Subglacial volcanic seismicity in Marie Byrd Land detected by the POLENET/ANET seismic deployment
Abstract
The deployment of 37 seismic stations in West Antarctica during 2010-2012 as part of the POLENET/ANET project offers an unprecedented opportunity to detect any active seismicity associated with Marie Byrd Land volcanoes. Several of the largest volcanic centers, such as Mt. Sidley and Mt. Berlin, extend above the ice sheet with eruptive histories that can be constrained by lava samples but there are presumably other unknown smaller volcanoes in this poorly surveyed region. We detect, associate, and locate seismic events in West Antarctica in three high frequency bands (0.5-1.5 Hz, 1.5-4.0 Hz, 4.0-8.0 Hz) by identifying first arriving P and S phases using both automated STA/LTA detection and visual inspection. We find strong evidence of an active subglacial magmatic system beneath a poorly mapped topographic feature about 60 km from Mt. Sidley along the trend of the Executive Committee Range (ECR). This site shows hundreds of deep long period (DLP) volcanic events at depths of 25-30 km that resemble DLP events at numerous temperate volcanoes. These events occur in temporal clusters and show a DLP characteristic spectrogram with corner frequencies around 3 Hz and a maximum frequency of about 4 Hz. The corner frequencies of a corresponding tectonic event (average local magnitude ml 1.6) should be greater than 15 Hz. We also locate several events on Mt. Berlin that we classify as volcano-tectonic (VT). These events are higher frequency, up to 15 Hz, and have depths between 10-25 km, as is typical of VT sources. Mt. Moulton, Mt. Andrus, Mt. Frakes, Mt. Hampton, Mt. Sidley, and Mt. Waesche all have at least one event located on or very near to the volcano that are probably VT earthquakes, but in some cases may result from ice movement occurring along the flanks. This evidence of volcanic activity suggests high heat flow in the region, which would affect the dynamics of the overlying icecap. A major subglacial volcanic eruption could drastically affect the ice sheets by melting, the formation of a large sub-ice water reservoir, and by likely producing increases in ice velocity. We have also located several events from 2010 near the location of the June 1, 2012 Mw 5.5 earthquake along the coast near the Ford Ranges, showing that this region has long term earthquake and tectonic activity. In contrast, we find only a couple small earthquakes located within the West Antarctic Rift system itself. This supports the idea, consistent with POLENET/ANET geodetic results, that much of the rift is no longer tectonically active. Large clusters of shallow events occur near the grounding lines of several glaciers/ice streams along the north coast of MBL. These events are most likely related to glacial motion and may specifically occur when ice transitions from grounded to floating conditions.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFM.T41B2587L
- Keywords:
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- 0700 CRYOSPHERE;
- 7200 SEISMOLOGY;
- 7280 SEISMOLOGY / Volcano seismology