Geomorphic and Structural Evidence for Rolling Hinge Style Deformation in the Footwall of an Active Low Angle Normal Fault, Mai'iu Fault, Woodlark Rift, SE Papua New Guinea

NASA Astrophysics Data System (ADS)

Mizera, M.; Little, T.; Norton, K. P.; Webber, S.; Ellis, S. M.; Oesterle, J.

2016-12-01

While shown to operate in oceanic crust, rolling hinge style deformation remains a debated process in metamorpic core complexes (MCCs) in the continents. The model predicts that unloading and isostatic uplift during slip causes a progressive back-tilting in the upper crust of a normal fault that is more steeply dipping at depth. The Mai'iu Fault in the Woodlark Rift, SE Papua New Guinea, is one of the best-exposed and fastest slipping (probably >7 mm/yr) active low-angle normal faults (LANFs) on Earth. We analysed structural field data from this fault's exhumed slip surface and footwall, together with geomorphic data interpreted from aerial photographs and GeoSAR-derived digital elevation models (gridded at 5-30 m spacing), to evaluate deformational processes affecting the rapidly exhuming, domal-shaped detachment fault. The exhumed fault surface emerges from the ground at the rangefront near sea level with a northward dip of 21°. Up-dip, it is well-preserved, smooth and corrugated, with some fault remnants extending at least 29 km in the slip direction. The surface flattens over the crest of the dome, beyond where it dips S at up to 15°. Windgaps perched on the crestal main divide of the dome, indicate both up-dip tectonic advection and progressive back-tilting of the exhuming fault surface. We infer that slip on a serial array of m-to-km scale up-to-the-north, steeply S-dipping ( 75°) antithetic-sense normal faults accommodated some of the exhumation-related, inelastic bending of the footwall. These geomorphically well expressed faults strike parallel to the main Mai'iu fault at 110.9±5°, have a mean cross-strike spacing of 1520 m, and slip with a consistent up-to-the-north sense of throw ranging from <5 m to 120 m. Apparently the Mai'iu Fault was able to continue slipping despite having to negotiate this added fault-roughness. We interpret the antithetic faulting to result from bending stresses, and to provide the first clear examples of rolling hinge

Steep-dip seismic imaging of the shallow San Andreas Fault near Parkfield

USGS Publications Warehouse

Hole, J.A.; Catchings, R.D.; St. Clair, K.C.; Rymer, M.J.; Okaya, D.A.; Carney, B.J.

2001-01-01

Seismic reflection and refraction images illuminate the San Andreas Fault to a depth of 1 kilometer. The prestack depth-migrated reflection image contains near-vertical reflections aligned with the active fault trace. The fault is vertical in the upper 0.5 kilometer, then dips about 70° to the southwest to at least 1 kilometer subsurface. This dip reconciles the difference between the computed locations of earthquakes and the surface fault trace. The seismic velocity cross section shows strong lateral variations. Relatively low velocity (10 to 30%), high electrical conductivity, and low density indicate a 1-kilometer-wide vertical wedge of porous sediment or fractured rock immediately southwest of the active fault trace.

Surface morphology of active normal faults in hard rock: Implications for the mechanics of the Asal Rift, Djibouti

NASA Astrophysics Data System (ADS)

Pinzuti, Paul; Mignan, Arnaud; King, Geoffrey C. P.

2010-10-01

Tectonic-stretching models have been previously proposed to explain the process of continental break-up through the example of the Asal Rift, Djibouti, one of the few places where the early stages of seafloor spreading can be observed. In these models, deformation is distributed starting at the base of a shallow seismogenic zone, in which sub-vertical normal faults are responsible for subsidence whereas cracks accommodate extension. Alternative models suggest that extension results from localised magma intrusion, with normal faults accommodating extension and subsidence only above the maximum reach of the magma column. In these magmatic rifting models, or so-called magmatic intrusion models, normal faults have dips of 45-55° and root into dikes. Vertical profiles of normal fault scarps from levelling campaign in the Asal Rift, where normal faults seem sub-vertical at surface level, have been analysed to discuss the creation and evolution of normal faults in massive fractured rocks (basalt lava flows), using mechanical and kinematics concepts. We show that the studied normal fault planes actually have an average dip ranging between 45° and 65° and are characterised by an irregular stepped form. We suggest that these normal fault scarps correspond to sub-vertical en echelon structures, and that, at greater depth, these scarps combine and give birth to dipping normal faults. The results of our analysis are compatible with the magmatic intrusion models instead of tectonic-stretching models. The geometry of faulting between the Fieale volcano and Lake Asal in the Asal Rift can be simply related to the depth of diking, which in turn can be related to magma supply. This new view supports the magmatic intrusion model of early stages of continental breaking.

Normal Faulting at the Western Margin of the Altiplano Plateau, Southern Peru

NASA Astrophysics Data System (ADS)

Schildgen, T. F.; Hodges, K. V.; Whipple, K. X.; Perignon, M.; Smith, T. M.

2004-12-01

Although the western margin of the Altiplano Plateau is commonly used to illustrate the marked differences in the evolution of a mountain range with strong latitudinal and longitudinal precipitation gradients, the nature of tectonism in this semi-arid region is poorly understood and much debated. The western margin of the Altiplano in southern Peru and northern Chile marks an abrupt transition from the forearc region of the Andes to the high topography of the Cordillera Occidental. This transition has been interpreted by most workers as a monocline, with modifications due to thrust faulting, normal faulting, and gravity slides. Based on recent fieldwork and satellite image analysis, we suggest that, at least in the semi-arid climate of southern Peru, this transition has been the locus of significant high-angle normal faulting related to the block uplift of the Cordillera Occidental. We have focused our initial work in the vicinity of 15\\deg S latitude, 71\\deg W longitude, where the range front crosses Colca Canyon, a major antecedent drainage northwest of Arequipa. In that area, Oligocene to Miocene sediments of the Moquegua Formation, which were eroded from uplifted terrain to the northeast, presently dip to the northeast at angles between 2 and 10º. Field observations of a normal fault contact between the Moquegua sedimentary rocks and Jurassic basement rocks, as well as 15-m resolution 3-D images generated from ASTER satellite imagery, show that the Moquegua units are down-dropped to the west across a steeply SW-dipping normal fault of regional significance. Morphology of the range front throughout southern Peru suggests that normal faulting along the range front has characterized the recent tectonic history of the region. We present geochronological data to constrain the timing of movement both directly from the fault zone as well as indirectly from canyon incision that likely responded to fault movement.

Surface Morphology of Active Normal Faults in Hard Rock: Implications for the Mechanics of the Asal Rift, Djibouti

NASA Astrophysics Data System (ADS)

Pinzuti, P.; Mignan, A.; King, G. C.

2009-12-01

Mechanical stretching models have been previously proposed to explain the process of continental break-up through the example of the Asal Rift, Djibouti, one of the few places where the early stages of seafloor spreading can be observed. In these models, deformation is distributed starting at the base of a shallow seismogenic zone, in which sub-vertical normal faults are responsible for subsidence whereas cracks accommodate extension. Alternative models suggest that extension results from localized magma injection, with normal faults accommodating extension and subsidence above the maximum reach of the magma column. In these magmatic intrusion models, normal faults have dips of 45-55° and root into dikes. Using mechanical and kinematics concepts and vertical profiles of normal fault scarps from an Asal Rift campaign, where normal faults are sub-vertical on surface level, we discuss the creation and evolution of normal faults in massive fractured rocks (basalt). We suggest that the observed fault scarps correspond to sub-vertical en echelon structures and that at greater depth, these scarps combine and give birth to dipping normal faults. Finally, the geometry of faulting between the Fieale volcano and Lake Asal in the Asal Rift can be simply related to the depth of diking, which in turn can be related to magma supply. This new view supports the magmatic intrusion model of early stages of continental breaking.

Three Least-Squares Minimization Approaches to Interpret Gravity Data Due to Dipping Faults

NASA Astrophysics Data System (ADS)

Abdelrahman, E. M.; Essa, K. S.

2015-02-01

We have developed three different least-squares minimization approaches to determine, successively, the depth, dip angle, and amplitude coefficient related to the thickness and density contrast of a buried dipping fault from first moving average residual gravity anomalies. By defining the zero-anomaly distance and the anomaly value at the origin of the moving average residual profile, the problem of depth determination is transformed into a constrained nonlinear gravity inversion. After estimating the depth of the fault, the dip angle is estimated by solving a nonlinear inverse problem. Finally, after estimating the depth and dip angle, the amplitude coefficient is determined using a linear equation. This method can be applied to residuals as well as to measured gravity data because it uses the moving average residual gravity anomalies to estimate the model parameters of the faulted structure. The proposed method was tested on noise-corrupted synthetic and real gravity data. In the case of the synthetic data, good results are obtained when errors are given in the zero-anomaly distance and the anomaly value at the origin, and even when the origin is determined approximately. In the case of practical data (Bouguer anomaly over Gazal fault, south Aswan, Egypt), the fault parameters obtained are in good agreement with the actual ones and with those given in the published literature.

Directly imaging steeply-dipping fault zones in geothermal fields with multicomponent seismic data

DOE PAGES

Chen, Ting; Huang, Lianjie

2015-07-30

For characterizing geothermal systems, it is important to have clear images of steeply-dipping fault zones because they may confine the boundaries of geothermal reservoirs and influence hydrothermal flow. Elastic reverse-time migration (ERTM) is the most promising tool for subsurface imaging with multicomponent seismic data. However, conventional ERTM usually generates significant artifacts caused by the cross correlation of undesired wavefields and the polarity reversal of shear waves. In addition, it is difficult for conventional ERTM to directly image steeply-dipping fault zones. We develop a new ERTM imaging method in this paper to reduce these artifacts and directly image steeply-dipping fault zones.more » In our new ERTM method, forward-propagated source wavefields and backward-propagated receiver wavefields are decomposed into compressional (P) and shear (S) components. Furthermore, each component of these wavefields is separated into left- and right-going, or downgoing and upgoing waves. The cross correlation imaging condition is applied to the separated wavefields along opposite propagation directions. For converted waves (P-to-S or S-to-P), the polarity correction is applied to the separated wavefields based on the analysis of Poynting vectors. Numerical imaging examples of synthetic seismic data demonstrate that our new ERTM method produces high-resolution images of steeply-dipping fault zones.« less

Displacement-length relationship of normal faults in Acheron Fossae, Mars: new observations with HRSC.

NASA Astrophysics Data System (ADS)

Charalambakis, E.; Hauber, E.; Knapmeyer, M.; Grott, M.; Gwinner, K.

2007-08-01

For Earth, data sets and models have shown that for a fault loaded by a constant remote stress, the maximum displacement on the fault is linearly related to its length by d = gamma · l [1]. The scaling and structure is self-similar through time [1]. The displacement-length relationship can provide useful information about the tectonic regime.We intend to use it to estimate the seismic moment released during the formation of Martian fault systems and to improve the seismicity model [2]. Only few data sets have been measured for extraterrestrial faults. One reason is the limited number of reliable topographic data sets. We used high-resolution Digital Elevation Models (DEM) [3] derived from HRSC image data taken from Mars Express orbit 1437. This orbit covers an area in the Acheron Fossae region, a rift-like graben system north of Olympus Mons with a "banana"-shaped topography [4]. It has a fault trend which runs approximately WNW-ESE. With an interactive IDL-based software tool [5] we measured the fault length and the vertical offset for 34 faults. We evaluated the height profile by plotting the fault lengths l vs. their observed maximum displacement (dmax-model). Additionally, we computed the maximum displacement of an elliptical fault scarp where the plane has the same area as in the observed case (elliptical model). The integration over the entire fault length necessary for the computation of the area supresses the "noise" introduced by local topographic effects like erosion or cratering. We should also mention that fault planes dipping 60 degree are usually assumed for Mars [e.g., 6] and even shallower dips have been found for normal fault planes [7]. This dip angle is used to compute displacement from vertical offset via d = h/(h*sinα), where h is the observed topographic step height, and ? is the fault dip angle. If fault dip angles of 30 degree are considered, the displacement differs by 40% from the one of dip angles of 60 degree. Depending on the data

Continentward-dipping detachment fault system and asymmetric rift structure of the Baiyun Sag, northern South China Sea

NASA Astrophysics Data System (ADS)

Zhou, Zhichao; Mei, Lianfu; Liu, Jun; Zheng, Jinyun; Chen, Liang; Hao, Shihao

2018-02-01

The rift architecture and deep crustal structure of the distal margin at the mid-northern margin of the South China Sea have been previously investigated by using deep seismic reflection profiles. However, one fundamental recurring problem in the debate is the extensional fault system and rift structure of the hyperextended rift basins (Baiyun Sag and Liwan Sag) within the distal margin because of the limited amount of seismic data. Based on new 3D seismic survey data and 2D seismic reflection profiles, we observe an array of fault blocks in the Baiyun Sag, which were tilted towards the ocean by extensional faulting. The extensional faults consistently dip towards the continent. Beneath the tilted fault blocks and extensional faults, a low-angle, high-amplitude and continuous reflection has been interpreted as the master detachment surface that controls the extension process. During rifting, the continentward-dipping normal faults evolved in a sequence from south to north, generating the asymmetric rift structure of the Baiyun Sag. The Baiyun Sag is separated from the oceanic domain by a series of structural highs that were uplifted by magmatic activity in response to the continental breakup at 33 Ma and a ridge jump to the south at 26-24 Ma. Therefore, we propose that magmatism played a significant role in the continental extension and final breakup in the South China Sea.

Map of normal faults and extensional folds in the Tendoy Mountains and Beaverhead Range, Southwest Montana and eastern Idaho

USGS Publications Warehouse

Janecke, S.U.; Blankenau, J.J.; VanDenburg, C.J.; VanGosen, B.S.

2001-01-01

Compilation of a 1:100,000-scale map of normal faults and extensional folds in southwest Montana and adjacent Idaho reveals a complex history of normal faulting that spanned at least the last 50 m.y. and involved six or more generations of normal faults. The map is based on both published and unpublished mapping and shows normal faults and extensional folds between the valley of the Red Rock River of southwest Montana and the Lemhi and Birch Creek valleys of eastern Idaho between latitudes 45°05' N. and 44°15' N. in the Tendoy and Beaverhead Mountains. Some of the unpublished mapping has been compiled in Lonn and others (2000). Many traces of the normal faults parallel the generally northwest to north-northwest structural grain of the preexisting Sevier fold and thrust belt and dip west-southwest, but northeastand east-striking normal faults are also prominent. Northeaststriking normal faults are subparallel to the traces of southeast-directed thrusts that shortened the foreland during the Laramide orogeny. It is unlikely that the northeast-striking normal faults reactivated fabrics in the underlying Precambrian basement, as has been documented elsewhere in southwestern Montana (Schmidt and others, 1984), because exposures of basement rocks in the map area exhibit north-northwest- to northwest-striking deformational fabrics (Lowell, 1965; M’Gonigle, 1993, 1994; M’Gonigle and Hait, 1997; M’Gonigle and others, 1991). The largest normal faults in the area are southwest-dipping normal faults that locally reactivate thrust faults (fig. 1). Normal faulting began before middle Eocene Challis volcanism and continues today. The extension direction flipped by about 90° four times.

Pre-existing normal faults have limited control on the rift geometry of the northern North Sea

NASA Astrophysics Data System (ADS)

Claringbould, Johan S.; Bell, Rebecca E.; Jackson, Christopher A.-L.; Gawthorpe, Robert L.; Odinsen, Tore

2017-10-01

Many rifts develop in response to multiphase extension with numerical and physical models suggesting that reactivation of first-phase normal faults and rift-related variations in bulk crustal rheology control the evolution and final geometry of subsequent rifts. However, many natural multiphase rifts are deeply buried and thus poorly exposed in the field and poorly imaged in seismic reflection data, making it difficult to test these models. Here we integrate recent 3D seismic reflection and borehole data across the entire East Shetland Basin, northern North Sea, to constrain the long-term, regional development of this multiphase rift. We document the following key stages of basin development: (i) pre-Triassic to earliest Triassic development of multiple sub-basins controlled by widely distributed, NNW- to NE-trending, east- and west-dipping faults; (ii) Triassic activity on a single major, NE-trending, west-dipping fault located near the basins western margin, and formation of a large half-graben; and (iii) Jurassic development of a large, E-dipping, N- to NE-trending half-graben near the eastern margin of the basin, which was associated with rift narrowing and strain focusing in the Viking Graben. In contrast to previous studies, which argue for two discrete periods of rifting during the Permian-Triassic and Late Jurassic-Early Cretaceous, we find that rifting in the East Shetland Basin was protracted from pre-Triassic to Cretaceous. We find that, during the Jurassic, most pre-Jurassic normal faults were buried and in some cases cross-cut by newly formed faults, with only a few being reactivated. Previously developed faults thus had only a limited control on the evolution and geometry of the later rift. We instead argue that strain migration and rift narrowing was linked to the evolving thermal state of the lithosphere, an interpretation supporting the predictions of lithosphere-scale numerical models. Our study indicates that additional regional studies of

Growth and linkage of the quaternary Ubrique Normal Fault Zone, Western Gibraltar Arc: role on the along-strike relief segmentation

NASA Astrophysics Data System (ADS)

Jiménez-Bonilla, Alejandro; Balanya, Juan Carlos; Exposito, Inmaculada; Diaz-Azpiroz, Manuel; Barcos, Leticia

2015-04-01

Strain partitioning modes within migrating orogenic arcs may result in arc-parallel stretching that produces along-strike structural and topographic discontinuities. In the Western Gibraltar Arc, arc-parallel stretching has operated from the Lower Miocene up to recent times. In this study, we have reviewed the Colmenar Fault, located at the SW end of the Subbetic ranges, previously interpreted as a Middle Miocene low-angle normal fault. Our results allow to identify younger normal fault segments, to analyse their kinematics, growth and segment linkage, and to discuss its role on the structural and relief drop at regional scale. The Colmenar Fault is folded by post-Serravallian NE-SW buckle folds. Both the SW-dipping fault surfaces and the SW-plunging fold axes contribute to the structural relief drop toward the SW. Nevertheless, at the NW tip of the Colmenar Fault, we have identified unfolded normal faults cutting quaternary soils. They are grouped into a N110˚E striking brittle deformation band 15km long and until 3km wide (hereafter Ubrique Normal Fault Zone; UNFZ). The UNFZ is divided into three sectors: (a) The western tip zone is formed by normal faults which usually dip to the SW and whose slip directions vary between N205˚E and N225˚E. These segments are linked to each other by left-lateral oblique faults interpreted as transfer faults. (b) The central part of the UNFZ is composed of a single N115˚E striking fault segment 2,4km long. Slip directions are around N190˚E and the estimated throw is 1,25km. The fault scarp is well-conserved reaching up to 400m in its central part and diminishing to 200m at both segment terminations. This fault segment is linked to the western tip by an overlap zone characterized by tilted blocks limited by high-angle NNE-SSW and WNW-ESE striking faults interpreted as "box faults" [1]. (c) The eastern tip zone is formed by fault segments with oblique slip which also contribute to the downthrown of the SW block. This kinematic

Folding associated with extensional faulting: Sheep Range detachment, southern Nevada

DOE Office of Scientific and Technical Information (OSTI.GOV)

Guth, P.L.

1985-01-01

The Sheep Range detachment is a major Miocene extensional fault system of the Great Basin. Its major faults have a scoop shape, with straight, N-S traces extending 15-30 km and then abruptly turning to strike E-W. Tertiary deformation involved simultaneous normal faulting, sedimentation, landsliding, and strike-slip faulting. Folds occur in two settings: landslide blocks and drag along major faults. Folds occur in landslide blocks and beneath them. Most folds within landslide blocks are tight anticlines, with limbs dipping 40-60 degrees. Brecciation of the folds and landslide blocks suggests brittle deformation. Near Quijinump Canyon in the Sheep Range, at least threemore » landslide blocks (up to 500 by 1500 m) slid into a small Tertiary basin. Tertiary limestone beneath the Paleozoic blocks was isoclinally folded. Westward dips reveal drag folds along major normal faults, as regional dips are consistently to the east. The Chowderhead anticline is the largest drag fold, along an extensional fault that offsets Ordovician units 8 km. East-dipping Ordovician and Silurian rocks in the Desert Range form the hanging wall. East-dipping Cambrian and Ordovician units in the East Desert Range form the foot wall and east limb of the anticline. Caught along the fault plane, the anticline's west-dipping west limb contains mostly Cambrian units.« less

Elasto-plastic deformation and plate weakening due to normal faulting in the subducting plate along the Mariana Trench

NASA Astrophysics Data System (ADS)

Zhou, Z.; Lin, J.

2017-12-01

We investigated variations in the elasto-plastic deformation of the subducting plate along the Mariana Trench through an analysis of flexural bending, normal fault characteristics, and geodynamic modeling. It was observed that most of the normal faults were initiated along the outer-rise region and grew toward the trench axis with strikes that are mostly subparallel to the local trend of the trench axis. The average trench relief is more than 5 km in the southern region while only about 2 km in the northern and central regions. Fault throws were measured to be significantly greater in the southern region (maximum 320 m) than the northern and central regions (maximum 200 m). The subducting plate was modeled as an elasto-plastic slab subjected to tectonic loading along the trench axis. The "apparent" slab-pull dip angle of the subducting plate, calculated from the ratio of the inverted vertical loading versus horizontal tensional force, was significantly larger in the southern region (51-64°) than in the northern (22-35°) and central (20-34°) regions, which is consistent with the seismologically determined dip angle within the shallow part of the subducting slab. This result suggests that the differences in the plate flexure and normal faulting characteristics along the Mariana Trench might be influenced, at least in part, by significant variations in the dip angle within the shallow part of the subducting plate. Normal faults were modeled to penetrate to a maximum depth of 15, 14, and 25 km in the upper mantle for the northern, central, and southern regions, respectively, which is consistent with the depths of available relocated normal faulting earthquakes in the central region. We calculated that the average reduction of the effective elastic plate thickness Te due to normal faulting is 31% in the southern region, which is almost twice that in both the northern and central regions ( 16%). Furthermore, model results revealed that the stress reduction associated

Rare normal faulting earthquake induced by subduction megaquake: example from 2011 Tohoku-oki earthquake

NASA Astrophysics Data System (ADS)

Ishiyama, T.; Sugito, N.; Echigo, T.; Sato, H.; Suzuki, T.

2012-04-01

A month after March 11 gigantic M9.0 Tohoku-oki earthquake, M7.0 intraplate earthquake occurred at a depth of 5 km on April 11 beneath coastal area of near Iwaki city, Fukushima prefecture. Focal mechanism of the mainshock indicates that this earthquake is a normal faulting event. Based on field reconnaissance and LIDAR mapping by Geospatial Information Authority of Japan, we recognized coseismic surface ruptures, presumably associated with the main shock. Coseismic surface ruptures extend NNW for about 11 km in a right-stepping en echelon manner. Geomorphic expressions of these ruptures commonly include WWS-facing normal fault scarps and/or drape fold scarp with open cracks on their crests, on the hanging wall sides of steeply west-dipping normal fault planes subparallel to Cretaceous metamorphic rocks. Highest topographic scarp height is about 2.3 m. In this study we introduce preliminary results of a trenching survey across the coseismic surface ruptures at Shionohira site, to resolve timing of paleoseismic events along the Shionohira fault. Trench excavations were carried out at two sites (Ichinokura and Shionohira sites) in Iwaki, Fukushima. At Shionohira site a 2-m-deep trench was excavated across the coseismic fault scarp emerged on the alluvial plain on the eastern flank of the Abukuma Mountains. On the trench walls we observed pairs of steeply dipping normal faults that deform Neogene to Paleogene conglomerates and unconformably overlying, late Quaternary to Holocene fluvial units. Sense of fault slip observed on the trench walls (large dip-slip with small sinistral component) is consistent with that estimated from coseismic surface ruptures. Fault throw estimated from separation of piercing points on lower Unit I and vertical structural relief on folded upper Unit I is consistent with topographic height of the coseismic fault scarp at the trench site. In contrast, vertical separation of Unit II, unconformably overlain by Unit I, is measured as about 1.5 m

Frictional properties of low-angle normal fault gouges and implications for low-angle normal fault slip

NASA Astrophysics Data System (ADS)

Haines, Samuel; Marone, Chris; Saffer, Demian

2014-12-01

The mechanics of slip on low-angle normal faults (LANFs) remain an enduring problem in structural geology and fault mechanics. In most cases, new faults should form rather than having slip occur on LANFs, assuming values of fault friction consistent with Byerlee's Law. We present results of laboratory measurements on the frictional properties of natural clay-rich gouges from low-angle normal faults (LANF) in the American Cordillera, from the Whipple Mts. Detachment, the Panamint range-front detachment, and the Waterman Hills detachment. These clay-rich gouges are dominated by neoformed clay minerals and are an integral part of fault zones in many LANFs, yet their frictional properties under in situ conditions remain relatively unknown. We conducted measurements under saturated and controlled pore pressure conditions at effective normal stresses ranging from 20 to 60 MPa (corresponding to depths of 0.9-2.9 km), on both powdered and intact wafers of fault rock. For the Whipple Mountains detachment, friction coefficient (μ) varies depending on clast content, with values ranging from 0.40 to 0.58 for clast-rich material, and 0.29-0.30 for clay-rich gouge. Samples from the Panamint range-front detachment were clay-rich, and exhibit friction values of 0.28 to 0.38, significantly lower than reported from previous studies on fault gouges tested under room humidity (nominally dry) conditions, including samples from the same exposure. Samples from the Waterman Hills detachment are slightly stronger, with μ ranging from 0.38 to 0.43. The neoformed gouge materials from all three localities exhibits velocity-strengthening frictional behavior under almost all of the experimental conditions we explored, with values of the friction rate parameter (a - b) ranging from -0.001 to +0.025. Clast-rich samples exhibited frictional healing (strength increases with hold time), whereas clay-rich samples do not. Our results indicate that where clay-rich neoformed gouges are present along

Structure of a normal seismogenic fault zone in carbonates: The Vado di Corno Fault, Campo Imperatore, Central Apennines (Italy)

NASA Astrophysics Data System (ADS)

Demurtas, Matteo; Fondriest, Michele; Balsamo, Fabrizio; Clemenzi, Luca; Storti, Fabrizio; Bistacchi, Andrea; Di Toro, Giulio

2016-09-01

The Vado di Corno Fault Zone (VCFZ) is an active extensional fault cutting through carbonates in the Italian Central Apennines. The fault zone was exhumed from ∼2 km depth and accommodated a normal throw of ∼2 km since Early-Pleistocene. In the studied area, the master fault of the VCFZ dips N210/54° and juxtaposes Quaternary colluvial deposits in the hangingwall with cataclastic dolostones in the footwall. Detailed mapping of the fault zone rocks within the ∼300 m thick footwall-block evidenced the presence of five main structural units (Low Strain Damage Zone, High Strain Damage Zone, Breccia Unit, Cataclastic Unit 1 and Cataclastic Unit 2). The Breccia Unit results from the Pleistocene extensional reactivation of a pre-existing Pliocene thrust. The Cataclastic Unit 1 forms a ∼40 m thick band lining the master fault and recording in-situ shattering due to the propagation of multiple seismic ruptures. Seismic faulting is suggested also by the occurrence of mirror-like slip surfaces, highly localized sheared calcite-bearing veins and fluidized cataclasites. The VCFZ architecture compares well with seismological studies of the L'Aquila 2009 seismic sequence (mainshock MW 6.1), which imaged the reactivation of shallow-seated low-angle normal faults (Breccia Unit) cut by major high-angle normal faults (Cataclastic Units).

Geochemistry, mineralization, structure, and permeability of a normal-fault zone, Casino mine, Alligator Ridge district, north central Nevada

NASA Astrophysics Data System (ADS)

Hammond, K. Jill; Evans, James P.

2003-05-01

We examine the geochemical signature and structure of the Keno fault zone to test its impact on the flow of ore-mineralizing fluids, and use the mined exposures to evaluate structures and processes associated with normal fault development. The fault is a moderately dipping normal-fault zone in siltstone and silty limestone with 55-100 m of dip-slip displacement in north-central Nevada. Across-strike exposures up to 180 m long, 65 m of down-dip exposure and 350 m of along-strike exposure allow us to determine how faults, fractures, and fluids interact within mixed-lithology carbonate-dominated sedimentary rocks. The fault changes character along strike from a single clay-rich slip plane 10-20 mm thick at the northern exposure to numerous hydrocarbon-bearing, calcite-filled, nearly vertical slip planes in a zone 15 m wide at the southern exposure. The hanging wall and footwall are intensely fractured but fracture densities do not vary markedly with distance from the fault. Fault slip varies from pure dip-slip to nearly pure strike-slip, which suggests that either slip orientations may vary on faults in single slip events, or stress variations over the history of the fault caused slip vector variations. Whole-rock major, minor, and trace element analyses indicate that Au, Sb, and As are in general associated with the fault zone, suggesting that Au- and silica-bearing fluids migrated along the fault to replace carbonate in the footwall and adjacent hanging wall rocks. Subsequent fault slip was associated with barite and calcite and hydrocarbon-bearing fluids deposited at the southern end of the fault. No correlation exists at the meter or tens of meter scale between mineralization patterns and fracture density. We suggest that the fault was a combined conduit-barrier system in which the fault provides a critical connection between the fluid sources and fractures that formed before and during faulting. During the waning stages of deposit formation, the fault behaved as

Strain partitioning and deformation mode analysis of the normal faults at Red Mountain, Birmingham, Alabama

NASA Astrophysics Data System (ADS)

Wu, Schuman

1989-12-01

In a low-temperature environment, the thin-section scale rock-deformation mode is primarily a function of confining pressure and total strain at geological strain rates. A deformation mode diagram is constructed from published experimental data by plotting the deformation mode on a graph of total strain versus the confining pressure. Four deformation modes are shown on the diagram: extensional fracturing, mesoscopic faulting, incipient faulting, and uniform flow. By determining the total strain and the deformation mode of a naturally deformed sample, the confining pressure and hence the depth at which the rock was deformed can be evaluated. The method is applied to normal faults exposed on the gently dipping southeast limb of the Birmingham anticlinorium in the Red Mountain expressway cut in Birmingham, Alabama. Samples of the Ordovician Chickamauga Limestone within and adjacent to the faults contain brittle structures, including mesoscopic faults and veins, and ductile deformation features including calcite twins, intergranular and transgranular pressure solution, and deformed burrows. During compaction, a vertical shortening of about 45 to 80% in shale is indicated by deformed burrows and relative compaction of shale to burrows, about 6% in limestone by stylolites. The normal faults formed after the Ordovician rocks were consolidated because the faults and associated veins truncate the deformed burrows and stylolites, which truncate the calcite cement. A total strain of 2.0% was caused by mesoscopic faults during normal faulting. A later homogenous deformation, indicated by the calcite twins in veins, cement and fossil fragments, has its major principal shortening strain in the dip direction at a low angle (about 22°) to bedding. The strain magnitude is about 2.6%. By locating the observed data on the deformation mode diagram, it is found that the normal faulting characterized by brittle deformation occurred under low confining pressure (< 18 MPa) at shallow

The Padul normal fault activity constrained by GPS data: Brittle extension orthogonal to folding in the central Betic Cordillera

NASA Astrophysics Data System (ADS)

Gil, Antonio J.; Galindo-Zaldívar, Jesús; Sanz de Galdeano, Carlos; Borque, Maria Jesús; Sánchez-Alzola, Alberto; Martinez-Martos, Manuel; Alfaro, Pedro

2017-08-01

The Padul Fault is located in the Central Betic Cordillera, formed in the framework of the NW-SE Eurasian-African plate convergence. In the Internal Zone, large E-W to NE-SW folds of western Sierra Nevada accommodated the greatest NW-SE shortening and uplift of the cordillera. However, GPS networks reveal a present-day dominant E-W to NE-SW extensional setting at surface. The Padul Fault is the most relevant and best exposed active normal fault that accommodates most of the NE-SW extension of the Central Betics. This WSW-wards dipping fault, formed by several segments of up to 7 km maximum length, favored the uplift of the Sierra Nevada footwall away from the Padul graben hanging wall. A non-permanent GPS network installed in 1999 constrains an average horizontal extensional rate of 0.5 mm/yr in N66°E direction. The fault length suggests that a (maximum) 6 magnitude earthquake may be expected, but the absence of instrumental or historical seismic events would indicate that fault activity occurs at least partially by creep. Striae on fault surfaces evidence normal-sinistral kinematics, suggesting that the Padul Fault may have been a main transfer fault of the westernmost end of the Sierra Nevada antiform. Nevertheless, GPS results evidence: (1) shortening in the Sierra Nevada antiform is in its latest stages, and (2) the present-day fault shows normal with minor oblique dextral displacements. The recent change in Padul fault kinematics will be related to the present-day dominance of the ENE-WSW regional extension versus NNW-SSE shortening that produced the uplift and northwestwards displacement of Sierra Nevada antiform. This region illustrates the importance of heterogeneous brittle extensional tectonics in the latest uplift stages of compressional orogens, as well as the interaction of folding during the development of faults at shallow crustal levels.

Normal Faulting in the 1923 Berdún Earthquake and Postorogenic Extension in the Pyrenees

NASA Astrophysics Data System (ADS)

Stich, Daniel; Martín, Rosa; Batlló, Josep; Macià, Ramón; Mancilla, Flor de Lis; Morales, Jose

2018-04-01

The 10 July 1923 earthquake near Berdún (Spain) is the largest instrumentally recorded event in the Pyrenees. We recover old analog seismograms and use 20 hand-digitized waveforms for regional moment tensor inversion. We estimate moment magnitude Mw 5.4, centroid depth of 8 km, and a pure normal faulting source with strike parallel to the mountain chain (N292°E), dip of 66° and rake of -88°. The new mechanism fits into the general predominance of normal faulting in the Pyrenees and extension inferred from Global Positioning System data. The unique location of the 1923 earthquake, near the south Pyrenean thrust front, shows that the extensional regime is not confined to the axial zone where high topography and the crustal root are located. Together with seismicity near the northern mountain front, this indicates that gravitational potential energy in the western Pyrenees is not extracted locally but induces a wide distribution of postorogenic deformation.

The influence of normal fault geometry on porous sandstone deformation: Insights from mechanical models into conditions leading to Coulomb failure and shear-enhanced compaction

NASA Astrophysics Data System (ADS)

Allison, K.; Reinen, L. A.

2011-12-01

Slip on non-planar faults produces stress perturbations in the surrounding host rock that can yield secondary faults at a scale too small to be resolved on seismic surveys. Porosity changes during failure may affect the ability of the rock to transmit fluids through dilatant cracking or, in porous rocks, shear-enhanced compaction (i.e., cataclastic flow). Modeling the mechanical behavior of the host rock in response to slip on non-planar faults can yield insights into the role of fault geometry on regions of enhanced or inhibited fluid flow. To evaluate the effect of normal fault geometry on deformation in porous sandstones, we model the system as a linear elastic, homogeneous, whole or half space using the boundary-element modeling program Poly3D. We consider conditions leading to secondary deformation using the maximum Coulomb shear stress (MCSS) as an index of brittle deformation and proximity to an elliptical yield envelope (Y), determined experimentally for porous sandstone (Baud et al., JGR, 2006), for cataclastic flow. We model rectangular faults consisting of two segments: an upper leg with a constant dip of 60° and a lower leg with dips ranging 15-85°. We explore far-field stress models of constant and gradient uniaxial strain. We investigate the potential damage in the host rock in two ways: [1] the size of the damage zone, and [2] regions of enhanced deformation indicated by elevated MCSS or Y. Preliminary results indicate that, along a vertical transect passing through the fault kink, [1] the size of the damage zone increases in the footwall with increasing lower leg dip and remains constant in the hanging wall. [2] In the footwall, the amount of deformation does not change as a function of lower leg dip in constant stress models; in gradient stress models, both MCSS and Y increase with dip. In the hanging wall, Y decreases with increasing lower leg dip for both constant and gradient stress models. In contrast, MCSS increases: as lower leg dip

Up-dip partitioning of displacement components on the oblique-slip Clarence Fault, New Zealand

NASA Astrophysics Data System (ADS)

Nicol, Andrew; Van Dissen, Russell

2002-09-01

Active strike-slip faults in New Zealand occur within an obliquely-convergent plate boundary zone. Although the traces of these faults commonly delineate the base of mountain ranges, they do not always accommodate significant shortening at the free surface. Along the active trace of Clarence Fault in northeastern South Island, New Zealand, displaced landforms and slickenside striations indicate predominantly horizontal displacements at the ground surface, and a right-lateral slip rate of ca. 3.5-5 mm/year during the Holocene. The Inland Kaikoura mountain range occupies the hanging wall of the fault and rises steeply from the active trace to altitudes of ca. 3 km. The geomorphology of the range indicates active uplift and mountain building, which is interpreted to result, in part, from a vertical component of fault slip at depth. These data are consistent with the fault accommodating oblique-slip at depth aligned parallel to the plate-motion vector and compatible with regional geodetic data and earthquake focal-mechanisms. Oblique-slip on the Clarence Fault at depth is partitioned at the free surface into: (1) right-lateral displacement on the fault, and (2) hanging wall uplift produced by distributed displacement on small-scale faults parallel to the main fault. Decoupling of slip components reflects an up-dip transfer of fault throw to an off-fault zone of distributed uplift. Such zones are common in the hanging walls of thrusts and reverse faults, and support the idea that the dip of the oblique-slip Clarence Fault steepens towards the free surface.

3D geometries of normal faults in a brittle-ductile sedimentary cover: Analogue modelling

NASA Astrophysics Data System (ADS)

Vasquez, Lina; Nalpas, Thierry; Ballard, Jean-François; Le Carlier De Veslud, Christian; Simon, Brendan; Dauteuil, Olivier; Bernard, Xavier Du

2018-07-01

It is well known that ductile layers play a major role in the style and location of deformation. However, at the scale of a single normal fault, the impact of rheological layering is poorly constrained and badly understood, and there is a lack of information regarding the influence of several décollement levels within a sedimentary cover on the single fault geometry under purely extensive deformation. We present small-scale experiments that were built with interbedded layers of brittle and ductile materials and with minimum initial constraints (only a velocity discontinuity at the base of the experiment) on the normal fault geometry in order to investigate the influence of controlled parameters such as extension velocity, rate of extension, ductile thickness and varying stratigraphy on the 3D fault geometry. These experiments showed a broad-spectrum of tectonic features such as grabens, ramp-flat-ramp normal faults and reverse faults. Forced folds are associated with fault flats that develop in the décollement levels (refraction of the fault angle). One of the key points is that the normal fault geometry displays large variations in both direction and dip, despite the imposed homogeneous extension. This result is exclusively related to the presence of décollement levels, and is not associated with any global/regional variation in extension direction and/or inversion.

The Origin of High-angle Dip-slip Earthquakes at Geothermal Fields in California

NASA Astrophysics Data System (ADS)

Barbour, A. J.; Schoenball, M.; Martínez-Garzón, P.; Kwiatek, G.

2016-12-01

We examine the source mechanisms of earthquakes occurring in three California geothermal fields: The Geysers, Salton Sea, and Coso. We find source mechanisms ranging from strike slip faulting, consistent with the tectonic settings, to dip slip with unusually steep dip angles which are inconsistent with local structures. For example, we identify a fault zone in the Salton Sea Geothermal Field imaged using precisely-relocated hypocenters with a dip angle of 60° yet double-couple focal mechanisms indicate higher-angle dip-slip on ≥75° dipping planes. We observe considerable temporal variability in the distribution of source mechanisms. For example, at the Salton Sea we find that the number of high angle dip-slip events increased after 1989, when net-extraction rates were highest. There is a concurrent decline in strike-slip and strike-slip-normal faulting, the mechanisms expected from regional tectonics. These unusual focal mechanisms and their spatio-temporal patterns are enigmatic in terms of our understanding of faulting in geothermal regions. While near-vertical fault planes are expected to slip in a strike-slip sense, and dip slip is expected to occur on moderately dipping faults, we observe dip slip on near-vertical fault planes. However, for plausible stress states and accounting for geothermal production, the resolved fault planes should be stable. We systematically analyze the source mechanisms of these earthquakes using full moment tensor inversion to understand the constraints imposed by assuming a double-couple source. Applied to The Geysers field, we find a significant reduction in the number of high-angle dip-slip mechanisms using the full moment tensor. The remaining mechanisms displaying high-angle dip-slip could be consistent with faults accommodating subsidence and compaction associated with volumetric strain changes in the geothermal reservoir.

Transfer zones in listric normal fault systems

NASA Astrophysics Data System (ADS)

Bose, Shamik

Listric normal faults are common in passive margin settings where sedimentary units are detached above weaker lithological units, such as evaporites or are driven by basal structural and stratigraphic discontinuities. The geometries and styles of faulting vary with the types of detachment and form landward and basinward dipping fault systems. Complex transfer zones therefore develop along the terminations of adjacent faults where deformation is accommodated by secondary faults, often below seismic resolution. The rollover geometry and secondary faults within the hanging wall of the major faults also vary with the styles of faulting and contribute to the complexity of the transfer zones. This study tries to understand the controlling factors for the formation of the different styles of listric normal faults and the different transfer zones formed within them, by using analog clay experimental models. Detailed analyses with respect to fault orientation, density and connectivity have been performed on the experiments in order to gather insights on the structural controls and the resulting geometries. A new high resolution 3D laser scanning technology has been introduced to scan the surfaces of the clay experiments for accurate measurements and 3D visualizations. Numerous examples from the Gulf of Mexico have been included to demonstrate and geometrically compare the observations in experiments and real structures. A salt cored convergent transfer zone from the South Timbalier Block 54, offshore Louisiana has been analyzed in detail to understand the evolutionary history of the region, which helps in deciphering the kinematic growth of similar structures in the Gulf of Mexico. The dissertation is divided into three chapters, written in a journal article format, that deal with three different aspects in understanding the listric normal fault systems and the transfer zones so formed. The first chapter involves clay experimental models to understand the fault patterns in

Fault geometries and deformation mechanisms in the evolution of low-angle normal faults (Kea, Greece)

NASA Astrophysics Data System (ADS)

Iglseder, C.; Grasemann, B.; Schneider, D.; Rice, A. H. N.; Stöckli, D.; Rockenschaub, M.

2009-04-01

The overall tectonic regime in the Cyclades since the Oligocene has been characterized by crustal extension, accommodated by movements on low-angle normal faults (LANFs). On Kea, structural investigations have demonstrated the existence of an island-wide LANF within a large-scale ductile-brittle shear-zone traceable over a distance of 19.5 km parallel to the stretching lineation. The tectonostratigraphy comprises Attic-Cycladic Crystalline lithologies with a shallowly-dipping schist-calcite marble unit overlain by calcitic and dolomitic fault rocks. Notably, the calcitic marbles have been mylonitized, with a mean NNE/NE-SSW/SW trending, pervasive stretching lineation and intense isoclinal folding with fold axes parallel to the stretching lineation. Numerous SC-SCĆ-fabrics and monoclinic clast-geometries show a consistent top-to-SSW shear-sense. Recorded within all lithologies is a consistent WNW/NW-ESE/SE and NNE/NE-SSW/SW striking network of conjugated brittle, brittle-ductile high-angle faults perpendicular and (sub)parallel to the main stretching direction. Field evidence and microstructural investigations indicate high-angle normal faults formed synchronously with movement on LANFs. This interplay of LANFs with high-angle structures, initiated and evolved from brittle-ductile to brittle conditions, indicates initial stages of movement below the calcite brittle-ductile transition but above the dolomite transition. Weakening processes related to syntectonic fluid-rock interactions highlight these observations. In particular, grain-size reduction and strain localisation in fine-grained (ultra)-cataclasites and fine-grained aggregates of phyllosilicate-rich fault-rocks promoted fluid-flow and pressure-solution-accommodated ‘frictional-viscous' creep. These mechanisms show the importance for LANF slip and movement in the progressive development and interaction between contemporaneous active normal faults in the Andersonian-Byerlee frictional mechanics.

Salt flow direction and velocity during subsalt normal faulting and syn-kinematic sedimentation—implications from analytical calculations

NASA Astrophysics Data System (ADS)

Warsitzka, M.; Kukowski, N.; Kley, J.

2018-04-01

Salt flow induced by subsalt normal faulting is mainly controlled by tilting of the salt layer, the amount of differential loading due to syn-kinematic deposition, and tectonic shearing at the top or the base of the salt layer. Our study addresses the first two mechanisms and aims to examine salt flow patterns above a continuously moving subsalt normal fault and beneath a syn-kinematic minibasin. In such a setting, salt either tends to flow down towards the basin centre driven by its own weight or is squeezed up towards the footwall side owing to loading differences between the minibasin and the region above the footwall block. Applying isostatic balancing in analytical models, we calculated the steady-state flow velocity in a salt layer. This procedure gives insights into (1) the minimum vertical offset required for upward flow to occur, (2) the magnitude of the flow velocity, and (3) the average density of the supra-salt cover layer at the point at which upward flow starts. In a sensitivity study, we examined how the point of flow reversal and the velocity patterns are influenced by changes of the salt and cover layer thickness, the geometry of the cover flexure, the dip of the subsalt fault, compaction parameters of the supra-salt cover, the salt viscosity and the salt density. Our model results reveal that in most geological scenarios, salt flow above a continuously displacing subsalt normal fault goes through an early phase of downward flow. At sufficiently high fault offset in the range of 700-2600 m, salt is later squeezed upward towards the footwall side. This flow reversal occurs at smaller vertical fault displacement, if the thickness of the pre-kinematic layer is larger, the sedimentation rate of the syn-kinematic cover is higher, the compaction coefficient of cover sediments (i.e. the density increase with depth) is larger or the average density of the salt is lower. Other geometrical parameters such as the width of the cover monocline, the dip of the

Initiation of a Low-Angle Normal Fault Active Across the Upper Brittle-Plastic Transition, Chemehuevi Mountains, CA

NASA Astrophysics Data System (ADS)

LaForge, J.; John, B. E.; Grimes, C. B.; Stunitz, H.; Heilbronner, R.

2016-12-01

The Chemehuevi detachment fault system, part of the regionally developed Colorado River extensional corridor, hosts exceptional exposures of a denuded fault system related to Miocene extension. Here, we characterize the early history of extension associated with a small slip (1-2 km) low-angle normal fault, the Mohave Wash fault (MWF), initially active across the brittle-plastic transition. Strain localized in three principal ways across the 23-km down-dip exposure (T <150° to >400°C): a brittle fault zone, localized, disseminated quartz mylonites, and syntectonic dikes hosting mylonitic fabrics. Brittle deformation in these crystalline rocks was concentrated into a 10-62-m thick brittle fault zone hosting localized, unmineralized to chlorite-epidote-quartz mineralized zones of cataclasite series fault rocks ≤3 m thick and rare pseudotachylite. Mylonitic deformation played an increased role in deformation down dip (NE), with mylonites increasing in quantity and average thickness. At shallow structural levels, footwall mylonites are absent; at 9-18 km down dip, cm-scale quartz mylonites are common; ≥18 km down dip, meter-scale syntectonic intermediate-felsic dikes are mylonitic, are attenuated into parallelism with the MWF, and host well-developed L-S fabric; 23 km down dip, the footwall hosts meter-thick zones of disseminated mylonitic quartz of varying intensities. These mylonites host microstructures that record progressively higher deformation temperature down dip, with dislocation-creep in quartz indicative of T of 280-400°C to ≥500°C, and diffusion creep with grain boundary sliding in dikes suggestive of even higher T deformation. Dike emplacement in the system is syntectonic with MWF slip; mafic-intermediate composition dikes intruded damage zone fractures and cataclasites, and were in turn fractured; Pb/U zircon ages of intermediate-felsic dikes range from ca. 1.5 ± 1 Ma to 3.8 ± 1 Ma after the onset of regional extension, but predate rapid slip

Brittle extension of the continental crust along a rooted system of low-angle normal faults: Colorado River extensional corridor

NASA Technical Reports Server (NTRS)

John, B. E.; Howard, K. A.

