排序方式： 共有23条查询结果，搜索用时 15 毫秒
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Kristy F. Tiampo Francois-Alexis Ouegnin Sreeram Valluri Sergey Samsonov José Fernández Garrett Kapp 《Pure and Applied Geophysics》2012,169(8):1443-1456
Historically, surface subsidence as a result of subsurface groundwater fluctuations have produced important and, at times, catastrophic effects, whether natural or anthropogenic. Over the past 30?years, numerical and analytical techniques for the modeling of this surface deformation, based upon elastic and poroelastic theory, have been remarkably successful in predicting the magnitude of that deformation (Le Mouélic and Adragna in Geophys Res Lett 29:1853, 2002). In this work we have extended the formula for a circular-shaped aquifer (Geertsma in J Petroleum Tech 25:734–744, 1973) to a more realistic elliptical shape. We have improved the accuracy of the approximation by making use of the cross terms of the expansion for the elliptic coordinates in terms of the eccentricity, e, and the mean anomaly angle, M, widely used in astronomy. Results of a number of simulations, in terms of e and M developed from the transcendental Kepler equation, are encouraging, giving realistic values for the elliptical approximation of the vertical deformation due to groundwater change. Finally, we have applied the algorithm to modeling of groundwater in southern California. 相似文献
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Nithin V. George Kristy F. Tiampo Sitanshu S. Sahu Stéphane Mazzotti Lalu Mansinha Ganapati Panda 《Pure and Applied Geophysics》2012,169(8):1507-1517
Over the years, a number of different models and techniques have been proposed to both quantify and explain the glacial isostatic adjustment (GIA) process. There are serious challenges, however, to obtaining accurate results from measurements, due to noise in the data and the long periods of time necessary to identify the relatively small-magnitude signal in certain regions. The primary difficulty, in general, is that most of the geophysical signals that occur in addition to GIA are nonstationary in nature. These signals are also corrupted by random as well as correlated noise added during data acquisition. The nonstationary characteristic of the data makes it difficult for traditional frequency-domain denoising approaches to be effective. Time–frequency filters present a more robust and reliable alternative to deal with this problem. This paper proposes an extended S transform filtering approach to separate the various signals and isolate that associated with GIA. Continuous global positioning system (GPS) data from eastern Canada for the period from June 2001 to June 2006 are analyzed here, and the vertical velocities computed after filtering are consistent with the GIA models put forward by other researchers. 相似文献
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Jos Fernndez Kristy F. Tiampo John B. Rundle Gerhard Jentzsch 《Journal of Geodynamics》2005,39(5):475-492
A method for the computation and interpretation of gravity and height changes and vertical gravity gradients produced by magmatic intrusions in a layered elastic–gravitational medium is presented. The methodology assumes a planar medium geometry, which consists of welded layers overlying a half-space. The medium is elastic and gravitating. The intrusion is treated as a point source and can be located at any depth inside the medium. The theoretical elastic–gravitational model allows the computation of the so-called geometric and orthometric vertical displacements as well as gravity changes of different types. The corresponding vertical gravity gradients can also be computed. We present several examples of theoretical computations and study different types of these geometric and orthometric gravity gradients and the information we can get from the application of the methodology described. The results presented show that the use of these gradients is a useful tool to obtain information on the dynamics of the injection processes, including the detection of new magma recharge. We show that using the elastic–gravitational deformation model we can explain non-linear gravity–height relationships that appear in volcanic areas. We also present the application of the methodology to Mayon volcano, Philippines, delineating the intrusion of new magma, consistent with the produced eruptions after the observation period. 相似文献
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Patricia A. Perlock Pablo J. González Kristy F. Tiampo Gema Rodríguez-Velasco Sergey Samsonov José Fernández 《Pure and Applied Geophysics》2008,165(8):1531-1554
Differential interferometry is a very powerful tool for detecting changes in the Earth’s crust where coherence conditions
are good, but is difficult to employ in some volcanic areas due to dense vegetation. We apply two differential InSAR methods
using the time series associated with the interferograms to perform a phase analysis on a data set for La Palma island (Canary
Islands) from the ERS-1 and ERS-2 European Space Agency (ESA) satellites for the time period 1992 to 2000. Both methods involve
choosing a master image from the database and creating a series of interferograms with respect to this image. The “Coherent
Pixel Time Series” (CPTS) technique chooses pixels with good average coherence, aligns the unwrapped interferograms with a
stable area and then performs an inversion to calculate the linear velocity to quantify the deformation. The Coherent Target
Modeling (CTM) method calculates the temporal coherence of each pixel to identify stable targets and then determines the best
velocity for each pixel by using a linear fit that maximizes the temporal coherence. Using these two methods we have been
able to detect deformation on La Palma Island that has been previously undetectable by conventional InSAR methods. There is
a roughly circular region on the Southern part of the island that is actively deforming at ~ −4 to −8 mm/yr. This region is
located near the Teneguia valcano, the host of the last known eruption on La Palma in 1971. A thorough investigation of the
possible sources for this deformation revealed that it was most likely created by a subsurface thermal source. 相似文献
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Michaela E. Larsson Penelope A. Ajani Ana M. Rubio Kristy Guise Ross G. McPherson Steven J. Brett Kevin P. Davies Martina A. Doblin 《Marine pollution bulletin》2017,114(1):227-238
Sixteen years (1997–2013) of physicochemical, nutrient and phytoplankton biomass (Chlorophyll-a (Chl-a)) data and a decade (2003-2013) of phytoplankton composition and abundance data were analyzed to assess how the algal community in a temperate southeastern Australian estuary has responded to decreased chronic point source nitrogen loading following effluent treatment upgrade works in 2003. Nitrogen concentrations were significantly lower (P < 0.05) following enhanced effluent treatment and Chl-a levels decreased (P < 0.05) during the warmer months. Temperature and nutrient concentrations significantly influenced temporal changes of Chl-a (explaining 55% of variability), while salinity, temperature, pH and nutrient concentrations influenced phytoplankton abundance and composition (25% explained). Harmful Algal Bloom (HAB) dynamics differed between sites likely influenced by physical attributes of the estuary. This study demonstrates that enhanced effluent treatment can significantly decrease chronic point source nitrogen loading and that Chl-a concentrations can be lowered during the warmer months when the risk of blooms and HABs is greatest. 相似文献