Digital data for the geologic map of Scoggins Dam, Henry Hagg Lake, and Scoggins Valley, Washington County, Oregon

Scoggins Dam in northwest Oregon lies within the Gales Creek fault zone (GCF), a northwest-striking system of active faults forming the boundary between the Coast Range and the Tualatin Valley about 25 km east of Portland, Oregon. Geologic mapping published in 2020 shows the dam to lie within a block-faulted releasing stepover between the right-lateral, NW-striking Scoggins Creek and Parsons Creek strands of the GCF. The Scoggins Creek strand is presently mapped beneath the existing dam about 200 m north of the south abutment. Preliminary results from paleoseismic trenching by the U.S. Bureau of Reclamation, Portland State University, and the U.S. Geological Survey indicate that these two major fault strands have had multiple surface rupturing earthquakes in the Holocene. To confirm the accuracy of the 2020 geologic map and the geometry of the GCF in the releasing stepover region, we completed additional geologic mapping of the dam, reservoir, and an alternative dam site downstream between July 2018 and May 2020. Using high-resolution lidar topographic data and satellite imagery on handheld digital tablets, we collected data at ~500 field sites in the heavily forested terrain. We used these detailed field observations to locate and digitally map the main Scoggins Creek and Parsons Creek fault strands, as well as the cross faults linking the two main strands, to produce an improved and more detailed geologic map and cross sections of Scoggins Valley and its existing and proposed dam sites.

位于俄勒冈州西北部的斯科金斯大坝（Scoggins Dam）地处盖尔斯溪断裂带（Gales Creek fault zone, GCF）内部。该断裂带为北西向展布的活动断裂系统，构成了海岸山脉与图拉丁谷的分界，其位置距俄勒冈州波特兰市以东约25千米。2020年发表的地质填图成果显示，该大坝位于右旋北西向展布的GCF斯科金斯溪段与帕森斯溪段之间的块体断裂拉张阶区内。当前地质填图结果表明，斯科金斯溪断裂段位于现有大坝坝体下方，距大坝南坝肩以北约200米处。美国垦务局（U.S. Bureau of Reclamation）、波特兰州立大学（Portland State University）与美国地质调查局（U.S. Geological Survey）开展的古地震探槽初步研究结果表明，这两条主要断裂段在全新世时期曾发生过多次地表破裂型地震。为验证2020年地质填图成果的准确性，以及GCF拉张阶区内部的断裂几何形态，研究团队于2018年7月至2020年5月期间，针对该大坝、水库以及下游一处备选坝址开展了补充地质填图工作。研究团队依托手持数位平板搭载的高分辨率激光雷达地形数据与卫星影像，在植被茂密的野外区域完成了约500个野外测点的数据采集工作。基于上述详细的野外观测数据，研究团队对斯科金斯溪、帕森斯溪主断裂段以及连接二者的横向断裂进行了定位与数字化填图，最终生成了斯科金斯谷及其现有、拟建坝址区域的高精度精细化地质图与地质剖面图。