RU2395820C2 - System to detect killer quake signs - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: proposed system consists of ground and underwater modules. Underwater module consists of streamer hydrophone and hardware modules. Said hardware module comprises filtration and amplification unit, ADC, data reception-transmission unit and power supply arranged in strong housing. In operation of the system, hydrophone module signal comes to filtration and amplification unit to get digitised in ADC and fed to ground hardware module data processing unit. Ground hardware module incorporates also power supply, satellite communication subscriber station, antenna and analysis and decision making unit. Decision making unit can lock SLF-amplitude modulation signal.

EFFECT: higher validity.

5 dwg

Description

The invention relates to the field of seismology and may find application in national systems for observing geophysical measurements for predicting earthquakes.

At present, many works on earthquake prediction have been published. Consider some of them that we have chosen as analogues.

In [1], a method for earthquake prediction is considered, based on measurements of at least three prognostic stations equipped with geophones, which measure the amplitude and repetition frequency of pulse signals, the slew rate and the duration of pulse signals and select anomalous signals from the data obtained. Then measure the duration of the stage of increase, decrease and fading of the intensity of the anomalous signal at each forecast station.

In [2], a method of earthquake control is considered, which includes recording seismic signals corresponding to seismic events of certain energy classes, on the surface and inside it in the bottom hole of the proposed focal area. For each energy class, the statistical parameter S = Nk · ln (N / Nk) is determined, where Nk is the number of seismic events of a certain energy class k, N is the total number of observed seismic events. The measurement range is divided into four frequency measurement sub-ranges: 100-500, 500-1000, 1000-1500 and 1500-2000 Hz. The anomalous behavior of the monitored factors, as a harbinger of an upcoming event, is defined as the corresponding increase in the recorded amplitude levels of the seismic signal by a factor of two compared to the background values of the seismic field while lowering the parameter S.

In [3], a method is considered for determining earthquake precursors, including the recording of seismic oscillations, the use of digital records of seismic oscillations in real time, which are converted into statistical diagnostic parameters. Diagnostic parameters R = А _в / А _н , where А _н , А _в are the amplitudes of vibrational velocities of seismic oscillations in the low-frequency and high-frequency regions of the amplitude-frequency spectra, respectively. Upon reaching the diagnostic parameters of values exceeding the maximum permissible values, an alert signal is issued about the possibility of a seismic event.

In [4], a forecast based on data from seismic sensors and a geophone is considered. In the phase of occurrence, the maximum of activation is observed 4-6 months before the main shock (for acoustic radiation measured in the well using a geophon in the frequency band 500-1000 Hz) and for high-frequency seismic noise (measured using geophones in the frequency band 30-50 Hz) . At the climax phase (2-3 months before the main event), along with a decrease in high-frequency seismic noise and acoustic radiation, an increase in the number of micro-earthquakes is observed.

In [5], a method for earthquake prediction is considered, based on the registration of ultralow seismic waves with a period of the order of several thousand seconds; on a rectangular test site consisting of N ² seismic receivers spaced apart by a distance of λ / 4, the signal amplitude with a duty cycle of less than 1 s is measured where λ is the seismic wavelength.

It was assumed in [6] that ultralow-frequency seismic waves are commensurate with the equator length, i.e. the reach is the entire earth's surface. In the space of propagation of such waves, it is possible to distinguish sections of compression and rarefaction, as well as a section of a continuous, almost linear change in the density of the medium. The dispersion of rock density leads to a dispersion of the propagation velocities of lithospheric waves, and the latter leads to a change in the shape of the oscillatory process. In the frequency language, the process considered is equivalent to parametric modulation of the seismic background. The method of earthquake prediction [6], based on the registration of a seismic background wave in the form of a continuous sequence of discrete samples of the signal amplitude, calculates the spectrum, autocorrelation functions, determines the correlation intervals using two spatially separated stations. When ultra-low frequency modulation signals are detected, the direction to the focus is determined and an earthquake prediction is given.

All of the above analogs make their predictions based only on data from seismic stations, firstly, based on the statistical properties of weak earthquakes [1-4] as precursors of strong earthquakes, and secondly, based on the ultra-low-frequency modulation effect [5-6] of seismic background excluding data from sonar stations. This fact is a significant drawback of the analogues considered above by the authors.

It is desirable to carry out control over the seismic situation in the region both by the traditional method using land-based seismic stations, and by the use of hydroacoustic stations installed in water bodies (not necessarily deep-sea), which is the subject of the invention.

The experimental data by the authors say that at low frequencies, the hydrophone (acoustic channel) transforms seismic oscillation almost linearly into an acoustic signal. So a hydrophone at low frequencies can replace the seismic receiver. The second advantage of the hydrophone is related to the width of the frequency band: the hydrophone has a significantly wider bandwidth than the seismic channel.

