[S-CG39] Science of slow earthquakes: Toward unified understandings of whole earthquake process

[SCG39-P07] Extension of aseismic slip propagation theory to slow earthquake migration

*有吉 慶介¹、バーグマン ローランド²、アンプエロ ジャンポール³ (1.国立研究開発法人海洋研究開発機構、2.カリフォルニア大学バークレー校、3.コート・ダジュール大学)

キーワード：速度状態依存摩擦構成則、沈み込み帯、海溝型巨大地震

Recent observations have revealed various types of migrating slow earthquake phenomena. Very low-frequency earthquakes, one of the major types of slow earthquake, have migration speed in the range of about 1-10 km/day, which is much lower than shear wave speeds. Slow earthquakes also have anomalous moment-duration scaling, compared to regular earthquakes, and they are one possible mechanism of precursory slip before large earthquakes. To model and improve our understanding of the migration process of slow earthquakes and their longer duration relative to regular earthquakes, we assume a chain reaction model of numerous asperities along the strike direction, governed by rate- and state-dependent friction on a 3-D subduction plate boundary. From the simulation results, we find that the migration speed is quantitatively explained by an analytical derivation of frictional properties. By applying the analytical results to the simulation and observational results, we conclude that (i) the migration speed of slow slip transients can increase before megathrust earthquakes due to an increase of the background slip velocity, (ii) the longer duration of slow earthquakes given their seismic moment may be explained by the chain reaction model with time delay for stress transfer between nearby asperities mediated by aseismic slip propagation, and (iii) the characteristic slip distance for very low-frequency earthquakes can be roughly estimated in the range of 0.1 μm~2 mm.