All ICDP Publications with Abstracts
From parent-sysfolder "Publications" + 2 folder-levels deep
1969.
Cross-correlation-based detection and characterisation of microseismicity adjacent to the locked, late-interseismic Alpine Fault, South Westland, New Zealand
Earth and Planetary Science Letters,
45763-72
2017
ISSN: 0012821X
Publisher: Elsevier B.V.
Keywords:▾
Fault detection; Locks (fasteners); Matched filters; Seismic waves; Seismographs; Signal detection; Singular value decomposition; Strike-slip faults, Alpine Faults; Earthquake swarms; Inter-seismic periods; Magnitude estimation; Matched filter detections; Microseismicity; South Westland , New Zealand; Strike slip faulting, Earthquakes, detection method; earthquake magnitude; earthquake swarm; fault zone; focal mechanism; seismicity; singular value decomposition, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ The Alpine Fault is inferred on paleoseismological grounds to produce magnitude 8 earthquakes approximately every 330 yrs and to have last ruptured almost 300 yrs ago in 1717 AD. Despite approximately 90% of its typical interseismic period having elapsed since the last major earthquake, the Alpine Fault exhibits little present-day microseismicity and no geodetic evidence for shallow creep. Determining the mechanical state of the fault ahead of a future earthquake is a key objective of several studies, including the Deep Fault Drilling Project (DFDP). Here we use a network of borehole seismometers installed in conjunction with DFDP to detect and characterise low-magnitude seismicity adjacent to the central section of the Alpine Fault. We employ matched-filter detection techniques, automated cross-correlation phase picking, and singular value decomposition-derived magnitude estimation to construct a high-precision catalogue of 283 earthquakes within 5 km of the fault trace in an otherwise seismically quiet zone. The newly recognised seismicity occurs in non-repeating, spatially and temporally limited sequences, similar to sequences previously documented using standard methods but at significantly lower magnitudes of ML<1.8. These earthquakes are not clustered on a single distinctive structure, and we infer that they are distributed throughout a highly fractured zone surrounding the Alpine Fault. Focal mechanisms computed for 13 earthquakes using manual polarity picks exhibit predominantly strike-slip faulting, consistent with focal mechanisms observed further from the fault. We conclude that the Alpine Fault is locked and accumulating strain throughout the seismogenic zone at this location. © 2016 Elsevier B.V.
1968.
Cyclical Changes in the Pleistocene Climate from an Analysis of Biogenic Silica in a Bottom Sediment Core Sample of Lake Baikal
Geomagnetism and Aeronomy,
57
(7)
877 – 885
2017
ISSN: 00167932
Publisher: Maik Nauka-Interperiodica Publishing
Abstract: ▾ An inhomogeneous time series of measurements of the percentage content of biogenic silica in the samples of joint cores BDP-96-1 and BDP-96-2 from the bottom of Lake Baikal drilled at a depth of 321 m under water has been analyzed. The composite depth of cores is 77 m, which covers the Pleistocene Epoch to 1.8 Ma. The time series was reduced to a regular form with a time step of 1 kyr, which allowed 16 distinct quasi-periodic components with periods from 19 to 251 kyr to be revealed in this series at a significance level of their amplitudes exceeding 4σ. For this, the combined spectral periodogram (a modification of the spectral analysis method) was used. Some of the revealed quasi-harmonics are related to the characteristic cyclical oscillations of the Earth’s orbital parameters. Special focus was payed to the temporal change in the parameters of the revealed quasi-harmonic components over the Pleistocene Epoch, which was studied by constructing the spectral density of the analyzed data in the running window of 201 and 701 kyr. © 2017, Pleiades Publishing, Ltd.
1967.
Deep drilling at the Chalco lake: A technical report [Perforación profunda en el lago de Chalco: Reporte técnico]
Boletin de la Sociedad Geologica Mexicana,
69
(2)
299-311
2017
ISSN: 14053322
Publisher: Instituto de GeologÃa, Universidad Nacional Autónoma de México
Abstract: ▾ This paper presents a short description of the coring operations undertaken to recover the full lacustrine sedimentary sequence from Chalco. Geophysical techniques were used to determine the distribution and thickness of the sediments in order to select the drilling site. Resonance frequencies determined from H/V spectral ratios were used to determine an area where lake sediments reached 300 m thickness. Electromagnetic survey showed two changes in electric resistivity which were related to changes in sediment composition, the first from 100 to 120 m, related to an increase in volcanoclastic sediments and the second from 330 to 400 m related to the presence of a basaltic flows. Three wells were drilled with continuous recovery, reaching depths of 420 m in well A, 310 in B and 520 in C. Samples for geomicrobiological and metagenomics studies were collected during drilling operations. A total of 1152 m of core sediments were recovered reaching a maximum depth of 520 m. Recovery percentages were between 88 and 92 % in the three wells. Magnetic susceptibility analyses in the three sequences show that the first 260 m are mostly lake sediments, between 260 and 300 m sediments are coarser and below 300 m they are mostly volcaniclastic. Analysis of the sedimentary sequence of Lake Chalco that covers the last ~300000 years will allow documenting and extending the knowledge of climate variability in area, the paleoenvironmental history, basin closure history, lacustrian system development and volcanic activity recurrence. Studies of the physical properties of this sequence will be important for seismic propagation and basin structure modeling, and also will improve modeling of the subsidence process that this region experiences.
