[H-TT15] Geographic Information Systems and Cartography

[HTT15-02] Geomorphologic mapping and analysis to understand fault activities along the northern margin of the Yanfan Basin, China

*JIAJUN SUN^1,4、HONGLIN HE¹、TAKASHI OGUCHI^2,5、ZHANYU WEI¹、YUEREN XU³ (1.Institute of Geology, China Earthquake Administration、2.Center for Spatial Information Science, The University of Tokyo、3.Institute of Earthquake Forecasting, China Earthquake Administration、4.Beijing Earthquake Agency, China、5.Department of Natural Environment Studies, The University of Tokyo)

キーワード：High-resolution terrain data, geomorphological mapping, normal fault, vertical slip

The risk of strong earthquakes around the Capital City of Beijing has attracted scientific community concern since the 1976 Tangshan M 7.8 earthquake. Active faults at the northeastern end of the Shanxi Rift System have received particular attention for their short distance to the metropolitan. This study focuses on one of the faults, a normal fault along the northern margin of the Yanfan Basin, China, spanning ca. 105 km. The fault was displaced during past large earthquakes. Using 0.5-m resolution terrain data, we identified four surface levels of alluvial fans and river terraces with different relative elevations. We measured 378 vertical fault displacements on the geomorphic surfaces and uncovered the five groups of fault offsets. We used information from the previous trench surveys to infer the ages of the offsets, indicating that the five groups reflect repeated faulting since ca. 14 ka. The youngest offset group was due to the 1484 M 6 3/4 Juyongguan earthquake in the northeastern part of the fault and the 1337 M 6 1/2 Huailai earthquake in the southwestern part. The earthquake magnitudes are consistent with the estimated rapture lengths of the fault. Similar offset values for all five groups (ca. 2 m) suggest that each of the four older offset groups also consists of displacements from two or a bit more earthquakes that occurred at different parts of the fault but without a long interval. The method presented here may be applied to normal faults in other seismically active regions to examine paleoseismicity and future earthquake risks.