Seismic exploration methods, underground monitoring methods, seismic exploration systems, and seismic source devices.

Abstract

To provide a technology enabling more accurate underground monitoring.SOLUTION: An earthquake survey method includes a vibration generation step of allowing a seismic center device 10 arranged underground to generate vibration, and an acquisition step of allowing a signal acquisition device 20 to acquire a vibration signal based on vibration generated by the seismic center device 10. The seismic center device 10 includes eccentric rotors 170, 180 that rotate around a rotation shaft, and a drive unit 160 that rotates the rotors to generate vibration.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a seismic exploration method, a method for monitoring underground, a seismic exploration system, and a seismic source device.

Background Art

[0002] Conventionally, exploration of geological structures has been carried out by observing the propagation of artificially generated seismic waves. For example, in Patent Document 1, a pair of eccentric rotors having equal eccentricity amounts are pivotally supported with their rotation axes parallel, and the phases are adjusted so that one of the eccentric portions of the two eccentric rotors is symmetric with each other, and the two eccentric rotors are driven in opposite directions at the same rotational speed, thereby continuously generating seismic waves that reciprocate in one axial direction. A rotary seismic source device is described.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] However, the inventor of the present application has come to recognize the following problems. That is, when a rotary seismic source device is installed on the ground, the seismic waves are affected by the ground environment, and the accuracy of geological structure exploration decreases. Therefore, with the technique described in Patent Document 1 using a rotary seismic source device installed on the ground, it was not possible to accurately monitor underground.

[0005] The present invention has been made in view of such a situation, and one of its exemplary objects is to provide a technique that enables more accurate underground monitoring.

Means for Solving the Problems

[0006] One aspect of the present invention is a seismic exploration method. The seismic exploration method includes a vibration generation step in which a seismic source device located underground generates vibrations, and an acquisition step in which a signal acquisition device acquires vibration signals based on the vibrations generated by the seismic source device. The seismic source device comprises an eccentric rotating body that rotates around a rotation axis, and a drive unit that generates vibrations by rotating the rotating body.

[0007] Another aspect of the present invention is a method for monitoring underground structures. The underground monitoring method includes the seismic exploration method described above.

[0008] Another aspect of the present invention is an earthquake exploration system. The earthquake exploration system comprises a seismic source device located underground that generates vibrations, and a signal acquisition device that acquires vibration signals based on the vibrations generated by the seismic source device. The seismic source device has an eccentric rotating body that rotates around a rotation axis, and a drive unit that generates vibrations by rotating the rotating body.

[0009] Another aspect of the present invention is a seismic source device. The seismic source device comprises a seismic source section having an eccentric rotating body that rotates about a rotation axis and a drive section that generates vibrations by rotating the rotating body, and a housing section that houses the seismic source section in an internal space. The housing section houses the seismic source section so that it can be attached to and detached through an opening in the internal space.

[0010] Furthermore, any combination of the above components, as well as conversions of the expression of the present invention between methods, apparatus, systems, etc., are also valid embodiments of the present invention. [Effects of the Invention]

[0011] According to the present invention, a technology is available that enables more accurate underground monitoring. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic diagram of the seismic exploration system according to the first embodiment. [Figure 2] This is a functional block diagram of the control device according to the same embodiment. [Figure 3] It is a diagram showing a schematic configuration of a seismic exploration system according to the same embodiment and a cross-section of the underground. [Figure 4] It is a diagram showing a schematic configuration of a seismic source unit according to the same embodiment. [Figure 5] It is a schematic cross-sectional view of a seismic source section according to the same embodiment. [Figure 6] It is a flowchart showing an operation example of a seismic exploration system according to the same embodiment. [Figure 7] It is a diagram showing a schematic configuration of a seismic exploration system according to the second embodiment and a cross-section of the underground. [Figure 8] It is a diagram showing a schematic configuration of a seismic exploration system according to the third embodiment and a cross-section of the underground. [Figure 9] It is a diagram showing a schematic configuration of a seismic exploration system according to the fourth embodiment and a cross-section of the underground. [Figure 10] It is a functional block diagram of a laser device according to the same embodiment. [Figure 11] It is a diagram showing a schematic configuration of a seismic source unit according to the fifth embodiment. [Figure 12] It is a cross-sectional view showing a schematic configuration of a seismic source section according to the sixth embodiment. [Figure 13] It is a cross-sectional view showing a schematic configuration of a seismic source section according to the seventh embodiment. <00000​​​​​​​​​​​​​In recent years, CCS (Carbon Capture and Storage), a technology for treating carbon dioxide, a greenhouse gas, underground, has attracted attention as a practical means. In CCS, carbon dioxide is injected underground using a well (hereinafter also referred to as an "injection well") for sending carbon dioxide from the ground to underground, and the carbon dioxide is stored underground.

[0014] The IEA (International Energy Agency) has recommended a 15% reduction in carbon dioxide emissions by 2020. However, this goal of a 15% reduction is a very high goal, and in order to achieve this with CCS, thousands of large-scale sites for storing carbon dioxide (hereinafter also referred to as "CO2 storage sites") around the world are required, and it is considered that about 240 to 480 injection wells are needed in Japan.

[0015] It is necessary to monitor the CO2 storage site to ensure safety, but a practical method for realizing this has not been established. In view of such a situation, the inventor of the present application has come up with a seismic exploration system capable of continuously monitoring the CO2 storage site as described in the following embodiments.

[0016] (Embodiment) Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description of the drawings, the same elements are denoted by the same reference numerals, and overlapping descriptions will be omitted as appropriate. Also, the configurations described below are examples and do not limit the scope of the present invention in any way.

[0017] Furthermore, in this specification and drawings, multiple components having substantially the same functional configuration may be distinguished by adding a different alphabet after the same reference numeral. However, if there is no need to particularly distinguish each of multiple components having substantially the same functional configuration, each of the multiple components will be assigned only the same reference numeral. In the description of the drawings, the same element will be assigned the same reference numeral, and redundant descriptions will be omitted as appropriate. For example, when coupling mechanism 140a and coupling mechanism 140b are not particularly distinguished, they will simply be referred to as "coupling mechanism 140".

[0018] (First Embodiment) Figure 1 is a schematic diagram of the seismic exploration system 1 according to the first embodiment. As shown in Figure 1, the seismic exploration system 1 according to this embodiment includes a seismic source device 10, a signal acquisition device 20, and a management device 30. The seismic exploration system 1 according to this embodiment performs underground monitoring based on seismic exploration. Specifically, the seismic exploration system 1 conducts investigations of the geological structure by seismic exploration multiple times at regular intervals. If there are changes in the underground conditions during these investigation intervals, the seismic exploration system 1 can detect these changes as differences in the results of the seismic exploration.

[0019] The seismic source device 10 according to this embodiment is placed in a hole formed in the ground and generates vibrations inside the hole. The seismic source device 10 generates vibrations with a waveform (chirp) that includes a wide range of frequencies, and the management device 30 performs cross-coherence analysis on the oscillation waveform recorded by the first receiver 20a (described later) installed near the seismic source device 10 and the waveform recorded by the second receiver 20b (described later) installed at a distance from the seismic source device 10. This makes it possible to obtain results equivalent to those obtained when the seismic source device 10 oscillates an impulse seismic source and records it with the second receiver 20b. The seismic source device 10 according to this embodiment generates vibrations by rotating an eccentric rotating body that rotates around a rotation axis. The seismic source device 10 may be configured to generate vibrations underground by driving a piston into a hole formed in the ground and generating vibrations underground by the impact.

