青海拉脊山断裂带新活动特征的初步研究

拉脊山断裂带由拉脊山北缘断裂和拉脊山南缘断裂两条向NE凸出的弧形断裂所组成，分别长约230km和220km。它们是介于NNW向的热水一日月山右旋走滑断裂带和NWW向的西秦岭北缘左旋走滑断裂带之间的一个大型挤压构造区和构造转换带，也是分隔拉脊山南北两侧的西宁一民和盆地和循化一化隆盆地的重要边界断裂。沿断裂带的追踪考察，发现了其新活动的部分地质地貌证据。其最新活动时代为晚更新世晚期(仅局部为全新世早期)，性质以挤压逆冲为主稍具左旋特征。该断裂的新活动可能导致了该区20余次5级左右中等地震的发生。可以说，拉脊山地区既是反映构造活动，又是反映地震活动的地震构造窗。

A Preliminary Study on the New Activity Features of the Lajishan Mountain Fault Zone in Qinghai Province

The Lajishan Mountain fault zone, an arc fault zone which bulge to the NE direction,is consist of two fault zones:the northern margin fault zone and the southern margin fault zone of the Lajishan Mountain.Their lengths are about 230km and 220km,respectively.They are a large scale compressive tectonic area and tectonic transformation zone which are situated between the NNW oriented Reshui-Riyueshan right-lateral strike-slip fault zone and the NWW oriented northern margin fault zone of the west Qinling mountain which is an left-lateral strike-slip fault zone. They are also important boundary fault zones which seqarate the Xining-Minhe basin and the Xunhua-Hualong basin which situated at south and north sides of the Lajishan Mountain.According to the field investigation,the geomorphological evidences indicate that the Lajishan fault zone is still active in late Pleistocene,only a few segments are active in early Holocene,their features are main compressive thrust,a part of areas have left-lateral strike slip components. The newest activity of the fault zone had caused about 20 moderate earthquakes happened on the both sides of the Lajishan mountain since documented history. The Lajishan area is an earthquake tectonic window to reflect the tectonic activity and earthquake activity.