A New Source Function of the 1964 Alaska Tsunami Based on the Near-field Numerical Modeling and Observations
Abstract
Near-field observations of tsunami waves generated by the MW9.2 1964 Alaska earthquake reveal a complex relationship between the tsunami wave field in the source area and regional coseismic slip in south-central Alaska. The documented times and amplitudes of first arrivals, measured runup heights and inundation areas along the coasts of the Kenai Peninsula and Kodiak Island suggest that secondary splay faults played an important role in generating destructive tsunami waves. We conduct a tsunami numerical modeling study to test a hypothesis that a significant amount of slip needs to be placed on intraplate splay faults, and to evaluate the extent of these faults in order to explain the coseismic displacements and near-field tsunami observations. The newly revised coseismic deformation model of the 1964 earthquake extends the Patton Bay fault offshore beyond its mapped dimensions on land to about 150°W, which approximately corresponds to the boundary of plate coupling along the Kenai Peninsula coast derived from previous GPS and postseismic deformation studies. The results of tsunami numerical modeling in the Kodiak Island region demonstrate that the new coseismic deformation model provides a good estimate of slip on the megathrust in the Kodiak asperity, and confirm that it was an important feature of the 1964 tsunami generation mechanism. We investigate the possible contribution of coseismic horizontal displacements into the initial tsunami wave field by calculating the component of the ocean surface uplift due to horizontal motion of the steep ocean bottom slopes. The tsunami simulations reveal that including deformation due to horizontal displacements in the source function results in an increase of far-field tsunami amplitudes at all distant locations, while this modification of the tsunami source produces only very localized effects in the near field. Our approach for discretization of the fault geometry and redistribution of slip can augment future research of the 1964 tsunami source as well as inversion studies that use tsunami observations and measurements in the near field, where the modeling results are highly susceptible to the complexity of the tsunami source.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2011
- Bibcode:
- 2011AGUFM.T33A2376S
- Keywords:
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- 0545 COMPUTATIONAL GEOPHYSICS / Modeling;
- 4564 OCEANOGRAPHY: PHYSICAL / Tsunamis and storm surges;
- 7240 SEISMOLOGY / Subduction zones;
- 4304 NATURAL HAZARDS / Oceanic