ACTIVE FOLDING AND ACTIVE FLEXURAL-SLIP FAULT SCARPS ON MINGYAOLE ANTICLINE, WEST MARGIN OF TARIM

doi:10.3969/j.issn.0253-4967.2014.02.002

Abstract

Abstract: In recent times, some moderate-large earthquakes occurred in active folds and thrusts, which seem not directly related with known active faults on the surface and did not form surface ruptures. Although such individual earthquakes might correspond to a known surface active fault, most of them occurred under active folds, formed by displacement of burial thrusts which are located at depth of tens kilometers beneath the folds. Stein named such earthquake as "folding earthquake". It is quite a challenging issue to study and assess the seismic hazards of folding earthquakes occurring in compressive tectonic regions with active folds and burial thrusts. Derived from active folding secondary faults such as flexural-slip faults, bend-moment faults, it is easier to identify that the fold itself. These secondary faults have coseismic slip at the surface and record the active history of seismogenic thrusts which provide an effective way to study the seismic activity of blind thrusts. Many flexural-slip fault scarps are developed on several terrace surfaces at the two limbs of Mingyaole anticline, located along the western margin of the Tarim Basin. These scarps mainly form on the limb of steep beds closest to active axial surfaces(dips of 74°～89°, 18°～20° and 45°～60°, separately), within a range of 50～1 200m from active axial surface, and most are 90～1 000m wide. Overall, the height of the flexural-slip fault scarps gradually deceases away from the active axial surface. These scarps occur at nearly equidistant or multiple distance spacing on the same terrace surface. The strike of the flexural-slip fault scarp is consistent with the strike of underlying bedrock, which is dominated by interbedded medium-thick layered sandstone or fine-grain sandstone with similar rock mechanical properties. Since the abandonment of terrace T3 at the south limb of the Mingyaole anticline, the shortening rate and uplift rate absorbed by flexural-slip faults are at least (1.0±0.2)mm/a, (1.2±0.1)mm/a, respectively. Movement of the flexural-slip faults is characterized by repeatability and neo-activity.

Key words: active fold, active axial surface, flexural-slip fault scarp, Mingyaole anticline

摘要： 塔里木西缘明尧勒活动背斜两翼河流阶地面上多处发育活动弯滑断层陡坎。这些断坎主要分布在活动轴面附近较陡的等斜岩层（地层倾角分别为74°～89°、18°～20°和45°～60°）一翼，往往成排发育在距活动轴面50～1 200m范围内，宽90～1 000m，长40～950m，随着离活动轴面的距离加大弯滑断层陡坎规模渐小。同一阶地面上发育的弯滑断层陡坎几乎以等间距或间距倍数关系产出。这些断坎走向与下伏基岩地层走向一致，基岩地层大多为中-厚层块状砂岩或粉砂岩互层，岩层间力学性质差异较小。明尧勒背斜南翼克孜勒苏河北岸T₃阶地面废弃以来，单条弯滑断层的地表最大缩短速率为0.31mm/a，地表最大抬升速率为0.34mm/a。这些弯滑断层的活动具有重复性和新生性。

关键词: 活动褶皱, 活动轴面, 弯滑断层陡坎

CLC Number:

P315.2

YANG Xiao-dong, CHEN Jie, LI Tao, LI Wen-qiao, LIU Lang-tao, YANG Hui-li. ACTIVE FOLDING AND ACTIVE FLEXURAL-SLIP FAULT SCARPS ON MINGYAOLE ANTICLINE, WEST MARGIN OF TARIM[J]. SEISMOLOGY AND GEOLOGY, 2014, 36(1): 14-27.

杨晓东, 陈杰, 李涛, 李文巧, 刘浪涛, 杨会丽. 塔里木西缘明尧勒背斜的弯滑褶皱作用与活动弯滑断层陡坎[J]. 地震地质, 2014, 36(1): 14-27.

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[1]	LI Tao, CHEN Jie, XIAO Wei-peng. DEFORMATION CHARACTERISTICS AND KINEMATICS OF ACTIVE DETACHMENT FOLD SCARP：A CASE STUDY FROM THE MINGYAOLE ANTICLINE, PAMIR-SOUTHERN TIANSHAN FORELAND [J]. SEISMOLOGY AND GEOLOGY, 2014, 36(3): 677-691.
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[4]	Yang Xiaoping, Zhou Bengang, Li Jun, Sun Jianbao. SHORTENING AND UPLIFT OF THE ACTIVE YAKEN ANTICLINE, SOUTHERN TIANSHAN, CHINA SINCE LATE PLEISTOCENE [J]. SEISMOLOGY AND GEOLOGY, 2001, 23(4): 501-509.