1966.
Deep drilling reveals puzzling history of campi flegrei caldera
Eos (United States),
98
(4)
41
2017
ISSN: 00963941
Publisher: American Geophysical Union
1965.
Deep in a South African gold mine, scientists drill for the heart of an earthquake
Science
2017
1964.
Detection of a new sub-lithospheric discontinuity in Central Europe with S-receiver functions
Tectonophysics,
700-70119 – 31
2017
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Bohemian Massif; East European Craton; Pannonian Basin; Laboratories; Bohemian massifs; East-European craton; Lithosphere-asthenosphere boundary; Lithospheric; Pannonian basin; S-receiver functions; asthenosphere; craton; discontinuity; lithosphere; Moho; seismograph; upper mantle; Structural geology
Abstract: ▾ We used S-receiver functions (i.e. S-to-P converted signals) to study seismic discontinuities in the upper mantle between the Moho and the 410 km discontinuity beneath central Europe. This was done by using c. 49,000 S-receiver functions from c. 700 permanent and temporary broadband stations made available by the open EIDA Archives. Below Phanerozoic Europe we observed expected discontinuities like the Moho, the lithosphere-asthenosphere boundary (LAB), the Lehmann discontinuity and the 410 km discontinuity with an additional overlying low velocity zone. Below the East European Craton (EEC), we observed the Mid-Lithospheric Discontinuity (MLD) at c. 100 km depth as well as the controversial cratonic LAB at c. 200 km depth. At the boundary of the EEC but still below the Phanerozoic surface, we observed downward velocity reductions below the LAB in the following regions: the North German-Polish Plain at about 200 km depth; the Bohemian Massive, north-west dipping from 200 to 300 km depth; the Pannonian Basin, north-east dipping from 150 to 200 km depth underneath the western Carpathians and the EEC. We named this newly observed structure Sub-Lithospheric Discontinuity (SLD). At the northern edge of the Bohemian Massive, we see a sharp vertical step of about 100 km between the SLD below the Bohemian Massive and the North German-Polish Plain. This step follows the surface trace of the Rheic Suture between the continental Saxo-Thuringian and Rheno-Herzynian zones of the Variscan orogen. A preliminary interpretation of these features is that a prong of the cratonic mantle lithosphere penetrated the Phanerozoic asthenosphere during the continental collision at the western and south-western edges of the EEC. © 2017 Elsevier B.V.
1963.
Campanian–Maastrichtian palynomorph from the Sifangtai and Mingshui formations, Songliao Basin, Northeast China: Biostratigraphy and paleoflora
Palaeoworld,
26
(2)
352-368
2017
ISSN: 1871174X
Publisher: Elsevier B.V.
Keywords:▾
angiosperm; biostratigraphy; Campanian; core analysis; flora; gymnosperm; lacustrine deposit; levee; lithofacies; lithostratigraphy; Maastrichtian; mudstone; paleoenvironment; palynology; palynomorph; pollen; pteridophyte; sandstone; terrestrial deposit, China; Songliao Basin, Gymnospermae; Magnoliophyta; Pteridophyta
Abstract: ▾ We recovered a Campanian–Maastrichtian palynological record in transitional succession from the Sifangtai to Mingshui formations of the Songke Core-1 (North) (SK1 (N)) in the Songliao Basin, Northeast China. These formations are composed mainly of various colored mudstones and sandstones. The lithofacies variation suggests that the paleoenvironment changed from flood plain to lake. Most of the palynomorph assemblages are dominated by gymnosperm pollen, followed by spore of pteridophyte, and angiosperm pollen. On the basis of the first occurrences of marker genera within the succession, we identified four palynomorph interval zones (in ascending order): the Jianghanpollis, Chenopodipollis, Toroisporis, and Betulaceoipollenites interval zones. The first two interval zones are found from flood plain and levee deposits. The third one is recognized from lake basin plain–lake basin slope deposits. The last one is found in delta deposits within lakeshore. We consider that environmental changes are the major factors that formed component of Campanian–Maastrichtian assemblage in the Songliao Basin. In addition, the Jianghanpollis and Chenopodipollis interval zones are assigned to the Campanian, whereas the Toroisporis and Betulaceoipollenites interval zones date as the Maastrichtian. Thus, the Chenopodipollis/Toroisporis zonal boundary approximates the C/M boundary. Triprojectate pollen such as Aquilapollenites is regarded as marker taxa in the study section and other areas within the Aquilapollenites Province during the Campanian–Maastrichtian. However, Wodehouseia spp. have yet been confirmed within the study section, although this genus has appeared in Campanian–Maastrichtian deposits in other areas. This is one of the important clues to understand regional difference of local flora in these ages. © 2016 Elsevier B.V. and Nanjing Institute of Geology and Palaeontology, CAS
1962.
Biomarkers in Lake Van sediments reveal dry conditions in eastern Anatolia during 110.000–10.000 years B.P.
