RU2405176C2 - Drift buoy hydroacoustic station to reveal signs of large earthquake and tsunami - Google Patents

Abstract

FIELD: mining.

SUBSTANCE: proposed station comprises hardware module, satellite communication and navigation system unit, analyser unit, control units and power supplies. Said station incorporates vertical string of hydrophones. Analyser unit can detect super low-frequency amplitude modulation of hydroacoustic signals, i.e. signs of large earthquakes, isolate pulsed signals by amplitude, repetition rate, duration and speed of seismic wave edge rising and that of T-waves of large earthquakes, i.e. signs of tsunami.

EFFECT: higher validity of forecast.

4 dwg

Description

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

With the advent of the satellite communication system (CCC), especially the low-orbit CCC “Gonets” as a part of autonomous hydrophysical stations [1], the satellite navigation system “Glonass”, buoy stations drifting on the sea surface will become widespread [2].

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

In [3], an earthquake prediction method 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 [4], a method of earthquake control is considered, including the registration of 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 [5], 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 = A _a / A _n, where A _n, A respectively _in seysmokolebany amplitude vibration in low-frequency and high-frequency areas of the amplitude-frequency spectra. 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 [6], a forecast based on data from seismic sensors and geophones 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 borehole using a geophone 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 [7], a method for earthquake prediction is considered, based on the registration of ultra-low seismic waves with a period of the order of several thousand seconds, and a signal amplitude with a duty cycle of less than 1 is measured at a rectangular polygon consisting of N ² seismic receivers spaced apart by a distance of λ / 4. c, where λ is the seismic wavelength.

It was assumed in [8] that ultralow seismic waves with a period of several thousand seconds are commensurate with the length of the earth's equator, 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 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. In the earthquake prediction method [8], based on recording a seismic background wave in the form of a continuous sequence of discrete samples of the signal amplitude, the spectrum, autocorrelation functions are calculated, and correlation intervals are determined 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. This phenomenon is observed 5-7 hours before the earthquake.

All of the above analogs build their predictions based only on data obtained by seismic stations, firstly, based on the statistical properties of weak earthquakes as precursors of strong earthquakes, and secondly, based on the ultra-low-frequency modulation effect of the seismic background. No sonar data is used here. This fact is a significant drawback of the analogues considered above by the authors.

The use of hydroacoustic components of the seismic signal complement and significantly enhance the effectiveness of various methods of earthquake prediction proposed in [3–8]. We can say that hydroacoustic methods for predicting earthquakes can be implemented, especially when working in regions washed by oceans and seas. Particularly relevant for the Sea of Okhotsk, surrounded by seismically active regions of Kamchatka, the Kuril Islands, Hokkaido and Sakhalin.

Note that in the Sea of Okhotsk, the underwater sound channel (CCP) is located, depending on the season, at shallow depths of 60-80 m. Acoustic T-waves generated from the underwater slopes of the islands of the Kuril-Kamchastka Trench, Sakhalin, Hokkaido and the Kamchatka Peninsula are captured from the very beginning PZK. Therefore, T-waves mainly propagate in slam-shut devices until the receivers are reached. Moreover, if the hydrophone is also located in the slam-shut device, then the signal loss during propagation will be minimal. Under such conditions, T-waves of weak earthquakes can be detected even in the absence of seismic P-, S-waves. As an example, figure 1 shows the waveform and envelope of the T-wave, where there are practically no seismic P-, S-waves (the P-wave exceeds the background levels by 3-4 dB). When developing prognostic parameters using the technology proposed in [3-6], the seismic component (P-S-waves) of an earthquake of this earthquake cannot be used here, since they are hidden against the background of interference. For such cases, sonar components can and should be used. The use of the acoustic component in prognostic tasks allows telemetric monitoring (for earthquake prediction) using hydroacoustic stations installed on the shelf of Sakhalin Island beyond the region covering seismically active areas: Kamchatka, Kuril Islands, and Hokkaido Island.

