基于高精度机载LiDAR数据在GIS平台的地貌因子渲染分析，对海原断裂老虎山段松山地区古地震研究点进行高精度大比例尺（1∶1000）地貌填图，勾勒出研究点微地貌空间展布和断裂高精度几何形态。通过对松山古地震研究点2个新探槽的开挖，结合细致的探槽解译、地震事件识别与分期、年代学样品测试，得出5次37380±880BP以内的不连续古地震序列。通过对比此处已经开挖的各自相距不足150m、分布于断裂同一段落的4个古地震探槽的微地貌位置、沉积特征和地震事件信号强弱，发现即使相距不远，不同微地貌位置古地震探槽揭示的古地震现象也会有显著差别。这种差别凸显了古地震研究结果，如揭示的事件证据和个数等与探槽点位置的选取有较强的依赖性。综合对比分析表明，较低的地势、低能静水环境、高沉积速率、细粒的沉积物源区及连续的沉积环境是走滑断裂上开展古地震研究的优选地貌位置。实例表明，基于高精度地形数据对研究点开展精细地貌填图揭示微地貌时空演化，从而在探槽开挖前对古地震研究点的构造地貌优劣进行充分评价是提高古地震研究质量的必要程序，同时也显示出高精度机载LiDAR数据在活动构造研究中的重要新应用。%In this paper, the authors first carried out a large-scale (1∶1000) tecto-geomorphic mapping in the vicinity of the Song⁃shan paleoseismic study site on the Laohushan section of the Haiyuan fault by using high resolution ( 1m) airborne LiDAR DEM and with the aid of topographic enhancement through GIS tools. New paleoseismic results in two trenches opened near two previously published ones less than 150m to the east were reported, which allows a comprehensive comparison of four trenches in such aspects as geomorphic setting, sedimentary environment, number of paleoseismic events and their deformation styles. The new paleoseismic re⁃sults reveal a discontinuous paleoseismic sequence at 37380 ± 880BP including 5 events with different levels of certainty. The authors found that despite the fact that these trenches are located within short distances from each other, the stratigraphic resolution and paleo⁃ seismic event evidence exposed considerable difference from trench to trench. This implies that paleosiesmic results, such as the total number and robustness of stratigraphic evidence of paleoearthquakes, strongly depend on site location. Favorable depositional environ⁃menrts for an excellent preservation of paleoseismic record include topographic lows such as pull-apart basins allowing for low-ener⁃gy and fine graine size deposition as well as high sedimentation rate for strike-slip fault. Examples presented here suggest that large-scale tecto-geomorphic mapping, especially based on the high-resolution topography, is important for site selection, and such an ex⁃ercise is a necesssary reconnaissance step before opening a trench to maximize the quality of paleoseismic investigation. Such a prac⁃tice also shows the great potential and usefulness of airborne LiDAR data in better quantification of fault rupture behavior and fault ac⁃tivity in general.
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