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Geological constraints on the kinematics and fault-plane solution of the Quiches Fault Zone reactivated during the 10 November 1946 Ancash earthquake, northern Peru

Abstract:

The earthquake (Mw=6.8) produced surface faulting along the Quiches normal-slip fault. Field studies reported discontinuous NW-SE to NNW-SSE-striking seismic scarps that displace Quaternary glacial moraines and outwash, as well as Mesozoic sedimentary rocks. Structural analyses show that the 1946 normal displacement was accompanied by a small left-lateral slip component. There is evidence of a single normal-fault displacement before the 1946 seismic event that offset late Pleistocene glacial moraines. This indicates an approximate recurrence interval of more than 13 000 ± 1000 years for the major events, suggesting a rate of net vertical displacement on the fault of less than 0.25 mm/yr. Kinematic analysis suggests that the state of stress in the High Andes is regionally and locally homogeneous with only minor changes in the stress directions adjacent to major structures such as the Maranon Thrust and Fold Belt. The regional stress field is also discussed. -from Authors