1985-01-01

A transect across the 100 km wide Colorado River extensional corridor of mid-Tertiary age shows that the upper 10 to 15 km of crystalline crust extended along an imbricate system of brittle low-angle normal faults. The faults cut gently down a section in the NE-direction of tectonic transport from a headwall breakaway in the Old Woman Mountains, California. Successively higher allochthons above a basal detachment fault are futher displaced from the headwall, some as much as tens of kilometers. Allochthonous blocks are tilted toward the headwall as evidenced by the dip of the cappoing Tertiary strata and originally horizontal Proterozoic diabase sheets. On the down-dip side of the corridor in Arizona, the faults root under the unbroken Hualapai Mountains and the Colorado Plateau. Slip on faults at all exposed levels of the crust was unidirectional. Brittle thinning above these faults affected the entire upper crust, and wholly removed it locally along the central corridor or core complex region. Isostatic uplift exposed metamorphic core complexes in the domed footwall. These data support a model that the crust in California moved out from under Arizona along an asymmetric, rooted normal-slip shear system. Ductile deformation must have accompanied mid-Tertiary crustal extension at deeper structural levels in Arizona.

Scissoring Fault Rupture Properties along the Median Tectonic Line Fault Zone, Southwest Japan

NASA Astrophysics Data System (ADS)

Ikeda, M.; Nishizaka, N.; Onishi, K.; Sakamoto, J.; Takahashi, K.

2017-12-01

The Median Tectonic Line fault zone (hereinafter MTLFZ) is the longest and most active fault zone in Japan. The MTLFZ is a 400-km-long trench parallel right-lateral strike-slip fault accommodating lateral slip components of the Philippine Sea plate oblique subduction beneath the Eurasian plate [Fitch, 1972; Yeats, 1996]. Complex fault geometry evolves along the MTLFZ. The geomorphic and geological characteristics show a remarkable change through the MTLFZ. Extensional step-overs and pull-apart basins and a pop-up structure develop in western and eastern parts of the MTLFZ, respectively. It is like a "scissoring fault properties". We can point out two main factors to form scissoring fault properties along the MTLFZ. One is a regional stress condition, and another is a preexisting fault. The direction of σ1 anticlockwise rotate from N170°E [Famin et al., 2014] in the eastern Shikoku to Kinki areas and N100°E [Research Group for Crustral Stress in Western Japan, 1980] in central Shikoku to N85°E [Onishi et al., 2016] in western Shikoku. According to the rotation of principal stress directions, the western and eastern parts of the MTLFZ are to be a transtension and compression regime, respectively. The MTLFZ formed as a terrain boundary at Cretaceous, and has evolved with a long active history. The fault style has changed variously, such as left-lateral, thrust, normal and right-lateral. Under the structural condition of a preexisting fault being, the rupture does not completely conform to Anderson's theory for a newly formed fault, as the theory would require either purely dip-slip motion on the 45° dipping fault or strike-slip motion on a vertical fault. The fault rupture of the 2013 Barochistan earthquake in Pakistan is a rare example of large strike-slip reactivation on a relatively low angle dipping fault (thrust fault), though many strike-slip faults have vertical plane generally [Avouac et al., 2014]. In this presentation, we, firstly, show deep subsurface

A Non-linear Geodetic Data Inversion Using ABIC for Slip Distribution on a Fault With an Unknown dip Angle

NASA Astrophysics Data System (ADS)

Fukahata, Y.; Wright, T. J.

2006-12-01

We developed a method of geodetic data inversion for slip distribution on a fault with an unknown dip angle. When fault geometry is unknown, the problem of geodetic data inversion is non-linear. A common strategy for obtaining slip distribution is to first determine the fault geometry by minimizing the square misfit under the assumption of a uniform slip on a rectangular fault, and then apply the usual linear inversion technique to estimate a slip distribution on the determined fault. It is not guaranteed, however, that the fault determined under the assumption of a uniform slip gives the best fault geometry for a spatially variable slip distribution. In addition, in obtaining a uniform slip fault model, we have to simultaneously determine the values of the nine mutually dependent parameters, which is a highly non-linear, complicated process. Although the inverse problem is non-linear for cases with unknown fault geometries, the non-linearity of the problems is actually weak, when we can assume the fault surface to be flat. In particular, when a clear fault trace is observed on the EarthOs surface after an earthquake, we can precisely estimate the strike and the location of the fault. In this case only the dip angle has large ambiguity. In geodetic data inversion we usually need to introduce smoothness constraints in order to compromise reciprocal requirements for model resolution and estimation errors in a natural way. Strictly speaking, the inverse problem with smoothness constraints is also non-linear, even if the fault geometry is known. The non-linearity has been dissolved by introducing AkaikeOs Bayesian Information Criterion (ABIC), with which the optimal value of the relative weight of observed data to smoothness constraints is objectively determined. In this study, using ABIC in determining the optimal dip angle, we dissolved the non-linearity of the inverse problem. We applied the method to the InSAR data of the 1995 Dinar, Turkey earthquake and obtained

Subduction of thick oceanic plateau and high-angle normal-fault earthquakes intersecting the slab

NASA Astrophysics Data System (ADS)

Arai, Ryuta; Kodaira, Shuichi; Yamada, Tomoaki; Takahashi, Tsutomu; Miura, Seiichi; Kaneda, Yoshiyuki; Nishizawa, Azusa; Oikawa, Mitsuhiro

2017-06-01

The role of seamounts on interplate earthquakes has been debated. However, its impact on intraslab deformation is poorly understood. Here we present unexpected evidence for large normal-fault earthquakes intersecting the slab just ahead of a subducting seamount. In 1995, a series of earthquakes with maximum magnitude of 7.1 occurred in northern Ryukyu where oceanic plateaus are subducting. The aftershock distribution shows that conjugate faults with an unusually high dip angle of 70-80° ruptured the entire subducting crust. Seismic reflection images reveal that the plate interface is displaced over 1 km along one of the fault planes of the 1995 events. These results suggest that a lateral variation in slab buoyancy can produce sufficient differential stress leading to near-vertical normal-fault earthquakes within the slab. On the contrary, the upper surface of the seamount (plate interface) may correspond to a weakly coupled region, reflecting the dual effects of seamounts/plateaus on subduction earthquakes.

Fluid involvement in normal faulting

NASA Astrophysics Data System (ADS)

Sibson, Richard H.

2000-04-01

Evidence of fluid interaction with normal faults comes from their varied role as flow barriers or conduits in hydrocarbon basins and as hosting structures for hydrothermal mineralisation, and from fault-rock assemblages in exhumed footwalls of steep active normal faults and metamorphic core complexes. These last suggest involvement of predominantly aqueous fluids over a broad depth range, with implications for fault shear resistance and the mechanics of normal fault reactivation. A general downwards progression in fault rock assemblages (high-level breccia-gouge (often clay-rich) → cataclasites → phyllonites → mylonite → mylonitic gneiss with the onset of greenschist phyllonites occurring near the base of the seismogenic crust) is inferred for normal fault zones developed in quartzo-feldspathic continental crust. Fluid inclusion studies in hydrothermal veining from some footwall assemblages suggest a transition from hydrostatic to suprahydrostatic fluid pressures over the depth range 3-5 km, with some evidence for near-lithostatic to hydrostatic pressure cycling towards the base of the seismogenic zone in the phyllonitic assemblages. Development of fault-fracture meshes through mixed-mode brittle failure in rock-masses with strong competence layering is promoted by low effective stress in the absence of thoroughgoing cohesionless faults that are favourably oriented for reactivation. Meshes may develop around normal faults in the near-surface under hydrostatic fluid pressures to depths determined by rock tensile strength, and at greater depths in overpressured portions of normal fault zones and at stress heterogeneities, especially dilational jogs. Overpressures localised within developing normal fault zones also determine the extent to which they may reutilise existing discontinuities (for example, low-angle thrust faults). Brittle failure mode plots demonstrate that reactivation of existing low-angle faults under vertical σ1 trajectories is only likely if

Static stress changes associated with normal faulting earthquakes in South Balkan area

NASA Astrophysics Data System (ADS)

Papadimitriou, E.; Karakostas, V.; Tranos, M.; Ranguelov, B.; Gospodinov, D.

2007-10-01

Activation of major faults in Bulgaria and northern Greece presents significant seismic hazard because of their proximity to populated centers. The long recurrence intervals, of the order of several hundred years as suggested by previous investigations, imply that the twentieth century activation along the southern boundary of the sub-Balkan graben system, is probably associated with stress transfer among neighbouring faults or fault segments. Fault interaction is investigated through elastic stress transfer among strong main shocks ( M ≥ 6.0), and in three cases their foreshocks, which ruptured distinct or adjacent normal fault segments. We compute stress perturbations caused by earthquake dislocations in a homogeneous half-space. The stress change calculations were performed for faults of strike, dip, and rake appropriate to the strong events. We explore the interaction between normal faults in the study area by resolving changes of Coulomb failure function ( ΔCFF) since 1904 and hence the evolution of the stress field in the area during the last 100 years. Coulomb stress changes were calculated assuming that earthquakes can be modeled as static dislocations in an elastic half-space, and taking into account both the coseismic slip in strong earthquakes and the slow tectonic stress buildup associated with major fault segments. We evaluate if these stress changes brought a given strong earthquake closer to, or sent it farther from, failure. Our modeling results show that the generation of each strong event enhanced the Coulomb stress on along-strike neighbors and reduced the stress on parallel normal faults. We extend the stress calculations up to present and provide an assessment for future seismic hazard by identifying possible sites of impending strong earthquakes.

Late Cenozoic extensional faulting in Central-Western Peloponnesus, Greece

NASA Astrophysics Data System (ADS)

Skourtsos, E.; Fountoulis, I.; Mavroulis, S.; Kranis, H.

2012-04-01

A series of forearc-dipping, orogen-parallel extensional faults are found in the central-western Peloponnesus, (south-western Aegean) which control the western margin of Mt Mainalon. The latter comprises HP/LT rocks of the Phyllites-Quartzites Unit (PQ), overlain by the carbonates and flysch of the Tripolis Unit while the uppermost nappe is the Pindos Unit, a sequence of Mesozoic pelagic sequence, topped by a Paleocene flysch. Most of the extensional structures were previously thought of as the original thrust between the Pindos and Tripolis Units. However, the cross-cutting relationships among these structures indicate that these are forearc (SW-dipping) extensional faults, downthrowing the Pindos thrust by a few tens or hundreds of meters each, rooting onto different levels of the nappe pile. In SW Mainalon the lowermost of the extensional faults is a low-angle normal fault dipping SW juxtaposing the metamorphic rocks of the PQ Unit against the non-metamorphic sequence of the Tripolis Unit. High-angle normal faults, found further to the west, have truncated or even sole onto the low-angle ones and control the eastern margin of the Quaternary Megalopolis basin. All these extensional structures form the eastern boundary of a series of Neogene-Quaternary tectonic depressions, which in turn are separated by E-W horsts. In the NW, these faults are truncated by NE to NNE-striking, NW-dipping faults, which relay the whole fault activity to the eastern margin of the Pyrgos graben. The whole extensional fault architecture has resulted (i) in the Pindos thrust stepping down from altitudes higher than 1000 m in Mainalon in the east, to negative heights in North Messinia and Southern Ilia in the west; and (ii) the gradual disappearance of the Phyllite-Quartzite metamorphics of Mainalon towards the west. The combination of these extensional faults (which may reach down to the Ionian décollement) with the low-angle floor thrusts of the Pindos, Tripolis and Ionian Units leads

Steeply-dipping extension fractures in the Newark basin, New Jersey

USGS Publications Warehouse

Herman, G.C.

2009-01-01

Late Triassic and Early Jurassic bedrock in the Newark basin is pervasively fractured as a result of Mesozoic rifting of the east-central North American continental margin. Tectonic rifting imparted systematic sets of steeply-dipping, en ??chelon, Mode I, extension fractures in basin strata including ordinary joints and veins. These fractures are arranged in transitional-tensional arrays resembling normal dip-slip shear zones. They contributed to crustal stretching, sagging, and eventual faulting of basin rift deposits. Extension fractures display progressive linkage and spatial clustering that probably controlled incipient fault growth. They cluster into three prominent strike groups correlated to early, intermediate, and late-stage tectonic events reflecting about 50- 60?? of counterclockwise rotation of incremental stretching directions. Finite strain analyses show that extension fractures allowed the stretching of basin strata by a few percent, and these fractures impart stratigraphic dips up to a few degrees in directions opposing fracture dips. Fracture groups display three-dimensional spatial variability but consistent geometric relations. Younger fractures locally cut across and terminate against older fractures having more complex vein-cement morphologies and bed-normal folds from stratigraphic compaction. A fourth, youngest group of extension fractures occur sporadically and strike about E-W in obliquely inverted crustal blocks. A geometric analysis of overlapping fracture sets shows how fracture groups result from incremental rotation of an extending tectonic plate, and that old fractures can reactivate with oblique slip components in the contemporary, compressive stress regime. ?? 2008 Elsevier Ltd. All rights reserved.

Effects induced by an earthquake on its fault plane:a boundary element study

NASA Astrophysics Data System (ADS)

Bonafede, Maurizio; Neri, Andrea

2000-04-01

Mechanical effects left by a model earthquake on its fault plane, in the post-seismic phase, are investigated employing the `displacement discontinuity method'. Simple crack models, characterized by the release of a constant, unidirectional shear traction are investigated first. Both slip components-parallel and normal to the traction direction-are found to be non-vanishing and to depend on fault depth, dip, aspect ratio and fault plane geometry. The rake of the slip vector is similarly found to depend on depth and dip. The fault plane is found to suffer some small rotation and bending, which may be responsible for the indentation of a transform tectonic margin, particularly if cumulative effects are considered. Very significant normal stress components are left over the shallow portion of the fault surface after an earthquake: these are tensile for thrust faults, compressive for normal faults and are typically comparable in size to the stress drop. These normal stresses can easily be computed for more realistic seismic source models, in which a variable slip is assigned; normal stresses are induced in these cases too, and positive shear stresses may even be induced on the fault plane in regions of high slip gradient. Several observations can be explained from the present model: low-dip thrust faults and high-dip normal faults are found to be facilitated, according to the Coulomb failure criterion, in repetitive earthquake cycles; the shape of dip-slip faults near the surface is predicted to be upward-concave; and the shallower aftershock activity generally found in the hanging block of a thrust event can be explained by `unclamping' mechanisms.

Architectural and microstructural characterization of a seismogenic normal fault in dolostones (Central Apennines, Italy)

NASA Astrophysics Data System (ADS)

Demurtas, Matteo; Fondriest, Michele; Clemenzi, Luca; Balsamo, Fabrizio; Storti, Fabrizio; Di Toro, Giulio

2015-04-01

Fault zones cutting carbonate sequences represent significant seismogenic sources worldwide (e.g. L'Aquila 2009, MW 6.1). Though seismological and geophysical techniques (double differences method, trapped waves, etc.) allow us to investigate down to the decametric scale the structure of active fault zones, further geological field surveys and microstructural studies of exhumed seismogenic fault zones are required to support interpretation of geophysical data, quantify the geometry of fault zones and identify the fault processes active during the seismic cycle. Here we describe the architecture (i.e. fault geometry and fault rock distribution) of the well-exposed footwall-block of the Campo Imperatore Fault Zone (CIFZ) by means of remote sensed analyses, field surveys, mineralogical (XRD, micro-Raman spectroscopy) and microstructural (FE-SEM, optical microscope cathodoluminescence) investigations. The CIFZ dips 58° towards N210 and its strike mimics that of the arcuate Gran Sasso Thrust Belt (Central Apennines). The CIFZ was exhumed from 2-3 km depth and accommodated a normal throw of ~2 km starting from the Early-Pleistocene. In the studied area, the CIFZ puts in contact the Holocene deposits at the hangingwall with dolomitized Jurassic carbonate platform successions (Calcare Massiccio) at the footwall. From remote sensed analyses, structural lineaments both inside and outside the CIFZ have a typical NW-SE Apenninic strike, which is parallel to the local trend of the Gran Sasso Thrust. Based on the density of the fracture/fault network and the type of fault zone rocks, we distinguished four main structural domains within the ~300 m thick CIFZ footwall-block, which include (i) a well-cemented (white in color) cataclastic zone (up to ~40 m thick) at the contact with the Holocene deposits, (ii) a well-cemented (brown to grey in color) breccia zone (up to ~15 m thick), (iii) an high strain damage zone (fracture spacing < 2-3 cm), and (iv) a low strain damage zone

Fault reactivation: The Picuris-Pecos fault system of north-central New Mexico

NASA Astrophysics Data System (ADS)

McDonald, David Wilson

The PPFS is a N-trending fault system extending over 80 km in the Sangre de Cristo Mountains of northern New Mexico. Precambrian basement rocks are offset 37 km in a right-lateral sense; however, this offset includes dextral strike-slip (Precambrian), mostly normal dip-slip (Pennsylvanian), mostly reverse dip-slip (Early Laramide), limited strike-slip (Late Laramide) and mostly normal dip-slip (Cenozoic). The PPFS is broken into at least 3 segments by the NE-trending Embudo fault and by several Laramide age NW-trending tear faults. These segments are (from N to S): the Taos, the Picuris, and the Pecos segments. On the east side of the Picuris segment in the Picuris Mountains, the Oligocene-Miocene age Miranda graben developed and represents a complex extension zone south of the Embudo fault. Regional analysis of remotely sensed data and geologic maps indicate that lineaments subparallel to the trace of the PPFS are longer and less frequent than lineaments that trend orthogonal to the PPFS. Significant cross cutting faults and subtle changes in fault trends in each segment are clear in the lineament data. Detailed mapping in the eastern Picuris Mountains showed that the favorably oriented Picuris segment was not reactivated in the Tertiary development of the Rio Grande rift. Segmentation of the PPFS and post-Laramide annealing of the Picuris segment are interpreted to have resulted in the development of the subparallel La Serna fault. The Picuris segment of the PPFS is offset by several E-ESE trending faults. These faults are Late Cenozoic in age and interpreted to be related to the uplift of the Picuris Mountains and the continuing sinistral motion on the Embudo fault. Differential subsidence within the Miranda graben caused the development of several synthetic and orthogonal faults between the bounding La Serna and Miranda faults. Analysis of over 10,000 outcrop scale brittle structures reveals a strong correlation between faults and fracture systems. The dominant

Fault and joint geometry at Raft River Geothermal Area, Idaho

NASA Astrophysics Data System (ADS)

Guth, L. R.; Bruhn, R. L.; Beck, S. L.

1981-07-01

Raft River geothermal reservoir is formed by fractures in sedimentary strata of the Miocene and Pliocene salt lake formation. The fracturing is most intense at the base of the salt lake formation, along a decollement that dips eastward at less than 50 on top of metamorphosed precambrian and lower paleozoic rocks. Core taken from less than 200 m above the decollement contains two sets of normal faults. The major set of faults dips between 500 and 700. These faults occur as conjugate pairs that are bisected by vertical extension fractures. The second set of faults dips 100 to 200 and may parallel part of the basal decollement or reflect the presence of listric normal faults in the upper plate. Surface joints form two suborthogonal sets that dip vertically. East-northeast-striking joints are most frequent on the limbs of the Jim Sage anticline, a large fold that is associated with the geothermal field.

Fluid-driven normal faulting earthquake sequences in the Taiwan orogen

NASA Astrophysics Data System (ADS)

Wang, Ling-hua; Rau, Ruey-Juin; Lee, En-Jui

2017-04-01

Seismicity in the Central Range of Taiwan shows normal faulting mechanisms with T-axes directing NE, subparallel to the strike of the mountain belt. We analyze earthquake sequences occurred within 2012-2015 in the Nanshan area of northern Taiwan which indicating swarm behavior and migration characteristics. We select events larger than 2.0 from Central Weather Bureau catalog and use the double-difference relocation program hypoDD with waveform cross-correlation in the Nanshan area. We obtained a final count of 1406 (95%) relocated earthquakes. Moreover, we compute focal mechanisms using USGS program HASH by P-wave first motion and S/P ratio picking and 114 fault plane solutions with M 3.0-5.87 were determined. To test for fluid diffusion, we model seismicity using the equation of Shapiro et al. (1997) by fitting earthquake diffusing rate D during the migration period. According to the relocation result, seismicity in the Taiwan orogenic belt present mostly N25E orientation parallel to the mountain belt with the same direction of the tension axis. In addition, another seismic fracture depicted by seismicity rotated 35 degree counterclockwise to the NW direction. Nearly all focal mechanisms are normal fault type. In the Nanshan area, events show N10W distribution with a focal depth range from 5-12 km and illustrate fault plane dipping about 45-60 degree to SW. Three months before the M 5.87 mainshock which occurred in March, 2013, there were some foreshock events occurred in the shallow part of the fault plane of the mainshock. Half a year following the mainshock, earthquakes migrated to the north and south, respectively with processes matched the diffusion model at a rate of 0.2-0.6 m2/s. This migration pattern and diffusion rate offer an evidence of 'fluid-driven' process in the fault zone. We also find the upward migration of earthquakes in the mainshock source region. These phenomena are likely caused by the opening of the permeable conduit due to the M 5

Syn-Extensional Constrictional Folding of the Gwoira Rider Block, a Large Fault-Bounded Slice Atop the Mai'iu Low-Angle Normal Fault, Woodlark Rift.

NASA Astrophysics Data System (ADS)

Little, T. A.; Webber, S. M.; Norton, K. P.; Mizera, M.; Oesterle, J.; Ellis, S. M.

2016-12-01

The Mai'iu Fault is an active and corrugated low-angle normal fault (LANF) in Woodlark Rift, Eastern Papua New Guinea, which dips 21° NNE, accommodating rapid N-S extension. The Gwoira rider block is a large fault-bounded sedimentary slice comprising the Gwoira Conglomerate, located within a large synformal megamullion in the Mai'iu Fault surface. The Gwoira Conglomerate was originally deposited on the Mai'iu Fault hanging wall concurrent with extension, and has since been buried to a maximum depth of 1600-2100 m (evidenced by vitrinite reflectance data), back-tilted, and synformally folded. Both the Gwoira Conglomerate (former hanging wall) and mylonitic foliation (footwall) of the Mai'iu Fault have been shortened E-W, perpendicular to the extension direction. We show that E-W synformal folding of the Gwoira Conglomerate was concurrent with ongoing sedimentation and extension on the Mai'iu Fault. Structurally shallower Gwoira Conglomerate strata are folded less than deeper strata, indicating that folding was progressively accrued concurrent with N-S extension. We also show that abandonment of the inactive strand of the Mai'iu Fault in favor of the Gwoira Fault, which resulted in formation of the Gwoira rider block, occurred in response to progressive megamullion amplification and resultant misorientation of the inactive strand of the Mai'iu Fault. We attribute E-W folding to extension-perpendicular constriction. This is consistent with observations of outcrop-scale conjugate strike-slip faults that deform the footwall and hanging wall of the Mai'iu Fault, and accommodate E-W shortening. Constrictional folding remains active in the near-surface as evidenced by synformal tilting of inferred Late Quaternary fluvial terraces atop the Gwoira rider block. This sequence of progressive constrictional folding is dated using 26Al/10Be terrestrial cosmogenic nuclide burial dating of the Gwoira Conglomerate. Finally, because rider block formation records abandonment of the

Geometric effects resulting from the asymmetry of dipping fault: Hanging wall/ footwall effects

NASA Astrophysics Data System (ADS)

Wang, Dong; Xie, Li-Li; Hu, Jin-Jun

2008-05-01

Root-mean-square distance D rms with characteristic of weighted-average is introduced in this article firstly. D rms can be used to capture the general proximity of a site to a dipping fault plane comparing with the rupture distance D rup and the seismogenic distance D seis. Then, using D rup, D seis and D rms, the hanging wall/footwall effects on the peak ground acceleration (PGA) during the 1999 Chi-Chi earthquake are evaluated by regression analysis. The logarithm residual shows that the PGA on hanging wall is much greater than that on footwall at the same D rup or D seis when the D rup or D seis is used as site-to-source distance measure. In contrast, there is no significant difference between the PGA on hanging wall and that on footwall at the same D rms when D rms is used. This result confirms that the hanging wall/footwall effect is mainly a geometric effect caused by the asymmetry of dipping fault. Therefore, the hanging wall/footwall effect on the near-fault ground motions can be ignored in the future attenuation analysis if the root-mean-square distance D rms is used as the site-to-source distance measure.

Effects of fault dip and slip rake angles on near-source ground motions: Why rupture directivity was minimal in the 1999 Chi-Chi, Taiwan, earthquake

USGS Publications Warehouse

Aagaard, Brad T.; Hall, J.F.; Heaton, T.H.

2004-01-01

We study how the fault dip and slip rake angles affect near-source ground velocities and displacements as faulting transitions from strike-slip motion on a vertical fault to thrust motion on a shallow-dipping fault. Ground motions are computed for five fault geometries with different combinations of fault dip and rake angles and common values for the fault area and the average slip. The nature of the shear-wave directivity is the key factor in determining the size and distribution of the peak velocities and displacements. Strong shear-wave directivity requires that (1) the observer is located in the direction of rupture propagation and (2) the rupture propagates parallel to the direction of the fault slip vector. We show that predominantly along-strike rupture of a thrust fault (geometry similar in the Chi-Chi earthquake) minimizes the area subjected to large-amplitude velocity pulses associated with rupture directivity, because the rupture propagates perpendicular to the slip vector; that is, the rupture propagates in the direction of a node in the shear-wave radiation pattern. In our simulations with a shallow hypocenter, the maximum peak-to-peak horizontal velocities exceed 1.5 m/sec over an area of only 200 km2 for the 30??-dipping fault (geometry similar to the Chi-Chi earthquake), whereas for the 60??- and 75??-dipping faults this velocity is exceeded over an area of 2700 km2 . These simulations indicate that the area subjected to large-amplitude long-period ground motions would be larger for events of the same size as Chi-Chi that have different styles of faulting or a deeper hypocenter.

Overview of the Mechanics of the Active Mai'iu Low Angle Normal Fault (Dayman Dome), Southeastern Papua New Guinea

NASA Astrophysics Data System (ADS)

Little, T. A.; Boulton, C. J.; Webber, S. M.; Mizera, M.; Oesterle, J.; Ellis, S. M.; Norton, K. P.; Wallace, L.; Biemiller, J.; Seward, D.; Boles, A.

2016-12-01

The Mai'iu Fault is a corrugated low-angle normal fault (LANF) that has slipped >24 km. It emerges near sea level at 21° N dip, and flattens southward over the dome crest at 3000 m. This reactivated Paleogene suture is slipping at up to 1 cm/year based on previous GPS data and preliminary 10Be cosmogenic nuclide exposure scarp dating. An alignment of microseismicity (Eilon et al. 2015) suggests a dip of 30° N at 15-25 km depth. Pseudotachylites are abundant in lower, mylonitic parts of the footwall. One vein yielded 40Ar/39Ar ages of 1.9-2.2 Ma, implying seismicity at 8-10 km depth at the above slip rate. Widespread, antithetic normal faults in the footwall are attributed to rolling-hinge controlled yielding during exhumation. A single rider block is downfolded into synformal megamullion. Unconformities within this block, and ductile folding and conjugate strike-slip faulting of mylonitic footwall fabrics record prolonged EW shortening and constriction. Many normal and strike-slip faults cut the metabasaltic footwall recording Andersonian stresses and flipping between σ1 and σ2. To exhume the steep faults, the LANF must have remained active despite differential stress being locally high enough to initiate well-oriented faults—relationships that bracket the frictional strength of the LANF. Quantitative XRD on mafic and serpentinitic gouges reveal the Mai'iu fault core is enriched in weak clays corrensite and saponite. Hydrothermal friction experiments were done at effective normal stresses of 30-210 MPa, and temperatures of 50-450oC. At shallow depths (T≤200 oC), clay-rich fault gouges are frictionally weak (μ=0.13-0.15 and 0.20-0.28) and velocity-strengthening. At intermediate depths (T>200 oC), the footwall is frictionally strong (μ=0.71-0.78 and 0.50-0.64) and velocity-weakening. Velocity-strengthening is observed at T≥400 oC. The experiments provide evidence for deep unstable slip, consistent with footwall pseudotachylites and microseismicity at

Controls of earthquake faulting style on near field landslide triggering: The role of coseismic slip

NASA Astrophysics Data System (ADS)

Tatard, L.; Grasso, J. R.

2013-06-01

compare the spatial distributions of seven databases of landslides triggered by Mw=5.6-7.9 earthquakes, using distances normalized by the earthquake fault length. We show that the normalized landslide distance distributions collapse, i.e., the normalized distance distributions overlap whatever the size of the earthquake, separately for the events associated with dip-slip, buried-faulting earthquakes, and surface-faulting earthquakes. The dip-slip earthquakes triggered landslides at larger normalized distances than the oblique-slip event of Loma Prieta. We further identify that the surface-faulting earthquakes of Wenchuan, Chi-Chi, and Kashmir triggered landslides at normalized distances smaller than the ones expected from their Mw ≥ 7.6 magnitudes. These results support a control of the seismic slip (through amplitude, rake, and surface versus buried slip) on the distances at which landslides are triggered. In terms of coseismic landslide management in mountainous areas, our results allow us to propose distances at which 95 and 75% of landslides will be triggered as a function of the earthquake focal mechanism.

E-Cigs, Menthol & Dip

MedlinePlus

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Miocene extension in the East Range, Nevada: A two-stage history of normal faulting in the northern basin and range

USGS Publications Warehouse

Fosdick, J.C.; Colgan, J.P.

2008-01-01

The East Range in northwestern Nevada is a large, east-tilted crustal block bounded by west-dipping normal faults. Detailed mapping of Tertiary stratigraphic units demonstrates a two-phase history of faulting and extension. The oldest sedimentary and volcanic rocks in the area record cumulative tilting of -30??-45??E, whereas younger olivine basalt flows indicate only a 15??-20??E tilt since ca. 17-13 Ma. Cumulative fault slip during these two episodes caused a minimum of 40% extensional strain across the East Range, and Quaternary fault scarps and seismic activity indicate that fault motion has continued to the present day. Apatite fission track and (U-Th)/He data presented here show that faulting began in the East Range ca. 17-15 Ma, coeval with middle Miocene extension that occurred across much of the Basin and Range. This phase of extension occurred contemporaneously with middle Miocene volcanism related to the nearby northern Nevada rifts, suggesting a link between magmatism and extensional stresses in the crust that facilitated normal faulting in the East Range. Younger fault slip, although less well constrained, began after 10 Ma and is synchronous with the onset of low-magnitude extension in many parts of northwestern Nevada and eastern California. These findings imply that, rather than migrating west across a discrete boundary, late Miocene extension in western Nevada is a distinct, younger period of faulting that is superimposed on the older, middle Miocene distribution of extended and unextended domains. The partitioning of such middle Miocene deformation may reflect the influence of localized heterogeneities in crustal structure, whereas the more broadly distributed late Miocene extension may reflect a stronger influence from regional plate boundary processes that began in the late Miocene. ?? 2008 Geological Society of America.

Crustal Density Variation Along the San Andreas Fault Controls Its Secondary Faults Distribution and Dip Direction

NASA Astrophysics Data System (ADS)

Yang, H.; Moresi, L. N.

2017-12-01

The San Andreas fault forms a dominant component of the transform boundary between the Pacific and the North American plate. The density and strength of the complex accretionary margin is very heterogeneous. Based on the density structure of the lithosphere in the SW United States, we utilize the 3D finite element thermomechanical, viscoplastic model (Underworld2) to simulate deformation in the San Andreas Fault system. The purpose of the model is to examine the role of a big bend in the existing geometry. In particular, the big bend of the fault is an initial condition of in our model. We first test the strength of the fault by comparing the surface principle stresses from our numerical model with the in situ tectonic stress. The best fit model indicates the model with extremely weak fault (friction coefficient < 0.1) is requisite. To the first order, there is significant density difference between the Great Valley and the adjacent Mojave block. The Great Valley block is much colder and of larger density (>200 kg/m3) than surrounding blocks. In contrast, the Mojave block is detected to find that it has lost its mafic lower crust by other geophysical surveys. Our model indicates strong strain localization at the jointer boundary between two blocks, which is an analogue for the Garlock fault. High density lower crust material of the Great Valley tends to under-thrust beneath the Transverse Range near the big bend. This motion is likely to rotate the fault plane from the initial vertical direction to dip to the southwest. For the straight section, north to the big bend, the fault is nearly vertical. The geometry of the fault plane is consistent with field observations.

Structural expression of a rolling hinge in the footwall of the Brenner Line normal fault, eastern Alps

NASA Astrophysics Data System (ADS)

Axen, Gary J.; Bartley, John M.; Selverstone, Jane

1995-12-01

The kinematic and temporal sequence of structures observed to overprint mylonites along the Brenner Line low-angle normal fault may record passage of the footwall through two rolling hinges, at the top and bottom of a ramp in the shear zone. The structures comprise west down brittle and brittle-ductile structures and east down brittle structures. PT conditions of formation (250° to >400°C and 2-23 km depth), obtained from analysis of oriented fluid inclusion planes, indicate that west down structures were formed at greater depths and temperatures, and therefore earlier, than the east down structures. These data suggest that the brittle structures formed under conditions that permit crystal-plastic deformation at long-term geologic strain rates and therefore probably reflect transient rapid strain rates and/or high fluid pressure. Structures inferred to have formed at a lower hinge are consistent with viscous flow models of rolling-hinge deformation and support the concept of a crustal asthenosphere. Such high temperatures at shallow crustal depth also suggest significant upward advection of heat by extensional unroofing of warm rocks, which may have reduced the flexural rigidity of the footwall and thus affected mechanical behavior at the upper rolling hinge. Exposed mylonitic foliation within a few hundred meters of the Brenner line and on top of the east-west trending anticlines in the footwall dips ˜15° west. Our data favor a ramp dip of ˜25° but permit a dip as great as 45°. Fluid inclusion data suggest that structures related to the hinge at the base of the ramp formed at depths of 12-25 km. If the average dip of the Brenner shear zone to those depths was 20°, intermediate between the favored ramp dip and the dip of exposed foliation, then the horizontal component of slip could be as high as 33-63 km. The two discrete sets of structures with opposite shear senses, formed in the temporal sequence indicated by PT data, are consistent with subvertical

Methods to enhance seismic faults and construct fault surfaces

NASA Astrophysics Data System (ADS)

Wu, Xinming; Zhu, Zhihui

2017-10-01

Faults are often apparent as reflector discontinuities in a seismic volume. Numerous types of fault attributes have been proposed to highlight fault positions from a seismic volume by measuring reflection discontinuities. These attribute volumes, however, can be sensitive to noise and stratigraphic features that are also apparent as discontinuities in a seismic volume. We propose a matched filtering method to enhance a precomputed fault attribute volume, and simultaneously estimate fault strikes and dips. In this method, a set of efficient 2D exponential filters, oriented by all possible combinations of strike and dip angles, are applied to the input attribute volume to find the maximum filtering responses at all samples in the volume. These maximum filtering responses are recorded to obtain the enhanced fault attribute volume while the corresponding strike and dip angles, that yield the maximum filtering responses, are recoded to obtain volumes of fault strikes and dips. By doing this, we assume that a fault surface is locally planar, and a 2D smoothing filter will yield a maximum response if the smoothing plane coincides with a local fault plane. With the enhanced fault attribute volume and the estimated fault strike and dip volumes, we then compute oriented fault samples on the ridges of the enhanced fault attribute volume, and each sample is oriented by the estimated fault strike and dip. Fault surfaces can be constructed by directly linking the oriented fault samples with consistent fault strikes and dips. For complicated cases with missing fault samples and noisy samples, we further propose to use a perceptual grouping method to infer fault surfaces that reasonably fit the positions and orientations of the fault samples. We apply these methods to 3D synthetic and real examples and successfully extract multiple intersecting fault surfaces and complete fault surfaces without holes.

Fault orientations in extensional and conjugate strike-slip environments and their implications

USGS Publications Warehouse

Thatcher, W.; Hill, D.P.

1991-01-01

Seismically active conjugate strike-slip faults in California and Japan typically have mutually orthogonal right- and left-lateral fault planes. Normal-fault dips at earthquake nucleation depths are concentrated between 40?? and 50??. The observed orientations and their strong clustering are surprising, because conventional faulting theory suggests fault initiation with conjugate 60?? and 120?? intersecting planes and 60?? normal-fault dip or fault reactivation with a broad range of permitted orientations. The observations place new constraints on the mechanics of fault initiation, rotation, and evolutionary development. We speculate that the data could be explained by fault rotation into the observed orientations and deactivation for greater rotation or by formation of localized shear zones beneath the brittle-ductile transition in Earth's crust. Initiation as weak frictional faults seems unlikely. -Authors

Seismic reflection evidence for a northeast-dipping Hayward fault near Fremont, California: Implications for seismic hazard

USGS Publications Warehouse

Williams, R.A.; Simpson, R.W.; Jachens, R.C.; Stephenson, W.J.; Odum, J.K.; Ponce, D.A.

2005-01-01

A 1.6-km-long seismic reflection profile across the creeping trace of the southern Hayward fault near Fremont, California, images the fault to a depth of 650 m. Reflector truncations define a fault dip of about 70 degrees east in the 100 to 650 m depth range that projects upward to the creeping surface trace, and is inconsistent with a nearly vertical fault in this vicinity as previously believed. This fault projects to the Mission seismicity trend located at 4-10 km depth about 2 km east of the surface trace and suggests that the southern end of the fault is as seismically active as the part north of San Leandro. The seismic hazard implication is that the Hayward fault may have a more direct connection at depth with the Calaveras fault, affecting estimates of potential event magnitudes that could occur on the combined fault surfaces, thus affecting hazard assessments for the south San Francisco Bay region.

Normal fault earthquakes or graviquakes

PubMed Central

Doglioni, C.; Carminati, E.; Petricca, P.; Riguzzi, F.

2015-01-01

Earthquakes are dissipation of energy throughout elastic waves. Canonically is the elastic energy accumulated during the interseismic period. However, in crustal extensional settings, gravity is the main energy source for hangingwall fault collapsing. Gravitational potential is about 100 times larger than the observed magnitude, far more than enough to explain the earthquake. Therefore, normal faults have a different mechanism of energy accumulation and dissipation (graviquakes) with respect to other tectonic settings (strike-slip and contractional), where elastic energy allows motion even against gravity. The bigger the involved volume, the larger is their magnitude. The steeper the normal fault, the larger is the vertical displacement and the larger is the seismic energy released. Normal faults activate preferentially at about 60° but they can be shallower in low friction rocks. In low static friction rocks, the fault may partly creep dissipating gravitational energy without releasing great amount of seismic energy. The maximum volume involved by graviquakes is smaller than the other tectonic settings, being the activated fault at most about three times the hypocentre depth, explaining their higher b-value and the lower magnitude of the largest recorded events. Having different phenomenology, graviquakes show peculiar precursors. PMID:26169163

Three-dimensional geologic map of the Hayward fault, northern California: Correlation of rock unites with variations in seismicity, creep rate, and fault dip

USGS Publications Warehouse

Graymer, R.W.; Ponce, D.A.; Jachens, R.C.; Simpson, R.W.; Phelps, G.A.; Wentworth, C.M.

2005-01-01

In order to better understand mechanisms of active faults, we studied relationships between fault behavior and rock units along the Hayward fault using a three-dimensional geologic map. The three-dimensional map-constructed from hypocenters, potential field data, and surface map data-provided a geologic map of each fault surface, showing rock units on either side of the fault truncated by the fault. The two fault-surface maps were superimposed to create a rock-rock juxtaposition map. The three maps were compared with seismicity, including aseismic patches, surface creep, and fault dip along the fault, by using visuallization software to explore three-dimensional relationships. Fault behavior appears to be correlated to the fault-surface maps, but not to the rock-rock juxtaposition map, suggesting that properties of individual wall-rock units, including rock strength, play an important role in fault behavior. Although preliminary, these results suggest that any attempt to understand the detailed distribution of earthquakes or creep along a fault should include consideration of the rock types that abut the fault surface, including the incorporation of observations of physical properties of the rock bodies that intersect the fault at depth. ?? 2005 Geological Society of America.

The 2011 Hawthorne, Nevada, Earthquake Sequence; Shallow Normal Faulting

NASA Astrophysics Data System (ADS)

Smith, K. D.; Johnson, C.; Davies, J. A.; Agbaje, T.; Knezevic Antonijevic, S.; Kent, G.

2011-12-01

An energetic sequence of shallow earthquakes that began in early March 2011 in western Nevada, near the community of Hawthorne, has slowly decreased in intensity through mid-2011. To date about 1300 reviewed earthquake locations have been compiled; we have computed moment tensors for the larger earthquakes and have developed a set of high-precision locations for all reviewed events. The sequence to date has included over 50 earthquakes ML 3 and larger with the largest at Mw 4.6. Three 6-channel portable stations configured with broadband sensors and accelerometers were installed by April 20. Data from the portable instruments is telemetered through NSL's microwave backbone to Reno where it is integrated with regional network data for real-time notifications, ShakeMaps, and routine event analysis. The data is provided in real-time to NEIC, CISN and the IRIS DMC. The sequence is located in a remote area about 15-20 km southwest of Hawthorne in the footwall block of the Wassuk Range fault system. An initial concern was that the sequence might be associated with volcanic processes due to the proximity of late Quaternary volcanic flows; there have been no volcanic signatures observed in near source seismograms. An additional concern, as the sequence has proceeded, was a clear progression eastward toward the Wassuk Range front fault. The east dipping range bounding fault is capable of M 7+ events, and poses a significant hazard to the community of Hawthorne and local military facilities. The Hawthorne Army Depot is an ordinance storage facility and the nation's storage site for surplus mercury. The sequence is within what has been termed the 'Mina Deflection' of the Central Walker Lane Belt. Faulting along the Whiskey Flat section of the Wassuk front fault would be primarily down-to-the-east, with an E-W extension direction; moment tensors for the 2011 earthquake show a range of extension directions from E-W to NW-SE, suggesting a possible dextral component to the Wassuk

Elasto-plastic deformation and plate weakening due to normal faulting in the subducting plate along the Mariana Trench

NASA Astrophysics Data System (ADS)

Zhou, Zhiyuan; Lin, Jian

2018-06-01

We investigated variations in the elasto-plastic deformation of the subducting plate along the Mariana Trench through an analysis of flexural bending and normal fault characteristics together with geodynamic modeling. Most normal faults were initiated at the outer-rise region and grew toward the trench axis with strikes mostly subparallel to the local trench axis. The average trench relief and maximum fault throws were measured to be significantly greater in the southern region (5 km and 320 m, respectively) than the northern and central regions (2 km and 200 m). The subducting plate was modeled as an elasto-plastic slab subjected to tectonic loading at the trench axis. The calculated strain rates and velocities revealed an array of normal fault-like shear zones in the upper plate, resulting in significant faulting-induced reduction in the deviatoric stresses. We then inverted for solutions that best fit the observed flexural bending and normal faulting characteristics, revealing normal fault penetration to depths of 21, 20, and 32 km beneath the seafloor for the northern, central, and southern regions, respectively, which is consistent with the observed depths of the relocated normal faulting earthquakes in the central Mariana Trench. The calculated deeper normal faults of the southern region might lead to about twice as much water being carried into the mantle per unit trench length than the northern and central regions. We further calculated that normal faulting has reduced the effective elastic plate thickness Te by up to 52% locally in the southern region and 33% in both the northern and central regions. The best-fitting solutions revealed a greater apparent angle of the pulling force in the southern region (51-64°) than in the northern (22-35°) and central (20-34°) regions, which correlates with a general southward increase in the seismically-determined dip angle of the subducting slab along the Mariana Trench.

Apparent stress, fault maturity and seismic hazard for normal-fault earthquakes at subduction zones

USGS Publications Warehouse

Choy, G.L.; Kirby, S.H.

2004-01-01

The behavior of apparent stress for normal-fault earthquakes at subduction zones is derived by examining the apparent stress (?? a = ??Es/Mo, where E s is radiated energy and Mo is seismic moment) of all globally distributed shallow (depth, ?? 1 MPa) are also generally intraslab, but occur where the lithosphere has just begun subduction beneath the overriding plate. They usually occur in cold slabs near trenches where the direction of plate motion across the trench is oblique to the trench axis, or where there are local contortions or geometrical complexities of the plate boundary. Lower ??a (< 1 MPa) is associated with events occurring at the outer rise (OR) complex (between the OR and the trench axis), as well as with intracrustal events occurring just landward of the trench. The average apparent stress of intraslab-normal-fault earthquakes is considerably higher than the average apparent stress of interplate-thrust-fault earthquakes. In turn, the average ?? a of strike-slip earthquakes in intraoceanic environments is considerably higher than that of intraslab-normal-fault earthquakes. The variation of average ??a with focal mechanism and tectonic regime suggests that the level of ?? a is related to fault maturity. Lower stress drops are needed to rupture mature faults such as those found at plate interfaces that have been smoothed by large cumulative displacements (from hundreds to thousands of kilometres). In contrast, immature faults, such as those on which intraslab-normal-fault earthquakes generally occur, are found in cold and intact lithosphere in which total fault displacement has been much less (from hundreds of metres to a few kilometres). Also, faults on which high ??a oceanic strike-slip earthquakes occur are predominantly intraplate or at evolving ends of transforms. At subduction zones, earthquakes occurring on immature faults are likely to be more hazardous as they tend to generate higher amounts of radiated energy per unit of moment than

How do normal faults grow?