[0020] The signal acquisition device 20 acquires vibration signals based on vibrations generated by the seismic source device 10 and transmits these vibration signals to the management device 30. The signal acquisition device 20 may have various known seismometers, specifically, receivers. In this embodiment, the signal acquisition device 20 has a first receiver 20a installed near the seismic source device 10 and a second receiver 20b installed further away from the seismic source device 10 than the first receiver 20a. The first receiver 20a acquires a first vibration signal based on vibrations generated by the seismic source device 10 and transmits the first vibration signal to the management device 30. The second receiver 20b acquires a second vibration signal based on vibrations generated by the seismic source device 10 and transmits the second vibration signal to the management device 30.

[0021] The control device 30 manages the operation of the seismic exploration system 1. Specifically, the control device 30 controls the operation of the seismic source device 10, instructs the signal acquisition device 20 to acquire vibration signals, and performs various processes based on the detection results of the signal acquisition device 20. For example, the control device 30 can supply power to the seismic source device 10 or generate vibrations in the seismic source device 10. The control device 30 can also transmit a trigger signal to the receiver to instruct it to record vibration signals, record vibration signals along with time information, and analyze the geology using vibration signals from the signal acquisition device 20. The control device 30 may be equipped with a CPU (Central Processing Unit), RAM (Read Access Memory), and ROM (Read Only Memory). The control device 30 may also be equipped with a GPS (Global Positioning System) for recording accurate time.

[0022] Figure 2 is a functional block diagram of the management device 30 according to the first embodiment. As shown in Figure 2, the management device 30 according to this embodiment includes a processing unit 300, a storage unit 320, an output unit 340, a communication unit 360, and a power supply unit 380.

[0023] The processing unit 300 performs various processes, specifically transmitting control signals to the seismic source device 10, receiving vibration signals from the signal acquisition device 20, and performing calculations using those vibration signals. The functions of the processing unit 300 are realized by the control unit 302, the receiving unit 304, and the calculation unit 306. Note that the control unit 302, the receiving unit 304, and the calculation unit 306 may be provided individually.

[0024] The control unit 302 transmits control signals to the seismic source device 10 and controls the operation of the seismic source device 10. Specifically, the control unit 302 may control the operating conditions of the motor of the seismic source device 10 (for example, the rotation speed).

[0025] The receiving unit 304 receives vibration signals from the signal acquisition device 20 and transmits these vibration signals to the calculation unit 306. The calculation unit 306 performs various calculations based on the vibration signals and transmits the results to the storage unit 320 and the output unit 340. For example, the calculation unit 306 may perform processing related to geological analysis based on the vibration signals.

[0026] In this embodiment, the calculation unit 306 analyzes the vibration signals (first vibration signal and second vibration signal) acquired by the two receivers (first receiver 20a and second receiver 20b). Specifically, the calculation unit 306 synchronizes the first vibration signal and the second vibration signal and performs geological analysis based on these synchronized vibration signals using various known analysis techniques.

[0027] More specifically, the calculation unit 306 uses the first vibration signal as the original function and, using the cross-coherence method (see the reference below), obtains an original signal for analyzing the geology based on the first and second vibration signals. The calculation unit 306 can then analyze the geology using this original signal.

[0028] Nakata, N., Snieder, R., Tsuji, T., Larner, K., Matsuoka, T. (2011). Shear wave imaging from traffic noise using seismic interferometry by cross-coherence. Geophysics, 76:SA97-SA106. https : / / doi.org / 10.1190 / geo2010-0188.1

[0029] The memory unit 320 stores various types of information. For example, the memory unit 320 may store a control program for the control unit 302 to control the earthquake source device 10, a calculation program for the calculation unit 306 to perform various calculations, and the calculation results of the calculation unit 306.

[0030] The output unit 340 outputs various types of information. The output unit 340 may consist of various known display devices or audio output devices. For example, the output unit 340 may display the calculation results of the calculation unit 306. Specifically, the output unit 340 may display images for monitoring CO2 storage sites.

[0031] The communication unit 360 is a communication interface for sending and receiving various types of information with other devices. For example, the communication unit 360 may transmit the analysis results from the calculation unit 306 to other devices. The communication unit 360 may also be used when remotely controlling the device.

[0032] The power supply unit 380 supplies power to the seismic source device 10. The power supply unit 380 may, for example, convert power from a commercial power source (not shown) as needed and supply that power to the seismic source device 10. The power supply unit 380 may also supply power to the control device 30. Furthermore, in the case of a small seismic source device, a 12V DC battery may be used. In that case, power may be supplied from a solar panel.

[0033] Figure 3 shows a schematic configuration and underground cross-section of the seismic exploration system 1 according to the first embodiment. The seismic exploration system 1 according to this embodiment includes a seismic source unit 12 located underground, a receiver 20b (second receiver) located above ground 422, and a control device 30.

[0034] The seismic source unit 12 according to this embodiment includes a seismic source device 10 and a vibrator 20a (first vibrator). The seismic source device 10 of the seismic source unit 12 can generate vibrations in response to control by the control device 30. The vibrator 20a acquires a first vibration signal based on the vibrations generated by the seismic source device 10 and transmits the acquired first vibration signal to the control device 30.

[0035] In this embodiment, a vertically extending hole 42 (also called a "well") is formed in the ground. The seismic source unit 12 according to this embodiment is placed inside this hole 42, and the seismic source unit 12 can be removed from or inserted into the hole 42 as needed. The depth d of the position where the seismic source unit 12 is placed in the hole 42 is not particularly limited, but may be, for example, about 100m or 1000m. Furthermore, seismic source units may be installed at multiple locations at different depths, and oscillation operations may be performed. Moreover, if the seismic source unit can be installed near the target to be monitored, it is expected that more accurate data can be obtained.

[0036] In this embodiment, an aquifer 43, which is a geological layer filled with groundwater, is formed underground. The hole 42 in this embodiment is formed to penetrate this aquifer 43. Therefore, groundwater from the aquifer 43 accumulates in the hole 42.

[0037] The seismic source unit 12 may be positioned deeper than the aquifer 43. If the seismic source unit 12 is positioned higher than the aquifer 43 and is normally above the water level, the water level of the groundwater accumulated in the hole 42 may change due to rainfall, etc., and the operation of the seismic source unit 12 (for example, the vibrations it generates) may be affected by the change in groundwater, which may reduce the accuracy of monitoring. On the other hand, by positioning the seismic source unit 12 deeper than the groundwater level (for example, the water level 432 of the aquifer 43 shown in Figure 3) as in this embodiment, the seismic source unit 12 is submerged in groundwater regardless of fluctuations in the groundwater level due to rainfall, etc., making it possible to suppress the impact of fluctuations in the groundwater level on monitoring.

[0038] The receiver 20b acquires a second vibration signal based on the vibrations generated by the seismic source unit 12 and transmits the acquired second vibration signal to the control device 30. The control device 30 according to this embodiment can analyze, for example, the geology based on the vibration signal, which includes the first and second vibration signals transmitted from receivers 20a and 20b. It can also monitor changes occurring underground from the time change of the vibration signal. In this embodiment, there is only one receiver 20b, but it is preferable to install multiple receivers (for example, 100). Multiple receivers are especially necessary when conducting reflection seismic surveys, refraction seismic surveys, or surface wave seismic surveys.

