Neotectonic Active Characteristics And Dynamic Mechanism Of The Shandong Segement Of The The Tan-lu Fault Zone

The Shandong segment of the Tan-Lu Fault Zone, also referred to as theYishu Fault Zone, is an important mobile tectonic zone in eastern China.Romote sensing and DEM image interpretation results show that the YishuFault Zone consists of five large and a series of small-scale active faults. Ourdetailed field investigation shows that the neotectonic activities of the YishuFault Zone are mainly concentrated on five major faults of F₁to F₅whichstrike NNE in general and exposed from Anqiu to Tancheng. According tomarks of affected rock ages, topographical features, offset of rivers andchannels as well as features of section structures, it is suggested that there arecrashed-type and gouge-type active faults in the Yishu Fault Zone. Acrashed-type active fault contains a fault gouge belt, an incohesive brecciabelt, and a cataclastic belt from its main fault plane to outside, and the threebelts are several to tens of meters wide. These type active faults mostlydistribute along the Tancheng earthquake fault which belongs to the F₁and F2faults, F₅fault, and middle and southern segements of the F₃fault and middlesegement of F₄faults. A gouge-type active fault only contains a gouge belt ofservel centimeters wide without an incohesive breccia belt and a cataclasticbelt. These type active faults occurred along the northern segement of the F₁and F₃fault, northern and middle segements of the F2fault, northern andsouthern segements of the F₄faults. Beside all of those segments in the YishuFault Zone are inactive faults that appeare as faults with cohesive fault rocks.Detailed obverservation on kinematic indicators such as striationsdemonstrates that reverse dextral slipping predominated in neotectonicactivities of the faults since Quaternary. Varitation of the active fault beltwidth shows their active intensity increases eastwards and southwards.Fault-slip data from many active faults in the fault zone demonstrate thatENE-WSE compression predominated in the neotectonic period, which areconsistent with stress fields indicated by the present stress measurementresults, focal mechanism solution and GPS data. Therefore, the consistent stress fields of the neotectonic period are responsible for formation of theactive faults in the Yishu Fault Zone.Condering previous studies on active time of the Yishu Fault Zone,analyses of geology, geomorphology and seismic activity have conducted forunderstanding their active time. It is demonstrated that the F₁, F2, F₃, F₄and F₅faults have been active since the Quaternary. Activities of the active faults inthe eastern graben triggered the1668M8.5Tancheng earthquake and AnqiuM7.0earthquake70year before century.According to relations to the pre-existing boundary faults, formationmechanisms of shallow active faults in the Yishu Fault Zone can be dividedinto four types, i.e., direct reactivity of previous graben boundary faults,upward propagation of buried faults, reactivity of antithetic and truncatingfaults. In most cases, shallow, active faults in the fault zone are developedthrough direct reactivity or upward propagation of the previous four grabenboundary faults.