活动褶皱陡坎的识别、变形、运动学模型与强震

The blind thrust, a type of faults that do not cut up to the surface, can trigger strong, destroyed earthquakes. It is challenged to assess seismic hazards of these active faults due to their weak coseismic surface deformation and unclear coseismic colluvial wedge deposits. Recently, the discovery of fold scarp, which is formed by blind thrust related fold, make it is possible to constrain the activity, evolving process and paleo-earthquake history of the blind thrust, through analyzing folding deformation on the surface. The blind thrust related fold can be categorized into fault-bend, fault-propagate and detachment fold. Till now, however, only fold scarp formed by fault-bend fold has been well studied. For other types, such as fault-propagate fold and detachment fold, can they produce fold scarp or not, and what deformation characteristics do they have? There is no related report. Located in the interfering zone of the Pamir and the Tianshan, the Mingyaole anticline is an active detachment anticline. A series of impressive fold scarps are occurred on the terrace surfaces in the Mingyaole fold, providing an excellent chance to study the fold scarp formed by detachment fold. Combining detailed geologic and geomorphic mapping, differential GPS survey, analysis of water pattern and Quaternary chronology (Optical Stimulated Luminescence or Cosmogenic Nuclides dating methods and so on), we plan to investigate deformation characteristics and identification methods of detachment fold scarp, to build its geometric and kinematic models, and try to constrain paleo-earthquake history of the Mingyaole fold via trenching the growth strata at front of fold scarps.

不出露地表的隐伏逆断层会诱发强破坏性地震，如何识别和研究该类发震构造是一新的课题和挑战。最近提出的褶皱陡坎的概念模型，通过对隐伏逆断层在地表形成的褶皱变形的分析，可限定断层的活动性、演化过程和古地震历史，这就为隐伏逆断层地震危险性评估提供了可能。隐伏逆断层形成的褶皱包括断弯、断展和滑脱褶皱等类型，但到目前只对断弯褶皱形成的褶皱陡坎进行了研究，对于断展褶皱和滑脱褶皱能否形成褶皱陡坎、具有怎样的变形特征等至今没有相关报道。在帕米尔-天山碰撞带明尧勒背斜的河流阶地上发育有一系列特征显著的褶皱陡坎。由于明尧勒背斜为滑脱褶皱，通过该研究，就有可能建立滑脱褶皱陡坎模型。拟通过对明尧勒背斜活动褶皱陡坎的地质地貌填图、地形测量、水系相关地貌参数分析和第四纪年代学研究，探讨滑脱褶皱陡坎变形特征和识别方法，建立相应的几何学和运动学模型，并尝试利用褶皱陡坎前缘的生长地层限定背斜下伏断层的古地震历史。

褶皱陡坎是褶皱生长过程中由于局部集中应变而形成的一种有别于断层陡坎的构造地貌类型。对该类陡坎的识别、变形特征的分析对于限定褶皱变形机制和生长演化历史至关重要。在帕米尔-天山碰撞带明尧勒背斜两翼的河流阶地上发育有一系列特征显著的褶皱陡坎。通过对这些褶皱陡坎详细的地质地貌填图、地形测量和分析，我们建立了基于地层几何形态分析的褶皱陡坎运动学模型。根据该模型，褶皱陡坎的坡度受控于枢纽两侧地层倾角和枢纽迁移距离/枢纽宽度(ratio)。陡坎形成初期，随着枢纽迁移距离的增大陡坎高度、宽度和坡度逐渐增大。当枢纽迁移距离达到枢纽宽度时(ratio=1)，陡坎坡度将达到最大值。此后尽管陡坎高度和宽度逐渐增大，其坡度将保持恒定。陡坎的最大坡度是枢纽两侧地层倾角的函数。利用褶皱陡坎的高度和下伏地层倾角，可估算褶皱陡坎吸收的缩短量。在背斜两翼发育有褶皱陡坎的河流阶地上还同时发育有大量保存完好的弯滑断层陡坎。弯滑断层坎只发育在褶皱陡坎顶面、下伏较陡的基岩一侧；断层作用下河流阶地发生了掀斜，远离枢纽掀斜角度逐渐减小。通过对褶皱陡坎和弯滑断层陡坎的分析，结合光释光和宇宙成因核素法测定的河流阶地的年龄，可得在全新世明尧勒背斜南、北两翼的缩短速率分别为~2.0和3.0mm/a；整个背斜缩短速率≥5.0mm/a，约占整个帕米尔-天山碰撞带会聚速率的一半。