Figure 1

Tectonic context. Of the (a) Himalaya-Sumatra and (b) Taiwan-Ryukyu collision subduction systems. The red beach ball shows the location and focal mechanism of the Mw 9.3 Sumatra-Andaman earthquake on December 26, 2004. The red rectangle shows the position of Figure 2. LOFZ, Luzon-Okinawa fracture zone; IFZ, Investigator fracture zone. (c, d) The color bars show the stress orientations obtained from different fault types, which were retrieved from the World Stress Map (WSM) (http://dc-app3-14.gfz-potsdam.de/) (Heidbach et al.2010). Red indicates normal faulting, green indicates strike slip, and blue indicates thrust faulting. Numbered circles show the orientations of the P-axis (red dot) and T-axis (green dot) in an equal-area projection of the lower hemispheres of the focal spheres from the global centroid-moment-tensor (CMT) catalog from 1976 to December 26, 2004 for the Sumatra subduction system and from 1976 to December 31, 2011 along the Ryukyu subduction system. The patterns for groups 1 and 2 were calculated from the thrust and normal faulting earthquakes along the subduction zone shown by the yellow contour, respectively. Group 3 used the events in the collision zones (yellow dashed contour), and group 4 used the events in the oceanic domain of the subducting plate (yellow dotted contour). Relative plate motions, shown by the white arrows, are based on the MORVEL model from the plate motion calculator (http://www.unavco.org/community_science/science-support/crustal_motion/dxdt/model.html) (DeMets et al.2010).