JP2870407B2 - Remote tsunami forecast support system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distant tsunami forecasting support system installed under the sea, and particularly to a distant tsunami forecasting earthquake-related device.
The epicenter and oscillation time are obtained using underwater propagation acoustic signals associated with crustal movements caused by fault movement and crustal activity involving rapid changes in the volume of seawater such as submarine volcanic explosions and submarine landslides. The present invention relates to a distant tsunami forecasting support device having a function of predicting the arrival time of a tsunami.

[0002]

2. Description of the Related Art Conventional tsunami warnings include, for example, "Ocean Physics II".
I "(Marine Science Basic Course 3.295 pages, Tokai University Press, 19
(1981), this method uses only the information on the seismic waveforms observed on land to determine whether or not a tsunami has occurred using a tsunami forecast map, and then makes a forecast.

[0003] Specifically, the conventional tsunami forecasting method comprises a large number of seismometers (71 _{1 to} 71 _n ) installed on land, an epicenter estimator 72, a tsunami determiner 73, and a tsunami arrival time estimator. The tsunami forecast is basically performed as follows (FIG. 7).

That is, a large number of seismographs (71 _{1 to} 71) installed on land are used to transmit seismic waves generated at the epicenter and transmitted underground.
_n ) and record the arrival time and amplitude. Using the arrival time information from each seismograph, the epicenter is estimated by the epicenter estimator 72. The tsunami determiner 73 determines whether the epicenter is below the sea floor, and plots the amplitude and epicentral distance (distance between the epicenter and each seismograph) recorded on each seismograph on a tsunami forecast map as shown in Fig. 8. Then, the magnitude of the tsunami expected by the approximate curve is estimated. When the presence or absence of a tsunami is determined, a tsunami arrival time estimator 74 calculates a tsunami arrival time in an area to be predicted, such as an important port, and issues a tsunami forecast.

[0005]

By the way, the tsunami propagates the vertical movement of the sea surface caused by large-scale seafloor crustal deformation caused by fault movement accompanied by seismic waves.
Some occur mainly due to rapid changes in seawater volume, such as submarine volcanic explosions and submarine landslides. Among them, in the case where the earthquake occurrence area is far away from the observation point or in the case of a tsunami caused by a change in the volume of seawater, the amplitude of the observed seismic wave may be smaller than the damage caused by the tsunami.

Therefore, the conventional tsunami forecasting method using a seismometer at a land-based observation point cannot detect a seismic wave signal due to a seafloor landslide hardly becoming energy of a seismic motion or a seafloor crustal deformation generated at a distant place where the seismic motion is greatly attenuated. However, there was a problem that a tsunami warning could not be issued.

[0007] Further, when issuing a warning for a tsunami caused by crustal activity generated in distant places such as Hawaii and Chile, where the difference in signal arrival time at each observation point is small, which observation point was used to determine the arrival direction of the seismic wave. There was also a problem that the epicenter estimation ability was low and the estimation error of the epicenter was large or impossible to estimate.

An object of the present invention is to solve these problems by making an epicenter determination using underwater propagation acoustic signals, and furthermore, making the tsunami propagation velocity dependent only on the average water depth and gravitational acceleration of the propagation path. It is an object of the present invention to provide a distant tsunami forecasting support device that can calculate a tsunami arrival time in an arbitrary coastal area using the system.

[0009]

Means for Solving the Problems In order to achieve the above object, a remote tsunami forecasting support apparatus of the present invention has the following configuration. In other words, far-field tsunami forecast support apparatus of the present invention is, in the far-field
Oceans such as crustal deformation accompanied by seismic waves and submarine volcanic explosions
Water generated by crustal activity with rapid volume change of water
Tsunami for specific area based on reception of medium propagation acoustic signal
Tsunami Forecasting of Underwater Mounted Sensor for Supporting Forecasting
The information support device, wherein each one of the pair of hydrophones arranged in parallel to each of two orthogonal axes is separated by a predetermined distance.
A shared hydraulic that occupies the origin of the two orthogonal axes.
Means for receiving an underwater propagation sound signal with each of the hydrophones ; means for calculating the direction of arrival of the signal from the received sound signal; means for measuring the time of arrival of the signal from the received sound signal When; in that it comprises: means for estimation <br/> constant the intersection seeking intersection of direction of arrival calculated by the plurality of pairs means that a set of the three means signal source as (hypocenter) It is a feature.

Then, it is determined whether the estimated signal generation source is near the seabed or inland, and when it is near the seabed,
Is equipped with a means for issuing an alarm notifying the arrival of a tsunami .