[0039] Figure 3 shows an example in which the seismic exploration system 1 has one source unit 12 placed in one hole 42. However, it is not limited to this; multiple holes may be formed, in which case the seismic exploration system 1 may have multiple source units placed in each of the multiple holes. This makes it possible to generate vibrations at more locations and analyze the geology of a wider area or monitor the subsurface.

[0040] Figure 4 shows a schematic configuration of the earthquake source unit 12 according to the first embodiment. The Z-axis represents the vertical direction, and the X-axis and Y-axis represent the horizontal direction, respectively. The X-axis is perpendicular to the Z-axis, and the Y-axis is perpendicular to both the Z-axis and the X-axis.

[0041] The seismic source device 10 according to this embodiment mainly comprises a housing section 100, a support body 120, a seismic source section 130, and coupling mechanisms 140a and 140b.

[0042] The housing section 100 houses the support 120, the seismic source section 130, and the receiver 20b. The housing section 100 has a cylindrical shape, and its size may be, for example, about 10 cm in length and about 10 cm in diameter. The housing section 100 comprises a housing 102 and a lid 104, and an internal space 106 is formed inside it, surrounded by the housing 102 and the lid 104.

[0043] The housing 102 has a hollow cylindrical shape extending in the Z-axis direction, with one lower end closed by a bottom portion 103 that forms part of the housing 102, and one upper end closed by a lid portion 104.

[0044] The lid 104 is fixed to the housing 102 so that it can open and close the opening at the top of the housing 102. When the lid 104 is closed, the inside of the storage section 100 is sealed, preventing groundwater accumulated in the hole 42 from entering the internal space 106. When the lid 104 is opened, the support 120 can be removed from the housing 102.

[0045] Various sensors (not shown) may be placed in the housing section 100. For example, temperature sensors and water pressure sensors may be placed there. These sensors may be connected to the control device 30 and arranged to transmit measurement results regarding temperature, water pressure, etc., to the control device 30.

[0046] The support 120 has a hollow cylindrical shape extending in the Z-axis direction and supports the seismic source 130 and the receiver 20b inside. The support 120 is detachably fixed to the housing 102 of the housing 100. The support 120 may be directly fixed to the housing 102 or fixed to the housing 102 via fasteners. Although Figure 4 depicts a gap between the housing 100 and the support 120 in the internal space 106, there does not need to be a gap between the housing 100 and the support 120. For example, it is preferable that the support 120 is fixed in close contact with the housing 102.

[0047] The seismic source unit 130 generates vibrations used for seismic exploration. In this embodiment, the seismic source unit 130 is equipped with a motor (drive unit) and an eccentric rotating body, and vibrations are generated when the motor rotates the rotating body. A cable 31 connected to the control device 30 is connected to the seismic source unit 130. Power is supplied to the motor of the seismic source unit 130 from the control device 30 via the cable 31, and control signals are transmitted. As a result, the seismic source unit 130 can generate vibrations.

[0048] A first vibration signal based on vibrations generated by the seismic source 130 is acquired by a receiver 20a installed inside the housing 100. Furthermore, vibrations generated by the seismic source 130 are transmitted to the area around the hole 42 via the sides of the housing 100 or through coupling mechanisms 140a and 140b. A second vibration signal based on these vibrations is acquired, for example, by a receiver 20b located on the ground. The first vibration signal based on vibrations from the seismic source 130 may be recorded by a receiver installed inside the housing 100.

[0049] The vibration conditions generated by the seismic source 130 can be adjusted by changing various parts of the seismic source 130. For example, the vibration conditions can be adjusted by changing the motor in the seismic source 130, the gears for transmitting the motor's driving force to the rotating body, and the weight of the counterweight (described later) used to eccentricate the rotating body.

[0050] When replacing parts of the seismic source unit 130, first, the seismic source unit 12 is removed from the hole 42 to the ground. Then, the cover 104 is opened, and the fasteners that secure the support 120 to the housing 102 are released, for example, to remove the support 120 from the housing 102. After that, the conditions for the vibrations generated by the seismic source unit 130 can be adjusted by replacing each part of the seismic source unit 130. By placing the seismic source unit 12 back into the hole 42 after replacing the parts, it becomes possible to generate vibrations with new conditions in the seismic source unit 130.

[0051] The coupling mechanisms 140a and 140b connect (couple) the housing 102 of the housing 100 to the inner circumferential surface 420 of the hole 42. The coupling mechanisms 140a and 140b have substantially the same configuration.

[0052] The coupling mechanism 140 has a pressing portion 142 and a coupling portion 144. One end of the pressing portion 142 is connected to the housing 102 and extends away from the housing 102, while the other end is connected to the coupling portion 144. The pressing portion 142 is configured to press the coupling portion 144 against the inner circumferential surface 420 of the hole 42. Specifically, the pressing portion 142 is configured to be extendable and retractable in the horizontal direction (for example, in the Y-axis direction), and presses the coupling portion 144 by extending in the direction indicated by the arrow in Figure 4. The configuration for the pressing portion 142 to press the coupling portion 144 is not particularly limited, but may be, for example, a hydraulic type or an electrically controlled type. If the pressing portion 142 has an electrically controlled pressing mechanism, the strength of the force with which the pressing mechanism presses the coupling portion 144 may be adjusted by controlling the pressing mechanism with the control device 30.

[0053] When the pressing parts 142a and 142b press the connecting parts 144a and 144b against the inner circumferential surface 420 of the hole 42, the housing part 100 is coupled to the inner circumferential surface 420 of the hole 42. As a result, the vibrations generated by the seismic source part 130 are transmitted to the surroundings more reliably through the housing part 100, the coupling mechanism 140, and the inner circumferential surface 420 of the hole 42.

[0054] In this example, two coupling mechanisms 140a and 140b are provided on the housing 102, but the number of coupling mechanisms may be one or three or more. Also, although an example was described in which the coupling mechanism connects the housing 100 to the inner circumferential surface 420 in one direction (Y-axis direction), the invention is not limited to this, and multiple coupling mechanisms may be provided so that the housing 100 is connected to the inner circumferential surface 420 in multiple different directions. For example, multiple coupling mechanisms may be arranged in the circumferential direction on the outer circumferential surface of the housing 102, and the housing 100 may be connected in multiple directions.

[0055] Figure 5 is a schematic cross-sectional view of the seismic source section 130 according to the first embodiment. As shown in Figure 5, the seismic source section 130 according to this embodiment includes a motor 160 (drive unit), a first rotating body 170, and a second rotating body 180.

[0056] The motor 160 is driven in accordance with the control of the control device 30 and transmits its driving force to the first rotating body 170. The motor 160 according to this embodiment has a main body 162, a rotating shaft 164, and a transmission unit 166. A part of the rotating shaft 164 is housed in the main body 162. The rotating shaft 164 extends in the X-axis direction and is configured to be rotatable around its length. The transmission unit 166 has a cylindrical shape that extends in the X-axis direction, is arranged to cover the rotating shaft 164, and is configured to be rotatable integrally with the rotating shaft 172.

[0057] A speed sensor (not shown) may be provided on the motor 160. The speed sensor may be connected to the control device 30, measure the rotational speed of the rotating shaft 164, and transmit the measurement result to the control device 30.

[0058] The first rotating body 170 includes a rotating shaft 172, a transmission unit 174, a weight support unit 176, a gear 178, and a weight 179. The rotating shaft 172 extends in the X-axis direction and is configured to rotate around its length. The transmission unit 174 has a cylindrical shape extending in the X-axis direction, is positioned to cover the rotating shaft 172, and is configured to rotate integrally with the rotating shaft 172. A belt 168 is provided around the transmission unit 166 and around the transmission unit 174.

