Seismological Investigations of Earthquakes and Deep Earth Structure

该项目将利用世界各地数千次地震产生的数十年地震波记录来了解地震和地球深层结构。对地震的分析将重点放在地震图的高频成分上，这些成分提供了对地震辐射能量的关键限制，以及有关断层破裂的速度和复杂性的信息。这些结果应该有助于改善对强震造成的破坏性地面运动的预测。计划中的地球结构分析将检查发生在地表以下50至400英里深处的地震波速度的急剧变化，这些变化与晶体结构的变化或水或岩浆等流体的存在有关。一个相关的项目将研究地震波的散射，这提供了从地表到地球液态核深处岩石性质的小尺度变化的线索。这些结果将有助于理解地球的内部组成及其与构造作用的关系。该项目将支持本科生、研究生和研究生，并让他们参与研究。教育部分包括研究生和博士后支持，以及赞助一个长期且成功的SIO项目的本科生暑期实习生，该项目旨在增加学生的多样性。对世界各地永久和临时地震台站记录的大数据集进行系统分析，为研究有关地震和地球结构的问题提供了丰富的机会。计划进行的研究包括：对过渡带和岩石圈-软流圈边界内和附近的上地幔不连续结构进行创新性调查；观测地震散射并对其进行模拟，以确定地幔小规模成分的不均质性；以及对地震辐射进行频谱分析，以限制地震破裂的尺寸和动力学。该项目计划研究的一些关键问题包括：(1)在地幔对流和水循环的410公里不连续面上方的低速层(LVL)起什么作用？(2)是什么导致了在许多大陆克拉通下观察到的中岩石圈不连续(MLD)？(3)660公里不连续面的尖锐和粗糙程度是如何变化的，这对地幔成分意味着什么？(4)中下地幔小尺度不均匀的强度是什么，它是否横向变化？(5)是什么导致了地震应力降估计中的大分散，(6)地震应力降是否随构造区域而有系统地变化？(7)改进的全球高频体波衰减模型与层析模型和面波衰减模型相比如何？这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project will use decades of records of seismic waves generated by thousands of earthquakes all over the world to learn about both earthquakes and deep Earth structure. Analyses of earthquakes will focus on the high-frequency components of the seismograms, which provide key constraints on the energy radiated by earthquakes and information about the speed and complexity of fault ruptures. These results should help improve forecasts of damaging ground motions produced by strong earthquakes. Planned analyses for Earth structure will examine sharp changes in seismic wave velocities that occur at depths of 50 to 400 miles below the surface that are related to changes in crystal structure or the presence of fluids, such as water or magma. A related project will examine scattering of seismic waves, which provides clues regarding small-scale variability in rock properties at depths extending from the surface to Earth's liquid core. These results will help in understanding the internal composition of the Earth and its relation to tectonic processes. The project will support undergraduate, graduate, and postgraduate students and involve them in research. Educational components include graduate student and postdoc support, as well as sponsoring an undergraduate summer intern in a long-standing and successful SIO program designed to increase student diversity. Systematic analyses of large datasets recorded by both permanent and temporary seismic stations all over the world provide rich opportunities to study problems concerning earthquakes and Earth structure. Planned research includes innovative investigations of upper-mantle discontinuity structure within and near the transition zone and the lithosphere-asthenosphere boundary, observing and modeling of seismic scattering to characterize small-scale compositional heterogeneity in the mantle, and spectral analyses of earthquake radiation to constrain earthquake rupture dimensions and dynamics. Some key questions this project plans to examine include: (1) What is the role of the low-velocity layer (LVL) above the 410-km discontinuity in mantle convection and water recycling? (2) What causes the mid-lithospheric discontinuity (MLD) observed under many continental cratons? (3) How variable is the sharpness and roughness of the 660-km discontinuity and what does that imply for mantle composition? (4) What is the strength of small-scale heterogeneity in the mid- to lower mantle and does it vary laterally? (5) What causes the large scatter in earthquake stress drop estimates, i.e., how much is due to modeling uncertainties versus real differences in earthquake dynamics? (6) Does earthquake stress drop vary systematically with tectonic region? (7) How do improved global high-frequency body-wave attenuation models compare to tomographic models and to surface-wave attenuation models?This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.