JP2800911B2 - Seismic intensity measurement method for control - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a seismic intensity used for a control seismometer or the like.

[0002]

2. Description of the Related Art In the event of an earthquake, there is a control seismometer as a device for controlling various systems according to the intensity of the earthquake to prevent the spread of damage and the occurrence of secondary disasters.
2. Description of the Related Art Control seismometers have been incorporated in various facilities such as transportation, city gas, electric power, and water as an automatic emergency stop device at the time of a large earthquake.

In such a control seismometer, in order to perform a control having a high correlation with the degree of damage to a structure, for example, as shown in Japanese Patent Publication No. 4-35035, the SI value is measured as a measure of the intensity of earthquake motion. A measurement method has been proposed and implemented. In this method of measuring the intensity of seismic motion, the acceleration of the seismic motion is input to an arithmetic unit that satisfies the equation of motion of the one-degree-of-freedom vibration system, and the speed response is obtained every moment, and the spectrum of the maximum value of the speed response, that is, the speed response spectrum SV is used. Is used to calculate the SI value as the intensity of. Specifically, in this method, the calculation unit sets the attenuation constant to 20
% And the natural period are set to 1.5 seconds and 2.5 seconds, respectively, to form two sets, and the maximum value of the speed response of each natural period, which is the output of these arithmetic units, is set to the larger one. Constant 0.7
The SI value is approximately obtained by multiplying by 3.

[0004] This SI value is the natural period of the velocity response spectrum of a one-degree-of-freedom vibration system having a damping constant of 20% from 0.1 second to 2.5 seconds.
It is defined by the average value of the response speed in the range up to seconds, and if this SI value is calculated by the defined formula based on the acceleration obtained by the seismometer, a great deal of calculation is required. Is not practical. Therefore, in the method of the above document, the flat portion of the natural cycle of the velocity response spectrum of 1.5 to 2.5 seconds is represented by a value of the natural cycle of 1.5 seconds or 2.5 seconds, so that the value of 0.1 is obtained. The velocity response spectrum in the range from second to 2.5 seconds is approximated by a bent line that is bent at a point of a natural period of 1.5 seconds, an average value thereof is obtained, and this is estimated as the SI value.

[0005]

Therefore, the present inventors have made a large number of correlations between the SI value obtained by the above-described method, that is, the estimated SI value, and the SI value obtained by the definition formula, that is, the true SI value. As a result of a thorough investigation of the earthquake records, the estimated SI value obtained by the method of the above-mentioned document, which changes the natural period of interest in approximation of the velocity response spectrum of the ground motion when calculating the SI value according to the magnitude of each velocity response Does not include systematic errors, and from this viewpoint it is found that the accuracy is good, and from the possibility that the change of the natural period affects the value variation, the possibility of improvement regarding the value variation is Was obtained. The present invention has been made in view of such a point, and it is an object of the present invention to provide a highly accurate seismic intensity measurement method having a small degree of variation as compared with the above-described conventional method.

[0006]

According to the present invention, in order to solve the above-mentioned problems, an acceleration of a seismic motion is input, and a calculation is performed which satisfies a motion equation of a one-degree-of-freedom vibration system at a set damping constant and a natural period. In a method of obtaining a speed response momentarily and substituting the maximum value into a preset estimation formula to obtain an estimated SI value, the SI value obtained by a definition formula for a large number of earthquake records under the desired setting conditions and the above estimation formula The regression coefficient of a regression linear equation using the estimated SI value as a dependent variable and the SI value obtained from the definition equation as an independent variable from the estimated SI value obtained by the above and substituting this regression coefficient into the regression linear equation. , A relational expression in which the estimated SI value is the dependent variable and the correction value of the SI value is the independent variable is obtained, and by modifying this relational expression, the correction value of the SI value is determined by the dependent variable and the estimated value. Obtains the form of a correction formula as an independent variable the I value, the correction in the correction formula, by substituting the estimated SI value obtained by inputting the acceleration of the ground motion of interest S
It is characterized in that I value is obtained.

In the present invention, the damping constant in the above method is set to 20% similarly to the definition formula of the SI value.
It is suggested to set a value other than 20%.