Thus, the use of the T-wave in forecasting problems of strong earthquakes using the technologies proposed in analogues [3–8] is not only possible, but necessary. Firstly, there is the possibility of using hydroacoustic antennas to detect weak signals (for earthquakes with M≤2 points); secondly, it is possible to study hydroacoustic background characteristics for detecting ultra-low-frequency amplitude modulations, which will make it possible to use the technologies described in [3–8].

Strong earthquakes are in a certain way connected with tsunami waves. Underwater earthquakes with a magnitude of M≥7 and an epicenter located near the seabed are considered potentially tsunamigenic [9]. Tsunamigenic earthquakes can cause both elastic vibrations of the seabed and its discontinuous movements with a vertical displacement component. The presence of the vertical displacement component causes the generation of tsunami waves, as well as the effective generation of hydroacoustic T-waves in the water layer due to the formation of the acoustic Mach cone by a discontinuity moving at a speed exceeding the phase velocity of sound in water. The fact of registration in the aquatic environment of high-frequency sound waves due to the large attenuation of these frequencies in the soil may indicate processes developing in the very top of the seabed. High-frequency sonar signals [9] (with frequencies of 100-400 Hz) captured by an underwater sound channel (CCD) can travel a distance of several thousand kilometers without significant attenuation, forming the high-frequency part of the T phase. The combination of these properties (strong attenuation in the rocks that make up the bed of the ocean, and the ability to propagate over significant distances in the CCD) leads to the fact that hydroacoustic waves with frequencies of 100-400 Hz are an independent source of information about the tsunamigenicity of an underwater earthquake.

The criterion for making a decision on the tsunamigenicity of the underwater earthquake that has occurred can be the fact of registering oscillations in the indicated frequency range, understood as the excess of the ratio of the T-phase signal intensity in the frequency range 100-400 Hz to the average intensity of background noise in this region of a certain threshold value [9].

There is another way to determine the tsunami precursor [10], which includes placing groups of devices for recording hydroacoustic signals at deep observation horizons in the coastal zone located at depth horizons that are multiples of 25 m, with a maximum observation horizon of 100 m, registration of hydroacoustic signals is performed with phase separation type P, S and T. Recommended frequency range is 30-100 Hz.

The more powerful the earthquake with the epicenter near the seabed, the wider the region of T-wave generation, i.e. there will be many T-wave maxima with significant energy levels, which in a certain way serve as an indicator of tsunami wave excitation.

An addition of the prognostic parameters proposed in [9] is proposed, namely: to analyze the relations of T-wave levels in the frequency band 100-500 Hz relative to the T-wave level in the frequency band 100-2000 Hz; analysis of the relations of T-wave levels in the frequency band 10-100 Hz to the T-wave level in the frequency band 0.5-100 Hz; analysis of the relationship of the duration of the T-wave in the frequency band 10-100 Hz to the duration of the T-wave in the frequency band 0.5-100 Hz.

Thus, the problems of forecasting strong earthquakes are significantly related to the problems of forecasting tsunami waves, so these questions can and should be linked into a single technological complex.

An interesting option is the installation of a buoy hydroacoustic station in the middle of the Sea of Okhotsk, where there are virtually no ice fields all year round. With the advent of the GLONASS satellite navigation system (SNA) in Russia, drifting buoy sonar devices (DBGAS) are widely used. In this case, it is possible to monitor the seismic situation in Kamchatka, the Kuril Islands and Sakhalin Island.

It is proposed to install drifting buoyal hydroacoustic stations (DBGAS) equipped with a vertical 8-element equidistant garland of hydrophones (the distance between hydrophones is 25 m) installed in the underwater sound channel (the total signal is recorded, i.e. we form a linear antenna with a radiation pattern oriented along the horizon ) on the surface layer of the Sea of Okhotsk. The frequency range of 0.5-2000 Hz, although as a garland antenna can be considered in the frequency range of 30-2000 Hz.

Drifting buoy sonar station (BGAS) is designed for long-term observations in the ocean. Such buoys can be installed in the seas and oceans. Equipped with a daisy chain of DBGAS hydrophones, they regularly measure and transmit the processing results to a data processing center (DPC) via a radio channel, including via the Gonets satellite communication system. For DBGAS, the GLONASS satellite navigation system is provided.

