JP2020079716A - Bottom tremor survey apparatus - Google Patents

Abstract

To do work for installing a tremor measuring device on the bottom of the water simply and efficiently.SOLUTION: A buoy 2 is able to float on the surface of the water 10 and is connected to a tremor measuring device 3. The tremor measuring device 3 is installed in or on the bottom of the water 20 for detecting a tremor of the bottom of the water 20. A main body unit 4 comprises a recording unit 41 for recording the output of the tremor measuring device 3. The main body unit 4 is mounted on the buoy 2, thereby being able to be arranged in the vicinity of the surface of the water 10.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a technique for performing microtremor array exploration on a water bottom such as a sea bottom or a lake bottom.

  The following Patent Document 1 describes a technique for microtremor array exploration used to obtain ground information up to a depth of about 100 m. The microtremor array exploration is a method in which a plurality of sensors (microtremor) are installed on the ground surface to observe microtremors, and the observed microtremors can be analyzed to estimate the S wave velocity structure of the ground.

  According to such a microtremor array survey, information on the underground structure of the ground can be obtained by a simple and nondestructive method of arranging a sensor on the ground surface.

  In recent years, microtremor array exploration on the seabed has also been proposed (Non-Patent Document 1 below). In the technique of Non-Patent Document 1, a cable is arranged from the microtremor installed on the seabed to the ship, and a signal from the micromotion meter is sent to the ship for observation.

  However, in general, when performing microtremor surveys on the seabed, it is expected that the water depth will be, for example, on the order of 10 m to 100 m. The distance between the micromotion meters arranged in an array is, for example, about 50 m to 200 m. Under such circumstances, pulling the cables from each microtremor onto the ship is expected to be quite difficult in reality. It is conceivable to distribute the cables to multiple ships, but in that case the cost of chartered ships will increase. In addition, pulling a cable on a ship in rough seas also increases the burden on the ship.

  Further, in this technology, in order to install the microtremor on the seabed, it is assumed that the microtremor will be dropped into the sea from above the sea surface. However, due to the influence of the ocean current, etc., the drop position and the position of the microtremor on the seabed will be displaced. Therefore, the conventional technique has a problem that it is difficult to grasp the accurate position of the microtremor on the seabed.

JP 2006-349491 A

Yoshiya Inoue, Takeshi Kazeran, Takeshi Yoshida, Tatsuaki Miyoshi, "Exploration of submarine tremor array", Jour. Japan Soc. Eng. Geol., Vol.42, No.4, pp.231-237, 2001

  The present invention has been made in view of the above situation. A main object of the present invention is to provide a technique capable of easily and efficiently performing the work of installing a micromotion meter on the water bottom such as the seabed. Another object of the present invention is to provide a technique for grasping the position of the micromotion meter on the bottom of the water.

  The present invention can be expressed as the inventions described in the following items.

(Item 1)
An exploration device used for microtremor array exploration at the bottom of the water,
It has a buoy, a tremor, and a main body.
The buoy is floatable on the surface of the water, and is connected to the microtremor,
The microtremor, in a state of being installed on the water bottom, is configured to detect a micromotion of the water bottom,
The main body unit includes a recording unit that records the output of the microtremor,
Moreover, the main body part is attached to the buoy, and thereby, the water bottom microtremor exploration device which can be arranged near the water surface.

(Item 2)
The main body section further includes a GPS signal receiving section,
Item 2. The water bottom tremor survey apparatus according to Item 1, wherein the GPS signal receiving unit is configured to receive time information and/or position information included in the GPS signal and record the time information and/or position information in the recording unit.

(Item 3)
The main body further includes a battery,
The water bottom microtremor surveying apparatus according to Item 1 or 2, wherein the battery is configured to supply power to the recording unit.

(Item 4)
Furthermore, it is provided with an anchor for suppressing the movement of the microtremor when installed on the bottom of the water,
The water bottom microtremor survey apparatus according to any one of Items 1 to 3, wherein the anchor is detachably attached to the microtremor.

(Item 5)
A water bottom tremor surveying method using the water bottom tremor surveying device according to any one of Items 1 to 4,
Dropping the micromotion meter into the water to dispose the micromotion meter at the bottom of the water, and to dispose the buoy and the body portion near the water surface,
Recording data of the vibration detected by the microtremor in the recording unit,
A step of searching the state of the water bottom using the vibration data recorded in the recording unit.

