The macroseismic intensity of the 18 October 1992 Murindo-Atrato earthquake that\ud affected the northwestern states of Colombia (Choco´ and Antioquia) is reassessed using the\ud newly developed INQUA Environmental Seismic Intensity Scale (ESI 2007) which is based on\ud the evaluation of earthquake environmental effects. To generate the ESI 2007 isoseismal map of\ud northwestern Colombia, a geographical information system was used. Unifying the available\ud information on the seismological and active tectonics framework including historical seismicity,\ud hypocentral depths, foreshocks, aftershocks, focal mechanism, macroseismic data under the\ud same GIS and the map of Quaternary faults allowed us to reinterpret the geological and environmental\ud effects of the 1992 earthquakes sequence. A total of 24 sites from the areas of Quibdo´ ,\ud Bojaya´, Rio Sucio, Murindo, Vigı´a del Fuerte and Turbo were evaluated. A systematic comparison\ud among evaluated intensities (Modified Mercalli and ESI scale) revealed differences from one to\ud two degrees. According to the ESI 2007 scale, the epicentral intensity Io is XI. This represents\ud one degree higher than the epicentral intensity obtained using MM and Medveded Sponhauer\ud Karnik (MSK) intensity scales, probably due to the lack of suitable observations on building\ud damage in this poorly populated and developed region. This information is also useful in order\ud to shed some light on the persistent question of the exact location and dimension of the main\ud rupture zone associated with the earthquake. The isoseismal map derived from the integration of\ud the whole set of environmental effects with other macroseismic data strongly suggests that the causative\ud tectonic structure is the Murindo fault. However, the rupture length derived from the distribution\ud of ground effects is greater than the Murindo fault length, implying that other nearby fault\ud segments were activated during the 1992 event. The new isoseismal map resulting from this work is\ud relevant for the assessment of future seismic risk in the northwestern region of Colombia. Overall,\ud the application of the ESI 2007 scale to the 18 October 1992 earthquake, and to similar strong\ud events in the region, can be useful for disaster management and planning, estimation of damage,\ud and post-earthquake recovery efforts
The aim of this investigation was the paleoseismological characterization of eastern Antioquia, using trenches analysis and detailed study of indicators of neotectonic activity, some of which had been reported in previous seismic hazard assessment studies of the Aburra Valley.Through techniques of neotectonic, paleoseismology and also age correlation of Quaternary deposits obtained by several authors, it was found at Alcaravanes site (Marinilla Town), evidences of three seismic events with magnitudes Mw 6.4, 6.6 and 6.5 which displaced recent deposits with maximum ages of 440,000, 37,000 and 8,000 years respectively. Likewise, two prehistoric earthquakes, both with magnitude Mw 6.5 were recognized at the Hamburgo site (Guarne Town), dated between 880,000 and 37,000 years respectively, which proves the existence and activity of La Mosca fault. Finally, the Manantiales site (Rionegro Town) revealed a couple of seismic events with magnitude Mw 6.7 and 6.6 that displaced alluvial terraces in Rio Negro basin with a maximum age of onset of neotectonic deformation of 880,000 years.Latest neotectonic findings change the perspective of seismic hazard in Medellin city and surroundings. Prehistoric earthquakes have occurred in the last million years and created small surface rupture and faulting not related with active mountain fronts. Furthermore, the evidence shows obliterated active faults and efficiency of erosion factors in modeling relief and alluvial fill in the basins of Rionegro Erosion Surface.
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