DAS Observations of Crustal Thickness From a 56 km Infrastructure Fiber

In June 2025 a collaboration between Terēan ® , Sintela, and the Center for Transformative Environmental Monitoring Programs (CTEMPs) at the University of Nevada, Reno (UNR) made distributed acoustic sensing (DAS) recordings for ground-imaging trials. Recording employed Sintela’s ONYX™ peta DAS interrogator. One of the trials was on infrastructure dark fiber operated by the State of Nevada. A 56 km segment of this fiber runs from the UNR campus in Reno eastward to the town of Fernley, closely following Interstate Highway 80. The route east of Reno is in the narrow Truckee River Canyon cutting through the Virginia Range. The canyon hosts a busy freight railroad (up to 3 dozen 200-car trains each day), natural gas and petroleum pipelines, frequent overflights by airliners coming in and out of the Reno-Tahoe Airport, and major industrial and logistics operations all within 200 m of the interstate highway. The Truckee River in this stretch pours over several rapids and had a high volume of spring outflow at the time. All these are sources of seismic microtremor and together contributed high-amplitude, broadband microtremor signals along the cableway. The trial recording of this fiber lasted more than 24 hours and used a channel spacing of 3.12 m derived from a gauge length several times longer. Test processing of a snippet of the recording used Terēan’s VsSurf ReMi ® 2dS+ software, revealing fundamental-mode Rayleigh-wave dispersion between periods of 1.0 to 15.4 sec. A sharp rise in phase velocity, from 2.35 km/s at 2.8 s period to 3.33 km/s at 7.7 s period, suggests the presence of the Moho interface at approximately 35 km depth, consistent with prior observations in the area. While the picked dispersion curve does not tightly constrain the shear-wave velocity (Vs) below the Moho, it is consistent with an upper-mantle Vs of 4.5 km/s. The average crustal Vs is well-constrained at 3.59 km/s. Additional dispersion processing and modeling will examine the entire 24 hours of data, to determine the uncertainties on the dispersion picks and on the model features. One noteworthy feature requiring validation is a 3.3 km thick high-Vs layer (possibly around 5.0 km/s) beginning at 5.9 km depth, which may represent gabbroic or ultramafic material.