NASA Astrophysics Data System (ADS)

Jackson, Christopher; Bell, Rebecca; Rotevatn, Atle; Tvedt, Anette

2016-04-01

Normal faulting accommodates stretching of the Earth's crust, and it is arguably the most fundamental tectonic process leading to continent rupture and oceanic crust emplacement. Furthermore, the incremental and finite geometries associated with normal faulting dictate landscape evolution, sediment dispersal and hydrocarbon systems development in rifts. Displacement-length scaling relationships compiled from global datasets suggest normal faults grow via a sympathetic increase in these two parameters (the 'isolated fault model'). This model has dominated the structural geology literature for >20 years and underpins the structural and tectono-stratigraphic models developed for active rifts. However, relatively recent analysis of high-quality 3D seismic reflection data suggests faults may grow by rapid establishment of their near-final length prior to significant displacement accumulation (the 'coherent fault model'). The isolated and coherent fault models make very different predictions regarding the tectono-stratigraphic evolution of rift basin, thus assessing their applicability is important. To-date, however, very few studies have explicitly set out to critically test the coherent fault model thus, it may be argued, it has yet to be widely accepted in the structural geology community. Displacement backstripping is a simple graphical technique typically used to determine how faults lengthen and accumulate displacement; this technique should therefore allow us to test the competing fault models. However, in this talk we use several subsurface case studies to show that the most commonly used backstripping methods (the 'original' and 'modified' methods) are, however, of limited value, because application of one over the other requires an a priori assumption of the model most applicable to any given fault; we argue this is illogical given that the style of growth is exactly what the analysis is attempting to determine. We then revisit our case studies and demonstrate

The regional structural setting of the 2008 Wells earthquake and Town Creek Flat Basin: implications for the Wells earthquake fault and adjacent structures

USGS Publications Warehouse

Henry, Christopher S.; Colgan, Joseph P.

2011-01-01

The 2008 Wells earthquake occurred on a northeast-striking, southeast-dipping fault that is clearly delineated by the aftershock swarm to a depth of 10-12 km below sea level. However, Cenozoic rocks and structures around Wells primarily record east-west extension along north- to north-northeast-striking, west-dipping normal faults that formed during the middle Miocene. These faults are responsible for the strong eastward tilt of most basins and ranges in the area, including the Town Creek Flat basin (the location of the earthquake) and the adjacent Snake Mountains and western Windermere Hills. These older west-dipping faults are locally overprinted by a younger generation of east-dipping, high-angle normal faults that formed as early as the late Miocene and have remained active into the Quaternary. The most prominent of these east-dipping faults is the set of en-échelon, north-striking faults that bounds the east sides of the Ruby Mountains, East Humboldt Range, and Clover Hill (about 5 km southwest of Wells). The northeastern-most of these faults, the Clover Hill fault, projects northward along strike toward the Snake Mountains and the approximately located surface projection of the Wells earthquake fault as defined by aftershock locations. The Clover Hill fault also projects toward a previously unrecognized, east-facing Quaternary fault scarp and line of springs that appear to mark a significant east-dipping normal fault along the western edge of Town Creek Flat. Both western and eastern projections may be northern continuations of the Clover Hill fault. The Wells earthquake occurred along this east-dipping fault system. Two possible alternatives to rupture of a northern continuation of the Clover Hill fault are that the earthquake fault (1) is antithetic to an active west-dipping fault or (2) reactivated a Mesozoic thrust fault that dips east as a result of tilting by the west-dipping faults along the west side of the Snake Mountains. Both alternatives are

Pseudotachylyte: Reading the Record of Paleoseismicity in Low-Angle Normal Faults

NASA Astrophysics Data System (ADS)

Smith, D. M.; Goodwin, L. B.; Feinberg, J. M.; Ellis, A. P.

2012-12-01

Whether or not low-angle normal faults (LANFs, dipping <30°) can produce earthquakes is hotly debated. Pseudotachylyte - rapidly quenched frictional melt generated during seismic failure - has been noted in several LANF sites but not extensively studied. We recently documented significant pseudotachylyte exposures in both the South Mountains and Catalina-Rincon metamorphic core complexes of Arizona. In both field areas, pseudotachylyte is located below detachment faults, where it is best exposed in fractured areas beneath chlorite breccia zones. Generation veins dip 7-24°, are locally parallel to host rock foliations, and range from 1 mm to 3 cm thick. Where subvertical exposures are available, generation and injection veins either form networks up to 1 m thick or are stacked, such that multiple veins spaced < 1m apart are exposed in zones 2 to 3 m thick. Outcrops do not permit mapping of pseudotachylytes' full lateral extent, but do allow a minimum length of 50 m oblique to strike to be estimated. The magnitude of pseudotachylyte exposure in these core complexes implies significant seismicity. A key question is whether the generation surfaces were in their present orientations when they failed seismically. To answer this, we are applying a fault paleogeometry test. The cornerstone of this test is a comparison of two paleomagnetic vectors. The first will be determined through standard paleomagnetic analyses of oriented pseudotachylyte samples. The second will represent the vector expected if no LANF rotation has occurred and will be determined through correlation of a sample's 40Ar/39Ar age with its coeval magnetic pole location. Any discrepancy between the vectors will be interpreted to represent rotation of the fault since seismicity. Anderson-Byerlee compatible slip will be supported by discrepancies requiring a seismically active dip >30°. An active dip of <30° suggests that additional factors have reduced effective stress and/or frictional resistance to

Fault-zone structure and weakening processes in basin-scale reverse faults: The Moonlight Fault Zone, South Island, New Zealand

NASA Astrophysics Data System (ADS)

Alder, S.; Smith, S. A. F.; Scott, J. M.

2016-10-01

The >200 km long Moonlight Fault Zone (MFZ) in southern New Zealand was an Oligocene basin-bounding normal fault zone that reactivated in the Miocene as a high-angle reverse fault (present dip angle 65°-75°). Regional exhumation in the last c. 5 Ma has resulted in deep exposures of the MFZ that present an opportunity to study the structure and deformation processes that were active in a basin-scale reverse fault at basement depths. Syn-rift sediments are preserved only as thin fault-bound slivers. The hanging wall and footwall of the MFZ are mainly greenschist facies quartzofeldspathic schists that have a steeply-dipping (55°-75°) foliation subparallel to the main fault trace. In more fissile lithologies (e.g. greyschists), hanging-wall deformation occurred by the development of foliation-parallel breccia layers up to a few centimetres thick. Greyschists in the footwall deformed mainly by folding and formation of tabular, foliation-parallel breccias up to 1 m wide. Where the hanging-wall contains more competent lithologies (e.g. greenschist facies metabasite) it is laced with networks of pseudotachylyte that formed parallel to the host rock foliation in a damage zone extending up to 500 m from the main fault trace. The fault core contains an up to 20 m thick sequence of breccias, cataclasites and foliated cataclasites preserving evidence for the progressive development of interconnected networks of (partly authigenic) chlorite and muscovite. Deformation in the fault core occurred by cataclasis of quartz and albite, frictional sliding of chlorite and muscovite grains, and dissolution-precipitation. Combined with published friction and permeability data, our observations suggest that: 1) host rock lithology and anisotropy were the primary controls on the structure of the MFZ at basement depths and 2) high-angle reverse slip was facilitated by the low frictional strength of fault core materials. Restriction of pseudotachylyte networks to the hanging-wall of the

High resolution t-LiDAR scanning of an active bedrock fault scarp for palaeostress analysis

NASA Astrophysics Data System (ADS)

Reicherter, Klaus; Wiatr, Thomas; Papanikolaou, Ioannis; Fernández-Steeger, Tomas

2013-04-01

Palaeostress analysis of an active bedrock normal fault scarp based on kinematic indicators is carried applying terrestrial laser scanning (t-LiDAR or TLS). For this purpose three key elements are necessary for a defined region on the fault plane: (i) the orientation of the fault plane, (ii) the orientation of the slickenside lineation or other kinematic indicators and (iii) the sense of motion of the hanging wall. We present a workflow to obtain palaeostress data from point cloud data using terrestrial laser scanning. The entire case-study was performed on a continuous limestone bedrock normal fault scarp on the island of Crete, Greece, at four different locations along the WNW-ESE striking Spili fault. At each location we collected data with a mobile terrestrial light detection and ranging system and validated the calculated three-dimensional palaeostress results by comparison with the conventional palaeostress method with compass at three of the locations. Numerous kinematics indicators for normal faulting were discovered on the fault plane surface using t-LiDAR data and traditional methods, like Riedel shears, extensional break-outs, polished corrugations and many more. However, the kinematic indicators are more or less unidirectional and almost pure dip-slip. No oblique reactivations have been observed. But, towards the tips of the fault, inclination of the striation tends to point towards the centre of the fault. When comparing all reconstructed palaeostress data obtained from t-LiDAR to that obtained through manual compass measurements, the degree of fault plane orientation divergence is around ±005/03 for dip direction and dip. The degree of slickenside lineation variation is around ±003/03 for dip direction and dip. Therefore, the percentage threshold error of the individual vector angle at the different investigation site is lower than 3 % for the dip direction and dip for planes, and lower than 6 % for strike. The maximum mean variation of the complete

Spatiotemporal analysis of Quaternary normal faults in the Northern Rocky Mountains, USA

NASA Astrophysics Data System (ADS)

Davarpanah, A.; Babaie, H. A.; Reed, P.

2010-12-01

, are located. The GIS based autocorrelation method, applied to the trace orientation, length, frequency, and spatial distribution for each age-defined fault set, revealed spatial homogeneity for each specific set. The results of the method of Moran`sI and Geary`s C show no spatial autocorrelation among the trend of the fault traces and their location. Our results suggest that while lineaments of similar age define a clustered pattern in each domain, the overall distribution pattern of lineaments with different ages seems to be non-uniform (random). The directional distribution analysis reveals a distinct range of variation for fault traces of different ages (i.e., some displaying ellipsis behavior). Among the Quaternary normal fault sets, the youngest lineament set (i.e., last 150 years) defines the greatest ellipticity (eccentricity) and the least lineaments distribution variation. The frequency rose diagram for the entire Quaternary normal faults, shows four major modes (around 360o, 330o, 300o, and 270o), and two minor modes (around 235 and 205).

First-order and subsidiary faults controlling the time-space evolution of the Central Italy 2016 seismic sequence - a multi-source data detailed 3D reconstruction

NASA Astrophysics Data System (ADS)

Lavecchia, Giusy; de nardis, Rita; Ferrarini, Federica; Cirillo, Daniele; Brozzetti, Francesco

2017-04-01

. At the light of the reconstructed geometric pattern integrated with the evidences of primary co-seismic fractures, it results evident that the Central Italy seismic sequence represents a "classic", although complex, intra-Apennine normal-faulting event, reactivating a long-term quiescent seismogenic alignment (e.g. VEGO). The reactivated and inverted compressional structures are confined at shallow depth within the Vettore footwall, and in no way control the major events of the sequence. Conversely, an important regional role is played by the east-dipping detachment. It represents the missing geometric link between the Altotiberina LANF of northern Umbria and the recently discovered LANF of Latium-Abruzzi.

Tectono-stratigraphic evolution of normal fault zones: Thal Fault Zone, Suez Rift, Egypt

NASA Astrophysics Data System (ADS)

Leppard, Christopher William

The evolution of linkage of normal fault populations to form continuous, basin bounding normal fault zones is recognised as an important control on the stratigraphic evolution of rift-basins. This project aims to investigate the temporal and spatial evolution of normal fault populations and associated syn-rift deposits from the initiation of early-formed, isolated normal faults (rift-initiation) to the development of a through-going fault zone (rift-climax) by documenting the tectono-stratigraphic evolution of the Sarbut EI Gamal segment of the exceptionally well-exposed Thai fault zone, Suez Rift, Egypt. A number of dated stratal surfaces mapped around the syn-rift depocentre of the Sarbut El Gamal segment allow constraints to be placed on the timing and style of deformation, and the spatial variability of facies along this segment of the fault zone. Data collected indicates that during the first 3.5 My of rifting the structural style was characterised by numerous, closely spaced, short (< 3 km), low displacement (< 200 m) synthetic and antithetic normal faults within 1 - 2 km of the present-day fault segment trace, accommodating surface deformation associated with the development of a fault propagation monocline above the buried, pre-cursor strands of the Sarbut El Gamal fault segment. The progressive localisation of displacement onto the fault segment during rift-climax resulted in the development of a major, surface-breaking fault 3.5 - 5 My after the onset of rifting and is recorded by the death of early-formed synthetic and antithetic faults up-section, and thickening of syn-rift strata towards the fault segment. The influence of intrabasinal highs at the tips of the Sarbut EI Gamal fault segment on the pre-rift sub-crop level, combined with observations from the early-formed structures and coeval deposits suggest that the overall length of the fault segment was fixed from an early stage. The fault segment is interpreted to have grown through rapid lateral

Modeling the effect of preexisting joints on normal fault geometries using a brittle and cohesive material

NASA Astrophysics Data System (ADS)

Kettermann, M.; van Gent, H. W.; Urai, J. L.

2012-04-01

, stereo-photography at the final stage of deformation enabled the creation of 3D models to preserve basic geometric information. The models showed that at the surface the deformation localized always along preexisting joints, even when they strike at an angle to the basement-fault. In most cases faults intersect precisely at the maximum depth of the joints. With increasing fault-joint angle the deformation occurred distributed over several joints by forming stepovers with fractures oriented normal to the strike of the joints. No fractures were observed parallel to the basement fault. At low angles stepovers coincided with wedge-shaped structures between two joints that remain higher than the surrounding joint-fault intersection. The wide opening gap along the main fault allowed detailed observations of the fault planes at depth, which revealed (1) changing dips according to joint-fault angles, (2) slickenlines, (3) superimposed steepening fault-planes, causing sharp sawtooth-shaped structures. Comparison to a field analogue at Canyonlands National Park, Utah/USA showed similar structures and features such as vertical fault escarpments at the surface coinciding with joint-surfaces. In the field and in the models stepovers were observed as well as conjugate faulting and incremental fault-steepening.

Neotectonic Geomorphology of the Owen Stanley Oblique-slip Fault System, Eastern Papua New Guinea

NASA Astrophysics Data System (ADS)

Watson, L.; Mann, P.; Taylor, F.

2003-12-01

Previous GPS studies have shown that the Australia-Woodlark plate boundary bisects the Papuan Peninsula of Papua New Guinea and that interplate motion along the boundary varies from about 19 mm/yr of orthogonal opening in the area of the western Woodlark spreading center and D'Entrecasteaux Islands, to about 12 mm/yr of highly oblique opening in the central part of the peninsula, to about 10 mm/yr of transpressional motion on the western part of the peninsula. We have compiled a GIS database for the peninsula that includes a digital elevation model, geologic map, LANDSAT and radar imagery, and earthquake focal mechanisms. This combined data set demonstrates the regional importance of the 600-km-long Owen Stanley fault system (OSFS) in accommodating interplate motion and controlling the geomorphology and geologic exposures of the peninsula. The OSFS originated as a NE-dipping, reactivated Oligocene-Early Miocene age ophiolitic suture zone between an Australian continental margin and the Melanesian arc system. Pliocene to recent motion on the plate boundary has reactivated motion on the former NE-dipping thrust fault either as a NE-dipping normal fault in the eastern area or as a more vertical strike-slip fault in the western area. The broadly arcuate shape of the OSFS is probably an inherited feature from the original thrust fault. Faults in the eastern area (east of 148° E) exhibit characteristics expected for normal and oblique slip faults including: discontinuous fault traces bounding an upthrown highland block and a downthrown coastal plain or submarine block, transfer faults parallel to the opening direction, scarps facing to both the northeast and southwest, and spatial association with recent volcanism. Faults in the western area (west of 148° E) exibit characteristics expected for left-lateral strike-slip faults including: linear and continuous fault trace commonly confined to a deep, intermontane valley and sinistral offsets and deflections of rivers and

How Do Normal Faults Grow?

NASA Astrophysics Data System (ADS)

Jackson, C. A. L.; Bell, R. E.; Rotevatn, A.; Tvedt, A. B. M.

2015-12-01

Normal faulting accommodates stretching of the Earth's crust and is one of the fundamental controls on landscape evolution and sediment dispersal in rift basins. Displacement-length scaling relationships compiled from global datasets suggest normal faults grow via a sympathetic increase in these two parameters (the 'isolated fault model'). This model has dominated the structural geology literature for >20 years and underpins the structural and tectono-stratigraphic models developed for active rifts. However, relatively recent analysis of high-quality 3D seismic reflection data suggests faults may grow by rapid establishment of their near-final length prior to significant displacement accumulation (the 'coherent fault model'). The isolated and coherent fault models make very different predictions regarding the tectono-stratigraphic evolution of rift basin, thus assessing their applicability is important. To-date, however, very few studies have explicitly set out to critically test the coherent fault model thus, it may be argued, it has yet to be widely accepted in the structural geology community. Displacement backstripping is a simple graphical technique typically used to determine how faults lengthen and accumulate displacement; this technique should therefore allow us to test the competing fault models. However, in this talk we use several subsurface case studies to show that the most commonly used backstripping methods (the 'original' and 'modified' methods) are, however, of limited value, because application of one over the other requires an a priori assumption of the model most applicable to any given fault; we argue this is illogical given that the style of growth is exactly what the analysis is attempting to determine. We then revisit our case studies and demonstrate that, in the case of seismic-scale growth faults, growth strata thickness patterns and relay zone kinematics, rather than displacement backstripping, should be assessed to directly constrain

Dips, ramps, and rolls- Evidence for paleotopographic and syn-depositional fault control on the Western Kentucky No. 4 coal bed, tradewater formation (Bolsovian) Illinois Basin

USGS Publications Warehouse

Greb, S.F.; Eble, C.F.; Williams, D.A.; Nelson, W.J.

2001-01-01

The Western Kentucky No. 4 coal is a high-volatile B to high-volatile C bituminous coal that has been heavily mined along the southern margin of the Western Kentucky Coal Field. The seam has a reputation for rolling floor elevation. Elongate trends of floor depressions are referred to as "dips" and "rolls" by miners. Some are relatively narrow and straight to slightly curvilinear in plan view, with generally symmetric to slightly asymmetric cross-sections. Others are broader and asymmetric in section, with sharp dips on one limb and gradual, ramp-like dips on the other. Some limbs change laterally from gradual dip, to sharp dip, to offset of the coal. Lateral changes in the rate of floor elevation dip are often associated with changes in coal thickness, and in underground mines, changes in floor elevation are sometimes associated with roof falls and haulage problems. In order to test if coal thickness changes within floor depressions were associated with changes in palynology, petrography and coal quality, the coal was sampled at a surface mine across a broad. ramp-like depression that showed down-dip coal thickening. Increment samples of coal from a thick (150 cm), down-ramp and thinner (127 cm), up-ramp position at one surface mine correlate well between sample sites (a distance of 60 m) except for a single increment. The anomalous increment (31 cm) in the lower-middle part of the thick coal bed contained 20% more Lycospora orbicula spores. The rolling floor elevations noted in the study mines are inferred to have been formed as a result of pre-peat paleotopographic depressions, syn-depositional faulting, fault-controlled pre-peat paleotopography, and from compaction beneath post-depositional channels and slumps. Although the association of thick coal with linear trends and inferred faults has been used in other basins to infer syn-depositional faulting, changes in palynology within increment samples of the seam along a structural ramp in this study provide

Fault zone processes in mechanically layered mudrock and chalk

NASA Astrophysics Data System (ADS)

Ferrill, David A.; Evans, Mark A.; McGinnis, Ronald N.; Morris, Alan P.; Smart, Kevin J.; Wigginton, Sarah S.; Gulliver, Kirk D. H.; Lehrmann, Daniel; de Zoeten, Erich; Sickmann, Zach

2017-04-01

A 1.5 km long natural cliff outcrop of nearly horizontal Eagle Ford Formation in south Texas exposes northwest and southeast dipping normal faults with displacements of 0.01-7 m cutting mudrock, chalk, limestone, and volcanic ash. These faults provide analogs for both natural and hydraulically-induced deformation in the productive Eagle Ford Formation - a major unconventional oil and gas reservoir in south Texas, U.S.A. - and other mechanically layered hydrocarbon reservoirs. Fault dips are steep to vertical through chalk and limestone beds, and moderate through mudrock and clay-rich ash, resulting in refracted fault profiles. Steeply dipping fault segments contain rhombohedral calcite veins that cross the fault zone obliquely, parallel to shear segments in mudrock. The vertical dimensions of the calcite veins correspond to the thickness of offset competent beds with which they are contiguous, and the slip parallel dimension is proportional to fault displacement. Failure surface characteristics, including mixed tensile and shear segments, indicate hybrid failure in chalk and limestone, whereas shear failure predominates in mudrock and ash beds - these changes in failure mode contribute to variation in fault dip. Slip on the shear segments caused dilation of the steeper hybrid segments. Tabular sheets of calcite grew by repeated fault slip, dilation, and cementation. Fluid inclusion and stable isotope geochemistry analyses of fault zone cements indicate episodic reactivation at 1.4-4.2 km depths. The results of these analyses document a dramatic bed-scale lithologic control on fault zone architecture that is directly relevant to the development of porosity and permeability anisotropy along faults.

Active tectonic extension across the Alto Tiberina normal fault system from GPS data modeling and InSAR velocity maps: new perspectives within TABOO Near Fault Observatory

NASA Astrophysics Data System (ADS)

Vadacca, Luigi; Anderlini, Letizia; Casarotti, Emanuele; Serpelloni, Enrico; Chiaraluce, Lauro; Polcari, Marco; Albano, Matteo; Stramondo, Salvatore

2014-05-01

The Alto Tiberina fault (ATF) is a low-angle (east-dipping at 15°) normal fault (LANF) 70 km long placed in the Umbria-Marche Apennines (central Italy), characterized by SW-NE oriented extension occurring at rates of 2-3 mm/yr. These rates were measured by continuous GPS stations belonging to several networks, which are denser in the study area thanks to additional sites recently installed in the framework of the INGV national RING network and of the ATF observatory. In this area historical and instrumental earthquakes mainly occur on west-dipping high-angle normal faults. Within this context the ATF has accumulated 2 km of displacement over the past 2 Ma, but at the same time the deformation processes active along this misoriented fault, as well as its mechanical behavior, are still unknown. We tackle this issue by solving for interseismic deformation models obtained by two different methods. At first, through the 2D and 3D finite element modeling, we define the effects of locking depth, synthetic and antithetic fault activity and lithology on the velocity gradient measured along the ATF system. Subsequently through a block modeling approach, we model the GPS velocities by considering the major fault systems as bounds of rotating blocks, while estimating the corresponding geodetic fault slip-rates and maps of heterogeneous fault coupling. Thanks to the latest imaging of the ATF deep structure obtained from seismic profiles, we improve the proposed models by modeling the fault as a complex rough surface to understand where the stress accumulations are located and the interseismic coupling changes. The preliminary results obtained show firstly that the observed extension is mainly accommodated by interseismic deformation on both the ATF and antithetic faults, highlighting the important role of this LANF inside an active tectonic contest. Secondarily, using the ATF surface "topography", we find an interesting correlation between microseismicty and creeping portions

Automatic fault tracing of active faults in the Sutlej valley (NW-Himalayas, India)

NASA Astrophysics Data System (ADS)

Janda, C.; Faber, R.; Hager, C.; Grasemann, B.

2003-04-01

In the Sutlej Valley the Lesser Himalayan Crystalline Sequence (LHCS) is actively extruding between the Munsiari Thrust (MT) at the base, and the Karcham Normal Fault (KNF) at the top. The clear evidences for ongoing deformation are brittle faults in Holocene lake deposits, hot springs activity near the faults and dramatically younger cooling ages within the LHCS (Vannay and Grasemann, 2001). Because these brittle fault zones obviously influence the morphology in the field we developed a new method for automatically tracing the intersections of planar fault geometries with digital elevation models (Faber, 2002). Traditional mapping techniques use structure contours (i.e. lines or curves connecting points of equal elevation on a geological structure) in order to construct intersections of geological structures with topographic maps. However, even if the geological structure is approximated by a plane and therefore structure contours are equally spaced lines, this technique is rather time consuming and inaccurate, because errors are cumulative. Drawing structure contours by hand makes it also impossible to slightly change the azimuth and dip direction of the favoured plane without redrawing everything from the beginning on. However, small variations of the fault position which are easily possible by either inaccuracies of measurement in the field or small local variations in the trend and/or dip of the fault planes can have big effects on the intersection with topography. The developed method allows to interactively view intersections in a 2D and 3D mode. Unlimited numbers of planes can be moved separately in 3 dimensions (translation and rotation) and intersections with the topography probably following morphological features can be mapped. Besides the increase of efficiency this method underlines the shortcoming of classical lineament extraction ignoring the dip of planar structures. Using this method, areas of active faulting influencing the morphology, can be

Subsurface structures of the active reverse fault zones in Japan inferred from gravity anomalies.

NASA Astrophysics Data System (ADS)

Matsumoto, N.; Sawada, A.; Hiramatsu, Y.; Okada, S.; Tanaka, T.; Honda, R.

2016-12-01

The object of our study is to examine subsurface features such as continuity, segmentation and faulting type, of the active reverse fault zones. We use the gravity data published by the Gravity Research Group in Southwest Japan (2001), the Geographical Survey Institute (2006), Yamamoto et al. (2011), Honda et al. (2012), and the Geological Survey of Japan, AIST (2013) in this study. We obtained the Bouguer anomalies through terrain corrections with 10 m DEM (Sawada et al. 2015) under the assumed density of 2670 kg/m3, a band-pass filtering, and removal of linear trend. Several derivatives and structural parameters calculated from a gravity gradient tensor are applied to highlight the features, such as a first horizontal derivatives (HD), a first vertical derivatives (VD), a normalized total horizontal derivative (TDX), a dip angle (β), and a dimensionality index (Di). We analyzed 43 reverse fault zones in northeast Japan and the northern part of southwest Japan among major active fault zones selected by Headquarters for Earthquake Research Promotion. As the results, the subsurface structural boundaries clearly appear along the faults at 21 faults zones. The weak correlations appear at 13 fault zones, and no correlations are recognized at 9 fault zones. For example, in the Itoigawa-Shizuoka tectonic line, the subsurface structure boundary seems to extend further north than the surface trace. Also, a left stepping structure of the fault around Hakuba is more clearly observed with HD. The subsurface structures, which detected as the higher values of HD, are distributed on the east side of the surface rupture in the north segments and on the west side in the south segments, indicating a change of the dip direction, the east dipping to the west dipping, from north to south. In the Yokote basin fault zone, the subsurface structural boundary are clearly detected with HD, VD and TDX along the fault zone in the north segment, but less clearly in the south segment. Also, Di

The influence of topographic stresses on faulting, emphasizing the 2008 Wenchuan, China earthquake rupture

NASA Astrophysics Data System (ADS)

Styron, R. H.; Hetland, E. A.; Zhang, G.

2013-12-01

distribution, considering several published fault models. These models differ primarily in slip magnitude and planar vs. listric fault geometry at depth. Preliminary results indicate that topographic stresses are generally resistive to tectonic deformation, especially above ~10 km depth, where the faults are steep in all models. Down-dip topographic shear stresses on the fault are normal sense where the faults dip steeply, and reach 20 MPa on the fault beneath the Pengguan massif. Reverse-sense shear up to ~15 MPa is present on gently-dipping thrust flats at depth on listric fault models. Strike-slip shear stresses are sinistral on the steep, upper portions of faults but may be dextral on thrust flats. Topographic normal stress on the faults reaches ~80 MPa on thrust ramps and may be higher on flats. Coseismic slip magnitude is negatively correlated with topographic normal and down-dip shear stresses. The spatial patterns of topographic stresses and slip suggest that topographic stresses have significantly suppressed slip in certain areas: slip maxima occur in areas of locally lower topographic stresses, while areas of higher down-dip shear and normal stress show less slip than adjacent regions.

A Classification of Geometric Styles for Paleoseismic Trenches across Normal Faults in the North Island, New Zealand: An Interplay between Tectonic and Erosional/Depositional Processes

NASA Astrophysics Data System (ADS)

Villamor, P.; Berryman, K.; Langridge, R.; van Dissen, R.; Persaud, M.; Canora, C.; Nicol, A.; Alloway, B.; Litchfield, N.; Cochran, U.; Stirling, M.; Mouslopoulou, V.; Wilson, K.

2006-12-01

Over the last ~15 years we have excavated 73 trenches across active normal faults in the Taupo and Hauraki Rifts, North Island, New Zealand. The stratigraphy in these trenches is quite similar because of the predominance of volcanic and volcanic-derived deposits, sourced from the active Taupo Volcanic Zone. These deposits, whether alluvial (reworked, mainly volcanics) or volcanic (tephra), are all characterized by relative loose, to moderately loose, medium-size gravel and sands, and cohesive (sticky) clays. The homogeneity of the materials and of the sedimentation rates across these paleoseismic trenches has allowed us to assess the influence of different materials on the faulting style. The predominant types of material, their relative thickness, and their stratigraphic order (e.g. whether cohesive materials are overlying or underlying loose materials) in the trench strongly determine the deformation style when subjected to normal faulting. However, the final geometric relation between the sedimentary layers and the faults also depends on the sediment depositional environment (e.g., alluvial vs air fall deposition), the fault dip, and cumulative displacement (i.e., the size of the scarp). For example, the cumulative displacement of the fault conditions the amount of erosion/deposition at/derived from the scarp itself. When we combine observations from the tectonic deformation style and from geometries derived from erosional/depositional processes, we can define at least five "geometric styles" present in paleoseismic trenches in our study area: 1) folding, where the fault does not reach the upper layers, and relative displacement of the fault walls is achieved by folding (dragging of the layer); 2) folding-large cracks, where relative movement of the fault walls is achieved by folding and opening of large fissures; 3) faulting, the most common style where a layer is displaced along the fault plane; 4) faulting- erosion, similar to the previous style but with

Taking apart the Big Pine fault: Redefining a major structural feature in southern California

USGS Publications Warehouse

Onderdonk, N.W.; Minor, S.A.; Kellogg, K.S.

2005-01-01

New mapping along the Big Pine fault trend in southern California indicates that this structural alignment is actually three separate faults, which exhibit different geometries, slip histories, and senses of offset since Miocene time. The easternmost fault, along the north side of Lockwood Valley, exhibits left-lateral reverse Quaternary displacement but was a north dipping normal fault in late Oligocene to early Miocene time. The eastern Big Pine fault that bounds the southern edge of the Cuyama Badlands is a south dipping reverse fault that is continuous with the San Guillermo fault. The western segment of the Big Pine fault trend is a north dipping thrust fault continuous with the Pine Mountain fault and delineates the northern boundary of the rotated western Transverse Ranges terrane. This redefinition of the Big Pine fault differs greatly from the previous interpretation and significantly alters regional tectonic models and seismic risk estimates. The outcome of this study also demonstrates that basic geologic mapping is still needed to support the development of geologic models. Copyright 2005 by the American Geophysical Union.

Vertical deformation associated with normal fault systems evolved over coseismic, postseismic, and multiseismic periods

USGS Publications Warehouse

Thompson, George A.; Parsons, Thomas E.

2016-01-01

Vertical deformation of extensional provinces varies significantly and in seemingly contradictory ways. Sparse but robust geodetic, seismic, and geologic observations in the Basin and Range province of the western United States indicate that immediately after an earthquake, vertical change primarily occurs as subsidence of the normal fault hanging wall. A few decades later, a ±100 km wide zone is symmetrically uplifted. The preserved topography of long-term rifting shows bent and tilted footwall flanks rising high above deep basins. We develop finite element models subjected to extensional and gravitational forces to study time-varying deformation associated with normal faulting. We replicate observations with a model that has a weak upper mantle overlain by a stronger lower crust and a breakable elastic upper crust. A 60° dipping normal fault cuts through the upper crust and extends through the lower crust to simulate an underlying shear zone. Stretching the model under gravity demonstrates that asymmetric slip via collapse of the hanging wall is a natural consequence of coseismic deformation. Focused flow in the upper mantle imposed by deformation of the lower crust localizes uplift under the footwall; the breakable upper crust is a necessary model feature to replicate footwall bending over the observed width ( < 10 km), which is predicted to take place within 1-2 decades after each large earthquake. Thus the best-preserved topographic signature of rifting is expected to occur early in the postseismic period. The relatively stronger lower crust in our models is necessary to replicate broader postseismic uplift that is observed geodetically in subsequent decades.

Effects of lateral variations of crustal rheology on the occurrence of post-orogenic normal faults: The Alto Tiberina Fault (Northern Apennines, Central Italy)

NASA Astrophysics Data System (ADS)

Pauselli, Cristina; Ranalli, Giorgio

2017-11-01

The Northern Apennines (NA) are characterized by formerly compressive structures partly overprinted by subsequent extensional structures. The area of extensional tectonics migrated eastward since the Miocene. The youngest and easternmost major expression of extension is the Alto Tiberina Fault (ATF). We estimate 2D rheological profiles across the NA, and conclude that lateral rheological crustal variations have played an important role in the formation of the ATF and similar previously active faults to the west. Lithospheric delamination and mantle degassing resulted in an easterly-migrating extension-compression boundary, coinciding at present with the ATF, where (i) the thickness of the upper crust brittle layer reaches a maximum; (ii) the critical stress difference required to initiate faulting at the base of the brittle layer is at a minimum; and (iii) the total strengths of both the brittle layer and the whole lithosphere are at a minimum. Although the location of the fault is correlated with lithospheric rheological properties, the rheology by itself does not account for the low dip ( 20°) of the ATF. Two hypotheses are considered: (a) the low dip of the ATF is related to a rotation of the stress tensor at the time of initiation of the fault, caused by a basal shear stress ( 100 MPa) possibly related to corner flow associated with delamination; or (b) the low dip is associated to low values of the friction coefficient (≤ 0.5) coupled with high pore pressures related to mantle degassing. Our results establishing the correlation between crustal rheology and the location of the ATF are relatively robust, as we have examined various possible compositions and rheological parameters. They also provide possible general indications on the mechanisms of localized extension in post-orogenic extensional setting. The hypotheses to account for the low dip of the ATF, on the other hand, are intended simply to suggest possible solutions worthy of further study.

The SCEC 3D Community Fault Model (CFM-v5): An updated and expanded fault set of oblique crustal deformation and complex fault interaction for southern California

NASA Astrophysics Data System (ADS)

Nicholson, C.; Plesch, A.; Sorlien, C. C.; Shaw, J. H.; Hauksson, E.

2014-12-01

Southern California represents an ideal natural laboratory to investigate oblique deformation in 3D owing to its comprehensive datasets, complex tectonic history, evolving components of oblique slip, and continued crustal rotations about horizontal and vertical axes. As the SCEC Community Fault Model (CFM) aims to accurately reflect this 3D deformation, we present the results of an extensive update to the model by using primarily detailed fault trace, seismic reflection, relocated hypocenter and focal mechanism nodal plane data to generate improved, more realistic digital 3D fault surfaces. The results document a wide variety of oblique strain accommodation, including various aspects of strain partitioning and fault-related folding, sets of both high-angle and low-angle faults that mutually interact, significant non-planar, multi-stranded faults with variable dip along strike and with depth, and active mid-crustal detachments. In places, closely-spaced fault strands or fault systems can remain surprisingly subparallel to seismogenic depths, while in other areas, major strike-slip to oblique-slip faults can merge, such as the S-dipping Arroyo Parida-Mission Ridge and Santa Ynez faults with the N-dipping North Channel-Pitas Point-Red Mountain fault system, or diverge with depth. Examples of the latter include the steep-to-west-dipping Laguna Salada-Indiviso faults with the steep-to-east-dipping Sierra Cucapah faults, and the steep southern San Andreas fault with the adjacent NE-dipping Mecca Hills-Hidden Springs fault system. In addition, overprinting by steep predominantly strike-slip faulting can segment which parts of intersecting inherited low-angle faults are reactivated, or result in mutual cross-cutting relationships. The updated CFM 3D fault surfaces thus help characterize a more complex pattern of fault interactions at depth between various fault sets and linked fault systems, and a more complex fault geometry than typically inferred or expected from

Surface faulting along the inland Itozawa normal fault (eastern Japan) and relation to the 2011 Tohoku-oki megathrust earthquake

NASA Astrophysics Data System (ADS)

Ferry, Matthieu; Tsutsumi, Hiroyuki; Meghraoui, Mustapha; Toda, Shinji

2013-04-01

The 11 March 2011 Mw 9 Tohoku-oki earthquake ruptured ~500 km length of the Japan Trench along the coast of eastern Japan and significantly impacted the stress regime within the crust. The resulting change in seismicity over the Japan mainland was exhibited by the 11 April 2011 Mw 6.6 Iwaki earthquake that ruptured the Itozawa and Yunodake faults. Trending NNW and NW, respectively, these 70-80° W-dipping faults bound the Iwaki basin of Neogene age and have been reactivated simultaneously both along 15-km-long sections. Here, we present initial results from a paleoseismic excavation performed across the Itozawa fault within the Tsunagi Valley at the northern third of the observed surface rupture. At the Tsunagi site, the rupture affects a rice paddy, which provides an ideally horizontal initial state to collect detailed and accurate measurements. The surface break is composed of a continuous 30-to-40-cm-wide purely extensional crack that separates the uplifted block from a gently dipping 1-to-2-m-wide strip affected by right-stepping en-echelon cracks and locally bounded by a ~0.1-m-high reverse scarplet. Total station across-fault topographic profiles indicate the pre-earthquake ground surface was vertically deformed by ~0.6 m while direct field examinations reveal that well-defined rice paddy limits have been left-laterally offset by ~0.1 m. The 12-m-long, 3.5-m-deep trench exposes the 30-to-40-cm-thick cultivated soil overlaying a 1-m-thick red to yellow silt unit, a 2-m-thick alluvial gravel unit and a basal 0.1-1-m-thick organic-rich silt unit. Deformation associated to the 2011 rupture illustrates down-dip movement along a near-vertical fault with a well-expressed bending moment at the surface and generalized warping. On the north wall, the intermediate gravel unit displays a deformation pattern similar to granular flow with only minor discrete faulting and no splay to be continuously followed from the main fault to the surface. On the south wall, warping

Surface faulting along the inland Itozawa normal fault (eastern Japan) and relation to the 2011 Tohoku-oki megathrust earthquake

NASA Astrophysics Data System (ADS)

Ferry, M.; Tsutsumi, H.; Meghraoui, M.; Toda, S.

2012-12-01

The 11 March 2011 Mw 9 Tohoku-oki earthquake ruptured ~500 km length of the Japan Trench along the coast of eastern Japan and significantly impacted the stress regime within the crust. The resulting change in seismicity over the Japan mainland was exhibited by the 11 April 2011 Mw 6.6 Iwaki earthquake that ruptured the Itozawa and Yunodake faults. Trending NNW and NW, respectively, these 70-80° W-dipping faults bound the Iwaki basin of Neogene age and have been reactivated simultaneously both along 15-km-long sections. Here, we present initial results from a paleoseismic excavation performed across the Itozawa fault within the Tsunagi Valley at the northern third of the observed surface rupture. At the Tsunagi site, the rupture affects a rice paddy, which provides an ideally horizontal initial state to collect detailed and accurate measurements. The surface break is composed of a continuous 30-to-40-cm-wide purely extensional crack that separates the uplifted block from a gently dipping 1-to-2-m-wide strip affected by right-stepping en-echelon cracks and locally bounded by a ~0.1-m-high reverse scarplet. Total station across-fault topographic profiles indicate the pre-earthquake ground surface was vertically deformed by ~0.6 m while direct field examinations reveal that well-defined rice paddy limits have been left-laterally offset by ~0.1 m. The 12-m-long, 3.5-m-deep trench exposes the 30-to-40-cm-thick cultivated soil overlaying a 1-m-thick red to yellow silt unit, a 2-m-thick alluvial gravel unit and a basal 0.1-1-m-thick organic-rich silt unit. Deformation associated to the 2011 rupture illustrates down-dip movement along a near-vertical fault with a well-expressed bending moment at the surface and generalized warping. On the north wall, the intermediate gravel unit displays a deformation pattern similar to granular flow with only minor discrete faulting and no splay to be continuously followed from the main fault to the surface. On the south wall, warping

Porosity variations in and around normal fault zones: implications for fault seal and geomechanics

NASA Astrophysics Data System (ADS)

Healy, David; Neilson, Joyce; Farrell, Natalie; Timms, Nick; Wilson, Moyra

2015-04-01

Porosity forms the building blocks for permeability, exerts a significant influence on the acoustic response of rocks to elastic waves, and fundamentally influences rock strength. And yet, published studies of porosity around fault zones or in faulted rock are relatively rare, and are hugely dominated by those of fault zone permeability. We present new data from detailed studies of porosity variations around normal faults in sandstone and limestone. We have developed an integrated approach to porosity characterisation in faulted rock exploiting different techniques to understand variations in the data. From systematic samples taken across exposed normal faults in limestone (Malta) and sandstone (Scotland), we combine digital image analysis on thin sections (optical and electron microscopy), core plug analysis (He porosimetry) and mercury injection capillary pressures (MICP). Our sampling includes representative material from undeformed protoliths and fault rocks from the footwall and hanging wall. Fault-related porosity can produce anisotropic permeability with a 'fast' direction parallel to the slip vector in a sandstone-hosted normal fault. Undeformed sandstones in the same unit exhibit maximum permeability in a sub-horizontal direction parallel to lamination in dune-bedded sandstones. Fault-related deformation produces anisotropic pores and pore networks with long axes aligned sub-vertically and this controls the permeability anisotropy, even under confining pressures up to 100 MPa. Fault-related porosity also has interesting consequences for the elastic properties and velocity structure of normal fault zones. Relationships between texture, pore type and acoustic velocity have been well documented in undeformed limestone. We have extended this work to include the effects of faulting on carbonate textures, pore types and P- and S-wave velocities (Vp, Vs) using a suite of normal fault zones in Malta, with displacements ranging from 0.5 to 90 m. Our results show a

High-angle faults control the geometry and morphology of the Corinth Rift

NASA Astrophysics Data System (ADS)

Bell, R. E.; Duclaux, G.; Nixon, C.; Gawthorpe, R.; McNeill, L. C.

2016-12-01

Slip along low-angle normal faults is mechanically difficult, and the existence of low angle detachment faults presents one of most important paradoxes in structural geology. Only a few examples of young continental rifts where low-angle faults may be a mechanism for accommodating strain have been described in the literature, and an important example is the Gulf of Corinth, central Greece. Here, microseismicity, the geometry of onshore faults and deep seismic reflection images have been used to argue for the presence of <30o dipping faults. However, new and reinterpreted data calls into question whether low-angle faults have been influential in controlling rift geometry. We seek to definitively test whether slip on a mature low-angle normal fault can reproduce the long-term geometry and morphology of the Corinth Rift, which involves i) significant uplift of the southern margin, ii) long-term uplift to subsidence ratios across south coast faults of 1 -2, and iii) a northern margin that does not undergo significant long-term uplift. We use PyLith, an open-source finite-element code for quasi-static viscoelastic simulations of crustal deformation and model the uplift and subsidence fields associated with the following fault geometries: i) planar faults with dips of 45-60° that sole onto a 10° detachment at a depth of 6 to 8 km, ii) 45-60° faults, which change to a dip angle of 25-45° at a depth of 3 km and continue to a brittle-ductile transition at 10 km and iii) planar faults which dip 45-60° to the brittle-ductile transition at a depth of 10 km. We show that models involving low-angle detachments, shallower than 8 km produce very minor coseismic uplift of the southern margin and post-seismic relaxation results in the southern margin experiencing net subsidence over many seismic cycles, incompatible with geological observations. Models involving planar faults produce long-term displacement fields involving uplifted southern margin with uplift to subsidence

Sandstone-filled normal faults: A case study from central California

NASA Astrophysics Data System (ADS)

Palladino, Giuseppe; Alsop, G. Ian; Grippa, Antonio; Zvirtes, Gustavo; Phillip, Ruy Paulo; Hurst, Andrew

2018-05-01

Despite the potential of sandstone-filled normal faults to significantly influence fluid transmissivity within reservoirs and the shallow crust, they have to date been largely overlooked. Fluidized sand, forcefully intruded along normal fault zones, markedly enhances the transmissivity of faults and, in general, the connectivity between otherwise unconnected reservoirs. Here, we provide a detailed outcrop description and interpretation of sandstone-filled normal faults from different stratigraphic units in central California. Such faults commonly show limited fault throw, cm to dm wide apertures, poorly-developed fault zones and full or partial sand infill. Based on these features and inferences regarding their origin, we propose a general classification that defines two main types of sandstone-filled normal faults. Type 1 form as a consequence of the hydraulic failure of the host strata above a poorly-consolidated sandstone following a significant, rapid increase of pore fluid over-pressure. Type 2 sandstone-filled normal faults form as a result of regional tectonic deformation. These structures may play a significant role in the connectivity of siliciclastic reservoirs, and may therefore be crucial not just for investigation of basin evolution but also in hydrocarbon exploration.

Geometrical and mechanical constraints on the formation of ring-fault calderas

NASA Astrophysics Data System (ADS)

Folch, A.; Martí, J.

2004-04-01

Ash-flow, plate-subsidence (piston-like) calderas are bounded by a set of arcuated sub-vertical collapse faults named ring-faults. Experimental studies on caldera formation, performed mostly using spherical or cylindrical magma chamber geometries, find that the resulting ring-faults correspond to steeply outward dipping reverse faults, and show that pre-existing fractures developed during pre-eruptive phases of pressure increase may play a major role in controlling the final collapse mechanism, a situation that should be expected in small to medium sized ring-fault calderas developed on top of composite volcanoes or volcanic clusters. On the other hand, some numerical experiments indicate that large sill-like, elongated magma chambers may induce collapse due to roof bending without fault reactivation, as seems to occur in large plate-subsidence calderas formed independently of pre-existing volcanoes. Also, numerical experiments allow the formation of nearly vertical or steeply inward dipping normal ring-faults, in contrast with most of the analogue models. Using a thermoelastic model, we investigate the geometrical and mechanical conditions to form ring-fault calderas, in particular the largest ones, without needing a previous crust fracturing. Results are given in terms of two dimensionless geometrical parameters, namely λ and e. The former is the chamber extension to chamber depth ratio, whereas the latter stands for the chamber eccentricity. We propose that the ( λ, e) pair determinates two different types of ring-fault calderas with different associated collapse regimes. Ring-fault region A is related to large plate-subsidence calderas (i.e. Andean calderas or Western US calderas), for which few depressurisation is needed to set up a collapse initially governed by flexural bending of the chamber roof. In contrast, ring-fault region B is related to small to moderate sized calderas (i.e. composite volcano calderas), for which much depressurisation is needed

Quaternary marine terraces as indicators of neotectonic activity of the Ierapetra normal fault SE Crete (Greece)

NASA Astrophysics Data System (ADS)

Gaki-Papanastassiou, K.; Karymbalis, E.; Papanastassiou, D.; Maroukian, H.

2009-03-01

Along the southern coast of the island of Crete, a series of east-west oriented Late Pleistocene marine terraces exist, demonstrating the significant coastal uplift of this area. Five uplifted terraces were mapped in detail and correlated with Middle-Late Pleistocene sea-level stands following the global sea-level fluctuations. These terraces are deformed by the vertical movements of the NNE-SSW trending and dipping west Ierapetra normal fault. The elevation of the inner edges of the terraces was estimated at several sites by using aerial photographs and detailed topographic maps and diagrams, supported by extensive field observations. In this way detailed geomorphological maps were constructed utilizing GIS technology. All these allowed us to obtain rates of 0.3 mm/yr for the regional component of uplift and 0.1 mm/yr for the vertical slip movements of the Ierapetra fault. Based on the obtained rates and the existence of coastal archaeological Roman ruins it is concluded that Ierapetra fault should have been reactivated sometime after the Roman period.

