DOI: 10.5285/147baf64-b9af-4a97-8091-26aec0d3c0bb
title: Seismic refraction data from two sites on Antarctica's Larsen C Ice Shelf, Nov 2017, following the calving of Iceberg A68

description: Seismic refraction data were acquired at two sites on Antarctica's Larsen C Ice Shelf, in November 2017. The acquisition was performed to measure seismic anisotropy, a proxy for the stress condition, in the ice shelf following the calving of Iceberg A68 in July 2017. 2D seismic profiles were acquired at two sites: S1, close to the new calving front of the ice shelf, and S2, advected downstream from the site surveyed in the NERC funded project NE/E013414/1 (SOLIS). Profiles were rotated about a common midpoint to examine the variation in seismic properties with azimuth. Throughout, 24 geophones were deployed at 10 m offset, with data recorded at a Geometrics GEODE system; data are presented here in SEG-2 format. All acquisitions were performed by Dr Jim White (British Geological Survey) and Emma Pearce (University of Leeds, School of Earth and Environment), with support from BAS. The data is part of the NERC RACE project, NE/R012334/1. Associated datasets are an archive of ground penetrating radar data from S2, and velocity products derived from satellite remote sensing.
description: Seismic data were recorded using Geometrics GEODE instrumentation, deploying 24 10 Hz geophones at 10 m intervals. Each record is 1 s long, sampled at 62.5 us. A hammer-and-plate seismic source was deployed, with offsets from the first geophone extending to ±200 m, typically recording 5 shots at each location. The line was sequentially rotated about a common midpoint, relative to the dominant ~easterly flow direction. As the acquisition azimuth varies, variations in the travel-time of either first-breaks or reflections can be used to infer any trends in anisotropy and therefore stress condition. The acquisition is fully documented within the Observer's Logs which accompany these data.
description: Instrumentation: Geometrics GEODE seismic system. 24x10 Hz geophones.
description: Data from S2, acquired on 22/11/2017, are generally of good quality, with clear first breaks and visible bed reflections after minimal processing; the reflection from the underlying sea-bed is also typically visible, even in unstacked data. Data are supplied in raw format here, but an Ormsby bandpass filter with corner frequencies at 75-150-300-600 Hz, plus a 100 ms AGC window, provides good improvement to the visibility of arrivals. The good quality of these data is attributed to simple structure at the site, plus calm weather conditions at the time of acquisition (22/11/2017). Note that the time was incorrectly recorded until shot record 150. A 2 hour shift is needed, then a one hour shift after note. Data from S1 are rather noisier, likely a result of windy weather at the time of acquisition (28/11/2017). The same processing parameters reveal base-ice reflections, but these are typically less coherent than the equivalents at S2. On stacking, base-ice reflections are improved but the data would benefit from ground-roll suppression. S1 central location: 67.79944383°S, 61.825091°W S2 central location: 68.00410°S, 62.568916°W The acquisition is fully documented within the Observer's Logs which accompany these data.