Thomas ForbrigerKarlsruhe Institute of Technology, Nasim KaramzadehKarlsruhe Institute of Technologynow at University of Münster Institut für Geophysik, Münster, Germany, Jérôme AzzolaKarlsruhe Institute of Technology, Emmanuel GaucherKarlsruhe Institute of Technology, Rudolf Widmer-SchnidrigInstitute of Geodesy, University of Stuttgart, Stuttgart, Germany, Andreas RietbrockKarlsruhe Institute of Technology
{"title":"Calibration of the strain amplitude recorded with DAS using a strainmeter array","authors":"Thomas ForbrigerKarlsruhe Institute of Technology, Nasim KaramzadehKarlsruhe Institute of Technologynow at University of Münster Institut für Geophysik, Münster, Germany, Jérôme AzzolaKarlsruhe Institute of Technology, Emmanuel GaucherKarlsruhe Institute of Technology, Rudolf Widmer-SchnidrigInstitute of Geodesy, University of Stuttgart, Stuttgart, Germany, Andreas RietbrockKarlsruhe Institute of Technology","doi":"arxiv-2408.01151","DOIUrl":null,"url":null,"abstract":"The power of distributed acoustic sensing (DAS) lies in its ability to sample\ndeformation signals along an optical fiber at hundreds of locations with only\none interrogation unit (IU). While the IU is calibrated to record 'fiber\nstrain', the properties of the cable and its coupling to the rock control the\n'strain transfer rate' and hence how much of 'rock strain' is represented in\nthe recorded signal. We use DAS recordings in an underground installation\ncolocated with an array of strainmeters in order to calibrate the 'strain\ntransfer rate' in situ, using earthquake signals between 0.05 Hz and 0.1 Hz. A\ntight-buffered cable and a standard loose-tube telecommunication cable (running\nin parallel) are used, where a section of both cables loaded down by loose sand\nand sand bags is compared to a section, where cables are just unreeled on the\nfloor. The 'strain transfer rate' varies between 0.13 and 0.53 depending on\ncable and installation type. The sandbags show no obvious effect and the\ntight-buffered cable generally provides a larger 'strain transfer rate'.\nCalibration of the 'strain transfer rate' with respect to the strainmeter does\nnot depend on wave propagation parameters. Hence it is applicable to the large\namplitude surface wave signal in a strain component almost perpendicular to the\ngreat-circle direction for which a waveform comparison with seismometer data\ndoes not work. The noise background for 'rock strain' in the investigated band\nis found at about an rms-amplitude of 0.1 nstrain in 1/6 decade for the\ntight-buffered cable. This allows a detection of marine microseisms at times of\nhigh microseism amplitude.","PeriodicalId":501270,"journal":{"name":"arXiv - PHYS - Geophysics","volume":"90 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-08-02","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - PHYS - Geophysics","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2408.01151","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
The power of distributed acoustic sensing (DAS) lies in its ability to sample
deformation signals along an optical fiber at hundreds of locations with only
one interrogation unit (IU). While the IU is calibrated to record 'fiber
strain', the properties of the cable and its coupling to the rock control the
'strain transfer rate' and hence how much of 'rock strain' is represented in
the recorded signal. We use DAS recordings in an underground installation
colocated with an array of strainmeters in order to calibrate the 'strain
transfer rate' in situ, using earthquake signals between 0.05 Hz and 0.1 Hz. A
tight-buffered cable and a standard loose-tube telecommunication cable (running
in parallel) are used, where a section of both cables loaded down by loose sand
and sand bags is compared to a section, where cables are just unreeled on the
floor. The 'strain transfer rate' varies between 0.13 and 0.53 depending on
cable and installation type. The sandbags show no obvious effect and the
tight-buffered cable generally provides a larger 'strain transfer rate'.
Calibration of the 'strain transfer rate' with respect to the strainmeter does
not depend on wave propagation parameters. Hence it is applicable to the large
amplitude surface wave signal in a strain component almost perpendicular to the
great-circle direction for which a waveform comparison with seismometer data
does not work. The noise background for 'rock strain' in the investigated band
is found at about an rms-amplitude of 0.1 nstrain in 1/6 decade for the
tight-buffered cable. This allows a detection of marine microseisms at times of
high microseism amplitude.