Three-Dimensional Imaging of Earthquake-induced Liquefaction Features with Ground Penetrating Radar Near Marianna, Arkansas

Abstract

Ground penetrating radar (GPR) is a powerful tool used to study earthquake-related features such as sand blows and faults. The study area is near Marianna, Arkansas, and the work involves GPR surveys of large elliptical sand deposits. Our primary goal was to locate feeder dikes of sand blows and to image the contact between sand blows and the buried paleosurface in order to optimize the location of trenches. A secondary goal was to image the sand blows in three dimensions to define their sizes and morphology. Trenching large sand blows is costly and provides a limited view of the overall structure. GPR helps to identify possible locations for the venting dikes and to visualize the subsurface features. It also helps to map the locations in the sand blows of tree stumps that are useful for dating. The surveys imaged sharp contacts in near-surface sediments that were confirmed in trenches to represent boundaries between sand blows and buried soils. One survey in particular showed a sharp discontinuity in the boundary related to a large feeder dike. Because sand thickness was no more than 4 m, a 400 MHz antenna was used. This antenna is designed to provide high-resolution images of the upper 5 m of soil. Data acquisition was along parallel profiles oriented normal to the long axes of the sand deposits at all sites. Data reduction and analysis procedures included removal of direct and ground surface effects, frequency filtration, gain control, profile migration, and three-dimensional visualization. In future work, we plan to refine field procedures and test additional survey configurations to ensure the best results. We will survey additional sites to help with the follow-up trenching and sampling work.