According to the present invention, in the above-described method, one point from 1.5 seconds to 2.5 seconds is set as a natural period, and the value of this point represents a flat portion of the velocity response spectrum. The estimation formula is a formula that approximates the speed response spectrum by a bent line that is bent at a point of a natural period of 1.5 seconds to obtain an average of the speed response in a section of the natural period of 0.1 to 2.5 seconds, and in particular, It is proposed to set the natural period to a point at or near 1.5 seconds.

Further, in the present invention, in the above method, a plurality of points having a natural period of 0.1 second to 2.5 seconds are selected, and the estimation expression is obtained by dividing the velocity response spectrum by a broken line connecting the values of the above points. It is proposed to use an equation that approximates the average of the speed response in the section of the natural period of 0.1 second to 2.5 seconds.

In the present invention, in the above-mentioned method, a natural period of at least 1.5 seconds and 2.5 seconds is selected, and the natural period is set to 1.5 seconds and 2.5 seconds.
It is suggested to add 3 points to add points.

[0011]

In the approximation of the velocity response spectrum of the seismic motion when calculating the SI value, there is a systematic error in the estimated SI value obtained without changing the preset natural period, and this systematic error is determined by Although the number of cycles is relatively large when the number of cycles is two or less, the degree of variation is smaller than the degree of variation of the estimated SI value obtained by the method of the above-mentioned document even when the set natural cycle is one point.

The above systematic error can be easily removed by correcting with a correction formula using a regression coefficient of a regression linear equation using the estimated SI value as a dependent variable and the SI value obtained from the definition formula as an independent variable. .

Therefore, even when the number of natural periods set at the time of calculating the SI value is small, it is possible to obtain a highly accurate seismic intensity with a small degree of variation for the target earthquake. By increasing the number, the degree of variation is further reduced, and the seismic intensity can be obtained with higher accuracy.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings. FIG. 1 conceptually shows the configuration of a control seismometer to which the present invention is applied. Reference numeral 1 denotes an accelerometer, 2 denotes an estimated SI value calculation unit, 3 denotes a regression correction unit, and 4 denotes a control unit. Estimated SI
The value calculation unit 1 inputs the acceleration of the seismic motion detected by the accelerometer 1 at every sampling time of, for example, about 1/100 second, and calculates a predetermined damping constant and a motion equation of a one-degree-of-freedom vibration system at a natural period. There is a process of calculating the speed response every moment by performing a calculation that satisfies the conditions, and a process of obtaining the maximum value of the speed response and substituting this maximum value into an estimation formula described in detail later to obtain an estimated SI value. These processes can be realized by, for example, combining various arithmetic elements such as various arithmetic units and filters as disclosed in the above document in terms of hardware, or by software using an apparatus to which a microcomputer is applied. Can be realized in a practical manner. The regression correction unit 3 holds the regression coefficient of a linear regression equation using the estimated SI value as a dependent variable and the true SI value as an independent variable as data, as described later, and estimates the estimated SI value obtained by the estimated SI value calculation unit 1. In this configuration, a value is corrected by a correction formula using a regression coefficient, and this can also be realized by software using a device to which a microcomputer is applied. The control unit 4 controls various systems based on the corrected SI value corrected by the regression correction unit 3 in the event of an earthquake that has a high possibility of damaging the structure, and automatically stops operation, for example. Action can be taken. As a specific method of such control, an appropriate method such as performing control in consideration of the maximum acceleration can be applied as described in the above document.

According to the present invention, as described above, the SI value is estimated by approximating the velocity response spectrum of the seismic motion without changing the set natural period. One of the points from 5 seconds to 2.5 seconds is set to represent the flat part of the velocity response spectrum, and the estimation equation is obtained by approximating the velocity response spectrum by a broken line that bends at a point with a natural period of 1.5 seconds. A method of calculating the average of the speed response in the section of the natural period of 0.1 second to 2.5 seconds, a method of selecting a plurality of points of the natural period from 0.1 second to 2.5 seconds, and an estimating expression The velocity response spectrum is approximated by a broken line connecting the above points to obtain a natural period of 0.1 second to 2.
A formula for calculating the average of the speed response in the section of 5 seconds. Next, these methods will be described in detail with reference to examples.

