JP3345644B2 - Apparatus and method for detecting small electromagnetic field anomaly that predicts earthquake, and method for estimating distance to wave source - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention makes it possible to detect an abnormality of an electromagnetic field, which is a precursor of an earthquake, based on electromagnetic field observation, and to predict the possibility and location of an earthquake. The present invention relates to an apparatus for detecting a small electromagnetic field abnormality that is a precursor of an earthquake, a method for detecting the abnormality, and a method for estimating a distance to a wave source.

[0002]

2. Description of the Related Art A large number of pulsating signals due to an abnormal electromagnetic field, which is a precursor of an earthquake, have been observed so far. In order to predict the occurrence of an earthquake, it is necessary to clearly detect the signal due to the abnormal electromagnetic field. ing. In this detection, reference is made to the literature (Kozo Takahashi, the current state of earthquake precursor radio wave observation in China and the proposal of the observation method in Japan, Quarterly Report of the Communications Research Laboratory, Vol. 3).
4, no. 173, Dec. 1988, pp. 245-
As described in (249), in the past, when observing an abnormality in the pre-earthquake electromagnetic field using, for example, a radio wave having a frequency of 100 Hz or more, the received radio wave was detected and the amplitude of the detected signal was smoothed. . In this case, by detecting, the pulse signal or noise and the continuous wave signal or noise are added without distinction, so that much of the pulse information due to the pre-earthquake electromagnetic field is lost and overwhelming. Masked by continuous strong electromagnetic fields caused by artificially strong noise and distant lightning,
Magnitude (Richter-scale magnitude, abbreviated as M below) was difficult to detect signals due to electromagnetic field anomalies that signaled a small earthquake of about 6 or less.

In addition, literature (Takeo Yoshino, elucidation of the mechanism of electromagnetic wave excitation in the epicenter and above the source of electromagnetic field fluctuation as an earthquake precedent phenomenon in the frequency band above VLF, Cond
Activity Anomaly Study Group, 1997 Transactions, March 1997, pp. 82-89), a pre-earthquake electromagnetic field is generated at a frequency of 100H, for example.
When observing with radio waves of z or more, it is possible to observe without detection, but in this case also, despite the difference in characteristics between the pulse signal or noise and the continuous wave signal or noise, Attention has not been paid to this point, and no means has been taken to discriminate the signal due to the abnormal electromagnetic field which is a sign of an earthquake from other noises. For this reason, even in the case of observation without detection, similarly to the case of the above-described detection, it was difficult to detect a small electromagnetic field abnormality of about M6 or less before the earthquake.

[0004] As an invention relatively close to the present invention,
U. S. Pat. No. (. United States Patent No.)
No. 4,825,165. In the invention disclosed in this publication, the configuration disclosed in FIG. 1 is particularly close to the present invention. The disclosed configuration includes an antenna, a preamplifier, a filter, a rectifier circuit having an averaging effect over a specific time, an analog-to-digital converter, and a numerical operation device. This publication describes that the averaging time in a rectifier circuit having an averaging action over a specific time is shorter than the time when the observed transient phenomenon occurs. On the other hand, in the present invention, an antenna,
It includes an amplifier, a filter, an amplifier, an analog-to-digital converter, and a numerical operation device, and performs signal averaging processing as described below. In particular, the averaging process of the present invention differs from that of the above-described invention in the averaging time of the signal. This is because the signal averaging time is shorter in the case of the above-described invention than the time when the observed transient occurs, whereas in the case of the present invention, the individual transient is directly observed. However, they are different in this respect because they accumulate over a time sufficiently longer than the time when the individual transients occur.

Conventionally, the distance from the source of the pre-earthquake electromagnetic field to the observation point has been obtained empirically and subjectively from the magnitude of the amplitude, or from the phase difference by multipoint observation. In the present invention, since the distance from the waveform of the observation signal to the wave source is obtained, the difference from the conventional method is clear.

