[S-CG44] Science of slow-to-fast earthquakes

[SCG44-P30] Extension of aseismic slip propagation theory to slow earthquake migration

*有吉 慶介¹ (1.国立研究開発法人海洋研究開発機構)

キーワード：超低周波地震、低周波微動、速度状態依存摩擦構成則

Natural faults host various types of migrating slow earthquake phenomena, with migration speeds much lower than seismic wave speeds and different moment-duration scaling from regular earthquakes. To advance our quantitative understanding of the migration process and long duration of slow earthquakes and their possible relation to earthquake precursors, I study a chain reaction model in a population of brittle asperities based on a rate- and state-dependent friction on a 3-D subduction plate boundary. Simulation results show that the migration speed is quantitatively related to frictional properties by an analytical relation derived here. By applying the analytical solution to observational results, I conclude that (i) the temporal change of migration speed of foreshock swarms preceding the 2011 Tohoku earthquake may be explained by an acceleration of background slip velocity increasing up to several times above plate convergence rate; (ii) assuming a fixed stress drop, the faster migration observed in Kii regions can be explained by a reduction of effective normal stress (66-73%); (iii) focusing on the difference of tremor migration speed in Shikoku, I estimate the ratio of aσ for the western to the central parts as 1.5; (iv) the long duration of slow earthquakes is explained in the chain reaction model by the time delay of stress transfer between neighboring asperities mediated by aseismic slip propagation; (v) the characteristic slip distance of rate-and-state friction for low-frequency earthquakes is roughly between 30μm and 30mm; (vi) the stress and strength drops of very low-frequency earthquakes is much smaller than 1 MPa.