JP4463729B2 - Depth value calculation method and depth value calculation device - Google Patents

Description

  The present invention relates to a depth value calculation method and a depth value calculation device.

Conventionally, it has been requested to grasp the underground structure, and in response to this request, public institutions etc. have published data on the underground structure at a specific point. However, there are cases where it is necessary to grasp the underground structure of a point other than the specific point (so-called interpolation point). For example, when building a building at the interpolation point, it is necessary to grasp the underground structure (depth to the earthquake base) from the viewpoint of seismic isolation or the like. Therefore, conventionally, an interpolation method for estimating the underground structure of the interpolation point by smoothing data related to the underground structure of a specific point around the interpolation point has been adopted.
The Generic Mapping Tools Version 3.4.1 A Map-Making Tutorial, March 2002, p.24

However, in the above method, there is a possibility that the underground structure at the interpolation point cannot be appropriately interpolated when the number of specific points to which data is given is small.
This invention is made | formed in view of this subject, The place made into the objective is to provide the simple method which can interpolate the underground structure of an interpolation point appropriately.

  In order to solve the above-mentioned problem, the main present invention is a first step of obtaining a residual gravity value of an interpolation point, a residual gravity value of a surrounding point around the interpolation point, and a A second step of acquiring a depth value up to a predetermined layer, and based on the residual gravity value and the depth value of the surrounding point acquired in the second step, a residual gravity value and a depth value; A third step of calculating a linear coefficient that defines the linear relationship of: the residual gravity value of the interpolation point acquired in the first step, and the coefficient calculated in the third step And a fourth step of calculating a depth value of the interpolation point, based on the depth value calculation method.

  Other features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

  At least the following will be made clear by the description of the present specification and the accompanying drawings.

A first step of obtaining a residual gravity value of the interpolation point; a second step of obtaining a residual gravity value of a surrounding point around the interpolation point and a depth value to a predetermined layer in the formation at the surrounding point; A linear coefficient defining a linear relationship between the residual gravity value and the depth value is calculated based on the residual gravity value and the depth value of the surrounding points acquired in the step and the second step. Calculating a depth value of the interpolation point based on the third step, the residual gravity value of the interpolation point acquired in the first step, and the coefficient calculated in the third step; A depth value calculation method comprising: four steps.
The residual gravity value is related to the underground structure (especially the sedimentary layer). Therefore, according to the present invention, in the linear form in which the residual gravity and the depth value are in a linear relationship, the depth value is calculated based on the coefficient corresponding to the surrounding point and the residual gravity at the interpolation point. Even when the number of points given is small, the depth value of the interpolation point (depth to each layer in the sedimentary layer or depth to the earthquake base) can be obtained more appropriately. And it becomes possible to interpolate an underground structure appropriately by calculating the depth value of a some interpolation point as mentioned above.

Further, in this depth value calculation method, the predetermined layer may be an earthquake base.
In such a case, it is possible to appropriately calculate the depth to the earthquake base at the interpolation point.

Further, in this depth value calculation method, there are a plurality of interpolation points, and in the third step, the coefficient is calculated for each interpolation point, and in the fourth step, the coefficient is calculated for each interpolation point. As calculating the depth value of the interpolation point based on the coefficient of the interpolation point calculated in the third step and the residual gravity value of the interpolation point acquired in the first step. Also good.
In such a case, since the depth value at the interpolation point is calculated using the coefficient calculated for each interpolation point, the depth value at each interpolation point can be set to a more optimal value.

Further, in this depth value calculation method, the surrounding points are a plurality of points having different distances from the interpolation point, and in the third step, the plurality of the points that are within a predetermined distance from the interpolation point The coefficient may be calculated based on the residual gravity value and the depth value of surrounding points.
In such a case, it is possible to calculate the optimum value of the coefficient by using only surrounding points in the vicinity of the interpolation point.