[0006]

In a conventional method and apparatus for detecting an electromagnetic field abnormality which is a precursor of an earthquake, a pulse signal or noise and a continuous wave signal or noise are handled without discrimination. Therefore, it has been difficult to detect electromagnetic field abnormalities that signal a small-scale (M6 or less) earthquake. In addition, the distance from the source of the pre-earthquake electromagnetic field to the observation point was conventionally estimated empirically and subjectively from the magnitude of the amplitude, or from the phase difference obtained by multipoint observation, so it was estimated correctly. Was hard to say.

[0007] The present invention has been proposed in view of the above,
An electromagnetic field anomaly that is a precursor to a small-scale (M6 or less) earthquake is detected, the location of the occurrence of an abnormal electromagnetic field is estimated, and the possibility and location of an earthquake can be predicted. It is an object of the present invention to provide a detection apparatus for detecting a minute electromagnetic field abnormality, a method for detecting the abnormality, and a method for estimating a distance to a wave source.

[0008]

Means for Solving the Problems In order to achieve the above object, the invention according to claim 1 is an apparatus for detecting a small electromagnetic field abnormality which is a precursor of an earthquake, comprising an antenna for receiving an electromagnetic wave of 30 kHz or less. A receiving device comprising an amplifier, a filter, an analog-to-digital converter, and a numerical processing device, wherein the numerical processing device obtains an accumulated value of the digital data over a predetermined time longer than an individual transient phenomenon. ,
Obtain the time series of the accumulated value of the above digital data, and
Of the signal waveform and the wave source
It is characterized in that it has a configuration for obtaining the distance to the wave source in comparison with the relationship with the distance .

[0009] The invention according to claim 2 is a method for detecting a small electromagnetic field abnormality which is a precursor of an earthquake.
The following electromagnetic wave is received and amplified, passed through a filter, converted into a signal having a substantially specific frequency component, the signal having the substantially specific frequency component is converted into digital data, and a predetermined time longer than each transient phenomenon. Formation of the digital data over the
The product value is calculated and the time series of the accumulated value of the above digital data
And obtain the signal wave by the electromagnetic wave
Distance to the source compared to the relationship between the shape and the distance to the source
It is characterized by seeking .

Further, the invention according to claim 3 relates to a method for estimating a distance to a wave source of a minute electromagnetic field abnormality which is a precursor of an earthquake, and receives an electromagnetic wave of 30 kHz or less from the wave source, and generates a waveform of the received signal. The ratio between the first extreme value where the electromagnetic field is positive or negative and the amplitude of the second extreme value of an extreme point having a phase shifted by π and having the opposite sign is calculated in advance. The obtained distance to the wave source and the electromagnetic field are positive or negative first extreme value, and the amplitude of the second extreme value of the extreme point whose phase is shifted by π and opposite in sign to the first extreme value. It is characterized in that the distance to the wave source is obtained using the relationship with the ratio.

The invention according to claim 4 relates to a method for estimating a distance to a wave source of a minute electromagnetic field abnormality which is a precursor of an earthquake, comprising the steps of: receiving an electromagnetic wave of 30 kHz or less from the wave source; Evaluate the similarity with the signal waveform determined in advance and reduce the signal waveform from the signal waveform determined in advance.
Select the two similar ones, and determine the relationship between the signal waveform and the distance to the wave source obtained in advance and at least the two above.
The distance to the wave source is obtained by performing interpolation using the similarity with the signal waveform .

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention is based on the principle described below. It is known that electromagnetic field abnormalities that signal an earthquake emit pulsed signals or noise.
Since many artificial signals are continuous waves, the present invention
Focusing on the difference between the characteristics of the pulsed signal or noise and the signal or noise of the continuous wave, removing the continuous wave, and detecting the electromagnetic field of an earthquake sign that is a kind of the pulsed signal or noise. Things. Hereinafter, the theoretical background of the present invention will be described using an electric field as an example.

