Crustal Structure Across The Septentrional Region Of The Islas Marías Archipelago

Abstract:

The complex tectonic activity associated with the interaction of the Rivera and North American plates is clearly defined from Bahía de Banderas to the south, where the Mesoamerican Trench is the morphological expression of that convergence. However, there are not structural geological elements that indicate an active subduction north of Islas Marías Archipelago. During the spring of 2014, a geophysical experiment (Active stage of TsuJal project) was carried in order to clarify the shallow and deep structure of the Rivera plate - Jalisco Block contact zone and to be able to determine potential seismic and tsunamigenic sources. In this paper, we present the results of two seismic transects recording MCS and WAS data along the TS09 and RTSIM01b profiles, respectively, across the northern region of Islas Marías. These marine seismic lines are coincident with 110 km length for MCS and 240 km for WAS, and perpendicular to the coastline with SW-NE orientation. The seismic sources used in this work were provided by the RRS James Cook vessel and consisted of 12 guns with a volume of 5800 cu.in. every 120 s for WAS data and 3540 cu.in. every 50 m for MCS data. The MCS data were acquired with a 5.85 km length streamer, while the WAS data were recorded by a network of 4 OBS and 27 land seismic stations. After data processing and joint interpretation, it was possible to determine that shallow structure is mainly constituted by normal faults associated with graben structures forming sedimentary basins with non-deformed sediments in the basement. At the same time, the crust is 9 to 12 km depth in the oceanic region, while the continental crust reaches thicknesses of 18 to 21 km. The thickening towards the continent shows layers dipping between 6° and 8°.