Reassessment of macroseismic intensities for two earthquakes in Colombia: Tumaco (1979, Mw = 8.1) and Armenia (1999, Mw = 6.1), using the ESI-2007 scale

Abstract

A reassessment of the macroseismic intensities was performed for the Tumaco (December 12th, 1979, Mw = 8.1) and Armenia (January 25th, 1999, Mw = 6.1) earthquakes, based on the spatial distribution and quantification of dimensions of the surface geological and environmental effects in lists compiled from published documents. The newly constructed lists of 46 effects for the Tumaco earthquake (TE) and 123 effects for the Armenia earthquake (AE) were obtained by literature review and systematic searches of information in authoritative sources. The geological and environmental effects caused by the two earthquakes were then used to estimate seismic intensities and construct new isoseismal maps following the methodology of the ESI-2007 scale. Comparisons were made between the ESI-2007 isoseismal maps and those using data from traditional intensity scales (Modified Mercalli MM-31 and EMS-98) in terms of the percentage overlap between affected areas for each intensity level. For the AE, the newly computed intensities indicate epicentral intensity I0AE = 10 and the ESI-2007 intensities show best agreement with EMS-98 values, with a maximum of 54.2% overlap for intensities in the range 7–8. The new isoseismal maps for the TE indicate maximum intensity IMaxTE ~ I0TE = 11 and best agreement with MM-31 values, with a maximum of 48.8% overlap for intensities in the range 7–8. It is concluded that ESI-2007 intensities exhibit close agreement in most cases with MM-31 and EMS-98 values and provide new details for maximum intensities and the extent of affected areas which can be used in future plans of land use for earthquake-prone areas in Colombia.