Geophysical Surveys of Bear Lake, Utah-Idaho, 2002 - JPEG Images of Seismic Data

Bear Lake is a tectonic lake that has existed for at least several hundred thousand years. The lake basin is a relatively simple half graben, a spoon-shaped depression tilted toward the main fault on the east side of the lake. The U.S. Geological Survey, in cooperation with researchers from several universities, has been studying the sediments of Bear Lake since 1996. The general purpose of this effort is to reconstruct past limnological conditions and regional climate on a range of timescales, from hundreds of years to hundreds of thousands of years. This research relates to a variety of human concerns, including water usage in the Bear River basin. Past work has included several coring operations, a seismic-reflection survey, sediment-trap deployments, a barge-mounted drilling operation with the GLAD800 drill rig, and a variety of other studies. The objectives of the September, 2002 operations, preliminarily reported here, were (1) to compile a detailed bathymetric map of the lake using swath-mapping techniques, in order to provide baseline data for a variety of applications and studies, and (2) to complete a sidescan-sonar survey of the lake, providing a nearly complete acoustic image of the lake floor. Limited amounts of subbottom acoustic-reflection data (CHIRP) were also collected, along with samples of lake-floor sediments representative of different kinds of backscatter patterns. These surveys followed an earlier subbottom acoustic-reflection survey (1997), using boomer and 3.5 kHz systems (S. M. Colman, unpublished data).贝尔湖（Bear Lake）是一处构造湖（tectonic lake），其存在历史至少已达数十万年。湖盆属于相对简单的半地堑（half graben）结构，为朝湖东侧主断层倾斜的勺状凹陷。美国地质调查局（U.S. Geological Survey）联合多所高校的研究人员，自1996年起开展贝尔湖沉积物研究。本研究的总体目标是重建数百年至数十万年时间尺度下的古湖沼学环境与区域气候特征，相关研究涉及诸多人类关切的议题，其中包括贝尔河流域的水资源利用情况。此前的研究工作涵盖多次取芯钻探作业、地震反射勘探（seismic-reflection survey）、沉积物捕集器布设、搭载GLAD800钻机（GLAD800 drill rig）的驳船钻探作业，以及其他多项相关研究。 2002年9月的勘探作业目标（本文在此初步汇报）分为两项：(1) 采用条带测深（swath-mapping）技术绘制高精度湖泊水深图，为各类应用与研究提供基准数据；(2) 完成湖泊全域侧扫声呐（sidescan-sonar）勘探，获取近乎全覆盖的湖底声学影像。本次作业还同步采集了少量亚底声学反射（subbottom acoustic-reflection）数据（CHIRP系统），以及对应不同反向散射特征的湖底沉积物样本。本次勘探接续1997年开展的亚底声学反射勘探作业，当时采用了电火花震源（boomer）与3.5kHz系统（S. M. Colman，未公开数据）。