地震研究

利用垂直向Pg和Sg波振幅比方法计算了2003年1月至2009年10月间宁夏南部及邻区的40个中小地震的震源机制解,然后对计算所得的40个地震的震源机制解进行系统聚类及应力场分析,利用格点尝试法研究灵武—吴忠地区(I区)和宁夏南部地区(II区)的平均震源机制解。结果表明:该区域主要受北东东向压应力作用而形成右旋走滑型断层,同时又带有张性分量; I区域构造应力场主压应力方向以水平作用为主,地震产生的震源区构造变形是北东向发生压缩,北西向发生相对扩张; II区域构造应力场主压应力方向以水平作用为主,地震产生的震源区构造变形是北东东向发生压缩,北北西向发生相对扩张。

Firstly, we calculated the focal mechanism solutions of 40 small and moderate earthquakes in southern Ningxia and its adjacent areas from Jan. 2003 to Oct. 2009 by the amplitude ratio method of Pg and Sg waves in vertical direction and did the system clustering of the calculated focal mechanism solutions to analyze the stress field. Secondly, we studied the average focal mechanism of Lingwu-Wuzhong region(I)and southern Ningxia region(II)by grid testing method. The results show that it is easy to develop dextral strike slip fault with stretching component in the study area under the compressive stress in NEE. The direction of principal compressive stress of tectonic stress field in I and II region is mainly horizontal. The structure deformations in the focal region caused by earthquake are compression in NE and expansion in NW in I region, and are compression in NEE and expansion in NNW in II region.

引言
1 方法与原理
2 资料处理
3 结果分析
4 结论与讨论

表1 研究区域地壳速度模型<br/>Tab.1 The crustal velocity model in the study region

表1 研究区域地壳速度模型
Tab.1 The crustal velocity model in the study region

图1 研究区内的地震震中分布<br/>Fig.1 Distribution of epicenters in the study region

图1 研究区内的地震震中分布
Fig.1 Distribution of epicenters in the study region

图2 研究区内的地震震源机制解<br/>Fig.2 Distribution of focal mechanisms in the study region

图2 研究区内的地震震源机制解
Fig.2 Distribution of focal mechanisms in the study region

图3 研究区中小地震震源机制解聚类分析给出的3种类型平均解<br/>Fig.3 Average solutions of 3 types of focal mechanism of the medium and small earthquakes in the study area by system clustering method

图3 研究区中小地震震源机制解聚类分析给出的3种类型平均解
Fig.3 Average solutions of 3 types of focal mechanism of the medium and small earthquakes in the study area by system clustering method

表2 研究区3种类型的中小地震震源机制平均解参数(单位:(°))<br/>Tab.2 Parameters of average solutions of 3 types of focal mechanism of the medium and small earthquakes in the study area

表2 研究区3种类型的中小地震震源机制平均解参数(单位:(°))
Tab.2 Parameters of average solutions of 3 types of focal mechanism of the medium and small earthquakes in the study area

表3 利用格点尝试法给出的两个研究分区的平均震源机制解(单位:(°))<br/>Tab.3 Average focal mechanism solutions of two research areas by grid testing method

表3 利用格点尝试法给出的两个研究分区的平均震源机制解(单位:(°))
Tab.3 Average focal mechanism solutions of two research areas by grid testing method

图4 灵武—吴忠地区(Ⅰ区)震源机制P、T、N轴方位和仰角及节面解玫瑰图<br/>Fig.4 Azimuth,elevation angles and rose diagram of nodal plane solutions of P,T,N axis of focal solution in Lingwu-Wuzhong region(Ⅰarea)

图4 灵武—吴忠地区(Ⅰ区)震源机制P、T、N轴方位和仰角及节面解玫瑰图
Fig.4 Azimuth,elevation angles and rose diagram of nodal plane solutions of P,T,N axis of focal solution in Lingwu-Wuzhong region(Ⅰarea)

图5 灵武—吴忠地区(Ⅰ区)震源机制平均解<br/>Fig.5 Average focal mechanism solutions in Lingwu-Wuzhong region(Ⅰarea)

图5 灵武—吴忠地区(Ⅰ区)震源机制平均解
Fig.5 Average focal mechanism solutions in Lingwu-Wuzhong region(Ⅰarea)

图6 宁夏南部地区(II区)震源机制P、T、N轴方位和仰角及节面解玫瑰图<br/>Fig.6 Azimuth,elevation angles and rose diagram of nodal plane solutions of P,T,N axis of focal solution in southern Ningxia region(Ⅱarea)

图6 宁夏南部地区(II区)震源机制P、T、N轴方位和仰角及节面解玫瑰图
Fig.6 Azimuth,elevation angles and rose diagram of nodal plane solutions of P,T,N axis of focal solution in southern Ningxia region(Ⅱarea)

图7 宁夏南部地区(II区)震源机制平均解<br/>Fig.7 Average focal mechanism solutions in southern Ningxia region(Ⅱ area)

图7 宁夏南部地区(II区)震源机制平均解
Fig.7 Average focal mechanism solutions in southern Ningxia region(Ⅱ area)

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备注

引言

1 方法与原理

2 资料处理

3 结果分析

4 结论与讨论

期刊信息