Depth variation of seismic source scaling relations: implications for earthquake hazard in southeastern Australia

Advances in earthquake data acquisition and processing techniques have allowed for improved quantification of source parameters for local Australian earthquakes. Until recently, only hypocentral locations and local magnitudes (M_L) had been determined routinely, with little attention given to the inversion of additional source parameters. The present study uses these new source data (e.g. seismic moment, stress drop, source dimensions) to further extend our understanding of seismicity and the continental stress regime of the Australian landmass and its peripheral regions.

Earthquake activity within Australia is typically low, and the proportion of small to large events (i.e. the b value) is also low. It is observed that average stress drops for southeastern Australian earthquakes appear to increase with seismic moment to relatively high levels, up to approximately 10 MPa for M_L 5.0 earthquakes. This is thought to be indicative of high compressive crustal stress, coupled with strong rocks and fault asperities. Furthermore, the data indicates that shallow focus earthquakes (shallower than 6 km) appear to produce lower than average stress drops than deeper earthquakes (between 6 and 20 km) with similar moment.

Recurrence estimates were obtained for a discrete seismogenic zone in southeastern Australia. Decreasing b values with increasing focal depth for this zone indicate that larger earthquakes (with high stress drops) tend to occur deeper in the crust. This may offer an explanation for the apparent increase of stress drop with hypocentral depth. Consequently, earthquake hazard estimates that assume a uniform Gutenburg–Richter distribution with depth (i.e. constant b value) may be too conservative and therefore slightly overestimate seismic hazard for surface sites in southeastern Australia.     

Terminal Pleistocene/Early Holocene Environmental Change at the Sunshine Locality, North-Central Nevada, U.S.A.

Sedimentological, faunal, and archaeological investigations at the Sunshine Locality, Long Valley, Nevada reveal a history of human adaptation and environmental change at the last glacial–interglacial transition in North America's north-central Great Basin. The locality contains a suite of lacustrine, alluvial, and eolian deposits associated with fluvially reworked faunal remains and Paleoindian artifacts. Radiocarbon-dated stratigraphy indicates a history of receding pluvial lake levels followed by alluvial downcutting and subsequent valley filling with marsh-like conditions at the end of the Pleistocene. A period of alluvial deposition and shallow water tables (9,800 to 11,000 ¹⁴C yr B.P.) correlates to the Younger Dryas. Subsequent drier conditions and reduced surface runoff mark the early Holocene; sand dunes replace wetlands by 8,000 ¹⁴C yr B.P. The stratigraphy at Sunshine is similar to sites located 400 km south and supports regional climatic synchroneity in the central and southern Great Basin during the terminal Pleistocene/early Holocene. Given regional climate change and recurrent geomorphic settings comparable to Sunshine, we believe that there is a high potential for buried Paleoindian features in primary association with extinct fauna elsewhere in the region yet to be discovered due to limited stratigraphic exposure and consequent low visibility.     

The Geography of Racisms in NSW: A theoretical exploration and some preliminary findings from the mid-1990s

The spatial variation of racisms is an under-researched field of inquiry, certainly in Australia. This paper explores the geographies of racism in New South Wales. Responses to three opinion polls conducted between 1994 and 1996 were used to construct patterns of racisms across NSW. Preliminary findings suggest a substantive degree of racism in NSW. There was little evidence of an urban-rural variation in terms of ethnocentrism. Examination of regional variations confounds this simple division. Social Constructionist theory is put forward as a spatially sensitive theory for understanding and responding to the geographies of racism. The identification of regional variations in racism is crucial to the development of regionally specific anti-racism campaigns. This paper highlights the need for more comprehensive analyses of the varying causes and remedies for racisms.     

Plant and insect remains from the Wisconsinan interstadial/stadial transition at Wedron, north-central Illinois

Organic material exposed within a small swale fill in Pit 6 of the Wedron Silica Sand Co. near Wedron in LaSalle County, Illinois, includes well-preserved pollen, plant macrofossils, and insect remains. This material occurs in slackwater sediment in the lower part of the Peddicord Formation, which was deposited as existing valleys were dammed by fluvial aggradation during the initial late Wisconsinan advance of Laurentide ice into the Wedron area. Wood from the organic horizon has a radiocarbon age of 21,460 ± 470 yr B.P. (ISGS-1486). The pollen spectrum is dominated by Picea, Pinus, and Cyperaceae. Plant macrofossils comprise a mix of boreal-forest taxa, including Picea, Larix laricina, and the moss Campylium stellatum; subarctic species including Betula glandulosa, Empetrum nigrum, and Selaginella selaginoides; along with the predominantly arctic Vaccinium uliginosum var. alpinum, Dryas integrifolia, and Rhododendron lapponicum. The insect fauna contains the western montane ground beetle Opisthius richardsoni; several arctic-subarctic ground beetles including Diacheila polita, Helophorus sibiricus, and Pterostichus (Cryobius) caribou; and a diverse assemblage of insects that today inhabit the boreal forest. We interpret the biotic record to record a phase in the transition from closed boreal forest to open tundra as climatic conditions deteriorated in advance of continental glaciation.     

