強震動シミュレーションのためのすべり速度時間関数の近似式

Abstract

Nakamura and Miyatake (2000) had proposed an approximate expression of slip rate time function on the basis of the dynamic rupture model simulation on narrow fault. In the present paper, it is applied to strong ground motion simulation from strike slip fault in order to study the validity of the expression by comparison with dynamic rupture models in several cases. The following three fault rupture processes are considered in the present paper, and the waveforms generated from the approximate slip rate time function for these cases are compared with corresponding dynamic rupture models.(a) almost unilateral rupture on 20km×10km single strike slip fault with uniform 10MPa stress drop distrubution. (b) two asperity models, i. e., b-1) single 8km×6km single asperity located near the center of a 20km×10km strike slip fault and b-2), three asperites located on the same fault. Stress drop is 10MPa in asperity part, and 0MPa in another part. These cases correspond to the heterogeneous fault. (c) 10km×10km fault on which rupture starts from the deepest corner of the fault, and propagate circularly. Since this situation is very different from that assumed in Nakamura and Miyatake (2000), the approximate function might not be valid. In all the cases, the uppermost depth is assumed to be 1km, and the speed of rupture propagation is assumed to be 0.8 times shear wave velocity.In case A, approximate slip rates and the generated seismic waves gave the good agreement with those calculated from dynamic faulting model, although at the initial part of the rupture some discrepancy exists. In case B, the agreement is also good, except the initial part of the rupture. It is possible to improve the agreement by adjusting the rise time and peak slip rate using simple correction function.In case C, it is impossible to apply uniform slip rate function. Slip rates time functions from dynamic model for case C are different from point to point on the fault plane. So rise time and peak slip rate distributions need to be adjusted using the above function.