SiGOG: simulated GPS observation generator   总被引：3，自引：0，他引：3  

Elsa Mohino  Mauricio Gende  Claudio Brunini  Miguel Heraiz 《GPS Solutions》2005,9(3):250-254

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Identification and modeling of earthquake ground response - I. Site amplification     

A.-W. Elgamal  M. Zeghal  E. Parra  R. Gunturi  H.T. Tang  J.C. Stepp 《Soil Dynamics and Earthquake Engineering》1996,15(8):499-522

Seismic downhole-array data provide a unique source of information on actual soil (and overall site) behavior over a wide range of loading conditions that are not readily covered by in-situ or laboratory experimentation procedures. In this paper, free-field downhole-array seismic records are employed to identify and model the recorded response at the Lotung (Taiwan) and Treasure Island (California) sites. At Lotung, a five-accelerometer array recorded the site response during 18 earthquakes (1985–1986). The Treasure Island site was instrumented in 1992 with an array of six accelerometers that recorded a low amplitude earthquake in 1993. Using this downhole data, correlation and spectral analyses are performed to evaluate shear wave propagation characteristics, variation of shear wave velocity with depth and site resonant frequencies and model configurations. In addition, the actual seismic shear stress-strain histories are directly evaluated from the recorded downhole accelerations. These histories provide valuable insight into the mechanisms of site amplification, damping and pore-pressure build-up. Computational simulations of these case histories are performed based on the identified mechanisms of site response. In a companion paper, two additional case histories of site liquefaction are analyzed using records of downhole seismic response.  相似文献   

Identification and modeling of earthquake ground response - II. Site liquefaction   总被引：1，自引：0，他引：1  

Mourad Zeghal  Ahmed-W. Elgamal  Ender Parra 《Soil Dynamics and Earthquake Engineering》1996,15(8):523-547

Downhole records of seismically-induced soil liquefaction are a valuable source of information on the associated mechanisms of stiffness degradation and lateral spreading. In this paper, free-field downhole array seismic records are employed to identify and model the recorded response at Wildlife Refuge (California, USA) and Port Island (Kobe, Japan) sites. The Wildlife Refuge site was instrumented in 1982 with a two-accelerometer array and six piezometers that recorded a case of seismically induced site liquefaction. At Port Island, a four-accelerometer down-hole array recorded strong motion during the recent 1995 Hyogoken-Nanbu earthquake. This earthquake resulted in widespread liquefaction and major ground deformations at Port Island. Using the recorded downhole accelerations at these two sites, the actual seismic shear stress-strain histories are directly evaluated. These histories provide valuable insight into the mechanisms of site liquefaction and associated loss of stiffness and strength. Based on the identified dynamic soil behaviors, computational simulations of the observed seismic response are performed. Optimization techniques are employed to estimate the necessary computational modeling parameters. This document constitutes the second part of a set of two companion papers about site amplification and liquefaction.  相似文献   

Late Quaternary western Mediterranean pollen records and African winds     

D. Magri  I. Parra   《Earth and Planetary Science Letters》2002,200(3-4):401-408

Late Quaternary vegetation changes of regional and global significance in the Mediterranean region are generally interpreted as being controlled by changes in the circulation patterns of North Atlantic air masses. However, the possibility cannot be excluded that they may also be related to winds blowing from Africa. Long pollen records from southwest Europe show that Cedrus pollen of northwest African provenance is found during the glacial periods, and occasionally during abrupt deforestation events in the forest-dominated periods of the interglacials. A pollen concentration record from central Italy shows that during the Holocene the presence of Cedrus pollen coincides with two abrupt deforestation events, around 8.1 and 4.2 cal kyr BP. These observations raise the question of a possible influence of eolian activity on arboreal vegetation during phases of climatic stress towards aridity, and suggest the use of modern pollen monitoring as a strategy for revealing tendencies towards aridification in southwestern Europe.  相似文献   

Assessing the geochemical reactivity of inorganic phosphorus along estuaries by means of laboratory simulation experiments     

