Localized Fault Slip to the Trench in the 2010 Maule, Chile M­w = 8.8 Earthquake from Joint Inversion of High-Rate GPS, Teleseismic Body Waves, InSAR, and Tsunami Observations

Abstract:

The 27 February 2010, M_w 8.8 Maule earthquake ruptured ~500 km along the plate boundary offshore of central Chile between 34°S and 38.5°S. Intense ground shaking and large tsunami inundation combined to take more than 500 lives. The co-seismic slip distribution has previously been investigated using geodetic, seismic and tsunami observations, yielding consistent locations of the largest slip in a region extending from 34°S to 35.5°S. However, it remains uncertain whether co-seismic fault offset extended to the trench, which is important for interpreting both shallow frictional behavior and potential for tsunami earthquakes in the region. Joint inversion of high-rate GPS, teleseismic body waves, InSAR, and tsunami observations yields a kinematic rupture model with improved resolution of slip near the trench. Two up-dip large-slip (>15 m) patches are resolved along a bi-lateral rupture with relatively uniform 5-10 m slip down-dip beneath the coast. Both up-dip patches have significant slip in localized regions extending to the trench. The peak slip is ~22 m at a depth of ~15 km on the central megathrust, located ~200 km north from the hypocenter and overlapping the rupture zone of the 1928 M ~8 event. The slip decreases at shallower depth, but is still about ~20 m near the trench. The peak slip is ~15 m in a shallow near-trench patch located ~150 km southwest of the hypocenter. Checker-board resolution tests demonstrate that the tsunami data are critical to resolution of slip near the trench, with other data sets allowing, but not requiring slip far offshore. The stability of the joint inversion reduces the need for regularization. Larger events in the aftershock sequence have a complementary distribution to the co-seismic slip pattern, filling in gaps or outlining edges of large-slip zones. Two clusters of normal faulting events locate seaward along the plate motion direction from the localized regions of large near-trench slip, suggesting that proximity of slip to the trench enhanced extensional faulting in the underthrusting plate.