New techniques for the analysis of earthquake sources from local array data with an application to the 1993 Scotts Mills, Oregon, aftershock sequence

We analysed aftershocks recorded by a temporary digital seismic network following the moderate M _w = 5.5 1993, Scotts Mills, Oregon, earthquake. A technique to retrieve source moment tensors from local waveforms was developed, tested, and applied to 41 small earthquakes ( M _w ranging from 1.6 to 3.2). The derived focal mechanisms, although well resolved, are highly variable and do not share a common nodal plane. In contrast, the majority of the events, relocated with a joint hypocentre determination algorithm, collapse to a well-focused plane. The incompatibility of the nodal planes of most events with the plane defined by their locations suggests that the aftershocks did not occur on the fault plane, but tightly around it, outlining the rupture area rather than defining it. Furthermore, the moment tensors reveal stable P -axes, whereas T  -axes plunges are highly dispersed. We detect a rotation of average T  -axis plunge with depth, indicating a change from shallower, predominantly dip-slip mechanisms to deeper strike-slip mechanisms. These characteristics are difficult to explain by remnant stress concentrations on the main-shock rupture plane or asperity- and barrier-type models. We suggest that the aftershocks occurred under the ambient regional stress, triggered by a sudden weakening of the region surrounding the main-shock slip, rather than from a shear stress increase due to the main shock.     

Biodegradation of NOM in Rapid Sand Filters for Removing Iron and Manganese

In order to examine the Corg flow in rapid sand filter columns for the elimination of iron and manganese, reduced groundwater was treated in a pilot plant consisting of a trickling filter column (TF I) followed by a wet type filter column (WF II) and a separate wet type filter column (WF sep). Additionally the effect of filtration on BOM was studied by measuring AOC and BDOC. The biological processes in TF I and WF sep led to an elimination of iron, ammonia, and manganese. Moreover, the filtration decreased the NOM content. 21% and 23% of the TOC were eliminated in TF I and in WF sep, respectively. WF II caused no significant Corg reduction. The calculation of the Corg flow in the filter columns showed that bacteria took part in the TOC elimination. From the TOC removed, about 24% was eliminated by metabolic activities of the bacterial population whereas 86% was adsorbed onto iron sludge. Similar results were obtained for the TF I column and for the WF sep column as well. The calculated Corg flow was confirmed by the BDOC measurements. The filtration process led to a BDOC decrease. TF I and WF sep reduced appoximately 35% of the biodegradable organic carbon. In contrast there was no significant elimination by WF II. The AOC results suggest that an AOC production and an AOC elimination process exist in rapid sand filters for groundwater treatment. In the trickling filter column significant AOC production was found, whereas in the wet type filter columns AOC elimination was predominating.     

The geochemistry of aliphatic and polar organic tracers in sediments from Lake Bera, Malaysia

The molecular distributions of homologous aliphatic lipid compounds (n-alkanes, n-alkanoic acids, n-alkanols, n-alkanals and n-alkan-2-ones) were investigated in sediments of Lake Bera, Malaysia as well as in plant waxes from the vicinity using gas chromatography-mass spectrometry. In addition, triterpenoids of the oleanane, ursane, lupane and friedelane series, and their diagenetic products were also identified. Using the aquatic proxy P_aq, it was found that the n-alkanes present in surface sediments S1, S5 and S6 correspond to an input from emergent macrophytes, whereas in sediments collected from open water (S2, S3 and S4) they correspond to input from submerged/floating macrophytes. The presence of n-alkan-2-ols, a commonly found homologous series in the sediments as well as in the plant wax, is novel here. In addition, the presence of 24-methylcycloart-22-enol and 24-ethylcycloart-22-enol in sediments as well as the plant wax of Pandanus helicopus, a dominant reed around the lake, also supports the input of plant biomarkers to the sediments. The occurrence of 5-membered ring triterpenoid derivatives as major diagenetic products of the triterpenoids identified (e.g. friedelan-2,3-dione) shows that the degradation of the organic matter in the sediments occurs mainly under oxic conditions. Also, the presence of ring-A degraded triterpenoids (dihydroputranjivic acid, 3-nor-2,4-seco-friedelane, 4α- and 4β-3-norfriedelanes, A-norfriedel-10-one, and A-norfriedel-8-en-10-one) and the aromatized triterpenoid hydrocarbons (mono- and triaromatic derivatives) as minor diagenetic products indicates photochemical and microorganism-mediated alteration reactions of natural products in the sediments. Additional novel polyfunctional friedelane derivatives, namely friedelane-2,3-dione, friedelane-1,3-diol-2-one and friedel-1(10)-ene-1,3-diol-2-one were identified for the first time in this study. These novel polyfunctional triterpenoids were inferred to derive from the oxidation of the triterpenoids from higher plants in this oxic tropical environment. For future reference purposes, the mass spectra of the identified polar triterpenoids are also presented here. This study provides important data on the biogeochemistry of organic matter in a tropical lake of SE Asia.     

