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Porosity reduction in rocks from a fault core can cause elevated pore fluid pressures and consequently influence the recurrence time of earthquakes. We investigated the porosity distribution in the New Zealand's Alpine Fault core in samples recovered during the first phase of the Deep Fault Drilling Project (DFDP-1B) by using two-dimensional nanoscale and three-dimensional microscale imaging. Synchrotron X-ray microtomography-derived analyses of open pore spaces show total microscale porosities in the range of 0.1 %–0.24 %. These pores have mainly non-spherical, elongated, flat shapes and show subtle bipolar orientation. Scanning and transmission electron microscopy reveal the samples' microstructural organization, where nanoscale pores ornament grain boundaries of the gouge material, especially clay minerals. Our data imply that (i) the porosity of the fault core is very small and not connected; (ii) the distribution of clay minerals controls the shape and orientation of the associated pores; (iii) porosity was reduced due to pressure solution processes; and (iv) mineral precipitation in fluid-filled pores can affect the mechanical behavior of the Alpine Fault by decreasing the already critically low total porosity of the fault core, causing elevated pore fluid pressures and/or introducing weak mineral phases, and thus lowering the overall fault frictional strength. We conclude that the current state of very low porosity in the Alpine Fault core is likely to play a key role in the initiation of the next fault rupture.

Graphitization in fault zones is associated both with fault weakening and orogenic gold mineralization. We examine processes of graphitic carbon emplacement and deformation in the active Alpine Fault Zone, New Zealand by analysing samples obtained from Deep Fault Drilling Project (DFDP) boreholes. Optical and scanning electron microscopy reveal a microtextural record of graphite mobilization as a function of temperature and ductile then brittle shear strain. Raman spectroscopy allowed interpretation of the degree of graphite crystallinity, which reflects both thermal and mechanical processes. In the amphibolite-facies Alpine Schist, highly crystalline graphite, indicating peak metamorphic temperatures up to 640°C, occurs mainly on grain boundaries within quartzo-feldspathic domains. The subsequent mylonitization process resulted in the reworking of graphite under lower temperature conditions (500–600°C), resulting in clustered (in protomylonites) and foliation-aligned graphite (in mylonites). In cataclasites, derived from the mylonitized schists, graphite is most abundant (

Fragments of optically flat silica discs embedded in synthetic gouge were deformed to examine the relationship between the development of striations and slickenlines, and deformation mechanisms, conditions, and fault rheology. Experiments were performed under hydrothermal conditions in a rotary shear apparatus at 100°C or 450°C, to shear strains of 2.02 < γ < 8.25. Slip hardening and softening prevail at low and high temperatures, respectively. In recovered samples, disc fragment surfaces are decorated by fine gouge, sometimes arranged in trails, pits, and scratch marks. Prominent grooves—inferred slickenlines—with constant orientation, wavelength

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

The orientations and densities of fractures in the foliated hanging-wall of the Alpine Fault provide insights into the role of a mechanical anisotropy in upper crustal deformation, and the extent to which existing models of fault zone structure can be applied to active plate-boundary faults. Three datasets were used to quantify fracture damage at different distances from the Alpine Fault principal slip zones (PSZs): (1) X-ray computed tomography (CT) images of drill-core collected within 25 m of the PSZs during the first phase of the Deep Fault Drilling Project that were reoriented with respect to borehole televiewer (BHTV) images, (2) field measurements from creek sections at

We report the results of our observing campaign on GRB140903A, a nearby (z=0.351) short duration (T90~0.3 s) gamma-ray burst discovered by Swift. We monitored the X-ray afterglow with Chandra up to 21 days after the burst, and detected a steeper decay of the X-ray flux after approximately 1 day. Continued monitoring at optical and radio wavelengths showed a similar decay in flux at nearly the same time, and we interpret it as evidence of a narrowly collimated jet. By using the standard fireball model to describe the afterglow evolution, we derive a jet opening angle of 5 deg and a collimation-corrected total energy release of 2E50 erg. We further discuss the nature of the GRB progenitor system. Three main lines disfavor a massive star progenitor: the properties of the prompt gamma-ray emission, the age and low star-formation rate of the host galaxy, and the lack of a bright supernova. We conclude that this event was likely originated by a compact binary merger., Comment: 12 pages, 7 figures, accepted for publication in ApJ

