Digital Data for a Three-Dimensional Geologic Map of the San Andreas Fault Zone Between Gold Hill and Pinnacles National Park, California

A three-dimensional geologic map was created by assembling eight geologic cross sections derived from geologic mapping, potential field geophysics, and petroleum well logs. The central feature of the map is the San Andreas Fault, with many other prominent structural features depicted that express the regional transpressional tectonic setting. The subsurface interpretation was based on existing two-dimensional geologic mapping and modified by new geologic mapping by USGS geologists between 2005-2014. Existing gravitational anomaly and magnetic anomaly maps helped guide subsurface interpretations. The result is a three-dimensional model that depicts the geologic units, faults, and folds of the region in a model that can be viewed from any perspective and sliced in any direction. Once the map was assembled, kinematic modeling was conducted using the modeling software’s forward and reverse deformation algorithms. These exercises were in part experimental, to assess how well the software’s kinematic algorithms work in this setting. But these experiments have also yielded insights into the geologic history of the region. An experiment with fault motion algorithms revealed a possible mechanism for the creation of secondary faults. Retro-deforming a syncline was also performed to approximate the amount of contraction caused by compressional stress in the region.

本三维地质图通过整合8条由地质填图、位场地球物理及石油钻井测井资料衍生得到的地质剖面制作而成。该图的核心构造为圣安德烈亚斯断层（San Andreas Fault），同时还描绘了诸多其他显著构造特征，直观体现了区域的压扭构造背景。地下解译工作以已有的二维地质填图成果为基础，并由美国地质调查局（USGS）地质学家在2005至2014年间开展的新地质填图进行了修正完善。已有的重力异常图与磁异常图为地下解译工作提供了重要指导。最终生成的三维模型可展示该区域的地质单元、断层与褶皱构造，支持任意视角浏览与任意方向剖切。该三维地质图搭建完成后，研究人员借助建模软件的正、反向变形算法开展了运动学建模。本次建模工作部分属于实验性探索，旨在评估该软件的运动学算法在该区域构造背景下的适配效果。但此类实验同时也为解析该区域的地质演化历史提供了新认知。针对断层运动算法的实验揭示了次级断层形成的一种潜在机制。研究人员还通过对向斜进行回退变形，估算了该区域由挤压应力引发的收缩量。