First, the SI value estimation formula set in the estimated SI value calculation unit 1 in the present invention will be described below together with the SI value definition formula and the SI value estimation formula according to the above document. First,
As described above, the SI value is the natural period of the velocity response spectrum SV of the one-degree-of-freedom vibration system having a damping constant of 20% from 0.1 second to 2.
It is defined by the average value of the response speed in the range up to 5 seconds, and is expressed by the following equation.

(Equation 1)

On the other hand, the method of estimating the SI value shown in the above-mentioned document, that is, with a damping constant of 20%, a natural period of 1.5 seconds, and 2.
An equation for estimating the SI value in the method of estimating the SI value by multiplying the larger one of the maximum values of the speed response of the 5-second one-degree-of-freedom vibration system by a constant is expressed by the following equation. SIk (20) = max [SV (2.5), SV (1.5)] × 1.7 / 2.4 Here, SV (1.5) and SV (2.5) are the maximum values of the speed response at the natural periods of 1.5 seconds and 2.5 seconds, respectively. And max [a.
b] is an operator for adopting the larger value of a or b, and “20” of SIk (20) emphasizes that 20% is adopted as the damping constant. But the same is true.

On the other hand, the estimated SI value obtained by the above method in the present invention is represented by the following equation. However, the following equation is for a case where a damping constant of 20% is applied. A method of setting any one point of the natural period from 0.1 second to 2.5 seconds SI ₁ (20) = SV (T) × 1.7 / 2.4 T is the set natural period and is 1.5 seconds to 2 seconds. The value is up to .5 seconds. For example, in the case of 1.5 seconds, the value is expressed by the following equation. SI ₁ (20) = SV (1.5) × 1.7 / 2.4 In this method, as shown conceptually in FIG. 2, the flat portion of the velocity response spectrum SV is represented by the maximum value of the velocity response in the natural period T, and The response spectrum is set to the natural period 1.
The natural period is approximated by a broken line that is bent at a point of 5 seconds.
The estimated SI value is obtained by calculating the average of the speed response in the section from 1 second to 2.5 seconds.

A method in which the natural period is set by selecting a plurality of points from 0.1 seconds to 2.5 seconds

(Equation 2) As shown in the conceptual diagram of FIG. 3, the above equation expresses the section of the natural period of the velocity response spectrum from 0.1 second to 2.5 seconds by a broken line connecting the values of the points of the plurality of natural periods selected and set. This is a general expression that approximates and averages the speed response in this section.
The maximum value of Tj + 1 is 2.5 (seconds). When the natural period set in this method is set to two points of 1.5 seconds and 2.5 seconds, it is expressed by the following equation and shown in FIG. SI ₂ (20) = [SV (1.5) × 0.7 + {SV (1.5) + SV (2.5)} ×
0.5] /2.4

The results of obtaining the estimated SI value represented by the above equation and the SI value of the definition equation for a large number of earthquake records are shown below. The earthquake records are based on the records used in the "Research Report on Information for Judgment of Emergency Measures in the Event of an Earthquake" (April 1991, Japan Gas Association). Forty earthquake records observed in a famous earthquake are used.

First, FIGS. 5 to 7 show SIk (20), SI ₁ (20), and SI ₂ (20) obtained from the above-mentioned earthquake record, respectively, as SI values (hereinafter simply referred to as SI or SI This is shown in comparison with the value. In these figures, the horizontal axis represents the SI value.
When there is a linear relationship between the value and the linear relationship, particularly the gradient 1, the estimation accuracy is good and there is no systematic error. From FIG. 5, although SIk (20) has a relatively large variation,
When the relationship with SI is approximated by a straight line on average, the gradient of the straight line Lk is approximately 1, which indicates that no systematic error is included. Incidentally, since, in a linear gradient 1 are shown as L _0. Next, as shown in FIGS. 6 and 7, SI ₁ (20) and SI ₂ (20) have a linear relationship with SI, but the gradients of the straight lines L ₁ and L ₂ are different from 1, and therefore the systematic It can be seen that an error is included.
Therefore, these values cannot be directly used as the estimated SI values. However, it can be seen that the value variation is smaller than SIk (20). By the way, in order to compare SI ₂ (20) and SIk (20), as shown in FIG. 8, when the horizontal axis represents SI ₂ (20) / SI and the vertical axis represents SIk (20) / SI, The value varies around 1.0, but the latter varies around 1.0, and the range of variation is larger in the latter. These numerical points and SIi (20) (i ≧ 3) will be described later.