[0059] The disc-shaped weight support portion 176 is provided around the transmitted portion 174 and is configured to rotate integrally with the transmitted portion 174. The disc-shaped gear 178 is provided around the weight support portion 176 and is configured to rotate integrally with the weight support portion 176. A weight 179 is provided on a part of the circumference of the weight support portion 176. Due to this weight 179, the first rotating body 170 is eccentric from its center (the position of the rotation axis 172 on the YZ plane) toward the center of the weight 179. In the state shown in Figure 5, the first rotating body 170 is eccentric to a position r1 away from its center in the Y-axis direction.

[0060] The second rotating body 180 has a rotating shaft 182, a weight support 184, a gear 186, and a weight 188. The rotating shaft 182 extends in the X-axis direction and is configured to rotate around its length. The disc-shaped weight support 184 is provided around the rotating shaft 182 and is configured to rotate integrally with the rotating shaft 182. The disc-shaped gear 186 is provided around the weight support 184 and is configured to rotate integrally with the weight support 184. The gear 186 is also arranged to engage with the gear 178.

[0061] A weight 188 is provided on a part of the circumference of the weight support portion 184. Due to this weight 188, the second rotating body 180 is eccentrically positioned from its center (the position of the rotation axis 182 on the YZ plane) toward the center of the weight 188. In the state shown in Figure 5, the second rotating body 180 is eccentrically positioned at a distance r2 away from its center in the direction opposite to the Y-axis direction.

[0062] In this embodiment, the mass of weight 179 and the mass of weight 188 are equal in m1. Furthermore, weights 179 and 188 are positioned on the first rotating body 170 and the second rotating body 180 such that their eccentricities are equal. That is, weights 179 and 188 are positioned such that m1 × r1 = m1 × r2.

[0063] When the motor 160 is driven, the rotating shaft 164 rotates, and as a result of this rotation, the transmission unit 166 rotates together with the rotating shaft 164. At this time, the driving force is transmitted from the transmission unit 166 to the transmitted unit 174 via the belt 168. As a result, the transmitted unit 174, together with the other members constituting the first rotating body 170, rotates clockwise around the rotating shaft 172. At this time, the gear 186 of the second rotating body 180 receives driving force from the gear 178 of the first rotating body 170. As a result, the gear 186, together with the other members constituting the second rotating body 180, rotates around the rotating shaft 182 in the opposite direction to the first rotating body 170 (counterclockwise).

[0064] Focusing on the movement of weights 179 and 188 during the rotation of the first rotating body 170 and the second rotating body 180, the horizontal components (e.g., in the Y-axis direction) of the rotational speeds of weights 179 and 188 cancel each other out, while the vertical components (in the Z-axis direction) of the rotational speeds of weights 179 and 188 reinforce each other. Therefore, the vibration source 130 can generate vertical vibrations by rotating the first rotating body 170 and the second rotating body 180 using the drive of the motor 160.

[0065] In this embodiment, the seismic source unit 130 continuously generates the same vibrations, thereby superimposing them. This allows vibrations to travel long distances even if the energy of the generated vibrations is small. The seismic source unit 130 can transmit vibrations up to 1 km away, even when the weight of the counterweight is only about 10 g.

[0066] The rotational speed of the rotating shaft 164 is not particularly limited, but it may be a speed that generates vibrations of approximately 20 to 60 Hz. Generally, the higher the vibration frequency, the higher the resolution of the seismic survey, and the lower the vibration frequency, the less the vibration is attenuated and the more it can be transmitted to distant locations. It is preferable for the vibration to have a wide frequency range.

[0067] The various components of the seismic source section 130 described above can be replaced as appropriate to adjust the vibration conditions. For example, the weights of the counterweights 179 and 188 can be changed to adjust the vibration conditions depending on the target of monitoring in the seismic survey. For example, if the target of monitoring is a dam, the weights of the counterweights 179 and 188 may be set to about 10g. If the target of monitoring is a wide area or deep area, the weights of the counterweights may be set to about 100g.

[0068] Figure 6 is a flowchart illustrating an example of the operation of the seismic exploration system 1 according to the first embodiment. The operation example of the seismic exploration system 1 will be described below in accordance with the flowchart.

[0069] First, the control device 30 transmits a control signal to the seismic source device 10 (S101). Next, the seismic source device 10 generates vibrations based on the control signal transmitted in S101 (S103: vibration generation process). Next, the signal acquisition device 20 acquires a vibration signal based on the vibrations generated in S103 (S105: signal acquisition process). Next, the signal acquisition device 20 transmits the vibration signal acquired in S105 to the control device 30 (S107). Next, the control device 30 acquires the vibration signal (S109) and analyzes the vibration signal (S111).

[0070] Note that the processing steps shown in the flowchart in Figure 6 do not necessarily have to be performed in the order shown in Figure 6. The order of the steps may be changed or multiple steps may be processed in parallel, as long as it is logically consistent. Furthermore, by repeatedly and continuously performing the processes from S101 to S109, it is possible to increase the signal-to-noise ratio of the vibration signal.

[0071] (Effects of this embodiment) Traditionally, seismic source devices installed on the ground have been developed. However, surface-level influences such as rainfall and ice / snow strongly affect the results of monitoring in seismic exploration. In particular, when repeatedly exploring geological structures through seismic exploration and monitoring subtle changes, the influence of the surface environment becomes apparent. For this reason, seismic exploration using conventional seismic source devices is susceptible to surface influences, making it difficult to monitor geological changes.

[0072] According to the seismic exploration system 1 of this embodiment, the management device 30 can perform seismic exploration using vibration signals based on vibrations generated from the seismic source device 10 located underground. Therefore, compared to monitoring using vibrations from a seismic source device installed on the ground, the seismic exploration system 1 of this embodiment can suppress the influence of the ground environment, making it possible to monitor with higher accuracy.

[0073] Furthermore, according to the seismic exploration system 1 of this embodiment, since the target to be monitored is underground, vibrations can be generated at a location closer to the target. Therefore, according to the seismic exploration system 1 of this embodiment, it is possible to monitor the underground by seismic exploration with higher accuracy.

[0074] Furthermore, the seismic exploration system 1 according to this embodiment enables environmentally friendly monitoring. Specifically, because the seismic exploration system 1 according to this embodiment generates vibrations underground, it is possible to reduce noise caused by vibrations compared to cases where vibrations are generated above ground. Therefore, the seismic exploration system 1 according to this embodiment can be used even in urban areas and at night.

[0075] Conventional seismic source devices (such as vibroseis) used in seismic exploration are large, difficult to operate in hard-to-reach locations, and are expensive. In contrast, the seismic exploration system 1 according to this embodiment can generate vibrations even in limited locations with poor access by utilizing a small seismic source unit 12. Therefore, the seismic exploration system 1 according to this embodiment makes it possible to conduct seismic exploration at a lower cost in a wider variety of locations. For example, by drilling numerous holes, placing a seismic source unit 12 according to this embodiment in each hole, and analyzing the vibration signals based on the vibrations generated by these seismic source units 12, many CO2 storage sites can be monitored simultaneously.