Employment Trends in Geography,Part 2: Current Demand Conditions*

This paper, the second in a series dealing with employment trends in geography, focuses on current labor market conditions. Two windows on the current labor market are (1) the employment experiences of recent graduates of geography programs and (2) the activities of the Association of American Geographers Convention Placement Services (CoPS). The former provides a perspective primarily on the nonacademic labor market in geography and includes bachelor's, master's, and doctoral recipients of geography degrees. The latter covers both academic and nonacademic jobs but focuses on geographers who hold advanced degrees.     

Cations in olivine,Part 2: Diffusion in olivine xenocrysts,with applications to petrology and mineral physics

Diffusivities for calcium, iron, magnesium, manganese and aluminum have been measured for St. John's olivine undergoing cation exchange with synthetic basaltic melts. The variety of temperature, pressure and fO₂ conditions under which the diffusivities were measured complement the equilibrium-partitioning study of calcium in olivine-bearing basalts by Jurewicz and Watson, 1988. Olivine was found to be anisotropic with respect to the diffusion of calcium, iron, magnesium and manganese. This anisotropy is a weak function of temperature, but strongly dependent upon oxygen fugacity.Because diffusion is independent of olivine composition over the small range of compositions used in this study, it could be shown that the absolute values of the diffusion coefficients were also functions of temperature and fO₂. At near-atmospheric total pressure and an oxygen fugacity of 10^–8atm, D _Fe>D _Mn>D _Ca and D _MgD _Mn for a range of geologically reasonable temperatures. These relative diffusivities were shown to change with oxygen fugacity. The power-law dependence of diffusion on oxygen partial-pressure was determined for each cation and the results are consistent with the range of values given by Stocker (1978) and by other workers.For Ca and Fe, the effect of hydrostatic pressure on diffusion appears to be weak, at least for transport parallel to the c crystallographic direction. Unfortunately, no true activation volumes (or other pressure-related parameters) could be computed because the oxygen fugacity was not held constant over changes in pressure, and because accurate post-experiment reconstruction of sample orientation was not possible. Al was found to enter high-pressure olivines at concentrations of up to 0.14 weight percent, thus allowing aluminum diffusion to be characterized. The diffusivity of aluminum is, within error, the same as iron at 20 kb at 1430° C at the ambient fO₂ of our piston-cylinder cells. This correspondence suggests that diffusion of Al may depend on transport of either Fe or of Fe ⁺³ defects. While the results of these experiments are generally consistent with results published elsewhere, there are important inconsistencies. Tracer diffusion and interdiffusion in pure, ordered, olivine endmembers (e.g., tephroite and forsterite) showed significantly higher activation energies. This discrepancy could reflect the role of Fe⁺³ defects in diffusion; however, it may also suggest that order-disorder phenomena may be significant factors influencing diffusion in analog systems.The results of this study are applied to four petrologic problems: (1) calculation of rates of equilibration for olivine xenocrysts; (2) calculation of closure temperatures for the CaO/MgO olivine/basalt geothermometer (Jurewicz and Watson 1988); (3) delineation of an intrinsic-/O₂ geobarometer; and (4) investigation of the dependence of olivine dissolution upon crystallographic orientation. In addition, it is demonstrated that diffusion-exchange experiments are useful for studying the dominant point-defect mechanisms for cation diffusion.Currently, a visiting scientist with Air Force Wright Aeronautical Laboratories Materials Laboratory (MLLM), Wright-Patterson AFB, OH 45433     

Bringing geography to the community: community-based learning and the geography classroom