Further, in this depth value calculation method, in the third step, the residual gravity value of the surrounding point, the depth value of the surrounding point, and the distance from the interpolation point of the surrounding point The coefficient may be calculated based on a weight value that gives weight to the residual gravity value and the depth value.
The farther the interpolation point is from the surrounding point, the higher the possibility that the underground structure is different from the surrounding point. Therefore, when calculating the coefficient in consideration of the weighting that gives weight to the residual gravity value and depth value corresponding to the distance from the interpolation point of the surrounding points, weight the surrounding points closer to the interpolation point. Thus, it is possible to effectively calculate the optimum value of the coefficient.

Further, (a) a memory for storing a residual gravity value at an interpolation point, a residual gravity value at a surrounding point around the interpolation point, and a depth value to a predetermined layer in the formation at the surrounding point And (b) calculating a linear coefficient defining a linear relationship between the residual gravity value and the depth value based on the residual gravity value and the depth value of the surrounding points stored in the memory; A depth calculating unit that calculates a depth value of the interpolation point based on the calculated coefficient and a residual gravity value of the interpolation point stored in the memory; and (c). Value calculation device.
According to such a depth value calculation device, it is possible to appropriately interpolate the underground structure.

=== About Underground Structure ===
Next, an outline of the underground structure will be described with reference to FIG. FIG. 1 is a schematic diagram showing an underground structure.

  As shown in FIG. 1, a stratum is formed under the ground surface. This stratum is composed of a plurality of layers, and in general, the layers farther from the ground surface are formed in the older times. This stratum includes an earthquake base composed of hard rock and a sedimentary layer located between the base and the ground surface.

  The earthquake base is defined by the speed at which seismic waves travel. Specifically, a layer having a speed of transmission of S waves, which are seismic waves, of about 3 (km / s) is called an earthquake base. The depth d (km) to the earthquake base varies depending on the location. The deposited layer is further composed of a plurality of layers, and is divided according to the constituent state of the deposit constituting each layer. The deposited layer shown in FIG. 1 has a four-layer structure of a first layer, a second layer, a third layer, and a fourth layer from the ground surface toward the earthquake base.

  By the way, a building on the surface of the earth is constructed in consideration of an earthquake shake at a point where the building is located. Since earthquakes vary in magnitude depending on the underground structure, it is desirable to properly understand the underground structure. Regarding this underground structure, observation data and analysis data at a specific point are publicly disclosed by public institutions. However, it is necessary to properly grasp the underground structure at a point away from this specific point (hereinafter also referred to as an interpolation point).

  Therefore, in order to appropriately grasp the underground structure of the interpolation point, a computer system 100 that is an example of a depth value calculation device described below is used. The computer system 100 can calculate a depth value to a predetermined layer in the formation at the interpolation point. At this time, the computer system 100 calculates the depth value of the interpolation point using data such as the depth value of the specific point (hereinafter also referred to as the surrounding point) around the interpolation point.

=== Overview of Depth Value Calculation Device ===
An outline of the computer system 100 will be described with reference to FIGS.

  FIG. 2 is a diagram showing an external configuration of the computer system 100. The computer system 100 includes a computer 110, a display device 120, an input device 130, and a reading device 140.

  In this embodiment, the computer 110 is housed in a mini tower type housing. As the display device 120, a CRT (Cathode Ray Tube), a plasma display, a liquid crystal display device, or the like is used. In this embodiment, the input device 130 uses a keyboard 130A and a mouse 130B. In this embodiment, the reading device 140 uses a flexible disk drive device 140A and a CD-ROM drive device 140B. However, the reading device 140 is not limited to this. For example, an MO (Magneto Optical) disk drive device or a DVD (Digital Versatile) is used. Disk) etc. may be used.

  FIG. 3 is a block diagram showing a configuration of the computer system 100 shown in FIG. The computer 110 is provided with a CPU 111 that is an example of a calculation unit, a memory 113 such as a RAM, and an interface 114.

