Imaging the Rivera and Cocos Plates below Jalisco and Michoacan Blocks from Seismicity Data

Abstract:

We review the local seismicity recorded by the project “Mapping the Riviera Subduction Zone” (MARS), a temporary seismic network that was installed in the states of Jalisco, Colima and Michoacán between January 2006 and June 2007, and the data collected by Jalisco Seismic and Accelerometric Network (RESAJ). We did a relocation of all MARS events using Hypo71 and the P-wave velocity model used by the RESAJ. The data comprise more than 2,000 earthquakes with local magnitude between 1.4 and 5.9 and depths between 1.0 and 109 km. Some crustal seismicity alignments are observed on the Jalisco Block. The geometry of the slabs is different; both are clearly separated beneath the Colima Graben. The Cocos plate, residing south of the graben, presents a typical flat slab dipping with an angle of about 21º extending eastward 200 km from the trench. Meanwhile, the more northerly Rivera plate exhibits a curvature or bend, possibly the result of an oblique suduction process, dipping from the trench with an angle of about 10º just south of Bahía Banderas to a dip angle of 25º at the Eastern contact with the Colima Graben. We have produced profiles parallel to the trench, in a profile along the shore line and a second one 50 km inland. A subduction dip angle of 12º towards the SE direction is observed in the Rivera plate in profiles inland from Bahia de Banderas to the Colima Graben, but the seismicity ceases to define the plate for more westerly profiles which enounter the graben.