02031 : Geophysical Surveys of Bear Lake, Utah-Idaho, September 2002 - Seismic Navigation: Start of Line (CHRP_SOL)

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followed an earlier subbottom acoustic-reflection survey (1997), using boomer and 3.5 kHz systems (S. M. Colman, unpublished data).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）为至少存在数十万年的构造湖。其湖盆为相对简单的半地堑构造，系朝湖东侧主断裂倾斜的勺状凹陷。美国地质调查局（U.S. Geological Survey）自1996年起联合多所高校的研究人员，持续开展贝尔湖沉积物研究工作，核心宗旨为重建数百年至数十万年尺度下的古湖沼环境与区域气候。该研究关联诸多人类关切议题，其中涵盖贝尔河流域的水资源利用问题。此前的研究工作已完成多次取芯钻探作业、地震反射调查、沉积物捕集器布设、搭载GLAD800钻机的驳船钻探实验，以及其他多项相关研究。
本文初步报道的2002年9月野外作业目标为：（1）采用条带测深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）完成全湖侧扫声呐调查，获取近乎全覆盖的湖底声学影像。本次调查还同步采集了少量亚底声学反射（chirp）数据，以及代表不同反向散射特征的湖底沉积物样品。本次调查基于1997年开展的亚底声学反射调查（采用boomer震源与3.5 kHz系统，S. M. Colman，未发表数据）完成。