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The available historical information and modeled historical scenarios for tsunami
affecting San Francisco Bay are combined with analysis of the tsunami response from
displacements along the various subduction zone segments on the Pacific Rim, to deter-mine
the worst case scenario. All of the results suggest that the largest wave will hit
San Francisco Bay from a tsunami triggered along the AASZ, when the hypothetical
Mw = 9.2 earthquake occurs along 700km of the fault, in the area of the most sensitive
response for San Francisco Bay. The magnitude and the size of the displacement for this
case was designed to be similar to that of 1964 Alaskan earthquake and 2004 Sumatra
earthquakes.
Figure 2.22 shows the comparison between the “designed” Mw = 9.2 AASZ III
event and the 1964 tide gauge records at the Presidio and Alameda tide gauge stations.
The worst case scenario produces two to three times larger wave heights than does the
1964 event. This AASZ III scenario produces larger waveheights at the station compared
with all modeled scenarios. It also features the highest tsunami current speeds at Outer
Richmond, East of Carquinez, Golden Gate and Presidio.
Table 2.7 lists the maximum modeled values for positive and negative water surface
level at 6 regions inside San Francisco Bay. The computed maximum values are in the
range of values that Magoon’s (1966) amplitude attenuation suggests. The maximum
wave heights at the Carquinez Strait are on the order of 25% of the values at Rich-mond
and 10% of those modeled for the Golden Gate. Similarly, the attenuation of the
outer Richmond area is of the order of 53% of the Presidio value, whereas in the inner
Richmond area, it is only 30%.
76
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 91 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | The available historical information and modeled historical scenarios for tsunami affecting San Francisco Bay are combined with analysis of the tsunami response from displacements along the various subduction zone segments on the Pacific Rim, to deter-mine the worst case scenario. All of the results suggest that the largest wave will hit San Francisco Bay from a tsunami triggered along the AASZ, when the hypothetical Mw = 9.2 earthquake occurs along 700km of the fault, in the area of the most sensitive response for San Francisco Bay. The magnitude and the size of the displacement for this case was designed to be similar to that of 1964 Alaskan earthquake and 2004 Sumatra earthquakes. Figure 2.22 shows the comparison between the “designed” Mw = 9.2 AASZ III event and the 1964 tide gauge records at the Presidio and Alameda tide gauge stations. The worst case scenario produces two to three times larger wave heights than does the 1964 event. This AASZ III scenario produces larger waveheights at the station compared with all modeled scenarios. It also features the highest tsunami current speeds at Outer Richmond, East of Carquinez, Golden Gate and Presidio. Table 2.7 lists the maximum modeled values for positive and negative water surface level at 6 regions inside San Francisco Bay. The computed maximum values are in the range of values that Magoon’s (1966) amplitude attenuation suggests. The maximum wave heights at the Carquinez Strait are on the order of 25% of the values at Rich-mond and 10% of those modeled for the Golden Gate. Similarly, the attenuation of the outer Richmond area is of the order of 53% of the Presidio value, whereas in the inner Richmond area, it is only 30%. 76 |
