Modeling of the Subsurface Structure from the Seismic Bedrock to the Ground Surface for a Broadband Strong Motion Evaluation in Japan

Session: Near-Surface Effects: Advances in Site Response Estimation and Its Applications [Poster]
Type: Poster
Date: 4/28/2020
Time: 08:00 AM
Room: Ballroom
Description: 

To improve the accuracy of the estimation of strong ground motions, establishing a subsurface structure model is important for evaluating broadband motion characteristics in an approximate range of 0.1 to 10 sec. Integrating the ground surface and seismic bedrock models, which have been modeled separately so far, to construct an integrated model for reproducing observed data is essential for that purpose. In this study, boring data from the whole area of several prefectures were collected from local governments to construct an initial geological structure model from the ground surface to the engineering bedrock, which was further integrated with the existing seismic bedrock model to obtain an initial subsurface structure model (geological model). Seismic records from the observation points of K-NET, KiK-net, the Japan Meteorological Agency and local governments, as well as records from array surveys with a multitude of continuous microtremors were collected to obtain the S-wave velocity structure of the ground, Q-values and amplitude characteristics using this initial subsurface structure model to improve it. We also assessed an areal interpolation method, thereby constructing an integrated ground surface/seismic bedrock subsurface structure model with 250-m mesh grids. Additionally, the one-dimensional multi-reflection method was used to compare seismic observation records and site amplification characteristics for a period shorter than 2 sec, while the finite‐difference method was used for comparison with a period longer than 2 sec to verify that the model is more accurate than existing subsurface structure models. As the final achievement of this investigation, we constructed period and amplitude characteristic maps calculated by the one-dimensional multi-reflection method with the subsurface structure model having a 250-m mesh as the seismic response characteristics of the entire Kanto, Tokai and Kumamoto region.

Presenting Author: Shigeki Senna

Authors