CN117590458A - Method for evaluating monitoring shock level threshold of Pn wave signal of seismic station based on reciprocity principle - Google Patents
Method for evaluating monitoring shock level threshold of Pn wave signal of seismic station based on reciprocity principle Download PDFInfo
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Abstract
The invention relates to a monitoring capability evaluation method of a seismic station, in particular to a monitoring magnitude threshold evaluation method of a Pn wave signal of the seismic station based on a reciprocity principle, which solves the technical problem that the monitoring magnitude threshold evaluation of the Pn wave signal of the seismic station is difficult because observation data of an area of the seismic station to be built cannot be directly obtained or a temporary seismic station is difficult to build. Based on the reciprocity principle of seismology, the method evaluates the Pn wave signal monitoring magnitude threshold value of the earthquake station of the area of the to-be-constructed earthquake station to the earthquake in the reference area through the existing earthquake station in the reference area, can be used for potential monitoring capability evaluation of the to-be-constructed earthquake station, monitoring capability evaluation of the existing earthquake station to a specific low earthquake activity area and monitoring upper and lower limit capability evaluation of some earthquake stations which can not acquire recorded data, and has important application value for guiding construction of an earthquake station network and optimizing layout of the earthquake station of the station network.
Description
Technical Field
The invention relates to a monitoring capability evaluation method of a seismic station, in particular to a monitoring magnitude threshold evaluation method of a Pn wave signal of the seismic station based on a reciprocity principle.
Background
The Pn wave signal is the first arrival signal of regional seismic waveform record, the time-to-time reading accuracy of the signal is higher, and the Pn wave signal is used as the first choice signal of in-shell seismic positioning in seismic monitoring. The ability of a seismic station to monitor an earthquake in a particular region is generally characterized by the magnitude threshold of the monitoring of the Pn wave signal of the earthquake in that region by the seismic station.
The method is only suitable for the evaluation scene with the observation data, and the observation data of the seismic signals of the area with the established seismic station on the seismic station of the area with the to-be-constructed seismic station needs to be acquired, and the observed earthquake level is required to have a certain range. For example, the earthquake station is built and operates for a long time, a large amount of observation data is accumulated, or temporary observation equipment is erected in the area of the earthquake station to be built for data accumulation. However, in actual situations, an evaluation result needs to be given before the construction of the seismic station, or it is difficult to erect a temporary seismic station in the area of the seismic station to be constructed (for example, in an unmanned area of Qinghai-Tibet plateau), and the conventional method for evaluating the monitoring magnitude threshold of the Pn wave signal cannot conveniently give the monitoring magnitude threshold of the Pn wave signal of the seismic event of the seismic station to be constructed to the target area.
Disclosure of Invention
The invention aims to solve the technical problem that the monitoring magnitude threshold value of the Pn wave signal of the seismic station is difficult to evaluate because the observation data of the area of the seismic station to be built cannot be directly obtained or the temporary seismic station is difficult to build, and provides a method for evaluating the monitoring magnitude threshold value of the Pn wave signal of the seismic station based on the reciprocity principle.
The design idea of the invention is as follows:
the invention provides a method for evaluating a monitoring magnitude threshold of a Pn wave signal of a seismic station based on a seismology reciprocity principle.
Because the Pn wave signals mainly propagate on the top of the upper mantle and are greatly influenced by the non-uniform scattering attenuation and the inelastic attenuation of the upper mantle, the amplitude of the Pn wave signals passing through some high attenuation areas is obviously smaller, so that the Pn wave signal monitoring capability of the corresponding seismic station is obviously lower. The attenuation difference of the Pn wave signal at the top of the upper mantle is a main factor for causing the amplitude difference of the Pn wave signal, and according to the reciprocity principle of seismology, the following can be obtained: the Pn wave signal from source to seismic station will experience the same attenuation as the Pn wave signal from seismic station to source. Therefore, to evaluate the Pn wave signal monitoring magnitude threshold of the earthquake station in the area a (the earthquake station is not actually built yet) to the earthquake in the area B (the earthquake station is built already), the Pn wave signal intensity of the earthquake in the area a monitored by the earthquake station in the area B can be equivalently analyzed and evaluated.
The reciprocity principle in seismology is utilized to convert the problem of monitoring the threshold value of the level of Pn wave signals of the earthquake station of the evaluation area A to the earthquake in the shell of the area B into the monitoring nominal level of the earthquake station of the calculation area B to the signals of different frequency bands of Pn waves of the earthquake in the shell of the area A, and the corresponding threshold value of the monitoring level of the Pn wave signals is obtained by utilizing the difference of the levels of the monitoring nominal level and the monitoring level of the earthquake.
The magnitude of the earthquake (including local magnitude, remote body magnitude, and surface magnitude) has the general form shown below:
M＝alg(V)+σ(△)
wherein V is the amplitude of a certain type of seismic signal measured by various methods; alpha is a relation coefficient (Amplitude-magnitide relation) between the Amplitude of the signal and the Magnitude, and is caused by the corner frequency difference of the frequency spectrums of the seismic sources of different magnitudes; sigma (delta) is a gauge function of magnitude calculation reflecting the attenuation of the seismic signal with the mid-range for calculating the magnitude, and for a magnitude or frequency of alpha equal to 1, sigma (delta) corresponds to the logarithmic value of the magnitude of a certain type of signal in a 0-level earthquake monitored by a station with a mid-range delta, also the magnitude-mid-range relation model (Amplitude-Distance) of a particular signal, can be expressed by using an n-th order polynomial of the magnitude logarithmic value:
σ n (△)＝b 0 +b 1 lg△+b 2 (lg△) 2 +…+b n (lg△) n +K△
Wherein b 0 ，b 1 ，……，b n K is a polynomial coefficient, and in order to compare with the magnitude calculated by the Pn wave signal, a measurement method which has better region portability and can uniformly measure the seismic source intensities of different regions under the same standard needs to be established. The earthquake magnitude obtained based on the earthquake signals with stable attenuation and simple attenuation correction generally has better region portability.
The Lg wave signal mainly propagates in the crust, has the characteristics of stable attenuation and small influence by the directional change of the radiation intensity of the seismic source in a larger area range, and is more suitable for measuring the seismic source intensity of the area seismic. Numerous research results indicate that the attenuation of the amplitude of the in-shell seismic excitation Lg wave signal can be expressed as:
wherein A is Lg (delta, f) is the signal amplitude at the mid-shock distance delta of the Lg wave with dominant frequency f, delta 0 For the reference distance, U is the propagation average velocity of the Lg wave, and Q (f) is the Lg wave quality factor at frequency f.
Selecting a reference distance (for example, 10 km), correcting the Lg wave signal amplitude at different distances to the signal amplitude at the reference distance by using a corresponding Q (f), and then calculating the mb equivalent magnitude of the seismic event by using the following formula:
mb Lg ＝5.0+log 10 (A Lg (△ 0 ,f)/C(f))
wherein C (f) is a correction coefficient, and the corresponding value is the amplitude of the Lg wave signal of the mb5.0 level earthquake at the reference distance, and the signal amplitude A can be observed through the gazette magnitude and the Lg wave of the earthquake event Lg (Δ 0 F) calibrating.
