Mercurian impact ejecta: Meteorites and mantle     

Brett GLADMAN  Jaime COFFEY 《Meteoritics & planetary science》2009,44(2):285-291

Abstract— We have examined the fate of impact ejecta liberated from the surface of Mercury due to impacts by comets or asteroids, in order to study 1) meteorite transfer to Earth, and 2) reaccumulation of an expelled mantle in giant‐impact scenarios seeking to explain Mercury's large core. In the context of meteorite transfer during the last 30 Myr, we note that Mercury's impact ejecta leave the planet's surface much faster (on average) than other planets in the solar system because it is the only planet where impact speeds routinely range from 5 to 20 times the planet's escape speed; this causes impact ejecta to leave its surface moving many times faster than needed to escape its gravitational pull. Thus, a large fraction of Mercurian ejecta may reach heliocentric orbit with speeds sufficiently high for Earth‐crossing orbits to exist immediately after impact, resulting in larger fractions of the ejecta reaching Earth as meteorites. We calculate the delivery rate to Earth on a time scale of 30 Myr (typical of stony meteorites from the asteroid belt) and show that several percent of the high‐speed ejecta reach Earth (a factor of 2–3 less than typical launches from Mars); this is one to two orders of magnitude more efficient than previous estimates. Similar quantities of material reach Venus. These calculations also yield measurements of the re‐accretion time scale of material ejected from Mercury in a putative giant impact (assuming gravity is dominant). For Mercurian ejecta escaping the gravitational reach of the planet with excess speeds equal to Mercury's escape speed, about one third of ejecta reaccretes in as little as 2 Myr. Thus collisional stripping of a silicate proto‐Mercurian mantle can only work effectively if the liberated mantle material remains in small enough particles that radiation forces can drag them into the Sun on time scale of a few million years, or Mercury would simply re‐accrete the material.  相似文献   

Middle Eocene deformation–sedimentation in the Luracatao Valley: Tracking the beginning of the foreland basin of northwestern Argentina     

Patricio Payrola Bosio  Jaime Powell  Cecilia del Papa  Fernando Hongn 《Journal of South American Earth Sciences》2009,28(2):142-154

The Andean foreland basin overlaps the Cretaceous-Paleogene Salta rift basin in northwestern Argentina. Knowledge of the relationship between rift and foreland basins is key to understanding the initial stages of foreland basin development related to Andean shortening. We present a new stratigraphic scheme for the Luracatao Valley, revealing that the Quebrada de los Colorados Formation (Payogastilla Group) lies over the Santa Bárbara Subgroup (Salta Group) through an erosional unconformity that turns into an angular unconformity close to folds and faults recorded in the Santa Bárbara Subgroup. The base of the Quebrada de los Colorados Formation shows growth strata along the west frontal limb of an anticline with Santa Bárbara units in its core. The finding of a mammalian fossil at the base of the Quebrada de los Colorados Formation allows us to assign a Middle-Upper Eocene age to the sedimentation; therefore, the time elapsed between the deposition of the final postrift strata and the beginning of Andean sedimentation was brief and constrained to the Lower-Middle Eocene. This data indicates that the Eocene deformation phase described in other portions of the Puna-Cordillera Oriental transition (e.g., the northern Calchaquí Valley and Aguilar range) is also present in the Luracatao Valley, offering new tools for interpreting the ages and distributions of the initial episodes of sedimentation and deformation related to the Andean shortening. Thus, the Luracatao Valley provides new evidence for tracking the distribution of the Paleogene deformation in northwestern Argentina.  相似文献   

A Blocking Markov Chain Monte Carlo Method for Inverse Stochastic Hydrogeological Modeling   总被引：3，自引：2，他引：1  

Jianlin Fu  J. Jaime Gómez-Hernández 《Mathematical Geosciences》2009,41(2):105-128

An adequate representation of the detailed spatial variation of subsurface parameters for underground flow and mass transport simulation entails heterogeneous models. Uncertainty characterization generally calls for a Monte Carlo analysis of many equally likely realizations that honor both direct information (e.g., conductivity data) and information about the state of the system (e.g., piezometric head or concentration data). Thus, the problems faced is how to generate multiple realizations conditioned to parameter data, and inverse-conditioned to dependent state data. We propose using Markov chain Monte Carlo approach (MCMC) with block updating and combined with upscaling to achieve this purpose. Our proposal presents an alternative block updating scheme that permits the application of MCMC to inverse stochastic simulation of heterogeneous fields and incorporates upscaling in a multi-grid approach to speed up the generation of the realizations. The main advantage of MCMC, compared to other methods capable of generating inverse-conditioned realizations (such as the self-calibrating or the pilot point methods), is that it does not require the solution of a complex optimization inverse problem, although it requires the solution of the direct problem many times.  相似文献   

On the potential of time series InSAR for subsidence and ground rupture evaluation: application to Texcoco and Cuautitlan–Pachuca subbasins,northern Valley of Mexico     

Gabriela Ll. Siles  Juan Carlos Alcérreca-Huerta  Penélope López-Quiroz  Jaime Carrera Hernández 《Natural Hazards》2015,78(2):1091-1110

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Ocean versus atmosphere control on western European wintertime temperature variability     

Ayako Yamamoto  Jaime B. Palter  M. Susan Lozier  Michel S. Bourqui  Susan J. Leadbetter 《Climate Dynamics》2015,45(11-12):3593-3607

