Dr. Shuo Ma and Evan Hirakawa’s poster presentation for the Seismological Society of America 2014 Annual Meeting in Anchorage, Alaska

Session: Great Earthquakes and Slip to the Trench (Seismological Society of Japan/Seismological Society of America Joint Session)

Can Compaction Further Enhance Inelastic Wedge Failure in Shallow Subduction Zone Earthquakes?
HIRAKAWA, E. T., San Diego State University, San Diego, CA, USA, ehirakaw@ucsd.edu; MA, S., San Diego State University, San Diego, CA, USA, sma@mail.sdsu.edu
One of the distinct features of a convergent plate boundary is the continuous flux of sediments carried by the oceanic plate into the subduction zone. Sediments under various pressure and temperature conditions in the subduction zone experience substantial changes that are considered to contribute greatly to the complexities of subduction zone earthquakes. In this work, we focus on the compaction of sediments and sedimentary rocks in the accretionary wedge that are highly porous. Compaction of porous materials in the accretionary wedge was once considered to contribute to the aseismic nature of the plate interface in the shallow subduction zone (Zhang, Davis, and Wong, 1993). When porous materials are compacted in the undrained condition (as in the rapid loading of earthquake rupture) the pore pressure increases significantly when pore space closes while pore fluids are nearly incompressible, resulting in a much larger pore pressure increase than that by the elastic compression alone. In this work, we will incorporate compaction in our poroplastic model of shallow subduction zone earthquakes (Ma, 2012; Ma and Hirakawa, 2013) by using an end-cap yield criterion (e.g., Wong, 1997). A likely scenario is that material in the wedge is on the verge of compactant failure initially. Compaction induces the pore pressure increase that in turn reduces effective stress and causes shear failure. We hypothesize that compaction can significantly enhance coseismic wedge failure, which will make our wedge-failure mechanism more plausible in explaining well-documented anomalous observations for shallow subduction zone earthquakes, such as slow rupture velocity, large seafloor uplift, deficiency in high-frequency radiation, and low energy-to-moment ratio.

Thursday, May 1st / Poster #15 / Cook/Arteaga