Analyzing shallow faulting at a site in the Wasatch fault zone, Utah, USA, by integrating seismic, gravity, magnetic, and trench data

Gravity, magnetic, and seismic surveys were conducted across the Wasatch fault zone east of Springville, Utah, near the mouth of Hobble Creek Canyon. The geophysical data were acquired, processed, and interpreted to determine possible locations of larger [total offset greater than 6 ft (1.8 m)], shallow normal faults within the fault zone. Interpretations of the individual data sets were integrated to help eliminate spurious readings and to strengthen the interpretations. Visual methods of integration, along with computer modeling, were chosen for this study. Furthermore, the geophysical data were correlated and integrated with available trench data and surface data. In addition to verifying locations of known faults, the geophysical surveys detected numerous possible additional faults not previously mapped. Of particular interest is a newly discovered graben structure near the southern end of the site, where building of new homes has recently been proposed.

New structural information about fault densities and styles was also determined from the surveys. The fault concentration for this site is 1.3 faults/100 ft (30.5 m), or one fault per 77 ft (23.5 m). Interpreted antithetic faults at the Hobble Creek site account for 65% of the total, while synthetic faults account for 35% with respect to the main fault strand.

Information derived from this study should be useful during planning and development of areas within the Wasatch fault zone. The characteristics of subsurface deformation can be used to gain a better understanding of the potential for surface rupture at a given site. This is also useful in planning appropriate site development and remedial measures to help mitigate hazards associated with large-magnitude earthquakes.     

Industrial sulfur demand: Analysis and prospect

Weak growth in industrial (nonagricultural) U.S. sulfur demand has slowed the growth of total sulfur demand. Evaluating prospects for trend reversal is hampered by inadequate detailed data published by industry, and the lack of an easily measured demand component that reliably depicts total demand. In this article, I try to overcome this data deficiency by constructing an industry-by-industry breakdown of published data on total industrial sulfur consumption. Industrial sulfur consumptions were estimated from data on consuming industry activity, characteristics of relevant industrial processes, and analyses of the conditions affecting choice among alternative industrial processes. Subjective projections of the industry detail data are presented.In addition to cyclical factors, past declines in industrial sulfur demand were due to replacement of sulfur-using industrial processes with alternative processes that use less or no sulfur to achieve production cost economies. In some, but not all, cases, changeovers of process were in response to impositions of environmental-related requirements. The demand for industrial sulfur has good prospects for positive growth as shrinkage of some markets reaches natural limits and total market growth comes increasingly to be dominated by markets with positive growth prospects. Positive growth has been generated by environmentally related regulation in several markets, such as petroleum alkylation and copper production.     

Hydraulics of recirculating well pairs for ground water remediation

Recirculating well pairs are a proven means of implementing bioremediation and may also be useful for applying other in situ ground water remediation technologies. A bromide tracer test was performed to characterize the hydraulic performance of a recirculating well pair installed at Moffett Field, California. In particular, we estimate two important properties of the recirculating well pair: (1) the fraction of captured water that is recycled between the wells, and (2) the travel-time distribution of ground water in the induced zone of recirculation. We also develop theoretical estimates of these two properties and demonstrate they depend upon a dimensionless pumping rate, denoted xi. The bromide breakthrough curve predicted from theory agrees well with that determined experimentally at Moffett Field. The minimum travel time between the wells is denoted t(min). In theory, t(min) depends inversely on Q, the pumping rate in the recirculating wells, and is proportional to a2, the square of the distance between the wells. Both the experimental and theoretical travel-time distributions indicate that at least half the recirculating water travels between the wells along fast flowpaths (travel time < 2*t(min)). Therefore, when designing recirculating well pairs, engineers should ensure that t(min) will be sufficiently high to allow biologically mediated reactions (or other in situ remediation processes) sufficient time to proceed.     

