Modeling the poroelastic response to megathrust earthquakes: A look at the 2012 Mw 7.6 Costa Rican event
Modeling the poroelastic response to megathrust earthquakes: A look at the 2012 Mw 7.6 Costa Rican event
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DOI：
10.1016/j.advwatres.2018.02.014
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发表时间：
2017-12
影响因子：
4.7
通讯作者：
K. Mccormack;M. Hesse
中科院分区：
文献类型：
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作者：
K. Mccormack;M. Hesse
我们模拟了2012年9月5日发生在哥斯达黎加尼科亚半岛板块界面上的7.6兆瓦俯冲带地震的地下水文响应。上覆板块的区域尺度孔隙弹性模型综合了地震、大地测量和水文数据集，用于预测地震后的孔隙弹性响应。一个有代表性的二维模型表明，滑动宽度小于其深度三分之一的逆冲地震在浅层地下产生复杂的多叶压力扰动。这导致多个孔弹性松弛时间尺度可能与较长的粘弹性时间尺度重叠。在三维模型中，2012年Nicoya事件的复杂滑动分布和较小的宽深比导致孔隙压力分布由多个海沟平行的高、低压脊组成。这导致了复杂的地下水流动模式，预测井水位的非单调变化，以及多时间尺度上的孔隙弹性松弛。该模型还预测了大量由构造驱动的海底地下水向近海排放。在地震发生后的几周内，预测研究区域的海底地下水净流量增加，在前30天内，相对于地形驱动的流量，净流量增加了100倍。我们的模型表明，陆地上的水文响应比构造研究中通常承认的要复杂得多。这可能使地震后瞬态地表变形的解释复杂化。构造-水文联合观测网有可能减少这种模糊性。
We model the subsurface hydrologic response to the 7.6Mwsubduction zone earthquake that occurred on the plate interface beneath the Nicoya peninsula in Costa Rica on September 5, 2012. The regional-scale poroelastic model of the overlying plate integrates seismologic, geodetic and hydrologic data sets to predict the post-seismic poroelastic response. A representative two-dimensional model shows that thrust earthquakes with a slip width less than a third of their depth produce complex multi-lobed pressure perturbations in the shallow subsurface. This leads to multiple poroelastic relaxation timescales that may overlap with the longer viscoelastic timescales. In the three-dimensional model, the complex slip distribution of 2012 Nicoya event and its small width to depth ratio lead to a pore pressure distribution comprising multiple trench parallel ridges of high and low pressure. This leads to complex groundwater flow patterns, non-monotonic variations in predicted well water levels, and poroelastic relaxation on multiple time scales. The model also predicts significant tectonically driven submarine groundwater discharge off-shore. In the weeks following the earthquake, the predicted net submarine groundwater discharge in the study area increases, creating a 100 fold increase in net discharge relative to topography-driven flow over the first 30 days. Our model suggests the hydrological response on land is more complex than typically acknowledged in tectonic studies. This may complicate the interpretation of transient post-seismic surface deformations. Combined tectonic-hydrological observation networks have the potential to reduce such ambiguities.