GOALI: Application of Wave Gradiometry to Exploration Seismology

寻找能源资源主要是基于地震波的使用，它使地球物理学家能够对地球地下的地质结构进行成像。这些成像实验的地震波通常是通过小型爆炸的爆炸或使用大型卡车上安装的振动器产生的，这些振动器将波传播到地球上，在那里它们从断层、地质地层和碳氢化合物储层反射和散射。该项目的研究重点是应用一种新的数学方法来分析从数百台地震仪器阵列收集的地震波数据，这些仪器可以对地球表面的地震波进行高保真记录。这种方法被称为“波梯度法”，它能够量化地震波在空间和时间上的传播方式，由此推断出的波特征可以更直接地与震源和记录仪器阵列之间的地质结构联系起来。这种方法以前没有尝试过，因为直到现在还没有合适的数据集。全球地球物理服务公司（Global Geophysical Services）在俄亥俄州东部的一个天然气勘探区部署了一个实验性地震阵列，目的是收集可以用波浪梯度法分析的数据。我们将研究在野外数据集上使用这种新技术，以发现新的地震处理方法，这些方法将改善地球结构成像，用于资源开发和地壳科学研究。全球地球物理服务公司（Global Geophysical Services）与俄亥俄州东部的一个三维地震反射实验一起，收集了一个密集的二维阵列的数据，该阵列由400个单元组成，每个单元相距30米，每个单元有3个垂直传感器。该阵列记录了大约7600个2磅炸药和辅助填充可控震源信号，形成了约1Tbyte的数据集。这些独特的数据是在与孟菲斯大学的研究人员协商后收集的，目的是测试以波浪梯度法为中心的新地震处理技术。密集、冗余的阵列元素间距将允许计算波的空间梯度，当与原始波场结合时，将得到波场的慢度、方位角、几何扩展变化和辐射方向变化等波属性，作为阵列面积上时间的函数。在此之前，该大学已经部署了小型梯度仪和现成的地震检波器，以证明像这次这样的大规模实验的可行性。我们将研究波梯度法在生成波属性层析图中的应用，该层析图将用于估计近地表速度结构，以计算地面滚动的静校正，研究部分阵列下浅层开采空洞的性质和特征，并研究可用于叠加、迁移或AVO的近垂直反射波特征。在地震波长的一小部分的空间尺度上收集数据代表了研究地震波场随位置的稳定性的丰富新领域。我们将开发计算波空间梯度的处理技术，并从特定地震波中反演不同波属性的层析图，以确定地震速度结构或像AVO分析一样检查结构的特定方面。这项工作代表了对一个独特数据集的初步探索，使用了一种新的波分析范式，很可能会产生地震波传播的新见解和知识。

The search for energy resources is primarily based on the use of seismic waves that allow geophysicists to image geological structures in the subsurface of the Earth. Seismic waves for these imaging experiments are usually created through detonation of small explosions or use of large truck-mounted vibrators that propagate waves into the Earth where they reflect and scatter from faults, geological strata, and hydrocarbon reservoirs. Research in this project is centered about the application of a new mathematical method to analyze seismic wave data collected from arrays of hundreds of seismic instruments that give a high-fidelity recording of the seismic wave over the Earth's surface. This method, called "wave gradiometry", is able to quantify how a seismic wave propagates in space and in time in such a way that the resulting inferred wave characteristics can be related more directly to the geological structure between the seismic source and recording array of instruments. This approach has not been tried before because appropriate datasets have not been available until now. Global Geophysical Services has deployed an experimental seismic array over a gas prospect in eastern Ohio that was designed to collect data that can be analyzed with wave gradiometry. We will be researching the use of this new technique on the field dataset to discover new seismic processing methods that will improve the imaging of Earth structure for resource development and scientific studies of the crust.Data from a dense, 2D array consisting of 400 elements 30m apart with 3 vertical sensors at each element have been collected by Global Geophysical Services (Global) in conjunction with a 3D seismic reflection experiment in eastern Ohio. Approximately 7600 2-lb dynamite shots and auxiliary fill-in vibroseis signals were recorded by this array resulting in a ~1Tbyte dataset. These unique data were collected in consultation with investigators at the University of Memphis to test new seismic processing techniques centered on wave gradiometry. The dense, redundant array element spacing will allow computation of wave spatial gradients that, when combined with the original wave field, will yield wave attributes of slowness, azimuth, geometrical spreading change, and radiation pattern change for the wave field as a function of time over the area of the array. Small-scale gradiometers have been previously deployed at the University with off-the-shelf geophones to demonstrate feasibility of larger scale experiments such as this one. We will investigate the use of wave gradiometry in producing tomographic maps of wave attributes that will be used to estimate near-surface velocity structure to compute statics corrections from ground roll, investigate the nature and signature of shallow mined out voids under part of the array, and investigate wave characteristics of near-vertical reflections that could be used in stacking, migration, or AVO. Collecting data over spatial scales of a fraction of a seismic wavelength represents fertile new terrain in examining how stable the seismic wave field is with position. We will be developing processing techniques in computing wave spatial gradients and inverting tomographic maps of diverse wave attributes from particular seismic waves to determine seismic velocity structures or to examine particular aspects of the structure as in AVO analysis. This work represents an initial exploration of a unique dataset using a new paradigm of wave analysis that will very likely result in new insights and knowledge of seismic wave propagation.