In order to achieve the above purpose, the invention adopts the following technical scheme:
a method for evaluating a monitoring magnitude threshold of a Pn wave signal of a seismic station based on the reciprocity principle is characterized by comprising the following steps:
step 1, marking a region of a station to be constructed as a region A, selecting a reference region according to the distance between the region A and the attenuation change of Lg waves, and marking the reference region as a region B;
step 2, collecting observed waveforms of seismic events in the area B, measuring Pn wave signal amplitudes of the observed waveforms, and calculating a magnitude amplitude coefficient and a source radiation intensity correction coefficient of the Pn wave signals to obtain a Pn wave signal magnitude gauge function of the area B;
step 3, selecting an A area seismic event, and calculating the equivalent earthquake magnitude of an Lg wave station of the A area seismic event and the earthquake magnitude of an A area seismic event Pn wave station monitored by the B area seismic station according to the observed waveform of the A area seismic event monitored by the B area seismic station and the Pn wave signal earthquake magnitude gauge function of the B area obtained in the step 2;
step 4, calculating the equivalent magnitude of the Lg wave station of the seismic event in the area A and the difference of the magnitude of the seismic event Pn wave station in the area A, which is monitored by the seismic station in the area B;
Step 5, predicting the noise floor amplitude of the earthquake station in the area A by using the earth noise floor model or the noise floor signal amplitude of the earthquake station in other areas similar to the natural geography and the humane environment in the area A, setting a monitoring signal to noise ratio, and then calculating the Pn wave signal monitoring nominal magnitude of the earthquake event in the area A monitored by the earthquake station in the area B according to the Pn wave signal magnitude gauge function of the area B obtained in the step 2 and the magnitude difference obtained in the step 4;
and 6, monitoring the nominal magnitude according to the magnitude difference obtained in the step 4 and the Pn wave signal obtained in the step 5, and calculating a threshold value of the monitoring magnitude of the Pn wave signal of the earthquake in the shell of the area B by the earthquake station in the area A.
Further, the step 2 specifically comprises:
2.1, selecting J B area seismic events in the B area, wherein J is an integer and J is more than 10; m B area seismic stations are arranged in the B area, M is an integer, and M is more than 50;
2.2, selecting Q earthquake stations in the area with the earthquake center distance smaller than 15 degrees from J B area earthquake events, and collecting the observation waveforms of each B area earthquake event on the Q earthquake stations, wherein Q is an integer and Q is more than 50;
2.3, selecting K seismic stations with the epicenter distance of 2.0-15 degrees from J B area seismic events from Q seismic stations and Pn wave signal records, wherein K is an integer, and J is more than or equal to K and less than or equal to Q multiplied by J; filtering observed waveforms on the K seismic stations by adopting band-pass filters with I different pass bands, and then respectively calculating Pn wave signal amplitudes of J B area seismic events monitored by the K seismic stations in different filtering frequency bands, wherein I is an integer and is more than or equal to 1;
2.4, selecting P earthquake stations with the earthquake center distance smaller than 1 degree from J B area earthquake events from Q earthquake stations, and calculating to obtain the earthquake source frequency spectrum corner frequency and mb-f of the J B area earthquake events according to the observed waveforms of the J B area earthquake events monitored by the P earthquake stations c The relation model is used for calculating magnitude amplitude coefficients of J B-region seismic events in different filtering frequency bands according to the frequency of the corners of a seismic source frequency spectrum, wherein P is a positive integer, P is less than Q, mb represents the magnitude of a seismic event gazette, and f c Source spectrum corner frequencies representing seismic events;
2.5, inquiring or inverting the source mechanism solutions of J B-area seismic events, and calculating Pn wave source radiation intensity correction coefficients of the J B-area seismic events according to the source mechanism solutions;
2.6, obtaining the magnitude gauge functions of Pn waves of J B area seismic events monitored by K seismic stations in different filtering frequency bands according to the Pn wave signal amplitude obtained in the step 2.3, the magnitude amplitude coefficient obtained in the step 2.4 and the Pn wave source radiation intensity correction coefficient obtained in the step 2.5:
wherein,the magnitude gauge function, delta, of the Pn wave of the jth B region seismic event at the ith filter band monitored for the kth seismic station jk For the center distance, mb, from the jth zone B seismic event to the kth seismic station j Gazette magnitude for the jth zone B seismic event,>magnitude coefficient at the ith filter band for the jth B-zone seismic event, c j k The correction coefficient of Pn wave source radiation intensity for the jth B region seismic event monitored by the kth seismic station, i V k j the peak-to-peak amplitude of Pn wave signals in the ith filtering frequency band of the jth B area seismic event monitored by the kth seismic station is that I, J and K are integers, I is more than 0 and less than or equal to I, J is more than 0 and less than or equal to J, and K is more than 0 and less than or equal to K;
2.7 obtaining Pn wave signal amplitude values of the B area seismic events in different frequency bands and the value of the Pn wave amplitude value gauge functions of the B area seismic events in different frequency bands and the epicenter distance according to the gazette amplitude values of the J B area seismic events, the Pn wave signal amplitude values of the J B area seismic event observation waveforms in different filtering frequency bands, which are obtained in the step 2.3, and the Pn wave amplitude value gauge functions of the Pn wave in the different filtering frequency bands, which are obtained in the step 2.6, and then carrying out fitting regression on the Pn wave signal amplitude value gauge functions of the B area seismic events
Further, the step 3 specifically comprises:
3.1, selecting L seismic events with complete seismic record signals on a seismic station in the area B from the area A as the seismic events in the area A, wherein L is an integer and L is more than 10;
3.2, collecting the seismic signals of L A-area seismic events monitored by M B-area seismic stations to obtain L A-area seismic signal waveforms monitored by the M B-area seismic stations;
3.3, calculating the Lg wave station equivalent earthquake magnitude of the L A area earthquake events according to the L A area earthquake signal waveforms monitored by the M B area earthquake stations;
3.4, inquiring or inverting the source mechanism solutions of the L A-area seismic events, and calculating Pn wave source radiation intensity correction coefficients of the L A-area seismic events according to the source mechanism solutions;
3.5, obtaining Pn wave signal amplitude values of L A area seismic event observation waveforms monitored by M B area seismic stations in different filtering frequency bands by adopting the same method in the step 2.3;
3.6 using the mb-f obtained in step 2.4 c The relation model obtains the frequency of the frequency spectrum corner of the seismic source of the L A-area seismic events, and then the magnitude coefficients of the L A-area seismic events in different filtering frequency bands are calculated according to the following formula:
wherein,magnitude coefficient in the ith filter band for the ith A-zone seismic event, f 0 i For the center frequency of the ith filter band, < >>Source spectrum corner frequencies for the first a-zone seismic event;
3.7, calculating Pn wave station mb magnitudes of L A area seismic events monitored by M B area seismic stations in different filtering frequency bands according to the Pn wave source radiation intensity correction coefficient obtained in the step 3.4, the Pn wave signal amplitude obtained in the step 3.5, the magnitude amplitude coefficient obtained in the step 3.6 and the Pn wave signal magnitude gauge function of the B area seismic events obtained in the step 2 by the following formulas:
Wherein,the Mb magnitude of the Pn wave station in the ith filtering frequency band is the first A area seismic event monitored by the mth B area seismic station; />A Pn wave source radiation intensity correction coefficient of a first A area seismic event monitored by an mth B area seismic station; i V l m pn wave signal amplitude of the ith A area seismic event in the ith filtering frequency band, which is monitored by the mth B area seismic station; />The value of the Pn wave signal magnitude gauge function of the B area seismic event at the midrange of the m-th B area seismic station and the first A area seismic event is taken; l and M are integers, and L is more than 0 and less than or equal to L, and M is more than 0 and less than or equal to M;
and 3.8, calculating the average value of the Mb magnitudes of the Pn wave stations of the first A area seismic event in the ith filtering frequency band, which are monitored by M B area seismic stations, to obtain the Mn wave stations of the L A area seismic events in different filtering frequency bands.
