JP4069177B2 - Fault fracture zone determination method and determination support device - Google Patents

Description

  The present invention relates to a fault fracture zone determination method and a determination support device, and in particular, a fault fracture zone determination method for determining whether or not a fault fracture zone candidate that may exist actually exists, and the fault The present invention relates to a fault fracture zone determination support apparatus that can be used in a fracture zone determination method.

  For example, it is very important to understand the existence and characteristics of fault crushing zones in the candidate site and its surroundings when formulating a construction plan for a structure that requires high safety, such as a high-level waste disposal site. It is. Currently, exploration of the fault fracture zone is mainly carried out by applying the reflection method. As described in Non-Patent Document 1, the reflection method uses a phenomenon in which elastic waves are reflected and refracted at a boundary surface with different acoustic impedances, and uses an artificial seismic source such as a vibrator or a blast to be below the ground surface. CDP polymerization method, etc., repeating the measurement of the elastic wave incident on the ground layer and measuring the elastic wave reflected at the boundary of the formation at multiple locations on the ground surface while moving the positions of the artificial seismic source and the measurement location of the elastic wave This is a method for investigating the underground structure of the survey area including the presence or absence of fault fracture zone and the inclination direction by analyzing the measurement results of elastic waves. The reflection method is technically almost complete and highly reliable.

In relation to the above, Patent Document 1 discloses a three-dimensional reflection method in which an oscillation point and a receiving point are arranged in a plane, and a geological structure is three-dimensionally explored by observing and processing signals from all directions. In seismic exploration, a high-density three-dimensional reflection seismic exploration device having a configuration in which a plurality of oscillation devices and vibration receiving devices are mounted on a non-stretchable planar member is disclosed.
Illustrated Geophysical Exploration, Geophysical Exploration Society, June 1, 1992, p.3-18 JP 2004-20448 A

  However, the exploration of the fault fracture zone by the reflection method means that an elastic wave is incident below the ground surface using an artificial seismic source, and elastic waves are measured at multiple locations on the ground surface. Since it is necessary to repeat the position many times while moving the position, there is a problem that measurement is very expensive and difficult to implement at the very early stage of construction planning. In particular, when there are many candidate construction sites, or when it is predicted that there are many fault fracture zones and the area to be surveyed is wide, investigate the fault fracture zone by the reflection method. Then, since enormous cost is required, establishment of a method capable of determining the presence or absence of a fault fracture zone at a lower cost has been demanded.

  Note that the high-density three-dimensional reflection seismic exploration device described in Patent Document 1 is a device intended for three-dimensional exploration of shallow geological structures at high density, and the technology described in Patent Document 1 is applied. In order to investigate the deeper underground structure, the oscillation device and the vibration receiving device must be separated from each other, so that the area of the planar member becomes very large, which is not realistic.

  The present invention has been made in view of the above facts, and an object of the present invention is to obtain a fault fracture zone determination method and a fault fracture zone determination support device that can easily determine the presence or absence of a fault fracture zone.

  In addition to the reflection method described above, the presence or absence of a fault fracture zone can also be estimated by a lineament based on an aerial photograph (aerial photograph or satellite photograph). However, with lineaments and the like, it is understood that “there seems to be a fault crushing zone may exist”, and determination accuracy is remarkably insufficient to determine the presence or absence of a fault crushing zone alone. For this reason, the inventors of the present application determine / confirm whether or not a fault crush zone candidate exists for a fault zone candidate that has been determined to be possibly present by a lineament or the like. For the purpose of developing the method, in order to investigate the influence of the fault fracture zone on seismic waves, the simulation described below was performed.

  In this simulation, as shown in Fig. 1, a two-dimensional plane in which a bedrock layer with a layer thickness of 3000 (m) exists on a basement layer with a base of 8000 (m) and a layer thickness of 1000 (m). Using a strain model as an analysis model, the horizontal and vertical components of the seismic wave measured at each position on the ground surface (upper surface of the rock layer) when a seismic wave is incident on this analysis model Each of the cases with and without the fault fracture zone was determined by frequency response analysis by FEM (Finite Element Method). In addition, as the fault crush zone, the fault crush zone is inclined at an inclination angle (angle with respect to the upper surface of the base) θ = 80 °, penetrates the bedrock layer and continues in the depth direction of FIG. Applied. Seismic waves are assumed to be incident from the bottom. Then, the initial motion part of the horizontal component of the seismic wave and the initial motion part of the vertical component at each position on the ground surface obtained by the simulation calculation are converted into a frequency spectrum (response spectrum), respectively. By dividing the frequency spectrum of the initial motion part by the frequency spectrum of the initial motion part of the vertical component of the seismic wave at each position, the H / V spectrum of the seismic wave at each position was obtained. The results are shown in FIGS. 2 (A) and (C). Note that the two-dimensional plane strain model provides sufficient accuracy under the present conditions, and the same model is used. However, the same study can be performed using a three-dimensional model.

  2A and 2C, p0k, p2k, pfl, pfr, p6k, and p8k are the measurement point positions on the ground surface of the analysis model (these measurement points are the fault fracture zone on the ground surface). The p0k is located at one end (reference position) on the ground surface of the analysis model, as shown in FIG. 1 as well. P2k is the position of the measurement point located at a distance of 2000m from the reference position on the ground surface of the analysis model to the other end, pfl is the position of the fault crush zone on the ground surface of the analysis model The measurement point position that is slightly shifted to the reference position side (left side in FIG. 1) with respect to the position of the fault fracture zone on the ground surface of the analysis model, pfr P6k is the ground surface of the analysis model where the measurement point position is slightly shifted to the right) P8k is located at the other end on the ground surface of the analysis model (position 8000m away from the reference position to the other end side), the measurement point position located 6000m away from the upper reference position to the other end side. Each measurement point position is shown.

