Verification of the Apparent Crustal Stress Anomaly in the Western Midcontinent

最近的两项独立研究，一项是在南部的东南角， 达科他州和另一个在堪萨斯中北部，表明了一个惊人的 中大陆裂谷（MCR）以西应力状态的偏离 从威斯康星州、伊利诺斯州和东部各州建立的 直到现在都被认为在整个中大陆应力中占主导地位 省 南达科他州近地表地应力测量 和一个堪萨斯地震的震源机制解（深度 1.3公里或更大）都表明90度旋转的方向 最大水平应力均匀分布在东北方向 在所有以前的中大陆测量中。 这些新发现 得到了两个早期焦点机制解决方案的支持， 西-西北应力方向 然而，这个迷人的， 重要的观察，这可能需要重新分配 美国大陆的压力省份，是不完整的， 代表地壳上部的应力值很难 从近地表测试中确定，并且不可能 从震源机制解确定。 这个项目的目标 是为了验证MCR以西的意外结果，并补充 他们与可靠的估计，在原地主要的大小， 强调，通过进行一系列全面的液压 深部基底花岗岩破裂应力测量 约600米使用现有的昆比，爱荷华州科学孔。

Two recent independent studies, one in the SE corner of South Dakota, and the other in north central Kansas, indicate a striking departure in the stress regime west of the Midcontinent Rift (MCR) from that established in Wisconsin-Illinois and more eastern states and assumed until now to prevail throughout the Midcontinent stress province. Near-surface in situ stress measurements in South Dakota and a focal mechanism solution of an earthquake in Kansas (depth 1.3 km or greater) both indicate a 90o rotation in the direction of the maximum horizontal stress which is uniformly northeastern in all the previous Midcontinent measurements. The new findings are supported by two earlier focal mechanism solutions suggesting west-northwest stress direction. However, this fascinating and important observation, which may require a redistribution of the stress provinces in the continental U.S., is incomplete in that stress magnitudes representative of the upper crust are difficult to ascertain from near-surface tests, and are impossible to determine from focal mechanism solutions. The goal of this project is to verify the unexpected results west of the MCR, and complement them with credible estimates of the magnitudes of in situ principal stresses, by conducting a comprehensive series of hydraulic fracturing stress measurements in basement granite at depths of about 600 m using the existing Quimby, Iowa Scientific hole.