Faulting processes of the 1956 San Miguel,Baja California,earthquake sequence     

Diane I. Doser 《Pure and Applied Geophysics》1992,139(1):3-16

Body waveform modeling is used to determine the source processes of three large earthquakes (magnitude 6.8, 6.4, 6.3) occurring between February 9 and 15, 1956 along the San Miguel fault in northern Baja California, Mexico. Results of the modeling suggest that the mainshock on February 9 was responsible for the 20 km of surface faulting observed during the sequence. Although previous researchers have suggested a complex rupture history for the mainshock, uncertainty estimates of source-time function shape indicate single or double source models fit the observed waveforms equally well. The February 15 aftershock, however, appears to have consisted of two events. Locations and focal mechanisms obtained for the three events suggest that the rupture process may have been controlled by cross faults to the main trace of the San Miguel fault. The good correlation between source parameter information and the surficial geology/geometry of the San Miguel fault zone demonstrates the usefulness of waveform modeling studies in unravelling the complexities of historic multi-event earthquake sequences.  相似文献   

Complete Trace Elemental Characterisation of Granitoid (USGS G-2, GSP-2) Reference Materials by High Resolution Inductively Coupled Plasma-Mass Spectrometry     

Wilma Pretorius  Dominique Weis  Gwen Williams  Diane Hanano  Bruno Kieffer  James Scoates 《Geostandards and Geoanalytical Research》2006,30(1):39-54

The United States Geological Survey granitic and granodioritic reference materials G‐2 and GSP‐2 were decomposed in high‐pressure bombs using both HF‐HNO₃ and HF‐HNO₃‐HClO₄ in order to evaluate the feasibility of characterising the entire suite of geologically relevant trace elements through direct analysis with a high‐resolution inductively coupled plasma‐mass spectrometer (HR‐ICP‐MS). The digested samples were diluted to the appropriate levels and analysed at low, medium and high resolution depending on the required sensitivity and potential interferences for each element. Memory effects during analysis of the high field strength elements (HFSE) were negligible when analysed using an all‐Teflon, uncooled sample introduction system and combined with adequate wash times with 4% v/v aqua regia + 0.5% v/v HF between samples. The concentration of the remaining lithophile elements was determined with a conventional, cooled, Scott‐type spray chamber using a wash solution of 1% v/v HNO₃. Total procedural blanks contributed between 0.01 to 0.5% to final sample concentrations and blank subtractions were typically unnecessary. Abundances for Li, Hf, Ba, Zr, Ga, Rb, Sr, La, Ce, Th and U were systematically higher, while those for the heavy rare earth elements (HREEs), Cu and Y were systematically lower in this study compared to USGS values for G‐2 and GSP‐2. This is likely to be related to, respectively, higher recoveries from more efficient digestion of refractory phases (i.e., zircon, tourmaline), and better resolution of interferences when using a HR‐ICP‐MS. Sample digestion experiments also showed that perchloric acid digestion in high pressure bombs resulted in superior recoveries and better precision for the bulk of the trace elements analysed. The concentration of the remaining elements overlapped within uncertainty with recommended reference values and with values determined in other studies using isotope‐dilution TIMS, ICP‐MS and XRF. Concentrations for the elements Cd, Sn, Sb, Ta, Bi, Tb, Ni and Mo are also reported for G‐2 and GSP‐2 reference materials. Our study shows therefore that it is feasible to determine thirty‐nine geologically relevant trace elements accurately and directly in granitoid sample digests when using a HR‐ICP‐MS, thereby negating the need for ion exchange or isotopic spiking.  相似文献   

Sources of osmium to the modern oceans: new evidence from the Pt-Os system     

Diane K. McDaniel  Richard J. Walker  Mary F. Horan  Richard I. Grauch 《Geochimica et cosmochimica acta》2004,68(6):1243-1252