  The response of “free ground” was used to investigate the effect of the fault fracture zone. “Free ground” means a stratified ground having the same stratum structure as the analysis model and infinitely extending in the horizontal direction. The same seismic wave as the analysis model shown in Fig. 1 is incident on the free ground, and the response on the ground surface is obtained based on the one-dimensional wave propagation theory, and the H / V spectrum of the seismic wave as in the analysis model shown in Fig. 1 Ask for. The H / V spectrum of seismic waves in free ground is not affected by the fault fracture zone. In addition, there is no error in numerical analysis due to the side boundary of the analysis model, the size of the analysis mesh, and the like. From the above viewpoint, the H / V spectrum of seismic waves in free ground can be used as a reference.

  As is clear from comparison between FIG. 2A and FIG. 2C, when there is no fault fracture zone (see FIG. 2A), the measurement is performed at each position on the ground surface of the analysis model. The seismic wave H / V spectrum is almost the same as the seismic wave H / V spectrum measured on free ground, but in the case of a fault zone (see Fig. 2 (C)), the analysis model The H / V spectrum of the seismic wave measured at each position on the ground surface is different from that of the seismic wave measured on the free ground. In this way, the result that the H / V spectrum of the seismic wave measured at each position on the ground surface of the analysis model is greatly different depending on the presence or absence of the fault fracture zone was obtained. It can be judged that the H / V spectrum of the seismic wave at the nearby measurement point has a large effect, and even in the actual underground structure survey, the presence or absence of the fault fracture zone is determined based on the H / V spectrum of the seismic wave at each measurement point. It can be understood that there is a possibility of determination.

In the results shown in FIGS. 2 (A) and 2 (C), the inventors of the present application show that the H / V spectrum of the seismic wave at each position substantially matches the H / V spectrum of the seismic wave in the free ground when there is no fault fracture zone. On the other hand, when there is a fault fracture zone, the H / V spectrum of the seismic wave at each position is different from the H / V spectrum of the seismic wave at the free ground. It was predicted that the presence or absence of a fault fracture zone could be determined by using the H / V spectrum of seismic waves at a position where there was no influence as a reference. Then, the value obtained by integrating the absolute value of the difference between the seismic wave H / V spectrum and the seismic wave H / V spectrum on the free ground at a plurality of predetermined frequencies (also expressed by the following equation (1)) Reference) was defined as an index value at an arbitrary measurement point, and the above index values were calculated for each position on the ground surface of the analysis model.
Index value = Σ | H / V spectrum at an arbitrary measurement point−H / V spectrum at free ground | (1)
FIG. 2B shows the calculation result of the index value when there is no fault crushing zone, and FIG. 2D shows the calculation result of the index value when there is a fault crushing zone.

  As is clear from a comparison between FIG. 2B and FIG. 2D, the index value is substantially constant regardless of the position of the measurement point when there is no fault fracture zone (see FIG. 2B). On the other hand, when there is a fault crush zone (see Fig. 2 (D)), the index value of the measurement point existing at a position close to the fault crush zone is particularly large and large depending on the location. It has fluctuated. The inventors of the present application based on the result shown in FIG. 2D, “If the fault fracture zone exists, the difference between the index values of a pair of measurement points adjacent to each other across the fault fracture zone is relatively large. In order to establish the hypothesis of “becoming” and to confirm the suitability of this hypothesis, the index at each position when the tilt angle θ of the fault fracture zone is 60 ° and the incident angles of the seismic waves are 0 °, 45 ° and −45 °. A simulation was also performed to determine the value. The results are shown in FIG. As is clear from FIGS. 3A to 3C, the above hypothesis holds even when the tilt angle of the fault crushing zone and the incident angle of the seismic wave are different. It was confirmed that when the difference between the index values is relatively large, it can be determined that there is a high possibility that a fault fracture zone exists between the pair of measurement points.

Based on the above, the fault fracture zone determination method according to the invention described in claim 1 is set on a survey line that intersects the strike direction of the fault fracture zone candidate that may exist. The horizontal direction component and the vertical direction component of the incoming seismic wave are measured at a plurality of measurement points on the ground surface, respectively, and the frequency spectrum of the initial motion portion of the horizontal component obtained from the measurement result of the horizontal component of the seismic wave, and the seismic wave It performed a plurality of times each determined that for each measurement point the H / V spectrum is the ratio of the frequency spectrum of the initial portion of the vertical component obtained from the measurement results of the vertical component and is not affected by the cross-sectional layer fracture zone as estimated reference H / V spectrum, the calculation based on the ground structure recognized by performing candidate Drilling around the point that the position of the fault zone Calculated from the measured H / V spectrum or the horizontal component and the vertical component of the seismic wave arriving at a point more than a predetermined distance from the point where the candidate for the fracture zone is located. Using the H / V spectrum or a combination of these H / V spectra, as an index value at each measurement point in each seismic wave measurement , the absolute difference between the obtained H / V spectrum and the reference H / V spectrum Each of the integrated values is calculated, and for the index value of each measurement point obtained from the measurement result of a certain seismic wave, the difference between the index values of the adjacent measurement point pairs on the line is calculated between the individual measurement point pairs. A comparison is made for each index value at each measurement point obtained from the seismic wave measurement results, and the difference between the index values of adjacent measurement point pairs across the fault crush zone candidate position. Each time If they represent the respective relatively large value in the index value obtained from the measurement results of Shinnami determines that a candidate of the fault zone is existent.

  In the first aspect of the present invention, a fault crush zone candidate that may exist (for example, a fault crush zone candidate determined to be real by a lineament or the like) The horizontal component obtained from the measurement result of the horizontal component of the seismic wave by measuring the horizontal component and the vertical component of the incoming seismic wave at multiple measurement points on the ground surface set on the survey line that intersects the strike direction of the belt candidate The H / V spectrum, which is the ratio of the frequency spectrum of the initial motion part of the vertical direction component obtained from the measurement result of the vertical direction component of the seismic wave and the frequency spectrum of the initial motion part of the seismic wave, is obtained for each measurement point a plurality of times. The seismic wave (measurement target seismic wave) arriving at each measurement point may be a seismic wave due to a naturally occurring earthquake as described in claim 2, for example, or an explosive using an artificial seismic source (for example, dynamite) It may be an elastic wave generated by vibrating the ground using an epicenter or a non-explosive seismic source such as a vibrator or an air gun, and the “seismic wave” in the present invention includes both the above-mentioned seismic wave and elastic wave. It is.

