Snowmelt-Triggered Earthquake Swarms at the Margin of Long Valley Caldera, California
Snowmelt-Triggered Earthquake Swarms at the Margin of Long Valley Caldera, California
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DOI：
10.1029/2019gl082254
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发表时间：
2019-04-16
影响因子：
5.2
通讯作者：
Hsieh, P. A.
中科院分区：
文献类型：
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作者：
Montgomery-Brown, E. K.;Shell, D. R.;Hsieh, P. A.
众所周知，流体会影响地震，但地震很少与降水有令人信服的联系。微弱的调制或有限的数据常常导致模棱两可的解释。相反，这里我们发现，在长谷火山口附近的内华达山脉的浅层地震活动受到融雪的强烈调节。33年来，浅层地震活动率在非常潮湿的时期比非常干燥的时期高37倍。2017年一群地震的相对重新定位显示，沿着一个陡峭的斜面，从类似1至3公里的深度向下迁移。陡倾地层可能提供高渗透通道和断裂面。在这里，我们将地震活动性和水文时间序列与在相对定位的地震中观测到的传播相结合。从这些综合证据中，我们推断地下水补给的压力扩散极大地加速了浅层地震活动率，造成了与火山作用无关的地震群。在长谷火山口附近的山上，融雪的水沿着向上的元沉积层向下过滤，引发了地震群。地震位置显示蝗群向下传播；与渗透水的方向相同，与附近其他火山地震群相反。在33年的河流流量和地震数据记录中，潮湿时期的地震活跃度是干旱时期的37倍。这一增加幅度大大大于其他有类似触发记录的地区。结合河流流量与地震的长期相关性和向下传播的群，我们推断泉水地下水补给的压力扩散显著增加了地震活动性。
Fluids are well known to influence earthquakes, yet rarely are earthquakes convincingly linked to precipitation. Weak modulation or limited data often leads to ambiguous interpretations. In contrast, here we find that shallow seismicity in the Sierra Nevada range near Long Valley Caldera is strongly modulated by snowmelt. Over 33years, shallow seismicity rates were similar to 37 times higher during very wet periods versus very dry periods. Relative earthquake relocations from a swarm in 2017 reveal downward migration from similar to 1- to 3-km depth along a steeply inclined plane. Steeply dipping strata may provide high-permeability pathways and faulting plane. Here we combine the correlated seismicity and hydrologic time series with the propagation observed in the relatively relocated earthquakes. From this combined evidence, we infer that pressure diffusion from groundwater recharge dramatically accelerated shallow seismicity rates, causing seismic swarms unrelated to volcanic processes.Plain Language Summary Water from melting snow in the mountains near Long Valley Caldera filters down along upturned metasedimentary layers and triggers earthquake swarms. Earthquake locations show that the swarms propagate downward; the same direction as the infiltrating water and opposite from other nearby volcanic earthquake swarms. Over a 33-year record of stream flow and earthquake data, the earthquakes are similar to 37 times more active during wet periods than dry periods. This amount of increase is substantially larger than other regions where similar triggering has been documented. Combining the long-term correlation of the stream flow and earthquakes, with the downward propagating swarm we infer that pressure diffusion from the spring groundwater recharge dramatically increases the seismicity rates.