JPH0263194B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention is an epicenter distance calculation device that continuously calculates the distance from an observation point of seismic waves to the epicenter (epicenter distance) in real time.

(Prior art) Conventional methods for calculating the epicenter distance include detecting the arrival time of earthquake waves at three or more observation points, determining the epicenter, and then calculating the epicenter distance;
There is a method of detecting the difference between the arrival times of P waves and S waves (P to S time) at one observation point, and calculating the epicenter distance by utilizing the fact that the P to S time is proportional to the epicenter distance. In either case, the epicenter distance cannot be determined until several tens of seconds to several minutes have passed after the arrival of the seismic waves.

(Object of the Invention) An object of the present invention is to provide a device that calculates the epicenter distance of an earthquake from observation outputs obtained with different natural periods.

(Structure of the Invention) The present invention sets earthquake observation outputs from two types of seismometers with different natural periods into one set, and a set includes the seismometer with the longest natural period and a set includes the seismometer with the shortest natural period. means for inputting two sets of observation outputs and calculating an exponentially smoothed value of each set of observation outputs, and the exponentially smoothed value of the observed waveform of each set of seismometers and the natural period of each set of seismometers, Predominant frequency calculation means for calculating the predominant frequency and its component amplitude in two high and low frequency bands, and the logarithm of the ratio of the two component amplitudes obtained by the two sets of predominant frequency calculation means, and the predominant frequency calculation means for the two sets. This apparatus is characterized in that it obtains the epicenter distance of an observation point by calculating the ratio of the difference between the two dominant frequencies obtained from the method.

(First Example) It can be considered that waves of all frequency components are uniformly radiated to the surrounding area from the vicinity of the epicenter.
However, when seismic waves propagate, generally higher frequency vibrations are more easily attenuated, so the ratio of the amplitude of high frequency components to the amplitude of low frequency components in seismic waves becomes smaller as the distance of wave propagation increases. Therefore, it is possible to estimate how far that point is from the epicenter by combining the frequencies and component amplitude values of the two dominant frequencies in seismic waves observed at a certain point. Furthermore, when one earthquake is observed simultaneously by several seismometers with different natural periods, each seismometer is strongly sensitive to vibrations close to its own natural period, so their output waveforms will be different, as shown in Figure 1. However, if the natural period of a seismometer is known in advance, the dominant period and amplitude of earthquake motion can be estimated from the output amplitude of these seismometers. The present invention uses one set of seismic wave observation outputs from two types of seismometers with different natural periods, and calculates the dominant frequency and amplitude in each frequency band based on two sets of seismic wave observation outputs belonging to two frequency bands. The idea is to use these calculations to estimate the epicenter distance.

FIG. 2 is a block diagram showing the first embodiment. 1, 2, 3, and 4 are sensors that detect ground motion at the same point, and their respective natural frequencies are, for example, the first
Sensor 1 is 0.1 Hz, second sensor 2 is 0.5 Hz, third sensor 3 is 1 Hz, and fourth sensor 4 is 5 Hz. 51, 52, 53, 54 are amplifiers that amplify the detection signals from the sensors 1, 2, 3, 4; 61, 62, 63, 64 are buffer amplifiers;
8 is a processing device that processes ground motion data from detection signals from sensors 1, 2, 3, and 4 to calculate the epicenter distance. The processing device 8 includes sampling means 111,1
12, 113, 114, exponential smoothing means 121,
122, 123, 124, dominant period calculation means 13
1,132, an epicenter distance calculation means 14, and an epicenter distance output means 15. FIG. 3 is a flowchart of the embodiment.

The sensors 1 to 4 constantly detect ground motion at the location where they are installed, convert this into an electrical signal, and send it to the processing device 8. The processing device 8 includes the sensor 1,
2, 3, 4 detected and amplifiers 51, 52, 5
3, 54, buffer amplifier 61, 62, 63, 6
It takes in ground motion information that is constantly sent through 4.

The sampling means 11 includes each of the sensors 1, 2, 3,
4 information at predetermined time intervals (for example, 1/50 to 1/15
0), and the offset level, which is the direct current component of the input data, is calculated from the average value of the past sampling information. This offset level is constantly updated based on sampling information obtained from time to time. In addition, sensors 1, 2,
The values obtained by removing the offset level from the four sampling values of ground motion information detected by 3 and 4 and sent from time to time x ₁ (t), x ₂ (t), x ₃ (t), x ₄
(t) is calculated. If the sampling value is x _si (t) and the offset level is x _pi , then x _i (t) = x _si (t)
−x _pi (i=1, 2, 3, 4).