In the invention described in claim 1, the reference H / V spectrum estimated not to be affected by the fault fracture zone is recognized by conducting a boring survey in the vicinity of the location where the fault fracture zone candidate is located. The H / V spectrum obtained by calculation based on the ground structure, or the horizontal component and the vertical component of the seismic wave that arrived at a point more than a predetermined distance away from the point where the fault zone candidate is located The H / V spectrum obtained from the above, or a combination of these H / V spectra, and the index value at each measurement point in each seismic wave measurement , the difference of the obtained H / V spectrum from the reference H / V spectrum Each value obtained by integrating the absolute values is calculated . This ensures that for each measurement point, a plurality of index values corresponding to the seismic waves were measured each time is that each obtained.

According to the first aspect of the present invention, with respect to the index value of each measurement point obtained from the measurement result of a certain seismic wave, the difference between the index values of the measurement point pairs adjacent to each other on the survey line is calculated between each measurement point pair. To each index value of each measurement point obtained from the measurement result of each seismic wave, the difference between the index values of the adjacent measurement point pair across the position of the fault crush zone candidate, When the index values obtained from the seismic wave measurement results show relatively large values (or when the majority shows relatively large values), the fault crush zone candidate actually exists. It is determined that As described above, in the first aspect of the present invention, an elastic wave is incident below the ground surface using an artificial seismic source and an elastic wave is measured at a plurality of locations on the ground surface, as in the case of a fault fracture zone search using a reflection method. It is not necessary to repeat this many times while moving the position of the artificial seismic source and elastic wave measurement location, and it is not necessary to move at least the position of each measurement point in multiple seismic wave measurements. Can be easily determined. In addition, if there are loose constraints on the time required to determine the presence or absence of a fault shatter zone, the use of seismic waves from a naturally occurring earthquake as the seismic wave to be measured eliminates the need for an artificial seismic source. Presence / absence can be determined more easily. Further, in the first aspect of the invention, the seismic wave is measured a plurality of times, and it is determined whether or not the fault crush zone candidate actually exists by using the index value at each measurement point obtained by each seismic wave measurement. By doing so, it is possible to ensure a certain level of determination accuracy.

  By the way, in the simulation results shown in FIG. 2D and FIGS. 3A to 3C, the average of the measurement point group located on the reference position side of the analysis model with the position of the fault crush zone candidate as a boundary. The magnitude of the index value is different from the average index value of the measurement point group located on the opposite side of the reference position of the analysis model with the position of the candidate for the fault fracture zone as a boundary. In the above simulation results, the inventors of the present application have determined that the average index of the measurement point group located on the opposite side is the size of the average index value of the measurement point group located on the reference position side. Since it is larger than the value and the slope direction of the fault crush zone is the same, we hypothesized that there is a correlation between the two, and conducted a simulation to confirm this hypothesis. Although the illustration of the simulation result is omitted, as a result, when the fault fracture zone is inclined toward one measurement point group from the ground surface to the ground, the average index value of the one measurement point group It was confirmed that the size tends to be larger than the average index value of the other measurement point group.

Based on the above, the invention described in claim 3 is the index of each measurement point obtained from the measurement result of a certain seismic wave when it is determined in the invention described in claim 1 that a candidate for a fault fracture zone exists. With respect to the values, the index value of each measurement point constituting the first measurement point group located on one end side on the survey line with reference to the position of the fault crush zone candidate and the position of the fault crush zone candidate as a reference Compare the index value of each measurement point that constitutes the second measurement point group located on the other end side on the survey line, with respect to the index value of each measurement point obtained from the measurement result of each seismic wave In the index value obtained from the measurement results of each seismic wave, the index value of each measurement point constituting one measurement point group is larger than the index value of each measurement point constituting the other measurement point group. If each shows a relatively large value (or the majority is relatively large) If they represent the values), that are characterized by determining a candidate of the fault zone is inclined to the one measuring point group side toward from the surface into the ground.

Since the fault fracture zone has a large influence on the flow of groundwater, the inclination direction of the fault fracture zone is very important information when it is desired to understand the behavior of groundwater. On the other hand, in the invention described in claim 3, among the index values of the respective measurement points obtained from the measurement result of a certain seismic wave, the index values of the respective measurement points constituting the first measurement point group, and the second The index values of each measurement point constituting each measurement point group are compared with each other for each measurement point index value obtained from the seismic wave measurement results, and based on the comparison results, Since the candidate inclination direction is determined, even when it is determined that the fault crush zone candidate exists, the fault crush zone is searched by the reflection method in order to determine the inclination direction of the fault crush zone candidate. There is no need, and the inclination direction of the fault fracture zone can be easily determined.

According to a fourth aspect of the present invention, there is provided a fault fracture zone determination support device for a fault fracture zone candidate that may actually exist, on a survey line set on a survey line that intersects the strike direction of the fault fracture zone candidate. Information indicating the measurement result of the horizontal component and vertical component of the seismic wave measured each time a seismic wave arrives at a plurality of measurement points, and information indicating the position of each measurement point on the survey line Obtaining the frequency spectrum of the initial movement portion of the horizontal component from the acquisition means to acquire and information representing the measurement result of the horizontal component of the seismic wave measured at a specific measurement point among the information acquired by the acquisition means And obtaining the frequency spectrum of the initial motion part of the vertical component from the information representing the measurement result of the vertical component of the seismic wave measured at the specific measurement point, and obtaining the horizontal direction The H / V spectrum, which is the ratio of the frequency spectrum of the initial motion part of the minute and the frequency spectrum of the initial motion part of the vertical component, is calculated for each measurement result obtained by the measurement at each measurement point. a first calculation means, as the reference H / V spectra is estimated that not affected by the cross-sectional layer fracture zone, soil structure recognized by performing boring survey near the point where the candidate of the fault zone is located From the results of measuring the H / V spectrum obtained by calculation based on the above, or the horizontal component and the vertical component of the seismic wave arriving at a point more than a predetermined distance away from the point where the fault fracture zone candidate is located obtained H / V spectra, or used in combination of H / V spectra, as an index value at each measurement point, with respect to the reference H / V spectra, The second calculation means for calculating the value obtained by integrating the absolute values of the difference of the H / V spectrum calculated by the first calculation means, and the index value at each measurement point calculated by the second calculation means, And output means for outputting a chart in which the position of each measurement point on the survey line is plotted on the coordinates with the first coordinate axis and the index value as the second coordinate axis.

