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Garcia and Houston’s (1975) 100–year and 500–year values do not mimic the atten-uation
relation suggested by Magoon (1966). Their recurrence estimate for Alaska and
Aleutian events was based only on historic events. The mid-20th century might had been
anomalous for large Alaska tsunamigenic events, hence these recurrence relationships
need to be re-evaluated using paleoseismic data, as now available. The restriction of
tsunami sources affecting California from Alaska and the Aleutians also needs to be re-examined,
particularly in light of the CSZ megathrust events that are believed to have an
approximate 500–year return period, and are capable of producing tsunami amplitudes
in the source area comparable to the 1964 Alaska or 2004 Sumatra events.
The Houston and Garcia’s studies, while ground–breaking at the time undertaken,
are computationally crude, when compared to the level of sophistication in modern
numerical tools or the resolution of bathymetric data now available.
Houston and Garcia computed tsunami wave amplitudes outside of San Francisco
Bay, then performed their calculations inside the bay using a forced wave input for a
monochromatic wave with the precomputed amplitude and a set period of 38min, a
value based on observations during the 1964 Alaskan event. The present study differs
in that it considers a wider variety of input sources from subduction zones around the
Pacific, and directly computes the tsunami wave from the source to the study area, using
a single model, when necessary inundation is computed directly at high resolution.
Parsons et al. (2003) performed hydrodynamic modeling to examine the tsunami-genic
potential of the Hayward – Rodgers Creek “stepover”, i.e., the lateral offset
between two strike–slip segments. Subsidence in the stepover region was modeled as a
slip of 0.35m on a high–angle 18km wide normal fault. The maximum wave height in
the Bay predicted by this model was 0.1m, well below the # 0.6m reported for the 1898
Mw # 6.7 Rodgers Creek event by the Union Record newspaper. It is possible these
13
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 28 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | Garcia and Houston’s (1975) 100–year and 500–year values do not mimic the atten-uation relation suggested by Magoon (1966). Their recurrence estimate for Alaska and Aleutian events was based only on historic events. The mid-20th century might had been anomalous for large Alaska tsunamigenic events, hence these recurrence relationships need to be re-evaluated using paleoseismic data, as now available. The restriction of tsunami sources affecting California from Alaska and the Aleutians also needs to be re-examined, particularly in light of the CSZ megathrust events that are believed to have an approximate 500–year return period, and are capable of producing tsunami amplitudes in the source area comparable to the 1964 Alaska or 2004 Sumatra events. The Houston and Garcia’s studies, while ground–breaking at the time undertaken, are computationally crude, when compared to the level of sophistication in modern numerical tools or the resolution of bathymetric data now available. Houston and Garcia computed tsunami wave amplitudes outside of San Francisco Bay, then performed their calculations inside the bay using a forced wave input for a monochromatic wave with the precomputed amplitude and a set period of 38min, a value based on observations during the 1964 Alaskan event. The present study differs in that it considers a wider variety of input sources from subduction zones around the Pacific, and directly computes the tsunami wave from the source to the study area, using a single model, when necessary inundation is computed directly at high resolution. Parsons et al. (2003) performed hydrodynamic modeling to examine the tsunami-genic potential of the Hayward – Rodgers Creek “stepover”, i.e., the lateral offset between two strike–slip segments. Subsidence in the stepover region was modeled as a slip of 0.35m on a high–angle 18km wide normal fault. The maximum wave height in the Bay predicted by this model was 0.1m, well below the # 0.6m reported for the 1898 Mw # 6.7 Rodgers Creek event by the Union Record newspaper. It is possible these 13 |
