Analysis of afterslip distribution following the 2007 September 12 southern Sumatra earthquake using poroelastic and viscoelastic media

作者：Lubis Ashar Muda^*; Hashima Akinori; Sato Toshinori

来源：Geophysical Journal International, 2013, 192(1): 18-37.

DOI：10.1093/gji/ggs020

• Inverse theory
• Space geodetic surveys
• Subduction zone processes
• Dynamics and mechanics of faulting
• Rheology: crust and lithosphere
• Rheology: mantle

Most studies of afterslip distribution consider only elastic media. However, the effects of poroelastic rebound in the upper crust and viscoelastic relaxation in the asthenosphere are part of the observed post-seismic deformation. Therefore, these effects should be removed to give a more reliable and correct afterslip distribution. We developed a method for calculating an afterslip distribution in elastic, poroelastic and viscoelastic media, and we applied this method to the case of the 2007 southern Sumatra earthquake (M-w 8.5). To estimate the coseismic slip and time evolution of the afterslip distribution, we applied Akaike%26apos;s Bayesian Information Criterion (ABIC) inversion method of coseismic displacement, and analysed 15 months of GPS post-seismic deformation data in 3-month observation periods. To calculate afterslip in each period, we considered not only viscoelastic responses to coseismic slip but also viscoelastic responses to afterslip in the preceding periods. We used viscoelastic model to compute post-seismic deformation models every 3 months during the 15 months after the earthquake. The viscosity value for the asthenosphere layer is a crucial unknown parameter. To overcome this problem, we used a grid search method to determine the best-viscosity value, and we found that the best viscosity for the Sumatra subduction zone was 2.5 x 10(18) Pa.s. After removing the poroelastic and viscoelastic responses, we obtained maximum afterslip of 0.5 m during the 15-month investigation (the same as maximum afterslip estimated using the elastic medium only), but the poroelastic and viscoelastic responses brought the afterslip distribution to a shallower depth than the main coseismic rupture area. The results showed that the poroelastic and viscoelastic responses added significant corrections to the afterslip distribution. Compared with the traditional method, this method improved the determination of the afterslip distribution. We conclude that consideration of poroelastic and viscoelastic behaviours is essential for calculating the afterslip distribution. We propose that these parameters should be considered to obtain more reliable and correct afterslip distribution models following earthquakes.

• 出版日期2013-1