In the invention according to claim 4, a plurality of measurement points on the ground surface set on a survey line that intersects the strike of the fault crushing zone candidate with respect to the fault crushing zone candidate that may exist by the acquisition means. , Information indicating the measurement result of the horizontal component and vertical component of the seismic wave measured each time the seismic wave arrives is acquired, and information indicating the position of each measurement point on the survey line is acquired. The first computing means obtains the frequency spectrum of the initial motion part of the horizontal component from the information representing the measurement result of the horizontal component of the seismic wave measured at the specific measurement point among the information obtained by the obtaining means, Obtain the frequency spectrum of the initial motion part of the vertical component from the information representing the measurement result of the vertical component of the seismic wave measured at a specific measurement point, and obtain the frequency spectrum of the initial motion part of the horizontal component and the initial motion part of the vertical component The H / V spectrum, which is the ratio of the frequency spectra, is calculated for each measurement result obtained by measurement at each measurement point.

In addition, the second calculation means uses, as an index value at each measurement point, a reference H / V spectrum that is estimated to be unaffected by the fault fracture zone, and is drilled near the location where the fault fracture zone candidate is located. H / V spectrum obtained by calculation based on the ground structure recognized by the investigation, or horizontal component and vertical component of the seismic wave arriving at a point more than a predetermined distance from the point where the fault fracture zone candidate is located The H / V spectrum obtained from the result of measuring each direction component, or a combination of these H / V spectra, is used as an index value at each measurement point by the first calculation means for the reference H / V spectrum . Each of the values obtained by integrating the absolute values of the H / V spectrum differences is calculated, and the output means calculates the index value at each measurement point calculated by the second calculation means on the line. The position of each measurement point first coordinate axis, it outputs a chart obtained by plotting the index value on the coordinates of the second coordinate axis (e.g. display means on the display, or printed on the recording sheet) to.

As a result, the horizontal direction component and vertical direction component of the seismic wave are measured each time the seismic wave arrives at a plurality of measurement points on the ground surface set on the survey line, and the information indicating the measurement result together with the information indicating the position of each measurement point If it inputs into the fault fracture zone determination assistance apparatus based on invention of Claim 7 (if it is made to acquire by an acquisition means), FIG. 2 (B) or FIG. 2 (D) and FIG. 3 (A)-(C). As shown in FIG. 8, a chart (discrete chart as shown in FIG. 8 described later) representing the distribution of the index values is output. By referring to the output chart, fault crush zone candidates can be obtained. It can be easily and intuitively determined whether or not it exists, and the inclination direction of the fault crush zone candidate when it is determined that the fault crush zone candidate exists can be easily and intuitively determined. Therefore, according to the invention described in claim 4, it is possible to realize labor saving of the determination of the presence or absence of the fault fracture zone.

As described above, the invention according to claim 1 is capable of performing a plurality of measurements on the ground surface set on a survey line that intersects the strike direction of the fault fracture zone candidate that may exist. Measure the horizontal component and vertical component of the incoming seismic wave at the point, and obtain the frequency spectrum of the initial motion part of the horizontal component obtained from the measurement result of the horizontal component of the seismic wave and the measurement result of the vertical component of the seismic wave. The H / V spectrum, which is the ratio of the frequency spectrum of the initial motion part of the vertical component, is obtained multiple times for each measurement point, and as a reference H / V spectrum that is estimated not to be affected by the fault fracture zone, H / V spectrum obtained by calculation based on the ground structure recognized by conducting a boring survey near the point where the candidate for the fracture zone is located, or The H / V spectrum obtained from the result of measuring the horizontal component and the vertical component of the seismic wave that has arrived at a predetermined distance or more from the point where the candidate for the crush zone is located, or these H / V spectra combined using, respectively calculates the value obtained by integrating the absolute value of the difference between the H / V spectra at each measurement point for the index value to criteria H / V spectra at each measurement point in each time of the measurement of seismic waves, some As for the index value of each measurement point obtained from the measurement result of the seismic wave, the difference in index value between adjacent measurement point pairs on the survey line is compared with each other between each pair of measurement points. The index values obtained from the seismic wave measurement results are shown as the difference between the index values of adjacent measurement points across the fault crush zone candidate position. Each relative in value If they represent a large value, since the candidates for fault zone is the so determined to be real, it can be determined whether the fault zone easily and has an excellent effect that.

In the invention according to claim 4, the frequency spectrum of the initial movement portion of the horizontal component is obtained from the information representing the measurement result of the horizontal component of the seismic wave measured at the specific measurement point, and measured at the specific measurement point. Obtaining the frequency spectrum of the initial motion part of the vertical component from the information representing the measurement result of the vertical component of the seismic wave and calculating the H / V spectrum, respectively, for the measurement results obtained by the measurement at each measurement point As a reference H / V spectrum that is estimated to be unaffected by the fault fracture zone, the calculation is based on the ground structure recognized by conducting a boring survey near the location where the fault zone candidate is located. H / V spectrum, or horizontal component and vertical component of seismic waves that arrive at a point more than a predetermined distance away from the point where the fault zone candidate is located Each H / V spectrum obtained from the result of measurement, or using a combination of these H / V spectra, the H / V spectra at each measurement point for the index value to criteria H / V spectra at each measurement point Each of the values obtained by integrating the absolute values of the differences is calculated, and the index value at each measurement point is output on the coordinates plotted with the position of each measurement point as the first coordinate axis and the index value as the second coordinate axis. Therefore, it has an excellent effect that labor-saving in determining the presence or absence of a fault fracture zone can be realized.

