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

利用2008年进行的一项试验性研究的成功，该研究测试了沿着密西西比河采集海洋地震数据的可行性，孟菲斯大学和德克萨斯大学的研究人员正在计划两个实地项目，以采集沿着密西西比河约600公里的高分辨率海洋地震反射和海底下剖面数据。这两项活动将以前所未有的分辨率对新马德里地震带活动断层系统和一系列推测的断层进行成像，这些断层被怀疑是新马德里地震带地震活动之前地震诱发液化特征的原因。发挥海上采办优势（时效性强，成本低），新数据将确定活动断层系统内变形的位置和时间（每年发生200多次1. 5 - 4. 0级地震），而在新马德里地震带之外，并有助于理解长期变形是如何在时间和空间上划分在密西西比湾内的断层。这一信息对于解决由小大地矢量的对比证据、令人困惑的缺乏实质性变形以及高水平的仪器和历史地震活动性所引起的明显矛盾至关重要。板块构造学的支柱之一是假设主要板块的刚性。事实上，GPS研究表明，大多数板块内部表现为刚性，因此，大多数地震发生在板块边界的沿着狭窄或扩散带。新马德里地震带位于北美大陆中心，距离最近的板块边界2,000公里，是世界上最活跃的板内地震区之一，也是最臭名昭著的偏离板块刚性的地区之一。古地震学观测表明，该地区在历史和史前时期经历了一系列灾难性地震，越来越多的证据表明，长期地震活动不仅限于目前活跃的断层系统，而且在密西西比湾内的其他地区也发生了大地震，其中负责的断层（或断层系统）尚未确定。这项研究将提供观测约束的理论模型，提出解释的时间，规模和位置的板内地震活动在美国中部。这一项目的成果还将对地震危险评估产生重大影响，确定发震断层的位置和特点，提高地震危险图的质量和效用。

Capitalizing on the success of a pilot study conducted in 2008, which tested the feasibility of marine seismic data acquisition along the Mississippi River, University of Memphis and University of Texas researchers are planning two field programs to acquire approximately 600 km of high-resolution, marine seismic reflection and sub-bottom profile data along the Mississippi River. The two campaigns will image with unprecedented resolution the New Madrid Seismic Zone active fault system and a series of inferred faults suspected to be responsible for earthquake induced liquefaction features predating the seismic activity of the New Madrid Seismic Zone. Exploiting the advantages of marine acquisition (time effective, low cost), the new data will identify the location and timing of deformation within the active fault system (which generates more than 200 magnitude 1.5-4.0 earthquakes a year), and outside the New Madrid Seismic Zone, and contribute to the understanding of how long-term deformation is partitioned in time and space among faults within the Mississippi Embayment. This information is critical to solve the apparent paradox raised by the contrasting evidence of small geodetic vectors, a puzzling lack of substantial deformation, and the high level of instrumental and historical seismicity. One of the pillars of plate tectonics is the assumption of the rigidity of major plates. Indeed GPS studies show that most plate interiors behave rigidly and, as a result, the majority of earthquakes occur along narrow or diffuse belts at plate boundaries. Located in the heart of the North American continent and 2,000 km away from the nearest plate boundary, the New Madrid Seismic Zone is one of the most active intraplate seismic areas in the world, and one of the most notorious deviations from plate rigidity. Paleoseismological observations show that the area experienced a series of catastrophic earthquakes in historic and prehistoric time and evidence is mounting that the long-term seismicity is not limited to the presently active fault system, but that large earthquakes have occurred in other areas within the Mississippi Embayment, for which the responsible fault (or system of faults) are yet to be identified. This study will provide observational constraints on theoretical models proposed to explain the timing, magnitude and location of intraplate seismicity in the Central United States. The results of this project will also have a crucial impact for earthquake hazard assessments by localizing and characterizing seismogenic faults, and improving the quality and usefulness of seismic hazard maps.