RUI: Deployment of a simultaneous broadband gradiometers to quantify the effects of aperture and near-surface geology on gradient-derived wavefield attributes

这是一个由两部分组成的项目，将利用一套灵活的小规模地震阵列。优化阵列的设计，以估计区域和远震波场的空间梯度。在项目的第一部分，将部署一个单独的14元阵列，目标是确定最佳阵列几何形状和孔径，以估计波场梯度，以及量化这些测量的不确定性。第二部分将包括在两个相邻位置同时部署两个地震阵列。第一个地点是以前的洪泛区，基岩上覆盖着大约700米的未固结冲积层。第二个地点的基岩距地表不到一米。这部分项目的目标是严格记录近地表地质对地震空间梯度（如应变、旋转、P-S能量分配等）估计参数的影响。到目前为止，还没有研究使用小尺度地震阵列（称为梯度仪）来量化地震波场梯度的准确度和/或精度。然而，以往的研究表明，梯度仪对仪器位置的不确定性、记录的地震记录中的噪声和当地地下地质情况高度敏感。本研究将详细探讨这些问题，并尝试1)制定一套部署地震梯度仪的指导方针，2)量化当地地质条件对从梯度估计中得出的地震属性估计的影响。通过制定地震阵列设计标准，未来的梯度测量将是统一的，从而可以更直接地比较不同实验之间的差异。此外，通过严格量化地下地质对地震梯度参数的影响，我们对地球结构的解释将更加准确，我们对震源性质的解释也将更加准确。

This is a two part project that will make use of a set of flexible, small scale seismic arrays. The design of the arrays will be optimized to estimate the spatial gradients of regional and teleseismic wavefields. In the first portion of the project, a single, fourteen-element array will be deployed with the goal of determining the optimal array geometry and aperture to estimate wavefield gradients, as well as to quantify the uncertainty of these measurements. The second portion will consist of two, simultaneous deployments of seismic arrays in two adjacent locations. The first location is a former floodplain, with approximately 700m of unconsolidated alluvium overlying bedrock. The second location has bedrock within one meter of the surface. The goal of this portion of the project is to rigorously document the effects of near-surface geology on parameters estimated from seismic spatial gradients (such as strain, rotation, P-S energy partitioning, etc).Up to now, there has been no study to quantify the accuracy and/or precision of seismic wavefield gradients using small-scale seismic arrays (termed gradiometers). However, previous studies suggest that gradiometers are highly sensitive to uncertainties in instrument location, noise in the recorded seismograms, and local subsurface geology. This study will investigate these issues in detail and attempt to 1) produce a set of guidelines for deploying seismic gradiometers, and 2) quantify the effects of local geologic conditions on the estimation of seismic attributes derived from gradient estimations. By developing a standard of seismic array design, future gradient measurements will be uniform allowing a more direct comparison from one experiment to another. Furthermore, by rigorously quantifying the effects of subsurface geology on parameters derived from seismic gradients, our interpretations of Earth structure will be more accurate, as well as our interpretations of the nature of the seismic source.