[0076] Furthermore, conventional seismic source devices were not designed for permanent installation and could not be used for continuous underground monitoring. In earthquake surveys using conventional seismic source devices, monitoring was typically conducted only once every few years. In contrast, according to the earthquake survey system 1 of this embodiment, the seismic source unit 12 is small, making permanent installation possible. In addition, because the seismic source unit 12 has a mechanism that can continuously generate vibrations, constant and continuous underground monitoring becomes possible. For example, by constantly monitoring a CO2 storage site, it becomes possible to respond to sudden CO2 leaks.

[0077] Furthermore, conventional attempts have been made to generate vibrations by placing a seismic source device using a piezoelectric element underground. However, when using a piezoelectric element, the vibrations are weak, making it impossible to achieve vibrations strong enough for seismic exploration. In contrast, according to the seismic exploration system 1 of this embodiment, by rotating an eccentric rotating body and reinforcing the coupling between the seismic source unit 12 and the inner circumferential surface 420 of the hole 42 with the coupling mechanism 140, vibrations of sufficient strength can be generated, enabling underground monitoring through seismic exploration.

[0078] When installing a seismic source device on the lunar surface or elsewhere, the coupling between the device and the lunar surface is weaker compared to when it is installed on Earth due to the low-gravity environment. According to the seismic exploration system 1 of this embodiment, the seismic source unit 12 is coupled to a hole formed in the ground using a coupling mechanism, thereby achieving good coupling even in low gravity and generating stable vibrations.

[0079] The seismic exploration system 1 according to this embodiment can also be used for monitoring reservoirs beneath the seabed. Because the surface portion of the seabed is soft, even if a seismic source device is placed on the surface to generate vibrations, the vibrations are greatly attenuated, making it difficult to conduct effective seismic exploration. In contrast, the bedrock is harder at greater depths of the seabed than at the surface. Therefore, according to the seismic exploration system 1 according to this embodiment, by drilling a hole in the seabed and placing the seismic source device underground and fixing it to the hard bedrock, vibration attenuation can be suppressed, making it possible to perform accurate subsurface monitoring even at the seabed.

[0080] Furthermore, the seismic exploration system 1 according to this embodiment can be used for various applications, including the examples described above. For example, the seismic exploration system 1 can be used in resource energy and decarbonization fields such as monitoring the distribution of stored CO2 and induced earthquakes at CO2 underground storage sites, monitoring reservoirs toward carbon neutrality such as CO2 underground storage and hydrogen underground storage, monitoring geothermal reservoirs, monitoring groundwater, and monitoring resource reservoirs in oil and gas development; in civil engineering fields such as monitoring the integrity of civil engineering structures such as embankments, tunnels, and dams; in outer space such as the lunar surface and Mars; and for underground imaging in hard-to-access areas such as mountainous regions.

[0081] (Second Embodiment) Figure 7 shows a schematic configuration and subsurface cross-section of the seismic exploration system 2 according to the second embodiment. The seismic exploration system 2 according to the second embodiment comprises three source units 14a to 14c, a receiver 22 (second receiver), and a control device 32. The receiver 22 and the control device 32 may have substantially the same configuration as the receiver 20b and control device 30 described in the first embodiment.

[0082] Each of the seismic source units 14a to 14c may have substantially the same configuration as the seismic source unit 12 described in the first embodiment and may be capable of generating vibrations. The seismic source units 14a to 14c according to the second embodiment are arranged in one hole 44, and more specifically, are arranged in the direction in which the hole 44 extends (i.e., the vertical direction). Although three seismic source units are shown in Figure 7, two seismic source units may be arranged, or four or more seismic source units may be arranged.

[0083] The vibration signals generated by the source unit 14 are acquired by the receiver (first receiver) and receiver 22 installed in the source unit 14. The control device 32 can analyze these vibration signals. Therefore, the control device 32 can analyze the geology using the vibration signals generated by each of the source units 14a to 14c. Furthermore, by modifying and characterizing the waveforms of the vibrations generated by each of the multiple source units 14, it becomes possible to distinguish and analyze the vibrations from each source unit 14 even when multiple source units 14 oscillate simultaneously.

[0084] By utilizing multiple source units 14a to 14c in this manner, it becomes possible to conduct more detailed seismic surveys. Furthermore, by arranging the multiple source units 14a to 14c in the direction in which the hole 44 extends, it becomes possible to monitor the subsurface using seismic surveys with higher spatial resolution.

[0085] (Third embodiment) Figure 8 shows a schematic configuration and subsurface cross-section of the seismic exploration system 3 according to the third embodiment. The seismic exploration system 3 according to the third embodiment comprises a seismic source unit 16, a receiver 24 (second receiver), and a control device 34. The seismic source unit 16, the receiver 24, and the control device 34 may each have substantially the same configuration as the seismic source unit 12, receiver 20b, and control device 30 described in the first embodiment.

[0086] As shown in Figure 8, in the third embodiment, two vertically extending holes 46a and 46b are formed in the ground. A seismic source unit 16 is placed in one hole 46a, and a receiver 24 is placed in the other hole 46b. Thus, in the third embodiment, unlike the above embodiment, the receiver 24 is located underground.

[0087] The receiver (first receiver) on the seismic source unit 16 acquires a first vibration signal based on the vibrations generated by the seismic source unit 16. The receiver 24 acquires a second vibration signal based on the vibrations generated by the seismic source unit 16. The control device 34 receives the vibration signals (first and second vibration signals) and performs analysis based on the vibration signals. At this time, since the receiver 24 is located underground, the vibration signals acquired by the receiver 24 are less affected by the surface environment. Therefore, according to the seismic exploration system 3 of this embodiment, it is possible to monitor underground changes with greater accuracy.

[0088] In Figure 8, only the seismic source unit 16 is shown in hole 46a, and only the receiver 24 is shown in hole 46b. However, this is not limited to this arrangement; in addition to the seismic source unit 16, receivers and other seismic source units may be placed in hole 46a, and in addition to receiver 24, seismic source units and other receivers may be placed in hole 46b. Furthermore, multiple seismic source units 16 may be installed in hole 46a, and multiple receivers may be installed in hole 46b.

[0089] (Fourth Embodiment) Figure 9 shows a schematic configuration and subsurface cross-section of the seismic exploration system 4 according to the fourth embodiment. The seismic exploration system 4 according to the fourth embodiment comprises a seismic source unit 18, a signal acquisition device 26, and a management device 36. The seismic source unit 18 may have substantially the same configuration as the seismic source unit 12 according to the first embodiment, but it does not have to have a receiver 20a. Also, the management device 36 may have substantially the same configuration as the management device 30 according to the first embodiment.

[0090] The signal acquisition device 26 according to the fourth embodiment includes a laser device 37 and an optical fiber 260. The laser device 37 emits laser light into the optical fiber 260 and acquires a vibration signal based on the vibrations generated by the seismic source unit 18 based on the laser light reflected in the optical fiber 260. The laser device 37 transmits the acquired vibration signal to the management device 36.

[0091] As shown in Figure 9, in the fourth embodiment, two vertically extending holes 48a and 48b are formed in the ground. A seismic source unit 18 is placed in one of the holes 48a, and an optical fiber 260 is placed in the other hole 48b along the direction in which the hole 48b extends.

[0092] Figure 10 is a functional block diagram of the laser device 37 according to the fourth embodiment. As shown in Figure 10, the laser device 37 according to the fourth embodiment includes a light source 370 and an acquisition unit 372.

[0093] The light source 370 emits laser light and may be composed of various known laser light source devices, for example. In this embodiment, the light source 370 emits laser light into the optical fiber 260. As a result, the laser light propagates through the optical fiber 260, and at least a portion of it is reflected back to the laser device 37.

