Crustal‐scale pure shear foreland deformation of western Argentina

New analyses of teleseismic body waves from moderate earthquakes in western Argentina demonstrate that active shortening of the Andean foreland occurs on reverse faults extending to 40–50 km depth. Existing crustal‐scale models of foreland deformation invoke thin‐skinned fault geometries, which root into an east‐dipping mid‐crustal décollement. Whereas thin‐skinned thrust sheets dominate shallow‐crustal structure, seismological and geological data illustrate that planar reverse faults and pure‐shear deformation involving more than 75% of the crust characterizes this thick‐skinned structural province

Growth of the South Pyrenean orogenic wedge

A six-step reconstruction of the South Pyrenean foreland fold-and-thrust belt in Spain delineates the topographic slope, basal décollement angle, internal deformation, and thrust-front advance from the Early Eocene until the end of contractional deformation in the Late Oligocene. Style of thrust-front advance, dip of the basal décollement, slope of the upper surface, and internal deformation are decoupled and not simply related. Internal deformation increased, decreased, and maintained surface slope angle at different stages. From the onset to the cessation of deformation, the basal décollement angle decreased overall suggesting translation of the thrust belt onto stronger crust with time. Taper angle of the Pyrenean thrust wedge was fundamentally controlled by the flexural rigidity of the lower plate, the relative rate of creation of structural relief in the rear versus the front of the wedge, the extent of deposition of eroded material within the deforming wedge, and the taper of the pretectonic stratigraphic wedge

Imaging Fourier transform spectrometers for environmental sensing

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/77073/1/AIAA-1998-291-523.pd

Effect of toroidal field ripple on plasma rotation in JET

Dedicated experiments on TF ripple effects on the performance of tokamak plasmas have been carried out at JET. The TF ripple was found to have a profound effect on the plasma rotation. The central Mach number, M, defined as the ratio of the rotation velocity and the thermal velocity, was found to drop as a function of TF ripple amplitude (3) from an average value of M = 0.40-0.55 for operations at the standard JET ripple of 6 = 0.08% to M = 0.25-0.40 for 6 = 0.5% and M = 0.1-0.3 for delta = 1%. TF ripple effects should be considered when estimating the plasma rotation in ITER. With standard co-current injection of neutral beam injection (NBI), plasmas were found to rotate in the co-current direction. However, for higher TF ripple amplitudes (delta similar to 1%) an area of counter rotation developed at the edge of the plasma, while the core kept its co-rotation. The edge counter rotation was found to depend, besides on the TF ripple amplitude, on the edge temperature. The observed reduction of toroidal plasma rotation with increasing TF ripple could partly be explained by TF ripple induced losses of energetic ions, injected by NBI. However, the calculated torque due to these losses was insufficient to explain the observed counter rotation and its scaling with edge parameters. It is suggested that additional TF ripple induced losses of thermal ions contribute to this effect

Debris flow initiation in proglacial gullies on Mount Rainier, Washington

Effects of climate change, retreating glaciers, and changing storm patterns on debris flow hazards concern managers in the Cascade Range (USA) and mountainous areas worldwide. During an intense rainstorm in November 2006, seven debris flows initiated from proglacial gullies of separate basins on the flanks of Mount Rainier. Gully heads at glacier termini and widespread failure of gully walls imply that overland flow was transformed into debris flow along gullies. We characterized gully change and morphology, and assessed spatial distributions of debris flows to infer the processes and conditions for debris flow initiation. Slopes at gully heads were greater than ~0.35 m m⁻¹ (19°) and exhibited a significant negative relationship with drainage area. A break in slope–drainage area trends among debris flow gullies also occurs at ~0.35 m m⁻¹, representing a possible transition to fluvial sediment transport and erosion. An interpreted hybrid model of debris flow initiation involves bed failure near gully heads followed by sediment recruitment from gully walls along gully lengths. Estimates of sediment volume loss from gully walls demonstrate the importance of sediment inputs along gullies for increasing debris flow volumes. Basin comparisons revealed significantly steeper drainage networks and higher elevations in debris flow-producing than non-debris flow-producing proglacial areas. The high slopes and elevations of debris flow-producing proglacial areas reflect positive slope–elevation trends for the Mount Rainier volcano. Glacier extent therefore controls the slope distribution in proglacial areas, and thus potential for debris flow generation. As a result, debris flow activity may increase as glacier termini retreat onto slopes inclined at angles above debris flow initiation thresholds.Keywords: Hazards, Cascade volcanoes, Debris flow, Glacier retreat, Climate change, In-gully debris flow initiatio

