Abstract
Most of the recent published geodetic models of the 2010 Maule, Chile mega-thrust earthquake (Mw=8.8) show a pronounced slip maximum of 15-20 m offshore Iloca (~35°S), indicating that co-seismic slip was largest north of the epicenter of the earthquake rupture area. A secondary slip maximum 8-10 m appears south of the epicenter west of the Arauco Peninsula. During the first weeks following the main shock and seaward of the main slip maximum, an outer rise seismic cluster of >450 events, mainly extensional, with magnitudes Mw=4-6 was formed. In contrast, the outer rise located seaward of the secondary slip maximum presents little seismicity. This observation suggests that outer rise seismicity following the Maule earthquake is strongly correlated with the heterogeneous coseismic slip distribution of the main megathrust event. In particular, the formation of the outer-rise seismic cluster in the north, which spatially correlates with the main maximum slip, is likely linked to strong extensional stresses transfered from the large slip of the subducting oceanic plate. In addition, high resolution bathymetric data reveals that bending-related faulting is more intense seaward of the main maximum slip, where well developed extensional faults strike parallel to the trench axis. Also published seismic constraints reveal reduced P-wave velocities in the uppermost mantle at the trench-outer rise region (7.5-7.8 km/s), which suggest serpentinization of the uppermost mantle. Seawater percolation up to mantle depths is likely driven by bending related-faulting at the outer rise. Water percolation into the upper mantle is expected to be more efficient during the co-seismic and early post-seismic periods of large megathrust earthquakes when intense extensional faulting of the oceanic lithosphere facilitates water infiltration seaward of the trench.
Highlights
IntroductionThe occurrence of megathrust earthquakes has a profound impact on the regional intraplate stresses in the vicinity of the rupture area
The outer rise located seaward of the secondary slip maximum presents little seismicity. This observation suggests that outer rise seismicity following the Maule earthquake is strongly correlated with the heterogeneous coseismic slip distribution of the main megathrust event
The occurrence of megathrust earthquakes has a profound impact on the regional intraplate stresses in the vicinity of the rupture area
Summary
The occurrence of megathrust earthquakes has a profound impact on the regional intraplate stresses in the vicinity of the rupture area. The rupture area of this megathrust event is characterized by two regions of high co-seismic slip (asperities) (Delouis et al, 2010; Lay et al, 2010; Lorito et al, 2011; Pollitz et al, 2011). Between these asperities, the rupture bridged a zone that was creeping interseismically with consistently low co-seismic slip. Our observations, based on available data, provide new insights in how the occurrence of a megathrust event affects the stress regime in the outer rise area, and how this is closely related to the hydration process of the upper oceanic lithosphere
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