JP4721945B2 - Crustal deformation detection device and crustal deformation detection method - Google Patents

Description

  The present invention relates to a crustal movement detection device and a crustal movement detection method for detecting earthquakes and predicting earthquakes.

  In recent years, various methods have been studied to predict earthquakes in order to minimize earthquake damage. If it is possible to predict earthquakes, before an earthquake occurs, escape from the building, shut down chemical plants and nuclear power plants, stop running cars or evacuate to safe places, use gas It becomes possible to stop the equipment and the like, and the earthquake damage can be greatly reduced.

  Many methods have been proposed for crustal deformation observation and earthquake prediction. For example, a method has been proposed in which the movement of the crust is detected by position measurement using GPS (Global Positioning System) or triangulation, and the possibility of generating a fault from the distribution state of strain energy accumulated in the ground has been proposed. . In addition, a method for predicting the occurrence of periodic earthquakes due to asperity in the subducted part of the continental plate from past history, occurrence frequency of microearthquakes around asperity, crustal deformation, etc. has also been proposed. Yes. In addition, a method using a VAN (Varotsos Alexopouls Nomicos) method for observing current generation due to crustal stress and predicting an earthquake has also been proposed (for example, see Patent Document 1).

  In addition, there have been proposed a method of capturing abnormalities in a living body by some method and a method of performing earthquake prediction by detecting electromagnetic noise when an earthquake occurs (see, for example, Patent Document 2).

  In addition, a method for predicting earthquakes by observing the waveform of omega radio waves, which are VLF (Very Low Frequency) radio waves, and detecting the occurrence of atmospheric plasma that is a sign of an earthquake by detecting waveform anomalies has also been proposed. (For example, refer to Patent Document 3).

  In addition, a method has been proposed for measuring changes in the ionosphere (ionosphere) corresponding to changes in the crust from radio wave propagation abnormalities. Methods for detecting such ionospheric changes include the use of GPS radio waves of different frequencies to observe ion concentration changes and disturbances in the ionosphere to predict earthquakes, and the observation of abnormal propagation of radio waves from VHF / FM transmitter stations. A method to do this has also been proposed. In addition, long-term observations of changes in received intensity and phase of LF (Low Frequency) radio waves reflected by the D layer, which is the lowest ionosphere near the ground surface, predict earthquakes based on the opening of the terminator time in the morning and evening There has also been proposed a method (see, for example, Non-Patent Document 1).

JP 2004-251713 A Japanese Patent Laid-Open No. 9-90051 Japanese Patent Application Laid-Open No. 8-33469 International Workshop on Seismo Electromagnetics IWSE-2005 Program and Extended Abstract, March 15-17, 2005

  In the above-mentioned conventional technology, an attempt is made to predict earthquakes by detecting crustal movements by various methods, but any method is still under study, and there is no method that can reliably predict earthquakes. .

  An object of the present invention is to provide a crustal movement detecting device and a crustal movement detecting method capable of detecting crustal movement with higher accuracy and performing more accurate earthquake prediction.

[Crustal deformation detector]
In order to achieve the above object, the crustal movement detection device of the present invention receives a radio wave reflected by the ionosphere, and uses a phase synchronization circuit to generate a signal having a frequency that is a rational multiple of the carrier frequency of the received radio wave. A receiving device that is generated in a phase-synchronized state with
Frequency measuring means for measuring the frequency of the signal generated by the receiving device.

  Preferably, the radio wave reflected by the ionosphere is a long wave radio wave or a super long wave radio wave.

  Preferably, the time constant of the loop filter of the phase locked loop circuit is 2 seconds or more and 100 seconds or less.

  Preferably, the frequency measuring means measures the frequency of the signal generated by the receiving device with a frequency accuracy of 8 digits or more per second.