From the observations so far, it is considered that the change of the precursor electric field is pulse-like and its generation is caused by electric discharge. In this case, it is known that the amplitude of the change in the electric field along the direction of the discharge path (the phase term is omitted) is expressed by the following equation.

(Equation 1) Here, ds is the discharge path length, D is the distance from the discharge path to the observation point (perpendicular to the discharge path), Q is the discharge amount, and μ. Is the magnetic permeability, c
Is the speed of light.

FIG. 3 shows the amplitude of the change of the electric field expressed by the equation 1 for each term. FIG. 3 is a diagram showing the amplitude of the change in the electric field along the direction of the discharge path, where (a) is an electrostatic field proportional to D ^-3 corresponding to the first term of Equation 1,
(B) is an induced electric field proportional to D ⁻² corresponding to the second term of Equation 1, and (c) is a diagram illustrating a radiated electric field proportional to D ⁻¹ corresponding to the third term of Equation ¹ . It is.

The waveform of the electric field, which is the sum of the electric fields described above, changes as shown in FIG. FIG. 4 is a diagram showing that the waveform of the electric field along the direction of the discharge path changes according to the propagation distance D. In FIG. 4, when it comes to a long distance,
The radiated electric field of the third term of
Is larger than the above, which is natural from the above equation (1).

[0016] In this case, a positive electric field strength (A ⁺⁾ and negative electric field strength (A ^-) when attention is paid to the, the following can be said. For signals from far away sources, the ratio A ⁺ / A ^- is approximately equal to one. However, at short distances, it diverges to infinity. From this, it can be said that the ratio A ⁺ / A ^- is a parameter that characterizes the distance to the wave source.

[0017] The ratio A ⁺ / A ^- In areas where diverges to infinity, obtaining the distance from the wave itself to the wave source. Therefore, to determine the distance to the wave source in this region, the waveforms for some representative distances are calculated numerically or from the measured values, and the waveforms are compared with the observed waveforms. The distance to the wave source of the observed waveform can be obtained. In addition, in order to estimate the distance between the waveforms by associating the above-described representative distances with the waveforms, a morphing technique that is already well known in the field of computer graphics is used. Performs interpolation. According to this method, the distance to the wave source can be obtained even in a region where the ratio A ⁺ / A ⁻ diverges to infinity.

The component having more than one cycle is
For the following reasons. The radio wave generated by the discharge is not a radio wave having a single frequency component but a wave packet (Wave Packet) including a radio wave having many frequency components. That is, at the time of discharging, many radio waves having the same waveform as those in FIGS. 3B and 3C and having different amplitudes and periods are generated. For this reason, the radio waves of each frequency component interfere with each other, and at a propagation distance of about 2λ (where λ is a wavelength) or more, the waveform has a component of one cycle or more, as shown in FIG.

In general, when observation is made in a plurality of frequency bands, the accuracy of estimating the propagation distance increases in accordance with the number of observation frequency bands. Further, by observing at a plurality of observation points, the transmission source can be obtained by a well-known method. This is a method in which a circle is drawn with each observation point as the center and a distance as a radius, and the intersection point is estimated as an occurrence point. However,
If there are two observation points, they cannot be uniquely determined.

Hereinafter, the method of the present invention will be described based on the above principle. Most of the artificial noise is a continuous wave that attenuates and its time integral over a long time becomes zero as shown in FIG. In addition, as shown in FIG.
When separated by more than λ, the wave becomes an attenuated continuous wave. In this case, the time integral becomes zero as shown in FIG. Also, even in the case of pulse noise from a short distance within 5λ,
When a large number of independent and similar noises are generated, such as noise generated from electric motors and switches in home appliances, the time integral of each waveform does not become zero as shown in FIG. 1 (b). However, since the number of waveforms that swing greatly in the negative direction and the number of waveforms that swing in the positive direction are often almost the same, the total pulse noise from short-distance home appliances and the like can also be integrated over a certain period of time. The integral approaches zero.

