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Goetz Observatory, Department of Meteorology, Ascot, Bulawayo, Zimbabwe
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- PublicationOpen AccessSeismic hazard assessment in Eastern and Southern Africa(1999-12)
; ; ; ; ; ; ; ; ;Midzi, V.; Goetz Observatory, Department of Meteorology, Ascot, Bulawayo, Zimbabwe ;Hlatywayo, D. J.; Applied Physics Department, Faculty of Applied Sciences, Bulawayo, Zimbabwe ;Chapola, L. S.; Geological Survey of Malawi, Zomba, Malawi ;Kebede, F.; Geophysical Observatory, Faculty of Sciences, Addis Ababa University, Addis Ababa, Ethiopia ;Atakan, K.; Kuvvet Atakan Institute of Solid Earth Physics, University of Bergen, Norway ;Lombe, D. K.; Geological Survey of Zambia, Geological Section, Lusaka, Zambia ;Turyomurugyendo, G.; Department of Geological Survey and Mines, Entebbe, Uganda ;Tugume, F. A.; Department of Geological Survey and Mines, Entebbe, Uganda; ; ; ; ; ; ; Seismic hazard assessment for the Eastern and Southern Africa region was done using the probabilistic approach. Seismic hazard maps for 10% exceedance in 50 years, 10% exceedance in 100 years, as well as for 50 and 100 years return periods were prepared using the FRISK88M software. The area involved covers a wide region bounded by latitudes 40°S-25°N and longitudes 10°E and 55°E. Input parameters for the computations were obtained using the recent earthquake catalogue compiled by Turyomurugyendo. The catalogue which covers the time period 627-1994, contains earthquakes within the area bounded by 40°S-25°N and 10°E-55°E, with homogeneous magnitudes (M S ). Since a Poisson model of earthquake occurrence is assumed, dependent events were cleaned from the catalogue. Attenuation relations for the Eastern and Southern Africa region based on the strong motion data are virtually non-existent. However, attempts have been made recently by Jonathan and Twesigomwe to establish an average attenuation relation for the region. These relations were used in the computations. Possible uncertainties in the attenuation relations were accounted for using the logic-tree formalism. The results are presented in seismic hazard maps in terms of Peak Ground Acceleration (PGA) for the mean and the 85th percentile. The distribution of PGA values indicate relatively high hazard along the East African rift system. In the northern segments of the rift system, they exceed 250 gals for 10% probability of exceedence in 50 years.387 520 - PublicationRestrictedAn intensity database for earthquakes in South Africa from 1912 to 2011(2013)
; ; ; ; ; ; ; ;Midzi, V.; Council for Geoscience ;Bommer, J. J.; Imperial College ;Strasser, F. O.; Council for Geoscience ;Albini, P.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Milano-Pavia, Milano, Italia ;Zulu, B. S.; Council for Geoscience ;Prasad, K.; Council for Geoscience ;Flint, N. S.; Council for Geoscience; ; ; ; ; ; A database of intensity observations from instrumentally-recorded earthquakes in South Africa has been compiled as a contribution to the characterisation of seismic hazard. The database contains about 1,000 intensity data points (IDPs) that have been assigned from macroseismic observations retrieved from newspaper reports and questionnaires, and also digitised from previously published isoseismal maps. The database includes IDPs from 57 earthquakes with magnitudes in the range of Mw 2.2 to 6.4, for epicentral distances up to 1,000 km. Sixteen events have 20 or more IDPs, with half of these events having more than 80 IDPs. The database is dominated by relatively low intensity values, mostly determined from human perception of shaking rather than structural damage. However, 19 IDPs correspond to intensity values greater than VI MMI-56. Using geological maps of South Africa, the sites of 60% the IDPs were geologically classified as either ‘rock’ or ‘soil’, the uncertainty in locations precluding such a classification for the remaining data points. A few of the IDPs identified as being from soil sites appear to be strongly influenced by site effects and these were removed from the trimmed database created for exploring ground-motion levels. The trimmed database included 15 earthquakes which have a minimum of five useful IDPs, excluding those with intensity MMI=I and those based on a single observation. After removing such points, and those identified as clear ‘outliers’, a total of 436 useful IDPs were selected.443 23