  The CPU 111 is for performing various calculations (calculations). And CPU111 calculates the depth value of the interpolation point mentioned later. The memory 113 stores data (information on the interpolation points and the surrounding points) stored by the reading device 140 on a recording medium such as a CD-ROM or a flexible disk (FD). The interface 114 is for connecting to an external device via a public line or the like.

=== Method of calculating depth value of interpolation point ===
Next, a method for calculating the depth value of the interpolation point will be described with reference to FIGS. FIG. 4 is a flowchart showing a depth value calculation method. FIG. 5 is a flowchart showing a method for calculating a linear coefficient. FIG. 6 is a diagram showing the positional relationship between the interpolation points and the surrounding points. FIG. 7A is a table showing data related to the interpolation points stored in the memory 113. FIG. 7B is a table showing data related to surrounding points stored in the memory 113. FIG. 8 is a table showing the weight values for the surrounding points.

  In the following description, the interpolation point is the interpolation point k as shown in FIG. 6, and the surrounding points are a plurality of surrounding points 1, 2, 3, 4, 5 as shown in FIG. And Further, the depth values of the interpolation point k and the surrounding points are assumed to be the depth d to the earthquake base at each point.

  First, the computer 110 acquires (calculates) the residual gravity value g at the interpolation point k (hereinafter, the residual gravity value at the interpolation point k is referred to as gk in order to distinguish it from the residual gravity value at other points). (Step s102). Hereinafter, a detailed calculation method of the residual gravity value gk at the interpolation point k will be described.

  The computer 110 obtains gravity anomaly data for a wide area including the interpolation point k (specifically, a distribution map showing gravity anomaly values at each point, hereinafter also referred to as “gravity anomaly distribution map”) from a public institution or the like. Acquired via a recording medium such as the Internet or a CD-ROM. Here, the gravity anomaly data is data relating to gravity or the like at a predetermined observation point. The magnitude of gravity at each observation point varies depending on the underground structure. For example, the magnitude of gravity differs between a place where the density of the formation is high and a place where the density of the formation is low. The gravity anomaly data is data reflecting the sedimentary layer, the earthquake base, and the structure deeper than the earthquake base shown in FIG.

  The computer 110 that has acquired the gravity anomaly distribution map removes the influence of the structure of the layer deeper than the layer whose depth value is to be calculated and the influence of the heterogeneous structure near the ground surface on the gravity anomaly distribution map. Apply filtering. Then, the computer 110 can calculate the residual gravity value gk at the interpolation point k by performing the above filtering process. The residual gravity value gk calculated in this way reflects the structure of the sedimentary layer, but does not reflect the structure deeper than the earthquake basement. Therefore, by using this residual gravity value, it becomes possible to calculate the structure of the deposited layer and the thickness of the deposited layer (that is, the depth to the earthquake base). In the present embodiment, it is assumed that the residual gravity value gk of the interpolation point k calculated as described above is 1.5 (mGal).

  Then, the computer 110 stores the acquired (calculated) residual gravity value gk of the interpolation point k in the memory 113. In addition, as shown in FIG. 7A, the memory 113 stores the coordinates (30, 10) of the interpolation point together with the residual gravity value gk.

  The computer 110 that has calculated the residual gravity value gk at the interpolation point k in step s102 calculates the residual gravity value g at each of the surrounding points 1, 2, 3, 4, and 5 and the depth value d at each of the surrounding points. Obtain (step s104). The residual gravity values g and depth values of the surrounding points 1, 2, 3, 4, and 5 are measured or analyzed in advance by a public institution or the like, and are published via the Internet or a recording medium. Then, the computer 110 acquires the residual gravity values g1, g2, g3, g4, and g5 and the depth values d1, d2, d3, d4, and d5 at the surrounding points, for example, via the Internet. The computer 110 also acquires information regarding the position of each surrounding point, that is, the coordinates of each surrounding point. Then, the computer 110 calculates the distance r (r1, r2, r3, r4, r5) between the interpolation point k and each surrounding point from the coordinates of each surrounding point 1, 2, 3, 4, 5 and the coordinate of the interpolation point k. Is calculated. Note that the residual gravity value g, depth value d, and distance r at each surrounding point are stored in the memory 113 as shown in FIG. 7B.

