Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise
Relative seismic velocity variations in the Earth’s crust can be estimated by using ambient seismic noise records from a pair of stations. Velocity variations can be caused by stress perturbations in the subsurface. Therefore, information on stress changes in the crust can possibly be retrieved from...
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Uppsala universitet, Institutionen för geovetenskaper
2018
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ftuppsalauniv:oai:DiVA.org:uu-353619 2023-05-15T16:21:48+02:00 Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise Jonsdottir, Frida 2018 application/pdf http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353619 eng eng Uppsala universitet, Institutionen för geovetenskaper Examensarbete vid Institutionen för geovetenskaper, 1650-6553 427 http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353619 info:eu-repo/semantics/openAccess Katla volcano Iceland ambient seismic noise coda waves relative velocity variations Katla vulkan Island omgivande seismiskt brus codavågor relativa hastighetsvariationer Geophysics Geofysik Student thesis info:eu-repo/semantics/bachelorThesis text 2018 ftuppsalauniv 2023-02-23T21:47:51Z Relative seismic velocity variations in the Earth’s crust can be estimated by using ambient seismic noise records from a pair of stations. Velocity variations can be caused by stress perturbations in the subsurface. Therefore, information on stress changes in the crust can possibly be retrieved from measured velocity variations in the medium. The measurement is done by comparing the coda part of two cross-correlation functions (CCFs) obtained from ambient noise recordings at two seismic stations; a current CCF that is considered to represent the actual state in the study medium at a specific time and a reference CCF that is considered to represent its average state. Here, the method is applied to the area around Katla volcano in southern Iceland. Katla is an active subglacial volcano and therefore frequent stress changes can be expected to take place there. Long-term changes (of the order of 1-2 months) in relative seismic velocity were estimated over a period of 7 months in 2011. These changes were of the order of about 0.1% for a frequency range of 0.2-1.0 Hz. For this frequency range, surface waves around Katla have been estimated to be most sensitive to velocity changes taking place at depths of about 1-5 km but the sensitivity kernels also have a peak at the surface. The scattering volume (in this case area since we are working with surface waves) depends on both the inter-station distance and how far into the coda the measurements are made. The inter-station distances vary between 5.8 and 23.4 km. Measurements are made 30 s into the coda. This results in scattering areas on the order of 100 km2. The velocity variations have a negative trend over July and over a two month period from the end of August until early November, and a positive trend in August and from early November until the end of the study period in late December. These variations are possibly the results of a combination of changes in the ground water level beneath the glacier, surface load changes and possibly hydrothermal and magmatic ... Bachelor Thesis glacier Iceland Katla Uppsala University: Publications (DiVA) Brus ENVELOPE(87.789,87.789,67.651,67.651) Katla ENVELOPE(-19.062,-19.062,63.631,63.631) Vulkan ENVELOPE(156.404,156.404,61.679,61.679) |
institution |
Open Polar |
collection |
Uppsala University: Publications (DiVA) |
op_collection_id |
ftuppsalauniv |
language |
English |
topic |
Katla volcano Iceland ambient seismic noise coda waves relative velocity variations Katla vulkan Island omgivande seismiskt brus codavågor relativa hastighetsvariationer Geophysics Geofysik |
spellingShingle |
Katla volcano Iceland ambient seismic noise coda waves relative velocity variations Katla vulkan Island omgivande seismiskt brus codavågor relativa hastighetsvariationer Geophysics Geofysik Jonsdottir, Frida Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise |
topic_facet |
Katla volcano Iceland ambient seismic noise coda waves relative velocity variations Katla vulkan Island omgivande seismiskt brus codavågor relativa hastighetsvariationer Geophysics Geofysik |
description |
Relative seismic velocity variations in the Earth’s crust can be estimated by using ambient seismic noise records from a pair of stations. Velocity variations can be caused by stress perturbations in the subsurface. Therefore, information on stress changes in the crust can possibly be retrieved from measured velocity variations in the medium. The measurement is done by comparing the coda part of two cross-correlation functions (CCFs) obtained from ambient noise recordings at two seismic stations; a current CCF that is considered to represent the actual state in the study medium at a specific time and a reference CCF that is considered to represent its average state. Here, the method is applied to the area around Katla volcano in southern Iceland. Katla is an active subglacial volcano and therefore frequent stress changes can be expected to take place there. Long-term changes (of the order of 1-2 months) in relative seismic velocity were estimated over a period of 7 months in 2011. These changes were of the order of about 0.1% for a frequency range of 0.2-1.0 Hz. For this frequency range, surface waves around Katla have been estimated to be most sensitive to velocity changes taking place at depths of about 1-5 km but the sensitivity kernels also have a peak at the surface. The scattering volume (in this case area since we are working with surface waves) depends on both the inter-station distance and how far into the coda the measurements are made. The inter-station distances vary between 5.8 and 23.4 km. Measurements are made 30 s into the coda. This results in scattering areas on the order of 100 km2. The velocity variations have a negative trend over July and over a two month period from the end of August until early November, and a positive trend in August and from early November until the end of the study period in late December. These variations are possibly the results of a combination of changes in the ground water level beneath the glacier, surface load changes and possibly hydrothermal and magmatic ... |
format |
Bachelor Thesis |
author |
Jonsdottir, Frida |
author_facet |
Jonsdottir, Frida |
author_sort |
Jonsdottir, Frida |
title |
Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise |
title_short |
Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise |
title_full |
Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise |
title_fullStr |
Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise |
title_full_unstemmed |
Estimation of Relative Seismic Velocity Changes Around Katla Volcano, Using Coda in Ambient Seismic Noise |
title_sort |
estimation of relative seismic velocity changes around katla volcano, using coda in ambient seismic noise |
publisher |
Uppsala universitet, Institutionen för geovetenskaper |
publishDate |
2018 |
url |
http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353619 |
long_lat |
ENVELOPE(87.789,87.789,67.651,67.651) ENVELOPE(-19.062,-19.062,63.631,63.631) ENVELOPE(156.404,156.404,61.679,61.679) |
geographic |
Brus Katla Vulkan |
geographic_facet |
Brus Katla Vulkan |
genre |
glacier Iceland Katla |
genre_facet |
glacier Iceland Katla |
op_relation |
Examensarbete vid Institutionen för geovetenskaper, 1650-6553 427 http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-353619 |
op_rights |
info:eu-repo/semantics/openAccess |
_version_ |
1766009781982593024 |