1-D and 2-D analyses of weak motion data in Fraser Delta from 1966 Duvall earthquake     

W. D. Liam Finn  E. Zhai  T. Thavaraj  X. -S. Hao  C. E. Ventura 《Soil Dynamics and Earthquake Engineering》2003,23(4):323-329

The 1996 Duvall earthquake in Washington State triggered ground motion stations in the Fraser Delta, British Columbia, located on varying depths of Holocene and Pleistocene soils to a maximum depth of 800 m and one station on bedrock. Recorded ground motions were used to examine the applicability of 1-D and 2-D site response analyses for amplification studies in the Delta. 1-D response analysis gave a good indication of the period of peak response. Response spectra computed by 1-D analysis did not compare well with recorded spectra except at very deep sites. The use of 2-D analyses to include buried topography generally improved the predictions of site response spectra at the shallow sites. However, for the shallow earth sites, the recorded motions showed a strong spectral response at short periods in the range of 0.1–0.25 s. Neither 1-D nor 2-D analysis predicted this response.  相似文献   

Platinum–palladium–gold mineralization in the Nkenja mafic–ultramafic body, Ubendian metamorphic belt, Tanzania     

David M. Evans  Finn M. Barrett  Hazel M. Prichard  Peter C. Fisher 《Mineralium Deposita》2012,47(1-2):175-196

Significant and widespread enrichment of platinum, palladium, and gold has been found within the Nkenja mafic–ultramafic body located in southern Tanzania in the central part of the Ubendian metamorphic belt. This body is dominated by partly serpentinized chromitiferous dunite, wehrlite and olivine clinopyroxenite, which are tectonically intercalated with amphibolitized metagabbro. The dunites contain both disseminated and seam-type chrome spinel with an Al-rich composition. The seams are thin, impersistent and, together with enclosing dunite, often show deformation at granulite facies conditions. Forsterite contents of olivine in the dunite range from 87 to 92?mol%. Clinopyroxene in wehrlite and clinopyroxenite is diopsidic with significant contents of Al and Na. Clinopyroxene forms irregular bands and crosscutting veins in the dunite, as well as occurring as weakly dispersed isolated grains in the dunite. Elevated levels of Pt, Pd and Au occur in all ultramafic rocks, but not amphibolitized metagabbro, and there is a weak correlation between high abundances of platinum-group element (PGE) and chromitites. PGE values are erratically distributed and are associated with trace to minor amounts of disseminated sulphides (pyrrhotite, pentlandite, heazlewoodite, chalcopyrite and bornite). The abundances of all PGE are consistently anomalous, suggesting a primary igneous control by sulphides in ultramafic rock. However, there has evidently been a strong metamorphic and/or hydrothermal overprint on what was probably an original magmatic concentration of PGE-bearing sulphides. Geological mapping and petrological evidence, as well as the style of PGE sulphide mineralization, are consistent with the Nkenja ultramafic body being part of the crustal section of a dismembered Palaeoproterozoic ophiolite.  相似文献   

Salt Marsh Fucoid Algae: Overlooked Ecosystem Engineers of North Temperate Salt Marshes     

Megan C. Tyrrell  Michele Dionne  Sarah A. Eberhardt 《Estuaries and Coasts》2012,35(3):754-762

Salt marsh fucoid algae are a conspicuous component of north temperate marshes, yet comparatively little research has been conducted to examine their ecological effects. We examined the influence of salt marsh fucoids on physical conditions and the biotic community in a manipulative experiment conducted in a southern Maine back-barrier salt marsh. The biomass of salt marsh fucoids was higher than that of aboveground Spartina alterniflora in the zone where we conducted the experiment. Average daytime temperatures at the sediment surface were significantly reduced by the presence of salt marsh fucoids. Density and biomass of standing-dead S. alterniflora was significantly higher when salt marsh fucoids were removed. In contrast, the abundance of various species of epifauna and infauna were significantly enhanced by the presence of salt marsh fucoids. A regional survey indicated that results from the study site may be conservative because the biomass of salt marsh fucoids was lowest among other back-barrier marshes. Salt marsh fucoids are little studied ecosystem engineers whose presence affects the microclimate and biotic community, especially the animals that constitute the basal components of the salt marsh trophic relay.  相似文献   