DBGAS consists (Fig. 2) of a sealed cylindrical hardware module DBGAS 1 as part of a control unit 3, a power supply 4. Outside, under the radio-transparent cap 5, an antenna of the satellite communications system “Gonets” and navigation “Glonass” 6 with a subscriber station 7, flashing light a beacon 8 and a radio antenna 9, which are mounted on a float 10 made of syntactic material. The signal cable 11 is introduced into the hardware module 1 using a pressure-tight input 2-1; to insure the signal cable from jerks, safety halyards 13 are used, which are attached to the signal cable 11 using special clamps 14. In series, all eight elements of the “garland” of hydrophone modules 2 are connected to the signal cable (Fig. 3).

Power supply 4 is assembled from MPL-200 lithium batteries, which provide continuous operation of DBGAS for at least 100 days.

The float 10, made of syntactic materials, provides DBGAS necessary buoyancy.

The subscriber station of the Gonets satellite communication system 7, using the antenna 6, transmits hydrophysical and service information to a data processing center (DPC), and the Glonass navigation system determines the location of the DBGAS. The light beacon (SM) is turned on in the dark (turned on by the LED) and operates in a cyclic mode, with a frequency of 30 s.

Using the radio antenna 9, a radio is exchanged between the DBGAS and the supply vessel. At the same time, the radio antenna plays the role of an active radar transponder.

Control unit 3 is a microcontroller that controls all DBGAS devices according to a given program or by a command received via a radio channel.

BU 3 (Fig. 2, item 17) turns on (turns off) a light beacon (SM) 8, a subscriber unit of a satellite communications and navigation system (CCCH) 7. BU 3 through antenna 9 is ready to reflect the location signal from a standard radar, allowing clearly mark the location of the station on the sea surface.

In Fig. 3, pos. 2 corresponds to a hydrophone module of a garland of hydrophones 2. The hydrophone module 2 is a hydrophone with a preamplifier. The station is equipped with a vertical equidistant 8-element garland of hydrophones (a total signal is recorded, i.e. a linear antenna is formed with a radiation pattern oriented along the horizon) installed in an underwater sound channel (CCD). To align the garland of hydrophones in line, a load is used (item 12). The frequency range of 0.5-2000 Hz, as a garland antenna of hydrophones 2 is used in the frequency range of 30-2000 Hz.

Figure 4 shows the structural diagram of the sonar station. The analysis block 17 consists of two components: pos. 17-1 correspond to the signal conversion block, where the signal is amplified and limited in the frequency band 0.5-2000 Hz 18, digitized using an 8-channel analog-to-digital converter 19 with a quantization frequency of 4800 Hz, Further, the summation of the signals 20 for the formation of the antenna with a diagram oriented horizontally, and pos. 17-2 correspond to the analysis and decision making unit. Here, positions 21 and 22 correspond to the low-pass (low-pass) and high-pass (high-pass) filters with a cut-off frequency 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.

Thinning out of samples 23 is performed 16 times by summing 16 consecutive time samples, the sum of which will correspond to the current time sample. At the output from pos.23, we have a time series with a sampling frequency of 300 Hz.

Pos.24-25, 28-31 correspond to digital band-pass filters, respectively, in the frequency band: 0.5-10 Hz (infra-low-frequency sonar channel); 10-100 Hz (low-frequency sonar channel); 100-500 Hz; 500-1000 Hz; 1000-1500 Hz; 1500-2000 Hz.

Further decimation of time samples corresponding to a sampling frequency of 300 Hz by a factor of 10 is performed by summing 10 consecutive time samples, the sum of which will correspond to the current time sample. At the output from pos. 33, we have a time series with a sampling frequency of 30 Hz.

Pos. 34 is a threshold device that starts analysis block 26, which implements an algorithm for searching for statistical parameters of weak earthquakes that precede strong earthquakes, considered in analogues [3-6]. The threshold device 34 starts the analysis unit 26 when the current signal value is exceeded by 6 dB, the averaged predetermined background level, after which the threshold device itself is turned off. When prognostic statistical parameters are detected, a certain code is generated in the shaper 27.

