地震災害を考える 予測と対策 ナショナルセンターを目指した活断層研究センターの試み

Abstract

Active Fault Research Center (AFRC) was launched in April 2001 as one of major research units for the new Geological Survey of Japan (GSJ), according to the establishment of the National Institute of Advanced Industrial Science and Technology (AIST) AFRC is one of the responsible organizations for active fault studies in Japan under the Japanese government Headquarters for Earthquake Research Promotion (HQERP) AFRC conducts the following researches that is closely related to active faults.Study of active faults : HQERP has selected 98 active faults that are subject to prompt survey. These major active faults will be surveyed using various methods such as geological mapping, trenching and boring, in order to reveal the distribution and extent of each fault, timing of the last rupture event and recurrence intervals. On the basis of such paleoseismological data, the AFRC evaluates the possibility of future rupture and earthquake magnitude for each fault.Study of fault segmentation : A long active fault consists of several segments which can produce both single- and multiple-segment earthquakes. The important factors for segmentation study are the geometry, length, displacement and paleoseismicity of the surface faults of recent earthquakes to reveal the characteristics of fault segments. Modeling a faulting behavior using seismological and geodetic data for the evaluating future earthquakes on long active faults is also an essential part of this study. The North Anatolian fault in Turkey and the San Andreas fault in California, USA are two major on going international studies field being undertaken with the cooperation of the MTA-Turkey and the US Geological Survey, respectively.Studies in earthquake hazard assessment : On the basis of active fault study and fault modeling, AFRC estimates ground shaking from earthquakes. Earthquake ground shaking and damage is strongly dependent upon the epicentral distance, the way rupture propagates in a fault, and the characteristics of the subsurface structure. Considering these factors, simulation of the generation and propagation of seismic waves will be studied.Maintenance of an active fault database : AFRC publishes Annual Reports on Active Fault and Paleoearthquake Researches, and also publishes active fault strip maps and 1 : 500, 000- scale seismotectonic maps. There are plans to publish maps showing possible hazards from future earthquakes, in addition to maps showing rupture probabilities of major active faults in Japan. The AFRC will collect as much existing geological data as possible that is related to active faults and their activities. The AFRC will also create and maintain a database for longterm evaluation dataset and survey results of major active faults. All literature and databases will be open to the public and researchers.The author sincerely hopes that the new AFRC will become a key research institutes for earthquake hazard mitigation in Japan and play an important role as the national center for active faults in Japan.