New Madrid Seismic Zone

The New Madrid Seismic Zone (NMSZ) has been responsible for producing some of the largest intraplate earthquakes on record (Tuttle et al., 2002). Paleoseismologic studies of sand blows and the Reelfoot fault show that earthquakes occurred in the last 4000 years at intervals of approximately 400-600 years (Kelson et al., 1995; Tuttle et al., 2002; Holbrook et al., 2006). The 1811-1812 NMSZ sequence produced three major earthquakes (M 7-8) followed by several large aftershocks and hundreds of smaller ones, resulting in a felt area that reached the east coast of the United States and caused destruction of several settlements along the Mississippi River due to liquefaction and strong shaking (Nuttli 1973, Johnston and Schweig, 1996). The risk of another large destructive earthquake in this region is of great concern to the USGS and local and federal authorities because several large metropolitan areas (Memphis, Little Rock, Nashville, St. Louis), and hundreds of smaller communities lie in or near the NMSZ.<br><br>The mechanism for occurrence of earthquakes in the NMSZ is widely debated. Studies reveal the NMSZ is underlain by a failed rifting event, dating from late Precambrian. During the failed rifting event, emplacement of mafic plutons throughout the crustal column took place. Further studies show a correlation between the rift and current seismic activity. This correlation suggests that the source of the earthquakes was from slippage along weak zones within the failed rift caused by the E-W compressive stress of the region, a result of plate motion. Seismic monitoring shows that there is a spatial correlation of the active seismic zone with the failed Reelfoot Rift.

新马德里地震带（NMSZ）曾引发史上部分最大的板块内地震（Tuttle 等人，2002年）。通过对沙丘和雷尔富特断层进行古地震学研究，表明在过去4000年间，地震以大约400至600年的周期发生（Kelson 等人，1995年；Tuttle 等人，2002年；Holbrook 等人，2006年）。1811-1812年的NMSZ序列产生了三次主要地震（震级7-8级），随后发生数次较大余震以及数百次较小余震，影响范围扩展至美国东海岸，并导致密西西比河沿岸数个定居点因液化作用和强烈震动而遭受破坏（Nuttli，1973年，Johnston 和 Schweig，1996年）。鉴于该地区存在另一次大型破坏性地震的风险，美国地质调查局以及地方和联邦当局深感忧虑，因为数个大型都市区（如孟菲斯、小石城、纳什维尔、圣路易斯）以及数百个小社区均位于或靠近NMSZ。<br><br>NMSZ地震发生的机制一直是学术界广泛讨论的焦点。研究揭示，NMSZ位于一次失败的裂谷事件之下，该事件始于晚前寒武纪。在这次失败的裂谷事件中，基性岩浆体在整个地壳柱中沉积。进一步的研究表明，裂谷与当前的地震活动存在相关性。这种相关性暗示，地震的源起是因区域板块运动产生的E-W压缩应力，导致失败裂谷内部薄弱带发生滑动。地震监测显示，活动地震区与失败的雷尔富特裂谷在空间上存在相关性。