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

孟菲斯大学和得克萨斯大学的科学家正在利用海洋地震方法获取密西西比河沿着从阿肯色州海伦娜到密苏里州卡鲁瑟斯维尔的300公里长的高分辨率地震反射数据和海底剖面数据。研究区位于密西西比海湾，神秘的新马德里地震带南部，这是北美大陆中心的一个异常活跃的地震区，距离最近的板块边界2000公里。在这个板内区域，历史上和仪器记录的高水平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湾的晚白垩世后沉积层中令人困惑的缺乏实质性变形不一致。为了调和这一明显的矛盾，有人提出，新马德里地震带的地震活动要么是1）偶发性的;要么是非常年轻的（至少在目前的情况下）;要么是在大陆或区域尺度上迁移到整个广阔的区域。为了验证这些假设，研究小组正在对密西西比河沿着的大部分海湾进行勘测地震剖面。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，这表明过去在海湾发生过地震。地震采集经过校准以照亮浅部，将提供密西西比河沉积物和隐藏在平缓地形下的疑似断层的前所未有的高分辨率图像，提供关于新马德里地震带界限以外的关键结构之间的变形划分的详细信息。它不能解释为什么地震发生在远离板块边界的地区，那里的变形率低，板块运动提供的驱动能量不足。该研究项目将使用海洋地球物理数据采集技术沿着密西西比河研究美国中部神秘的新马德里地震带。这些技术将允许非常具有成本效益的检查地下的300公里长的密西西比河谷，在那里发生了毁灭性的地震在历史和史前的过去。这些数据还将为解释构造板块中部地震活动性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各种应用。最重要的应用将是在中部大陆的地震灾害评估和地震损失和风险降低。这些数据对于通过评估河床和边坡稳定性来了解地震对密西西比河航行的影响也将是有价值的。此外，这些数据将对孟菲斯等大都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.