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131.
Vanessa Andrews Joann Stock Carlos Ariel Ram��rez V��zquez Gabriel Reyes-D��vila 《Pure and Applied Geophysics》2011,168(8-9):1331-1338
On 22 January 2003, the M w?=?7.6 Tecomán earthquake struck offshore of the state of Colima, Mexico, near the diffuse triple junction between the Cocos, Rivera, and North American plates. Three-hundred and fifty aftershocks of the Tecomán earthquake with magnitudes between 2.6 and 5.8, each recorded by at least 7 stations, are relocated using the double difference method. Initial locations are determined using P and S readings from the Red Sismológica Telemétrica del Estado de Colima (RESCO) and a 1-D velocity model. Because only eight RESCO stations were operating immediately following the Tecomán earthquake, uncertainties in the initial locations and depths are fairly large, with average uncertainties of 8.0?km in depth and 1.4?km in the north?Csouth and east?Cwest directions. Events occurring between 24 January and 31 January were located using not only RESCO phase readings but also additional P and S readings from 11 temporary stations. Average uncertainties decrease to 0.8?km in depth, 0.3?km in the east?Cwest direction, and 0.7?km in the north?Csouth direction for events occurring while the temporary stations were deployed. While some preliminary studies of the early aftershocks suggested that they were dominated by shallow events above the plate interface, our results place the majority of aftershocks along the plate interface, for a slab dipping between approximately 20° and 30°. This is consistent with the slab positions inferred from geodetic studies. We do see some upper plate aftershocks that may correspond to forearc fault zones, and faults inland in the upper plate, particularly among events occurring more than 3?months after the mainshock. 相似文献
132.
Thierry Calmus Carlos Pallares Ren�� C. Maury Alfredo Aguill��n-Robles Herv�� Bellon Mathieu Benoit Fran?ois Michaud 《Pure and Applied Geophysics》2011,168(8-9):1303-1330
The study of the geochemical compositions and K-Ar or Ar-Ar ages of ca. 350 Neogene and Quaternary lavas from Baja California, the Gulf of California and Sonora allows us to discuss the nature of their mantle or crustal sources, the conditions of their melting and the tectonic regime prevailing during their genesis and emplacement. Nine petrographic/geochemical groups are distinguished: ??regular?? calc-alkaline lavas; adakites; magnesian andesites and related basalts and basaltic andesites; niobium-enriched basalts; alkali basalts and trachybasalts; oceanic (MORB-type) basalts; tholeiitic/transitional basalts and basaltic andesites; peralkaline rhyolites (comendites); and icelandites. We show that the spatial and temporal distribution of these lava types provides constraints on their sources and the geodynamic setting controlling their partial melting. Three successive stages are distinguished. Between 23 and 13 Ma, calc-alkaline lavas linked to the subduction of the Pacific-Farallon plate formed the Comondú and central coast of the Sonora volcanic arc. In the extensional domain of western Sonora, lithospheric mantle-derived tholeiitic to transitional basalts and basaltic andesites were emplaced within the southern extension of the Basin and Range province. The end of the Farallon subduction was marked by the emplacement of much more complex Middle to Late Miocene volcanic associations, between 13 and 7 Ma. Calc-alkaline activity became sporadic and was replaced by unusual post-subduction magma types including adakites, niobium-enriched basalts, magnesian andesites, comendites and icelandites. The spatial and temporal distribution of these lavas is consistent with the development of a slab tear, evolving into a 200-km-wide slab window sub-parallel to the trench, and extending from the Pacific coast of Baja California to coastal Sonora. Tholeiitic, transitional and alkali basalts of subslab origin ascended through this window, and adakites derived from the partial melting of its upper lip, relatively close to the trench. Calc-alkaline lavas, magnesian andesites and niobium-enriched basalts formed from hydrous melting of the supraslab mantle triggered by the uprise of hot Pacific asthenosphere through the window. During the Plio-Quaternary, the ??no-slab?? regime following the sinking of the old part of the Farallon plate within the deep mantle allowed the emplacement of alkali and tholeiitic/transitional basalts of deep asthenospheric origin in Baja California and Sonora. The lithospheric rupture connected with the opening of the Gulf of California generated a high thermal regime associated to asthenospheric uprise and emplaced Quaternary depleted MORB-type tholeiites. This thermal regime also induced partial melting of the thinned lithospheric mantle of the Gulf area, generating calc-alkaline lavas as well as adakites derived from slivers of oceanic crust incorporated within this mantle. 相似文献
133.