Next, the computer 110 causes the CPU 111 to determine the residual gravity value g and the depth value based on the residual gravity value g and the depth value d of the surrounding points 1, 2, 3, 4, and 5 acquired in step s104. A linear coefficient that defines a linear relationship with d is calculated (step s106). Here, the line format is expressed by the following formula 1, and the coefficients are A and B in formula 1.
d = A + Bg (1)

Then, the CPU 111 calculates the coefficient A and the coefficient B by Expression 2 and Expression 3 derived from Expression 1.

Here, how Formula 2 and Formula 3 are derived from Formula 1 will be described.
Λ is defined from Equation 1 to Equation 4 below.

  Note that Wn in Equation 4 is a weighting value. This weight value corresponds to the distance r from the interpolation point k of the surrounding points 1, 2, 3, 4, 5 and the residual gravity values g1, g2, g3, g4, g5 of the surrounding points, and the depth value. Weights are given to d1, d2, d3, d4, and d5. Further, ε in Expression 4 is a constant for preventing the value of the denominator in the expression from becoming 0 when the value of the capture radius R (described later) or the distance r becomes 0. The value of ε is 0.01 (km).

Then, when λ in Equation 4 is solved as in Equation 5 below, Equation 6 is derived.

Further, when λ in Equation 4 is solved as in Equation 7 below, Equation 8 is derived.

  Then, Equations 2 and 3 are derived from Equations 6 and 8.

Next, the calculation of the coefficients A and B (step s106) using the equations 2 and 3 will be described in detail with reference to FIG.
First, the capture radius R is set (step s202). Here, the capture radius R indicates the radius (km) from the interpolation point k. The range in which the capture radius R can be set is determined in advance. Specifically, the minimum value of the capturing radius R is 10 (km), and the maximum value is 35 (km). In this embodiment, the capture radius R is set at intervals of 5 (km) so that the number of surrounding points used for calculating the coefficients A and B is a predetermined number from the distribution state of the surrounding points.

  Then, by setting the capture radius R, the surrounding points used when calculating the coefficients A and B are determined (step s204). Specifically, among the surrounding points 1, 2, 3, 4, and 5 acquired in step s104, the surrounding points whose distance r from the interpolation point k is smaller than the capture radius R are used for calculating the coefficients A and B. It is done. For example, in the present embodiment, if the capturing radius R is 35 (km), the surrounding points used for calculating the coefficients A and B are the four surrounding points 1, 2, 3, and 4.

  Next, the CPU 111 calculates weighting values W1, W2, W3, and W4 for each surrounding point (step s206). The weight values W1, W2, W3, and W4 of each surrounding point are calculated by using Wn in Equation 4. The calculated result is the table shown in FIG. The table shown in FIG. 8 is also stored in the memory 113. The weighting value W becomes smaller as the distance r between the interpolation point and the surrounding point is larger. That is, as shown in FIG. 8, among the four surrounding points 1, 2, 3, and 4, the surrounding point 1 closest to the interpolation point k has the largest weight value W3, and the surrounding point 1 farthest from the interpolation point k. Is the smallest weight value W1.

  Next, the CPU 111 converts the residual gravity values g1, g2, g3, and g4 at the surrounding points 1, 2, 3, and 4 to the depth values d1, d2, d3, and d4, and the weighting value W1. , W2, W3, and W4 are substituted to calculate coefficients A and B (step s208). As a result of the calculation, A = 0 (km) and B = 0.5 (km / mGal). Thereby, the calculation of the coefficients A and B is completed. The values of the coefficients A and B are stored in the memory 113.

