Donald J. Stierman

Mapping hydraulic fractures using a borehole-to-surface electrical resistivity method

Abstract A series of shallow-depth hydraulic fracturing experiments was carried out in the summer of 1988 at the Elda landfill near Cincinatti, Ohio and mise-a-la-masse (MLM) borehole-to-surface resistivity measurements were obtained in an attempt to detect the fracturing. The well casing of an injection borehole was energized and potentials were measured at various points on the surface near the borehole before and after hydraulic fracturing was performed with a conductive fluid. Forward and inverse modeling algorithms based on the DC alpha center method were developed and tested with synthetic data to create a tool for interpretation of the experimental data. The alpha center forward algorithm incorporates a vertical line source of current to model an energized steel well casing. The advantages of the alpha center method are its speed and simplicity, and its ability to handle 3D geometry and indicate positions of conductive inhomogeneities. The forward solution is incorporated into an iterative least-squares inversion algorithm, with constraints applied to the alpha center parameters to facilitate modeling of fractures.

Electrical methods of detecting contaminated groundwater at the stringfellow waste disposal site, riverside county, California

At the Stringfellow Class I waste-disposal site near Riverside, California, the influence of variations in groundwater chemistry and saturation on electrical measurements made from the surface was tested Spontaneous potential, D C electrical sounding, dipole-dipole resistivity profiles, and mise-a-la-masse measurements were employed to investigate the sub-surface migration of the acidic fluids deposited in this site between 1956 and 1972 Mise-a-la-masse exploration conducted at the downstream edge of the site detected a major anomaly which, on excavation, proved to be the signature of a previously unsuspected leak from the surface disposal ponds on the site Downstream from the site, a dipole-dipole profile and electrical soundings correlate well with electrical conductivity of groundwater obtained from monitoring wells This study demonstrates that geophysical methods may be used to search for and map leaks from toxic chemical waste dumps

A study of the depth of weathering and its relationship to the mechanical properties of near-surface rocks in the Mojave Desert

Weathered granite extends 70 m deep at Hi Vista in the arid central Mojave Desert of southern California. The low strength of this granite is due to the alteration of biotite and chlorite montmorillonite. Deep weathering probably occurs in most granites, although we cannot rule out some anomalous mechanisms at Hi Vista. Geophysical instruments set in these slightly altered rocks are limited by the unstable behavior of the rocks. Thus, tectonic signals from instruments placed in shallow boreholes give vague results. Geophysical measurements of these weathered rocks resemble measurements of granitic rocks near major faults. The rheology of the rocks in which instruments are placed limits the useful sensitivity of the instruments.

Hydrologic and geochemical properties of the San Andreas fault at the Stone Canyon well

The Stone Canyon well penetrates 600 m of highly fractured and severely altered quartz diorite intimately associated with the creeping segment of the San Andreas fault of central California. Geophysical logs reveal a complex hydrology dominated by major fractures. Fluid pressure in some fractures is sufficient to prevent invasion of the formation by heavy drilling mud, implying pore pressures at least 10% higher than hydrostatic ones. At least three chemically distinct waters are encountered, including a chloride brine clearly segregated from the shallow, potable groundwater. Chemical alteration of the quartz diorite persists throughout the well, far below the depth where the water-rock reactions responsible for the ubiquitous chlorite and mixed-layer clays can be considered weathering. Whole-rock δ18O analyses indicate significant interaction of the rocks with a low δ18O fluid within some of the fractured and altered zones, whereas a deeper sample shows18O enrichment. High pore pressures encountered in Stone Canyon may be due to tectonic compression. Measurements of temporal variations in the pore pressure at the well may provide a means of predicting earthquakes along this segment of the San Andreas fault.

Electrical resistivity mapping of landscape modifications at the Talgua site, Olancho, Honduras

Geophysical reconnaissance in 1995 provided information useful in developing a successful strategy for the 1996 field season in resistivity mapping of subsurface cultural features at Talgua Village, an archaeological site in eastern Honduras. Ground truth excavations confirmed that high-resistivity anomalies detected by modified dipole–dipole apparent resistivity pseudosections correlate with a layer of small cobbles imported to fill low spots of this prehistoric settlement. Resistivity measurements reveal that mounds on this site were erected on normal subsoil, while at least one plaza was originally a topographic low that has been filled. The volume of imported stones is at least 500 m3, which represents a significant public improvement effort. Similar imported fill under the rest of Talgua Village could be mapped by similar means, and other prehistoric sites of the region could be geophysically tested for similar features. Resistivity profiles provide archaeologists with a quick, inexpensive, accurate, and noninvasive method of determining the extent of landscape modification at Talgua Village.

Remains of Prehistoric Human in Strata Deformed by the San Andreas Fault Near Stone Canyon, San Benito County, California

(Accepted for publication May 22, 1978) ABSTRACT: Stierman, D.J., Zubrow, E. and Atkinson, L., 1979. Remains of prehistoric human in strata deformed by the San Andreas fault. In: C.A. Whitten, R. Green and B.K. Meade (Editors), Recent Crustal Movements, 1977. Tectonophysics, 52: 381-387. Human bones discovered in a river terrace about 20 m from an actively creeping trace of the San Andreas fault place an upper limit on the age of a sand deposit which has been deformed by fault-related movements. Amino-acid racemization infers these bones are about 5000 years old. No evidence was found associating this burial with cultural activity. The relationship between these bones and the surrounding soils, as well as the disarticulation and mixing of the bones, suggests that these human remains were buried by stream action. Sorted materials in this terrace dip 20° to the southwest, and other features of this exposure show that fault-related vertical displacements occur along this segment of the San Andreas fault. This style of deformation is consistent with dip-slip movement postulated by published results of dynamic modeling of creep-related strain events at the Stone Canyon Geophysical Observatory, only a few hundred meters from the burial, and with published models of tilt events recorded at Melondy Ranch, 6 km to the southeast. However, extrapolation of deformation rates based on these models and with the short-term creep rate cannot be reconciled with deformation observed in the terrace. The bone fragments lie in the zone of complex deformation within the San Andreas fault zone. Holocene movements in this zone have occurred at least 20 m beyond the fault trace currently monitored for fault creep.