Multiple-event relocation of historic earthquakes along Blanco Transform Fault Zone, NE Pacific

Abstract

Blanco Transform Fault Zone (BTFZ) is part of the Juan de Fuca Ridge system located ∼200-500 km west of the Oregon coastline. Individually located epicenters reported by the International Seismological Center (ISC) and National Earthquake Information Center along the BTFZ are not well correlated spatially with the activetransform boundary. More accurate locations of 120 mb ≥ 5.0 earthquakes relative to each other have been obtained using a joint-relocation process that yields improved epicenter locations relative to each other. Six of these earthquakes have been independently located using data from the U.S. Navy's SOSUS hydrophone array, enabling specification of a static correction to improve absolute locations for all 120 relocated epicenters relative to the BTFZ. The final locations average ∼34.6 ± 15.2 km toward azimuth 196° ± 28° relative to the original ISC locations. The 95% confidence ellipses of most of the relocated epicenters fall on or very near active structural features along the BTFZ.