Suboceanic earthquake location and seismic structure in the Kanto district,central Japan     

《Earth and Planetary Science Letters》2006,241(3-4):789-803

We present a combined method, using sP depth-phase data and double-difference arrival times, to determine the precise hypocenter locations of earthquakes that occur under the Pacific Ocean outside of the area covered by the land-based seismic network. We assess the effectiveness of the combined method using a data set of P- and S-wave arrival times and sP depth phase from suboceanic earthquakes recorded by both land-based seismic stations and offshore seismic stations (OFS). The hypocenters of the offshore earthquakes relocated using the combined method are consistent with those determined using the standard location method and OFS data. The differences in the hypocenters relocated by the two methods are less than 4 km. We applied the method to the subduction region that underlies the Kanto district, central Japan, and located a large number of earthquakes that occurred beneath the Pacific Ocean. We then determined the detailed 3D seismic velocity structure by inverting a large number of arrival times of P- and S-waves and sP depth phase from the relocated earthquakes in the study region. High-velocity anomalies related to the cold subducting Pacific slab and low-velocity anomalies related to the hot mantle wedge are clearly imaged. Beneath active volcanoes, low-velocity zones are visible from the surface to a depth of 100 km, reflecting fluids released by dehydration of the subducting Pacific slab. Strong lateral heterogeneities are revealed on the upper boundary of the Pacific slab beneath the forearc region. The low-velocity areas under the offshore region are associated with low seismicity and weak interplate coupling. A low-velocity layer is imaged along the upper boundary of the Philippine Sea slab in the northern part of Kanto district, which may reflect dehydration of the slab. Our tomographic images indicate that the overlaying Philippine Sea plate has effects on the spatial distribution of active volcanoes related to the subducting Pacific slab in the study region.  相似文献   

The Infrared Spectral Energy Distribution And Polarization Of Comet C/1995 O1 (Hale–Bopp) During 1997     

Woodward  Charles E.  Gehrz  R. D.  Mason  C. G.  Jones  T. J.  Williams  D. M. 《Earth, Moon, and Planets》1998,81(3):217-222

Comets, such as C/1995 O1 (Hale-Bopp), are important to studies of the origins of the solar system because they are believed to be frozen reservoirs of the most primitive pre-solar dust grains and ices. Here, we report 1.2–18.5 μm infrared (IR) spectrophotometric and polarimetric observations of comet Hale-Bopp. Our measurements of the spectral energy distribution (SED) and IR polarization near perhelion passage suggest that emission from the coma was dominated by scattering and thermal emission from sub-micron sized dust grains. Hale-Bopp's surprising brightness may have been largely a result of the properties of its coma grains rather than the size of its nucleus. The thermal emission continuum from the grains had a superheat of S = T_color/T_BB ≥ 1.7, the peak of the 10 μm silicate emission feature was 1.7 mags above the carbon grain continuum, and the albedo (reflectivity) of the grains was ≥ 0.4 at a scattering angles, θ ≥ 135° This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

A groundwater vortex hypothesis for mima-like mounds, Laramie Basin, Wyoming     

Richard G. Reider  Joseph M. Huss  Timothy W. Miller 《Geomorphology》1996,16(4):295-317

Mima-like mounds in the Laramie Basin occur where: (1) impervious bedrock (shale) is at a shallow depth (∼ 2–5 m); (2) bedrock is overlain by a thin veneer (∼ 1–4 m) of alluvial gravels; and (3) a strong argillic/calcic or petrocalcic soil caps the landform, typically a terrace. Active and inactive mounds contain churned materials, including pebbles derived from adjacent/subjacent units. The mounds are circular in plan view and lens- or funnel-shaped in cross-section. The strong intermound (premound) soil collapses beneath the mound, is entirely or partly destroyed at its base, or is truncated at the mound edge. Stratigraphic relationships on the youngest terrace of the Laramie River indicate that the inactive mounds are Holocene in age.Sodium concentrations (used as a tracer) in mound material and adjacent/subjacent units suggest that the mounds rotate counterclockwise. This movement may be driven by free spiral vortices (low hydraulic head) in confined (artesian) groundwater flow in alluvium between shallow bedrock and strong surface soil. The vortices (similar to water draining from a bathtub or a whirlpool in a river) may result from enlargements, constrictions, or changes in permeability of the aquifer — or meandering of groundwater flow. Groundwater, dissolved ions, and materials in suspension, or through friction and turbidity, then would move from adjacent high-hydraulic head areas into and down the vortex. In effect, the high head (intermound) areas would act as a pump whereas the vortex (which would form a mound) would act as a turbine — responding, therefore, to energy transformations between groundwater velocity and pressure according to the Bernoulli principle and Newton's Second Law of Motion. Soil or sediment, incapable of being fully moved into and down the vortex, would amass at the land surface as a circular mound that in cross-section would have a lens or funnel (turbine) shape. Computer modelling shows that mounds tend to form over deep bedrock and thick alluvium.The groundwater vortex hypothesis can account for the building of the mound higher at its center, the circular plan view and lens (or funnel) shape in cross-section, the inward spiral of sodium, the churned character of mound material, and the collapse (or truncation) of soils and other units beneath and along mound edges. The hypothesis, however, must not be applied to all other Mima or mima-like mounds, unless vortex motion can be determined and if stratigraphic similarities can be demonstrated.  相似文献   

