Crustal deformation in the Western Solomon Islands revealed by GPS observation and D_InSAR during 2009 - 2013

The Solomon Islands are located in the southwestern Pacific, where the Australian Plate underthrusts the Solomon Plate towards ~N70 E at a rate of ~100 mm/yr. The Coleman seamount on the Australian plate is impinging on the forearc at Rendova Island and may cause both the seismicity and tectonic behavior to be more complicated than usual. Hence, an understanding o f the ongoing crustal deformation is essential to reconstructing the structural framework that controls the entire subduction system, particularly earthquake generation on the megathrust fault and possible subsidiary faults. Based on the results from GPS and D_InSAR, the horizontal velocity profiles across the trench for areas of the forearc to the west and to the east of the impinging Coleman seamount show different characteristics. The eastern profile shows convergence rates of ~100 mm/yr only 10 km from the trench at the western end of the Tetepare Island, and the western profile reaches 70 mm/yr at 30 km from the trench. This difference might be caused by the shallow locked depth consistent with co-seismic slip located extremely close to the trench during the Mw 7.1 Solomon Earthquake on 3rd January, 2010. We have a hypothesis to argue that the behavior of the fault geometry should be very different on the two sides of the seamount. However, the coupling ratio could be realized by further detailed analysis.