Results from 60 Years of Crustal-Scale Active-Source Wide-Angle Seismic Profiling in Cascadia

Session: Amphibious Seismic Studies of Plate Boundary Structure and Processes [Poster]
Type: Poster
Date: 4/29/2020
Time: 08:00 AM
Room: Ballroom
Description: 

Sixty years of crustal-scale active-source wide-angle profiling, much of it amphibious, provide significant insights into Cascadia crustal and upper mantle structure as well as the tectonic and magmatic processes that formed it. This profiling has imaged (1) several km-thick basins beneath Puget Lowland, (2) widespread underthrusting of the accretionary wedge beneath the forearc crust that uplifted the Crescent Terrane, eroding it completely in Olympic Peninsula, (3) magmatic underplating in the backarc forming a lower-crustal rift pillow, (4) the geometry and structure of the subducting oceanic plates and (5) widespread hydration (serpentinization) of the forearc upper mantle wedge. These datasets, whose resolution has steadily increased over time, also provide important constraints for 3D seismic velocity models for Cascadia. Seismic imaging of volcanic centers in Cascadia first focused on Medicine Lake and Mt. Shasta in northern California (1978-1982) and Newberry Crater in Oregon (1984), and but recent profiling using 1000’s of receivers has imaged the magmatic system at Mt. St. Helens in Washington (2014). In the 1980s, profiling was conducted in the Cascadia backarc, imaging the Modoc Plateau in California, the Columbia Plateau near Hanford, Washington, the Yakima Fold Belt and southern British Columbia. Onshore profiling of the British Columbia, Oregon and Washington forearcs and the Mendocino triple junction was conducted between 1980 and 1995. Imaging of the incoming Juan de Fuca plate, the accretionary complex and the forearc commenced offshore Vancouver Island (1980), followed by studies in central Oregon (1989 and 2012), near Cape Blanco and the Mendocino triple junction (1994), the Washington margin (1996 and 2012) and in Georgia Basin (2002). Wide-angle profiling in the Puget Lowland (1998 and 1999) imaged the structure of the Seattle and other deep sedimentary basins, the Crescent Terrane, the subducting Juan de Fuca plate and the serpentinized forearc mantle wedge.

Presenting Author: Tom Brocher

Authors