RU2462734C1 - Method for determining probability of catastrophic phenomena - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: method of determining probability of catastrophic phenomena, involving measuring geophysical field parameters in the monitored zone and using the obtained data to determine the probability of catastrophic phenomena via continuous measurement with detection of fluctuation of the measured parameter, wherein variation of the magnetic field is further measured at frequencies 0.05-0.4 Hz, and the probability of a catastrophic phenomenon is determined from change in amplitude of the zero mode, wherein to increase accuracy and reliability of prediction, seismic signals are picked up in the frequency range of 0.003-20 Hz, wherein the tsunami wave pressure is detected at the bottom at frequencies lower than 0.01 Hz.

EFFECT: broader functional capabilities and higher accuracy of prediction.

Description

The invention relates to geophysics, and more specifically to methods for detecting the possibility of the onset of catastrophic phenomena mainly at sea, and can be used to solve the following fundamental problems:

studying the structure of the earth's crust in the waters of the oceans, studying the totality of the manifestation of geophysical fields in tectonic fault zones directly at the bottom of the ocean, studying the state of the marine environment in the bottom zone and its interaction with tectonic processes, geophysical monitoring of complex hydraulic structures, operational assessment of the seismic and hydrodynamic conditions of regions and prediction of possible seismic and environmental impacts, as well as early warning of earthquakes iah and tsunami.

A known method of detecting the possibility of the onset of catastrophic phenomena [1], including measuring the parameter of the geophysical field in a controlled area and judging by the data on the possibility of the onset of catastrophic events, in which measurements are carried out continuously, detect fluctuations of the measured parameter and when detecting sinusoidal oscillations of increasing frequency with amplitude , statistically significantly different from the background for the controlled area, and the period from 100 to 1,000,000 s, judge about the availability the onset of catastrophic events.

The disadvantage of this method is that it has a low reliability of the forecast, since they measure only one parameter of the geophysical field. In addition, the sinusoidal oscillations of the measured parameter when superimposed on them by anthropogenic acoustic and hydrodynamic noises can be both periodic and aperiodic, which requires the receipt of numerous arrays of the measured parameter to identify the amplitude, which is statistically significantly different from the background to achieve a positive technical result.

A known method of seismic micro-zoning [2], including the placement of the investigated and reference points of observation in areas with different engineering and geological conditions, registration of seismic vibrations from earthquakes from potentially dangerous and other focal zones, determination of the dynamic parameters of seismic vibrations and their variations in each studied observation point relative to the reference in a given frequency range of studies, in which, with the aim of increasing reliability by taking into account the lateral effect In addition to the heterogeneity of the rock base and deeper horizons of the geological section, three-component seismic vibrations are additionally recorded along an orthogonal profile network oriented to potentially dangerous focal zones, while the distance between the observation points does not exceed 1 / 3-1 / 4 of the wavelength of the most high-frequency seismic vibrations forming informative amplitude variations, and the distance between the profiles is 1 / 3-1 / 4 of the minimum spatial period of informative amplitude amplitudes iatsy highband seismic vibrations.

Performing a three-component registration of seismic oscillations along an orthogonal profile network oriented to potentially dangerous focal zones does increase the reliability of the classification of a possible earthquake. However, due to the fact that in the known method the determination of dynamic parameters is carried out by analyzing only the most high-frequency seismic vibrations, the achievement of the technical result, which consists in increasing the reliability of the forecast, is possible only with time-stable oscillatory processes and in the absence of interference caused by acoustic and hydrodynamic noise of natural and technogenic character. And if in land conditions with some assumptions this method has a positive technical effect, then in marine conditions it is practically not applicable.

In addition, a significant role in improving the accuracy of measuring signals, which establish the precursors of catastrophic phenomena, is the measurement base and the orientation of the measuring instruments relative to the source. For example, the spacing of meters at high and equatorial latitudes over 10 km when measuring electrical and magnetic components leads to large (up to 50%) errors in impedance measurements.

Similar disadvantages are also known methods and devices designed to register signals of seismic origin in marine conditions [3-19]. In the known methods, the significant value of the error is due to the fact that when processing the registered signals, the average signal propagation field is used. While the maximum deviations of the real field from the average differ precisely at the horizons of maximum gradients. In this case, the real field differs sharply from the ideal model. Under the influence of external factors using acoustic means of recording signals, a shadow zone is formed located in a strip from 5 to 16 km from the source. Moreover, its length in different directions is not the same and can differ by 5 times or more, and with an increase in the distance between the receiver and the signal source, the errors increase. For marine conditions up to 15 km, they are within 2 dB, then in the interval from 15 to 30 km there is a sharp increase to 6 dB. Subsequently, in the interval from 30 to 60 km, the error value monotonically increases to 7.5 dB.

