Taishi OSANAI

Evaluation of distance attenuation formula for earthquake motion in Niigata prefecture

Takaaki IKEDA

The distance attenuation formula is used to predict the ground motion. If the magnitude and distance of the earthquake are known, the maximum ground motion can be estimated.The distance attenuation formula is an empirical formula and does not reflect records of earthquakes since 2000. In addition, since the topography and underground structure peculiar to the region are not taken into account, the accuracy of earthquake prediction may be reduced in detail.
From this, my research is to construct a high-precision distance attenuation formula limited to Niigata prefecture in order to improve the accuracy of the distance attenuation formula.
Earthquake data were collected using a strong motion observation network(KiK-net).There are four conditions to collect, that they occur all over Niigata Prefecture, and that M4.0 to M7.0 records are collected about 5 records every 0.1, that the waveform of the earthquake is not disturbed, and that underground records are used.To find the shortest distance, it is necessary to set a fault plane. The fault plane is determined by strike, dip, and fault length. In this case, we used the broadband seismic network to collect strike and dip information.The fault length was obtained using Matsuda's formula. The width of the fault is defined as half its length.
In this study, the formula was constructed based on the formula for the shortest fault plane constructed by Hongjun SI and Saburoh MIDORIKWA.When magnitude was small, the information of strike and dip was not obtained. Therefore, the shortest distance was calculated by considering the hypocenter below M4.5 as a point epicenter and the one above M4.5 with a surface epicenter.
This time, the equation was constructed by changing k, which is the coefficient of viscous damping in the propagation path of the equation.As a result, we thought that the value of k in Niigata Prefecture was optimally around 0.003.