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Lithosphere in some regions undergoes slow, distributed deformation, contrary to the plate tectonic assumption that deformation is localized along narrow plate boundaries. The nature and magnitude of slow, distributed deformation can be studied using rigid-plate models as a tool for locating and modeling this slow deformation. Here, four regions of slow deformation are examined, the Pacific-North America boundary in western North America, the Owen Fracture Zone, the diffuse India-Australia plate boundary, and the southern Indian Ocean. To construct the rigid-plate models, over 600 data, including 0-3 Ma spreading rates derived from marine magnetic anomalies, transform azimuths derived from bathymetric and Seasat altimetric data, earthquake epicenters, and offset magnetic lineations, and earthquake slip vectors are used. The first study resolves a long-standing discrepancy between Pacific-North America motion predicted by rigid-plate models and Pacific-North America motion measured using geodetic, geologic, and seismologic observations of deformation in western North America. The rate of motion inferred from magnetic anomalies in the Gulf of California is 48 mm/yr, 10 mm/yr lower than prior models, but consistent with the rate predicted by global plate motions. The reduced rate implies that strike-slip motion on faults west of the San Andreas is 60% less than thought before, a result consistent with independent observations. The final three studies attempt a synthesis of present-day plate motions in the Indian ocean. India-Arabia-Africa and Africa-Antarctica-Australia motions are modeled and shown to be consistent with circuit closure, with the exception of data near the Macquarie triple junction, which suggest deformation of the Australian plate in the Tasman Sea. Using these two three-plate models, the final study examines how well motion between Australia and India along a boundary characterized by slow, distributed deformation can be predicted. The predictions of the rigid-plate model agree well with the rate and direction of motion inferred from independent observations. Unlike published models of global and Indian Ocean plate motions, our model has no systematic misfits exceeding 2 mm/yr, suggesting the Indian Ocean will be a strong link in future global plate motion models.
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