The Alpine Fault, South Island, New Zealand, constitutes a globally significant natural laboratory for research into how active plate-bounding continental faults work and, in particular, how rocks exposed at the surface today relate to deep-seated processes of tectonic deformation, seismogenesis, and mineralization. The along-strike homogeneity of the hanging wall, rapid rate of dextral-reverse slip on an inclined fault plane, and relatively shallow depths to mechanical and chemical transitions make the Alpine Fault and the broader South Island plate boundary an important international site for multi-disciplinary research and a realistic target for an ambitious long-term program of scientific drilling investigations.

New Zealand’s Alpine Fault is a site of global importance for the study of active geological faults. The Alpine Fault provides an opportunity to study a major fault late in the cycle of stress accumulation ahead of a future earthquake, to search for precursors to large earthquakes, and to understand the long-term evolution of faults and the formation of fault rocks. The fault’s self-exhuming geometry, relative geological simplicity, and rapid and precisely-known slip rates, mean its accessible surface exposures have already been the subject of >40 years of intensive research. The goal of the Alpine Fault, Deep Fault Drilling Project (DFDP) is to go beneath the surface, to sample and make observations of the fault rocks and physical conditions at a range of depths, and monitor these over coming decades. To date, no active fault drilling experiment has targeted the mid-crustal roots of a long-lived active fault, or addressed fault zone evolution throughout the seismogenic zone and towards the brittle-ductile transition. DFDP-2A drilling started in August 2014 and DFDP-2B was completed in January 2015, having reached a maximum depth of 893 m. Technical problems, most notably the loss (and recovery) of the bottom-hole assembly on two occasions, caused delays in the drilling schedule, and the failure of a casing string ultimately caused drilling to be terminated at a shallower depth than planned and before the fault had been intersected. A very extensive data set was collected including geological, geophysical, geochemical and hydraulic measurements extending the length of the DFDP-2B borehole. Samples of rocks and fluids were collected, and a long-term observatory installed. Of particular significance are the observations that the geothermal gradient is extremely high, exceeding 140°C/km in the upper part of the borehole, and that the hangingwall is overpressured, as predicted prior to drilling. This report documents the technical planning and execution of DFDP-2 drilling, summarizes the scientific methods and types of data collected, and describes the observatory constructed.

The first phase of the Deep Fault Drilling Project (DFDP-1), Alpine Fault, was carried out in January and February 2011 at Gaunt Creek, South Westland, New Zealand. Two boreholes, DFDP-1A and DFDP-1B, were drilled to depths of 101 m and 151 m respectively. DFDP-1A cored a hangingwall mylonite sequence containing cataclasite zones that increase in frequency downward; 20–30 m of cemented and hydrothermally altered cataclasites; a >5 cm-thick principal slip surface of ultracatalasite and gouge at 90 m; and footwall fluvial gravels to a total depth of 100.6 m. DFDP-1B cored a similar hangingwall sequence; encountered a principal slip surface with a thickness of about 20 cm at depth of 128 m; penetrated a footwall sequence of quartz- and feldspar-rich, extensively altered and variably cataclased rock including a significant fault at 130 m; and reached a total depth of 151.4 m. A broad suite of downhole geophysical logs was collected using acoustic televiewer, neutron, full-waveform sonic, density, dipmeter, and electromagnetic flowmeter sondes. A fault zone observatory was installed in the DFDP-1B borehole, consisting of a seismometer near the base; a 25 mm internal diameter alkathene fluid sampling tube (perforated above the seismometer in the footwall); four vibrating-wire piezometers with inbuilt temperature sensors; 20 platinum RTD temperature sensors on two separate strings; and surface infrastructure providing security and housing the power supply and recording equipment. DFDP-1A was cased to 81 m depth and had a seismometer installed at the base of the casing, connected to the observatory equipment mounted above DFDP-1B.