Further, step 2.4 specifically includes:
2.4.1, selecting P earthquake stations with the earthquake center distance smaller than 1.0 degree from the B area earthquake events from the Q earthquake stations, and acquiring observation waveforms of the J B area earthquake events on the P earthquake stations;
2.4.2, measuring and fitting Pg signal spectrums of J B area seismic events by a parameter searching and fitting method according to observed waveforms of the J B area seismic events on P seismic stations to obtain source spectrum corner frequencies of the J B area seismic events;
2.4.3 regressing the source spectrum corner frequencies of J B-region seismic events to obtain mb-f c A relationship model;
2.4.4, calculating the center frequencies of the I different pass bands to obtain the center frequencies of different filter frequency bands;
2.4.5, calculating magnitude coefficients of J B-area seismic events in different filtering frequency bands according to the following formulas by using a source spectrum model of a natural earthquake, the source spectrum corner frequencies of the J B-area seismic events obtained in the step 2.4.2 and the center frequencies of the different filtering frequency bands obtained in the step 2.4.4 respectively:
wherein,magnitude coefficient in the ith filter band for the jth B-zone seismic event, f 0 i For the center frequency of the ith filter band, < >>Source spectrum corner frequency for the jth B zone seismic event.
Further, step 2.3 specifically includes:
2.3.1, selecting K seismic stations with the epicenter distance of 2.0-15 degrees from J B area seismic events from Q seismic stations and Pn wave signal records, wherein K is an integer, and J is more than or equal to K and less than or equal to Q multiplied by J; marking Pn wave signal arrival times and subsequent following signal arrival times on observed waveforms of J B area seismic events monitored by K seismic stations respectively;
2.3.2, calculating the time difference between the follow-up signal and the Pn wave signal, selecting an observed waveform with the time difference being more than or equal to 5.0s, and recording the observed waveform as seismic observation data;
2.3.3, performing instrument response correction on the seismic observation data to obtain a ground vibration waveform taking mu m/s as a unit;
2.3.4, respectively filtering the ground vibration waveforms by using band-pass filters with I different pass bands to obtain ground vibration waveforms of J B area seismic events monitored by K seismic stations in I filtering frequency bands;
2.3.5, in the ground vibration waveform, waveform data in the time of 5.0s from the first 0.1s of the arrival time position of the Pn wave signal are taken, and Pn wave signal peak-to-peak amplitude values of J B area seismic events detected by K seismic stations in I filtering frequency bands are respectively calculated;
2.3.6 in the ground vibration waveforms of the I filtering frequency bands, noise data of Pn wave signals in 5.2s before reaching the time and in 5.0s long are taken, and noise peak-to-peak amplitude values of K seismic stations are calculated respectively;
2.3.7, respectively calculating signal to noise ratios of Pn wave signals of J B area seismic events monitored by K seismic stations in I filtering frequency bands according to the Pn wave signal peak-to-peak amplitude obtained in the step 2.3.5 and the noise peak-to-peak amplitude obtained in the step 2.3.6, wherein the Pn wave signal peak-to-peak amplitude of the Pn wave signals with the signal to noise ratio being more than or equal to 5.0 is the Pn wave signal amplitude of J B area seismic events monitored by K seismic stations in different filtering frequency bands.
Further, the step 3.3 specifically includes:
3.3.1, filtering L A area seismic signal waveforms monitored by M B area seismic stations to obtain L A area seismic event observation waveforms monitored by the M B area seismic stations;
3.3.2, selecting an observed waveform of an A-region seismic event on one of the B-region seismic stations, and marking the arrival time position of the Lg wave seismic phase;
3.3.3 setting a velocity window according to the Lg wave vibration phase, calculating the Lg wave amplitude value by using the velocity window to measure the time window length TL Lg ；
3.3.4 measuring the starting time of the Lg wave vibration phase arrival time and the length of TL on the observed waveform of the seismic event of the area A Lg Maximum peak-to-peak amplitude of Lg wave signals;
3.3.5, correcting the maximum peak-to-peak amplitude of the Lg wave signal of the seismic event in the area A obtained in the step 3.3.4 to the signal amplitude at the reference distance according to the Lg wave quality factor in the area B by the following formula to obtain corrected Lg wave observation signal amplitude:
wherein A is Lg (delta, f) is the time of arrival of the Lg wave vibration phase with the starting time of the observed waveform of the A area earthquake event and the length of TL Lg Maximum peak-to-peak amplitude, A, of Lg wave signal of (2) Lg (Δ 0 F) is the corrected Lg wave observed signal amplitude, representing the amplitude of the seismic signal where the dominant frequency f of the Lg wave is at the mid-seismic distance Δ; f is the center frequency of the filter passband, delta is the center distance of the epicenter, delta 0 For reference distance, delta-delta 0 For the difference of the epicenter distance, U is the propagation average speed of the Lg wave, and Q (f) is the quality factor of the Lg wave with the frequency f;
3.3.6 calibrating the correction coefficient of the A-area seismic event according to the gazette magnitude of the A-area seismic event and the corrected Lg wave observation signal amplitude obtained in the step 3.3.5, and calculating the Lg wave magnitude mb of the A-area seismic event on one of the B-area seismic stations according to the following formula Lg ：
mb Lg ＝5.0+log 10 (A Lg (△ 0 ,f)/C(f))
Wherein C (f) is a correction coefficient of the A-region seismic event;
3.3.7, repeating the steps 3.3.2-3.3.6 until the Lg wave magnitudes of L A area seismic events on M B area seismic stations are obtained;
3.3.8, respectively calculating the average value of the Lg wave magnitudes of the A-area seismic events on the M B-area seismic stations to obtain the Lg wave station equivalent magnitudes of the L A-area seismic events.
Further, in step 5, the nominal magnitude of Pn wave signal monitoring of the seismic event in the a zone monitored by the B zone seismic station is calculated by the following formula:
wherein,area A land monitored for area B seismic stationsMonitoring nominal magnitude, δmb, of Pn wave signals of seismic events in the ith filtering band i Is the difference between the equivalent amplitude of the Lg wave station of the A area seismic event and the amplitude of the Pn wave station in the ith frequency band of the A area seismic event monitored by the B area seismic station, c is the source radiation intensity coefficient, p is the monitoring signal to noise ratio, i A noise Noise floor amplitude in the ith filter band for the seismic station in zone A, +.>A Pn wave signal magnitude gauge function of the B region; />Is of the magnitude +.>Magnitude coefficient of earthquake in ith filtering band, +.> Is of the magnitude +.>Source spectrum corner frequency of the earthquake.
Further, in step 6, the threshold value of the monitoring magnitude of the Pn wave signal of the earthquake in the shell of the area B by the area a earthquake station is calculated by the following formula:
wherein, i mb th the magnitude threshold is monitored for Pn wave signals of an earthquake in the B zone shell in the ith filtering band for the a zone seismic station.