  Next, based on the residual gravity value gk at the interpolation point k acquired at step s102 and the coefficients A and B calculated at step s208, the CPU 111 determines the depth value d (others) at the interpolation point k. In order to distinguish from the depth value of the point, a depth value dk) is calculated (step s108). As a result of the calculation, the depth value dk = 0.75 (km). The calculated depth value dk is stored in the memory 113.

  Furthermore, the CPU 111 can calculate the depth value dm of the interpolation point m by repeating steps s102 to s108 for other interpolation points (for example, the interpolation point m shown in FIG. 6) other than the interpolation point k. It becomes. In calculating the depth value dm, the coefficients A and B for the interpolation point m are calculated. Thus, when there are a plurality of interpolation points, the coefficients A and B are calculated for each interpolation point.

  In the above description, the computer 110 obtains the residual gravity value gk at the interpolation point k (step s102), and then obtains the residual gravity value g and the depth value d at the surrounding points 1, 2, 3, 4, and 5. Although acquisition (step s104) was decided, it is not limited to this. For example, the computer 110 may acquire the residual gravity value gk of the interpolation point k after acquiring the residual gravity value g and the depth value d of the surrounding points.

=== Effect of Depth Value Calculation Method According to the Present Embodiment ===
Next, the effect of the depth value calculation method according to the present embodiment will be described. In this depth value calculation method, as shown in FIG. 4, the first step (step s102) of acquiring the residual gravity value gk of the interpolation point k and the surrounding points 1, 2, 3, 4 around the interpolation point k are obtained. Second step (step) of acquiring the residual gravity values g1, g2, g3, g4 and the depth value d to a predetermined layer (for example, earthquake basement) in the formation at the surrounding points 1, 2, 3, 4 s104) and the residual gravity values g1, g2, g3, g4 and the depth values d1, d2, d3, d4 of the surrounding points 1, 2, 3, 4 acquired in step s104. a third step (step s106) for calculating linear coefficients A and B that define the linear relationship between g and the depth value d, a residual gravity value gk of the interpolation point k obtained in step s102, and a step Based on the coefficients A and B calculated in s106 Has a fourth step of calculating a depth value dk of the interpolation point k (step s108), the.

  FIG. 9 is a diagram showing PS-P time (s) corresponding to the depth value calculated by the depth value calculation method. The curve in FIG. 9 is a line connecting the points where the PS-P time is the same, and ● in FIG. 9 indicates the surrounding points. The same applies to FIG. 11 described later.

  Here, the PS-P time (s) will be described with reference to FIG. FIG. 10 is a diagram for explaining the transmission of P waves and S waves, which are seismic waves. When an earthquake occurs, a P wave and an S wave are generated from the hypocenter X shown in FIG. Here, since the P wave is faster than the S wave, the P wave transmitted through the earthquake base enters the deposited layer earlier than the S wave. When the P wave enters the sedimentary layer, an S wave is generated from the P wave at the boundary surface between the earthquake basement and the sedimentary layer. The S wave generated from the P wave is distinguished from the S wave generated from the epicenter and is called a PS wave. On the other hand, a part of the P wave incident on the deposited layer remains the P wave.

Since the P wave is earlier than the P wave and the PS wave, the PS wave reaches the ground surface after the P wave transmitted through the sedimentary layer reaches the ground surface. Here, the above-described PS-P time (s) is the difference between the time (s) when the P wave reaches the ground surface and the time (s) when the PS wave reaches the ground surface. This PS-P time can be regarded as having a proportional relationship represented by the following formula 9 with the thickness of the deposited layer, that is, the depth to the earthquake base. This is because the P wave is faster than the PS wave, and the greater the depth to the earthquake base, the greater the difference between the time for the P wave to reach the ground and the time for the PS wave to reach the ground. Note that C (km / s) in Equation 9 is a constant.

d = C × [PS-P time] (9)

  The PS-P time corresponding to the depth value calculated by the depth value calculation method according to the present embodiment is the PS-P time shown in FIG. On the other hand, FIG. 11 is a diagram showing the PS-P time calculated by the conventional calculation method.