Potential Implications of PCM Climate Change Scenarios for Sacramento–San Joaquin River Basin Hydrology and Water Resources

The potential effects of climate change on the hydrology and water resources of the Sacramento–San Joaquin River Basin were evaluated using ensemble climate simulations generated by the U.S. Department of Energy and National Center for Atmospheric Research Parallel Climate Model (DOE/NCAR PCM). Five PCM scenarios were employed. The first three were ensemble runs from 1995–2099 with a `business as usual' global emissions scenario, eachwith different atmospheric initializations. The fourth was a `control climate'scenario with greenhouse gas emissions set at 1995 levels and run through 2099. The fifth was a historical climate simulation forced with evolving greenhouse gas concentrations from 1870–2000, from which a 50-yearportion is taken for use in bias-correction of the other runs. From these global simulations, transient monthly temperature and precipitation sequences were statistically downscaled to produce continuous daily hydrologic model forcings, which drove a macro-scale hydrology model of theSacramento–San Joaquin River Basins at a 1/8-degree spatial resolution, and produceddaily streamflow sequences for each climate scenario. Each streamflow scenario was used in a water resources system model that simulated current and predicted future performance of the system. The progressive warming of the PCM scenarios (approximately 1.2 °C at midcentury, and 2.2 °C by the 2090s), coupled with reductions in winter and spring precipitation (from 10 to 25%), markedly reduced late spring snowpack (by as much as half on average by the end of the century). Progressive reductions in winter, spring, and summer streamflow were less severe in the northern part of the study domain than in the south, where a seasonality shift was apparent. Results from the water resources system model indicate that achieving and maintaining status quo (control scenario climate) system performance in the future would be nearly impossible, given the altered climate scenario hydrologies. The most comprehensive of the mitigation alternatives examined satisfied only 87–96% of environmental targets in the Sacramento system, and less than 80% in the San Joaquin system. It is evident that demand modification and system infrastructure improvements will be required to account for the volumetric and temporal shifts in flows predicted to occur with future climates in the Sacramento–San JoaquinRiver basins.     

Active intracontinental transpressional mountain building in the Mongolian Altai: Defining a new class of orogen

Mountain ranges that are actively forming around the western and northern perimeter of the Indo-Eurasia collisional deformational field, such as the Mongolian Altai, comprise a unique class of intracontinental intraplate transpressional orogen with structural and basinal elements that are distinct from contractional and extensional orogens. Late Cenozoic uplift and mountain building in the Mongolian Altai is dominated by regional-scale dextral strike-slip faults that link with thrust and oblique-slip faults within a 300-km-wide deforming belt sandwiched between the more rigid Junggar Basin block and Hangay Precambrian craton. Dominant orogenic elements in the Mongolian Altai include double restraining bends, terminal restraining bends, partial restraining bends, single thrust ridges, thrust ridges linked by strike-slip faults, and triangular block uplifts in areas of conjugate strike-slip faults. The overall pattern is similar to a regional strike-slip duplex array; however, the significant amount of contractional and oblique-slip displacement within the range and large number of historical oblique-slip seismic events renders the term “transpressional duplex” more accurate. Intramontane and range flanking basins can be classified as ramp basins, half-ramp basins, open-sided thrust basins, pull-apart basins, and strike-slip basins. Neither a classic fold-and-thrust orogenic wedge geometry nor a bounding foredeep exists. The manner in which upper crustal transpressional deformation is balanced in the lower crust is unknown; however, crustal thickening by lower crustal inflation and northward outflow of lower crustal material are consistent with existing geological and geodetic data and could account for late Cenozoic regional epeirogenic uplift in the Russian Altai and Sayan regions.     

