tsunami.oregonstate.edu

Motivation

Earthquake scientists and engineers are well aware of the importance of detailed field (reconnaissance) surveys immediately after an event. The surveys provide valuable lessons learned from real effects of the actual events. However, it is difficult to collect sufficient and accurate data from surveys because the data/information are ephemeral and difficult to obtain. International boundaries and rescue efforts cause understandably delayed access to the field sites. News media, time and trauma alter the memories of actual eyewitnesses. Marks of tsunami passage and destroyed structures are quickly removed in the effort to recover normalcy in a tsunami-damaged community. Furthermore, there is no way to make advance preparations to obtain data since it would be a formidable task to install a sufficient number of sensors in the field prior to a very unpredictable and rare tsunami event.

An alternative to a full-scale field investigation is to perform repeatable and precisely controlled “scenario” simulations. A scenario simulation means a case study, either in a real or hypothetical background setup. Tsunami phenomena and effects are simulated for given geographical, seismological, geological, and societal conditions. Simulations must be comprehensive and integrate not only tsunami generation, propagation, runup motion (flow velocities and inundation) and flow-structure interactions, but also other types of simulations such as warning transmission to the public, evacuation, environmental impacts, rescue tactics and short-term and long-term recovery strategies. The simulation exercises should include physical models, numerical models, informatics, human behavior, communi cation simulations, and other exercises that will integrate the tsunami source with its eventual effects on communities and the environment. This activity is by nature a multi-university, multi-community, and multi-disciplinary effort.

The concept of scenario simulation is not new and numerous cases have been performed especially for purposes of disaster response and disaster preparedness. Many of the tsunami-related simulations are conducted by a small number of participants in a specific discipline or are limited to a specific geographic location. For example, a study entitled “Planning Scenario in Humboldt and Del Norte Counties for a Great Earthquake on the Cascadia Subduction Zone,” was conducted in 1992 by FEMA, NOAA, and the State of California (Toppozada, 1995). For a given hypothetical generation condition in the Cascadia subduction zone, inundation areas, shaking intensity, liquefaction and other effects of the earthquake were identified. Although inundation estimates are very valuable, it should be realized that they are usually based on only one numerical model, i.e., one of a number that are currently available in the U.S. and overseas. Considering the critical nature of such estimates, it is important that model results used for inundation be confirmed by several means (including large-scale laboratory simulations where appropriate) so that their limits of applicability can be clearly defined.

It is not our immediate objective to determine specific tsunami mitigation measures for specific coastal towns and cities. Instead, we will set up a fully integrated scenario for a hypothetical situation (which could be based on an existing real coastal community) to be investigated by researchers from a wide variety of disciplines working to solve a common problem from different angles. The outcome of the exercise will provide the participants, the sponsors and coastal communities with valuable experi ence, lessons learned from the model event, and will enhance and maintain further research collaboration for tsunami hazard reduction. The simulation exercise based upon a hypothetical but realistic coastal situation would result in realistic engineering evaluation, but it would not cause the potential social and political concerns of a direct study of a specific location. An additional and important benefit of the use of a hypothetical scenario is to provide a better means for technology transfer from basic research. Results from research in academia generally end up in journal publication, but not be extended beyond in spite of their potential usefulness. Presence of the hypothetical scenario would encourage a researcher to validate her/his model for the ideal and common scenario, and the results would be effectively disseminated to the broader community.

Involvement in the scenario simulation and work on the common problem will lead each researcher in their specialized area to interact closely with researchers in other areas. The researchers will obtain a broader picture for tsunami research, and identify critical problems and linkages to be examined for improvement. For example, through this program, a numerical specialist will simulate tsunami propagation and runup for a given scenario bathymetry and topography. She/he must determine the initial condition for the hydrodynamics with seismologists and geologists who evaluate seafloor displacement from a predetermined set of seismic signals. The numerical results will be carefully examined, compared and discussed with other numerical models as well as the laboratory data taken by experimentalists (e.g. NEES facilities). The numerical specialists will also play a role in the determination of tsunami forces and sediment scour on model structures. This task will necessitate close collaboration with structural and geotechnical engineers. The numerically simulated tsunami arrival t ime and the temporal and spatial flow patterns will provide critical information for warning transmission systems and evacuation and rescue simulations. These require detailed flow information such as velocities, runup/rundown flow depths, sediment interaction, and behavior of water-born missiles (timbers, automobiles, washed-out houses, etc). It is certain that, through this exercise, any in the deficiencies in the numerical models will be identified that can then be a focus for future refinements. Similarly, the data needs for the numerical models and the use of model data will also highlight any needed improvements in linkages either further up or further down the chain.

An example of an integrated program in the area of seismic hazards is Seismic Performance for Urban Regions (SPUR), a joint project between engineering groups at Mississippi State University, Carnegie Mellon University, and the University of California, Berkeley (http://www.erc.msstate.edu/vail/projects/SPUR/). The long-term objective of SPUR is to advance the state-of-the-art in simulating the effects of a major earthquake on an urban region by the integration of earthquake-ground-motion modeling with modeling of structural and infrastructure systems using a distributed interactive simulation. The goal is to provide damage estimates based on best available information ultimately leading to earthquake related risk analysis for an urban region and to provide a rich problem-solving environment for the education of students. A tsunami scenario simulation must actually expand this concept to include the modeling of human behavior since a primary emphasis of tsunami hazard mitigation is not only minimization of structural damage but also the saving of lives through evacuation: recall that tsunami attack has typically a sufficient lead time for evacuation.

In summary, through this type of integrat ed scenario simulation exercise, each researcher will earn experience just like that obtained through a real field investigation. Critical problems will be identified for improvement in her/his specialized area. The exercise will provide a common background for all researchers working in the tsunami area and maintain communication and coherence in this broadly distributed multi-disciplinary community. In addition, because of the integrated and highly visual output of the simulations, the exercise outcomes will be a valuable educational tool for not only for K-12, but also for public education in general.