Exponential smoothing means 121, 122, 123, 12
4 performs the smoothing of x _i (t) described above. That is,
The exponential smoothing value x _ai (t) is calculated using the following formula.

x _ai (t)=x _ai (t-1)×α _i +x _i ² (t) ……(1) α _i is a constant of about 0.9. Moreover, x _ai (t-1) is an exponentially smoothed value one sample before time t.

With this smoothing method, it is possible to suppress the influence of noise components superimposed on the signal, and to grasp fluctuations in the envelope of the vibration waveform in real time.

Incidentally, it is obvious that the meaning of this equation (1) indicates the following.

x _ai (t)=x _ai (t-1)×α _i +x _i ² (t)=(x _ai (
t-2)×α _i +x _i ² (t-1))×α _i +x ₁ ² (t) =x _ai (t-2)×α _i ² +x _i ² (t-1)×α _i +x ₁ (
t)=(x _ai (t-3)×α _i +x _i ² (t-2))×α _i ²
+x _i ² (t-1)×
α _i +x _i ² (t) =x _ai (t-3)×α _i ³ +x _i ² (t-2)×α _i ² +x _i ²
(t-1)×α _i +x _i ² (t) =…+x _i ² (t-n)×α _i ⁿ +…+x _i ² (t-3) ×α _i ³ +x _i ² (t-2) ×α _i ² +x _i ² (t−1)×α
_i + x _i ² (t) In other words, Equation (1) expresses the effect of the current instantaneous squared amplitude as it is, but each time you go back one step to the past, the influence of the instantaneous squared amplitude at that time increases by α _i times. It represents the accumulation of squared amplitudes. If x _i ² (t)
If is constant, then Equation (1) will be obtained by multiplying this constant value by the sum of the geometric series of the initial value 1 common ratio α _i . If α _i
If is less than 1, the sum of this geometric series is finite and becomes 1/(1-α _i ). Therefore, equation (1) multiplied by (1-α _i ) represents the envelope amplitude obtained by smoothing the squared amplitude value. Such smoothing reduces the influence of past instantaneous amplitudes exponentially, so
It's called exponential smoothing. This smoothing method digitally imitates an electrical smoothing circuit,
Smoothing circuits are commonly used in electricity.

With this smoothing method, it is possible to suppress the influence of noise components superimposed on the signal, and to grasp fluctuations in the envelope of the vibration waveform in real time. Note that, as is clear from the expansion of the equation, the amplitude values such as x _i in equation (2) are not instantaneous amplitude values but amplitude values expressed by fluctuations in the envelope of the vibration waveform.
Further, since the ratio thereof is calculated, there is no problem even if the envelope amplitude value is multiplied by a constant. Therefore, in order to simplify the calculation, when defining the smoothing method for calculating the envelope amplitude value, (1-α _i ) was not multiplied.

Natural period of one sensor ₁ Hz, output signal x ₁
(t), the natural frequency of the other one _{is 2} Hz, the output signal is x ₂
(t), the dominant frequency (t) is calculated using the following formula.

(t) ² = {( ₂ ² ×x ₂ (t) − ₁ ² ×x ₁ (t) / ₂ ² ×x ₁ ²
(t) − ₁ ² ×x ₂ ² (t)} ^1/2・_{1 2} Let the natural frequencies of sensors 1 and 2 be ω ₁ , ω ₂ , the damping constants be h ₁ , h ₂ , and the true acceleration of ground vibration waveform y
Then, the output waveform is output as an electrical signal according to the motion system shown in equations (2) and (3).

x¨ ₁ +2h ₁ ω ₁ x〓 ₁ +ω ₁ ² x ₁ =2h _{1 ω} 1 y¨ (2) x¨ ₂ +2h ₂ ω ₂ x〓 ₂ +ω _{2 2} ^x ₂ =2h ₂ ω ₂ y¨ (3) In this case, the sensors 1 and 2 convert the vibration of the pendulum directly into an electrical signal and output it.
x ₁ , x ₂ are relative displacements, x〓 ₁ , x〓 ₂ are relative velocities, x ¨ ₁ ,
x¨2 is _the output waveform corresponding to relative acceleration.

