Geophysical properties within the San Andreas Fault Zone at the San Andreas Fault Observatory at Depth and their relationships to rock properties and fault zone structure
Geophysical properties within the San Andreas Fault Zone at the San Andreas Fault Observatory at Depth and their relationships to rock properties and fault zone structure
复制标题
圣安德烈亚斯断层深度观测站圣安地列斯断层带内的地球物理特性及其与岩石特性和断层带结构的关系
DOI：
10.1029/2010jb007563
复制
发表时间：
2010
影响因子：
--
通讯作者：
James P. Evans
中科院分区：
文献类型：
--
作者：
T. Jeppson;K. Bradbury;James P. Evans
[1]我们检查钻孔地球物理数据和断层相关岩石的物理性质之间的关系，确定从数据的圣安德烈亚斯断层观测站在深度钻孔的圣安德烈亚斯断层。地球物理测井、岩屑数据和钻孔深度为3至4公里的钻井数据涵盖了圣安德烈亚斯断层的活动部分。该断裂带位于一系列变形砂岩、粉砂岩、页岩、含蛇纹岩的块状基质岩和剪切千枚状粉砂岩中。钻孔地球物理测井显示，在3190 - 3410 m测量深度处存在低速带，Vp和Vs值比围岩低10 - 30%，在3301 - 3303 m测量深度处存在1 - 2 m厚的活动剪切带。在断裂带中存在七个低速偏移，其孔隙度增加、密度降低和泥浆气反冲特征。地质数据的粒度变形和蚀变的钻孔数据进行比较，并揭示弱相关性和地球物理数据的逆关系。在某些地方，Vp和Vs随断裂带中粒度变形和蚀变而增加，随孔隙度而减小。低速带与向低速岩石的显著岩性和结构过渡有关，低速岩石主要由层状硅酸盐和渗透性片理化剪切岩石组成。活跃的剪切带和低声速区域似乎与富含粘土的岩石有关，这些岩石表现出细尺度的面理和较高的孔隙度，这可能是断层相关的面理和细粒沉积岩剪切的结果。
[1] We examine the relationships between borehole geophysical data and physical properties of fault-related rocks within the San Andreas Fault as determined from data from the San Andreas Fault Observatory at Depth borehole. Geophysical logs, cuttings data, and drilling data from the region 3- to 4-km measured depth of the borehole encompass the active part of the San Andreas Fault. The fault zone lies in a sequence of deformed sandstones, siltstone, shale, serpentinite-bearing block-in-matrix rocks, and sheared phyllitic siltstone. The borehole geophysical logs reveal the presence of a low-velocity zone from 3190 to 3410 m measured depth with Vp and Vs values 10–30% lower than the surrounding rocks and a 1–2 m thick zone of active shearing at 3301–3303 m measured depth. Seven low-velocity excursions with increased porosity, decreased density, and mud-gas kick signatures are present in the fault zone. Geologic data on grain-scale deformation and alteration are compared to borehole data and reveal weak correlations and inverse relationships to the geophysical data. In places, Vp and Vs increase with grain-scale deformation and alteration and decrease with porosity in the fault zone. The low-velocity zone is associated with a significant lithologic and structural transition to low-velocity rocks, dominated by phyllosilicates and penetratively foliated, sheared rocks. The zone of active shearing and the regions of low sonic velocity appear to be associated with clay-rich rocks that exhibit fine-scale foliation and higher porosities that may be a consequence of the fault-related shearing of foliated and fine-grained sedimentary rocks.
影响因子：
3.4
作者：
T. Wiersberg;J. Erzinger
通讯作者：
T. Wiersberg;J. Erzinger