Crust and Mantle Anisotropy Variations from the Coast to Inland In Central and Southern Mexico

Abstract:

We examine radial and tangential receiver functions (RFs) obtained along the Meso America Subduction Experiment (MASE), a profile from the Pacific coast in central-southern Mexico to the Gulf of Mexico. Tangential RFs show waveform variations in timing and polarity, both in the Moho and the slab Ps phases in function of its backazimuth; also, radial RFs show arrivals timing variation; all of which suggests a non-homogeneous horizontal layer medium. Using a particle motion analysis and a cross-correlation procedure, we are able to quantify the shear wave splitting in the continental crust, the subducted oceanic crust and the mantle below each station of the array in terms of a time delay, and a fast azimuth direction. From these variations, we distinguish between three major regions: 1) dipping subducted slab, 2) horizontal subducted slab, 3) absence of subducted slab. Results for region 1 are consistent with the geometry of the Cocos plate previously determined by other studies, showing a minimum energy content in the tangential RFs for the NE-SW geographic quadrants. In region 2, we identify a strong azimuthal dependence with a variable periodicity of 180° and 360° as well as the existence of “split” Ps phases in our data, possibly related to the presence of fluids and the ultra low velocity layer (ULVL) localized between the continental and oceanic crust. We compare these results with previous silent earthquakes (SSE) and non-volcanic tremors (NVT) studies in the area.