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  • 1
    Publication Date: 2020-02-12
    Description: Fault rock assemblages reflect interaction between deformation, stress, temperature, fluid, and chemical regimes on distinct spatial and temporal scales at various positions in the crust. Here we interpret measurements made in the hanging-wall of the Alpine Fault during the second stage of the Deep Fault Drilling Project (DFDP-2). We present observational evidence for extensive fracturing and high hanging-wall hydraulic conductivity (∼10−9 to 10−7 m/s, corresponding to permeability of ∼10−16 to 10−14 m2) extending several hundred meters from the fault's principal slip zone. Mud losses, gas chemistry anomalies, and petrophysical data indicate that a subset of fractures intersected by the borehole are capable of transmitting fluid volumes of several cubic meters on time scales of hours. DFDP-2 observations and other data suggest that this hydrogeologically active portion of the fault zone in the hanging-wall is several kilometers wide in the uppermost crust. This finding is consistent with numerical models of earthquake rupture and off-fault damage. We conclude that the mechanically and hydrogeologically active part of the Alpine Fault is a more dynamic and extensive feature than commonly described in models based on exhumed faults. We propose that the hydrogeologically active damage zone of the Alpine Fault and other large active faults in areas of high topographic relief can be subdivided into an inner zone in which damage is controlled principally by earthquake rupture processes and an outer zone in which damage reflects coseismic shaking, strain accumulation and release on interseismic timescales, and inherited fracturing related to exhumation.
    Language: English
    Type: info:eu-repo/semantics/article
    Format: application/pdf
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  • 2
    Publication Date: 2020-02-12
    Description: 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.
    Type: info:eu-repo/semantics/article
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  • 3
    Publication Date: 2020-02-12
    Description: Temperature and fluid pressure conditions control rock deformation and mineralization on geological faults, and hence the distribution of earthquakes1. Typical intraplate continental crust has hydrostatic fluid pressure and a near-surface thermal gradient of 31 ± 15 degrees Celsius per kilometre2, 3. At temperatures above 300–450 degrees Celsius, usually found at depths greater than 10–15 kilometres, the intra-crystalline plasticity of quartz and feldspar relieves stress by aseismic creep and earthquakes are infrequent. Hydrothermal conditions control the stability of mineral phases and hence frictional–mechanical processes associated with earthquake rupture cycles, but there are few temperature and fluid pressure data from active plate-bounding faults. Here we report results from a borehole drilled into the upper part of the Alpine Fault, which is late in its cycle of stress accumulation and expected to rupture in a magnitude 8 earthquake in the coming decades4, 5. The borehole (depth 893 metres) revealed a pore fluid pressure gradient exceeding 9 ± 1 per cent above hydrostatic levels and an average geothermal gradient of 125 ± 55 degrees Celsius per kilometre within the hanging wall of the fault. These extreme hydrothermal conditions result from rapid fault movement, which transports rock and heat from depth, and topographically driven fluid movement that concentrates heat into valleys. Shear heating may occur within the fault but is not required to explain our observations. Our data and models show that highly anomalous fluid pressure and temperature gradients in the upper part of the seismogenic zone can be created by positive feedbacks between processes of fault slip, rock fracturing and alteration, and landscape development at plate-bounding faults.