(Item 6)
A method for estimating the position in water of the microtremor in the water bottom microtremor exploration device according to any one of Items 1 to 4,
Propagating sound waves from a predetermined position in water,
Receiving the vibration due to the sound wave by the microtremor installed on the bottom of the water;
Estimating the position of the micromotion meter itself using the vibration received by the micromotion meter.

(Item 7)
The microtremor used in the water bottom microtremor exploration device according to any one of Items 1 to 4,
The micromotion meter includes a plurality of micromotion meter bodies capable of receiving the micromotion of the water bottom.

(Item 8)
The microtremor used in the water bottom microtremor exploration device according to any one of Items 1 to 4,
The micromotion meter comprises a micromotion meter main body and a frame capable of receiving micromotion of the water bottom,
The frame is formed with an opening that allows passage of a water flow inside the micromotion meter when the micromotion meter is installed on the water bottom.

  According to the water bottom tremor exploration apparatus of the present invention, it becomes possible to easily and efficiently perform the work of installing the tremor on the sea floor.

  Further, according to the position estimation method of the present invention, it is possible to relatively accurately estimate the position of the micromotion meter on the bottom of the water.

It is a typical explanatory view in the state where the water bottom tremor exploration device concerning one embodiment of the present invention is arranged underwater. It is a typical explanatory view in the state where a plurality of water bottom tremor exploration devices are arranged in water. It is explanatory drawing which expands and shows the part of the buoy in the water bottom microtremor search apparatus of FIG. It is a block diagram of the main body part in the water bottom microtremor survey apparatus of FIG. FIG. 2 is a perspective view of a microtremor in the water bottom microtremor exploration apparatus of FIG. 1. It is a top view of FIG. It is a front view of FIG. FIG. 7 is a left side view of FIG. 6. FIG. 6 is an enlarged perspective view of a case in the micromotion meter of FIG. 5. FIG. 12 is a right side view of FIG. 11. It is a front view of FIG. It is a schematic sectional drawing which follows the AA line of FIG. FIG. 2 is an enlarged perspective view of a main part of an anchor in the water bottom tremor exploration device of FIG. 1. It is a flowchart for demonstrating the procedure which searches using the water bottom microtremor search apparatus of FIG. It is a graph which shows an example of the fine motion waveform obtained by a fine motion meter, and a horizontal axis is time (minute) and a vertical axis is velocity amplitude (cm/s). It is a graph which shows an example of the S wave velocity structure obtained by the procedure of FIG. 14, the horizontal axis is the S wave velocity, and the vertical axis is the depth of the ground. 3 is a flowchart for explaining a procedure for estimating the position of a microtremor in the water bottom microtremor exploration apparatus of FIG. 1. It is explanatory drawing for demonstrating the procedure of FIG. It is explanatory drawing for demonstrating the procedure of FIG. It is a graph which shows the transmitted waveform from a sound wave oscillating device, and the waveform received by a microtremor. It is XY coordinate which shows the position estimation result on the horizontal plane of the micromotion meter obtained by the procedure of FIG.

  A bottom tremor survey apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings.

  The water bottom microtremor exploration apparatus (hereinafter, may be simply referred to as “exploration apparatus” or “apparatus”) 1 of the present embodiment includes a buoy 2, a micromotion meter 3, and a main body 4 (see FIG. 1). ). Further, the device 1 includes a waterproof container 5, an anchor 6, and a signal cable 7 as additional components.

  The device 1 of the present embodiment is installed at a plurality of positions in water as shown in FIG. For microtremor array exploration, at least four devices 1 are used. Since each device 1 has basically the same configuration, one device 1 will be basically described below.

  Further, in the following description, it is assumed that the device 1 is used in the sea, but it can be used in a place other than the sea such as a lake or a river.

(buoy)
The buoy 2 includes a buoy body 21 that can float on the water surface 10 (see FIGS. 1 and 2), and a hook 22 for attaching the signal cable 7 to the buoy body 21 (see FIGS. 2 and 3). .. The buoy body 21 preferably has a buoyancy capable of floating the waterproof container 5 and the body portion 4 attached to the buoy body 21 on the water surface. As such a buoy body 21, an existing one can be used, and a detailed description thereof will be omitted. The hook 22 is preferably configured so that the signal cable 7 can be easily attached to and detached from the buoy body 21. Since the existing hook 22 can be used, detailed description thereof will be omitted. With the above configuration, the buoy 2 of the present embodiment can float on the water surface 10 and is connected to the fine motion meter 3 via the signal cable 7.

