Abstract: Along the northern piedmont of Mt. Lishan, the characteristics and locations of the active normal Lishan fault in west of Huaqing Pool provide important evidences for determining the seismotectonic environment, seismic stability evaluation of engineering in the eastern Weihe Basin. After reviewing the results from high-density resistivity method, seismic profile data, geological drillhole section and trenching in west of the Huaqing Pool, it is found that the strike of western normal Lishan Fault changes from EW direction at the eastern part to the direction of N60°W, and the fault consists of two branches, dipping NE with a high dip angle of~75°. The artificial shallow seismic profile data reveals that the attitude of strata near Lishan Fault mainly dips to south, which is presumed to be related to the southward tilt movement of Mt. Lishan since the Cenozoic. The section of geological drillhole reveals that since the late middle Pleistocene, the displacement of the paleo-soil layer S₂ is about 10m. And the maximum displacement of western Lishan Fault recorded in the paleo-soil layer S₁ reaches 7.8m since the late Pleistocene.
In addition, evidences from trench profile show that the western Lishan Fault was active at least 3 times since Malan loess deposition with ¹⁴ C dating age(32 170±530)Cal a BP. The multiple activities of the Lishan Fault result in a total displacement about 3.0m in the Malan loess layer L₁. The latest activity of the western Lishan Fault produced a displacement of about 0.9m in the early Holocene loess layer L₀((8 630±20)Cal a BP)and caused obvious tensile cracks in the Holocene dark leoss layer S₀((4 390±20)Cal a BP). Briefly, we have obtained a vertical movement rate of about 0.11~0.19mm/a since the Holocene((8 630±20)Cal a BP)in the western extension of the Lishan Fault, the recurrence interval of earthquakes on the fault is about(10.7±0.5)ka, and the co-seismic surface rupture in a single event is inferred to be about 0.9m.

Key words: Lishan Fault, fault activity, co-seismic surface rupture, setback from fault

摘要： 骊山山前断裂位于骊山北侧，其华清池以西段向渭河盆地延伸，该断裂的几何展布和活动习性是准确认识渭河盆地东部区域地震构造及地震安全性评价的重要依据。跨断裂推测位置布设高密度电法、人工浅层地震及联合钻孔剖面并通过探槽开挖等多种手段进行探测，所得结果显示，华清池以西段的走向由其西段的近EW向变为N60°W，断裂由2支次级正断层构成，倾向NE，倾角约75°。其中，南支次级断层自晚更新世以来没有明显的活动证据，北支次级断层最新活动时代为全新世。人工浅层地震探测揭示断裂附近的地层产状整体倾向S，推测与骊山断块自新生代以来向S掀斜运动有关；联合钻探剖面揭示北支断层自中更新世晚期以来古土壤层S₂断错位移量约10m；晚更新世早期以来古土壤层S₁垂直错距最大约7.8m。探槽剖面揭示西延段断裂自马兰黄土沉积（（32 170±530） Cal a BP）以来至少发生过3次古地震事件，并造成马兰黄土最大总错距约3.0m。其中，断裂最新一次活动使全新世早期的黄土层L₀（（8 630±20） Cal a BP）产生了约0.9m的垂直错距，并在全新统黑垆土地层S₀（（4 390±20） Cal a BP）中形成了明显的张裂缝。最终分析得到骊山山前断裂西延段全新世（（8 630±20） Cal a BP）以来的垂直活动速率为0.11~0.19mm/a，推测单次事件产生的垂直位错量约0.9m。

关键词: 骊山山前断裂, 断裂活动性, 同震垂直位移, 断裂避让