We present results from differential Global Positioning System (GPS) surveys of seven alignment arrays and four continuous GPS sites along the creeping segment of the San Andreas fault. Surveys of four alignment arrays from the central creeping segment yield 33-to 36-year average minimum slip rates of 21-26 mm/yr. These rates are consistent with previous alignment array surveys spanning a 10-year period and with rates determined by creepmeters, indicating approximate steadystate creep along the central creeping segment for at least 35 years. Motion between continuous GPS sites that span the central creeping segment is 28.2 ‫ע‬ 0.5 mm/yr for two sites that are 1 km apart and 33.6 ‫ע‬ 1 mm/yr for two sites that are 70 km apart. Slip rates therefore increase with distance from the creeping segment of the San Andreas fault. All rates reported here are significantly slower than the 39 ‫ע‬ 2 mm/yr rate predicted for motion between the Sierra Nevada-Great Valley block and the Pacific plate. Repeat surveys of three alignment arrays following the 2004 Parkfield earthquake demonstrate that its coseismic and short-term postseismic offsets decrease rapidly with distance from the epicenter, from 150 mm to 15 mm to Ͻ5 mm at respective distances of 9, 36, and 54 km to the northwest. Continuous GPS data confirm that little coseismic and postseismic slip occurred along the central creeping segment. Geodetic and geologic slip rates are compared and different models for the accommodation of transcurrent deformation across the creeping segment are discussed.

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Decades ago, pioneering petroleum geologist Wallace Pratt pointed out that oil is first found in the human mind. His insight remains true today: Across geoscience specialties, the human mind is arguably the geoscientist's most important tool. It is the mind that converts colors and textures of dirt, or blotches on a satellite image, or wiggles on a seismogram, into explanatory narratives about the formation and migration of oil, the rise and fall of mountain ranges, the opening and closing of oceans. Improved understanding of how humans think and learn about the Earth can help geoscientists and geoscience educators do their jobs better, and can highlight the strengths that geoscience expertise brings to interdisciplinary problem solving.

[1] We use GPS data to measure the aseismic slip along the central San Andreas fault (CSAF) and the deformation across adjacent faults. Comparison of EDM and GPS data sets implies that, except for small-scale transients, the fault motion has been steady over the last 40 years. We add 42 new GPS velocities along the CSAF to constrain the regional strain distribution. Shear strain rates are less than 0.083 ± 0.010 mstrain/yr adjacent to the creeping SAF, with 1 -4.5 mm/yr of contraction across the Coast Ranges. Dislocation modeling of the data gives a deep, long-term slip rate of 31-35 mm/yr and a shallow (0 -12 km) creep rate of 28 mm/yr along the central portion of the CSAF, consistent with surface creep measurements. The lower shallow slip rate may be due to the effect of partial locking along the CSAF or reflect reduced creep rates late in the earthquake cycle of the adjoining SAF rupture zones.

New continuous and differential global positioning system (GPS) measurements of recent slip rates and 30 yr alignment-array offsets from the central creeping segment of the San Andreas fault yield a maximum right-lateral slip rate of 25 ؎ 1 mm/yr. This slip rate is 20% slower than the 30 mm/yr slip rate accepted for this segment of the fault and 35% slower than the 39 mm/yr slip rate predicted between the Sierra Nevada-Great Valley block and the Pacific plate. New continuous GPS measurements between pairs of sites that flank the creeping segment at intersite distances of 1.0 km and 70 km give relative fault-parallel slip rates of 28 ؎ 2 and 30 ؎ 2 mm/yr, respectively. These observations indicate that right-lateral deformation rates increase with distance from the fault. Possible explanations for the gradient observed in the geodetic data are elastic strain accumulation along the creeping segment or significant distributed deformation on off-fault structures.