On the other hand, it is well known that the pre-earthquake pulse does not occur almost at the same time but occurs in a time series. The generation of the pre-earthquake pulse oscillates positively or negatively. It is presumed to be a waveform, each of which is not accidental and occurs by a series of mechanisms. As shown in Fig. 1 (b), a single pulse waveform that is a precursor to an earthquake within about 4λ from the epicenter area is greatly shifted negatively or positively, and its integral value is not zero, but the integral value includes a plurality of pulse waveforms. The value is no longer zero. This occurs within about 4λ from the epicenter. For example, when observing at 3 kHz, such a waveform is observed if the distance to the epicenter is 400 km or less.

Regarding the frequency of the pulse, for example, the Hokkaido Toho-oki earthquake (occurred on October 4, 1994, M = 8.
In the case of 1), pulsed signals or noise are observed several times a second, and even in the case of other earthquakes, in the epicenter area before the earthquake, the frequency is about several times a second. It is estimated that discharge has occurred.

The above phenomenon is similar to the case of observation of an electric field due to lightning discharge described in the literature (Kazuo Sao, Seiden, Seizando Shoten, 1981, pp. 15-17).
As is well known in lightning observations, the electric field due to lightning discharge is far distant from the wave source and about 5 times longer than the wavelength, and the received electric field is dominated by the AC radiated electric field, and the integral value is Approaching zero. On the contrary, the wave source is close and the wavelength is about 4
In the case of close lightning at a distance of less than twice, the received electric field is dominated by a pulse-like induced electric field, and the above-mentioned integral value does not become zero. In the case of a close lightning, the integrated value is not zero, but since the pulse width of the electric field of the lightning is about 10 μs, for example, the time average of the integrated value for 15 minutes = 900 seconds is about one hundred millionth of the maximum value. .

Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 2 shows a detection apparatus 100 for detecting a small electromagnetic field abnormality that is a precursor of an earthquake.

The electric field received by the antenna 1 is amplified only in a specific frequency band by a filter 2 and an amplifier 3, converted into a digital signal by an analog-to-digital (AD) converter 4, and transmitted to a personal computer (PC) 5. Read and processed. That is, the electric field is time-integrated by the PC 5 at regular intervals, for example, about every 15 minutes, continuous waves having equal positive and negative areas are removed, and only short-range (about 4λ or less) pulse noise is recorded. Are output to the recording medium 6 as necessary. In addition, the processing result is input to a digital-to-analog (DA) converter 7, and the output is recorded in an analog recorder 8.

As a first embodiment, FIG.
Shows a first observation example using the device shown in FIG. The observation frequency band is 80 Hz to 10 kHz, the sampling rate of the AD converter is 25 kHz, the antenna is a vertical minute dipole, the material is titanium, and the length of the element antenna is 515 mm. The sensitivity of this device was 0.25 mV / m.
The observation point where this device is installed is 35 ゜ 42 'north latitude, 140 ゜ 51' east longitude, and the altitude is about 60m. 1999 3
The observation shown in FIG. 5 was obtained by observation over 1st to 2nd (UT) of the month. The vertical axis in FIG. 5 is a value proportional to the value integrated by the following Equation 2, and the horizontal axis is time.

(Equation 2) Here, E (x) is the vertical electric field at the antenna position, t is time, and the above equation indicates that the electric field is integrated for 900 seconds. In FIG. 5, the appearance of a waveform that is greatly reduced to the negative side is considered to be a precursor of the earthquake, and the time of occurrence of the corresponding earthquake is 07:12 on March 2, 1999 (U.S.
T), the epicenter was 35 ゜ 40 'north latitude, 142 ゜ 0 east longitude
4 ', depth about 68 km, magnitude (Richter scale) is 6.2. Here, the above integration need not be limited to 900 seconds, and it is desirable to set an optimum value from 1 ms to about 60 minutes according to the situation.

