Seismic sensor, earthquake detection method, and earthquake detection program

Abstract

To provide a seismic sensor, an earthquake detection method, and an earthquake detection program that can accurately determine whether a detected vibration is an earthquake or noise.SOLUTION: A seismic sensor 10 comprises an acceleration acquisition unit 21, an internal angle calculation unit 23, an internal angle frequency distribution generation unit 24, and an earthquake determination unit 25. The acceleration acquisition unit 21 detects a vibration and acquires the acceleration of the vibration. The internal angle calculation unit 23 calculates, for the acceleration acquired by the acceleration acquisition unit 21, internal angles of two acceleration vectors continuous on a predetermined coordinate plane. The internal angle distribution generation unit 24 generates the frequency distribution of the internal angles calculated by the internal angle calculation unit 23. The earthquake determination unit 25 determines whether or not the vibration is an earthquake on the basis of the frequency distribution generated by the internal angle frequency distribution generation unit 24.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a seismic sensor for detecting seismic motion, an earthquake detection method, and an earthquake detection program. [Background technology]

[0002] In recent years, seismic sensors have been used that are built into gas meters, electricity meters, distribution boards, outlets, etc., and that output a cut-off signal to cut off the supply of gas, electricity, etc. when they detect earthquake motion of a magnitude above a predetermined value (for example, seismic intensity 5 or higher). For example, Patent Document 1 discloses a seismic sensor that outputs a shutoff signal when an index value indicating the magnitude of an earthquake is equal to or greater than a threshold value during an earthquake processing period following a judgment period, and that includes a continuing earthquake judgment unit that judges whether an earthquake has occurred based on the acceleration measured during the earthquake processing period, and a shutoff judgment unit that prevents the shutoff signal from being output regardless of the index value when the continuing earthquake judgment unit judges that an earthquake has not occurred. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6465257 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the above-mentioned conventional seismic sensors have the following problems. That is, in the seismic sensor disclosed in the above publication, when analyzing the frequency of the acceleration measured by the acceleration sensor, the frequency of each axis (e.g., X-axis and Y-axis) of the acceleration sensor is calculated. Therefore, it is difficult to analyze vibrations taking into account the vibration characteristics of both axes (e.g., X-axis and Y-axis), making it difficult to accurately determine whether an earthquake has occurred.

[0005] An object of the present invention is to provide a seismic sensor, an earthquake detection method, and an earthquake detection program that can accurately determine whether a detected vibration is an earthquake or noise. [Means for solving the problem]

[0006] The seismic sensor according to the first aspect of the present invention includes an acceleration acquisition unit, an interior angle calculation unit, an interior angle frequency distribution generation unit, and an earthquake determination unit. The acceleration acquisition unit detects vibrations and acquires the acceleration of the vibrations. The interior angle calculation unit calculates the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane based on the acceleration acquired by the acceleration acquisition unit. The interior angle frequency distribution generation unit generates a frequency distribution of the interior angles calculated by the interior angle calculation unit. The earthquake determination unit determines whether the vibrations are an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit.

[0007] Here, for example, the interior angle between two consecutive acceleration vectors on the coordinate plane of an acceleration sensor that acquires the acceleration of the vibration is calculated, and based on the frequency distribution generated, it is determined whether the vibration is an earthquake or not. Here, the interior angle between two successive acceleration vectors means the angle formed by the two successive acceleration vectors when the starting points of the two acceleration vectors are aligned with the origin over elapsed time.

[0008] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration. Generally, when vibrations are caused by earthquakes, they are characterized by low frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0009] Therefore, this seismic sensor determines whether an earthquake has occurred based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. This means that if the interior angle between two consecutive acceleration vectors has many acute components and few obtuse components, it can be determined that it matches the characteristics of an earthquake and that the vibration in question is likely to be an earthquake. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0010] The seismic sensor of the second invention is the seismic sensor of the first invention, wherein the earthquake determination unit determines that the vibration is an earthquake if the proportion of obtuse angle components in the frequency distribution of interior angles is smaller than a predetermined threshold value. As a result, if the frequency distribution of the interior angles of two consecutive acceleration vectors shows that the number of obtuse angle components, which are characteristic of noise such as daily vibrations, is less than a predetermined threshold, the vibration can be determined to be an earthquake.

[0011] The seismic sensor of the third invention is the seismic sensor of the first or second invention, and the earthquake determination unit determines that the vibration is not an earthquake if the proportion of obtuse angle components in the frequency distribution of interior angles is equal to or greater than a predetermined threshold value. As a result, if the frequency distribution of the interior angles of two consecutive acceleration vectors shows that the number of obtuse angle components, which are characteristic of noise such as daily vibrations, is greater than a predetermined threshold, it is possible to determine that the vibration is not an earthquake.

[0012] The seismic sensor of the fourth invention is the seismic sensor of the first or second invention, wherein the earthquake determination unit determines whether the vibration is an earthquake using any of the mean, median, or mode of the frequency distribution generated by the interior angle frequency distribution generation unit. This allows highly accurate earthquake detection by analyzing the characteristics of the detected vibrations using any of the mean, median, and mode in the interior angle frequency distribution.

[0013] The seismic sensor of the fifth invention is a seismic sensor of the first or second invention, wherein the earthquake determination unit determines whether the vibration is an earthquake using any of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit. This allows highly accurate earthquake detection by analyzing the characteristics of detected vibrations using any of the standard deviation, variance, coefficient of variation, skewness, and kurtosis in the interior angle frequency distribution.

[0014] The seismic sensor of the sixth invention is a seismic sensor of the first or second invention, in which the earthquake determination unit determines whether the vibration is an earthquake or not by using the result of weighting the frequency distribution generated by the interior angle frequency distribution generation unit according to the angle. This allows for angle-dependent weighting of the frequency distribution to emphasize the characteristic features of earthquakes or noise, making it possible to more accurately determine whether the detected vibrations are earthquakes or noise.

