Constraining the Oceanic Lithosphere Seismogenic Zone Using Teleseismic Relocations of the 2012 Wharton Basin Great Earthquake Sequence

摘要

The great 2012 M_w 8.6 strike-slip earthquake beneath the Wharton Basin generated a complex aftershock sequence that maps onto a system of conjugate faults. Analysis of high-precision aftershock locations with improved depth constraint is used here to characterize the seismogenic limits of the oceanic lithosphere. The study presents teleseismic double-difference earthquake relocation results for 695 events in and around the 2012 Wharton Basin intraplate earthquake sequence. We highlight seven major clusters of seismicity and show that the 2012 earthquake sequence ruptured in the oceanic crust and upper mantle. The refined aftershock locations projected onto available mainshock finite-fault models show that aftershocks occur outside the largest coseismic slip region and tend to cluster in low slip areas, a pattern commonly seen for large continental and megathrust sequences. For events with depth phases, the relocated focal depths generally correspond to predicted depths from pP-P time observations. Reported pP-P observations for intraplate events correspond to depths ranging from ~5 to 35-40 km, such that the deepest events occur within the expected limit of brittle seismic failure at 600 °C, here defined by a half-space cooling model of the region. The 74 low magnitude events in our catalog that locate below the 600 °C isotherm do not have consistent depth phase observations and cannot be interpreted as strong evidence of rupture into the ductile regime. The refined double-difference catalog supports that, along with deep coseismic rupture, moderate-sized earthquakes ruptured across the full extent of the elastic oceanic lithosphere in the Wharton Basin.