According to the present invention, when a long wave radio wave or a super long wave radio wave reflected by the ionosphere is received and a signal phase-synchronized with the received radio wave is generated using the phase synchronization circuit, the time constant of the loop filter is set to 2. By setting the second time to 100 seconds or less, it is possible to make a prediction immediately before the occurrence of an earthquake by detecting a short-time frequency fluctuation that has not been detected by the conventional method.
The time constant described in the present invention refers to a time constant that is set in a range in which the output of the phase comparator is not saturated and is operating linearly. When the output (dudy) of the phase comparator saturates and deviates from linear operation, the speed at which the maximum current that can be output by the phase comparator charges the loop filter capacitor becomes a problem. The time constant described here is a time twice as long as the frequency variation reaches 2. Furthermore, if the influence of the resistor, capacitor, etc. for smoothing the output voltage when detecting it as a phase output instead of a frequency or a capacitor, a switch for decoupling, or a frequency is not negligible A time constant described here is a time twice as long as the time required for the operation of the included circuit to reach half of the target frequency variation.

  The frequency measuring means can also measure the frequency of the signal generated by the receiving device by detecting a control voltage of a voltage controlled oscillator constituting the phase locked loop.

Preferably, the frequency measurement means includes a GPS frequency reference device that generates a reference frequency signal using received GPS radio waves, and
And a time interval counter for measuring the frequency of the signal generated by the receiving device based on the reference frequency signal generated by the GPS frequency reference device.

  As described above, according to the present invention, by setting the time constant of the loop filter of the phase synchronization circuit used when generating the signal synchronized with the radio wave reflected by the ionosphere to 2 seconds or more and 100 seconds or less, The effect that it becomes possible to perform more accurate earthquake prediction is obtained.

[background]
First, in order to help understanding of the present invention, its background and outline will be described.
As described above, when an ionospheric propagation abnormality is detected using LF (or VLF) radio waves, radio waves from radio transmission stations such as omega transmission stations, Laurent transmission stations, and JJY (standard frequency stations) are used. In the receiving apparatus to be used, the time constant of the phase synchronization circuit is set to be as long as several minutes to several tens of minutes. For this reason, most of the conventional crustal movement detection methods observe signal intensity changes and phase changes in units of days or weeks even when detecting ionospheric propagation anomalies using LF radio waves. In such a method of observing changes in signal intensity and phase in units of days or weeks, the detected crustal movement has a long period of days.

  Here, the inventors of the present application have found that the reception frequency of the LF radio wave emitted from the transmitter fluctuates immediately before or after the crustal movement. This is considered to cause frequency fluctuations due to the Doppler effect due to the fluctuation of the reflection area due to the crustal movement when the LF radio wave emitted from the transmitter is reflected by the ionosphere (D layer). The reason for this phenomenon is that a huge current flows through the crust immediately before the occurrence of the earthquake due to crustal stress, and a magnetic field is generated by this current, which may affect the lowermost ionosphere D layer. The inventors of the present application have come to consider performing earthquake prediction by detecting crustal deformation by detecting this frequency fluctuation.

  When LF radio waves are reflected by the ionosphere, how the frequency fluctuations are caused by the fluctuation of the reflection area due to the crustal movement is shown in FIG. The ionosphere is divided into four layers, D layer, E layer, F1 layer, and F2 layer, in order from the surface of the earth. The VLF / LF wave used by the present invention is reflected by the lowermost D layer among these ionospheres. The LF wave is a radio wave having a frequency of 30 to 300 kHz (wavelength 10 km to 1 km), and the VLF wave is a radio wave having a frequency of 3 to 30 kHz (wavelength 100 km to 10 km).

  In FIG. 1, the LF wave transmitted from the transmitting station 100 is reflected by the ionosphere of the D layer and reaches the receiving station 200. Here, immediately before an earthquake occurs somewhere along the path between the transmitting station 100 and the receiving station 200, the reflection area of the D layer fluctuates, and the frequency of the LF wave after being reflected by the Doppler effect changes. Conceivable. That is, if the frequency received by the receiving station 200 can be monitored and frequency fluctuations can be detected, the occurrence of crustal fluctuations can be detected in advance, and so-called earthquake prediction can be performed.

  However, as described above, in the conventional standard radio wave receiver, the time constant of the phase synchronization circuit is set to be a long time. Cannot be detected.

  Therefore, in the present invention, the time constant of the loop filter of the phase locked loop in the standard radio wave receiver is set short, and the crustal movement is detected by observing the frequency fluctuation of the VLF / LF wave reflected by the ionosphere in a short time. To predict the occurrence of an earthquake.

[Embodiment]
Next, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 2 is a block diagram showing a configuration of a crustal movement detecting device according to an embodiment of the present invention.

