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Application of the spatially smoothed seismicity and Monte Carlo methods to estimate the seismic hazard of Eritrea and the surrounding region
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.
Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences.
2006 (English)In: Natural Hazards, ISSN 0921-030X, E-ISSN 1573-0840, Vol. 39, no 3, 395-418 p.Article in journal (Refereed) Published
Abstract [en]

The region of interest is characterized by incomplete data sets and little information about the tectonic features. Therefore, two methodologies for estimating seismic hazard were used in order to elucidate the robustness of the results: the method of spatially smoothed seismicity introduced by Frankel (1995) and later extended by Lapajne et al. (1997) and a Monte Carlo approach presented by Ebel and Kafka (1999). In the first method, fault-rupture oriented elliptical Gaussian smoothing was performed to estimate future activity rates along the causative structures. Peak ground accelerations were computed for a grid size of 15 km x 415 km assuming the centre of the grids as epicentres, from which the seismic hazard map was produced. The attenuation relationship by Ambraseys et al. (1996) was found suitable for the region under study. PGA values for 10% probability of exceedence in 50 years (return period of 475 years) were computed for each model and a combined seismic hazard map was produced by subjectively assigning weights to each of these models. A worst-case map is also obtained by picking the highest value at each grid point from values of the four hazard maps. The Monte Carlo method is used to estimate seismic hazard, for comparison to the results from our previous approach. Results obtained from both methods are comparable except values in the first set of maps estimate greater hazard in areas of low seismicity. Both maps indicate a higher hazard along the main tectonic features of the east African and Red Sea rift systems. Within Eritrea, the highest PGA exceeded a value 25% of g, located north of Red Sea port of Massawa. In areas around the capital, Asmara, PGA values exceed 10% of g.

Place, publisher, year, edition, pages
2006. Vol. 39, no 3, 395-418 p.
Keyword [en]
spatially smoothed seismicity, Monte Carlo methods, seismic hazard, peak ground acceleration, Eritrea
National Category
Earth and Related Environmental Sciences
Identifiers
URN: urn:nbn:se:uu:diva-95146DOI: 10.1007/s11069-005-6127-9ISI: 000241613400003OAI: oai:DiVA.org:uu-95146DiVA: diva2:169246
Available from: 2006-11-09 Created: 2006-11-09 Last updated: 2017-12-14Bibliographically 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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