Strong Aftershock Study Based on Coulomb Stress Triggering—A Case Study on the 2016 Ecuador Mw 7.8 Earthquake

Jianchao Wu,Qian Feng,Yongjian Cai,Weijie Li

doi:10.3390/app7010088

Abstract

The 2016 Ecuador M 7.8 earthquake ruptured the subduction zone boundary between the Nazca plate and the South America plate. This M 7.8 earthquake may have promoted failure in the surrounding crust, where six M ≥ 6 aftershocks occurred following this mainshock. These crustal ruptures were triggered by the high coulomb stress changes produced by the M 7.8 mainshock. Here, we investigate whether the six M ≥ 6 aftershocks are consistent with the positive coulomb stress region due to the mainshock. To explore the correlation between the mainshock and the aftershocks, we adopt a recently published high-quality finite fault model and focal mechanisms to study the coulomb stress triggers during the M 7.8 earthquake sequence. We compute the coulomb failure stress changes (ΔCFS) on both of the focal mechanism nodal planes. We compare the ΔCFS imparted by the M 7.8 mainshock on the subsequent aftershocks with the epicenter location of each aftershock. In addition, the shear stress, normal stress, and coulomb stress changes in the focal sources of each aftershock are also computed. Coulomb stress changes in the focal source for the six M ≥ 6 aftershocks are in the range of −2.17–7.564 bar. Only one computational result for the M 6.9 aftershock is negative; other results are positive. We found that the vast majority of the six M ≥ 6 aftershocks occurred in positive coulomb stress areas triggered by the M 7.8 mainshock. Our results suggest that the coulomb stress changes contributed to the development of the Ecuador M 7.8 earthquake sequence.

Highlights

The 2016 M 7.8 earthquake occurred offshore of the west coast of Northern Ecuador, where the plate boundary between the Nazca and the South America plates lies (Figure 1)
For the other five M ≥ 6 aftershocks, the coulomb stress changes on both fault planes increased at varying degrees
Based on the seismic stress triggering theory and elastic dislocation theory, we compute the coulomb stress changes on two inferred rupture planes according to the focal mechanism solutions of each M ≥ 6 aftershock

Summary

Introduction

The 2016 M 7.8 earthquake occurred offshore of the west coast of Northern Ecuador, where the plate boundary between the Nazca and the South America plates lies (Figure 1). Much research on large earthquake sequences has concluded that stress changes from the affect the locations of subsequent aftershocks [4,5,6]. The coulomb stress triggering theory has been mainshock affect the locations of subsequent aftershocks [4,5,6]. It was thought that small coulomb stress changes can alter the trigger the occurrence of some aftershocks. Small changes in coulomb stress due to anincreases earlier mainshock can0.1 trigger subsequent earthquakes. The coulomb stress change triggered by a mainshock has been widely studied to explore interaction with aftershock activities. 2016 Ecuador earthquake sequence provides a unique opportunity interactionstudied between a largeThe subduction earthquake that imparted coulomb stress changes and the seismicity. We want to determine whether the coulomb stress triggering theory can explain the Ecuador M 7.8 earthquake sequence

Coulomb Failure Criterion

Finite Fault Model

Coulomb

Coulomb Stress Changes Computed in the Focal Source

Discussion and Conclusions