In addition, the known methods are based on the registration of excitation of high-frequency sonar fields (the so-called phase T), which occurs over a large area and significantly depends on the topography of the bottom. Therefore, high-frequency hydroacoustic fields contain relatively less information per se about the forms of bottom movement in the epicenter of an earthquake.

The known shortcomings are deprived of the known method for detecting the possibility of the onset of catastrophic phenomena, which includes measuring the parameters of the geophysical field in a controlled area and judging by the data obtained on the possibility of the onset of catastrophic phenomena by continuous measurements with the detection of fluctuations of the measured parameter with the detection of sinusoidal oscillations of increasing frequency, with an amplitude that is statistically significant different from the background for the controlled area judged by availability the possibility of the onset of catastrophic phenomena, additionally measure the variation of the magnetic field at frequencies of 0.05-0.4 Hz, and the possibility of a catastrophic phenomenon is judged by a change in the magnitude of the zero mode [20]. New distinctive features in comparison with analogs, consisting in measuring the variation of the magnetic field at frequencies of 0.05-0.4 Hz, and the ability to judge the onset of a catastrophic phenomenon by a change in the magnitude of the zero mode, allow for earlier warning of impending earthquakes and tsunamis.

Known methods allow to achieve a technical result, which consists in increasing reliability, only in an isotropic field, since the nature of the decrease in the intensity of the sound signal with distance from the source in a horizontally inhomogeneous field (especially in the ocean) differs sharply from the same dependence in an isotropic field. Mesoscale inhomogeneities of the ocean (fronts, rings) dramatically rearrange the sound field, causing fluctuations in signal intensity up to 5 dB when predicting their range (D) up to 10 km. Therefore, for an effective forecast of hydroacoustic conditions in abnormal areas, a clear establishment of centers and boundaries, as well as determination of the parameters of disturbing formations, are necessary. Uncertainty in the calculation of the sound field by climatic data or the reference field is expressed in standard deviations of the real level from the reference at 4-9 dB, at D = 90 km, which corresponds to an error in the forecast of the expected range of hydroacoustic systems by 60-90%. The use of a single curve of the vertical distribution of the speed of sound for acoustic calculations is permissible only at short distances (up to 10 km), which is extremely rare in real conditions. By the magnitude and direction (sign) of the horizontal gradient along the signal propagation path, one can judge the degree of variability of the intensity of the sound field at the receiving horizon relative to a fixed source. For calculations of the acoustic field, the parameter is the sound velocity profile, which exactly matches the actual profile at the source location. However, when using regime information, the mean-square profile, as a rule, does not coincide with the actual one, which leads to additional random errors in the final result.

In addition, in the known methods, as models for the generation of tsunamis, water is considered as an incompressible liquid in which, in principle, acoustic fields cannot arise and propagate. Or vice versa, with a compressible fluid, the bottom is made absolutely rigid. In this case, low-frequency hydroacoustic fields are localized in the deep part of the ocean and cannot spread over large distances along oceanic waveguides. In a waveguide with a hard bottom, there can only be a discrete acoustic field in an aqueous medium at frequencies higher than critical. With decreasing water depth near the continents, the critical frequency decreases and the low-frequency hydroacoustic field should decay. More realistic is the model of a waveguide with an elastic bottom. In such a waveguide, along with a discrete sonar field in the aquatic environment, there is a continuous seismic field in the bottom massif (zero mode). Discrete field modes are interconnected through an elastic bottom. In fact, a single seismic-hydroacoustic field propagates in the waveguide. With a change in depth, an adiabatic transformation of the modes occurs in accordance with the new critical frequency. With a fairly smooth change in the steepness of the continental slope, the order of the modes decreases, as a result of which the first mode becomes zero, which propagates on land as a surface Rayleigh wave.

However, analysis of a number of recorded seismic signals during earthquakes (Levchenko DG Features of designing broadband bottom seismographs. / Oceanology, 2001, vol. 41, No. 4, p. 644) showed that the recorded signals include both bulk P and S waves, so and surface waves of Love and Rayleigh. In this case, dispersive long-period oscillations were recorded in the frequency range 0.0125-0.05 Hz, which are the low-frequency component of the Love wave, the high-speed Love wave recorded at the beginning of the dispersive train with minimal distortion, and 10 minutes after the arrival of Love waves, dispersive oscillations were observed which can be attributed to the Rayleigh wave complicated by interference with the Love wave (Voronina E.V., Levchenko D.G., Soloviev S.V., Sonkin A.V. Features of recording a strong Himalayan earthquakes at the bottom of the central part of the Atlantic Ocean and the dispersion of long-period Love waves. // Physics of the Earth. 1955. No. 2, pp. 3-17). This circumstance may introduce ambiguity into the forecast of a catastrophic phenomenon.

