Evidence for deep icequakes in an Alpine glacier
To obtain more reliable information about the focal-depth distribution of icequakes, in April 1997 we operated an array of seven portable digital seismographs on Unteraargletscher, central Swiss Alps. Over 5000 events were detected by at least two instruments during the 9 day recording period. P-wav...
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International Glaciological Society
2000
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Online Access: | https://nrl.northumbria.ac.uk/id/eprint/38154/ https://doi.org/10.3189/172756400781820462 |
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ftunivnorthumb:oai:nrl.northumbria.ac.uk:38154 2023-05-15T13:29:22+02:00 Evidence for deep icequakes in an Alpine glacier Deichmann, N. Ansorge, J. Scherbaum, F. Aschwanden, A. Bernard, F. Gudmundsson, Hilmar 2000 https://nrl.northumbria.ac.uk/id/eprint/38154/ https://doi.org/10.3189/172756400781820462 unknown International Glaciological Society Deichmann, N., Ansorge, J., Scherbaum, F., Aschwanden, A., Bernard, F. and Gudmundsson, Hilmar (2000) Evidence for deep icequakes in an Alpine glacier. Annals of Glaciology, 31. pp. 85-90. ISSN 0260-3055 F800 Physical and Terrestrial Geographical and Environmental Sciences Article PeerReviewed 2000 ftunivnorthumb https://doi.org/10.3189/172756400781820462 2022-09-25T06:09:19Z To obtain more reliable information about the focal-depth distribution of icequakes, in April 1997 we operated an array of seven portable digital seismographs on Unteraargletscher, central Swiss Alps. Over 5000 events were detected by at least two instruments during the 9 day recording period. P-wave velocities (3770 m f) were determined from several calibration shots detonated at the glacier surface as well as in a 49 m deep borehole, whereas S-wave velocities (1860 ms–1) were derived from a simultaneous inversion for Vp/Vs6 applied to 169 icequakes. So far, hypocentral locations have been calculated for over 300 icequakes. Besides confirming the occurrence of shallow events associated with the opening of crevasses, our results show that a small but significant fraction of the hypocenters are located at or near the glacier bed. One event was found at an intermediate depth of about 120 m. Three-dimensional particle-motion diagrams of both explosions and icequakes clearly demonstrate that all vertical component seismograms from shallow sources are dominated by the Rayleigh wave. On the other hand, for events occurring at depths greater than about 40 m, the Rayleigh wave disappears almost entirely. Therefore, a qualitative analysis of the signal character provides direct information on the focal depth of an event and was used as an independent check of the locations obtained from traditional arrival-time inversions. Thus, our results demonstrate that deep icequakes do occur and that simple rheological models, according to which brittle deformation is restricted to the uppermost part of a glacier, may need revision. Article in Journal/Newspaper Annals of Glaciology Northumbria University, Newcastle: Northumbria Research Link (NRL) Annals of Glaciology 31 85 90 |
institution |
Open Polar |
collection |
Northumbria University, Newcastle: Northumbria Research Link (NRL) |
op_collection_id |
ftunivnorthumb |
language |
unknown |
topic |
F800 Physical and Terrestrial Geographical and Environmental Sciences |
spellingShingle |
F800 Physical and Terrestrial Geographical and Environmental Sciences Deichmann, N. Ansorge, J. Scherbaum, F. Aschwanden, A. Bernard, F. Gudmundsson, Hilmar Evidence for deep icequakes in an Alpine glacier |
topic_facet |
F800 Physical and Terrestrial Geographical and Environmental Sciences |
description |
To obtain more reliable information about the focal-depth distribution of icequakes, in April 1997 we operated an array of seven portable digital seismographs on Unteraargletscher, central Swiss Alps. Over 5000 events were detected by at least two instruments during the 9 day recording period. P-wave velocities (3770 m f) were determined from several calibration shots detonated at the glacier surface as well as in a 49 m deep borehole, whereas S-wave velocities (1860 ms–1) were derived from a simultaneous inversion for Vp/Vs6 applied to 169 icequakes. So far, hypocentral locations have been calculated for over 300 icequakes. Besides confirming the occurrence of shallow events associated with the opening of crevasses, our results show that a small but significant fraction of the hypocenters are located at or near the glacier bed. One event was found at an intermediate depth of about 120 m. Three-dimensional particle-motion diagrams of both explosions and icequakes clearly demonstrate that all vertical component seismograms from shallow sources are dominated by the Rayleigh wave. On the other hand, for events occurring at depths greater than about 40 m, the Rayleigh wave disappears almost entirely. Therefore, a qualitative analysis of the signal character provides direct information on the focal depth of an event and was used as an independent check of the locations obtained from traditional arrival-time inversions. Thus, our results demonstrate that deep icequakes do occur and that simple rheological models, according to which brittle deformation is restricted to the uppermost part of a glacier, may need revision. |
format |
Article in Journal/Newspaper |
author |
Deichmann, N. Ansorge, J. Scherbaum, F. Aschwanden, A. Bernard, F. Gudmundsson, Hilmar |
author_facet |
Deichmann, N. Ansorge, J. Scherbaum, F. Aschwanden, A. Bernard, F. Gudmundsson, Hilmar |
author_sort |
Deichmann, N. |
title |
Evidence for deep icequakes in an Alpine glacier |
title_short |
Evidence for deep icequakes in an Alpine glacier |
title_full |
Evidence for deep icequakes in an Alpine glacier |
title_fullStr |
Evidence for deep icequakes in an Alpine glacier |
title_full_unstemmed |
Evidence for deep icequakes in an Alpine glacier |
title_sort |
evidence for deep icequakes in an alpine glacier |
publisher |
International Glaciological Society |
publishDate |
2000 |
url |
https://nrl.northumbria.ac.uk/id/eprint/38154/ https://doi.org/10.3189/172756400781820462 |
genre |
Annals of Glaciology |
genre_facet |
Annals of Glaciology |
op_relation |
Deichmann, N., Ansorge, J., Scherbaum, F., Aschwanden, A., Bernard, F. and Gudmundsson, Hilmar (2000) Evidence for deep icequakes in an Alpine glacier. Annals of Glaciology, 31. pp. 85-90. ISSN 0260-3055 |
op_doi |
https://doi.org/10.3189/172756400781820462 |
container_title |
Annals of Glaciology |
container_volume |
31 |
container_start_page |
85 |
op_container_end_page |
90 |
_version_ |
1766000220852715520 |