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Extension related to a high topography : results from a microearthquake survey in the Andes of Peru and tectonic implications

Authors
Publication Date
Keywords
  • Sismotectonique
  • Faille
  • Contrainte De Cisaillement
  • Compression Tectonique
  • Extension Tectonique
  • Topographie
  • Orogenese
Disciplines
  • Computer Science
  • Earth Science

Abstract

Extension related to a high topography : results from a microearthquake survey in the Andes of Peru and tectonic implications Geophys. J . Int. (1989) 98, 281-292 Extension related to a high topography: results from a microearthquake survey in the Andes of Peru and tectonic implications Jacques Deverch*re*, Catherine Dorbatht and Louis Dorbatht Loborotoire de Giophysique, Britiment 509, UA du CNRS 730, Universiti Poris-Sud, 91405 Orsay Cedex, Fronce ond t ORSTOM, 213 rue Lofoyette, 75480 Pork Cedex 10, ond lnstitut de Physique du Globe de Strasbourg, 5 rue RenP Descortes, 67084 Strasbourg, Fronce Accepted 1989 February 6. Received 1989 February 2; in original form 1988 April I I SUMMARY A microearthquake study performed in 1985 October-November in the Cordillera Blanca (western Cordillera of northern Peru) allowed us to make a precise mapping of its shallow seismicity. 160 local events are accurately located in the vicinity of an active normal fault system showing a vertical displacement of 4500 m over the last 7Myr. Part of the seismic activity can be related to this west-dipping system, but a great number of events indicate a new seismic zone situated under the highest peaks of the chain. By using an inversion algorithm of P-wave polarities, we show a regional deviatoric stress tensor which defines an extensional axis in a direction approximately orthogonal to the Andean structures. This result is in good agreement with the theoretical distribution of stresses expected in an elongated high topography bordered by tectonic convergent zones. Moreover, we suggest that an absolute uplift of this young batholith occurs on a normal fault system and that this phenomenon is partly due to buoyancy forces originating in its crustal root. Key words: intraplate seismicity, active fault, extension, Andes, Peru, stress tensor, gravita- tional body force 1 INTRODUCTION Evidence of an extensional state of stress has been reported in many parts of the highest ch

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