Chen, P., C. R. Bina, and E. A. Okal, A global survey of stress orientations in the slab as revealed by intermediate-depth earthquakes, Eos, Transactions of the American Geophysical Union, 83, Fall Meeting Supplement, S51A-1012, 2002.
Several mechanisms have been proposed as contributors to the states of stress in downgoing slabs at intermediate depths (70-300 km). To appraise these models, we first determine the regional strike and dip of subducting slabs from relocated seismicity (Engdahl et al., 1998) for the circum-Pacific area. Cylindrical projections are adopted for arcuate areas (e.g., Mariana and Ryukyu arc, etc.). The regional slab coordinates thus derived are used to project the P and T axes of intermediate-depth earthquakes, using seismicity from the Harvard CMT catalogue enhanced by pre-1976 events inverted from hand-digitized seismograms (Chen et al., 2001). We characterize each region as either down-dip-stress-dominant or non-down-dip-stress-dominant, according the number of events. For the former regions, we find that: (1) The regional seismic distributions associated with down-dip compression or down-dip extension are consistent with a thermo-mechanical model, except for the Ryukyu arc. (2) Slab thermal parameters indicate that colder slabs are more likely to exhibit down-dip compression, suggesting a role for thermally induced perturbations of phase transition boundaries. (3) In most regions, conjugate P (or T) axes are oriented in a slab-normal direction, supporting the hypothesis of earthquake occurrence by reactivation of fossil faults. For the latter regions, we find that lateral extension is associated with regions of both small arc radius and steep dip angles (e.g., Mariana arc and South Sandwich islands), and that lateral compression is associated with linear arcs and shallow dips, consistent with the predictions of the punctured-ping-pong-ball model (Frank, 1968).Copyright © 2002 American Geophysical Union