Numerical Studies Of Tectonic And Landslide-Generated Tsunamis Caused By The 1964 Great Alaska Earthquake

Abstract

The focus of my thesis is on the complex source mechanism of tsunami waves generated by the MW9.2 1964 Alaska earthquake, the largest instrumentally recorded earthquake in North America. The vertical seafloor displacements produced a trans-Pacific tectonic tsunami that caused loss of life and great damage in Alaska and the west coast of the United States and Canada. In addition to the major tectonic wave, about 20 local tsunamis were generated by submarine mass failures in a number of bays and fjords in south-central Alaska. These locally generated waves caused most of the damage and accounted for 76% of tsunami fatalities. I use numerical modeling to study tectonic and landslide tsunamis of the 1964 earthquake. The first part of the thesis presents numerical analysis of tsunami inundation at Seward and other locations in Resurrection Bay caused by the combined impact of landslide-generated waves and the tectonic tsunami. This study utilizes the recent geological findings of large-scale submarine slope failures in the bay during the 1964 earthquake and confirms the hypothesis that tsunami waves observed in Seward during and immediately after the earthquake resulted from multiple underwater landslides. The analysis of the simulated composite inundation area caused by the two different tsunami sources explains their relative contributions and demonstrates good agreement with observations. The second major topic is the source of the 1964 tectonic tsunami. The results of inundation modeling in Kodiak Island show that tsunami runup in the near field strongly depends on coseismic slip in the Kodiak asperity. I test the hypothesis that splay faults played a major role in tsunami generation and evaluate the extent of the Patton Bay fault using near-field tsunami observations. The new source function of the 1964 tsunami is presented, which includes the effects of the splay fault displacements and the component of the vertical deformation of the sea surface due to horizontal displacements on the megathrust. The results of numerical modeling studies included in this thesis complement the Alaska Tsunami Inundation Mapping Project. This activity provides emergency officials in coastal Alaska with tsunami hazard assessment tools and helps mitigate future tsunami risk.