Studies in quaternary geology of Arizona: Active tectonics relationship of soils to surficial geology

The Quaternary geology of Arizona contains a record of deformation, erosion, and transport of rock and alluvium. The Colorado Plateau shows an interesting contrast between low deformation rates and distinctive tectonic geomorphology. The 250-km long Hurricane fault, the most active locus of deformation in Arizona, is an excellent area to examine the geomorphic response to tectonic change; it presents a seismic hazard to the rapidly growing populations of southwestern Utah.; Paleoseismic studies on the Shivwitz section of the Hurricane fault in northwestern Arizona yielded slip rates of ∼0.05 to 0.3 mm/year using displaced alluvial fans. The 0.85 ± 0.06 Ma Moriah Knoll basalt has been offset 204m that indicates a maximum long-term slip rate of 0.24 ± 0.02 mm/yr. Fault trenching of a late Quaternary fan suggests two surface-rupturing events in the last 15–78 ky with the total vertical surface offset of 4.6 m; recurrence interval is estimated at 2.5 to 22 ky. The most recent event produced displacement of up to ∼2.5 m. A radiocarbon age of soil related to the most recent event produced a calibrated age of 8900–10,300 (2-σ) years before present; the results from the trenching indicate a 0.06 to 0.28 mm/yr slip rate. Ruptures of this size on the Shivwitz could potentially produce M6–7.2 earthquakes.; Bedrock scarps are common evidence of fault displacement and fluvial incision. Weathering rinds as a proxy were tested to estimate the amount and timing of surface exposure. Observations did not fit the simple model; the rind thickness appeared to increase towards the base of the scarp. The implications are for progressive removal of the scarp surface over time, probably primarily by chemical weathering.; Expansive and collapsible soils cause damage to infrastructure in semi-arid parts of the United States. The spatial correlation of geology to soil engineering properties was tested for estimating the distribution of problem soils in the Phoenix metropolitan area. Pleistocene fluvial terrace units may contain higher percentages of expansive clay and silt than other units. Older geomorphic surfaces (>250 ka) were found to have strong caliche development and clay accumulation that may affect soil moisture infiltration and cause problems with shrink/swell.