  As shown in FIG. 2, the crustal movement detection device of the present embodiment includes a loop antenna 10, a preamplifier 20, a receiver 30, a GPS antenna 40, a GPS frequency reference device 50, a time interval counter 60, And a data recording device 70.

  In this embodiment, a case where crustal movement is detected using a 40 kHz standard radio wave from a JJY transmitting station under the jurisdiction of the Ministry of Internal Affairs and Communications that transmits a reference frequency / time will be described. The crustal movement may be detected using the carrier signal.

  The preamplifier 20 amplifies the 40 kHz standard radio wave received by the loop antenna 10.

  The receiving device 30 receives the 40 kHz standard radio wave amplified by the preamplifier 20, and uses a phase synchronization circuit to phase-synchronize the signal having a frequency that is a rational multiple of the carrier frequency of 40 kHz of the standard radio wave to the standard radio wave ( It is generated in a phase locked state.

  In the present embodiment, the description will be made assuming that the receiver 30 outputs a signal of 10 MHz, 250 times the standard frequency of 40 kHz, to the time interval counter 60 in phase synchronization with the standard radio wave.

  The GPS frequency reference device 50 receives GPS radio waves from GPS satellites and generates a highly accurate 10 MHz reference frequency signal.

  In the crustal movement detection device of the present embodiment, the signal generated by the GPS frequency reference device 50 is used as a reference frequency signal. You may make it use the signal produced | generated using this as a reference frequency signal. Further, the reference frequency signal may be generated using an LF wave received as a direct wave from the standard transmission station.

  The time interval counter 60 stores a 10 MHz signal synchronized with the standard radio wave from the receiver 30 and a waveform of a 10 MHz reference frequency signal from the GPS frequency reference device 50, respectively, and stores digits of 1 Hz or less, for example, 10,000. This is a device that can measure 1,000,000 mHz with a gate time of 1 second. With a general frequency counter, 1000 seconds or more are required to measure a digit of 1 mHz.

With such a function, the time interval counter 60 measures the frequency of the signal generated by the receiving device 30 based on the reference frequency signal generated by the GPS frequency reference device 50.
Here, 1 mHz (millihertz) represents a frequency of 1/1000 of 1 Hz.

  The GPS frequency reference device 50 and the time interval counter 60 constitute frequency measuring means, and the frequency of the 10 MHz signal generated by the receiving device 30 is measured.

  As shown in FIG. 3, the receiver 30 includes amplifiers 31, 33, 39, a full-wave rectifier 32, a phase comparator 34, a division period 35, and a voltage controlled oscillator (VCO). 36, a changeover switch 37, and a loop filter 38.

The full-wave rectifier 32 performs full-wave rectification on the 40 kHz high-frequency signal input via the preamplifier 20 and the amplifier 31 and outputs the result as an 80 kHz signal. The full-wave rectifier 32 extracts a time code signal superimposed on the standard radio wave and outputs it to the changeover switch 37.
Here, the time code signal is a signal indicating that time information is included in the standard radio wave.

  The phase comparator 34 detects the phase difference between the 80 kHz signal amplified by the amplifier 33 and the 80 kHz signal from the dividing period 35, and outputs a signal that reduces the detected phase difference.

In the division period 35, the signal generated by the voltage controlled oscillator 36 is divided by 1/125 and output to the phase comparator 34.
The voltage controlled oscillator 36 outputs a signal having a frequency corresponding to the control voltage generated by the loop filter 38.

  The changeover switch 37 outputs the output from the phase comparator 34 to the loop filter 38 when the time code signal is output from the full-wave rectifier 32. Therefore, the loop filter 38 takes in the output from the phase comparator 34 only when the time information is included in the standard radio wave.

  The loop filter 38 is a filter for removing a high frequency component contained in the output signal of the phase comparator 34 input via the changeover switch 37 and generating a DC control voltage to be output to the voltage controlled oscillator 36. .

  Here, if the time constant of a loop filter constituting a PLL (Phase-Locked Loop) circuit is generally increased, stable reception can be performed, but followability is deteriorated. On the contrary, if the time constant is set short, the followability is improved, but the reception stability is deteriorated.