  As can be seen by comparing FIG. 9 and FIG. 11, the curve shown in FIG. 9 has a more intricate shape than the curve shown in FIG. A portion where the curve shown in FIG. 9 is complicated indicates a place where the depth value d changes suddenly. On the other hand, in the conventional calculation method, since the data of each point is smoothed and a curve is drawn, as shown in FIG. For this reason, according to the depth value calculation method according to the present embodiment, it is possible to appropriately interpolate even a complicated underground structure.

  From the above, according to the depth value calculation method according to the present embodiment, it is possible to appropriately interpolate the underground structure.

=== Other Embodiments ===
Although the computer system and the like as one embodiment have been described, the above embodiment is for facilitating the understanding of the present invention, and is not intended to limit the present invention. The present invention can be changed and improved without departing from the gist thereof, and it is needless to say that the present invention includes equivalents thereof.

  In the above embodiment, the computer 110 calculates the residual gravity value gk of the interpolation point k. However, the present invention is not limited to this. For example, another device may calculate the residual gravity value gk of the interpolation point k.

  Moreover, in said embodiment, although Formula 1 decided to be a primary type | formula, it is good also as a formula more than secondary. In such a case, the number of coefficients increases. However, since it is known that Expression 1 is a linear expression, the depth value of the interpolation point can be appropriately calculated even with the linear expression.

Furthermore, in the above embodiment, the predetermined layer is an earthquake base, but is not limited thereto. For example, the predetermined layer may be a layer in the deposited layer (for example, the third layer in FIG. 1).
When the predetermined layer is an earthquake base, it is possible to appropriately calculate the depth to the earthquake base. On the other hand, the seismic ground motion tends to be amplified by the sedimentary layer. For this reason, when the predetermined layer is an earthquake base, it is possible to appropriately interpolate the structure of the sedimentary layer that has a large influence on the shaking of the earthquake. Therefore, the above embodiment is more desirable.

Further, in the above embodiment, there are a plurality of interpolation points (interpolation points k and m in FIG. 6). In the third step (step s106), the coefficients A and B are calculated for each interpolation point. Further, in the fourth step (step s108), the coefficients A and B of the interpolation point calculated in step s106 for each interpolation point and the residual gravity at the interpolation point acquired in the first step (step s102). Based on the value g, the depth value d of the interpolation point is calculated. However, it is not limited to the above. For example, the coefficients A and B may be values common to the interpolation points.
However, when the coefficients A and B are calculated for each interpolation point, the depth value d of each interpolation point is calculated using the coefficients A and B calculated for each interpolation point. Can be set to a more optimal value. Therefore, the above embodiment is more desirable.

Furthermore, in the above embodiment, the surrounding points are a plurality of points (around points 1, 2, 3, 4, 5 shown in FIG. 6) having different distances from the interpolation point k. Further, in the third step (step s106), within a range of a predetermined distance from the interpolation point k, that is, within a range where the capture value R can be set (in FIG. 6, the capture value R is set within a range of 10 ( km) to 35 (km)), the coefficients A and B are calculated based on the residual gravity values g and depth values d of a plurality of surrounding points. However, it is not limited to the above. For example, it is possible to use all surrounding points that already have data without setting the capture value R.
However, when the capture value R is set, the optimum values of the coefficients A and B can be calculated by using only the surrounding points near the interpolation point k. Therefore, the above embodiment is more desirable.

