| AbstractThe
shallow, mb = 5.3, 1986 earthquake that affected the Cuzco region
reactivated the 18-km-long Chincheros-Qoricocha faults in the central
part of the Cuzco fault system. Although the event has a moderate
magnitude, clear surface ruptures were observed to total 3 km in length,
with maximum 10-cm normal displacements. Fault kinematics related to the
earthquake, analyzed where the Qoricocha fault had a maximum surface
fault displacement, is in agreement with roughly N-S extension. The
normal fault mechanism proposed for this earthquake is compatible with
the surface kinematic analysis. Seismic activity prior to the 1986
earthquake is deduced from analysis of Holocene scarps. Trench exposures
give evidence for at least three fault displacements, suggesting an
average recurrence interval of the order of a few thousand years for
surface-rupturing seismic events. These fault reactivations, with
vertical displacement ranging from 0.6 to 2 m, were related to seismic
events of Mw magnitude probably ranging from 5.8 to 6.9.
Structural analyses of Holocene faults indicate that the
Chincheros-Qoricocha fault activity was related to roughly N-S-trending
extension, characterized by a horizontal N-S-trending 3 axis and a vertical
1 axis. The N-S
extensional tectonics that controlled the Holocene and 1986
Chincheros-Qoricocha fault activity are the typical deformational
pattern of the Peruvian High Andes and seem to be in agreement with
compensated high topography.Return to Table of
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