The variability of volcanic activity at Zamama, Culann, and Tupan Patera on Io as seen by the Galileo Near Infrared Mapping Spectrometer     

Ashley Gerard Davies  Megan Elizabeth Ennis 《Icarus》2011,215(1):401-416

Zamama, Culann, and Tupan Patera are three large, persistent volcanic centers on the jovian moon Io. As part of an ongoing project to quantify contributions from individual volcanic centers to Io’s thermal budget, we have quantified the radiant flux from all suitable observations made by the Galileo Near Infrared Mapping Spectrometer (NIMS) of these volcanoes, in some cases filling omissions in previous analyses. At Zamama, after a long period of cooling, we see a peak in thermal emission that corresponds with new plume activity. Subsequently, toward the end of the Galileo epoch, thermal emission from Zamama drops off in a manner consistent with a greatly reduced eruption rate and the cooling of emplaced flows. Culann exhibits possible episodic activity. We present the full Tupan Patera NIMS dataset and derive new estimates of thermal output and temporal behavior. Eruption rates at these three volcanoes are on the order of 30 m³ s⁻¹, consistent with a previous analysis of NIMS observations of Prometheus, and nearly an order of magnitude greater than Kilauea volcano, Hawai’i, Earth’s most active volcano. We propose that future missions to the jovian system could better constrain activity at these volcanoes and others where similar styles of activity are taking place by obtaining data on a time scale of, ideally, at least one observation per day. Observations at similar or even shorter timescales are desirable during initial waxing phases of eruption episodes. These eruptions are identifiable from their characteristic spectral signatures and temporal behavior.  相似文献   

Reuse of Drinking Water Treatment Waste for Remediation of Heavy Metal Contaminated Groundwater     

Ryan R. Holmes  Megan L. Hart  John T. Kevern 《Ground Water Monitoring & Remediation》2019,39(4):69-79

Lime softening produces an estimated 10,000 metric tons of dry drinking water treatment wastes (DWTW) per year, costing an estimated one billion dollars annually for disposal worldwide. Lime softening wastes have been investigated for reuse as internal curing agents or supplementary cementitious materials in concrete as well as a high-capacity sorbent for heavy metal removal. Lead, cadmium, and zinc are common heavy metals in groundwater contaminated by mine tailings. Cement-based filter media (CBFM) are a novel material-class for heavy metal remediation in groundwater. This study investigated the incorporation of DWTW as a recycled, low-cost additive to CBFM for the removal of lead, cadmium, and zinc. Jar testing at three different metal concentrations and breakthrough column testing using synthetic groundwater were performed to measure removal capacity and reaction kinetics. Jar testing results show as DWTW content increases at low concentrations, removal approaches 100% but at high metal concentrations removal decreases due to saturation or exhaustion of the removal mechanisms. Removal occurs through the formation of metal carbonate precipitates, surface sorption, and ion exchange with calcium according to the preferential series Pb⁺² > Zn⁺² > Cd²⁺. Removal kinetics were also measured through column testing and exceeded estimated calculations derived from batch jar testing isotherms due to the large formation of oolitic metal carbonates. Lead, cadmium, and zinc was concentrated in the column precipitates from 0.29, 0.23, and 20.0 μg/g in the influent solution to approximately 200, 130, 14,000 μg/g in the reacted DWTW-CBFM. The control and DWTW-CBFM columns had statically similar removal for zinc and lead. In the DWTW-CBFM, cadmium had decreased removal of approximately 25% due to proportionately decreased hydroxide content from cement replacement with 25% DWTW. This study shows the potential for DWTW as an enhancement to CBFM, thereby valorizing an otherwise waste material. Furthermore, the concentrative abilities of CBFM through precipitate and oolitic mineral formation could provide a minable waste product and close the waste-product cycle for DWTW.  相似文献