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100公里厚的大陆板块的破裂，但只有经过数百万年的地球深部地幔加热，并在板块边界的力的作用下拉伸。在这些板块伸展和加热的区域之上，有着活火山的深的、以断层为边界的山谷被称为大陆裂谷带。阿法尔洼地的东非裂谷系统是世界上少数几个大陆断裂过程发生在陆地上的地方之一，提供了一个直接观察和量化板块分离过程的机会。大陆断裂过程的时间平均速度非常缓慢，大约是指甲生长的速度。地震和火山活动表明，板块也承受着10到100年的压力。当板块不再能够承受来自板块拉伸的应力时，在一系列地震中会发生更快的，有时甚至是灾难性的变形。同样地，来自板块下方热区的熔融岩石（岩浆）的密度比固体岩石低，它可能会在板块内聚集，导致火山爆发。如果熔融的岩石聚集在一个脆弱的或高应力的板块区域之下，它将上升为一个被称为岩脉的薄片，填充脆性地壳的裂缝和裂缝。这些事件中的火山和地震活动只影响狭长裂谷带的一部分，产生了一个规则的沿轴裂谷分段，并在随后的事件中保持。2005年9月至10月，埃塞俄比亚东非裂谷系统的一个60公里长的部分经历了一个强烈的局部变形期。在3周内发生了超过163次中等地震（5.3 mb 3.9）和一次爆炸性火山爆发。野外、地震、遥感和模拟研究表明，熔融的岩石（岩浆）侵入了这个60公里长的裂谷段下方的板块，在岩浆注入的狭窄区域上方的脆性岩石中形成了裂缝和断层。裂谷幕可能是由一个60公里长，约8米宽的玄武岩浆（岩脉）的注入触发，断层滑动以上的岩脉。玄武岩在这一幕中没有到达地表，或者在2006年6月的第二次不那么强烈的事件中。 对地震活动的持续监测，地面相对于距离活动区约100公里的稳定地区的垂直和水平运动，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板块破裂与岩浆注入事件之一。然后将观测结果与计算机模拟的岩浆通过正在伸展开的板块上升进行比较。这项研究的重大影响之一是，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.