  For this reason, the ionosphere fluctuates considerably rapidly in a short time, and if the time constant of the loop filter 38 of the phase locked loop circuit is too short, the ionosphere changes greatly, making it difficult to capture the average movement of the ionosphere. If the time constant is too long, it will not be possible to follow a large change. Therefore, the time constant of the loop filter in the receiving apparatus for measuring the frequency fluctuation of the LF wave reflected by the ionosphere is preferably about 2 seconds or more and 100 seconds or less. Therefore, the time constant of the loop filter 38 in the crustal movement detection device of this embodiment is set to 50 seconds.

Next, the operation of the crustal movement detection device of the present embodiment will be described in detail with reference to the drawings.
The 40 kHz standard radio wave supplemented by the loop antenna 10 is amplified by the preamplifier 20 and then input to the receiver 30. In the receiver 30, the frequency of 40 kHz is full-wave rectified by the full-wave rectifier 32 to generate a signal having a frequency of 80 kHz. The 10 MHz signal generated by the voltage controlled oscillator 36 is generated by the full wave rectifier 32 by the phase locked loop composed of the phase comparator 34, the frequency divider 35, the voltage controlled oscillator 36, and the loop filter 38. It will be synchronized with the 80 kHz signal. Then, the 10 MHz signal generated by the voltage controlled oscillator 36 is output to the time interval counter 60 via the amplifier 39.

  Then, the 10 MHz signal generated by the voltage controlled oscillator 36 has a gate time of 1 second and an interval of 10 with an accuracy of 10 digits / second in the time interval counter 60 using the reference frequency signal from the GPS frequency reference device 50 as a reference. It is measured in seconds and taken into a data recording device 70 such as a personal computer.

  Here, the time interval counter 60 needs to measure the frequency of the signal generated by the receiving device 30 with a frequency accuracy of at least 8 digits / second (8 digits per second) or more.

  The frequency fluctuation factor is due to factors such as solar activity in addition to the purpose of the present invention of crustal stress, crustal current, magnetism or magnetic field / electromagnetic wave generation, influence on the ionosphere, occurrence of reception frequency shift, etc. There is. Accordingly, it is preferable to use a stable ionosphere in order to perform earthquake prediction with high accuracy by observation according to the present invention. For example, when the D layer, which is the lowest ionosphere, is used in the LF band, the ionosphere of the D layer can be used during the day, so relatively small crustal movements can be captured, but the D layer disappears at night. And since it becomes E layer reflection, the detection sensitivity of a fluctuation | variation will fall large. Also, when solar flare is occurring, it is difficult to observe crustal deformation due to the effect of solar flare even during the day.

  The frequency when the radio wave of the Fukushima JJY transmitting station (Fukushima Prefecture Tamura City: Otakadoya Yamayama Standard Radio Transmission Station) is received in Machida City, Tokyo, by the crustal movement detection device of this embodiment shown in FIG. The change is shown in FIG. The graph shown in FIG. 4 shows a change in average reception frequency for about 3 days in which no major abnormality was observed. Referring to FIG. 4, frequency fluctuations of about ± 5 mHz during the day and ± 100 mHz at night were observed.

  As can be seen from FIG. 4, it is difficult to detect a frequency shift of about ± 100 mHz at night, but it can be detected in the daytime if the frequency fluctuation is ± 10 mHz or more.

[Observation example 1]
Next, FIG. 5 shows an observation example at the time of abnormality when the radio wave of the Fukushima JJY transmitting station is received in Machida City, Tokyo, using the crustal movement detection device of the present embodiment.

  FIG. 5 shows observed waveforms before and after the earthquake of M3.4 that occurred in Tochigi Prefecture on June 12, 2005 at 9:05 in the morning. Referring to FIG. 5, it can be seen that the nighttime fluctuations are reduced and an abnormality is detected in a stable state during the day.

  A decrease in the frequency of the voltage controlled oscillator of 10 MHz was observed from about 8:40, the frequency fluctuation reached about −30 mHz at 8:46 and 8:50, and then increased to about +10 mHz at 9:02. It has become. That is, it can be seen that the frequency starts decreasing about 25 minutes before the occurrence of the earthquake, and the abnormality is clear 15 minutes before. FIG. 5 shows that it is possible to predict before an earthquake occurs by detecting an abnormality in frequency fluctuation.

