A narrowly spaced double-seismic zone in the subducting Nazca plate

LDEO Publication: 
Publication Type  Journal Article
Year of Publication  2004
Authors  Rietbrock, A.; Waldhauser, F.
Journal Title  Geophysical Research Letters
Volume  31
Issue  10
Pages  -
Journal Date  May 22
ISBN Number  0094-8276
Accession Number  ISI:000221609800004
LDEO Publication Number  6688
Key Words  intermediate-depth earthquakes; dehydration; crustal; mantle; chile

High-precision relocations of intermediate-depth earthquakes (80-130 km) below the Central Andes reveal a fine-scale double-layeredWadati-Benioffzone (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.


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URL  http://www.ldeo.columbia.edu/~felixw/papers/Rietbrock_Waldhauser_GRL2004.pdf
DOI  Doi 10.1029/2004gl019610