GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 3.3 GNGTS 2024 Diferental arrival tmes for event locaton with DAS data E. Bozzi 1 , L. Gebraad 2 ,A. Fichtner 3 , N. Piana Agostnet 1 , G. Saccorot 4 , T. Kiers 3 , T. Nishimura 5 1 University of Milano-Bicocca (Milan, Italy) 2 Mondaic Ltd (Zurich, Switzerland) 3 ETH Zurich, Insttute of Geophysics (Zurich, Switzerland) 4 Insttuto Nazionale di Geofsica e Vulcanologia (Pisa, Italy) 5 Tohoku University, Department of Geophysics (Tohoku, Japan) Standard seismic networks typically use absolute arrival tmes of specifc seismic phases to estmate source locatons. In this context, multple sensors are positoned over a monitored area, aiming to minimize the azimuthal gap to known seismicity clusters. Distributed Acoustc Sensing (DAS) technology, which converts fber optc cables (FOCs) into very dense seismic arrays, is nowadays used for similar purposes. DAS has the additonal advantage of being able to exploit preexistng telecommunicaton FOCs (Telecom-FOCs). However, since the original installaton purpose for Telecom-FOCs doesn’t align with seismological needs, the spanned azimuthal directons can be limited. Hence, relying on absolute arrival tmes for event locaton might result in uncertain locatons, given poor waveform moveouts and site-specifc sources of noise in the data. Nevertheless, the intrinsic DAS channels’ spatal density provide a good opportunity to test mult- channel cross-correlaton techniques. Here, to assess the potental beneft from using diferental arrival tmes for event locaton, we cross-correlate all possible DAS channel pairs and identfy P-wave tme delays. We focus on well-known test environments (i.e., known event locatons) and use a Hamiltonian Monte Carlo algorithm to estmate hypocentral parameter uncertaintes, considering both absolute and diferental arrival tmes. We demonstrate how diferental arrival tmes beter constrain the events' azimuthal directons compared to absolute arrival tmes. However, computatonal costs are inevitably higher due to the signifcant increase in data points when considering all the P-wave delays. A mitgaton to this issue is reached by selectng measurements based on thresholds for the minimum cross-correlaton index and maximum interchannel distance. This work illustrates how to potentally alleviate DAS geometrical limitatons on event locaton by exploitng selected diferental arrival tmes. Corresponding author: e.bozzi3@campus.unimib.it