The Mw8.8 2010 Maule, Chile Earthquake: Significant slip occurred only above the continental Moho

Radar interferometry from the ALOS satellite captured the coseismic ground deformation associated with the 2010 Mw 8.8 Maule, Chile earthquake. We processed the ALOS interferograms with our newly developed GMTSAR software. The ScanSAR to stripe mode and the ScanSAR to ScanSAR interferograms along the descending orbits are critical to recover a nearly complete deformation field. The fringe patterns of the coseismic interferograms are diagnostic of the downdip rupture limit of the Maule earthquake. Nine tracks of the stripe mode ascending interferograms reveal a sharp transition from high fringe rate to low fringe rate at ~150 km from the trench axis. The descending interferograms exhibit a trough at the similar location. An elastic dislocation model based on both ascending and descending ALOS interferograms and near-field 3-components GPS measurements shows that the coseismic slip decreases rapidly from a maximum of 17 m (average of 6.5 m) at 18 km depth to approximately zero at 43-48 km depth, quantitatively indicating the downdip limit of the seismogenic zone. The depth at which slip drops to near-zero appears to be at the intersection of the subducting plate with the continental Moho. Our model also suggests that the depth where coseismic slip vanishes is almost uniform in strike direction for a rupture length of ~600 km. We are investigating the effects of the layered velocity models in the slip-depth estimation of the Maule earthquake. The inferred slip-depth distributions from the Maule earthquake and past megathrust earthquakes over subduction zones might assist a reevaluation on different mechanisms that control the seismic coupling.