Description
On June 18, 2019, there was a magnitude 6.7 earthquake at a depth of about 15 km off the coast of Yamagata Prefecture. A seismic intensity [Japan Meteorological Agency Seismic Intensity Class; JMA] of 6+ [larger] was observed in Murakami City, Niigata Prefecture, and a seismic intensity of 6- [smaller] was observed in Tsuruoka City, Yamagata Prefecture. The authors conducted a damage survey from June 29 to July 1 after the earthquake and conducted microtremor array observations at nine points centred on the strong motion observation points in October. The ground structure [layer thickness and Shear wave velocity] of the surface layer was estimated from the observation of the microtremor array and compared with the existing ground structure. In addition, a comparison of the ground amplification characteristics obtained from the ground structure and the strong motion observation records could be divided into three groups. That is, a group that is consistent and has a peak in a short period of 0.2 s or less. Consistent group with peaks around 0.2-0.4s. A group in which the predominant period of strong motion records is slightly longer. Therefore, a simple study using equivalent linear analysis was carried out in order to consider the non-linearity of the ground. As a result, considering the non-linearity of the ground, the result can be explained including the group with a long period of predominance.
| DOI | https://doi.org/10.5592/CO/1CroCEE.2021.79 |
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| Keywords | strong motion observation, microtremor observation, amplification characteristics, nonlinearity, |