Further, based on the estimated signal source and the signal measurement time , the underwater propagation acoustic signal generated due to the crustal activity.
Signal generating time and means for estimating the (oscillation time) of No.; calculating a tsunami predicted arrival time at a specific position from the depth data of the sea with a built-signal source and the signal generation time and advance, Tsu
Means for issuing an alarm notifying the arrival of a wave .

[0012]

Next, the operation of the present invention configured as described above will be described. Underwater acoustic signals are less likely to attenuate signals from distant places than seismic signals, tend to reflect crustal activity in the vicinity of the sea floor, especially inducing rapid volume changes in seawater, and propagation speed propagates through the crust Earthquake wave (5-10
km / s) (1.5 km / s), the arrival time difference of each observation point is large, and the accuracy of determining the signal arrival direction is high.

Accordingly, the present invention provides a method in which one of the two pairs of spaced apart hydrophones is placed at the origin.
A plurality of orthogonally arranged acoustic sensors are arranged underwater as shared hydrophones, and the direction of arrival and the time of arrival can be obtained from the received signals of each acoustic sensor to estimate the epicenter.

As a result, it can be determined whether the epicenter is near the sea floor or inland, and an appropriate alarm can be issued. Also, by providing the water depth data of the monitored sea area, the predicted tsunami arrival time can be calculated, and a more accurate forecast of a distant tsunami that could not be predicted conventionally or has low accuracy can be performed.

[0015]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 shows a distant tsunami forecasting support device according to one embodiment of the present invention. As shown in FIG. 1, the apparatus of this embodiment includes an acoustic signal direction / time detector (11 _{1 to} 11 _n ), an epicenter estimator 12, an oscillation time estimator 13, and a tsunami arrival time estimator 14. It is basically composed of

Sound signal azimuth / time detector (11 _{1 to} 11)
_n ), as shown in FIG. 2, an acoustic sensor unit 21, a phase processing unit 22, an arrival direction calculation unit 23, and a time measurement unit 24.
And an arrival time measuring unit 25, and are arranged, for example, underwater along the coast.

The acoustic sensor section 21 is configured by arranging a pair of hydrophones separated by a predetermined distance in parallel with each of two orthogonal axes, and each hydrophone receives a wave signal in the sea. For example, it is as shown in FIG.
Incidentally, it indicated by circular as an acoustic sensor 21, a housing cylindrical acoustic signal azimuth-time detector (11 ₁ ~11 _n), each component including the acoustic sensor unit 21 therein It is intended to be incorporated.

In FIG. 3, the acoustic sensor section 21
It is shown that it is basically composed of three hydrophones 31, 32 and 33. That is, (31, 32) and (31, 33) of the three hydrophones are paired hydrophones that are separated from each other by a predetermined distance. Are installed so as to be orthogonal. The hydrophones (31, 32) correspond to the x axis, and the hydrophones (31, 33) correspond to the y axis. There is a time difference between the received signals of these hydrophones with respect to the hydrophones.

Therefore, the phase processing unit 22 calculates the arrival time difference τ _x from the received signal of the hydrophone (31, 32),
The arrival time differences τ _y are calculated from the reception signals of the hydrophones (31, 33), respectively, and provided to the arrival direction calculation unit 23.
Here, the arrival time difference between each hydrophone is represented by the angle θ from the x-axis as shown in FIG.
In the direction of, if the distance between the hydrophones is d, it is expressed by Equation 1.

[0020]

Τ _x = (d · cos θ) / V τ _y = (d · sin θ) / V

The arrival direction calculation unit 23 calculates the arrival direction θ in the horizontal plane by the following equation (2), and gives it to the arrival time measurement unit 25.

[0022]

## EQU2 ## θ = tan ⁻¹ (τ _y / τ _x )

The arrival time measuring section 25 records the time at which the arrival of the signal is recognized among the time data of the time measuring section 24 which constantly counts the time.

Returning to FIG. 1, the epicenter estimator 12 estimates the epicenter based on the directions of arrival estimated by the plurality of acoustic signal direction / time detectors 11 as described above. Specifically, as shown in FIG. 5, the sound signal azimuth and time detectors (11 ₁ to 11 ₁ )
The point connecting the azimuth lines 51 to 54 calculated in 11 _n ) is estimated as the epicenter 55. This makes it possible to determine whether the epicenter is in the ocean or inland.

[0025] In the oscillation time estimator 13, epicenter 55 and the acoustic signal azimuth-time detector (11 ₁ to 11 _n) distance delta _n between each (n = 1,2, ..., n : hereinafter the same) The oscillation time is calculated from Equation 3 based on the arrival time T _n previously measured by the acoustic signal direction / time detector 11 _n .

