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

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 (Mw = 6.6) is capable of triggering another (Mw = 6.9) at a remote distance (~4750 km). On September 11, 2008, two strong earthquakes with magnitudes (Mw) 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