Bawden G W, Thatcher W, Stein R S, Hudnut K W, Peltzer G
United States Geological Survey, Menlo Park, California 94025, USA.
Nature. 2001 Aug 23;412(6849):812-5. doi: 10.1038/35090558.
After the 1987 Whittier Narrows and 1994 Northridge earthquakes revealed that blind thrust faults represent a significant threat to metropolitan Los Angeles, a network of 250 continuously recording global positioning system (GPS) stations was deployed to monitor displacements associated with deep slip on both blind and surface faults. Here we augment this GPS data with interferometric synthetic aperture radar imagery to take into account the deformation associated with groundwater pumping and strike-slip faulting. After removing these non-tectonic signals, we are left with 4.4 mm yr-1 of uniaxial contraction across the Los Angeles basin, oriented N 36 degrees E (perpendicular to the major strike-slip faults in the area). This indicates that the contraction is primarily accommodated on thrust faults rather than on the northeast-trending strike-slip faults. We have found that widespread groundwater and oil pumping obscures and in some cases mimics the tectonic signals expected from the blind thrust faults. In the 40-km-long Santa Ana basin, groundwater withdrawal and re-injection produces 12 mm yr-1 of long-term subsidence, accompanied by an unprecedented seasonal oscillation of 55 mm in the vertical direction and 7 mm horizontally.
1987年惠蒂尔窄道地震和1994年北岭地震表明，隐伏逆冲断层对洛杉矶大都市构成重大威胁，之后部署了一个由250个连续记录的全球定位系统（GPS）站组成的网络，以监测与隐伏断层和地表断层深部滑动相关的位移。在此，我们用干涉合成孔径雷达图像增强这些GPS数据，以考虑与地下水抽取和走滑断层作用相关的变形。去除这些非构造信号后，我们得到洛杉矶盆地每年4.4毫米的单轴收缩，方向为北偏东36度（垂直于该地区主要走滑断层）。这表明收缩主要发生在逆冲断层上，而非东北走向的走滑断层上。我们发现，广泛的地下水和石油抽取掩盖了，在某些情况下还模拟了隐伏逆冲断层预期的构造信号。在40公里长的圣安娜盆地，地下水抽取和回灌产生了每年12毫米的长期沉降，同时伴有垂直方向55毫米、水平方向7毫米的前所未有的季节性振荡。