Geochemistry, Geophysics, Geosystems,
18
(2)
571-583
2017
ISSN: 15252027
Publisher: Blackwell Publishing Ltd
Keywords:▾
Evaporation; Glycerol; Isotopes; Lakes; Paraffins; Sediments, ACE index; Halophilic archaea; Hydrogen isotope; Hydrogen isotopic composition; Lake vans; Long chain n-alkanes; Occurrence and distribution; Pore water salinities, Biomarkers, biomarker; hydrogen isotope; isotopic composition; lacustrine deposit; lipid; paleoclimate; porewater; salinity, Anatolia; Lake Van; Turkey, algae; Euryarchaeota
Abstract: ▾ Lipid biomarkers were analyzed in Lake Van sediments covering the last 600 ka, with a focus on the period between 110 and 10 ka, when a broad maximum in pore water salinity as a relict from the past suggests dry conditions. The occurrence and distribution of biomarkers indicative for terrestrial plants (long-chain n-alkane C29), haptophyte algae (methyl alkenones C37) and halophilic archaea (archaeol) all point toward a dry climate in Lake Van region during this time interval. The hydrogen isotopic composition of C29 n-alkanes (δDC29) and C37 alkenones (δDC37) is enriched between MIS 4 and MIS 2, which is interpreted as a decrease in the regional ratio of precipitation to evaporation. Similarly, the low abundance of the acyclic glycerol dialkyl glycerol tetraether GDGT-0 relative to archaeol, quantified by the Archaeol and Caldarchaeol Ecometric (ACE) is assumed to reflect the presence of halophilic euryarchaeota adapted to high salinity water. The climate around Lake Van appears in phase with the Yammouneh basin 800 km southwest and Lake Urmia 250 km southeast of Lake Van over the last two glacial periods. The results highlight the potential of combining ACE, δDC29, and δDC37 for reconstructing salinity changes and regional precipitation to evaporation ratio from lake sediments. © 2017. American Geophysical Union. All Rights Reserved.
1961.
Drilling into an active mofette: Pilot-hole study of the impact of CO2-rich mantle-derived fluids on the geo-bio interaction in the western Eger Rift (Czech Republic)
Scientific Drilling,
2313-27
2017
ISSN: 18168957
Publisher: Copernicus GmbH
Keywords:▾
Beverages; Calcium; Carbon dioxide; Drilling fluids; Earthquakes; Faulting; Geodynamics; Reservoirs (water); Sodium; Sodium compounds; Sulfur compounds; Water, Cenozoic sediments; Czech Republic; Deformation structure; Earthquake swarms; Geodynamic process; Microbial life; Seismic activity; Well location, Calcium compounds
Abstract: ▾ Microbial life in the continental "deep biosphere" is closely linked to geodynamic processes, yet this interaction is poorly studied. The Cheb Basin in the western Eger Rift (Czech Republic) is an ideal place for such a study because it displays almost permanent seismic activity along active faults with earthquake swarms up to ML 4.5 and intense degassing of mantle-derived CO2 in conduits that show up at the surface in form of mofettes. We hypothesize that microbial life is significantly accelerated in active fault zones and in CO2 conduits, due to increased fluid and substrate flow. To test this hypothesis, pilot hole HJB-1 was drilled in spring 2016 at the major mofette of the Hartoušov mofette field, after extensive pre-drill surveys to optimize the well location. After drilling through a thin caprock-like structure at 78.5 m, a CO2 blowout occurred indicating a CO2 reservoir in the underlying sandy clay. A pumping test revealed the presence of mineral water dominated by Na+, Ca2+, HCO3-, SO42- (Na-Ca-HCO3-SO4 type) having a temperature of 18.6 °C and a conductivity of 6760 μScm-1. The high content of sulfate (1470 mg L-1) is typical of Carlsbad Spa mineral waters. The hole penetrated about 90 m of Cenozoic sediments and reached a final depth of 108.50m in Palaeozoic schists. Core recovery was about 85 %. The cored sediments are mudstones with minor carbonates, sandstones and lignite coals that were deposited in a lacustrine environment. Deformation structures and alteration features are abundant in the core. Ongoing studies will show if they result from the flow of CO2-rich fluids or not. © Author(s) 2017.
1960.
A numerical approach for modelling fault-zone trapped waves
Geophysical Journal International,
210
(2)
919-930
2017
ISSN: 0956540X
Publisher: Oxford University Press
Keywords:▾
Finite element method; Guided electromagnetic wave propagation; Water waves, Absorbing boundary condition; Computationally efficient; Fault-zone trapped waves; Finite element matrices; High-order finite elements; Numerical approximations and analysis; Numerical solution; Seismic anisotropy, Computational efficiency, boundary condition; fault zone; finite element method; Green function; numerical model; seismic anisotropy; transverse isotropy; trapped wave; wave generation; waveform analysis
Abstract: ▾ We develop a computationally efficient approach to compute the waveforms and the dispersion curves for fault-zone trapped waves guided by arbitrary transversely isotropic across-fault velocity models. The approach is based on a Green's function type representation for FL and FR type fault-zone trapped waves. The model can be used for simulation of the waveforms generated by both infinite line sources (2-D) and point sources (3-D). The numerical scheme is based on a high order finite element approximation and, to increase computational efficiency, we make use of absorbing boundary conditions and mass lumping of finite element matrices. © The Authors 2017.
