Linear versus non-linear earthquake location and seismogenic fault detection in the southern Tyrrhenian Sea, Italy     

D. Presti  B. Orecchio  G. Falcone  G. Neri 《Geophysical Journal International》2008,172(2):607-618

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A multidisciplinary effort to assign realistic source parameters to models of volcanic ash-cloud transport and dispersion during eruptions   总被引：6，自引：1，他引：5  

L.G. Mastin  M. Guffanti  R. Servranckx  P. Webley  S. Barsotti  K. Dean  A. Durant  J.W. Ewert  A. Neri  W.I. Rose  D. Schneider  L. Siebert  B. Stunder  G. Swanson  A. Tupper  A. Volentik  C.F. Waythomas 《Journal of Volcanology and Geothermal Research》2009,186(1-2):10

During volcanic eruptions, volcanic ash transport and dispersion models (VATDs) are used to forecast the location and movement of ash clouds over hours to days in order to define hazards to aircraft and to communities downwind. Those models use input parameters, called “eruption source parameters”, such as plume height H, mass eruption rate Ṁ, duration D, and the mass fraction m₆₃ of erupted debris finer than about 4 or 63 μm, which can remain in the cloud for many hours or days. Observational constraints on the value of such parameters are frequently unavailable in the first minutes or hours after an eruption is detected. Moreover, observed plume height may change during an eruption, requiring rapid assignment of new parameters. This paper reports on a group effort to improve the accuracy of source parameters used by VATDs in the early hours of an eruption. We do so by first compiling a list of eruptions for which these parameters are well constrained, and then using these data to review and update previously studied parameter relationships. We find that the existing scatter in plots of H versus Ṁ yields an uncertainty within the 50% confidence interval of plus or minus a factor of four in eruption rate for a given plume height. This scatter is not clearly attributable to biases in measurement techniques or to well-recognized processes such as elutriation from pyroclastic flows. Sparse data on total grain-size distribution suggest that the mass fraction of fine debris m₆₃ could vary by nearly two orders of magnitude between small basaltic eruptions ( 0.01) and large silicic ones (> 0.5). We classify eleven eruption types; four types each for different sizes of silicic and mafic eruptions; submarine eruptions; “brief” or Vulcanian eruptions; and eruptions that generate co-ignimbrite or co-pyroclastic flow plumes. For each eruption type we assign source parameters. We then assign a characteristic eruption type to each of the world's  1500 Holocene volcanoes. These eruption types and associated parameters can be used for ash-cloud modeling in the event of an eruption, when no observational constraints on these parameters are available.  相似文献   

Field Survey of the 2015 Chile Tsunami with Emphasis on Coastal Wetland and Conservation Areas     

Manuel Contreras-López  Patricio Winckler  Ignacio Sepúlveda  Adolfo Andaur-Álvarez  Fernanda Cortés-Molina  Camila J. Guerrero  Cyntia E. Mizobe  Felipe Igualt  Wolfgang Breuer  José F. Beyá  Hernán Vergara  Rodrigo Figueroa-Sterquel 《Pure and Applied Geophysics》2016,173(2):349-367

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The Coupling State of an Idealized Stable Boundary Layer   总被引：1，自引：1，他引：0  

Otávio C. Acevedo  Felipe D. Costa  Gervásio A. Degrazia 《Boundary-Layer Meteorology》2012,145(1):211-228

The coupling state between the surface and the top of the stable boundary layer (SBL) is investigated using four different schemes to represent the turbulent exchange. An idealized SBL is assumed, with fixed wind speed and temperature at its top. At the surface, two cases are considered, first a constant temperature, 20 K lower than the SBL top, and later a constant 2 K h⁻¹ cooling rate is assumed for 10 h after a neutral initial condition. The idealized conditions have been chosen to isolate the influence of the turbulence formulations on the coupling state, and the intense stratification has the purpose of enhancing such a response. The formulations compared are those that solve a prognostic equation for turbulent kinetic energy (TKE) and those that directly prescribe turbulence intensity as a function of atmospheric stability. Two TKE formulations are considered, with and without a dependence of the exchange coefficients on stability, while short and long tail stability functions (SFs) are also compared. In each case, the dependence on the wind speed at the SBL top is considered and it is shown that, for all formulations, the SBL experiences a transition from a decoupled state to a coupled state at an intermediate value of mechanical forcing. The vertical profiles of potential temperature, wind speed and turbulence intensity are shown as a function of the wind speed at the SBL top, both for the decoupled and coupled states. The formulation influence on the coupling state is analyzed and it is concluded that, in general, the simple TKE formulation has a better response, although it also tends to overestimate turbulent mixing. The consequences are discussed.  相似文献   

