CC - CATEGORY CODES: 26B-Economic-geology,-general,-economics
DT - DOCUMENT TYPE: Serial
BL - BIB LEVEL: Analytic
IL - ILLUSTRATION: illus. incl. sketch maps.
RF - REFERENCE SOURCE: GeoRef, Copyright 2000, American Geological Institute.
IS - ISSN: 0746-729X
CO - CODEN: WOCODN
AN - ACCESSION NUMBER: 1984-047679
UD - UPDATE CODE: 1984
Registro 988 de 5614 - GeoRef Disc 2: 1975-1984
TI - TITLE: Seismicity associated with the great Colombia-Ecuador earthquakes of 1942, 1958, and 1979; implications for barrier models of earthquake rupture.
AU - AUTHORS: Mendoza-Carlos; Dewey-James-W
AF - AUTHOR AFFILIATION: U. S. Geol. Surv., Denver, CO, United States
SO - SOURCE: Bulletin of the Seismological Society of America. 74; 2, Pages 577-593. 1984.
PB - PUBLISHER: Seismological Society of America. Berkeley, CA, United States. 1984.
RP - RESEARCH PROGRAM: USGSOP (Non-USGS publications with USGS authors)
CP - COUNTRY OF PUBLICATION: United-States
PY - PUBLICATION YEAR: 1984
LA - LANGUAGE: English
AB - ABSTRACT: We have relocated earthquakes with Joint Hypocenter Determination in order to examine the nature of fault heterogeneities that controlled northward propagation of plate-boundary rupture from the source region of the earthquake of 14 May 1942, to the source region of the 19 January 1958 earthquake, and eventually to the source region of the earthquake of 12 December 1979. The entire region had previously ruptured in the earthquake of 1906. The relocated hypocenters lie on the same plane to within the approximately 20-km uncertainty of the focal depths. Also, the main shocks nucleated at nearly the same distance from the Colombia Trench. These observations suggest that the heterogeneities between the 1942 and 1958 ruptures and between the 1958 and 1979 ruptures do not correspond to a major distortion of the downgoing slab but rather to either minor distortions of the slab or to regions of high friction or low available strain energy on a continuous fault surface. In particular, the heterogeneity between the 1958 and 1979 rupture zones seems to have been a high-strength barrier with dimensions much smaller than the dimensions of either of the rupture zones. The 1942 and 1958 earthquakes had source dimensions no larger than the 1979 main shock, but they had stronger aftershocks.This suggests that the arrest of earthquake rupture in 1979 left the plate boundary segment that had ruptured in 1906 in a state of lower stress than after the 1942 and 1958 earthquakes. Long-term seismicity in the decades preceding the 1979 earthquake occurred mostly outside or on the boundaries of the rupture area defined by the distribution of 1979 aftershocks. The intense aftershocks in 1958 within tens of kilometers of the eventual 1979 hypocenter may correspond to a long-term precursory seismic swarm for the 1979 earthquake.--Modified journal abstract.
AB - ABSTRACT: Late Cretaceous Diabase Group pillow basalts which make up much of the Western Cordillera are at least 81+ or -5 Ma in the El Tambo-El Penol area. 105-97 Ma hornblende and whole-rock dates from the ophiolitic Los Azules Complex indicate an Albian age of formation, although many dates are lower (65-62 Ma) owing the low-grade ocean-floor metamorphism. The metamorphic age distribution here supports an end of Cretaceous emplacement for the complex rather than the Early-Mid Cretaceous emplacement suggested for North Colombian ophiolites similarly aligned along the Romeral fault system. Tertiary dacites intruding the Los Azules Complex are 36-15 Ma.--Modified journal abstract.