断層滑りの支配的な変形機構の遷移を考慮に入れた動的地震サイクルシミュレーション

Abstract

Development of suitable algorithms and an increase in computational capability have enabled dynamic earthquake cycle simulations (ECS) to be conducted in which both coseismic rapid slip associated with inertial effects and interseismic quasistatic processes are simulated in a single framework. The rate- and state-dependent friction (RSF) law is a very useful tool in ECS, because it is able to reproduce a spectrum of fault behaviors including steady slip, aseismic transient, and earthquakes when coupled with an elastic medium. The RSF law has, however, been developed with a rather narrow range of experimental conditions where cataclasis dominates. Recent experimental and theoretical studies have developed fault constitutive laws that are applicable to different conditions where different deformation mechanisms are important. The ECS is useful for realizing and quantifying fault motions based on different hypotheses of fault slip deformation mechanisms, such as brittle-plastic transition at a deeper extent of a seismogenic fault, pressure solution creep, and remarkable weakening at a coseismic high slip rate. In the field of structural geology, conceptual fault models, which represents distribution of dominant deformation mechanisms and strength along the depth of a major fault, have been proposed and updated since the 1970s on a basis of field observations of fault rocks and laboratory experiments. Since the development of ECS, it has become possible to build them as objective numerical models once fault constitutive laws are formulated, and to compare behaviors under different hypotheses. Recent studies on the significance of changes in deformation mechanisms of a fault slip for fault behavior and reviewed and perspectives are discussed.