Seasonal and Long-Term Groundwater Unloading in the Central Valley Modifies Crustal Stress.
Seasonal and Long-Term Groundwater Unloading in the Central Valley Modifies Crustal Stress.
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DOI：
10.1029/2019jb018490
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发表时间：
2020-01
期刊：
影响因子：
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通讯作者：
Ojha C
中科院分区：
文献类型：
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作者：
Carlson G;Shirzaei M;Werth S;Zhai G;Ojha C
陆地水含量的变化会引起地壳的弹性变形。这种形变被认为在储水量波动较大的地区对地壳应力和地震活动起到了调节作用。地下水是加州总蓄水量变化的重要组成部分，有助于推动每年的蓄水量波动和干旱期间的损失。在这里，我们使用从基于高分辨率干涉合成孔径雷达的垂直陆地运动数据中获得的2007-2010年加州中央山谷干旱期间地下水体积损失的直接估计来研究地下水体积变化对应力场演化的影响。结果表明，基于GPS的弹性载荷模型可能无法反映地下水对地表水载荷的贡献，从而低估了非构造地应力的变化。我们发现，干旱期间地下水的卸载导致孕震深度库仑应力变化高达5.5kpa，季节波动高达2.6kpa。我们发现山谷附近的断裂应力变化最大，而圣安德烈亚斯断裂由于地下水储量的变化，在一年的时间里只经历了约40Pa库仑应力变化。地下水位较低时，库仑应力年变化主要在秋季达到峰值，但一些断层在地下水位较高时，在春季出现应力峰值。此外，我们发现，应力增加的周期与高于平均地震矩释放相关，但与地震次数的增加无关。这表明地下水负荷可能对断层的非构造负荷有贡献，特别是在山谷边缘附近，但不是加州地震活动调制的主导因素，因为应力变化的幅度随着距离山谷的距离而迅速下降。通过仔细量化和空间定位地下水波动，我们将提高我们对驱动加州地震活动的非构造应力和作用力的理解。中央河谷外由于地下水量损失引起的弹性垂直陆地运动很小。中央河谷地下水量波动调节地壳应力由水负荷引起的季节性应力变化可能调制地震活动
Changes in terrestrial water content cause elastic deformation of the Earth's crust. This deformation is thought to play a role in modulating crustal stress and seismicity in regions where large water storage fluctuations occur. Groundwater is an important component of total water storage change in California, helping to drive annual water storage fluctuations and loss during periods of drought. Here we use direct estimates of groundwater volume loss during the 2007–2010 drought in California's Central Valley obtained from high resolution Interferometric Synthetic Aperture Radar‐based vertical land motion data to investigate the effect of groundwater volume change on the evolution of the stress field. We show that GPS‐derived elastic load models may not capture the contribution of groundwater to terrestrial water loading, resulting in an underestimation of nontectonic crustal stress change. We find that groundwater unloading during the drought causes Coulomb stress change of up to 5.5 kPa and seasonal fluctuations of up to 2.6 kPa at seismogenic depth. We find that faults near the Valley show the largest stress change and the San Andreas fault experiences only ~40 Pa of Coulomb stress change over the course of a year from groundwater storage change. Annual Coulomb stress change peaks dominantly in the fall, when the groundwater level is low; however, some faults experience peak stress in the spring when groundwater levels are higher. Additionally, we find that periods of increased stress correlate with higher than average seismic moment release but are not correlated with an increase in the number of earthquakes. This indicates groundwater loading likely contributes to nontectonic loading of faults, especially near the Valley edge, but is not a dominant factor in modulation of seismicity in California because the amplitude of stress change declines rapidly with distance from the Valley. By carefully quantifying and spatially locating groundwater fluctuations, we will improve our understanding of what drives nontectonic stress and forces that modulate seismicity in California. Elastic vertical land motion due to groundwater volume loss is minute outside of the Central Valley Groundwater volume fluctuations in the Central Valley modulates crustal stress Seasonal stress changes due to water loading might modulate seismicity