High precision Os isotope analysis of young marine manganese nodules indicate that whereas the composition of modern seawater is radiogenic with respect to ¹⁸⁷Os/¹⁸⁸Os, it has ¹⁸⁶Os/¹⁸⁸Os that is within uncertainty of the chondritic value. Marine Mn nodule compositions thus indicate that the average continental source of Os to modern seawater had long-term high Re/Os compared to Pt/Os. Analyses of loess and freshwater Mn nodules support existing evidence that average upper continental crust (UCC) has resolvably suprachondritic ¹⁸⁶Os/¹⁸⁸Os, as well as radiogenic ¹⁸⁷Os/¹⁸⁸Os. Modeling the composition of seawater as a two-component mixture of oceanic/cosmic Os with chondritic Os compositions and continentally-derived Os demonstrates that, insofar as estimates for the composition of average UCC are accurate, congruently weathered average UCC cannot be the sole continental source of Os to seawater. Our analysis of four Cambrian black shales confirm that organic-rich sediments can have ¹⁸⁷Os/¹⁸⁸Os ratios that are much higher than average UCC, but ¹⁸⁶Os/¹⁸⁸Os compositions that are generally between those of chondrites and average-UCC. Preferential weathering of black shales can result in dissolved Os discharged to the ocean basins that has a much lower ¹⁸⁶Os/¹⁸⁸Os than does average upper crust. Modeling the available data demonstrates that augmentation of estimated average UCC compositions with less than 0.1% additional black shale and 1.4% additional ultramafic rock can produce a continental end-member Os isotopic composition that satisfies the requirements imposed by the marine Mn nodule data. The interplay of these two sources provides a mechanism by which the ¹⁸⁷Os/¹⁸⁸Os of seawater can change as sources and weathering conditions change, yet seawater ¹⁸⁶Os/¹⁸⁸Os varies only minimally.  相似文献   

The seismicity, seismotectonics and earthquake hazards of Libya, with detailed analysis of the 1935 April 19, M = 7.1 earthquake sequence     

Abdunnur S. Suleiman  Diane I. Doser 《Geophysical Journal International》1995,120(2):312-322

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Projections of Future Trends in Biogeochemical Conditions in the Northwest Atlantic Using CMIP5 Earth System Models     

Diane Lavoie  Nicolas Lambert  Denis Gilbert 《大气与海洋》2019,57(1):18-40

We use the results from eight of the Earth System Models (ESMs) made available for the Fifth Assessment Report of the Intergovernmental Panel on Climate Change to analyze the projected changes in biogeochemical conditions over the next 50 years in the northwest Atlantic. We looked at the projected changes using the Representative Concentration Pathway 8.5 scenario in the 100–400?m depth range over a large region and at more specific locations to assess the relevance of using these outputs to force a regional climate downscaling model of the Gulf of St. Lawrence. The projected trends for dissolved oxygen (decrease), pH (decrease), and nitrate (variable although negative in general) represent a continuation of the recently observed trends in the area. For primary production, no firm conclusions can be drawn because of large differences in the trends from one model to another. The consistency of the trends near the regional model lateral boundaries leads us to conclude that the ESM trends can be used to set up future boundary conditions to evaluate regional impacts of climate change although the uncertainty of the results for the Scotian Shelf will be greater than for the Gulf of St. Lawrence.  相似文献   

Channel responses to varying sediment input: A flume experiment modeled after Redwood Creek, California   总被引：1，自引：0，他引：1  

Mary Ann Madej  Diane G. Sutherland  Thomas E. Lisle  Bonnie Pryor   《Geomorphology》2009,103(4):507-519

At the reach scale, a channel adjusts to sediment supply and flow through mutual interactions among channel form, bed particle size, and flow dynamics that govern river bed mobility. Sediment can impair the beneficial uses of a river, but the timescales for studying recovery following high sediment loading in the field setting make flume experiments appealing. We use a flume experiment, coupled with field measurements in a gravel-bed river, to explore sediment transport, storage, and mobility relations under various sediment supply conditions. Our flume experiment modeled adjustments of channel morphology, slope, and armoring in a gravel-bed channel. Under moderate sediment increases, channel bed elevation increased and sediment output increased, but channel planform remained similar to pre-feed conditions. During the following degradational cycle, most of the excess sediment was evacuated from the flume and the bed became armored. Under high sediment feed, channel bed elevation increased, the bed became smoother, mid-channel bars and bedload sheets formed, and water surface slope increased. Concurrently, output increased and became more poorly sorted. During the last degradational cycle, the channel became armored and channel incision ceased before all excess sediment was removed. Selective transport of finer material was evident throughout the aggradational cycles and became more pronounced during degradational cycles as the bed became armored. Our flume results of changes in bed elevation, sediment storage, channel morphology, and bed texture parallel those from field surveys of Redwood Creek, northern California, which has exhibited channel bed degradation for 30 years following a large aggradation event in the 1970s. The flume experiment suggested that channel recovery in terms of reestablishing a specific morphology may not occur, but the channel may return to a state of balancing sediment supply and transport capacity.  相似文献   

Remote sensing analysis of physical complexity of North Pacific Rim rivers to assist wild salmon conservation     

Matthew Luck  Niels Maumenee  Diane Whited  John Lucotch  Samantha Chilcote  Mark Lorang  Daniel Goodman  Kyle McDonald  John Kimball  Jack Stanford 《地球表面变化过程与地形》2010,35(11):1330-1343

