The hydraulic properties of aquitards are not easily obtained because monitoring wells are usually installed in aquifers for groundwater resources management. Earthquake‐induced crust stress (strain) triggers groundwater level variations over a short period of time in a large area. These groundwater anomalies can be used to investigate aquifer systems. This study uses a poroelastic model to fit the postseismic variations of groundwater level triggered by the Chi‐Chi earthquake to evaluate the hydraulic properties of aquitards in the Jhoushuei River alluvial fan (JRAF), Taiwan. Six of the adopted eight wells with depths of 70 to 130 m showed good agreement with the recovery theory. The mean hydraulic conductivities (K) of the aquifers for the eight wells are 1.62 × 10?4 to 9.06 × 10?4 m/s, and the thicknesses are 18.8 to 46.1 m. The thicknesses of the aquitards are 11.3 to 42.0 m. Under the isotropic assumption for K, the estimated values of K for the aquitards are 3.0 × 10?8 to 2.1 × 10?6 m/s, corresponding to a silty medium. The results match the values obtained for the geological material of the drilling core and those reported in previous studies. The estimated values were combined with those given in previous studies to determine the distribution of K in the first two aquitards in the JRAF. The distribution patterns of the aquitards reflect the sedimentary environments and fit the geological material. The proposed technique can be used to evaluate the K value of aquitards using inverse methods. The inversion results can be used in hydrogeological analyses, contaminant modeling, and subsidence evaluation. 相似文献
We study scattering of antiplane shear waves induced by a deep semielliptic canyon with a horizontal edge. We employ the region-point-matching technique to cope with the problem considered. Through an auxiliary boundary, a part of the circumference of a semiellipse, the whole analyzed region is divided into two subregions. We express the displacement fields in terms of Mathieu functions. We unify two distinct elliptic coordinates via a simple coordinate transformation relation. Integration of the coordinate transformation relation into the region-point-matching technique simplifies the procedure for constructing simultaneous equations. Imposing the continuity conditions and traction-free ones, we obtain the expansion coefficients. Frequency-domain results demonstrate ground motion variability based on several key factors. Ground surface responses under seismic shaking are also simulated in the time domain. 相似文献
This study measures the reaction rate of dolomite and aragonite (calcite) into Mg-calcite at 800, 850, and 900°C and 1.6 GPa. The dry synthetic dolomite-aragonite aggregate transformed very rapidly into dolomite-calcite polycrystalline aggregate while Mg-calcites formed at a relatively slow rate, becoming progressively richer in Mg with run time. We modeled the reaction progress semi-empirically by the first-order rate law. The temperature dependence of the overall transport rate of MgCO3 into calcite can be described by the kinetic parameters (E?=?231.7 kJ/mol and Ao?=?22.69 h?1). Extrapolation using the Arrhenius equation to the conditions during exhumation of UHPM rocks indicates that the reaction of dolomite with aragonite into Mg-saturated calcite can be completed as the P-T path enters the Mg-calcite stability field in a geologically short time period (<1 Ky). On the other hand, the extrapolation of the rate to prograde metamorphic conditions reveals that the Mg-calcite formed from dolomitic marble in the absence of metamorphic fluid may not reach Mg-saturation until temperatures corresponding to high-grade metamorphism (e.g., >340°C and >10 My). SEM-EDS analysis of individual calcite grains shows compositional gradients of Mg in the calcite grains. The Mg-Ca inter-diffusion coefficient at 850°C is around 1.68?×?10?14 m2/sec if diffusion is the major control of the reaction. The calculated closure temperatures for Ca-Mg inter-diffusion as a function of cooling rate and grain size reveal that Ca/Mg resetting in calcite in a dry polycrystalline carbonate aggregate (with grain size around 1 mm) may not occur at temperatures below 480°C at a geological cooling rate around 10°C/My, unless other processes, such as short-circuit interdiffusion along grain boundaries and dislocations, are involved. 相似文献
Hurricane surge events have caused devastating damage in active-hurricane areas all over the world. The ability to predict surge elevations and to use this information for damage estimation is fundamental for saving lives and protecting property. In this study, we developed a framework for evaluating hurricane flood risk and identifying areas that are more prone to them. The approach is based on the joint probability method with optimal sampling (JPM-OS) using surge response functions (SRFs) (JPM-OS-SRF). Derived from a discrete set of high-fidelity storm surge simulations, SRFs are non-dimensional, physics-based empirical equations with an algebraic form, used to rapidly estimate surge as a function of hurricane parameters (i.e., central pressure, radius, forward speed, approach