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Authors: Midzi, V.* 
Bommer, J. J.* 
Strasser, F. O.* 
Albini, P.* 
Zulu, B. S.* 
Prasad, K.* 
Flint, N. S.* 
Title: An intensity database for earthquakes in South Africa from 1912 to 2011
Journal: Journal of Seismology 
Series/Report no.: /17 (2013)
Publisher: Springer Science+Business Media B.V.
Issue Date: 2013
DOI: 10.1007/s10950-013-9387-y
Keywords: Intensity database; South Africa
Subject Classification04. Solid Earth::04.06. Seismology::04.06.05. Historical seismology 
Abstract: 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.
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