[0094] The acquisition unit 372 acquires a vibration signal based on the laser light propagated in the optical fiber 260. Specifically, the acquisition unit 372 has a light receiving unit, which detects the laser light that is reflected in the optical fiber 260 and returned to the laser device 37. At this time, if the seismic source unit 18 is generating vibrations, the optical fiber 260 expands and contracts in the longitudinal direction in response to those vibrations. Because the state of the laser light returning to the laser device 37 changes due to the expansion and contraction of the optical fiber 260, the acquisition unit 372 can acquire a vibration signal based on the vibrations generated by the seismic source unit 18 by detecting the optical laser of the optical fiber 260.

[0095] According to the seismic exploration system 4 of this embodiment, vibration signals can be acquired using optical fibers 260 placed in the hole 48b. By using optical fibers 260, the same functionality as when multiple seismometers are placed in the hole 48b at regular intervals can be achieved. For example, when the length of the optical fibers 260 placed in the hole 48 is 1000m, it is possible to acquire vibration signals equivalent to those obtained when seismometers are arranged every 10m. Therefore, according to the seismic exploration system 4 of this embodiment, detailed underground monitoring by seismic exploration can be performed at a low cost without using a large number of seismometers. Furthermore, because the optical fibers 260 are placed underground, the vibration signals can be suppressed from being affected by the ground surface.

[0096] Although Figure 9 shows an example where only the optical fiber 260 is placed in hole 48b, a seismic source unit may also be placed in hole 48b. In this case, it is also possible to use the optical fiber 260 to acquire vibration signals based on vibrations generated by the seismic source unit placed in the same hole 48b.

[0097] (Fifth embodiment) Figure 11 shows a schematic configuration of the earthquake source unit 19 according to the fifth embodiment. The earthquake source unit 19 according to the fifth embodiment differs from the earthquake source unit 12 according to the first embodiment mainly in the configuration of the coupling mechanism.

[0098] The seismic source unit 19 according to the fifth embodiment comprises a housing section 100, a support body 120, a seismic source section 130, a vibrator 20a, and a coupling mechanism 62.

[0099] The coupling mechanism 62 according to the fifth embodiment has an arm structure and is connected to the housing 100. Specifically, the coupling mechanism 62 extends away from the housing 100, and one end is connected to the housing 100 via a joint (not shown) configured to rotate about an axis parallel to the horizontal plane (e.g., the X-axis). Therefore, the coupling mechanism 62 is rotatable about the joint. The operation of the coupling mechanism 62 may be electrically controlled, for example, based on a control signal from a control device located on the ground.

[0100] For example, the coupling mechanism 62 can rotate in the direction of the arrow shown in Figure 11 so that its other end 622 approaches the inner circumferential surface 490 of the hole 49. The other end 622 of the coupling mechanism 62 contacts and presses against the inner circumferential surface 490 of the hole 49, thereby coupling the seismic source unit 19 with the inner circumferential surface 490 of the hole 49. This ensures that the vibrations generated by the seismic source unit 19 are transmitted more reliably to the area around the hole 49 via the side surface of the housing 100 or the coupling mechanism 62.

[0101] (Sixth Embodiment) Figure 12 is a schematic cross-sectional view showing the configuration of the seismic source section 70 according to the sixth embodiment. In Figure 12, the seismic source section 70 is shown as viewed in the horizontal direction (X-axis direction in Figure 12). As shown in Figure 12, the seismic source section 70 according to the sixth embodiment includes a motor 700, a first rotating body 720, and a second rotating body 740.

[0102] The motor 700 comprises a main body 702, a rotating shaft 704, and a transmission unit 706. A portion of the rotating shaft 704 is housed within the main body 702. The rotating shaft 704 extends in the X-axis direction and is configured to rotate around its longitudinal direction. The transmission unit 706 has a cylindrical shape extending in the X-axis direction, is provided to cover the rotating shaft 704, and is configured to rotate integrally with the rotating shaft 704.

[0103] The first rotating body 720 includes a rotating shaft 722, a transmission unit 724, a weight support unit 726, a gear 728, and a weight 729. The rotating shaft 722 extends in the X-axis direction and is configured to rotate around its length. The transmission unit 724 has a cylindrical shape extending in the X-axis direction, is positioned to cover the rotating shaft 722, and is configured to rotate integrally with the rotating shaft 722. A belt 708 is provided around the transmission unit 706 and around the transmission unit 724 so that driving force is transmitted from the transmission unit 706 to the transmission unit 724.

[0104] The disc-shaped weight support portion 726 is provided around the transmitted portion 724 and is configured to rotate integrally with the transmitted portion 724. The disc-shaped gear 728 is provided around the weight support portion 726 and is configured to rotate integrally with the weight support portion 726. A weight 729 is provided on a part of the circumference of the weight support portion 726. Due to this weight 729, the first rotating body 720 is eccentric from its center (the position of the rotation axis 722 on the YZ plane) toward the center of the weight 729. In the state shown in Figure 12, the first rotating body 720 is eccentric to a position r3 away from its center in the Y-axis direction.

[0105] The second rotating body 740 has a rotating shaft 742, a weight support portion 744, a gear 746, and a weight 748. The rotating shaft 742 extends in the X-axis direction and is configured to rotate around its length. The disc-shaped weight support portion 744 is provided around the rotating shaft 742 and is configured to rotate integrally with the rotating shaft 742. The disc-shaped gear 746 is provided around the weight support portion 744 and is configured to rotate integrally with the weight support portion 744.

[0106] A weight 748 is provided on a portion of the circumference of the weight support portion 744. Due to this weight 748, the second rotating body 740 is eccentrically positioned away from its center (the position of the rotation axis 742 on the YZ plane). In the state shown in Figure 12, the second rotating body 740 is eccentrically positioned at a distance r4 in the Y-axis direction from its center.

[0107] In this embodiment, the masses of weight 729 and weight 748 are equal by m². Furthermore, weights 729 and 748 are positioned on the first rotating body 720 and the second rotating body 740 such that their eccentricities are equal. Therefore, weights 729 and 748 are positioned such that m² × r³ = m² × r⁴.

[0108] When the motor 700 is driven, the rotating shaft 704 rotates, and in conjunction with this rotation, the transmission unit 706 rotates together with the rotating shaft 704. At this time, the driving force is transmitted from the transmission unit 706 to the transmitted unit 724 via the belt 708. As a result, the transmitted unit 724, together with the other members constituting the first rotating body 720, rotates clockwise around the rotating shaft 722. At this time, the gear 746 of the second rotating body 740 receives driving force from the gear 728 of the first rotating body 720, and the gear 746, together with the other members constituting the second rotating body 740, rotates in the opposite direction (counterclockwise) to the first rotating body 720 around the rotating shaft 742.

[0109] Focusing on the movement of weights 729 and 748 during the rotation of the first rotating body 720 and the second rotating body 740, the vertical (Z-axis direction) components of the rotational speeds of weights 729 and 748 cancel each other out, while the horizontal (e.g., Y-axis component) components of the rotational speeds of weights 729 and 748 reinforce each other. As a result, the vibration source 70 can generate horizontal vibrations by rotating the first rotating body 720 and the second rotating body 740 through the drive of the motor 700.

[0110] Thus, according to the seismic source unit 70 of this embodiment, it is possible to generate vibrations with a unidirectional component on the horizontal plane and utilize these vibrations for seismic exploration.