The influence of normal fault on initial state of stress in rock mass

NASA Astrophysics Data System (ADS)

Tajduś, Antoni; Cała, Marek; Tajduś, Krzysztof

2016-03-01

Determination of original state of stress in rock mass is a very difficult task for rock mechanics. Yet, original state of stress in rock mass has fundamental influence on secondary state of stress, which occurs in the vicinity of mining headings. This, in turn, is the cause of the occurrence of a number of mining hazards, i.e., seismic events, rock bursts, gas and rock outbursts, falls of roof. From experience, it is known that original state of stress depends a lot on tectonic disturbances, i.e., faults and folds. In the area of faults, a great number of seismic events occur, often of high energies. These seismic events, in many cases, are the cause of rock bursts and damage to the constructions located inside the rock mass and on the surface of the ground. To estimate the influence of fault existence on the disturbance of original state of stress in rock mass, numerical calculations were done by means of Finite Element Method. In the calculations, it was tried to determine the influence of different factors on state of stress, which occurs in the vicinity of a normal fault, i.e., the influence of normal fault inclination, deformability of rock mass, values of friction coefficient on the fault contact. Critical value of friction coefficient was also determined, when mutual dislocation of rock mass part separated by a fault is impossible. The obtained results enabled formulation of a number of conclusions, which are important in the context of seismic events and rock bursts in the area of faults.

Slip localization on the southern Alpine Fault, New Zealand

NASA Astrophysics Data System (ADS)

Barth, N. C.; Boulton, C.; Carpenter, B. M.; Batt, G. E.; Toy, V. G.

2013-06-01

of a detailed field study of the southern onshore portion of New Zealand's Alpine Fault reveal that for 75 km along-strike, dextral-normal slip on this long-lived structure is highly localized in phyllosilicate-rich fault core gouges and along their contact with more competent rocks. At three localities (Martyr River, McKenzie Creek, and Hokuri Creek), we document complete cross sections through the fault. New 40Ar/39Ar dates on mylonites, combined with microstructural and mechanical data on phyllosilicate-rich fault core gouges show that modern slip is localized onto a single, steeply dipping 1 to 12 m-thick fault core composed of impermeable (k = 10-20 to 10-22 m2), frictionally weak (μs = 0.12-0.37), velocity-strengthening, illite-chlorite, and saponite-chlorite-lizardite fault gouges. Fault core materials are (1) comparable to those of other major weak-cored faults (e.g., San Andreas Fault) and (2) most compatible with fault creep, despite paleoseismic evidence of quasiperiodic large magnitude earthquakes (Mw > 7) on this portion of the Alpine Fault. We conclude that frictional properties of gouges at the surface do not characterize the overall seismogenic behavior of the southern Alpine Fault.

DipTest: A litmus test for E. coli detection in water.

PubMed

Gunda, Naga Siva Kumar; Dasgupta, Saumyadeb; Mitra, Sushanta K

2017-01-01

We have developed a new litmus paper test (DipTest) for detecting Escherichia coli (E. coli) in water samples by performing enzymatic reactions directly on the porous paper substrate. The paper strip consists of a long narrow piece of cellulose blotting paper coated with chemoattractant (at bottom edge), wax hydrophobic barrier (at the top edge), and custom formulated chemical reagents (at reaction zone immediately below the wax hydrophobic barrier). When the paper strip is dipped in water, E. coli in the water sample is attracted toward the paper strip due to a chemotaxic mechanism followed by the ascent along the paper strip toward the reaction zone due to a capillary wicking mechanism, and finally the capillary motion is arrested at the top edge of the paper strip by the hydrophobic barrier. The E. coli concentrated at the reaction zone of the paper strip will react with custom formulated chemical reagents to produce a pinkish-red color. Such a color change on the paper strip when dipped into water samples indicates the presence of E. coli contamination in potable water. The performance of the DipTest device has been checked with different known concentrations of E. coli contaminated water samples using different dip and wait times. The DipTest device has also been tested with different interfering bacteria and chemical contaminants. It has been observed that the different interfering contaminants do not have any impact on the DipTest, and it can become a potential solution for screening water samples for E. coli contamination at the point of source.

DipTest: A litmus test for E. coli detection in water

PubMed Central

Gunda, Naga Siva Kumar; Dasgupta, Saumyadeb

2017-01-01

We have developed a new litmus paper test (DipTest) for detecting Escherichia coli (E. coli) in water samples by performing enzymatic reactions directly on the porous paper substrate. The paper strip consists of a long narrow piece of cellulose blotting paper coated with chemoattractant (at bottom edge), wax hydrophobic barrier (at the top edge), and custom formulated chemical reagents (at reaction zone immediately below the wax hydrophobic barrier). When the paper strip is dipped in water, E. coli in the water sample is attracted toward the paper strip due to a chemotaxic mechanism followed by the ascent along the paper strip toward the reaction zone due to a capillary wicking mechanism, and finally the capillary motion is arrested at the top edge of the paper strip by the hydrophobic barrier. The E. coli concentrated at the reaction zone of the paper strip will react with custom formulated chemical reagents to produce a pinkish-red color. Such a color change on the paper strip when dipped into water samples indicates the presence of E. coli contamination in potable water. The performance of the DipTest device has been checked with different known concentrations of E. coli contaminated water samples using different dip and wait times. The DipTest device has also been tested with different interfering bacteria and chemical contaminants. It has been observed that the different interfering contaminants do not have any impact on the DipTest, and it can become a potential solution for screening water samples for E. coli contamination at the point of source. PMID:28877199

The 2015 M w 6.0 Mt. Kinabalu earthquake: an infrequent fault rupture within the Crocker fault system of East Malaysia

NASA Astrophysics Data System (ADS)

Wang, Yu; Wei, Shengji; Wang, Xin; Lindsey, Eric O.; Tongkul, Felix; Tapponnier, Paul; Bradley, Kyle; Chan, Chung-Han; Hill, Emma M.; Sieh, Kerry

2017-12-01

The M w 6.0 Mt. Kinabalu earthquake of 2015 was a complete (and deadly) surprise, because it occurred well away from the nearest plate boundary in a region of very low historical seismicity. Our seismological, space geodetic, geomorphological, and field investigations show that the earthquake resulted from rupture of a northwest-dipping normal fault that did not reach the surface. Its unilateral rupture was almost directly beneath 4000-m-high Mt. Kinabalu and triggered widespread slope failures on steep mountainous slopes, which included rockfalls that killed 18 hikers. Our seismological and morphotectonic analyses suggest that the rupture occurred on a normal fault that splays upwards off of the previously identified normal Marakau fault. Our mapping of tectonic landforms reveals that these faults are part of a 200-km-long system of normal faults that traverse the eastern side of the Crocker Range, parallel to Sabah's northwestern coastline. Although the tectonic reason for this active normal fault system remains unclear, the lengths of the longest fault segments suggest that they are capable of generating magnitude 7 earthquakes. Such large earthquakes must occur very rarely, though, given the hitherto undetectable geodetic rates of active tectonic deformation across the region.

Stress state and movement potential of the Kar-e-Bas fault zone, Fars, Iran

NASA Astrophysics Data System (ADS)

Sarkarinejad, Khalil; Zafarmand, Bahareh

2017-08-01

The Kar-e-Bas or Mengharak basement-inverted fault is comprised of six segments in the Zagros foreland folded belt of Iran. In the Fars region, this fault zone associated with the Kazerun, Sabz-Pushan and Sarvestan faults serves as a lateral transfer zone that accommodates the change in shortening direction from the western central to the eastern Zagros. This study evaluates the recent tectonic stress regime of the Kar-e-Bas fault zone based on inversion of earthquake focal mechanism data, and quantifies the fault movement potential of this zone based on the relationship between fault geometric characteristics and recent tectonic stress regimes. The trend and plunge of σ 1 and σ 3 are S25°W/04°-N31°E/05° and S65°E/04°-N60°W/10°, respectively, with a stress ratio of Φ = 0.83. These results are consistent with the collision direction of the Afro-Arabian continent and the Iranian microcontinent. The near horizontal plunge of maximum and minimum principle stresses and the value of stress ratio Φ indicate that the state of stress is nearly strike-slip dominated with little relative difference between the value of two principal stresses, σ 1 and σ 2. The obliquity of the maximum compressional stress into the fault trend reveals a typical stress partitioning of thrust and strike-slip motion in the Kar-e-Bas fault zone. Analysis of the movement potential of this fault zone shows that its northern segment has a higher potential of fault activity (0.99). The negligible difference between the fault-plane dips of the segments indicates that their strike is a controlling factor in the changes in movement potential.

Active normal fault network of the Apulian Ridge (Eastern Mediterranean Sea) imaged by multibeam bathymetry and seismic data

NASA Astrophysics Data System (ADS)

Pellegrini, Claudio; Marchese, Fabio; Savini, Alessandra; Bistacchi, Andrea

2016-04-01

The Apulian ridge (North-eastern Ionian margin - Mediterranean Sea) is formed by thick cretaceous carbonatic sequences and discontinuous tertiary deposits crosscut by a NNW-SSE penetrative normal fault system and is part of the present foreland system of both the Apennine to the west and the Hellenic arc to the east. The geometry, age, architecture and kinematics of the fault network were investigated integrating data of heterogeneous sources, provided by previous studies: regional scale 2D seismics and three wells collected by oil companies from the '60s to the '80s, more recent seismics collected during research projects in the '90s, very high resolution seismic (VHRS - Sparker and Chirp-sonar data), multi-beam echosounder bathymetry and results from sedimentological and geo-chronological analysis of sediment samples collected on the seabed. Multibeam bathymetric data allowed in particular assessing the 3D continuity of structures imaged in 2D seismics, thanks to the occurrence of continuous fault scarps on the seabed (only partly reworked by currents and covered by landslides), revealing the vertical extent and finite displacement associated to fault scarps. A penetrative network of relatively small faults, always showing a high dip angle, composes the NNW-SSE normal fault system, resulting in frequent relay zones, which are particularly well imaged by seafloor geomorphology. In addition, numerous fault scarps appear to be roughly coeval with quaternary submarine mass-wasting deposits colonised by Cold-Water Corals (CWC). Coral colonies, yielding ages between 11 and 14 kA, develop immediately on top of late Pleistocene mass-wasting deposits. Mutual cross-cutting relationships have been recognized between fault scarps and landslides, indicating that, at least in places, these features may be coeval. We suppose that fault activity lasted at least as far as the Holocene-Pleistocene boundary and that the NNW-SSW normal fault network in the Apulian Plateau can be

Hydrothermal Upflow, Serpentinization and Talc Alteration Associated with a High Angle Normal Fault Cutting an Oceanic Detachment, Northern Apennines, Italy

NASA Astrophysics Data System (ADS)

Alt, J.; Crispini, L.; Gaggero, L.; Shanks, W. C., III; Gulbransen, C.; Lavagnino, G.

2017-12-01

Normal faults cutting oceanic core complexes are observed at the seafloor and through geophysics, and may act as flow pathways for hydrothermal fluids, but we know little about such faults in the subsurface. We present bulk rock geochemistry and stable isotope data for a fault that acted as a hydrothermal upflow zone in a seafloor ultramafic-hosted hydrothermal system in the northern Apennines, Italy. Peridotites were exposed on the seafloor by detachment faulting, intruded by MORB gabbros, and are overlain by MORB lavas and pelagic sediments. North of the village of Reppia are fault shear zones in serpentinite, oriented at a high angle to the detachment surface and extending 300 m below the paleo-seafloor. The paleo-seafloor strikes roughly east-west, dipping 30˚ to the north. At depth the fault zone occurs as an anticlinal form plunging 40˚ to the west. A second fault strikes approximately north-south, with a near vertical dip. The fault rock outcrops as reddish weathered talc + sulfide in 0.1-2 m wide anastomosing bands, with numerous splays. Talc replaces serpentinite in the fault rocks, and the talc rocks are enriched in Si, metals (Fe, Cu, Pb), Light Rare Earth Elements (LREE), have variable Eu anomalies, and have low Mg, Cr and Ni contents. In some cases gabbro dikes are associated with talc-alteration and may have enhanced fluid flow. Sulfide from a fault rock has d34S=5.7‰. The mineralogy and chemistry of the fault rocks indicate that the fault acted as the upflow pathway for high-T black-smoker type fluids. Traverses away from the fault (up to 1 km) and with depth below the seafloor (up to 500 m) reveal variable influences of hydrothermal fluids, but there are no consistent trends with distance. Background serpentinites 500 m beneath the paleoseafloor have LREE depleted trends. Other serpentinites exhibit correlations of LREE with HFSE as the result of melt percolation, but there is significant scatter, and hydrothermal effects include LREE enrichment

Frictional heterogeneities on carbonate-bearing normal faults: Insights from the Monte Maggio Fault, Italy

NASA Astrophysics Data System (ADS)

Carpenter, B. M.; Scuderi, M. M.; Collettini, C.; Marone, C.

2014-12-01

Observations of heterogeneous and complex fault slip are often attributed to the complexity of fault structure and/or spatial heterogeneity of fault frictional behavior. Such complex slip patterns have been observed for earthquakes on normal faults throughout central Italy, where many of the Mw 6 to 7 earthquakes in the Apennines nucleate at depths where the lithology is dominated by carbonate rocks. To explore the relationship between fault structure and heterogeneous frictional properties, we studied the exhumed Monte Maggio Fault, located in the northern Apennines. We collected intact specimens of the fault zone, including the principal slip surface and hanging wall cataclasite, and performed experiments at a normal stress of 10 MPa under saturated conditions. Experiments designed to reactivate slip between the cemented principal slip surface and cataclasite show a 3 MPa stress drop as the fault surface fails, then velocity-neutral frictional behavior and significant frictional healing. Overall, our results suggest that (1) earthquakes may readily nucleate in areas of the fault where the slip surface separates massive limestone and are likely to propagate in areas where fault gouge is in contact with the slip surface; (2) postseismic slip is more likely to occur in areas of the fault where gouge is present; and (3) high rates of frictional healing and low creep relaxation observed between solid fault surfaces could lead to significant aftershocks in areas of low stress drop.

Fault geometries in basement-induced wrench faulting under different initial stress states

NASA Astrophysics Data System (ADS)

Naylor, M. A.; Mandl, G.; Supesteijn, C. H. K.

Scaled sandbox experiments were used to generate models for relative ages, dip, strike and three-dimensional shape of faults in basement-controlled wrench faulting. The basic fault sequence runs from early en échelon Riedel shears and splay faults through 'lower-angle' shears to P shears. The Riedel shears are concave upwards and define a tulip structure in cross-section. In three dimensions, each Riedel shear has a helicoidal form. The sequence of faults and three-dimensional geometry are rationalized in terms of the prevailing stress field and Coulomb-Mohr theory of shear failure. The stress state in the sedimentary overburden before wrenching begins has a substantial influence on the fault geometries and on the final complexity of the fault zone. With the maximum compressive stress (∂ 1) initially parallel to the basement fault (transtension), Riedel shears are only slightly en échelon, sub-parallel to the basement fault, steeply dipping with a reduced helicoidal aspect. Conversely, with ∂ 1 initially perpendicular to the basement fault (transpression), Riedel shears are strongly oblique to the basement fault strike, have lower dips and an exaggerated helicoidal form; the final fault zone is both wide and complex. We find good agreement between the models and both mechanical theory and natural examples of wrench faulting.

Does magmatism influence low-angle normal faulting?

USGS Publications Warehouse

Parsons, Thomas E.; Thompson, George A.

1993-01-01

Synextensional magmatism has long been recognized as a ubiquitous characteristic of highly extended terranes in the western Cordillera of the United States. Intrusive magmatism can have severe effects on the local stress field of the rocks intruded. Because a lower angle fault undergoes increased normal stress from the weight of the upper plate, it becomes more difficult for such a fault to slide. However, if the principal stress orientations are rotated away from vertical and horizontal, then a low-angle fault plane becomes more favored. We suggest that igneous midcrustal inflation occurring at rates faster than regional extension causes increased horizontal stresses in the crust that alter and rotate the principal stresses. Isostatic forces and continued magmatism can work together to create the antiformal or domed detachment surface commonly observed in the metamorphic core complexes of the western Cordillera. Thermal softening caused by magmatism may allow a more mobile mid-crustal isostatic response to normal faulting.

Quaternary low-angle slip on detachment faults in Death Valley, California

USGS Publications Warehouse

Hayman, N.W.; Knott, J.R.; Cowan, D.S.; Nemser, E.; Sarna-Wojcicki, A. M.

2003-01-01

Detachment faults on the west flank of the Black Mountains (Nevada and California) dip 29??-36?? and cut subhorizontal layers of the 0.77 Ma Bishop ash. Steeply dipping normal faults confined to the hanging walls of the detachments offset layers of the 0.64 Ma Lava Creek B tephra and the base of 0.12-0.18 Ma Lake Manly gravel. These faults sole into and do not cut the low-angle detachments. Therefore the detachments accrued any measurable slip across the kinematically linked hanging-wall faults. An analysis of the orientations of hundreds of the hanging-wall faults shows that extension occurred at modest slip rates (<1 mm/yr) under a steep to vertically oriented maximum principal stress. The Black Mountain detachments are appropriately described as the basal detachments of near-critical Coulomb wedges. We infer that the formation of late Pleistocene and Holocene range-front fault scarps accompanied seismogenic slip on the detachments.

Strength evolution of simulated carbonate-bearing faults: The role of normal stress and slip velocity

NASA Astrophysics Data System (ADS)

Mercuri, Marco; Scuderi, Marco Maria; Tesei, Telemaco; Carminati, Eugenio; Collettini, Cristiano

2018-04-01

A great number of earthquakes occur within thick carbonate sequences in the shallow crust. At the same time, carbonate fault rocks exhumed from a depth < 6 km (i.e., from seismogenic depths) exhibit the coexistence of structures related to brittle (i.e., cataclasis) and ductile deformation processes (i.e., pressure-solution and granular plasticity). We performed friction experiments on water-saturated simulated carbonate-bearing faults for a wide range of normal stresses (from 5 to 120 MPa) and slip velocities (from 0.3 to 100 μm/s). At high normal stresses (σn > 20 MPa) fault gouges undergo strain-weakening, that is more pronounced at slow slip velocities, and causes a significant reduction of frictional strength, from μ = 0.7 to μ = 0.47. Microstructural analysis show that fault gouge weakening is driven by deformation accommodated by cataclasis and pressure-insensitive deformation processes (pressure solution and granular plasticity) that become more efficient at slow slip velocity. The reduction in frictional strength caused by strain weakening behaviour promoted by the activation of pressure-insensitive deformation might play a significant role in carbonate-bearing faults mechanics.

The 2013 earthquake swarm in Helike, Greece: seismic activity at the root of old normal faults

NASA Astrophysics Data System (ADS)

Kapetanidis, V.; Deschamps, A.; Papadimitriou, P.; Matrullo, E.; Karakonstantis, A.; Bozionelos, G.; Kaviris, G.; Serpetsidaki, A.; Lyon-Caen, H.; Voulgaris, N.; Bernard, P.; Sokos, E.; Makropoulos, K.

2015-09-01

The Corinth Rift in Central Greece has been studied extensively during the past decades, as it is one of the most seismically active regions in Europe. It is characterized by normal faulting and extension rates between 6 and 15 mm yr-1 in an approximately N10E° direction. On 2013 May 21, an earthquake swarm was initiated with a series of small events 4 km southeast of Aigion city. In the next days, the seismic activity became more intense, with outbursts of several stronger events of magnitude between 3.3 and 3.7. The seismicity migrated towards the east during June, followed by a sudden activation of the western part of the swarm on July 15th. More than 1500 events have been detected and manually analysed during the period between 2013 May 21 and August 31, using over 15 local stations in epicentral distances up to 30 km and a local velocity model determined by an error minimization method. Waveform similarity-based analysis was performed, revealing several distinct multiplets within the earthquake swarm. High-resolution relocation was applied using the double-difference algorithm HypoDD, incorporating both catalogue and cross-correlation differential traveltime data, which managed to separate the initial seismic cloud into several smaller, densely concentrated spatial clusters of strongly correlated events. Focal mechanism solutions for over 170 events were determined using P-wave first motion polarities, while regional waveform modelling was applied for the calculation of moment tensors for the 18 largest events of the sequence. Selected events belonging to common spatial groups were considered for the calculation of composite mechanisms to characterize different parts of the swarm. The solutions are mainly in agreement with the regional NNE-SSW extension, representing typical normal faulting on 30-50° north-dipping planes, while a few exhibit slip in an NNE-SSW direction, on a roughly subhorizontal plane. Moment magnitudes were calculated by spectral analysis

Geometry and evolution of low-angle normal faults (LANF) within a Cenozoic high-angle rift system, Thailand: Implications for sedimentology and the mechanisms of LANF development

NASA Astrophysics Data System (ADS)

Morley, Chris K.

2009-10-01

At least eight examples of large (5-35 km heave), low-angle normal faults (LANFs, 20°-30° dip) occur in the Cenozoic rift basins of Thailand and laterally pass into high-angle extensional fault systems. Three large-displacement LANFs are found in late Oligocene-Miocene onshore rift basins (Suphan Buri, Phitsanulok, and Chiang Mai basins), they have (1) developed contemporaneous with, or after the onset of, high-angle extension, (2) acted as paths for magma and associated fluids, and (3) impacted sedimentation patterns. Displacement on low-angle faults appears to be episodic, marked by onset of lacustrine conditions followed by axial progradation of deltaic systems that infilled the lakes during periods of low or no displacement. The Chiang Mai LANF is a low-angle (15°-25°), high-displacement (15-35 km heave), ESE dipping LANF immediately east of the late early Miocene Doi Inthanon and Doi Suthep metamorphic core complexes. Early Cenozoic transpressional crustal thickening followed by the northward motion of India coupled with Burma relative to east Burma and Thailand (˜40-30 Ma) caused migmatization and gneiss dome uplift in the late Oligocene of the core complex region, followed by LANF activity. LANF displacement lasted 4-6 Ma during the early Miocene and possibly transported a late Oligocene-early Miocene high-angle rift system 35 km east. Other LANFs in Thailand have lower displacements and no associated metamorphic core complexes. The three LANFs were initiated as low-angle faults, not by isostatic rotation of high-angle faults. The low-angle dips appear to follow preexisting low-angle fabrics (thrusts, shear zones, and other low-angle ductile foliations) predominantly developed during Late Paleozoic and early Paleogene episodes of thrusting and folding.

Active tectonics in southern Xinjiang, China: Analysis of terrace riser and normal fault scarp degradation along the Hotan-Qira fault system

NASA Technical Reports Server (NTRS)

Avouac, Jean-Philippe; Peltzer, Gilles

1993-01-01

The northern piedmont of the western Kunlun mountains (Xinjiang, China) is marked at its easternmost extremity, south of the Hotan-Qira oases, by a set of normal faults trending N50E for nearly 70 km. Conspicuous on Landsat and SPOT images, these faults follow the southeastern border of a deep flexural basin and may be related to the subsidence of the Tarim platform loaded by the western Kunlun northward overthrust. The Hotan-Qira normal fault system vertically offsets the piedmont slope by 70 m. Highest fault scarps reach 20 m and often display evidence for recent reactivations about 2 m high. Successive stream entrenchments in uplifted footwallls have formed inset terraces. We have leveled topographic profiles across fault scarps and transverse abandoned terrace risers. The state of degradation of each terrace edge has been characterized by a degradation coefficient tau, derived by comparison with analytical erosion models. Edges of highest abandoned terraces yield a degradation coefficient of 33 +/- 4 sq.m. Profiles of cumulative fault scarps have been analyzed in a similar way using synthetic profiles generated with a simple incremental fault scarp model.

Geology of the Elephanta Island fault zone, western Indian rifted margin, and its significance for understanding the Panvel flexure

NASA Astrophysics Data System (ADS)

Samant, Hrishikesh; Pundalik, Ashwin; D'souza, Joseph; Sheth, Hetu; Lobo, Keegan Carmo; D'souza, Kyle; Patel, Vanit

2017-02-01

The Panvel flexure is a 150-km long tectonic structure, comprising prominently seaward-dipping Deccan flood basalts, on the western Indian rifted margin. Given the active tectonic faulting beneath the Panvel flexure zone inferred from microseismicity, better structural understanding of the region is needed. The geology of Elephanta Island in the Mumbai harbour, famous for the ca. mid-6th century A.D. Hindu rock-cut caves in Deccan basalt (a UNESCO World Heritage site) is poorly known. We describe a previously unreported but well-exposed fault zone on Elephanta Island, consisting of two large faults dipping steeply east-southeast and producing easterly downthrows. Well-developed slickensides and structural measurements indicate oblique slip on both faults. The Elephanta Island fault zone may be the northern extension of the Alibag-Uran fault zone previously described. This and two other known regional faults (Nhava-Sheva and Belpada faults) indicate a progressively eastward step-faulted structure of the Panvel flexure, with the important result that the individual movements were not simply downdip but also oblique-slip and locally even rotational (as at Uran). An interesting problem is the normal faulting, block tectonics and rifting of this region of the crust for which seismological data indicate a normal thickness (up to 41.3 km). A model of asymmetric rifting by simple shear may explain this observation and the consistently landward dips of the rifted margin faults.

Seismic reflection images of shallow faulting, northernmost Mississippi embayment, north of the New Madrid seismic zone

USGS Publications Warehouse

McBride, J.H.; Nelson, W.J.

2001-01-01

High-resolution seismic reflection surveys document tectonic faults that displace Pleistocene and older strata just beyond the northeast termination of the New Madrid seismic zone, at the northernmost extent of the Mississippi embayment. These faults, which are part of the Fluorspar Area fault complex in southeastern Illinois, are directly in line with the northeast-trending seismic zone. The reflection data were acquired using an elastic weight-drop source recorded to 500 msec by a 48-geophone array (24-fold) with a 10-ft (??3.0m) station interval. Recognizable reflections were recorded to about 200 msec (100-150 m). The effects of multiple reflections, numerous diffractions, low apparent velocity (i.e., steeply dipping) noise, and the relatively low-frequency content of the recorded signal provided challenges for data processing and interpreting subtle fault offsets. Data processing steps that were critical to the detection of faults included residual statics, post-stack migration, deconvolution, and noise-reduction filtering. Seismic migration was crucial for detecting and mitigating complex fault-related diffraction patterns, which produced an apparent 'folding' of reflectors on unmigrated sections. Detected individual offsets of shallow reflectors range from 5 to 10 m for the top of Paleozoic bedrock and younger strata. The migrated sections generally indicate vertical to steeply dipping normal and reverse faults, which in places outline small horsts and/or grabens. Tilting or folding of stratal reflectors associated with faulting is also locally observed. At one site, the observed faulting is superimposed over a prominent antiformal structure, which may itself be a product of the Quaternary deformation that produced the steep normal and reverse faults. Our results suggest that faulting of the Paleozoic bedrock and younger sediments of the northern Mississippi embayment is more pervasive and less localized than previously thought.

Influence of crystallised igneous intrusions on fault nucleation and reactivation during continental extension

NASA Astrophysics Data System (ADS)

Magee, Craig; McDermott, Kenneth G.; Stevenson, Carl T. E.; Jackson, Christopher A.-L.

2014-05-01

Continental rifting is commonly accommodated by the nucleation of normal faults, slip on pre-existing fault surfaces and/or magmatic intrusion. Because crystallised igneous intrusions are pervasive in many rift basins and are commonly more competent (i.e. higher shear strengths and Young's moduli) than the host rock, it is theoretically plausible that they locally intersect and modify the mechanical properties of pre-existing normal faults. We illustrate the influence that crystallised igneous intrusions may have on fault reactivation using a conceptual model and observations from field and subsurface datasets. Our results show that igneous rocks may initially resist failure, and promote the preferential reactivation of favourably-oriented, pre-existing faults that are not spatially-associated with solidified intrusions. Fault segments situated along strike from laterally restricted fault-intrusion intersections may similarly be reactivated. This spatial and temporal control on strain distribution may generate: (1) supra-intrusion folds in the hanging wall; (2) new dip-slip faults adjacent to the igneous body; or (3) sub-vertical, oblique-slip faults oriented parallel to the extension direction. Importantly, stress accumulation within igneous intrusions may eventually initiate failure and further localise strain. The results of our study have important implications for the structural of sedimentary basins and the subsurface migration of hydrocarbons and mineral-bearing fluids.

Magnetotelluric study to characterize Kachchh Mainland Fault (KMF) and Katrol Hill Fault (KHF) in the western part of Kachchh region of Gujarat, India

NASA Astrophysics Data System (ADS)

Mohan, Kapil; Chaudhary, Peush; Patel, Pruthul; Chaudhary, B. S.; Chopra, Sumer

2018-02-01

The Kachchh Mainland Fault (KMF) is a major E-W trending fault in the Kachchh region of Gujarat extending >150 km from Lakhpat village in the west to the Bhachau town in the east. The Katrol Hill Fault (KHF) is an E-W trending intrabasinal fault located in the central region of Kachchh Basin and the south of KMF. The western parts of both of the faults are characterized, and the sediment thickness has been estimated in the region using a Magnetotelluric (MT) survey at 17 sites along a 55 km long north-south profile with a site spacing of 2-3 km. The analysis reveals that the maximum sediment thickness is 2.3 km (Quaternary, Tertiary, and Mesozoic) in the region, out of which, the Mesozoic sediments feature a maximum thickness of 2 km. The estimated sediment thickness is found consistent with the thickness suggested by a deep borehole (depth approx. 2.5 km) drilled by Oil and Natural Gas Corporation (ONGC) at Nirona (Northern part of the study area). From 2-D inversion of the MT data, three conductive zones are identified from north to south. The first conductive zone is dipping nearly vertical down to 7-8 km depth. It becomes north-dipping below 8 km depth and is inferred as KMF. The second conductive zone is found steeply dipping into the southern limbs near Manjal village (28 km south of Nirona), which is inferred as the KHF. A vertical-dipping (down to 20 km depth) conductive zone has also been observed near Ulat village, located 16 km north of Manjal village and 12 km south of Nirona village. This conductive zone becomes listric north-dipping beyond 20 km depth. It is reported first time by a Geophysical survey in the region.

The role of rock anisotropy in developing non-Andersonian faults: staircase trajectories for strike-slip faults

NASA Astrophysics Data System (ADS)

Barchi, M. R.; Collettini, C.; Lena, G.

2012-04-01

Thrust and normal faults affecting mechanically heterogeneous multilayers often show staircase trajectories, where flat segments follow less competent units. Within flat segments the initiation/reactivation angle, θ, which is the angle that the fault makes with the σ1 direction, is different from that predicted by the Andersonian theory. This suggests that fault trajectory is mainly controlled by rock anisotropy instead of frictional properties of the material. Our study areas are located in the Umbria-Marche fold-thrust belt, within the Northern Apennines of Italy. The area is characterized by a lithologically complex multilayer, about 2000 m thick, consisting of alternated competent (mainly calcareous) and less competent (marls or evaporites) units. At the outcrop scale, some units show a significant mechanical layering, consisting of alternated limestones and shales. Due to the complex tectonic evolution of the Apennines, well developed sets of conjugate normal, thrust and strike-slip faults are exposed in the region. The study outcrop, Candigliano Gourge, is characterized by steep (dip > 60°) NE dipping beds, affected by conjugate sets of strike-slip faults, exposed in the eastern limb of a NE verging anticline. The faults develop within the Marne a Fucoidi Fm., a Cretaceous sedimentary unit, about 70 m thick, made of competent calcareous beds (about 20 cm thick), separated by marly beds (1-20 cm thick). The conjugate strike-slip faults are formed after the major folding phase: in fact the strike-slip faults cut both minor folds and striated bedding surfaces, related to syn-folding flexural slip. Faults show marked staircase trajectories, with straight segments almost parallel to the marly horizons and ramps cutting through the calcareous layers. Slip along these faults induces local block rotation of the competent strata, dilational jogs (pull-aparts), extensional duplexes and boudinage of the competent layers, while marly levels are strongly laminated. In

Evolution of triangular topographic facets along active normal faults

NASA Astrophysics Data System (ADS)

Balogun, A.; Dawers, N. H.; Gasparini, N. M.; Giachetta, E.

2011-12-01

Triangular shaped facets, which are generally formed by the erosion of fault - bounded mountain ranges, are arguably one of the most prominent geomorphic features on active normal fault scarps. Some previous studies of triangular facet development have suggested that facet size and slope exhibit a strong linear dependency on fault slip rate, thus linking their growth directly to the kinematics of fault initiation and linkage. Other studies, however, generally conclude that there is no variation in triangular facet geometry (height and slope) with fault slip rate. The landscape of the northeastern Basin and Range Province of the western United States provides an opportunity for addressing this problem. This is due to the presence of well developed triangular facets along active normal faults, as well as spatial variations in fault scale and slip rate. In addition, the Holocene climatic record for this region suggests a dominant tectonic regime, as the faulted landscape shows little evidence of precipitation gradients associated with tectonic uplift. Using GIS-based analyses of USGS 30 m digital elevation data (DEMs) for east - central Idaho and southwestern Montana, we analyze triangular facet geometries along fault systems of varying number of constituent segments. This approach allows us to link these geometries with established patterns of along - strike slip rate variation. For this study, we consider major watersheds to include only catchments with upstream and downstream boundaries extending from the drainage divide to the mapped fault trace, respectively. In order to maintain consistency in the selection criteria for the analyzed triangular facets, only facets bounded on opposite sides by major watersheds were considered. Our preliminary observations reflect a general along - strike increase in the surface area, average slope, and relief of triangular facets from the tips of the fault towards the center. We attribute anomalies in the along - strike geometric

Normal Fault Type Earthquakes Off Fukushima Region - Comparison of the 1938 Events and Recent Earthquakes -

NASA Astrophysics Data System (ADS)

Murotani, S.; Satake, K.

2017-12-01

Off Fukushima region, Mjma 7.4 (event A) and 6.9 (event B) events occurred on November 6, 1938, following the thrust fault type earthquakes of Mjma 7.5 and 7.3 on the previous day. These earthquakes were estimated as normal fault earthquakes by Abe (1977, Tectonophysics). An Mjma 7.0 earthquake occurred on July 12, 2014 near event B and an Mjma 7.4 earthquake occurred on November 22, 2016 near event A. These recent events are the only M 7 class earthquakes occurred off Fukushima since 1938. Except for the two 1938 events, normal fault earthquakes have not occurred until many aftershocks of the 2011 Tohoku earthquake. We compared the observed tsunami and seismic waveforms of the 1938, 2014, and 2016 earthquakes to examine the normal fault earthquakes occurred off Fukushima region. It is difficult to compare the tsunami waveforms of the 1938, 2014 and 2016 events because there were only a few observations at the same station. The teleseismic body wave inversion of the 2016 earthquake yielded with the focal mechanism of strike 42°, dip 35°, and rake -94°. Other source parameters were as follows: source area 70 km x 40 km, average slip 0.2 m, maximum slip 1.2 m, seismic moment 2.2 x 1019 Nm, and Mw 6.8. A large slip area is located near the hypocenter, and it is compatible with the tsunami source area estimated from tsunami travel times. The 2016 tsunami source area is smaller than that of the 1938 event, consistent with the difference in Mw: 7.7 for event A estimated by Abe (1977) and 6.8 for the 2016 event. Although the 2014 epicenter is very close to that of event B, the teleseismic waveforms of the 2014 event are similar to those of event A and the 2016 event. While Abe (1977) assumed that the mechanism of event B was the same as event A, the initial motions at some stations are opposite, indicating that the focal mechanisms of events A and B are different and more detailed examination is needed. The normal fault type earthquake seems to occur following the

The Dip. H.E. Coombe Lodge Report, Study Confererence 74/43.

ERIC Educational Resources Information Center

Further Education Staff Coll., Blagdon (England).

Papers presented on the Dip. H.E., a two-year course in higher education recently developed in Britain include: the future of higher education (W. Taylor); the colleges of education perspective on the Dip. H.E. (N. Payne); the colleges of further education perspective (W. Bosley); the polytechnics perspective (A. Sandbach); validating the diploma…

Holocene tectonics and fault reactivation in the foothills of the north Cascade Mountains, Washington

USGS Publications Warehouse

Sherrod, Brian L.; Barnett, Elizabeth; Schermer, Elizabeth; Kelsey, Harvey M.; Hughes, Jonathan; Foit, Franklin F.; Weaver, Craig S.; Haugerud, Ralph; Hyatt, Tim

2013-01-01

We use LiDAR imagery to identify two fault scarps on latest Pleistocene glacial outwash deposits along the North Fork Nooksack River in Whatcom County, Washington (United States). Mapping and paleoseismic investigation of these previously unknown scarps provide constraints on the earthquake history and seismic hazard in the northern Puget Lowland. The Kendall scarp lies along the mapped trace of the Boulder Creek fault, a south-dipping Tertiary normal fault, and the Canyon Creek scarp lies in close proximity to the south-dipping Canyon Creek fault and the south-dipping Glacier Extensional fault. Both scarps are south-side-up, opposite the sense of displacement observed on the nearby bedrock faults. Trenches excavated across these scarps exposed folded and faulted late Quaternary glacial outwash, locally dated between ca. 12 and 13 ka, and Holocene buried soils and scarp colluvium. Reverse and oblique faulting of the soils and colluvial deposits indicates at least two late Holocene earthquakes, while folding of the glacial outwash prior to formation of the post-glacial soil suggests an earlier Holocene earthquake. Abrupt changes in bed thickness across faults in the Canyon Creek excavation suggest a lateral component of slip. Sediments in a wetland adjacent to the Kendall scarp record three pond-forming episodes during the Holocene—we infer that surface ruptures on the Boulder Creek fault during past earthquakes temporarily blocked the stream channel and created an ephemeral lake. The Boulder Creek and Canyon Creek faults formed in the early to mid-Tertiary as normal faults and likely lay dormant until reactivated as reverse faults in a new stress regime. The most recent earthquakes—each likely Mw > 6.3 and dating to ca. 8050–7250 calendar years B.P. (cal yr B.P.), 3190–2980 cal. yr B.P., and 910–740 cal. yr B.P.—demonstrate that reverse faulting in the northern Puget Lowland poses a hazard to urban areas between Seattle (Washington) and Vancouver

Earthquake Clustering on Normal Faults: Insight from Rate-and-State Friction Models

NASA Astrophysics Data System (ADS)

Biemiller, J.; Lavier, L. L.; Wallace, L.

2016-12-01

Temporal variations in slip rate on normal faults have been recognized in Hawaii and the Basin and Range. The recurrence intervals of these slip transients range from 2 years on the flanks of Kilauea, Hawaii to 10 kyr timescale earthquake clustering on the Wasatch Fault in the eastern Basin and Range. In addition to these longer recurrence transients in the Basin and Range, recent GPS results there also suggest elevated deformation rate events with recurrence intervals of 2-4 years. These observations suggest that some active normal fault systems are dominated by slip behaviors that fall between the end-members of steady aseismic creep and periodic, purely elastic, seismic-cycle deformation. Recent studies propose that 200 year to 50 kyr timescale supercycles may control the magnitude, timing, and frequency of seismic-cycle earthquakes in subduction zones, where aseismic slip transients are known to play an important role in total deformation. Seismic cycle deformation of normal faults may be similarly influenced by its timing within long-period supercycles. We present numerical models (based on rate-and-state friction) of normal faults such as the Wasatch Fault showing that realistic rate-and-state parameter distributions along an extensional fault zone can give rise to earthquake clusters separated by 500 yr - 5 kyr periods of aseismic slip transients on some portions of the fault. The recurrence intervals of events within each earthquake cluster range from 200 to 400 years. Our results support the importance of stress and strain history as controls on a normal fault's present and future slip behavior and on the characteristics of its current seismic cycle. These models suggest that long- to medium-term fault slip history may influence the temporal distribution, recurrence interval, and earthquake magnitudes for a given normal fault segment.

Laboratory observations of fault strength in response to changes in normal stress

USGS Publications Warehouse

Kilgore, Brian D.; Lozos, Julian; Beeler, Nicholas M.; Oglesby, David

2012-01-01

Changes in fault normal stress can either inhibit or promote rupture propagation, depending on the fault geometry and on how fault shear strength varies in response to the normal stress change. A better understanding of this dependence will lead to improved earthquake simulation techniques, and ultimately, improved earthquake hazard mitigation efforts. We present the results of new laboratory experiments investigating the effects of step changes in fault normal stress on the fault shear strength during sliding, using bare Westerly granite samples, with roughened sliding surfaces, in a double direct shear apparatus. Previous experimental studies examining the shear strength following a step change in the normal stress produce contradictory results: a set of double direct shear experiments indicates that the shear strength of a fault responds immediately, and then is followed by a prolonged slip-dependent response, while a set of shock loading experiments indicates that there is no immediate component, and the response is purely gradual and slip-dependent. In our new, high-resolution experiments, we observe that the acoustic transmissivity and dilatancy of simulated faults in our tests respond immediately to changes in the normal stress, consistent with the interpretations of previous investigations, and verify an immediate increase in the area of contact between the roughened sliding surfaces as normal stress increases. However, the shear strength of the fault does not immediately increase, indicating that the new area of contact between the rough fault surfaces does not appear preloaded with any shear resistance or strength. Additional slip is required for the fault to achieve a new shear strength appropriate for its new loading conditions, consistent with previous observations made during shock loading.

The growth of geological structures by repeated earthquakes: 2, Field examples of continental dip-slip faults

USGS Publications Warehouse

Stein, R.S.; King, G.C.P.; Rundle, J.B.

1988-01-01

A strong test of our understanding of the earthquake cycle is the ability to reproduce extant faultbounded geological structures, such as basins and ranges, which are built by repeated cycles of deformation. Three examples are considered for which the structure and fault geometry are well known: the White Wolf reverse fault in California, site of the 1952 Kern County M=7.3 earthquake, the Lost River normal fault in Idaho, site of the 1983 Borah Peak M=7.0 earthquake, and the Cricket Mountain normal fault in Utah, site of Quaternary slip events. Basin stratigraphy and seismic reflection records are used to profile the structure, and coseismic deformation measured by leveling surveys is used to estimate the fault geometry. To reproduce these structures, we add the deformation associated with the earthquake cycle (the coseismic slip and postseismic relaxation) to the flexure caused by the observed sediment load, treating the crust as a thin elastic plate overlying a fluid substrate. -from Authors

Reverse fault growth and fault interaction with frictional interfaces: insights from analogue models

NASA Astrophysics Data System (ADS)

Bonanno, Emanuele; Bonini, Lorenzo; Basili, Roberto; Toscani, Giovanni; Seno, Silvio

2017-04-01

The association of faulting and folding is a common feature in mountain chains, fold-and-thrust belts, and accretionary wedges. Kinematic models are developed and widely used to explain a range of relationships between faulting and folding. However, these models may result not to be completely appropriate to explain shortening in mechanically heterogeneous rock bodies. Weak layers, bedding surfaces, or pre-existing faults placed ahead of a propagating fault tip may influence the fault propagation rate itself and the associated fold shape. In this work, we employed clay analogue models to investigate how mechanical discontinuities affect the propagation rate and the associated fold shape during the growth of reverse master faults. The simulated master faults dip at 30° and 45°, recalling the range of the most frequent dip angles for active reverse faults that occurs in nature. The mechanical discontinuities are simulated by pre-cutting the clay pack. For both experimental setups (30° and 45° dipping faults) we analyzed three different configurations: 1) isotropic, i.e. without precuts; 2) with one precut in the middle of the clay pack; and 3) with two evenly-spaced precuts. To test the repeatability of the processes and to have a statistically valid dataset we replicate each configuration three times. The experiments were monitored by collecting successive snapshots with a high-resolution camera pointing at the side of the model. The pictures were then processed using the Digital Image Correlation method (D.I.C.), in order to extract the displacement and shear-rate fields. These two quantities effectively show both the on-fault and off-fault deformation, indicating the activity along the newly-formed faults and whether and at what stage the discontinuities (precuts) are reactivated. To study the fault propagation and fold shape variability we marked the position of the fault tips and the fold profiles for every successive step of deformation. Then we compared

Investigating the Influence of Regional Stress on Fault and Fracture Permeability at Pahute Mesa, Nevada National Security Site

DOE Office of Scientific and Technical Information (OSTI.GOV)

Reeves, Donald M.; Smith, Kenneth D.; Parashar, Rishi

Regional stress may exert considerable control on the permeability and hydraulic function (i.e., barrier to and/or conduit for fluid flow) of faults and fractures at Pahute Mesa, Nevada National Security Site (NNSS). In-situ measurements of the stress field are sparse in this area, and short period earthquake focal mechanisms are used to delineate principal horizontal stress orientations. Stress field inversion solutions to earthquake focal mechanisms indicate that Pahute Mesa is located within a transtensional faulting regime, represented by oblique slip on steeply dipping normal fault structures, with maximum horizontal stress ranging from N29°E to N63°E and average of N42°E. Averagemore » horizontal stress directions are in general agreement with large diameter borehole breakouts from Pahute Mesa analyzed in this study and with stress measurements from other locations on the NNSS.« less

New constraints shed light on strike-slip faulting beneath the southern Apennines (Italy): The 21 August 1962 Irpinia multiple earthquake

NASA Astrophysics Data System (ADS)

Vannoli, Paola; Bernardi, Fabrizio; Palombo, Barbara; Vannucci, Gianfranco; Console, Rodolfo; Ferrari, Graziano

2016-11-01

On 21 August 1962 an earthquake sequence set off near the city of Benevento, in Italy's southern Apennines. Three earthquakes, the largest having Mw 6.1, struck virtually the same area in less than 40 min (at 18:09, 18:19 and 18:44 UTC, respectively). Several historical earthquakes hit this region, and its seismic hazard is accordingly among the highest countrywide. Although poorly understood in the past, the seismotectonics of this region can be revealed by the 1962 sequence, being the only significant earthquake in the area for which modern seismograms are available. We determine location, magnitude, and nodal planes of the first event (18:09 UTC) of the sequence. The focal mechanism exhibits dominant strike-slip rupture along a north-dipping, E-W striking plane or along a west-dipping, N-S striking plane. Either of these solutions is significantly different from the kinematics of the typical large earthquakes occurring along the crest of the Southern Apennines, such as the 23 November 1980 Irpinia earthquake (Mw 6.9), caused by predominant normal faulting along NW-SE-striking planes. The epicentre of the 21 August 1962, 18:09 event is located immediately east of the chain axis, near one of the three north-dipping, E-W striking oblique-slip sources thought to have caused one of the three main events of the December 1456 sequence (Io XI MCS), the most destructive events in the southern Apennines known to date. We maintain that the 21 August 1962, 18:09 earthquake occurred along the E-W striking fault system responsible for the southernmost event of the 1456 sequence and for two smaller but instrumentally documented events that occurred on 6 May 1971 (Mw 5.0) and 27 September 2012 (Mw 4.6), further suggesting that normal faulting is not the dominant tectonic style in this portion of the Italian peninsula.

