Dynamic rupture simulation of 2018, Hokkaido Eastern Iburi earthquake: role of non-planar geometry

Tatsuya Hisakawa,Tomoko Elizabeth Yano,Ryosuke Ando,Makoto Matsubara

doi:10.1186/s40623-020-01160-y

Abstract

The 2018, Hokkaido Eastern Iburi, Japan, earthquake is an event characterized by complexity of the rupture process and slip pattern, which may involve both reverse and strike-slip motion depending on the locations on the fault surface. We perform dynamic rupture simulations based on simple physical laws, conditions for stressing and fault friction, and the non-planar fault geometry constrained by the aftershock observation. The complex fault geometry is numerically treated by the boundary integral equation method accelerated by the fast domain portioning method. The fault geometry is characterized primarily by the combination of six fault planes. As a result, we are able to explain several observed features of the event, including the spatial variation of the final fault slip and rupture velocity, which are inferred from the kinematic slip inversion. We also succeed in refining the constraint of the regional stress field in the focal area based on the simulation. Our results show that the overall patterns of the complex rupture event can be reproduced by a relatively simple model of the regional stress and the fault friction, if the geometrical complexity of the fault is properly taken into account.

Highlights

The 2018, Hokkaido Eastern Iburi earthquake occurred on September 6 (JST) with an estimated local magnitude ( MJMA ) of 6.7
Rupture process we focus on the case of φ = 0.1 and S1 axis N 48° E (Model 5) in Case A to illustrate the characteristic pattern of the rupture process on the main fault because it reproduces the feature of the inversion result in that it shows the largest slip on the middle of shallower part and small slip on the deeper part
We investigate the origin of the complex pattern observed in the centroid moment tensor (CMT) solutions, the slip profile and the rupture process of the 2018, Hokkaido Eastern Iburi earthquake and what kind of stress field underlying the observed characteristics

Summary

Introduction

The 2018, Hokkaido Eastern Iburi earthquake occurred on September 6 (JST) with an estimated local magnitude ( MJMA ) of 6.7. The event occurred in so-called the Hokkaido corner region, where the northern Japan island arc is considered to transit to the Kurile island arc (Kita et al 2012; Kimura 1994). The Kurile island arc is moving in the southwest direction and is colliding with the Japan island arc (Kita et al 2012; Kimura 1994), which causes the overall tendency of the stress field in the region to be northeast–southwest compression (Fig. 1 inset). The centroid moment tensor (CMT) solution determined by Japan Meteorological Agency (JMA) (https:// www.data.jma.go.jp/svd/eqev/data/mech/cmt/fig/cmt20 180906030759.html) showed that the event ruptured. While previous studies provided insights into the kinematic feature of this earthquake (Asano and Iwata 2019), physical conditions such as stress field underlying the event are poorly understood. We conducted dynamic rupture simulations by giving minimal assumptions constrained with observed facts

Objectives

Results

Conclusion