Open AccessExtension related to a high topography: results from a microearthquake survey in the Andes of Peru and tectonic implications
Author(s) -
Deverchère Jacques,
Dorbath Catherine,
Dorbath Louis
Publication year - 1989
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.1989.tb03352.x
Subject(s) - geology , microearthquake , seismology , tectonics , induced seismicity , crust , extensional definition , fault (geology) , lithosphere , cauchy stress tensor , geodesy , inversion (geology) , geophysics , physics , classical mechanics
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 7 Myr. 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.