The output values of sensors 1 and 2 can take various values, but in this example, x ₁ and x ₂ corresponding to displacement
This example shows what outputs .

y=ae ^j 〓 ^t (a＞0) (4) x ₁ ＝x ₁ e ^j( 〓 ^t+ 〓 ¹⁾ (x ₁ ＞0) (5) x ₂ ＝x ₂ e ^j( 〓 ^t+ 〓 ²⁾ ( x ₂ > 0) (6) Then, from equation (2), (ω ₁ ² −ω ² +j2h ₁ ω ₁ ω) x ₁ e ^j( 〓 ^t+ 〓 ¹⁾ = −2h ₁ ω ₁ aω ² e ^j 〓 ^t ∴x ₁ = −2h ₁ ω ₁ aω ² /ω ₁ −ω ² +j2h ₁ ω ₁ ω・e ^-j 〓 ¹ (7) x ₁ is an output proportional to speed and is a real number (positive) from, Similarly, The input speed amplitude is a〓, and this is set as the unknown number X.
Also, the input frequency is ω, which is also considered an unknown quantity, and X,
Derive ω from x ₁ and x ₂ .

From equations (8) and (9), x ₁ ² {(ω ₁ ² −ω ² ) ² + (2h ₁ ω ₁ ω) ² }=4h ₁ ² ω ₁ ^{2
ω 2} _{_} ^_ _{_} ^{_ _ _} _{_ _} ^_ _{_} ^_ _{_} ^{_
ω 2} _{_} ^_ _{_} ^_ _{_} ^_ _{_} ^{_ _ _} _{_ _} ^_ _{_} ^_
ω ₁ ² x ₂ ² {(ω ₂ ² −ω ² ) ² + (2h ₂ ω ₂ ω) ² }=0 (h ₂ ² ω _{2 2} ^x ₁ ² −h ₁ ² ω ₁ ² x ₂ ² )ω ⁴ + (-2h ₂ ² x ₁ ² +4h ₁ ² h ₂
² x ₁ ² +2h ₁ ² x ₂ ² −4h ₂ ² h ₁ ² x ₂ ² )ω ₁ ² ω ₂ ² ω ² +h ₂ ² ω ₂ ² x ₁ ² ω
₁ ⁴ −h ₁ ² ω ₁ ² x ₂ ² ω ₂ ⁴ = 0 (h ₂ ² ω ₂ ² x ₁ ² −h ₁ ² ω ₁ ² x ₂ ² ) ω ⁴ + {−2h ₂ ² x ₁ (1 −2h ₁
² ) +2h ₁ ² x ₂ ² (1 −2h ₂ ² )}ω ₁ ² ω ₂ ² ω ² +h ₂ ² ω _{2 2} ^x 1 ² −h _{1 2} ^ωx _{2 2} ^ω ₂ ⁴
=0(12) Here, A=h ₂ ² ω ₂ ² x ₁ ² −h ₁ ² ω ₁ ² x ₂ ² (13) B={−h ₂ ² x ₁ ² (1−2h ₁ ² )+h ₁ ² x ₂ ² (1-2h ₂ ² )
}ω ₁ ² ω ₂ ² (14) C=h ₂ ² ω ₂ ² x ₁ ² ω ₁ ⁴ −h ₁ ² ω ₁ ² x ₂ ² ω ₂ ⁴ (15) Then, equation (12) becomes Aω ⁴ +2Bω ² +C=0 (16). If we solve equation (16) for ω ² considering ω ² >0, then becomes. In order for ω ² >0, B ² −AC>0 and AC<0.