    Type: info:eu-repo/semantics/article
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  • 4
    Publication Date: 2020-02-12
    Description: These data are supplementary material to “Bedrock Geology of DFDP-2B, Central Alpine Fault, New Zealand” (Toy et al., 2017, http://doi.org/10.1080/00288306.2017.1375533). The data tables SF3 and SF4 are provided as well as Excel as well as CSV and PDF versions (in the zip folder). The table numbers below are referring to Toy et al. (2017): Toy_SF1.pdf (Data Description): Supplementary Data to “Bedrock Geology of DFDP-2B, Central Alpine Fault, New Zealand”, including supplementary methods, Information on reference frames and corrections, and protocols for thin section preparation and scanning electron microscopic analyses. Toy_SF2: Table S1. Time vs. depth during drilling, with lag dip corrections Toy_SF3: Table S2. Energy dispersive spectroscopy (EDS) data acquired using a TESCAN Integrated Mineral Analyzer (TIMA) and phases detected by mineral liberation analysis (MLA) Toy_SF4: Table S3. Electron backscatter diffraction (EBSD) grain sizes
    Language: English
    Type: info:eu-repo/semantics/workingPaper
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 150 (1997), S. 249-267 
    ISSN: 1420-9136
    Keywords: Key words: Seismic quiescence, numerical simulation, rate- and state-dependent friction, preseismic sliding, stress relaxation.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —We propose a new model to physically explain the seismic quiescence precursory to a large interplate earthquake. A numerical simulation is performed to quantitatively examine possible stress changes prior to a great interplate earthquake in a subduction zone. In the present study, the frictional force following a laboratory-derived friction law, in which the friction coefficient is dependent on slip rate and slip history, is assumed to act on a dip-slip fault plane of infinite width in a uniform elastic half-space. The values of friction parameters are determined so that the result of numerical simulation may explain some properties of great interplate earthquakes in subduction zones, such as the recurrence interval and the seismic coupling coefficient. The result of simulation reveals that significant quasi-stable sliding occurs prior to a great earthquake and, accordingly, stresses are changed on and around the plate boundary. In a relatively wide area of the overriding continental plate, the compres sional horizontal-stress perpendicular to the trench axis is decreased for a few years before the occurrence of a great earthquake. This decrease in regional compressional stress may account for the appearance of seismic quiescence prior to a great interplate earthquake.
    Type of Medium: Electronic Resource
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  • 6
    ISSN: 1420-9136
    Keywords: Key words: Rate- and state-dependent friction law, subduction zone, seismic activity, aseismic sliding.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —A numerical study is conducted to simulate complicated sliding behavior and earthquake activity on a subducting plate boundary. A 2-D model of a uniform elastic half-space with a semi-infinite thrust fault is set up, and the frictional stress prescribed by a rate- and state-dependent friction law is assumed to act on the plate boundary fault. Spatial nonuniformity of friction parameters representing rate-dependence of friction and of slip-dependence of friction are introduced in the model to obtain complicated sliding behavior in the numerical simulation. Analogs of great earthquakes that break the entire seismogenic plate boundary repeatedly occur at a constant time interval. Smaller events of seismic or aseismic sliding occur during a great earthquake cycle. Regions of rate-strengthening of friction and of a large characteristic distance in slip-dependence of friction behave as barriers or asperities. Rupture propagation is often arrested in such a region and a great earthquake occurs later when the region is broken. The variety of earthquake activity observed in many regions along real plate boundaries may be explained by similar nonuniformity in friction parameters. Conversely, the friction parameters on plate boundaries might be estimated from comparison of theoretical simulations with observations of earthquake activity. Simulation results indicate that spatiotemporal variation in stress due to aseismic sliding may play an important part in generating earthquakes.
    Type of Medium: Electronic Resource
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  • 7
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 155 (1999), S. 425-442 
    ISSN: 1420-9136
    Keywords: Key Words: A rate- and state-dependent friction law, seismic cycle, precursory seismic quiescence, postseismic sliding, intermediate-depth earthquake, episodic sliding.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract — Numerical simulation of recurring large interplate earthquakes in a subduction zone is conducted to explore the effects of aseismic sliding on the variation of stresses and the activity of small earthquakes. The frictional force obeying a rate- and state-dependent friction law is assumed to act on the plate interface in a 2-D model of uniform elastic half-space. The simulation results show that large earthquakes repeatedly occur at a constant time interval on a shallow part of the plate interface and that aseismic sliding migrates from the upper aseismic zone as well as from the lower aseismic zone into the central part of the seismogenic zone before the occurrence of a large interplate earthquake. This spatiotemporal variation of aseismic sliding significantly perturbs the stresses in the overriding plate and in the subducting oceanic plate, leading to the precursory seismic quiescence in the overriding plate and the activation of the intermediate-depth earthquakes of down-dip tension type. After the occurrence of a large interplate earthquake, the activity of the intermediate-depth earthquakes of down-dip compression type in the subducting slab is expected to increase and migrate downward. This is because the downward propagation of postseismic sliding causes the downward migration of compressional-stress increase in the down-dip direction of the plate interface. The simulation result further indicates that episodic events of aseismic sliding may occur when the spatial distributions of friction parameters are significantly nonuniform. The variation of stresses due to episodic sliding is expected to cause seismicity changes.