Next, a description will be given of a correction formula for setting the regression correction unit 3 to remove the systematic error. First, for the SI value obtained by the definition equation, SIi (20) (where i = k, 1,2,
..) Is represented as SIi, and a linear regression equation obtained by regression analysis is given by SIi = aSI + b,
The establishment variable [SIi (20)] of Ii (20) can be expressed by the following equation. [SIi (20)] = aSI + b + ε (where ε is a residual variable) The regression coefficients a and b of the above linear regression equation are obtained by applying the least squares method to SIi (20) and SIi for a large number of earthquake records. Can be obtained as a value that minimizes the sum of the squares of the differences. Conversely, the regression coefficients a and b of the regression linear equation
Is determined, the relationship between each estimated SI value and the corrected SI value sii from which the systematic error has been removed is SIi (20) = asii + b, the estimated SI value is a dependent variable, and the corrected SI value sii is independent. It can be represented by a relational expression in the form of a variable. This is corrected S
The following equation, which is transformed into a correction equation in which the I value sii is a dependent variable and the estimated SI value is an independent variable, is a correction equation to be set in the regression correction unit 3. sii = SIi (20) / ab / a

[0023] 9-11, estimated SI value shown in FIGS. 5 to 7, SIk (20), SI 1 (20), a value obtained by correcting by the correction equation SI ₂ (20), i.e. sik, si ₁ and si ₂ are shown in comparison with SI. In these figures, the standard deviation σ of the residual ε is entered to show the degree of variation.

As shown in FIG. 10 and FIG.
The systematic errors of ₁ (20) and SI ₂ (20) are removed by the correction formula. When the relationship between si ₁ and si ₂ with SI is approximated by straight lines on average, these straight lines L ₂ ′ and L ₂ gradient of ₃ 'is 1, overlapping with the straight line L _0. Further, as shown in FIG.
A straight line Lk 'indicating the relationship between ik and SI is represented by SIk (2
0), and overlaps the straight line L _0, and sik and SIk (20) are
The same applies to the degree of variation. And sik, si _1, s
The standard deviations indicating the degree of variation of i ₂ are 8.79, respectively.
(cm / s), 6.43 (cm / s), and 3.38 (cm / s), indicating that the sik varies most.

Therefore, from the above, even when the set natural period is set to one point in the method of the present invention, by performing the correction, it is possible to obtain a highly accurate ground motion with a small degree of variation with respect to the target earthquake. The strength can be obtained, and if the natural period is set to two points and the velocity response spectrum is approximated by a broken line using the values of these points, it is possible to obtain a more accurate seismic intensity with a smaller degree of variation. Recognize.

Next, an embodiment for SIi (20) (i ≧ 3) will be described with reference to FIGS. First, FIG.
Shows the relationship between SI ₃ and SI ₃ obtained by correcting SI ₃ (20) (set natural period T (second): 1.0, 1.5, 2.5) by a correction formula. FIG. 13 shows the relationship between SI ₃ and SI obtained by correcting SI ₃ (20) (set natural period T (second): 0.7, 1.5, 2.5) using the above correction formula. FIG.
4 is SI ₄ (20) (setting natural period T (second): 0.44, 0.8, 1.
5, 2.5) shows the relationship between SI ₄ and SI obtained by correcting with a correction formula. FIG. 15 shows a relationship between SI ₅ and SI ₅ obtained by correcting SI ₅ (20) (set natural period T (second): 0.44, 0.8, 1.5, 2.0, 2.5) by a correction formula. .

From these figures, it can be seen that, by increasing the number of eigenperiods to be set to three or more, the degree of variation is further reduced and the correlation with SI is increased. As shown in FIGS. 12 and 13, it can be seen that the degree of variation varies depending on the positions of points of the natural periods even if the set natural periods are the same. FIG.
4. As shown in FIG. 15, when the number of eigenperiods to be set becomes four and further five, the correlation with SI becomes very high. It can be seen that this is not a good idea in view of the time required for the calculation in the value calculation unit 2. However, when there is sufficient reserve for the calculation speed in the estimated SI value calculation unit 2,
A better correlation can be obtained by further increasing the number of eigencycles to be set.

