Remote Triggering of the Mw 6.9 Hokkaido Earthquake as a Result of the Mw 6.6 Indonesian Earthquake on September 11, 2008

Cheng-Horng Lin

doi:10.3319/tao.2012.01.12.01(t)

Abstract

Only just recently, the phenomenon of earthquakes being triggered by a distant earthquake has been well established. Yet, most of the triggered earthquakes have been limited to small earthquakes (M ＜ 3). Also, the exact triggering mechanism for earthquakes is still not clear. Here I show how one strong earthquake (M(subscript w) = 6.6) is capable of triggering another (M(subscript w) = 6.9) at a remote distance (~4750 km). On September 11, 2008, two strong earthquakes with magnitudes (M(subscript w)) of 6.6 and 6.9 hit respectively in Indonesia and Japan within a short interval of ~21 minutes time. Careful examination of broadband seismograms recorded in Japan shows that the Hokkaido earthquake occurred just as the surface waves generated by the Indonesia earthquake arrived. Although the peak dynamic stress estimated at the focus of the Hokkaido earthquake was just reaching the lower bound for the capability of triggering earthquakes in general, a more plausible mechanism for triggering an earthquake might be attributed to the change of a fault property by fluid infiltration. These observations suggest that the Hokkaido earthquake was likely triggered from a remote distance by the surface waves generated from the Indonesia earthquake. If some more cases can be observed, a temporal warning of possible interaction between strong earthquakes might be concerned in the future.

Highlights

The phenomenon of earthquake triggering is one of the most interesting subjects in seismological studies and can help researchers improve the understanding of how earthquakes occur and may mitigate potential seismic hazards in the future
Among seismic data recorded at from broadband seismic stations (F-net), seismograms at Station KMU show that the inception time of the Hokkaido earthquake corresponds very well to the arrivals of the Rayleigh waves generated by the Indonesia earthquake (Fig. 4)
Since the Hokkaido earthquake occurred right at the arrivals of Rayleigh waves generated by the Indonesia earthquake, it is interesting to ask whether they occurred as a coincidence or the 2nd earthquake was associated with the dynamic stress carried by seismic waves by the 1st one

Summary

Introduction

The phenomenon of earthquake triggering is one of the most interesting subjects in seismological studies and can help researchers improve the understanding of how earthquakes occur and may mitigate potential seismic hazards in the future. The peak dynamic stresses carried by large surface waves greater than ~0.1 bar (~0.01 MPa) are capable of triggering micro-earthquakes or tremors at remote distances as far as 10000 km (Hill and Prejean 2007). A lower bound for dynamic stress of ~1 KPa has been suggested by the modulation between the Earth’s tides and the occurrence of crustal thrust earthquakes in convergent margins around the Pacific basin (Cochran et al 2004) and in Japan (Tanaka et al 2004) Such a lower bound or threshold for initiating an earthquake is consistent with laboratory results showing that cyclical stressing at 1 - 4 KPa level should modulate the occurrence of background seismicity (Lockner and Beeler 1999; Beeler and Lockner 2003). Tectonic characteristics at the triggered earthquake are discussed for understanding that one strong earthquake (M > 6) might be triggered by oscillatory surface waves generated by another event at remote distances

The 2008 Hokkaido and Indonesia Earthquakes

Temporal correlation between two earthquakes

Peak dynamic stress

Discussion

Conclusion