Further, in step 1, the selection principle of the B region is as follows:
the vibration center distance between the station and the area A is 3-10 degrees, the Lg wave attenuation is the same as that of the area A, and the earthquake stations are dense;
in step 2.1, the selection principle of the seismic event in the area B is as follows:
the number of the earthquake stations for monitoring the earthquake event is more than 50, pn waves and Lg waves are complete in earthquake phase development, and the range of the earthquake magnitude is more than 2.5 levels.
Further, in step 2.3, the selection principle of the band-pass filter is as follows: the passband of the bandpass filter evaluates relevant signal frequency selections according to regional seismic monitoring capability;
in step 3.1, L of the a-zone seismic events are repeating seismic clusters.
Compared with the prior art, the invention has the following beneficial technical effects:
according to the method for evaluating the Pn wave signal monitoring magnitude threshold of the seismic station based on the reciprocity principle, which is provided by the invention, the seismic station data of the seismic station area to be built is not required to be acquired, the temporary station is not required to be built in the seismic station area to be built, the Pn wave signal monitoring magnitude threshold of the seismic station in the seismic station area to be built is evaluated by referring to the existing seismic stations in the area, so that the Pn wave signal monitoring magnitude threshold evaluation is more economical and wider in application, and the method can be used for potential monitoring capability evaluation of the seismic station to be built, monitoring capability evaluation of the existing seismic station to a specific low seismic activity area and monitoring upper and lower limit capability evaluation of some seismic stations incapable of acquiring record data, and has important application value for guiding the construction of a seismic station network and the optimization of the layout of the seismic station network.
Drawings
FIG. 1 is a flow chart of an embodiment of the present invention;
FIG. 2 is a schematic diagram of the equivalent vibration level of an Lg wave station and the vibration level of a Pn wave station in an embodiment of the present invention.
Detailed Description
The invention provides a method for evaluating the monitoring shock level threshold value of the Pn wave signal of the seismic station based on the reciprocity principle, which is further described in detail below with reference to the accompanying drawings and the detailed description. It should be understood by those skilled in the art that these embodiments are merely for explaining the technical principles of the present invention, and are not intended to limit the scope of the present invention.
A method for evaluating a monitoring magnitude threshold of a Pn wave signal of a seismic station based on the reciprocity principle, as shown in figure 1, comprises the following steps:
and 1, marking the area of the earthquake station to be built as an area A, selecting a reference area according to the distance between the area A and the attenuation change of the Lg wave, and marking the reference area as an area B. M B area seismic stations are arranged in the B area, M is an integer, and M is more than 50.
The selection principle of the area B is as follows: the vibration center distance between the station and the area A is between 3 degrees and 10 degrees, the Lg wave attenuation is the same as that of the area A, and the earthquake stations are dense. The selection principle of the seismic event in the area B is as follows: the number of the earthquake stations for monitoring the earthquake event is more than 50, pn waves and Lg waves are complete in earthquake phase development, and the range of the earthquake magnitude is more than 2.5 levels.
And 2, collecting observation waveforms of the seismic events in the area B, measuring Pn wave signal amplitudes of the observation waveforms, and calculating a magnitude amplitude coefficient and a source radiation intensity correction coefficient of the Pn wave signals to obtain a magnitude gauge function of the Pn wave signals in the area B.
To facilitate quantitative comparison with the Pn wave signal monitoring magnitude threshold of an existing seismic station, the intensity of the Pn wave signal is converted into a magnitude. Although different regions have established gauge functions that use regional seismic signal amplitudes to calculate the magnitude, these gauge functions are applicable to calculating the magnitude using the maximum signal amplitude of the entire wave train of the seismic signal. For continental-shell earthquakes, the maximum amplitude signal monitored at a regional seismic station is typically Lg wave, so these magnitude gauge functions are not applicable to Pn wave signals and an mb (Pn) magnitude gauge function applicable to Pn wave signals needs to be established. The specific steps of the step 2 are as follows:
2.1, selecting J B area seismic events in the B area, wherein J is an integer, and J is more than 10.
2.2, selecting Q earthquake stations in the area with the earthquake center distance smaller than 15 degrees from J B area earthquake events, and collecting the observation waveforms of each B area earthquake event on the Q earthquake stations, wherein Q is an integer and Q is more than 50.
2.3, selecting K seismic stations with the epicenter distance of 2.0-15 degrees from J B area seismic events from Q seismic stations and Pn wave signal records, wherein K is an integer, and J is not less than K and not more than Q multiplied by J. 5 band-pass filters with pass bands of 0.75 Hz-1.5 Hz, 2.0 Hz-4.0 Hz, 3.0 Hz-6.0 Hz, 4.0 Hz-8.0 Hz and 8.0 Hz-16.0 Hz are adopted to filter the observed waveform, and then Pn wave signal amplitudes of J B area seismic event observed waveforms monitored by K seismic stations in different filtering frequency bands are calculated respectively. The selection principle of the band-pass filter is as follows: the passband of the bandpass filter evaluates the relevant signal frequency selections based on the regional seismic monitoring capabilities. The specific steps of the step 2.3 are as follows:
2.3.1, selecting K seismic stations with the epicenter distance of 2.0-15 degrees from J B area seismic events from Q seismic stations and Pn wave signal records, wherein K is an integer, and J is more than or equal to K and less than or equal to Q multiplied by J; marking Pn wave signal arrival times and subsequent following signal arrival times on observed waveforms of J B area seismic events monitored by K seismic stations respectively;
2.3.2, calculating the time difference between the follow-up signal and the Pn wave signal, selecting an observed waveform with the time difference being more than or equal to 5.0s, and recording the observed waveform as seismic observation data;
2.3.3, performing instrument response correction on the seismic observation data to obtain a ground vibration waveform taking mu m/s as a unit;
2.3.4, filtering the ground vibration waveform by adopting 5 band-pass filters with pass bands of 0.75 Hz-1.5 Hz, 2.0 Hz-4.0 Hz, 3.0 Hz-6.0 Hz, 4.0 Hz-8.0 Hz and 8.0 Hz-16.0 Hz respectively, so as to obtain the ground vibration waveform of J B area seismic events monitored by K seismic stations in I filtering frequency bands respectively;
2.3.5, in the ground vibration waveform, waveform data in the time of 5.0s from the first 0.1s of the arrival time position of the Pn wave signal are taken, and Pn wave signal peak-to-peak amplitude values of J B area seismic events detected by K seismic stations in I filtering frequency bands are respectively calculated;
2.3.6 in the ground vibration waveforms of the I filtering frequency bands, noise data of Pn wave signals in 5.2s before reaching the time and in 5.0s long are taken, and noise peak-to-peak amplitude values of K seismic stations are calculated respectively;
2.3.7, respectively calculating signal to noise ratios of Pn wave signals of J B area seismic events monitored by K seismic stations in I filtering frequency bands according to the Pn wave signal peak-to-peak amplitude obtained in the step 2.3.5 and the noise peak-to-peak amplitude obtained in the step 2.3.6, wherein the Pn wave signal peak-to-peak amplitude of the Pn wave signals with the signal to noise ratio being more than or equal to 5.0 is the Pn wave signal amplitude of J B area seismic events monitored by K seismic stations in different filtering frequency bands.