Further, in the above embodiment, in the third step (step s106), the residual gravity value g of the surrounding points 1, 2, 3, and 4, the depth value d of the surrounding points, and the interpolation point of the surrounding points The coefficients A and B are calculated based on the residual gravity value g and the weight value W that gives weight to the depth value d corresponding to the distance from k. However, the present invention is not limited to this. . For example, the weighting value W may not be considered when calculating the coefficients A and B.
The farther the interpolation point is from the surrounding point, the higher the possibility that the underground structure is different from the surrounding point. Therefore, when calculating the coefficients A and B in consideration of the weighting value W that gives weight to the residual gravity value g and the depth value d corresponding to the distance from the interpolation point of the surrounding points, it is close to the interpolation point. By assigning weights to the surrounding points, it is possible to calculate the optimum values of the coefficients A and B. Therefore, the above embodiment is more desirable.

It is the schematic diagram which showed the underground structure. 1 is a diagram showing an external configuration of a computer system 100. FIG. FIG. 3 is a block diagram illustrating a configuration of the computer system 100 illustrated in FIG. 2. It is the flowchart which showed the calculation method of the depth value. It is the flowchart which showed the calculation method of the coefficient of a line format. It is the figure which showed the positional relationship of an interpolation point and a surrounding point. FIG. 7A is a table showing data related to the interpolation points stored in the memory 113. FIG. 7B is a table showing data related to surrounding points stored in the memory 113. It is the table which showed the weighting value with respect to each surrounding point. It is the figure which showed PS-P time (s) corresponding to the depth value calculated by the depth value calculation method concerning this embodiment. It is a figure for demonstrating transmission of the P wave and S wave which are seismic waves. It is the figure which showed PS-P time calculated by the conventional calculation method.

Explanation of symbols

100 Computer System 110 Computer 111 CPU
112 Calculation unit 113 Memory 114 Interface 120 Display device 130 Input device 130A Keyboard 130B Mouse 140 Reading device 140A Flexible disk drive device 140B CD-ROM drive device

Claims (6)

A first step of obtaining a residual gravity value of the interpolation point;
A second step of obtaining a residual gravity value of surrounding points around the interpolation point and a depth value to a predetermined layer in the formation at the surrounding point;
A third step of calculating a linear coefficient defining a linear relationship between the residual gravity value and the depth value based on the residual gravity value and the depth value of the surrounding point acquired in the second step. When,
A fourth step of calculating a depth value of the interpolation point based on the residual gravity value of the interpolation point acquired in the first step and the coefficient calculated in the third step;
A depth value calculation method characterized by comprising: The depth value calculation method according to claim 1,
The depth calculation method, wherein the predetermined layer is an earthquake base. The depth value calculation method according to claim 1 or 2,
There are a plurality of interpolation points,
In the third step, the coefficient is calculated for each interpolation point,
In the fourth step, based on the coefficient of the interpolation point calculated in the third step for each interpolation point and the residual gravity value of the interpolation point acquired in the first step. And calculating a depth value of the interpolation point. The depth value calculation method according to any one of claims 1 to 3,
The surrounding points are a plurality of points having different distances from the interpolation point,
In the third step, the coefficient is calculated based on the residual gravity value and the depth value of a plurality of the surrounding points within a predetermined distance from the interpolation point. . The depth value calculation method according to claim 4,
In the third step, the residual gravity value and the depth value of the surrounding point, the depth value of the surrounding point, and the residual gravity value and the depth value corresponding to the distance from the interpolation point of the surrounding point are weighted. A depth value calculation method, wherein the coefficient is calculated based on a weighting value for providing (A) a memory for storing a residual gravity value of an interpolation point, a residual gravity value of surrounding points around the interpolation point, and a depth value to a predetermined layer in the formation at the surrounding point;
(B) Based on the residual gravity value and the depth value of the surrounding points stored in the memory, calculate a linear coefficient that defines a linear relationship between the residual gravity value and the depth value;
A calculation unit that calculates a depth value of the interpolation point based on the calculated coefficient and a residual gravity value of the interpolation point stored in the memory;
A depth value calculation apparatus comprising (c).