Magmatic CO2 and saline melts from the Sybille Monzosyenite,Laramie Anorthosite Complex,Wyoming     

B. Ronald Frost  Jacques L. R. Touret 《Contributions to Mineralogy and Petrology》1989,103(2):178-186

There are three populations of fluid inclusions in quartz from the Sybille Monzosyenite: early CO₂, secondary CO₂, and rare secondary brines. The oldest consist of low density CO₂ (0.70) inclusions that appear to be co-magmatic. The densities of these inclusions are consistent with the inferred crystallization conditions of the Sybille Monzosyenite, namely 3 kilobars and 950–1000° C. The other types of inclusions are secondary; they contain CO₂ (0.50) and secondary brine inclusions that form trains radiating out from a decrepitated inclusion. The sites of these decrepitated inclusions are now marked by irregularly shaped fluid inclusions and solid inclusions of salt and carbonate. Rather than fluid inclusions, feldspar contain abundant solid inclusions. These consist of magmatic minerals, hedenbergite, hornblende, ilmenite, apatite, and graphite, intimately associated with K, Na chlorides. We interpret these relations as follows: The Sybille Monzosyenite formed from a magma that contained immiscible droplets of a halide-rich melt along with a CO₂ vapor phase. The salt was trapped along with the other obvious magmatic minerals during growth of the feldspars. CO₂ may have also been included in the feldspars but it probably leaked later during exsolution of the feldspars and was not preserved. Both the saline melt and the CO₂ vapor were trapped in the quartz. The melt inclusions in the quartz later decrepitated, perhaps due to progressive exsolution of fluids, to produce the secondary H₂O and CO₂ inclusions. These observations indicate that the Sybille Monzosyenite, which is a markedly anhydrous rock, was actually vapor-saturated. Rather than being H₂O, however, the vapor was CO₂-rich and possibly related to an immiscible chloride-rich melt.  相似文献   

An evaluation of trace element release associated with acid mine drainage     

Patrick J. Sullivan  Jennifer L. Yelton 《Environmental Geology》1988,12(3):181-186

The determination of trace element release from geologic materials, such as oil shale and coal overburden, is important for proper solid waste management planning. The objective of this study was to determine a correlation between trace element residency and concentration to trace element release using the following methods: (1) sequential selective dissolution for determining trace element residencies, (2) toxicity characteristic leaching procedure (TCLP), and (3) humidity cell weathering study simulating maximum trace element release. Two eastern oil shales were used, a New albany shale that contains 4.6 percent pyrite, and a Chattanooga shale that contains 1.5 percent pyrite. Each shale was analyzed for elemental concentrations by soluble, adsorbed, organic, carbonate, and sulfide phases. All leachates were analyzed to determine total trace element concentrations. The results of the selective dissolution studies show that each trace element has a unique distribution between the various phases. Thus, it is possible to predict trace element release based on trace element residency. The TCLP results show that this method is suitable for assessing soluble trace element release but does not realistically assess potential hazards. The results of the humidity cell studies do demonstrate a more reasonable method for predicting trace element release and potential water quality hazards. The humidity cell methods, however, require months to obtain the required data with a large number of analytical measurements. When the selective dissolution data are compared to the trace element concentrations in the TCLP and humidity cell leachates, it is shown that leachate concentrations are predicted by the selective dissolution data. Therefore, selective dissolution may represent a rapid method to assess trace element release associated with acid mine drainage.  相似文献   