  Hereinafter, an example of an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 4 shows a personal computer (PC) 10 that can be used to implement the method for determining a fault fracture zone according to the present invention. The PC 10 is configured by connecting a CPU 10A, a ROM 10B, a RAM 10C, and an input / output port 10D to each other via a bus 10E including a data bus, a control bus, an address bus, and the like. The input / output port 10D includes a display 12, a keyboard 14, a mouse 16, a hard disk drive (HDD) 18, and a CD-ROM drive for reading information from a CD-ROM as various input / output devices. 20 are connected to each other. Further, a connector 22 is connected to the input / output port 10D, and a seismometer (denoted as a seismometer group 24 in the figure) can be connected via the connector 22.

The HDD 18 of the PC 10 is installed with a fault fracture zone determination support program for performing a fault fracture zone determination support process described later. There are several methods for installing (transferring) the fault fracture zone determination support program to the PC 10. For example, the fault fracture zone determination support program is recorded on a CD-ROM together with a setup program, and the CD-ROM is stored in the CD. -When the ROM drive 20 is set and the CPU 10A is instructed to execute the setup program, the fault fracture zone determination support program is sequentially read from the CD-ROM. In order, the fault fracture zone determination support program is installed. The PC 10 functions as a fault crush zone determination support apparatus according to the invention of claim 4 by the CPU 10A executing the fault crush zone determination support program. Instead of the PC 10, for example, a workstation or a general-purpose large computer can be used.

  Next, as a function of this embodiment, when formulating a construction plan for a construction that requires high safety such as a high-level waste disposal site, a fault crush zone in the study area including the candidate site and its surroundings is proposed. The fault fracture zone determination process performed for the purpose of grasping the presence / absence and characteristics thereof will be described with reference to the flowchart of FIG. This fault fracture zone determination process is a process to which the fault fracture zone determination method according to the present invention is applied.

  In the fault fracture zone determination process, the investigator first obtains an aerial photograph of the survey area from the sky, and estimates that it corresponds to the fault fracture zone among the long linear patterns appearing on the obtained aerial photograph. A lineament is extracted to extract the linear pattern to be used as a fault fracture zone candidate (step 100). In addition, the line patterns appearing on the aerial photographs include not only those that reflect fault fracture zones, but also those that reflect displacement topography caused by erosion, etc., and lines created by natural phenomena in the surface layer such as wind and waves. Since there are some patterns and it may be difficult to discriminate on aerial photographs, the lineament has a remarkably insufficient accuracy for judging the presence or absence of a fault fracture zone alone. In addition, the lineament cannot determine the inclination direction of the fault fracture zone. For this reason, in the subsequent step 102 and subsequent steps, the operation for determining (confirming) whether or not the fault fracture zone candidate extracted by the lineament in step 100 actually exists is applied (step). Process).

  That is, subsequently, the investigator determines the position of each measurement point where the seismometer is installed and the seismic wave is measured for each fault fracture zone candidate extracted by the lineament in step 100 (step 102). As shown in FIG. 6 as an example, the determination of the measurement point position for a single fault crush zone candidate is a fault line representing the position of a fault crush zone candidate on the ground surface (shown as a thick straight line in FIG. 6). ), A survey line (shown as a broken line in FIG. 6) substantially at the center of the fault line is set, and approximately the same number of measurement points are located on both sides of the fault line (fault fracture zone candidate). This can be done by arranging a plurality of measurement points on the survey line so that they exist. Note that the interval between individual measurement points on the survey line need not be constant, and as shown in FIG. 6, the interval between a pair of measurement points adjacent to each other across the fault line (fault crush zone candidate) is also different. It is preferable to make it smaller than the interval between the measurement points. In addition, in order to obtain the reference seismic wave data (seismic wave data not affected by the fault shattering zone) at the same time, measurement points are set at a point that is more than a predetermined distance from the fault shattering zone candidate in the survey area. (Hereinafter, this measurement point is referred to as a reference measurement point).

  After determining the position of the measurement points, the investigator prepares the same number of seismometers as the number of measurement points whose positions have been determined, goes to the survey area, and installs the seismometers at each determined measurement point position (Step) 104). In this embodiment, the seismometer installed at each measurement point position can measure the horizontal component and the vertical component of the seismic wave arriving at the measurement point location, and records the measurement result of the seismic wave as data on a built-in recording medium. It has a function to do. Such a seismometer is, for example, an existing seismometer having a function of measuring seismic waves, and a recording device (a dedicated recorder or a computer such as a PC) having a function of recording seismic wave measurement results. It can be realized by adding or the like. In addition, when a seismometer was installed in the survey area, if there was a fault zone that could clearly be judged as a fault of lineament and not a fault zone at first glance, Needless to say, it is not necessary to install a seismometer at the measurement point position corresponding to the crush zone candidate.

  When the installation of the seismometer is completed, the investigator once withdraws from the survey target area, and waits until multiple natural earthquakes occur in the survey target area (step 106). Whether or not a natural earthquake has occurred in the survey area can be determined by, for example, connecting at least one of the installed seismometers to a communication line and monitoring the measurement results of the seismic waves from the seismometer. Alternatively, it may be performed by monitoring the presence or absence of natural earthquakes in the survey target area and its surroundings announced by the Japan Meteorological Agency or other seismic measurement organizations. It is also possible to go to the survey area regularly and check the seismic wave measurement results recorded on the seismometer.

  Until the determination in step 106 is affirmed, the seismometer installed at each measurement point position always measures the seismic wave that arrives at the measurement point position, and the seismic wave measurement result is correlated with the measurement date and time as seismic wave data. Recorded sequentially. When it is confirmed that a natural earthquake has occurred several times in the survey target area, the investigator goes to the survey target area again, collects the seismometers installed at each measurement point position, and lifts them from the survey target area (step 108). The investigator turns on the power of the PC 10 and instructs the execution of the fault fracture zone determination support program installed in the HDD 18 of the PC 10, thereby causing the PC 10 to function (start) as a fault fracture zone determination support device (step) 110). Thus, in the next step 112 to step 134, the fault fracture zone determination support processing is performed by the PC 10 (hereinafter referred to as the fault fracture zone determination support device 10). (It is realized by the cooperation of the support device 10).

