IRS-P5影像提取DEM技术在大青山山前断裂古地震研究的应用

Application of DEM Extracted from IRS-P5 Stereo Images on Paleo-Earthquake Study of Daqingshan Piedmont Fault

以内蒙古大青山山前断裂中间三段的IRS-P5全色立体像对为例生成DEM,利用检查点法对DEM进行精度评定,DEM的高程精度能达到1∶10 000地形图山地和高山地测图中误差要求。在DEM数据中提取了横穿断裂的25条冲沟,并在冲沟纵剖面中提取了该断裂在全新世活动形成的裂点。在从左到右三段断裂上升盘的冲沟中分别识别出6、5和3级裂点序列。通过土右西段和土左西段最新一级裂点后退距离和公元849年地震距今时间,分别计算了这两段上各条冲沟最新一级裂点的后退速率,并以此速率作为各条冲沟裂点的后退速率。利用土右西和土左西两条冲沟最新一级裂点的后退速率平均值作为毕克齐段冲沟裂点后退速率。结合三段上各条冲沟裂点后退距离,分别得到断裂上升盘冲沟各级裂点形成时间,从而得到三段断裂全新世古地震事件序列。本研究得到的大青山山前断裂中间三段全新世古地震序列与前人通过探槽开挖和利用断层下降盘全新世古土壤揭露的古地震序列能够很好地对比。

A case DEMwas extracted from IRS-P5 stereo images of middle three segments （Tuyou,Tuzuo and Bikeqi）in Daqingshan piedmont fault,and this DEM’s vertical accuracy was tested to meet hilly-area and mountainous-region requirement of 1∶10,000 topographic maps.Twenty-five gullies across the fault on the foot-wall have been extracted from this DEM,and the knickpoints caused by fault activities in Holocene have further been extracted from profiles of gullies,and the six-,five-and three-ranks of knickpoints are identified in the gullies from west to east.The newest rank knickpoints in the Tuyou and Tuzuo segments are regarded as those caused by the A.D.849 earthquake to get their retreat rates.The retreat rate of the newest knickpoint in each gully is also considered as that of other points in the same gully;the average retreat-rate value of the newest rank knickpoints in the Tuyou and Tuzuo segments is considered as that of the knickpoints in the Bikeqi seg-ment;then the formation time of the six-,five-and three-ranks of knickpoints in the three segments is computed combining with the retreat distances of knickpoints on the gullies,thus the paleo-earthquake series in the study area in Holocene have been obtained.These paleo-earthquake series are close to the results that are derived from trench techniques and Holocene paleosols in paleo-alluvial-pluvial fans in previous studies.