Sampling Strategies for Uncertainty Reduction in Categorical Random Fields: Formulation,Mathematical Analysis and Application to Multiple-Point Simulations     

Santibañez  Felipe  Silva  Jorge F.  Ortiz  Julián M. 《Mathematical Geosciences》2019,51(5):579-624

Mathematical Geosciences - The task of optimal sampling for the statistical simulation of a discrete random field is addressed from the perspective of minimizing the posterior uncertainty of...  相似文献   

Variability of carbon dioxide flux from tropical (Cerrado) hydroelectric reservoirs   总被引：4，自引：0，他引：4  

Fábio Roland  Luciana O. Vidal  Felipe S. Pacheco  Nathan O. Barros  Arcilan Assireu  Jean P. H. B. Ometto  André C. P. Cimbleris  Jonathan J. Cole 《Aquatic Sciences - Research Across Boundaries》2010,72(3):283-293

Hydroelectric reservoirs generate energy without significant combustion of fossil fuels. However, these systems can, potentially, emit greenhouse gases (GHG’s) at a rate which may be significant at the global scale, and, possible, co-equal, per kilowatt-hour, to that from conventional coal or oil-fired systems. Although much of the new construction of hydroelectric reservoirs is in the tropics, most of the data on GHG emissions comes from temperate regions. Further, much of the existing data on reservoir gas emissions comes from single sites, usually near the terminal dams. Large tropical reservoirs often involve the impoundments of river systems with complex morphology which in turn can cause spatial heterogeneity in gas flux. We evaluated spatial and seasonal variability in CO₂ concentrations and gas flux for five large (50–1,400 km²) reservoirs in the Cerrado region of Brazil. Most of data set (87% of all measurements) showed CO₂ supersaturation and net efflux to the atmosphere. There was as much or more variation in pCO₂ over space and among seasons. The large studied reservoirs showed different zones in terms of CO₂ emission because those fluxes are dependent on flooded biomass, watershed input of organic matter and dam operation regime. Here we demonstrate that the reservoirs in the Brazilian Cerrado have low rates of CO₂ emissions compared to existing global comparisons. Our results suggest that ignoring the spatial variability can lead to more than 25% error in total system gas flux.  相似文献   

Tracing anthropogenically driven groundwater discharge into a coastal lagoon from southern Brazil     

Isaac R. Santos  Felipe Niencheski  William Burnett  Richard Peterson  Jeffrey Chanton  Carlos F.F. Andrade  Idel B. Milani  Axel Schmidt  Kay Knoeller 《Journal of Hydrology》2008,353(3-4):275-293

We investigated the distribution of naturally occurring geochemical tracers (²²²Rn, ²²³Ra, ²²⁴Ra, ²²⁶Ra, CH₄, δ¹⁸O, and δ²H) in the water column and adjacent groundwater of Mangueira Lagoon as proxies of groundwater discharge. Mangueira Lagoon is a large (90 km long), shallow (4–5 m deep), fresh, and non-tidal coastal lagoon in southern Brazil surrounded by extensively irrigated rice plantations and numerous irrigation canals. We hypothesized that the annual, intense irrigation for rice agriculture creates extreme conditions that seasonally change groundwater discharge patterns in the adjacent lagoon. We further supposed that dredging of irrigation canals alters groundwater fluxes.

While the activities of ²²²Rn in shallow groundwater were 2–3 orders of magnitude higher than in surface water, CH₄ and radium isotopes were only 1 order of magnitude higher. Therefore, ²²²Rn appears to be the preferred groundwater tracer in this system. Radon concentrations and conductivities were dramatically higher near the pump house of rice irrigation canals, consistent with a groundwater source. Modeling of radon inventories accounting for total inputs (groundwater advection, diffusion from sediments, and decay of ²²⁶Ra) and losses (atmospheric evasion, horizontal mixing and decay) indicated that groundwater advection rates in the irrigation canals (25 cm/d) are over 2 orders of magnitude higher than along the shoreline (0.1 cm/d). Nearly 75% of the total area of the canals is found in the southern half of the lagoon, where groundwater inputs seem to be higher as also indicated by methane and stable isotope trends. In spite of the relatively small area of the canals, we estimate that they contribute nearly 70% of the total (57,000 m³/d) groundwater input into the entire Mangueira Lagoon. We suggest that the dredging of these canals cut through aquitards which previously restricted upward advection from the underlying permeable strata. The irrigation channels may therefore represent an important but previously overlooked source of nutrients and other dissolved chemicals derived from agricultural practices into the lagoon.  相似文献   

