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Chapter 3
Probabilistic Tsunami Hazard
Assessment
3.1 Introduction
Probabilistic hazard analysis in tsunami studies involves determining the probability of
exceedance of specific runup values in specific time windows through the superposition
of runup predictions from specific sources and their probabilities of occurrence during
the same time windows. An extreme event may have small probability but high impact,
as opposed to a more frequent event with lower impact. The sum of individual probabili-ties
of exceedance of a set of particular runup heights in a given analysis over all possible
scenarios for a specific return period will provide the total probability of exceedance of
the smallest runup height in the set.
Consider the probability of 2m runup in a given location 10% in a five year interval
from a given source A, while the probability of 10m runup from another source B is
1% in the same interval. Then one could conclude that the expected runup value for
five years for this location from sources A and B is 0.21m. This prediction is less use-ful
than the probability of exceedance of a given runup value in the same time interval
from different sources, because the two sources A and B are unlikely to rupture simul-taneously
in the same time interval. For example, one expects that, if the probability
of exceeding 10m in any given year is 1% from source A, and 0.01% from source B,
112
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 127 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | Chapter 3 Probabilistic Tsunami Hazard Assessment 3.1 Introduction Probabilistic hazard analysis in tsunami studies involves determining the probability of exceedance of specific runup values in specific time windows through the superposition of runup predictions from specific sources and their probabilities of occurrence during the same time windows. An extreme event may have small probability but high impact, as opposed to a more frequent event with lower impact. The sum of individual probabili-ties of exceedance of a set of particular runup heights in a given analysis over all possible scenarios for a specific return period will provide the total probability of exceedance of the smallest runup height in the set. Consider the probability of 2m runup in a given location 10% in a five year interval from a given source A, while the probability of 10m runup from another source B is 1% in the same interval. Then one could conclude that the expected runup value for five years for this location from sources A and B is 0.21m. This prediction is less use-ful than the probability of exceedance of a given runup value in the same time interval from different sources, because the two sources A and B are unlikely to rupture simul-taneously in the same time interval. For example, one expects that, if the probability of exceeding 10m in any given year is 1% from source A, and 0.01% from source B, 112 |