(Main body)
The main body portion 4 of the present embodiment is attached to the buoy 2 so that it can be arranged near the water surface 10. Specifically, the body portion 4 is housed inside a waterproof container 5 attached to the tip of the buoy body 21. That is, the body portion 4 is attached to the tip of the buoy body 21 via the waterproof container 5 (see FIG. 3).

  The main body unit 4 of this embodiment includes a recording unit 41, a GPS signal receiving unit 42, and a battery 43 (see FIG. 4).

  The recording unit 41 includes an amplifier 411 that amplifies a signal sent via the signal cable 7, an A/D converter 412 that A/D converts the amplified signal, and a recording medium 413 that records the converted signal. And have.

  The GPS signal receiving unit 42 is configured to receive the GPS signal transmitted from the GPS satellite 50 (see FIG. 2), and is specifically configured by a GPS antenna. The GPS data (for example, time data and position data) recorded by the GPS signal receiving unit 42 can also be recorded in the recording medium 413 of the recording unit 41 in this embodiment.

  With this configuration, the GPS signal receiving unit 42 of the present embodiment receives the time information and/or the position information included in the GPS signal and records the time information and/or the position information in the recording unit 41.

  The battery 43 is configured to supply electric power for driving the operating portion of the main body portion 4, for example, the recording portion 41. Since a recording time of about several hours is sufficient for general seabed tremor array exploration, the battery 43 has a capacity corresponding to a driving time of, for example, 10 hours or more, more preferably 50 hours or more, correspondingly. Is used.

  With this configuration, the main body portion 4 of the present embodiment can record the output of the fine motion meter 3.

(Microtremor)
The fine motion meter 3 of the present embodiment includes a frame 31, a case 32 supported by the frame, a first fine motion meter body 33 and a second fine motion meter body 34 housed in the case 32. (See FIGS. 5 to 12).

  The frame 31 is configured by connecting the periphery of two coaxially arranged circular rings 311 with a connection plate 312 (see FIGS. 5 to 8 ). An opening 313 is formed between the two circular rings 311. The inside of the two circular rings 311 is an opening 314. These openings 313 and 314 are designed to allow passage of a water flow inside the micromotion meter 3 when the micromotion meter 3 is installed on the water bottom.

  The case 32 is fixed to the one annular ring 311 of the frame 31 by using an appropriate fixing tool. The case 32 has a base 321 and a cover 322 that is watertightly and detachably attached to the base 321 (see FIG. 12 ). The first fine motion meter body 33 and the second fine motion meter body 34 are arranged inside the cover 322.

  In the present embodiment, normally, only the first fine motion meter main body 33 operates and the second fine motion meter main body 34 does not operate. Specifically, as the first and second fine motion meter main bodies 33 and 34, known vibrometers that become inoperable by being placed upside down are used. By setting the arrangement direction of such a vibrometer, only one can be in the operating state and the other can be in the inoperative state. Further, by arranging the case 32 upside down with respect to the initial state, it is possible to switch the operating microtremor body.

  A connector 323 for connecting the signal cable 7 is incorporated at the end of the base 321. With this, the output of the micromotion meter 3 can be taken out to the outside.

  With the above configuration, the micromotion meter of the present embodiment can detect the micromotion of the water bottom 20 when installed in the water bottom 20.

(Waterproof container)
The waterproof container 5 has a box-like shape that is hermetically sealed so that the inside is watertight (see FIG. 3 ). The main body 4 is housed inside the waterproof container 5. The signal cable 7 passes through the waterproof container 5 and is connected to the main body 4 by using a means that does not impair the water tightness of the waterproof container 5, for example, a sealing member (not shown). As the waterproof container 5, a pressure resistant container that can be used even at a certain depth of water can be used if necessary, but generally, it does not have to have a pressure resistance enough to be used at the water bottom.

(anchor)
The anchor 6 includes an anchor body 61, a hook 62, and a chain 63 (see FIGS. 1 and 13). One end of the chain 63 is connected to the frame 31 of the micromotion meter 3. The other end of the chain 63 is detachably attached to the hook 62 attached to the end of the anchor body 61. A so-called carabiner is used as the hook 62.

