Robert L. Baskin

The Great Salt Lake Ecosystem (Utah, USA): long term data and a structural equation approach

Great Salt Lake (Utah, USA) is one of the worlds largest hypersaline lakes, supporting many of the western U.S.s migratory waterbirds. This unique ecosystem is threatened, but it and other large hypersaline lakes are not well understood. The ecosystem consists of two weakly linked food webs: one phytoplankton-based, the other organic particle/benthic algae-based. Seventeen years of data on the phytoplankton-based food web are presented: abundances of nutrients (N and P), phytoplankton (Chlorophyta, Bacillariophyta, Cyanophyta), brine shrimp (Artemia franciscana), corixids (Trichocorixa verticalis), and Eared Grebes (Podiceps nigricollis). Abundances of less common species, as well as brine fly larvae (Ephydra cinerea and hians) from the organic particle/benthic algae-based food web are also presented. Abiotic parameters were monitored: lake elevation, temperature, salinity, PAR, light penetration, and DO. We use these data to test hypotheses about the phytoplankton-based food web and its weak linkage with the organic particle/benthic algae-based food web via structural equation modeling. Counter to common perceptions, the phytoplankton-based food web is not limited by high salinity, but principally through phytoplankton production, which is limited by N and grazing by brine shrimp. Annual N abundance is highly variable and depends on lake volume, complex mixing given thermo- and chemo-clines, and recycling by brine shrimp. Brine shrimp are food-limited, and predation by corixids and Eared Grebes does not depress their numbers. Eared Grebe numbers appear to be limited by brine shrimp abundance. Finally, there is little interaction of brine fly larvae with brine shrimp through competition, or with corixids or grebes through predation, indicating that the lakes two food webs are weakly connected. Results are used to examine some general concepts regarding food web structure and dynamics, as well as the lakes future given expected anthropogenic impacts.

Paleoseismic history of the Fallen Leaf segment of the West Tahoe–Dollar Point fault reconstructed from slide deposits in the Lake Tahoe Basin, California-Nevada

The West Tahoe–Dollar Point fault (WTDPF) extends along the western margin of the Lake Tahoe Basin (northern Sierra Nevada, western United States) and is characterized as its most hazardous fault. Fallen Leaf Lake, Cascade Lake, and Emerald Bay are three subbasins of the Lake Tahoe Basin, located south of Lake Tahoe, and provide an opportunity to image primary earthquake deformation along the WTDPF and associated landslide deposits. Here we present results from high-resolution seismic Chirp (compressed high intensity radar pulse) surveys in Fallen Leaf Lake and Cascade Lake, multibeam bathymetry coverage of Fallen Leaf Lake, onshore Lidar (light detection and ranging) data for the southern Lake Tahoe Basin, and radiocarbon dates from piston cores in Fallen Leaf Lake and Emerald Bay. Slide deposits imaged beneath Fallen Leaf Lake appear to be synchronous with slides in Lake Tahoe, Emerald Bay, and Cascade Lake. The temporal correlation of slides between multiple basins suggests triggering by earthquakes on the WTDPF system. If this correlation is correct, we postulate a recurrence interval of ∼3–4 k.y. for large earthquakes on the Fallen Leaf Lake segment of the WTDPF, and the time since the most recent event (∼4.5 k.y. ago) exceeds this recurrence time. In addition, Chirp data beneath Cascade Lake image strands of the WTDPF offsetting the lake floor as much as ∼7.5 m. The Cascade Lake data combined with onshore Lidar allow us to map the WTDPF continuously between Fallen Leaf Lake and Cascade Lake. This improved mapping of the WTDPF reveals the fault geometry and architecture south of Lake Tahoe and improves the geohazard assessment of the region.

Strike-slip faulting along the Wassuk Range of the northern Walker Lane, Nevada

A strike-slip fault is present outboard and subparallel to the Wassuk Range front within the central Walker Lane (Nevada, USA). Recessional shorelines of pluvial Lake Lahontan that reached its highstand ca. 15,475 ± 720 cal. yr B.P. are displaced ∼14 m and yield a right-lateral slip-rate estimate approaching 1 mm/yr. The strike-slip fault trace projects southeastward toward the eastern margin of Walker Lake, which is ∼15 km to the southeast. The trace is obscured in this region by recessional shorelines features that record the historical dessication of the lake caused by upstream water diversion and consumption. High-resolution seismic CHIRP (compressed high intensity radar pulse) profiles acquired in Walker Lake reveal ∼20 k.y. of stratigraphy that is tilted westward ∼20–30 m to the Wassuk Range front, consistent with ∼1.0–1.5 mm/yr (20–30 m/20 k.y.) of vertical displacement on the main range-bounding normal fault. Direct evidence of the northwest-trending right-lateral strike-slip fault is not observed, although a set of folds and faults trending N35°E, conjugate to the trend of the strike-slip fault observed to the north, is superimposed on the west-dipping strata. The pattern and trend of folding and faulting beneath the lake are not simply explained; they may record development of Riedel shears in a zone of northwest-directed strike slip. Regardless of their genesis, the faults and folds appear to have been inactive during the past ∼10.5 k.y. These observations begin to reconcile what was a mismatch between geodetically predicted deformation rates and geological fault slip rate studies along the Wassuk Range front, and provide another example of strain partitioning between predominantly normal and strike-slip faults that occurs in regions of oblique extension such as the Walker Lane.

