Urgent deployment of GPS in Afar (Ethiopia): determining the rheology of incipient oceanic lithosphere

当板块运动时，新的洋壳最终会形成。随着岩浆沿着大洋中脊的垂直裂缝(岩墙)侵入，地壳呈间歇性增长(对于任何给定的地段来说，每隔几百年左右)。世界上大部分大洋地壳都在几公里深的水下，在那里不可能直接观察到堤坝的入侵过程。9月14日，在东非裂谷系统北端的阿法尔(埃塞俄比亚)的陆地上，发生了一次堤坝入侵事件--那里的大陆地壳刚刚被拉伸到足以形成“大洋”地壳的程度。一段60公里长的裂谷打开了9米之多，侵入了超过2立方公里的岩浆。有许多地震和喷发来自地表的长而开放的裂缝，覆盖了大片地区的火山灰，使大约25,000名牧民和他们的牲畜流离失所。这是自20世纪70年代以来陆地上第一次重大的堤坝入侵事件，也是第一次发生在精密天基测量技术时代。除了希望了解未来任何活动的可能性外，该事件还建立了一个简单的自然实验，将帮助我们了解地球外层的属性。从本质上说，入侵给了地球一个突然的打击。通过测量它对这种冲击的反应，我们可以了解到岩石在深处的表现。我们尤其感兴趣的是，我们是否能看到这些岩石随着踢球的压力而流动，以及它们流动的速度有多快。我们计划在地面上安装GPS仪器，连续监测地壳的运动，并使用卫星雷达图像获取变形的快照。结合这些测量，我们将能够了解大陆分裂和海洋板块生长的过程。

When tectonic plates move apart, new oceanic crust is eventually formed. This crust grows episodically (every few hundred years or so for any given segment) by the intrusion of magma along vertical cracks (dykes) at mid-ocean ridges. Most of the world's oceanic crust is under several kilometres of water where it is impossible to directly observe the dyke intrusion process. On the 14 September a dyke intrusion event began on land at the northern end of the East African Rift system, in Afar (Ethiopia) - where continental crust has just been stretched sufficiently for 'oceanic' crust to be formed. A 60 km long segment of the rift opened by as much as 9 m, and more than 2 cubic kilometres of magma was intruded. There were many 10s of earthquakes and eruptions from long, open fissures at the surface, blanketed a wide area in ash, displacing some 25,000 pastoralists and their livestock. This is the first major dyke intrusion event on land since the 1970s, and the first to occur in the era of precision space-based measuring techniques. As well as wishing to understand the likelihood of any future activity, the event sets up a simple natural experiment that will help us understand the properties of the earth's outer layers. In essence, the intrusion has given the earth a sudden kick. Measuring how it responds to that kick tells us about how the rocks at depth behave. In particular, we are interested in whether we can see those rocks flow in response to the stress of the kick, and how quickly they flow. We plan to install GPS instruments on the ground that will monitor the movement of the crust continuously, and to use satellite radar images to get snapshots of the deformation. From the combination of these measurements, we will be able to learn about the processes by which continents split apart and oceanic plates grow.