  However, in the nighttime zone where layer D has disappeared, frequency fluctuations during normal times are large due to unstable E-layer reflections, so it seems that frequency fluctuations associated with such small-scale earthquakes cannot be detected in the nighttime zone. It is.

[Observation example 2]
Next, another example of observation at the time of abnormality when the radio wave of the Fukushima JJY transmitting station is received in Machida City, Tokyo, using the crustal movement detection device of the present embodiment is shown in FIGS. However, the measurement was performed using a time interval counter 60 having a precision of 12 digits / second.

  6 and 7 are observation waveforms before and after the occurrence of the M5.7 Chiba Prefecture northwest earthquake that occurred at 16:35 on July 23, 2005. FIG. 6 is an observation waveform from 14:13 on July 23 to immediately after the occurrence of the earthquake, and FIG. 7 is a waveform showing the frequency change immediately before the occurrence of the earthquake with the time axis extended.

  Referring to FIG. 6, it can be seen that a large frequency fluctuation of about +300 mHz to −170 mHz is observed from around 14:16. 6 and 7, it can be seen that a frequency fluctuation of −250 mHz is observed immediately before the occurrence of the earthquake. Furthermore, referring to FIG. 7, it can be seen that the frequency starts decreasing about 7 minutes before the occurrence of the earthquake and reaches the lowest point of −250 mHz about 4 minutes before the occurrence of the earthquake. The frequency fluctuation at the time of the earthquake occurrence was +50 mHz.

  In the examples shown in FIGS. 6 and 7, crustal deformation is detected about 2 hours before the occurrence of the earthquake, and it is possible to make a prediction before the occurrence of the earthquake.

  Thus, according to the crustal movement detection device of the present embodiment, by observing the frequency fluctuation of the LF radio wave reflected by the ionosphere, as shown in the above observation examples 1 and 2, 25 minutes of the occurrence of the earthquake. It was possible to predict the occurrence of an earthquake two hours ago.

  That is, according to the crustal movement detection device of the present embodiment, the time constant of the phase synchronization circuit of the receiver 30 is shortened, and the short-time frequency fluctuation of the LF radio wave reflected by the ionosphere is detected, so that the earthquake is It is possible to make a prediction immediately before detecting a sign of an earthquake occurring several hours to several minutes ago.

  Note that the crustal movement detection device of the present embodiment detects crustal movement using the fact that the reception frequency fluctuates due to the Doppler effect when the LF radio wave emitted from the standard radio wave transmission station is reflected by the ionosphere. Yes. Therefore, it is necessary to set the distance between the transmitting station and the receiving device so that direct waves do not reach. Then, when a frequency fluctuation is detected by the crustal movement detection device of the present embodiment, it is predicted that a crustal movement has occurred at any location between the transmitting station and the receiving device. However, as long as measurement is possible with pulsed radio waves, the distance between the two transmission and reception points may be within the range where the direct wave reaches.

  Furthermore, in order to specify in more detail the location where the crustal movement has occurred, radio waves from transmission facilities set in different locations are received by one receiving device, and receiving devices set in different locations are provided. By connecting and exchanging information with each other through communication means such as the Internet, it is possible to limit the occurrence location and predict earthquakes with higher accuracy.

[Modification]
In the above embodiment, the case where the fluctuation of the output frequency of the receiver 30 is observed using the frequency measuring means including the GPS frequency reference device 50 and the time interval counter 60 has been described, but the present invention is not limited to this. Any means may be used as long as it can measure the output frequency variation of the receiver 30 with high accuracy.

  Further, the frequency fluctuation may be indirectly observed by measuring the control voltage of the voltage controlled oscillator 36 in the receiver 30 without directly measuring the output frequency of the receiver 30.

  Since the voltage controlled oscillator 36 changes the frequency of the signal generated based on the control voltage from the loop filter 38, the frequency change of the signal generated by the voltage controlled oscillator 36 is monitored by monitoring this control voltage. It is because it is possible to detect.

  Thus, if the frequency fluctuation is detected by measuring the control voltage to the voltage controlled oscillator 36, the GPS frequency reference device 50 and the time interval counter 60 become unnecessary, and a crustal movement detecting device is realized at low cost. It becomes possible to do.

