Tracking melt injection under the Mid-Atlantic Rift near Askja, central Iceland

追踪冰岛中部阿斯贾附近大西洋中裂谷下的熔体注入

• 批准号: NE/F011407/1
• 负责人: Robert White
• 金额: $ 3.88万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FF011407%2F1
• 关键词: Tracking; melt; injection; under; Mid

The crust of the large oceanic island of Iceland in the North Atlantic is formed almost entirely from successive volcanic eruptions which fill the gap caused by the separation (rifting) of the plates on which North America and Europe sit. The massive volcanism in Iceland is caused by the deep mantle there being hotter than normal, and so melting more than normal to produce large amounts of molten rock, or magma. Although the melt is formed in the deep mantle at depths of 40-100 kilometres, it is very buoyant and bleeds rapidly up towards the surface. Normally it ponds in the crust in a magma chamber about 5-6 kilometres beneath the surface until a sufficiently large volume has built up to cause an eruption. Our main objective is to investigate some exceptionally deep earthquakes occurring 15-30 kilometres beneath the surface under the active volcanic system of Askja in central Iceland. These occur at depths where the crust should be hot enough to prevent brittle failure generating any earthquakes. We first discovered these deep earthquakes in summer 2006, and will now target an array of seismometers specifically to investigate them further. Our hypothesis is that they are caused by melt moving in the deep crust. This is an exciting observation, since such deep earthquakes have only rarely been observed before, and never in a rift zone; it means that we can catch the volcano in the act of transferring molten rock through the crust. A second objective is to monitor a new area of activity, again thought to be caused by melt injection, which started in February 2007 beneath a previously seismically quiet area on the edge of the rift zone some 20 km east of Askja. Over 3000 events have occurred up to mid-August 2007, gradually decreasing in depth from 20 to 15 km and latterly extending almost to the surface. This may represent injection of molten rock into a shallow magma chamber which may result in a volcanic eruption. Previous experience suggests that activity is likely to persist for around 2 years, so we have an opportunity to track almost the entire development of a melt injection (and possibly eruption) episode. Thirdly we will map the location of the underground storage reservoirs (magma chambers), by using the fact that the crust above them is cold and brittle, therefore allowing numerous small earthquakes to occur as it fractures, whereas the hot magma chambers deform ductilely without fracturing. So by mapping where the earthquakes are absent, or where seismic waves are absorbed by passing through rock containing some melt, or rock at high temperatures, we can map the region of the magma chamber. Our seismic data will also be used to calculate the crustal thickness in this region, which is presently poorly known. Results form our studies will be integrated with information from other researchers investigating deformation in the region using satellite measurements which can detect motions at a millimetre scale, together with surface mapping of faults in the crust and evidence from detailed petrological studies of the rocks which provide control on the depths at which the molten rock has ponded in the crust during its ascent to the surface. The Askja area is inhospitable, and is easily accessible only in the summer months of July-August when snow is absent. Winter temperatures plummet to -25C. We shall install our seismometer array during summer 2008, but leave them operating remotely through the winter to gain a complete picture of the seismicity through time. The seismometers include a satellite clock receiver which provides accurately timing. Solar panels with large batteries will power the instruments through the dark winter months. Data from one of the stations will be radio-telemetered to Reykjavik and hence accessible via the internet from Cambridge, while the remainder will record data internally, to be collected in summer 2009.