CO2 Push-Pull Single Fault Injection Simulations

DOE Data Explorer

Borgia, Andrea; Oldenburg, Curtis (ORCID:0000000201326016); Zhang, Rui; Pan, Lehua; Daley, Thomas M.; Finsterle, Stefan; Ramakrishnan, T.S.; Doughty, Christine; Jung, Yoojin; Lee, Kyung Jae; Altundas, Bilgin; Chugunov, Nikita

2017-09-21

ASCII text files containing grid-block name, X-Y-Z location, and multiple parameters from TOUGH2 simulation output of CO2 injection into an idealized single fault representing a dipping normal fault at the Desert Peak geothermal field (readable by GMS). The fault is composed of a damage zone, a fault gouge and a slip plane. The runs are described in detail in the following: Borgia A., Oldenburg C.M., Zhang R., Jung Y., Lee K.J., Doughty C., Daley T.M., Chugunov N., Altundas B, Ramakrishnan T.S., 2017. Carbon Dioxide Injection for Enhanced Characterization of Faults and Fractures in Geothermal Systems. Proceedings of the 42st Workshop on Geothermal Reservoir Engineering, Stanford University, Stanford, California, February 13-17.

Shallow Seismic Reflection Study of Recently Active Fault Scarps, Mina Deflection, Western Nevada

NASA Astrophysics Data System (ADS)

Black, R. A.; Christie, M.; Tsoflias, G. P.; Stockli, D. F.

2006-12-01

During the spring and summer of 2006 University of Kansas geophysics students and faculty acquired shallow, high resolution seismic reflection data over actively deforming alluvial fans developing across the Emmigrant Peak (in Fish Lake Valley) and Queen Valley Faults in western Nevada. These normal faults represent a portion of the transition from the right-lateral deformation associated with the Walker Lane/Eastern California Shear Zone to the normal and left-lateral faulting of the Mina Deflection. Data were gathered over areas of recent high resolution geological mapping and limited trenching by KU students. An extensive GPR data grid was also acquired. The GPR results are reported in Christie, et al., 2006. The seismic data gathered in the spring included both walkaway tests and a short CMP test line. These data indicated that a very near-surface P-wave to S-wave conversion was taking place and that very high quality S-wave reflections were probably dominating shot records to over one second in time. CMP lines acquired during the summer utilized a 144 channel networked Geode system, single 28 hz geophones, and a 30.06 downhole rifle source. Receiver spacing was 0.5 m, source spacing 1.0m and CMP bin spacings were 0.25m for all lines. Surveying was performed using an RTK system which was also used to develop a concurrent high resolution DEM. A dip line of over 400m and a strike line over 100m in length were shot across the active fan scarp in Fish Lake Valley. Data processing is still underway. However, preliminary interpretation of common-offset gathers and brute stacks indicates very complex faulting and detailed stratigraphic information to depths of over 125m. Depth of information was actually limited by the 1024ms recording time. Several west-dipping normal faults downstep towards the basin. East-dipping antithetic normal faulting is extensive. Several distinctive stratigraphic packages are bound by the faults and apparent unconformitites. A CMP dip line

Faulting and hydration of the Juan de Fuca plate system

NASA Astrophysics Data System (ADS)

Nedimović, Mladen R.; Bohnenstiehl, DelWayne R.; Carbotte, Suzanne M.; Pablo Canales, J.; Dziak, Robert P.

2009-06-01

Multichannel seismic observations provide the first direct images of crustal scale normal faults within the Juan de Fuca plate system and indicate that brittle deformation extends up to ~ 200 km seaward of the Cascadia trench. Within the sedimentary layering steeply dipping faults are identified by stratigraphic offsets, with maximum throws of 110 ± 10 m found near the trench. Fault throws diminish both upsection and seaward from the trench. Long-term throw rates are estimated to be 13 ± 2 mm/kyr. Faulted offsets within the sedimentary layering are typically linked to larger offset scarps in the basement topography, suggesting reactivation of the normal fault systems formed at the spreading center. Imaged reflections within the gabbroic igneous crust indicate swallowing fault dips at depth. These reflections require local alteration to produce an impedance contrast, indicating that the imaged fault structures provide pathways for fluid transport and hydration. As the depth extent of imaged faulting within this young and sediment insulated oceanic plate is primarily limited to approximately Moho depths, fault-controlled hydration appears to be largely restricted to crustal levels. If dehydration embrittlement is an important mechanism for triggering intermediate-depth earthquakes within the subducting slab, then the limited occurrence rate and magnitude of intraslab seismicity at the Cascadia margin may in part be explained by the limited amount of water imbedded into the uppermost oceanic mantle prior to subduction. The distribution of submarine earthquakes within the Juan de Fuca plate system indicates that propagator wake areas are likely to be more faulted and therefore more hydrated than other parts of this plate system. However, being largely restricted to crustal levels, this localized increase in hydration generally does not appear to have a measurable effect on the intraslab seismicity along most of the subducted propagator wakes at the Cascadia margin.

High-resolution seismic profiling reveals faulting associated with the 1934 Ms 6.6 Hansel Valley earthquake (Utah, USA)

USGS Publications Warehouse

Bruno, Pier Paolo G.; Duross, Christopher; Kokkalas, Sotirios

2017-01-01

The 1934 Ms 6.6 Hansel Valley, Utah, earthquake produced an 8-km-long by 3-km-wide zone of north-south−trending surface deformation in an extensional basin within the easternmost Basin and Range Province. Less than 0.5 m of purely vertical displacement was measured at the surface, although seismologic data suggest mostly strike-slip faulting at depth. Characterization of the origin and kinematics of faulting in the Hansel Valley earthquake is important to understand how complex fault ruptures accommodate regions of continental extension and transtension. Here, we address three questions: (1) How does the 1934 surface rupture compare with faults in the subsurface? (2) Are the 1934 fault scarps tectonic or secondary features? (3) Did the 1934 earthquake have components of both strike-slip and dip-slip motion? To address these questions, we acquired a 6.6-km-long, high-resolution seismic profile across Hansel Valley, including the 1934 ruptures. We observed numerous east- and west-dipping normal faults that dip 40°−70° and offset late Quaternary strata from within a few tens of meters of the surface down to a depth of ∼1 km. Spatial correspondence between the 1934 surface ruptures and subsurface faults suggests that ruptures associated with the earthquake are of tectonic origin. Our data clearly show complex basin faulting that is most consistent with transtensional tectonics. Although the kinematics of the 1934 earthquake remain underconstrained, we interpret the disagreement between surface (normal) and subsurface (strike-slip) kinematics as due to slip partitioning during fault propagation and to the effect of preexisting structural complexities. We infer that the 1934 earthquake occurred along an ∼3-km wide, off-fault damage zone characterized by distributed deformation along small-displacement faults that may be alternatively activated during different earthquake episodes.

Faulting, Seismicity and Stress Interaction in the Salton Sea Region of Southern California

NASA Astrophysics Data System (ADS)

Kilb, D. L.; Brothers, D. S.; Lin, G.; Kent, G.; Newman, R. L.; Driscoll, N.

2009-12-01

The Salton Sea region in southern California provides an ideal location to study the relationship between transcurrent and extensional motion in the northern Gulf of California margin, allowing us to investigate the spatial and temporal interaction of faults in the area and better understand their kinematics. In this region, the San Andreas Fault (SAF) and Imperial Fault present two major transform faults separated by the Salton Sea transtensional domain. Earthquakes over magnitude 4 in this area almost always have associated aftershock sequences. Recent seismic reflection surveys in the Salton Sea reveal that the majority of faults under the southern Salton Sea trend ~N15°E, appear normal-dominant and have very minimal associated microseismicity. These normal faults rupture every 100-300 years in large earthquakes and most of the nearby microseismicity locates east of the mapped surface traces. For example, there is profuse microseismicity in the Brawley Seismic Zone (BSZ), which is coincident with the southern terminus of the SAF as it extends offshore into the Salton Sea. Earthquakes in the BSZ are dominantly swarm-like, occurring along short (<5 km) ~N45°E oriented sinistral and N35°W oriented dextral fault planes. This mapped seismicity makes a rung-and-ladder pattern. In an effort to reconcile differences between processes at the surface and those at seismogenic depths we integrate near surface fault kinematics, geometry and paleoseismic history with seismic data. We identify linear and planer trends in these data (20 near surface faults, >20,000 relocated earthquakes and >2,000 earthquake focal mechanisms) and when appropriate estimate the fault strike and dip using principal component analysis. With our more detailed image of the fault structure we assess how static stress changes imparted by magnitude ~6.0 ruptures along N15E oriented normal faults beneath the Salton Sea can modulate the stress field in the BSZ and along the SAF. These tests include

The offshore Palos Verdes fault zone near San Pedro, Southern California

USGS Publications Warehouse

Fisher, M.A.; Normark, W.R.; Langenheim, V.E.; Calvert, A.J.; Sliter, R.

2004-01-01

High-resolution seismic-reflection data are combined with a variety of other geophysical and geological data to interpret the offshore structure and earthquake hazards of the San Pedro shelf, near Los Angeles, California. Prominent structures investigated include the Wilmington graben, the Palos Verdes fault zone, various faults below the west part of the San Pedro shelf and slope, and the deep-water San Pedro basin. The structure of the Palos Verdes fault zone changes markedly along strike southeastward across the San Pedro shelf and slope. Under the north part of the shelf, this fault zone includes several strands, with the main strand dipping west. Under the slope, the main fault strands exhibit normal separation and mostly dip east. To the southeast near Lasuen Knoll, the Palos Verdes fault zone locally is low angle, but elsewhere near this knoll, the fault dips steeply. Fresh seafloor scarps near Lasuen Knoll indicate recent fault movement. We explain the observed structural variation along the Palos Verdes fault zone as the result of changes in strike and fault geometry along a master right-lateral strike-slip fault at depth. Complicated movement along this deep fault zone is suggested by the possible wave-cut terraces on Lasuen Knoll, which indicate subaerial exposure during the last sea level lowstand and subsequent subsidence of the knoll. Modeling of aeromagnetic data indicates a large magnetic body under the west part of the San Pedro shelf and upper slope. We interpret this body to be thick basalt of probable Miocene age. This basalt mass appears to have affected the pattern of rock deformation, perhaps because the basalt was more competent during deformation than the sedimentary rocks that encased the basalt. West of the Palos Verdes fault zone, other northwest-striking faults deform the outer shelf and slope. Evidence for recent movement along these faults is equivocal, because we lack age dates on deformed or offset sediment.

Extension across Tempe Terra, Mars, from measurements of fault scarp widths and deformed craters

USGS Publications Warehouse

Golombek, M.P.; Tanaka, K.L.; Franklin, B.J.

1996-01-01

Two independent methods, with no common assumptions, have been used to estimate the extension across the heavily deformed Tempe Terra province of the Tharsis region of Mars. One method uses measurements of normal fault scarp width with average scarp slope data for simple grabens and rifts on Mars to estimate the fault throw, which, combined with sparse fault dip data, can be used to estimate extension. Formal uncertainties in this method are only slightly greater than those in other methods, given that the total uncertainty is dominated by the likely uncertainty in the fault dip (assumed to be 60????15??). Measurement of normal fault scarp widths along two N25??-50??W directed traverses across Tempe Terra both yield about 22??16 km of extension (or ???2% strain across the northern traverse and nearly 3% across the southern one). About three quarters of the extension has occurred during the two main phases of Tharsis-related deformation from Middle/Late Noachian to Early Hesperian and from Late Hesperian to Early Amazonian, with more extension closer to the center of Tharsis during the first phase. Extension across the region was also determined by measuring the elongation and elongation direction of all ancient Noachian impact craters without ejecta blankets, which predate most of the deformation. Results have been corrected for initial non circularity of craters, established from similar measurements of young (post deformation) impact craters, yielding a statistically significant mean strain of 1.96??0.35% in a N38????10??W direction across Tempe Terra (extension of ???20??4, comparable in magnitude and direction to the average result from the scarp measurement method). Both methods indicate an average extension for single normal fault scarps (and shortening across wrinkle ridges for the crater method) of ???100 m. The agreement between the results of the two independent methods in overall extension and average single normal fault extension argues that the average

Extension across Tempe Terra, Mars, from measurements of fault scarp widths and deformed craters

NASA Astrophysics Data System (ADS)

Golombek, M. P.; Tanaka, K. L.; Franklin, B. J.

Two independent methods, with no common assumptions, have been used to estimate the extension across the heavily deformed Tempe Terra province of the Tharsis region of Mars. One method uses measurements of normal fault scarp width with average scarp slope data for simple grabens and rifts on Mars to estimate the fault throw, which, combined with sparse fault dip data, can be used to estimate extension. Formal uncertainties in this method are only slightly greater than those in other methods, given that the total uncertainty is dominated by the likely uncertainty in the fault dip (assumed to be 60°+/-15°). Measurement of normal fault scarp widths along two N25°-50°W directed traverses across Tempe Terra both yield about 22+/-16 km of extension (or ~2% strain across the northern traverse and nearly 3% across the southern one). About three quarters of the extension has occurred during the two main phases of Tharsis-related deformation from Middle/Late Noachian to Early Hesperian and from Late Hesperian to Early Amazonian, with more extension closer to the center of Tharsis during the first phase. Extension across the region was also determined by measuring the elongation and elongation direction of all ancient Noachian impact craters without ejecta blankets, which predate most of the deformation. Results have been corrected for initial non circularity of craters, established from similar measurements of young (post deformation) impact craters, yielding a statistically significant mean strain of 1.96+/-0.35% in a N38°+/-10°W direction across Tempe Terra (extension of ~20+/-4, comparable in magnitude and direction to the average result from the scarp measurement method). Both methods indicate an average extension for single normal fault scarps (and shortening across wrinkle ridges for the crater method) of ~100 m. The agreement between the results of the two independent methods in overall extension and average single normal fault extension argues that the average

Magnetic Fabric Associated with Faulting of Poorly Consolidated Basin Sediments of the Rio Grande Rift, New Mexico, USA

NASA Astrophysics Data System (ADS)

Hudson, M. R.; Minor, S. A.; Caine, J. S.

2015-12-01

Permanent strain in sediments associated with shallow fault zones can be difficult to characterize. Anisotropy of magnetic susceptibility (AMS) data were obtained from 120 samples at 6 sites to assess the nature of fault-related AMS fabrics for 4 faults cutting Miocene-Pliocene basin fill sediments of the Rio Grande rift of north-central New Mexico. The San Ysidro (3 sites), Sand Hill, and West Paradise faults within the northern Albuquerque basin have normal offset whereas an unnamed fault near Buckman in the western Española basin has oblique strike-slip offset. Previous studies have shown that detrital magnetite controls magnetic susceptibility in rift sandstones, and in a 50-m-long hanging wall traverse of the San Ysidro fault, non-gouge samples have typical sedimentary AMS fabrics with Kmax and Kint axes (defining magnetic foliation) scattered within bedding. For the 5 normal-fault sites, samples from fault cores or adjacent mixed zones that lie within 1 m of the principal slip surface developed common deformation fabrics with (1) magnetic foliation inclined in the same azimuth but more shallowly dipping than the fault plane, and (2) magnetic lineation plunging down foliation dip with nearly the same trend as the fault striae, although nearer for sand versus clay gouge samples. These relations suggest that the sampled fault materials deformed by particulate flow with alignment of magnetite grains in the plane of maximum shortening. For a 2-m-long traverse at the Buckman site, horizontal sedimentary AMS foliation persists to < 15 cm to the fault slip surface, wherein foliation in sand and clay gouge rotates toward the steeply dipping fault plane in a sense consistent with sinistral offset. Collectively these data suggest permanent deformation fabrics were localized within < 1 m of fault surfaces and that AMS fabrics from gouge samples can provide kinematic information for faults in unconsolidated sediments which may lack associated slickenlines.

Seismic and Aseismic Behavior of the Altotiberina Low-angle Normal Fault System (Northern Apennines, Italy) through High-resolution Earthquake Locations and Repeating Events

NASA Astrophysics Data System (ADS)

Valoroso, L.; Chiaraluce, L.

2017-12-01

Low-angle normal faults (dip < 30°) are geologically widely documented and considered responsible for accommodating the crustal extension within the brittle crust although their mechanical behavior and seismogenic potential is enigmatic. We study the anatomy and slip-behavior of the actively slipping Altotiberina low-angle (ATF) normal fault system using a high-resolution 5-years-long (2010-2014) earthquake catalogue composed of 37k events (ML<3.9 and completeness magnitude MC=0.5 ML), recorded by a dense permanent seismic network of the Altotiberina Near Fault Observatory (TABOO). The seismic activity defines the fault system dominated at depth by the low-angle ATF surface (15-20°) coinciding to the ATF geometry imaged through seismic reflection data. The ATF extends for 50km along-strike and between 4-5 to 16km of depth. Seismicity also images the geometry of a set of higher angle faults (35-50°) located in the ATF hanging-wall (HW). The ATF-related seismicity accounts for 10% of the whole seismicity (3,700 events with ML<2.4), occurring at a remarkably constant rate of 2.2 events/day. This seismicity describes an about 1.5-km-thick fault zone composed by multiple sub-parallel slipping planes. The remaining events are instead organized in multiple mainshocks (MW>3) seismic sequences lasting from weeks to months, activating a contiguous network of 3-5-km-long syn- and antithetic fault segments within the ATF-HW. The space-time evolution of these minor sequences is consistent with subsequence failures promoted by fluid flow. The ATF-seismicity pattern includes 97 clusters of repeating events (RE) made of 299 events with ML<1.9. RE are located around locked patches identified by geodetic modeling, suggesting a mixed-mode (stick-slip and stable-sliding) slip-behavior along the fault plane in accommodating most of the NE-trending tectonic deformation with creeping dominating below 5 km depth. Consistently, the seismic moment released by the ATF-seismicity accounts

The role of thin, mechanical discontinuities on the propagation of reverse faults: insights from analogue models

NASA Astrophysics Data System (ADS)

Bonanno, Emanuele; Bonini, Lorenzo; Basili, Roberto; Toscani, Giovanni; Seno, Silvio

2016-04-01

Fault-related folding kinematic models are widely used to explain accommodation of crustal shortening. These models, however, include simplifications, such as the assumption of constant growth rate of faults. This value sometimes is not constant in isotropic materials, and even more variable if one considers naturally anisotropic geological systems. , This means that these simplifications could lead to incorrect interpretations of the reality. In this study, we use analogue models to evaluate how thin, mechanical discontinuities, such as beddings or thin weak layers, influence the propagation of reverse faults and related folds. The experiments are performed with two different settings to simulate initially-blind master faults dipping at 30° and 45°. The 30° dip represents one of the Andersonian conjugate fault, and 45° dip is very frequent in positive reactivation of normal faults. The experimental apparatus consists of a clay layer placed above two plates: one plate, the footwall, is fixed; the other one, the hanging wall, is mobile. Motor-controlled sliding of the hanging wall plate along an inclined plane reproduces the reverse fault movement. We run thirty-six experiments: eighteen with dip of 30° and eighteen with dip of 45°. For each dip-angle setting, we initially run isotropic experiments that serve as a reference. Then, we run the other experiments with one or two discontinuities (horizontal precuts performed into the clay layer). We monitored the experiments collecting side photographs every 1.0 mm of displacement of the master fault. These images have been analyzed through PIVlab software, a tool based on the Digital Image Correlation method. With the "displacement field analysis" (one of the PIVlab tools) we evaluated, the variation of the trishear zone shape and how the master-fault tip and newly-formed faults propagate into the clay medium. With the "strain distribution analysis", we observed the amount of the on-fault and off-fault deformation

Evidence of post-Pleistocene faults on New Jersey Atlantic outer continental shelf

USGS Publications Warehouse

Sheridan, R.E.; Knebel, H.J.

1976-01-01

Recently obtained high-resolution seismic profiles (400-4,000-Hz band) show evidence of faults in shallow sedimentary strata near the edge of the Atlantic continental shelf off New Jersey. Apparent normal faults having a throw of about 1.5 m displace sediments to within 7 m of the sea floor. The faults appear to be overlain by undeformed horizontal beds of relatively recent age. Several faults 1 to 2 km apart strike approximately N70°E and dip northwest. The data suggest that the faults are upthrown on the southeast.Projection of the faults on the high-resolution profiles to a nearby multichannel seismic-reflection profile indicates that these shallow faults might be the near-surface expression of a more fundamental deep-seated fault. Several prominent reflectors in the multichannel records are offset by a high-angle normal fault reaching depths of 4.0 to 5.0 sec (6.0 to 6.5 km). The deep fault on the multichannel line also is upthrown on the southeast. Throws of as much as 90 m are apparent at depth, but offsets of as much as 10 m could be present in the shallower parts of the section that may not be resolved in the multichannel data.The position and strike of these faults coincide with and parallel the East Coast magnetic anomaly interpreted as the fundamental seaward basement boundary of the Baltimore Canyon trough. Recurring movements along such boundary faults are expected theoretically if the marginal basins are subsiding in response to the plate rotation of North America and seafloor spreading in the Atlantic.

Aksu-Dinar Fault System: Its bearing on the evolution of the Isparta Angle (SW Turkey)

NASA Astrophysics Data System (ADS)

Kaymakci, Nuretdin; Özacar, Arda; Langereis, Cornelis G.; Özkaptan, Murat; Gülyüz, Erhan; van Hinsbergen, Douwe J. J.; Uzel, Bora; McPhee, Peter; Sözbilir, Hasan

2017-04-01

The Isparta Angle is a triangular structure in SW Turkey with NE-SW trending western and NW-SE trending eastern flanks. Aksu Fault is located within the core of this structure and have been taken-up large E-W shortening and sinistral translation since the Late Miocene. It is an inherited structure which emplaced Antalya nappes over the Beydaǧları Platform during the late Eocene to Late Miocene and was reactivated by the Pliocene as a high angle reverse fault to accommodate the counter-clockwise rotation of Beydaǧları and SW Anatolia. On the other hand, the Dinar Fault is a normal fault with slight sinistral component has been active since Pliocene. These two structures are collinear and delimit areas with clockwise and counter-clockwise rotations. The areas to the north and east of these structures rotated clockwise while southern and western areas are rotated counter-clockwise. We claim that the Dinar-Aksu Fault System facilitate rotational deformation in the region as a scissor like mechanism about a pivot point north of Burdur. This mechanism resulted in the normal motion along the Dinar and reverse motion along the Aksu faults with combined sinistral translation component on both structures. We claim that the driving force for the motion of these faults and counter-clockwise rotation of the SW Anatolia seems to be slab-pull forces exerted by the east dipping Antalya Slab, a relic of Tethys oceanic lithosphere. The research for this paper is supported by TUBITAK - Grant Number 111Y239. Key words: Dinar Fault, Aksu Fault, Isparta Angle, SW Turkey, Burdur Pivot, Normal Fault, Reverse Fault

Flexure in the Corinth rift: reconciling marine terraces, rivers, offshore data and fault modeling

NASA Astrophysics Data System (ADS)

de Gelder, G.; Fernández-Blanco, D.; Jara-Muñoz, J.; Melnick, D.; Duclaux, G.; Bell, R. E.; Lacassin, R.; Armijo, R.

2016-12-01

The Corinth rift (Greece) is an exceptional area to study the large-scale mechanics of a young rift system, due to its extremely high extension rates and fault slip rates. Late Pleistocene activity of large normal faults has created a mostly asymmetric E-W trending graben, mainly driven by N-dipping faults that shape the southern margin of the Corinth Gulf. Flexural footwall uplift of these faults is evidenced by Late Pleistocene coastal fan deltas that are presently up to 1700m in elevation, a drainage reversal of some major river systems, and flights of marine terraces that have been uplifted along the southern margin of the Gulf. To improve constraints on this footwall uplift, we analysed the extensive terrace sequence between Xylokastro and Corinth - uplifted by the Xylokastro Fault - using 2m-resolution digital surface models developed from Pleiades satellite imagery (acquired through the Isis and Tosca programs of the French CNES). We refined and improved the spatial uplift pattern and age correlation of these terraces, through a detailed analysis of the shoreline angles using the graphical interface TerraceM, and 2D numerical modeling of terrace formation. We combine the detailed record of flexure provided by this analysis with a morphometric analysis of the major river systems along the southern shore, obtaining constraints of footwall uplift on a longer time scale and larger spatial scale. Flexural subsidence of the hanging wall is evidenced by offshore seismic sections, for which we depth-converted a multi-channel seismic section north of the Xylokastro Fault. We use the full profile of the fault geometry and its associated deformation pattern as constraints to reproduce the long-term flexural wavelength and uplift/subsidence ratio through fault modeling. Using PyLith, an open-source finite element code for quasi-static viscoelastic simulations, we find that a steep-dipping planar fault to the brittle-ductile transition provides the best fit to reproduce

Fault kinematics and active tectonics of the Sabah margin: Insights from the 2015, Mw 6.0, Mt. Kinabalu earthquake

NASA Astrophysics Data System (ADS)

Wang, Y.; Wei, S.; Tapponnier, P.; WANG, X.; Lindsey, E.; Sieh, K.

2016-12-01

A gravity-driven "Mega-Landslide" model has been evoked to explain the shortening seen offshore Sabah and Brunei in oil-company seismic data. Although this model is considered to account simultaneously for recent folding at the edge of the submarine NW Sabah trough and normal faulting on the Sabah shelf, such a gravity-driven model is not consistent with geodetic data or critical examination of extant structural restorations. The rupture that produced the 2015 Mw6.0 Mt. Kinabalu earthquake is also inconsistent with the gravity-driven model. Our teleseismic analysis shows that the centroid depth of that earthquake's mainshock was 13 to 14 km, and its favored fault-plane solution is a 60° NW-dipping normal fault. Our finite-rupture model exhibits major fault slip between 5 and 15 km depth, in keeping with our InSAR analysis, which shows no appreciable surface deformation. Both the hypocentral depth and the depth of principal slip are far too deep to be explained by gravity-driven failure, as such a model would predict a listric normal fault connecting at a much shallower depth with a very gentle detachment. Our regional mapping of tectonic landforms also suggests the recent rupture is part of a 200-km long system of narrowly distributed active extension in northern Sabah. Taken together, the nature of the 2015 rupture, the belt of active normal faults, and structural consideration indicate that active tectonic shortening plays the leading role in controlling the overall deformation of northern Sabah and that deep-seated, onland normal faulting likely results from an abrupt change in the dip-angle of the collision interface beneath the Sabah accretionary prism.

Multistory duplexes with forward dipping roofs, north central Brooks Range, Alaska

USGS Publications Warehouse

Wallace, W.K.; Moore, Thomas E.; Plafker, G.

1997-01-01

The Endicott Mountains allochthon has been thrust far northward over the North Slope parautochthon in the northern Brooks Range. Progressively younger units are exposed northward within the allochthon. To the south, the incompetent Hunt Fork Shale has thickened internally by asymmetric folds and thrust faults. Northward, the competent Kanayut Conglomerate forms a duplex between a floor thrust in Hunt Fork and a roof thrust in the Kayak Shale. To the north, the competent Lisburne Group forms a duplex between a floor thrust in Kayak and a roof thrust in the Siksikpuk Formation. Both duplexes formed from north vergent detachment folds whose steep limbs were later truncated by south dipping thrust faults that only locally breach immediately overlying roof thrusts. Within the parautochthon, the Kayak, Lisburne, and Siksikpuk-equivalent Echooka Formation form a duplex identical to that in the allochthon. This duplex is succeeded abruptly northward by detachment folds in Lisburne. These folds are parasitic to an anticlinorium interpreted to reflect a fault-bend folded horse in North Slope "basement," with a roof thrust in Kayak and a floor thrust at depth. These structures constitute two northward tapered, internally deformed wedges that are juxtaposed at the base of the allochthon. Within each wedge, competent units have been shortened independently between detachments, located mainly in incompetent units. The basal detachment of each wedge cuts upsection forward (northward) to define a wedge geometry within which units dip regionally forward. These dips reflect forward decrease in internal structural thickening by forward vergent folds and hindward dipping thrust faults. Copyright 1997 by the American Geophysical Union.

Identification of Lembang fault, West-Java Indonesia by using controlled source audio-magnetotelluric (CSAMT)

NASA Astrophysics Data System (ADS)

Sanny, Teuku A.

2017-07-01

The objective of this study is to determine boundary and how to know surrounding area between Lembang Fault and Cimandiri fault. For the detailed study we used three methodologies: (1). Surface deformation modeling by using Boundary Element method and (2) Controlled Source Audiomagneto Telluric (CSAMT). Based on the study by using surface deformation by using Boundary Element Methods (BEM), the direction Lembang fault has a dominant displacement in east direction. The eastward displacement at the nothern fault block is smaller than the eastward displacement at the southern fault block which indicates that each fault block move in left direction relative to each other. From this study we know that Lembang fault in this area has left lateral strike slip component. The western part of the Lembang fault move in west direction different from the eastern part that moves in east direction. Stress distribution map of Lembang fault shows difference between the eastern and western segments of Lembang fault. Displacement distribution map along x-direction and y-direction of Lembang fault shows a linement oriented in northeast-southwest direction right on Tangkuban Perahu Mountain. Displacement pattern of Cimandiri fault indicates that the Cimandiri fault is devided into two segment. Eastern segment has left lateral strike slip component while the western segment has right lateral strike slip component. Based on the displacement distribution map along y-direction, a linement oriented in northwest-southeast direction is observed at the western segment of the Cimandiri fault. The displacement along x-direction and y-direction between the Lembang and Cimandiri fault is nearly equal to zero indicating that the Lembang fault and Cimandiri Fault are not connected to each others. Based on refraction seismic tomography that we know the characteristic of Cimandiri fault as normal fault. Based on CSAMT method th e lembang fault is normal fault that different of dip which formed as

Rupture Process During the Mw 8.1 2017 Chiapas Mexico Earthquake: Shallow Intraplate Normal Faulting by Slab Bending

NASA Astrophysics Data System (ADS)

Okuwaki, R.; Yagi, Y.

2017-12-01

A seismic source model for the Mw 8.1 2017 Chiapas, Mexico, earthquake was constructed by kinematic waveform inversion using globally observed teleseismic waveforms, suggesting that the earthquake was a normal-faulting event on a steeply dipping plane, with the major slip concentrated around a relatively shallow depth of 28 km. The modeled rupture evolution showed unilateral, downdip propagation northwestward from the hypocenter, and the downdip width of the main rupture was restricted to less than 30 km below the slab interface, suggesting that the downdip extensional stresses due to the slab bending were the primary cause of the earthquake. The rupture front abruptly decelerated at the northwestern end of the main rupture where it intersected the subducting Tehuantepec Fracture Zone, suggesting that the fracture zone may have inhibited further rupture propagation.

On the use of imaginary faults in palaeostress analysis

NASA Astrophysics Data System (ADS)

Shan, Yehua; Liang, Xinquan

2017-11-01

The imaginary fault refers to the counterpart of a certain given fault that has a similar expression about the Wallace-Bott hypothesis. It is included to further reduce the feasible fields for the principal stress directions using the right dihedra method. The given fault and its imaginary fault have a similar dip-slip sense under the extensional or compressional regime but, as proved in this paper, a different dip-slip sense under the strike-slip regime. Their relation in dip-slip sense does no change with the rotation of the coordinate system, thus making possible the general use in the reduction of the imaginary faults under any tectonic regime. A procedure for this use is proposed and applied to a real example to demonstrate the feasibility of this method.

Internal architecture, permeability structure, and hydrologic significance of contrasting fault-zone types

NASA Astrophysics Data System (ADS)

Rawling, Geoffrey C.; Goodwin, Laurel B.; Wilson, John L.

2001-01-01

The Sand Hill fault is a steeply dipping, large-displacement normal fault that cuts poorly lithified Tertiary sediments of the Albuquerque basin, New Mexico, United States. The fault zone does not contain macroscopic fractures; the basic structural element is the deformation band. The fault core is composed of foliated clay flanked by structurally and lithologically heterogeneous mixed zones, in turn flanked by damage zones. Structures present within these fault-zone architectural elements are different from those in brittle faults formed in lithified sedimentary and crystalline rocks that do contain fractures. These differences are reflected in the permeability structure of the Sand Hill fault. Equivalent permeability calculations indicate that large-displacement faults in poorly lithified sediments have little potential to act as vertical-flow conduits and have a much greater effect on horizontal flow than faults with fractures.

Aftershocks of the june 20, 1978, Greece earthquake: A multimode faulting sequence

USGS Publications Warehouse

Carver, D.; Bollinger, G.A.

1981-01-01

A 10-station portable seismograph network was deployed in northern Greece to study aftershocks of the magnitude (mb) 6.4 earthquake of June 20, 1978. The main shock occurred (in a graben) about 25 km northeast of the city of Thessaloniki and caused an east-west zone of surface rupturing 14 km long that splayed to 7 km wide at the west end. The hypocenters for 116 aftershocks in the magnitude range from 2.5 to 4.5 were determined. The epicenters for these events cover an area 30 km (east-west) by 18 km (north-south), and focal depths ranges from 4 to 12 km. Most of the aftershocks in the east half of the aftershock zone are north of the surface rupture and north of the graben. Those in the west half are located within the boundaries of the graben. Composite focalmechanism solutions for selected aftershocks indicate reactivation of geologically mapped normal faults in the area. Also, strike-slip and dip-slip faults that splay off the western end of the zone of surface ruptures may have been activated. The epicenters for four large (M ??? 4.8) foreshocks and the main shock were relocated using the method of joint epicenter determination. Collectively, those five epicenters form an arcuate pattern convex southward, that is north of and 5 km distant from the surface rupturing. The 5-km separation, along with a focal depth of 8 km (average aftershock depth) or 16 km (NEIS main-shock depth), implies that the fault plane dips northward 58?? or 73??, respectively. A preferred nodal-plane dip of 36?? was determined by B.C. Papazachos and his colleagues in 1979 from a focal-mechanism solution for the main shock. If this dip is valid for the causal fault and that fault projects to the zone of surface rupturing, a decrease of dip with depth is required. ?? 1981.

Fault kinematics and localised inversion within the Troms-Finnmark Fault Complex, SW Barents Sea

NASA Astrophysics Data System (ADS)

Zervas, I.; Omosanya, K. O.; Lippard, S. J.; Johansen, S. E.

2018-04-01

The areas bounding the Troms-Finnmark Fault Complex are affected by complex tectonic evolution. In this work, the history of fault growth, reactivation, and inversion of major faults in the Troms-Finnmark Fault Complex and the Ringvassøy Loppa Fault Complex is interpreted from three-dimensional seismic data, structural maps and fault displacement plots. Our results reveal eight normal faults bounding rotated fault blocks in the Troms-Finnmark Fault Complex. Both the throw-depth and displacement-distance plots show that the faults exhibit complex configurations of lateral and vertical segmentation with varied profiles. Some of the faults were reactivated by dip-linkages during the Late Jurassic and exhibit polycyclic fault growth, including radial, syn-sedimentary, and hybrid propagation. Localised positive inversion is the main mechanism of fault reactivation occurring at the Troms-Finnmark Fault Complex. The observed structural styles include folds associated with extensional faults, folded growth wedges and inverted depocentres. Localised inversion was intermittent with rifting during the Middle Jurassic-Early Cretaceous at the boundaries of the Troms-Finnmark Fault Complex to the Finnmark Platform. Additionally, tectonic inversion was more intense at the boundaries of the two fault complexes, affecting Middle Triassic to Early Cretaceous strata. Our study shows that localised folding is either a product of compressional forces or of lateral movements in the Troms-Finnmark Fault Complex. Regional stresses due to the uplift in the Loppa High and halokinesis in the Tromsø Basin are likely additional causes of inversion in the Troms-Finnmark Fault Complex.

Spatial arrangement and size distribution of normal faults, Buckskin detachment upper plate, Western Arizona

NASA Astrophysics Data System (ADS)

Laubach, S. E.; Hundley, T. H.; Hooker, J. N.; Marrett, R. A.

2018-03-01

Fault arrays typically include a wide range of fault sizes and those faults may be randomly located, clustered together, or regularly or periodically located in a rock volume. Here, we investigate size distribution and spatial arrangement of normal faults using rigorous size-scaling methods and normalized correlation count (NCC). Outcrop data from Miocene sedimentary rocks in the immediate upper plate of the regional Buckskin detachment-low angle normal-fault, have differing patterns of spatial arrangement as a function of displacement (offset). Using lower size-thresholds of 1, 0.1, 0.01, and 0.001 m, displacements range over 5 orders of magnitude and have power-law frequency distributions spanning ∼ four orders of magnitude from less than 0.001 m to more than 100 m, with exponents of -0.6 and -0.9. The largest faults with >1 m displacement have a shallower size-distribution slope and regular spacing of about 20 m. In contrast, smaller faults have steep size-distribution slopes and irregular spacing, with NCC plateau patterns indicating imposed clustering. Cluster widths are 15 m for the 0.1-m threshold, 14 m for 0.01-m, and 1 m for 0.001-m displacement threshold faults. Results demonstrate normalized correlation count effectively characterizes the spatial arrangement patterns of these faults. Our example from a high-strain fault pattern above a detachment is compatible with size and spatial organization that was influenced primarily by boundary conditions such as fault shape, mechanical unit thickness and internal stratigraphy on a range of scales rather than purely by interaction among faults during their propagation.

How do horizontal, frictional discontinuities affect reverse fault-propagation folding?

NASA Astrophysics Data System (ADS)

Bonanno, Emanuele; Bonini, Lorenzo; Basili, Roberto; Toscani, Giovanni; Seno, Silvio

2017-09-01

The development of new reverse faults and related folds is strongly controlled by the mechanical characteristics of the host rocks. In this study we analyze the impact of a specific kind of anisotropy, i.e. thin mechanical and frictional discontinuities, in affecting the development of reverse faults and of the associated folds using physical scaled models. We perform analog modeling introducing one or two initially horizontal, thin discontinuities above an initially blind fault dipping at 30° in one case, and 45° in another, and then compare the results with those obtained from a fully isotropic model. The experimental results show that the occurrence of thin discontinuities affects both the development and the propagation of new faults and the shape of the associated folds. New faults 1) accelerate or decelerate their propagation depending on the location of the tips with respect to the discontinuities, 2) cross the discontinuities at a characteristic angle (∼90°), and 3) produce folds with different shapes, resulting not only from the dip of the new faults but also from their non-linear propagation history. Our results may have direct impact on future kinematic models, especially those aimed to reconstruct the tectonic history of faults that developed in layered rocks or in regions affected by pre-existing faults.

Normal block faulting in the Airport Graben, Managua pull-apart rift, Nicaragua: gravity and magnetic constraints

NASA Astrophysics Data System (ADS)

Campos-Enriquez, J. O.; Zambrana Arias, X.; Keppie, D.; Ramón Márquez, V.

2012-12-01

Regional scale models have been proposed for the Nicaraguan depression: 1) parallel rifting of the depression (and volcanic front) due to roll back of the underlying subducted Cocos plate; 2) right-lateral strike-slip faulting parallel to the depression and locally offset by pull-apart basins; 3) right-lateral strike-slip faulting parallel to the depression and offset by left-lateral transverse or bookshelf faults. At an intermediate scale, Funk et al. (2011) interpret the depression as half graben type structures. The E-W Airport graben lies in the southeastern part of the Managua graben (Nicaragua), across which the active Central American volcanic arc is dextrally offset, possibly the result of a subducted transform fault where the subduction angle changes. The Managua graben lies within the late Quaternary Nicaragua depression produced by backarc rifting during roll back of the Middle American Trench. The Managua graben formed as a pull-apart rift associated with dextral bookshelf faulting during dextral shear between the forearc and arc and is the locus of two historical, large earthquakes that destroyed the city of Managua. In order to asses future earthquake risk, four E-W gravity and magnetic profiles were undertaken to determine its structure across the Airport graben, which is bounded by the Cofradia and Airport fault zones, to the east and west, respectively. These data indicated the presence of a series of normal faults bounding down-thrown and up-thrown fault blocks and a listric normal fault, Sabana Grande Fault. The models imply that this area has been subjected to tectonic extension. These faults appear to be part of the bookshelf suite and will probably be the locus of future earthquakes, which could destroy the airport and surrounding part of Managua. Three regional SW-NE gravity profiles running from the Pacific Ocean up to the Caribbean See indicate a change in crustal structure: from north to south the crust thins. According to these regional

Geophysical data reveal the crustal structure of the Alaska Range orogen within the aftershock zone of the Mw 7.9 Denali fault earthquake

USGS Publications Warehouse

Fisher, M.A.; Ratchkovski, N.A.; Nokleberg, W.J.; Pellerin, L.; Glen, J.M.G.

2004-01-01

Geophysical information, including deep-crustal seismic reflection, magnetotelluric (MT), gravity, and magnetic data, cross the aftershock zone of the 3 November 2002 Mw 7.9 Denali fault earthquake. These data and aftershock seismicity, jointly interpreted, reveal the crustal structure of the right-lateral-slip Denali fault and the eastern Alaska Range orogen, as well as the relationship between this structure and seismicity. North of the Denali fault, strong seismic reflections from within the Alaska Range orogen show features that dip as steeply as 25?? north and extend downward to depths between 20 and 25 km. These reflections reveal crustal structures, probably ductile shear zones, that most likely formed during the Late Cretaceous, but these structures appear to be inactive, having produced little seismicity during the past 20 years. Furthermore, seismic reflections mainly dip north, whereas alignments in aftershock hypocenters dip south. The Denali fault is nonreflective, but modeling of MT, gravity, and magnetic data suggests that the Denali fault dips steeply to vertically. However, in an alternative structural model, the Denali fault is defined by one of the reflection bands that dips to the north and flattens into the middle crust of the Alaska Range orogen. Modeling of MT data indicates a rock body, having low electrical resistivity (>10 ??-m), that lies mainly at depths greater than 10 km, directly beneath aftershocks of the Denali fault earthquake. The maximum depth of aftershocks along the Denali fault is 10 km. This shallow depth may arise from a higher-than-normal geothermal gradient. Alternatively, the low electrical resistivity of deep rocks along the Denali fault may be associated with fluids that have weakened the lower crust and helped determine the depth extent of the after-shock zone.

Structure of the San Andreas Fault Zone in the Salton Trough Region of Southern California: A Comparison with San Andreas Fault Structure in the Loma Prieta Area of Central California

NASA Astrophysics Data System (ADS)

Fuis, G. S.; Catchings, R.; Scheirer, D. S.; Goldman, M.; Zhang, E.; Bauer, K.

2016-12-01

The San Andreas fault (SAF) in the northern Salton Trough, or Coachella Valley, in southern California, appears non-vertical and non-planar. In cross section, it consists of a steeply dipping segment (75 deg dip NE) from the surface to 6- to 9-km depth, and a moderately dipping segment below 6- to 9-km depth (50-55 deg dip NE). It also appears to branch upward into a flower-like structure beginning below about 10-km depth. Images of the SAF zone in the Coachella Valley have been obtained from analysis of steep reflections, earthquakes, modeling of potential-field data, and P-wave tomography. Review of seismological and geodetic research on the 1989 M 6.9 Loma Prieta earthquake, in central California (e.g., U.S. Geological Survey Professional Paper 1550), shows several features of SAF zone structure similar to those seen in the northern Salton Trough. Aftershocks in the Loma Prieta epicentral area form two chief clusters, a tabular zone extending from 18- to 9-km depth and a complex cluster above 5-km depth. The deeper cluster has been interpreted to surround the chief rupture plane, which dips 65-70 deg SW. When double-difference earthquake locations are plotted, the shallower cluster contains tabular subclusters that appear to connect the main rupture with the surface traces of the Sargent and Berrocal faults. In addition, a diffuse cluster may surround a steep to vertical fault connecting the main rupture to the surface trace of the SAF. These interpreted fault connections from the main rupture to surface fault traces appear to define a flower-like structure, not unlike that seen above the moderately dipping segment of the SAF in the Coachella Valley. But importantly, the SAF, interpreted here to include the main rupture plane, appears segmented, as in the Coachella Valley, with a moderately dipping segment below 9-km depth and a steep to vertical segment above that depth. We hope to clarify fault-zone structure in the Loma Prieta area by reanalyzing active

Evolution of the Median Tectonic Line fault zone, SW Japan, during exhumation

NASA Astrophysics Data System (ADS)

Shigematsu, Norio; Kametaka, Masao; Inada, Noriyuki; Miyawaki, Masahiro; Miyakawa, Ayumu; Kameda, Jun; Togo, Tetsuhiro; Fujimoto, Koichiro

2017-01-01

Like many crustal-scale fault zones, the Median Tectonic Line (MTL) fault zone in Japan preserves fault rocks that formed across a broad range of physical conditions. We examined the architecture of the MTL at a large new outcrop in order to understand fault behaviours under different crustal levels. The MTL here strikes almost E-W, dips to the north, and juxtaposes the Sanbagawa metamorphic rocks to the south against the Izumi Group sediments to the north. The fault core consists mainly of Sanbagawa-derived fault gouges. The fault zone can be divided into several structural units, including two slip zones (upper and lower slip zones), where the lower slip zone is more conspicuous. Crosscutting relationships among structures and kinematics indicate that the fault zone records four stages of deformation. Microstructures and powder X-ray diffraction (XRD) analyses indicate that the four stages of deformation occurred under different temperature conditions. The oldest deformation (stage 1) was widely distributed, and had a top-to-the-east (dextral) sense of slip at deep levels of the seismogenic zone. Deformation with the same sense of slip, then became localised in the lower slip zone (stage 2). Subsequently, the slip direction in the lower slip zone changed to top-to-the-west (sinistral-normal) (stage 3). The final stage of deformation (stage 4) involved top-to-the-north normal faulting along the two slip zones within the shallow crust (near the surface). The widely distributed stage 1 damage zone characterises the deeper part of the seismogenic zone, while the sets of localised principal slip zones and branching faults of stage 4 characterise shallow depths. The fault zone architecture described in this paper leads us to suggest that fault zones display different behaviours at different crustal levels.

In-situ stress and fracture permeability in a fault-hosted geothermal reservoir at Dixie Valley, Nevada

USGS Publications Warehouse

Hickman, Stephen; Barton, Colleen; Zoback, Mark; Morin, Roger; Sass, John; Benoit, Richard; ,

1997-01-01

As part of a study relating fractured rock hydrology to in-situ stress and recent deformation within the Dixie Valley Geothermal Field, borehole televiewer logging and hydraulic fracturing stress measurements were conducted in a 2.7-km-deep geothermal production well (73B-7) drilled into the Stillwater fault zone. Borehole televiewer logs from well 73B-7 show numerous drilling-induced tensile fractures, indicating that the direction of the minimum horizontal principal stress, Shmin, is S57 ??E. As the Stillwater fault at this location dips S50 ??E at approximately 3??, it is nearly at the optimal orientation for normal faulting in the current stress field. Analysis of the hydraulic fracturing data shows that the magnitude of Shmin is 24.1 and 25.9 MPa at 1.7 and 2.5 km, respectively. In addition, analysis of a hydraulic fracturing test from a shallow well 1.5 km northeast of 73B-7 indicates that the magnitude of Shmin is 5.6 MPa at 0.4 km depth. Coulomb failure analysis shows that the magnitude of Shmin in these wells is close to that predicted for incipient normal faulting on the Stillwater and subparallel faults, using coefficients of friction of 0.6-1.0 and estimates of the in-situ fluid pressure and overburden stress. Spinner flowmeter and temperature logs were also acquired in well 73B-7 and were used to identify hydraulically conductive fractures. Comparison of these stress and hydrologic data with fracture orientations from the televiewer log indicates that hydraulically conductive fractures within and adjacent to the Stillwater fault zone are critically stressed, potentially active normal faults in the current west-northwest extensional stress regime at Dixie Valley.