    Type of Medium: Electronic Resource
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  • 8
    Electronic Resource
    Electronic Resource
    Springer
    Pure and applied geophysics 155 (1999), S. 669-687 
    ISSN: 1420-9136
    Keywords: Key Words: Locked subduction, microearthquake seismicity, frictional sliding.
    Source: Springer Online Journal Archives 1860-2000
    Topics: Geosciences , Physics
    Notes: Abstract —A tectonic state of a locked subduction is considered to be a possible source of a future interplate earthquake. Discriminating an actually locked state to verify its extent is therefore essential in constructing an accurate prospect against the forthcoming earthquake. Micorearthquake seismicity is an effective tool for such an analysis because it is considered to be a faithful indicator of the stress state, and is expected to exhibit a characteristic pattern in the area where the locked state in the subduction appears with a certain stress concentration. Focusing on the microearthquake seismicity around the Tokai district in central Japan, where a large interplate earthquake is feared to occur, we tried to identify such an area of locked subduction on the Philippine Sea plate, possibly related to the future earthquake. We investigated the microearthquake seismicity from various perspectives. First, the hypocenter distribution was analyzed to identify the extent of the locked area. The characteristic profile of the distribution was presumed to represent a stress concentrated area induced from the mechanical contact between both plates. The second approach is to interpret stress patterns reflected in focal mechanisms. The locked state was recognized and verified by a comparison of the P-axis distribution pattern with that expected from a model imaging a partially locked subduction. The third approach is to monitor the temporal change of the seismic wave spectrum. Analyzing predominant frequencies of P and S waves and monitoring their changes for a period of 10 years, we found a trend of gradual increase common to both waves. This means an increase of stress drop in microfracturings, and in its turn implies accumulation of stress around the focus area. The rate of the stress change converted from the frequency change was compared with the result derived from a numerical simulation. The simulation, performed on the basis of a constitutive friction law for a stick sliding on the plate interface, computed a changing rate of the maximum shear stress around the locked zone and showed its spatial variation along the subduction axis. Thus the simulated result indicated a certain compatibility with the observed one. Although ambiguities and uncertainties still exist in the study, all the results derived here seem to indicate an identical conclusion that the plate subduction is actually locked in this region at present.
    Type of Medium: Electronic Resource
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  • 9
    Electronic Resource
    Electronic Resource
    Springer
    Physics of the solid state 41 (1999), S. 688-692 
    ISSN: 1063-7834
    Source: Springer Online Journal Archives 1860-2000
    Topics: Physics
    Notes: Abstract Multi-purpose nonlinear optical microscope is an optical microscope which images 2D distribution of the optical second harmonic (SH) waves from a specimen. Image contrast can be obtained either by inhomogeneous distribution of nonlinear optical tensor components or by the interference between SH waves from a specimen and a standard plate. This microscope also functions as a fluorescence (FL) microscope, and SH and FL images can be obtained from the same part of a specimen. Absorption and FL spectra from a specific part of a specimen are measured through an optical fiber which connects an ocular with a polychromator. These functions are especially useful for investigation of the J-aggregate state of polar dye molecules. Several photographs taken by the microscope revealed the structure of merocyanine dye/arachidic acid mixed monolayer and the role of bridge ions in the subphase.
    Type of Medium: Electronic Resource
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  • 10
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Publishing Ltd
    FEMS microbiology letters 20 (1983), S. 0 
    ISSN: 1574-6968
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Abstract Polyvinyl alcohol (PVA) was utilized by a symbiotic mixed culture which was composed of Pseudomonas putida VM15A and Pseudomonas sp. VM14C. The PVA oxidase was found in the culture fluid, membrane, and cytosol fractions of VM15C. The membrane-bound PVA oxidase was purified by several steps of chromatography. The enzyme (pI= 9.6) exhibited the maximum activity at pH 8.0 to 8.4 and 45°C, and utilized secondary alcohol as well as PVA. The enzyme showed the PVA dehydrogenating activity linking with phenazine ethosulfate, indicating the possibility that PVA oxidation is coupled with an electron transport chain on the bacterial membrane.
    Type of Medium: Electronic Resource
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