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New insights into the crustal structure of the England, Wales and Irish Seas areas from local earthquake tomography and associated seismological studies

机译：从当地地震层析成像和相关的地震学研究中获得对英格兰，威尔士和爱尔兰海地区地壳结构的新见解

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For the past three decades, deep crustal studies of the British Isles have been restricted to the interpretation of 2-D seismic reflection and refraction profiles, mostly acquired offshore. During this period, the British Geological Survey (BGS) seismic monitoring network has developed to an unrivalled density for a region of low intraplate seismicity. In an average year, the modern network records approximately 40 earthquakes in the crust beneath the British Isles with local magnitudes > 2. Statistical tests show the modern and historical pattern is not random. Understanding of the tectonic processes behind the pattern are hindered by the sparseness of onshore deep crustal studies where the majority of earthquakes are concentrated.\udFor the first time local earthquake tomography, a method more commonly applied to tectonically active regions, is used to produce high resolution 3-D images of seismic P-wave velocity (Vp) and the P- to S-wave velocity ratio (Vp/Vs) in the crust beneath England, Wales and the Irish Sea. To account for low seismicity, over 1,000 earthquakes are utilised from the past 25 years of monitoring. The existing BGS digital catalogue is enhanced by a two-fold increase in seismic arrival time picks, significantly reducing earthquake location errors in the input dataset.\udThe tomographic models establish a strong and previously undemonstrated link between Palaeocene magmatism and more widespread earlier phases of Caledonian magmatism. A regional Vp anomaly (> 7.2 km/s) in the lower crust centred on the East Irish Sea Basin is inferred as Palaeocene magmatic underplate with seismicity concentrated around its eastern and southern margins. In the mid- and lower-crust earthquake clusters are evident around the edges of local Vp/Vs anomalies (> 1.80), most significantly beneath the Ordovician volcanic centre in Snowdonia. The models are supplemented by the inversion of 185 independently determined focal mechanisms to consider the influence of local variations in far-field intraplate stresses alongside lithostatic stress from overburden pressure.
机译：在过去的三十年中，对不列颠群岛进行的深入地壳研究仅限于二维地震反射和折射剖面的解释，这些剖面大多是在海上采集的。在此期间，对于低板内地震活动性地区，英国地质调查局（BGS）地震监测网络已发展到无与伦比的密度。现代网络平均每年在不列颠群岛下方的地壳中记录大约40次地震，局部震级大于2。统计测试表明，现代和历史模式不是随机的。陆上深部地壳研究的稀疏性阻碍了对模式背后构造过程的理解，因为大部分地震都集中在地震研究上。\ ud首次使用局部地震层析成像技术，是一种更普遍地应用于构造活动区域的方法，可以产生高强度的地震。英格兰，威尔士和爱尔兰海下方地壳中地震P波速度（Vp）和P波与S波速度比（Vp / Vs）的高分辨率3-D图像。为了降低地震活动性，在过去25年的监测中，共利用了1000多次地震。现有的BGS数字目录通过地震到达时间选择的两倍增加而得到增强，从而显着减少了输入数据集中的地震位置误差。\ ud断层摄影模型在古新世岩浆作用和古苏格兰时期的更广泛的早期阶段之间建立了牢固而未经证实的联系。岩浆作用。推测以东爱尔兰海盆地为中心的下地壳区域出现了Vp异常（> 7.2 km / s），推测为古新世岩浆底板，地震活动集中在其东部和南部边缘。在中地壳和下地壳中，在局部Vp / Vs异常（> 1.80）的边缘附近可见地震群，最明显的是在斯诺登尼亚的奥陶纪火山中心以下。通过对185个独立确定的震源机制进行反演来补充模型，以考虑远场板内应力的局部变化以及上覆岩层压力引起的岩石静应力的影响。

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    Hardwick, Anthony James;

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  • 年度 2009
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