The Bear River Fault Zone, Wyoming and Utah: Complex Ruptures on a Young Normal Fault

NASA Astrophysics Data System (ADS)

Schwartz, D. P.; Hecker, S.; Haproff, P.; Beukelman, G.; Erickson, B.

2012-12-01

The Bear River fault zone (BRFZ), a set of normal fault scarps located in the Rocky Mountains at the eastern margin of Basin and Range extension, is a rare example of a nascent surface-rupturing fault. Paleoseismic investigations (West, 1994; this study) indicate that the entire neotectonic history of the BRFZ may consist of two large surface-faulting events in the late Holocene. We have estimated a maximum per-event vertical displacement of 6-6.5 m at the south end of the fault where it abuts the north flank of the east-west-trending Uinta Mountains. However, large hanging-wall depressions resulting from back rotation, which front scarps that locally exceed 15 m in height, are prevalent along the main trace, obscuring the net displacement and its along-strike distribution. The modest length (~35 km) of the BRFZ indicates ruptures with a large displacement-to-length ratio, which implies earthquakes with a high static stress drop. The BRFZ is one of several immature (low cumulative displacement) normal faults in the Rocky Mountain region that appear to produce high-stress drop earthquakes. West (1992) interpreted the BRFZ as an extensionally reactivated ramp of the late Cretaceous-early Tertiary Hogsback thrust. LiDAR data on the southern section of the fault and Google Earth imagery show that these young ruptures are more extensive than currently mapped, with newly identified large (>10m) antithetic scarps and footwall graben. The scarps of the BRFZ extend across a 2.5-5.0 km-wide zone, making this the widest and most complex Holocene surface rupture in the Intermountain West. The broad distribution of Late Holocene scarps is consistent with reactivation of shallow bedrock structures but the overall geometry of the BRFZ at depth and its extent into the seismogenic zone are uncertain.

Voltage dips at the terminals of wind power installations

NASA Astrophysics Data System (ADS)

Bollen, Math H. J.; Olguin, Gabriel; Martins, Marcia

2005-07-01

This article gives an overview of the kind of voltage dips that can be expected at the terminals of a wind power installation. The overview is based on the study of those dips at the terminals of industrial installations and provides a guideline for the testing of wind power installations against voltage dips. For voltage dips due to faults, a classification into different types is presented. Five types appear at the terminals of sensitive equipment and thus have to be included when testing the wind power installation against disturbances coming from the grid. A distinction is made between installations connected at transmission level and those connected at distribution level. For the latter the phase angle jump has to be considered. Dips due to other causes (motor, transformer and capacitor switching) are briefly discussed as well as the voltage recovery after a dip. Finally some thoughts are presented on the way in which voltage tolerance requirements should be part of the design process for wind power installations. Copyright

New insights on active fault geometries in the Mentawai region of Sumatra, Indonesia, from broadband waveform modeling of earthquake source parameters

NASA Astrophysics Data System (ADS)

WANG, X.; Wei, S.; Bradley, K. E.

2017-12-01

Global earthquake catalogs provide important first-order constraints on the geometries of active faults. However, the accuracies of both locations and focal mechanisms in these catalogs are typically insufficient to resolve detailed fault geometries. This issue is particularly critical in subduction zones, where most great earthquakes occur. The Slab 1.0 model (Hayes et al. 2012), which was derived from global earthquake catalogs, has smooth fault geometries, and cannot adequately address local structural complexities that are critical for understanding earthquake rupture patterns, coseismic slip distributions, and geodetically monitored interseismic coupling. In this study, we conduct careful relocation and waveform modeling of earthquake source parameters to reveal fault geometries in greater detail. We take advantage of global data and conduct broadband waveform modeling for medium size earthquakes (M>4.5) to refine their source parameters, which include locations and fault plane solutions. The refined source parameters can greatly improve the imaging of fault geometry (e.g., Wang et al., 2017). We apply these approaches to earthquakes recorded since 1990 in the Mentawai region offshore of central Sumatra. Our results indicate that the uncertainty of the horizontal location, depth and dip angle estimation are as small as 5 km, 2 km and 5 degrees, respectively. The refined catalog shows that the 2005 and 2009 "back-thrust" sequences in Mentawai region actually occurred on a steeply landward-dipping fault, contradicting previous studies that inferred a seaward-dipping backthrust. We interpret these earthquakes as `unsticking' of the Sumatran accretionary wedge along a backstop fault that separates accreted material of the wedge from the strong Sunda lithosphere, or reactivation of an old normal fault buried beneath the forearc basin. We also find that the seismicity on the Sunda megathrust deviates in location from Slab 1.0 by up to 7 km, with along strike

Frictional response of simulated faults to normal stresses perturbations probed with ultrasonic waves

NASA Astrophysics Data System (ADS)

Shreedharan, S.; Riviere, J.; Marone, C.

2017-12-01

We report on a suite of laboratory friction experiments conducted on saw-cut Westerly Granite surfaces to probe frictional response to step changes in normal stress and loading rate. The experiments are conducted to illuminate the fundamental processes that yield friction rate and state dependence. We quantify the microphysical frictional response of the simulated fault surfaces to normal stress steps, in the range of 1% - 600% step increases and decreases from a nominal baseline normal stress. We measure directly the fault slip rate and account for changes in slip rate with changes in normal stress and complement mechanical data acquisition by continuously probing the faults with ultrasonic pulses. We conduct the experiments at room temperature and humidity conditions in a servo controlled biaxial testing apparatus in the double direct shear configuration. The samples are sheared over a range of velocities, from 0.02 - 100 μm/s. We report observations of a transient shear stress and friction evolution with step increases and decreases in normal stress. Specifically, we show that, at low shear velocities and small increases in normal stress (<5% increase), the shear stress on the fault does not increase instantaneously with the normal stress step while the ultrasonic wave amplitude and normal displacement do. In other words, the shear stress does not follow the load point stiffness curve. At high shear velocities and larger normal stress steps (> 5% increases), the shear stress evolves immediately with normal stress. We show that the excursions in slip rate resulting from the changes in normal stress must be accounted for in order to predict fault strength evolution. Ultrasonic wave amplitudes which first increase immediately in response to normal stress steps, then decrease approximately linearly to a new steady state value, in part due to changes in fault slip rate. Previous descriptions of frictional state evolution during normal stress perturbations have not

Geometry of Thrust Faults Beneath Amenthes Rupes, Mars

NASA Technical Reports Server (NTRS)

Vidal, A.; Mueller, K. M.; Golombek, M. P.

2005-01-01

Amenthes Rupes is a 380 km-long lobate fault scarp located in the eastern hemisphere of Mars near the dichotomy boundary. The scarp is marked by about 1 km of vertical separation across a northeast dipping thrust fault (top to the SW) and offsets heavily-cratered terrain of Late Noachian age, the visible portion of which was in place by 3.92 Ga and the buried portion in place between 4.08 and 4.27 Ga. The timing of scarp formation is difficult to closely constrain. Previous geologic mapping shows that near the northern end of Amenthes Rupes, Hesperian age basalts terminate at the scarp, suggesting that fault slip predated the emplacement of these flows at 3.69 to 3.9 Ga. Maxwell and McGill also suggest the faulting ceased before the final emplacement of the Late Hesperian lavas on Isidis Planitia. The trend of the faults at Amenthes, like many thrust faults at the dichotomy boundary, parallels the boundary itself. Schultz and Watters used a dislocation modeling program to match surface topography and vertical offset of the scarp at Amenthes Rupes, varying the dip and depth of faulting, assuming a slip of 1.5 km on the fault. They modeled faulting below Amenthes Rupes as having a dip of between 25 and 30 degrees and a depth of 25 to 35 km, based on the best match to topography. Assuming a 25 degree dip and surface measurements of vertical offset of between 0.3 and 1.2 km, Watters later estimated the maximum displacement on the Amenthes Rupes fault to be 2.90 km. However, these studies did not determine the geometry of the thrust using quantitative constraints that included shortening estimates. Amenthes Rupes deforms large preexisting impact craters. We use these craters to constrain shortening across the scarp and combine this with vertical separation to infer fault geometry. Fault dip was also estimated using measurements of scarp morphology. Measurements were based on 460 m (1/128 per pixel) digital elevation data from the Mars Orbiter Laser Altimeter (MOLA), an

Distribution and nature of fault architecture in a layered sandstone and shale sequence: An example from the Moab fault, Utah

USGS Publications Warehouse

Davatzes, N.C.; Aydin, A.

2005-01-01

We examined the distribution of fault rock and damage zone structures in sandstone and shale along the Moab fault, a basin-scale normal fault with nearly 1 km (0.62 mi) of throw, in southeast Utah. We find that fault rock and damage zone structures vary along strike and dip. Variations are related to changes in fault geometry, faulted slip, lithology, and the mechanism of faulting. In sandstone, we differentiated two structural assemblages: (1) deformation bands, zones of deformation bands, and polished slip surfaces and (2) joints, sheared joints, and breccia. These structural assemblages result from the deformation band-based mechanism and the joint-based mechanism, respectively. Along the Moab fault, where both types of structures are present, joint-based deformation is always younger. Where shale is juxtaposed against the fault, a third faulting mechanism, smearing of shale by ductile deformation and associated shale fault rocks, occurs. Based on the knowledge of these three mechanisms, we projected the distribution of their structural products in three dimensions along idealized fault surfaces and evaluated the potential effect on fluid and hydrocarbon flow. We contend that these mechanisms could be used to facilitate predictions of fault and damage zone structures and their permeability from limited data sets. Copyright ?? 2005 by The American Association of Petroleum Geologists.

Shallow subsurface imaging of the Piano di Pezza active normal fault (central Italy) by high-resolution refraction and electrical resistivity tomography coupled with time-domain electromagnetic data

NASA Astrophysics Data System (ADS)

Villani, Fabio; Tulliani, Valerio; Sapia, Vincenzo; Fierro, Elisa; Civico, Riccardo; Pantosti, Daniela

2015-12-01

The Piano di Pezza fault is the central section of the 35 km long L'Aquila-Celano active normal fault-system in the central Apennines of Italy. Although palaeoseismic data document high Holocene vertical slip rates (˜1 mm yr-1) and a remarkable seismogenic potential of this fault, its subsurface setting and Pleistocene cumulative displacement are still poorly known. We investigated for the first time the shallow subsurface of a key section of the main Piano di Pezza fault splay by means of high-resolution seismic and electrical resistivity tomography coupled with time-domain electromagnetic soundings (TDEM). Our surveys cross a ˜5-m-high fault scarp that was generated by repeated surface-rupturing earthquakes displacing Holocene alluvial fans. We provide 2-D Vp and resistivity images, which show significant details of the fault structure and the geometry of the shallow basin infill material down to 50 m depth. Our data indicate that the upper fault termination has a sub-vertical attitude, in agreement with palaeoseismological trench evidence, whereas it dips ˜50° to the southwest in the deeper part. We recognize some low-velocity/low-resistivity regions in the fault hangingwall that we relate to packages of colluvial wedges derived from scarp degradation, which may represent the record of some Holocene palaeo-earthquakes. We estimate a ˜13-15 m throw of this fault splay since the end of the Last Glacial Maximum (˜18 ka), leading to a 0.7-0.8 mm yr-1 throw rate that is quite in accordance with previous palaeoseismic estimation of Holocene vertical slip rates. The 1-D resistivity models from TDEM soundings collected along the trace of the electrical profile significantly match with 2-D resistivity images. Moreover, they indicate that in the fault hangingwall, ˜200 m away from the surface fault trace, the pre-Quaternary carbonate basement is at ˜90-100 m depth. We therefore provide a minimal ˜150-160 m estimate of the cumulative throw of the Piano di Pezza

Sub-Moho Reflectors, Mantle Faults and Lithospheric Rheology

NASA Astrophysics Data System (ADS)

Brown, L. D.

2013-12-01

One of the most unexpected and dramatic observations from the early years of deep reflection profiling of the continents using multichannel CMP techniques was the existing of prominent reflections from the upper mantle. The first of these, the Flannan thrust/fault/feature, was traced by marine profiling of the continental margin offshore Britain by the BIRPS program, which soon found them to be but one of several clear sub-crustal discontinuities in that area. Subsequently, similar mantle reflectors have been observed in many areas around the world, most commonly beneath Precambrian cratonic areas. Many, but not all, of these mantle reflections appear to arise from near the overlying Moho or within the lower crust before dipping well into the mantle. Others occur as subhorizontal events at various depths with the mantle, with one suite seeming to cluster at a depth of about 75 km. The dipping events have been variously interpreted as mantle roots of crustal normal faults or the deep extension of crustal thrust faults. The most common interpretation, however, is that these dipping events are the relicts of ancient subduction zones, the stumps of now detached Benioff zones long since reclaimed by the deeper mantle. In addition to the BIRPS reflectors, the best known examples include those beneath Fennoscandia in northern Europe, the Abitibi-Grenville of eastern Canada, and the Slave Province of northwestern Canada (e.g. on the SNORCLE profile). The most recently reported example is from beneath the Sichuan Basin of central China. The preservation of these coherent, and relatively delicate appearing, features beneath older continental crust and presumably within equally old (of not older) mantle lithosphere, has profound implications for the history and rheology of the lithosphere in these areas. If they represent, as widely believe, some form of faulting with the lithosphere, they provide corollary constraints on the nature of faulting in both the lower crust and

Deformation pattern during normal faulting: A sequential limit analysis

NASA Astrophysics Data System (ADS)

Yuan, X. P.; Maillot, B.; Leroy, Y. M.

2017-02-01

We model in 2-D the formation and development of half-graben faults above a low-angle normal detachment fault. The model, based on a "sequential limit analysis" accounting for mechanical equilibrium and energy dissipation, simulates the incremental deformation of a frictional, cohesive, and fluid-saturated rock wedge above the detachment. Two modes of deformation, gravitational collapse and tectonic collapse, are revealed which compare well with the results of the critical Coulomb wedge theory. We additionally show that the fault and the axial surface of the half-graben rotate as topographic subsidence increases. This progressive rotation makes some of the footwall material being sheared and entering into the hanging wall, creating a specific region called foot-to-hanging wall (FHW). The model allows introducing additional effects, such as weakening of the faults once they have slipped and sedimentation in their hanging wall. These processes are shown to control the size of the FHW region and the number of fault-bounded blocks it eventually contains. Fault weakening tends to make fault rotation more discontinuous and this results in the FHW zone containing multiple blocks of intact material separated by faults. By compensating the topographic subsidence of the half-graben, sedimentation tends to slow the fault rotation and this results in the reduction of the size of the FHW zone and of its number of fault-bounded blocks. We apply the new approach to reproduce the faults observed along a seismic line in the Southern Jeanne d'Arc Basin, Grand Banks, offshore Newfoundland. There, a single block exists in the hanging wall of the principal fault. The model explains well this situation provided that a slow sedimentation rate in the Lower Jurassic is proposed followed by an increasing rate over time as the main detachment fault was growing.

Deriving earthquake history of the Knidos Fault Zone, SW Turkey, using cosmogenic 36Cl surface exposure dating of the fault scarp.

NASA Astrophysics Data System (ADS)

Yildirim, Cengiz; Ersen Aksoy, Murat; Akif Sarikaya, Mehmet; Tuysuz, Okan; Genc, S. Can; Ertekin Doksanalti, Mustafa; Sahin, Sefa; Benedetti, Lucilla; Tesson, Jim; Aster Team

2016-04-01

Formation of bedrock fault scarps in extensional provinces is a result of large and successive earthquakes that ruptured the surface several times. Extraction of seismic history of such faults is critical to understand the recurrence intervals and the magnitude of paleo-earthquakes and to better constrain the regional seismic hazard. Knidos on the Datca Peninsula (SW Turkey) is one of the largest cities of the antique times and sits on a terraced hill slope formed by en-echelon W-SW oriented normal faults. The Datça Peninsula constitutes the southern boundary of the Gulf of Gökova, one of the largest grabens developed on the southernmost part of the Western Anatolian Extensional Province. Our investigation relies on cosmogenic 36Cl surface exposure dating of limestone faults scarps. This method is a powerful tool to reconstruct the seismic history of normal faults (e.g. Schlagenhauf et al 2010, Benedetti et al. 2013). We focus on one of the most prominent fault scarp (hereinafter Mezarlık Fault) of the Knidos fault zone cutting through the antique Knidos city. We collected 128 pieces of tablet size (10x20cm) 3-cm thick samples along the fault dip and opened 4 conventional paleoseismic trenches at the base of the fault scarp. Our 36Cl concentration profile indicates that 3 to 4 seismic events ruptured the Mezarlık Fault since Last Glacial Maximum (LGM). The results from the paleoseismic trenching are also compatible with 36Cl results, indicating 3 or 4 seismic events that disturbed the colluvium deposited at the base of the scarp. Here we will present implications for the seismic history and the derived slip-rate of the Mezarlık Fault based on those results. This project is supported by The Scientific and Technological Research Council of Turkey (TUBITAK, Grant number: 113Y436) and it was conducted with the Decision of the Council of Ministers with No. 2013/5387 on the date 30.09.2013 and was done with the permission of Knidos Presidency of excavation in

Subsurface geometry of the San Andreas-Calaveras fault junction: influence of serpentinite and the Coast Range Ophiolite

USGS Publications Warehouse

Watt, Janet Tilden; Ponce, David A.; Graymer, Russell W.; Jachens, Robert C.; Simpson, Robert W.

2014-01-01

While an enormous amount of research has been focused on trying to understand the geologic history and neotectonics of the San Andreas-Calaveras fault (SAF-CF) junction, fundamental questions concerning fault geometry and mechanisms for slip transfer through the junction remain. We use potential-field, geologic, geodetic, and seismicity data to investigate the 3-D geologic framework of the SAF-CF junction and identify potential slip-transferring structures within the junction. Geophysical evidence suggests that the San Andreas and Calaveras fault zones dip away from each other within the northern portion of the junction, bounding a triangular-shaped wedge of crust in cross section. This wedge changes shape to the south as fault geometries change and fault activity shifts between fault strands, particularly along the Calaveras fault zone (CFZ). Potential-field modeling and relocated seismicity suggest that the Paicines and San Benito strands of the CFZ dip 65° to 70° NE and form the southwest boundary of a folded 1 to 3 km thick tabular body of Coast Range Ophiolite (CRO) within the Vallecitos syncline. We identify and characterize two steeply dipping, seismically active cross structures within the junction that are associated with serpentinite in the subsurface. The architecture of the SAF-CF junction presented in this study may help explain fault-normal motions currently observed in geodetic data and help constrain the seismic hazard. The abundance of serpentinite and related CRO in the subsurface is a significant discovery that not only helps constrain the geometry of structures but may also help explain fault behavior and the tectonic evolution of the SAF-CF junction.

Fault zone architecture of a major oblique-slip fault in the Rawil depression, Western Helvetic nappes, Switzerland

NASA Astrophysics Data System (ADS)

Gasser, D.; Mancktelow, N. S.

2009-04-01

The Helvetic nappes in the Swiss Alps form a classic fold-and-thrust belt related to overall NNW-directed transport. In western Switzerland, the plunge of nappe fold axes and the regional distribution of units define a broad depression, the Rawil depression, between the culminations of Aiguilles Rouge massif to the SW and Aar massif to the NE. A compilation of data from the literature establishes that, in addition to thrusts related to nappe stacking, the Rawil depression is cross-cut by four sets of brittle faults: (1) SW-NE striking normal faults that strike parallel to the regional fold axis trend, (2) NW-SE striking normal faults and joints that strike perpendicular to the regional fold axis trend, and (3) WNW-ESE striking normal plus dextral oblique-slip faults as well as (4) WSW-ENE striking normal plus dextral oblique-slip faults that both strike oblique to the regional fold axis trend. We studied in detail a beautifully exposed fault from set 3, the Rezli fault zone (RFZ) in the central Wildhorn nappe. The RFZ is a shallow to moderately-dipping (ca. 30-60˚) fault zone with an oblique-slip displacement vector, combining both dextral and normal components. It must have formed in approximately this orientation, because the local orientation of fold axes corresponds to the regional one, as does the generally vertical orientation of extensional joints and veins associated with the regional fault set 2. The fault zone crosscuts four different lithologies: limestone, intercalated marl and limestone, marl and sandstone, and it has a maximum horizontal dextral offset component of ~300 m and a maximum vertical normal offset component of ~200 m. Its internal architecture strongly depends on the lithology in which it developed. In the limestone, it consists of veins, stylolites, cataclasites and cemented gouge, in the intercalated marls and limestones of anastomosing shear zones, brittle fractures, veins and folds, in the marls of anastomosing shear zones, pressure

Active simultaneous uplift and margin-normal extension in a forearc high, Crete, Greece

NASA Astrophysics Data System (ADS)

Gallen, S. F.; Wegmann, K. W.; Bohnenstiehl, D. R.; Pazzaglia, F. J.; Brandon, M. T.; Fassoulas, C.

2014-07-01

The island of Crete occupies a forearc high in the central Hellenic subduction zone and is characterized by sustained exhumation, surface uplift and extension. The processes governing orogenesis and topographic development here remain poorly understood. Dramatic topographic relief (2-6 km) astride the southern coastline of Crete is associated with large margin-parallel faults responsible for deep bathymetric depressions known as the Hellenic troughs. These structures have been interpreted as both active and inactive with either contractional, strike-slip, or extensional movement histories. Distinguishing between these different structural styles and kinematic histories here allows us to explore more general models for improving our global understanding of the tectonic and geodynamic processes of syn-convergent extension. We present new observations from the south-central coastline of Crete that clarifies the role of these faults in the late Cenozoic evolution of the central Hellenic margin and the processes controlling Quaternary surface uplift. Pleistocene marine terraces are used in conjunction with optically stimulated luminesce dating and correlation to the Quaternary eustatic curve to document coastal uplift and identify active faults. Two south-dipping normal faults are observed, which extend offshore, offset these marine terrace deposits and indicate active N-S (margin-normal) extension. Further, marine terraces preserved in the footwall and hanging wall of both faults demonstrate that regional net uplift of Crete is occurring despite active extension. Field mapping and geometric reconstructions of an active onshore normal fault reveal that the subaqueous range-front fault of south-central Crete is synthetic to the south-dipping normal faults on shore. These findings are inconsistent with models of active horizontal shortening in the upper crust of the Hellenic forearc. Rather, they are consistent with topographic growth of the forearc in a viscous orogenic

Fault-scale controls on rift geometry: the Bilila-Mtakataka Fault, Malawi

NASA Astrophysics Data System (ADS)

Hodge, M.; Fagereng, A.; Biggs, J.; Mdala, H. S.

2017-12-01

Border faults that develop during initial stages of rifting determine the geometry of rifts and passive margins. At outcrop and regional scales, it has been suggested that border fault orientation may be controlled by reactivation of pre-existing weaknesses. Here, we perform a multi-scale investigation on the influence of anisotropic fabrics along a major developing border fault in the southern East African Rift, Malawi. The 130 km long Bilila-Mtakataka fault has been proposed to have slipped in a single MW 8 earthquake with 10 m of normal displacement. The fault is marked by an 11±7 m high scarp with an average trend that is oblique to the current plate motion. Variations in scarp height are greatest at lithological boundaries and where the scarp switches between following and cross-cutting high-grade metamorphic foliation. Based on the scarp's geometry and morphology, we define 6 geometrically distinct segments. We suggest that the segments link to at least one deeper structure that strikes parallel to the average scarp trend, an orientation consistent with the kinematics of an early phase of rift initiation. The slip required on a deep fault(s) to match the height of the current scarp suggests multiple earthquakes along the fault. We test this hypothesis by studying the scarp morphology using high-resolution satellite data. Our results suggest that during the earthquake(s) that formed the current scarp, the propagation of the fault toward the surface locally followed moderately-dipping foliation well oriented for reactivation. In conclusion, although well oriented pre-existing weaknesses locally influence shallow fault geometry, large-scale border fault geometry appears primarily controlled by the stress field at the time of fault initiation.

The Dandridge-Vonore Fault Zone in the Eastern Tennessee Seismic Zone (and Rejuvenation of the Smokies?)

NASA Astrophysics Data System (ADS)

Cox, R. T.; Hatcher, R. D., Jr.; Forman, S. L.; Gamble, E. D. S.; Warrell, K. F.

2017-12-01

The eastern Tennessee seismic zone (ETSZ) trends 045o from NE Alabama and NW Georgia through Tennessee to SE Kentucky, and seismicity is localized 5-26 km deep in the basement. The ETSZ is the second most seismically active region in North America east of the Rocky Mountains, although no historic earthquakes larger than Mw 4.8 have been recorded here. Late Quaternary paleoiseismic evidence suggests that the ETSZ is capable of M7+ earthquakes and that neotectonic faults may have significantly influenced the regional relief. We have identified an 80 km-long, 060o-trending corridor in eastern Tennessee that contains collinear northeast-striking thrust, strike-slip, and normal Quaternary faults with displacements of 1-2 m, herein termed the Dandridge-Vonore fault zone (DVFZ). French Broad River alluvium in the northeast DVFZ near Dandridge, TN, is displaced by a 050o-striking, SE-dipping thrust fault and by a set of related fissures that record at least two significant post 25 ka paleo-earthquakes. Southwest of Dandridge near Alcoa, TN, a 060o-striking, SE-dipping thrust fault cuts Little River alluvium and records two significant post-15 ka paleo-earthquakes. Farther southwest at Vonore, colluvium with alluvial cobbles is thrust >1 m by a 057o-striking, steeply SE-dipping fault that may also have a significant strike-slip component, and Little Tennessee River alluvium is dropped >2 m along a 070o- striking normal fault. The DVFZ partly overlaps and is collinear with a local trend of maximum seismicity that extends 30 km farther SW of the DVFZ (as currently mapped), for a total length of 110 km. The DVFZ is coincident with a steep gradient in S-wave velocities (from high velocity on the SE to low velocity on the NW) at mid-crustal depths of 20 to 24 km, consistent with a fault and source zone at hypocentral depths in the crystalline basement. Moreover, the DVFZ parallels the NW foot of Blue Ridge Mountains, and the sense of thrusting at all sites of Quaternary faulting

Development, Interaction and Linkage of Normal Fault Segments along the 100-km Bilila-Mtakataka Fault, Malawi

NASA Astrophysics Data System (ADS)

Fagereng, A.; Hodge, M.; Biggs, J.; Mdala, H. S.; Goda, K.

2016-12-01

Faults grow through the interaction and linkage of isolated fault segments. Continuous fault systems are those where segments interact, link and may slip synchronously, whereas non-continuous fault systems comprise isolated faults. As seismic moment is related to fault length (Wells and Coppersmith, 1994), understanding whether a fault system is continuous or not is critical in evaluating seismic hazard. Maturity may be a control on fault continuity: immature, low displacement faults are typically assumed to be non-continuous. Here, we study two overlapping, 20 km long, normal fault segments of the N-S striking Bilila-Mtakataka fault, Malawi, in the southern section of the East African Rift System. Despite its relative immaturity, previous studies concluded the Bilila-Mtakataka fault is continuous for its entire 100 km length, with the most recent event equating to an Mw8.0 earthquake (Jackson and Blenkinsop, 1997). We explore whether segment geometry and relationship to pre-existing high-grade metamorphic foliation has influenced segment interaction and fault development. Fault geometry and scarp height is constrained by DEMs derived from SRTM, Pleiades and `Structure from Motion' photogrammetry using a UAV, alongside direct field observations. The segment strikes differ on average by 10°, but up to 55° at their adjacent tips. The southern segment is sub-parallel to the foliation, whereas the northern segment is highly oblique to the foliation. Geometrical surface discontinuities suggest two isolated faults; however, displacement-length profiles and Coulomb stress change models suggest segment interaction, with potential for linkage at depth. Further work must be undertaken on other segments to assess the continuity of the entire fault, concluding whether an earthquake greater than that of the maximum instrumentally recorded (1910 M7.4 Rukwa) is possible.

Fault creep rates of the Chaman fault (Afghanistan and Pakistan) inferred from InSAR

NASA Astrophysics Data System (ADS)

Barnhart, William D.

2017-01-01

The Chaman fault is the major strike-slip structural boundary between the India and Eurasia plates. Despite sinistral slip rates similar to the North America-Pacific plate boundary, no major (>M7) earthquakes have been documented along the Chaman fault, indicating that the fault either creeps aseismically or is at a late stage in its seismic cycle. Recent work with remotely sensed interferometric synthetic aperture radar (InSAR) time series documented a heterogeneous distribution of fault creep and interseismic coupling along the entire length of the Chaman fault, including an 125 km long creeping segment and an 95 km long locked segment within the region documented in this study. Here I present additional InSAR time series results from the Envisat and ALOS radar missions spanning the southern and central Chaman fault in an effort to constrain the locking depth, dip, and slip direction of the Chaman fault. I find that the fault deviates little from a vertical geometry and accommodates little to no fault-normal displacements. Peak-documented creep rates on the fault are 9-12 mm/yr, accounting for 25-33% of the total motion between India and Eurasia, and locking depths in creeping segments are commonly shallower than 500 m. The magnitude of the 1892 Chaman earthquake is well predicted by the total area of the 95 km long coupled segment. To a first order, the heterogeneous distribution of aseismic creep combined with consistently shallow locking depths suggests that the southern and central Chaman fault may only produce small to moderate earthquakes (

Fault geometry and cumulative offsets in the central Coast Ranges, California: Evidence for northward increasing slip along the San Gregorio-San Simeon-Hosgri fault

USGS Publications Warehouse

Langenheim, V.E.; Jachens, R.C.; Graymer, R.W.; Colgan, J.P.; Wentworth, C.M.; Stanley, R.G.

2012-01-01

Estimates of the dip, depth extent, and amount of cumulative displacement along the major faults in the central California Coast Ranges are controversial. We use detailed aeromagnetic data to estimate these parameters for the San Gregorio–San Simeon–Hosgri and other faults. The recently acquired aeromagnetic data provide an areally consistent data set that crosses the onshore-offshore transition without disruption, which is particularly important for the mostly offshore San Gregorio–San Simeon–Hosgri fault. Our modeling, constrained by exposed geology and in some cases, drill-hole and seismic-reflection data, indicates that the San Gregorio–San Simeon–Hosgri and Reliz-Rinconada faults dip steeply throughout the seismogenic crust. Deviations from steep dips may result from local fault interactions, transfer of slip between faults, or overprinting by transpression since the late Miocene. Given that such faults are consistent with predominantly strike-slip displacement, we correlate geophysical anomalies offset by these faults to estimate cumulative displacements. We find a northward increase in right-lateral displacement along the San Gregorio–San Simeon–Hosgri fault that is mimicked by Quaternary slip rates. Although overall slip rates have decreased over the lifetime of the fault, the pattern of slip has not changed. Northward increase in right-lateral displacement is balanced in part by slip added by faults, such as the Reliz-Rinconada, Oceanic–West Huasna, and (speculatively) Santa Ynez River faults to the east.

Active backstop faults in the Mentawai region of Sumatra, Indonesia, revealed by teleseismic broadband waveform modeling

NASA Astrophysics Data System (ADS)

Wang, Xin; Bradley, Kyle Edward; Wei, Shengji; Wu, Wenbo

2018-02-01

Two earthquake sequences that affected the Mentawai islands offshore of central Sumatra in 2005 (Mw 6.9) and 2009 (Mw 6.7) have been highlighted as evidence for active backthrusting of the Sumatran accretionary wedge. However, the geometry of the activated fault planes is not well resolved due to large uncertainties in the locations of the mainshocks and aftershocks. We refine the locations and focal mechanisms of medium size events (Mw > 4.5) of these two earthquake sequences through broadband waveform modeling. In addition to modeling the depth-phases for accurate centroid depths, we use teleseismic surface wave cross-correlation to precisely relocate the relative horizontal locations of the earthquakes. The refined catalog shows that the 2005 and 2009 "backthrust" sequences in Mentawai region actually occurred on steeply (∼60 degrees) landward-dipping faults (Masilo Fault Zone) that intersect the Sunda megathrust beneath the deepest part of the forearc basin, contradicting previous studies that inferred slip on a shallowly seaward-dipping backthrust. Static slip inversion on the newly-proposed fault fits the coseismic GPS offsets for the 2009 mainshock equally well as previous studies, but with a slip distribution more consistent with the mainshock centroid depth (∼20 km) constrained from teleseismic waveform inversion. Rupture of such steeply dipping reverse faults within the forearc crust is rare along the Sumatra-Java margin. We interpret these earthquakes as 'unsticking' of the Sumatran accretionary wedge along a backstop fault separating imbricated material from the stronger Sunda lithosphere. Alternatively, the reverse faults may have originated as pre-Miocene normal faults of the extended continental crust of the western Sunda margin. Our waveform modeling approach can be used to further refine global earthquake catalogs in order to clarify the geometries of active faults.

Seismic reflection study of the East Potrillo Fault, southwestern Dona Ana County, New Mexico

NASA Astrophysics Data System (ADS)

Carley, Shane Alan

The East Potrillo Mountains are located just north of the U.S.-Mexico border in southwestern Dona Ana County, New Mexico. Laramide and Rio Grande rift deformation has formed low-angle and high-angle Tertiary normal faults that are exposed in the area. Along the east flank of the range is the East Potrillo Fault identified on the surface as a north-striking scarp. Fault scarps associated with the East Potrillo Fault have been dated using slope degradation models and they range between 56 ka and 377 ka in age. Offset of geomorphic surfaces interpreted to be tectonic terraces records at least four earthquakes over that period of time, leading to an estimated recurrence interval of 33.5 kyr. Because of this paleoseismic history, the East Potrillo Fault potentially poses a significant seismic hazard to the over 2 million residents living in the border region. Our study presents two 2D seismic reflection profiles to give the first subsurface image of the East Potrillo Fault and potentially other subsidiary faults that have not broken the surface. Three faults are identified in the subsurface, two of which were previously unknown. The range bounding fault is identified 300 m west of observed fault scarps. The fault scarp is found to be formed from one of two secondary faults. It dips 75°s east and has a fault offset of 150 m. The other secondary fault is an antithetic fault dipping 75°s west and forms a graben within the EPF system. The vibroseis source data acquisition is found to be beneficial for characterizing unknown subsurface features.

Extensional faulting in the southern Klamath Mountains, California

USGS Publications Warehouse

Schweickert, R.A.; Irwin, W.P.

1989-01-01

Large northeast striking normal faults in the southern Klamath Mountains may indicate that substantial crustal extension occurred during Tertiary time. Some of these faults form grabens in the Jurassic and older bedrock of the province. The grabens contain continental Oligocene or Miocene deposits (Weaverville Formation), and in two of them the Oligocene or Miocene is underlain by Lower Cretaceous marine formations (Great Valley sequence). At the La Grange gold placer mine the Oligocene or Miocene strata dip northwest into the gently southeast dipping mylonitic footwall surface of the La Grange fault. The large normal displacement required by the relations at the La Grange mine is also suggested by omission of several kilometers of structural thickness of bedrock units across the northeast continuation of the La Grange fault, as well as by significant changes in bedrock across some northeast striking faults elsewhere in the Central Metamorphic and Eastern Klamath belts. The Trinity ultramafic sheet crops out in the Eastern Klamath terrane as part of a broad northeast trending arch that may be structurally analogous to the domed lower plate of metamorphic core complexes found in eastern parts of the Cordillera. The northeast continuation of the La Grange fault bounds the southeastern side of the Trinity arch in the Eastern Klamath terrane and locally cuts out substantial lower parts of adjacent Paleozoic strata of the Redding section. Faults bounding the northwestem side of the Trinity arch generally trend northeast and juxtapose stacked thrust sheets of lower Paleozoic strata of the Yreka terrane against the Trinity ultramafic sheet. Geometric relations suggest that the Tertiary extension of the southern Klamath Mountains was in NW-SE directions and that the Redding section and the southern part of the Central Metamorphic terrane may be a large Tertiary allochthon detached from the Trinity ultramafic sheet. Paleomagnetic data indicate a lack of rotation about a

Systematic assessment of fault stability in the Northern Niger Delta Basin, Nigeria: Implication for hydrocarbon prospects and increased seismicities

NASA Astrophysics Data System (ADS)

Adewole, E. O.; Healy, D.

2017-03-01

Accurate information on fault networks, the full stress tensor, and pore fluid pressures are required for quantifying the stability of structure-bound hydrocarbon prospects, carbon dioxide sequestration, and drilling prolific and safe wells, particularly fluid injections wells. Such information also provides essential data for a proper understanding of superinduced seismicities associated with areas of intensive hydrocarbon exploration and solid minerals mining activities. Pressure and stress data constrained from wells and seismic data in the Northern Niger Delta Basin (NNDB), Nigeria, have been analysed in the framework of fault stability indices by varying the maximum horizontal stress direction from 0° to 90°, evaluated at depths of 2 km, 3.5 km and 4 km. We have used fault dips and azimuths interpreted from high resolution 3D seismic data to calculate the predisposition of faults to failures in three faulting regimes (normal, pseudo-strike-slip and pseudo-thrust). The weighty decrease in the fault stability at 3.5 km depth from 1.2 MPa to 0.55 MPa demonstrates a reduction of the fault strength by high magnitude overpressures. Pore fluid pressures > 50 MPa have tendencies to increase the risk of faults to failure in the study area. Statistical analysis of stability indices (SI) indicates faults dipping 50°-60°, 80°-90°, and azimuths ranging 100°-110° are most favourably oriented for failure to take place, and thus likely to favour migrations of fluids given appropriate pressure and stress conditions in the dominant normal faulting regime of the NNDB. A few of the locally assessed stability of faults show varying results across faulting regimes. However, the near similarities of some model-based results in the faulting regimes explain the stability of subsurface structures are greatly influenced by the maximum horizontal stress (SHmax) direction and magnitude of pore fluid pressures.

Sub-volcanic slope influencing the development of major structures at volcanoes during strike-slip faulting

NASA Astrophysics Data System (ADS)

Andrade, Daniel; van Wyk de Vries, Benjamin; Robin, Claude

2014-05-01

Volcano-basement interactions can deeply determine the structural development of volcanoes basically by the propagation of stress and strain fields from the basement into the volcanic edifice, and vice versa. An extensively studied case of such interactions is the propagation of a strike-slip fault through a volcanic edifice, which gives place to a strong tendency of major volcanic construction and destruction events to occur in a sub-parallel trend with respect to the strike of the fault. During precedent studies, however, both scaled and natural prototypes have always considered that the surfaces on which volcanoes stand (i.e. the sub-volcanic slope) are horizontal. The scaled experiments presented here show that the dip-angle and dip-direction of the subvolcanic slopes can systematically and significantly change the deformation patterns developed by the volcanic edifice during strike-slip faulting. When the dip-direction of the sub-volcanic slope and the strike of the fault are nearly parallel, an increased development and concentration of the deformation on the down-slope side of the volcanic cone occurs. In medium to long-term, this would imply again a tendency of major volcanic structures growing in a sub-parallel trend with respect to the strike of the fault, but with one preferred direction: that of the dip-direction. In the experiments, the dip-direction of the sub-volcanic slope was set progressively oblique, up to perpendicular, with respect to the strike of the fault by: 1) rotating in the same sense as the strike-slip fault, or 2) rotating in the opposite sense as the fault. In both cases, the downslope side of the volcanic cone still concentrates the deformation, but the deformed sectors progressively rotate which results in a structural development (construction and destruction) of the edifice occurring clearly oblique with respect to the strike of the fault. Imbabura volcano (Ecuador) is traversed by the strike-slip El Angel-Río Ambi fault, whose

Comparative study of two tsunamigenic earthquakes in the Solomon Islands: 2015 Mw 7.0 normal-fault and 2013 Santa Cruz Mw 8.0 megathrust earthquakes

NASA Astrophysics Data System (ADS)

Heidarzadeh, Mohammad; Harada, Tomoya; Satake, Kenji; Ishibe, Takeo; Gusman, Aditya Riadi

2016-05-01

The July 2015 Mw 7.0 Solomon Islands tsunamigenic earthquake occurred ~40 km north of the February 2013 Mw 8.0 Santa Cruz earthquake. The proximity of the two epicenters provided unique opportunities for a comparative study of their source mechanisms and tsunami generation. The 2013 earthquake was an interplate event having a thrust focal mechanism at a depth of 30 km while the 2015 event was a normal-fault earthquake occurring at a shallow depth of 10 km in the overriding Pacific Plate. A combined use of tsunami and teleseismic data from the 2015 event revealed the north dipping fault plane and a rupture velocity of 3.6 km/s. Stress transfer analysis revealed that the 2015 earthquake occurred in a region with increased Coulomb stress following the 2013 earthquake. Spectral deconvolution, assuming the 2015 tsunami as empirical Green's function, indicated the source periods of the 2013 Santa Cruz tsunami as 10 and 22 min.

Sudden aseismic fault slip on the south flank of Kilauea volcano.

PubMed

Cervelli, Peter; Segall, Paul; Johnson, Kaj; Lisowski, Michael; Miklius, Asta

2002-02-28

One of the greatest hazards associated with oceanic volcanoes is not volcanic in nature, but lies with the potential for catastrophic flank failure. Such flank failure can result in devastating tsunamis and threaten not only the immediate vicinity, but coastal cities along the entire rim of an ocean basin. Kilauea volcano on the island of Hawaii, USA, is a potential source of such flank failures and has therefore been monitored by a network of continuously recording geodetic instruments, including global positioning system (GPS) receivers, tilt meters and strain meters. Here we report that, in early November 2000, this network recorded transient southeastward displacements, which we interpret as an episode of aseismic fault slip. The duration of the event was about 36 hours, it had an equivalent moment magnitude of 5.7 and a maximum slip velocity of about 6[?]cm per day. Inversion of the GPS data reveals a shallow-dipping thrust fault at a depth of 4.5[?]km that we interpret as the down-dip extension of the Hilina Pali--Holei Pali normal fault system. This demonstrates that continuously recording geodetic networks can detect accelerating slip, potentially leading to warnings of volcanic flank collapse.

Geometry and active tectonics of the Los Osos-Hosgri Fault Intersection in Estero Bay, CA: Reconciling seismicity patterns with near-surface geology

NASA Astrophysics Data System (ADS)

Watt, J. T.; Hardebeck, J.; Johnson, S. Y.; Kluesner, J.

2016-12-01

Characterizing active structures within structurally complex fault intersections is essential for unraveling the deformational history and for assessing the importance of fault intersections in regional earthquake hazard assessments. We employ an integrative, multi-scale geophysical approach to describe the 3D geometry and active tectonics of the offshore Los Osos fault (LOF) in Estero Bay, California. The shallow structure of the LOF, as imaged with multibeam and high-resolution seismic-reflection data, reveals a complex west-diverging zone of active faulting that bends into and joins the Hosgri fault. The down-dip geometry of the LOF as revealed by gravity, magnetic, and industry multi-channel seismic data, is vertical to steeply-dipping and varies along strike. As the LOF extends offshore, it is characterized by SW-side-up motion on a series of W-NW trending, steeply SW-dipping reverse faults. The LOF bends to the north ( 23°) as it approaches the Hosgri fault and dips steeply to the NE along a magnetic basement block. Inversion of earthquake focal mechanisms within Estero Bay yields maximum compressive stress axes that are near-horizontal and trend approximately N15E. This trend is consistent with dextral strike-slip faulting along NW-SE trending structures such as the Hosgri fault and northern LOF, and oblique dip-slip motion along the W-NW trending section of the LOF. Notably, NW-SE trending structures illuminated by seismicity in Estero Bay coincide with, but also appear to cross-cut, LOF structures imaged in the near-surface. We suggest this apparent disconnect reflects ongoing fault reorganization at a dynamic and inherently unstable fault intersection, in which the seismicity reflects active deformation at depth that is not clearly expressed in the near-surface geology. Direct connectivity between the Hosgri and Los Osos faults suggests a combined earthquake rupture is possible; however, the geometrical complexity along the offshore LOF may limit the

The distribution of deformation in parallel fault-related folds with migrating axial surfaces: comparison between fault-propagation and fault-bend folding

NASA Astrophysics Data System (ADS)

Salvini, Francesco; Storti, Fabrizio

2001-01-01

In fault-related folds that form by axial surface migration, rocks undergo deformation as they pass through axial surfaces. The distribution and intensity of deformation in these structures has been impacted by the history of axial surface migration. Upon fold initiation, unique dip panels develop, each with a characteristic deformation intensity, depending on their history. During fold growth, rocks that pass through axial surfaces are transported between dip panels and accumulate additional deformation. By tracking the pattern of axial surface migration in model folds, we predict the distribution of relative deformation intensity in simple-step, parallel fault-bend and fault-propagation anticlines. In both cases the deformation is partitioned into unique domains we call deformation panels. For a given rheology of the folded multilayer, deformation intensity will be homogeneously distributed in each deformation panel. Fold limbs are always deformed. The flat crests of fault-propagation anticlines are always undeformed. Two asymmetric deformation panels develop in fault-propagation folds above ramp angles exceeding 29°. For lower ramp angles, an additional, more intensely-deformed panel develops at the transition between the crest and the forelimb. Deformation in the flat crests of fault-bend anticlines occurs when fault displacement exceeds the length of the footwall ramp, but is never found immediately hinterland of the crest to forelimb transition. In environments dominated by brittle deformation, our models may serve as a first-order approximation of the distribution of fractures in fault-related folds.

Multidisciplinary approach for fault detection: Integration of PS-InSAR, geomorphological, stratigraphic and structural data in the Venafro intermontane basin (Central-Southern Apennines, Italy)

NASA Astrophysics Data System (ADS)

Amato, Vincenzo; Aucelli, Pietro P. C.; Bellucci Sessa, Eliana; Cesarano, Massimo; Incontri, Pietro; Pappone, Gerardo; Valente, Ettore; Vilardo, Giuseppe

2017-04-01

A multidisciplinary methodology, integrating stratigraphic, geomorphological and structural data, combined with GIS-aided analysis and PS-InSAR interferometric data, was applied to characterize the relationships between ground deformations and the stratigraphic and the morphostructural setting of the Venafro intermontane basin. This basin is a morphostructural depression related to NW-SE and NE-SW oriented high angle normal faults bordering and crossing it. In particular, a well-known active fault crossing the plain is the Aquae Juliae Fault, whose recent activity is evidenced by archeoseismological data. The approach applied here reveals new evidence of possible faulting, acting during the Lower to Upper Pleistocene, which has driven the morphotectonic and the environmental evolution of the basin. In particular, the tectonic setting emerging from this study highlights the influence of the NW-SE oriented extensional phase during the late Lower Pleistocene - early Middle Pleistocene, in the generation of NE-SW trending, SE dipping, high-angle faults and NW-SE trending, high-angle transtensive faults. This phase has been followed by a NE-SW extensional one, responsible for the formation of NW-SE trending, both NW and SE dipping, high-angle normal faults, and the reactivation of the oldest NE-SW oriented structures. These NW-SE trending normal faults include the Aquae Juliae Fault and a new one, unknown until now, crossing the plain between the Venafro village and the Colle Cupone Mt. (hereinafter named the Venafro-Colle Cupone Fault, VCCF). This fault has controlled deposition of the youngest sedimentary units (late Middle Pleistocene to late Upper Pleistocene) suggesting its recent activity and it is well constrained by PS-InSAR data, as testified by the increase of the subsidence rate in the hanging wall block.