When setting a plurality of natural periods,
Each natural period can be set to an appropriate point from 0.1 to 2.5 seconds, but the flat part of the velocity response spectrum SV starts at or near 1.5 seconds,
Considering the definition formula of the value, it is preferable that the plurality of eigencycles to be set include at least 1.5 seconds and 2.5 seconds. In addition, it is preferable to select a point on a longer period side than the natural period other than the above, particularly near 0.1 second where the SV value is small at 1.5 seconds or less.

The degree of variation of the estimated SI value and the regression coefficients a and b of the above linear equation
Are shown in Table 1. Estimated S before and after regression correction
FIG. 16 shows the relationship between the degree of variation of the I value and the set number of the natural periods. However, in Table 1 and FIG. 16, the degree of variation is not the standard deviation σ, but a value obtained by dividing the standard deviation σ by the average SI value (μ = 38 cm / sec) of the 40 earthquake records, ie, It is represented by the coefficient of variation (σ / μ). Further, in FIG. 16, the mark x indicates the variation coefficient before correction, the symbol ■ indicates the variation coefficient after correction, and the symbol □ indicates the variation coefficient of the estimated SI value according to the above document.

[Table 1]

The following is evident from Table 1 and FIG. When the set number of the natural periods is one, the coefficient of variation of the estimated SI value is larger than the coefficient of variation of the estimated SI value according to the method described in the above document, but is corrected by the regression coefficients a and b. It can be smaller than the latter coefficient of variation. When the set number of the natural periods is two, the coefficient of variation of the estimated SI value is slightly smaller than the coefficient of variation of the estimated SI value according to the method described in the above-mentioned document. By performing the correction, the coefficient of variation can be made smaller than the latter. When the set number of the natural periods is three or more, the coefficient of variation of the estimated SI value is much smaller than the coefficient of variation of the estimated SI value by the method of the above-mentioned document, and is corrected by the regression coefficients a and b. By doing so, the coefficient of variation can be made even smaller than the latter.

The broken line in FIG. 16 is a standard variation coefficient introduced for obtaining a standard value of the variation of the estimated SI value.
The speed response spectrum is normalized so that the SI value becomes 1, and the normalized speed response spectrum is statistically processed to obtain a normalized speed response spectrum. The SI value obtained from the average value and the SI value obtained from (average value + standard deviation) Is used as a criterion for variation. That is, FIG. 17 shows the normalized velocity response spectrum obtained from the 40 examples of the above-mentioned earthquake records. The solid line is the average value, and the broken line is the average value ± standard deviation. In each of the normalized speed response spectra, the SI value obtained from these by the definition formula is entered, and the deviation by the standard deviation of the normalized speed response spectrum corresponds to a change of about 25% in SI value. You can see that it is. Therefore, all data of the earthquake record
%, The standard deviation σ of the SI values calculated as varying by% is 10.79 (cm / s). From the average μ = 38 cm / sec, the coefficient of variation (σ / μ) is 0.284, which is the standard coefficient of variation described above. And

FIG. 18 shows the standard deviation of the variation of the normalized speed response spectrum on a common logarithmic scale.
It can be seen that it is smallest around 5 seconds. For this reason, SI
₁ (20) It can be seen that the accuracy is highest when the natural period in the calculation is 1.5 seconds or near.

In the above description, the damping constant to be set is SI
Although 20% in the value definition formula is set, a value other than 20% may be set as the attenuation constant in some cases by using the method of correcting with the correction formula using the regression coefficient as described above. it can.

[0034]

As described above, the present invention has the following effects. It is possible to reduce the variation of the estimated SI value as compared with the method of the above-mentioned document which selects the larger value of the maximum value of the speed response of the natural period 1.5 seconds or 2.5 seconds and obtains the estimated SI value. It is possible to measure the seismic intensity with high accuracy by removing the systematic error by regression correction. By setting the number of natural periods to be set to one, the SI
The calculation time required for estimating the value can be reduced. The accuracy can be further improved by setting the number of eigencycles to three or more.

[Brief description of the drawings]

FIG. 1 is a system diagram conceptually showing a configuration of a control seismometer to which a method of the present invention is applied.

FIG. 2 is an explanatory diagram showing a first approximation method of a velocity response spectrum in the method of the present invention.

