Ps receiver function imaging of crustal structure and Moho topography beneath the Northeast Caribbean

Abstract:

Due to its tectonic history, the Caribbean plate contains complex fault systems that are likely to have disrupted the Moho. To study the region's subsurface structure we computed a 3D image of the Northeast Caribbean via “velocity analysis” with Ps receiver functions. In this technique we simultaneously find, via an optimization procedure, depths to major discontinuities (in this case the Moho) and P and S velocity profiles beneath each seismic station. Ps receiver functions are time series computed from three-component seismograms that identify waves converted from P- to S-type at velocity discontinuities, such as the Moho and subducting lithosphere.

Data were requested from the IRIS Data Management Center for events that occurred in the 2005-15 time period with magnitudes of 5.5-8.0 and epicentral distances of 30°-95° from stations in the study region. Data pre-processing steps include tapering, removing the trend and mean, and rotating from Z-N-E to L-Q-T (ray-based) coordinate systems. Ps receiver functions were then computed via iterative deconvolution in the time domain and the best receiver functions were stacked and modeled to generate a 3D image of the subsurface. Shear velocity profiles for each station are varied in a procedure, driven by simulated annealing, that seeks to optimize the correlation of a target feature—in this case the Moho—in the set of pre-processed Ps receiver functions. This procedure is feasible only when station spacing is relatively dense, which limits its success in this region to the islands of Puerto Rico and Hispaniola. Individual receiver functions were computed for isolated stations in the NE Caribbean, as well, but velocity analysis is limited to the two islands that have the densest station coverage.

Moho depths beneath Puerto Rico range from 24 km, in the north, to 37 km, in the south. Moho depths beneath Hispaniola range from 23 km to 36 km but exhibit a more complex pattern of variation than beneath Puerto Rico, with the Moho generally shallower in the east, deepening in central and western Dominican Republic, and shallowing again in the southwest, although values beneath Haiti are poorly constrained. The interpretation of the images places constraints on the structure of the subsurface and may elucidate the causes and styles of deformation occurring in the region.