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An application of relative moment tensor inversion to aftershocks of the June 1998 Hengill earthquake in southwest Iceland
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, Geophysics.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
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2008 (English)In: Bulletin of The Seismological Society of America (BSSA), ISSN 0037-1106, Vol. 98, no 2, 636-650 p.Article in journal (Refereed) Published
Abstract [en]

Using spectral amplitudes from the South Iceland Lowland (SIL) seismic network, we conduct a relative moment tensor inversion (RMTI) on aftershocks of the June 1998 M-w 5: 4 event that occurred at the Hengill triple junction, southwest Iceland. Three distinct groups of spatially clustered events are observed in the region for 25 selected events that occurred during the period from 4-5 June 1998. These clusters have previously been relocated with very high accuracy using cross-correlation techniques. We use the RMTI method to determine the focal mechanisms of these events and compare our results with the SIL network mechanisms obtained using spectral amplitudes. Most focal mechanisms obtained in this study show a predominantly right-lateral strike-slip motion, similar to those obtained by the SIL network, but more consistently in agreement with the orientations of the surface faults in the area. The spectral amplitude grouping method was used to investigate discrepancies between some of the focal mechanisms obtained using RMTI and the method used in the SIL network. This resolved apparent differences in the focal mechanism solutions for two of the studied events. Cluster alignment across the presumed fault and the individual event mechanisms agree well, suggesting the occurrence of the events along a fault plane dipping steeply towards the east. Consistency in the pressure and tension axes of the focal mechanisms suggests that the region was under northeast-southwest-oriented compression during the activity. Decomposition of the moment tensors into double-couple and isotropic components and the resulting insignificant isotropic component also suggests that the styles of failure for the analyzed events was mainly due to shearing.

Place, publisher, year, edition, pages
2008. Vol. 98, no 2, 636-650 p.
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95148DOI: 10.1785/0120060163ISI: 000254528000009OAI: oai:DiVA.org:uu-95148DiVA: diva2:169248
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2017-01-25Bibliographically approved
In thesis
1. Earthquake Sources, the Stress Field and Seismic Hazard: A Study in Eritrea and its Surrounding
Open this publication in new window or tab >>Earthquake Sources, the Stress Field and Seismic Hazard: A Study in Eritrea and its Surrounding
2006 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Presented in this thesis are some basic concepts and applications of seismic hazard analysis and the elements that influence the amplitude and geometric attenuation of earthquake ground motion. This thesis centers on the identification of the styles of failure, focal mechanisms, and the state of regional stress in the study area. Seismic hazard is a complex problem often involving considerable uncertainties. Therefore it is reasonable to consider different seismic hazard analysis approaches in order to as robustly as possible define zones of different levels of hazard. With the aim of characterizing and quantifying hazard in the east African region of Eritrea and its surroundings, a study is included in the thesis presenting hazard maps constructed using two non-parametric probabilistic seismic hazard analysis (PSHA) approaches. Peak ground acceleration (PGA) values for 10% probability of exceedence in 50 years are computed at given grid points for the whole selected area and results from both methods are compared.

Other aspects addressed in the thesis include the determination of source parameters of selected earthquakes that occur in the Afar region. The styles of faulting, the mechanisms involved during the rupture process and the states of stress along the major tectonic features are also highlighted. Source parameters for selected events in the region were re-evaluated and improved solutions obtained. An aftershock sequence in the Hengill volcanic area in SW Iceland, following the major event that occurred on June 4, 1998, was used to investigate improved methodologies for moment tensor using a relative approach. The sensitive and spatially dense seismic network in this area reveals large sets of clustered events allowing the power of the new methodology to be demonstrated and providing greater insight into the tectonic implications of the activity in the area.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2006. 55 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 242
Keyword
Earth sciences, Seismic hazard, Focal mechanism, Moment tensor inversion, Stress field, Afar depression, Eritrea, Geovetenskap
National Category
Earth and Related Environmental Sciences
Identifiers
urn:nbn:se:uu:diva-7292 (URN)91-554-6721-0 (ISBN)
Public defence
2006-12-06, Axel Hambergsalen, Geocentrum, Villavägen 16, Uppsala, 10:00 (English)
Opponent
Supervisors
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2009-05-28Bibliographically approved

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Lund, Björn

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