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IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS006 Poster presentation 1943 A fresh fault scarp identified in an urban district by LiDAR survey: A case study on the Itoigawa-Shizuoka Tectonic Line, central Japan Dr. Hisao Kondo Active Fault Research Center Geological Survey of JapanAIST Shinji Toda, Koji Okumura, Keita Takada, Tatsuro Chiba A light detection and ranging (LiDAR) survey that provides us high-resolution DEM has been successfully applied to the field of active tectonics recently to reveal invisible and obscure active faults, especially in forested areas. Here, we apply the LiDAR to an urban district in which detailed fault mapping is normally difficult due to densely built-up area in central Japan. Matsumoto City, which is located on a ca. 3 km square basin along the middle section of the Itoigawa-Shizuoka Tectonic Line active fault system (ISTL), one of the major active fault systems in Japan, shows us a large gap of the fault continuity. As the result of the survey, we found obvious fault scarps in the densely populated area. For the LiDAR, the data were acquired from a Cessna, which basically flew at the position of 750m above ground surface with laser scanning angle of 15 degrees. Along the expected fault traces, in order to avoid loss of laser returns to ground surface insulated with buildings, data was acquired from the position of 1000m above ground surface with a scanning angle of 12 degrees. GPS position control and Inertial Measurement Unit (IMU) data were combined with the time of flight for the laser data to produce DSM data. After filtering process to remove noise data, and laser returns to buildings and vegetations, DEM data at 0.5-m-grid interval was processed. Based on the high-resolution DEM, a continuous one-meter-high scarp was clearly recognized on alluvial fan surfaces in the urban district, west of the Matsumoto castle built in the ca. 16th century. Since the trend of west-facing scarp is almost perpendicular to the general flowdirection of streams, the scarp can be geomorphologically interpreted as tectonic origin. Taking distribution of adjacent active faults into considerations, the newly found fault traces probably contribute to form a pull-apart basin related to a fault step-over between the Gofukuji fault and the East Matsumoto Basin faults of which predominant slip component are left-lateral strike-slip. Since the Gofukuji fault has 14% earthquake probability for the next 30 years based on previous paleoseismic studies, the existence of such a fault scarp in urban district and its tectonic interpretation in Matsumoto City is crucial not only for evaluation of the future surface rupturing and direct strong shaking from the source but also for fault segmentation of the ISTL. Thus, the application of the current LiDAR survey technology to other urban areas would provide advantages in various aspects of seismic hazard mitigation. Keywords: paleoseismology, lidar

IUGG XXIV General Assembly July 2-13, 2007 Perugia, Italy (S) - IASPEI - International Association of Seismology and Physics of the Earth's Interior JSS006 Poster presentation 1944 NEotectonic derived models for crustal deformation in a stable continental region setting: insight from the Southwest Of western Australia. Dr. Mark Leonard Geoscience Australia Geohazards IASPEI Dan Clark In recent times, high resolution digital elevation models (DEMs) have emerged as an important tool for finding and characterising earthquake related geomorphology, and particularly fault scarps. The results of a reconnaissance investigation of two DEM datasets covering a large portion of southwest and central Western Australia are presented. A total of thirty-three new fault scarps of probable Quaternary age have been identified, bringing the total number of neotectonic features in the area to sixty. The scarps are spatially isolated and range in length from ~15 km to over 45 km, and from ~1.5 m to 20 m in height. Most scarps where a displacement sense could be determined from the DEM data suggest reverse displacement on the underlying fault. In the few instances where high-resolution aeromagnetic data is coincident with a scarp location the ruptures are seen to exploit pre-existing crustal weaknesses. Twenty-one of the features have been verified as fault scarps by ground-truthing, and range in apparent age from perhaps less than a thousand years to many tens of thousands of years. Only four have been quantitatively examined to determine source parameters (e.g. timing of events, recurrence, magnitude). However, three important characteristics are revealed in the extant data: 1) recurrence of surface breaking earthquakes on an individual fault is typical (ie. areas hosting active fault scarps are earthquake-prone), 2) temporal clustering of events is apparent on many faults (ie. large earthquake recurrence in active phases might be much less than during inactive phases), and 3) significantly larger events than have been seen in historic times (MW>7.2) might be expected in the future, Australia-wide. This rich neotectonic record also provides an opportunity to understand the characteristics of intraplate deformation at the scale of the entire Precambrian shield region (the Yilgarn Craton). An uniform distribution of the northerly trending scarps suggests that strain is uniformly accommodated over the Yilgarn Craton at geologic timescales, and that the easterly-trending compressive contemporary stress field has pertained for hundreds of thousands of years or more. This evidence supports a model whereby the lower, ductile part of the lithosphere is uniformly strong and deforms uniformly, and the upper (seismogenic) layer accommodates this large-scale flow by localised, transient and recurrent brittle deformation in zones of pre-existing crustal weakness. The proposed model implies uniform seismic hazard across the southwest of Western Australia, but at a timescale much greater than useful for most seismic hazard assessment applications. Palaeoseismological data on individual faults is playing an important role in bridging the gap between this seismicity model and the historic record of seismicity in , upon which all current seismic hazard assessments are based. Keywords: neotectonic, paleoseismicity, earthquake

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