Enrique García‐Luque  Jesús M. Forja Pajares  Abelardo Gmez‐Parra 《水文研究》2006,20(16):3555-3566

Phosphate behaviour in natural estuarine systems can be studied by performing field measurements and by undertaking laboratory simulation experiments. Thus, in this paper we describe the use of a dynamic automated estuarine simulator to characterize the geochemical reactivity of phosphate in varying salinity gradients in order to study possible mechanisms of phosphate removal from the dissolved phase (e.g. formation of some kind of apatite) and how changes in pH and salinity values influence this removal. Six laboratory assays, representing various salinity and pH gradients (average pH values between 7 and 8), were carried out. The geochemical equilibrium model MINTEQA2 was employed to characterize removal of phosphate. Among the minerals from which dissolved phosphate can originate, it seems that hydroxyapatite is by far the mineral that shows the greatest saturation indexes in the experiments. Thus, there is evidence that a type of calcium phosphate (hydroxyapatite) is involved in phosphate removal in the assays. Phosphate removal by Ca²⁺ occurs sharply at salinity values of 1–2, whereas by Fe³⁺ it is relatively gradual, at least until a salinity value of 7. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

The La Luna formation: chemostratigraphy and organic facies in the Middle Magdalena Basin     

A. Rangel  P. Parra  C. Nio 《Organic Geochemistry》2000,31(12):2694

A detailed geochemical study and a sequence stratigraphic interpretation have been conducted on a sedimentary sequence of the Upper Cretaceous La Luna Formation, in a section outcropping in the eastern flank of the Middle Magdalena Basin (MMB), Colombia. The goals were to evaluate geochemical variability related to lithofacies and organic facies changes, characterize depositional environment and investigate the possible relationship between geochemical data and sequence stratigraphic cycles. The La Luna Formation is composed of organic-rich sediments of monotonous appearance, with good to excellent potential for oil generation. Most of the bulk, petrographic and biomarker parameters display a relatively narrow range of variation. However, the geochemical variations are sufficient to differentiate organic facies types B, BC and C in the Salada Member, B and D in the Pujamana Member and B in the Galembo Member. Certain biomarker ratios are consistent within the La Luna Formation and are characteristic of its depositional environment, for example, average ratios of diasterane/sterane are lower than 1, Ts/Tm averages are less than 0.33, the C₃₅/C₃₄ hopane ratio is more than 0.92, and oleanane/C₃₀ hopane ratios range from 0.02 to 0.19. Regarding depositional condition indicators, the C₃₅/C₃₄ hopane ratio shows a good positive correlation with HI. This suggests that in carbonate environment changes in this parameter are more strongly related to redox condition than to changes in carbonate content. Regarding the possible relationship between organic matter characteristics and sea level changes, in regressive carbonate shelves during shallow stages, HI tends to increase and TOC tends to decrease, while in regressive siliciclastic shelves, both TOC and HI decrease continuously. Some biomarker ratios (oleanane/C₃₀ hopane, C₂₀/C₂₃ tricyclic, Ts/Tm) increase during base level falls. Regarding δ ¹³C/¹²C isotope composition, the aromatic fraction and whole bitumen display an isotopic shift associated to the main deepening event in the section.  相似文献   

Possible detection of an old bipolar shell associated with η Carinae     

Joaquín Bohigas  Mauricio Tapia  María Teresa Ruiz †  Miguel Roth 《Monthly notices of the Royal Astronomical Society》2000,312(2):295-300

Continuum-subtracted dereddened images in the light of several atomic lines show the presence of an extended bipolar nebula surrounding η Carinae with size ∼100×45 arcsec² (1.3×0.5 pc²). This feature is best delineated in [O  iii ] 5007. The geometrical disposition and mass of the shell suggest that it was formed by mass ejections from η Carinae. The dynamic age of the nebula is ∼13 000/ V ₇ yr, where V ₇ is the mean expansion velocity in 100 km s⁻¹, and its mass is between 5 and 10 M_⊙. The nebula is photoionized and composed of unprocessed material. The major axes of the nebula and of the Homunculus are nearly perpendicular. We also report the discovery of elongated emission knots prominent in [N  ii ] located 64 to 100 arcsec away from η Carinae, which implies that they were ejected either centuries ago or at a more recent date but with extremely large velocities.  相似文献   

