Seismic array constraints on the D discontinuity beneath Central America

We analyzed 16,150 transverse component seismic recordings from 54 deep-focus earthquakes in the South American and Caribbean regions recorded at broadband stations in North America between 2005 and 2012. We treated subgroups of seismic stations within 3 degrees radius geographical bins as seismic arrays and performed vespagram analysis. We focused on the S, ScS, and Scd arrivals and collected data in the epicentral distance range from 55 degrees to 90 degrees. In particular, we searched for D. discontinuity presence in the vespagrams in a 25 degrees by 35 degrees (or 1520 by 2130 km) area beneath Central America. Analysis of these data showed 125 clear Scd observations, 180 Scd observations of lesser quality, and 343 nonobservations. We produced a new map of the discontinuity height beneath Central America. Our map shows an average discontinuity height of 286 +/- 6 km (sigma = 76 km). The region is punctuated by a large topographic high centered at approximately 10 degrees N and 90 degrees W with a maximum height of 380 km. Two smaller topographic highs are located at approximately 4 degrees N and 81 degrees W (discontinuity height of 320 km) and at 4 degrees N and 70 degrees W (height of 315 km). The observation of multiple Scd arrivals collocated with the strongest gradients in inferred topography provides evidence for topographic variation on the discontinuity rather than multiple discontinuities. The regions where the discontinuity has the greatest height can be explained by localized enrichment of mid-ocean ridge basalt from the subducted Farallon slab impinging on the core-mantle boundary.