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and analytical methods. They considered tsunamis emanating from both AASZ and
SASZ, based on the 1964 Alaska and 1960 Chilean earthquakes.
In their methodology, they discretized AASZ into twelve segments, and then they
recreated “worst case scenarios” by assuming initial ground deformations by a hypo-thetical
uplifting mass of ellipsoidal shape, about 1000km long, with an aspect ratio of
1 : 5 and maximum vertical uplift of 8–10m. Using a one–dimensional linearized shal-low
water equation in spherical coordinates, they propagated their initial waves from
the Alaskan and Chilean sources to California. At the continental shelf, an analyti-cal
expression was derived to match the inner and outer wave amplitudes. Then, they
obtained a simple amplification factor for a sinusoidal wave to generate the final wave
amplitude offshore of the target. Their 100–year (R100) and 500–year (R500) results are
summarized in Table 1.1, with a comparison of Houston and Garcia’s (1974) results
with the 1964 Alaska tsunami tide gauge record shown on Table 1.2.
Houston and Garcia’s (1974) results showed greater accuracy than even what would
had been optimistically anticipated when compared to the 1964 tidal gauge records
(Synolakis et al., 1997). Yet, their solution had three areas that warranted improve-ment.
First, a one dimensional model was applied for the solution of nearfield events,
and this solution is not a priori appropriate for complex nearshore bathymetry, such as
in narrow bays. Second, they used a sinusoidal wave in the analytical solution close
to shore, and this can lead to substantial errors in the solutions of the runup. Third,
small scale nearshore features affect local inundation and runup to first order, and were
neglected in the coarse gridded computation of Houston and Garcia (1974).
A few years later, Houston (1980) performed a further comprehensive study, uti-lizing
finite elements solutions of nonlinear shallow–water wave equations including
friction terms. His work was an improvement over Houston and Garcia (1974), but was
4
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 19 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | and analytical methods. They considered tsunamis emanating from both AASZ and SASZ, based on the 1964 Alaska and 1960 Chilean earthquakes. In their methodology, they discretized AASZ into twelve segments, and then they recreated “worst case scenarios” by assuming initial ground deformations by a hypo-thetical uplifting mass of ellipsoidal shape, about 1000km long, with an aspect ratio of 1 : 5 and maximum vertical uplift of 8–10m. Using a one–dimensional linearized shal-low water equation in spherical coordinates, they propagated their initial waves from the Alaskan and Chilean sources to California. At the continental shelf, an analyti-cal expression was derived to match the inner and outer wave amplitudes. Then, they obtained a simple amplification factor for a sinusoidal wave to generate the final wave amplitude offshore of the target. Their 100–year (R100) and 500–year (R500) results are summarized in Table 1.1, with a comparison of Houston and Garcia’s (1974) results with the 1964 Alaska tsunami tide gauge record shown on Table 1.2. Houston and Garcia’s (1974) results showed greater accuracy than even what would had been optimistically anticipated when compared to the 1964 tidal gauge records (Synolakis et al., 1997). Yet, their solution had three areas that warranted improve-ment. First, a one dimensional model was applied for the solution of nearfield events, and this solution is not a priori appropriate for complex nearshore bathymetry, such as in narrow bays. Second, they used a sinusoidal wave in the analytical solution close to shore, and this can lead to substantial errors in the solutions of the runup. Third, small scale nearshore features affect local inundation and runup to first order, and were neglected in the coarse gridded computation of Houston and Garcia (1974). A few years later, Houston (1980) performed a further comprehensive study, uti-lizing finite elements solutions of nonlinear shallow–water wave equations including friction terms. His work was an improvement over Houston and Garcia (1974), but was 4 |