  With the above configuration, the anchor 6 of the present embodiment can suppress the movement of the micromotion meter 3 when it is installed on the water bottom 20. Further, by using the hook 62, the anchor 6 of the present embodiment is detachably attached to the fine motion meter 3.

(Water bottom tremor exploration method of the present embodiment)
Next, with further reference to FIG. 14, an example of a method for exploring the micromotion of the water bottom (sea bottom in the following example) 20 using the device 1 will be described.

(Step SA-1 in FIG. 14)
In this example, it is assumed that the required number of devices 1 are mounted on a ship that can receive GPS signals. In this state, the position where the fine motion meter 3 should be dropped is determined based on the GPS signal. In the case of general microtremor array exploration, it is desirable to dispose microtremor 3 at the positions of the vertices of the triangle and the center of gravity of the triangle, as shown in FIG. Of course, it is possible to arrange the fine motion meter 3 at other positions.

(Step SA-2 in FIG. 14)
When the ship reaches a predetermined position, the entire device 1 (the whole including the fine motion meter 3) mounted therein is dropped into water at the predetermined position. This operation is performed for the required number of devices 1. The state of the device 1 dropped in water is shown in FIGS. 1 and 2. As shown in these drawings, in the state of being dropped in water, the tremometer 3 and the anchor 6 are arranged on the water bottom (sea bottom) 20. In addition, the upper portion of the buoy 2 is arranged above the water surface 10, whereby the main body portion 4 is also arranged at a position higher than the water surface 10. Here, the length of the signal cable 7 is made sufficiently longer than the water depth assumed in advance. Note that the accurate estimation of the installation position of the micromotion meter 3 will be described later.

(Step SA-3 in FIG. 14)
The micromotion meter 3 grounded on the water bottom 20 receives the micromotion of the water bottom (that is, the ground) 20, and records the micromotion in the recording unit 41 of the main body unit 4. Further, the GPS signal receiving unit 42 of the main body unit 4 receives the GPS signal from the GPS satellite 50. In the present embodiment, the recording time of vibration can be accurately grasped by using the time information included in this GPS signal.

  The vibration waveform of the recorded slight movement is shown in FIG. The vertical axis of FIG. 15 is the velocity amplitude (cm/s), but the four waveforms are shown separated from each other in the vertical axis direction.

(Step SA-4 in FIG. 14)
After a lapse of a predetermined time (for example, 1 hour to 2 hours or more), the entire apparatus 1 including the micromotion meter 3 is collected. By using the position of the buoy 2 as a mark, this recovery can be performed relatively easily using a ship.

(Step SA-5 in FIG. 14)
Then, by analyzing the vibration data recorded in the main body portion 4 of the collected device 1, the state of the ground, for example, the S wave velocity structure can be estimated. FIG. 16 shows an example of the obtained S wave velocity structure.

  According to the exploration device 1 of the present embodiment, since each device 1 can independently acquire vibration and time, it is not necessary to pull a cable from the individual device 1 onto the ship. Therefore, there is an advantage that the actual microtremor survey can be performed easily.

  Moreover, in the device 1 of the present example, since only the fine motion meter 3 is disposed on the water bottom 20 and the main body part 4 is disposed on or near the water surface, the fine motion meter 3 disposed on the water bottom 20 is a pressure resistant container. No need to fence For this reason, it becomes possible to simplify the device configuration and make the device 1 lightweight. In the case of a structure in which various instruments and batteries are attached to the microtremor part and they are surrounded by a pressure-resistant container that is strong enough to withstand the water pressure at the bottom of the water, it is likely that a crane will be required to handle the device due to the weight of the pressure-resistant container. . On the other hand, in the device of the present embodiment, since the device can be made lightweight, it is possible to drop the device manually without using a crane. Then, it becomes possible to carry out exploration using a small boat, for example, a fishing boat, and it can be expected that the actual exploration cost will be reduced.

  Further, in this embodiment, since the fine motion meter 3 is provided with the openings 313 and 314, the pressure applied to the fine motion meter 3 from the water current such as the sea current can be reduced. Then, even if the fine motion meter 3 is made lightweight, it is possible to suppress the unexpected movement of the fine motion meter 3. Therefore, according to the present embodiment, the weight of the micromotion meter can be reduced, and as a result, the weight of the entire device can be reduced.

