--> Abstract: Deterministic and Stochastic Approaches for Evaluating Multiple Scales of Santa Clara Valley Hydrostratigraphy, by N. M. Johnson; #90958 (1995).

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Abstract: Deterministic and Stochastic Approaches for Evaluating Multiple Scales of Santa Clara Valley Hydrostratigraphy

Nicholas M. Johnson

Approaches for evaluating Santa Clara Valley hydrostratigraphy range from deterministic to stochastic depending on the scale of structure considered. Tectonic, eustatic, and climatic influences have imparted an overall basin structure that accounts conceptually for recognized major aquifer and aquitard zones. Nevertheless, the basin fill consists of complexly interfingered fan and channel deposits derived from the valley's commingling streams. As such, these major zones have obscure boundaries and highly heterogeneous internal structures. A statistical evaluation of well perforations reveals four major aquifer-aquitard cycles within 800 ft (250 m) depth. This subdivision provides a framework for interpreting the distribution of depositional environments from available geo ogic cross sections. Geostatistical correlations among well-perforation indicators confirm a eustatic influence on hydrostratigraphy toward the basin center, but caution against the inference of large channel structures in most proximal fan areas. Detailed geostatistical analysis of shallow (130 ft, 40 m) borehole data from proximal, medial, and distal sites demonstrates widely ranging spatial correlation among aquifer-aquitard indicators at relatively small scales. Channel deposits along Coyote Creek in the proximal Edenvale area are correlated up to 80% within distances of about 1,600 ft (500 m). Near the baylands in Sunnyvale, aquifer-aquitard indicators are correlated only about 40% within distances of 20 ft to 250 ft (6 m to 80 m). In a medial fan area near downtown San Jose, maximum correlation distances are similar to Eden vale but the maximum degree of correlation is only about 40% at distances >=40 ft (12 m), similar to Sunnyvale.

AAPG Search and Discovery Article #90958©1995 AAPG Pacific Section Meeting, San Francisco, California