[0015] The seismic sensor of the seventh invention is the seismic sensor of the first or second invention, wherein the acceleration acquisition unit extracts and acquires acceleration in a non-gravity direction from the acceleration measured by the three-axis acceleration sensor. This allows for the extraction and acquisition of acceleration components other than those in the direction of gravity, thereby obtaining an acceleration vector on a predetermined coordinate plane.

[0016] The seismic sensor of the eighth invention is a seismic sensor of the first or second invention, and further comprises an earthquake magnitude calculation unit that, when the earthquake determination unit determines that an earthquake has occurred, determines whether the earthquake is of a predetermined seismic intensity or greater. For example, if the magnitude of the earthquake is judged to be upper 5 on the seismic intensity scale or higher, there is a risk of fire or gas leaks, and a shut-off signal can be output to stop the supply of energy such as electricity or gas, thereby improving the safety of users.

[0017] The seismic sensor of the ninth invention is a seismic sensor of the first or second invention, and further includes an activation determination unit that calculates the vibration intensity from the results acquired by the acceleration acquisition unit, and when the vibration intensity is equal to or greater than a predetermined magnitude, transitions from a power saving mode to a measurement mode that consumes more power than the power saving mode. This allows the device to switch to a measurement mode that performs earthquake detection processing using the vibration acceleration waveform only when the strength of the detected vibration is equal to or greater than a predetermined magnitude (e.g., equivalent to a seismic intensity of 4), thereby enabling highly accurate earthquake detection while reducing power consumption.

[0018] The seismic sensor of the tenth invention is the seismic sensor of the first or second invention, and further comprises an output control unit that outputs a predetermined signal when the earthquake determination unit determines that an earthquake has occurred. This allows, for example, when an earthquake occurs, the output unit to output a cutoff signal to stop the supply of energy such as electricity or gas, or a warning signal to warn of danger.

[0019] An earthquake detection method according to an eleventh aspect of the present invention includes an acceleration acquisition step, an interior angle calculation step, an interior angle frequency distribution generation step, and an earthquake determination step. In the acceleration acquisition step, vibrations are detected and the acceleration of the vibrations is acquired. In the interior angle calculation step, the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane is calculated for the accelerations acquired in the acceleration acquisition step. In the interior angle frequency distribution generation step, a frequency distribution of the interior angles calculated in the interior angle calculation step is generated. In the earthquake determination step, it is determined whether the vibrations are an earthquake or not based on the frequency distribution generated in the interior angle frequency distribution generation step.

[0020] Here, for example, the interior angle between two consecutive acceleration vectors on the coordinate plane of an acceleration sensor that acquires the acceleration of the vibration is calculated, and based on the frequency distribution generated, it is determined whether the vibration is an earthquake or not. Here, the interior angle between two successive acceleration vectors means the angle formed by the two successive acceleration vectors when the starting points of the two acceleration vectors are aligned with the origin over elapsed time.

[0021] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration. Generally, when vibrations are caused by earthquakes, they are characterized by low frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0022] Therefore, this seismic sensor determines whether an earthquake has occurred based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. This means that if the interior angle between two consecutive acceleration vectors has many acute components and few obtuse components, it can be determined that it matches the characteristics of an earthquake and that the vibration in question is likely to be an earthquake. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0023] An earthquake detection program according to a twelfth aspect of the present invention causes a computer to execute an earthquake detection method including an acceleration acquisition step, an interior angle calculation step, an interior angle frequency distribution generation step, and an earthquake determination step. In the acceleration acquisition step, vibrations are detected and the acceleration of the vibrations is acquired. In the interior angle calculation step, the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane is calculated for the accelerations acquired in the acceleration acquisition step. In the interior angle frequency distribution generation step, a frequency distribution of the interior angles calculated in the interior angle calculation step is generated. In the earthquake determination step, it is determined whether the vibrations are an earthquake based on the frequency distribution generated in the interior angle frequency distribution generation step.

[0024] Here, for example, the interior angle between two consecutive acceleration vectors on the coordinate plane of an acceleration sensor that acquires the acceleration of the vibration is calculated, and based on the frequency distribution generated, it is determined whether the vibration is an earthquake or not. Here, the interior angle between two successive acceleration vectors means the angle formed by the two successive acceleration vectors when the starting points of the two acceleration vectors are aligned with the origin over elapsed time.

[0025] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration. Generally, when vibrations are caused by earthquakes, they are characterized by low frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0026] Therefore, this seismic sensor determines whether an earthquake has occurred based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. This means that if the interior angle between two consecutive acceleration vectors has many acute components and few obtuse components, it can be determined that it matches the characteristics of an earthquake and that the vibration in question is likely to be an earthquake. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0027] A seismic sensor according to a thirteenth aspect of the present invention includes an acceleration acquisition unit, an interior angle calculation unit, and an interior angle frequency distribution generation unit. The acceleration acquisition unit detects vibrations and acquires the acceleration of the vibrations. The interior angle calculation unit calculates the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane for the acceleration acquired by the acceleration acquisition unit. The interior angle frequency distribution generation unit generates a frequency distribution of the interior angles calculated by the interior angle calculation unit.

[0028] Here, for example, the interior angle between two successive acceleration vectors on a coordinate plane of an acceleration sensor that acquires the acceleration of the vibration is calculated, and the vibration is analyzed. Here, the interior angle between two successive acceleration vectors means the angle formed by the two successive acceleration vectors when the starting points of the two acceleration vectors are aligned with the origin over elapsed time.

[0029] Furthermore, the predetermined coordinate plane set when calculating the interior angle means, for example, the XY plane, XZ plane, or YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor that measures acceleration, or, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration. Generally, when vibrations are caused by earthquakes, they are characterized by low frequency vibrations, containing various frequency components, and vibrating in various directions on a horizontal plane.

[0030] For this reason, this seismic sensor analyzes vibrations based on the frequency distribution of the interior angle formed by two consecutive acceleration vectors over time. This means that if the interior angle between two consecutive acceleration vectors has many acute components and few obtuse components, it can be analyzed as matching the characteristics of an earthquake and determined that the vibration in question is likely to be an earthquake.