Injection-extraction treatment well pairs: an alternative to permeable reactive barriers

Two of the biggest drawbacks of using permeable reactive barriers (PRBs) to treat contaminated ground water are the high capital cost of installation, particularly when the contaminated ground water is deep below ground surface, and the uncertainty of whether or not PRBs remain effective for the long time scales (e.g., decades) needed for many contaminant plumes. The use of an injection-extraction treatment well pair (IETWP) for capture and treatment of contaminated ground water can circumvent these difficulties, while still providing many of the same advantages offered by PRBs. In this paper, the hydraulics of IETWPs and PRBs are compared, focusing primarily on the width of the captured plume. It is demonstrated that IETWPs act as hydraulic barriers in a manner similar to PRBs, and that IETWPs provide excellent plume capture. A mathematical expression is presented for the plume capture width of an IETWP oriented perpendicular to the ground water flow direction in a homogeneous aquifer. Also discussed are other practical considerations that might determine whether an IETWP is better suited than a PRB for a particular contaminated site; these considerations include operating and maintenance costs, and the conditions under which an IETWP system can be used for in situ remediation.     

Subduction influence on magma supply at the East Scotia Ridge

Despite a spreading rate of 65–70 km Ma⁻¹, the East Scotia Ridge has, along most of its length, a form typically associated with slower rates of sea floor spreading. This may be a consequence of cooler than normal mantle upwelling, which could be a feature of back-arc spreading. At the northern end of the ridge, recently acquired sonar data show a complex, rapidly evolving pattern of extension within 100 km of the South Sandwich Trench. New ridge segments appear to be nucleating at or near the boundary between the South American and Scotia Sea plates and propagating southwards, supplanting older segments. The most prominent of these, north of 56°30′S, has been propagating at a rate of approximately 60 km Ma⁻¹ for at least 1 Ma, and displays a morphology unique on this plate boundary. A 40 km long axial high exists at the centre of this segment, forming one of the shallowest sections of the East Scotia Ridge. Beneath it, seismic reflection profiles reveal an axial magma chamber, or AMC, reflector, similar to those observed beneath the East Pacific Rise and Valu Fa Ridge. Simple calculations indicate the existence here of a narrow (<1 km wide) body of melt at a depth of approximately 3 km beneath the sea floor. From the topographic and seismic data, we deduce that a localised mantle melting anomaly lies beneath this segment. Rates of spreading in the east Scotia Sea show little variation along axis. Hence, the changes in melt supply are related to the unique tectonic setting, in which the South American plate is tearing to the east, perhaps allowing mantle flow around the end of the subducting slab. Volatiles released from the torn plate edge and entrained in the flow are a potential cause of the anomalous melting observed. A southward mantle flow may have existed beneath the axis of the East Scotia Ridge throughout its history.     

Amino acid biogeochemistry and dating of offshore Peru/Chile phosphorites

Amino acid biogeochemical results for a suite of indurated sea-floor phosphate nodules from the Peru/Chile margin confirm the youthful nature of these deposits as previously indicated by uranium-series disequilibrium dating. Isoleucine epimerization is significant in the hydrolyzed acid soluble fraction of the nodules with a range in the D-alloisoleucine/L-isoleucine ratio from 0.06 to 0.32. Amino acid compositional patterns are uniform for all nodules and are similar to unlithified surface sediments from the region suggesting that the nodules and sediments constitute a single genetic series.     

Mass consistent models for wind distribution in complex terrain — Fast algorithms for three dimensional problems

Mass consistent models for wind distribution in complex terrain are extremely useful and readily applied to many practical situations, such as the siting of wind turbines, or as input in the estimation of diffusion and transport of pollutants in complex terrain. These models are based on the numerical solution of the steady state three dimensional continuity equation for the mean wind components. The momentum and energy equations are not solved explicitly, but considered indirectly using parametric relations and wind data. In practical applications the equations must be solved numerous times (e.g. for each time interval). Standard techniques for numerical solution of three dimensional problems are frequently very expensive and thus not suitable for practical needs. In the present work, great emphasis is given to the development of fast algorithms, and techniques based on the multigrid approach are shown. Two mass consistent programs are described, the first based on the parametric representation of one of the wind components, and the second based on a few wind measurements and a variational principle. To verify the reliability of the variational approach, a measurement program related to a project of wind energy, is being performed at Har-Ahim, a site located in the Galilee.