However, to implement the known method, seismographs are used in which to increase the life of the bottom seismic signals are recorded in the start-stop (standby) mode of the information storage device. The drive is controlled from a special device in which the average level of the seismic background is continuously determined for a large period of time and simultaneously for a small period of time, commensurate with the average duration of earthquake signals. The ratio of these levels is used as a threshold value for turning on the drive. Since such a control device has inertia, a limited amount of buffer memory is used to eliminate the loss of the initial part of the signal. If the threshold value is exceeded, the signal is overwritten from the buffer to the drive. Moreover, such a system only responds to earthquakes of a certain duration and intensity. At the same time, the duration of earthquake signals can leave from units of seconds (local weak earthquakes) to units of hours (strong distant earthquakes), and their intensity can vary by many orders of magnitude. On the other hand, such a system is highly susceptible to interference, which leads to false signal recordings. For example, periodic signals from the airgun used in seismic exploration, or signals from underwater sonar communication, as well as pulsed interference of biological origin, can completely fill the drive and lead to premature discharge of the power source.

In addition, the determination of the coordinates of the hypocenter of a sea earthquake and its magnitude using ground-based seismographs to assess the possibility of a tsunami is not accurate, since it is impossible to determine the nature of the bottom deformation at significant distances (large focal sizes), and a significant tsunami wave occurs only when vertical or inclined his movements. False alarms lead to large material losses, etc. (Levin B.V., Nosov M.A. Tsunami Physics. - M.: “Janus-K”, 2005. 360 p.).

In addition, the registration of seismic signals by one seismic station does not allow to determine the epicenter of the earthquake with the necessary reliability.

The objective of the proposed technical solution is to expand the functionality of known methods with increasing the reliability of the forecast.

The problem is solved due to the fact that in the method of detecting the possibility of the onset of catastrophic phenomena, including measuring the parameters of the geophysical field in a controlled area and judging by the data obtained on the possibility of the onset of catastrophic phenomena by continuous measurements with the detection of fluctuations in the measured parameter, magnetic field variations are additionally measured at frequencies 0.05-0.4 Hz, and the possibility of a catastrophic event is judged by a change in the magnitude of the zero mode, in contrast to stnogo method recorded seismic signals in the frequency range 0,003-20 Hz, the recorded pressure at the bottom of the tsunami waves at frequencies below 0.01 Hz.

A set of new features from the prior art has not been identified, which allows us to conclude that the claimed technical solution meets the patentability criterion of "inventive step".

The essence of the method is as follows.

A device for implementing the method consists of sensors of weak seismic signals (3 components), sensors of strong bottom movements (3 components), a digital multichannel information storage device, buffer memory, control device, surface relay buoy, sonar channel, satellite communication channel, magnetic field sensor and power source.

As a magnetic field sensor designed to measure the absolute value of the magnetic induction of the earth's field in marine areas to depths of 6000 meters, a sensor with a range of measured values of magnetic induction of 20,000-100,000 nT is used.

As seismic sensors, for the implementation of the proposed method, an acoustic seismic sensor is used, which is a three-component seismic-acoustic sensor, which is designed to convert the third derivative of soil vibrations into an electrical signal in the frequency range of 20-1000 Hz, the dynamic range of which is in the 1/3 octave and central band with a frequency of 30 Hz is not less than 60 dB, as well as an SM-5 seismic receiver (cycle meter), which includes three seismic sensors with a frequency range for recording seismic 0.05-0.4 Hz latter is present, the full dynamic range of at least 120 dB.

Broadband seismic channels (0.003–20 Hz) allow tsunami wave pressure to be recorded to the bottom (frequencies below 0.01 Hz).

The control device continuously analyzes the level of signals coming from the sensors of weak seismic signals, and in case of exceeding the threshold level includes sensors and channels for recording strong movements. Next, the control device analyzes the signals received from the sensors of strong movements (after they are turned on), determines the elements of the bottom movement and, in the case of significant vertical or inclined speeds of its displacement, generates and transmits an alarm signal through the communication lines.

