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There is growing concern about seismicity triggered by human activities, whereby small increases in stress bring tectonically loaded faults to failure. Examples of such activities include mining, impoundment of water, stimulation of geothermal fields, extraction of hydrocarbons and water, and the injection of water, CO.sub.2 and methane into subsurface reservoirs.sup.1. In the absence of sufficient information to understand and control the processes that trigger earthquakes, authorities have set up empirical regulatory monitoring-based frameworks with varying degrees of success.sup.2,3. Field experiments in the early 1970s at the Rangely, Colorado (USA) oil field.sup.4 suggested that seismicity might be turned on or off by cycling subsurface fluid pressure above or below a threshold. Here we report the development, testing and implementation of a multidisciplinary methodology for managing triggered seismicity using comprehensive and detailed information about the subsurface to calibrate geomechanical and earthquake source physics models. We then validate these models by comparing their predictions to subsequent observations made after calibration. We use our approach in the Val d'Agri oil field in seismically active southern Italy, demonstrating the successful management of triggered seismicity using a process-based method applied to a producing hydrocarbon field. Applying our approach elsewhere could help to manage and mitigate triggered seismicity. A multidisciplinary method for managing triggered seismicity is developed using detailed subsurface information to calibrate geomechanical and earthquake source physics models, and is applied to the Val d'Agri oil field in seismically active southern Italy., Author(s): Bradford H. Hager [sup.1] , James Dieterich [sup.2] , Cliff Frohlich [sup.3] , Ruben Juanes [sup.4] [sup.5] , Stefano Mantica [sup.6] , John H. Shaw [sup.7] , Francesca Bottazzi [...]

We present a new, 3D description of crust and upper mantle velocity structure in southern California implemented as a Unified Structural Representation (USR). The USR is comprised of detailed basin velocity descriptions that are based on tens of thousands of direct velocity (Vp, Vs) measurements and incorporates the locations and displacement of major fault zones that influence basin structure. These basin descriptions were used to developed tomographic models of crust and upper mantle velocity and density structure, which were subsequently iterated and improved using 3D waveform adjoint tomography. A geotechnical layer (GTL) based on Vs30 measurements and consistent with the underlying velocity descriptions was also developed as an optional model component. The resulting model provides a detailed description of the structure of the southern California crust and upper mantle that reflects the complex tectonic history of the region. The crust thickens eastward as Moho depth varies from 10 to 40 km reflecting the transition from oceanic to continental crust. Deep sedimentary basins and underlying areas of thin crust reflect Neogene extensional tectonics overprinted by transpressional deformation and rapid sediment deposition since the late Pliocene. To illustrate the impact of this complex structure on strong ground motion forecasting, we simulate rupture of a proposed M 7.9 earthquake source in the Western Transverse Ranges. The results show distinct basin amplification and focusing of energy that reflects crustal structure described by the USR that is not captured by simpler velocity descriptions. We anticipate that the USR will be useful for a broad range of simulation and modeling efforts, including strong ground motion forecasting, dynamic rupture simulations, and fault system modeling. The USR is available through the Southern California Earthquake Center (SCEC) website (http://www.scec.org).

© 2014 The American Ceramic Society. This article addresses the effects of small holes (1-2 mm in diameter) on the tensile properties of a woven C/SiC composite. Holes are introduced by one of two methods: by insertion of fugitive rods into the woven preform before adding the matrix or by drilling after panel fabrication. The tensile strength exhibits only a weak sensitivity to the presence of holes, regardless of the manner in which the holes are introduced. Nevertheless, woven holes appear to be somewhat less detrimental to strength. The effects are attributed to the fact that the tows in specimens with woven holes are locally intact and thus contribute to load-bearing. Full-field strain maps reveal strong spatial periodicity, reflecting the underlying crack pattern and weave geometry. Even when averaged over lengths equal to the unit cell dimensions, the strains exhibit periodicity, with a wavelength dictated by the unit cell dimensions. When holes are present, the strain patterns reflect a convolution of the effects of weave geometry and strain concentrations near the holes. The results have implications for development of high-fidelity models for these composites: notably, in selection of a suitable representative volume element and for modeling schemes that capture the stochastic nature of cracking.