[0031] As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise. [Effects of the Invention]

[0032] The seismic sensor according to the present invention can accurately determine whether the detected vibration is an earthquake or noise. [Brief explanation of the drawings]

[0033] [Figure 1] FIG. 1 is a control block diagram showing the configuration of a seismic sensor according to an embodiment of the present invention. [Figure 2]Functional block diagram generated within the seismic sensor in Figure 1. [Figure 3] 2 is a graph showing the acceleration on the horizontal plane (XY plane) of earthquake vibrations detected by the seismic sensor of FIG. 1. [Figure 4] (a) is a diagram showing an example of two consecutive acceleration vectors in the earthquake vibration of Figure 3. (b) is a diagram showing the interior angle of the two acceleration vectors in (a) when their origins are aligned with the origin. (c) is a graph showing the frequency distribution of the interior angle in (b). [Figure 5] 2 is a graph showing the acceleration on the horizontal plane (XY plane) of noise vibration detected by the seismic sensor of FIG. 1. [Figure 6] (a) is a diagram showing an example of two consecutive acceleration vectors in the daily vibration (noise) of Figure 5. (b) is a diagram showing the interior angle of the two acceleration vectors in (a) when their starting points are aligned with the origin. (c) is a graph showing the frequency distribution of the interior angle in (b). [Figure 7] (a) is a graph showing the acceleration on the horizontal plane (XY plane) of earthquake vibrations detected by a seismic sensor. (b) is a graph showing the frequency distribution of the interior angle of the acceleration in (a). [Figure 8] (a) is a graph showing the acceleration on the horizontal plane (XY plane) of noise (high-frequency) vibration detected by a seismic sensor. (b) is a graph showing the frequency distribution of the interior angle of the acceleration in (a). [Figure 9] (a) is a graph showing the acceleration on the horizontal plane (XY plane) of noise (same frequency) vibration detected by a seismic sensor. (b) is a graph showing the frequency distribution of the interior angle of the acceleration in (a). [Figure 10] (a) is a graph showing the acceleration on the horizontal plane (XY plane) of noise (linear motion) vibration detected by a seismic sensor. (b) is a graph showing the frequency distribution of the interior angle of the acceleration in (a). [Figure 11] 3 is a flowchart showing the flow of processing in an earthquake detection method executed by the seismic sensor of FIG. 2; [Figure 12]As an example of earthquake determination using the mode, mean, or median of the interior angle frequency distribution generated by a seismic sensor according to another embodiment of the present invention, (a) is a graph showing the interior angle frequency distribution when the detected vibration is an earthquake. (b) and (c) are graphs showing the interior angle frequency distribution of noise. [Figure 13] As an example of an interior angle frequency distribution generated by a seismic sensor according to yet another embodiment of the present invention, (a) is a graph showing the case where the detected vibration is an earthquake, and (b) is a graph showing weights for assigning positive and negative weights to earthquake features and noise features, respectively, for the interior angle frequency distribution in (a). [Figure 14] As an example of an interior angle frequency distribution generated by a seismic sensor according to yet another embodiment of the present invention, (a) is a graph showing a case where the detected vibration is noise, and (b) is a graph showing weights for assigning positive and negative weights to earthquake features and noise features, respectively, for the interior angle frequency distribution in (a). DETAILED DESCRIPTION OF THE INVENTION

[0034] A seismic sensor according to one embodiment of the present invention will be described below with reference to FIGS. 1 to 11. FIG. In the present embodiment, more detailed explanation than necessary may be omitted. For example, detailed explanation of well-known matters or redundant explanation of substantially the same configuration may be omitted. This is to avoid unnecessary redundancy in the following explanation and to facilitate understanding by those skilled in the art. Furthermore, the applicant provides the accompanying drawings and the following description to enable those skilled in the art to fully understand the present invention, and they are not intended to limit the subject matter described in the claims.

[0035] (1) Configuration of the seismic sensor 10 As shown in FIG. 1, the seismic sensor 10 according to this embodiment includes an acceleration sensor 11, a controller 12, and a memory 13.

[0036] The acceleration sensor 11 is, for example, an acceleration sensor using a piezoelectric element or an acceleration sensor that detects electrostatic capacitance between electrodes. The acceleration measured (also called “sampling”) by the acceleration sensor 11 is output to the controller 12. The acceleration sensor 11 has virtual three-dimensional axes (X-axis, Y-axis, Z-axis), detects acceleration on each axis, and outputs the detected acceleration to the controller 12.

[0037] The controller 12 is, for example, a general-purpose integrated circuit that acquires the acceleration measured by the acceleration sensor 11 at a predetermined period, detects the occurrence of an earthquake based on the acquired acceleration, and calculates an index value indicating the magnitude of the earthquake. Also, the controller 12 operates in different modes, active mode or sleep mode, depending on the situation.

[0038] The sleep mode is a mode in which the controller 12 operates with limited functions, such as stopping the execution of instructions while accepting interrupts, stopping the supply of clocks, etc. In this sleep mode, power consumption can be reduced more than in the active mode. The active mode is a mode in which a process is performed to determine whether the detected vibration is an earthquake or noise, and an index value indicating the magnitude of the earthquake is calculated.

[0039] The function blocks (see FIG. 2) generated when the CPU in the seismic sensor 10 reads the earthquake detection program stored in the memory 13 will be described in detail later. The memory 13 is a temporary storage means such as a RAM (Random Access Memory) or a non-volatile memory such as an EPROM (Erasable Programmable Read Only Memory), and stores, for example, the acceleration measured by the acceleration sensor 11 and threshold values ​​used for earthquake determination.

[0040] The memory 13 may be a memory built into the acceleration sensor 11 or the controller 12 . The output unit 14 is, for example, an output terminal included in the controller 12, and when the controller 12 determines that, for example, an earthquake has occurred, information indicating the occurrence and scale of the earthquake is output to another device via the output unit 14. Furthermore, when an earthquake of a predetermined scale or greater is detected, the output unit 14 outputs, for example, a cutoff signal to an external device to stop the supply of energy such as electricity or gas.

