Triggered tremor and slow slip in the Western Solomon Islands

Abstract:

Slow slip events are often accompanied by an emergent and long-duration seismic signal called tectonic tremor, keeping pace with the slow slip event. In some cases, tectonic tremor can also be triggered in fault zones during the passing of surface waves from distant events. Since the presence of tectonic tremor may indicate the frictional transition between areas that typically undergo steady aseismic sliding and large megathrust earthquakes, identifying tectonic tremor in various locations allows us to possibly forecast future earthquake rupture areas. The Western Solomon Islands are unique amongst the subduction zones of the world due to islands directly overlying the shallowest part of the plate interface. For example, two islands that are ~8 km apart straddle the trench and most of the larger islands are closer to the trench than any other subduction zone in the world. In 2007, an Mw 8.1 earthquake ruptured across a triple junction, all the way out to the trench. This unique shallow coupling is plausibly the result of young (~5 Ma) subducting oceanic crust. Since early 2000, colleagues from the National Taiwan University, Academica Sinica, the University of Texas at Austin, and Ohio State University have operated a few continuous GPS stations in the Western Solomon Islands, which was augmented in 2009 to include 10 GPS and 7 seismic stations. Our preliminary results suggest evidence for triggering of tectonic tremor for a few large, distant earthquakes. In addition, GPS results indicate a major slow slip event occurring in 2001 and possibly other minor ones. For this contribution, we will report on our systematic search for triggered tremor in the Western Solomon Islands. Since this area is possibly an end-member amongst subduction zones with respect to its relatively shallow coupling, the presence of triggered tectonic tremor here suggests that slow slip processes are indeed ubiquitous.