The Mugi Mélange located in western Shikoku of the Shimanto Belt shows systematic Y‐P deformation fabrics formed by microshear and pressure solution that penetrate throughout the mélange pile. Magnetic susceptibility ellipsoids obtained from the anisotropy of magnetic susceptibility (AMS) are highly oblate. Maximum and minimum axes of the ellipsoids are consistent with the shear orientation of the mélange and the mean pole of P surfaces, respectively. This agreement suggests that the Mugi Mélange was formed as a result of underthrusting of trench filling sediment. Vitrinite reflectance ranges from 2.52% to 3.08%, which corresponds to a maximum paleotemperature of ∼180–200°C. Pseudotachylyte, evidence of a seismogenic slip, was found in the upper boundary roof fault of the Mugi Mélange. However, there is not a thermal gap between the mélange and the overlying coherent piles, and the temperature from vitrinite reflectance gradually rises downward from the coherent piles to the mélange beyond the boundary fault, which suggests that paleoisotherms parallel the boundary fault orientation. The isotherms in the seismogenic zone are estimated as subparallel to the plate boundary décollement. Therefore the setting of the cataclastic boundary fault, which includes pseudotachylyte, appears to be a major plate boundary thrust or a subhorizontal splay fault. A probable geologic setting that accounts for the Mugi Mélange and the seismogenic roof fault is partitioning of the slip along the plate boundary fault in space and time: interseismic slip in the mélange and seismic slip along the roof fault.

Systematic changes in fabrics of melanges have been detected in rocks of the Shimanto Belt, Japan. Several shear indicators, including S-C structures, Riedel shears, and folds, in the melanges indicate consistent sense of shear both in outcrop and microscopic scales. The deformation mechanisms, independent particulate flow and pressure solution, suggest that the deformation started under unlithified conditions and progressed through lithification due to strain hardening. After lithification, cataclastic deformation occurred locally, but most of the earlier deformation features are preserved. This process appears to have taken place along the decollement beneath the off-scraped accretionary prism. Sinistral reverse sense of shear is observed in the Campanian melange, whereas a dextral reverse sense of shear is preserved in the early Eocene melange in the Shimanto Belt. This change in fabric is interpreted to be linked to a change in relative convergence between the subducting and overriding plates. Three different plate models have been proposed for the Late Cretaceous to Early Tertiary western Pacific margin: (1) subduction of the Kula-Pacific ridge along the continental margin, (2) subduction of the Pacific Plate since 85 Ma, and (3) subduction of the aborted Kula-Pacific ridge after 43 Ma. The observed change in fabric of melange is consistent only with the third model, which predicts a change in relative convergence from sinistral to dextral at the appropriate time. the South Armonian Shear Zone, J. Struct. Geol., 1, 31-42, 1979. Byrne, T., Early deformation in melangeterranes of the Ghost Rocks Formation, Kodiak Islands, Alaska, Spec. Pap. Geol. Soc. Am., 198, 21-51, 1984. Byrne, T., and L. DiTullio, Evidence for changing plate motions in southwest Japan and reconstructions of the Philippine Sea Plate, Island Arc, 1, 148-165, 1992. Charvet, J., M. Faure, O. Fabbri, D. Cluzel, and H. Lapierre, Accretion and collision during East-Asiatic margin building-A new insight on the peri-Pacific orogenies, vectors and fault mechanics in the Makran accretionary wedge, southwestern Pakistan,

In this study, we investigate the extent to which viscoelastic velocity perturbations (or “ghost transients”) from individual fault segments can affect elastic block model‐based inferences of fault slip rates from GPS velocity fields. We focus on the southern California GPS velocity field, exploring the effects of known, large earthquakes for two end‐member rheological structures. Our approach is to compute, at each GPS site, the velocity perturbation relative to a cycle average for earthquake cycles on particular fault segments. We then correct the SCEC CMM4.0 velocity field for this perturbation and invert the corrected field for fault slip rates. We find that if asthenosphere viscosities are low (3 × 1018 Pa s), the current GPS velocity field is significantly perturbed by viscoelastic earthquake cycle effects associated with the San Andreas Fault segment that last ruptured in 1857 (Mw = 7.9). Correcting the GPS velocity field for this perturbation (or “ghost transient”) adds about 5 mm/a to the SAF slip rate along the Mojave and San Bernardino segments. The GPS velocity perturbations due to large earthquakes on the Garlock Fault (most recently, events in the early 1600s) and the White Wolf Fault (most recently, the Mw = 7.3 1952 Kern County earthquake) are smaller and do not influence block‐model inverted fault slip rates. This suggests that either the large discrepancy between geodetic and geologic slip rates for the Garlock Fault is not due to a ghost transient or that un‐modeled transients from recent Mojave earthquakes may influence the GPS velocity field.

Map to microscopic‐scale structural analysis of the Hanazono Assemblage of the Shimanto Belt in SW Japan, an excellent example of a deeply buried accretionary complex, indicates a detailed process from underthrusting to underplating. The earliest underthursting process is recorded in fabric of melange, which has deformed by shear along the decollement, characterized by thinning strain due to extensional breakage of blocks of sandstone and exotic materials, such as basalt and pelagic sediments of oceanic affinities. The deformation mechanism for melange formation for domain I is plastic flow, concordant with metamorphic grade, which is higher than that of domain II. The deformation mechanism for domain II is predominantly pressure solution partly with grain‐scale brittle breakage for the less metamorphosed part of the Hanazono Assemblage. The posterior underplating process recorded is contraction and thickening due to thrust stacking and folding. Locations of the folds developed beneath thrusts are emphasized because they are a line of evidence of thickening. The main deformation mechanism of the second stage is plastic flow for domain I and cataclasis for domain II. The cataclasis in domain II may be a result of change in strain rate and seems to be related to seismicity at the time of underplating. Kinematics deduced from fabric analysis of the earliest deformed melange indicates a good consistency with a relative plate motion between the Eurasian and oceanic plates that is estimated from a hot spot reference plate circuit model by Engebretson et al. [1985], while that of the subsequent thrusting is not. This fact suggests that strain partitioning in association with oblique subduction of oceanic plate was minimum during subduction. Another possibility for strain partitioning is the requirement of coupling between plates that are recorded by the deformation mechanisms.

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