Microseismicity and focal mechanisms of the intermediate-depth Bucaramanga nest, Colombia
The Bucaramanga nest of intermediate-depth seismicity in northern Colombia was investigated from microearthquakes (m/sub b/less than or equal to4.3) recorded from June 20 to July 6, 1979, by a local array of 12 digital three-component seismographs. Of 161 events studied, 142 are from the nest and 19 define a thin Wadati-Benioff (W-B) zone, mainly from 110 to 190 km depth. The W-B zone, part of the Bucaramanga segment, strikes N10/sup 0/ E with a dip increasing wtih depth from 30/sup 0/ E to near-vertical beneath the nest. The 89 best located events from within the nest define a volume of about 8 km (NW) by 4 km (NE) by 4 km (depth) centered at 161 km depth, with relative location accuracies of +- 0.5 to +- 1.0 km. Double-couple fault plane solutions of 59 events were determined from an objective procedure using P wave polarities and S/P amplitude ratios. There is no dominant trend in focal mechanisms nor any reasonable correlation with regional stress patterns or previously determined mechanisms from teleseismic data. The subduction and assimilation of a linear feature (such as an island arc undergoing a phase transformation) may explain the existence of the Bucaramanga nest. However, the extraordinarily high rate of seismicity suggests that the nest may be moving rate several orders of magnitude faster than the rate of relative plate motion alone. The intense seismicity and variation in focal mechanisms suggest that the nest represents some aspect of stress release associated with the ascent of fluids, perhaps brine or magma, that will ultimately result in the initiation of volcanic activity over this recently emplaced W-B zone. copyright American Geophysical Union 1987
- Research Organization:
- Department of Geology and Geophysics, University of Wisconsin-Madison
- OSTI ID:
- 5466313
- Journal Information:
- J. Geophys. Res.; (United States), Vol. 92:B13
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
COLOMBIA
EARTHQUAKES
BENIOFF ZONE
DEPTH
DIGITAL SYSTEMS
DYNAMICS
EARTHQUAKE MAGNITUDE
MAGMA
PHASE TRANSFORMATIONS
SEISMIC P WAVES
SEISMIC SURVEYS
SEISMICITY
SEISMOGRAPHS
THREE-DIMENSIONAL CALCULATIONS
DIMENSIONS
GEOPHYSICAL SURVEYS
LATIN AMERICA
MEASURING INSTRUMENTS
MECHANICS
SEISMIC ARRAYS
SEISMIC DETECTORS
SEISMIC EVENTS
SEISMIC WAVES
SOUTH AMERICA
SURVEYS
580201* - Geophysics- Seismology & Tectonics- (1980-1989)