Collaborative Research: High-Resolution Study of Subduction Zone Seismicity and Structure

合作研究：俯冲带地震活动和构造的高分辨率研究

• 批准号: 0337743
• 负责人: E.Robert Engdahl
• 金额: --
• 依托单位: University of Colorado at Boulder
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2004
• 资助国家: 美国
• 起止时间: 2004-01-01 至 2008-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0337743&HistoricalAwards=false
• 关键词: Collaborative; Research; Resolution; Study; Subduction

Abstract Subduction zones are one of the most important components of the Earth's plate tectonic system. This is reflected by the existence of two major international science initiatives focused on subduction zones: the Subduction Factory (SubFac) and the Seismogenic Zone Experiment (SEIZE), both part of the MARGINS initiative. The SubFac initiative has motivated substantial mineralogical and petrologic work on stability fields of candidate slab constituents (especially hydrated phases) and their relation to intermediate-depth seismicity. One working hypothesis is that the intermediate-depth earthquakes are related to metamorphic dehydration reactions in the subducting slab. Tests of this hypothesis are imperfect for four main reasons - uncertainties in slab thermal structure, slab composition, slab seismic velocity structure, and earthquake locations. The latter impacts earthquake locations and also affects the association between seismic velocities in slab models and candidate mineralogies. This project involves a multi-faceted seismological investigation of subduction zones around the world. The principal project goals are refining knowledge of the distribution of seismic activity within down-going slabs and improving seismic models of their structure. Analysis methods that are being applied in the project include (1) improved waveform alignment techniques, (2) high-precision teleseismic and local earthquake location, (3) associated focal mechanism determination, and (4) double-difference (DD) seismic tomography. Methods 1, 2 and 3 are applied to a broad suite of subduction zones, especially where the presence or absence of a double seismic zone is in question. Methods 1 and 4 are applied to a selected set of subduction zones where adequate local earthquake data are available - Northern Chile, Alaska, Costa Rica, and Taiwan. Previous work indicates that waveform cross-correlation (WCC) time delays verified with the bispectrum waveform alignment method provide better relocation results than those selected with the standard threshold criterion. This improvement is expected for two main reasons. First, unreliable WCC time delay data can be removed using bispectrum checking. Second, the bispectrum verification process can provide more time delay measurements for two close earthquakes and thus more control over their relative positions. Based on previous work with both teleseismic and local events, close to an order of magnitude reduction in relative location scatter can be expected. Refined waveform alignment techniques and a new DD seismic tomography method are applied to local datasets from several subduction zones to sharpen images of seismic velocity structure. All of the proposed target areas have been the subject of one or more previous local earthquake tomography studies, and thus have datasets suitable for DD tomography. Based on initial results applying the DD tomography method to catalog data from northern Honshu, the production of subduction zone seismic images of unprecedented clarity can be anticipated. This project will contribute in a fundamental way to the understanding of subduction zones and related processes. Subduction zones are a fundamental feature of the plate tectonic engine that drives the evolution of the Earth. The structure, state of stress, and evolution of down-going slabs are topics that have received substantial scientific attention yet remain relatively poorly understood. This project will provide improved information on the distribution of seismic activity within down-going slabs along with detailed models of the seismic structure of the slab and overlying mantle wedge, which are critical constraints for geodynamic and petrologic models. In particular, there are several competing hypotheses about the nature of intermediate-depth earthquakes. Through a detailed study of several different subduction zones, seismic evidence for or against these hypotheses will be obtained. This project will take advantage of the new NSF-supported Center for the Integration of Research Teaching and Learning (CIRTL) at UW-Madison in preparing web-based outreach materials based on the research results. Software and data will be shared with other scientists, particularly by providing training on the use of DD tomography.

摘要 俯冲带是地球板块构造体系的重要组成部分。这反映在存在两个主要的国际科学倡议，重点是俯冲带：俯冲工厂（SubFac）和地震带实验（SEIZE），两者都是MARGINS倡议的一部分。SubFac倡议激发了大量的矿物学和岩石学工作的稳定性领域的候选板成分（特别是水化相）和他们的关系，中深度地震活动。一种工作假设是，中深地震与俯冲板片中的变质脱水反应有关。这一假设的测试是不完善的四个主要原因-在板热结构，板组成，板地震速度结构，和地震位置的不确定性。后者影响地震位置，也影响板块模型和候选矿物的地震速度之间的关联。 该项目涉及对世界各地的俯冲带进行多方面的地震学调查。项目的主要目标是完善下行板块内地震活动分布的知识，并改进其结构的地震模型。在该项目中应用的分析方法包括（1）改进的波形对准技术，（2）高精度地震定位和当地地震定位，（3）相关震源机制确定，以及（4）双差（DD）地震层析成像。方法1，2和3适用于一个广泛的一套俯冲带，特别是在存在或不存在的双地震带的问题。方法1和4适用于一组选定的俯冲带，其中有足够的当地地震数据-北方智利，阿拉斯加，哥斯达黎加，和台湾。 以往的工作表明，波形互相关（WCC）的时间延迟验证的双谱波形对齐方法提供更好的重新定位结果比那些选择与标准的阈值标准。预计这一改善有两个主要原因。首先，不可靠的WCC时间延迟数据可以使用双谱检查。其次，双谱验证过程可以为两个近距离地震提供更多的时间延迟测量，从而更好地控制它们的相对位置。根据以前的工作与气象和当地的事件，接近一个数量级的减少相对位置分散可以预期。 应用精细波形对齐技术和一种新的DD地震层析成像方法，对几个俯冲带的局部数据集进行了地震速度结构图像的锐化处理。所有拟议的目标区域都是以前一个或多个当地地震层析成像研究的主题，因此具有适合DD层析成像的数据集。根据应用DD层析成像方法对本州北方编目数据的初步结果，可以预期将产生前所未有的清晰度的俯冲带地震图像。 该项目将从根本上促进对俯冲带和相关过程的理解。俯冲带是驱动地球演化的板块构造引擎的一个基本特征。下行板块的结构、应力状态和演化是受到大量科学关注但仍相对知之甚少的主题。该项目将提供关于下行板块内地震活动分布的更好信息，沿着板块和上覆地幔楔的地震结构的详细模型，这是地球动力学和岩石学模型的关键制约因素。特别是，关于中深度地震的性质，有几种相互竞争的假设。通过对几个不同俯冲带的详细研究，将获得支持或反对这些假设的地震证据。 该项目将利用新的NSF支持的研究性教学和学习（CIRTL）在威斯康星大学麦迪逊分校的整合中心，根据研究结果准备基于网络的宣传材料。将与其他科学家分享软件和数据，特别是通过提供关于使用DD断层扫描的培训。