[0026]

T ₀ = {(T _n −Δ _n / V)} / n

Next, the tsunami arrival time estimator 14 having the configuration shown in FIG. 6, to estimate the tsunami arrival time of any local based estimated epicenter 55 the oscillation time T ₀ as described above .

That is, in FIG. 6, the tsunami propagation path average water depth calculation unit 64 calculates the tsunami arrival time, which is input to the estimated point coordinate input unit 61, and the epicenter location estimation unit 62 which inputs the tsunami arrival time. The average water depth up to the coordinates of each estimated point is obtained from the epicenter coordinates automatically input from the vessel and the water depth data from the water depth data recording unit 63.

[0029] As is well known, the average water depth is h, the acceleration of gravity as g, since the tsunami average propagation velocity V _n is expressed by Equation 4, at the expected tsunami arrival time calculating unit 65, the estimated location If the tsunami arrival time is calculated by Expression 5, a warning can be given.

[0030]

V _n = √ (gh)

[0031]

T _n = T ₀ + Δ _n / V _n

[0032]

As described above, the tsunami forecasting support apparatus of the present invention uses an acoustic signal that has a slower propagation speed than seismic waves and is sensitive to crustal activity that has occurred near the sea floor, and uses a sound arrival direction. The tsunami was estimated by measuring the arrival time with multiple sensors, and the estimated tsunami arrival time was calculated, so that more accurate forecasts of tsunamis that could not be predicted before or had low accuracy were made possible. it can.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a remote tsunami forecasting support apparatus according to an embodiment of the present invention.

FIG. 2 is a configuration block diagram of an acoustic signal direction / time detector.

FIG. 3 is a diagram showing an arrangement of hydrophones constituting an acoustic sensor unit.

FIG. 4 is a diagram illustrating a positional relationship between an arrival direction of a wave signal and an acoustic sensor unit.

FIG. 5 is a schematic diagram showing an epicenter determination procedure by an epicenter estimator.

FIG. 6 is a configuration block diagram of a tsunami arrival time estimator.

FIG. 7 is a block diagram of a conventional tsunami forecast method.

FIG. 8 is a tsunami forecast diagram used for a conventional tsunami forecast.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 11 Acoustic signal direction and time detector 12 Epicenter estimator 13 Oscillation time estimator 14 Tsunami arrival time estimator 21 Acoustic sensor unit 22 Phase processing unit 23 Arrival direction calculation unit 24 Time measurement unit 25 Arrival time measurement unit 31-33 Hydro Phone 61 Estimated point coordinate input section 62 Epicenter coordinate input section 63 Water depth data recording section 64 Tsunami propagation path average water depth calculation section 65 Predicted tsunami arrival time calculation section 71 Seismograph 72 Epicenter estimator 73 Tsunami determiner 74 Tsunami arrival time estimation Device θ signal arrival direction

Claims (3)

(57) [Claims] 1. Crustal deformation accompanied by seismic waves generated at a distance
Crustal activity with rapid volume change of seawater such as submarine volcanic explosion
Based on the reception of underwater acoustic signal generated by motion
A sensor sea that supports forecasting of tsunami arrivals in specific areas
A distant tsunami forecasting support device of a middle installation type, wherein one of each pair of hydrophones arranged in parallel to each of the two orthogonal axes and separated by a predetermined distance is occupied at the origin position of the two orthogonal axes.
With or without the shared hydrophone
Means for receiving an underwater propagating acoustic signal at each of the
Means for calculating the direction of arrival of the signal from the received signal;
Means for measuring the arrival time of the received signal from the acoustic signal; estimating the intersections obtain the intersection of direction of arrival calculated by the plurality of pairs means that a set of the three means signal source as (hypocenter) Means for performing a distant tsunami forecasting support apparatus, comprising: Wherein determining whether the estimated signal source is in the inland or near the sea floor, when in the vicinity of the seabed
The distant tsunami forecast support apparatus according to claim 1, further comprising: means for issuing an alarm notifying the arrival of a tsunami. 3. A water propagation acoustic signal occurring along with the crustal activity from said estimated signal source and the signal measurement time
Means for estimating the signal generation time (oscillation time) of the tsunami; calculating the estimated arrival time of the tsunami at a specific position from the signal generation source, the signal generation time, and the built-in water depth data of the tsunami;
Means for issuing an alarm notifying the arrival of the distant tsunami forecasting support device according to claim 1, characterized by comprising: