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

2008年，美国孟菲斯大学（University of Memphis）和德克萨斯大学（University of Texas）的研究人员成功进行了一项试点研究，该研究测试了密西西比河沿岸海洋地震数据采集的可行性。基于此，他们计划开展两个实地项目，以获取密西西比河沿岸约600公里的高分辨率海洋地震反射和海底剖面数据。这两项活动将以前所未有的分辨率成像新马德里地震带的活动断层系统和一系列被怀疑是导致地震诱发液化特征的推断断层，这些断层在新马德里地震带地震活动之前就已存在。利用海洋采集的优势（时间有效，成本低），新数据将确定活动断层系统（每年产生超过200次1.5-4.0级地震）和新马德里地震带外的变形位置和时间，并有助于了解密西西比海湾内断层之间的长期变形是如何在时间和空间上划分的。这些信息对于解决一个明显的悖论是至关重要的，这个悖论是由小大地测量矢量的对比证据、令人费解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。板块构造学的支柱之一是主要板块的刚性假设。事实上，GPS研究表明，大多数板块内部的行为是刚性的，因此，大多数地震发生在板块边界的狭窄或扩散带上。新马德里地震带位于北美大陆的中心地带，距离最近的板块边界2000公里，是世界上最活跃的板块内地震区之一，也是最臭名昭著的板块刚性偏差之一。古地震学观察表明，该地区在历史上和史前时期经历了一系列灾难性的地震，越来越多的证据表明，长期的地震活动不仅限于目前活跃的断层系统，而且在密西西比海湾内的其他地区也发生了大地震，造成这些地震的断层（或断层系统）尚未确定。这项研究将为解释美国中部板内地震活动的时间、震级和位置的理论模型提供观测约束。该项目的成果还将通过定位和描述发震断层，以及提高地震危险度图的质量和实用性，对地震危险性评估产生至关重要的影响。

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.