1605年琼山大地震深部构造和应力状态研究

A Study on Deep Crust Structures and Stress Situation of the 1605 Qiongshan Strong Earthquake

利用1605年琼山地震区已有的浅部地质、物探和钻井等资料,采用空间域三维重力正反演计算,消除了地壳浅部影响,依次得到由浅到深的各剩余深部重力异常值。然后由基底剩余重力异常值反演得到莫霍界面深度及起伏形态。分析上述结果可知:1605年的琼山大地震是一个以垂直向差异运动为主的地震,位于琼北莫霍面隆起区东北部、隆起向外凸出部位的陡坡上;北东东向的马袅-铺前断裂(中东段)呈反扭(左旋)状态,而北西向的铺前-清澜断裂(北段)呈顺扭(右旋)状态;云龙地区地下地幔物质上涌,造成云龙地块的上隆;如果1605年地震区出现NE30°左右的主压应力场作用和云龙地块异常上隆时,应考虑地震的复发问题。另外,分析各剩余深部重力异常等值线分布,还可以判定地质学给出的各断裂构造展布和延伸情况。

Using the method of 3-dimension forward calculation in spatial field to eliminate the gravity contributions of shallow crust with data of geology, geophysical prospect and drilling, the different deep residue gravitational anomalies from shallow to deep layer were obtained in turn. We gained the depth and fluctuant situation Moho surface from residue gravitational anomaly of basement by means of inversion. The above results show that： The rupture direction of the 1605 Qiongshan strong earthquake was mainly vertical, and its epicenter located on the steep slope of northeast part of Moho surface＇s ridgy region in Northeast Hainan Island; the middle and east portion of Maniao-Puqian Fault of NEE presents reverse twist （left whirl）, and the north portion of Puqian-Qinglan fault of NW presents forward twist （right whirl） ; the uplift of mantle material under Yunlong region resulted in the upthrust of Yunlong tectonic block; when the direction of stress field in 1605 earthquake＇s region is nearly NE30 and Yunlong tectonic block uplifts abnormally, recrudescence of the strong earthquake is possible. To analyze the contours of different residue deep gravitational anomaly, we can determine the distribution and extension of the faults found by geology.