2022 CSDMS meeting-083


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Modeling Tsunami Inundation and Sediment Transport to Characterize Earthquake Source Parameters from Tsunami Deposits

Guy Gelfenbaum, U.S. Geological Survey Santa Cruz California, United States. ggelfenbaum@usgs.gov
SeanPaul La Selle, USGS Santa Cruz California, United States. slaselle@usgs.gov

Assessing the tsunami hazard in regions with infrequent or no instrumental or historical records of tsunamis is a challenge for emergency managers. In the absence of these records, coastal geologists rely on evidence of past tsunami inundation from buried sedimentary deposits to identify the presence of a tsunami hazard and to determine the recurrence of past events. One persistent challenge in assessing tsunami hazard from sandy coastal deposits is inferring the relative magnitude of past tsunamis from characteristics of the deposits. Recent reanalysis of field data from the 2011 Tohoku-oki earthquake and tsunami show that the volume of onshore sandy tsunami deposits is highly correlated with offshore tsunami magnitude, seafloor deformation, and fault slip. To further explore these relationships, we employ a Delft3D-FLOW hydrodynamic and sediment transport model to simulate onshore tsunami deposit volume from offshore slip of the 2011 Tohoku-oki earthquake and tsunami. We use the Satake et al. (2013) tsunami source model to derive the hydrodynamic boundary conditions for the sediment transport simulations. The Delft3D-FLOW model uses van Rijn (2007) sediment transport formulations and coefficients and a two-dimensional, vertically layered grid to model sediment transport with the effect of suspended-sediment induced density stratification on the vertical turbulent mixing. We model how variation in offshore slip affects tsunami deposit volume for a wide range of sediment sources, offshore and onshore slopes, and boundary roughness conditions. Model results show a strong correlation between onshore tsunami deposit volume and adjacent offshore co-seismic slip if ample sediment is available in the model to be eroded and transported. These results are consistent with data from the 2011 Tohoku tsunami at sites with sufficiently wide beaches and without shoreline armoring. We continue to test the model to evaluate sensitivity to parameters that may not be well known for paleo-tsunamis such as width of fault rupture, paleo-topography, and changes in sea level. Ultimately, this approach may be able to reconstruct past tsunami magnitudes and improve assessment of tsunami hazard.
  • Satake, K., Fujii, Y., Harada, T., & Namegaya, Y. (2013). Time and space distribution of coseismic slip of the 2011 Tohoku earthquake as inferred from tsunami waveform data. Bulletin of the seismological society of America, 103(2B), 1473-1492.