Geophysical studies across Rivera Plate and Jalisco Block, Mexico: TsuJal Project

Abstract

In the spring of 2014, an onshore–offshore geophysical experiment (“Crustal Characterization of the Rivera plate–Jalisco Block Boundary and Its Implications for Seismic and Tsunami Hazard Assessment”) was carried out in the frame of the TsuJal project to define the crustal architecture of the western Mexican active margin and identify potential structural sources that can trigger earthquakes and tsunamis at the convergence between the Rivera plate (RP) and the Jalisco Block (JB) within the North American plate. In this work, we present the preliminary results about bathymetric, structural geology, and wide‐angle seismic data of the southern coast of Bahía de Banderas. These data indicate the slab thickness in this area is about 10 km and presents a dip angle of about 8°. Continental crustal thickness below Puerto Vallarta is about 20 km, but no evidences of continental Moho and clear subduction features (trench, accretionary prism) are observed. Nevertheless, this model supports the hypothesis that the region of Bahía de Banderas is under strong crustal stresses generating structural lineaments with the same trends offshore and inland due to the convergence of the RP against the JB. Most of the seismicity reported can be associated with the main structural lineaments. Moreover, the Banderas Canyon (BC) is apparently in an eastward opening process, which seems to continue through the Rio Pitillal river valley; no seismic or morphological evidences were found to suggest the BC is a continuation of the Vallarta graben. Offshore, the Sierra de Cleofas, located south of María Cleofas Island, marks the limit between the RP and the JB along 100 km. It may be the result of the RP pushing against the JB establishing the beginning of the current subduction process, with associated seismic activity. If a subduction type earthquake occurs in this area, the associated magnitude will be about 7.5 and could have a tsunamigenic effect.