蔚广盆地南缘断裂带唐山口段山前断层活动性研究

蔚广盆地是山西地堑系北端京西北盆岭构造区内的一个半地堑盆地,蔚广盆地南缘断裂带为控制该盆地形成的边界断裂。该断裂带位于唐山口段的山前断裂在冲洪积扇体上形成了线性特征显著的断层陡坎。横跨断层陡坎开挖的探槽表明该条山前断裂属于全新世活动断裂,探槽揭示了2条活动断层以及相应的3次古地震事件。在距今约9ka时其中一条断层首次活动,之后在距今约7.3ka时该条断层再次活动并引发了另一条断层的形成与同步活动。最后它们又发生了第三次活动,而最新一次活动的时间由于相应地表沉积的缺失而无法获得。这3次古地震事件的累积垂直位错约为8.1m。估算出整条山前断裂的平均复发周期约为1.7ka、平均滑动速率约为1.6mm/a。此外还依据经验公式估算出了各次古地震的参考震级。

The Activity of the Piedmont Fault along the Tangshankou Segment of Yuguang Basin Southern Marginal Fault

The Yuguang basin is a half-graben basin in the basin-range tectonic zone northwest to Beijing, wherethe Yuguang basin southern marginal fault (YBSMF) that is located at the northern end of the Shanxi graben system controlled the formation of the basin. A linear fault escarpment formed in the pluvialfan along the piedmont fault zone of the Tangshankou segment of YBSMF. A trench across this escarpment revealed three paleoearthquake events in two active faults. The first activity occurred in one fault at about 9ka for the first time, and then the second activity occurred at about 7.3ka, which caused the formation and synchronous activity of another fault. For the third fault activity we cannot determine the active time due to lack of relevant surface deposition. The accumulative vertical displacement of these three events is about 8.1m. We estimate that the average recurrence period of the piedmont fault is about 1.7ka, and the average slip rate of the piedmont fault is about 1.6mm/a. Besides, we estimate the reference magnitude of each event according to the empirical formula.