Mantle Structures between Guatemala and the Eastern USArray

Abstract:

While cratons are stable features based on their ages, they apparently can be disturbed by flattened slabs and hidden hotspots. When these slabs break up they provide a host of volatiles which interact with the old lithosphere producing complicated structures. These have been imaged by a host of techniques involving modeling regional waveforms and an assortment of tomography models. Here we test these models against a deep March 25^th, 2013 Guatemala event at a depth of 190 km, which produced an excellent set of TA record sections that provide dense sampling of the structure, spanning the ranges from 15 to 35 degrees. Because the structure in the southern Gulf of Mexico is uncertain, we first concentrated on deriving a pure-path model for this region. Both P and SH triplication data is well sampled by stations located in Florida from 13 degrees and beyond. The best fitting model is modified from the SH model ATL (Grand and Helmberger, 1984) with a P-model in Zhao and Helmberger (1993). These models contain a high-velocity lid structure along with a low-velocity gradient at depth. This allows the up-going S wave (direct) to remain the first arrival traveling in the fast lid to beyond 180 degrees. The modeling of the direct S along with the diving phases and depth phase triplications, pP, sP, sS allows for a well constrained model. This model ATLm and the earlier craton model CR along with mixture of the two are tested with the Cut-and-Paste (CAP) code on whole 3 component records. Over large paths of data produced by the southern US support the so-called X-phase arrivals which are produced by a 300 km transition. This feature breas down at large distance (>25 degree) along a northwest-southeast boundary. Data at larger distances indicate a complexity in the 660 transition which appears to be caused by a fast slab located at the top of the lower mantle. Variation in the EF-CD branches of pP and sP display changes of up to 5 s and sS up to 10 s, associated with the transition from CR to ATLm on the east coast.