International Symposium on Tsunami Disaster Mitigation in Future
Jan. 17-18, 2005, Kobe, Japan
determined after re-analysis that the 100-year data from far-field events is probably still adequate, but
that the 500-year data is more dominated by local tectonic or offshore landslide events..
In 1996, the U.S. National Tsunami Hazard Mitigation Program (NTHMP) was established to
provide resources for mitigating tsunami hazards, including inundation maps for the five states on the
Pacific Ocean. In 1998, the Tsunami Research Program at USC was funded to prepare the first
generation of inundation maps for California based on realistic worst-case scenarios. The mapping
priority for the state was based on population densities with Santa Barbara and San Francisco in year 1,
Los Angeles and San Diego in year 2, and Monterrey Bay in the final year. Offshore faults and
landslide-prone areas were identified, initial tsunami waves developed, and inundation heights and
penetration distances along target coastlines predicted using the propagation and runup model MOST
(Method Of Splitting Tsunami) of Titov and Gonzalez (1997). These inundation maps represent
maximum penetration from relocating worst-case scenario events along the coast, rather than any
particular event or characteristic earthquake (Synolakis et al. 2002).
For southern California, recent work has focused on nearshore tectonic sources created by
restraining bends in offshore strike slip faults (Legg et al. 2004, Borrero et al., 2004). Where strike
slip faults have curved traces, stresses created during earthquakes can result in tsunamigenic vertical
deformation of the sea floor. Figure 7 shows three such restraining bends offshore of southern
California, The Catalina Fault (CAT), Lasuen Knoll (LAS) and The San Mateo Thrust Fault (SAM).
Modeling the tsunamis generated by these events results in tsunami runup heights between 2 and 5
m along the coast of Southern California.
The modeling also shows that the shallow San Pedro
Shelf offshore of the Posts of Los Angeles and Long Beach acts to amplify tsunami waves while
retarding their arrival time. Scenarios modeled by Borrero et al. (2004) suggest that there may be as
much as 15 minutes delay in tsunami wave arrival into the Port areas from local sources. This time lag
suggests the possibility of a local warning system for the Ports that could suspend cargo handling or oil
transfer activities in the event of a large local earthquake.
The ports of LALB are the busiest in the U.S. and are located on the San Pedro Bay, adjacent to
the Palos Verdes (PV) Peninsula (Figure 7). In addition to the tectonic sources mentioned above,
landslide scars and deposits have been observed and described in this region since the 1950's
(McCulloch et al. 1985). One feature in particular, the Palos Verdes Debris Avalanche, is believed to
be the signature of a tsunamigenic submarine landslide. Although most of the extreme runup is located
around the PV cliffs, there is significant impact in the LALB, with projected losses of .5B (Borrero
et al. 2002). The broad San Pedro Shelf, although retarding tsunami arrival times, contributes to
tsunami wave focusing. Disruption of operations at the LALB port facilities due to tsunami attack
could severely impact the regional, national, and even global economies.
Currently the inundation mapping effort is focusing on nearshore and distant sources for the
northern part of the State and revised inundation maps for that area are expected to be completed in
2005.
Conclusions
This paper has described the current state of the Corps of Engineers tsunami disaster mitigation and
research in the United States. Because the U.S. has not had any major tsunami disasters in recent
years, the Corps does not have a formal mission or policy for incorporating tsunami runup
considerations in the design wave height for coastal structures. In the 1990's the Corps' Coastal and
Hydraulics Laboratory did participate in substantial physical modeling of tsunami runup on beaches,
vertical walls, and islands, as part of the National Science Foundation's Joint Tsunami Runup Study.
Flume and basin facilities, including a newer version of the DSWG used in the NSF study, are
available for future tsunami research at the CHL. The University of Southern California (USC) has
recently developed tsunami inundation maps for California based on far field and local tectonic and
landslide sources. An example using the ports of Los Angeles and Long Beach in southern California
was presented showing the potential for .5B in damages and disruption of port operations that could
significantly impact national and global economies.
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