This study used high-resolution, two- and three-dimensional, seismic-reflection data from the Niger Delta, Sichuan Basin, and Magdalena Basin to analyze displacement profile patterns and scaling relationships between the maximum displacement and length ([D.sub.max] v. L) of thrust faults, referred to as displacement-length scaling relationships. The thrust faults mapped in this study exhibited highly variable displacement profiles, both in terms of shape and overall magnitude of displacement. A robust power-law displacement-length scaling relationship was obtained for all three data sets combined, yielding a scaling relationship (n = 0.87) close to the linear fit most often observed for normal faults and thrust faults. At the regional scale, however, a robust fit was obtained only for the Sichuan Basin, and with a nonlinear displacement-length scaling relationship (n = 0.58) suggesting scale dependence in this region. Many displacement profiles exhibited steep displacement gradients at the fault tips and shallow gradients in between, often with multiple maxima. These features are interpreted with conceptual growth models for thrust faults: hard linkage and soft linkage fault interaction models, a detachment linkage fault interaction model, and an overburden-limited, fault-growth model. doi: 10.1130/B26373.1

The Longmen Shan mountain range, site of the devastating 12 May 2008 Wenchuan (M = 7.9) earthquake, defines the eastern margin of the Himalayan orogen and exhibits greater topographic relief than anywhere else in the Tibetan plateau. However, before the earthquake, geodetic and geologic surveys measured little shortening across the range front (1-3), inspiring a vigorous debate about the process by which the topography of the mountain belt is produced and maintained. Two endmember models have been proposed: (1) brittle crustal thickening, in which thrust faults with large amounts of slip that are rooted in the lithosphere cause uplift (4), and (2) crustal flow, in which low-viscosity material in the lower crust extrudes outward from the Tibetan plateau and inflates the crust north and east of the Himalayas (5-7). Here we use balanced geologic cross-sections to show that crustal shortening, structural relief, and topography are strongly correlated in the range front. This suggests that crustal shortening is a primary driver for uplift and topography of the Longmen Shan on the flanks of the plateau. The 2008 Wenchuan (M = 7.9) earthquake, which ruptured a large thrust fault along the range front causing tens of thousands of fatalities and widespread damage, is an active manifestation of this shortening process., India began colliding with Eurasia over 50 million years ago, progressively accommodating at least 1,400 km of north-south shortening (8). This plate collision uplifted the highest mountains in the world [...]

A numerical grid search using the trishear kinematic model can be used to extract both slip and the distance that a fault tip line has propagated during growth of a fault-propagation fold. The propagation distance defines the initial position of the tip line at the onset of slip. In the Santa Fe Springs anticline of the Los Angeles basin, we show that the tip line of the underlying Puente Hills thrust fault initiated at the same position as the 1987 magnitude 6.0 Whittier Narrows earthquake. Keywords: folding, faulting, kinematics, earthquakes.

We develop new methods to identify blind-thrust fault systems, determine fault slip rates, and estimate potential earthquake magnitudes and recurrence intervals in active fold-and-thrust belts. These methods are applied to compressive folds along the Offshore Oak Ridge and Blue Bottle trends, which overlie active blind-thrust faults in the eastern Santa Barbara Channel. These folds and their causative faults are interpreted using fault-bend fold theory and are represented in balanced models and cross sections that integrate surface and subsurface data. The structures are mapped using a new technique of axial-surface mapping in seismic reflection grids, which defines three-dimensional structural geometries and shows changes in slip and subsurface fault geometry along strike. Analysis of syntectonic (growth) sediments yields Pliocene and Quaternary fault slip rates of 1.3 mm/yr on a deep thrust (greater than or equal to 16 km) and 1.3 mm/yr on shallower faults (2-5 km). The combined 2.6 mm/yr slip rate represents only part of the 6 mm/yr of shortening measured by geodesy across the channel and estimated from relative Pacific-North American plate motions across the Transverse Ranges. Additional shortening is probably accommodated on other active thrusts in the western Transverse Ranges and in the northern channel along the Santa Barbara coast. Deformed seafloor sediments and a swarm of axial surface seismicity along the fold trends indicate that the underlying thrusts are active and may pose significant earthquake hazards to coastal southern California. Unsegmented fault surfaces are used through empirical relationships between fault surface area and rupture magnitude to estimate the sizes of potential earthquakes. This analysis suggests that a ramp in the Channel Islands fault beneath the Offshore Oak Ridge trend is capable of rupturing in a M(sub s) greater than or equal to 7.2 earthquake. Earthquakes of this magnitude may release approximately 2 m of slip, which, when combined with the estimated slip rate (1.3 mm/yr), yields an earthquake recurrence interval of approximately 1500 yr for this Channel Islands fault ramp.

We define the Wilmington blind-thrust as a tectonically active fault capable of generating large damaging earthquakes, through analysis of 2D and 3D seismic reflection surveys, petroleum and water wells, and recent mapping of groundwater aquifers in the southwestern Los Angeles basin. This overturns the long-held view that the fault became dormant in the Late Pliocene, barring its inclusion in state-of-the-art regional earthquake hazard assessments. The size of the fault suggests that it is capable of generating moderate-magnitude earthquakes (Mw 6.3-6.4), whereas potential linkages with other nearby faults (e.g., Huntington Beach, Torrance, and Compton) pose the threat of larger multisegment events (Mw>7). These earthquakes would directly impact the overlying Ports of Los Angeles and Long Beach, as well as the broader Los Angeles metropolitan area. [ABSTRACT FROM AUTHOR]