Simulating spatial and temporal evolution of multiple wing cracks around faults in crystalline basement rocks

Fault zones are structurally highly spatially heterogeneous and hence extremely complex. Observations of fluid flow through fault zones over several scales show that this structural complexity is reflected in the hydrogeological properties of faults. Information on faults at depth is scarce, hence, it is highly valuable to understand the controls on spatial and temporal fault zone development. In this paper we increase our understanding of fault damage zone development in crystalline rocks by dynamically simulating the growth of single and multiple splay fractures produced from failure on a pre-existing fault. We present a new simulation model, MOPEDZ (Modeling Of Permeability Evolution in the Damage Zone surrounding faults), that simulates fault evolution through solution of Navier's equation with a combined Mohr-Coulomb and tensile failure criteria. Simulations suggest that location, frequency, mode of failure and orientation of splay fractures are significantly affected both by the orientation of the fault with respect to the maximum principal compressive stress and the conditions of differential stress. Model predictions compare well with published field outcrop data, confirming that this model produces realistic damage zone geometries

Data report: Seismic structure beneath the North Cascadia drilling transect of IODP Expedition 311

Between 1999 and 2004, new seismic data became available for the study of gas hydrates on the northern Cascadia margin. These data consist of multi- and single-channel data with two- and partly three-dimensional subsurface coverage and were acquired and used in support of the proposal for Integrated Ocean Drilling Program (IODP) Expedition 311 carried out in 2005. The working area lies across the continental slope off the coast of central Vancouver Island, British Columbia, Canada, with water depths ranging from 2600 m in the trench to 500 m on the upper slope, where it is well above the minimum depth for gas hydrate stability. This paper gives the details of the data acquisition and conventional processing and then focuses on describing the new data at six individual sites along a transect across the gas hydrate zone. Five of the sites were drilled during the Expedition 311. The transect of sites commences at the almost undeformed incoming sediments seaward of the region where gas hydrates are observed; these ocean basin sediments were drilled at a site 40 km southeast during Ocean Drilling Program (ODP) Leg 146. The transect continues up the continental slope into the area of hydrate stability, with a site on top of the frontal accretionary ridge where normal faulting indicates margin parallel extension; a site in the first slope basin overlying a buried ridge near a reflectivity wipe-out zone; a site adjacent to Site 889 of Leg 146 and therefore acting as a tie hole; the most landward site at the shallowest end of the hydrate stability field; and a cold vent site at one of several blank zones close to a bright spot region in the seismic records

Deterministic Computations on a PRAM with Static Processor and Memory Faults.

We consider Parallel Random Access Machine (PRAM) which has some processors and memory cells faulty. The faults considered are static, i.e., once the machine starts to operate, the operational/faulty status of PRAM components does not change. We develop a deterministic simulation of a fully operational PRAM on a similar faulty machine which has constant fractions of faults among processors and memory cells. The simulating PRAM has $n$ processors and $m$ memory cells, and simulates a PRAM with $n$ processors and a constant fraction of $m$ memory cells. The simulation is in two phases: it starts with preprocessing, which is followed by the simulation proper performed in a step-by-step fashion. Preprocessing is performed in time $O((\frac{m}{n}+ \log n)\log n)$. The slowdown of a step-by-step part of the simulation is $O(\log m)$

Role of tectonic stress in seepage evolution along the gas hydrate‐charged Vestnesa Ridge, Fram Strait

Methane expulsion from the world ocean floor is a broadly observed phenomenon known to be episodic. Yet the processes that modulate seepage remain elusive. In the Arctic offshore west Svalbard, for instance, seepage at 200–400 m water depth may be explained by ocean temperature‐controlled gas hydrate instabilities at the shelf break, but additional processes are required to explain seepage in permanently cold waters at depths \u3e1000 m. We discuss the influence of tectonic stress on seepage evolution along the ~100 km long hydrate‐bearing Vestnesa Ridge in Fram Strait. High‐resolution P‐Cable 3‐D seismic data revealed fine‐scale (\u3e10 m width) near‐vertical faults and fractures controlling seepage distribution. Gas chimneys record multiple seepage events coinciding with glacial intensification and active faulting. The faults document the influence of nearby tectonic stress fields in seepage evolution along this deepwater gas hydrate system for at least the last ~2.7 Ma

An equivalent circuit for the evaluation of cross-country fault currents in medium voltage (MV) distribution networks

A Cross-Country Fault (CCF) is the simultaneous occurrence of a couple of Line-to-Ground Faults (LGFs), affecting different phases of same feeder or of two distinct ones, at different fault locations. CCFs are not uncommon in medium voltage (MV) public distribution networks operated with ungrounded or high-impedance neutral: despite the relatively small value of LGF current that is typical of such networks, CCF currents can be comparable to those that are found in Phase-To-Phase Faults, if the affected feeder(s) consists of cables. This occurs because the faulted cables' sheaths/screens provide a continuous, relatively low-impedance metallic return path to the fault currents. An accurate evaluation is in order, since the resulting current magnitudes can overheat sheaths/screens, endangering cable joints and other plastic sheaths. Such evaluation, however, requires the modeling of the whole MV network in the phase domain, simulating cable screens and their connections to the primary and secondary substation earth electrodes by suitable computer programs, such as ATP (which is the acronym for alternative transient program) or EMTP (the acronym for electromagnetic transient program), with substantial input data being involved. This paper presents a simplified yet accurate circuit model of the faulted MV network, taking into account the CCF currents' return path (cable sheaths/screens, ground conductors, and earthing resistances of secondary substations). The proposed CCF model can be implemented in a general-purpose simulation program, and it yields accurate fault currents estimates: for a 20 kV network case study, the comparison with accurate ATP simulations evidences mismatches mostly smaller than 2%, and never exceeding 5%

Simulation of subseismic joint and fault networks using a heuristic mechanical model

Flow simulations of fractured and faulted reservoirs require representation of subseismic structures about which subsurface data are limited. We describe a method for simulating fracture growth that is mechanically based but heuristic, allowing for realistic modelling of fracture networks with reasonable run times. The method takes a triangulated meshed surface as input, together with an initial stress field. Fractures initiate and grow based on the stress field, and the growing fractures relieve the stress in the mesh. We show that a wide range of bedding-plane joint networks can be modelled simply by varying the distribution and anisotropy of the initial stress field. The results are in good qualitative agreement with natural joint patterns. We then apply the method to a set of parallel veins and demonstrate how the variations in thickness of the veins can be represented. Lastly, we apply the method to the simulation of normal fault patterns on salt domes. We derive the stress field on the bedding surface using the horizon curvature. The modelled fault network shows both radial and concentric faults. The new method provides an effective means of modelling joint and fault networks that can be imported to the flow simulator