Equilibrium experiments in the system MgO–SiO2–H2O (MSH): stability fields of clinohumite-OH [Mg9Si4O16(OH)2], chondrodite-OH [Mg5Si2O8(OH)2] and phase A (Mg7Si2O8(OH)6)

The water-pressure and temperature stability fields of clinohumite-OH, chondrodite-OH and phase A were determined in reversed equilibrium experiments up to 100 kbar within the system MgO–SiO₂–H₂O. Their PT-fields differ from results from former synthesis experiments. Bracketing experiments on the reaction phase A + low P-clinoenstatite ⇆ forsterite + water resulted in a slightly steeper dP/dT-slope compared to earlier experiments for this equilibrium. Clinohumite-OH and chondrodite-OH both have large stability fields which extend over pressure ranges of more than 80 kbar. However, they are hardly relevant as hydrous minerals within the subducted oceanic lithosphere. Both are too Mg-rich for a typical mantle bulk composition. In addition, the dehydration of subducted oceanic lithosphere – due to (forsterite + water)-forming reactions – will occur before the two humite-group phases even become stable. Restricted to the cool region of cold subducting slabs, phase A, however, might be formed via the reactions phase A + low P-/high P-clinoenstatite ⇆ forsterite + water or antigorite + brucite ⇆ phase A + water, before dehydration of the oceanic lithosphere occurs. Received: 22 July 1997 / Accepted: 12 March 1998     

Organic tracers from biomass burning in atmospheric particulate matter over the ocean

Particulate matter from the atmosphere over the Atlantic Ocean along the South American and African Continents has been analyzed for organic tracers from natural and biomass burning emissions. The major biomarker compounds characterized are natural products from continental vegetation consisting primarily of epicuticular wax components. For example, n-alkanes ranged from C₂₅ to C₃₅, with an odd carbon number predominance and carbon maxima (C_max) at 29 or 31. Concentrations of n-alkanes varied from 0.3 to 680 ng/m³. Nevertheless, n-alkanols are the dominant terrestrial tracers in almost all samples (concentrations from 0.1 to 780 ng/m³) and ranged from C₂₂ to C₃₄ with an even carbon number predominance. Despite the major presence of the natural tracers, organic components from biomass burning emissions are also present in the particulate matter. The major tracers from this source are thermal degradation products from the biopolymer cellulose, namely the dianhydromonosaccharide derivatives levoglucosan, galactosan, and mannosan. In general, the concentrations of levoglucosan, the major derivative from this source in all samples, varied from 0.0008 to 0.15 ng/m³ in atmospheric samples collected over the ocean and from 0.04 to 4860 ng/m³ in terrestrial particulate matter, used as reference in this study. Dehydroabietic acid, another marker compound emitted from burning of Gymnosperm fuel, is also detectable in most oceanic samples at concentrations ranging from 0.0001 to 0.4 ng/m³, whereas in terrestrial aerosol particulate matter, this component is present at much higher concentrations (0.23–440 ng/m³). The presence of these tracers in atmospheric particulate matter over the ocean confirms the long-range transport of smoke from biomass burning off the continents.     

A Precambrian core sample from the Altiplano/Bolivia

Drilling in the Bolivian Altiplano discovered the Precambrian basement at 2.744 m of depth, Paleozoic strata lacking. The core is composed of hornblende meta-granite (hornblende granoblastite), in the upper part of biotite meta-granite (biotite granoblastite). Radiometric dating provides evidence for a Grenvillian magmatic or anatectic rock formation (1.050±100 my) and a later metamorphic event of 530±30 my in age.

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Zusammenfassung In einem Bohraufschluß vom Altiplano in Bolivien wurde in 2.744 m Teufe unter tertiärer und kretazischer Bedeckung das präkambrische Basement angetroffen. Der präkambrische Bohrkern besteht teils aus Hornblende-Meta-Granit (Hornblende-Kalifeldspat-Quarz-Plagioklas-Gneis), teils aus Biotit-Meta-Granit (Biotit-Kalifeldspat-Quarz-Plagioklas-Gneis). Nach Rb-Sr Datierung dürfte das Bildungsalter etwa 1.050±100 my betragen, eine Aufheizungsperiode um 530±30 my ist nach K-Ar Analyse zu vermuten.

