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为查明南、西华山北缘大断裂的活动性质、活动量及大地震重复间隔,我局于1983年10月在1920年海原大地震震中区沿干盐池至小山地段挖了12条探槽。在4条探槽的全新世地层中,见到该断裂多次活动的证据,其中以海原城西南约12公里的刺儿沟探槽揭露的古地震剖面最为精彩和典型,现对它简报如下:探槽呈北东—南西向,位于南华山北缘刺儿沟旁Ⅱ级阶地上,由不连续的两截组成。揭露了主断裂面F_3和1920年地震断裂F_2及地表形变带(图1)。南华山北缘断裂主断面F_3出露非常清楚,断裂南西盘为前寒武系浅灰绿色片岩与大理岩,已强烈破碎;
In order to find out the nature and amount of activity of the large faults in the north and west Huashan Mountains and the intervals of major earthquakes, the bureau dug 12 exploration trenches along the Yanyanchi-Hill area in 1920 in the epicenter of the Haiyuan earthquake . In the Holocene stratigraphy of the four trenches, there is evidence of multiple activities of the fault. Among them, the paleoseismic profile revealed by the Thier ditch trench about 12 km southwest of Haiyuan City is the most exciting and typical. : The exploration trough is north-south-westward and is located on the grade II terrace beside the pedicle of the South Huashan Mountain, consisting of two discontinuous sections. Revealed the main fracture surface F_3 and 1920 Earthquake fracture F_2 and surface deformation bands (Figure 1). It is very clear that F_3 of the main fracture of the northern margin of South Huashan is clear, and the fault has the characteristics of pale-green-green schist and marble in the Precambrian.