Spectral Analysis of Surface Waves with Simultaneous Fiber Optic Distributed Acoustic Sensing and Vertical Geophones

Abstract

Experiments were performed comparing the response of fiber optic distributed acoustic sensing (DAS) to vertical geophones installed on the surface. The DAS consisted of an optical interrogator attached to an optical fiber. The fiber was part of an optical cable that was installed at depths of 0.3 to 0.76 meters in a coastal environment composed of unconsolidated sand. Seismic signals generated with an impact hammer were recorded simultaneously with both systems and directly compared. Experiments were performed with two different configurations, broadside and end-fire, between the source and the fiber optic cable. The seismic signals recorded in the two configurations and with the two sensor systems were processed identically using the Spectral Analysis of Surface Wave method. The results demonstrate the suitability and limitations of using DAS for near-surface seismic measurements.