Assessing the causes of slab seismicity through dehydration, temperature and strain: A global approach

通过脱水、温度和应变评估板片地震活动的原因：全球方法

• 批准号: 1246955
• 负责人: Clifford Thurber
• 金额: $ 10.66万
• 依托单位: University of Wisconsin-Madison
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-01-01 至 2014-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1246955&HistoricalAwards=false
• 关键词: Assessing; causes; slab; seismicity; through

The majority of Earth's seismicity is focused at subduction zones, either in the shallow thrust zone or as intermediate-depth (~50 to 300 km depth) or deep (to ~600 km depth) slab seismicity. Intermediate-depth seismicity is commonly thought to be caused by dehydration embrittlement, in which the dehydration of hydrous minerals in the subducted crust or mantle increases the pore fluid pressure in low-permeability rocks, allowing rocks to behave brittlely; although recent studies have called this hypothesis into question due to a lack up supporting laboratory observations. Double seismic zones are obvious in some subducting slabs (e.g., Honshu), but their presence in other slabs is less clear due to the relatively large errors in hypocentral locations relative to the spacing between the two layers of seismicity, which varies among different slabs. As the lower layer of seismicity is thought to be caused by the dehydration of serpentine in the slab mantle, having a limited view of the global prevalence of double seismic zones limits the constraints on slab mantle serpentinization and dehydration. In this project, we will relocate teleseismic earthquakes within 54 small arc sections and compare these seismicity distributions with pre-existing 2D thermal and mineralogical models, with a focus on the locations of greatest dehydration of slab minerals. The double-difference relocation technique teletomoDD will be used with nested regional-global 3D velocity models, which will significantly reduce scatter and improve the absolute locations of earthquake hypocenters in comparison to existing global catalogs. By better understanding intermediate-depth seismicity and its relation to thermal and petrological models, we can gain insight to the seismogenic processes in slabs and contribute to the understanding of six key questions pertaining to subduction zones:1) What phenomenon is responsible for the majority of intermediate-depth seismicity?2) Where are double seismic zones observable?3) In double seismic zones, what is responsible for the lower layer of seismicity?4) What controls the maximum depth of slab seismicity?5) Is the distribution of slab seismicity correlated with changes in volcanism?6) Is there a relationship between slab seismicity and changes in deep plate coupling?The majority of Earth's seismicity is focused at subduction zones, where cold, dense oceanic crust and mantle descend beneath a more buoyant plate, with the ability of producing large earthquakes and volcanism. Seismicity occurs either in the shallow thrust zone, or as intermediate-depth (~50 to 300 km depth) or deep (to ~600 km depth) slab seismicity. The mechanisms that cause shallow earthquakes are relatively well understood, whereas the cause of intermediate-depth seismicity is less certain. This is due in part to the expected ductile behavior of Earth materials at high pressures and temperatures, conditions that are difficult to reproduce in the laboratory. However, by combining numerical models of temperature and mineralogical reactions within subducting crust and mantle to observations of seismicity, we can better understand what slab conditions are most closely associated with observed seismicity. In this project, we will relocate intermediate-depth earthquakes using techniques that more accurately reproduce the paths of seismic wave propagation and reduce errors in earthquake locations from existing global seismicity catalogs. We will then comprehensively compare the distributions of slab seismicity with existing temperature and mineralogical models to identify which particular reactions contribute most to the creation of potentially large intermediate-depth earthquakes.

地球的大部分地震性都集中在俯冲区域，无论是在浅层推力带还是中间深度（〜50至300 km的深度）或深度（〜600 km深度）平板地震。通常认为中等深度的地震性是由脱水的封闭膜引起的，其中俯冲壳或地幔中含水矿物质的脱水会增加低渗透性岩石中的孔隙流体压力，从而使岩石的表现稳固；尽管由于缺乏支持实验室的观察，最近的研究称该假设提出了疑问。在某些俯冲平板（例如，亨森）中，双重地震区是显而易见的，但是由于在地震性的两个层之间的间距相对于次中心位置的相对较大的误差，因此它们在其他板块中的存在尚不清楚，这在不同的板片之间各不相同。由于较低的地震性被认为是由蛇纹石地幔中蛇纹石脱水引起的，因此对双重地震区域的全局患病率的看法有限，这限制了对平板地幔蛇形化和脱水的约束。在这个项目中，我们将在54个小弧形段内重新降低远距离地震，并将这些地震性分布与现有的2D热和矿物学模型进行比较，重点关注平板矿物质最大脱水的位置。双向重定位技术Teletomodd将与嵌套的区域 - 全球3D速度模型一起使用，与现有的全球目录相比，这将显着减少散射并改善地震降压器的绝对位置。通过更好地理解中等深度及其与热和岩石学模型的关系，我们可以深入了解板中的地震生成过程，并有助于理解与俯冲区有关的六个关键问题：1）哪些现象是什么现象是什么责任中等程度的ZESIS ZONES ZONES的大多数？地震性层？4）什么控制平板地震性的最大深度？5）平板地震性的分布是否与火山主义的变化相关？6）平板地震性与深层耦合之间的变化之间存在关系吗？地球上的大部分地球性都集中在更冷的deScultion zones，而deaste to的刺激性，coldecte骨的colly脚，构成了一个coldecte骨的象征，象征着大海的象征，象征着大海的象征。产生大型地震和火山。地震性发生在浅推力区域，或中间深度（〜50至300 km的深度）或深度（深度为〜600 km）的平板地震性。引起浅层地震的机制相对充分理解，而中等深度地震的原因则不太确定。这部分是由于地球材料在高压和温度下的预期延性行为，这些条件在实验室中难以繁殖。但是，通过将俯冲和地幔中温度和矿物质反应的数值模型结合到地震性观察中，我们可以更好地理解哪些平板条件与观察到的地震性最紧密相关。在这个项目中，我们将使用更准确地重现地震波传播路径并减少地震位置中现有的全球地震性目录中地震位置的误差的技术重现中等深度地震。然后，我们将全面地比较平板地震性与现有温度和矿物学模型的分布，以确定哪些特定反应对创造潜在的大型中间深度地震最大​​。