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GNS Science, NZ
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- PublicationRestrictedJoint Geophysical Observations of Ice Stream Dynamics(2008)
; ; ; ; ; ;Danesi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Dubbini, M.; DiMec, Università di Modena e Reggio Emilia ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Vittuari, L.; DISTART, Università di Bologna ;Bannister, S.; GNS Science, NZ; ; ; ; ; ; ; ;Capra, A.; DiMec, Università di Modena e Reggio Emilia ;Dietrich, R.; Technische Universitat Dresden, G; Ice streams play a major role in the ice mass balance and in the reckoning of the global sea level; they have therefore been object of wide scientific interest in the last three decades. During the 21st Italian Antarctic Expedition, in the austral summer 2005–06, we deployed a joint seismographic and geodetic network in the area of the David Glacier, Southern Victoria Land. This campaign followed a similar experiment carried out in the same area during the austral summer 2003–04 with the deployment of a seismographic network that recorded significant microseismicity beneath the David Glacier, primarily occurring as a few small clusters. In the latest 2005–06 deployment, 7 seismographic stations and 3 GPS geodetic receivers operated continuously for a period of 3 months (November 2005–early February 2006) in an area of about 100×150 km2 around the David Glacier. We have carried out several analyses using the combined data sets. These included the examination of the temporal evolution in earthquake magnitude and location and also the contemporaneous observation of both seismic activity and surface kinematics of the ice stream to possibly correlate the recorded microseismicity with the movement of the glacier, affected by the Ross Sea tides. Unfortunately, a clear correlation between the occurrence of seismic events and the movement of the glacier is not evident. Here we present some details of the two temporary networks and preliminary results and implications.398 410 - PublicationRestrictedRepeating earthquakes from rupture of an asperity under an Antarctic outlet glacier(2007-01-15)
; ; ; ;Danesi, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Bannister, S.; GNS Science, PO Box 30368, Lower Hutt, New Zealand ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; The inner regions of the Antarctic continent are generally regarded as nearly aseismic, although microseismicity is known to occur beneath some outlet ice streams, related to the interaction between the fast flowing ice and the bedrock. Here we show the occurrence of unusual earthquakes beneath an Antarctic outlet glacier that share almost the same magnitude, pointing to the repeated rupture of a single asperity. These seismic events produce waveforms with very high similarity and uncommon spectrum and are tightly clustered in space but, unlike other reported instances of repeating earthquakes on a patch of the San Andreas Fault, they occur in frequent irregular swarms. Evidence locates these events at the rock–ice interface under the glacier, and shows the existence of stick–slip motion on a smaller scale than the large slow slip events detected by global seismographs. Seismic behaviour of large glaciers can presumably be connected to surges in ice motion. This study determines a little known environment for fracture dynamics studies, while also contributing to the understanding of the coupling processes between fast flowing glaciers and bedrock that influence ice stream evolution and stability.325 25 - PublicationRestrictedThe 2010–2011 Canterbury, New Zealand, seismic sequence: Multiple source analysis from InSAR data and modeling(2012)
; ; ; ; ; ; ; ; ; ; ; ; ;; ;The 2010–2011 Canterbury sequence is a complex system of seismic events that started with a Mw 7.1 earthquake and continued with large aftershocks with dramatic consequences, particularly for the city of Christchurch. We model the main earthquakes using InSAR data, providing displacement maps and the respective modeling for the September 4th, 2010, February 22nd, 2011 and June 13th, 2011 events. Relocated aftershocks, field and GPS surveys are used to constrain models obtained by inversion of InSAR data; the fault slip distribution is retrieved with a variable patch size approach aimed at maximizing the spatial resolution on the fault plane. For the September 2010 earthquake we estimated significant slip values below 10 km depth; the calamitous February 2011 event in Christchurch is modeled with a double fault source with slip values less than 2 m down to 7 km depth; for the second June 13th event in Christchurch we identified a NW-SE striking fault as responsible for the earthquake. Last, we introduce the use of InSAR coherence maps to quickly detect the areas subject to soil liquefaction in Christchurch, as shown for the two main events.771 1