Abstract The macroseismic intensity of the 18 October 1992 Murindo-Atrato earthquake that affected the northwestern states of Colombia (Chocó and Antioquia) is reassessed using the newly developed INQUA Environmental Seismic Intensity Scale (ESI 2007) which is based on the evaluation of earthquake environmental effects. To generate the ESI 2007 isoseismal map of northwestern Colombia, a geographical information system was used. Unifying the available information on the seismological and active tectonics framework including historical seismicity, hypocentral depths, foreshocks, aftershocks, focal mechanism, macroseismic data under the same GIS and the map of Quaternary faults allowed us to reinterpret the geological and environmental effects of the 1992 earthquakes sequence. A total of 24 sites from the areas of Quibdó, Bojayá, Rio Sucio, Murindo, Vigía del Fuerte and Turbo were evaluated. A systematic comparison among evaluated intensities (Modified Mercalli and ESI scale) revealed differences from one to two degrees. According to the ESI 2007 scale, the epicentral intensity I o is XI. This represents one degree higher than the epicentral intensity obtained using MM and Medveded Sponhauer Karnik (MSK) intensity scales, probably due to the lack of suitable observations on building damage in this poorly populated and developed region. This information is also useful in order to shed some light on the persistent question of the exact location and dimension of the main rupture zone associated with the earthquake. The isoseismal map derived from the integration of the whole set of environmental effects with other macroseismic data strongly suggests that the causative tectonic structure is the Murindo fault. However, the rupture length derived from the distribution of ground effects is greater than the Murindo fault length, implying that other nearby fault segments were activated during the 1992 event. The new isoseismal map resulting from this work is relevant for the assessment of future seismic risk in the northwestern region of Colombia. Overall, the application of the ESI 2007 scale to the 18 October 1992 earthquake, and to similar strong events in the region, can be useful for disaster management and planning, estimation of damage, and post-earthquake recovery efforts.

Abstract More than 75% of Colombia's 42 million people live in urban areas located in the mountains and are exposed to numerous natural hazards: floods, flash floods, landslides, earthquakes and volcanism. The Armero disaster of 1985 triggered the creation of the National System for Disaster Prevention and Relief. National, regional and local committees started to operate across the country, accompanied by education commissions that produced diverse audiovisual materials to help educate people living in these areas. The experiences of working with local committees gained during the last two decades are presented here. Case histories are from cities such as Pereira, Manizales and Medellín, where the local committees are run by people with little or no formal education but who understand that they must participate as a group to prevent or mitigate the effects of natural disasters. The co-operation between technical experts and trained residents represents an outstanding example of good communication and co-operation for urban populations living in dangerous areas. Although many problems have yet to be resolved, these case histories show that this type of organization seems to be more effective than direct intervention from national government agencies. The models of community participation and communication developed and refined here may have application to similar social environments in other countries.