JPH057674B2 - - Google Patents

Description

[Detailed description of the invention]

(1) Technical Field of the Invention The present invention relates to a method for determining the time of seismic wave generation, that is, the time point of seismic wave generation with high accuracy. (2) Conventional technology and problems Conventionally, in order to determine the time of earthquake occurrence, observation signals from multiple seismic wave observation telemeter devices were collected at a data center, and the time of earthquake wave occurrence was determined using the moving average method. In other words, as shown in Figure 1, when seismic waves are converted to voltage levels and observed, the average voltage level a _L for a short time of about 1 second is a ₀ to a ₄₀ , and the average voltage level a L for a long time of about 40 seconds b ₄₀ to b ₀ The average value b _L is compared, and the start time of any one of the short periods a ₄₀ to a ₀ when b _L ×α<a _L is determined as the time of seismic wave generation. However, α is 1
A larger arbitrary constant is selected in accordance with the magnitude of earthquakes that are likely to occur. In Figure 1, a ₄₀ and a ₃₉
..., and when a predetermined threshold level is exceeded at a ₀ , the long-term average value b _L does not change suddenly, so the average value at short-time a ₀ changes suddenly and greatly. . In this case, it is difficult to obtain theoretically appropriate values for the length of time and the size of α, and appropriate values have been used based on experience. It is also being considered that it would be better to determine α in response to weather changes. Furthermore, since the data center determines that an earthquake has occurred when noise occurs in the same frequency band as the seismic wave at time a, there is a drawback that the actual earthquake cannot be distinguished from the noise and the earthquake occurrence time is incorrect. (3) Purpose of the Invention The purpose of the present invention is to improve the above-mentioned drawbacks and to provide a method for determining the time of seismic wave generation with high accuracy by performing multiple data processing at the same time. (4) Structure of the invention The structure of the present invention to achieve the above object is as follows:
In a method in which observation signals from seismic wave observation telemeter equipment are collected in a data center and the occurrence of an earthquake is determined based on changes in the observation signals, the observation signals are constantly subjected to fast Fourier transform and the integrated value of the spectrum in a frequency range specific to seismic waves is calculated. and a second comparison circuit that calculates a moving average of the observed signal and compares it with the normal value; It is determined that an earthquake has occurred when the second comparison circuit (described below) also detects that the specified level has been exceeded. The time when it is determined that the earthquake occurred is the time when the earthquake occurred. (5) Embodiment of the invention FIG. 2 is a diagram showing the configuration of an embodiment of the invention.
Observation signals from the seismometer EQ and its telemeter device TM are collected at the data center DTC. In the data center DTC, the telemeter receiving device TRV performs A/D conversion, and a determination is made on the obtained digital signal. The digital signal is input to the moving average processing circuit TD using the above-mentioned moving average method and the fast Fourier transform processing circuit FFT according to the present invention.
The fast Fourier transform process is to obtain frequency versus amplitude values for a digital signal at a certain time, as shown in FIGS. 3A and 3B. That is, when a signal exceeding the above-mentioned threshold level shown in FIG. 3A is input for the characteristic frequency range W1 to W2 of seismic waves, the amplitude integral value A1 and the so-called normal state shown in FIG. 3B are At a certain time t1 at the noise level of
is compared with the amplitude integral value A2. Then, the time t0 when A2×β<A1 (where β is an arbitrary constant greater than 1) is determined to be the time of seismic wave generation. The central processing unit CPU performs fast Fourier transform processing and operates as a first comparison circuit that compares the integrated values A1 and A2. Furthermore, since the central processing unit CPU performs determination using the moving average method as in conventional devices, it also operates as a second comparison circuit. As a result, the central processing unit CPU detects the occurrence of seismic waves using the same moving average method as described above, and further uses the FFT
When the occurrence of seismic waves is detected by the method, it is judged as a true seismic wave occurrence, and in this case, the earthquake occurrence time is the time obtained by the moving average method or the time obtained by the FFT method, for example, the time obtained by the latter FFT method. It is determined in advance that If the moving average method determines that an earthquake has occurred, but the FFT method does not determine that an earthquake has occurred, the central processing unit assumes that it is due to external noise and does not perform any further processing. Furthermore, when calculating using FFT, noise in the band specific to seismic waves is constantly investigated, so
By subtracting the noise signal from the observed signal in a band specific to seismic waves and then performing arithmetic processing, it is possible to remove the influence of noise mixed in the seismic waves. (6) Effects of the Invention As described above, according to the present invention, by using determination based on fast Fourier transform together with determination based on conventional moving average, when determining seismic waves from different points, geological conditions along the way and , it is possible to reduce errors based on weather conditions and obtain highly accurate seismic wave generation times. In addition, even when sudden external noise arrives and the background noise changes, the effects can be easily removed.
Time observation becomes more accurate, and the location of earthquake occurrence can be determined more accurately.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram for determining seismic waves by the moving average method, FIG. 2 is a diagram showing the configuration of an embodiment of the present invention, and FIG. 3 is an explanatory diagram of fast Fourier transform processing. EQ...seismograph, TM...telemeter device,
DTC...Data center, TRV...Moving average processing circuit, FFT...Fast Fourier transform processing circuit,
CPU...Central processing unit.

Claims (1)

[Claims] 1. A method in which observation signals from a seismic wave observation telemeter device are collected in a data center and the occurrence of an earthquake is determined based on changes in the observation signals, the observation signals being constantly subjected to fast Fourier transform to determine the frequency characteristic of seismic waves. a first comparison circuit that compares the integrated value of the spectrum in the range with the integrated value during normal times; and a second comparing circuit that calculates a moving average of the observed signal and compares it with the normal value; When the comparison circuit detects that the specified level has been exceeded, and the second comparison circuit (described below) also detects that the specified level has been exceeded, it is determined that an earthquake has occurred. An earthquake occurrence determination method characterized by setting the time when a circuit determines that a specified level has been exceeded as the earthquake wave occurrence time.