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2.6.3 Discussion and Conclusion for the Tsunami Hazard in Cres-cent
City
Detailed inundation modeling was presented for tsunamis affecting CC using both near
and farfield sources. The computations simulated fairly accurately the water level his-tory
produced by the March 28, 1964 Alaska earthquake and the November 15, 2006,
Kuril Islands earthquake. The main result is that a tsunami caused by ruptures on the
Cascadia Subduction Zone would impact Crescent City worse than in 1964. Such an
event would inundate 3.8km inland, twice as far as the 1964 event. Inundation dis-tances
of this order were observed in Aceh during the 2004 mega–tsunami (Synolakis
and Kong, 2006; Borrero, 2005). Note that the maximum seismic slip in any of the
scenarios for the Gorda rupture is 8m; substantially larger slips, would result in greater
wave heights and inundation extents.
Rupture of the Gorda segment of the Cascadia subduction zone controls the tsunami
hazard at Crescent City. The full rupture (scenario CSZ L) produces marginally larger
inundation than the four other scenarios that only involve a Gorda rupture. The width
of the rupture and the amount of slip partitioning between the CSZ megathrust and the
Little Salmon fault has little effect into the wave field. In contrast, the northern rupture
(CSZ N), an event nearly as large in magnitude as the full rupture and significantly larger
than any of the Gorda segment events, produces less inundation than the 1964 tsunami,
possibly due to directivity effects.
The onset of the tsunami for all Gorda ruptures is only minutes after the trigger-ing
earthquake is initiated. The crest of the first tsunami wave arrives at the tide gauge
in CC in 25 min (Figure 2.27c). Because the north coast of California is so close to
the leading edge of the subduction zone, the adjacent offshore area is predominantly
100
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 115 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 2.6.3 Discussion and Conclusion for the Tsunami Hazard in Cres-cent City Detailed inundation modeling was presented for tsunamis affecting CC using both near and farfield sources. The computations simulated fairly accurately the water level his-tory produced by the March 28, 1964 Alaska earthquake and the November 15, 2006, Kuril Islands earthquake. The main result is that a tsunami caused by ruptures on the Cascadia Subduction Zone would impact Crescent City worse than in 1964. Such an event would inundate 3.8km inland, twice as far as the 1964 event. Inundation dis-tances of this order were observed in Aceh during the 2004 mega–tsunami (Synolakis and Kong, 2006; Borrero, 2005). Note that the maximum seismic slip in any of the scenarios for the Gorda rupture is 8m; substantially larger slips, would result in greater wave heights and inundation extents. Rupture of the Gorda segment of the Cascadia subduction zone controls the tsunami hazard at Crescent City. The full rupture (scenario CSZ L) produces marginally larger inundation than the four other scenarios that only involve a Gorda rupture. The width of the rupture and the amount of slip partitioning between the CSZ megathrust and the Little Salmon fault has little effect into the wave field. In contrast, the northern rupture (CSZ N), an event nearly as large in magnitude as the full rupture and significantly larger than any of the Gorda segment events, produces less inundation than the 1964 tsunami, possibly due to directivity effects. The onset of the tsunami for all Gorda ruptures is only minutes after the trigger-ing earthquake is initiated. The crest of the first tsunami wave arrives at the tide gauge in CC in 25 min (Figure 2.27c). Because the north coast of California is so close to the leading edge of the subduction zone, the adjacent offshore area is predominantly 100 |
