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Glacial long period seismic events at Katla volcano, Iceland
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences. Uppsala University, Disciplinary Domain of Science and Technology. Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL. (glacologi)
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
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2009 (English)In: Geophysical Research Letters, ISSN 0094-8276, E-ISSN 1944-8007, Vol. 36, L11402- p.Article in journal (Refereed) Published
Abstract [en]

Repeating long-period (lp) earthquakes are commonly8 observed in volcanic regions worldwide. They are usually9 explained in terms of a volcanic source effect or anomalous10 propagation through the volcano. Recently, large lp events11 have also been associated with the motion of massive ice12 streams. Our joint analysis of climatic and new seismic data13 shows that small lp events observed at Katla volcano, Iceland,14 are in fact related to ice movement in a steep outlet glacier and15 not, as previously thought, to volcanic intrusive activity. The16 over 13000 lp events recorded since 2000 are consistent in17 character and magnitude with seasonal changes of the glacier.18 As the current global warming trend could cause similar19 earthquake sequences at other glacier covered volcanoes,20 identifying them as glacial rather than eruption precursors21 is vital.

Place, publisher, year, edition, pages
2009. Vol. 36, L11402- p.
Keyword [en]
Mýrdalsjökull, Katla volcano, seismic tilt, vlp-signals, lp-signals, acceleration, static deformation
National Category
Earth and Related Environmental Sciences
Research subject
Geophysics with specialization in Seismology
Identifiers
URN: urn:nbn:se:uu:diva-117549DOI: 10.1029/2009GL038234ISI: 000267000000004OAI: oai:DiVA.org:uu-117549DiVA: diva2:297898
Available from: 2009-04-16 Created: 2009-04-16 Last updated: 2017-12-12Bibliographically approved
In thesis
1. Studies of Unusual Seismicity and Long Period Events at the Glacier Overlain Katla Volcano, Iceland
Open this publication in new window or tab >>Studies of Unusual Seismicity and Long Period Events at the Glacier Overlain Katla Volcano, Iceland
2009 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Earthquake catalogues are usually dominated by diffusive behaviour consistent with the Omori law of aftershocks. This is investigated in terms of waiting times, i.e. the time between successive events in a time-sorted earthquake catalogue. The theoretical waiting time probability distribution for the Omori law is derived and shown to predict the numerically produced Omori aftershock sequence well. These results enhance our understanding of aftershock processes and demonstrate that previous waiting time interpretations were severely flawed.

Iceland earthquake catalogues are studied in terms of waiting times. Omori aftershock sequences are shown to predict most datasets well but there are some significant exceptions. One of these is data from the glacier covered Katla volcano in South Iceland, with few aftershocks. This dataset can be further split into two geographical groups: Several hundred volcano-tectonic earthquakes occurring within the caldera, reaching depths down to 15 km, and thousands of emergent low frequency earthquakes with a poorly defined shallow source in Goðabunga, in the western part of Katla. These events are investigated further.

The lp events at Goðabunga have been recorded for decades and show a clear seasonal and climate-related correlation where their number increases in the autumn as well as during warmer years. Many of them form groups with very with similar waveforms. New broad-band seismic data suggests that the lp events originate in a steep outlet glacier covering Katla. Here, ice movement leads to ice falls over the steep escarpment, and we now believe that the lp events are generated by large ice falls rather than being related to gas or magma movements within the volcano, and are not precursors to an eruption as previously suspected. This observation probably has major significance for hazard estimation at the many ice-covered volcanoes around the world.

We report near-field (vlp) signals simultaneous with the largest lp events. Our data is partly consistent in character with surface deformation (displacement and tilt) due to the ice movements. However, in line with results from elsewhere, the magnitudes of the observed effects are large relative to those from mathematical modelling. Our analysis suggests that the signal is not an instrumental artefact. Possible explanations are discussed.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2009. 85 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 636
National Category
Geophysics
Research subject
Geophysics Specialized In Seismology
Identifiers
urn:nbn:se:uu:diva-100771 (URN)978-91-554-7500-0 (ISBN)
Public defence
2009-05-08, Hambergssalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2009-04-16 Created: 2009-04-07 Last updated: 2009-04-27

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