From equations (10) and (11), x ₁ ² = (2h ₁ ω ₁ ωX) ² / (ω ₁ ² −ω ² ) ² + (2h ₁ ω ₁ ω
) ² (18) x ₂ ² = (2h ₂ ω ₂ ωX) ² / (ω ₂ ² −ω ² ) ² + (2h ₂ ω ₂ ω
) ² (19) Substituting equations (18) and (19) into equation (13), A=4h ₁ ² h _{2 2} ^ω ₁ ² ω ₂ ² ω ² X ² / (ω ₁ ² −ω ² ) ² +(2h ₁ ω ₁
ω) ² −4h ₁ ² h ₂ ² ω ₁ ² ω ₂ ² ω ² X ² / (ω ₂ ² −ω ² ) ² + (2h ₂
ω ₂ ω) ² =4h ₁ ² h ₂ ² ω ₁ ² ω ₂ ² ωX ² / {(ω ₁ ² −ω ² ) ² + (2h ₁ ω
₁ ω) ² }{(ω ₂ ² −ω) ² }+(2h ₂ ω ₂ ω) ² } ・{(ω ₂ ² +ω ₁ ² )(ω ₂ ² −ω ₁ ² )−2(ω ₂ ² −ω ₁ ²
)ω ² +4(h ₂ ² ω ₂ ² −h ₁ ² ω ₁ ² )ω ² }(20) Substituting equations (18) and (19) into equation (15), C=h ₂ ² ω ₂ ²・(2h ₁ ω ₁ ωX) ² / (ω ₁ ² −ω ² ) ² + (2h ₁
ω ₁ ω) ²・ω ₁ ⁴ −h ₁ ² ω ₁ ²・(2h ₂ ω ₂ ωX) ² / (ω ₂ ² −
ω ² ) ² + (2h ₂ ω ₂ ω) ²・ω ₂ ⁴ = 4h ₁ h ₂ ² ω ₁ ² ω _{2 2} ^{ω 2} X ² / {(ω ₁ ² −ω ² ) ² + (2h ₁ ω
₁ ω) ² } {(ω ₂ ² −ω ² ) ² + (2h ₂ ω ₂ ω) ² } ・[ω ₁ ⁴ {(ω ₂ ² −ω ² ) ² + (2h ₂ ω ₂ ω) ² − ω ₂ ⁴ {
(ω ₁ ² −ω ² ) ² + (2h ₁ ω ₁ ω) ² }] (21) (ω ₁ ² −ω ² ) ² + (2h ₁ ω ₁ ω) ² >0, (ω ₂ ² −ω ² ) ² + 2 (h ₂ ω ₂ ω) ² > 0 ω ₂ ² > ω ₁ ² , so equation (20) x equation (21) = AC
<0, {(ω ₂ ² +ω ₁ ² )(ω ₂ ² −ω ₁ ² ) −2(ω ₂ ² −ω ₁ ² )ω ² +4(h ₂ ² ω ₂ ² −h ₁ ² ω ₁ ² )ω ² } ・[ω ₁ ⁴ {(ω ₂ ² −ω ² ) ² + (2h ₂ ω ₂ ω) ² } −ω ₂ ⁴ {(ω ₁ ² −ω ² ) ² + (2h ₁ ω ₁ ω) ² }〕<0. Rearranging the left side of the above equation, ω ² [(ω ₂ ² + ω ₁ ² ) (ω ₂ ² −ω ₁ ² ) + 2ω ² {(1−2h ₁
² )ω ₁ ² −(1−2h ₂ ² )ω ₂ ² )}]・[ω ² (ω ₁ ² +ω ₂ ² )(ω ₁ ² −ω ₂ ² )−2ω ₁ ² ω ₂ ² {(1 −2h ₂ ² )
ω ₁ ² −(1−2h ₁ ² )ω ₂ ² }〕＜0(22) Therefore, (1−2h ₁ ² )ω ₁ ² −(1−2h ₂ ² )ω ₂ ² 0 (1−2h ₂ ² ) ω ₁ ² −(1−2 ₁ ² )ω ₂ ² 0, then formula (22) is satisfied.