[0111] (Seventh Embodiment) Figure 13 is a schematic cross-sectional view of the seismic source section 75 according to the seventh embodiment. The seismic source section 75 according to the seventh embodiment mainly comprises a motor 750, a first rotating body 760, a second rotating body 770, a third rotating body 780, and a fourth rotating body 790. The seismic source section 75 according to the seventh embodiment differs from the seismic source section 130 according to the first embodiment in that it mainly comprises a third rotating body 780 and a fourth rotating body 790.

[0112] Since the configurations of the motor 750, the first rotating body 760, and the second rotating body 770 according to the seventh embodiment are substantially the same as those of the motor 160, the first rotating body 170, and the second rotating body 180 according to the first embodiment, a detailed explanation is omitted here.

[0113] The third rotating body 780 has a rotating shaft 782, a transmission part 784, a weight support part 786, a gear 788, and a weight 789. The rotating shaft 782 extends in the X-axis direction and is configured to rotate around its length. The transmission part 784 has a cylindrical shape extending in the X-axis direction and is positioned to cover the rotating shaft 782 and is configured to rotate integrally with the rotating shaft 782. In this embodiment, the radius of the transmission part 784 of the third rotating body 780 is smaller than the radius of the transmission part 764 of the first rotating body 760.

[0114] In this embodiment, a belt 758 is provided so that driving force is transmitted from the transmission unit 754 of the motor 750 to the transmitted unit 784 and the transmitted unit 764 of the first rotating body 760. Specifically, the belt 758 is provided around the transmitted unit 784, around the transmission unit 754, and around the transmitted unit 764.

[0115] The disc-shaped weight support portion 786 is provided around the transmitted portion 784 and is configured to rotate integrally with the transmitted portion 784. The disc-shaped gear 788 is provided around the weight support portion 786 and is configured to rotate integrally with the weight support portion 786. A weight 789 is provided on a part of the circumference of the weight support portion 786. Due to this weight 789, the third rotating body 780 is eccentric from its center (the position of the rotation axis 782 on the YZ plane) toward the center of the weight 789. In the state shown in Figure 13, the third rotating body 780 is eccentric to a position r5 away from its center in the opposite direction in the Y-axis direction.

[0116] The fourth rotating body 790 has a rotating shaft 792, a weight support 794, a gear 796, and a weight 798. The rotating shaft 792 extends in the X-axis direction and is configured to rotate around its length. The disc-shaped weight support 794 is provided around the rotating shaft 792 and is configured to rotate integrally with the rotating shaft 792. The disc-shaped gear 796 is provided around the weight support 794 and is configured to rotate integrally with the weight support 794.

[0117] A weight 798 is provided on a portion of the circumference of the weight support portion 794. Due to this weight 798, the fourth rotating body 790 is eccentrically positioned away from its center (the position of the rotation axis 792 on the YZ plane). In the state shown in Figure 13, the fourth rotating body 790 is eccentrically positioned at a distance of r5 in the Y-axis direction from its center.

[0118] In this embodiment, the mass of weight 789 and the mass of weight 798 are equal by m3. Note that m3 may be lighter than the mass of weight 769 of the first rotating body 760 and the mass of weight 778 of the second rotating body 770. Furthermore, weights 789 and 798 are positioned on the third rotating body 780 and the fourth rotating body 790 such that their eccentricities are equal. Therefore, weights 789 and 798 are positioned such that m3 × r5 = m3 × r5.

[0119] In this embodiment, when the motor 750 is driven, the transmission unit 754 rotates, and its driving force is transmitted to the transmitted unit 764 of the first rotating body 760 and the transmitted unit 784 of the third rotating body 780. At this time, the first rotating body 760 and the second rotating body 770 generate vertical vibrations in the same manner as in the first embodiment.

[0120] The transmitted portion 784 of the third rotating body 780 receives the driving force from the motor 750 and rotates clockwise around the rotation axis 782 together with the other members constituting the third rotating body 780. At this time, the gear 796 of the fourth rotating body 790 receives the driving force from the gear 788 of the third rotating body 780 and rotates counterclockwise around the rotation axis 792 together with the other members constituting the fourth rotating body 790 in the opposite direction to the third rotating body 780. At this time, the weights 789 and 798 cancel out the horizontal components of their rotational speeds, causing the third rotating body 780 and the fourth rotating body 790 to generate vertical vibrations.

[0121] The transmitted portion 784 of the third rotating body 780 receives the driving force from the motor 750 and rotates around the rotating shaft 782. At this time, since the radius of the transmitted portion 784 is smaller than the radius of the transmitted portion 764, the transmitted portion 784 rotates faster than the transmitted portion 764. As a result, the set of the third rotating body 780 and the fourth rotating body 790 (hereinafter also referred to as the "second set") generates vibrations of a higher frequency than the set of the first rotating body 760 and the second rotating body 770 (hereinafter also referred to as the "first set").

[0122] Thus, according to the seismic source unit 75 of this embodiment, by rotating the first and second sets via the transmitted parts 764 and 784 which have different radii, vibrations of different frequencies can be generated. This makes it possible to generate vibrations of a wider frequency range. As a result, the seismic source exploration system can generate vibrations that are more suitable for the target.

[0123] Furthermore, in this embodiment, when the second set generates vibrations with a higher frequency than the first set, it is desirable for the weights of the second set to be lighter than those of the first set in order to generate equivalent vibration energy over a wide frequency range.

[0124] (Eighth embodiment) Figure 14 is a schematic diagram showing the seismic source section 80 according to the eighth embodiment. In Figure 14, the seismic source section 80 is shown as viewed in the horizontal direction (X-axis direction in Figure 14). As shown in Figure 14, the seismic source section 80 according to the eighth embodiment mainly includes a motor 800, a transmission section 810, a first rotating body 820a, a second rotating body 820b, a third rotating body 820c, a fourth rotating body 820d, and bearings 812, 814, and 816.

[0125] The motor 800 has a main body 802 and a rotating shaft 804. Part of the rotating shaft 804 is housed in the main body 802, extends in the Z-axis direction, and is configured to be rotatable around its length.

[0126] The transmission unit 810 has a cylindrical shape extending in the Z-axis direction and is provided on the opposite side of the rotating shaft 804 from the main body 802, so as to be rotatable integrally with the rotating shaft 804.

[0127] The first rotating body 820a, the second rotating body 820b, the third rotating body 820c, and the fourth rotating body 820d are arranged around the transmission unit 810 in this order, starting from the side closest to the motor 800, so as to be rotatable integrally with the transmission unit 810. The first rotating body 820a, the second rotating body 820b, the third rotating body 820c, and the fourth rotating body 820d all have substantially the same configuration.

[0128] Furthermore, bearing 812 is provided around the transmission unit 810 on the motor 800 side of the first rotating body 820a, to rotatably support the transmission unit 810. Also, bearing 814 is provided around the transmission unit 810 on the opposite side of the motor 800 from the fourth rotating body 820d, to rotatably support the transmission unit 810. In addition, bearing 816 is provided around the transmission unit 810 between the second rotating body 820b and the third rotating body 820c, to rotatably support the transmission unit 810. Although Figure 14 shows three bearings, the number of bearings may be two or fewer, or four or more. The more bearings there are, the more stable the rotation of, for example, the first to fourth rotating bodies 820a to 820d will be, and furthermore, bearing wear will be reduced, which is advantageous for long-term operation.

