共查询到20条相似文献，搜索用时 15 毫秒
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Donald B. Percival Donald W. Denbo Marie C. Eblé Edison Gica Harold O. Mofjeld Michael C. Spillane Liujuan Tang Vasily V. Titov 《Natural Hazards》2011,58(1):567-590
The ability to accurately forecast potential hazards posed to coastal communities by tsunamis generated seismically in both
the near and far field requires knowledge of so-called source coefficients, from which the strength of a tsunami can be deduced.
Seismic information alone can be used to set the source coefficients, but the values so derived reflect the dynamics of movement
at or below the seabed and hence might not accurately describe how this motion is manifested in the overlaying water column.
We describe here a method for refining source coefficient estimates based on seismic information by making use of data from
Deep-ocean Assessment and Reporting of Tsunamis (DART
\circledR^{\circledR}) buoys (tsunameters). The method involves using these data to adjust precomputed models via an inversion algorithm so that
residuals between the adjusted models and the DART
\circledR^{\circledR} data are as small as possible in a least squares sense. The inversion algorithm is statistically based and hence has the
ability to assess uncertainty in the estimated source coefficients. We describe this inversion algorithm in detail and apply
it to the November 2006 Kuril Islands event as a case study. 相似文献
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Rapid accumulation of CaCO3 is occurring in Littlefield Lake, a marl lake located in central Michigan. The sediment, which is 95% CaCO3, primarily consists of eight different genetic groups of carbonate allochems. These include calcite muds, sands, algal oncoids and Chara encrustations, as well as the dominant aragonitic gastropods Valvota tricarinota. Gyraulus deflectus and Amnicola integra. and the dominant aragonitic pelecypod Sphaerium partumeium. Samples of each of these groups were analyzed for Ca, Sr and Mg. Molar ratios are primarily controlled by allochem mineralogy, with calcitic forms having ratios 5–10 times larger than aragonitic (shelled) forms. The ratios are primarily controlled by biochemical fractionation, and are significantly lower than ratios of inorganically precipitated aragonite from other settings. Partition coefficients were determined for both Sr and Mg for each carbonate allochem group and, based on comparisons with results reported by other workers, the partition coefficients determined here are generally considered ‘typical’ or representative values for biogeneous freshwater carbonates. An analysis of variance of the data indicates that most genera and species of carbonate-secreting organisms in marl lakes have highly characteristic and ratios. These ratios can potentially serve as geochemical tracers in future investigations of lacustrine carbonate diagenesis. Both Sr and Mg are influenced by grain size and/or surface area, probably due to the presence of these elements in non-lattice-held (exchangeable) positions. 相似文献
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James W.C. White Edward R. Cook James R. Lawrence 《Geochimica et cosmochimica acta》1985,49(1):237-246
Measurements of ratios of tree sap can be used to determine the source water for a tree. Based on these measurements, trees can be separated into three categories: those which rely solely on summertime rainfalls, those which rely solely on groundwaters and those which utilize both water sources. For trees in the last category, ratios of sap can be used to quantify the relative contributions to the tree's source water of summertime rainfalls and groundwaters. These measurements can be used to select trees for tree ring isotope studies. Single source trees, those which rely solely on summertime rain or groundwaters, appear to be the best choices for measuring long records of tree ring ratios. 相似文献
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Concentrations of potassium and rubidium are reported for 62 Precambrian shield whole-rock samples belonging to the pyroxene granulite facies of world-wide distribution. Compared with the Main Trend established by Shaw (1968) for igneous and quasi-igneous rocks of the upper crust, the high-grade metamorphic granulites exhibit a similar correlation but with a measurable depletion in Rb for a given K content. The Metamorphic Trend may be described by the equations: log10 (ppm Rb) = 1.136 log10 (per cent K) + 1.495 or ppm Rb = 31.28 (per cent K)1.136. The square of the product moment correlation coefficient shows that 80 per cent of the variation in Rb is associated with variation in K.All suites studied have initial ratios less than 0.707. This low value argues against repeated extraction of Rb and K through time on a regional scale. Rather, the major depletion in these lithophile elements occurred in the early stages of crustal evolution. 相似文献
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Jacques Touret 《Lithos》1971,4(3):239-249
