Spectral characteristics of auroral region scintillation using 100 Hz sampling

GPS Solutions - With advances in Global Positioning System (GPS) receiver hardware, increased sampling rates have become available, allowing for more robust spectral analysis in the field of...     

The 1979 Cadoux earthquake and intraplate stress in Western Australia

The 1979 Cadoux earthquake (magnitude Ms ～ 6.0), which caused over $4 million damage in 1979, occurred in the Southwest Seismic Zone (SWSZ) of Western Australia and produced a shallow dipping thrust fault with an average strike close to north‐south. The fault length was approximately 15 km and the maximum displacement close to 1 m. The seismic moment is estimated to be 1.8 ±0.1 X 10¹⁸ Nm and the earthquake was, like the 1968 Meckering earthquake, caused by east‐west compressive stress in the crust. Aftershocks of the Cadoux earthquake are still continuing (1986) at the northern and southern ends of the area affected by the main earthquake; strain‐release data from the aftershocks indicate that significant strain energy is yet to be released in the region. Overcoring measurements in the SWSZ indicated high stress (up to 30 MPa) at shallow depths (～ 10 m). Near the epicentre of the Cadoux earthquake overcoring measurements revealed stress levels ranging from about 4 MPa, less than 1 km from the fault trace, to about 20 MPa at 15 km from the fault. This difference in stress at the two locations is much larger than the stress drop associated with the Cadoux earthquake (～ 1 MPa) obtained from seismological observations. However, the maximum compressive stress direction is consistent with the direction of the P‐axis obtained from the focal mechanism. Reliable hydro fracturing results, from a depth of 65 m, were similar to the stress directions and magnitudes obtained from overcoring measurements made at the same site. It appears that the crust in the SWSZ is under compressive stress and that earthquake activity releases this stress in small areas rather than along linear fault zones. Shallow earthquakes of similar magnitude could well take place in the SWSZ during the next 50 years.     

Intra-clinothem variability in sedimentary texture and process regime recorded down slope profiles

Shelf-margin clinothem successions can archive process interactions at the shelf to slope transition, and their architecture provides constraints on the interplay of factors that control basin-margin evolution. However, detailed textural analysis and facies distributions from shelf to slope transitions remain poorly documented. This study uses quantitative grain-size and sorting data from coeval shelf and slope deposits of a single clinothem that crops out along a 5 km long, dip-parallel transect of the Eocene Sobrarbe Deltaic Complex (Ainsa Basin, south-central Pyrenees, Spain). Systematic sampling of sandstone beds tied to measured sections has captured vertical and basinward changes in sedimentary texture and facies distributions at an intra-clinothem scale. Two types of hyperpycnal flow-related slope deposits, both rich in mica and terrestrial organic matter, are differentiated according to grain size, sorting and bed geometry: (i) sustained hyperpycnal flow deposits, which are physically linked to coarse channelized sediments in the shelf setting and which deposit sand down the complete slope profile; (ii) episodic hyperpycnal flow deposits, which are disconnected from, and incise into, shelf sands and which are associated with sediment bypass of the proximal slope and coarse-grained sand deposition on the medial and distal slope. Both types of hyperpycnites are interbedded with relatively homogenous, organic-free and mica-free, well-sorted, very fine-grained sandstones, which are interpreted to be remobilized from wave-dominated shelf environments; these wave-dominated deposits are found only on the proximal and medial slope. Coarse-grained sediment bypass into the deeper-water slope settings is therefore dominated by episodic hyperpycnal flows, whilst sustained hyperpycnal flows and turbidity currents remobilizing wave-dominated shelf deposits are responsible for the full range of grain sizes in the proximal and medial slope, thus facilitating clinoform progradation. This novel dataset highlights previously undocumented intra-clinothem variability related to updip changes in the shelf process-regime, which is therefore a key factor controlling downdip architecture and resulting sedimentary texture.     

Sedimentary architecture of detached deep‐marine canyons: Examples from the East Coast Basin of New Zealand

Submarine canyons are conduits for the distribution of sediment across continental margins. Although many canyons connect directly with fluvial or marine littoral system feeders, canyons detached from direct hinterland supply are also recognized. The fill of detached canyons remains enigmatic, because their deep‐water setting restricts analysis of their evolution and stratigraphic architecture. Therefore, this study aims to investigate the sedimentary processes that infilled deep‐water canyons and the resulting architecture. Miocene outcrops of an exhumed deep‐water system from the East Coast Basin, New Zealand, are documented and compared with the morphology and seismic scale architecture of a modern detached canyon system on the same convergent margin. The outcropping system preserves the downstream margin of a sub‐basin deposited at palaeo‐water depths >700 m. A 6 km wide by 430 m deep incision is filled by heterogeneous siliciclastic sediments, 50% of which comprise graded thin‐beds with traction structures, interpreted to result from oscillatory flows. These are intercalated with concave‐up lenses, up to 15 m thick, of sigmoidally‐bedded, amalgamated sandstones, which preserve ripple casts on bed bases, interpreted as deposits at the head of a deep‐marine canyon. Palaeo‐flow was eastward, into the sub‐basin margin. On the adjacent margin of the sub‐basin down‐dip, stacked and amalgamated sandstones and conglomerates represent the fill of a submarine channel complex, at least 3 km wide. The channels are inferred to have been fed by the up‐dip canyon, which traversed the intervening structural high; similar relationships are seen in the bathymetry data. Seismic studies on this margin demonstrate that multiple phases of canyon cut and fill may occur, with downstream architectural evolution comparable to that seen at outcrop, demonstrating that detached canyons may act as sediment conduits. Breaching of developing sea‐floor structures by detached canyons can modify tortuous sediment pathways, supplying sediment to otherwise starved areas of the slope.     

Longitudinal Social Science Research in Natural Resource Communities: Lessons and Considerations

The majority of social science research is cross-sectional in nature, with data collected at a single point in time. However, social systems are dynamic and many of the variables of interest to social scientists may change over time. Longitudinal research methods enable data collection at two or more points in time among a population of interest to examine change in measured variables and influencing factors. Despite the opportunities it affords, longitudinal research is relatively uncommon in natural-resource-based social science research as compared to other fields (e.g., medical, criminal, education). We feel that the field of natural resource social science is ripe for a proliferation of longitudinal studies, now that a substantial body of cross-sectional data has been built. In the spirit of encouraging more of this type of research, we draw on our collective experiences in longitudinal studies to share lessons learned in research design, sampling, and data management.