The dynamics of dyke injection during rifting - combining geodetic and seismic methodologies

地球上几百公里的地方是由不同的构造板块组成的，这些板块在板块边界处分离、碰撞或滑动，这一过程被称为板块构造。板块沿着位于大陆内部的边界分离，可能导致大陆分裂成两个或更多部分，最终形成和生长一个新的海洋盆地。这是通过向板块中添加新物质来实现的，这些新物质来自于地表以下深处部分熔融的岩浆，并作为冻结岩浆的近垂直壁（称为岩脉）添加到上层地壳中。因此，岩脉在分离板块边界处的侵位过程是板块构造的基础。然而，大多数这样的板块边界位于地球主要海洋的底部，被几公里厚的海水所掩盖。由于缺乏观察，科学家们不知道在板块分离过程中如何、在何处以及何时发生脉结的准确细节。形成堤坝的分离板块之间的一小部分边界暴露在海平面以上。例子包括冰岛和阿法尔（吉布提和埃塞俄比亚）。以前的观察表明，堤防侵入并不是连续发生的，而是每隔几千年发生的一周、一个月或一年的重复堤防侵入事件。堤坝形成通常伴随着强烈的地震、地球表面的破裂和火山爆发。然而，在上个世纪只观察到两次堤防侵入，自现代科学仪器出现以来没有一次。因此，我们仍然不确定注入岩脉的熔融岩石的来源在哪里，以及在岩脉形成过程中熔融岩石是如何以及何时在地球内部移动的。只有把对地震的精确观测与现代全球定位系统和空间卫星提供的对实际板块运动的高分辨率测量相结合，才能回答这些基本问题。2005年9月，埃塞俄比亚阿法尔裂谷发生了一条长达60公里、厚达8米的玄武岩堤坝的侵入。这一事件伴随着火山爆发和两周多的强烈地震。我参加了在阿法尔部署记录设备的紧急响应，以准确测量地震、活火山下岩浆房的膨胀和收缩，并测量构造板块的运动，因为我知道未来可能会有堤坝被安置。2006年6月，人们为获取这一独特数据所付出的巨大努力得到了回报，在裂谷下修建了第二条堤（长15公里，宽2米）。因此，我现在有机会获得来自一代人一次的堤防侵入事件的非凡数据，以准确地探测堤防是如何、何时以及在分离板块边界发生的。我将能够准确地确定岩浆来自哪里，岩浆在地球内部移动的时间，以及有多少岩浆被冻结在板块中形成垂直的堤坝。我提出的研究结果对于提高我们对平板分离的一般过程的理解至关重要。与来自埃塞俄比亚、冰岛、美国和英国的一流科学家合作，我将学习处理、分析和解释科学数据的新技能，同时解决地球如何继续进化的基本问题。我提出的研究结果对于埃塞俄比亚政府了解火山和地震的危害，以及与阿法尔壮观的地质特征相关的地热能源的潜在来源将是无价的。

The upper few hundred kilometres of the earth is comprised of a jigsaw of tectonic plates that separate, collide, or slide past each other at plate boundaries in a process called plate tectonics. Separation of a plate along a boundary located within a continent can result in the division of the continent into two or more parts and eventual formation and growth of a new ocean basin. This is achieved through the addition of new material to the plate, sourced from partially molten magma deep below the surface, and added to the upper crust as near vertical walls of frozen magma called dykes. Therefore, the process by which dykes are emplaced at separating plate boundaries is fundamental to plate tectonics. However, the majority of such plate boundaries lie at the bottom of the Earth's major oceans, and obscured by several kilometers of overlying water. Due to a lack of observations, scientists do not know accurate details of how, where and when dyking actually occurs during plate separation. A tiny proportion of the boundaries between separating plates where dykes occurs are exposed above sea-level. Examples include Iceland, and Afar (Djibouti and Ethiopia). Previous observations show that dyke intrusion does not occur on a continuous basis, but is rather restricted to week, month, or year long episodes of repeated dyke intrusions that occur every couple thousand years. Dyking is generally accompanied by violent earthquakes, fracturing of the Earth's surface, and volcanic eruptions. However, only two dyke intrusions have been observed over the last century, and none since the advent of modern scientific instrumentation. We are therefore still not sure where the source of the molten rock that feeds dykes is located, and how and when molten rock moves within the earth during the formation of a dyke. These fundamental questions can only be answered by combining accurate observations of earthquakes with high resolution measurements of actual plate movements provided by modern global positioning systems and space borne satellites. In September 2005, the intrusion of a 60 km-long basalt dyke, up to 8 metres thick, occurred in the Afar rift, Ethiopia. The event was accompanied by a volcanic eruption and swarm of violent earthquakes over two weeks. I participated in an urgent response to deploy recording equipment in Afar to accurately measure earthquakes, the expansion and contraction of magma chambers beneath the active volcanoes, and measure the movement of the tectonic plates, in the knowledge that future dykes are likely to be emplaced. The extreme effort to acquire this unique data was rewarded in June 2006 when a second dyke (15 km long, 2 metres wide) was injected beneath the rift. I thus now have access to extraordinary data from a once in a generation dyke intrusion event to accurately probe how, when and where dyking occurs at separating plate boundaries. I will be able to accurately determine where the magma came from, when the magma moved within the earth, and how much magma was frozen into the plate as a vertical dyke. The results of my proposed study are of critical importance in improving our understanding of the general process of plate separation. In collaboration with first class scientists from Ethiopia, Iceland, USA and the U.K., I will learn new skills in processing, analyzing and interpreting scientific data while solving a fundamental question on how the Earth continues to evolve. The results of my proposed research will be invaluable to the Ethiopian government in understanding the volcanic and seismic hazards, and potential sources of geothermal energy associated with the spectacular geological features in Afar.