Collaborative Research: Magma-Tectonic Processes in an Active Transitional Rift from Seismic, Global Positioning System (GPS), and Modelling Studies in Afar

一个新的海洋盆地的形成始于一个100公里厚的大陆板块的破裂，但这是在地球深层地幔数百万年的加热和板块边界力量的作用下拉伸之后才开始的。在这些板块伸展和加热带之上有活火山的深的、有断层的山谷被称为大陆裂谷带。阿法尔坳陷中的东非裂谷系统是世界上为数不多的陆地上发生大陆破裂过程的地方之一，为直接观察和量化板块分离过程提供了机会。大陆破裂过程的时间平均速度极其缓慢；关于指甲生长的速度。地震和火山活动表明，板块也承受着10年到100年的压力。当板块不能再承受板块拉伸产生的应力时，在地震群中就会发生更快的、有时甚至是灾难性的变形。同样，来自板块下方热区的熔融岩石（岩浆）比固体岩石密度小，它可能在板块内聚集，导致火山爆发。如果熔融岩石积聚在一个弱或高应力板块带之下，它就会上升成一层叫做岩脉的薄片，填满脆弱地壳的裂缝和裂缝。这些时期的火山和地震活动只影响了狭长的裂谷带的一部分，产生了规律的沿轴裂谷分割，并在随后的时期保持不变。2005年9月至10月，位于埃塞俄比亚的东非裂谷系统60公里长的一段经历了剧烈的局部变形。在3周的时间里，发生了163次中等（5.3 mb 3.9）地震和一次火山爆发。野外、地震、遥感和模拟研究表明，熔融岩石（岩浆）侵入了这个60公里长的裂谷段下方的板块，在狭窄的岩浆注入带上方的脆性岩石中形成了裂缝和断层。裂谷事件可能是由一条60公里长、8米宽的玄武岩岩浆（岩脉）的注入引发的，断层在岩脉上滑动。玄武岩并没有在这次喷发中到达地表，2006年6月的第二次喷发强度较低。对地震活动的持续监测、相对于离活跃区约100公里的稳定地区地表的垂直和水平运动，以及每月的卫星雷达图像，使我们能够直接测量这些罕见的岩浆注入板块破裂事件之一。然后将观测结果与岩浆通过被拉伸的板块上升的计算机模拟结果进行比较。这项研究的一个重要的更广泛的影响是，对活动的持续监测为减轻东非的地震和火山灾害提供了重要信息。该项目由两个NSF项目共同资助：地球物理学和国际科学与工程办公室。

The formation of a new ocean basin begins with the rupture of a 100 km-thick continental plate, but only after millions of years of heating from Earth's deep mantle, and stretching in response to forces at the plate boundaries. Deep, fault-bounded valleys with active volcanoes above these zones of plate stretching and heating are termed continental rift zones. The East African rift system in the Afar Depression is one of few places worldwide where this process of continental rupture is occurring on land, affording an opportunity to directly observe and quantify the plate separation process.The time-averaged rate of the continental rupture process is extremely slow; about the rate of fingernail growth. Earthquakes and volcanic activity demonstrate that the plate also sustains stresses for periods of 10's to 100's of years. When the plate can no longer support the stresses from the plate stretching, much more rapid and sometimes catastrophic deformation occurs in a swarm of earthquakes. Likewise, molten rock (magma) from the hot zone beneath the plate is less dense than solid rock, and it may pond within the plate, leading to volcanic eruptions. If molten rock has accumulated beneath a weak or highly stressed plate zone, it will rise as a thin sheet called a dike that fills the fissures and cracks in the brittle crust. Volcanic and earthquake activity in these episodes affects only a sector of the long narrow rift zones, producing a regular along-axis rift segmentation that is maintained in subsequent episodes. One of these 60 km-long segments of the East African rift system in Ethiopia experienced an intense period of localized deformation in September-October, 2005. Over 163 moderate (5.3 mb 3.9) earthquakes and an explosive volcanic eruption occurred over a 3 week-period. Field, earthquake, remote sensing, and modelling studies show that molten rock (magma) was intruded into the plate beneath this 60 km-long rift segment, with cracks and faults forming in brittle rocks above the narrow zones of magma injection. The rifting episode was probably triggered by the injection of a 60 km-long, ~ 8m-wide sheet of basaltic magma (dike), with faults slipping above the dikes. The basalts did not reach the surface in this episode, or a second, less intense episode in June, 2006. The ongoing monitoring of earthquake activity, vertical and horizontal motion of the ground surface relative to stable areas ~100 km away from the active zone, and monthly satellite radar images allow us to directly measure one of these rare episodes of plate rupture with magma injection. The observations are then compared with computer simulations of the rise of magma through a plate that is being stretched apart. Among the significant broader impacts of this study are that continued monitoring of the activity provides vital information for seismic and volcanic hazard mitigation in East Africa. This project is co-funded by two NSF programs: Geophysics and the Office of International Science and Engineering.