15:30 〜 16:30
[J06-P-18] Trench-parallel sliver motion in the Mexican oblique subduction zone
Large, equivalent to Mw~7.5, subduction thrust slow slip events (tSSE) in Guerrero, Mexico have a period of ~4years. The secular GPS velocity vectors are oblique to the Middle America trench (MAT). The lateral velocity components abruptly diminish to the north by 4-5mm/year across La Venta-Chacalapa fault zone (LVC), striking along the Pacific coast of Guerrero and Oaxaca for ~650km. 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.
Long-term GPS records show that the tSSEs are accompanied by strike-slip SSEs (sSSE) on
the LVC fault. GPS displacement records in Guerrero reveal that during the interSSE periods (~3 years) the LVC fault is mainly locked, and the shear strain rate across it remains constant at ~14nrad/year. During the tSSE there is an increase of lateral sinistral displacement of the GPS stations on the coast, south of the fault while the stations to the north off the LVC undergo minor dextral displacements. The secular shear strain rate drastically changes across the fault from 64 nrad/year south of it to 11nrad/year to the north. The LVC fault is currently active but the slow accumulation of shear strain on it is periodically interrupted by sSSEs highly synchronized with the tSSEs.
According to the analysis of thrust events from local catalogs slip vectors lay between the vectors of plate convergence and trench normal. Obliquity of thrust slip vectors (1-5') grows southward along the coast. The oblique subduction motion is partitioned into trench parallel displacement along LVC fault zone at the rate of ~8mm/yr. Secular trench parallel velocity calculated from GPS data is ~6.5mm/yr. Slower motion at the surface (GPS) compared to the subduction interface (thrust events) may be due to the properties of the media.
Long-term GPS records show that the tSSEs are accompanied by strike-slip SSEs (sSSE) on
the LVC fault. GPS displacement records in Guerrero reveal that during the interSSE periods (~3 years) the LVC fault is mainly locked, and the shear strain rate across it remains constant at ~14nrad/year. During the tSSE there is an increase of lateral sinistral displacement of the GPS stations on the coast, south of the fault while the stations to the north off the LVC undergo minor dextral displacements. The secular shear strain rate drastically changes across the fault from 64 nrad/year south of it to 11nrad/year to the north. The LVC fault is currently active but the slow accumulation of shear strain on it is periodically interrupted by sSSEs highly synchronized with the tSSEs.
According to the analysis of thrust events from local catalogs slip vectors lay between the vectors of plate convergence and trench normal. Obliquity of thrust slip vectors (1-5') grows southward along the coast. The oblique subduction motion is partitioned into trench parallel displacement along LVC fault zone at the rate of ~8mm/yr. Secular trench parallel velocity calculated from GPS data is ~6.5mm/yr. Slower motion at the surface (GPS) compared to the subduction interface (thrust events) may be due to the properties of the media.