Seismogenesis of megathrust earthquakes at the Costa Rican erosive continental margin

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The Mw=9.0 2011 Tohoku earthquake ruptured an erosive continental margin and reached unexpectedly the trench axis. Our current understanding is thus challenged as the material and thrust fault properties should have caused a negative stress drop, stopping rupture well landward of the trench. In 2002 the Mw=6.4 Osa earthquake may have shown a similar behavior offshore of Costa Rica. However, global event localization is associated with too large errors and temperature estimates – critical to assess the frictional state of the megathrust – suffer from uncertainties related to the thermal properties of the upper plate. We will use a unique suite of available local seismological data from the rupture area of the Osa earthquake and determine a 3-D velocity model that will allow us to yield precise source parameters of the main and aftershocks that can be rated against structural information from seismic surveying and drilling. Further, the Costa Rica Seismogenesis Project (CRISP) was designed to study the processes that control nucleation and seismic rupture propagation of large earthquakes at erosive subduction zones and IODP drilling provides with last year’s leg 334 and this year’s leg 344 unique data to constraint the thermal structure of the seismogenic zone. The seismological data will be interpreted jointly with thermal and drilling data from both IODP drilling expeditions to refine the link between temperature and seismogenesis at erosive convergent margins.