2.4, selecting P earthquake stations with the earthquake center distance smaller than 1 degree from J B area earthquake events from Q earthquake stations, and calculating to obtain the earthquake source frequency spectrum corner frequency and mb-f of the J B area earthquake events according to the observed waveforms of the J B area earthquake events monitored by the P earthquake stations c The relation model is used for calculating magnitude amplitude coefficients of J B-region seismic events in different filtering frequency bands according to the frequency of the corners of a seismic source frequency spectrum, wherein P is a positive integer, P is less than Q, mb represents the magnitude of a seismic event gazette, and f c Source spectrum corner frequencies representing seismic events. The method comprises the following specific steps:
2.4.1, selecting P earthquake stations with the earthquake center distance smaller than 1.0 degree from the B area earthquake events from the Q earthquake stations, and acquiring observation waveforms of the J B area earthquake events on the P earthquake stations;
2.4.2, measuring and fitting Pg signal spectrums of J B area seismic events by a parameter searching and fitting method according to observed waveforms of the J B area seismic events on P seismic stations to obtain source spectrum corner frequencies of the J B area seismic events;
2.4.3 regressing the source spectrum corner frequencies of J B-region seismic events to obtain mb-f c A relationship model;
2.4.4, calculating the center frequencies of the I different pass bands to obtain the center frequencies of different filter frequency bands;
2.4.5, calculating magnitude coefficients of J B-area seismic events in different filtering frequency bands according to the following formulas by using a source spectrum model of a natural earthquake, the source spectrum corner frequencies of the J B-area seismic events obtained in the step 2.4.2 and the center frequencies of the different filtering frequency bands obtained in the step 2.4.4 respectively:
wherein,magnitude coefficient in the ith filter band for the jth B-zone seismic event, f 0 i For the center frequency of the ith filter band, < >>The frequency of the frequency spectrum corner of the seismic source is the J-th B area seismic event, i and J are integers, i is more than 0 and less than or equal to 5, and J is more than 0 and less than or equal to J.
And 2.5, inquiring or inverting the source mechanism solutions of J B-area seismic events, and calculating Pn wave source radiation intensity correction coefficients of the J B-area seismic events according to the source mechanism solutions.
2.6, obtaining the magnitude gauge functions of Pn waves of J B area seismic events monitored by K seismic stations in different filtering frequency bands according to the Pn wave signal amplitude obtained in the step 2.3, the magnitude amplitude coefficient obtained in the step 2.4 and the Pn wave source radiation intensity correction coefficient obtained in the step 2.5:
wherein,the magnitude gauge function, delta, of the Pn wave of the jth B region seismic event at the ith filter band monitored for the kth seismic station jk For the center distance, mb, from the jth zone B seismic event to the kth seismic station j Gazette magnitude for the jth zone B seismic event,>magnitude coefficient at the ith filter band for the jth B-zone seismic event, c j k The correction coefficient of Pn wave source radiation intensity for the jth B region seismic event monitored by the kth seismic station, i V k j the peak-to-peak amplitude of Pn wave signals in the ith filtering frequency band of the jth B area seismic event monitored by the kth seismic station is provided, K is an integer, and K is more than 0 and less than or equal to K.
2.7 obtaining Pn wave signal amplitude values of the B area seismic events in different frequency bands and the value of the Pn wave amplitude value gauge functions of the B area seismic events in different frequency bands and the epicenter distance according to the gazette amplitude values of the J B area seismic events, the Pn wave signal amplitude values of the J B area seismic event observation waveforms in different filtering frequency bands, which are obtained in the step 2.3, and the Pn wave amplitude value gauge functions of the Pn wave in the different filtering frequency bands, which are obtained in the step 2.6, and then carrying out fitting regression on the Pn wave signal amplitude value gauge functions of the B area seismic events
Step 3, selecting an A area seismic event, and calculating the Lg wave station equivalent magnitude of the A area seismic event and the A area seismic event Pn wave station magnitude monitored by the B area seismic station according to the observed waveform of the A area seismic event monitored by the B area seismic station and the Pn wave signal magnitude gauge function of the B area obtained in the step 2, wherein the specific steps are as follows:
And 3.1, selecting L repeated seismic clusters with complete seismic record signals on the B area seismic station from the A area as A area seismic events, wherein L is an integer and L is more than 10. When the A-region seismic event is a repeated seismic group, the Pn wave source radiation intensity correction coefficient of the A-region seismic eventIs a fixed value.
And 3.2, collecting the seismic signals of L A-area seismic events monitored by the M B-area seismic stations, and obtaining L A-area seismic signal waveforms monitored by the M B-area seismic stations.
And 3.3, calculating the Lg wave station equivalent earthquake magnitude of the L A area earthquake events according to the L A area earthquake signal waveforms monitored by the M B area earthquake stations. The method comprises the following specific steps:
3.3.1, filtering L A area seismic signal waveforms monitored by M B area seismic stations to obtain L A area seismic event observation waveforms monitored by the M B area seismic stations;
3.3.2, selecting an observed waveform of an A-region seismic event on one of the B-region seismic stations, and marking the arrival time position of the Lg wave seismic phase;
3.3.3 setting a velocity window according to the Lg wave vibration phase, calculating the Lg wave amplitude value by using the velocity window to measure the time window length TL Lg ；
3.3.4 measuring the starting time of the Lg wave vibration phase arrival time and the length of TL on the observed waveform of the seismic event of the area A Lg Maximum peak-to-peak amplitude of Lg wave signals;
3.3.5, correcting the maximum peak-to-peak amplitude of the Lg wave signal of the seismic event in the area A obtained in the step 3.3.4 to the signal amplitude at the reference distance according to the Lg wave quality factor in the area B by the following formula to obtain corrected Lg wave observation signal amplitude:
wherein A is Lg (delta, f) is the time of arrival of the Lg wave vibration phase with the starting time of the observed waveform of the A area earthquake event and the length of TL Lg Maximum peak-to-peak amplitude, A, of Lg wave signal of (2) Lg (Δ 0 F) is the corrected Lg wave observed signal amplitude, representing the amplitude of the seismic signal where the dominant frequency f of the Lg wave is at the mid-seismic distance Δ; f is the center frequency of the filter passband, delta is the center distance of the epicenter, delta 0 For reference distance, delta-delta 0 For the difference of the epicenter distance, U is the propagation average speed of the Lg wave, and Q (f) is the quality factor of the Lg wave with the frequency f;
3.3.6, calibrating the correction coefficient of the A-area seismic event according to the amplitude of the corrected Lg wave observation signal obtained in the step 3.3.5,the Lg wave magnitude mb of an A-zone seismic event on one of the B-zone seismic stations is calculated by the following formula Lg ：
mb Lg ＝5.0+log 10 (A Lg (△ 0 ,f)/C(f))
Wherein C (f) is a correction coefficient of the A-region seismic event;
3.3.7, repeating the steps 3.3.2-3.3.6 until the Lg wave magnitudes of L A area seismic events on M B area seismic stations are obtained;
3.3.8, respectively calculating the average value of the Lg wave magnitudes of the A-area seismic events on the M B-area seismic stations to obtain the Lg wave station equivalent magnitudes of the L A-area seismic events.
And 3.4, inquiring or inverting the source mechanism solutions of the L A-area seismic events, and calculating Pn wave source radiation intensity correction coefficients of the L A-area seismic events according to the source mechanism solutions.
And 3.5, obtaining Pn wave signal amplitudes of L A area seismic event observation waveforms monitored by M B area seismic stations in different filtering frequency bands by adopting the same method in the step 2.3.
