Relationship between bend‐faulting at trenches and intermediate‐depth seismicity

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  • César R. Ranero
    IFM‐GEOMAR and SFB754 Wischhofstrasse 1‐3, D‐24148 Kiel Germany
  • Antonio Villaseñor
    Institute of Earth Sciences “Jaume Almera,” CSIC, Lluis Solé i Sabarís s/n E‐08028 Barcelona Spain
  • Jason Phipps Morgan
    Department of Geological Sciences Cornell University EAS 4164 Snee Hall, Ithaca New York 14853 USA
  • Wilhelm Weinrebe
    IFM‐GEOMAR and SFB754 Wischhofstrasse 1‐3, D‐24148 Kiel Germany

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<jats:p>We have studied faulting associated with bending of the incoming oceanic plate along segments of Middle America and Chile subduction zones and its relationship to intermediate‐depth intraslab seismicity and slab geometry. Multibeam bathymetry shows that bending‐related faulting forms patterns made of sets of faults with orientations ranging from parallel to almost perpendicular to the trench axis. These fault patterns may change along a single subduction zone within along‐strike distances of several hundred kilometers or less. Where available, near‐trench intraplate earthquakes show normal‐fault focal mechanisms consistent with mapped bending‐related normal faults. The strike of bending‐related faults in the incoming oceanic plate is remarkably similar to the strike of the nodal planes of intermediate‐depth earthquakes for each segment of the study areas. This similarity in strike is observed even for faults oriented very oblique to the trench and slab strikes. Thus, in the studied subduction zones, results strongly support that many intraslab earthquakes do not occur along the planes of maximum shear within the slab and that much intermediate‐depth seismicity occurs by reactivation of faults formed by plate bending near the trench. Furthermore, a qualitative relationship between trench faulting and intraslab seismicity is indicated by segments of the incoming plate with pervasive bend‐faulting that correspond to segments of the slabs with higher intermediate‐depth seismicity.</jats:p>

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