Since the control device operates with inertia, in order to exclude the loss of the first arrivals of strong bottom motions, the signals from the outputs of the weak signal sensors are continuously recorded in the buffer memory and then used to determine the elements of the bottom motion and are recorded in the information storage device. The threshold level is determined by averaging over a long period of time the noise coming from the outputs of the sensors of weak signals.

Simultaneously with the registration of signals in the open sea, low-frequency fields are recorded by means of measuring equipment installed at seismic stations located on the shore or in the coastal zone in areas exposed to tsunami, for example, on the Kamchatka Peninsula, the Kuril Islands and Sakhalin Island. Measure the variation of the magnetic field at frequencies of 0.05-0.4 Hz.

The system of bottom seismographs is located in areas prone to strong earthquakes, which can cause tsunamigenic waves. In the event of a catastrophic earthquake (with a magnitude of about 8), bottom stations use strong motion sensors to detect bottom movement elements and transmit express information to the surface buoy using the sonar channel and via satellite or radio channels to ground control points. Such a system provides reliable registration and classification of tsunamigenic earthquakes and gives a timely (within a few minutes) warning of the danger of tsunamis.

The recorded seismic signals by bottom and coast stations are analyzed at ground control points and the possibility of a catastrophic event is judged by a change in the magnitude of the zero mode. At the same time, seismic signals are recorded in the frequency range 0.003-20 Hz if these signals exceed the threshold level, strong bottom movements are recorded, while determining the pressure of the tsunami waves to the bottom at frequencies below 0.01 Hz.

The proposed method, which consists in measuring at large distances from the epicenter of the earthquake, low-frequency hydroacoustic fields caused by bottom movements, allows remote sensing of tsunamigenicity of earthquakes. Since the propagation velocity of low-frequency hydroacoustic fields in the ocean is about five times higher than that of tsunami waves, they can serve as harbingers of the danger of tsunamis. At present, it has been theoretically proved that the excitation of tsunami waves by earthquakes in a compressible fluid should be accompanied by the generation of hydroacoustic fields in a wide frequency range, and their energy can exceed the energy of tsunami waves (Levin B.V., Nosov M.A. Tsunami physics. - M. : “Janus-K, 2005. 360 p.). In this case, low-frequency fields (F <1 Hz), like tsunami waves, are excited mainly due to vertical movements of the bottom in the epicenter of an earthquake. Excitation of high-frequency hydroacoustic fields (the so-called phase T) occurs on a much larger area and significantly depends on the topography of the bottom (Kadykov I.F. Acoustics of underwater earthquakes. 1986). Therefore, high-frequency hydroacoustic fields contain relatively less information per se about the forms of bottom movement in the epicenter of an earthquake. The presence of intense low-frequency acoustic fields in the tsunami center was confirmed experimentally during the earthquake of September 25, 2003, which occurred in the Pacific Ocean south of Hokkaido. The measurements were carried out using broadband bottom pressure sensors. The main energy of elastic vibrations was observed in the range of 0.05-0.4 Hz and exceeded the tsunami wave energy by about 300 times.

A specific implementation of the proposed method is based on a model of a waveguide with an elastic bottom. In such a waveguide, along with a discrete sonar field in the aquatic environment, there is a continuous seismic field in the bottom massif (zero mode). Discrete field modes are interconnected through an elastic bottom. In fact, a single seismic-hydroacoustic field propagates in the waveguide. When the depth changes, adiabatic mode transformation occurs in accordance with the new critical frequency, which necessitates the registration of seismic signals in the frequency range 0.003–20 Hz, and if these signals exceed the threshold level, strong bottom movements are recorded, determining pressure tsunami waves to the bottom at frequencies below 0.01 Hz.

Placing a system of bottom seismographs in the region under study also makes it possible to determine the distance to the earthquake epicenter by solving a triangulation problem by extracting a characteristic signal.

The proposed method can also be used in land conditions.

Devices for implementing the method in a wide assortment are available on the market, which allows us to conclude that the claimed technical solution meets the patentability condition "industrial applicability".

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Claims (1)

A method for detecting the possibility of the onset of catastrophic phenomena, including measuring the parameters of the geophysical field in a controlled area and judging by the data obtained on the possibility of the onset of catastrophic phenomena by continuous measurements with the detection of fluctuations in the measured parameter, in which magnetic field variations are additionally measured at frequencies 0.05-0.4 Hz, and the possibility of a catastrophic event is judged by a change in the magnitude of the zero mode, characterized in that they record a seismic signal in the frequency range 0,003-20 Hz, in the event that these signals exceed the threshold level, the strong motion record bottom, defining the pressure at the bottom of the tsunami waves at frequencies below 0.01 Hz.