GPS-derived interseismic fault locking along the Jalisco–Colima segment of the Mexico subduction zone

Abstract

Summary Northeastward subduction of the oceanic Rivera and Cocos plates in western Mexico poses a poorly understood seismic hazard to the overlying areas of the North America plate. We estimate the magnitude and distribution of interseismic locking along the northern ∼500 km of the Mexico subduction zone, with a series of elastic half-space inversions that optimize the fits to the velocities of 57 GPS stations in western Mexico. All velocities were corrected for the coseismic, afterslip and viscoelastic rebound effects of the 1995 Colima-Jalisco and 2003 Tecomán earthquakes. We explore the robustness of interseismic locking estimates to a variety of mantle Maxwell times that are required for the viscoelastic corrections, to the maximum permitted depth for locking of the subduction interface, and to the location assigned to the Rivera-Cocos-North America plate triple junction offshore from western Mexico. The best fitting locking solutions are associated with a maximum locking depth of 40 km, a triple junction location ∼50 km northwest of the Manzanillo Trough, and a mantle Maxwell time of 15 yr (viscosity of 2 × 1019 Pa·s). Checkerboard tests show that the locking distribution is best resolved at intermediate depths (10-40 km). All of our inversions define a gradual transition from strong locking (i.e. 70-100 percent) of most (70%) of the Rivera-North America subduction interface to strong but less uniform locking below the Manzanillo Trough, where oceanic lithosphere transitional between the Cocos and Rivera plate subducts, to weak to moderate locking (averaging 55 percent) of the Michoacán segment of the Cocos-North America interface. Strong locking of the ∼125-km-long trench segment offshore from Puerto Vallarta and other developed coastal areas, where our modelling indicates an average annual elastic slip-rate deficit of ∼20 mm yr−1, implies that ∼1.8 m of unrelieved plate slip has accrued since the segment last ruptured in 1932, sufficient for a M ∼ 8.0 earthquake.

Analysis of the Current Dynamic of the Jalisco Block, Mexico through GNSS Observations

“…Likewise, the stations located in the south-southeast zone and in the coastal zone present the highest velocities, with values ranging from 6.29 to 10.81 mm/year, while the stations located to the north-northwest, near the Tepic-Zacoalco rift present values of approximately 3.0 mm/year (Figure 2). On the other hand, in the central zone of the Jalisco Block, a decrease in velocity was observed at station G, which could be related to a blockage of the Rivera plate at the subduction interface proposed by Cosenza-Muralles et al [20] in this zone. The velocities obtained in our study suggest a counterclockwise rotation of the JB, with a preferential direction towards north-northwest in most stations, which agrees with the subduction direction estimated by the Rivera plate movement model proposed by DeMets et al [21].…”

“…Considering the information presented above, the ground velocity shortening observed near station G could be related to the blocking zone observed at the subduction interface in this same region [20], which would indicate that it is observing a deformation within the JB due to the coupling between the Rivera plates and said block.…”

Co-seismic and post-seismic deformation for the 1995 Colima–Jalisco and 2003 Tecomán thrust earthquakes, Mexico subduction zone, from modelling of GPS data

“…We also estimate the long-term velocities of all the GPS sites fully corrected for the co-seismic and post-seismic effects of the 1995 and 2003 earthquakes. In the second part of our study we invert the new velocities to estimate interseismic locking along the JCSZ and hence its seismic hazard (Cosenza-Muralles et al 2021). Hereafter, we refer to the secondstage study as CM21-II.…”