[S-CG46] New Insights of Fluid-Rock Interactions: From Surface to Deep Subduction Zone

[SCG46-11] Does an asperity recover its shear strength in a short interval?

*Junichi Nakajima¹, Akira Hasegawa² (1.Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2.Graduate School of Science, Tohoku University)

Repeating earthquakes (repeaters), which are interpreted as repeated ruptures in the same asperity patch, are often found on the San Andreas fault and subduction plate boundaries. For example, there is a repeater sequence off the coast of Kamaishi where earthquakes of M4.8 occur repeatedly at intervals of about 5.5 years. It is understood that such repeater sequences are caused by ruptures of isolated asperities due to the steady subduction of the Pacific plate. On the other hand, there was also known to be a burst-type repeaters that occur over short intervals ranging from a few days to a few months. However, the mechanism of burst-type repeaters remains elusive.
In recent years, it has been found that repeaters also occur in the inland crust and slabs. Many of these repeaters repeat from a few minutes to a few hours. Furthermore, we observed that repeaters belonging to the same group possess variable stress drops. If repeated rupture of isolated asperities is the cause of repeaters, these results strongly suggest that asperity strength recovers in a short time and that fault strength changes over time. In the talk, we will introduce recent seismological observations and discuss the process of asperity strength recovery.