  In the above-described embodiment, the case where the phase synchronization with respect to the received radio wave is performed using one phase synchronization circuit has been described. However, two phase synchronization circuits are provided, and the received voltage is first controlled by the first voltage control. It may be supplemented by an oscillator, and a second voltage-controlled oscillator having a longer time constant may be synchronized with this (under the condition that the frequency of the real number of each other matches).

  Apart from this, the control voltage to the voltage controlled oscillator synchronized by a lag reed filter having a short time constant that can be synchronized in a short time may be converted into a digital signal by an A / D converter and averaged. . By performing averaging in this way, it is possible to obtain an accurate frequency. Alternatively, the averaged digital signal may be given a predetermined time constant, converted to an analog signal control voltage by a D / A converter, and returned to the voltage controlled oscillator. Furthermore, a receiving facility having a plurality of different time constants can be provided.

  Furthermore, in this embodiment, although the case where the fluctuation | variation of D layer which is the lowest ionosphere is detected using LF radio wave is demonstrated, this invention is not limited to such a case. Of course, the fluctuation of the D layer may be detected using the VLF radio wave. Furthermore, if the magnitude of the crustal deformation exceeds a certain level, the state of the E layer may be affected, and the fluctuation of the E layer is detected by radio waves having a frequency different from that of VLF / LF radio waves or VLF / LF radio waves. It may be possible to detect crustal movements.

It is a figure which shows a mode that a frequency fluctuation | variation is caused by the Doppler effect by the fluctuation | variation of the reflective area by a crustal movement, when the electromagnetic wave emitted from the transmitter is reflected in an ionosphere. It is a system diagram showing a configuration of a crustal movement detection device of one embodiment of the present invention. It is a block diagram which shows the structure of the receiver 30 in FIG. It is a graph which shows the change of the average receiving frequency for about 3 days when especially big abnormality was not recognized. It is a graph which shows an example of the change of the receiving frequency when abnormality is detected by the crustal movement detection apparatus of one Embodiment of this invention. It is a graph which shows the other example of the change of the receiving frequency at the time of detecting abnormality by the crustal movement detection apparatus of one Embodiment of this invention. In the graph of FIG. 6, it is the graph which showed the waveform which extended the time axis | shaft the frequency change just before the occurrence of an earthquake.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Loop antenna 20 Preamplifier 30 Receiver 31 Amplifier 32 Full wave rectifier 33 Amplifier 34 Phase comparator 35 Minute period 36 Voltage control oscillator 37 Changeover switch 38 Loop filter 39 Amplifier 40 GPS antenna 50 GPS frequency reference apparatus 60 Time interval counter 70 Data recording Device 100 Transmitting station 200 Receiving station

Claims (5)

A standard radio wave, which is a long wave radio wave reflected by the D layer, which is the lowest ionosphere near the ground surface, is received, and a signal having a frequency that is a rational multiple of the carrier frequency of the received standard radio wave is 2 seconds. A receiving device that generates a phase-synchronized state with the standard radio wave using a phase-locked loop that is 100 seconds or shorter ;
Frequency measuring means for measuring the frequency of the signal generated by the receiving device;
A crustal movement detector. It said frequency measurement means, tectonic detecting apparatus according to claim 1, wherein measuring the frequency of the signal generated by the receiving device by per second 8 digits or more frequency accuracy. The crustal movement detecting device according to claim 1 or 2 , wherein the frequency measuring means measures a frequency of a signal generated by the receiving device by detecting a control voltage of a voltage controlled oscillator constituting the phase locked loop circuit. The frequency measuring means includes a GPS frequency reference device that generates a reference frequency signal using received GPS radio waves, and
The time interval counter which measures the frequency of the signal produced | generated by the said receiver based on the reference frequency signal produced | generated by the said GPS frequency reference apparatus, The any one of Claim 1 to 3 comprised. Crustal deformation detector. And receive radio signals is a long wave radio waves reflected by the D layer is the lowest layer of the ionosphere close to the surface, a signal having a rational multiple of the frequency of the carrier frequency of the standard radio wave received, the time constant of the loop filter 2 Using a phase synchronization circuit that is not less than 100 seconds and not more than 100 seconds, it is generated while being phase-synchronized with the standard radio wave,
A crustal movement detection method for measuring a frequency of a signal generated by the phase synchronization circuit.

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