LAND SUBSIDENCE IN THE LOS BANOS–KETTLEMAN CITY AREA,CALIFORNIA: PAST AND FUTURE OCCURRENCE     

Hakan Başağaoğlu  Miguel A. Mariño  Tudor M. Botzan 《自然地理学》2013,34(1):67-82

Land subsidence in the western San Joaquin Valley has been studied and monitored for almost six decades. Especially in the 1950s and 1960s, land subsidence had tremendous negative environmental and socioeconomic implications. The rate of land subsidence in the Los Banos–Kettleman City area, however, has decreased during the last three decades as a result of a decrease in groundwater withdrawal, following the importation of surface water to the Valley in late 1960s. The land subsidence in the Valley potentially could be a serious issue if the existing surface water supplies cannot meet increasing water demands during future critical drought periods. In this respect, this paper proposes a preliminary analysis to predict magnitudes of subsidence for the period 2000 to 2040, based on historical occurrences. In this study, extrapolation from earlier subsidence is based on: (1) knowledge of recent post-drought records at extensometers, (2) assumption of a single time porosity scenario, and (3) the premise that pumpage from the confined aquifer gradually will decrease as a result of progressive water quality degradation. Predicted magnitudes of land subsidence in the Los Banos–Kettleman City area are expected to be in the range 0.5 to 4.0 m for the next 4 to 5 decades under the scenario considered in this paper. [Key words: subsidence, groundwater extraction, aquitard, inelastic compaction, active porosity, Los Banos-Kettleman City, California.]  相似文献   

Glacial and Fluvial Deposits in the Aragón Valley,Central‐Western Pyrenees: Chronology of the Pyrenean Late Pleistocene Glaciers     

José M. García‐Ruiz  Carlos Martí‐Bono  José L. Peña‐Monné  Carlos Sancho  Edward J. Rhodes  Blas Valero‐Garcés  Penélope González‐Sampériz  Ana Moreno 《Geografiska Annaler: Series A, Physical Geography》2013,95(1):15-32

The Aragón Valley glacier (Central Western Pyrenees) has been studied since the late nineteenth century and has become one of the best areas in the Pyrenees to study the occurrence of Pleistocene glaciations and the relationships between moraines and fluvial terraces. New morphological studies and absolute ages for moraines and fluvial terraces in the Aragón Valley allow a correlation with other Pyrenean glaciers and provide solid chronologies about the asynchroneity between global last glacial maximum (LGM) and the maximum ice extent (MIE). Six frontal arcs and three lateral morainic ridges were identified in the Villanúa basin terminal glacial complex. The main moraines (M1 and M2) correspond to two glacial stages (oxygen isotopic stages MIS 6 and MIS 4), dated at 171 ± 22 ka and 68 ± 7 ka, respectively. From a topographical point of view, moraine M1 appears to be linked to the 60 m fluvioglacial terrace, dated in a tributary of the Aragón River at 263 ± 21 ka. The difference in age between M1 moraine and the 60 m fluvioglacial terrace suggests that the latter belongs to an earlier glacial stage (MIS 8). Moraine M2 was clearly linked to the fluvioglacial 20 m terrace. Other minor internal moraines were related to the 7–8 m terrace. The dates obtained for the last glacial cycle (20–18 ka) are similar to other chronologies for Mediterranean mountains, and confirm the occurrence of an early MIE in the Central Pyrenees that does not coincide with the global LGM.  相似文献   

Examining regulatory reform for bus operations in Latin America     

Laurel Paget-Seekins  Onesimo Flores Dewey  Juan Carlos Muñoz 《Urban geography》2013,34(3):424-438

Governments in Latin American cities are pursuing regulatory reforms to address the negative externalities of informal public transportation service providers. This is achieved by regulatory actions that work to consolidate many small operators competing “in the market” into fewer larger companies competing “for the market.” This reform addresses problems in the previous phase of the regulatory cycle, but requires a larger role for public authorities. The cities of Bogotá, Santiago and Mexico City took different approaches and have achieved different levels of formalization. Under these cities’ new regulatory regimes, bus companies have consolidated and public authorities now rely on renegotiation of contracts instead of open rebidding. However, industry formalization increases costs, requiring public subsidy or higher fares, and puts financial pressure on the public sector. These results imply a continued instability in the regulatory cycle; without increased public sector capacity, it is possible that large, entrenched operators and increasing costs will create a new market opening for informal service.  相似文献   

A Spectral Diagnostic for Density-Bounded HII Regions     

J. Iglesias-Páramo  C. Muñoz-Tuñón 《Astrophysics and Space Science》2001,277(1):99-99

Our spectral diagnostic based on the intensity of the [OI]λ6300Å line indicates that many observed HII regions are indeed density-bounded. The estimated fractions of escaping Lyman continuum photons range from 15 to even more than 50%.  相似文献   

Is the supersonic turbulence observed in HII regions sustained by the presence of magnetic fields?     