M. Teresa Ram��rez-Herrera Vladimir Kostoglodov Jaime Urrutia-Fucugauchi 《Pure and Applied Geophysics》2011,168(8-9):1415-1433
Holocene and Pleistocene tectonic deformation of the coast in the Mexico subudction margin is recorded by geomorphic and stratigraphic markers. We document the spatial and temporal variability of active deformation on the coastal Mexican subduction margin. Pleistocene uplift rates are estimated using wave-cut platforms at ca. 0.7?C0.9?m/ka on the Jalisco block coast, Rivera-North America tectonic plate boundary. We examine reported measurements from marine notches and shoreline angle elevations in conjunction with their radiocarbon ages that indicate surface uplift rates increasing during the Holocene up to ca. 3?±?0.5?m/ka. In contrast, steady rates of uplift (ca. 0.5?C1.0?m/ka) in the Pleistocene and Holocene characterize the Michoacan coastal sector, south of El Gordo graben and north of the Orozco Fracture Zone (OFZ), incorporated within the Cocos-North America plate boundary. Significantly higher rates of surface uplift (ca. 7?m/ka) across the OFZ subduction may reflect the roughness of subducting plate. Absence of preserved marine terraces on the coastal sector across El Gordo graben likely reflects slow uplift or coastal subsidence. Stratigraphic markers and their radiocarbon ages show late Holocene (ca. last 6?ka bp) coastal subsidence on the Guerrero gap sector in agreement with a landscape barren of marine terraces and with archeological evidence of coastal subsidence. Temporal and spatial variability in recent deformation rates on the Mexican Pacific coast may be due to differences in tectonic regimes and to localized processes related to subduction, such as crustal faults, subduction erosion and underplating of subducted materials under the southern Mexico continental margin. 相似文献
134.
Modern engineering design methods require ground motion time histories as input for non-linear dynamic structural analysis. Non-linear dynamic methods of analysis are increasingly applied in the context of probabilistic risk assessments and for cost-effective design of critical infrastructures. In current engineering practice artificial time histories matching deterministic design spectra or probabilistic uniform hazard spectra are most frequently used for engineering analysis. The intermediate step of generation of response spectra can lead to a biased estimate of the potential damage from earthquakes because of insufficient consideration of the true energy content and strong motion duration of earthquakes. Thus, assessment of seismic risk may seem unrealistic. An engineering approach to the development of three-component ground motion time histories has been established which enables consideration of the typical characteristics of seismic sources, regional ground motion attenuation, and the main geotechnical characteristics of the target site. Therefore, the approach is suitable for use in scenario-based risk analysis a larger number of time histories are required for representation of the seismic hazard. Near-field effects are implemented in the stochastic source model using engineering approximations. The approach is suggested for use in areas of low seismicity where ground motion records of larger earthquakes are not available. Uncertainty analysis indicates that ground motions generated by individual earthquakes are well constrained and that the usual lognormal model is not the best choice for predicting the upper tail of the distribution of the ground motions. 相似文献
135.
Hubert Gall��e C��cile Agosta Luc Gential Vincent Favier Gerhard Krinner 《Surveys in Geophysics》2011,32(4-5):507-518
The Antarctic ice sheet surface mass balance shows high spatial variability over the coastal area. As state-of-the-art climate models usually require coarse resolutions to keep computational costs to a moderate level, they miss some local features that can be captured by field measurements. The downscaling approach adopted here consists of using a cascade of atmospheric models from large scale to meso-?? scale. A regional climate model (Modèle Atmosphérique Régional) forced by meteorological reanalyses provides a diagnostic physically-based rain- and snowfall downscaling model with meteorological fields at the regional scale. Although the parameterizations invoked by the downscaling model are fairly simple, the knowledge of small-scale topography significantly improves the representation of spatial variability of precipitation and therefore that of the surface mass balance. Model evaluation is carried out with the help of shallow firn cores and snow height measurements provided by automatic weather stations. Although downscaling of blowing snow still needs to be implemented in the model, the net accumulation gradient across Law Dome summit is shown to be induced mostly by orographic effects on precipitation. 相似文献
136.
137.
Classifying wave forecasts with model-based Geostatistics and the Aitchison distribution 总被引：1，自引：1，他引：0
Raimon Tolosana-Delgado Juan Jos�� Egozcue Agust��n S��nchez-Arcilla Jes��s G��mez 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(8):1091-1100
This paper proposes a non-parametric method of classification of maps (i.e., variable fields such as wave energy maps for
the Western Mediterranean Sea) into a set of D typical regimes (calm, E-, SW- or N/NW-wind dominated storms, the 4 synoptic situations more often occurring in this region).
Each map in the training set is described by its values at P measurement points and one of these regime classes. A map is thus identified as a labelled point in a P-dimensional feature space, and the problem is to find a discrimination rule that may be used for attaching a classification
probability to future unlabelled maps. The discriminant model proposed assumes that some log-contrasts of these classification
probabilities form a Gaussian random field on the feature space. Then, available data (labelled maps of the training set)
are linked to these latent probabilities through a multinomial model. This model is quite common in model-based Geostatistics
and the Gaussian process classification literature. Inference is here approximated numerically using likelihood based techniques.
The multinomial likelihood of labelled features is combined in a Bayesian updating with the Gaussian random field, playing
the role of prior distribution. The posterior corresponds to an Aitchison distribution. Its maximum posterior estimates are
obtained in two steps, exploiting several properties of this family. The first step is to obtain the mode of this distribution
for labelled features, by solving a mildly non-linear system of equations. The second step is to propagate these estimates
to unlabelled features, with simple kriging of log-contrasts. These inference steps can be extended via Markov-chain Monte
Carlo (MCMC) sampling to a hierarchical Bayesian problem. This MCMC sampling can be improved by further exploiting the Aitchison
distribution properties, though this is only outlined here. Results for the application case study suggest that E- and N/NW-dominated
storms can be successfully discriminated from calm situations, but not so easily distinguished from each other. 相似文献
138.
