摘要
利用2007年8月1日至2013年7月21日发生在鄂尔多斯块体周缘的8499个地震的49844个P波初动符号资料,应用综合震源机制解法获得了鄂尔多斯块体周缘0.25°×0.25°的精细地壳应力场,所得应力场结果基本上覆盖了整个鄂尔多斯周缘地区.研究结果表明鄂尔多斯周缘地壳应力场具有以下特征:(1)在环绕鄂尔多斯周缘的银川—吉兰泰断陷带、河套断陷带、岱海断陷带、山西断陷带和渭河断陷带内,综合震源机制解结果以正断层型为主,且综合震源机制解节面走向大体与控制断陷带边界的主要断裂走向相一致,与鄂尔多斯周缘断陷带现今的拉张状态相一致.(2)在鄂尔多斯西南缘,综合震源机制解类型主要为逆冲、逆冲走滑和走滑型,反映了鄂尔多斯块体在西南缘受到青藏高原北东向挤压作用.鄂尔多斯西南缘的应力场的主压应力方向在远处为东向,源自于青藏高原向东北挤压作用,靠近鄂尔多斯块体表现为北东—南西向.(3)P轴方位在局部地区变化较大,但总体呈现规律性变化.P轴方位在鄂尔多斯块体西缘,从南向北,主压应力轴方位更加偏北;在其北缘,由西向东,主压应力轴方位更加偏东.在其南缘和东缘,主压应力轴方位变化不大,大体上平行于控制各断陷带主要断裂走向.P轴倾角在西南缘为近水平,在其周缘各盆地内P轴倾角近直立.(4)T轴方位总体表现为北西—南东向;在鄂尔多斯周缘各断陷带内,T轴走向大体与控制断陷带主要断裂走向以及断陷盆地走向相垂直.(5)鄂尔多斯块体在其西南角受到来自青藏高原的北东向挤压和其东北角深部物质上涌形成的北西—南东向拉张力联合作用,上述作用使得鄂尔多斯块体周缘地区除西南区为挤压区外,其余区域均为剪切拉张区,与先前研究认为鄂尔多斯周缘地区处于引张应力场作用相符合,较好地解释了环鄂尔多斯周缘的断陷盆地构造,亦�
With more and more densely seismic stations deployed,a large number of P wave firstmotion data are observed,which provides us an opportunity to further study the tectonic stress field.In this paper,by using the 49844 Pwave first motion polarity data from 8499 earthquakes,which occurred in and around the Ordos block from August 1,2007 to July 21,2013,we obtained the precise and detailed stress field in the study area.The composite focal mechanism method was used in this study.By fitting the focal mechanism radiation pattern with P wave polarity data from a large number of earthquakes,this method can obtain the composite focal mechanism in specific grid,and P,B,Taxes can be regarded as the principal stress axes of the tectonic stress field.The grid search method is used to fit the focal mechanism radiation pattern,the focal mechanism which has the minimum contradictory ratio was regarded as the optimal solution.The inconsistent ratio is the ratio of the number of P wave first motion polarity which is inconsistent with the focal mechanism and the total number of P wave first motion polarity data,which is weighted by the distance of the earthquake epicenter to the grid point.The study results show that the stress field has the following characteristics：First,in the rift zone of the Yinchuan-Jilantai,Hetao,Daihai,Shanxi,and Weihe around the Ordos block,the main types of composite focal mechanism are normal types,and the strike of the nodal planes is consistent with the strike of the main fault which controls the boundary of the rift zone,that is,in accord with the extension regime in the rift zone around the Ordos block.Second,the main types of the composite focal mechanism are thrust,thrust-strike-slip and strike-slip types in the southwest boundary of the Ordos block,which reflects that the Ordos block is subjected to the northeastward squeezing of the Qinghai-Tibetan plateau.The principal compressive stress direction is eastward in the distance from the southwest boundary of Ordos block,that may derived from the
出处
《地球物理学报》
SCIE
EI
CAS
CSCD
北大核心
2015年第2期436-452,共17页
Chinese Journal of Geophysics
基金
地震行业专项(201208009
200808053)
中央高校基本科研业务专项资金(创新项目团队资助计划)(ZY20110101)
国家科技支撑计划项目(2012BAK19B03-4)共同资助
关键词
应力场
综合震源机制解
P波初动
鄂尔多斯块体
Stress field
Composite focal mechanism
P wave first motion polarity
Ordos block