If you choose h ₁ = h ₂ = 1/√2, then A=1/2 (ω ₂ ² x ₁ ² −ω ₁ ² x ₂ ² ) B=0 C=1/2ω ₁ ² ω ₂ ² (x ₁ ² ω ₁ ² −x ₂ ² ω ₂ ² ) Therefore, equation (14) is This equation (23) gives the dominant period. That is, ω={(x ₂ ² ω ₂ ² −x ₁ ² ω ₁ ² )/(x ₁ ² ω ₂ ² −x ₂ ² ω ₁ ² )
} ^1/4 (ω ₁ ω ₂ ) ^1/2 (24) = {(x ₂ ² ₂ ² −x ₁ ² ₁ ² )/(x _{1 2} ² ₂ ^−x ₂ ² ₁ ² )
^{} 1/4} ( _{1 2} ^{) 1/2} _On ^the other hand, regarding _X ^, from _equation ( ^{10 )} _, 4h ₁ ²
ω ₁ ² ω ² ) (25) Substituting h ₁ = 1/√2 into this equation, X ² = x ₁ (ω ₁ ⁴ + ω ⁴ )/2ω _{1 2} ^{ω 2} (26) Furthermore, equation (17) Substituting ω ² of accordingly The first dominant period calculation means 131 calculates the output signal x _a1 (t) of the first and second exponential smoothing means 121 and 122.
and the dominant period _L (t) and amplitude of the lower frequency than x _a2 (t)
Calculate a _L (t). Second dominant period calculation means 1
32 is the third and fourth exponential smoothing means 123, 124
The dominant period _H (t) and amplitude a _H (t) of the high frequency are calculated from the output signals x _a3 (t) and x _a4 (t). here,
The signal from the first sensor 1 is input to the predominant period calculation means 131 on the low frequency side, and the signal from the fourth sensor 4 is input to the predominant period calculation means 132 on the high frequency side. The natural period of the first sensor 1 is 0.1 Hz, and the natural period of the fourth sensor 4 is 5 Hz.
Therefore, the first dominant period calculating means 131 is on the low frequency side, and the second dominant period calculating means 132 is on the high frequency side.

The power source distance calculation means 14 calculates the dominant frequency _L from the first and second dominant period calculation means 131 and 132.
(t), _H (t) and the amplitudes a _L (t), a _H (t), the epicenter distance R(t) is calculated using the following formula.

R(t)=Q・V _p・log(a _L (t)/a _H (t))/π(l
oge) ( _H − _L ) (29) Here, Q is a constant indicating wave attenuation, and for example, 150 is adopted. V _p indicates the average velocity of P waves on the propagation path, and is set to 6.5 Km/sec, for example. π
is pi.

The estimation formula for the epicenter distance shown in equation (29) can be obtained as follows.

If the amplitude when R Km from the epicenter is a, and the amplitude when R _O Km is a _O , then a is expressed by the following formula.

a=(a _O /√ _O )e ^- 〓 ^R (30) α is a constant, α=2πh/λ=ωh/V _p =2πh/V _p λ=V _p If we take the logarithm of equation (30), we get log a=log a _O −αRlog e−0.5logR _O =log a _O −2πhR/V _p log e−1/2logR _OHere , the amplitudes observed by the two sensors are a _L , a _H
Then, log a _L = log a _O −2πh (log e) R/V _p・_L −1/2log R _O (31) log a _H = log a _O −2πh (loge) R/V _p・_H −1/ 2logR _O (32) Eliminating a _O from equations (31) and (32), log a _L − log a _H = 2πh (log e) R/V _p ( _H − _L ) (33) ∴R=V _p log(a _L /a _H )/2πh(log e)・( _H − _L
) = QV _p log (a _L / a _H ) / π (log e) ( _H − _L ) (34
) However, _H > _L and a _L > a _H.

The epicenter distance output means 15 is the epicenter distance calculation means 1
The epicenter distance R(t) at that time calculated in step 4 is output to the outside.

Earthquakes are vibrations caused when a fault breaks, and if the fault is large, it takes time for the fault to break. Additionally, the epicenter is where the destruction is currently occurring and is constantly moving. Therefore, to be precise, the epicenter distance changes while the fault movement continues, but if the distance between the observation point and the epicenter is sufficiently larger than the size of the fault, the estimated epicenter distance will not change much. , if the observation point is located close to the fault compared to its size, the epicenter distance may vary greatly. Therefore, rather, the present invention can encourage such changes that have been overlooked in the past, and the object of the present invention is more than achieved.

(Second Example) In the second example, three sensors are prepared,
The output of the sensor with a low natural period is sent to the first sampling means 121, the output of the sensor with a high natural period is sent to the fourth sampling means 124, and the output of the sensor with a natural period intermediate between the two natural periods is sent to the first sampling means 121. 2nd output
and third sampling means 122 and 123, respectively. In this way, the configuration can be configured with one less sensor than the first embodiment.

(Third Embodiment) FIG. 4 shows a block diagram of a third embodiment.
In FIG. 4, 5 is an amplifier, 6 is a buffer amplifier, 71, 72, and 73 are characteristic conversion devices, and the others are the same as those in FIG. 2.