Trace element distribution and oil yield data from the parachute creek member of the green river formation,colorado     

Patrick J. Sullivan  Robert C. Donovan 《Environmental Geology》1987,10(1):21-31

The determination of trace element concentrations in oil shale before mining and retorting is required for proper solid-waste management planning. Using routine Fischer assay oil yield data collected during resource characterization as indicators of potential trace element concentrations could lead to a standard method of identifying strata containing high trace element levels. In order to determine a correlation between trace element concentrations and oil yield, shale samples were selected from four statigraphic zones of the Parachute Creek Member of the Green River Formation for analysis. All samples were analyzed for total elemental concentrations, mineralogy, and Fischer assay oil yield. The results of these analyses demonstrated that the Mahogany zone shales contain significantly greater trace element concentrations (antimony, arsenic, cadmium, chromium, copper, lead, lithium, mercury, molybdenum, nickel, selenium, silver, and vanadium) than the other three shale zones. These high trace element concentrations have been identified within well-defined interbedded tuff deposits in the Mahogany zone. In addition, all trace elements evaluated, except boron, show either increasing or decreasing concentrations as oil yield increases within all oil shale zones. With an increased number of analyses of existing oil shale cores, oil yield data will be correlated to specific stratigraphic units containing high trace element concentrations.  相似文献   

Numerical modelling of multiphase flow in porous media     

Myron B. Allen III 《Advances in water resources》1985,8(4):162-187

The simultaneous flow of immiscible fluids in porous media occurs in a wide variety of applications. The equations governing these flows are inherently nonlinear, and the geometries and material properties characterizing many problems in petroleum and groundwater engineering can be quite irregular. As a result, numerical simulation often offers the only viable approach to the mathematical modelling of multiphase flows. This paper provides an overview of the types of models that are used in this field and highlights some of the numerical techniques that have appeared recently. The exposition includes discussions of multiphase, multispecies flows in which chemical transport and interphase mass transfers play important roles. The paper also examines some of the outstanding physical and mathematical problems in multiphase flow simulation. The scope of the paper is limited to isothermal flows in natural porous media; however, many of the special techniques and difficulties discussed also arise in artificial porous media and multiphase flows with thermal effects.  相似文献   

Caledonian Magma Genesis and Crustal Recycling     

FROST  C. D.; NIONS  R. K. O' 《Journal of Petrology》1985,26(2):515-544

The isotopic compositions of Sr, Nd, Pb and O together withabundance data for Rb, Sr, Sm, Nd, U and Pb are reported forsamples from the component parts of the c. 400 Ma old EtiveComplex, temporally and spatially related Lorne and Glencoelavas, and the Dalradian country rocks into which the Complexhas been emplaced. These and published data available for otherCaledonian granites are used to evaluate the petrogenesis ofthe Etive Complex in particular, and the role of crustal recyclingin the generation and evolution of the Caledonian granites ingeneral. Nd-isotope compositions of Etive samples at 400 Ma range from – 9.9 to – 4.7 compared with–8.4 < – 3.2 for the associated volcanics investigated here, and an estimatedvalue for depleted mantle 400 Ma ago at approximately ? 7. Dalradiancountry rocks have – 23.4 < – 7.5 and two partially digested metasedimentaryxenoliths within the granite have values of –9. 3 and -4.0. Initial ⁸⁷Sr/ ⁸⁶Sr ratios forthe Etive Complex range from 0–7043 to 0–7079, whereasDalradian metasediment in the immediate vicinity of the granitehas an initial ratio of 0–726. Oxygen isotopes in theComplex have 7. 6 per mil <¹⁸O < 10.0 per mil, all inexcess of typical values of mantle oxygen and reflect a crustalcomponent. An upper limit of 25 per cent Dalradian assimilationis set by the Nd-Sr isotopic variations with the granites andxenoliths. The Etive complex parent magma prior to Dalradian xenolith assimilationis estimated to have values between – 10 and – 5. In order to satisfy the Srand Pb isotope composition, additional components from a deepersource within the lithosphere (lower crust or continental lithosphericmantle) with relatively unradiogenic Sr, Nd and Pb are required. The crustal residence ages of the Etive Complex average about1.5 Ga, similar to those of many other late and post-tectonicCaledonian granites. The generation of the Etive Complex andCaledonian granites in general has been dominated by recyclingof the continental lithosphere, rather than the addition ofnew material from asthenospheric sources.  相似文献   

