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damage than any other state, except Alaska (Plafker, 1972). Eleven people lost their lives
and thirty–five were seriously injured at Crescent City, where the wave was observed
larger than in surrounding areas, possibly because of local topographic amplification.
Plafker (1972) reported that the earthquake deformation caused regional displace-ment
over an area of 140, 000km2, which is about the size of Greece. The zone of major
uplift was inferred was 950km long and 200km wide with a maximum uplift around
11m and 2m subsidence. Plafker (1969) determined the vertical displacements using
a comparison of pre and post tide gage records and survey level lines based on vege-tation
patterns. He also compared before and after depth soundings and measured the
runup of the tsunami along the coast, in what appears to be the first ever comprehensive
quantitative tsunami post-event field survey (Synolakis and Okal, 2005).
The Alaska–Aleutian Subduction Zone (AASZ) is the result of Pacific Plate subduct-ing
under the North American Plate. The AASZ is one of the longest subduction zones
known, starting from longitude 165!E to almost 140!W. The AASZ also has a history of
rupturing in large and great earthquakes(Johnson et al., 1996). Five great earthquakes
in the last century were the 1938, 1946 Unimak, 1957 Andreanof Islands, 1964 Prince
William Sound (or Alaskan) and 1965 Rat Island events. All five of them happened in
sequence, one of the longest in the 20th century, although not spatially distributed tem-porarily.
In this study, four scenarios have been modeled with the objective to identify
physically realistic extreme future events, but not necessarily to model any particular
historic events earthquakes, except for the 1964 event which was done for validation.
The fault mechanism suggested by (Plafker, 1969, 1972) for the 1964 earthquake
uses a fault length of 890km, different from his inferred zone of uplift (950km). The
northern segment was estimated as 600km, then the rupture continued E-W for another
200km. The down–dip width was proposed 290km at the north, and 175km on the
47
Object Description
| Title | Deterministic and probabilistic tsunami studies in California from near and farfield sources |
| Author | Uslu, Burak |
| Author email | uslu@usc.edu; burak.uslu@noaa.gov |
| Degree | Doctor of Philosophy |
| Document type | Dissertation |
| Degree program | Civil Engineering |
| School | Viterbi School of Engineering |
| Date defended/completed | 2007-09-21 |
| Date submitted | 2008 |
| Restricted until | Unrestricted |
| Date published | 2008-10-30 |
| Advisor (committee chair) | Synolakis, Costas E. |
| Advisor (committee member) |
Bardet, Jean-Pierre Okal, Emile A. Moore, James Elliott, II |
| Abstract | California is vulnerable to tsunamis from both local and distant sources. While there is an overall awareness of the threat, tsunamis are infrequent events and few communities have a good understanding of vulnerability. To quantitatively evaluate the tsunami hazard in the State, deterministic and probabilistic methods are used to compute inundation and runup heights in selected population centers along the coast.; For the numerical modeling of tsunamis, a two dimensional finite difference propagation and runup model is used. All known near and farfield sources of relevance to California are considered. For the farfield hazard analysis, the Pacific Rim is subdivided into small segments where unit ruptures are assumed, then the transpacific propagations are calculated. The historical records from the 1952 Kamchatka, 1960 Great Chile, 1964 Great Alaska, and 1994 and 2006 Kuril Islands earthquakes are compared to modeled results. A sensitivity analysis is performed on each subduction zone segment to determine the relative effect of the source location on wave heights off the California Coast.; Here, both time-dependent and time-independent methods are used to assess the tsunami risk. In the latter, slip rates are obtained from GPS measurements of the tectonic motions and then used as a basis to estimate the return period of possible earthquakes. The return periods of tsunamis resulting from these events are combined with computed waveheight estimates to provide a total probability of exceedance of given waveheights for ports and harbors in California. The time independent method follows the practice of past studies that have used Gutenberg and Richter type relationships to assign probabilities to specific tsunami sources.; The Cascadia Subduction Zone is the biggest nearfield earthquake source and is capable of producing mega-thrust earthquake ruptures between the Gorda and North American plates and may cause extensive damage north of Cape Mendocino, to Seattle. The present analysis suggests that San Francisco Bay and Central California are most sensitive to tsunamis originating from the Alaska and Aleutians Subduction Zone (AASZ). An earthquake with a magnitude comparable to the 1964 Great Alaska Earthquake on central AASZ could result in twice the wave height as experienced in San Francisco Bay in 1964.; The probabilistic approach shows that Central California and San Francisco Bay have more frequent tsunamis from the AASZ, while Southern California can be impacted from tsunamis generated on Chile and Central American Subduction Zone as well as the AASZ. |
| Keyword | assessment; California; hazard; model; probability; tsunami |
| Geographic subject | capes: Kamchatka; islands: Kuril Islands; fault zones: Cascadia Subduction Zone |
| Geographic subject (state) | California; Alaska |
| Geographic subject (country) | Chile |
| Coverage date | 1952/2008 |
| Language | English |
| Part of collection | University of Southern California dissertations and theses |
| Publisher (of the original version) | University of Southern California |
| Place of publication (of the original version) | Los Angeles, California |
| Publisher (of the digital version) | University of Southern California. Libraries |
| Provenance | Electronically uploaded by the author |
| Type | texts |
| Legacy record ID | usctheses-m1706 |
| Contributing entity | University of Southern California |
| Rights | Uslu, Burak |
| Repository name | Libraries, University of Southern California |
| Repository address | Los Angeles, California |
| Repository email | cisadmin@lib.usc.edu |
| Filename | etd-uslu-2434 |
| Archival file | uscthesesreloadpub_Volume40/etd-uslu-2434.pdf |
Description
| Title | Page 62 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | damage than any other state, except Alaska (Plafker, 1972). Eleven people lost their lives and thirty–five were seriously injured at Crescent City, where the wave was observed larger than in surrounding areas, possibly because of local topographic amplification. Plafker (1972) reported that the earthquake deformation caused regional displace-ment over an area of 140, 000km2, which is about the size of Greece. The zone of major uplift was inferred was 950km long and 200km wide with a maximum uplift around 11m and 2m subsidence. Plafker (1969) determined the vertical displacements using a comparison of pre and post tide gage records and survey level lines based on vege-tation patterns. He also compared before and after depth soundings and measured the runup of the tsunami along the coast, in what appears to be the first ever comprehensive quantitative tsunami post-event field survey (Synolakis and Okal, 2005). The Alaska–Aleutian Subduction Zone (AASZ) is the result of Pacific Plate subduct-ing under the North American Plate. The AASZ is one of the longest subduction zones known, starting from longitude 165!E to almost 140!W. The AASZ also has a history of rupturing in large and great earthquakes(Johnson et al., 1996). Five great earthquakes in the last century were the 1938, 1946 Unimak, 1957 Andreanof Islands, 1964 Prince William Sound (or Alaskan) and 1965 Rat Island events. All five of them happened in sequence, one of the longest in the 20th century, although not spatially distributed tem-porarily. In this study, four scenarios have been modeled with the objective to identify physically realistic extreme future events, but not necessarily to model any particular historic events earthquakes, except for the 1964 event which was done for validation. The fault mechanism suggested by (Plafker, 1969, 1972) for the 1964 earthquake uses a fault length of 890km, different from his inferred zone of uplift (950km). The northern segment was estimated as 600km, then the rupture continued E-W for another 200km. The down–dip width was proposed 290km at the north, and 175km on the 47 |
