Spatial distribution of similar aftershocks of a large inland earthquake, the 2000 Western Tottori earthquake, in Japan

Misaki Hayashi,Yoshihiro Hiramatsu

doi:10.5047/eps.2013.09.002

Abstract

We detected similar aftershocks of the 2000 Western Tottori earthquake and we have examined their spatial distribution on the source fault. Many similar aftershocks are distributed in the northern part of the source fault, but few in the southern part. Specifically, similar aftershocks on the source fault are located outside of the asperity. The cumulative slip estimated from the similar aftershocks is 0.4–2.4 cm. The largest one is found at the edge of the major asperity. We observe that shallower events show a larger cumulative slip than deeper events. Large cumulative slip in the shallow depth in the northern part is coincident with the geodetic observation of afterslip. These facts suggest that similar aftershocks can provide information related to afterslip. However, the slip velocity estimated from both the slip and the recurrence interval of the similar aftershocks shows no distinct distribution.

Highlights

Aftershocks following a large earthquake show striking features of a temporal decay rate, Omori’s law (Omori, 1894), and spatial distribution
No aftershocks occur in the largest slip area beyond 4 m, some aftershocks are located on the large slip area of 2–4 m. This feature enables us to compare the location of similar aftershocks with that of the asperity of the 2000 Western Tottori earthquake, the comparison might be less pronounced than in the case of the 2007 Noto
Hiramatsu et al (2011) reported that the distribution of similar aftershocks on the source fault reflects the area and the amount of afterslip. If this idea is adapted to the case of the 2000 Western Tottori earthquake, the spatial distribution of the similar aftershocks reported here implies that the afterslip occurred mainly in the northern shallow part on the source fault

Summary

Introduction

Aftershocks following a large earthquake show striking features of a temporal decay rate, Omori’s law (Omori, 1894), and spatial distribution. 2. Data and Method We analyze waveform data, provided by the Group for the Dense Aftershock Observations of the 2000 Western Tottori Earthquake, of 1089 events that occurred during October 15–25 determined by Shibutani et al (2005) (Fig. 1). Following the procedure described above, we select 28 groups of similar aftershocks on the source fault of the 2000 Western Tottori earthquake (Fig. 3).

Results

Conclusion