Combining physical-based models and satellite images for the spatio-temporal assessment of soil infiltration capacity 总被引：1，自引：1，他引：0
Daniele Pedretti Daniel Fern��ndez-Garcia Xavier Sanchez-Vila Marco Barahona-Palomo Diogo Bolster 《Stochastic Environmental Research and Risk Assessment (SERRA)》2011,25(8):1065-1075
The performance of managed artificial recharge (MAR) facilities by means of surface ponds (SP) is controlled by the temporal
evolution of the global infiltration capacity I
c
of topsoils. Cost-effective maintenance operations that aim to maintain controlled infiltration values during the activity
of the SP require the full knowledge of the spatio-temporal variability of I
c
. This task is deemed uncertain. The natural reduction in time of I
c
depends on complex physical, biological and chemical reactions that clog the soil pores and has been observed to decay exponentially
to an asymptotic non-zero value. Moreover, the relative influence of single clogging processes depend on some initial parameters
of the soil, such as the initial infiltration capacity (I
c,0). This property is also uncertain, as aquifers are typically heterogeneous and scarcely characterized in practical situations.
We suggest a method to obtain maps of I
c
using a geostatistical approach, which is suitable to be extended to engineering risk assessment concerning management of
SP facilities. We propose to combine geostatistical inference and a temporally-lumped physical model to reproduce non-uniform
clogging in topsoils of a SP, using field campaigns of local and large scale tests and additionally by means of satellite
images as secondary information. We then postulate a power-law relationship between the parameter of the exponential law,
λ, and I
c,0. It is found that calibrating the two parameters of the power law model it is possible to fit the temporal evolution of total
infiltration rate at the pond scale in a MAR test facility. The results can be used to design appropriate measures to selectively
limit clogging during operation, extending the life of the infiltration pond. 相似文献
139.
G. Milana R. M. Azzara E. Bertrand P. Bordoni F. Cara R. Cogliano G. Cultrera G. Di Giulio A.M. Duval A. Fodarella S. Marcucci S. Pucillo J. R��gnier G. Riccio 《Bulletin of Earthquake Engineering》2011,9(3):741-759
After the 2009 April 6th Mw 6.3 L??Aquila earthquake (Central Italy) the Italian Civil Defense Department promoted the microzoning study in the ten zones in the epicentral area that suffered major damage. In this paper we present the activities and the results concerning a temporary seismic network installed in the historical L??Aquila city center indicated as ??macroarea 1?? in the microzoning project. Seismic data were collected to investigate the amplification effects in the city and to support the microzoning activities in verifying both geological profiles and 1D numerical modeling of the seismic response of the city. The conventional spectral approaches using both microtremor and earthquake data allowed to determine the fundamental resonance frequencies and the amplification factors within the city respectively. The spatial variability of these quantities can be related to the geological and geomorphologic characteristics of the investigated area. A comparison between the network data and the data recorded by the two strong motion instruments installed in the city was also made. This allows verifying the relative response of the accelerometric stations that recorded in the city the major events of the sequence. 相似文献
140.
Davide Lenaz Brian O��Driscoll Francesco Princivalle 《Contributions to Mineralogy and Petrology》2011,162(6):1201-1213
Thirteen Cr-bearing spinels from major horizons of magma replenishment in the open-system Rum Layered Suite have been analysed by X-ray single crystal diffraction and electron microprobe analyses. On the basis of the structural parameters and the chemistry of these spinels the so-called Rum trend, in which Al-content increases at the expense of Cr and Fe3+, has been easily recognised. In addition, natural spinels with Fe3+ content similar to synthetic spinels on the MgCr2O4?CMgFe2O4 join have been analysed for the first time. Layers of chromitite, anorthosite and peridotite situated within several cm of one another have yielded different intracrystalline exchange temperatures using an intercrystalline spinel-olivine thermometer. The Rum anorthosite Cr-spinels are interpreted as having crystallised within the cumulus pile following rejuvenation of the crystal mush. Their low Al-content is a function of simultaneous plagioclase crystallisation, reducing the amount of Al3+ present for the Cr-spinel. By contrast, Cr-spinels in well-known Archean anorthosites (e.g. Ujaragssuit nunat and Fisken?sset, western Greenland) and Sittampundi (southern India) are very aluminous in composition, attributed to crystallisation of Cr-spinel from high-alumina basalts in lower crustal magma chambers and linked to the control exerted by plagioclase crystallisation on Al content of the melt, in the absence of clinopyroxene crystallisation. The compositional differences between the Rum anorthosite Cr-spinels and the Fisken?sset and Sittampundi Cr-spinels suggest that postcumulus reaction of Cr-spinel and melt to low (800?C900°C) temperatures, as invoked for the Rum crystals, may not have been as important a process in the Archean anorthosites. 相似文献