Analysis block 26, which implements an earthquake prediction algorithm, considered in analogues [3-6] from the moment it was turned on, analyzes the statistical parameters of weak earthquakes for 1 min. After 1 min, block 26 is turned off and issues a command to turn on threshold device 34.

Analysis block 32, which implements the earthquake prediction algorithm considered in taxes [7–8], works continuously and searches for amplitude modulations, with modulation periods from 1000-10000 s. Periods corresponding to periods of tidal currents of 6, 12 and 24 hours are excluded from consideration. When detecting amplitude modulation with a certain period, a certain code is generated in the shaper 27.

The analysis unit 37, which implements the analysis of the T-waves of strong earthquakes using the tsunami forecasting algorithms considered in [9-10] and proposed by the authors to detect the prognostic parameters of tsunami waves, runs in a cyclic mode triggered by the threshold device 38. The threshold device 38 starts the block analysis 37 when exceeding the current level modulo a signal of a strong earthquake by 10 dB of a given average background level. In this case, the block 38 is turned off. Block 44 analyzes the relationships 10 log x ₁ ² / x ₂ ² , 10 log t ₁ / t ₂ , 10 log x ₃ ² / x ₄ ² , 10 log t ₃ ² / t ₄ ² , where x ₁ ² , x ₂ ² , x ₃ ² , x ₄ ² is the sum of energy, respectively, in the frequency band 0.5-100, 0.5-10, 100-2000, 100-500 Hz during the time at which the signal level modulo exceeds the averaged predetermined background level by 6 dB. Moreover, if the time period is less than 1 min, the result is reset and the analysis process stops. A command is issued to start the threshold device 45. The time intervals t1, t2, t3, t4, during which the corresponding signal levels in the frequency band 0.5-100, 0.5-10, 100-2000, 100-500 Hz, exceed the specified background levels by 6 dB Upon reaching certain values of the relations, a certain code is generated in the shaper (pos. 27. Fig. 4) and transmitted to the subscriber station of the CCC "Messenger" (pos. 7. Fig. 2). In addition, the code contains the following service information: current time, location parameters of the determined GLONASS satellite navigation system.

Information is transmitted to the processing center using the subscriber station 7 and antenna 6 of the “Messenger” satellite communication system.

In the earthquake and tsunami forecasting system, it is proposed to use at least 4 spatially separated and synchronously operating DBGASs simultaneously. Replacement of DBGAS power sources is carried out at least 100 days. When replacing the sources, preventive maintenance of DBGAS can be carried out, after which re-setting is performed. Re-setting DBGAS can be performed at other geographical coordinate points.

Information sources

1. Malashenko A.E., Malashenko A.A., Derevnin V.A., Leonenkoa R.V., Sokhatyuk M.Yu. Equipment for transmitting hydrophysical information data using a satellite communication system. RF patent for PM No. 75117, Н04В 1/00, 03/15/2005

2. Malashenko A.E. Perunov V.V., Filimonov V.I., Rozhkov B.C. Autonomous displacing hydrophysical station. RF patent for ПМ №61245, G01S 1/00, 11/01/2005

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

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

5. 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

6. Karryev B.S., Kosarev V.G., Kurbanov M.K., Ashirov T.A. A method for predicting earthquakes. Patent No. 1389473, G01V 1/00, 1995

7. 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

8. 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

9. Stavrov K.G., Paramonov A.A., Anosov B.C. A method for determining the tsunami precursor. RF patent No. 2292569, G01V 1/38, 2005

10. Ivanov V.V., Lopatnikov S.L., Rock V.E. A method for establishing tsunamigenicity of an underwater earthquake. RF patent No. 1584585, G01V 1/00, 1995

Claims (1)

Drifting buoy hydroacoustic station for determining the precursors of strong earthquakes and tsunamis, equipped with a vertical garland of hydrophones, including a hardware module, a satellite communications and navigation unit, an analysis unit, a control unit and power sources, an analysis unit configured to detect ultra-low-frequency amplitude modulations of hydroacoustic signals - harbingers of strong earthquakes, as well as with the possibility of selecting pulsed signals in amplitude, repetition rate, length nosti and slew rate of the front of the seismic waves and T-waves of strong earthquakes - precursors of the tsunami.

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