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century may also have generated waves in excess of 0.5m; none were recorded on tide
gages and the height has been estimated from eyewitness accounts only (Lander et al.,
1993; Toppozada et al., 1992; Borrero et al., 2006a) .
Since 1854, there has been a tide gauge in operation in San Francisco Bay. It had
been originally installed at Fort Point, was moved to Sausalito in 1877, and then to its
present location at the Presidio in 1897 (Bromirski et al., 2002). Other stations inside
the bay have operated on an interim basis including Hunters Point, Alameda, Oakland
and Mare Island (see Figure 2.7). While the original tide gauge in Presidio has been in
operation since 1854, some of the records have been lost or events not recorded due to
instrument problems or severe weather conditions.
Forty-three of the 51 historic tsunamis recorded or observed in San Francisco Bay
originated from distant sources involving at least four hours travel time from the source
to the Bay. The most frequent source area appears to have been the northwestern Pacific
(Japan and the Kamchatka-Kuril Trenches), followed by South America and the Alaska–
Aleutian Islands. Two of the 51 tsunamis, the 1960 Mw = 9.5 Chile earthquake and
1964 Mw = 9.2 Alaska earthquake, did cause tsunami damage in San Francisco Bay.
The tsunami waves from the 1960 Chile earthquake arrived in the Bay at 10:12 UTC
(2:12 a.m. PST), fifteen hours after the earthquake. The tsunami was recorded on the
tide gauges at the Presidio and Alameda, as well as on a 33–gauge array of water level
recorders fortuitously present in San Francisco Bay during the tsunami (Magoon, 1962).
The waves were observed on six of the thirty three gauges, and the maximum recorded
wave heights are shown in Table 1.4.
The top two frames of Figure 1.6 show the 1960 Presidio and Alameda tide gauge
recordings. The plots illustrate a feature of many recorded tsunamis within the Bay.
22
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 37 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | century may also have generated waves in excess of 0.5m; none were recorded on tide gages and the height has been estimated from eyewitness accounts only (Lander et al., 1993; Toppozada et al., 1992; Borrero et al., 2006a) . Since 1854, there has been a tide gauge in operation in San Francisco Bay. It had been originally installed at Fort Point, was moved to Sausalito in 1877, and then to its present location at the Presidio in 1897 (Bromirski et al., 2002). Other stations inside the bay have operated on an interim basis including Hunters Point, Alameda, Oakland and Mare Island (see Figure 2.7). While the original tide gauge in Presidio has been in operation since 1854, some of the records have been lost or events not recorded due to instrument problems or severe weather conditions. Forty-three of the 51 historic tsunamis recorded or observed in San Francisco Bay originated from distant sources involving at least four hours travel time from the source to the Bay. The most frequent source area appears to have been the northwestern Pacific (Japan and the Kamchatka-Kuril Trenches), followed by South America and the Alaska– Aleutian Islands. Two of the 51 tsunamis, the 1960 Mw = 9.5 Chile earthquake and 1964 Mw = 9.2 Alaska earthquake, did cause tsunami damage in San Francisco Bay. The tsunami waves from the 1960 Chile earthquake arrived in the Bay at 10:12 UTC (2:12 a.m. PST), fifteen hours after the earthquake. The tsunami was recorded on the tide gauges at the Presidio and Alameda, as well as on a 33–gauge array of water level recorders fortuitously present in San Francisco Bay during the tsunami (Magoon, 1962). The waves were observed on six of the thirty three gauges, and the maximum recorded wave heights are shown in Table 1.4. The top two frames of Figure 1.6 show the 1960 Presidio and Alameda tide gauge recordings. The plots illustrate a feature of many recorded tsunamis within the Bay. 22 |