北大西洋大海洋冰岛的大洋岛的外壳几乎完全是由连续的火山喷发形成的，这些火山喷发填补了北美和欧洲所在的板块的分离（裂谷）造成的空白。冰岛的大量火山是由高地幔引起的，那里的火山比正常人高，因此熔化比正常融化以产生大量的熔融岩石或岩浆。尽管熔体是在40-100公里深的深度中形成的，但它非常浮力，并且出血迅速向上朝向表面。通常，它在地面下约5-6公里处的岩浆室中的地壳中池塘池塘，直到建立足够大的体积以引起喷发为止。我们的主要目的是研究冰岛中部的Askja活跃火山系统下面15-30公里处发生的一些非常深的地震。这些发生在地壳应该足够热以防止易碎破坏产生任何地震的深度。我们首先在2006年夏季发现了这些深层地震，现在将针对一系列专门调查它们的地震仪。我们的假设是它们是由融化在深层地壳中移动引起的。这是一个令人兴奋的观察，因为这样的深层地震很少以前没有观察到，而从未在裂谷区域中进行过观察。这意味着我们可以在将熔融岩石通过地壳转移的行为中捕获火山。第二个目标是监视一个新的活动区域，这再次被认为是由熔体注射引起的，该注射始于2007年2月，在先前在裂谷区域边缘约20公里以东约20公里处的裂谷区边缘下方。超过3000个事件发生到2007年8月中旬，逐渐从20 km逐渐减少，后来延伸到表面。这可能代表将熔融岩石注射到浅岩浆腔中，这可能会导致火山喷发。以前的经验表明，活动可能会持续大约2年，因此我们有机会跟踪熔体注射（甚至可能是喷发）发作的整个发展。第三，我们将使用以下事实来绘制地下储物库（岩浆腔）的位置，即使用它们上方的地壳冷又脆，因此使许多小地震在裂缝时发生，而热的岩浆腔室无需破裂而变形。因此，通过映射地震的位置，或通过在高温下穿过岩石或岩石的岩石来吸收地震波，我们可以绘制岩浆腔室的区域。我们的地震数据还将用于计算该区域的地壳厚度，该区域目前尚不清楚。结果表格我们的研究将与其他研究人员的信息进行整合，该研究人员使用卫星测量结果研究了该地区的变形，这些测量可以检测到毫米尺度的运动，以及在地壳中的故障的表面映射以及对岩石的详细岩石学研究的证据，这些岩石对岩石的详细岩石学研究提供了对深度的控制，从而可以控制熔融的岩石在其层状的甲壳中池塘在其沿沿沿沿表面进行岩石。 Askja地区是无处不在的，只有在7月至8月降雪的夏季，才能轻松到达。冬季温度下降至-25C。我们将在2008年夏季安装我们的地震仪阵列，但在整个冬季，它们都会远程操作，以全面了解地震性。地震仪包括一个卫星时钟接收器，该接收器提供了准确的计时。带有大电池的太阳能电池板将在黑暗的冬季为乐器提供动力。来自其中一个电台的数据将被广播电台到雷克雅未克，因此可以从剑桥从互联网访问，而其余的将在2009年夏季收集到内部的数据。

项目成果

Seismic Amplitude Ratio Analysis of the 2014-2015 Bárarbunga-Holuhraun Dike Propagation and Eruption

2014-2015年Bárarbunga-Holuhraun堤坝扩展和喷发地震振幅比分析

• DOI: 10.1002/2017jb014660
• 发表时间: 2018
• 期刊: Solid Earth
• 影响因子: 3.4
• 作者: Caudron C

Triggered earthquakes suppressed by an evolving stress shadow from a propagating dyke

• DOI: 10.1038/ngeo2491
• 发表时间: 2015-07
• 期刊: Nature Geoscience
• 影响因子: 18.3
• 作者: R. Green;T. Greenfield;R. White

Ambient noise tomography reveals upper crustal structure of Icelandic rifts

• DOI: 10.1016/j.epsl.2017.02.039
• 发表时间: 2017-05
• 期刊: Earth and Planetary Science Letters
• 影响因子: 5.3
• 作者: R. Green;K. Priestley;R. White

Seismic Amplitude Ratio Analysis of the 2014-2015 Bár ?arbunga-Holuhraun Dike Propagation and Eruption

2014-2015年Bár ?arbunga-Holuhraun岩脉扩展和喷发地震振幅比分析

• DOI: 10.17863/cam.21041
• 发表时间: 2018
• 作者: Caudron C

Coalescence microseismic mapping

• DOI: 10.1093/gji/ggt331
• 发表时间: 2013-12-01
• 期刊: GEOPHYSICAL JOURNAL INTERNATIONAL
• 影响因子: 2.8
• 作者: Drew, Julian;White, Robert S.;Tarasewicz, Jon
• 通讯作者: Tarasewicz, Jon