DEFORMATION ASSOCIATED WITH THE MW 8.8 2010 MAULE, CHILE EARTHQUAKE

The Maule earthquake of February 27 2010 affected about 500 km of the Nazca-South America plate boundary in south-central Chile producing spectacular tectonic deformation and a devastating tsunami. A compilation of pre-, co-, and post-earthquake geologic and geodetic data offers the opportunity of gain insight into the processes that controlled strain accumulation and release associated to this megathrust event. We inverted 160 GPS vectors together with InSAR and coastal land-level change data to obtain the distribution of coseismic megathrust slip using a Finite-Element model with a realistic geometry adapted from geophysical images. Slip was segmented in two main patches with up to 15 m of slip breached by an area with less than 10 m of slip. The northern patch was larger and accounted for 10 m of slip at the trench, which may have boosted the tsunami. The southern patch surrounded the Arauco Peninsula, a region of high Quaternary uplift rates, and overlapped with slip during the 1960 event of Mw 9.5. Coastal uplift of up to 2.5 m was measured in this region. We find that the area limiting the two patches of high slip is correlated with an inflection along strike of the megathrust; these two patches also exhibited high plate coupling rate prior to the Maule event. This correlation suggests that plate geometry may strongly influence strain accumulation and release. The segment boundary between the 2010 and 1960 events is an area of lower slab dip, high topography, and coincident with a major crustal-scale splay fault system. Though still speculative, we suggest that this geometrical boundary may account for the segment boundary. At Isla Santa Maria, north of Arauco, we observed the surface rupture of a series of normal faults. Surface breaks were also observed on side-scan sonar data near the coast of the island. Additionally, space and land geodesy suggest steep trench-parallel co-seismic tilting of the island. We associate both tilt and normal faulting to growth of a reverse-fault cored anticline, imaged by seismic reflection profiles below the island. Fault rupture occurred within the 2.5 hours following the mainshock, and was accompanied by the outflow of a minimum of 20000 m3 of fluids along the fault zone. The Maule event offered the opportunity to explore various processes associated to megathrust earthquakes.