This paper describes the impacts of the M5.8(5.1) Gyeongju earthquakes on groundwater levels using data obtained from a unique coastal monitoring well. The monitoring strategy integrates conventional water level monitoring with periodic, continuous measurements of temperature and electrical conductivity (EC) within the water column of the well. Another important component of the monitoring system is a new instrument, the InterfacEGG, which is capable of dynamically tracking the freshwater‐saltwater interface. Although the system was set up to monitor seawater intrusion related to over‐pumping, as well as rainfall and tidal effects, it recorded impacts associated with a large earthquake and aftershocks approximately 241 km away. Seismic energies associated with the M5.8(5.1) Gyeongju earthquakes induced groundwater flows to the monitoring well through fractures and joints in the crystalline basement rocks. Temperature and EC logging data showed that the EC vertical profile declined from an average of approximately 5300 to 4800 μS/cm following the earthquakes. The temperature profile showed a trend toward lower temperatures as the depth increased, a feature not commonly observed in previous studies. Data from the InterfacEGG suggested that the rise in EC was not due to the saltwater intrusion, but from the tendency for brackish water entering the borehole to induce convective mixing at deeper depths as the seismic waves travel through the well‐aquifer system. The increase in groundwater levels was caused by pulse of colder, less brackish water flowing into the well because of the earthquake. This behavior reflects an enhancement in rock permeability by removing precipitates and colloidal particles from clogged fractures, which improve the hydraulic connection with a nearby unit with a higher hydraulic head. This study suggests there is value added with a more aggressive monitoring strategy.

中文翻译：

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综合监测系统确定的韩国M5.8地震对地下水的影响

本文使用从独特的沿海监测井获得的数据来描述庆州M5.8（5.1）地震对地下水位的影响。监控策略将常规水位监控与井水柱内温度和电导率（EC）的定期，连续测量相结合。监测系统的另一个重要组成部分是新仪器InterfacEGG，它能够动态跟踪淡水-盐水界面。尽管建立了该系统来监视与过度泵入有关的海水入侵以及降雨和潮汐影响，但该系统记录了与大地震和大约241公里外的余震有关的影响。与M5.8（5。1）庆州地震导致地下水通过结晶基岩中的裂缝和节理流向监测井。温度和EC测井数据表明，地震后EC垂直剖面从平均约5300μS/ cm下降到4800μS/ cm。随着深度的增加，温度曲线显示出温度趋于降低的趋势，这是以前研究中通常没有观察到的特征。来自InterfacEGG的数据表明，EC的升高并不是由于盐水的入侵，而是由于微咸水进入井眼会在地震波穿过井-含水层系统时在更深的深度引起对流混合的趋势。地下水位的增加是由于地震造成的冷，微咸水流入井中而引起的。此行为反映出通过从堵塞的裂缝中去除沉淀物和胶体颗粒，岩石渗透性得到了增强，从而改善了与附近液压头更高的单元的液压连接。这项研究表明，更具积极性的监测策略可以带来附加值。