1959.
3-D P- And S-wave velocity structure along the central Alpine Fault, South Island, New Zealand
Geophysical Journal International,
209
(2)
935-947
2017
ISSN: 0956540X
Publisher: Oxford University Press
Keywords:▾
Acoustic wave velocity; Drills; Earthquakes; Faulting; Guided electromagnetic wave propagation; Infill drilling; Tomography, Double-difference tomography; Earthquake location; Earthquake relocation; P- and S-wave velocities; South Island , New Zealand; Structural feature; Velocity contrasts; Velocity structure, Shear waves
Abstract: ▾ The Deep Fault Drilling Project (DFDP) on the central Alpine Fault, South Island, New Zealand, has motivated a broad range of geophysical and geological studies intended to characterize the fault system in the locality of the drill site at various scales. In order to better understand the structural features of the central Alpine Fault, we have developed 3-D P- and S-wave velocity (VP and VS) models of the region by double-difference tomography using data sets from multiple seismic networks. In previous work, the quality of the S-wave model has been poor due to the small number of available S-wave picks. We have utilized a new high-accuracy automatic S-wave picker to increase the number of usable S-wave arrivals by more than a factor of two, thereby substantially improving the VS model. Compared to previous studies, our new higher-resolution VP model based on more observations shows a clear VP contrast (higher VP on the southeast hanging wall side) at depths of 5-10 km near the DFDP drill sites. With our better resolved VS model, in the same region, we detect a sharply defined high VS body (VS > 3.7 km s-1) within the hanging wall. Our earthquake relocations reveal the presence of clusters within and around low-velocity zones in the hanging wall southeast of the Alpine Fault. Together with the improved earthquake locations, the P- and S-wave tomography results reveal the Alpine Fault to be marked by a velocity contrast throughout most of the study region. The fault dips southeastwards at about 50° from 5 to 15 km depth, as inferred from the velocity structure, seismicity and observations of fault zone guided waves. © 2017 The Authors 2017. Published by Oxford University Press on behalf of The Royal Astronomical Society.
1958.
50 Years of 10 December 1967 M 6.3 Koyna earthquake: Preface
Journal of the Geological Society of India,
90
(6)
641-644
2017
ISSN: 00167622
Publisher: Geological Society of India
1957.
A ∼6000 yr diatom record of mid- to late Holocene fluctuations in the level of Lago Wiñaymarca, Lake Titicaca (Peru/Bolivia)
Quaternary Research (United States),
88
(2)
179 – 192
2017
Keywords:▾
Bacillariophyta; Phytoplankton; Water; Concomitant decrease; Ecological conditions; Environmental dynamics; Holocenes; Lake level fluctuations; Lake levels; Mid to late Holocene; Tropical Andes; Lakes
Abstract: ▾ A multidecadal-scale lake-level reconstruction for Lago Wiñaymarca, the southern basin of Lake Titicaca, has been generated from diatom species abundance data. These data suggest that ~6500 cal yr BP Lago Wiñaymarca was dry, as indicated by a sediment unconformity. At ~4400 cal yr BP, the basin began to fill, as indicated by the dominance of shallow epiphytic species. It remained somewhat saline with extensive wetlands and abundant aquatic plants until ~3800 cal yr BP, when epiphytic species were replaced by planktic saline-indifferent species, suggesting a saline shallow lake. Wiñaymarca remained a relatively shallow lake that fluctuated on a multidecadal scale until ~1250 cal yr BP, when freshwater planktic species increased, suggesting a rise in lake level with a concomitant decrease in salinity. The lake became gradually fresher, dominated by deep, freshwater species from ~850 cal yr BP. By ~80 cal yr BP, saline-tolerant species were rare, and the lake was dominated by freshwater planktic diatoms, resembling the fresh and deep lake of today. These results reveal a more dynamic and chronologically specific record of lake-level fluctuations and associated ecological conditions that provide important new data for paleoclimatologists and archaeologists, to better understand human-environmental dynamics during the mid- to late Holocene. Copyright © University of Washington. Published by Cambridge University Press, 2017.
1956.
A 1251m-thick Deccan flood basalt pile recovered by scientific drilling in the Koyna region, western India
Journal of the Geological Society of India,
90
(6)
788-794
2017
ISSN: 00167622
Publisher: Geological Society of India
Keywords:▾
basement rock; Deccan Traps; drilling; flood basalt; lava flow; petrography; plagioclase; volcanism; volcanology, India; Koyna; Maharashtra
Abstract: ▾ A 1251 m thick succession of Deccan lava flows has been recovered by scientific drilling in the Koyna region, western part of the Deccan Volcanic Province (DVP). Forty-six lava flows, starting with the first flow overlying the granitic basement in the region, have been identified through mesoscopic studies of cores obtained from a 1500 m deep borehole KBH7 in Panchgani village of Patan sub-division. Mesoscopic observations supported by petrographic studies bring out the characteristics of the basaltic pile. The salient findings are as follows. The thickness of Deccan trap in the Panchgani area is 1251.20 m, comprising a succession of 40 simple lava flows and 6 compound lava flows. The contact with the underlying granitic basement occurs over a short span of 90 cm. Infra-trappean sediments are absent. Overall, ∼74% of the basaltic pile is constituted of massive basalt and ∼24% vesicular/amygdaloidal basalt. Red bole horizons are observed in 7 flows. Nine giant plagioclase basalt (GPB) flows are identified in the single vertical section. The long basalt core may serve as a model Deccan trap section for correlation with the flows exposed at the surface in the Koyna and surrounding region and support detailed investigations to constrain the duration of Deccan volcanism. © 2017, Geological Society of India.
