1 Introduction and Background
 In subduction zones, strain and stress in the upper plate reflect conditions and mechanical properties along the underlying plate boundary fault, and the material properties of the overriding and downgoing plates [e.g., Davis et al., 1983; Wang and Hu, 2006]. Forearc basins, common features at many convergent margins [e.g., Berglar et al., 2008; Contardo et al., 2008; Dickinson, 1995], provide a record of sedimentation and deformation on the upper plate that has been linked to upper plate and subduction megathrust mechanical behavior. For example, Wells et al.  and Song and Simons  suggest that large forearc basins correlate with asperities on the plate boundary that may act as source regions for great earthquakes. On the basis of a mechanical model of upper plate stresses, Wang and Hu  suggest that forearc basins should form above a stable inner wedge, which overlies the interseismically locked portion of the plate interface. In the model of Fuller et al., , sedimentation in the forearc basin stabilizes the wedge through the maintenance of a horizontal slope above a steepening decollement. These models predict that large forearc basins and the underlying inner accretionary wedge should undergo little permanent deformation during the seismic cycle, and may be characterized by extensional stresses following large earthquakes [e.g., Wang and Hu, 2006]. However, direct observations of strain and stress in these settings are usually limited to the expression of deformation at the seafloor, and to regions accessible to drilling.
 Offshore southwest Japan, the Nankai Trough accretionary complex is the focus of the Nankai Trough Seismogenic Zone Experiment (NanTroSEIZE), a major Integrated Ocean Drilling Program (IODP) drilling project, and of a 3-D seismic survey acquired in support of drilling [Kinoshita et al., 2009; Moore et al., 2009] (Figure 1). The high-resolution seismic volume images a complete transect of the margin, and structures within 2 km of the seafloor are imaged in particularly excellent detail [e.g., Moore et al., 2009] (Figures 2 and 3). A large population of recent and active normal faults in the forearc basin provides an opportunity to document basin-wide patterns of both strain and stress. In this study, we (1) investigate the timing, orientation, and magnitude of strain and stress in the Kumano Basin over the last 0.44 Myr through structural and kinematic analyses of this fault population, and (2) discuss these results in the context of borehole and core-scale indicators of deformation and stress. This work follows from a companion paper by Moore et al. , which characterizes the orientations and timing of normal faults in the basin using seismic coherency analysis.
1.1 Geologic Setting and Previous Work
 The Nankai Trough is formed by the subduction of the Philippine Sea Plate beneath the Eurasian continental plate at an azimuth of 300°–315° and a velocity of 4.1–6.5 cm yr−1 [Seno et al., 1993; Miyazaki and Heki, 2001] (Figure 1). Along the NanTroSEIZE transect, the sediment section on the subducting plate includes ~1.1 km of Miocene pelagic and hemipelagic sediments of the Shikoku Basin, overlain by a ~1.3 km thick package of trench deposits [e.g., Moore et al., 2009] (Figure 2). The modern accretionary prism incorporates the entire thickness of the trench deposits and at least half of the underlying Shikoku Basin sequence [Park et al., 2002]. The Nankai Trough, with its long record of great earthquakes and tsunami [Ando, 1975], has been the focus of numerous studies investigating subduction zone processes, including geodetic surveys [Aoki et al., 1982], seismic reflection surveys [Park et al., 2002; Moore et al., 2009], and IODP and Ocean Drilling Program (ODP) drilling [e.g., Karig et al., 1975; Kagami et al., 1986; Taira et al., 1991; Moore et al., 2001; Kinoshita et al., 2009; Saffer et al., 2010]. As part of the NanTroSEIZE project, recent IODP expeditions have drilled 11 boreholes spanning from seaward of the frontal thrust to 25 km landward of the forearc high in the Kumano Basin (Figures 1 and 2).
 The Kumano forearc basin is bounded at its seaward edge (~30 km from the trench) by a prominent bathymetric “notch” associated with a network of transpressive faults termed the Kumano Basin Edge Fault Zone (KBEFZ) [Martin et al., 2010]. Just seaward of the KBEFZ, a major out of sequence splay fault, termed the “megasplay”, separates the active outer accretionary wedge from an inner wedge that is characterized by higher seismic velocity [Park et al., 2002; Moore et al, 2009] (Figure 2). The 3-D seismic survey covers the seaward-most ~25 km of the basin (Figures 1 and 2). The basin sediments consist primarily of mudstones with sandy intervals. The section ranges from ~1 to >2.5 km thick, and is <2 Myr old [Expedition 314 Scientists, 2009; Saffer et al., 2010]. The landward dip of strata increases progressively with proximity to the forearc high, and bed dips are progressively gentler in younger strata, indicating successive tilting associated with slip on the megasplay fault [Strasser et al., 2009; Gulick et al., 2010]. The forearc basin sediments unconformably overlie Miocene age sediments of the accretionary prism [Expedition 314 Scientists, 2009; Saffer et al., 2010]. The basin sediment package thickens significantly in the landward portion of the basin, generally due to an increased depth to the top of the prism, but also enhanced locally by the infilling of several major depressions. The entire section is cut by normal faults estimated to have initiated from ~1.0 to 0.3 Ma [Gulick et al., 2010]. Many of these faults are recently active, penetrating to within a few reflectors of the seafloor or forming seafloor scarps (Figure 3; see also supporting information).
 NanTroSEIZE drilling has recovered cores, collected logs, and measured a suite of downhole properties across a transect from the incoming plate to ~55 km landward of the trench [Kinoshita et al., 2009] (Figure 2). The orientations of maximum and minimum horizontal stresses (SHmax and Shmin, respectively) defined from wellbore failures (borehole breakouts and drilling-induced tensile fractures) in these holes demonstrate that in the outer wedge, the azimuth of maximum horizontal compression is subparallel to the subduction direction [Lin et al., 2010]. At Site C0002, ~5 km landward of the basin's seaward edge, SHmax is subparallel to the trench (rotated 90° relative to that in the outer wedge). At Site C0009, 20 km landward, SHmax is again subparallel to the subduction direction. This suite of results is consistent with horizontal stress orientations inferred from seismic velocity anisotropy within the upper plate, which indicates a gradual rotation of SHmax with distance landward from the area of Site C0002 [Tsuji et al., 2011].