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flooding about twice as far inland as in 1964 (Bernard et al., 1994; Toppozada et al.,
1995). Bernard et al. (1994) used an early generation hydrodynamic model to estimate
inundation in Crescent City. That model was never validated through benchmark testing
(Yeh et al., 1996; Liu et al., 2007) and the results were incompatible with some pale-otsunami
data, particularly in the Humboldt Bay region (PG&E, 2003; Synolakis et al.,
2007).
Here, the tsunami hazard in CC from Cascadia earthquakes is re-examined, using the
numerical model MOST (Titov and Synolakis, 1998; Gonz´alez et al., 2007; Synolakis
et al., 2007), the relative tsunami hazard posed by segmentary and full ruptures of the
CSZ and the sensitivity of the results to slip partitioning are investigated. 1
2.6.1 Tsunami Modeling
Three levels of nested grids were used, as shown in Figure 1.8e. The highest resolution
grid was itself sampled twice with uniform 3arc–sec (93 by 69 m at 41.7! N) and 1arc–
sec (31m×23mat 41.7! N) resolution. The outermost grid was resampled to 30arc–sec,
and the intermediate grid to 15arc–sec. Similar multi grid computations for southern
California are discussed in Borrero et al. (2006a).
2.6.2 Tsunami Hazard Assessment in Crescent City
Using the scenarios discussed in Section 2.2, as Tsunami Sources, modeled water level
histories at the site of the CC tide gauge are presented in Figure 2.27c. The four Gorda
scenarios (SN, SW, SP1 and SP2) show very similar results. The differences are well
within the error margins of the simulations. The full Cascadia rupture CSZ L is only
1This section follows Uslu et al. (2007)
97
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 112 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | flooding about twice as far inland as in 1964 (Bernard et al., 1994; Toppozada et al., 1995). Bernard et al. (1994) used an early generation hydrodynamic model to estimate inundation in Crescent City. That model was never validated through benchmark testing (Yeh et al., 1996; Liu et al., 2007) and the results were incompatible with some pale-otsunami data, particularly in the Humboldt Bay region (PG&E, 2003; Synolakis et al., 2007). Here, the tsunami hazard in CC from Cascadia earthquakes is re-examined, using the numerical model MOST (Titov and Synolakis, 1998; Gonz´alez et al., 2007; Synolakis et al., 2007), the relative tsunami hazard posed by segmentary and full ruptures of the CSZ and the sensitivity of the results to slip partitioning are investigated. 1 2.6.1 Tsunami Modeling Three levels of nested grids were used, as shown in Figure 1.8e. The highest resolution grid was itself sampled twice with uniform 3arc–sec (93 by 69 m at 41.7! N) and 1arc– sec (31m×23mat 41.7! N) resolution. The outermost grid was resampled to 30arc–sec, and the intermediate grid to 15arc–sec. Similar multi grid computations for southern California are discussed in Borrero et al. (2006a). 2.6.2 Tsunami Hazard Assessment in Crescent City Using the scenarios discussed in Section 2.2, as Tsunami Sources, modeled water level histories at the site of the CC tide gauge are presented in Figure 2.27c. The four Gorda scenarios (SN, SW, SP1 and SP2) show very similar results. The differences are well within the error margins of the simulations. The full Cascadia rupture CSZ L is only 1This section follows Uslu et al. (2007) 97 |