Evidence for slip partitioning and bimodal slip behavior on a single fault: Surface slip characteristics of the 2013 Mw7.7 Balochistan, Pakistan earthquake

USGS Publications Warehouse

Barnhart, William; Briggs, Richard; Reitman, Nadine G.; Gold, Ryan D.; Hayes, Gavin

2015-01-01

Deformation is commonly accommodated by strain partitioning on multiple, independent strike-slip and dip-slip faults in continental settings of oblique plate convergence. As a corollary, individual faults tend to exhibit one sense of slip – normal, reverse, or strike-slip – until whole-scale changes in boundary conditions reactivate preexisting faults in a new deformation regime. In this study, we show that a single continental fault may instead partition oblique strain by alternatively slipping in a strike-slip or a dip-slip sense during independent fault slip events. We use 0.5 m resolution optical imagery and sub-pixel correlation analysis of the 200+ km 200+km"> 2013 Mw7.7 Balochistan, Pakistan earthquake to document co-seismic surface slip characteristics and Quaternary tectonic geomorphology along the causative Hoshab fault. We find that the 2013 earthquake, which involved a ∼6:1 strike-slip to dip-slip ratio, ruptured a structurally segmented fault. Quaternary geomorphic indicators of gross fault-zone morphology reveal both reverse-slip and strike-slip deformation in the rupture area of the 2013 earthquake that varies systematically along fault strike despite nearly pure strike-slip motion in 2013. Observations of along-strike variations in range front relief and geomorphic offsets suggest that the Hoshab fault accommodates a substantial reverse component of fault slip in the Quaternary, especially along the southern section of the 2013 rupture. We surmise that Quaternary bimodal slip along the Hoshab fault is promoted by a combination of the arcuate geometry of the Hoshab fault, the frictional weakness of the Makran accretionary prism, and time variable loading conditions from adjacent earthquakes and plate interactions.

Evidence for slip partitioning and bimodal slip behavior on a single fault: Surface slip characteristics of the 2013 Mw7.7 Balochistan, Pakistan earthquake

NASA Astrophysics Data System (ADS)

Barnhart, W. D.; Briggs, R. W.; Reitman, N. G.; Gold, R. D.; Hayes, G. P.

2015-06-01

Deformation is commonly accommodated by strain partitioning on multiple, independent strike-slip and dip-slip faults in continental settings of oblique plate convergence. As a corollary, individual faults tend to exhibit one sense of slip - normal, reverse, or strike-slip - until whole-scale changes in boundary conditions reactivate preexisting faults in a new deformation regime. In this study, we show that a single continental fault may instead partition oblique strain by alternatively slipping in a strike-slip or a dip-slip sense during independent fault slip events. We use 0.5 m resolution optical imagery and sub-pixel correlation analysis of the 200 + km 2013 Mw7.7 Balochistan, Pakistan earthquake to document co-seismic surface slip characteristics and Quaternary tectonic geomorphology along the causative Hoshab fault. We find that the 2013 earthquake, which involved a ∼6:1 strike-slip to dip-slip ratio, ruptured a structurally segmented fault. Quaternary geomorphic indicators of gross fault-zone morphology reveal both reverse-slip and strike-slip deformation in the rupture area of the 2013 earthquake that varies systematically along fault strike despite nearly pure strike-slip motion in 2013. Observations of along-strike variations in range front relief and geomorphic offsets suggest that the Hoshab fault accommodates a substantial reverse component of fault slip in the Quaternary, especially along the southern section of the 2013 rupture. We surmise that Quaternary bimodal slip along the Hoshab fault is promoted by a combination of the arcuate geometry of the Hoshab fault, the frictional weakness of the Makran accretionary prism, and time variable loading conditions from adjacent earthquakes and plate interactions.

Post 4 Ma initiation of normal faulting in southern Tibet. Constraints from the Kung Co half graben

NASA Astrophysics Data System (ADS)

Mahéo, G.; Leloup, P. H.; Valli, F.; Lacassin, R.; Arnaud, N.; Paquette, J.-L.; Fernandez, A.; Haibing, L.; Farley, K. A.; Tapponnier, P.

2007-04-01

The timing of E-W extension of the Tibetan plateau provides a test of mechanical models of the geodynamic evolution of the India-Asia convergence zone. In this work we focus on the Kung Co half graben (Southern Tibet, China), bounded by an active N-S normal fault with a minimum vertical offset of 1600 m. To estimate the onset of normal faulting we combined high and medium temperature (U-Pb, Ar/Ar) and low temperature ((U-Th)/He) thermochronometry of the Kung Co pluton, a two-mica granite of the northern Himalayan granitic belt that outcrop in the footwall of the fault. Biotite and muscovite Ar/Ar ages , are close from each other [˜ 16 Ma ± 0.2 (Ms) and ˜ 15 ± 0.4 Ma (Bt)], which is typical of fast cooling. The zircon and apatite (U-Th)/He ages range from 11.3 to 9.6 Ma and 9.9 to 3.7 Ma respectively. These He ages are indicative of (1) fast initial cooling, from 11.3 to ˜ 9 Ma, gradually decreasing with time and (2) a high geothermal gradient (˜ 400 °C/km), close to the surface at ˜ 10 Ma. The Kung Co pluton was emplaced at about 22 Ma (U-Pb on zircon) at less than 10 km depth and 520-545 °C. Subsequent to its shallow emplacement, the pluton underwent fast thermal re-equilibration ending around 7.5 Ma, followed by a period of slow cooling caused either by the end of the thermal re-equilibration or by very slow exhumation (0.02-0.03 mm/yr) from ˜ 7.5 Ma to at least 4 Ma. In either case the data suggest that the exhumation rate increased after 4 Ma. We infer this increase to be related to the initiation of the Kung Co normal fault. A critical examination of previously published data show that most ˜ N-S Tibetan normal faults may have formed less than 5 Ma ago rather than in the Miocene as assumed by several authors. Such a young age implies that E-W extension is not related to the Neogene South Tibetan magmatism (25 to 8 Ma). Consequently, models relating E-W extension to magmatism, such as convective removal of the lower lithosphere, may be inappropriate

The role of bed-parallel slip in the development of complex normal fault zones

NASA Astrophysics Data System (ADS)

Delogkos, Efstratios; Childs, Conrad; Manzocchi, Tom; Walsh, John J.; Pavlides, Spyros

2017-04-01

Normal faults exposed in Kardia lignite mine, Ptolemais Basin, NW Greece formed at the same time as bed-parallel slip-surfaces, so that while the normal faults grew they were intermittently offset by bed-parallel slip. Following offset by a bed-parallel slip-surface, further fault growth is accommodated by reactivation on one or both of the offset fault segments. Where one fault is reactivated the site of bed-parallel slip is a bypassed asperity. Where both faults are reactivated, they propagate past each other to form a volume between overlapping fault segments that displays many of the characteristics of relay zones, including elevated strains and transfer of displacement between segments. Unlike conventional relay zones, however, these structures contain either a repeated or a missing section of stratigraphy which has a thickness equal to the throw of the fault at the time of the bed-parallel slip event, and the displacement profiles along the relay-bounding fault segments have discrete steps at their intersections with bed-parallel slip-surfaces. With further increase in displacement, the overlapping fault segments connect to form a fault-bound lens. Conventional relay zones form during initial fault propagation, but with coeval bed-parallel slip, relay-like structures can form later in the growth of a fault. Geometrical restoration of cross-sections through selected faults shows that repeated bed-parallel slip events during fault growth can lead to complex internal fault zone structure that masks its origin. Bed-parallel slip, in this case, is attributed to flexural-slip arising from hanging-wall rollover associated with a basin-bounding fault outside the study area.

Fault zone structure and inferences on past activities of the active Shanchiao Fault in the Taipei metropolis, northern Taiwan

NASA Astrophysics Data System (ADS)

Chen, C.; Lee, J.; Chan, Y.; Lu, C.

2010-12-01

The Taipei Metropolis, home to around 10 million people, is subject to seismic hazard originated from not only distant faults or sources scattered throughout the Taiwan region, but also active fault lain directly underneath. Northern Taiwan including the Taipei region is currently affected by post-orogenic (Penglai arc-continent collision) processes related to backarc extension of the Ryukyu subduction system. The Shanchiao Fault, an active normal fault outcropping along the western boundary of the Taipei Basin and dipping to the east, is investigated here for its subsurface structure and activities. Boreholes records in the central portion of the fault were analyzed to document the stacking of post- Last Glacial Maximum growth sediments, and a tulip flower structure is illuminated with averaged vertical slip rate of about 3 mm/yr. Similar fault zone architecture and post-LGM tectonic subsidence rate is also found in the northern portion of the fault. A correlation between geomorphology and structural geology in the Shanchiao Fault zone demonstrates an array of subtle geomorphic scarps corresponds to the branch fault while the surface trace of the main fault seems to be completely erased by erosion and sedimentation. Such constraints and knowledge are crucial in earthquake hazard evaluation and mitigation in the Taipei Metropolis, and in understanding the kinematics of transtensional tectonics in northern Taiwan. Schematic 3D diagram of the fault zone in the central portion of the Shanchiao Fault, displaying regional subsurface geology and its relation to topographic features.

Postseismic deformation associated with the 2008 Mw 7.9 Wenchuan earthquake, China: Constraining fault geometry and investigating a detailed spatial distribution of afterslip

NASA Astrophysics Data System (ADS)

Jiang, Zhongshan; Yuan, Linguo; Huang, Dingfa; Yang, Zhongrong; Chen, Weifeng

2017-12-01

We reconstruct two types of fault models associated with the 2008 Mw 7.9 Wenchuan earthquake, one is a listric fault connecting a shallowing sub-horizontal detachment below ∼20 km depth (fault model one, FM1) and the other is a group of more steeply dipping planes further extended to the Moho at ∼60 km depth (fault model two, FM2). Through comparative analysis of the coseismic inversion results, we confirm that the coseismic models are insensitive to the above two type fault geometries. We therefore turn our attention to the postseismic deformation obtained from GPS observations, which can not only impose effective constraints on the fault geometry but also, more importantly, provide valuable insights into the postseismic afterslip. Consequently, FM1 performs outstandingly in the near-, mid-, and far-field, whether considering the viscoelastic influence or not. FM2 performs more poorly, especially in the data-model consistency in the near field, which mainly results from the trade-off of the sharp contrast of the postseismic deformation on both sides of the Longmen Shan fault zone. Accordingly, we propose a listric fault connecting a shallowing sub-horizontal detachment as the optimal fault geometry for the Wenchuan earthquake. Based on the inferred optimal fault geometry, we analyse two characterized postseismic deformation phenomena that differ from the coseismic patterns: (1) the postseismic opposite deformation between the Beichuan fault (BCF) and Pengguan fault (PGF) and (2) the slightly left-lateral strike-slip motions in the southwestern Longmen Shan range. The former is attributed to the local left-lateral strike-slip and normal dip-slip components on the shallow BCF. The latter places constraints on the afterslip on the southwestern BCF and reproduces three afterslip concentration areas with slightly left-lateral strike-slip motions. The decreased Coulomb Failure Stress (CFS) change ∼0.322 KPa, derived from the afterslip with viscoelastic influence

Aftershocks illuminate the 2011 Mineral, Virginia, earthquake causative fault zone and nearby active faults

USGS Publications Warehouse

Horton, J. Wright; Shah, Anjana K.; McNamara, Daniel E.; Snyder, Stephen L.; Carter, Aina M

2015-01-01

Deployment of temporary seismic stations after the 2011 Mineral, Virginia (USA), earthquake produced a well-recorded aftershock sequence. The majority of aftershocks are in a tabular cluster that delineates the previously unknown Quail fault zone. Quail fault zone aftershocks range from ~3 to 8 km in depth and are in a 1-km-thick zone striking ~036° and dipping ~50°SE, consistent with a 028°, 50°SE main-shock nodal plane having mostly reverse slip. This cluster extends ~10 km along strike. The Quail fault zone projects to the surface in gneiss of the Ordovician Chopawamsic Formation just southeast of the Ordovician–Silurian Ellisville Granodiorite pluton tail. The following three clusters of shallow (<3 km) aftershocks illuminate other faults. (1) An elongate cluster of early aftershocks, ~10 km east of the Quail fault zone, extends 8 km from Fredericks Hall, strikes ~035°–039°, and appears to be roughly vertical. The Fredericks Hall fault may be a strand or splay of the older Lakeside fault zone, which to the south spans a width of several kilometers. (2) A cluster of later aftershocks ~3 km northeast of Cuckoo delineates a fault near the eastern contact of the Ordovician Quantico Formation. (3) An elongate cluster of late aftershocks ~1 km northwest of the Quail fault zone aftershock cluster delineates the northwest fault (described herein), which is temporally distinct, dips more steeply, and has a more northeastward strike. Some aftershock-illuminated faults coincide with preexisting units or structures evident from radiometric anomalies, suggesting tectonic inheritance or reactivation.

The role of fault surface geometry in the evolution of the fault deformation zone: comparing modeling with field example from the Vignanotica normal fault (Gargano, Southern Italy).

NASA Astrophysics Data System (ADS)

Maggi, Matteo; Cianfarra, Paola; Salvini, Francesco

2013-04-01

cell, the acting stress and strength are computed by analytical laws (Coulomb failure). Total brittle deformation for each cell is then computed by cumulating the brittle failure values along the path of each cell belonging to one side onto the facing one. The brittle failure value is provided by the DF function, that is the difference between the computed shear and the strength of the cell at each step along its path by using the Frap in-house developed software. The width of the FC and the FDZ are computed as a function of the DF distribution and displacement around the fault. This methodology has been successfully applied to model the brittle deformation pattern of the Vignanotica normal fault (Gargano, Southern Italy) where fracture intensity is expressed by the dimensionless H/S ratio representing the ratio between the dimension and the spacing of homologous fracture sets (i.e., group of parallel fractures that can be ascribed to the same event/stage/stress field).

The influence of joint parameters on normal fault evolution and geometry: a parameter study using analogue modeling

NASA Astrophysics Data System (ADS)

Kettermann, Michael; von Hagke, Christoph; Urai, Janos L.

2017-04-01

Dilatant faults often form in rocks containing pre-existing joints, but the effects of joints on fault segment linkage and fracture connectivity is not well understood. Studying evolution of dilatancy and influence of fractures on fault development provides insights into geometry of fault zones in brittle rocks and will eventually allow for predicting their subsurface appearance. In an earlier study we recognized the effect of different angles between strike direction of vertical joints and a basement fault on the geometry of a developing fault zone. We now systematically extend the results by varying geometric joint parameters such as joint spacing and vertical extent of the joints and measuring fracture density and connectivity. A reproducibility study shows a small error-range for the measurements, allowing for a confident use of the experimental setup. Analogue models were carried out in a manually driven deformation box (30x28x20 cm) with a 60° dipping pre-defined basement fault and 4.5 cm of displacement. To produce open joints prior to faulting, sheets of paper were mounted in the box to a depth of 5 cm at a spacing of 2.5 cm. We varied the vertical extent of the joints from 5 to 50 mm. Powder was then sieved into the box, embedding the paper almost entirely (column height of 19 cm), and the paper was removed. During deformation we captured structural information by time-lapse photography that allows particle imaging velocimetry analyses (PIV) to detect localized deformation at every increment of displacement. Post-mortem photogrammetry preserves the final 3-dimensional structure of the fault zone. A counterintuitive result is that joint depth is of only minor importance for the evolution of the fault zone. Even very shallow joints form weak areas at which the fault starts to form and propagate. More important is joint spacing. Very large joint spacing leads to faults and secondary fractures that form subparallel to the basement fault. In contrast, small

Controls on the Seafloor Exposure of Detachment Fault Surfaces

NASA Astrophysics Data System (ADS)

Olive, J. A. L.; Parnell-Turner, R. E.; Escartin, J.; Smith, D. K.; Petersen, S.

2017-12-01

Morphological and seismological evidence suggests that asymmetric accretion involving oceanic detachment faulting takes place along 40% of the Northern Mid-Atlantic Ridge. However, seafloor exposures of corrugated slip surfaces -a telltale sign of this kind of faulting- remain scarce and spatially limited according to multibeam bathymetric surveys. This raises the question of whether geomorphic processes can hinder the exposure of pristine fault surfaces during detachment growth. We address this problem by analyzing ≤2-m resolution bathymetry data from four areas where corrugated surfaces emerge from the seafloor (13º20'N, 16º25'N, 16º36'N, and TAG). We identify two key processes capable of degrading or masking a corrugated large-offset fault surface. The first is gravitational mass wasting of steep (>25º) slopes, which is widespread in the breakaway region of most normal faults. The second is blanketing of the shallow-dipping termination area by a thin apron of hanging wall-derived debris. We model this process using critical taper theory, and infer low effective friction coefficients ( 0.15) on the emerging portion of detachment faults. A corollary to this result is that faults emerging from the seafloor with an angle <10º are more likely to blanket themselves under an apron of hanging wall debris. Optimal exposure of detachment surfaces therefore occurs when the fault emerges at slopes between 10° and 25º. We generalize these findings into a simple model for the progressive exhumation and flexural rotation of detachment footwalls, which accounts for the continued action of seafloor geomorphic processes. Our model suggests that many moderate-offset `blanketed' detachments may exist along slow mid-ocean ridges, but their corrugated surfaces are unlikely to be detected in shipboard multibeam bathymetry (e.g., TAG). Furthermore, many `irregular massifs' may correspond to the degraded footwalls of detachment faults.

Paleomagnetic and structural evidence for oblique slip in a fault-related fold, Grayback monocline, Colorado

USGS Publications Warehouse

Tetreault, J.; Jones, C.H.; Erslev, E.; Larson, S.; Hudson, M.; Holdaway, S.

2008-01-01

Significant fold-axis-parallel slip is accommodated in the folded strata of the Grayback monocline, northeastern Front Range, Colorado, without visible large strike-slip displacement on the fold surface. In many cases, oblique-slip deformation is partitioned; fold-axis-normal slip is accommodated within folds, and fold-axis-parallel slip is resolved onto adjacent strike-slip faults. Unlike partitioning strike-parallel slip onto adjacent strike-slip faults, fold-axis-parallel slip has deformed the forelimb of the Grayback monocline. Mean compressive paleostress orientations in the forelimb are deflected 15??-37?? clockwise from the regional paleostress orientation of the northeastern Front Range. Paleomagnetic directions from the Permian Ingleside Formation in the forelimb are rotated 16??-42?? clockwise about a bedding-normal axis relative to the North American Permian reference direction. The paleostress and paleomagnetic rotations increase with the bedding dip angle and decrease along strike toward the fold tip. These measurements allow for 50-120 m of fold-axis-parallel slip within the forelimb, depending on the kinematics of strike-slip shear. This resolved horizontal slip is nearly equal in magnitude to the ???180 m vertical throw across the fold. For 200 m of oblique-slip displacement (120 m of strike slip and 180 m of reverse slip), the true shortening direction across the fold is N90??E, indistinguishable from the regionally inferred direction of N90??E and quite different from the S53??E fold-normal direction. Recognition of this deformational style means that significant amounts of strike slip can be accommodated within folds without axis-parallel surficial faulting. ?? 2008 Geological Society of America.

Initiation and Along-Axis Segmentation of Seaward-Dipping Volcanic Sequences Captured in Afar

NASA Astrophysics Data System (ADS)

Ebinger, C.; Wolfenden, E.; Yirgu, G.; Keir, D.

2003-12-01

The Afar triple junction zone provides a unique opportunity to examine the early development of magmatic margins, as respective limbs of the triple junction capture different stages of the breakup process. Initial rifting in the southernmost Red Sea occurred concurrent with, or soon after flood basaltic magmatism at ~31 Ma in the Ethiopia-Yemen plume province, whereas the northern part of the Main Ethiopian rift initiated after 12 Ma. Both rift systems initiated with the development of high-angle border fault systems bounding broad basins, but 8-10 My after rifting we see riftward migration of strain from the western border fault to narrow zones of increasingly more basaltic magmatism. These localised zones of faulting and volcanism (magmatic segments) show a segmentation independent of the border fault segmentation. The much older, more evolved magmatic segments in the southern Red Sea, where not onlapped by Pliocene-Recent sedimentary strata, dip steeply riftward and define a regional eastward flexure into transitional oceanic crust, as indicated by gravity models constrained by seismic refraction and receiver function data. The southern Red Sea magmatic segments have been abandoned in Pliocene-Recent triple junction reorganisations, whereas the process of seaward-dipping volcanic sequence emplacement is ongoing in the seismically and volcanically active Main Ethiopian rift. Field, remote sensing, gravity, and seismicity data from the Main Ethiopian and southern Red Sea rifts indicate that seaward-dipping volcanic sequences initiate in moderately stretched continental crust above a narrow zone of dike-intrusion. Our comparison of active and ancient magmatic segments show that they are the precursors to seaward-dipping volcanic sequences analogous to those seen on passive continental margins, and provides insights into the initiation of along-axis segmentation of seafloor-spreading centers.

Kinematic Model for the Sierra Nevada Frontal Fault Zone, California: Paleomagnetism of the Eureka Valley Tuff

NASA Astrophysics Data System (ADS)

Rood, D. H.; Burbank, D. W.; Luyendyk, B. P.

2005-12-01

We document the geometry, timing, rates, and kinematic style of Late Tertiary deformation between Sonora Pass and Mono Basin, central Sierra Nevada, California. Observed mismatches between geodetic and geologic deformation rates in the western Great Basin may be primarily due to underestimates of true geologic deformation. Relatively little attention has been paid to the role of permanent deformation between faults, i.e. folding or crustal block rotation. Current slip discrepancies may be accounted for if a significant component of off-fault transrotational deformation is present. We use geologic and paleomagnetic data to address the kinematic development of the Sierra Nevada frontal fault zone (SNFFZ), and to quantify both the elastic and inelastic strain accumulated across the Sierra Nevada-Basin and Range transition since ~9 Ma. The complex structure of this transition, between the regions of Sonora Pass and Mono Basin, may be a result of three distinct modes of dextral shear accommodation (transtensional, transpressional, and crustal thinning). The study area is characterized by four important structural elements that lie between the SNFFZ and Walker Lane Belt: (1) N- to NNW-striking normal and oblique faults, dominantly E-dipping, and associated W-tilted fault blocks; (2) NW-striking dextral faults; (3) ENE- to NE-striking left-lateral oblique faults that may accommodate overall dextral shear through clockwise vertical axis rotations of fault blocks; (4) E- to NE-trending folds, which may accommodate N-S shortening at large-scale left steps in the dextral transtensional fault system. Between Bridgeport and Mono Basins, a regional E- to NE-trending fold is present that affects both the Tertiary volcanic strata and a Quaternary glacial outwash surface. To the west, normal faulting rates on the SNFFZ are 1-2 mm/yr (Bursik and Sieh, 1989). This slip decreases to the north, into the folded region of the Bodie Hills. This kinematic relationship suggests that the

The Role of Coseismic Coulomb Stress Changes in Shaping the Hard Link Between Normal Fault Segments

NASA Astrophysics Data System (ADS)

Hodge, M.; Fagereng, Å.; Biggs, J.

2018-01-01

The mechanism and evolution of fault linkage is important in the growth and development of large faults. Here we investigate the role of coseismic stress changes in shaping the hard links between parallel normal fault segments (or faults), by comparing numerical models of the Coulomb stress change from simulated earthquakes on two en echelon fault segments to natural observations of hard-linked fault geometry. We consider three simplified linking fault geometries: (1) fault bend, (2) breached relay ramp, and (3) strike-slip transform fault. We consider scenarios where either one or both segments rupture and vary the distance between segment tips. Fault bends and breached relay ramps are favored where segments underlap or when the strike-perpendicular distance between overlapping segments is less than 20% of their total length, matching all 14 documented examples. Transform fault linkage geometries are preferred when overlapping segments are laterally offset at larger distances. Few transform faults exist in continental extensional settings, and our model suggests that propagating faults or fault segments may first link through fault bends or breached ramps before reaching sufficient overlap for a transform fault to develop. Our results suggest that Coulomb stresses arising from multisegment ruptures or repeated earthquakes are consistent with natural observations of the geometry of hard links between parallel normal fault segments.

Lithospheric "corner flow" via extensional faulting and tectonic rotation at non-volcanic, slow-spreading ridges

NASA Astrophysics Data System (ADS)

Schroeder, T.; Cheadle, M. J.; Dick, H. J.; Faul, U.

2005-12-01

Large degrees (up to 90°) of tectonic rotation may be the norm at slow-spreading, non-volcanic ridges. Vertically upwelling mantle beneath all mid-ocean ridges must undergo corner flow to move horizontally with the spreading plate. Because little or no volcanic crust is produced at some slow-spreading ridges, the uppermost lithospheric mantle must undergo this rotation in the regime of localized, rather than distributed deformation. Anomalous paleomagnetic inclinations in peridotite and gabbro cores drilled near the 15-20 Fracture Zone (Mid-Atlantic Ridge, ODP Leg 209) support such large rotations, with sub-Curie-temperature rotations up to 90° (Garces et al., 2004). Here, we present two end-member tectonic mechanisms, with supporting data from Leg 209 cores and bathymetry, to show how rotation is accomplished via extensional faults and shear zones: 1) long-lived detachment faults, and 2) multiple generations of high-angle normal faults. Detachment faults accommodate rotation by having a moderate to steep dip at depth, and rotating to horizontal through a rolling hinge as the footwall is tectonically denuded. Multiple generations of high-angle normal faults accommodate large rotations in a domino fashion; early faults become inactive when rotated to inopportune slip angles, and are cut by younger high-angle faults. Thus, each generation of high-angle faults accommodates part of the total rotation. There is likely a gradation between the domino and detachment mechanisms; transition from domino to detachment faulting occurs when a single domino fault remains active at inopportune slip angles and evolves into a detachment that accommodates all corner flow for that region. In both cases, the original attitude of layering within mantle-emplaced gabbro bodies must be significantly different than present day observed attitudes; sub-horizontal bodies may have been formed sub-vertically and vice-versa. Leg 209 cores record an average major brittle fault spacing of

Geophysical methods for identification of active faults between the Sannio-Matese and Irpinia areas of the Southern Apennines.

NASA Astrophysics Data System (ADS)

Gaudiosi, Germana; Nappi, Rosa; Alessio, Giuliana; Cella, Federico; Fedi, Maurizio; Florio, Giovanni

2014-05-01

The Southern Apennines is one of the Italian most active areas from a geodynamic point of view since it is characterized by occurrence of intense and widely spread seismic activity. Most seismicity of the area is concentrated along the chain, affecting mainly the Irpinia and Sannio-Matese areas. The seismogenetic sources responsible for the destructive events of 1456, 1688, 1694, 1702, 1732, 1805, 1930, 1962 and 1980 (Io = X-XI MCS) occurred mostly on NW-SE faults, and the relative hypocenters are concentrated within the upper 20 km of the crust. Structural observations on the Pleistocene faults suggest normal to sinistral movements for the NW-SE trending faults and normal to dextral for the NE-SW trending structures. The available focal mechanisms of the largest events show normal solutions consistent with NE-SW extension of the chain. After the 1980 Irpinia large earthquake, the release of seismic energy in the Southern Apennines has been characterized by occurrence of moderate energy sequences of main shock-aftershocks type and swarm-type activity with low magnitude sequences. Low-magnitude (Md<5) historical and recent earthquakes, generally clustered in swarms, have commonly occurred along the NE-SW faults. This paper deals with integrated analysis of geological and geophysical data in GIS environment to identify surface, buried and hidden active faults and to characterize their geometry. In particular we have analyzed structural data, earthquake space distribution and gravimetric data. The main results of the combined analysis indicate good correlation between seismicity and Multiscale Derivative Analysis (MDA) lineaments from gravity data. Furthermore 2D seismic hypocentral locations together with high-resolution analysis of gravity anomalies have been correlated to estimate the fault systems parameters (strike, dip direction and dip angle) through the application of the DEXP method (Depth from Extreme Points).

Mechanical Effects of Normal Faulting Along the Eastern Escarpment of the Sierra Nevada, California

NASA Astrophysics Data System (ADS)

Martel, S. J.; Logan, J. M.; Stock, G. M.

2013-12-01

Here we test whether the regional near-surface stress field in the Sierra Nevada, California, and the near-surface fracturing that heavily influences the Sierran landscape are a mechanical response to normal faulting along its eastern escarpment. A compilation of existing near-surface stress measurements for the central Sierra Nevada, together with three new measurements, shows the most compressive horizontal stresses are 3-21 MPa, consistent with the widespread distribution of sheeting joints (near-surface fractures subparallel to the ground surface). In contrast, a new stress measurement at Aeolian Buttes in the Mono Basin, east of the range front fault system, reveals a horizontal principal tension of 0.014 MPa, consistent with the abundant vertical joints there. To evaluate mechanical effects of normal faulting, we modeled both normal faults and grabens in three ways: (1) dislocations of specified slip in an elastic half-space, (2) frictionless sliding surfaces in an elastic half-space; and (3) faults in thin elastic beams resting on an inviscid fluid. The different mechanical models predict concave upward flexure and widespread near-surface compressive stresses in the Sierra Nevada that surpass the measurements even for as little as 1 km of normal slip along the eastern escarpment, which exhibits 1-3 km of structural and topographic relief. The models also predict concave downward flexure of the bedrock floors and horizontal near-surface tensile stresses east of the escarpment. The thin-beam models account best for the topographic relief of the eastern escarpment and the measured stresses given current best estimates for the rheology of the Sierran lithosphere. Our findings collectively indicate that the regional near-surface stress field and the widespread near-surface fracturing directly reflect the mechanical response to normal faulting along the eastern escarpment. These results have broad scientific and engineering implications for slope stability

First Results from a Forward, 3-Dimensional Regional Model of a Transpressional San Andreas Fault System

NASA Astrophysics Data System (ADS)

Fitzenz, D. D.; Miller, S. A.

2001-12-01

We present preliminary results from a 3-dimensional fault interaction model, with the fault system specified by the geometry and tectonics of the San Andreas Fault (SAF) system. We use the forward model for earthquake generation on interacting faults of Fitzenz and Miller [2001] that incorporates the analytical solutions of Okada [85,92], GPS-constrained tectonic loading, creep compaction and frictional dilatancy [Sleep and Blanpied, 1994, Sleep, 1995], and undrained poro-elasticity. The model fault system is centered at the Big Bend, and includes three large strike-slip faults (each discretized into multiple subfaults); 1) a 300km, right-lateral segment of the SAF to the North, 2) a 200km-long left-lateral segment of the Garlock fault to the East, and 3) a 100km-long right-lateral segment of the SAF to the South. In the initial configuration, three shallow-dipping faults are also included that correspond to the thrust belt sub-parallel to the SAF. Tectonic loading is decomposed into basal shear drag parallel to the plate boundary with a 35mm yr-1 plate velocity, and East-West compression approximated by a vertical dislocation surface applied at the far-field boundary resulting in fault-normal compression rates in the model space about 4mm yr-1. Our aim is to study the long-term seismicity characteristics, tectonic evolution, and fault interaction of this system. We find that overpressured faults through creep compaction are a necessary consequence of the tectonic loading, specifically where high normal stress acts on long straight fault segments. The optimal orientation of thrust faults is a function of the strike-slip behavior, and therefore results in a complex stress state in the elastic body. This stress state is then used to generate new fault surfaces, and preliminary results of dynamically generated faults will also be presented. Our long-term aim is to target measurable properties in or around fault zones, (e.g. pore pressures, hydrofractures, seismicity

Geophysical characterization of transtensional fault systems in the Eastern California Shear Zone-Walker Lane Belt

NASA Astrophysics Data System (ADS)

McGuire, M.; Keranen, K. M.; Stockli, D. F.; Feldman, J. D.; Keller, G. R.

2011-12-01

The Eastern California Shear Zone (ECSZ) and Walker Lane belt (WL) accommodate ~25% of plate motion between the North American and Pacific plates. Faults within the Mina deflection link the ECSZ and the WL, transferring strain from the Owens Valley and Death Valley-Fish Lake Valley fault systems to the transcurrent faults of the central Walker Lane. During the mid to late Miocene the majority of strain between these systems was transferred through the Silver Peak-Lone Mountain (SPLM) extensional complex via a shallowly dipping detachment. Strain transfer has since primarily migrated north to the Mina Deflection; however, high-angle faults bounding sedimentary basins and discrepancies between geodetic and geologic models indicate that the SPLM complex may still actively transfer a portion of the strain from the ECSZ to the WL on a younger set of faults. Establishing the pattern and amount of active strain transfer within the SPLM region is required for a full accounting of strain accommodation, and provides insight into strain partitioning at the basin scale within a broader transtensional zone. To map the active structures in and near Clayton Valley, within the SPLM region, we collected seismic reflection and refraction profiles and a dense grid of gravity readings that were merged with existing gravity data. The primary goals were to determine the geometry of the high-angle fault system, the amount and sense of offset along each fault set, connectivity of the faults, and the relationship of these faults to the Miocene detachment. Seismic reflection profiles imaged the high-angle basin-bounding normal faults and the detachment in both the footwall and hanging wall. The extensional basin is ~1 km deep, with a steep southeastern boundary, a gentle slope to the northwest, and a sharp boundary on the northwest side, suggestive of another fault system. Two subparallel dip-slip faults bound the southeast (deeper) basin margin with a large lateral velocity change (from ~2

Shallow-depth location and geometry of the Piedmont Reverse splay of the Hayward Fault, Oakland, California

USGS Publications Warehouse

Catchings, Rufus D.; Goldman, Mark R.; Trench, David; Buga, Michael; Chan, Joanne H.; Criley, Coyn J.; Strayer, Luther M.

2017-04-18

The Piedmont Thrust Fault, herein referred to as the Piedmont Reverse Fault (PRF), is a splay of the Hayward Fault that trends through a highly populated area of the City of Oakland, California (fig. 1A). Although the PRF is unlikely to generate a large-magnitude earthquake, slip on the PRF or high-amplitude seismic energy traveling along the PRF may cause considerable damage during a large earthquake on the Hayward Fault. Thus, it is important to determine the exact location, geometry (particularly dip), and lateral extent of the PRF within the densely populated Oakland area. In the near surface, the PRF juxtaposes Late Cretaceous sandstone (of the Franciscan Complex Novato Quarry terrane of Blake and others, 1984) and an older Pleistocene alluvial fan unit along much of its mapped length (fig. 1B; Graymer and others, 1995). The strata of the Novato Quarry unit vary greatly in strike (NW, NE, and E), dip direction (NE, SW, E, and NW), dip angle (15° to 85°), and lithology (shale and sandstone), and the unit has been intruded by quartz diorite in places. Thus, it is difficult to infer the structure of the fault, particularly at depth, with conventional seismic reflection imaging methods. To better determine the location and shallow-depth geometry of the PRF, we used high-resolution seismic imaging methods described by Catchings and others (2014). These methods involve the use of coincident P-wave (compressional wave) and S-wave (shear wave) refraction tomography and reflection data, from which tomographic models of P- and S-wave velocity and P-wave reflection images are developed. In addition, the coincident P-wave velocity (VP) and S-wave velocity (VS) data are used to develop tomographic models of VP/VS ratios and Poisson’s ratio, which are sensitive to shallow-depth faulting and groundwater. In this study, we also compare measurements of Swave velocities determined from surface waves with those determined from refraction tomography. We use the combination of

Complex permeability structure of a fault zone crosscutting a sequence of sandstones and shales and its influence on hydraulic head distribution

NASA Astrophysics Data System (ADS)

Cilona, A.; Aydin, A.; Hazelton, G.

2013-12-01

Characterization of the structural architecture of a 5 km-long, N40°E-striking fault zone provides new insights for the interpretation of hydraulic heads measured across and along the fault. Of interest is the contaminant transport across a portion of the Upper Cretaceous Chatsworth Formation, a 1400 m-thick turbidite sequence of sandstones and shales exposed in the Simi Hills, south California. Local bedding consistently dips about 20° to 30° to NW. Participating hydrogeologists monitor the local groundwater system by means of numerous boreholes used to define the 3D distribution of the groundwater table around the fault. Sixty hydraulic head measurements consistently show differences of 10s of meters, except for a small area. In this presentation, we propose a link between this distribution and the fault zone architecture. Despite an apparent linear morphological trend, the fault is made up of at least three distinct segments named here as northern, central and southern segments. Key aspects of the fault zone architecture have been delineated at two sites. The first is an outcrop of the central segment and the second is a borehole intersecting the northern segment at depth. The first site shows the fault zone juxtaposing sandstones against shales. Here the fault zone consists of a 13 meter-wide fault rock including a highly deformed sliver of sandstone on the northwestern side. In the sandstone, shear offset was resolved along N42°E striking and SE dipping fracture surfaces localized within a 40 cm thick strand. Here the central core of the fault zone is 8 m-wide and contains mostly shale characterized by highly diffuse deformation. It shows a complex texture overprinted by N30°E-striking carbonate veins. At the southeastern edge of the fault zone exposure, a shale unit dipping 50° NW towards the fault zone provides the key information that the shale unit was incorporated into the fault zone in a manner consistent with shale smearing. At the second site, a

Seismic swarms and diffuse fracturing within Triassic evaporites fed by deep degassing along the low-angle Alto Tiberina normal fault (central Apennines, Italy)

NASA Astrophysics Data System (ADS)

Piana Agostinetti, Nicola; Giacomuzzi, Genny; Chiarabba, Claudio

2017-01-01

We present high-resolution elastic models and relocated seismicity of a very active segment of the Apennines normal faulting system, computed via transdimensional local earthquake tomography (trans-D LET). Trans-D LET, a fully nonlinear approach to seismic tomography, robustly constrains high-velocity anomalies and inversions of P wave velocity, i.e., decreases of VP with depth, without introducing bias due to, e.g., a starting model, and giving the possibility to investigate the relation between fault structure, seismicity, and fluids. Changes in seismicity rate and recurring seismic swarms are frequent in the Apennines extensional belt. Deep fluids, upwelling from the delaminating continental lithosphere, are thought to be responsible for seismicity clustering in the upper crust and lubrication of normal faults during swarms and large earthquakes. We focus on the tectonic role played by the Alto Tiberina low-angle normal fault (ATF), finding displacements across the fault consistent with long-term accommodation of deformation. Our results show that recent seismic swarms affecting the area occur within a 3 km thick, high VP/VS, densely cracked, and overpressurized evaporitic layer, composed of dolostones and anhydrites. A persistent low VP, low VP/VS volume, present on top of and along the ATF low-angle detachment, traces the location of mantle-derived CO2, the upward flux of which contributes to cracking within the evaporitic layer.

San Antonio relay ramp: Area of stratal continuity between large-displacement barrier faults of the Edwards aquifer and Balcones fault zone, central Texas

DOE Office of Scientific and Technical Information (OSTI.GOV)

Collins, E.W.

1996-09-01

The San Antonio relay ramp, a gentle southwest-dipping monocline, formed between the tips of two en echelon master faults having maximum throws of >240 in. Structural analysis of this relay ramp is important to studies of Edwards aquifer recharge and ground-water flow because the ramp is an area of relatively good stratal continuity linking the outcrop belt recharge zone and unconfined aquifer with the downdip confined aquifer. Part of the relay ramp lies within the aquifer recharge zone and is crossed by several southeast-draining creeks, including Salado, Cibolo, and Comal Creeks, that supply water to the ramp recharge area. Thismore » feature is an analog for similar structures within the aquifer and for potential targets for hydrocarbons in other Gulf Coast areas. Defining the ramp is an {approximately}13-km-wide right step of the Edwards Group outcrop belt and the en echelon master faults that bound the ramp. The master faults strike N55-75{degrees}E, and maximum displacement exceeds the {approximately}165-m thickness of the Edwards Group strata. The faults therefore probably serve as barriers to Edwards ground-water flow. Within the ramp, tilted strata gently dip southwestward at {approximately}5 m/km, and the total structural relief along the ramp`s southwest-trending axis is <240 in. The ramp`s internal framework is defined by three fault blocks that are {approximately}4 to {approximately}6 km wide and are bound by northeast-striking faults having maximum throws between 30 and 150 m. Within the fault blocks, local areas of high fracture permeability may exist where smaller faults and joints are well connected.« less

RMT focal plane sensitivity to seismic network geometry and faulting style

USGS Publications Warehouse

Johnson, Kendra L.; Hayes, Gavin; Herrmann, Robert B.; Benz, Harley M.; McNamara, Daniel E.; Bergman, Eric A.

2016-01-01

Modern tectonic studies often use regional moment tensors (RMTs) to interpret the seismotectonic framework of an earthquake or earthquake sequence; however, despite extensive use, little existing work addresses RMT parameter uncertainty. Here, we quantify how network geometry and faulting style affect RMT sensitivity. We examine how data-model fits change with fault plane geometry (strike and dip) for varying station configurations. We calculate the relative data fit for incrementally varying geometries about a best-fitting solution, applying our workflow to real and synthetic seismograms for both real and hypothetical station distributions and earthquakes. Initially, we conduct purely observational tests, computing RMTs from synthetic seismograms for hypothetical earthquakes and a series of well-behaved network geometries. We then incorporate real data and station distributions from the International Maule Aftershock Deployment (IMAD), which recorded aftershocks of the 2010 MW 8.8 Maule earthquake, and a set of regional stations capturing the ongoing earthquake sequence in Oklahoma and southern Kansas. We consider RMTs computed under three scenarios: (1) real seismic records selected for high data quality; (2) synthetic seismic records with noise computed for the observed source-station pairings and (3) synthetic seismic records with noise computed for all possible station-source pairings. To assess RMT sensitivity for each test, we observe the ‘fit falloff’, which portrays how relative fit changes when strike or dip varies incrementally; we then derive the ranges of acceptable strikes and dips by identifying the span of solutions with relative fits larger than 90 per cent of the best fit. For the azimuthally incomplete IMAD network, Scenario 3 best constrains fault geometry, with average ranges of 45° and 31° for strike and dip, respectively. In Oklahoma, Scenario 3 best constrains fault dip with an average range of 46°; however, strike is best constrained

Fault stability under conditions of variable normal stress

USGS Publications Warehouse

Dieterich, J.H.; Linker, M.F.

1992-01-01

The stability of fault slip under conditions of varying normal stress is modelled as a spring and slider system with rate- and state-dependent friction. Coupling of normal stress to shear stress is achieved by inclining the spring at an angle, ??, to the sliding surface. Linear analysis yields two conditions for unstable slip. The first, of a type previously identified for constant normal stress systems, results in instability if stiffness is below a critical value. Critical stiffness depends on normal stress, constitutive parameters, characteristic sliding distance and the spring angle. Instability of the first type is possible only for velocity-weakening friction. The second condition yields instability if spring angle ?? <-cot-1??ss, where ??ss is steady-state sliding friction. The second condition can arise under conditions of velocity strengthening or weakening. Stability fields for finite perturbations are investigated by numerical simulation. -Authors

Outer Rise Faulting And Mantle Serpentinization

NASA Astrophysics Data System (ADS)

Ranero, C. R.; Phipps Morgan, J.; McIntosh, K.; Reichert, C.

Dehydration of serpentinized mantle of the downgoing slab has been proposed to cause both intermediate depth earthquakes (50-300 km) and arc volcanism at sub- duction zones. It has been suggested that most of this serpentinization occurs beneath the outer rise; where normal faulting earthquakes due to bending cut > 20 km deep into the lithosphere, allowing seawater to reach and react with underlying mantle. However, little is known about flexural faulting at convergent margins; about how many normal faults cut across the crust and how deeply they penetrate into the man- tle; about the true potential of faults as conduits for fluid flow and how much water can be added through this process. We present evidence that pervasive flexural faulting may cut deep into the mantle and that the amount of faulting vary dramatically along strike at subduction zones. Flexural faulting increases towards the trench axis indicat- ing that active extension occurs in a broad area. Multibeam bathymetry of the Pacific margin of Costa Rica and Nicaragua shows a remarkable variation in the amount of flexural faulting along the incoming ocean plate. Several parameters seem to control lateral variability. Off south Costa Rica thick crust of the Cocos Ridge flexes little, and little to no faulting develops near the trench. Off central Costa Rica, normal thick- ness crust with magnetic anomalies striking oblique to the trench displays small offset faults (~200 m) striking similar to the original seafloor fabric. Off northern Costa Rica, magnetic anomalies strike perpendicular to the trench axis, and a few ~100m-offset faults develop parallel to the trench. Further north, across the Nicaraguan margin, magnetic anomalies strike parallel to the trench and the most widespread faulting de- velops entering the trench. Multichannel seismic reflection images in this area show a pervasive set of trenchward dipping reflections that cross the ~6 km thick crust and extend into the mantle to depths of at

Slip accumulation and lateral propagation of active normal faults in Afar

NASA Astrophysics Data System (ADS)

Manighetti, I.; King, G. C. P.; Gaudemer, Y.; Scholz, C. H.; Doubre, C.

2001-01-01

We investigate fault growth in Afar, where normal fault systems are known to be currently growing fast and most are propagating to the northwest. Using digital elevation models, we have examined the cumulative slip distribution along 255 faults with lengths ranging from 0.3 to 60 km. Faults exhibiting the elliptical or "bell-shaped" slip profiles predicted by simple linear elastic fracture mechanics or elastic-plastic theories are rare. Most slip profiles are roughly linear for more than half of their length, with overall slopes always <0.035. For the dominant population of NW striking faults and fault systems longer than 2 km, the slip profiles are asymmetric, with slip being maximum near the eastern ends of the profiles where it drops abruptly to zero, whereas slip decreases roughly linearly and tapers in the direction of overall Aden rift propagation. At a more detailed level, most faults appear to be composed of distinct, shorter subfaults or segments, whose slip profiles, while different from one to the next, combine to produce the roughly linear overall slip decrease along the entire fault. On a larger scale, faults cluster into kinematically coupled systems, along which the slip on any scale individual fault or fault system complements that of its neighbors, so that the total slip of the whole system is roughly linearly related to its length, with an average slope again <0.035. We discuss the origin of these quasilinear, asymmetric profiles in terms of "initiation points" where slip starts, and "barriers" where fault propagation is arrested. In the absence of a barrier, slip apparently extends with a roughly linear profile, tapered in the direction of fault propagation.

A dense, intersecting array of normal faults on the outer shelf off Southern Costa Rica, associated with subducting Quepos ridge

NASA Astrophysics Data System (ADS)

Silver, E. A.; Kluesner, J. W.; Gibson, J. C.; Bangs, N. L.; McIntosh, K. D.; von Huene, R.; Orange, D.; Ranero, C. R.

