Combined Thickness of the Modeled Saddle Mountains Basalt and Mabton Interbed Geomodel Units (smthk_f)

The smthk_f grid represents the modeled combined thickness of the Saddle Mountains Basalt and Mabton interbed geomodel units at a 500 foot resolution. It is one grid of a geomodel that consists of eleven grids and a spatial extent polygon shapefile. As part of a U.S. Geological Survey Groundwater Resources Program study, a three-dimensional geomodel was constructed for approximately 53,000 mi2 of the Columbia Plateau in Washington, Oregon, and Idaho. This geomodel was constructed to define the general aquifer system geometry for use in a regional numerical groundwater flow model. Simplifications and assumptions consistent with this ultimate goal and the uncertainty in the available data were made. The geomodel units consist of Miocene age Columbia River Basalt Group strata and younger alluvial overburden covering approximately 44,000 mi2. Data were compiled from numerous databases and detailed studies completed during the past three decades. These data include stratigraphic interpretations made on more than 13,000 wells and a contiguous compilation of surficial geology and structural features spanning the study area. These data were simplified and used to construct piecewise-smooth trend surfaces that represent upper and lower subsurface geomodel unit boundaries in this complex folded and faulted terrain. The smoothness of the surfaces implicitly represents uncertainty in prediction of each surface resulting from data gaps, errors in borehole interpretations, errors in mapped contact locations, and uncertainty in the shape of the paleo-surface upon which flood basalts were emplaced. Using a rule-based algorithm, surfaces were then recombined to construct a fully three-dimensional model with a 500-foot grid resolution that is consistent with the data and for which error estimates may be made. The modeling process yielded improved estimates of unit volumes, refinement of location of large structural features, and identification of features that may be important for ongoing groundwater studies.

smthk_f网格代表了以500英尺为分辨率建模得到的鞍山脉玄武岩（Saddle Mountains Basalt）与梅普顿夹层（Mabton interbed）地质单元的组合厚度。该网格属于一套包含11个网格单元及一个空间范围多边形形状文件（shapefile）的地质模型（geomodel）。作为美国地质调查局（U.S. Geological Survey）地下水资源项目的研究内容之一，科研人员针对华盛顿州、俄勒冈州及爱达荷州境内约53000平方英里的哥伦比亚高原构建了三维地质模型。构建该模型的核心目标是明确区域含水层系统的整体几何形态，以供区域数值地下水流模型使用。本次建模遵循了与该终极目标及现有数据不确定性相匹配的简化原则与假设条件。地质模型单元涵盖中新世哥伦比亚河玄武岩群地层，以及覆盖约44000平方英里的年轻冲积覆盖层。研究数据汇编自过去三十年间完成的各类数据库与详细研究成果，包括对超过13000口钻井的地层解释，以及覆盖整个研究区的地表地质与构造特征的连续编录数据集。上述数据经简化处理后，被用于构建分段光滑趋势面，以表征该复杂褶皱断裂地形中地下地质单元的上下边界。这些曲面的平滑程度隐含了各边界预测的不确定性，其来源包括数据缺口、钻井解释误差、制图接触位置误差，以及玄武岩溢流喷发时古地表形态的不确定性。随后，科研人员通过基于规则的算法将这些曲面重新组合，构建出分辨率为500英尺的完整三维模型，该模型符合现有数据特征，且可对其误差进行量化估算。本次建模工作优化了单元体积的估算精度，细化了大型构造特征的空间定位，并识别出对后续地下水研究具有重要价值的相关地质要素。