1955.
Large eighteenth–nineteenth century earthquakes in western gulf of corinth with reappraised size and location
Bulletin of the Seismological Society of America,
107
(4)
1663 – 1687
2017
ISSN: 00371106
Publisher: Seismological Society of America
Keywords:▾
Achaea; Egion; Greece; Gulf of Corinth; Ionian Sea; Mediterranean Sea; Western Greece; Achaea; Geophysics; Location; Uncertainty analysis; Continuous monitoring; Earthquake process; Earthquake records; Epistemic uncertainties; Laboratory project; Macroseismic intensity; Multi-disciplinary research; New parameters; earthquake epicenter; earthquake event; earthquake magnitude; earthquake mechanism; eighteenth century; nineteenth century; paleoseismicity; seismicity; seismology; structural geology; Earthquakes
Abstract: ▾ The area of the western Gulf of Corinth around the city of Aigio (Achaea, northwest Peloponnese, Greece) represents an international pilot site for continuous monitoring and multidisciplinary research on earthquake processes. In the framework of the ANR-SISCOR Corinth Rift Laboratory project (2011–2014), a thorough reappraisal of the five largest (Mw >6) eighteenth–nineteenth century earthquakes was performed, namely those of 14 May 1748, 23 August 1817, 26 December 1861, 9 September 1888, and 25 August 1889. Written observations of earthquake effects were looked into in their original version and language and were placed in the context from which they originated, to avoid the translations and digests on which previous seismological studies had relied. Earthquake records were traced for 108 different localities, and 143 macroseismic intensities in European Macroseismic Scale 1998 (EMS-98) have been assigned. Earthquake-related geological phenomena have been identified and carefully mapped, to be used as a further constraint of the location and magnitude of the associated earthquakes. Finally, new parameters for the studied earthquakes have been assessed with two separate and independent strategies to quantify epistemic uncertainties. In conclusion, the 1748, 1817, and 1888 earthquakes were located in the area of Aigio; the 1861 earthquake is reckoned to be the largest in the area, with an epicentral location at sea; whereas the 1889 earthquake has been relocated to the northwest in mainland Greece, well outside the Gulf of Corinth. © 2017, Seismological Society of America. All rights reserved.
1954.
A magnetotelluric investigation of the Scandinavian Caledonides in western Jämtland, Sweden, using the COSC borehole logs as prior information
Geophysical Journal International,
208
(3)
1465 – 1489
2017
ISSN: 0956-540XKeywords:▾
inverse theory, Magnetotellurics, Europe, Downhole methods, Continental tectonics
1953.
A simple and inexpensive technique for assessing contamination during drilling operations
Limnology and Oceanography: Methods,
15
(2)
200 – 211
2017
ISSN: 15415856
Publisher: Wiley Blackwell
Abstract: ▾ Subsurface exploration relies on drilling. Normally drilling requires a drilling fluid that will infiltrate into the drill core. Drilling fluid contains non-indigenous materials and microbes from the surface, so its presence renders a sample unsuitable for microbiological and many other analyses. Because infiltration cannot be avoided, it is of paramount importance to assess the degree of contamination to identify uncontaminated samples for geomicrobiological investigations. To do this, usually a tracer is mixed into the drilling fluid. In past drilling operations a variety of tracers have been used, each has specific strengths and weaknesses. For microspheres the main problem was the high price, which limited their use to spot checks or drilling operations that require only small amounts of drilling fluid. Here, we present a modified microsphere tracer approach that uses an aqueous fluorescent pigment dispersion with a similar concentration of fluorescent particles as previously used microsphere tracers. However, it costs four orders of magnitude less, allowing for a more liberal use even in large operations. Its applicability for deep drilling campaigns was successfully tested during two drilling campaigns of the International Continental Drilling Program (ICDP) at Lake Towuti, Sulawesi, Indonesia, and Lake Chalco, Mexico. Quantification of the tracer requires only a fluorescence microscope or a flow cytometer. The latter allowing for high-resolution data to be obtained directly on-site within minutes and with minimal effort, decreasing sample processing times substantially relative to traditional tracer methods. This approach offers an inexpensive, rapid, but powerful alternative technique for contamination assessment during drilling campaigns. © 2017 Association for the Sciences of Limnology and Oceanography.
1952.
