Migration of seismic activity in strike-slip zones: A case study of the boundary between the North American and pacific plates

Abstract

The results of computer visualization of the spatiotemporal distribution of the total earthquake energy for the instrumental period are presented. This visualization was implemented to determine the parameters of slow earthquake migrations (of a few kilometers to a few hundreds of kilometers per year) in strike-slip zones. A case study of the San Andreas and Mendocino fault zones referring to the boundary between the North American and Pacific plates is considered. The obtained results are compared with the migration peculiarities revealed for the structures under other geodynamical conditions, in particular those in Trans-Bakalia. The spatiotemporal analysis is carried out with the use of strong, moderate, and weak events. Migration episodes are detected in the seismic data projection zones constructed for epicenter concentrations at the Mendocino triple junction, at the junction of the San Andreas and Calaveras faults, the Santa Monica and San Gabriel ones, and the Camp Rock Fault Zone; these areas host the strongest earthquakes of the instrumental period. Migration in these zones is manifested as a phenomena both preceding and following the seismic events and can reflect the dynamics of the stress redistribution in the zone of interaction between tectonic structures. The calculated migration rates vary from 7 ± 2 to 250 ± 50 km/yr. It is concluded that there is no dependence of the seismic activity migration on the geodynamical type of the fault zones, because similar rates (10–70 km/yr) are reported for the Mendocino and San Andreas faults and the Baikal Rift System. The migration rates for the Mendocino and San Andreas, exceeding 70 km/yr, are likely caused by a high rate of the interplate displacements, which is higher than that in the Baikal Rift System by more than an order. The extent of the seismoactive segments of faults zones along which migration episodes were detected is from 20 to 70 km. The results of the mutual correlation analysis of time series carried out for such parameters as the earthquake numbers and earthquake energy suggest that migrations are caused by local geodynamical conditions affecting the seismicity on the scale of zones where large segments of fault zone interact with each other.