[0041] (2) Functional block of seismic sensor 10 As shown in Figure 2, the seismic sensor 10 includes an acceleration acquisition unit 21, a vibration intensity classification / activation determination unit 22, an interior angle calculation unit 23, an interior angle frequency distribution generation unit 24, an earthquake determination unit 25, an earthquake magnitude calculation unit 26, an output control unit 27, an offset adjustment unit 28, and a memory unit 29. These functional blocks shown in FIG. 2 are configured by the controller 12 receiving acceleration data obtained from the acceleration sensor 11 and reading a program stored in the memory 13.

[0042] The acceleration acquisition unit 21 acquires measurement data of acceleration in the X-axis, Y-axis, and Z-axis measured at a predetermined cycle by the acceleration sensor 11. Note that the acceleration acquisition unit 21 normally acquires measurement data of acceleration measured repeatedly at a relatively low speed (i.e., at a relatively large measurement cycle). When performing such low-speed acceleration sampling, the controller 12 basically operates in a sleep mode (standby state or power-saving mode) with low power consumption. In the standby state, the acceleration sensor 11 is in an operating state where it samples at a low speed, so the controller 12 operates in a sleep mode with limited functionality, thereby reducing power consumption.

[0043] Furthermore, when the acceleration acquisition unit 21 acquires vibrations greater than a threshold value preset in the storage unit 29, the acceleration sensor 11 repeats measuring the acceleration at a higher speed (i.e., at a relatively short cycle) than during low-speed sampling. During such high-speed sampling, the controller 12 operates in a sleep mode or an active mode. When the earthquake determination unit 25 (described later) and the like execute processing, the controller 12 operates in active mode (measurement mode). The transition from the power saving mode to the measurement mode is called the activation of the seismic sensor 10.

[0044] The measurement mode is an operating state in which high-speed sampling is performed, so the controller 12 may operate in a sleep mode with limited functionality, or in an active mode with maximum computing power. In the measurement mode, the sampling period is shortened and the controller 12 switches from the sleep mode to the active mode, resulting in higher power consumption than in the power-saving mode.

[0045] Furthermore, the acceleration acquisition unit 21 extracts the acceleration in the non-gravity direction from the acceleration measured by the triaxial acceleration sensor 11, and acquires the acceleration on a coordinate plane (for example, an XY plane). The vibration intensity discrimination and activation determination unit 22 is a function on the acceleration sensor 11 side, which compares the acceleration value acquired by the acceleration acquisition unit 21 with the activation threshold value stored in the memory unit 29, and if the acceleration value exceeds the activation threshold value, transitions from power saving mode to measurement mode (activates the seismic sensor 10).

[0046] In addition, the vibration intensity discrimination / activation determination unit 22 calculates the vibration intensity from the measurement results of the acceleration acquisition unit 21, and if the vibration intensity is equal to or greater than a predetermined magnitude, transitions from the power saving mode to the measurement mode, which consumes more power than the power saving mode (activates the controller 12). Here, the vibration intensity classification process performed by the vibration intensity classification / activation determination unit 22 is performed by filtering the acceleration value acquired by the acceleration acquisition unit 21. At this time, the filtered acceleration is stored in the storage unit 29.

[0047] The interior angle calculation unit 23 calculates the interior angle between two successive acceleration vectors on a predetermined coordinate plane (for example, an XY plane) for the acceleration acquired by the acceleration acquisition unit 21. Here, the predetermined coordinate plane means a substantially horizontal XY plane formed by, for example, the X-axis and the Y-axis out of the X-axis, Y-axis, and Z-axis of the acceleration sensor 11. The interior angle between two consecutive accelerations refers to the interior angle between two acceleration vectors connecting three consecutive acceleration points on a coordinate plane acquired over time. Note that the interior angle between two acceleration vectors is the angle formed by the two vectors when the starting points of the two consecutive acceleration vectors are aligned with the origin.

[0048] Specifically, when the vibration detected by acceleration sensor 11 is an earthquake, the vibration caused by the earthquake is characterized by generating acceleration in all directions, for example, on the XY plane of the X, Y, and Z axes of acceleration sensor 11 or on the horizontal plane, as shown in FIG. 3. Here, as shown in FIG. 4(a), the interior angle calculation unit 23 extracts two acceleration vectors A and B connecting three consecutive points from the accelerations on the XY plane in FIG. 3, and calculates the angle formed by the two acceleration vectors with the starting points of the two acceleration vectors aligned with the origin as the interior angle, as shown in FIG. 4(b).

[0049] The interior angle frequency distribution generating unit 24 generates a frequency distribution of the interior angle formed by two successive acceleration vectors shown in FIG. 4(b). In this case, if the detected vibration is an earthquake as shown in Fig. 3, it has characteristics such as being a low-frequency vibration, containing various frequency components, vibrating in various directions on the horizontal plane, etc., and therefore has the characteristic of moving in a circular shape on the horizontal plane, so the interior angle between two consecutive acceleration vectors is often an acute angle and rarely an obtuse angle. Therefore, the interior angle frequency distribution generated by the interior angle frequency distribution generator 24 is a graph that peaks at around 20 degrees (part A) and decreases in frequency as the angle increases (part B), as shown in Fig. 4(c).

[0050] In the graph in Figure 4(c), when the interior angle between two consecutive acceleration vectors is 0° (part C), this means that the detected vibration is linear motion, and vibrations that are not characteristic of an earthquake are occurring. On the other hand, if the vibration detected by acceleration sensor 11 is not an earthquake, the vibration is characterized by noise such as everyday vibration, and generates acceleration in a substantially constant direction on the XY plane of the X, Y, and Z axes of acceleration sensor 11, or on the horizontal plane, as shown in FIG. 5.

[0051] Here, as shown in FIG. 6(a), the interior angle calculation unit 23 extracts two acceleration vectors A and B connecting three consecutive points from the accelerations on the XY plane in FIG. 5, and calculates the angle formed by the two acceleration vectors with the starting points of the two acceleration vectors aligned with the origin as the interior angle, as shown in FIG. 6(b). The interior angle frequency distribution generating unit 24 generates a frequency distribution of the interior angle formed by two successive acceleration vectors shown in FIG. 6(b).