Pyroclastic density currents resulting from the interaction of basaltic magma with hydrothermally altered rock: an example from the 2006 summit eruptions of Mount Etna,Italy   总被引：2，自引：1，他引：1  

B. Behncke  S. Calvari  S. Giammanco  M. Neri  H. Pinkerton 《Bulletin of Volcanology》2008,70(10):1249-1268

After 16 months of quiescence, Mount Etna began to erupt again in mid-July 2006. The activity was concentrated at and around the Southeast Crater (SEC), one of the four craters on the summit of Etna, and eruptive activity continued intermittently for 5 months. During this period, numerous vents displayed a wide range of eruptive styles at different times. Virtually all explosive activities took place at vents at the summit of the SEC and on its flanks. Eruptive episodes, which lasted from 1 day to 2 weeks, became shorter and more violent with time. Volcanic activity at these vents was often accompanied by dramatic mass-wasting processes such as collapse of parts of the cone, highly unusual flowage processes involving both old rocks and fresh magmatic material, and magma–water interaction. The most dramatic events took place on 16 November, when numerous rockfalls and pyroclastic density currents (PDCs) were generated during the opening of a large fracture on the SE flank of the SEC cone. The largest PDCs were clearly triggered explosively, and there is evidence that much of the energy was generated during the interaction of intruding magma with wet rocks on the cone’s flanks. The most mobile PDCs traveled up to 1 km from their source. This previously unknown process on Etna may not be unique on this volcano and is likely to have taken place on other volcanoes. It represents a newly recognized hazard to those who visit and work in the vicinity of the summit of Etna.  相似文献   

Assessing Uncertainty Associated with the Delineation of Geochemical Anomalies   总被引：2，自引：0，他引：2  

Costa  Joao Felipe  Koppe  Jair Carlos 《Natural Resources Research》1999,8(1):59-67

A pedogeochemical exploratory survey of gold deposits was carried out in the region of São Sepé (southernmost Brazil). The region comprises a predominantly metamorphosed belt of volcanoclastics, sediments, serpentinites, basalts, gabbros, chert, tuffs, and banded iron formation of the Proterozoic age. The anomalies were identified first by stream sediment heavy mineral survey at the regional scale of exploration. Once spatial continuity was modeled, ordinary block kriging was performed to generate geochemical maps. Indicator block kriging also was used as an alternative in analyzing and interpreting geochemical data. A novel approach is proposed, which combines both ordinary and indicator kriging for delineating geochemical anomalies. Probability maps proved to be appropriate for selecting new sites for further exploration. Gold anomalies in soils trending NE were well defined by geostatistical analysis and subsequently confirmed by drilling.  相似文献   

Seismogenic stress field beneath Mt. Etna (South Italy) and possible relationships with volcano-tectonic features     

O. Cocina  G. Neri  E. Privitera  S. Spampinato 《Journal of Volcanology and Geothermal Research》1998,83(3-4)

Shallow shear-type seismic activity occurring beneath the Etna volcano during 1990–1995 has been analysed for hypocenter locations, focal mechanisms and stress tensor inversion. The results have been examined jointly with Electronic Distance Measurements and tiltmeter data collected in the same period and reported in the literature. Significant seismicity located in the upper 10 km was found to be confined to the time intervals in which ground deformation data indicated inflation of the volcano edifice (e.g., the periods preceding the December 1991–March 1993 and August 1995–March 1996 eruptive phases). The shocks mostly occurred in a sector approximately centered on the crater area and elongated in the East–West direction. The causative seismogenic stress shows a low-dip East–West orientation of σ₁. In agreement with existing knowledge on relationships between local fault systems and magma uprise processes, the shallow seismicity in question is tentatively explained as being due to lateral compression by magma inside a nearly North–South system. The volcano deflation phase revealed by Electronic Distance Measurements and tilt data during the 1991–1993 major eruption was not accompanied by any significant shear-type shallow event. Below the depth of 10 km, the North–South prevailing orientation of σ₁ reflects the dominant role of the regional stress.  相似文献