FIG. 3 is an explanatory diagram showing a second approximation method of a velocity response spectrum in the method of the present invention.

FIG. 4 is an explanatory diagram showing a third approximation method of a velocity response spectrum in the method of the present invention.

FIG. 5 is an explanatory diagram showing a relationship between SIk (20) and SI.

FIG. 6 is an explanatory diagram showing a relationship between SI ₁ (20) and SI.

FIG. 7 is an explanatory diagram showing a relationship between SI ₂ (20) and SI.

FIG. 8 is an explanatory diagram showing a relationship between SIk (20) and SI ₂ (20).

FIG. 9 is an explanatory diagram showing a relationship between SIk (20) subjected to regression correction and SI.

FIG. 10 is an explanatory diagram showing a relationship between SI ₁ (20) subjected to regression correction and SI.

FIG. 11 is an explanatory diagram showing a relationship between SI ₂ (20) subjected to regression correction and SI.

FIG. 12 is an explanatory diagram showing a relationship between regression-corrected SI ₃ (20) and SI.

[13] The SI ₃ in FIG. 12 (20) is an explanatory diagram showing the relationship between SI and regression corrected SI ₃ (20) having different natural period.

FIG. 14 is an explanatory diagram showing a relationship between SI ₄ (20) subjected to regression correction and SI.

FIG. 15 is an explanatory diagram showing a relationship between SI ₅ (20) subjected to regression correction and SI.

FIG. 16 is an explanatory diagram showing the relationship between the degree of variation of estimated SI values before and after regression correction and the set number of natural periods.

FIG. 17 is an explanatory diagram showing a normalized velocity response spectrum obtained from 40 examples of earthquake records.

FIG. 18 is a graph showing the standard deviation of the variation of the normalized speed response spectrum of FIG. 17;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Accelerometer 2 Estimated SI value calculation part 3 Regression correction part 4 Control part

Claims (8)

(57) [Claims] 1. An acceleration equation of a seismic motion is input, and a speed response is obtained from time to time by performing an operation that satisfies a set damping constant and a motion equation of a one-degree-of-freedom vibration system at a natural period, and a maximum value thereof is an estimation formula set in advance. In the method of determining the estimated SI value by substituting the estimated SI value into the dependent variable, the desired SI value is obtained from the SI value obtained by the definition formula and the estimated SI value obtained by the above-mentioned estimation formula under a desired setting condition. The regression coefficient of the linear regression equation using the SI value obtained from the definition equation as an independent variable is obtained , and this regression coefficient is
Substituting the estimated SI value into the dependent equation
Calculate the relational expression in which the correction values of the numbers and SI values are used as independent variables.
By modifying this relational expression, the correction value of the SI value
Is a dependent variable and the estimated SI value is an independent variable.
Input the acceleration of the target seismic motion into this correction formula.
The corrected SI by substituting the estimated SI value obtained
Method for measuring seismic intensity for control, characterized by determining the value 2. The damping constant is defined as 2 in the equation for defining the SI value.
2. The method according to claim 1, wherein 0% is set. 3. The damping constant is defined as 2 in the SI value definition equation.
2. The method according to claim 1, wherein the value is set to a value other than 0%. 4. A natural period is set at any one point from 1.5 seconds to 2.5 seconds, and the value of this point represents a flat portion of the speed response spectrum. 4. An expression for approximating a speed response in a section having a natural period of 0.1 second to 2.5 seconds by approximating the equation with a bent line bent at a point of a natural period of 1.5 seconds. Seismic intensity measurement method for control of earthquakes 5. The method according to claim 4, wherein the natural period is set to a point at or near 1.5 seconds. 6. A plurality of points having a natural period of 0.1 second to 2.5 seconds are selected as the natural period, and a velocity response spectrum is approximated by a polygonal line connecting the values of the respective points in the estimation formula.
4. A method according to claim 1, wherein an equation for calculating an average of the speed response in a section of 1 second to 2.5 seconds is obtained. 7. The method according to claim 6, wherein a natural period of at least 1.5 seconds and 2.5 seconds is selected. 8. The method according to claim 7, wherein the natural period is three points obtained by adding one point of 1 second or less to 1.5 seconds and 2.5 seconds.
Seismic intensity measurement method for control described