Slow Slip Events on the Strike Slip Fault in Guerrero, Mexico

Abstract:

The secular GPS velocity vectors in the Pacific coast of Mexico are oblique to the Middle America trench (MAT). The along-trench, lateral velocity components abruptly diminish to the north by 4-5 mm/year across the area of La Venta-Chacalapa fault zone (LVC), which is striking at ~105 km inland from the MAT along the Pacific coast of Guerrero and Oaxaca states for almost 650 km. This velocity slump reveals a partitioning of the oblique convergence between the Cocos and North America plates with a sinistral motion of the Xolapa forearc sliver.

GPS displacement records in Guerrero provide clear evidence that the left lateral dislocation on the LVC fault occurs mainly during periodic episodes of strike-slip slow slip (sSSE), which coincide in time and duration with large thrust slow slip events on the subduction interface (tSSE). In the inter-SSE periods (~3 years) the LVC fault is locked, and the shear strain rate distributed across it remains constant at ~14 nrad/year. During the tSSEs, which happen about every 4 years in Guerrero, there is a noticeable increase of lateral sinistral displacement of the GPS stations located on the coast, south of the fault. Meanwhile the stations to the north off the LVC undergo minor dextral displacements. The secular shear train rate drastically changes across the fault from 64 nrad/year south of it to 11 nrad/year to the north. This means that the LVC fault is currently active but the slow accumulation of shear strain on it is periodically interrupted with sSSEs, which are highly synchronized with the subduction type tSSEs. This study was supported by PAPIIT IN110514 grant.