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Johnson, J.M., 1995

Asperity distribution of Alaskan-Aleutian earthquakes from inversion of tsunami waveforms

Bibliographic Reference

Johnson, J.M., 1995, Asperity distribution of Alaskan-Aleutian earthquakes from inversion of tsunami waveforms: University of Michigan, Ann Arbor, Ph.D. dissertation, 285 p., illust., maps.


The Alaskan-Aleutian arc has a history of rupturing in large and great earthquakes. The 20th century events include five great earthquakes: the 1938 Alaskan, 1946 Aleutian, 1957 Aleutian, 1964 Prince William Sound, and 1965 Rat Islands earthquakes. Due to the lack of seismic data for these earthquakes, a technique to invert tsunami waveforms is used to determine the source parameters of the Alaskan-Aleutian earthquakes. From the study of the 1965 earthquake, the results of tsunami waveform inversion are shown to be compatible with results of seismic wave studies. The areas of highest slip correspond to the tectonic blocks of the western Aleutians. The rupture area, slip distribution and seismic moment of the 1957 earthquake have been determined. The Unalaska Island area did not rupture in the 1957 event, making this area a seismic gap. The moment magnitude Mrm w of this earthquake is 8.6, and the slip was concentrated in the western half of the aftershock zone. The 1938 earthquake did not rupture into the Shumagin Islands seismic gap. The slip in this earthquake was concentrated in the eastern third of the aftershock area. The 1946 earthquake is a very unusual seismic event, but the tsunami data can be modeled using a simple underthrusting mechanism. The slip was highest near the trench. The moment magnitude Mrm w is 8.3. Tsunami data alone cannot resolve the entire slip distribution of the 1964 earthquake. Joint inversion of tsunami and geodetic data gives the complete slip distribution. The highest slip occurred in Prince William Sound and in the Gulf of Alaska where the Yakutat terrane is being subducted. High slip also occurred in the Kodiak Island region. Large near-trench slip was a major source of the transPacific tsunami. Areas of high slip correspond to seismologically determined areas of high moment release. The factors controlling asperity size and location are variable. This work can be used as a basis for future hypothesis testing concerning future earthquakes, asperities and seismic gaps.

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