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the more than 14 hours, to travel from South America. The model used assumes an
instantaneous rupture and displacement at the earthquake source, when in fact earth-quakes
of this size may take five minutes or longer to rupture the complete fault zone,
explaining at least a part of the time discrepancy. Tsunami travel times are also affected
by the shallow water bathymetry in the earthquake source region and the deep ocean
bathymetry along the tsunami travel path, neither of which are modeled perfectly given
the coarse grid resolution in the source region.
2.3.2 Comparison to Historical Measurements from the 1964
Alaska tsunami
A comparison of recorded and modeled waveheights for the 1964 event is shown in Fig-ures
2.9 and 2.10. While the model overpredicts the initial wave crest and first large
trough, especially on the Presidio tide gauge, the amplitudes and periods of the subse-quent
peaks match quite well. There is a slightly larger discrepancy in arrival times,
approximately 15 minutes, than for the 1960 case. It can be argued that this difference
is negligible in terms of hazard assessment for these distant events. The good fit of the
model data to the tide gauge recordings gives confidence in the computational formal-ism
and provides a strong foundation for investigating the relative influence of different
farfield sources.
For the Alameda gauge in Figure 2.8, the calculation captures the initial wave form
approximately the first several hours of the 1960 tsunami better, but does not reproduce
the large amplitude oscillations which begin some five hours after the first wave arrival
and persist for over three hours, see Figures 1.6. The exact cause for these late arriving
waves has not been explained before; they have been noticed in recent tsunamis, e.g.,
60
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 75 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | the more than 14 hours, to travel from South America. The model used assumes an instantaneous rupture and displacement at the earthquake source, when in fact earth-quakes of this size may take five minutes or longer to rupture the complete fault zone, explaining at least a part of the time discrepancy. Tsunami travel times are also affected by the shallow water bathymetry in the earthquake source region and the deep ocean bathymetry along the tsunami travel path, neither of which are modeled perfectly given the coarse grid resolution in the source region. 2.3.2 Comparison to Historical Measurements from the 1964 Alaska tsunami A comparison of recorded and modeled waveheights for the 1964 event is shown in Fig-ures 2.9 and 2.10. While the model overpredicts the initial wave crest and first large trough, especially on the Presidio tide gauge, the amplitudes and periods of the subse-quent peaks match quite well. There is a slightly larger discrepancy in arrival times, approximately 15 minutes, than for the 1960 case. It can be argued that this difference is negligible in terms of hazard assessment for these distant events. The good fit of the model data to the tide gauge recordings gives confidence in the computational formal-ism and provides a strong foundation for investigating the relative influence of different farfield sources. For the Alameda gauge in Figure 2.8, the calculation captures the initial wave form approximately the first several hours of the 1960 tsunami better, but does not reproduce the large amplitude oscillations which begin some five hours after the first wave arrival and persist for over three hours, see Figures 1.6. The exact cause for these late arriving waves has not been explained before; they have been noticed in recent tsunamis, e.g., 60 |
