|Report from Hokudan: Active Fault Research Moves Into the New Millennium
|Tim Dawson, Marco Shmulik, Takashi Nakata, Koji Okumura, Heidi Stenner|
|Over 150 participants representing nearly 25 countries gathered for the Hokudan International Symposium and School on Active Faulting, held in Hokudan, Japan between January 17-26, 2000. The meeting began on the fifth anniversary of 1995 Hansin-Awaji (Kobe) earthquake in Hokudan town, which killed nearly 6000 people and caused almost $115 billion in damage. The setting was particularly appropriate because the town of Hokudan has built an impressive earthquake memorial park and seminar house dedicated to earthquake education. Centerpiece of the park is a 140 m long structure erected over the surface trace of the Nojima fault. This structure protects the surface trace of the fault and offset cultural features and has served to educate millions of visitors since it first opened in 1997. It was in the spirit of education that the meeting participants convened to present developments in active fault research to fellow scientists and the Japanese public.
Sponsored by a number of institutions including Hokudan Town and the International Lithosphere Task Groups II-5: Earthquake Recurrence Through Time and II-2: World Map of Active Faults, the objective of the meeting was to gather the leading researchers to present the latest results of active fault research in an international forum. The meeting attracted disciplines ranging from geologists to engineers who presented a broad spectrum of research in active tectonics, from the collection of earthquake geologic data to their application in probabilistic seismic hazard analysis and disaster mitigation.
The meeting opened with a lecture delivered by Nobuyaki Yonekura (University of Tokyo), who summarized the rich 110 year history of active fault research in Japan. Beginning with the pioneering work by Bunjiro Koto, following the great 1891 surface-faulting Nobi earthquake, to the increasing number of investigations of active faults following the 1995 Hansin-Awaji earthquake, it is clear that the scientific community in Japan has been at the forefront of active fault research.
If the opening lecture's theme summarized the past and present of research in active tectonics, the second opening lecture, delivered by David Schwartz (USGS) took on a different tone. Preferring to focus on the future, Schwartz discussed the state of knowledge and the challenges ahead in the fields of paleoseismology and active faulting. Central to the talk was the role of the paleoseismologist who provides the geologic data through which fault behavior can be characterized. Despite nearly 30 years of paleoseismic studies, Schwartz expressed concern about the paucity of high-quality earthquake recurrence and slip-per-event data that is currently available. Of equal concern is the subjective nature of paleoseismic interpretation. However, Schwartz is optimistic that these limitations can be mitigated through in-the-field peer review, explicit listing of uncertainties, and additional exposures at a site, which all lead to interpretations that are reproducible and give a measure of redundancy through increasing the number of independent observations.
Other highlights of the opening day session was David Jackson's lecture "Estimating earthquake potential from faults", which generated much discussion about theoretical mechanics. Jackson's statistical modeling predicts the occurrence of very large and infrequent earthquakes on faults versus geologic observations that emphasizes a more quasi-periodic earthquake of a "characteristic" size. Lastly, the concluding talks of the first day highlighted the use of active fault studies as an end product in engineering applications and probabilistic seismic hazard analysis.
As the symposium and school progressed over the next few days, many participants were impressed at how far active tectonics research has come in recent decades. Highlights included a synthesis of earthquake geology studies applied to seismic hazard in New Zealand, presented by Kelvin Berryman (IGNS). Kerry Sieh (Caltech) presented the results of research along the Sumatran subduction zone, which has gone beyond paleoseismology and ventured into paleogeodesy. Shinji Toda (University of Tokyo) described the results of static stress modeling for the Parkfield section of the San Andreas fault. Such modeling has gained popularity in recent years as a way to examine fault interaction and gauge the effect that an earthquake has on nearby faults in terms of stress increase and transient changes in conditional probabilities
A recurrent theme of the symposium, to which a session titled "Application and Knowledge Transfer on Active Faulting and Hazard Mitigation", was devoted to, emphasized the interaction between the research scientist and the public. Earl Hart, former program manager of the Fault Education and Zoning Program for the California Division of Mines and Geology, described California's progressive efforts at disaster mitigation through the Alquist-Priolo Earthquake Fault Zoning Act, which prevents structures from being built on active fault traces. This lead to a spirited discussion as to whether such zonation was appropriate for Japan and other countries, given the limited amount of buildable land in urban areas. Mike Machette (USGS) unveiled the new WWW-based digital map and database of active faults and folds in the United States. This interactive database represents the future of data collection and information dissemination, where scientists will be able to enter their research results into a central database that is accessible over the World Wide Web. A similar worldwide database for earthquake recurrence information is being put together under the direction of Daniela Pantosti (ING Rome).
The knowledge transfer theme culminated with several public lectures and an open house where the public was invited to view the poster presentations of the symposium participants. Studies from China, India, Indonesia, Iran, Nepal, Pakistan, Philippines, and Vietnam, were just a few of the countries represented at the poster session. Although knowledge transfer from the scientist to the public was one of the primary purposes of the open house, this was far from a one way street. What made this meeting different and special was the involvement of the local community. Participants had an opportunity to listen to people who came to the meeting and gave us a moving account on the 1995 earthquake as well as their lessons learned from it.
In addition to the moving accounts of the 1995 earthquake described at the public session, the series of recent devastating earthquakes in Turkey and Taiwan, gave many scientists a sense of urgency to the research that is being conducted. Consequently, several presentations focused on the Izmit, Chi-Chi, and Duzce earthquakes. Aykut Barka (Istanbul Technical University) described efforts to characterize the seismic hazard posed to Istanbul through post-earthquake static stress change modeling coupled with paleoseismic trenching planned for this summer. This interdisciplinary approach represents the state of the art in seismic hazard assessment and will hopefully improve the ability of the scientist to provide meaningful earthquake forecasts to populations situated in seismically active regions.
A striking aspect of the meeting is the level of international collaboration that is being carried out. The Duzce earthquake investigation, whose results were presented by Omer Emre and colleagues, is a collaborative effort between the MTA of Turkey and Geological Survey of Japan. Ongoing cooperative agreements between agencies such as the Geological Survey of Japan and the United States Geological Survey have yielded a productive exchange of ideas and technology. One such example was the demonstration of the "geoslicer", a new tool developed by Japanese scientists for paleoseismic studies in wet environments. Many paleoseismologists were duly impressed by the demonstration, which recovered a 2x4m surface section containing the 1995 Nojima fault rupture, and eager to try the model donated by Takashi Nakata (Hiroshima University) for use in the United States. As the meeting progressed, it became obvious that international collaboration is now necessary in order to address the key issues of seismic hazard and distribute needed scientific expertise around the world.
As the meeting ended, most attendees appreciated the great strides in understanding earthquake processes that the field of active tectonics has made during the last few decades. However, it is clear much work remains in order to characterize the spectrum of fault behavior and seismic hazard posed to populations situated in seismically active zones around the world. Large data gaps still exist for some of the world's most studied faults such as the Median Tectonic Line in Japan and the San Andreas fault in California. The success of the Hokudan International Symposium and School on Active Faulting can be measured on many levels. The goals of presenting research, promoting discussion, and facilitating new scientific collaboration were all easily achieved by a group of scientists highly dedicated to their work. But most importantly, the Hokudan International Symposium and School on Active Faulting has inspired a new generation of scientists to accept the challenge and continue research in active tectonics into the new millennium.