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

这是一个两部分的项目，将利用一套灵活的，小规模的地震阵列。将优化阵列的设计，以估计区域和海洋波场的空间梯度。在该项目的第一部分，将部署一个单一的，十四元素阵列的目标是确定最佳的阵列几何形状和孔径估计波场梯度，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地点同时部署两个地震阵列。 第一个位置是前洪泛区，基岩上覆盖约700 m的未固结冲积层。 第二个位置有基岩，距离地表不到一米。 该项目这一部分的目标是严格记录近地表地质对地震空间梯度估计参数（如应变、旋转、P-S能量划分等）的影响。到目前为止，还没有研究使用小规模地震阵列（称为梯度仪）量化地震波场梯度的准确性和/或精度。 然而，以前的研究表明，梯度仪是高度敏感的仪器位置的不确定性，记录的地震图中的噪声，和当地地下地质。 本研究将详细调查这些问题，并试图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梯度估计得出的地震属性估计的影响。 通过制定地震台阵设计标准，未来的梯度测量将是统一的，从而允许从一个实验到另一个实验进行更直接的比较。 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.