[0052] At this time, if the detected vibration is noise such as everyday vibrations that are not earthquakes as shown in Figure 5, it has the characteristic of moving along a substantially constant straight line, so the interior angle between two consecutive acceleration vectors is often near 0° or an obtuse angle, and rarely an acute angle. For this reason, the interior angle frequency distribution generated by the interior angle frequency distribution generating unit 24 is a graph as shown in Figure 6(c), with many angles near 0° (part A), few acute angles (part B), and the frequency increasing as the angle becomes larger (part C).

[0053] Here, different acceleration distributions and interior angle frequency distributions are generated on a predetermined coordinate plane depending on whether the detected vibration is an earthquake or other types of noise (multiple types of noise). That is, when the detected vibration is an earthquake, it contains components of various frequency bands in all directions on the XY plane, as shown in FIG. 7(a). Therefore, as shown in FIG. 7(b), the frequency distribution generated by the interior angle frequency distribution generating unit 24 has a high frequency of acute angles and a low frequency of obtuse angles, similar to FIG. 4(c).

[0054] On the other hand, if the detected vibration is not an earthquake but high-frequency vibration noise, as shown in Figure 8(a), two consecutive acceleration components on the XY plane will be linear and contain high-frequency components. Therefore, the frequency distribution generated by the interior angle frequency distribution generating unit 24 has a high frequency of angles near 0° and obtuse angles, and a low frequency of acute angles, as shown in FIG. 8(b).

[0055] Furthermore, if the detected vibration is not an earthquake but a vibration noise having approximately the same frequency, it will contain an acceleration component that is approximately circular on the XY plane, as shown in FIG. 9(a). For this reason, the frequency distribution generated by the interior angle frequency distribution generating unit 24 has a particularly high frequency of certain angles, as shown in FIG. 9(b). Furthermore, if the detected vibration is not an earthquake but a noise of linear motion, two consecutive acceleration components on the XY plane will be linear components, as shown in FIG. 10(a).

[0056] Therefore, the frequency distribution generated by the interior angle frequency distribution generating unit 24 has a high frequency of angles near 0° and obtuse angles, and a low frequency of acute angles, as shown in FIG. 10(b). Here, a characteristic feature that appears as a characteristic of an earthquake is that, for example, the interior angle formed by two consecutive acceleration vectors often becomes an acute angle. Specifically, because earthquake vibrations are always vibrating in various directions, the frequency distribution of the interior angle formed by two consecutive acceleration vectors is high for acute angles and low for obtuse angles.

[0057] Therefore, in the seismic sensor 10 of this embodiment, since a characteristic of earthquakes is that the interior angle between two consecutive acceleration vectors is often an acute angle, if it detects that the frequency distribution of the interior angle is high at an acute angle, it determines that the vibration is an earthquake, and in any other cases it determines that the vibration is noise. The earthquake determination unit 25 determines whether or not the vibration is an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit 24. That is, the earthquake determination unit 25 determines that the vibration is not an earthquake if the proportion of obtuse angle components in the frequency distribution of interior angles is equal to or greater than a predetermined threshold, as shown in Figure 7(b). Also, the earthquake determination unit 25 determines that the vibration is an earthquake if the proportion of obtuse angle components in the frequency distribution of interior angles is smaller than a predetermined threshold, as shown in Figure 7(b).

[0058] Furthermore, the earthquake determination unit 25 may use any one of the mean value, median value, and mode value of the frequency distribution generated by the interior angle frequency distribution generation unit 24 to determine whether or not the vibration is an earthquake. Furthermore, the earthquake determination unit 25 may determine whether the vibration is an earthquake or not using any of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit 24.

[0059] As a result, in order to avoid mistakenly identifying noise with a frequency distribution that has a peak at a sharp angle, similar to the characteristics of an earthquake, as an earthquake, as shown in Figure 9(b), for example, when kurtosis is used and is greater than a predetermined threshold, noise of approximately the same frequency as shown in Figure 9(a), where a specific angle is prominently high, can be identified as vibration that is not an earthquake. When the earthquake determination unit 25 determines that an earthquake has occurred, the earthquake scale calculation unit 26 determines whether the earthquake has a seismic intensity of at least a predetermined level.

[0060] Furthermore, after the earthquake magnitude calculation unit 26 determines that the detected vibration is an earthquake and starts calculating an index indicating the magnitude of the earthquake, if an acceleration waveform that can be considered to be an impact is detected, the earthquake magnitude calculation unit 26 excludes the acceleration waveform and calculates the magnitude of the earthquake. The output control unit 27 controls the output of a signal from the output unit 14, which outputs a predetermined signal, depending on whether the magnitude of the earthquake calculated by the earthquake magnitude calculation unit 26 is equal to or greater than a predetermined seismic intensity.

[0061] Here, the predetermined signal output from the output unit 14 includes, for example, a shutoff signal sent to an external device such as an electricity supply device or a gas supply device in order to stop the supply of energy such as electricity or gas. When earthquake determination unit 25 determines that the vibration detected by acceleration acquisition unit 21 is noise, offset adjustment unit 28 adjusts the offset amount of the acceleration waveform according to the magnitude of the noise. Then, offset adjustment unit 28 adjusts the offset amount of the acceleration waveform according to the determination result of earthquake determination unit 25.

[0062] The offset adjustment performed by the offset adjuster 28 detects noise components contained in the measured acceleration as offset components, such as the amount of change in the measurement value that occurs with changes over time in the seismic sensor 10, the amount of change in the measurement value that occurs with temperature changes, and the amount of change in the measurement value that occurs when the orientation of the installed seismic sensor 10 tilts for some reason and the direction of gravitational acceleration relative to the seismic sensor 10 changes. Specifically, the offset adjuster 28 calculates, for example, the median of the maximum and minimum values ​​of the acceleration determined to be noise, or the average value of the acceleration, as the offset component. The memory unit 29 stores, for example, acceleration data acquired by the acceleration acquisition unit 21 or acceleration data after filtering processing, interior angle data calculated by the interior angle calculation unit 23, frequency distribution data generated by the interior angle frequency distribution generation unit 24, judgment results in the earthquake judgment unit 25, offset component data used in the offset adjustment unit 28, etc.