3.6 using the mb-f obtained in step 2.4 c The relation model obtains the frequency of the frequency spectrum corner of the seismic source of the L A-area seismic events, and then the magnitude coefficients of the L A-area seismic events in different filtering frequency bands are calculated according to the following formula:
wherein,magnitude coefficient in the ith filter band for the ith A-zone seismic event, f 0 i For the center frequency of the ith filter band, < >>The frequency of the corner of the frequency spectrum of the seismic source of the seismic event in the first area A is L, and L is an integer and is more than 0 and less than or equal to L.
3.7, calculating Pn wave station mb magnitudes of L A area seismic events monitored by M B area seismic stations in different filtering frequency bands according to the Pn wave source radiation intensity correction coefficient obtained in the step 3.4, the Pn wave signal amplitude obtained in the step 3.5, the magnitude amplitude coefficient obtained in the step 3.6 and the Pn wave signal magnitude gauge function of the B area seismic events obtained in the step 2 by the following formulas:
Wherein,the Mb magnitude of the Pn wave station in the ith filtering frequency band is the first A area seismic event monitored by the mth B area seismic station; />A Pn wave source radiation intensity correction coefficient of a first A area seismic event monitored by an mth B area seismic station; i V l m pn wave signal amplitude of the ith A area seismic event in the ith filtering frequency band, which is monitored by the mth B area seismic station; />The value of the Pn wave signal magnitude gauge function of the B area seismic event at the midrange of the m-th B area seismic station and the first A area seismic event is taken; m is an integer, and M is more than 0 and less than or equal to M.
And 3.8, calculating the average value of the Mb magnitudes of the Pn wave stations of the first A area seismic event in the ith filtering frequency band, which are monitored by M B area seismic stations, to obtain the Mn wave stations of the L A area seismic events in different filtering frequency bands.
Step 4, calculating the equivalent vibration level of the Lg wave station of the A area seismic event and the vibration level difference delta mb of the Pn wave station vibration level of the A area seismic event in different frequency bands, which is monitored by the B area seismic station i 。
As shown in FIG. 2, the dashed lines are i mb(Pn)＝mb(Lg)， i mb (Pn) is the Pn wave station magnitude of the A area seismic event in the ith filtering frequency band, and mb (Lg) is the Lg wave station equivalent magnitude of the A area seismic event. There are three cases of the current seismic location at the point in FIG. 2:
(I) Is positioned on the virtual line and is provided with a plurality of channels, i mb(Pn)-mb(Lg)＝δmb i =0, meaning that the attenuation of the propagation path of the Pn wave signal from the a region to the B region is the same as the attenuation of the propagation path of the same distance from the B region. A seismic station in the area A having the same noise floor level as the area B, and the monitoring magnitude threshold of the Pn wave signal is equivalent to that of the station in the area B (the point shown by the triangle in the drawing);
(II) is located above the dotted line, i mb(Pn)-mb(Lg)＝δmb i and > 0, the attenuation of the propagation path of the Pn wave signal from the A region to the B region is smaller than that of the propagation path with the same distance from the B region. The earthquake station with the same background noise level as the B area in the A area has smaller monitoring magnitude threshold value for Pn wave signals than the earthquake station in the B area and stronger monitoring capability (points shown by five-pointed star in the drawing);
(III) is located below the dashed line, i mb(Pn)-mb(Lg)＝δmb i < 0 means that the attenuation of the propagation path of the Pn wave signal from the a region to the B region is greater than that of the propagation path of the same distance from the B region. The seismic stations in zone a having the same noise floor level as zone B have a greater threshold magnitude for monitoring Pn wave signals than the seismic stations in zone B, with weaker monitoring capabilities (points shown as prisms in the drawing).
Step 5, predicting the background noise amplitude of the seismic station in the area A by using an earth background noise model or background noise signal amplitude of the seismic station in other areas similar to the natural geography and the humane environment in the area A, setting a monitoring signal to noise ratio, and calculating a Pn wave signal monitoring nominal magnitude threshold of the seismic event in the area A monitored by the seismic station in the area B according to the Pn wave signal magnitude gauge function of the area B obtained in the step 2 and the difference of the vibration levels obtained in the step 4 by using the following formula:
Wherein,monitoring nominal magnitude, δmb, for Pn wave signals of seismic events in region A in the ith filter band monitored by a region B seismic station i Is the difference between the equivalent amplitude of the Lg wave station of the A area seismic event and the amplitude of the Pn wave station in the ith frequency band of the A area seismic event monitored by the B area seismic station, c is the source radiation intensity coefficient, p is the monitoring signal to noise ratio, i A noise noise floor amplitude in the ith filter band for the seismic station in zone A, +.>A Pn wave signal magnitude gauge function of the B region; />Is of the magnitude +.>Magnitude coefficient of earthquake in ith filtering band, +.> Is of the magnitude +.>Source spectrum corner frequency of the earthquake.
And 6, calculating a Pn wave signal monitoring magnitude threshold value of the earthquake station in the area A for the earthquake in the area B by using the earthquake magnitude difference obtained in the step 4 and the monitoring nominal earthquake magnitude threshold value obtained in the step 5 according to the following formula:
wherein, i mb th the magnitude threshold is monitored for Pn wave signals of an earthquake in the B zone shell in the ith filtering band for the a zone seismic station.
According to the method for evaluating the Pn wave signal monitoring magnitude threshold of the earthquake station based on the reciprocity principle of seismology, the problem that the earthquake station of the earthquake station to be built monitors the Pn wave signal monitoring magnitude threshold of the earthquake in the shell of the reference area is converted into the monitoring nominal magnitude of the earthquake station of the reference area to be built on the Pn wave signals of different frequency bands of the earthquake in the shell of the earthquake station, and the corresponding Pn wave signal monitoring magnitude threshold is obtained by utilizing the difference of the monitoring nominal magnitude and the monitoring magnitude.
Claims (10)
1. A method for evaluating a monitoring magnitude threshold of a Pn wave signal of a seismic station based on the reciprocity principle is characterized by comprising the following steps:
step 1, marking a region of a station to be constructed as a region A, selecting a reference region according to the distance between the region A and the attenuation change of Lg waves, and marking the reference region as a region B;
step 2, collecting observed waveforms of seismic events in the area B, measuring Pn wave signal amplitudes of the observed waveforms, and calculating a magnitude amplitude coefficient and a source radiation intensity correction coefficient of the Pn wave signals to obtain a Pn wave signal magnitude gauge function of the area B;
step 3, selecting an A area seismic event, and calculating the equivalent earthquake magnitude of an Lg wave station of the A area seismic event and the earthquake magnitude of an A area seismic event Pn wave station monitored by the B area seismic station according to the observed waveform of the A area seismic event monitored by the B area seismic station and the Pn wave signal earthquake magnitude gauge function of the B area obtained in the step 2;
step 4, calculating the equivalent magnitude of the Lg wave station of the seismic event in the area A and the difference of the magnitude of the seismic event Pn wave station in the area A, which is monitored by the seismic station in the area B;
step 5, predicting the noise floor amplitude of the earthquake station in the area A by using the earth noise floor model or the noise floor signal amplitude of the earthquake station in other areas similar to the natural geography and the humane environment in the area A, setting a monitoring signal to noise ratio, and then calculating the Pn wave signal monitoring nominal magnitude of the earthquake event in the area A monitored by the earthquake station in the area B according to the Pn wave signal magnitude gauge function of the area B obtained in the step 2 and the magnitude difference obtained in the step 4;
And 6, monitoring the nominal magnitude according to the magnitude difference obtained in the step 4 and the Pn wave signal obtained in the step 5, and calculating a threshold value of the monitoring magnitude of the Pn wave signal of the earthquake in the shell of the area B by the earthquake station in the area A.