It is known that the wider the frequency band, the shorter the pulse duration. This fact will significantly simplify the detection of impulses (weak earthquakes), the statistics of which are among the essential signs of the foregoing earthquake precursors. Thus, the advantage of the acoustic channel in comparison with the seismic channel in the problem of fixing weak earthquakes following each other in the interval of 1 min or less is noticeable. The statistical parameters of weak earthquakes are known to be important prognostic parameters of strong earthquakes.

It should also be noted that the detection of ultra-low-frequency seismic precursors of earthquakes can be carried out (due to non-linear and parametric mechanisms of transformation of seismic waves into an acoustic wave, it can be converted into ultra-low-frequency oscillations of the envelope of the acoustic channel signal) by detecting ultra-low-frequency amplitude modulation of the hydroacoustic background.

To register sonar signals are used sonar stations installed on the bottom of the reservoir. Here, by a hydroacoustic station we mean a station equipped with a hydrophone, providing continuous registration of signals in the frequency band 0.5-2000 Hz.

The aim of the invention is to increase the reliability of methods for predicting earthquakes using hydroacoustic devices (stations) installed on natural and artificial reservoirs (lakes, ponds, etc.) in a seismically active zone. Most bodies of water have shallow depths (from several meters to tens of meters) and are small in size and, as a result, are not navigable. Therefore, the staging and sampling of the station can be performed manually without the use of mechanisms from the board of motor boats. As a result of this, the weight and size characteristics of the station should have the following parameters: station weight should not exceed 50 kg; station size - not exceed 1 m. Stations are designed to operate at depths of up to 100 m.

The hydroacoustic device consists of underwater and ground modules. The underwater module (Fig. 1) consists of hardware and hydrophone modules. The underwater equipment module includes a robust housing 1, frame 2, a secondary power source 17 (Fig. 3) (operating voltage 9 V), a filtering and amplification unit 14 (limits the frequency range of 0.5-2000 Hz), a 14-bit ADC 15 with a given quantization frequency of 4800 Hz, the data receiving and transmitting unit 16. The hydrophone module (Fig. 2) 4 is mounted on a cable 6, stretched using a ballast 7 and a float 5. Data from the hydrophone via cable 3 is fed to the input of the filtering and amplification unit . The cable 3 is inserted into the hardware module using a sealed cable entry. The signal limited in the band of 0.5-2000 Hz is digitized using an ADC, which is then fed through a cable to the transmitting unit 3 into the hardware module 8 (figure 2) of the ground module. The ground-based hardware module 8 includes: an analysis and decision-making block 19 (Fig. 3), a transmit-receive block 18, a primary power supply 21 (operating voltage 12 V), a subscriber station of the satellite communications system (CCC) “Messenger” 20. Processed information on cable 3 through the antenna CCC "Messenger" 9 is transmitted to the data center. The Gonets SSS antenna 9 is mounted on the mast 10, the stability of the mast is ensured by stretch marks 12 and the bed 13. On the territory of Russia in the winter and spring, especially in the Far Eastern and Northern regions, water bodies are covered with ice, therefore, to protect cable 3 from gusts during contact with the edges of the ice cable is laid in special channels 11.