[0063] <Earthquake detection method> The earthquake detection method using the seismic sensor 10 of this embodiment will be described below with reference to the flowchart shown in FIG.

[0064] That is, in step S11, the acceleration acquisition unit 21 of the seismic sensor 10 acquires the acceleration measured by the acceleration sensor 11. Next, in step S12, the interior angle calculation unit 23 calculates two consecutive acceleration vectors from the accelerations of the three consecutive points acquired in step S11. Next, in step S13, the interior angle calculation unit 23 calculates the interior angle between the two consecutive acceleration vectors calculated in step S12 using the inner product or the cross product.

[0065] Next, in step S14, the interior angle frequency distribution generating unit 24 counts up the frequency (number of times) of the interior angle calculated in step S13. Next, in step S15, it is determined whether or not the vibration determination process is to be ended. If it is to be ended, the process proceeds to step S16, and if it is not to be ended, the process returns to step S11 and the subsequent processes are repeated.

[0066] Next, in step S16, the interior angle frequency distribution generating unit 24 calculates the total number of frequencies of the interior angles counted up in step S14. Next, in step S17, the interior angle frequency distribution generating unit 24 calculates the total frequency of interior angles equal to or greater than 90° (obtuse angles) from the total frequency of interior angles calculated in step S16. Next, in step S18, the interior angle frequency distribution generating unit 24 calculates the proportion of obtuse angles to the total (total frequency of angles equal to or greater than 90° (obtuse angles) / total frequency of each interior angle).

[0067] Next, in step S19, the earthquake determination unit 25 determines whether or not the following relational expression (1) is satisfied. Percentage of obtuse angles < predetermined threshold (1) If the relational expression (1) is satisfied, the process proceeds to step S20, where the earthquake determination unit 25 determines that the frequency distribution of the interior angle formed by the vectors of two consecutive accelerations, which is a characteristic of noise, has a low proportion of obtuse angles, making it highly likely that the vibration is an earthquake, and ends the process.On the other hand, if the relational expression (1) is not satisfied, the process proceeds to step S21, where the earthquake determination unit 25 determines that the vibration has a high proportion of obtuse angles, which is a characteristic of noise, making it highly unlikely that the vibration is an earthquake, and ends the process.

[0068] <Major features> As shown in Fig. 2, the seismic sensor 10 of this embodiment includes an acceleration acquisition unit 21, an interior angle calculation unit 23, an interior angle frequency distribution generation unit 24, and an earthquake determination unit 25. The acceleration acquisition unit 21 detects vibrations and acquires the acceleration of the vibrations. The interior angle calculation unit 23 calculates the interior angle of two consecutive acceleration vectors on a predetermined coordinate plane based on the acceleration acquired by the acceleration acquisition unit 21. The interior angle frequency distribution generation unit 24 generates a frequency distribution of the interior angles calculated by the interior angle calculation unit 23. The earthquake determination unit 25 determines whether the vibrations are an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit 24. This means that if the interior angle between two consecutive acceleration vectors has many acute components and few obtuse components, it can be determined that it matches the characteristics of an earthquake and that the vibration in question is likely to be an earthquake. As a result, it is possible to accurately determine whether the detected vibration is an earthquake or noise.

[0069] [Other embodiments] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment, and various modifications are possible without departing from the gist of the invention.

[0070] (A) In the above embodiment, the present invention has been described as being implemented as a seismic sensor and an earthquake detection method, but the present invention is not limited to this. For example, the present invention may be realized as an earthquake detection program that causes a computer to execute the earthquake detection method using the seismic sensor described above.

[0071] This earthquake detection program is stored in a memory (storage unit) installed in the seismic sensor, and the CPU reads the earthquake detection program stored in the memory and causes the hardware to execute each step. More specifically, the CPU reads the earthquake detection program and executes the acceleration acquisition step, interior angle calculation step, interior angle frequency distribution generation step, and earthquake determination step described above, thereby achieving the same effects as those described above. The present invention may also be realized as a recording medium storing an earthquake detection program.

[0072] (B) In the above embodiment, an example has been described in which the earthquake determination unit 25 determines whether a detected vibration is an earthquake if the proportion of obtuse angles in the frequency distribution of the interior angles formed by two successive acceleration vectors is less than a predetermined threshold, but the present invention is not limited to this.

[0073] For example, the earthquake determination unit may be configured to determine whether the detected vibration is an earthquake by using any of the mean, median, and mode of the frequency distribution generated by the interior angle frequency distribution generation unit. Specifically, as shown in FIG. 12(a), the earthquake determination unit may be configured to determine that the vibration is an earthquake when the angle having a frequency (mode) higher than the average frequency is an acute angle. Furthermore, the earthquake determination unit may be configured to determine that an earthquake has occurred when an angle having a frequency higher than the median value of the frequencies is an acute angle, as shown in FIG. 12(a). Alternatively, the earthquake determination unit may be configured to determine that an earthquake has occurred when the most frequent value of the frequency is an acute angle, as shown in FIG. 12(a).

[0074] (C) In the above embodiment, an example has been described in which the earthquake determination unit 25 determines whether a detected vibration is an earthquake if the proportion of obtuse angles in the frequency distribution of the interior angles formed by two successive acceleration vectors is less than a predetermined threshold, but the present invention is not limited to this.

[0075] For example, the earthquake determination unit may be configured to determine whether an earthquake has occurred based on the degree of variation in angles when the standard deviation, variance, and coefficient of variation of the frequency in the frequency distribution are within predetermined thresholds. Specifically, the standard deviation, variance, and coefficient of variation represent the degree of dispersion in the distribution, and the smaller these values ​​are, the less dispersion there is. Furthermore, vibrations caused by earthquakes are characterized by the fact that the dispersion is neither extremely large nor extremely small around the angle of the most frequent value.

