No abstract

Interbasin ground water movement of 200 to 240 L/sec occurs as underflow beneath a mountainous surface water divide separating the topographically higher Salar de Michincha from the topographically lower Salar de Coposa internally drained basins in the Altiplano of northern Chile. Salt-encrusted flats (salars) and saline lakes occur on the lowest parts of the basin floors and comprise the principal evaporative discharge areas for the basins. Because a surface water divide separates the basins, surface water drainage boundaries do not coincide with ground water drainage boundaries. In the region, interbasin ground water movement is usually not recognized, but occurs for selected basins, and at places is an important component of ground water budgets. With increasing development of water for mining industry and potential exportation of ground water from the Altiplano for use at coastal cities, demonstration and quantification of interbasin movement is important for assessment of sustainable ground water development in a region of extreme aridity. Recognition and quantification of interbasin ground water underflow will assist in management of ground water resources in the arid Chilean Altiplano environment.

A seismic P wave velocity and bulk density model of the crust of the western Transverse Ranges of California along a north‐south profile near the city of Santa Barbara shows south to north crustal thickening and appreciable lateral inhomogeneity within the crust. The seismic model is developed by ray tracing based on data from a land‐sea refraction experiment, Pn arrivals from regional earthquakes, and near‐vertical arrivals from teleseisms. The density model is based on published gravity data (Bouguer on land and free air at sea). The model extends to the known oceanic lithospheric structure west of the southern California Borderland, providing a boundary condition for modeling crustal thickness. The Borderland crust south of the western Transverse Ranges is 23 km thick, and the Coast Ranges crust to the north is 31 km thick. A low‐density, low‐velocity feature associated with deep Neogene sediment in the Santa Barbara Channel extends to depths greater than 10 km. A local high‐density, high‐velocity feature is associated with exposures of Mesozoic mafic crystalline rock on Santa Cruz Island. Low‐density and velocity material is resolvable to 5‐km depth south of the East Santa Cruz Basin fault.

No abstract

A test‐stand experiment was conducted on neutron probe measurements using steel and Schedule 40 PVC access tubes to determine the effect of backfill grout in boreholes. The experiment used a moveable simulated vadose zone. Access tubes and grout do have masking effects on vadose zone measurements, but vadose zone moisture was detected through all configurations tested. Steel tubing has a smaller masking effect than PVC tubing. The masking effect of grout increased with borehole diameter. Although this experiment produced numerical results, conclusions drawn are qualitative in nature, rather than a quantitative calibration of the technique.