Constraints on rigid zones and other distinct layers at the top of the outer core using CMB underside reflected PKKP waves          下载免费PDF全文

Fenglin Niu  Cindi Kelly  Jianping Huang 《地震科学（英文版）》2012,25(1):17-24

Clear PKKP, a P wave reflects off the core-mantle boundary on the core side, is recorded by the transcontinental USArray from two deep earthquakes occurred in South America and Tonga, and one intermediate-depth earthquake in the Hindu Kush region. We compare the PKKP waveforms with the direct P waves to investigate the fine structures near the core-mantle boundary, with a primary focus on the core side. We find no evidence for the existence of a sedimentary layer of lighter elements with a thickness above a few hundreds of meters beneath the reflection points of the two deep events, which are located at the Ninety-East Ridge and South Africa. On the other hand the PKKP wave duration of the Hindu Kush event is almost twice as long as that of the P wave, suggesting that multiple reflections may be occurring at the core-mantle boundary located beneath the Antarctic, which is located inside the so-called tangent cylinder of the outer core. The tangent cylinder is an imaginary cylindrical region suggested by geodynamics studies, which has different flow pattern and may have a higher concentration in lighter elements as compared to the rest of the outer core. One possible explanation of the elongated PKKP is a thin distinct layer with a thickness of a few kilometers at the top of the outer core, suggesting that precipitation of lighter elements may occur at the core-mantle boundary. Our data also indicate an extremely low Q_P of 312, approximately 40% of the PREM average (~780), within the large-scale low-velocity anomaly in the lowermost mantle beneath Pacific.  相似文献   

USArray及其近期科学发现   总被引：2，自引：0，他引：2  

李秋生  陈凌  王良书  吴庆举  刘宏兵  张忠杰  赵俊猛  史大年  贺日政 《地质学报》2010,84(6):847-853

美国台阵(USArray)是EarthScope计划的主要内容之一。旨在探测北美大陆变形、结构及其演化。USArray主要由平移/滚动台阵和机动台阵两部分构成。滚动台阵由400个宽频带地震台站组成,以向前滚动的方式扫过美国本土和阿拉斯加。利用来自该台阵的数据,科学家能获得地球内部精细图像,藉此考察地震和火山的过程。作为滚动台阵的补充,机动台阵被用于对关键目标进行详细观测和短期测量。美国台阵计划启动5年来,采集的数据已经提供了足以令科学界考虑重新审视地震物理、火山过程、核幔结构、活动变形构造、大陆结构及其演化、地球动力学和地壳流体等基本科学问题的基础资料。  相似文献   

探索北美大陆地下奥秘——EarthScope计划十年进展     

刘刚  董树文  陈宣华 《地球学报》2016,37(S1):5-20

在地球透镜计划15年项目周期的前十年中, 这个多目标的科学计划阐明了一系列北美大陆的构造、演化和动力学特征, 采集了超过115 TB的数据资料, 利用这些数据发表了超过330篇高质量科学论文, 取得了巨大进展和成就。地球透镜计划不仅仅是科学技术的进步, 而且对整个国家科学事业产生深远影响。地球透镜计划综合研究和管理模式可以作为其它国家科学研究的示范。  相似文献