[0076] Therefore, as shown in FIG. 12(b), when there is an extremely small variation and bias around the angle of the most frequent value, the vibration can be determined to be noise. Similarly, as shown in FIG. 12(c), when there is an extremely large variation in the frequency distribution of the interior angles, the vibration can be determined to be noise. Furthermore, the earthquake determination unit may be configured to determine that an earthquake has occurred when the skewness of the frequency in the frequency distribution of interior angles is equal to or greater than a predetermined threshold (for example, 0). The skewness is equal to or greater than 0 when the frequency distribution of interior angles is biased to the left (high frequency of acute angles), and is equal to or less than 0 when biased to the right (high frequency of obtuse angles). Therefore, the predetermined threshold can be set to 0 to perform earthquake determination.

[0077] The earthquake determination unit may be configured to determine that an earthquake has occurred when the kurtosis of the frequency in the frequency distribution of the interior angles is equal to or less than a predetermined threshold. Here, kurtosis represents the degree of sharpness (degree of variation) in the frequency distribution of the interior angles, and a larger kurtosis represents less variation. As a result, if the kurtosis of the peak of the frequency distribution of the interior angles is within the threshold, it is determined that the degree of variation in angles is small, and the vibration can be determined to be an earthquake. On the other hand, for example, as shown in Figure 12(b), if the kurtosis of the frequency distribution of the interior angles is large, it is determined that the angle deviation is close to the characteristics of noise, and the vibration can be determined to be noise.

[0078] (D) In the above embodiment, an example has been described in which the earthquake determination unit 25 determines whether a detected vibration is an earthquake if the proportion of obtuse angles in the frequency distribution of the interior angles formed by two successive acceleration vectors is less than a predetermined threshold, but the present invention is not limited to this.

[0079] For example, the earthquake determination unit may be configured to focus on the fact that in the frequency distribution of interior angles, the frequency around approximately 20 to 50° is high as a characteristic of earthquakes, and the frequency around 0° and above approximately 150° is high as a characteristic of noise, and to assign a positive weight to the frequency of interior angles around 20 to 50° and a negative weight to the frequency of approximately 0° and above approximately 150°, and perform earthquake determination depending on whether the sum is positive or negative.

[0080] Specifically, as shown in Figure 13(a), when the detected vibration is an earthquake, the earthquake determination unit assigns a positive weight to the frequency of interior angles of approximately 20 to 50°, and a negative weight to the frequency of interior angles of approximately 0° and approximately 150° or greater, as shown in Figure 13(b), and calculates the sum from 0 to 180°. As a result, if the sum is positive, it can be determined that the characteristics of an earthquake are more pronounced than the characteristics of noise, and the vibration can be determined to be an earthquake.

[0081] On the other hand, when the detected vibration is noise as shown in FIG. 14(a), the earthquake determination unit assigns a positive weight to the frequency of interior angles of approximately 20 to 50°, and a negative weight to the frequency of interior angles of approximately 0° and approximately 150° or greater, as shown in FIG. 14(b), and calculates the sum from 0 to 180°. As a result, if the sum is negative, it can be determined that the characteristics of noise are more pronounced than the characteristics of an earthquake, and the vibration can be determined to be noise.

[0082] (E) In the above embodiment, an example has been described in which the XY plane of the acceleration sensor 11 is set as a predetermined coordinate plane and the interior angle between two consecutive acceleration vectors is calculated. However, the present invention is not limited to this. For example, the predetermined coordinate plane set for calculating the interior angle between two consecutive acceleration vectors may be the XZ plane or the YZ plane among the three axes (X-axis, Y-axis, and Z-axis) of the acceleration sensor, or may be, for example, a horizontal plane obtained by extracting acceleration in a non-gravity direction from the acceleration of the three axes of the acceleration sensor that measures acceleration.

[0083] (F) In the above embodiment, an example has been described in which the seismic sensor 10 is provided with the earthquake determination unit 25 that performs earthquake determination based on the frequency distribution generated by the interior angle frequency distribution generation unit 24. However, the present invention is not limited to this. For example, the seismic sensor may be configured to analyze the detected vibrations but not to determine whether an earthquake has occurred. In this case, the frequency distribution generated by the interior angle frequency distribution generation unit can be sent to an external device (e.g., an external server device, etc.), and earthquake determination can be performed on the external device side, thereby achieving the same effect as above.

[0084] <Additional Notes> The seismic sensor according to the first invention is an acceleration acquisition unit that detects vibration and acquires the acceleration of the vibration; an interior angle calculation unit that calculates an interior angle between two successive acceleration vectors on a predetermined coordinate plane for the acceleration acquired by the acceleration acquisition unit; an interior angle frequency distribution generation unit that generates a frequency distribution of the interior angles calculated by the interior angle calculation unit; an earthquake determination unit that determines whether the vibration is an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit; It is equipped with:

[0085] The seismic sensor according to the second invention is the seismic sensor according to the first invention, The earthquake determination unit determines that the vibration is an earthquake when a proportion of obtuse angle components in the frequency distribution of the interior angles is smaller than a predetermined threshold value. The seismic sensor according to the third invention is the seismic sensor according to the first or second invention, The earthquake determination unit determines that the vibration is not an earthquake when a proportion of obtuse angle components in the frequency distribution of the interior angles is equal to or greater than a predetermined threshold value.

[0086] A seismic sensor according to a fourth aspect of the present invention is a seismic sensor according to any one of the first to third aspects of the present invention, The earthquake determination unit determines whether the vibration is an earthquake using any one of the mean, median, and mode of the frequency distribution generated by the interior angle frequency distribution generation unit. The seismic sensor according to the fifth invention is the seismic sensor according to any one of the first to fourth inventions, The earthquake determination unit determines whether the vibration is an earthquake using any one of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit.

