Detection of asperities and barriers East off Tohoku.

本文以三维动态裂缝模型为基础，在前人波形反演结果的约束下，研究了1968年东北大地震的动态破裂过程。通过求解带断层滑动边界条件的三维平衡方程，估计了断层的应力降分布。并对其强度过剩分布和断裂韧性（临界应力强度因子）分布进行了估计。高应力降区和高强度过剩区分别对应凸起和障壁。我们为这次活动发现了两个障碍和三个难点。对比地形、地震活动、重力和热流数据，发现其中一个障碍位于复杂的地表地形。

Dynamic rupture process of the 1968 Tokachi-Oki earthquake has been investigated on the bais of a three-dimensional dynamic crack model with constraints of the results of previous waveform inversion. The stress drop distribution has been estimated by solving 3D equilibrium equations with the boundary condition of slip on the fault. The strength excess distribution and fracture toughness (critical stress intensity factor) distribution have been also estimated. The high stress drop regions and high strength excess regions, correspond asperities and barrier, respectively. We found two barriers and three asperities for the event. Comraring with topography, seismicity, gravity, and heat flow data, it seems that one of the barriers locates at the complicated surface topography.