[0129] The first rotating body 820a has a weight support portion 822a and a weight 824a, the second rotating body 820b has a weight support portion 822b and a weight 824b, the third rotating body 820c has a weight support portion 822c and a weight 824c, and the fourth rotating body 820d has a weight support portion 822d and a weight 824d. The weight support portion 822 is disc-shaped and is provided around the transmission portion 810. A weight 824 is also provided on a part of the circumference of the weight support portion 822. In this embodiment, when viewed in the Z-axis direction, the weights 824a to 824d are all positioned in the same location, and their relative positions do not change even when the weight support portion 822 rotates.

[0130] When the motor 800 is driven, the rotating shaft 804 rotates. As the rotating shaft 804 rotates, the transmission unit 810 rotates around the rotating shaft 804 in the direction indicated by the arrow in Figure 14. As a result of this rotation, the first rotating body 820a, the second rotating body 820b, the third rotating body 820c, and the fourth rotating body 820d rotate around the rotating shaft 804. At this time, the weights 824a to 824d all rotate in the same phase. Therefore, the forces generated by the rotation of the weights 824a to 824d reinforce each other. Accordingly, according to the seismic source unit 80 of this embodiment, it is possible to generate vibrations that rotate in the horizontal plane.

[0131] Unlike the seismic source unit 70 in the sixth embodiment, the vibration generated by the seismic source unit 80 in the eighth embodiment has two mutually orthogonal horizontal components. For this reason, the seismic source unit in the eighth embodiment may have two receivers arranged mutually orthogonally so as to be able to detect the two horizontal components of the vibration.

[0132] According to the above embodiments, the seismic source unit 130 according to the first embodiment can generate vertical vibrations, the seismic source unit 70 according to the sixth embodiment can generate unidirectional vibrations on the horizontal plane, and the seismic source unit 80 according to the eighth embodiment can generate vibrations in a rotational direction within the horizontal plane. Therefore, by removing the seismic source unit to the ground as needed and changing the configuration of the seismic source unit, the direction of the vibration components to be generated can be changed to desired conditions.

[0133] (Ninth Embodiment) Figure 15 is a perspective view of the seismic source unit 90 according to the ninth embodiment. The seismic source unit 90 according to this embodiment is located on the ground surface 98. The seismic source unit 90 according to the ninth embodiment includes a housing section 92 (coupler), a seismic source device 94, and a weight 96.

[0134] The housing section 92 has an internal space with an opening 922, which is made up of a cylindrical hole 920, and the seismic source device 94 is placed in this internal space. The housing section 92 may be made of concrete, for example. A weight 96 is placed on the upper surface of the housing section 92 to connect the housing section 92 to the ground surface 98. The housing section 92 is connected to the ground surface 98 by the weight of the weight 96 pressing the housing section 92 against the ground surface 98. This makes it easier for the vibrations generated by the seismic source device 94 to be transmitted to the ground. If the vibrations of the seismic source device are large, the number of weights 96 may be increased.

[0135] The seismic source device 94 may have the seismic source section described in the above embodiment. In this case, the direction corresponding to the Z-axis is the horizontal direction. Therefore, when using the seismic source section 130 shown in the first embodiment in Figure 5, horizontal vibrations can be generated. Furthermore, if the seismic source section 70 according to the sixth embodiment shown in Figure 12 is positioned so that the direction corresponding to the Y-axis direction is the vertical direction, vertical vibrations can be generated. Since the seismic source device 94 is detachably located in the internal space through the opening 922 of the internal space, the seismic source device 94 can be removed from the housing section 92 as needed. This makes it possible to change the components of the seismic source section (for example, gears, motors, and weights) and house the seismic source device back in the housing section 92, thereby enabling seismic exploration using vibrations under new conditions.

[0136] (supplement) The present invention has been described above based on embodiments. These embodiments are illustrative, and it will be understood by those skilled in the art that various modifications are possible in combinations of these components and processing processes, and that such modifications also fall within the scope of the present invention. [Explanation of Symbols]

[0137] 1,2,3,4 Earthquake exploration system, 10,94 Source device, 12,14,16,18,19,90 Source unit, 20,26 Signal acquisition device, 20,22,24 Receiver, 30,32,34,36 Management device, 37 Laser device, 42,44,46,48,49 Hole, 62,140 Coupling mechanism, 70,80 Source section, 92,100 Housing section, 120 Support, 130 Source section, 160 Motor, 170 First rotating body, 180 Second rotating body, 260 Optical fiber, 370 Light source, 372 Acquisition section

Claims

1. The vibration generation process involves a seismic source device located underground that generates vibrations, The process includes an acquisition step in which a signal acquisition device acquires a vibration signal based on vibrations generated by the aforementioned seismic source device, The aforementioned seismic source device comprises two eccentric rotating bodies that rotate around a rotation axis, and a drive unit that generates the vibration by rotating the rotating bodies. The aforementioned seismic source device is positioned in a hole formed underground, at a depth greater than the aquifer. The aforementioned axis of rotation is in the horizontal direction. The two rotating bodies are engaged with each other and rotate in conjunction to cancel out vibration components in a predetermined direction. Earthquake detection methods.

2. Multiple seismic source devices are arranged in the aforementioned hole. The aforementioned multiple seismic source devices are arranged in the direction in which the hole extends. The seismic exploration method according to claim 1.

3. The seismic source device further comprises a housing for housing the rotating body and the drive unit, and a coupling mechanism for connecting the housing for housing the inner surface of the hole. The seismic exploration method according to claim 1.

4. The signal acquisition device has a vibrator that acquires the vibration signal, The aforementioned receiver is located in a second hole, which is different from the first hole formed in the ground, when the hole in which the seismic source device is located is referred to as the first hole. The seismic exploration method according to claim 1.

5. The signal acquisition device comprises an optical fiber arranged in the hole along the direction in which the hole extends, a light source that propagates laser light through the optical fiber, and an acquisition unit that acquires the vibration signal based on the propagated laser light. The seismic exploration method according to claim 1.

6. A seismic exploration method according to any one of claims 1 to 5, Methods for monitoring underground areas.

7. A seismic source device that generates vibrations is located underground, The system includes a signal acquisition device that acquires vibration signals based on vibrations generated by the aforementioned seismic source device, The aforementioned seismic source device comprises two eccentric rotating bodies that rotate around a rotation axis, and a drive unit that generates the vibration by rotating the rotating bodies. The aforementioned seismic source device is positioned in a hole formed underground, at a depth greater than the aquifer. The aforementioned axis of rotation is in the horizontal direction. The two rotating bodies are engaged with each other and rotate in conjunction to cancel out vibration components in a predetermined direction. Earthquake detection system.

8. It is a seismic source device, A seismic source unit having two eccentric rotating bodies that rotate independently around a rotation axis, and a drive unit that generates vibrations by rotating the rotating bodies, It comprises a housing section that houses the aforementioned earthquake source section within an internal space, The housing unit houses the seismic source so that the seismic source can be attached to and detached through the opening in the internal space, The aforementioned seismic source device is positioned in a hole formed underground, at a depth greater than the aquifer. The aforementioned axis of rotation is in the horizontal direction. The two rotating bodies are engaged with each other and rotate in conjunction to cancel out vibration components in a predetermined direction. Epicenter device.

9. The drive unit rotates the two rotating bodies such that the two rotating bodies generate vibrations of different frequencies. The seismic source device according to claim 8.

10. The seismic source device further comprises a coupling mechanism for connecting the inner surface of the hole and the housing portion. The seismic source device according to claim 8.

11. The aforementioned housing includes a pressure vessel, The seismic source device according to claim 8.

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