Fennoscandia revisited: a spatially improved tree-ring reconstruction of summer temperatures for the last 900 years   总被引：1，自引：0，他引：1  

Hans W. Linderholm  Jesper Björklund  Kristina Seftigen  Björn E. Gunnarson  Mauricio Fuentes 《Climate Dynamics》2015,45(3-4):933-947

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Mesozoic–Cenozoic multistage tectonic evolution of the Pamir: Detrital fission-track constraints from the Tajik Basin     

Lin Li  Yani Najman  Guillaume Dupont-Nivet  Mauricio Parra  Pierrick Roperch  Mustafa Kaya  Niels Meijer  Paul O'Sullivan  Gilby Jepson  Jovid Aminov 《Basin Research》2023,35(2):530-550

Knowledge of the tectonic history of the Pamir contributes to our understanding of both the evolution of collisional orogenic belts as well as factors controlling Central Asian aridification. It is, however, not easy to decipher the Mesozoic–Cenozoic tectonics of the Pamir due to extensive Neogene deformation in an orogen that remains largely understudied. This study reports detrital apatite and zircon fission-track (FT) ages from both the eastern Tajik Basin sedimentary rocks and Pamir modern river sands. These FT data, supported by vitrinite reflectance and zircon and apatite U–Pb double dating, suggest that the majority of the FT ages are unreset and record exhumation stages of the Pamir, which has served as the source terrane of the Tajik Basin since the Cretaceous. Furthermore, we combine the new data with a compilation of published detrital apatite and zircon FT data from both the Tajik Basin sedimentary rocks and Pamir modern river sands, to explore the Mesozoic–Cenozoic tectonic history of Pamir. Deconvolved FT Peak Ages document two major Mesozoic exhumation events associated with the Late Triassic–Early Jurassic Cimmerian orogeny that reflects accretion of the Pamir terranes, as well as the Early–early Late Cretaceous deformation associated with the northward subduction of the Neo-Tethys Ocean beneath Pamir. The compiled data also show significant Late Eocene–Neogene exhumation associated with the ongoing formation of the Pamir, which peaks at ca. 36, 25, 14 and 7 Ma.  相似文献   

Source location of long period seismicity at Volcàn de Colima,México   总被引：1，自引：0，他引：1  

Simona Petrosino  Paola Cusano  Mario La Rocca  Danilo Galluzzo  Justo Orozco-Rojas  Mauricio Bretón  Jesus Ibáñez  Edoardo Del Pezzo 《Bulletin of Volcanology》2011,73(7):887-898

This paper presents an analysis of seismicity associated with the volcanic activity of Volcàn de Colima (México) and recorded in the period November 2005–April 2006 during a field survey by the Istituto Nazionale di Geofisica e Vulcanologia (INGV)–Osservatorio Vesuviano, the Observatorio Vulcanologico de Colima of Colima University and the Instituto Andaluz de Geofisica, University of Granada. Three different types of volcanic earthquakes have been identified on the basis of their spectral properties: Type A (0.3–1 Hz), Type B (1–5 Hz) and Type C (3–4 Hz). Results of polarization analysis applied to Type A events show a predominance of radial motion, indicating that the wavefield comprises compressional waves (P) and shear waves polarized in the vertical plane (SV), while the signal always begins with a negative polarity. Type A, B and C earthquakes have been located using both a flat layered model and a 3D model including topography. Hypocentre distributions indicate that the source of Type A signals is very shallow and confined to a small volume lying about 1 km below the crater. In contrast, the source of Type B and C events is significantly deeper, with most hypocentres located in a volume of about 1 km³ centred at 2.5–3 km depth. A cluster analysis based on the cross-correlation among the waveforms of different events recorded at the same station was applied to Type A earthquakes. Only two clusters, which include only a small percentage of events were found, indicating that earthquake families were uncommon during the period of our survey.  相似文献