Edited by ahmet cevdet yalçiner efim pelinovsky, emile okal, costas emmanuel synolakis nato Science Series

5-6. Vulnerability Assessment as a Tool for Hazard Mitigation

5-7. Producing Inundation Maps; the California Experience

PREFACE
Tsunamis can inflict significant damage and casualties both nearfield and after evolving over long propagation distances and impacting distant coastlines. Tsunamis can also effect geomorphologic changes along the coast. Tsunamis can be triggered by sea floor deformation, landslides, slumps, subsidence, volcanic eruptions and bolide impacts. Understanding tsunami generation is of paramount importance for protecting coastal population at risk, coastal structures and the natural environment.

Accurately and reliably predicting the initial waveform and the associated coastal effects of tsunamis remains one of the most vexing problems in geophysics, and -with few exceptions- has resisted routine numerical computation or off-the-shelf solutions.  While ten years ago, it was believed that the generation problem was adequately understood for useful predictions, it is now clear that it is not, in many cases of practical interest. By contrast, the runup problem earlier believed intractable is now well understood for all but the most extreme breaking wave events. Hence tsunami investigations have become highly interdisciplinary with contributions from basic and applied science to coastal zone management so that the overall hazard is better assessed in the context of the limits of our understanding. Most comprehensive modern investigations involve any number of marine surveys on tsunamigenic ocean floor, of underwater faults, studies of landslide and slump geology, of sediment stability and underwater ground failures, not to mention seismic considerations, theoretical and computational approaches and hydromechanics. At present, even applied engineering studies often extend to studying historical events, database management, instrumentation, risk, warning, preparedness, and hazards mitigation. Without mitigation, future tsunamis could be even more catastrophic than historic ones, due to steady growth in coastal land use and economic development, as seen in the last fifty years.

Protection from natural disasters is now undisputable one of the societal priorities all over the world. Following Plafker's classic analyses of the 1964 tsunami, recent tsunamis, including the 1979 Nice France, 1992 Nicaragua, 1992 Flores, 1993, Okushiri, Japan, 1994 Skagway, Alaska, 1994 East Java, Indonesia, 1994 Mindoro, Philippines, 1994 Kuril Islands, Russia, 1996, Chimbote, Peru 1998 Sissano, Papua New Guinea, 1999 Izmit, Turkey, 1999 Pentecost, Vanuatu, 2001 Camana, Peru, and 2002 Wewak, Papua New Guinea events, have all shown the importance of considering multiple ground failure tsunamigenic sources for the same event. Tsunamis generated by slope failures may cause higher runup along shorter lengths of coastlines and often cause very strong, near-shore currents.  Tsunamis generated by tectonic displacements often cause more widespread damage than those from slope failures, even though locally the inundation heights might be less extreme. Many events involve both types of tsunamigenesis.

Currently, sufficient quantitative comparison of different methods of tsunami generation is lacking, so that adequate discrimination of their sources from coastal inundation data is difficult and chancy. Even for the case of the 1998 Papua New Guinea tsunami, despite numerous extensive bathymetric surveys almost immediately following the event, only recently is consensus emerging about the crucial role of the landslide in the devastating tsunami. For many other events, necessary information on underwater ground failures is lacking, due to insufficient marine geologic data, or its unavailability for proprietary reasons. Even when provocative signatures of earlier events are identified on the seafloor, the timing and the sequence of failures remain very difficult to predict, thus allowing only for the calculation of worst-case scenarios, at least at present.
The NATO Advanced Research Workshop on "Underwater Ground Failures on Tsunami Generation Modeling Risk and Mitigation" was organized in Istanbul on May 2001 through support from NATO Science Committee, Division of Scientific and Environmental Affairs. The objective was to better understand tsunamigenesis in the light of recent results, in a forum encouraging frank and uninhibited discussion in the most classic collegial manner of academia. The deliberations were covered in the national and international press, notably in the August 17, 2001 issue of the SCIENCE Magazine. The workshop discussed existing theoretical and experimental studies and examined new ideas and techniques to investigate and model the source mechanisms of tsunamis and their impact. Advanced research papers selected from the presentations are presented in this book after peer review.

In two instances papers that would otherwise not have passed peer review were included in this volume. The editors felt that they present provocative work not often accessible in the worldwide scientific literature, and its wider dissemination will allow the extended community to evaluate its merits, consistent with the objectives of the ARW.

We hope that the new (and not so new) approaches, the comparisons among existing models and the development of newer ones, the coastal zone management and risk reduction considerations, will all help tsunami scientists, planners and policy makers to better mitigate present and future tsunami hazards.

Acknowledgements

The National Science Foundation (NSF) of the United States, Scientific and Technical Research Council (TUBITAK) of Turkey, Greek Ministry of Industry General Secretariat of Research&Technology International Organizations Department, Russian Fund for Basic Research, Middle East Technical University, University of Southern California, Northwestern University, Tohoku University, Yüksel Proje International Co, Kiska Komandit Co. are cheerfully acknowledged for their various and valuable forms of support to the workshop, either through travel grants or organizational funds.

February 2003

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