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3.4 Probabilistic Tsunami Hazard Assessment for Cali-fornia
In this study, five subduction zones are considered, i.e., the Kuril–Kamchatka and
Japan (KSZ), West Aleutians (WASZ), Alaska–East Aleutians (AASZ), Central Amer-ica
(including Mexico) (CASZ) and South America–Chile (SASZ) zones, also shown in
Figure 3.5. Note that Cascadia is not included.
For each of these zones, simulations were undertaken for a number of events of vari-able
size and extending over a corresponding number of segments of the NOAA FACTS
database. In turn, the return period of each event was computed from the rate of tec-tonic
convergence at the relevant boundary. This tacitly assumes that this convergence
is entirely taken up seismically, which has long been known to be incorrect in several
subduction zones (Kanamori, 1977a). Indeed, the fraction of tectonic motion expressed
seismically (sometimes referred to as the “seismic efficiency” of the boundary) is one
of the least well known parameters of seismo–tectonics (Stein et al., 1986), with some
subduction zones (e.g., Marianas) totally lacking large earthquakes with a significant
contribution to the convergence. The question of understanding to which extent a sub-duction
zone with given physical parameters (age of plate, convergence rate, sediment
load, etc.) can support a megathrust event remains unresolved, since the paradigm pro-posed
by (Ruff and Kanomori, 1980) was violated by the 2004 Sumatra earthquake
(Stein and Okal, 2007). In this context, the present study targets only subduction zones
where very large earthquakes are documented historically and where the seismic effi-ciency
is thought to be high.
126
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 141 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | 3.4 Probabilistic Tsunami Hazard Assessment for Cali-fornia In this study, five subduction zones are considered, i.e., the Kuril–Kamchatka and Japan (KSZ), West Aleutians (WASZ), Alaska–East Aleutians (AASZ), Central Amer-ica (including Mexico) (CASZ) and South America–Chile (SASZ) zones, also shown in Figure 3.5. Note that Cascadia is not included. For each of these zones, simulations were undertaken for a number of events of vari-able size and extending over a corresponding number of segments of the NOAA FACTS database. In turn, the return period of each event was computed from the rate of tec-tonic convergence at the relevant boundary. This tacitly assumes that this convergence is entirely taken up seismically, which has long been known to be incorrect in several subduction zones (Kanamori, 1977a). Indeed, the fraction of tectonic motion expressed seismically (sometimes referred to as the “seismic efficiency” of the boundary) is one of the least well known parameters of seismo–tectonics (Stein et al., 1986), with some subduction zones (e.g., Marianas) totally lacking large earthquakes with a significant contribution to the convergence. The question of understanding to which extent a sub-duction zone with given physical parameters (age of plate, convergence rate, sediment load, etc.) can support a megathrust event remains unresolved, since the paradigm pro-posed by (Ruff and Kanomori, 1980) was violated by the 2004 Sumatra earthquake (Stein and Okal, 2007). In this context, the present study targets only subduction zones where very large earthquakes are documented historically and where the seismic effi-ciency is thought to be high. 126 |
