Rapid Surface-Deployment of DAS Cable for Earthquake Hazard Assessment

Distributed Acoustic Sensing (DAS) is a relatively new technology used for a wide range of geophysical applications. DAS utilizes the principles of time domain reflectometry to provide dynamic strain measurements along the length of a fiber-optic cable. The versatility, relative low-cost, and high temporal-spatial resolution make DAS an ideal tool for rapid deployment surveys such as earthquake-aftershock monitoring and hazard assessment. These applications often rely on conventional coupling methods, such as burying the fiber, to ensure adequate contact between the fiber-optic cable and the ground for proper energy transfer resulting in a high signal-to-noise ratio. However, these methods are often time consuming and not always practical. Therefore, rapid deployment remains a goal amongst researchers and industry professionals. In this field study, we deployed a DAS array composed of six parallel linear subsections along the surface of Kafadar Commons located at the Colorado School of Mines. These linear subsections were deployed in pairs along the snow, grass, and cement under two coupling conditions: (1) the fiber optic cable was laid on the ground; and (2) pressed into the ground by several people walking on top of the cable. Ambient-noise interferometry is applied to the field data to estimate the average shear-wave velocity of the top 30m of subsurface (Vs30) for each linear profile. These results are compared with the Vs30 results from the co-located DAS array buried 1m beneath the surface that was previously installed as part of the Mines Underground Laboratory. We show that all linear profiles of the surface deployment provide robust Vs30 results and are consistent with the trenched cable profiles. This indicates adequate sensitivity to dynamic strain with DAS is possible under light coupling conditions along the ground surface. Implications of these findings suggest research and industry professionals can rapidly deploy DAS capturing high quality data for a variety of geophysical surveys.