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Résumé Lors d'un forage dans l'Altiplano bolivien le substratum précambrien a été rencontré à une profondeur de 2.744 m. La couverture sédimentaire comprend des couches tertiaires et crétaciques. La carotte précambrienne se compose d'un micro-granite gneissique de l'assemblage hornblende — feldspath potassique — quartz — plagioclase et d'un microgranite gneissique de biotite — feldspath potassique — quartz — plagioclase. L'âge de constitution de la roche est d'après l'analyse Rb-Sr de 1.050 ± 100 my. L'analyse K-Ar laisse supposer une transformation métamorphique de 530 ± 30 my.

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- , 2744 . — ( - -- —, - (- -- -). - 1050 ± 100 , , - , 530 ± 30 .

     

Deglaciation and catchment ontogeny in coastal south‐west Greenland: implications for terrestrial and aquatic carbon cycling

Here we present Holocene organic carbon, nitrogen, sulphur, carbon isotope ratio and macrofossil data from a small freshwater lake near Sisimiut in south‐west Greenland. The lake was formed c. 11 cal ka BP following retreat of the ice sheet margin and is located above the marine limit in this area. The elemental and isotope data suggest a complex deglaciation history of interactions between the lake and its catchment, reflecting glacial retreat and post‐glacial hydrological flushing probably due to periodic melting of local remnant glacial ice and firn areas between 11 and 8.5 cal ka BP. After 8.5 cal ka BP, soil development and associated vegetation processes began to exert a greater control on terrestrial–aquatic carbon cycling. By 5.5 cal ka BP, in the early Neoglacial cooling, the sediment record indicates a change in catchment–lake interactions with consistent δ¹³C while C/N exhibits greater variability. The period after 5.5 cal ka BP is also characterized by higher organic C accumulation in the lake. These changes (total organic carbon, C/N, δ¹³C) are most likely the result of increasing contribution (and burial) of terrestrial organic matter as a result of enhanced soil instability, as indicated by an increase in Cenococcum remains, but also Sphagnum and Empetrum. The impact of glacial retreat and relatively subdued mid‐ to late Holocene climate variation at the coast is in marked contrast to the greater environmental variability seen in inland lakes closer to the present‐day ice sheet margin. Copyright © 2012 John Wiley & Sons, Ltd.     

Discharge experiments simulating chemical evolution on the surface of Titan

Saturn's moon Titan has been considered as one of the few places in our Solar System, where atmospheric and surface conditions could have produced organic compounds essential as precursors for an evolution of life. The Cassini-Huygens mission has provided new data on Titan's atmosphere and surface, which enabled us to simulate the chemical processes occurring under these conditions. Possible lightning events on Titan cannot only produce higher hydrocarbons, but also allow surface water ice to participate in the reaction scenario, resulting in CHO, CHN, and CHON compounds including several molecules relevant for the formation of amino acids and nucleic acids.     

The effect of chrysotile nanotubes on the serpentine-fluid Li-isotopic fractionation

We determined the lithium isotope fractionation between synthetic Li-bearing serpentine phases lizardite, chrysotile, antigorite, and aqueous fluid in the P,T range 0.2–4.0 GPa, 200–500°C. For experiments in the systems lizardite-fluid and antigorite-fluid, ⁷Li preferentially partitioned into the fluid and Δ⁷Li values followed the T-dependent fractionation of Li-bearing mica-fluid (Wunder et al. 2007). By contrast, for chrysotile-fluid experiments, ⁷Li weakly partitioned into chrysotile. This contrasting behavior might be due to different Li environments in the three serpentine varieties: in lizardite and antigorite lithium is sixfold coordinated, whereas in chrysotile lithium is incorporated in two ways, octahedrally and as Li-bearing water cluster filling the nanotube cores. Low-temperature IR spectroscopic measurements of chrysotile showed significant amounts of water, whose freezing point was suppressed due to the Li contents and the confined geometry of the fluid within the tubes. The small inverse Li-isotopic fractionation for chrysotile-fluid results from intra-crystalline Li isotope fractionation of octahedral Li^[6] with preference to ⁶Li and lithium within the channels (Li^[Ch]) of chrysotile, favoring ⁷Li. The nanotubes of chrysotile possibly serve as important carrier of Li and perhaps also of other fluid-mobile elements in serpentinized oceanic crust. This might explain higher Li abundances for low-T chrysotile-bearing serpentinites relative to high-T serpentinites. Isotopically heavy Li-bearing fluids of chrysotile nanotubes could be released at relatively shallow depths during subduction, prior to complete chrysotile reactions to form antigorite. During further subduction, fluids produced during breakdown of serpentine phases will be depleted in ⁷Li. This behavior might explain some of the Li-isotopic heterogeneities observed for serpentinized peridotites.