Focal mechanisms and the state of stress on the San Andreas Fault in southern California
Focal mechanisms and the state of stress on the San Andreas Fault in southern California
复制标题
南加州圣安德烈亚斯断层的震源机制和应力状态
DOI：
10.1029/jb093ib08p08869
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发表时间：
1988
期刊：
影响因子：
--
通讯作者：
L. Jones
中科院分区：
文献类型：
--
作者：
L. Jones
根据1978 ~ 1985年发生在南加州圣安德烈亚斯断层地表迹线10 km以内的138次中小（2.6 ≤ M ≤ 4.3）地震的P波初动极性，确定了震源机制。在此基础上，将南圣安德烈亚斯断层划分为五个不同应力状态的区段。在Fort Tejon段的地震表现为东西向和北西向断层的斜向反转。莫哈韦段有西北走向的斜向反向和右行向上运动的地震。圣贝纳迪诺段在南北走向平面上发生正断层地震，而班宁段则在同一地区发生反向、走向和正断层地震。印第奥段地震在北西向至南北向的走向面上表现为走滑和斜向正断层活动。这些震源机制数据已被反演，以确定如何在南加州的圣安德烈亚斯断层上的应力随位置的变化沿着走向的故障。其中一个主应力在所有区域都是垂直的。垂直应力在Fort Tejon和莫哈韦是最小主应力，在Banning和印第奥是中等主应力，在圣贝纳迪诺是最大主应力。水平主应力的方向在不同的区域也不同。最大水平应力的走向旋转超过35°，从Fort Tejon的N15°W到印第奥的N20°。除圣贝纳迪诺段外，最大水平应力的走向与圣安德烈斯断层的局部走向成65°左右的恒定夹角，表明是一条软弱断层。目前应力状态的最大变化发生在1857年特洪堡地震破裂带的末端。似乎1857年的破裂在它传播到一个低应力幅度的区域时结束，这可能是由圣哈辛托和圣安德烈亚斯断层走向之间的15°角造成的。现今应力状态与以往地震分段性之间的强相关性表明，应力状态在控制破裂传播方面是重要的。
Focal mechanisms have been determined from P wave first motion polarities for 138 small to moderate (2.6 ≤ M ≤ 4.3) earthquakes that occurred within 10 km of the surface trace of the San Andreas fault in southern California between 1978 and 1985. On the basis of these mechanisms the southern San Andreas fault has been divided into five segments with different stress regimes. Earthquakes in the Fort Tejon segment show oblique reverse sup on east-west and northwest striking faults. The Mojave segment has earthquakes with oblique reverse and right-lateral strikesup motion on northwest strikes. The San Bernardino segment has normal faulting earthquakes on north-south striking planes, while the Banning segment has reverse, strike-sup, and normal faulting events all occurring in the same area. The earthquakes in the Indio segment show strike-slip and oblique normal faulting on northwest to north-south striking planes. These focal mechanism data have been inverted to determine how the stresses acting on the San Andreas fault in southern California vary with position along strike of the fault. One of the principal stresses is vertical in all of the regions. The vertical stress is the minimum principal stress in Fort Tejon and Mojave, the intermediate principal stress in Banning and Indio, and the maximum principal stress in San Bernardino. The orientations of the horizontal principal stresses also vary between the regions. The trend of the maximum horizontal stress rotates over 35°, from N15°W at Fort Tejon to N20° at Indio. Except for the San Bernardino segment, the trend of the maximum horizontal stress is at a constant angle of about 65° to the local strike of the San Andreas fault, implying a weak fault. The largest change in the present stress state occurs at the end of the rupture zone of the 1857 Fort Tejon earthquake. It appears that the 1857 rupture ended when it propagated into an area of low stress amplitude, possibly caused by the 15° angle between the strikes of the San Jacinto and San Andreas faults. The strong correlation between present state of stress and segmentation in previous earthquakes suggests that the stress state is important in controlling rupture propagation.