2. The method for evaluating the monitoring magnitude threshold of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 1, wherein the step 2 is specifically:
2.1, selecting J B area seismic events in the B area, wherein J is an integer and J is more than 10; m B area seismic stations are arranged in the B area, M is an integer, and M is more than 50;
2.2, the mid-seismic distance to J B-zone seismic events is less thanQ seismic stations are selected in the area of (1), and observation waveforms of the seismic events of each area B on the Q seismic stations are collected, wherein Q is an integer and Q is more than 50;
2.3 selecting the earthquake center distance between the Q earthquake stations and J B area earthquake events asK seismic stations recorded by Pn wave signals are arranged, wherein K is an integer, and J is not less than K and not more than Q multiplied by J; filtering observed waveforms on the K seismic stations by adopting band-pass filters with I different pass bands, and respectively calculating Pn wave signal amplitudes of J B area seismic events monitored by the K seismic stations in different filtering frequency bands, wherein I is an integer, and I is more than or equal to 1;
2.4 selecting and J B-zone seismic events from among the Q seismic stationsThe epicenter distance is smaller thanAccording to the observed waveforms of J B-area seismic events monitored by the P seismic stations, calculating to obtain the source spectrum corner frequency and mb-f of the J B-area seismic events c The relation model is used for calculating magnitude amplitude coefficients of J B-region seismic events in different filtering frequency bands according to the frequency of the corners of a seismic source frequency spectrum, wherein P is a positive integer, P is less than Q, mb represents the magnitude of a seismic event gazette, and f c Source spectrum corner frequencies representing seismic events;
2.5, inquiring or inverting the source mechanism solutions of J B-area seismic events, and calculating Pn wave source radiation intensity correction coefficients of the J B-area seismic events according to the source mechanism solutions;
2.6, obtaining the magnitude gauge functions of Pn waves of J B area seismic events monitored by K seismic stations in different filtering frequency bands according to the Pn wave signal amplitude obtained in the step 2.3, the magnitude amplitude coefficient obtained in the step 2.4 and the Pn wave source radiation intensity correction coefficient obtained in the step 2.5:
wherein,the magnitude gauge function, delta, of the Pn wave of the jth B region seismic event at the ith filter band monitored for the kth seismic station jk For the center distance, mb, from the jth zone B seismic event to the kth seismic station j Gazette magnitude for the jth zone B seismic event,>magnitude coefficient at the ith filter band for the jth B-zone seismic event, c j k The jth zone B seismic event monitored for the kth seismic stationPn wave source radiation intensity correction coefficient, +.>The peak-to-peak amplitude of Pn wave signals in the ith filtering frequency band of the jth B area seismic event monitored by the kth seismic station is that I, J and K are integers, I is more than 0 and less than or equal to I, J is more than 0 and less than or equal to J, and K is more than 0 and less than or equal to K;
2.7 obtaining Pn wave signal amplitude values of the B area seismic events in different frequency bands and the value of the Pn wave amplitude value gauge functions of the B area seismic events in different frequency bands and the epicenter distance according to the gazette amplitude values of the J B area seismic events, the Pn wave signal amplitude values of the J B area seismic event observation waveforms in different filtering frequency bands, which are obtained in the step 2.3, and the Pn wave amplitude value gauge functions of the Pn wave in the different filtering frequency bands, which are obtained in the step 2.6, and then carrying out fitting regression on the Pn wave signal amplitude value gauge functions of the B area seismic events
3. The method for evaluating the monitoring magnitude threshold of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 2, wherein the step 3 is specifically:
3.1, selecting L seismic events with complete seismic record signals on a seismic station in the area B from the area A as the seismic events in the area A, wherein L is an integer and L is more than 10;
3.2, collecting the seismic signals of L A-area seismic events monitored by M B-area seismic stations to obtain L A-area seismic signal waveforms monitored by the M B-area seismic stations;
3.3, calculating the Lg wave station equivalent earthquake magnitude of the L A area earthquake events according to the L A area earthquake signal waveforms monitored by the M B area earthquake stations;
3.4, inquiring or inverting the source mechanism solutions of the L A-area seismic events, and calculating Pn wave source radiation intensity correction coefficients of the L A-area seismic events according to the source mechanism solutions;
3.5, obtaining Pn wave signal amplitude values of L A area seismic event observation waveforms monitored by M B area seismic stations in different filtering frequency bands by adopting the same method in the step 2.3;
3.6 using the mb-f obtained in step 2.4 c The relation model obtains the frequency of the frequency spectrum corner of the seismic source of the L A-area seismic events, and then the magnitude coefficients of the L A-area seismic events in different filtering frequency bands are calculated according to the following formula:
wherein,magnitude coefficient in the ith filter band for the ith A-zone seismic event, f 0 i For the center frequency of the ith filter band, < >>The frequency of the frequency spectrum corner of the seismic source is the first A area seismic event, L is an integer, and L is more than 0 and less than or equal to L;
3.7, calculating Pn wave station mb magnitudes of L A area seismic events monitored by M B area seismic stations in different filtering frequency bands according to the Pn wave source radiation intensity correction coefficient obtained in the step 3.4, the Pn wave signal amplitude obtained in the step 3.5, the magnitude amplitude coefficient obtained in the step 3.6 and the Pn wave signal magnitude gauge function of the B area seismic events obtained in the step 2 by the following formulas:
wherein,the Mb magnitude of the Pn wave station in the ith filtering frequency band is the first A area seismic event monitored by the mth B area seismic station; />A Pn wave source radiation intensity correction coefficient of a first A area seismic event monitored by an mth B area seismic station; i V l m pn wave signal amplitude of the ith A area seismic event in the ith filtering frequency band, which is monitored by the mth B area seismic station; />The value of the Pn wave signal magnitude gauge function of the B area seismic event at the midrange of the m-th B area seismic station and the first A area seismic event is taken; m is an integer, and M is more than 0 and less than or equal to M;
and 3.8, calculating the average value of the Mb magnitudes of the Pn wave stations of the first A area seismic event in the ith filtering frequency band, which are monitored by M B area seismic stations, to obtain the Mn wave stations of the L A area seismic events in different filtering frequency bands.
4. The method for evaluating the monitoring magnitude threshold of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 3, wherein the step 2.4 is specifically:
2.4.1 selecting from among the Q seismic stations a seismic center distance from the B region seismic event less thanObtaining observed waveforms of J B area seismic events on the P seismic stations;
2.4.2, measuring and fitting Pg signal spectrums of J B area seismic events by a parameter searching and fitting method according to observed waveforms of the J B area seismic events on P seismic stations to obtain source spectrum corner frequencies of the J B area seismic events;
2.4.3 regressing the source spectrum corner frequencies of J B-region seismic events to obtain mb-f c A relationship model;
2.4.4, calculating the center frequencies of the I different pass bands to obtain the center frequencies of different filter frequency bands;
2.4.5, calculating magnitude coefficients of J B-area seismic events in different filtering frequency bands according to the following formulas by using a source spectrum model of a natural earthquake, the source spectrum corner frequencies of the J B-area seismic events obtained in the step 2.4.2 and the center frequencies of the different filtering frequency bands obtained in the step 2.4.4 respectively:
Wherein,magnitude coefficient in the ith filter band for the jth B-zone seismic event, f 0 i For the center frequency of the ith filter band, < >>Source spectrum corner frequency for the jth B zone seismic event.
