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Title: Narrowband signals recorded near a moulin that are not moulin tremor: a cautionary short note

Abstract

Geophysicists that deploy seismic sensors in ablation zones of glaciers and ice sheets to record glaciogenic signatures can confront recording challenges caused by instrument melt-out or tilt. These challenges often require installing sensors in boreholes to delay melt-out, or securing sensors to structures that improve coupling. We show that some of these structures that were buried near a moulin at a snow-free site in the ablation zone of the Western Greenland Ice Sheet resonated as they became exposed, and caused their geophones to record temporally evolving, narrowband signals that mimic features of glaciogenic sources like moulin tremor. We quantify these artifacts with a mechanical model that shows instruments undergo structural resonance as they melt-out, at exposure rates that we predict from an ablation model (RACMO). These models reproduce general spectral features in our data, and enable us to estimate what instrument exposure reduces ice-to-sensor coupling enough to prevent icequake detection. Last, we use our resonance data to quantitatively measure how narrowband signals that originate from either artificial or glaciogenic sources will reduce the ability of certain waveform detectors (correlators) to capture transient seismic events, even if sensors remain coupled.

Authors:
ORCiD logo [1]
  1. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Research Org.:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org.:
USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1526961
Report Number(s):
LA-UR-18-31409
Journal ID: ISSN 0260-3055
Grant/Contract Number:  
89233218CNA000001
Resource Type:
Accepted Manuscript
Journal Name:
Annals of Glaciology
Additional Journal Information:
Journal Name: Annals of Glaciology; Journal ID: ISSN 0260-3055
Publisher:
International Glaciological Society
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Glaciers, glaciology, cryosphere, seismic, seismology, geophysics, ice, polar regions, signal detection, tonal noise

Citation Formats

Carmichael, Joshua Daniel. Narrowband signals recorded near a moulin that are not moulin tremor: a cautionary short note. United States: N. p., 2019. Web. doi:10.1017/aog.2019.23.
Carmichael, Joshua Daniel. Narrowband signals recorded near a moulin that are not moulin tremor: a cautionary short note. United States. doi:10.1017/aog.2019.23.
Carmichael, Joshua Daniel. Tue . "Narrowband signals recorded near a moulin that are not moulin tremor: a cautionary short note". United States. doi:10.1017/aog.2019.23. https://www.osti.gov/servlets/purl/1526961.
@article{osti_1526961,
title = {Narrowband signals recorded near a moulin that are not moulin tremor: a cautionary short note},
author = {Carmichael, Joshua Daniel},
abstractNote = {Geophysicists that deploy seismic sensors in ablation zones of glaciers and ice sheets to record glaciogenic signatures can confront recording challenges caused by instrument melt-out or tilt. These challenges often require installing sensors in boreholes to delay melt-out, or securing sensors to structures that improve coupling. We show that some of these structures that were buried near a moulin at a snow-free site in the ablation zone of the Western Greenland Ice Sheet resonated as they became exposed, and caused their geophones to record temporally evolving, narrowband signals that mimic features of glaciogenic sources like moulin tremor. We quantify these artifacts with a mechanical model that shows instruments undergo structural resonance as they melt-out, at exposure rates that we predict from an ablation model (RACMO). These models reproduce general spectral features in our data, and enable us to estimate what instrument exposure reduces ice-to-sensor coupling enough to prevent icequake detection. Last, we use our resonance data to quantitatively measure how narrowband signals that originate from either artificial or glaciogenic sources will reduce the ability of certain waveform detectors (correlators) to capture transient seismic events, even if sensors remain coupled.},
doi = {10.1017/aog.2019.23},
journal = {Annals of Glaciology},
number = ,
volume = ,
place = {United States},
year = {2019},
month = {5}
}

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