angle and landfall location). The advantage of an SRF-based approach is that a continuum of storm scenarios can be efficiently evaluated and used to estimate continuous probability density functions for surge extremes, producing more statistically stable surge hazard assessments without adding measurably to epistemic uncertainty. SRFs were developed along the coastline and then used to estimate maximum surge elevations with respect to a set of hurricane parameters. Integrating information such as ground elevation, property value and population with the JPM-OS-SRF allows quantification of storm surge-induced hazard impacts over the continuum of storm possibilities, yielding a framework to create the following risk-based products, which can be used to assist in hurricane hazard management and decision making: (1) expected annual loss maps; (2) flood damage versus return period relationships; and (3) affected business (e.g., number of business, number of employees) versus return period relationships. By employing several simplifying assumptions, the framework is demonstrated at three northern Gulf of Mexico study sites exhibiting similar surge hazard exposure. The framework results reveal Gulfport, MS, USA is at relatively more risk of economic loss than Corpus Christi, TX, USA, and Panama City, FL, USA. Note that economic processes are complex and very interrelated to most other human activities. Our intention here is to present a methodology to quantify the flood damage (i.e., infrastructure economic loss, number of businesses affected, number of employees in these affected businesses and sales volume in these affected businesses) but not to discuss the complex interactions of these damages with other economic activities and recovery plans.
The horizontal-to-vertical spectral ratio has become popular in studies of the site effect and the determination of the predominant period of a site. 相似文献
This paper proposes a multiscale flow and transport model which can be used in three-dimensional fractal random fields. The
fractal random field effectively describes a field with a high degree of variability to satisfy the one-point statistics of
Levy-stable distribution and the two-point statistics of fractional Levy motion (fLm). To overcome the difficulty of using
infinite variance of Levy-stable distribution and to provide the physical meaning of a finite domain in real space, truncated
power variograms are utilized for the fLm fields. The fLm model is general in the sense that both stationary and commonly
used fractional Brownian motion (fBm) models are its special cases. When the upper cutoff of the truncated power variogram
is close to the lower cutoff, the stationary model is well approximated. The commonly used fBm model is recovered when the
Levy index of fLm is 2. Flow and solute transport were analyzed using the first-order perturbation method. Mean velocity,
velocity covariance, and effective hydraulic conductivity in a three-dimensional fractal random field were derived. Analytical
results for particle displacement covariance and macrodispersion coefficients are also presented. The results show that the
plume in an fLm field moves slower at early time and has more significant long-tailing behavior at late time than in fBm or
stationary exponential fields. The proposed fractal transport model has broader applications than those of stationary and
fBm models. Flow and solute transport can be simulated for various scenarios by adjusting the Levy index and cutoffs of fLm
to yield more accurate modeling results. 相似文献
We conducted a comprehensive 40Ar/39Ar geochronological study of the Jiali and Gaoligong shear zones to obtain a better understanding of crustal deformation and tectonic evolution around the Eastern Himalayan Syntaxis (EHS). The new age data reveal that the main phase of deformation in the Jiali and Gaoligong shear zones occurred from 22 to 11 Ma and from 18 to 13 Ma, respectively. Structural data collected during this study indicate that the Jiali shear zone underwent a change in shear sense from sinistral to dextral during its movement history. Based on a comparison with the deformation histories of other major shear zones in the region, we argue that the initial sinistral motion recorded by the Jiali shear zone was coincident with that of the Ailao Shan–Red River shear zone, which marked the northern boundary of the southeastward extrusion of the Indochina block during the Early Miocene. From the Middle Miocene (~18 Ma), the Jiali shear zone changed to dextral displacement, becoming linked with the dextral Gaoligong shear zone that developed as a consequence of continued northward indentation of the Indian continent into Asia. Since this time, the Jiali and Gaoligong shear zones have been united, defining the southwestern boundary of the EHS during clockwise rotation of the eastward-extruding Tibetan block, as revealed by recent GPS data. The temporal change in regional deformation pattern from southeastward block extrusion to clockwise rotation of crustal fragments may have played an important role in the development of the eastern Himalayan drainage system around the EHS. 相似文献