(Method of estimating the position of the tremor)
Next, an example of a method for estimating the position of the micromotion meter 3 installed on the water bottom 20 will be described with further reference to FIG.

(Step SB-1 in FIG. 17)
First, as a premise, it is assumed that the micromotion meter 3 has already been dropped into water (see FIGS. 1 and 2). In this state, sound waves are emitted from a plurality of positions into the water (see FIG. 18). Specifically, for example, the sound wave transmission device 401 (see FIG. 19) mounted on an appropriate ship 40 is used to transmit sound waves into the water. Then, while moving the ship 40, sound waves are emitted into the water from a plurality of positions. In the example of FIG. 18, one ship 40 is moved so as to circulate counterclockwise on the outside of the installed buoy 2. Then, after stopping the ship at an appropriate position, the work of transmitting a sound wave is repeated. Here, the position of the ship (hence the sound wave transmitting position) can be grasped by the GPS signal receiving device 402 (see FIG. 19) attached to the ship. In the present embodiment, the RTK-GPS is used as the GPS signal receiving device 402 to improve the position accuracy.

  Note that, in the example of FIG. 19, the shape of the buoy 2 is slightly different from that of FIG. 1, but is functionally the same. Further, in the example of FIG. 19, the anchor 6 and the buoy 2 are connected by an appropriate connecting tool (for example, a rope) 8 to improve the connection strength between the anchor 6 and the buoy 2.

(Step SB-2 in FIG. 17)
On the other hand, the micromotion meter 3 arranged on the water bottom 20 receives the vibration due to the sound wave transmitted toward the water during the execution of step SB-1. FIG. 20 shows an example of a reception waveform of a sound wave transmitted at one sound wave transmitting position. In FIG. 20, the received waveforms at the four fine motion meters 3 are shown in order from the top. The bottom waveform is the waveform of the emitted sound wave. It can be seen that after the sound waves are transmitted, the sound waves are received by each micromotion meter 3 with a slight time difference. This received waveform is also recorded in the recording section 41 of the main body section 4. Here, the time information is received by the GPS signal receiving section 42 of the main body section 4.

(Step SB-3 in FIG. 17)
Then, after collecting the micromotion meter 3, the position of the micromotion meter 3 is estimated by analyzing the vibration waveform received by the micromotion meter 3. The analysis method is not particularly limited, but the position of the micromotion meter 3 can be accurately estimated by inversely analyzing the sound wave transmission position and the sound wave reception timing, for example. Since this inverse analysis method can be easily implemented based on the existing estimation method, detailed description thereof will be omitted. Here, the micromotion meter 3 may receive the micromotion of the water bottom 20 and the sound wave for position estimation at the same time, but they can be separated relatively accurately by using, for example, a difference in frequency or reception intensity. it can.

  FIG. 21 shows the estimated position of the micromotion meter 3 (black circle), the planned installation point (x), and the position of the buoy 2 (+). It can be seen that the micromotion meter 3 is installed at a position relatively close to the planned installation site. On the other hand, it is far from the position of the buoy 2. It is presumed that this is because the buoy 2 easily moves due to wind and waves. The position of the buoy 2 was grasped from the GPS signal (positional information) received by the GPS signal receiving section 42 of the main body section 4.

  In the bottom tremor survey, it is difficult to accurately grasp the position of the tremometer 3 dropped from above the water. Even if it is dropped from an accurate position, the tremor 3 may be washed away due to the influence of ocean currents and waves. In addition, there is a possibility that the position of the tremor 3 may be displaced due to the topographical effect that cannot be grasped from the water. If the position of the micromotion meter 3 deviates from the expected value, an error will occur in the analysis result in the micromotion survey.

  Even in the conventional water bottom microtremor survey, it is possible to arrange a special additional equipment such as a transponder on the micromotion meter to accurately grasp the position of the micromotion meter. However, providing such special additional equipment has a problem that the apparatus becomes complicated and large-sized.

  On the other hand, according to the position estimation method of the present embodiment, the position of the fine motion meter 3 can be accurately estimated by using the sound wave reception waveform in the fine motion meter 3 for receiving the fine motion, which simplifies the apparatus.・There is an advantage that miniaturization can be expected.

  Further, in the device 1 of the present embodiment, since the anchor 6 is used, it is possible to suppress the movement of the microtremor 3 due to the ocean current during the microtremor observation.