Salmon populations are highly variable in both space and time. Accurate forecasting of the productivity of salmon stocks makes effective management and conservation of the resource extremely challenging. Furthermore, widespread and consistent data on the productivity of species‐specific and total salmon stocks in a river are almost nonexistent. Ranking rivers based on physical complexity derived from remote sensing allows rivers to be objectively compared. Our approach considered rivers with great geomorphic complexity (e.g. having expansive, multichanneled floodplains and/or on‐channel lakes) as likely to have greater productivity of salmon than rivers flowing in constrained or canyon‐bound channels. Our objective was to develop a database of landscape metrics that could be used to rank the rivers in relation to potential salmon productivity. We then examined the rankings in relation to existing empirical (monitoring) data describing productivity of salmon stocks. To extract the metrics for each river basin we used a digital elevation model and multispectral satellite imagery. We developed procedures to extract channel networks, floodplains, on‐channel lakes and other catchment features; variables such as catchment area, channel elevation, main channel length, floodplain area, and density of hydrojunctions (nodes) were measured. We processed 1509 catchments in the North Pacific Rim including the Kamchatka Peninsula in Russia and western North America. Overall, catchments were most physically complex in western Kamchatka and western Alaska, and particularly on the Arctic North Slope of Alaska. We could not directly examine coherence between potential and measured productivity except for a few rivers, but the expected relationship generally held. The resulting database and systematic ranking are objective tools that can be used to address questions about landscape structure and biological productivity at regional to continental extents, and provide a way to begin to efficiently prioritize the allocation of funding and resources towards salmon management and conservation. Copyright © 2010 John Wiley & Sons, Ltd.  相似文献   

Exhumation History of Southern Madagascar as Revealed by Zircon and Apatite Fission-Track Thermochronology     

Diane Seward  Djordje Grujic  Guido Schreurs   《Gondwana Research》1999,2(3):353

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Effects of coal contamination on early life history processes of a reef-building coral,Acropora tenuis     

Kathryn L.E. Berry  Mia O. Hoogenboom  Diane L. Brinkman  Kathryn A. Burns  Andrew P. Negri 《Marine pollution bulletin》2017,114(1):505-514

Successful reproduction and larval dispersal are important for the persistence of marine invertebrate populations, and these early life history processes can be sensitive to marine pollution. Coal is emerging as a contaminant of interest due to the proximity of ports and shipping lanes to coral reefs. To assess the potential hazard of this contaminant, gametes, newly developed embryos, larvae and juveniles of the coral Acropora tenuis were exposed to a range of coal leachate, suspended coal, and coal smothering treatments. Fertilisation was the most sensitive reproductive process tested. Embryo survivorship decreased with increasing suspended coal concentrations and exposure duration, effects on larval settlement varied between treatments, while effects on juvenile survivorship were minimal. Leachate exposures had negligible effects on fertilisation and larval settlement. These results indicate that coral recruitment could be affected by spills that produce plumes of suspended coal particles which interact with gametes and embryos soon after spawning.  相似文献   

Diel discharge variations in dormant and growing seasons in a headwater catchment suggest potential sources of an evapotranspiration signal     

John P. Gannon  David Kinner  Diane Styers  Mark Lord 《水文研究》2020,34(5):1228-1236

Diel fluctuations in discharge not associated with precipitation have been identified in streams around the world and attributed to evapotranspiration of both hillslope and near-stream vegetation. Several mechanisms have been hypothesized to explain the generation of these signals, but a consensus has not been reached. In order to investigate the origin of these daily discharge fluctuations, we measured discharge and groundwater levels in a 43-ha headwater catchment near Cullowhee, NC, USA. The catchment was logged at least twice in the past 120 years, allowing the evergreen invasive Chinese privet (Ligustrum sinense) to become established in near-stream areas. Stream discharge was measured at the outlet, and stream stage and near-stream groundwater level were measured at a second location higher in the catchment. Daily fluctuations in discharge were quantified and found to increase in magnitude with daily mean discharge. Interestingly, daily discharge fluctuations were observed in the dormant season, and our analysis suggests that their magnitude may increase more with discharge than during the growing season. Two previously hypothesized processes may explain our observations. A decrease in signal dampening due to faster transmission of an evapotranspiration signal at elevated flows may explain the increased diel fluctuation magnitude at higher flows. Additionally, because the primary active vegetation in our catchment in the dormant season is in near-stream areas, we suggest that this indicates most of the evapotranspiration signal in stream discharge is derived from near-stream vegetation, not hillslopes.  相似文献