Premium
A narrowly spaced double‐seismic zone in the subducting Nazca plate
Author(s) -
Rietbrock A.,
Waldhauser F.
Publication year - 2004
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1029/2004gl019610
Subject(s) - geology , seismology , induced seismicity , oceanic crust , crust , subduction , slab , extensional definition , mantle (geology) , plate tectonics , geophysics , tectonics
High‐precision relocations of intermediate‐depth earthquakes (80–130 km) below the Central Andes reveal a fine‐scale double‐layered Wadati‐Benioff zone (WBZ). Upper and lower band of seismicity are separated by about 9 km and occur at the top of the oceanic crust and in the uppermost oceanic mantle, respectively. Analysis of focal mechanisms and waveform similarities indicate that fluid processes are causing the events. Earthquakes in the oceanic crust occur on pre‐existing normal faults due to hydraulic embrittlement from metamorphic dehydration, and on subvertical faults that connect the two layers in a narrow depth range. Extensional faulting predominates in both layers, indicating that slab pull forces are the dominant stress source superseding possible unbending forces in this segment of the Nazca plate.