Collaborative Research: Inferences on Cascadia Deformation Front and Plate Interface Properties from Advanced Studies of Active Source Seismic Data
DESCRIPTION: This grant is supporting analysis of previously acquired marine seismic data to investigate properties of the shallow megathrust at the Cascadia subduction zone. Our project includes advanced studies of the basal sediment section and top oceanic crust just seaward of the deformation front spanning two contrasting regions, one offshore central Oregon that may currently be creeping and one offshore Washington that is believed to be fully locked at present with potential for rupture over a larger area in future earthquakes. Sediment properties are evaluated from compressional-wave velocity (Vp) models derived from Pre-Stack Depth Migration (PSDM) and Full Waveform Inversion, shear wave velocity (Vs) studies, and Amplitude vs Offset studies. The project makes use of 8 km long-streamer multi-channel seismic (MCS) and wide-angle ocean bottom seismometer (OBS) data acquired along two dip lines crossing the margin offshore central Oregon and Washington (OR and WA transects), and one ~400 km line strike line (MARGIN transect) located ~10-15 km seaward of the deformation front and spanning the 2 dip lines. The analysis is designed to address the following science questions: 1) What are the seismic characteristics (Vp, Vs, Vp/Vs, anisotropy) and derived physical properties (porosity, effective stress, pore fluid pressure, and crack density) of the basal sediment section prior to subduction, and how do they vary along the margin with the documented segmentation in the structure and hydration state of the incoming JdF plate? 2) What conditions control the stratigraphic position of the proto-décollement and how are these conditions related to the structural style of the forearc? 3) How do the physical properties of plate interface zone at Cascadia vary in the down-dip direction both in the strongly-coupled region (WA) as well as in the partially creeping region (OR), and how does this relate to upper plate forearc deformation?
This project is supporting advanced analysis of previously acquired marine seismic data that are available through the MGDS data repository: http://www.marine-geo.org/tools/search/entry.php?id=MGL1211