Recent faulting in western Nevada revealed by multi-scale seismic reflection

Roxanna N. Frary∗†, John N. Louie†, William J. Stephenson‡, Jackson K. Odum‡, Annie Kell†, Amy Eisses†, Graham M. Kent†, Neal W. Driscoll§, Robert Karlin¶, Robert L. Baskin‖, Satish Pullammanappallil∗∗, Lee M. Liberty†† †Nevada Seismological Laboratory, University of Nevada ‡United States Geological Survey, Golden, Colorado §Scripps Institution of Oceanography, University of California, San Diego ¶Department of Geological Sciences and Engineering, University of Nevada ‖United States Geological Survey, West Valley City, Utah ∗∗Optim, Reno, Nevada ††Center for the Geophysical Investigation of the Shallow Subsurface, Boise State University

New constraints on fault architecture, slip rates, and strain partitioning beneath Pyramid Lake, Nevada

A seismic compressed high-intensity radar pulse (CHIRP) survey of Pyramid Lake, Nevada, defines fault architecture and distribution within a key sector of the northern Walker Lane belt. More than 500 line-kilometers of high-resolution (decimeter) subsurface imagery, together with dated piston and gravity cores, were used to produce the first comprehensive fault map and attendant slip rates beneath the lake. A reversal of fault polarity is observed beneath Pyramid Lake, where down-to-the-east slip on the dextral Pyramid Lake fault to the south switches to down-to-the-west displacement on the Lake Range fault to the north. Extensional deformation within the northern two thirds of the basin is bounded by the Lake Range fault, which exhibits varying degrees of asymmetric tilting and stratal divergence due to along-strike segmentation. This structural configuration likely results from a combination of changes in slip rate along strike and the splaying of fault segments onshore. The potential splaying of fault segments onshore tends to shift the focus of extension away from the lake. The combination of normal- and oblique-slip faults in the northern basin gives Pyramid Lake its distinctive “fanning open to the north” geometry. The oblique-slip faults in the northwestern region of the lake are short and discontinuous in nature, possibly representing a nascent shear zone. In contrast, the Lake Range fault is long and well defined. Vertical slip rates measured across the Lake Range and other faults provide new estimates on extension across the Pyramid Lake basin. A minimum vertical slip rate of ∼1.0 mm/yr is estimated along the Lake Range fault. When combined with fault length, slip rates yield a potential earthquake magnitude range between M6.4 and M7.0. Little to no offset on the Lake Range fault is observed in the sediment rapidly emplaced at the end of Tioga glaciation (12.5–9.5 ka). In contrast, since 9.5 ka, CHIRP imagery provides evidence for three or four major earthquakes, assuming a characteristic offset of 2.5 m per event. Regionally, our CHIRP investigation helps to reveal how strain is partitioned along the boundary between the northeastern edge of the Walker Lane and the northwest Basin and Range Province proper.

Algorithm for the estimation of upper and lower bounds of the emissivity and temperature of a target from thermal multispectral airborne remotely sensed data

This paper describes a method to estimate the bounds of temperatures and emissivities from thermal data. This method is then tested with remotely sensed data obtained from NASAs Thermal Infrared Multispectral Scanner (TIMS) -- a 6 channel thermal sensor. Since this is an under-determined set of equations i.e., there are seven unknowns (six emissivities and one temperature) and six equations (corresponding to the 6 channel fluxes), there exist theoretically an infinite combination of values of emissivities and temperature that can satisfy these equations. However, using some realistic initial bounds on the emissivities, bounds on the temperature are calculated. These bounds on the temperature are refined to estimate a tighter bound on the emissivity of the source. An error analysis is also carried out to quantitatively determine the extent of uncertainty introduced in the estimate of these parameters. This method is useful only when a realistic set of bounds can be obtained for the emissivities of the data. In the case of water the lower and upper bounds were set at 0.97 and 1.00, respectively. A set of images obtained with the TIMS are then used as real imagery data. The data was acquired over Utah Lake, Utah, a large freshwater lake near Salt Lake City, Utah, in early April 1991. It will be used to identify water temperatures for detection of underwater thermal, saline, and fresh water springs. An image consisting mostly of water is analyzed. The temperatures of the pixels are calculated to an accuracy of less than 1 deg K and the emissivities are calculated to an accuracy of less than .01.

An algorithm for the estimation of water temperatures from thermal multispectral airborne remotely sensed data

The effective flux incident upon the detectors of the sensor, after is has been corrected for atmospheric effects, is a nonlinear function of the emissivity of the target for that channel and the temperature of the target. The sensor system cannot separate the contribution from the emissivity and the temperature that constitute the flux value. In this paper, we describe a method that estimates the water temperature from thermal data. This method is then tested with remotely sensed data obtained from NASAs Thermal Infrared Multispectral Scanner (TIMS)--a 6 channel thermal sensor. Since this is an under-determined set of equations i.e. there are 7 unknowns (6 emissivities and 1 temperature) and 6 equations (corresponding to the 6 channel fluxes), there exist theoretically an infinite combination of values of emissivities and temperature that can satisfy these equations. However using some realistic bounds on the emissivities, bounds on the temperature are calculated. These bounds on the temperature are refined to estimate a tighter bound on the emissivity of the source. An error analysis is also carried out to quantitatively determine the extent of uncertainty introduced in the estimate of these parameters. This method is useful only when a realistic set of bounds can be obtained for the emissivities of the data. In the case of water the lower and upper bounds were set at 0.97 and 1.00 respectively. A set of images obtained with the TIMS are then used as real imagery data. The data was acquired over Utah Lake, Utah, a large freshwater lake near Salt Lake City, in early April 1991. It will be used to identify water temperatures for detection of underwater thermal, saline, and fresh water springs. An image entirely consisting of water is analyzed. The temperatures of the pixels are calculated to an accuracy of less than 1 deg. K. The error histograms of the temperature estimates are also calculated.