英国剑桥大学A. Boyce的研究组建立了一个新的北美P波层析成像模型(CAP22)。这一研究成果发表在2023年2月27日出版的国际学术期刊《JGR地球》上。

研究小组使用绝对到达时间恢复方法(AARM)，提取了来自加拿大和阿拉斯加地震台超过18000个新的绝对到达时间残差，并将这些数据与美国阵列以及来自美国和阿拉斯加的全球到达时间数据结合起来。研究人员开发了一种新的绝对P波速度层析成像模型-CAP22，该模型覆盖北美，与之前的模型相比，显著提高了加拿大和阿拉斯加的分辨率。加拿大科迪勒拉山脉下面的慢波与加拿大西南部落基山海沟大陆内部的快波速非常接近。

麦肯齐山脉下的慢波速度在加拿大西北部继续向内陆延伸，这表明了元古宙-太古宙slave克拉通的交代作用。继承的构造特征与这一南北波速边界相结合，表明地壳和地幔都可能控制科迪勒纪的造山过程。在阿拉斯加，兰格尔火山场下的快速上地幔波速有利于常规的与俯冲有关的火山作用机制。最后，俯冲的Kula和Yukon板块的地震证据表明，北美西部的构造重建可能需要修正。

据悉，我们对加拿大和阿拉斯加地幔的现今状态和演化的理解受到缺乏绝对P波速度约束的阻碍，P波速度约束结合现有S波速度模型提供了对成分的补充敏感性。因此，克拉通改造、北美西部造山史以及阿拉斯加原太平洋俯冲系统的复杂性仍然是谜。一项挑战涉及从临时地震网络记录，从经常有噪声的数据中提取绝对到达时间测量值是极度困难的事，这些数据是填补大陆和全球数据库的空白所需要的。

附：英文原文

Title: A new P-wave Tomographic Model (CAP22) for North America: Implications for the Subduction and Cratonic Metasomatic Modification History of Western Canada and Alaska

Author: A. Boyce, M. V. Liddell, S. Pugh, J. Brown, E. McMurchie, A. Parsons, C. Est, S. Burdick, F. A. Darbyshire, S. Cottaar, I. D. Bastow, A. J. Schaeffer, P. Audet, D. L. Schutt, R. C. Aster

Issue&Volume: 2023-02-27

Abstract: Our understanding of the present-day state and evolution of the Canadian and Alaskan mantle is hindered by a lack of absolute P-wavespeed constraints that provide complementary sensitivity to composition in conjunction with existing S-wavespeed models. Consequently, cratonic modification, orogenic history of western North America and complexities within the Alaskan Proto-Pacific subduction system remain enigmatic. One challenge concerns the difficulties in extracting absolute arrival-time measurements from often-noisy data recorded by temporary seismograph networks required to fill gaps in continental and global databases. Using the Absolute Arrival-time Recovery Method (AARM), we extract > 180,000 new absolute arrival-time residuals from seismograph stations across Canada and Alaska and combine these data with USArray and global arrival-time data from the contiguous US and Alaska. We develop a new absolute P-wavespeed tomographic model, CAP22, spanning North America that significantly improves resolution in Canada and Alaska over previous models. Slow wavespeeds below the Canadian Cordillera sharply abut fast wavespeeds of the continental interior at the Rocky Mountain Trench in southwest Canada. Slow wavespeeds below the Mackenzie Mountains continue farther inland in northwest Canada, indicating Proterozoic-Archean metasomatism of the Slave craton. Inherited tectonic lineaments colocated with this north-south wavespeed boundary suggest that both the crust and mantle may control Cordilleran orogenic processes. In Alaska, fast upper mantle wavespeeds below the Wrangell Volcanic Field favor a conventional subduction related mechanism for volcanism. Finally, seismic evidence for the subducted Kula and Yukon slabs indicate tectonic reconstructions of western North America may require revision.

DOI: 10.1029/2022JB025745

Source: https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022JB025745