Collaborative Research: Toward an Understanding of the Long Term Deformation in the Mississippi Embayment

孟菲斯大学和德克萨斯大学的科学家正在使用海洋地震方法，沿着密西西比河从阿肯色州的海伦娜到密苏里州的卡鲁瑟斯维尔，获取300公里的高分辨率地震反射数据和海底剖面数据。研究区域位于密西西比湾，神秘的新马德里地震带以南，新马德里地震带是北美大陆心脏地带的一个异常活跃的地震区，距离最近的板块边界2000公里。在这个板内区，高水平的历史和仪器记录的地震活动似乎与密西西比湾的平坦地形、低大地测量确定的速度矢量以及令人费解的晚白垩世后海湾沉积中缺乏实质性变形的情况不符。为了调和这一明显的悖论，有人提出，新马德里地震带的地震活动要么是幕式的，要么是非常年轻的(至少在目前的情况下是如此)，或者是在大陆或区域尺度上在广泛的区域内迁移。为了验证这些假设，研究小组正在对密西西比河沿岸的一大部分海湾进行勘察地震剖面图。在研究区发现了与新马德里地震带事件无关的地震液化特征，表明该海湾过去曾发生过地震。经过校准以照亮浅部的地震采集将提供密西西比河沉积物和隐藏在低迷地形下的疑似断层的前所未有的高分辨率图像，提供有关新马德里地震带以外的关键结构之间形变划分的详细信息。尽管板块构造理论彻底改变了我们对地震过程的理解，但它不能解释为什么地震发生在远离板块边界的地区，那里变形速率低，板块运动提供的驱动能量不足。该研究项目将使用密西西比河沿岸的海洋地球物理数据采集技术来研究美国中部神秘的新马德里地震带。这些技术将使我们能够非常经济高效地检查密西西比河流域300公里长的地下，历史上和史前历史上曾在那里发生过毁灭性的地震。这些数据还将为提出的解释构造板块中部地震活动的理论模型提供观测约束。作为这项研究的一部分，获得的高分辨率地震数据将适用于不同的应用。最重要的应用将是在中部大陆的地震危险性评估和地震损失和减少风险方面。这些数据还将有助于通过评估河床和斜坡稳定性来了解地震对密西西比河航运的影响。此外，这些数据将对孟菲斯等大城市地区的地下水可持续性和水质研究至关重要。

University of Memphis and University of Texas scientists are acquiring 300 km of high-resolution seismic reflection data and sub-bottom profile data along the Mississippi River, from Helena, Arkansas, to Caruthersville, Missouri using marine seismic methods. The study area is located in the Mississippi embayment, south of the enigmatic New Madrid seismic zone, an extraordinarily active seismic area in the heart of the North American continent, 2000 km from the nearest plate boundary. In this intraplate area, the high level of historic and instrumentally-recorded seismicity seems at odds with the flat topography of the Mississippi Embayment, low geodetically-determined velocity vectors, and a puzzling lack of substantial deformation in the post-Late Cretaceous sedimentary deposits of the Embayment. To reconcile this apparent paradox it has been proposed that the seismicity in the New Madrid seismic zone is either 1) episodic; 2) very young (at least in its present incarnation); or 3) migrates throughout a broad region at the continental or regional scale. In order to test these hypotheses the research team is conducting reconnaissance seismic profiling of a large portion of the embayment along the Mississippi River. Earthquake-induced liquefaction features that do not correlate with the New Madrid seismic zone events have been identified in the study area, suggesting that earthquakes have occurred in the embayment in the past. The seismic acquisition, calibrated to illuminate the shallow section, will provide unprecedented high-resolution images of the Mississippi River sediments and the suspected faults concealed under the subdued topography, providing detailed information on the partitioning of the deformation among key structures beyond the limit of the New Madrid seismic zone. Although the theory of plate tectonics revolutionized our understanding of earthquake processes, it does not explain why earthquakes occur in regions distant from plate boundaries where deformation rates are low and where plate motions supply insufficient driving energy. This research project will use marine geophysical data acquisition techniques along the Mississippi River to examine the enigmatic New Madrid seismic zone of the central U.S. These techniques will allow very cost effective examination of the subsurface of a 300 km stretch of the Mississippi River Valley, where devastating earthquakes have occurred in the historic and prehistoric past. The data will also provide observational constraints on theoretical models proposed to explain seismicity in the middle of tectonic plates. The high-resolution seismic data acquired as part of this study will be suitable to diverse applications. The most important application will be in earthquake hazard assessment and earthquake loss and risk reduction in the mid continent. The data will be also valuable for understanding the impact of a earthquake on the Mississippi River navigation by evaluating the riverbed and slope stability. In addition, the data will be critical for ground water sustainability and water quality studies in large metropolitan areas, such as Memphis.