This study contributes to the understanding of shear failure development on the basis of macroscopic field data collected in latest Pleistocene-Holocene pyroclastic and fluvio-lacustrine deposits in the Pasto Valley, SW Colombia. Here there is a pervasive system of microfaults and joints. Right-lateral strike-slip microfaults strike N065 degrees, whereas left-lateral strike-slip microfaults strike N120 degrees. Three main joint sets strike N, N065 degrees and N020 degrees in decreasing order of frequency. Stress computation gives a horizontal a, trending similar to N060 degrees and a horizontal sigma(3) trending similar to N150 degrees, consistent with earthquake focal mechanisms and stress inversion of main faults. Synthetic shears dominate resulting from nucleation of older cracks. In the basement cropping out northeast of Pasto, the NE- to ENE-striking Buesaco, Aranda and Pasto Faults show evidence of latest Pleistocene-Holocene right-lateral strike-slip motions. The structures in the Pasto Valley can be interpreted as a Mode III damage zone representing the up-dip propagation of the main faults across the young volcano-sedimentary deposits. (C) 2005 Elsevier Ltd. All rights reserved.
Rovida, A., Tibaldi, A. (2005). Propagation of strike-slip faults across Holocene volcano-sedimentary deposits, Pasto, Colombia. JOURNAL OF STRUCTURAL GEOLOGY, 27(10), 1838-1855 [10.1016/j.jsg.2005.06.009].
Propagation of strike-slip faults across Holocene volcano-sedimentary deposits, Pasto, Colombia
TIBALDI, ALESSANDRO
2005
Abstract
This study contributes to the understanding of shear failure development on the basis of macroscopic field data collected in latest Pleistocene-Holocene pyroclastic and fluvio-lacustrine deposits in the Pasto Valley, SW Colombia. Here there is a pervasive system of microfaults and joints. Right-lateral strike-slip microfaults strike N065 degrees, whereas left-lateral strike-slip microfaults strike N120 degrees. Three main joint sets strike N, N065 degrees and N020 degrees in decreasing order of frequency. Stress computation gives a horizontal a, trending similar to N060 degrees and a horizontal sigma(3) trending similar to N150 degrees, consistent with earthquake focal mechanisms and stress inversion of main faults. Synthetic shears dominate resulting from nucleation of older cracks. In the basement cropping out northeast of Pasto, the NE- to ENE-striking Buesaco, Aranda and Pasto Faults show evidence of latest Pleistocene-Holocene right-lateral strike-slip motions. The structures in the Pasto Valley can be interpreted as a Mode III damage zone representing the up-dip propagation of the main faults across the young volcano-sedimentary deposits. (C) 2005 Elsevier Ltd. All rights reserved.
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