In the aftermath of the catastrophic M8.8 earthquake in Chile there is an urgent need to record aftershocks and capture ephemeral data that will help to assess both short term (immediate) and long term earthquake risk in the region and elsewhere. Reliable models of strain accumulation and seismogenic release along the fault zone, and improved tsunami models for the Pacific basin, are urgently needed. U.S. teams are already on the ground onshore, and another team is preparing to deploy a suite of ocean bottom seismometers offshore. The February 27th mainshock ruptured a 300 km long segment of the Peru-Chile subduction zone that borders South America, causing ground displacements of as much as 7 meters. This bathymetric survey of the offshore portion of the main rupture zone and the deployment of four highly sensitive pressure gauges to record vertical motions will complement efforts to document the surface effects and possible earthquake hazards, such as tsunamis. The principal broader impact of this study is its very high and immediate societal relevance.
On 27 February 2010, a magnitude 8.8 earthquake occurred offshore Maule, Chile. Initial estimates indicate a rupture extending approximately 500 km along the coast with slips on the deep fault of several meters. The R/V Melville was in the area working and its schedule permitted an 8?day leg to explore the submerged slope and trench above the rupture. From 17-25 March 2010, we conducted multibeam swath sonar survey and deployed four vertical geodetic sensors. We surveyed the seafloor from 37.5 S to 34.0 S from just seaward of the trench axis (~5200 m deep) to approximately 50 km landward (~ 1000 m deep) and up several canyons offshore river outlets (~100 m deep). The post?event Melville survey was compared with pre?event multibeam surveys collected by German and British research teams. Looking for changes between the pre- and post-event bathymetry were attempted to address: (i) add a submarine component to onshore assessments of surficial geologic effects of this major thrust event; (ii) clarify the relative importance for tsunami generation of co-seismic uplift and multiple (?) ground-shaken slope failures; and (iii) help selection of optimal sites for future seabed instrument arrays for monitoring post-thrusting activity (e.g., seabed geodesy, microseismicity, fluid flow, etc). The initial findings indicate that submarine landslides deeper than 1000 m played little if any role in the generation of tsunami offshore Chile due to the 27 Feb. 2010 EQ. Time constrains did not permit surveying significant portions of the seafloor shallower than 1000 m.
