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Fault Zone Material Heterogeneities May Trigger Repeating Earthquakes in Kanto, Japan

Description: 

Fault zones feature small-scale material heterogeneities that strongly affect where earthquake ruptures initiate and terminate. In this presentation, we show that fault zones that repeatedly rupture during earthquakes in Kanto, Japan also exhibit anomalous material properties. The Kanto region in Japan is situated in a special tectonic setting where the Philippine Sea plate is “sandwiched” between the Okhotsk and Pacific plates, generating small to moderate-magnitude earthquakes that repeat within days to years along the plate interface between the Pacific plate and the Philippine Sea plate at 60-70 km. We apply a waveform cross-correlation approach to measure the in-situ Vp/Vs ratios of earthquake patches. We find anomalously low Vp/Vs ratios (~1.5) in these earthquake source regions, suggesting the fault zone rocks may have distinct mineral compositions, e.g., high concentration of alpha-quartz. We also estimate the stress drop of M>3.4 earthquakes using the spectral ratio method, leading to a median stress drop of 4.6 MPa. The typical stress drop values suggest the effective normal stress is much lower than the lithostatic pressure and the fault zone may also contain abundant fluid. Thus, a combination of different mineral compositions and richness in fluid can promote velocity-weakening behaviors and generate repeating earthquakes at 60-70 km. Our earthquake cycle simulations based on the frictional parameters of wet quartz can reproduce M~4 earthquakes that alternate between full and partial ruptures every 2-5 years, which are similar to the recurrence intervals of M~4 earthquakes at 60-70 km.

Session: Characteristics and Mechanics of Fault Zone Rupture Processes, from Micro to Macro Scales - I

Type: Oral

Date: 5/2/2024

Presentation Time: 08:45 AM (local time)

Presenting Author: Yihe

Student Presenter: No

Invited Presentation: Yes

Authors