When the fault fracture zone determination support device 10 is activated, the investigator sequentially connects the collected individual seismometers to the fault fracture zone determination support device 10 in the next step 112. Each time the seismometer is connected, the fault fracture zone determination support device 10 reads out the seismic data recorded in the built-in recording medium of the connected seismometer and imports it into the memory (RAM 10C). Are stored in the HDD 18 in association with the ID of the connected seismometer among the IDs previously assigned to the individual seismometers. Of the seismic wave data sequentially taken into the fault fracture zone determination support device 10, seismic wave data taken from the seismometer installed at the reference measurement point is treated as reference seismic wave data. Further, the investigator operates the keyboard 14 of the fault fracture zone determination support device 10 and inputs measurement point position data representing the position of each measurement point where the seismometer is installed together with the ID of the corresponding seismometer. The input measurement point position data is also stored in the HDD 18 by the fault fracture zone determination support device 10. The above step 112 corresponds to the obtaining means described in claim 4 .

  The input of the seismic wave data to the fault fracture zone determination support apparatus 10 is not limited to being performed by sequentially connecting the seismometers as described above, and a recording medium on which the seismic data is recorded by the seismometers. If it is a removable medium, this removable medium may be taken out from each seismometer and set in the fault fracture zone determination support device 10, or each seismometer is installed at each measurement point position. A seismometer may be connected to the fault fracture zone determination support apparatus 10 via a communication line, and the measurement result of the seismic wave from each seismometer may be input to the fault fracture zone determination support apparatus 10 in real time.

  In the next step 114, the CPU 10 </ b> A of the fault fracture zone determination support device 10 selects the seismic wave data that has not been subjected to the processing subsequent to the next step 116 from among the seismic wave data that has been captured from each seismometer and stored in the HDD 18 in step 112. Capture from the HDD 18 to the memory. In the next step 116, the measurement result of the seismic wave when the natural earthquake occurs is searched by searching for data corresponding to the seismic wave measurement result when the natural earthquake occurs while sequentially referring to the captured seismic wave data in the order of the measurement time. It is determined whether or not seismic wave data corresponding to is included. If the corresponding seismic wave data is found, the determination in step 116 is affirmed and the process proceeds to step 118, and the found seismic wave data (the seismic wave representing the measurement result of the seismic wave over a certain time before and after the occurrence of the natural earthquake occurs). Data) is extracted as seismic wave data to be processed. An example of a seismic wave at the time of occurrence of a natural earthquake represented by the extracted seismic wave data is shown in FIG.

  In the next step 120, the frequency representing the frequency spectrum of the initial motion part of the horizontal component of the seismic wave is obtained by converting the data representing the horizontal component of the seismic wave in the extracted seismic wave data to be processed into the frequency domain by Fourier transform. Generate spectral data. In step 122, the frequency spectrum data representing the frequency spectrum of the initial motion part of the vertical component of the seismic wave is obtained by converting the data representing the vertical component of the seismic wave into the frequency domain by Fourier transform. Generate. In step 124, the value at each frequency in the frequency spectrum of the initial motion part of the horizontal component of the seismic wave obtained in step 120 is obtained at each frequency in the frequency spectrum of the initial motion part of the vertical component of the seismic wave obtained in step 122. By dividing by the value, the H / V spectrum of the seismic wave is calculated. An example of the calculation result of the H / V spectrum is shown in FIG. The H / V spectrum data representing the H / V spectrum obtained by the above calculation is associated with the seismometer ID corresponding to the original seismic wave data captured at step 114 and the occurrence date (measurement date) of the natural earthquake. Stored in the HDD 18.

  When the process of step 124 is completed, the process returns to step 116, and the search for data when a natural earthquake occurs is repeated. In this embodiment, the seismic wave measurement by the seismometers installed at each measurement point is continued until the natural earthquake occurs multiple times in the survey target area. Since a plurality of seismic wave data corresponding to the measurement result of the seismic wave at the time of the earthquake is included, the determination in step 116 is affirmed a plurality of times, and H / V spectrum data corresponding to each natural earthquake is calculated and stored. Will be.

If all the seismic wave data corresponding to the measurement result of the seismic wave when the natural earthquake occurred is extracted from the seismic wave data captured in step 114, the determination in step 116 is denied and the process proceeds to step 126, and the seismometer is captured from each seismometer. Judge whether all the seismic wave data has been processed. If the determination is negative, the process returns to step 114, and steps 114 to 126 are repeated until the determination of step 126 is negative. Thus, H / V spectrum data is calculated and stored for each seismic wave that arrives at each measurement point position including the reference measurement point when multiple natural earthquakes occur. In addition, from the reference seismic wave data taken from the seismometer installed at the reference measurement point, a plurality of reference H / V spectra (an example is shown in FIG. 7C) from which the influence of the fault fracture zone has been eliminated are represented. A plurality of reference H / V spectrum data is calculated and stored. Steps 114 to 126 described above correspond to the first calculation means described in claim 4 .

  If the determination in step 126 is affirmed, the process proceeds to step 128, where the position of each measurement point on the survey line set for the fault fracture zone candidate is taken as the first coordinate axis (for example, the X axis), and the present invention is applied. The same number of charts as the number of occurrences of natural earthquakes within the seismic wave measurement period are created with the index value taken on the second coordinate axis (for example, the Y axis). In addition, when there are a plurality of fault crush zone candidates, the above-described chart is created by the number corresponding to “the number of occurrences of natural earthquake × the number of fault crush zone candidates”. Note that marks, characters, etc. that clearly indicate the positions of the corresponding fault fracture zone candidates are added to the above chart (for example, the marks “●” and characters shown in FIGS. 8A to 8C). “Fracture zone” etc.).

  In the next step 130, among the H / V spectrum data calculated and stored in the previous step 124, the index value other than the reference H / V spectrum data and the index value is not calculated (H / V spectrum data to be processed). V spectrum data) is taken in from the HDD 18. In step 132, reference H / V spectrum data corresponding to the H / V spectrum data to be processed is fetched from the HDD 18. This reference H / V spectrum data is H / V spectrum data obtained from seismic wave data measured by a seismometer installed at a reference measurement point when a natural earthquake corresponding to the H / V spectrum data to be processed occurs. It can be recognized based on the occurrence date (measurement date) of the natural earthquake and the ID of the seismometer stored in the HDD 18 in association with each H / V spectrum data.