Spatiotemporal dynamics of recent mountain pine beetle and western spruce budworm outbreaks across the Pacific Northwest Region, USA

Across the western US, the two most prevalent native forest insect pests are mountain pine beetle (MPB; Dendroctonus ponderosae; a bark beetle) and western spruce budworm (WSB; Choristoneura freemani; a defoliator). MPB outbreaks have received more forest management attention than WSB outbreaks, but studies to date have not compared their cumulative mortality impacts in an integrated, regional framework. The objectives of this study are to: (1) map tree mortality associated with MPB and WSB outbreaks by integrating forest health aerial detection surveys (ADS; 1970–2012), Landsat time series (1984–2012), and multi-date forest inventory data; (2) compare the timing, extent, and cumulative impacts of recent MPB and WSB outbreaks across forested ecoregions of the US Pacific Northwest Region (PNW; Oregon and Washington). Our Landsat-based insect atlas facilitates comparisons across space, time, and insect agents that have not been possible to date, complementing existing ADS maps in three important ways. The new maps (1) capture variation of insect impacts within ADS polygons at a finer spatial resolution (30 m), substantially reducing estimated insect extent; (2) provide consistent estimates of change for multiple agents, particularly long-duration changes; (3) quantify change in terms of field-measured tree mortality (dead basal area). Despite high variation across the study region, spatiotemporal patterns are evident in both the aerial survey- and Landsat-based maps of insect activity. MPB outbreaks occurred in two phases – first during the 1970s and 1980s in eastern and central Oregon and then more synchronously during the 2000s throughout dry interior conifer forests of the PNW. Reflecting differences in habitat susceptibility and epidemiology, WSB outbreaks exhibited early activity in northern Washington and an apparent spread from the eastern to central PNW during the 1980s, returning to northern Washington during the 1990s and 2000s. At ecoregional and regional scales, WSB outbreaks have exceeded MPB outbreaks in extent as well as total tree mortality, suggesting that ongoing studies should account for both bark beetles and defoliators. Given projected increases of insect and fire activity in western forests, the accurate assessment and monitoring of these disturbances will be crucial for sustainable ecosystem management.Keywords: Bark beetle, Defoliator, Change detection, Landsat time series, Forest disturbance, Tree mortalit

Late Cenozoic Foreland-to-Hinterland Low-Temperature Exhumation History of the Kashmir Himalaya

New apatite and zircon (U-Th)/He cooling ages quantify late Cenozoic exhumation patterns associated with fault activity across the Kashmir Himalaya. Apatite (U-Th)/He (AHe) cooling ages of detrital grains from the Sub-Himalayan foreland sediments indicate significant resetting. AHe data and thermal modeling reveal cooling and exhumation initiated by 4Ma at the deformation front and by 2-4Ma throughout other Sub-Himalayan structures. Exhumation rates for Sub-Himalayan structures are 1mm/year. In the hinterland, thrust sheet samples from the Main Boundary thrust and Main Central thrust yield AHe cooling ages between 5.1 and 21.1Ma. Published apatite fission track cooling ages (<3Ma) and high exhumation rates (3.6-3.2mm/year) across the Kishtwar window further to the north are consistent with AHe data from the Sub-Himalayan structures. The pattern of cooling ages and rates indicates that exhumation occurs in association with changes in the Himalayan basal decollement ramp geometry. Hinterland zircon (U-Th)/He (ZHe) data show a pronounced abundance and probability spike in cooling ages between 14 and 21Ma, a period when Main Central thrust motion is well documented throughout the Himalaya. ZHe single-grain ages from Sub-Himalayan samples contain a nearly identical cluster from 16 to 23Ma. Cooling patterns across the Kashmir Himalayas do not correlate spatially with modern monsoon precipitation, suggesting that climate-related precipitation and exhumation are decoupled. Coeval translation over the basal decollement and distributed imbricate thrust deformation of the foreland in the upper plate characterizes fault-related exhumation of the Sub-Himalayan orogenic belt after 4Ma. Our new data document the timing of cooling of rocks brought to the surface during mountain building of the Kashmir Himalaya. Mineral grains eroded from the Himalaya and deposited in the plain are now exposed in the Sub-Himalayan belt. The ages of these rocks that we have measured constrain the timing of burial and subsequent return to the Earth's surface (exhumation) during thrust fault-related deformation. Analysis of apatite grains reveals that cooling and exhumation initiated by 4Ma on the southernmost structure of the Kashmir Himalaya and by 2-4Ma on other distributed faults in the Sub-Himalayan belt. In the core of the mountain range rocks have young cooling ages (<3Ma) related to high uplift rates within the Kishtwar window, a zone of localized deformation in the High Himalaya. Thus, outward growth of the Sub-Himalayan belt occurred in concert with uplift in the hinterland over the past 4Myr. Precipitation rates vary systematically from south to north across the Himalaya, but these variations are not synchronous with the pattern of cooling and exhumation in Kashmir Himalaya. This result suggests that climate does not drive crustal deformation. Instead exhumation patterns primarily reflect the location, geometry, and partitioning of faulting within the Himalaya