The basement of Southern Norway is a genetically homogeneous migmatite complex in which old supracrustals produced granitic and granodioritic ‘neosome’ during a late Precambrian (109 years ago) regional metamorphism. Observed isograds of critical minerals: muscovite, cordierite, orthopyroxene indicate that the Telemark amphibolite facies in the North passes into the coastal Bamble granulite facies in the South. The data of expeimental petrology suggest that the transition, which took place at temperatures of 700–800°C, is essentially due to a decrease of the partial water pressure. PH2O was equal to total pressure Ps in the amphibolite facies and lower than 2 kb in the granulite facies. 相似文献
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Coral proxy records of sea surface temperature (SST) and hydrological balance have become important tools in the field of tropical paleoclimatology. However, coral aragonite is subject to post-depositional diagenetic alteration in both the marine and vadose environments. To understand the impact of diagenesis on coral climate proxies, two mid-Holocene Porites corals from raised reefs on Muschu Island, Papua New Guinea, were analysed for Sr/Ca, δ18O, and δ13C along transects from 100% aragonite to 100% calcite. Thin-section analysis showed a characteristic vadose zone diagenetic sequence, beginning with leaching of primary aragonite and fine calcite overgrowths, transitional to calcite void filling and neomorphic, fabric selective replacement of the coral skeleton. Average calcite Sr/Ca and δ18O values were lower than those for coral aragonite, decreasing from 0.0088 to 0.0021 and −5.2 to −8.1‰, respectively. The relatively low Sr/Ca of the secondary calcite reflects the Sr/Ca of dissolving phases and the large difference between aragonite and calcite Sr/Ca partition coefficients. The decrease in δ18O of calcite relative to coral aragonite is a function of the δ18O of precipitation. Carbon-isotope ratios in secondary calcite are variable, though generally lower relative to aragonite, ranging from −2.5 to −10.4%. The variability of δ13C in secondary calcite reflects the amount of soil CO2 contributing 13C-depleted carbon to the precipitating fluids. Diagenesis has a greater impact on Sr/Ca than on δ18O; the calcite compositions reported here convert to SST anomalies of 115°C and 14°C, respectively. Based on calcite Sr/Ca compositions in this study and in the literature, the sensitivity of coral Sr/Ca-SST to vadose-zone calcite diagenesis is 1.1 to 1.5°C per percent calcite. In contrast, the rate of change in coral δ18O-SST is relatively small (−0.2 to 0.2°C per percent calcite). We show that large shifts in δ18O, reported for mid-Holocene and Last Interglacial corals with warmer than present Sr/Ca-SSTs, cannot be caused by calcite diagenesis. Low-level calcite diagenesis can be detected through X-ray diffraction techniques, thin section analysis, and high spatial resolution sampling of the coral skeleton and thus should not impede the production of accurate coral paleoclimate reconstructions. 相似文献
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Undifferentiated meteorites (chondrites) have the same relative abundances of refractory lithophile elements (Ca, Al, Ti, Sc, REE, etc.), despite variable absolute concentrations. The reasonable assumption of chondritic ratios among refractory elements in the bulk Earth is used to constrain the chemical composition of the upper mantle in the following way: Correlations of the compatible refractory elements Ca, Al, Ti, Sc and Yb with MgO are worldwide very similar in suites of spinel-lherzolite xenoliths from basaltic rocks. Such suites represent upper mantle material depleted to differing degrees by extraction of partial melts. From these refractory elements vs. MgO correlations, ratios of pairs of refractory elements were calculated at various MgO contents. Chondritic and ratios were only obtained for MgO contents below 36%. A chrondritic ratio requires an MgO content above 35%. We therefore accept 35.5% as the most reasonable MgO content of undepleted upper mantle. This MgO content is slightly below the spinel-lherzolite with the lowest measured MgO content (36.22%). The corresponding Al2O3 content of 4.75% is higher than in previous estimates of upper mantle composition. The concentrations of other elements were obtained from similar correlations at a MgO content of 35.5%. The resulting present upper mantle composition is enriched in refractory elements by a factor of 1.49 relative to Si and Cl and by a factor of 1.12 for Mg relative to Si and Cl. These enrichments are in the same range as those for the Vigarano type carbonaceous chondrites. The Mg/Mg + Fe ratio of 89 is slightly lower than previous estimates.The ratio in spinel lherzolite suites is, however, uniformly higher worldwide than the chondritic ratio by about 15%. Orogenic peridotites as well as komatiites appear to have similar non-chondritic ratios. It is therefore suggested that this non-chondritic ratio is a characteristic of the upper mantle, possibly since the Archean. A minor fractionation of about 4% of garnet in an early, global melting event (deep magma ocean?) is presented as the most likely cause for the high . In this case the addition of 4% of such a garnet component to the undepleted present upper mantle would be required to obtain the composition of the primordial upper mantle. The of this primordial mantle would be 15% higher than that of the undepleted present upper mantle, resulting in an enrichment of refractory elements of 1.70 ( relative to Cl) for the primordial upper mantle. 相似文献