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vary from north to south and it is possible that some events are segment ruptures. For
example, Clarke and Carver (1992) define a southern (Gorda) segment with dimensions
of about 240km×80km with a fault dip of 10–20!. Paleotsunami studies from southern
Oregon show several events not present in records from elsewhere on the subduction
zone (Nelson et al., 2006), thus they are possibly related to segment rutpures. This
apparently random alternation between segment ruptures and mega–events involving the
whole length of the fault was first described in Japan by Ando (1975) and more recently
documented in other provinces (Cisternas et al., 2005; Nanayama et al., 2005; Okal and
Synolakis, 2008). In addition to the main rupture zone, a number of subsidiary faults
in the CSZ acretionary fold and thrust belt pose an additional tsunami hazard (Clarke
and Carver, 1992). Finally, Toppozada et al. (1995) proposed a scenario involving a
simultaneous or triggered rupture of the Little Salmon fault (seen at the bottom of the
right of Figure 1.7), located along the northern edge of the Eel River basin and extending
offshore for at least 150km.
1.4.2 Local Tsunamis in San Francisco Bay
San Francisco Bay experienced six credible and several other possible tsunamis from
local sources and two additional credible tsunamis from other source regions in northern
California (Table 1.5). Of the six credible local source events, four were probably caused
by earthquakes and two by earthquake-triggered landslides. One event in 1887 was
associated with no known earthquakes and, if real, may represent slumping within the
bay. Perhaps the most notable aspect of historic local-source tsunamis is that they all
occurred in the 19th and early 20th century. Toppozada (2006) suggests that the high
29
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 44 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | vary from north to south and it is possible that some events are segment ruptures. For example, Clarke and Carver (1992) define a southern (Gorda) segment with dimensions of about 240km×80km with a fault dip of 10–20!. Paleotsunami studies from southern Oregon show several events not present in records from elsewhere on the subduction zone (Nelson et al., 2006), thus they are possibly related to segment rutpures. This apparently random alternation between segment ruptures and mega–events involving the whole length of the fault was first described in Japan by Ando (1975) and more recently documented in other provinces (Cisternas et al., 2005; Nanayama et al., 2005; Okal and Synolakis, 2008). In addition to the main rupture zone, a number of subsidiary faults in the CSZ acretionary fold and thrust belt pose an additional tsunami hazard (Clarke and Carver, 1992). Finally, Toppozada et al. (1995) proposed a scenario involving a simultaneous or triggered rupture of the Little Salmon fault (seen at the bottom of the right of Figure 1.7), located along the northern edge of the Eel River basin and extending offshore for at least 150km. 1.4.2 Local Tsunamis in San Francisco Bay San Francisco Bay experienced six credible and several other possible tsunamis from local sources and two additional credible tsunamis from other source regions in northern California (Table 1.5). Of the six credible local source events, four were probably caused by earthquakes and two by earthquake-triggered landslides. One event in 1887 was associated with no known earthquakes and, if real, may represent slumping within the bay. Perhaps the most notable aspect of historic local-source tsunamis is that they all occurred in the 19th and early 20th century. Toppozada (2006) suggests that the high 29 |
