CTSP: Coupling of Tectonic and Surface Processes

From Earthquakes to Landscapes in the Cascadia Subduction Zone

Alison Duvall

University of Washington From Earthquakes to Landscapes in the Cascadia Subduction Zone, United States

Increased computing power, high resolution imagery, new geologic dating techniques, and a more sophisticated comprehension of the geodynamic and geomorphic processes that shape our planet place us on the precipice of major breakthroughs in understanding links among tectonics and surface processes. In this talk, I will use University of Washington’s “M9 project” to highlight research progress and challenges in coupled tectonics and surface processes studies over both short (earthquake) and long (mountain range) timescales. A Cascadia earthquake of magnitude 9 (M9) would cause shaking, liquefaction, landslides and tsunamis from British Columbia to northern California. The M9 project explores this risk, resilience and the mechanics of Cascadia subduction. At the heart of the project are synthetic ground motions generated from 3D finite difference simulations for 50 earthquake scenarios including factors not previously considered, such as the distribution and timing of energy release on the fault, the coherent variation of frequency content of fault motion with fault depth, and the 3D effects of the deep basins along Puget Sound. Coseismic landslides, likely to number in the thousands, represent one of the greatest risks to the millions of people living in Cascadia. Utilizing the synthetic ground motions and a Newmark sliding block analysis, we compute the landscape response for different landslide failure modes. Because an M9 subduction earthquake is well known to have occurred just over 300 years ago, evidence of coseismic landslides triggered by this event should still be present in Washington and Oregon landscapes. We are systematically hunting for these landslides using a combination of radiocarbon dating and surface roughness analysis, a method first developed to study landslides near to the Oso 2014 disaster site, to develop more robust regional landslide chronologies to compare to model estimations. Resolved ground motions and hillslope response for a single earthquake can then be integrated into coupled landscape evolution and geodynamic models to consider the topographic and surface processes response to subduction over millions of years. This example demonstrates the power of an integrative, multidisciplinary approach to provide deeper insight into coupled tectonic and surface processes phenomena over a range of timescales.

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Of interest for:
  • Terrestrial Working Group
  • Geodynamics Focus Research Group