Modeling coseismic slip of the 2012 Nicoya Peninsula earthquake, Costa Rica : roles of megathrust geometry and surface displacement

Geomorphic and geodetic measurements of coseismic surface displacement due to the reported MW=7.6 2012 Nicoya earthquake are unprecedented datasets due to their location so near to the region of subduction zone slip (Protti et al. 2014). This unique situation presents an opportunity for an in-depth analysis of the plate interface geometry on which the earthquake occurred, and the surface displacement measurements constraining coseismic slip estimations. A strike-and-dip variant surface Geometry S (Hayes et al., 2012) is compared to two dipvariant segmented planes used in published analyses of the 2012 earthquake (Yue et al., 2013; Protti et al., 2014). Coseismic slip estimated on Geometry S yielded a MW=7.7 earthquake, producing 1.3x more moment than the published values. This is consistent with the depth contrast between Geometry S and the segmented planes, where the deeper surface geometry requires more slip to predict an equivalent amount of surface displacement. This result presents the possibility that the 2012 Nicoya Peninsula earthquake was larger than originally estimated, which has relevance to future earthquake hazards and signifies the importance of considering the true geometry of the plate interface when estimating earthquake slip from surface displacement data. Densely spaced geomorphic measurements of coseismic vertical displacement were taken along the SW coast of the Nicoya Peninsula, revealing local heterogeneities in deformation not captured by the sparser geodetic data. In addition to the spacing difference, a consistent disparity in vertical displacement of ~15 cm exists between the larger geomorphic to geodetic irecords. The vertical displacements predicted by the estimated slip distributions fit the geomorphic data significantly better than the discrepancy between measurement techniques, both in the context of spatial distribution and magnitude. This signifies that the slip distribution models can successfully fit local heterogeneities revealed by an independent dataset. A brief postseismic analysis is also performed, comparing preliminary results of geomorphic and geodetic measurements. This research has relevance to both Nicoya seismicity and earthquake research worldwide, as large-scale and interdisciplinary analysis of these unprecedented data provides novel insight into how we model earthquakes and analyze their hazards