Carter Lecture Series: Dr. Harold Tobin, "How the Structure of the Cascadia Accretionary Wedge Controls Shallow Megathrust Locking and tsunami-inducing Slip"

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Dr. Harold Tobin, Professor of Earth and Space Scienecs at the University of Washington, presents "How the Structure of the Cascadia Accretionary Wedge Controls Shallow Megathrust Locking and tsunami-inducing Slip"

Abstract: Using recent geophysical imaging of the offshore part of the Cascadia subduction zone at a range of scales, the evidence for recent activity of splay faults and the shallow megathrust can be newly evaluated. Central Cascadia off Washington and Oregon features a wide and flat wedge dominated by widely-spaced backthrusts, known as the landward-vergent zone. A synthesis of geology, geodesy, and mechanical analysis leads to the conclusion that this major portion of Cascadia is effectively locked right to the deformation front offshore, and that the most likely scenario for both past and future Cascadia magnitude 9 class events is a large-slip rupture of the megathrust, with slip extending efficiently up-dip to the frontal tip of the décollement fault and branching onto multiple frontal landward-verging splay faults. Furthermore, the existence and large-scale structure of the landward vergent zone is direct evidence of seismic rupture rather than aseismic slip. The implications for tsunami generation in a future Cascadia "Big One" will be explored.

This seminar is part of the Dr. james Carter Lecture Series hosted by the Department of Sustainable Earth Systems Sciences.