Tectonic controls for transverse drainage and timing of the Xin-Ding paleolake breach in the upper reach of the Hutuo River, North China

The upper reach of the Hutuo River flows along the Xin-Ding basin and cuts a transverse drainage through Xizhou Mountain and Taihang Range into the North China Plain. Previous studies showed that the Xin-Ding basin was occupied by a lake during the Early-Middle Pleistocene. However, the timing of the paleolake breach and the mechanism for the creation of the transverse drainage are unknown. We constructed the fluvial terrace sequence in the upper reach of the Hutuo drainage combined with thermoluminescence (TL) and optically stimulated luminescence (OSL) dating, as well as the timescale of the overlying loess-paleosol units. Our results reveal that (1) five terraces (T5-T1) are developed along the upper reach of the Hutuo River, amongst which terraces T4-T1 were formed synchronously at ~600 ka, ~120-130 ka, ~21-26 ka and ~6-7 ka, respectively; (2) the creation of the transverse drainage and breach of the Xin-Ding paleolake occurred between ~600 ka and ~130 ka; (3) the mechanism for the creation of the transverse drainage is via river piracy of paleostreams on both sides of the drainage divide. Localized differential uplift and associated tilting of the Xizhou Mountain block during the Middle Pleistocene result in the formation of the transverse drainage and breach of the Xin-Ding paleolake.Keywords: Hutuo River, River piracy, Tectonic uplift, Loess-paleosol sequence, Transverse drainage, Xin-Ding paleolake, Fluvial terrac

Paleoseismology of the Marquesado-La Rinconada thrust system, Eastern Precordillera of Argentina

Excavated trenches at two sites across the Marquesado–La Rinconada fault system along the eastern Precordilleran front south of San Juan, Argentina, reveal the earthquake history of this rapidly urbanizing region. Interpretation of earthquakes is based on both the generation of colluvial wedges and upward fault terminations, as well as folding events in fine-grained alluvium ponded behind upslope-facing fault scarps. The ages of the past five interpreted earthquakes at the Loma Negra site are E1 at 2.8 ± 2.8 ka, E2 at 7.1 ± 1.5 ka, E3 at 9.6 ± 1.3 ka, E4 at 14.4 ± 2.1 ka, and E5 at 17.2 ± 3.1 ka. At the Jejenes sites, we documented event ages of 2.7 ± 0.1 ka, 3.9 ± 0.6 ka, 5.9 ± 1.3 ka, and 11.4 ± 4 ka. These results indicate that the recurrence interval along the Marquesado–La Rinconada fault zone averages several thousand years. The inferred displacements at the Jejenes site are about 1.1 m for E1, E3, and E4 and 2.1 m for event E2, whereas the displacements at Loma Negra averaged about 1 m, but the most recent event displays less slip. Notably, the older events seem to have been larger and emergent, whereas the youngest event appears to have been smaller and blind in the ponded sediment; this may partially explain the poor expression of classic colluvial wedges associated with some events. Despite the fact that active surface faulting has an uncertain relationship with the primary seismic sources at depth in the crust, past and future events of Mw ∼7.5 are consistent with the length scale of active deformation, the ∼1–2 m slip per event scale of these ruptures, and the size of historical earthquakes