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Local seismicity studies of Arctic mid-ocean ridge processes with seismic arrays on drifting ice floes

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Schlindwein, V. , Läderach, C. and Korger, E. (2010): Local seismicity studies of Arctic mid-ocean ridge processes with seismic arrays on drifting ice floes , European Seimological Commission, 32nd General Assembly, MontpellierSept. 2010. .
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Abstract:

Active tectonic and magmatic processes at ultraslow spreading ridges are still poorly known because the main representatives of this class of mid-ocean ridges, the Arctic mid-ocean ridge system and the Southwest Indian Ridge, are situated in areas where permanent ice cover and adverse weather conditions, respectively, have prevented routine exploration. The first geological exploration of Gakkel Ridge during the Arctic Mid-Ocean Ridge Expedition in 2001 showed that predictions like decreasing magmatism with decreasing spreading rate are not valid at spreading rates below 20 mm/y full rate, challenging our models for crustal generation at mid-ocean ridges.In order to gain a first understanding of active spreading processes at ultraslow-spreading ridges we deployed seismic arrays on drifting ice floes to record the local seismicity in magmatic and amagmatic segments of Gakkel Ridge and Lena Trough. During four expeditions, we gathered a total of 63 days of seismicity data recorded by 3-12 stations clustered in up to three arrays. During all deployments we detected local and regional earthquakes with magnitudes well below magnitude 2 and event rates varying from three events/day in the amagmatic Lena Trough to one event/hour at the 85°E volcanic complex at eastern Gakkel ridge.At eastern Gakkel Ridge, the seismic arrays recorded 200 impulsive seismoacoustic signals and their multiple reflections in the water column. We analysed the character of these signals and located the sound source near major faults at the southern rift valley wall. Contemporaneous vigorous hydrothermal discharge, a preceding unusual teleseismic earthquake swarm and abundant pyroclastic deposits at the seafloor let us to interpret the seismoacoustic signals as deep submarine Strombolian eruption bursts. A dense network of recording stations, as a result of the ice drift, which recorded more than 400 local events will enable us to study the structure of the 85°E volcanic complex using seismic tomography.At Lena Trough, our arrays drifted across the area of a recent major seismic crisis in February and March 2009 which culminated in an mb 6.5 earthquake on March 6, 2009. We relocated the teleseismically recorded events in an outside corner setting at the junction of southern Lena Trough and the Spitzbergen Fracture Zone.

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