  In step 134, the difference between the H / V spectrum to be processed captured in step 130 and the reference H / V spectrum captured in step 132 is calculated for each of a plurality of predetermined frequencies, and the difference in the plurality of frequencies is calculated. A value obtained by integrating the absolute value of the difference of the H / V spectrum (see also the above formula (1)) is calculated as an index value corresponding to the H / V spectrum to be processed. In step 134, the processing target of the chart created in step 128 is generated based on the natural earthquake occurrence date (measurement date) and seismometer ID stored in the HDD 18 in association with the processing target H / V spectrum data. The chart corresponding to the H / V spectrum data (the chart corresponding to the same fault fracture zone and the same natural earthquake) is recognized, and the measurement point position data previously input and stored in the HDD 18 is also referred to. Plot the calculated index value on the recognized chart.

In the next step 136, it is determined whether or not the above index values have been calculated for all the H / V spectrum data stored in the HDD 18. If the determination is negative, the process returns to step 130, and steps 130 to 136 are repeated until the determination of step 136 is affirmed. As a result, index values are calculated for all H / V spectrum data except the reference H / V spectrum data, and the calculated index values are plotted on the corresponding chart. If the determination in step 136 is affirmed, the process proceeds to step 138, and each chart for which plotting has been completed is displayed on the display 12. As a result, charts as shown in FIGS. 8A to 8C (charts corresponding to any of a plurality of natural earthquakes) are displayed on the display 12 for an example of a single fault crush zone candidate. Will be. Steps 130 to 138 described above correspond to the second calculation means and the output means described in claim 4 , respectively.

  When the chart as shown in FIG. 8 is displayed on the display 12, the investigator determines whether or not a corresponding fault crush zone candidate actually exists by referring to and examining the displayed chart. . That is, first, the investigator compares a plurality of charts corresponding to specific fault fracture zone candidates displayed on the display 12, and compares the index value difference between adjacent measurement point pairs across the position of the fault fracture zone candidate. It is verified whether or not each indicates a relatively large value on each chart (step 140). For example, as shown in FIG. 2 (B), when there is almost no difference in index values between adjacent measurement points in each chart, or in a specific single chart, adjacent measurements across the position of a candidate for a fracture zone If the difference between the index values of the point pairs is relatively large, but the remaining charts show almost no difference in the index values between adjacent measurement point pairs across the position of the fault fracture zone candidate, Since it can be determined that the difference between the index values of adjacent measurement point pairs across the candidate position does not meet the above condition (determination in step 142 is negative), in this case, the investigator It is determined that the candidate does not exist.

  On the other hand, for example, as shown in FIGS. 8A to 8C, the difference between the index values of the pair of measurement points adjacent to each other across the position of the candidate for the fracture crush zone shows a relatively large value on each chart. If there is a difference between the index values of adjacent measurement point pairs across the fault crush zone candidate position in a specific single chart, the remaining charts pin the fault crush zone candidate position. In the case where the difference between the index values of adjacent measurement point pairs is relatively large, the difference in the index values of the adjacent measurement point pairs that meet the fault crush zone candidate position matches the above-mentioned conditions. (The determination in step 142 is affirmed), so in such a case, the investigator determines that the fault crush zone candidate actually exists.

  In addition, when it is determined that the fault crush zone candidate exists, the investigator further selects each measurement point group having a larger average index value from the measurement point groups on both sides with the fault crush zone position as a boundary. By determining each of the charts, the inclination direction of the fault crush zone determined to exist is determined. For example, in the charts shown in FIGS. 8A to 8C, the left measurement point group with the fault crush zone position as a boundary shows a larger average index value than the right measurement point group. ing. Therefore, in this case, it is determined that the fault crushing zone determined to exist is inclined to the left from the ground surface toward the ground. By performing the above determination on all the fault fracture zone candidates extracted by the lineament, it is possible to grasp the presence and characteristics (inclination direction) of the fault fracture zone in the investigation target area.

  As described above, in the present embodiment, the fault fracture zone determination method according to the present invention is applied to the fault fracture zone candidate extracted by the lineament to determine whether or not the fault fracture zone candidate actually exists. In addition, since the inclination direction is determined for the fault fracture zone that has been determined to exist, it is possible to grasp the presence and characteristics (inclination direction) of the fault fracture zone in the survey target area with a certain degree of accuracy. Therefore, it is not necessary to carry out exploration of the fault fracture zone by the high-cost and time-consuming reflection method in the investigation target area. Also, in this embodiment, since seismic waves due to naturally occurring earthquakes are the object of measurement, there is a possibility that the seismic wave measurement period may extend for a long time, but an aspect in which seismic waves generated using an artificial seismic source are to be measured and Even if it compares, it can implement at lower cost and it is suitable especially when restrictions on the time required for the presence or absence of a fault crushing zone and the judgment of an inclination direction are loose. Moreover, in the fault fracture zone determination processing according to the present embodiment, the fault fracture zone judgment support apparatus 10 performs the calculation of the H / V spectrum, the calculation of the index value, and the plot from the seismic wave data recorded by the seismometer. Therefore, it also has an effect that the determination of the presence or absence of the fault crushing zone and the inclination direction can be saved.

  In the above, the seismic wave data obtained by the seismometer installed at the reference measurement point at a predetermined distance or more from the fault fracture zone candidate in the survey area is set as the reference seismic wave data, and the H / O obtained from this reference seismic wave data is used. Although the V spectrum was used as the reference H / V spectrum, the present invention is not limited to this, and what kind of seismic wave is generated on the ground surface when an earthquake occurs when there is no fault fracture zone nearby. Whether it is observed can be determined approximately uniquely from the ground composition at that point (layer thickness of each layer, propagation velocity of seismic waves (s waves and p waves)). By conducting a boring survey near the point where the candidate is located), the ground composition near the point where the candidate for the fault crush zone is located is grasped and calculated from the grasped ground composition Therefore, based on the seismic wave waveform obtained, the reference H / V spectra may be obtained by calculation. Further, a reference H / V spectrum obtained by calculation from the result of the boring survey and a reference H / V spectrum obtained from the seismic wave data measured at the reference measurement point may be used in combination (for example, two types of reference H / V Each index value is obtained by using each V spectrum, two charts corresponding to each reference H / V spectrum are created, and the presence or absence of a fault crush zone and the inclination direction are determined by comparing them.

