DOI: 10.5285/b809a040-8305-4bc5-baff-76aa2b823734
title: Microseismic icequake catalogue, Rutford Ice Stream (West Antarctica), November 2018 to February 2019

description: This dataset contains ASCII files with hypocenter information, event times and magnitudes for 227029 micro-earthquakes with a magnitude range from -2.0 to -0.3 recorded from a 35-station seismic network located ~40 km upstream of the grounding line of Rutford Ice Stream, West Antarctica. For 87910 of these events, earthquake focal mechanisms (strike/dip/rake) are available. The seismic network, which recordings are the base for the event catalogue, broadly formed a rectangle with 1 km station spacing. Details on the station locations, instrument types and operation periods are included in these data files. The event catalogue encloses the geographic region between 084.142 to 083.760 degrees West and 78.204 to 78.113 degrees South. Events are located between 1.553 and 2.416 km depth. Recording took place between 20th November 2018 and 16th February 2019. The spatio-temporal arrangement of these micro-earthquakes can be used to characterize frictional properties at the ice-bed interface of Rutford Ice Stream. This work was funded within the BEAMISH project by NERC AFI award numbers NE/G014159/1 and NE/G013187/1. Seismic instruments were provided by NERC SEIS-UK (Loan 1017) and the Incorporated Research Institutions for Seismology (IRIS) through the PASSCAL Instrument Center at New Mexico Tech.
description: Event locations were gained from the continuous passive seismic records using the QuakeMigrate (Hudson et al., 2019; J. D. Smith et al., 2020) and Nonlinloc (Lomax et al., 2000) software. A two-layer velocity model (firn layer above an ice layer) according to E. C. Smith et al. (2015) was used in the Nonlinloc location step. Based on Nonlinloc locations, we accept only events with a total root-mean-square (RMS) value of 0.02 s, a maximum azimuthal gap of 280 degrees, maximum 10% of picks with a P/S residual larger than 0.02 s/0.2 s and at least 3 P picks and 2 S picks for the final event catalogue. We account for the movement of the seismic stations relative to the bed due to ice flow by shifting each event in the final catalogue downstream. Rutford Ice Stream moved ~94 m downstream during the 90 day survey period, whereas our stations are specified at fixed locations during event location, clearly evidencing the necessity for such a shift. We perform this shift by calculating the stations' locations at the time of each individual event relative to the start of the deployment, using their GPS locations, and apply this lateral shift to that event hypocenter. This is repeated for all events in the catalogue to compensate for ice flow. Magnitudes were calculated from the far-field displacement of the P-wave (Mw; Shearer (2009); implementation of Hudson (2019)) for a 1-day data subset. A local magnitude scale (ML) was then derived based on these Mw values. The local magnitude scale follows the equation: ML = log10(A) + m x depi - t where A is the maximum amplitude of either of the two horizontal components (in instrument counts corrected for the instrument type). The distance term m accounts for the decay of amplitudes with increasing epicentral distance, depi is the epicentral distance and t is a scaling parameter that bridges the offset between Mw and ML. Focal mechanisms were calculated from first motion polarities and P to S- amplitude ratios using the HASH software (Hardebeck & Shearer, 2002, 2003). The final set of good solutions is derived based on quality criteria, which are the stability of solution upon variations of input, the azimuthal gap of the final set of stations (should be smaller than 180 degrees) used and the final number of input picks (should be larger than seven). Detailed information on catalogue creation will be contained in Kufner et al. (in prep.).
description: Instrumentation: Each station of the seismic network consisted of a Reftek RT-130 data logger with a 4.5 Hz 3-component geophone (either GS11-3D or L28-3D), which was buried to ~1 m depth. The sampling frequency was set to 1000 Hz. Energy supply was ensured through a solar panel and batteries. Timing was obtained from an attached GPS antenna. Software: Event detection from continuous data: QuakeMigrate (https://github.com/QuakeMigrate/QuakeMigrate); October 2019-Version Event relocation: Nonlinloc (http://alomax.free.fr/nlloc/); Version 4, including updates until 2017 First motion focal mechanisms: HASH (https://www.usgs.gov/software/hash-12); Version 1.2, January 2008
description: See Lineage for quality restrictions applied to the event hypocenters and focal mechanisms. Location errors are given directly in the data file.