5. The method for evaluating the threshold value of monitoring the magnitude of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 4, wherein the step 2.3 is specifically:
2.3.1 selecting the seismic center distance from J B area seismic events in Q seismic stations asK seismic stations recorded by Pn wave signals are arranged, wherein K is an integer, and J is not less than K and not more than Q multiplied by J; marking Pn wave signal arrival times and subsequent following signal arrival times on observed waveforms of J B area seismic events monitored by K seismic stations respectively;
2.3.2, calculating the time difference between the follow-up signal and the Pn wave signal, selecting an observed waveform with the time difference being more than or equal to 5.0s, and recording the observed waveform as seismic observation data;
2.3.3, performing instrument response correction on the seismic observation data to obtain a ground vibration waveform taking mu m/s as a unit;
2.3.4, respectively filtering the ground vibration waveforms by using band-pass filters with I different pass bands to obtain ground vibration waveforms of J B area seismic events monitored by K seismic stations in I filtering frequency bands;
2.3.5, in the ground vibration waveform, waveform data in the time of 5.0s from the first 0.1s of the arrival time position of the Pn wave signal are taken, and Pn wave signal peak-to-peak amplitude values of J B area seismic events detected by K seismic stations in I filtering frequency bands are respectively calculated;
2.3.6 in the ground vibration waveforms of the I filtering frequency bands, noise data of Pn wave signals in 5.2s before reaching the time and in 5.0s long are taken, and noise peak-to-peak amplitude values of K seismic stations are calculated respectively;
2.3.7, respectively calculating signal to noise ratios of Pn wave signals of J B area seismic events monitored by K seismic stations in I filtering frequency bands according to the Pn wave signal peak-to-peak amplitude obtained in the step 2.3.5 and the noise peak-to-peak amplitude obtained in the step 2.3.6, wherein the Pn wave signal peak-to-peak amplitude of the Pn wave signals with the signal to noise ratio being more than or equal to 5.0 is the Pn wave signal amplitude of J B area seismic events monitored by K seismic stations in different filtering frequency bands.
6. The method for evaluating the threshold value of monitoring the magnitude of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 5, wherein the step 3.3 is specifically:
3.3.1, filtering L A area seismic signal waveforms monitored by M B area seismic stations to obtain L A area seismic event observation waveforms monitored by the M B area seismic stations;
3.3.2, selecting an observed waveform of an A-region seismic event on one of the B-region seismic stations, and marking the arrival time position of the Lg wave seismic phase;
3.3.3 setting a velocity window according to the Lg wave vibration phase, calculating the Lg wave amplitude value by using the velocity window to measure the time window length TL Lg ；
3.3.4 measuring the starting time of the Lg wave vibration phase arrival time and the length of TL on the observed waveform of the seismic event of the area A Lg Maximum peak-to-peak amplitude of Lg wave signals;
3.3.5, correcting the maximum peak-to-peak amplitude of the Lg wave signal of the seismic event in the area A obtained in the step 3.3.4 to the signal amplitude at the reference distance according to the Lg wave quality factor in the area B by the following formula to obtain corrected Lg wave observation signal amplitude:
wherein A is Lg (delta, f) is the time of arrival of the Lg wave vibration phase with the starting time of the observed waveform of the A area earthquake event and the length of TL Lg Maximum peak-to-peak amplitude, A, of Lg wave signal of (2) Lg (Δ 0 F) is the corrected Lg wave observed signal amplitude, representing the amplitude of the seismic signal where the dominant frequency f of the Lg wave is at the mid-seismic distance Δ; f is the center frequency of the filter passband, delta is the center distance of the epicenter, delta 0 For reference distance, delta-delta 0 For the difference of the epicenter distance, U is the propagation average speed of the Lg wave, and Q (f) is the quality factor of the Lg wave with the frequency f;
3.3.6 calibrating the correction coefficient of the A-area seismic event according to the gazette magnitude of the A-area seismic event and the corrected Lg wave observation signal amplitude obtained in the step 3.3.5, and calculating the Lg wave magnitude mb of the A-area seismic event on one of the B-area seismic stations according to the following formula Lg ：
mb Lg ＝5.0+log 10 (A Lg (△ 0 ,f)C(f))
Wherein C (f) is a correction coefficient of the A-region seismic event;
3.3.7, repeating the steps 3.3.2-3.3.6 until the Lg wave magnitudes of L A area seismic events on M B area seismic stations are obtained;
3.3.8, respectively calculating the average value of the Lg wave magnitudes of the A-area seismic events on the M B-area seismic stations to obtain the Lg wave station equivalent magnitudes of the L A-area seismic events.
7. The method for evaluating the monitoring magnitude threshold of the wave signal of the seismic station Pn based on the reciprocity principle according to any one of claims 3 to 6, wherein the method comprises the following steps: in step 5, the nominal magnitude of Pn wave signal monitoring of the seismic event in the area a monitored by the area B seismic station is calculated by the following formula:
wherein,monitoring nominal magnitude, δmb, for Pn wave signals of seismic events in region A in the ith filter band monitored by a region B seismic station i Is the difference between the equivalent amplitude of the Lg wave station of the A area seismic event and the amplitude of the Pn wave station in the ith frequency band of the A area seismic event monitored by the B area seismic station, c is the source radiation intensity coefficient, p is the monitoring signal to noise ratio, i A noise Noise floor amplitude in the ith filter band for the seismic station in zone A, +.>A Pn wave signal magnitude gauge function of the B region; />Is of the magnitude +.>Magnitude coefficient of earthquake in ith filtering band, +.> Is of the magnitude +.>Source spectrum corner frequency of the earthquake.
8. The method for evaluating the monitoring magnitude threshold of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 7, wherein the method comprises the following steps of: in step 6, the threshold value of the monitoring magnitude of the Pn wave signal of the earthquake in the shell of the area B by the area a earthquake station is calculated by the following formula:
wherein, i mb th the magnitude threshold is monitored for Pn wave signals of an earthquake in the B zone shell in the ith filtering band for the a zone seismic station.
9. The method for evaluating the monitoring magnitude threshold of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 8, wherein the method comprises the following steps of: in step 1, the selection principle of the region B is as follows:
the epicenter distance from region AThe Lg wave attenuation is the same as the area A, and the earthquake stations are dense;
in step 2.1, the selection principle of the seismic event in the area B is as follows:
the number of the earthquake stations for monitoring the earthquake event is more than 50, pn waves and Lg waves are complete in earthquake phase development, and the range of the earthquake magnitude is more than 2.5 levels.
10. The method for evaluating the monitoring magnitude threshold of the wave signal of the seismic station Pn based on the reciprocity principle according to claim 9, wherein the method comprises the following steps: in step 2.3, the selection principle of the band-pass filter is as follows:
the passband of the bandpass filter evaluates relevant signal frequency selections according to regional seismic monitoring capability;
in step 3.1, L of the a-zone seismic events are repeating seismic clusters.
Priority Applications (1)
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