[0087] A seismic sensor according to a sixth aspect of the present invention is a seismic sensor according to any one of the first to fifth aspects of the present invention, The earthquake determination unit determines whether the vibration is an earthquake or not by using a result of weighting the frequency distribution generated by the interior angle frequency distribution generation unit according to the angle. The seismic sensor according to the seventh invention is the seismic sensor according to any one of the first to sixth inventions, The acceleration acquisition unit extracts and acquires acceleration in a non-gravity direction from acceleration measured by a three-axis acceleration sensor.

[0088] The seismic sensor according to an eighth aspect of the present invention is the seismic sensor according to any one of the first to seventh aspects of the present invention, The earthquake detection unit further includes an earthquake magnitude calculation unit that determines whether the earthquake is equivalent to or greater than a predetermined seismic intensity when the earthquake determination unit determines that an earthquake has occurred. A seismic sensor according to a ninth aspect of the present invention is a seismic sensor according to any one of the first to eighth aspects of the present invention, The device further includes an activation determination unit that calculates the vibration intensity from the results acquired by the acceleration acquisition unit, and when the vibration intensity is equal to or greater than a predetermined magnitude, transitions from a power saving mode to a measurement mode that consumes more power than the power saving mode.

[0089] A seismic sensor according to a tenth aspect of the present invention is a seismic sensor according to any one of the first to ninth aspects of the present invention, The earthquake detection unit further includes an output control unit that outputs the predetermined signal when it is determined that an earthquake has occurred. [Industrial Applicability]

[0090] The seismic sensor of the present invention has the effect of being able to accurately determine whether detected vibrations are earthquakes or noise, and is therefore widely applicable to various devices that analyze vibrations such as earthquakes. [Explanation of symbols]

[0091] 10 Seismic Sensor 11 Acceleration sensor 12 Controllers 13. Memory 14 Output section 21 Acceleration acquisition section 22 Vibration intensity classification / startup determination section (startup determination section) 23 Interior angle calculation section 24 Internal angle frequency distribution generator 25 Earthquake Determination Department 26 Earthquake scale calculation department 27 Output control section 28 Offset adjustment section 29 Memory section

Claims

1. an acceleration acquisition unit that detects vibration and acquires the acceleration of the vibration; an interior angle calculation unit that calculates an interior angle between two successive acceleration vectors on a predetermined coordinate plane for the acceleration acquired by the acceleration acquisition unit; an interior angle frequency distribution generation unit that generates a frequency distribution of the interior angles calculated by the interior angle calculation unit; an earthquake determination unit that determines whether the vibration is an earthquake based on the frequency distribution generated by the interior angle frequency distribution generation unit; A seismic sensor equipped with:

2. the earthquake determination unit determines that the vibration is an earthquake when a proportion of obtuse angle components in the frequency distribution of the interior angles is smaller than a predetermined threshold value; The seismic sensor according to claim 1 .

3. The earthquake determination unit determines that the vibration is not an earthquake when a ratio of obtuse angle components in the frequency distribution of the interior angles is equal to or greater than a predetermined threshold. The seismic sensor according to claim 1 or 2.

4. the earthquake determination unit determines whether the vibration is an earthquake by using any one of a mean value, a median value, and a mode value of the frequency distribution generated by the interior angle frequency distribution generation unit. The seismic sensor according to claim 1 or 2.

5. the earthquake determination unit determines whether the vibration is an earthquake using any one of the standard deviation, variance, coefficient of variation, skewness, and kurtosis of the frequency distribution generated by the interior angle frequency distribution generation unit. The seismic sensor according to claim 1 or 2.

6. the earthquake determination unit determines whether the vibration is an earthquake or not by using a result of weighting the frequency distribution generated by the interior angle frequency distribution generation unit according to the angle. The seismic sensor according to claim 1 or 2.

7. the acceleration acquisition unit extracts and acquires acceleration in a non-gravity direction from acceleration measured by a three-axis acceleration sensor; The seismic sensor according to claim 1 or 2.

8. The apparatus further includes an earthquake magnitude calculation unit that, when the earthquake determination unit determines that an earthquake has occurred, determines whether the earthquake is equivalent to or greater than a predetermined seismic intensity. The seismic sensor according to claim 1 or 2.

9. The device further includes an activation determination unit that calculates the intensity of the vibration from the result of acquisition by the acceleration acquisition unit, and when the intensity of the vibration is equal to or greater than a predetermined magnitude, transitions from the power saving mode to a measurement mode that consumes more power than the power saving mode. The seismic sensor according to claim 1 or 2.

10. The earthquake detection unit further includes an output control unit that outputs the predetermined signal when the earthquake detection unit determines that an earthquake has occurred. The seismic sensor according to claim 1 or 2.

11. an acceleration acquisition step of detecting vibration and acquiring the acceleration of the vibration; an interior angle calculation step of calculating an interior angle between two successive acceleration vectors on a predetermined coordinate plane for the acceleration acquired in the acceleration acquisition step; an interior angle frequency distribution generating step of generating a frequency distribution of the interior angles calculated in the interior angle calculating step; an earthquake determination step of determining whether the vibration is an earthquake based on the frequency distribution generated in the interior angle frequency distribution generation step; An earthquake detection method comprising:

12. an acceleration acquisition step of detecting vibration and acquiring the acceleration of the vibration; an interior angle calculation step of calculating an interior angle between two successive acceleration vectors on a predetermined coordinate plane for the acceleration acquired in the acceleration acquisition step; an interior angle frequency distribution generating step of generating a frequency distribution of the interior angles calculated in the interior angle calculating step; an earthquake determination step of determining whether the vibration is an earthquake based on the frequency distribution generated in the interior angle frequency distribution generation step; An earthquake detection program that causes a computer to execute an earthquake detection method comprising:

13. an acceleration acquisition unit that detects vibration and acquires the acceleration of the vibration; an interior angle calculation unit that calculates an interior angle between two successive acceleration vectors on a predetermined coordinate plane for the acceleration acquired by the acceleration acquisition unit; an interior angle frequency distribution generation unit that generates a frequency distribution of the interior angles calculated by the interior angle calculation unit; A seismic sensor equipped with:

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