Bedrock geology of DFDP-2B, central Alpine Fault, New Zealand
New Zealand Journal of Geology and Geophysics,
60
(4)
497-518
2017
ISSN: 00288306
Publisher: Taylor and Francis Asia Pacific
Keywords:▾
bedrock; cataclasite; core analysis; drilling; fault zone; mylonite; sedimentary sequence; shear band; slip rate; structural geology, Alpine Fault Zone; New Zealand; South Island
Abstract: ▾ During the second phase of the Alpine Fault, Deep Fault Drilling Project (DFDP) in the Whataroa River, South Westland, New Zealand, bedrock was encountered in the DFDP-2B borehole from 238.5–893.2 m Measured Depth (MD). Continuous sampling and meso- to microscale characterisation of whole rock cuttings established that, in sequence, the borehole sampled amphibolite facies, Torlesse Composite Terrane-derived schists, protomylonites and mylonites, terminating 200–400 m above an Alpine Fault Principal Slip Zone (PSZ) with a maximum dip of 62°. The most diagnostic structural features of increasing PSZ proximity were the occurrence of shear bands and reduction in mean quartz grain sizes. A change in composition to greater mica:quartz + feldspar, most markedly below c. 700 m MD, is inferred to result from either heterogeneous sampling or a change in lithology related to alteration. Major oxide variations suggest the fault-proximal Alpine Fault alteration zone, as previously defined in DFDP-1 core, was not sampled. © 2017 The Royal Society of New Zealand.
1951.
A simple and inexpensive technique for assessing contamination during drilling operations
Limnology and Oceanography: Methods,
15
(2)
200-211
2017
ISSN: 15415856
Publisher: Wiley Blackwell
Abstract: ▾ Subsurface exploration relies on drilling. Normally drilling requires a drilling fluid that will infiltrate into the drill core. Drilling fluid contains non-indigenous materials and microbes from the surface, so its presence renders a sample unsuitable for microbiological and many other analyses. Because infiltration cannot be avoided, it is of paramount importance to assess the degree of contamination to identify uncontaminated samples for geomicrobiological investigations. To do this, usually a tracer is mixed into the drilling fluid. In past drilling operations a variety of tracers have been used, each has specific strengths and weaknesses. For microspheres the main problem was the high price, which limited their use to spot checks or drilling operations that require only small amounts of drilling fluid. Here, we present a modified microsphere tracer approach that uses an aqueous fluorescent pigment dispersion with a similar concentration of fluorescent particles as previously used microsphere tracers. However, it costs four orders of magnitude less, allowing for a more liberal use even in large operations. Its applicability for deep drilling campaigns was successfully tested during two drilling campaigns of the International Continental Drilling Program (ICDP) at Lake Towuti, Sulawesi, Indonesia, and Lake Chalco, Mexico. Quantification of the tracer requires only a fluorescence microscope or a flow cytometer. The latter allowing for high-resolution data to be obtained directly on-site within minutes and with minimal effort, decreasing sample processing times substantially relative to traditional tracer methods. This approach offers an inexpensive, rapid, but powerful alternative technique for contamination assessment during drilling campaigns. © 2017 Association for the Sciences of Limnology and Oceanography.
1950.
Active Magmatic Underplating in Western Eger Rift, Central Europe
Tectonics,
36
(12)
2846 – 2862
2017
ISSN: 02787407
Publisher: Blackwell Publishing Ltd
Keywords:▾
Eger; Heves; Hungary; Alkalinity; Reflection; Seismology; Velocity; Alkaline volcanism; Continental crusts; Eger Rift; Geodynamic process; Lateral variations; Lower crust; Magma bodies; Underplating; crust-mantle boundary; crustal movement; geodynamics; intraplate process; magmatic differentiation; rift zone; seismic reflection; underplating; Geodynamics
Abstract: ▾ The Eger Rift is an active element of the European Cenozoic Rift System associated with intense Cenozoic intraplate alkaline volcanism and system of sedimentary basins. The intracontinental Cheb Basin at its western part displays geodynamic activity with fluid emanations, persistent seismicity, Cenozoic volcanism, and neotectonic crustal movements at the intersections of major intraplate faults. In this paper, we study detailed geometry of the crust/mantle boundary and its possible origin in the western Eger Rift. We review existing seismic and seismological studies, provide new interpretation of the reflection profile 9HR, and supplement it by new results from local seismicity. We identify significant lateral variations of the high-velocity lower crust and relate them to the distribution and chemical status of mantle-derived fluids and to xenolith studies from corresponding depths. New interpretation based on combined seismic and isotope study points to a local-scale magmatic emplacement at the base of the continental crust within a new rift environment. This concept of magmatic underplating is supported by detecting two types of the lower crust: a high-velocity lower crust with pronounced reflectivity and a high-velocity reflection-free lower crust. The character of the underplated material enables to differentiate timing and tectonic setting of two episodes with different times of origin of underplating events. The lower crust with high reflectivity evidences magmatic underplating west of the Eger Rift of the Late Variscan age. The reflection-free lower crust together with a strong reflector at its top at depths of ~28–30 km forms a magma body indicating magmatic underplating of the late Cenozoic (middle and upper Miocene) to recent. Spatial and temporal relations to recent geodynamic processes suggest active magmatic underplating in the intracontinental setting. ©2017. American Geophysical Union. All Rights Reserved.
1949.
