The occurrence of induced earthquakes in crystalline rocks kilometers from deep wastewater injection wells poses questions about the influence nonconformity contacts have on the downward and lateral transmission of pore-fluid pressure and poroelastic stresses. We hypothesize that structural and mineralogical heterogeneities at the sedimentary–crystalline rock nonconformity control the degree to which fluids, fluid pressure, and associated poroelastic stresses are transmitted over long distances across and along the nonconformity boundary. We examined the spatial distribution of physical and chemical heterogeneities in outcrops and core samples of the Great Unconformity in the midcontinent of the United States, capturing a range of tectonic settings and rock properties that we use to characterize the degree of past fluid communication and the potential for future communication. We identify three end-member nonconformity types that represent a range of properties that will influence direct fluid pressure transmission and poroelastic responses far from the injection site. These nonconformity types vary depending on whether the contact is sharp and minimally altered (Type 0), dominated by phyllosilicates (Type I), or secondary non-phyllosilicate mineralization (Type II). Our observations provide geologic constraints for modeling fluid migration and the associated pressure communication and poroelastic effects at large-scale disposal projects by providing relevant subsurface properties and much needed data regarding common alteration minerals that may interact readily with brines or reactive fluids.

中文翻译：

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使用露头和岩心类似物对不整合面进行地质特征描述：注水地震活动的水文意义

在距污水深注入井数公里处的结晶岩中，诱发地震的发生引发了一个问题，即不整合接触对孔隙流体压力和孔隙弹性应力的向下和横向传输产生了影响。我们假设沉积-结晶岩石不整合面的结构和矿物异质性控制了流体，流体压力和相关的孔隙弹性应力在不整合面边界上或沿不整合面边界的长距离传输的程度。我们研究了美国中部大不整合面的露头和核心样本中物理和化学异质性的空间分布，捕获一系列构造背景和岩石属性，以表征过去的流体连通程度和未来的通信潜力。我们确定了三种末端成员不合格类型，它们代表了一系列特性，这些特性将影响远离注射部位的直接流体压力传递和孔隙弹性响应。这些不整合类型的变化取决于接触是尖锐的且变化最小（类型0），以层状硅酸盐为主（I型）还是次生的非层状硅酸盐矿化（II型）。