Slip distribution of the 2007 Bengkulu earthquake inferred from tsunami waveforms and InSAR data

Abstract

Joint inversion study using tsunami waveforms and InSAR data provides a new way to understand the magnitude and spatial extent of subduction zone earthquakes. A great earthquake (Mw 8.5) occurred on 12 September 2007 off the west coast of Bengkulu, Indonesia. The tsunami generated by the event was recorded by tide gauge stations around the Indian Ocean and by two bottom‐pressure sensors in the deep sea. The ground surface displacements produced by the earthquake on Pagai Islands and on Sumatra Island were observed by Interferometric Synthetic Aperture Radar (InSAR). We estimated the slip distribution of the earthquake by joint inversion incorporating a spatial smoothness constraint, using tsunami waveforms and InSAR data. The total released seismic moment calculated from the slip distribution is 6.7 × 1021 N m (Mw 8.5), consistent with the seismic moment of the Global CMT solution, 6.71 × 1021 N m. The maximum observed tsunami heights along the coast of Bengkulu agree with those computed from the slip distribution. The slip amount of the 2007 earthquake is smaller than the amount of potential slip that has been accumulated since after the 1797 and 1833 events. The premise is that, averaged over long periods of time, the entire fault must slip equal amounts. Therefore the 2007 great earthquake could be followed by several great earthquakes that will rupture the plate interface until the potential slip that has been accumulated is completely released.

Rupture Process of the 1969 and 1975 Kurile Earthquakes Estimated from Tsunami Waveform Analyses

“…In 2007, the Bengkulu earthquake occurred along the Sunda trench. Slip distribution of the 2007 Bengkulu earthquake was estimated using tsunami waveform data and InSAR data (Gusman et al 2010), and showed that the 2007 earthquake ruptured a deep part of the subducting plate. Subsequently, in 2010, the Mentawai tsunami earthquake occurred.…”

Randomly distributed unit sources to enhance optimization in tsunami waveform inversion

“…Without a smoothing constraint, the result of the tsunami waveform inversion might be bumpy and non-physical, especially for cases with high spatial resolution (Wu and Ho, 2011). In other studies on tsunami waveform inversion by Baba et al (2005) and Wu and Ho (2011), an equality constraint was imposed to maintain the smoothness of the inverted parameters to satisfy the long wave assumption, while by Saito et al (2010) and Gusman et al (2010) Figure 8. Scatter plots of each inversion method with respect to the waveforms of the target source at all gauges.…”

“…Therefore, both the uniqueness and the stability of solutions are sometimes difficult to attain without appropriate treatments. The most frequently employed techniques to maintain a stable solution is to use a smoothing constraint (Gusman et al, 2010(Gusman et al, , 2013Saito et al, 2010). Other than that, Koike et al (2003) suggested reducing the unknown parameters using the wavelet base to guarantee the uniqueness of the solution.…”

Interaction of Solid Earth, Atmosphere, and Ionosphere

“…They include the 2005 M w 8.6 Nias earthquake (Briggs et al, 2006) and the 2007 M w 8.5 Bengkulu earthquake (Gusman et al, 2010). Ionospheric disturbances by these earthquakes were studied by Cahyadi and Heki (2013) using a GPS network in Sumatra.…”