In the third embodiment, one sensor is installed, and the characteristic conversion devices 71, 72, 73 for converting the characteristics of the signal of the sensor 1 are connected to the buffer amplifier 6 and the second, third, and fourth samples. converting means 112, 11
3,114. The characteristic conversion devices 71, 72, 73 convert the outputs into the sampling means 112, 11 as if they were output from a sensor having a natural period different from that of the sensor 1.
3,114, for example, the natural period of sensor 1 is 0.1Hz as in the first embodiment,
Regarding the natural period, the first characteristic conversion device 71 is set to 0.5Hz,
The sampling means 11 sets the second characteristic converting device 72 to 1 Hz and the third characteristic converting device 73 to 5 Hz.
1, 112, 113 and 114, respectively. These characteristic conversion devices 71, 72, and 73 are disclosed in Japanese Patent Application Laid-Open No. 56-46479 (Japanese Patent Application No. 122559-1982). In other words, as shown in Fig. 5, the vibration waveform is input as an electrical signal, has arbitrarily settable frequency characteristics and damping characteristics, and there is a virtual seismometer function that simulates the sensor based on these, and a virtual seismometer function that simulates the sensor and the virtual seismometer function. a function of multiplying the output of the sensor by a constant determined by the format and characteristics of the seismograph function and inputting this to the virtual seismograph function;
A device that has the function of multiplying various output signals output from the simulation results of the virtual seismograph function by a constant derived from the frequency characteristics and braking characteristics of the sensor, and adding these together. It is. In FIG. 5, 501 is a sensor;
502 is an n multiplier, 503 is a virtual seismograph, and 504 is an adder. The outputs of the characteristic conversion devices 71, 72, 73 and the output of the buffer amplifier 6 obtained by such a configuration are sampled by sampling means 111, 1, respectively.
12, 113, and 114, the epicenter distance can be obtained in the same manner as in the first embodiment.

In addition, the first or second characteristic conversion device 71 or 7
2, for example, the second characteristic conversion device 7
2 is omitted and the output of the first characteristic conversion device 71 is used as a common input for the second and third sampling means 112, 113, thereby obtaining the epicenter distance in the same manner as in the second embodiment. Can be done.

(Effects of the Invention) According to the present invention, the epicenter distance of a seismic wave can be calculated immediately after the arrival of the seismic wave by observation at one point, and it is no longer necessary to arrange a large number of seismometers over a wide area as in the past. This has the advantage of being unnecessary. Additionally, since the distance to the epicenter can be determined in real time, it can be used as a basis for determining earthquake warning systems.

[Brief explanation of the drawing]

Fig. 1 is a waveform diagram showing an example of observation when one earthquake is observed simultaneously by seismometers with different natural periods, Fig. 2 is a block diagram showing the first embodiment, and Fig. 3 is a diagram of the embodiment. Outline processing flowchart, No. 4
The figure is a block diagram showing the third embodiment, and FIG. 5 is a block diagram explaining the characteristic conversion device. 1, 2, 3, 4...sensor, 51, 52, 5
3, 54...Amplifier, 61, 62, 63, 64...
... Buffer amplifier, 71, 72, 73 ... Characteristic conversion device, 8 ... Processing device, 111, 112, 11
3,114...Sampling means, 121,122,1
23, 124...exponential smoothing means, 131, 13
2... Predominant period calculation means, 14... Epicenter distance calculation means, 15... Epicenter distance output means.

Claims (1)

[Claims] 1 Set the seismic observation outputs from two types of seismometers with different natural periods as one set, and input the two sets of observation outputs: the set containing the seismometer with the longest natural period and the set containing the seismometer with the shortest natural period. Then, by means of calculating an exponentially smoothed value of the observation output of each set, and the exponentially smoothed value of the observed waveform of each set of seismometers and the natural period of each set of seismometers, the dominant frequency in two high and low frequency bands is calculated. and a dominant frequency calculation means for calculating the component amplitudes thereof, the logarithm of the ratio of the two component amplitudes obtained from the two sets of predominant frequency calculation means, and the two dominant frequencies obtained from the two sets of predominant frequency calculation means. What is claimed is: 1. An epicenter distance calculation device, comprising means for calculating a ratio between the difference and the difference, to obtain an epicenter distance of an observation point.