  Moreover, although the example which made the measurement object the seismic wave by the earthquake which occurred naturally was demonstrated above, it is not limited to this, Artificial seismic sources (For example, explosive seismic sources using dynamite etc., or non-explosives such as vibrators and air guns) It is also included in the present invention that a seismic wave generated using a seismic source is a measurement object. When using an artificial seismic source, the cost and effort required to measure the seismic wave increase, but the seismic wave measurement can be completed in a short period of time. It is suitable for the case where it is used.

It is a conceptual diagram which shows the analysis model used for the simulation which this inventor etc. implemented. When there is no fault fracture zone, (A) is the H / V spectrum at each position of the analysis model, (B) is a diagram showing the distribution of index values, and (C) is when there is a fault fracture zone. H / V spectrum at each position of the model, (D) is a diagram showing the distribution of index values. It is a diagram showing the distribution of index values when the incident angle of seismic waves is 0 °, (B) is 45 °, and (C) is −45 °. It is a block diagram which shows schematic structure of the fault fracture zone determination assistance apparatus which concerns on this embodiment. It is a flowchart which shows the content of a fault fracture zone determination process. It is an image figure which shows an example of a measurement point position. (A) is an example of a seismic wave measurement result, (B) is an example of a calculation result of an H / V spectrum, and (C) is a diagram showing an example of a reference H / V spectrum. It is a diagram which shows an example of the calculation result of an index value.

Explanation of symbols

10 Fault fracture zone determination support device 12 Display 14 Keyboard 18 HDD
24 Seismometers

Claims (4)

For the possible fault crush zones that may exist,
Measure the horizontal component and vertical component of the incoming seismic wave at multiple measurement points on the ground surface set on the survey line that intersects the strike direction of the candidate for the fault fracture zone. From the measurement result of the horizontal component of the seismic wave An H / V spectrum, which is a ratio of a frequency spectrum of the initial motion part of the horizontal component to be obtained and a frequency spectrum of the initial motion part of the vertical component to be obtained from a measurement result of the vertical component of the seismic wave, is obtained for each measurement point. Repeated several times,
Based H / V spectra is estimated that not affected by the cross-sectional layer fracture zone, determined by calculation based on the ground structure recognized by performing boring survey near the point where the candidate of the fault zone is located H / V obtained from the measured H / V spectrum or the horizontal component and vertical component of the seismic wave arriving at a point more than a predetermined distance from the point where the fault fracture zone candidate is located. Using the spectrum or a combination of these H / V spectra, the absolute value of the difference of the obtained H / V spectrum with respect to the reference H / V spectrum is integrated as an index value at each measurement point in each seismic wave measurement. Each of the calculated values,
For the index value of each measurement point obtained from the measurement result of a certain seismic wave, the difference between the index values of adjacent measurement point pairs on the survey line is mutually compared between the individual measurement point pairs. The index value of each measurement point obtained from the measurement results of each is performed, and the difference between the index values of adjacent measurement point pairs across the position of the candidate for the fracture zone is obtained from the seismic wave measurement results of each time. A fault crushing zone determination method for determining that a candidate for the fault crushing zone actually exists when each index value indicates a relatively large value .   The fault crush zone determination method according to claim 1, wherein a seismic wave caused by a naturally occurring earthquake or a seismic wave generated using an artificial seismic source is measured as the seismic wave arriving at each measurement point. When it is determined that the fault crush zone candidate exists, the index value of each measurement point obtained from the measurement result of a certain seismic wave is one end on the survey line based on the position of the fault crush zone candidate. The second measurement point located on the other end side of the survey line with reference to the index value of each measurement point constituting the first measurement point group located on the side and the candidate position of the fault crush zone The index values obtained from the measurement results of each seismic wave are obtained by comparing the index values of the measurement points constituting the group with respect to the index values at each measurement point obtained from the measurement results of each seismic wave. In the above, when the index value of each measurement point constituting one measurement point group shows a relatively larger value than the index value of each measurement point constituting the other measurement point group, The band candidate is inclined toward the one measurement point group from the ground to the ground. Fault zone determination method according to claim 1, wherein the determining a. Measured each time a seismic wave arrives at a plurality of measurement points on the ground surface set on a survey line that intersects the strike direction of the fault crush zone candidate that may exist. An acquisition means for acquiring information indicating the measurement result of the horizontal component and vertical component of the seismic wave, and acquiring information indicating the position of each measurement point on the survey line,
Among the information acquired by the acquisition means, the frequency spectrum of the initial motion portion of the horizontal component is obtained from information representing the measurement result of the horizontal component of the seismic wave measured at a specific measurement point, and the specific measurement The frequency spectrum of the initial motion part of the vertical component is obtained from the information indicating the measurement result of the vertical component of the seismic wave measured at the point, and the frequency spectrum of the initial motion part of the horizontal component and the initial motion of the vertical component are obtained. First calculating means for calculating the H / V spectrum, which is the ratio of the frequency spectra of the portions, for each measurement result obtained by measurement at each measurement point;
Based H / V spectra is estimated that not affected by the cross-sectional layer fracture zone, determined by calculation based on the ground structure recognized by performing boring survey near the point where the candidate of the fault zone is located H / V obtained from the measured H / V spectrum or the horizontal component and vertical component of the seismic wave arriving at a point more than a predetermined distance from the point where the fault fracture zone candidate is located. The spectrum, or a combination of these H / V spectra, is used as an index value at each measurement point, the absolute value of the difference of the H / V spectrum calculated by the first calculation means with respect to the reference H / V spectrum . A second calculation means for calculating each of the integrated values;
The index value at each measurement point calculated by the second calculation means is output as a chart in which the position of each measurement point on the survey line is plotted on the coordinates with the first coordinate axis and the index value as the second coordinate axis. Output means;
Fault fracture zone determination support device including

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