Further, in the present embodiment, the anchor 6 can be attached to and detached from the fine motion meter 3, so that the following advantages are provided.
-If the anchor is fixed to the micromotion meter, it will take a lot of time and labor to prepare the equipment for loading, the loading operation, and the recovery of the micromotion meter. On the other hand, by making the anchor removable, these problems can be reduced or eliminated.
-The shape and weight of the anchor and the installation position (positional relationship with the tremor) can be changed according to the conditions of the seabed and ocean current, and a more appropriate installation state can be easily realized.
-For these reasons, it can be expected that high-quality microtremor data can be acquired with good operability.

Here, the water bottom tremor survey method using the water bottom tremor survey device 1 of the present embodiment can be expressed as follows:
Placing the tremor 3 on the bottom of the water by dropping the tremor 3 into the water, and arranging the buoy 2 and the body 4 near the water surface;
Recording the vibration data (fine movement data) detected by the fine movement meter 3 in the recording unit 41;
And a step of exploring the state of the water bottom using the vibration data recorded in the recording unit 41.

  It should be noted that the above description of the embodiment is merely an example, and does not show an essential configuration of the present invention. The configuration of each part is not limited to the above as long as the object of the present invention can be achieved.

  For example, in the above description, the seabed was mainly assumed, but the device described above can be used not only on the seabed but also on the lake bottom or the river bottom.

1 Water Bottom Microtremor Exploration Device 2 Buoy 21 Buoy Main Body 22 Hook 3 Microtremor 31 Frame 311 Annulus 312 Connection Plate 313/314 Opening 32 Case 321 Base 322 Cover 323 Connector 33 1st Micrometer Main Body 34 2nd Micrometer Main Body 4 Main Body Part 41 Recording part 411 Amplifier 412 A/D converter 413 Recording medium 42 GPS signal receiving part 43 Battery 5 Waterproof container 6 Anchor 61 Anchor main body 62 Hook 63 Chain 7 Signal cable 8 Connector 10 Water surface (sea level)
20 Water floor (sea floor)
40 Ship 401 Sound wave transmitter 402 GPS signal receiver 50 GPS satellite

Claims (8)

An exploration device used for microtremor array exploration at the bottom of the water,
It has a buoy, a tremor, and a main body.
The buoy is floatable on the surface of the water, and is connected to the microtremor,
The microtremor, in a state of being installed on the water bottom, is configured to detect a micromotion of the water bottom,
The main body unit includes a recording unit that records the output of the microtremor,
Moreover, the main body part is attached to the buoy, and thereby, the water bottom microtremor exploration device which can be arranged near the water surface. The main body section further includes a GPS signal receiving section,
The water bottom tremor survey apparatus according to claim 1, wherein the GPS signal receiving unit is configured to receive time information and/or position information included in a GPS signal and record the time information and/or position information in the recording unit. The main body further includes a battery,
The water bottom tremor survey apparatus according to claim 1, wherein the battery is configured to supply electric power to the recording unit. Furthermore, it is provided with an anchor for suppressing the movement of the microtremor when installed on the bottom of the water,
The water bottom microtremor exploration device according to claim 1, wherein the anchor is detachably attached to the microtremor. A water bottom tremor surveying method using the water bottom tremor surveying device according to claim 1.
Dropping the micromotion meter into the water to dispose the micromotion meter at the bottom of the water, and to dispose the buoy and the body portion near the water surface,
Recording data of the vibration detected by the microtremor in the recording unit,
A step of searching the state of the water bottom using the vibration data recorded in the recording unit. A method for estimating the position in water of the microtremor in the water bottom microtremor exploration apparatus according to claim 1.
Propagating sound waves from a predetermined position in water,
Receiving the vibration due to the sound wave by the microtremor installed on the bottom of the water;
Estimating the position of the micromotion meter itself using the vibration received by the micromotion meter. The microtremor used in the water bottom microtremor exploration device according to any one of claims 1 to 4,
The micromotion meter includes a plurality of micromotion meter bodies capable of receiving the micromotion of the water bottom. The microtremor used in the water bottom microtremor exploration device according to any one of claims 1 to 4,
The micromotion meter comprises a micromotion meter main body and a frame capable of receiving the micromotion of the water bottom,
The frame is formed with an opening that allows passage of a water flow inside the micromotion meter when the micromotion meter is installed on the water bottom.