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TitleOnshore/offshore structure of the northern Cascadia Subduction Zone obtained from bayesian receiver function inversion
AuthorBrillon, C; Cassidy, J F; Dosso, S E
SourceSeismological Research Letters vol. 83, no. 2, 2012 p. 1
Alt SeriesEarth Sciences Sector, Contribution Series 20120043
MeetingSeismological Society of America Annual Meeting; San Diego, CA; US; April 17-19, 2012
Mediapaper; on-line; digital
RelatedThis publication is related to Brillon, C; Cassidy, J F; Dosso, S E; (2012). Onshore/offshore structure of the northern Cascadia Subduction Zone obtained from bayesian receiver function inversion, SSA 2012 Annual Meeting Abstracts
File formatpdf
ProvinceWestern offshore region
AreaJuan de Fuca Ridge
Subjectsgeophysics; seismic interpretations; seismic zones; seismicity; seismology; earthquakes; earthquake risk; earthquake magnitudes; Cascadia subduction zone; NEPTUNE
ProgramTargeted Hazard Assessments in Western Canada, Public Safety Geoscience
AbstractThis study applies Bayesian inversion to receiver functions (RFs) to solve for local shear wave velocity (Vs) structure of the crust and upper mantle beneath the northern Cascadia subduction zone at four sites from the Juan de Fuca Ridge (JdFR) to Vancouver Island, B.C.. We use passive seismic data recorded on NC89, a permanent NEPTUNE (North-East Pacific Time-series Undersea Networked Experiments) ocean bottom seismometer (OBS) located on the continental slope, and a temporary autonomous KECK foundation OBS, KEBB, located on the Endeavour segment of the JdFR. The two land based seismometers (OZB and PGC) are located on Vancouver Island and are part of the Canadian National Seismograph Network (CNSN). The introduction of NEPTUNE has helped to fill a gap in offshore seismic monitoring. However, due to high noise levels, few events are useful (to date) for RF analysis. In this study, we utilize three-component, broadband recordings of large (M6+), distant (30°-100°) earthquakes to compute RFs due to locally generated P to S converted waves. RFs are then inverted using a non-linear Bayesian approach which yields optimal Vs, Vp, strike and dip profiles, as well as rigorous uncertainty estimates of these parameters. Near the JdFR a thin sediment layer (<1km) overlying the oceanic crust containing a large velocity contrast at the depth of an expected axial magma chamber was resolved. The oceanic crust thickens to ~10km at the continental slope where it is overlain by ~5km of sediments. At the coastal station a low velocity zone is imaged at ~16km depth dipping approximately 12° NE. Evidence for this low velocity zone is also seen beneath southern Vancouver Island at a depth consistent with previous studies. Determining such models at a number of locations (from the spreading ridge to the coast) will provide new information regarding local structure and aid in hazard analysis.