Strontium isotopic and selected trace element variations between two Aleutian volcanic centers (Adak and Atka): implications for the development of arc volcanic plumbing systems     

James D. Myers  Bruce D. Marsh  A. Krishna Sinha 《Contributions to Mineralogy and Petrology》1985,91(3):221-234

Major and trace element concentrations and initial ⁸⁷Sr/⁸⁶Sr ratios of lavas from the Aleutian volcanic centers of Adak and Atka have been used to study the evolution of their respective lithospheric plumbing systems. The centers are within 150 km of one another and show similar overall silica ranges (47–67%), but Adak (40 km³) is smaller than Atka (200 km³). Adak's lavas are chemically and isotopically heterogeneous (⁸⁷Sr/⁸⁶Sr:0.70285–0.70330) and two units contain lithospheric xenoliths. The lavas of the much larger Atka, on the other hand, have much less variability in major and trace elements as well as ⁸⁷Sr/⁸⁶Sr (0.70320–0.70345). We suggest that these characteristics are a measure of the relative maturity and cleanliness of the lithospheric plumbing systems that supply magma to these centers. Because Aleutian volcanic centers often remain fixed for relatively long periods of time (5 m.y.), once established, magmatic passageways are repeatedly used. Young plumbing systems are relatively cool and contain large amounts of wallrock contaminant, and ascending magmas undergo contamination as well as concurrent crystallization and fractionation. With time, however, heat and mass transfer between ascending magmas and wallrock produce thermal and chemical boundary layers that insulate subsequent magmas. In effect, the plumbing system matures. The chemical heterogeneity displayed by young, dirty systems (like Adak) reflects not only the magma source but also the wallrock encountered during ascent and possibly the effects of extensive crystal fractionation. Thus, it is the petrologic data of mature, clean systems, like Atka, that yield the most direct and unambiguous information on the ultimate origin of the lavas and their near surface evolution.  相似文献   

Assimilation of Crustal Material by Basaltic Magma: Strontium Isotopic and Trace Element Data from the Edgecumbe Volcanic Field, SE Alaska     

MYERS  JAMES D.; SINHA  A. KRISHNA; MARSH  BRUCE D. 《Journal of Petrology》1984,25(1):1-26

The Edgecumbe volcanics, which range from basalt through rhyodacite,have Sr contents between 125 and 370 p.p.m., Rb contents of1 to 70 p.p.m., Ba ranging from 50–550 p.p.m. and initial⁸⁷Sr/⁸⁶Sr ratios between 0.70291 and 0.70404. No simple correlationexists between these components and silica. The highest ⁸⁷Sr/⁸⁶Srvalues occur in a group of intermediate lavas (55–60 wt.per cent SiO₂) while the rhyodacites have initial ratios between0.7035 and 0.7038. With increasing silica, Sr increases to amaximum in the andesites and then steadily decreases; Ba andRb increase over the same compositional range. The highest ⁸⁷Sr/⁸⁶Srlavas have major and trace element concentrations which departfrom trends defined by most of the lavas. The variation in strontiumisotopic compositions suggests interaction between parentalbasaltic magma and crustal material. Attempts to model the assimilationprocess using fixed end-member assimilation and assimilation-fractionalcrystallization models have failed to produce the observed chemicaltrends. Because the parental basaltic liquid underwent littlefractionation, the variability in hybrid lavas is attributedto variation in contaminant composition. Initial melts werelow in CaO, A1₂O₃, MgO and Sr and enriched in SiO₂. K₂O, Na₂O,Rb and Ba. As melting progressed, melts became enriched in themore refractory components. Because hybrid strontium isotopiccomposition is a function of Sr concentration as well as isotopiccompositions, the Sr content of the assimilant strongly influencesresultant isotopic systematics. The development of the assimilantssuggests plagioclase was a residual phase during early melting.This model of crustal assimilation represents one end-memberin the spectrum of processes responsible for the generationof continental volcanic suites.  相似文献