As a second embodiment, a description will be given of a second observation example in which this apparatus is used for observation from November 23 to 24, 1998 (UT). FIG. 6 shows a waveform obtained by this observation. In FIG. 6 as well, the appearance of a waveform having a large negative side is considered to be a precursor of the earthquake, and the time of occurrence of the corresponding earthquake is November 1998.
At 05:35 (UT) on March 24, the epicenter was north latitude 3
5 ゜ 59 ', 141 経 41' E longitude, 33km deep
And the magnitude (M) is 4.6. Like this
The present invention has made it possible to detect an extremely small electromagnetic field abnormality that is a precursor of an earthquake with a magnitude (M) of 6 or less, which was difficult with a conventional apparatus.

Next, as a third embodiment, from the waveform,
Determining the distance to the wave source will be described. FIG.
FIG. 4 is a diagram showing changes in the electric field when the same signal from the wave source is observed at each of Hasaki, Chikura, and Sagara points. From the time difference between the starting points of these signals, it is known that the distances between the wave source and the respective points of Hasaki, Chikura, and Sagara are 70 km, 70 km, and 190 km, respectively. As described above, it can be seen from FIG. 8 that the ratio A ⁺ / A ⁻ is a parameter of the distance to the wave source. FIG. 8 is a diagram plotting values from the data of FIG. 7 with the ratio A ⁺ / A ⁻ on the horizontal axis and the distance to the wave source on the vertical axis. In this figure, the number of plots is not sufficient, but it is possible to improve the estimation accuracy by further increasing the number of plots and obtaining an interpolation formula by the least squares method.

Further, it is apparent that the present invention can be used for other purposes than the detection of the above-mentioned precursor for the detection of a small electromagnetic field abnormality. For example, it is clear that it can be applied to the detection of general pulse noise and the estimation of the source.
In particular, for example, it can be used for detecting the occurrence of lightning and estimating the location of occurrence.

[0030]

Since the present invention has the above-described configuration,
The following effects can be obtained.

According to the first and second aspects of the present invention, 30
Receives and amplifies electromagnetic waves of less than kHz, passes through a filter into a signal of a substantially specific frequency component, converts the signal of the approximately specific frequency component into digital data, and is a predetermined longer than each individual transient phenomenon. Calculate the accumulated value of the digital data over time, and calculate the accumulated value of the digital data.
A series is acquired, and the
Signal and the distance to the source.
Since a method and an apparatus characterized by determining a distance are disclosed, an earthquake of a small-scale earthquake of about 6 or less, which has been difficult to detect because of being masked by overwhelmingly strong artificial noise or an electromagnetic field of a far-field lightning. It is now possible to obtain information from precursory electromagnetic fields, and therefore, for some earthquakes with M = 6 or less, it is possible to detect abnormalities in the electromagnetic field and predict earthquakes.

According to the third aspect of the present invention, the distance to the wave source is estimated by receiving an electromagnetic wave of 30 kHz or less from the wave source and comparing the amplitude of the received signal waveform with a calculated value or an observed value. Now you can.

According to the fourth aspect of the present invention, the distance to a wave source that is so close that the distance to the wave source cannot be estimated by the method of the third aspect can be estimated from the characteristics of the waveform.

[Brief description of the drawings]

FIG. 1 is a diagram for explaining a difference between time integration of a continuous wave and time integration of an earthquake precursor radio wave, and FIG.
Is a pulse signal waveform from a wave source at a relatively long distance,
(B) is a pulse signal waveform from a wave source located at a relatively short distance.

FIG. 2 is a diagram showing a block diagram of an apparatus for detecting a weak electromagnetic field signal.