Ambient noise tomography of the western Corinth Rift, Greece
Geophysical Journal International,
211
(1)
284 – 299
2017
ISSN: 0956540X
Publisher: Oxford University Press
Keywords:▾
Corinth Rift; Greece; Gulf of Corinth; Ionian Sea; Mediterranean Sea; Acoustic noise; Buildings; Coastal engineering; Group velocity dispersion; Interferometry; Light velocity; Rayleigh waves; Seismology; Surface waves; Tectonics; Three dimensional computer graphics; Ambient noise tomographies; Continuous waveforms; Crustal structure; Group velocity dispersion curve; Neighbourhood algorithms; Seismic tomography; Shear velocity models; Surface-wave tomography; algorithm; ambient noise; crustal structure; Green function; Rayleigh wave; seismic velocity; seismology; tomography; Shear flow
Abstract: ▾ Three years of continuous waveform data recorded at 22 stations from the Corinth Rift Laboratory and the Hellenic Unified Seismological Network are used to perform an ambient noise surface wave tomography of the western Corinth Rift. All available vertical component time-serieswere cross-correlated to extract empirical Rayleigh-wave Green's functions. Group velocity dispersion curves were measured for each station-pair by applying frequency-time analysis and then inverted to build 2-D group velocity maps between 1 and 6 s period. Finally, we locally inverted these velocity maps using a neighbourhood algorithm to assess the 3-D shear-velocity model of the shallow crustal structure of the western Corinth Rift. Across all studied periods the southern coast of the Corinth Gulf is generally imaged as a region of lower velocities compared to the northern coast. At periods up to 3 s, the spatial variation of the group velocities is correlated with the surface geology of the area. Lower velocities are observed in areas where mostly Plio-Quaternary syn-rift sediments are present, such as offshore regions of the rift, the Mornos delta and the largest part of the southern coast. Higher velocities are observed in pre-rift basement structures which are dominated mostly by carbonates. At periods above 3 s, where Rayleigh-waves begin to sense deeper structures below the sediments within the underlying basement, our study highlights the presence of a distinct zone of lower velocities across the southern part of the rift with an elongation in the WNW-ESE direction. The interpretation of this low velocity includes two arguments, the present-day active tectonic regime and the possible involvement of fluids circulation processes at depth within a highly fractured upper crust in the vicinity of the major faults zones. In general, the results demonstrate good agreement with the major geological and tectonic features of the area, as well as with previous local earthquake tomography studies and support the assumption of fluid circulations at depth. This work intends to be the base for further investigations towards the study of the Corinth Rift structure using long-time series of ambient noise data. © The Authors 2017.
1948.
Application of geochemical logging for palaeoenvironmental research in the Late Cretaceous Qingshankou Formation from the Chinese Continental Scientific Drilling Project-SK-2e, Songliao Basin, NE China
Journal of Geophysics and Engineering,
14
(4)
865 – 877
2017
ISSN: 17422132
Publisher: Institute of Physics Publishing
Keywords:▾
China; Songliao Basin; borehole; Chinese Continental Scientific Drilling Project; Cretaceous; deposition; environmental research; geochemistry; organic matter; paleoenvironment; productivity; proxy climate record; source rock; terrigenous deposit
Abstract: ▾ The Chinese Continental Scientific Drilling Project of the Cretaceous Songliao Basin (CCSD-SK) provides an excellent opportunity to understand the response of terrestrial environments to greenhouse climate change in the Cretaceous. We conducted a palaeoenvironmental study of the Late Cretaceous Qingshankou Formation (K2qn) based on geochemical log data from the SK-2 east borehole. According to the characteristic of Ti mainly from terrigenous minerals, the content of authigenic elements was calculated. Correlation space was proposed to study the variation of the correlation between two log curves along the depth. Palaeoenvironmental proxies were selected from log data to study the evolution of the climate and lake, productivity of the paleolake, and organic matter deposition. The results demonstrate that the productivity of the paleolake was driven by chemical weathering in K2qn, in which the first section of the Qingshankou Formation (K2qn1) has higher productivity than the second and third sections of the Qingshankou Formation (K2qn2+3). The high content of pyrite in several thin layers reveals lake water of high sulfate concentration. This may have been caused by acid rain related to large volcanic activity. In K2qn2+3, several periods of high productivity without the formation of source rocks and high organic matter content were identified. This may show that organic matter deposition was limited by low accommodation space or oxidation environment. Therefore, the preservation condition is suggested as the main controlling factor of organic matter deposition in K2qn. © 2017 Sinopec Geophysical Research Institute.
1947.