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Mid‐elevation ecosystems of Panama: future uncertainties in light of past global climatic variability          下载免费PDF全文

Alexander Correa‐Metrio  Maria I. Vélez  Jaime Escobar  Jeannine‐Marie St‐Jacques  Minerva López‐Pérez  Jason Curtis  Jason Cosford 《第四纪科学杂志》2016,31(7):731-740

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Families of periodic orbits in the planar Hill’s four-body problem     

Jaime Burgos-García 《Astrophysics and Space Science》2016,361(11):353

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Elastoplastic constitutive modelling of soil–structure interfaces under monotonic and cyclic loading     

Sofia Costa D’Aguiar  Arezou Modaressi-Farahmand-Razavi  Jaime Alberto dos Santos  Fernando Lopez-Caballero 《Computers and Geotechnics》2011

This paper is dedicated to the non-linear numerical modelling of the soil–structure interface. Thus, in a first part, after the presentation of the constitutive model, the soil–structure interface interaction is treated in terms of direct shear test simulations. A strategy for the interface model parameters’ identification is also presented. This strategy is linked to the similitude of soil–structure interface behavior and the soil behavior, regarding the interface surface roughness. In a second part, the performance of the numerical simulations are verified numerically against published results for soil–structure experimental shear tests. Finally, as an application, interface stress paths are studied in axially loaded pile–soil systems and load transfer mechanisms are identified.  相似文献   

Late Quaternary (24–10 ka BP) environmental history of the Neotropical lowlands inferred from ostracodes in sediments of Lago Petén Itzá, Guatemala     

Liseth Pérez  Peter Frenzel  Mark Brenner  Jaime Escobar  Philipp Hoelzmann  Burkhard Scharf  Antje Schwalb 《Journal of Paleolimnology》2011,46(1):59-74

We inferred late Pleistocene and early Holocene (24–10 ka BP) environmental conditions in and around Lago Petén Itzá, Guatemala from ostracode remains in the lake sediments. Multivariate statistics were run on autecological information for 29 extant ostracode species collected in 63 aquatic ecosystems on the Yucatán Peninsula along a steep, increasing NW–S precipitation gradient and across a large altitudinal range. Conductivity and water depth are the most important factors that shape ostracode communities. Transfer functions were developed and applied to fossil ostracode assemblages in a ~76-m sediment core (PI-6, ~85 ka) taken in 71 m of water from Lago Petén Itzá, to infer past shifts in conductivity and water level. Results suggest climate was cold and wet during the Last Glacial Maximum (LGM). Alternating dry and wet conditions characterized the deglacial. Early Holocene climate was warmer and wetter. The LGM was characterized by low ostracode species richness (4 spp.) and abundance (<940 valves g⁻¹), dominance of benthic over nektobenthic taxa, abundant Physocypria globula, conductivity as low as 190 μS cm⁻¹, and clay-rich sediments with relatively high total organic carbon and low C/N ratios (<14), suggesting relatively deeper water at the core site associated with abundant precipitation. Greatest water depth at the core site during the LGM occurred late in the period and was ~50 m. The deglacial was characterized by drier conditions, higher ostracode species richness (6 spp.) and abundances up to 18,115 valves g⁻¹, dominance of nektobenthic species, and presence of shallow-water and littoral-zone indicators such as Heterocypris punctata and Strandesia intrepida, conductivity up to 550 μS cm⁻¹, C/N ratios as high as 37, and gypsum deposition. Lowest inferred lake depth at the core site during the deglacial was ~20 m. The early Holocene was characterized by high numbers of ostracode remains, up to 25,500 valves g⁻¹, and the presence of L. opesta and P. globula. Cytheridella ilosvayi was absent from late Pleistocene sediments, suggesting it colonized northern Central America during the Holocene.  相似文献   

The DRASTIC-Sg model: an extension to the DRASTIC approach for mapping groundwater vulnerability in aquifers subject to differential land subsidence,with application to Mexico City   总被引：1，自引：1，他引：0  

Antonio Hernández-Espriú  J. Antonio Reyna-Gutiérrez  Emilio Sánchez-León  Enrique Cabral-Cano  Jaime Carrera-Hernández  Pedro Martínez-Santos  Sergio Macías-Medrano  Giacomo Falorni  Davide Colombo 《Hydrogeology Journal》2014,22(6):1469-1485

Mexico City relies on groundwater for most of its domestic supply. Over the years, intensive pumping has led to significant drawdowns and, subsequently, to severe land subsidence. Tensile cracks have also developed or reactivated as a result. All such processes cause damage to urban infrastructure, increasing the risk of spills and favoring contaminant propagation into the aquifer. The effects of ground deformation are frequently ignored in groundwater vulnerability studies, but can be relevant in subsiding cities. This report presents an extension to the DRASTIC methodology, named DRASTIC-Sg, which focuses on evaluating groundwater vulnerability in urban aquifers affected by differential subsidence. A subsidence parameter is developed to represent the ground deformation gradient (Sg), and then used to depict areas where damage risk to urban infrastructure is higher due to fracture propagation. Space-geodetic SqueeSAR data and global positioning system (GPS) validation were used to evaluate subsidence rates and gradients, integrating hydrogeological and geomechanical variables into a GIS environment. Results show that classic DRASTIC approaches may underestimate groundwater vulnerability in settings such as the one at hand. Hence, it is concluded that the Sg parameter is a welcome contribution to develop reliable vulnerability assessments in subsiding basins.  相似文献