Construction of an asperity model considering depth dependency of stress drop for more quantitative strong motion simulation

2022 Fiscal Year Final Research Report

• Project/Area Number: 19H02405
• Research Category: Grant-in-Aid for Scientific Research (B)
• Allocation Type: Single-year Grants
• Section: 一般
• Review Section: Basic Section 25030:Disaster prevention engineering-related
• Research Institution: Kyoto University
• Principal Investigator: Kawase Hiroshi 京都大学, 防災研究所, 寄附研究部門教員 (30311856)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: 強震動 / 動的破壊シミュレーション / SMGA / 滑り速度関数 / アスペリティ / 応力降下量

Outline of Final Research Achievements

A model for dynamic rupture simulation was constructed by considering depth dependence in the average stress drop in the asperity, and a parametric analysis was performed by setting random heterogeneity and a rectangular large stress drop region (stress asperity) in the heterogeneity on the fault surface. For the Kumamoto earthquake, we performed both the inversions using a kinematic model focusing on the slip-velocity time function and a forward modeling analysis using dynamic rupture simulation. The results show that the near-fault seismic ground motions are dominated by the slip-velocity function, that its identification by dynamic rupture simulation is possible, that short-period generation from the shallow part is difficult due to the shape of the slip-velocity function, and that the amount of stress drop in the shallow part is important for controlling the peak slip velocity in the shallow part.

Free Research Field

Strong motion seismology

Academic Significance and Societal Importance of the Research Achievements

従来の震源域の地震動予測では、比較的長周期域の地震動を用いた運動学的モデルによる変位不均質をターゲットにした逆解析を通して強震動生成領域（SMGA)として大変位域を把握、そのスケーリング則を構築して予測モデルとしてきた。しかし地表面に断層変位が表出した時、浅部の滑りが受動的か能動的かが判然とせず、そのモデル化が困難だった。我々は動的破壊シミュレーションを用いて、深部の能動的地震波生成領域を応力アスペリティとしてモデル化、得られる地震動を用いて観測地動を再現することを試みた。その結果これまでの運動学的モデル化には変位中心の弊害があり、滑り速度中心のモデル化に移行すべきであることを明らかにできた。