Let us consider in more detail the analysis and decision-making block 19. Figure 4 shows the structural diagram of the analysis and decision-making block of the sonar station. Pos. 18 correspond to the transmit-receive unit, where digital information is received from the underwater module. Pos. 22 and 33 correspond to low-pass and low-pass filters (high-pass filters) with cut-off frequencies of 100 Hz, i.e. the frequency range of 0.5-2000 Hz is divided into two frequency sub-ranges of 0.5-100 Hz and 100-2000 Hz. Pos. 24-25 correspond to digital low-pass and high-pass filters with cut-off frequencies of 10 Hz for the formation of two frequency subbands, respectively: 0.5-10 Hz (infra-low-frequency acoustic channel, which corresponds to a low-frequency seismic channel); 10-100 Hz (low-frequency acoustic channel, which corresponds to a high-frequency seismic channel); Pos. 28-31 correspond to digital band-pass filters (PF) in the frequency bands: 100-500 Hz; 500-1000 Hz; 1000-1500 Hz; 1500-2000 Hz. Pos. 23 corresponds to a decimation unit of time samples, where levels are summed over 16 consecutive time samples, the sum of which represents the level of a new time sample. The new time count, as can be seen, is the thinning of the time scale by 16 times, i.e. corresponds to a quantization frequency of 300 Hz = 4600 Hz / 16. Pos. 26 and 32 correspond to the analysis blocks that implement the transformation of the source data and the corresponding search for the statistical parameters described in [1-4] and the search for ultra-low-frequency amplitude modulations according to [5, 6]. Since the analysis unit 26 analyzes weak impulse signals (weak earthquakes), this unit is put into operation as follows. At the output of the low-frequency seismic channel (infra-low-frequency acoustic channel) (pos. 24), decimation is performed in the decimation unit (pos. 34), i.e. levels of 10 consecutive time samples are summed, the sum of which represents a new time sample. This corresponds to a sampling frequency of 30 Hz. In the threshold device (pos. 35), when the current level (in absolute value) of the sample of background noise is exceeded (the integral level of the background is averaged over 1800 time samples, which corresponds to a time interval of 60 s), a command to enable the analysis unit (pos. .26), at the same time the threshold device (pos. 35) is switched off. The analysis unit works continuously for 60 s, after which it is turned off, and the threshold device (pos. 35) is turned on. The analysis unit pos. 26 calculates the number of pulse signals for a time period of 6 hours. Estimates the ratio of the envelopes of the signal levels of the low-frequency channel 0.5-100 Hz to the band of 10-100 Hz, the ratio of the envelope of the acoustic channel in the frequency band of 100-2000 Hz to the envelopes in the frequency bands of 500-1000, 1000-1500 and 1500-2000 Hz. In the analysis block (pos. 32), the envelopes of signal levels in the frequency bands 0.5–10, 10–100, 100–500, 500–1000, 1000–1500, and 1500–2000 Hz are averaged over a time interval of 20 min. If a periodic trend with a period of more than 60 minutes is detected, the moment of detection of amplitude modulation is recorded and the corresponding code is generated (the code contains information divided into intervals by modulation periods). It does not consider periods with lengths of 6, 12 and 24 hours associated with tidal phenomena. Thus, the analysis unit (pos. 35) operates in a cyclic mode, and the analysis unit (pos. 32) operates in a continuous mode. When prognostic parameters are detected, an appropriate earthquake prediction code is generated with a fixation of the moment in time for further data transmission. Pos.27 - information transfer unit, designed for the operational preparation and transmission of information to the subscriber station of the CCC “Messenger” 20 for further operational transmission via CCC to a stationary data center.

The hydroacoustic station is sampled for preventive work using a submerged halyard, one end is tied to frame 2, the other end is washed ashore.

In the synchronous operation mode of several stations (in the case of operation of at least 4 stations, the epicenters of earthquakes are determined), they must be equipped with highly stable quartz watches. These stations can be installed on one or several bodies of water, spaced tens or hundreds of kilometers.

Consider the experimental material obtained on August 18, 2006 during a full-scale test of the underwater module of a hydroacoustic station. In mid-August 2006, a sonar station was installed north of the city of Kholmsk (the western coast of Sakhalin) in the area of water intake on the Malka River.

August 18, 2006 at 2:20:37 local time in the south of O. Sakhalin in the area of Nevelsk at a point with coordinates 46.583 ° N, 141.857 ° E at a depth of 32.3 kilometers an earthquake with a magnitude of ~ 5.6 on the Richter scale, recorded by many seismic stations in the world, including the city of Yuzhno-Sakhalinsk, occurred. Figure 5 shows the signalograms of an earthquake recorded by a sonar station in the band of 1.5-50 Hz and digitized with a quantization frequency of 200 Hz. In the signalogram of the earthquake, the arrivals of both P and S waves are well recorded.

The use of hydroacoustic components of the seismic signal complement and significantly enhance the effectiveness of various methods of earthquake prediction proposed in [1-6].

Information sources

1. Morgunov V.A. A method for the operational prediction of earthquakes, tectonic and technogenic movements. RF patent No. 2106001, G01V 9/00, 1996

2. Khamidulin Y. N. Earthquake control method. RF patent No. 2102780, G01V 9/00, 1996

3. Trofimov RS, Shahramanyan MA, Makhutov N.A., Nigmetov G.M., Petrov V.P. A method for determining medium-term earthquake precursors. RF patent No. 2233461, G01V 9/00, 2002

4. Karryev B.S., Kosarev V.G., Kurbanov M.K., Ashirov T.A. Earthquake prediction method, G01V 1/00, 1995

5. Davydov V.F., Scherbakov A.S., Komarov E.G., Malkov Y.V. Burkov V.D. Earthquake prediction method. RF patent No. 2130195, G01V 1/00, 1998

6. Davydov V.F., Shahramanyan M.A., Nigmetov G.M., Shalaev B.C., Shipov A.V. A short-term earthquake prediction method. RF patent No. 2181205, G01V 9/00, 2000

Claims (1)

A system for determining the precursor of strong earthquakes, consisting of underwater and ground modules, the underwater module consists of a hydrophone module and a hardware module, including a filtering and amplification unit, an ADC, a data transmitting and receiving unit, a power supply located in a durable case, and the signal from the hydrophone module it enters the filtering and amplification unit, is digitized in the ADC and, through the data receiving and transmitting unit, is supplied to the data receiving and transmitting unit of the ground-based equipment module, also equipped with a power supply, a subscriber station of a satellite communication system, an antenna, and a decision analysis and decision unit configured to detect the occurrence of ultra-low frequency amplitude modulation of the hydroacoustic signal.

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