John E. Beckman  Mónica Relaño 《Astrophysics and Space Science》2004,292(1-4):111-118

We describe a set of Hα emission line profiles from populations of H II regions in nearby spiral galaxies. These are characterized by a strong Gaussian central peak, and lower intensity higher velocity wing features. From the peak we extract a non-thermal velocity component, due to the internal turbulence of the region. The plot of the widths of these non-thermal components against Hα luminosity shows a lower envelope in line width, which we assign to regions in, or close to virial equilibrium, although the region mass derived on this assumption is higher than the mass obtained by summing all known mass components. We speculate that this discrepancy, as well as the supersonicity of the line widths, can be explained by the presence of turbulent magnetic fields within the H II regions, and make a very rough estimate of the fields implied, of order a few tens of microgauss.  相似文献   

A family of Coordinate Systems for Reissner-Nordstrom Geometry     

A. Patiño  H. Rago 《Astrophysics and Space Science》2001,278(3):305-309

In this work we integrate Einstein-Maxwell equations for a point charge, in a coordinate system first considered by Lake. The family of solutions obtained includes various well known metrics. A free metric function acting as a gauge in the solution, is related to the Lorentz contraction factor in infinity, considering a set of geodesic frames. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

3EG J2020+4017, the γ-Cygni source—before GLAST     

Alberto Carramiñana 《Astrophysics and Space Science》2007,309(1-4):373-378

The Cygnus region of the Milky Way is prolific in star formation and presents extended diffuse γ-ray emission with a few γ-ray point sources. Among them is 3EG J2020+4017, the brightest of the unidentified EGRET sources, positionally coincident with the supernova remnant G78.2+2.1. Even though the EGRET and multi-wavelength data have not provided a conclusive identification for this γ-ray loud, but otherwise faint object, the evidence favors a pulsar like source. The EGRET photon data lack the signal-to-noise ratio required for a period search, but will serve as a valuable timing baseline extension in the case that GLAST confirms the pulsar nature of the γ-Cygni source. Work sponsored by CONACyT grant SEP-2003-C02-42611.  相似文献   

On a universal structure for immiscible three-phase flow in virgin reservoirs     

Pablo Castañeda  Eduardo Abreu  Frederico Furtado  Dan Marchesin 《Computational Geosciences》2016,20(1):171-185

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Abandoned channel fill sequences in the tidal estuary of a small mountainous,dry‐summer river          下载免费PDF全文

Andrew B. Gray  Gregory B. Pasternack  Elizabeth B. Watson  Miguel A. Goñi 《Sedimentology》2016,63(1):176-206

This study proposes a modification of the current model for abandoned channel fill stratigraphy produced in unidirectional flow river reaches to incorporate seasonal tidal deposition. Evidence supporting this concept came from a study of two consecutive channel abandonment sequences in Ropers Slough of the lower Eel River Estuary in northern California. Aerial photographs showed that Ropers Slough was abandoned around 1943, reoccupied after the 1964 flood, and abandoned again in 1974 with fill continuing to the present. Planform geomorphic characteristics derived from these images were used in conjunction with sub‐centimetre resolution stratigraphic analyses to describe depositional processes and their resultant sedimentary deposits. Both abandonment sequences recorded quasi‐annual scale fluvial/tidal deposition couplets. In both cases, tidal deposits contained very little sand, were higher in organic and inorganic carbon content than the sandier, fluvially dominated deposits, and possessed millimetre‐scale horizontal laminations. The two abandonment fills differed significantly in terms of the temporal progression of channel narrowing and fluvial sediment deposition characteristics. Aerial photographic analysis showed that the first abandonment sequence led to a more rapid narrowing of Ropers Slough and produced deposits with a positive relationship between grain size/deposit thickness and discharge. The second abandonment resulted in a much slower narrowing of Ropers Slough and generally thinner fluvial deposits with no clear relationship between grain size/deposit thickness and discharge. The δ¹³C values and organic nitrogen to organic carbon ratios of deposits from the first phase overlapped with Eel River suspended sediment characteristics found for low flows (one to five times mean discharge), while those of the second phase were consistent with suspended sediment from higher flows (seven to ten times mean discharge). When considered together, the results indicate that the early fill sequence recorded a reach experiencing regular fluvial deposition through flow conditions during the wet season, while the latter fill sequence records a reach more disconnected from the main stem in terms of flow and sediment. The major factor affecting the difference in sedimentation between the two fill periods appears to have been the morphology of the upstream river bend in relation to the position of the bifurcation node. During the first fill period, the upstream entrance to Ropers Slough seems to have remained open, in part due to the placement of its entrance on the outside of the mainstem river bend, and despite stronger tidal effects caused by a larger tidal prism and closer proximity to the tidal inlet. By the second fill sequence, the upstream bend morphology had altered, placing the entrance to Ropers Slough on the inner bank of the mainstem bend, which resulted in more rapid plug bar formation. The role of tidal effects in the geomorphic trajectory of the two abandonment sequences is unclear, but appears to have been less important than local bifurcation geometry.  相似文献   

Demonstration of uncertainty resulting from MODerate resolution Imaging Spectroradiometer-like geometries: an albedo case study     

Enrique L. Montaño 《International Journal of Digital Earth》2016,9(5):520-544

This research examines uncertainty in MODerate resolution Imaging Spectroradiometer (MODIS) observations, and demonstrates the direct influence of geometric distortions resulting from the standard practice of geolocating swath observations. MODIS observations vary dependent on the ground sample distance, which varies dependent on the view zenith angle that changes with every orbit. MODIS Level 2G (L2G) land products are generated by applying a geolocation algorithm that resamples the variable observation geometries to a consistent grid of fixed pixel size and location, a process which itself introduces variability associated with the changing observational footprint. For this study, broadband albedo was simulated for five validation sites, representing five distinct land cover types, exhibiting quantifiable variability, with additional seasonal variability exhibited in some sites. All site simulations exhibit compounded uncertainty attributable to the geometric distortion sufficient to influence climate models (i.e. ranges from 0.01 to 0.045 albedo). These results indicate there is a minimum level of uncertainty associated with the variable geometry that should be factored into L2G-based products, particularly for nominal 250?m band data. Aggregating the data to coarser resolutions and smoothing the data through average resampling can mitigate the uncertainty.  相似文献