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spit in the Humboldt Bay will be having new residential developments, and thus has
been studied as a special interest locale in this section. Humboldt Bay area is a tsunami
high risk area, composed of north and south spit, where the south part of the spit of is
low terrain, extremely susceptible to any flooding. The northern part has sand dunes that
appeared to have protected Humboldt County during historical events (Dengler, 2007).
Computed Inundation Heights in Humboldt Bay and Discussion
Figures 2.30 and 2.31 compare computed results from the CSZ SP1 scenario earthquake.
The inundation from the CSZ SP1 and CSZ L cases was calculated at 30m resolution as
shown in Figure 2.31. Luckily, for each of the cases modeled, it appeared that the Samoa
area was being not inundated. The model suggests that for these events the dunes on the
northern sand spit might be high enough to prevent inundation directly from the sea.
This is shown in Figure 2.31, where cross sections of maximum tsunami wave height
are plotted over the local topography.
It is also interesting to note that the region is not inundated from the lagoon side,
either. Animations of the time histories of water levels from the simulations do not show
this area being flooded. This may be attributed to the degree of local co-seismic uplift
which is incorporated into the simulation. Because the ground level was raised during
the seismic event, the end result is that waves which would have otherwise inundated
the area are unable to flood over the new land level. This effect was observed in recent
tsunami events such as the March 28, 2005 Nias-Simeulue tsunami where local ground
uplift was on the order of 2–4m (Borrero et al., 2006b).
Figure 2.30 show time series histories of water levels on either side of the north spit.
The time histories are shown relative to ground levels before the earthquake event. The
time series are taken from gauges located in deep enough water to see the full cycle of
105
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 120 |
| Contributing entity | University of Southern California |
| Repository email | cisadmin@lib.usc.edu |
| Full text | spit in the Humboldt Bay will be having new residential developments, and thus has been studied as a special interest locale in this section. Humboldt Bay area is a tsunami high risk area, composed of north and south spit, where the south part of the spit of is low terrain, extremely susceptible to any flooding. The northern part has sand dunes that appeared to have protected Humboldt County during historical events (Dengler, 2007). Computed Inundation Heights in Humboldt Bay and Discussion Figures 2.30 and 2.31 compare computed results from the CSZ SP1 scenario earthquake. The inundation from the CSZ SP1 and CSZ L cases was calculated at 30m resolution as shown in Figure 2.31. Luckily, for each of the cases modeled, it appeared that the Samoa area was being not inundated. The model suggests that for these events the dunes on the northern sand spit might be high enough to prevent inundation directly from the sea. This is shown in Figure 2.31, where cross sections of maximum tsunami wave height are plotted over the local topography. It is also interesting to note that the region is not inundated from the lagoon side, either. Animations of the time histories of water levels from the simulations do not show this area being flooded. This may be attributed to the degree of local co-seismic uplift which is incorporated into the simulation. Because the ground level was raised during the seismic event, the end result is that waves which would have otherwise inundated the area are unable to flood over the new land level. This effect was observed in recent tsunami events such as the March 28, 2005 Nias-Simeulue tsunami where local ground uplift was on the order of 2–4m (Borrero et al., 2006b). Figure 2.30 show time series histories of water levels on either side of the north spit. The time histories are shown relative to ground levels before the earthquake event. The time series are taken from gauges located in deep enough water to see the full cycle of 105 |
