Comparison of Earthquake Wavefield Measurements from DAS and a Broadband Seismic Array in an Urban Setting

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Abstract
We compare earthquake wavefield measurements from a ∼95 km urban dark fiber distributed acoustic sensing (DAS) array and a collocated 16 km aperture broadband seismic array in Dallas, Texas. Using data from a regional M 5.2 earthquake, we assess the ability of DAS to recover ground-motion amplitudes and wavefield direction of arrival (DOA). Surface-wave (Rayleigh) amplitude ratios between broadband and DAS range from 0.25 to 22.15, revealing significantly more heterogeneous DAS coupling than previously reported. Although broadband sensors provide consistent amplitude and high-quality DOA estimates across all phases (P, S, and Rayleigh), DAS data show large amplitude variability unrelated to fiber orientation, suggesting coupling and emplacement differences as dominant factors. Signal coherence in DAS is also highly variable, with some segments showing stronger correlations during pre-event noise than during the earthquake signal. Nonetheless, by applying hierarchical clustering to interchannel cross-correlations, we identify a 36-channel DAS subgroup and obtain a DOA estimate for the Rayleigh wave within 4.5° of that derived from the broadband array. These results highlight both the promise and limitations of using urban dark fiber DAS for earthquake monitoring and underscore the need for careful characterization of fiber coupling and geometry to enable reliable wavefield reconstruction.

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