3A and 3B are diagrams showing an amplitude of a change in an electric field along a direction of a discharge path. FIG. 3A shows an electrostatic field proportional to D ^-3 corresponding to the first term of Expression 1, and FIG. FIG. 7C is a diagram illustrating an induced electric field proportional to D ⁻² corresponding to the second term of ^Equation 1, and FIG. 7C is a diagram illustrating a radiation electric field proportional to D ⁻¹ corresponding to the third term of Equation ¹ .

FIG. 4 is a diagram showing that a waveform of an electric field along a direction of a discharge path changes according to a propagation distance.

FIG. 5 is a diagram showing a first observation example.

FIG. 6 is a diagram showing a second observation example.

FIG. 7 is a diagram showing changes in the electric field when the same signal from the wave source is observed at each of Hasaki, Chikura, and Sagara points.

FIG. 8 is a diagram in which values from observed values are plotted with the ratio A ⁺ / A ⁻ on the horizontal axis and the distance to the wave source on the vertical axis.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Antenna 2 Filter 3 Amplifier 4 AD converter 5 Personal computer (PC) 6 Recording medium 7 DA converter 8 Analog recorder

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Eiji Kawai 1359-12-321 Hirai, Kashima City, Ibaraki Prefecture (72) Inventor Kozo Takahashi 7-14-7-7 Takiyama, Higashi Kurume-shi, Tokyo Kawanomura, Futaba-gun, Pref., Japan 20 Kainozaka, Shimokawauchi 20-72 Inventor Yukio Fujinawa 6-5-1, Nakamura-minami, Tsuchiura-shi, Ibaraki Pref. -80163 (JP, A) JP-A-9-90051 (JP, A) JP-A-11-194172 (JP, A) Registered utility model 3043622 (JP, U) (58) Fields investigated (Int. Cl. ⁷⁾ G01V 1/00 G01V 1/28 G01R 29/08

Claims (4)

(57) [Claims] 1. A receiving device comprising an antenna for receiving an electromagnetic wave of 30 kHz or less, an amplifier, a filter, an analog-to-digital converter, and a numerical processing device, wherein the numerical processing device has a predetermined length longer than each transient phenomenon. The accumulated value of the digital data is obtained over the specified time, and the digital
Time series of cumulative values of
Relationship between the signal waveform caused by the electromagnetic wave and the distance to the wave source
An apparatus for detecting a small electromagnetic field abnormality that is a precursor to an earthquake, characterized by having a configuration for obtaining a distance to a wave source as compared with the above . 2. An electromagnetic wave having a frequency of 30 kHz or less is received and amplified, passed through a filter to be converted into a signal having a substantially specific frequency component, and the signal having the substantially specific frequency component is converted into digital data. The accumulated value of the digital data is obtained over a long predetermined time, and
Obtain the time series of the cumulative value of the total data and obtain it in advance.
The relationship between the signal waveform due to electromagnetic waves and the distance to the wave source
A method for detecting a small electromagnetic field abnormality that is a precursor to an earthquake, characterized in that a distance to a wave source is obtained in comparison with a person in charge . 3. An electromagnetic wave having a frequency of 30 kHz or less from a wave source is received, and the phase of the first extreme value of the received signal waveform whose electromagnetic field is positive or negative and the first extreme value is shifted by π. Find the ratio of the extreme point with the opposite sign to the amplitude of the second extreme value,
The amplitude of the second extreme value of the first extreme value where the distance to the wave source and the electromagnetic field determined in advance is positive or negative and the phase of the first extreme value is shifted by π and the opposite sign is used A method for estimating a distance to a wave source, wherein the distance to the wave source is obtained using a relationship with the ratio of the wave source. 4. Receiving an electromagnetic wave of 30 kHz or less from a wave source, evaluating the similarity between the received signal waveform and a previously determined signal waveform,
At least two similar models are selected , and the relationship between the signal waveform determined in advance and the distance to the wave source and at least the two
By interpolating using the similarity between two signal waveforms,
A method for estimating a distance to a wave source, comprising determining a distance to the wave source.