Architecture and temporal variations of a terrestrial CO2 degassing site using electric resistivity tomography and self-potential
International Journal of Earth Sciences,
106
(8)
2915-2926
2017
ISSN: 14373254
Publisher: Springer Verlag
Keywords:▾
carbon dioxide; carbon flux; degassing; electrical resistivity; fumarole; mantle structure; mapping; temporal variation; tomography, Bohemia; Cheb Basin; Czech Republic; Karlovarsky
Abstract: ▾ The Hartoušov mofette field in NW Bohemia, Czech Republic, is characterized by strong CO2 degassing from the Lithospheric Mantle. In a test survey using electrical resistivity tomography, we observed changes over time in the subsurface structure beneath heavily CO2 degassing spots to depths of about 40 m and compared them to CO2 gas flux and soil gas mappings from previous studies. Changes in the electrical resistivity were measured between September 2012 and October 2013 at irregular intervals and highlight large variations in the resistivity distribution where the CO2 degassing was strongest (56 × 103 g m−2 day−1), indicating a fluid-induced change of properties of the underlying clayey sediments. Positive and negative anomalies in the electric self-potential parallel to the ERTs can be found where CO2 degassing occurs which indicates varying ascent or descent of fluids within these spots. Some degassing spots seem not to be actively degassing continuously over time, which can also be observed by other studies in the same area. We suggest that future gas mappings are accompanied by methods that observe the state of fluid systems at subsurface over time, e.g. electric resistivity tomography and self potential. © 2017, Springer-Verlag Berlin Heidelberg.
1946.
Arctic glacial and interglacial variability throughout the quaternary: Evidence from lake Elgygytgyn, northeastern Russia
Polarforschung,
87
(1)
43-60
2017
ISSN: 00322490
Publisher: Alfred Wegener Institut fur Polar- und Meeresforschung
Keywords:▾
climate variation; environmental change; glacial-interglacial cycle; lacustrine deposit; paleoclimate; paleoenvironment; paleolimnology; Quaternary, Chukchi; Elgygytgyn Lake; Russian Federation
Abstract: ▾ Lake Elgygytgyn in the north-eastern Russian Arctic became the target of extensive international site surveys in the late 1990s, with complex geoscientific fieldwork conducted in 1998, 2000, and 2003. The surveys strongly supported the hypothesis that the lake hosts a nearly continuous sediment record, which is highly sensitive to climatic and environmental changes and covers the time since the lake formation by a meteorite impact some 3.6 Ma ago. These promising findings led to deep drilling operations within the scope of the International Continental Scientific Drilling Program (ICDP) in 2008 and 2009, during which 141 m of permafrost deposits in the catchment, the 318 m thick lake sediment succession in the lake centre, and about 200 m of impact rocks underneath were drilled. Palaeoenvironmental and palaeoclimatological research on the Quaternary part of the lake sediment record revealed that full glacial conditions, with mean annual air temperatures at least 3.3 ±0.9 °C lower than today, first commenced at the Pliocene/ Pleistocene boundary 2.6 Ma ago. They gradually increased in frequency from ca. 2.3 to 1.8 Ma, eventually concurring with all global glacials and several stadials. The interglacials at Lake Elgygytgyn significantly differ in intensity. So-called super interglacials irregularly occurred throughout the Quaternary, including Marine Isotope Stages 11.3 and 31, when mean temperatures of the warmest month and annual precipitation were up to 4-5 °C and ~300 mm higher than today, respectively. According to climate modelling these climatic settings cannot in all cases be traced back to orbital forcing or greenhouse gas concentrations. They are, at least partly, the result of other processes and feedbacks in the climate system. A remarkable coincidence of the super interglacials with diatomite layers in the Antarctic ANDRILL 1B record suggests that they were associated with considerable retreats of the West Antarctic Ice Sheet. The ice decay may have caused reductions in Antarctic Bottom Water formation, its transport to the Pacific Ocean, and its upwelling in the north-western Pacific, and potentially increased warm-water intrusions through the Bering Strait into the Arctic Ocean. © Alfred Wegener Institut fur Polar- und Meeresforschung. All rights reserved.
1945.
Attenuation tomography in West Bohemia/Vogtland
Tectonophysics,
69564-75
2017
ISSN: 00401951
Publisher: Elsevier B.V.
Keywords:▾
Seismic waves, Body waves; Earthquake swarms; Europe; Seismic attenuation; Seismic tomography, Earthquakes, amplitude; body wave; earthquake hypocenter; earthquake swarm; P-wave; seismic attenuation; seismic tomography; seismicity; structural geology, Bohemia; Czech Republic; Germany; Vogtland
Abstract: ▾ We present a three-dimensional (3-D) P-wave attenuation (Qp) model for the geodynamically active swarm earthquake area of West Bohemia/Vogtland in the Czech/German border region. Path-averaged attenuation t* is calculated from amplitude spectra of time windows around the P-wave arrivals of local earthquakes. Average t/t* value or Qp for stations close to Nový Kostel are very low (< 150) compared to that of stations located further away from the focal zone (increases up to 500 within 80 km distance). The SIMUL2000 tomography scheme is used to invert the t* for P-wave attenuation perturbation. Analysis of resolution shows that our model is well-resolved in the vicinity of earthquake swarm hypocenters. The prominent features of the model are located around Nový Kostel focal zone and its northern vicinity. Beneath Nový Kostel a vertically stretched (down to depth of 11 km) and a highly attenuating body is observed. We believe that this is due to fracturing and high density of cracks inside the weak earthquake swarm zone in conjunction with presence of free gas/fluid. Further north of Nový Kostel two highly attenuating bodies are imaged which could represent fluid channels toward the surface. The eastern anomaly shows a good correlation with the fluid accumulation area which was suggested in 9HR seismic profile. © 2016 Elsevier B.V.