Community-based learning is a pedagogical technique designed to bring students out of the classroom and into their communities. Students typically pair with local nonprofit organizations to complete work which ties into their scholarship. Faculty, students, and community members can all benefit from these partnerships, and university-community relations are strengthened by them. These connections deepen the educational experience and improve student success and retention, and build civic engagement skills that benefit the university community and the student’s home community (Strait, Turk, and Nordyke in: JR Strait, K Nordyke (eds), Pedagogy Of Civic Engagement, High-Impact Practices, and e-Service- L Earning, Stylus Publishing, Virginian, 2015; Bednarz in Journal of Geography in Higher Education 32:87–100, 2008; Mohan in Journal of Geography in Higher Education 19:129–142, 1995). Spatial citizenship, while vital to such engagement and to effective community participation, is seldom taught in traditional pedagogy (Kanwischer, Schulze, and Gryl in: Thomas Jekel, Adrijana Car, Josef Strobl, and Gerald Griesebner (eds), Spatial citizenship—dimensions of a curriculum, Wichmann Verlag, Berlin, 2012). Connecting place to pedagogy with spatially-enabled learning helps students investigate complex global concepts at a manageable local scale. Geography is an intrinsic part of scholarship, to varying degrees, and spatial thinking can bring added dimension and value to the educational process (Vogler in: Thomas Jekel, Adrijana Car, Josef Strobl, and Gerald Griesebner (eds), Wichmann Verlag, Berlin, 2012). The intersectionalities which exist within the community, when examined with a spatial lens, are the core of community geography, a praxis-focused method of engaged scholarship (Shannon in Progress in Human Geography, 10.1177/0309132520961468, 2020). Community-based learning is not clearly defined, yet some established models exist. Place-based learning communities move cohorts of students through a curriculum that is centered on local community issues, with the community as both laboratory and lens, and building place attachment (Schweizer, Davis, and Thompson in Environmental Communication 7:42–62, 2013). Service learning, while less clearly defined, typically involves direct work with community organizations, identifying, investigating, and contributing to solutions for local issues (Strait, Turk, and Nordyke in: JR Strait, K Nordyke (eds), Pedagogy Of Civic Engagement, High-Impact Practices, and e-Service- L Earning, Stylus Publishing, Virginian, 2015; Cal Corps Public Service in Designing Community-Based Courses, 1–45, 2015). Built around the concept of place, the added dimension of improved spatial citizenship benefits both community and students. This paper will review community-based learning as practiced through upper-division service learning courses in geography at two universities, and the development of a new course, as methods of engagement with local communities through a spatial lens.

     

Review of factors affecting the distribution and abundance of waterfowl in shallow-water habitats of Chesapeake Bay

Long-term trends of waterfowl populations in Chesapeake Bay demonstrate the importance of shallow-water habitats for waterfowl species. Although recent increases in field feeding by geese and swans lessened the importance of shallow-water areas for these species, most duck species depend almost exclusively on shallow-water habitats. Many factors influenced the distribution and abundance of waterfowl in shallow-water habitats. Habitat degradation resulted in the decline in numbers of most duck species and a change in distribution of some species. Increased numbers of mallards (Anas platyrhynchos) in recent decades probably resulted from release programs conducted by the Maryland Department of Natural Resources and private individuals. Studies of food habits since 1885 showed a decline in submerged-aquatic vegetation in the diet of some species, such as the canvasback (Aythya valisineria), and an increase in the proportions of invertebrates in the diet. Diversity of food organisms for many waterfowl species has declined. Surveys of vegetation and invertebrates in the Chesapeake Bay generally reflect a degradation of shallow-water habitat. Human population increases in the Chesapeake Bay watershed directly and indirectly affected waterfowl distribution and abundance. The increase of exotic plant and invertebrate species in the bay, in most cases, benefited waterfowl populations. Increased contaminants have reduced the quality and quantity of habitat, although serious attempts to reverse this trend are underway. The use of shallow-water habitats by humans for fishing, hunting, boating, and other recreational and commercial uses reduced the use of shallow-water habitats by waterfowl. Humans can lessen the adverse influences on the valuable shallow-water habitats by restricting human population growth near these habitats and improving the water quality of the bay tributaries. Other affirmative actions that will improve these areas for waterfowl include greater restrictions on boat traffic in shallow-water habitats and establishing more sanctuaries in shallow-water areas that have complete protection from human disturbance. *** DIRECT SUPPORT *** A01BY074 00013     

Easing conservation? Conservation easements, public accountability and neoliberalism

This paper examines the use of conservation easements, with a focus on California. Conservation easements are now the dominant tool used for private land conservation in the United States. Easements are in many ways a paradigmatic neoliberal environmental policy tool. They privatize and re-scale a great deal of land conservation decision-making authority; they are market-based; they provide financial incentives for participation rather than punishment for non-compliance; and they commodify new property rights. However, these neoliberalisms are incorporated in uneven, and sometimes contradictory, ways that emphasize the gulf between neoliberal ideologies and “actually existing neoliberalisms.” Most critically, as a result of extensive public funding and management, conservation easements are not nearly as private (and thus not as neatly neoliberal) as they sometimes seem. Conservation easements are often heralded as a “win–win” land conservation strategy. I argue that the extent to which conservation easements may be construed as win–win solutions depends a great deal on who is included in the calculation of winners and losers. I contend that using and governing easements as if they are private elides complex questions about larger public costs and benefits. This obscures the large number of people and institutions (both state and private) that will likely need to be involved in governing conservation easements in the long term.