2012-12-01

Use of narrow, fixed swath multibeam data with high sounding densities has allowed order of magnitude improvement in image resolution with EM122 multibeam and backscatter data, as part of a 3D seismic study west of the Osa Peninsula. On the outer shelf, along the projection of the subducting Quepos Ridge, we mapped a dense array of faults cutting an arcuate, well-layered set of outcropping beds in the backscatter imagery (mosaicked at 2 m), with roughly N-S and E-W trends. The N-S trends dominate, and show inconsistent offsets, implying that the faults are normal and not strike-slip. The faults also show normal displacement in the 3D seismic data, consistent with the surface interpretation. The outcropping beds (of late Pleistocene age, based on Expedition 334 drilling), may have been truncated during the late Pleistocene low sea-level stand. The outermost shelf (edged by arcuate bathymetric contours) does not show these folded beds, as it was below wave base and buried by a thin sediment layer. However, narrow lines of small pockmarks and mounds follow the fault trends exactly, indicating that fluid flow through the faults is expressed at the surface, including a gas plume that extends to the sea-surface. The almost unprecedented increase in resolution of the EM122 data allows us to infer that the N-S, E-W grid of faults overlying the NE-trending Quepos Ridge projection (and NE directed subduction) formed by extensional arching above the ridge, not by collisional slip lines at a rigid indenter (as proposed earlier based on sandbox models). The extensional fault pattern also facilitates fluid and gas flow through the sedimentary section.

The Deformation of Overburden Soil and Interaction with Pile Foundations of Bridges Induced by Normal Faulting

NASA Astrophysics Data System (ADS)

Wu, Liang-Chun; Li, Chien-Hung; Chan, Pei-Chen; Lin, Ming-Lang

2017-04-01

According to the investigations of well-known disastrous earthquakes in recent years, ground deformation induced by faulting is one of the causes for engineering structure damages in addition to strong ground motion. Most of structures located on faulting zone has been destroyed by fault offset. Take the Norcia Earthquake in Italy (2016, Mw=6.2) as an example, the highway bridge in Arquata crossing the rupture area of the active normal fault suffered a quantity of displacement which causing abutment settlement, the piers of bridge fractured and so on. However, The Seismic Design Provisions and Commentary for Highway Bridges in Taiwan, the stating of it in the general rule of first chapter, the design in bridges crossing active fault: "This specification is not applicable of making design in bridges crossing or near active fault, that design ought to the other particular considerations ".This indicates that the safty of bridges crossing active fault are not only consider the seismic performance, the most ground deformation should be attended. In this research, to understand the failure mechanism and the deformation characteristics, we will organize the case which the bridges subjected faulting at home and abroad. The processes of research are through physical sandbox experiment and numerical simulation by discrete element models (PFC3-D). The normal fault case in Taiwan is Shanchiao Fault. As above, the research can explore the deformation in overburden soil and the influences in the foundations of bridges by normal faulting. While we can understand the behavior of foundations, we will make the bridge superstructures into two separations, simple beam and continuous beam and make a further research on the main control variables in bridges by faulting. Through the above mentioned, we can then give appropriate suggestions about planning considerations and design approaches. This research presents results from sandbox experiment and 3-D numerical analysis to simulate

Shear concentration in a collision zone: kinematics of the Chihshang Fault as revealed by outcrop-scale quantification of active faulting, Longitudinal Valley, eastern Taiwan

NASA Astrophysics Data System (ADS)

Angelier, J.; Chu, H.-T.; Lee, J.-C.

1997-06-01

Repeated measurements of active deformation were carried out at three sites along the active Chihshang Fault, a segment of the Longitudinal Valley Fault zone of eastern Taiwan (the present-day plate boundary between the Philippine Sea Plate and Eurasia). Reliable annual records of displacement along an active fault, were obtained based on detailed surveys of faulted concrete structures. Along the active Chihshang Fault striking N18°E, we determined average motion vectors trending N37°W with an average shortening of 2.2 cm/yr. Thus, the transverse component of motion related to westward thrusting is 1.8 cm/yr, whereas the left-lateral strike-slip component of motion is 1.3 cm/yr. The fault dips 39-45° to the east, so that the vertical displacement is 1.5-3 cm/yr and the actual oblique offset of the fault increases at a rate of 2.7-3.7 cm/yr. This is in good agreement with the results of regional geodetic and tectonic analyses in Taiwan, and consistent with the N54°W trend of convergence between the northernmost Luzon Arc and South China revealed by GPS studies. Our study provides an example of extreme shear concentration in an oblique collision zone. At Chihshang, the whole horizontal shortening of the Longitudinal Valley Fault, 2.2 cm/yr on average, occurs across a single, narrow fault zone, so that the whole reverse slip (about 2.7-3.7 cm/yr depending on fault dip) was entirely recorded by walls 20-200 m long where faults are tightly localized. This active faulting accounts for more than one fourth (27%) of the total shortening between the Luzon Arc and South China recorded through GPS analyses. Further surveys should indicate whether the decreasing shortening velocity across the fault is significant (revealing increasing earthquake risk due to stress accumulation) or not (revealing continuing fault creep and 'weak' behaviour of the Chihshang Fault).

Imaging the polarity switch between large seismogenic normal faults in the southern Apennines (Italy)

NASA Astrophysics Data System (ADS)

Fracassi, U.; Milano, G.; di Giovambattista, R.; Ventura, G.

2009-04-01

The backbone of Italy's Apennines hosts the majority of the seismic moment release in the Italian peninsula. In particular, the area among the southern Abruzzo, southeastern Lazio and Molise regions in central-southern Italy includes the polarity switch, from north to south, between the large SW-verging seismogenic normal faults (the southernmost one being the Aremogna-Cinque Miglia, responsible for a Mw 6.4 event dated 800 B.C-1030 A.D.) and those NE-verging ones (the northernmost one being the Boiano Basin, responsible for the 26 July 1805, Mw 6.6 Molise earthquake), including the Carpino-Le Piane fault system. In addition, the area between these two faults is the locus of extension parallel to the chain axis, as shown by a low-magnitude (M < 3.3) seismic sequence occurred in 2001. As GPS data illustrate, NE-SW striking extension predominates in the western and the inner sectors of the Apennines. All active normal faults along the crest of the Apennines are essentially parallel to the mountain range (NW-SE) and are governed by the current extensional regime that has been in place since the Middle-Upper Pleistocene. However, the occurrence of such polarity switch between antithetic, conjugate seismogenic normal faults in Italy is very uncommon. In addition, the area of research marks the abrupt end of the two (three?) sub-parallel seismogenic belts in Abruzzo (to the north) and the inception of the single, aligned one in Molise (to the south), including the western termination of E-W striking, large oblique-slip faulting in the foreland. In other words, this is a critical area concerning seismogenesis in central Italy and, therefore, the tectonic mechanism that either causes or influences such polarity switch could represent a key ingredient in the above scenario. Between January and May 2005, the RSN (Italy's National Seismometric Network) recorded a rise in the background seismicity, that has been recently relocated. This sequence is essentially a low magnitude

Fault zone structure and fluid-rock interaction of a high angle normal fault in Carrara marble (NW Tuscany, Italy)

NASA Astrophysics Data System (ADS)

Molli, G.; Cortecci, G.; Vaselli, L.; Ottria, G.; Cortopassi, A.; Dinelli, E.; Mussi, M.; Barbieri, M.

2010-09-01

We studied the geometry, intensity of deformation and fluid-rock interaction of a high angle normal fault within Carrara marble in the Alpi Apuane NW Tuscany, Italy. The fault is comprised of a core bounded by two major, non-parallel slip surfaces. The fault core, marked by crush breccia and cataclasites, asymmetrically grades to the host protolith through a damage zone, which is well developed only in the footwall block. On the contrary, the transition from the fault core to the hangingwall protolith is sharply defined by the upper main slip surface. Faulting was associated with fluid-rock interaction, as evidenced by kinematically related veins observable in the damage zone and fluid channelling within the fault core, where an orange-brownish cataclasite matrix can be observed. A chemical and isotopic study of veins and different structural elements of the fault zone (protolith, damage zone and fault core), including a mathematical model, was performed to document type, role, and activity of fluid-rock interactions during deformation. The results of our studies suggested that deformation pattern was mainly controlled by processes associated with a linking-damage zone at a fault tip, development of a fault core, localization and channelling of fluids within the fault zone. Syn-kinematic microstructural modification of calcite microfabric possibly played a role in confining fluid percolation.

Nucleation and growth of strike slip faults in granite.

USGS Publications Warehouse

Segall, P.; Pollard, D.P.

1983-01-01

Fractures within granodiorite of the central Sierra Nevada, California, were studied to elucidate the mechanics of faulting in crystalline rocks, with emphasis on the nucleation of new fault surfaces and their subsequent propagation and growth. Within the study area the fractures form a single, subparallel array which strikes N50o-70oE and dips steeply to the S. Some of these fractures are identified as joints because displacements across the fracture surfaces exhibit dilation but no slip. The joints are filled with undeformed minerals, including epidote and chlorite. Other fractures are identified as small faults because they display left-lateral strike slip separations of up to 2m. Slickensides, developed on fault surfaces, plunge 0o-20o to the E. The faults occur parallel to, and in the same outcrop with, the joints. The faults are filled with epidote, chlorite, and quartz, which exhibit textural evidence of shear deformation. These observations indicate that the strike slip faults nucleated on earlier formed, mineral filled joints. Secondary, dilational fractures propagated from near the ends of some small faults contemporaneously with the left-lateral slip on the faults. These fractures trend 25o+ or -10o from the fault planes, parallel to the direction of inferred local maximum compressive stress. The faults did not propagate into intact rock in their own planes as shear fractures. -from Authors

Orientations of Pre-existing Structures along the Scarp of the Bilila-Mtakataka Fault in the Central Malawi Rift.

NASA Astrophysics Data System (ADS)

Elifritz, E. A.; Johnson, S.; Beresh, S. C. M.; Mendez, K.; Mynatt, W. G.; Mayle, M.; Laó-Dávila, D. A.; Atekwana, E. A.; Chindandali, P. R. N.; Chisenga, C.; Gondwe, S.; Mkumbwa, M.; Kalindekafe, L.; Kalaguluka, D.; Salima, J.

2017-12-01

The NW-SE Bilila-Mtakataka Fault is suggested to be 100 km in length and is located in the Malawi Rift, a portion of the magma-poor Western Branch of the East African Rift System. This fault is exposed south of Lake Malawi and occurs close to the epicenter of the 1989 6.2 magnitude Salima Earthquake. Moreover, it traverses rocks with inherited Precambrian fabrics that may control the modern rifting process. The effect of the orientation of the pre-existing fabric on the formation of this potentially seismogenic fault has not been well studied. In this project, we measured the older foliations, dikes, and joints in addition to younger faults and striations to understand how the active faulting of the Bilila-Mtakataka Fault is affected by the older fabric. The Fault is divided into 5 segments and 4 linkage zones. All four linkage zones were studied in detail and a Brunton compass was used to determine orientations of structures. The linkage zone between segments 1 and 2 occurs between a regional WNW-ESE joint and the border fault, which is identified by a zig-zag pattern in SRTM data. Precambrian gneiss is cut by oblique steeply-dipping faults in this area. Striations and layer offsets suggest both right-lateral and normal components. This segment strikes NE-SW, in contrast with the NW-SE average strike of the entire fault. The foliations, faults, dikes, and joints collected in this area strike NE-SW, therefore running parallel to the segment. The last 3 southern linkage zones all strike NW-SE and the linkage zone between segment 3 and 4 has a steep dip angle. Dip angles of structures vary from segment to segment, having a wide range of results. Nonetheless, all four linkage zones show structures striking parallel to its segment direction. The results show that pre-existing meso-scale and regional structures and faults strike parallel to the fault scarp. The parallelism of the structures suggest that they serve as planes of weakness, controlling the localization of

Modeling of fault activation and seismicity by injection directly into a fault zone associated with hydraulic fracturing of shale-gas reservoirs

DOE PAGES

Rutqvist, Jonny; Rinaldi, Antonio P.; Cappa, Frédéric; ...

2015-03-01

We conducted three-dimensional coupled fluid-flow and geomechanical modeling of fault activation and seismicity associated with hydraulic fracturing stimulation of a shale-gas reservoir. We simulated a case in which a horizontal injection well intersects a steeply dip- ping fault, with hydraulic fracturing channeled within the fault, during a 3-hour hydraulic fracturing stage. Consistent with field observations, the simulation results show that shale-gas hydraulic fracturing along faults does not likely induce seismic events that could be felt on the ground surface, but rather results in numerous small microseismic events, as well as aseismic deformations along with the fracture propagation. The calculated seismicmore » moment magnitudes ranged from about -2.0 to 0.5, except for one case assuming a very brittle fault with low residual shear strength, for which the magnitude was 2.3, an event that would likely go unnoticed or might be barely felt by humans at its epicenter. The calculated moment magnitudes showed a dependency on injection depth and fault dip. We attribute such dependency to variation in shear stress on the fault plane and associated variation in stress drop upon reactivation. Our simulations showed that at the end of the 3-hour injection, the rupture zone associated with tensile and shear failure extended to a maximum radius of about 200 m from the injection well. The results of this modeling study for steeply dipping faults at 1000 to 2500 m depth is in agreement with earlier studies and field observations showing that it is very unlikely that activation of a fault by shale-gas hydraulic fracturing at great depth (thousands of meters) could cause felt seismicity or create a new flow path (through fault rupture) that could reach shallow groundwater resources.« less

Modeling of fault activation and seismicity by injection directly into a fault zone associated with hydraulic fracturing of shale-gas reservoirs

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rutqvist, Jonny; Rinaldi, Antonio P.; Cappa, Frédéric

We conducted three-dimensional coupled fluid-flow and geomechanical modeling of fault activation and seismicity associated with hydraulic fracturing stimulation of a shale-gas reservoir. We simulated a case in which a horizontal injection well intersects a steeply dip- ping fault, with hydraulic fracturing channeled within the fault, during a 3-hour hydraulic fracturing stage. Consistent with field observations, the simulation results show that shale-gas hydraulic fracturing along faults does not likely induce seismic events that could be felt on the ground surface, but rather results in numerous small microseismic events, as well as aseismic deformations along with the fracture propagation. The calculated seismicmore » moment magnitudes ranged from about -2.0 to 0.5, except for one case assuming a very brittle fault with low residual shear strength, for which the magnitude was 2.3, an event that would likely go unnoticed or might be barely felt by humans at its epicenter. The calculated moment magnitudes showed a dependency on injection depth and fault dip. We attribute such dependency to variation in shear stress on the fault plane and associated variation in stress drop upon reactivation. Our simulations showed that at the end of the 3-hour injection, the rupture zone associated with tensile and shear failure extended to a maximum radius of about 200 m from the injection well. The results of this modeling study for steeply dipping faults at 1000 to 2500 m depth is in agreement with earlier studies and field observations showing that it is very unlikely that activation of a fault by shale-gas hydraulic fracturing at great depth (thousands of meters) could cause felt seismicity or create a new flow path (through fault rupture) that could reach shallow groundwater resources.« less

Structural evolution and tectonic style of the Tunisian central Atlas; role of inherited faults in compressive tectonics (Ghoualguia anticline)

NASA Astrophysics Data System (ADS)

Briki, Haithem; Ahmadi, Riadh; Smida, Rabiaa; Rekhiss, Farhat

2018-04-01

Geological mapping, field cross sections, structural analyses and new subsurface data were used to characterize the geometry and tectonic setting of the Ghoualguia structure, which is an E-W-trending anticline located between the Kalaa Khasba and Rouhia troughs of the central Tunisian Atlas. The results show an important NE-SW extensional phase during the Mesozoic, as demonstrated by synsedimentary normal faults (NW-SE and E-W) and thickness variations. In the Aouled Mdoua area, the absence of Paleocene-Eocene rocks indicates that the eastern and western parts of the Ghoualguia structure were separated by high topography. In addition, the angular unconformity observed between the Upper Cretaceous unit (Abiod Fm.) and the upper Eocene series (Souar Fm.) provide evidence of a tilted-block structure delineated by North-South faults. A major compressional phase during the middle to late Miocene created various detachment levels that originated mainly in the Triassic and Cretaceous deposits. Faults were reactivated as thrust and strike-slip faults, creating fault-related fold structures. In the core of the Ghoualguia fold, an original S-dipping normal fault underwent reverse movement as a back thrust. Fault-slip data indicate that the area records a major NE-SW extensional phase that took place during the late Miocene and Pliocene. A balanced cross section provides insight into the existence of two main detachment levels rooted in the Triassic (depth ± 6 km) and the lower Cretaceous (depth ± 2.5 km). The balanced cross section highlights a shortening of about 2.5 km along cross section and 1.5 km in the central part of the Ghoualguia anticline. This work underlines the predominant role of the inherited Mesozoic structures during the evolution of the Atlassic range and their influence on the geometry of the central Tunisian atlas.

History of fault slip and interaction with deltaic depostion from the middle Miocene to the Present - Barataria Fault, coastal Louisiana

NASA Astrophysics Data System (ADS)

McLindon, C.

2017-12-01

The Barataria fault is a major component of the Terrebonne Trough, a structural system of faults and salt domes underlying coastal Louisiana. High-quality 3-D seismic reflection data, industry well logs, micro-paleontological data and published literature on regional depositional patterns are integrated to provide an evolutionary history of the Barataria fault. The fault is a segment within a series of south-dipping normal faults that define the northern boundary of the Terrebonne Trough. The fault segment tips at depth interact with the Lake Washington and Bay de Chene salt domes, which appear to have limited its along-strike length. This study shows that the Barataria fault has exhibited continuous but episodic slip since at least the middle Miocene and through the present. Periods of maximum rates of fault slip are related to periods of maximum rates of sediment accumulation associated with Miocene deltaic deposition. The expansion of interval thickness between biostratigraphic markers in the hanging wall section of the fault relative to the footwall section (expansion index) indicate that rates of subsidence on the footwall during active fault slip were substantially greater than on the footwall. Pliocene-Pleistocene stratigraphic intervals exhibiting lower expansion indexes indicate that the fault remained active, but with a pattern of slower slip rate in which stratigraphic thickening was more limited to the area immediately adjacent to the fault. The Barataria fault defines the modern-day width of Barataria Bay, and also has a surface expression in the coastal marsh indicating that recent episodic slip has been associated with patterns of Holocene deltaic deposition.

Stability of faults with heterogeneous friction properties and effective normal stress

NASA Astrophysics Data System (ADS)

Luo, Yingdi; Ampuero, Jean-Paul

2018-05-01

Abundant geological, seismological and experimental evidence of the heterogeneous structure of natural faults motivates the theoretical and computational study of the mechanical behavior of heterogeneous frictional fault interfaces. Fault zones are composed of a mixture of materials with contrasting strength, which may affect the spatial variability of seismic coupling, the location of high-frequency radiation and the diversity of slip behavior observed in natural faults. To develop a quantitative understanding of the effect of strength heterogeneity on the mechanical behavior of faults, here we investigate a fault model with spatially variable frictional properties and pore pressure. Conceptually, this model may correspond to two rough surfaces in contact along discrete asperities, the space in between being filled by compressed gouge. The asperities have different permeability than the gouge matrix and may be hydraulically sealed, resulting in different pore pressure. We consider faults governed by rate-and-state friction, with mixtures of velocity-weakening and velocity-strengthening materials and contrasts of effective normal stress. We systematically study the diversity of slip behaviors generated by this model through multi-cycle simulations and linear stability analysis. The fault can be either stable without spontaneous slip transients, or unstable with spontaneous rupture. When the fault is unstable, slip can rupture either part or the entire fault. In some cases the fault alternates between these behaviors throughout multiple cycles. We determine how the fault behavior is controlled by the proportion of velocity-weakening and velocity-strengthening materials, their relative strength and other frictional properties. We also develop, through heuristic approximations, closed-form equations to predict the stability of slip on heterogeneous faults. Our study shows that a fault model with heterogeneous materials and pore pressure contrasts is a viable framework

Fault strength in Marmara region inferred from the geometry of the principle stress axes and fault orientations: A case study for the Prince's Islands fault segment

NASA Astrophysics Data System (ADS)

Pinar, Ali; Coskun, Zeynep; Mert, Aydin; Kalafat, Dogan

2015-04-01

The general consensus based on historical earthquake data point out that the last major moment release on the Prince's islands fault was in 1766 which in turn signals an increased seismic risk for Istanbul Metropolitan area considering the fact that most of the 20 mm/yr GPS derived slip rate for the region is accommodated mostly by that fault segment. The orientation of the Prince's islands fault segment overlaps with the NW-SE direction of the maximum principle stress axis derived from the focal mechanism solutions of the large and moderate sized earthquakes occurred in the Marmara region. As such, the NW-SE trending fault segment translates the motion between the two E-W trending branches of the North Anatolian fault zone; one extending from the Gulf of Izmit towards Çınarcık basin and the other extending between offshore Bakırköy and Silivri. The basic relation between the orientation of the maximum and minimum principal stress axes, the shear and normal stresses, and the orientation of a fault provides clue on the strength of a fault, i.e., its frictional coefficient. Here, the angle between the fault normal and maximum compressive stress axis is a key parameter where fault normal and fault parallel maximum compressive stress might be a necessary and sufficient condition for a creeping event. That relation also implies that when the trend of the sigma-1 axis is close to the strike of the fault the shear stress acting on the fault plane approaches zero. On the other hand, the ratio between the shear and normal stresses acting on a fault plane is proportional to the coefficient of frictional coefficient of the fault. Accordingly, the geometry between the Prince's islands fault segment and a maximum principal stress axis matches a weak fault model. In the frame of the presentation we analyze seismological data acquired in Marmara region and interpret the results in conjuction with the above mentioned weak fault model.

ETS and tidal stressing: Fault weakening after main slip pulse

NASA Astrophysics Data System (ADS)

Houston, H.

2013-12-01

weakening of the fault plane following its initial rupture. Considering up- and down-dip sensitivities to tidal stress, tremor generation on the up-dip region is affected roughly 50% more by both positive and negative tidal stresses than tremor down-dip. Furthermore, for the down-dip tremor, there is less contrast in sensitivity to stress between the tremor at the main slip front and the later tremor, i.e., the fault downdip is both less sensitive to tidal stress and weakens less due to the rupture. These results are consistent with the timing and geometry of Rapid Tremor Reversals, which also indicate weakening of the fault after the main slip front has passed through a region (Houston et al., 2011). RTRs occur on updip parts of the fault, after the main slip front, and at times of encouraging tidal stress (Thomas et al., 2013).

Tectonic geomorphology of large normal faults bounding the Cuzco rift basin within the southern Peruvian Andes

NASA Astrophysics Data System (ADS)

Byers, C.; Mann, P.

2015-12-01

The Cuzco basin forms a 80-wide, relatively flat valley within the High Andes of southern Peru. This larger basin includes the regional capital of Cuzco and the Urubamba Valley, or "Sacred Valley of the Incas" favored by the Incas for its mild climate and broader expanses of less rugged and arable land. The valley is bounded on its northern edge by a 100-km-long and 10-km-wide zone of down-to-the-south systems of normal faults that separate the lower area of the down-dropped plateau of central Peru and the more elevated area of the Eastern Cordillera foldbelt that overthrusts the Amazon lowlands to the east. Previous workers have shown that the normal faults are dipslip with up to 600 m of measured displacements, reflect north-south extension, and have Holocene displacments with some linked to destructive, historical earthquakes. We have constructed topographic and structural cross sections across the entire area to demonstrate the normal fault on a the plateau peneplain. The footwall of the Eastern Cordillera, capped by snowcapped peaks in excess of 6 km, tilts a peneplain surface northward while the hanging wall of the Cuzco basin is radially arched. Erosion is accelerated along the trend of the normal fault zone. As the normal fault zone changes its strike from east-west to more more northwest-southeast, normal displacement decreases and is replaced by a left-lateral strike-slip component.

Criteria for Seismic Splay Fault Activation During Subduction Earthquakes

NASA Astrophysics Data System (ADS)

Dedontney, N.; Templeton, E.; Bhat, H.; Dmowska, R.; Rice, J. R.

2008-12-01

As sediment is added to the accretionary prism or removed from the forearc, the material overlying the plate interface must deform to maintain a wedge structure. One of the ways this internal deformation is achieved is by slip on splay faults branching from the main detachment, which are possibly activated as part of a major seismic event. As a rupture propagates updip along the plate interface, it will reach a series of junctions between the shallowly dipping detachment and more steeply dipping splay faults. The amount and distribution of slip on these splay faults and the detachment determines the seafloor deformation and the tsunami waveform. Numerical studies by Kame et al. [JGR, 2003] of fault branching during dynamic slip-weakening rupture in 2D plane strain showed that branch activation depends on the initial stress state, rupture velocity at the branching junction, and branch angle. They found that for a constant initial stress state, with the maximum principal stress at shallow angles to the main fault, branch activation is favored on the compressional side of the fault for a range of branch angles. By extending the part of their work on modeling the branching behavior in the context of subduction zones, where critical taper wedge concepts suggest the angle that the principal stress makes with the main fault is shallow, but not horizontal, we hope to better understand the conditions for splay fault activation and the criteria for significant moment release on the splay. Our aim is to determine the range of initial stresses and relative frictional strengths of the detachment and splay fault that would result in seismic splay fault activation. In aid of that, we conduct similar dynamic rupture analyses to those of Kame et al., but use explicit finite element methods, and take fuller account of overall structure of the zone (rather than focusing just on the branching junction). Critical taper theory requires that the basal fault be weaker than the overlying

Teleseismic body waves from dynamically rupturing shallow thrust faults: Are they opaque for surface-reflected phases?

USGS Publications Warehouse

Smith, D.E.; Aagaard, Brad T.; Heaton, T.H.

2005-01-01

We investigate whether a shallow-dipping thrust fault is prone to waveslip interactions via surface-reflected waves affecting the dynamic slip. If so, can these interactions create faults that are opaque to radiated energy? Furthermore, in this case of a shallow-dipping thrust fault, can incorrectly assuming a transparent fault while using dislocation theory lead to underestimates of seismic moment? Slip time histories are generated in three-dimensional dynamic rupture simulations while allowing for varying degrees of wave-slip interaction controlled by fault-friction models. Based on the slip time histories, P and SH seismograms are calculated for stations at teleseismic distances. The overburdening pressure caused by gravity eliminates mode I opening except at the tip of the fault near the surface; hence, mode I opening has no effect on the teleseismic signal. Normalizing by a Haskell-like traditional kinematic rupture, we find teleseismic peak-to-peak displacement amplitudes are approximately 1.0 for both P and SH waves, except for the unrealistic case of zero sliding friction. Zero sliding friction has peak-to-peak amplitudes of 1.6 for P and 2.0 for SH waves; the fault slip oscillates about its equilibrium value, resulting in a large nonzero (0.08 Hz) spectral peak not seen in other ruptures. These results indicate wave-slip interactions associated with surface-reflected phases in real earthquakes should have little to no effect on teleseismic motions. Thus, Haskell-like kinematic dislocation theory (transparent fault conditions) can be safety used to simulate teleseismic waveforms in the Earth.

Structure and mechanics of the Hayward-Rodgers Creek Fault step-over, San Francisco Bay, California

USGS Publications Warehouse

Parsons, T.; Sliter, R.; Geist, E.L.; Jachens, R.C.; Jaffe, B.E.; Foxgrover, A.; Hart, P.E.; McCarthy, J.

2003-01-01

A dilatational step-over between the right-lateral Hayward and Rodgers Creek faults lies beneath San Pablo Bay in the San Francisco Bay area. A key seismic hazard issue is whether an earthquake on one of the faults could rupture through the step-over, enhancing its maximum possible magnitude. If ruptures are terminated at the step-over, then another important issue is how strain transfers through the step. We developed a combined seismic reflection and refraction cross section across south San Pablo Bay and found that the Hayward and Rodgers Creek faults converge to within 4 km of one another near the surface, about 2 km closer than previously thought. Interpretation of potential field data from San Pablo Bay indicated a low likelihood of strike-slip transfer faults connecting the Hayward and Rodgers Creek faults. Numerical simulations suggest that it is possible for a rupture to jump across a 4-km fault gap, although special stressing conditions are probably required (e.g., Harris and Day, 1993, 1999). Slip on the Hayward and Rodgers Creek faults is building an extensional pull-apart basin that could contain hazardous normal faults. We investigated strain in the pull-apart using a finite-element model and calculated a ???0.02-MPa/yr differential stressing rate in the step-over on a least-principal-stress orientation nearly parallel to the strike-slip faults where they overlap. A 1- to 10-MPa stress-drop extensional earthquake is expected on normal faults oriented perpendicular to the strike-slip faults every 50-500 years. The last such earthquake might have been the 1898 M 6.0-6.5 shock in San Pablo Bay that apparently produced a small tsunami. Historical hydrographic surveys gathered before and after 1898 indicate abnormal subsidence of the bay floor within the step-over, possibly related to the earthquake. We used a hydrodynamic model to show that a dip-slip mechanism in north San Pablo Bay is the most likely 1898 rupture scenario to have caused the tsunami

Geometry and architecture of faults in a syn-rift normal fault array: The Nukhul half-graben, Suez rift, Egypt

NASA Astrophysics Data System (ADS)

Wilson, Paul; Gawthorpe, Rob L.; Hodgetts, David; Rarity, Franklin; Sharp, Ian R.

2009-08-01

The geometry and architecture of a well exposed syn-rift normal fault array in the Suez rift is examined. At pre-rift level, the Nukhul fault consists of a single zone of intense deformation up to 10 m wide, with a significant monocline in the hanging wall and much more limited folding in the footwall. At syn-rift level, the fault zone is characterised by a single discrete fault zone less than 2 m wide, with damage zone faults up to approximately 200 m into the hanging wall, and with no significant monocline developed. The evolution of the fault from a buried structure with associated fault-propagation folding, to a surface-breaking structure with associated surface faulting, has led to enhanced bedding-parallel slip at lower levels that is absent at higher levels. Strain is enhanced at breached relay ramps and bends inherited from pre-existing structures that were reactivated during rifting. Damage zone faults observed within the pre-rift show ramp-flat geometries associated with contrast in competency of the layers cut and commonly contain zones of scaly shale or clay smear. Damage zone faults within the syn-rift are commonly very straight, and may be discrete fault planes with no visible fault rock at the scale of observation, or contain relatively thin and simple zones of scaly shale or gouge. The geometric and architectural evolution of the fault array is interpreted to be the result of (i) the evolution from distributed trishear deformation during upward propagation of buried fault tips to surface faulting after faults breach the surface; (ii) differences in deformation response between lithified pre-rift units that display high competence contrasts during deformation, and unlithified syn-rift units that display low competence contrasts during deformation, and; (iii) the history of segmentation, growth and linkage of the faults that make up the fault array. This has important implications for fluid flow in fault zones.

Normal-faulting slip maxima and stress-drop variability: a geological perspective

USGS Publications Warehouse

Hecker, S.; Dawson, T.E.; Schwartz, D.P.

2010-01-01

We present an empirical estimate of maximum slip in continental normal-faulting earthquakes and present evidence that stress drop in intraplate extensional environments is dependent on fault maturity. A survey of reported slip in historical earthquakes globally and in latest Quaternary paleoearthquakes in the Western Cordillera of the United States indicates maximum vertical displacements as large as 6–6.5 m. A difference in the ratio of maximum-to-mean displacements between data sets of prehistoric and historical earthquakes, together with constraints on bias in estimates of mean paleodisplacement, suggest that applying a correction factor of 1.4±0.3 to the largest observed displacement along a paleorupture may provide a reasonable estimate of the maximum displacement. Adjusting the largest paleodisplacements in our regional data set (~6 m) by a factor of 1.4 yields a possible upper-bound vertical displacement for the Western Cordillera of about 8.4 m, although a smaller correction factor may be more appropriate for the longest ruptures. Because maximum slip is highly localized along strike, if such large displacements occur, they are extremely rare. Static stress drop in surface-rupturing earthquakes in the Western Cordillera, as represented by maximum reported displacement as a fraction of modeled rupture length, appears to be larger on normal faults with low cumulative geologic displacement (<2 km) and larger in regions such as the Rocky Mountains, where immature, low-throw faults are concentrated. This conclusion is consistent with a growing recognition that structural development influences stress drop and indicates that this influence is significant enough to be evident among faults within a single intraplate environment.

The Tjellefonna fault system of Western Norway: Linking late-Caledonian extension, post-Caledonian normal faulting, and Tertiary rock column uplift with the landslide-generated tsunami event of 1756

NASA Astrophysics Data System (ADS)

Redfield, T. F.; Osmundsen, P. T.

2009-09-01

On February 22, 1756, approximately 15.7 million cubic meters of bedrock were catastrophically released as a giant rockslide into the Langfjorden. Subsequently, three ˜ 40 meter high tsunami waves overwhelmed the village of Tjelle and several other local communities. Inherited structures had isolated a compartment in the hanging wall damage zone of the fjord-dwelling Tjellefonna fault. Because the region is seismically active in oblique-normal mode, and in accordance with scant historical sources, we speculate that an earthquake on a nearby fault may have caused the already-weakened Tjelle hillside to fail. From interpretation of structural, geomorphic, and thermo-chronological data we suggest that today's escarpment topography of Møre og Trøndelag is controlled to a first order by post-rift reactivation of faults parallel to the Mesozoic passive margin. In turn, a number of these faults reactivated Late Caledonian or early post-Caledonian fabrics. Normal-sense reactivation of inherited structures along much of coastal Norway suggests that a structural link exists between the processes that destroy today's mountains and those that created them. The Paleozoic Møre-Trøndelag Fault Complex was reactivated as a normal fault during the Mesozoic and, probably, throughout the Cenozoic until the present day. Its NE-SW trending strands crop out between the coast and the base of a c. 1.7 km high NW-facing topographic 'Great Escarpment.' Well-preserved kinematic indicators and multiple generations of fault products are exposed along the Tjellefonna fault, a well-defined structural and topographic lineament parallel to both the Langfjorden and the Great Escarpment. The slope instability that was formerly present at Tjelle, and additional instabilities currently present throughout the region, may be viewed as the direct product of past and ongoing development of tectonic topography in Møre og Trøndelag county. In the Langfjorden region in particular, structural geometry

Seismic investigation of the Kunlun Fault: Analysis of the INDEPTH IV 2-D active-source seismic dataset

NASA Astrophysics Data System (ADS)

Seelig, William George

The Tibetan Plateau has experienced significant crustal thickening and deformation since the continental subduction and collision of the Asian and Indian plates in the Eocene. Deformation of the northern Tibetan Plateau is largely accommodated by strike-slip faulting. The Kunlun Fault is a 1000-km long strike-slip fault near the northern boundary of the Plateau that has experienced five magnitude 7.0 or greater earthquakes in the past 100 years and represents a major rheological boundary. Active-source, 2-D seismic reflection/refraction data, collected as part of project INDEPTH IV (International Deep Profiling of Tibet and the Himalaya, phase IV) in 2007, was used to examine the structure and the dip of the Kunlun fault. The INDEPTH IV data was acquired to better understand the tectonic evolution of the northeastern Tibetan Plateau, such as the far-field deformation associated with the continent-continent collision and the potential subduction of the Asian continent beneath northern Tibet. Seismic reflection common depth point (CDP) stacks were examined to look for reflectivity patterns that may be associated with faulting. A possible reflection from the buried North Kunlun Thrust (NKT) is identified at 18-21 km underneath the East Kunlun Mountains, with an estimated apparent dip of 15°S and thrusting to the north. Minimally-processed shot gathers were also inspected for reflections off near-vertical structures such as faults and information on first-order velocity structure. Shot offset and nearest receiver number to reflection was catalogued to increase confidence of picks. Reflections off the North Kunlun (NKF) and South Kunlun Faults (SKF) were identified and analyzed for apparent dip and subsurface geometry. Fault reflection analysis found that the North Kunlun Fault had an apparent dip of approximately 68ºS to an estimated depth of 5 km, while the South Kunlun Fault dipped at approximately 78ºN to an estimated 3.5 km depth. Constraints on apparent dip and

The Corinth Rift Laboratory, Greece (CRL) : A Multidisciplinary Near Fault Observatory (NFO) on a Fast Rifting System

NASA Astrophysics Data System (ADS)

Bernard, P.; Lyon-Caen, H.; Deschamps, A.; Briole, P.; Lambotte, S.; Ford, M.; Scotti, O.; Beck, C.; Hubert-Ferrari, A.; Boiselet, A.; Godano, M.; Matrullo, E.; Meyer, N.; Albini, P.; Elias, P.; Nercessian, A.; Katsonopoulou, D.; Papadimitriou, P.; Voulgaris, N.; Kapetanidis, V.; Sokos, E.; Serpetsidaki, A.; el Arem, S.; Dublanchet, P.; Duverger, C.; Makropoulos, K.; Tselentis, A.

2014-12-01

The western rift of Corinth (Greece) is one of the most active tectonic structures of the euro-mediterranean area. Its NS opening rate is 1.5 cm/yr ( strain rate of 10-6/yr) results into a high microseismicity level and a few destructive, M>6 earthquakes per century, activating a system of mostly north dipping normal faults. Since 2001, monitoring arrays of the European Corinth Rift Laboratory (CRL, www.crlab.eu) allowed to better track the mechanical processes at work, with short period and broad band seismometers, cGPS, borehole strainmeters, EM stations, …). The recent (300 kyr) tectonic history has been revealed by onland (uplifted fan deltas and terraces) and offshore geological studies (mapping, shallow seismic, coring), showing a fast evolution of the normal fault system. The microseismicity, dominated by swarms lasting from days to months, mostly clusters in a layer 1 to 3 km thick, between 6 and 9 km in depth, dipping towards north, on which most faults are rooting. The diffusion of the microseismicity suggests its triggering by pore pressure transients, with no or barely detected strain. Despite a large proportion of multiplets, true repeaters seem seldom, suggesting a minor contribution of creep in their triggering, although transient or steady creep is clearly detected on the shallow part of some majors faults. The microseismic layer may thus be an immature, downward growing detachment, and the dominant rifting mechanism might be a mode I, anelastic strain beneath the rift axis , for which a mechanical model is under development. Paleoseismological (trenching, paleoshorelines, turbidites), archeological and historical studies completed the catalogues of instrumental seismicity, motivating attempts of time dependent hazard assessment. The Near Fault Observatory of CRL is thus a multidisciplinary research infrastructure aiming at a better understanding and modeling of multiscale, coupled seismic/aseismic processes on fault systems.

Fault Slip Distribution and Optimum Sea Surface Displacement of the 2017 Tehuantepec Earthquake in Mexico (Mw 8.2) Estimated from Tsunami Waveforms

NASA Astrophysics Data System (ADS)

Gusman, A. R.; Satake, K.; Mulia, I. E.

2017-12-01

An intraplate normal fault earthquake (Mw 8.2) occurred on 8 September 2017 in the Tehuantepec seismic gap of the Middle America Trench. The submarine earthquake generated a tsunami which was recorded by coastal tide gauges and offshore DART buoys. We used the tsunami waveforms recorded at 16 stations to estimate the fault slip distribution and an optimum sea surface displacement of the earthquake. A steep fault dipping to the northeast with strike of 315°, dip of 73°and rake of -96° based on the USGS W-phase moment tensor solution was assumed for the slip inversion. To independently estimate the sea surface displacement without assuming earthquake fault parameters, we used the B-spline function for the unit sources. The distribution of the unit sources was optimized by a Genetic Algorithm - Pattern Search (GA-PS) method. Tsunami waveform inversion resolves a spatially compact region of large slip (4-10 m) with a dimension of 100 km along the strike and 80 km along the dip in the depth range between 40 km and 110 km. The seismic moment calculated from the fault slip distribution with assumed rigidity of 6 × 1010 Nm-2 is 2.46 × 1021 Nm (Mw 8.2). The optimum displacement model suggests that the sea surface was uplifted up to 0.5 m and subsided down to -0.8 m. The deep location of large fault slip may be the cause of such small sea surface displacements. The simulated tsunami waveforms from the optimum sea surface displacement can reproduce the observations better than those from fault slip distribution; the normalized root mean square misfit for the sea surface displacement is 0.89, while that for the fault slip distribution is 1.04. We simulated the tsunami propagation using the optimum sea surface displacement model. Large tsunami amplitudes up to 2.5 m were predicted to occur inside and around a lagoon located between Salina Cruz and Puerto Chiapas. Figure 1. a) Sea surface displacement for the 2017 Tehuantepec earthquake estimated by tsunami waveforms. b

Structural controls of the Tuscarora geothermal field, Elko County, Nevada

NASA Astrophysics Data System (ADS)

Dering, G.; Faulds, J. E.

2012-12-01

Tuscarora is an amagmatic geothermal system located ~90 km northwest of Elko, Nevada, in the northern part of the Basin and Range province ~15 km southeast of the Snake River Plain. Detailed geologic mapping, structural analysis, and well data have been integrated to identify the structural controls of the Tuscarora geothermal system. The structural framework of the geothermal field is defined by NNW- to NNE-striking normal faults that are approximately orthogonal to the present extension direction. Boiling springs, fumaroles, and siliceous sinter emanate from a single NNE-striking, west-dipping normal fault. Normal faults west of these hydrothermal features mostly dip steeply east, whereas normal faults east of the springs primarily dip west. Thus, the springs, fumaroles, and sinter straddle a zone of interaction between fault sets that dip toward each other, classified as a strike-parallel anticlinal accommodation zone. Faults within the geothermal area are mostly discontinuous along strike with offsets of tens to hundreds of meters, whereas the adjacent range-bounding fault systems of the Bull Run and Independence Mountains accommodate several kilometers of displacement. The geothermal field lies within a broad step over between the southward terminating west-dipping Bull Run fault zone and the northward terminating west-dipping Independence Mountains fault zone. Neither of these major fault zones is known to host high temperature geothermal systems. The accommodation zone lies within the broad step over and contains both east-dipping antithetic and west-dipping synthetic faults. Accommodation zones are relatively common structural components of extended terranes that transfer strain between oppositely dipping fault sets via a network of subsidiary normal faults. This study has identified the hinge zone of an anticlinal accommodation zone as the site most conducive to fluid up-flow. The recognition of this specific portion of an accommodation zone as a favorable

3D Model of the McGinness Hills Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

The McGinness Hills geothermal system lies in a ~8.5 km wide, north-northeast trending accommodation zone defined by east-dipping normal faults bounding the Toiyabe Range to the west and west-dipping normal faults bounding the Simpson Park Mountains to the east. Within this broad accommodation zone lies a fault step-over defined by north-northeast striking, west-dipping normal faults which step to the left at roughly the latitude of the McGinness Hills geothermal system. The McGinness Hills 3D model consists of 9 geologic units and 41 faults. The basal geologic units are metasediments of the Ordovician Valmy and Vininni Formations (undifferentiated in the model) which are intruded by Jurassic granitic rocks. Unconformably overlying is a ~100s m-thick section of Tertiary andesitic lava flows and four Oligocene-to-Miocene ash-flow tuffs: The Rattlesnake Canyon Tuff, tuff of Sutcliffe, the Cambell Creek Tuff and the Nine Hill tuff. Overlying are sequences of pre-to-syn-extensional Quaternary alluvium and post-extensional Quaternary alluvium. 10-15º eastward dip of the Tertiary stratigraphy is controlled by the predominant west-dipping fault set. Geothermal production comes from two west dipping normal faults in the northern limb of the step over. Injection is into west dipping faults in the southern limb of the step over. Production and injection sites are in hydrologic communication, but at a deep level, as the northwest striking fault that links the southern and northern limbs of the step-over has no permeability.

Broadband Rupture Process of the 2001 Kunlun Fault (Mw 7.8) Earthquake

NASA Astrophysics Data System (ADS)

Antolik, M.; Abercrombie, R.; Ekstrom, G.

2003-04-01

We model the source process of the 14 November, 2001 Kunlun fault earthquake using broadband body waves from the Global Digital Seismographic Network (P, SH) and both point-source and distributed slip techniques. The point-source mechanism technique is a non-linear iterative inversion that solves for focal mechanism, moment rate function, depth, and rupture directivity. The P waves reveal a complex rupture process for the first 30 s, with smooth unilateral rupture toward the east along the Kunlun fault accounting for the remainder of the 120 s long rupture. The obtained focal mechanism for the main portion of the rupture is (strike=96o, dip=83o, rake=-8o) which is consistent with both the Harvard CMT solution and observations of the surface rupture. The seismic moment is 5.29×1020 Nm and the average rupture velocity is ˜3.5 km/s. However, the initial portion of the P waves cannot be fit at all with this mechanism. A strong pulse visible in the first 20 s can only be matched with an oblique-slip subevent (MW ˜ 6.8-7.0) involving a substantial normal faulting component, but the nodal planes of this mechanism are not well constrained. The first-motion polarities of the P waves clearly require a strike mechanism with a similar orientation as the Kunlun fault. Field observations of the surface rupture (Xu et al., SRL, 73, No. 6) reveal a small 26 km-long strike-slip rupture at the far western end (90.5o E) with a 45-km long gap and extensional step-over between this rupture and the main Kunlun fault rupture. We hypothesize that the initial fault break occurred on this segment, with release of the normal faulting energy as a continuous rupture through the extensional step, enabling transfer of the slip to the main Kunlun fault. This process is similar to that which occurred during the 2002 Denali fault (MW 7.9) earthquake sequence except that 11 days elapsed between the October 23 (M_W 6.7) foreshock and the initial break of the Denali earthquake along a thrust fault.

Crustal structure of norther Oaxaca terrane; The Oaxaca and caltepec faults, and the Tehuacan Valley. A gravity study.

NASA Astrophysics Data System (ADS)

Campos-Enriquez, J. O.; Alatorre-Zamora, M. A.; Ramón, V. M.; Belmonte, S.

2014-12-01

Northern Oaxaca terrane, southern Mexico, is bound by the Caltepec and Oaxaca faults to the west and east, respectively. These faults juxtapose the Oaxaca terrane against the Mixteca and Juarez terranes, respectively. The Oaxaca Fault also forms the eastern boundary of the Cenozoic Tehuacan depression. Several gravity profiles across these faults and the Oaxaca terrane (including the Tehuacan Valley) enables us to establish the upper crustal structure of this region. Accordingly, the Oaxaca terrane is downward displaced to the east in two steps. First the Santa Lucia Fault puts into contact the granulitic basamental rocks with Phanerozoic volcanic and sedimentary rocks. Finally, the Gavilan Fault puts into contact the Oaxaca terrane basement (Oaxaca Complex) into contact with the volcano-sedimentary infill of the valley. This gravity study reveals that the Oaxaca Fault system gives rise to a series of east tilted basamental blocks (Oaxaca Complex?). A structural high at the western Tehuacan depression accomadates the east dipping faults (Santa Lucia and Gavilan faults) and the west dipping faults of the Oaxaca Fault System. To the west of this high structural we have the depper depocenters. The Oaxaca Complex, the Caltepec and Santa Lucia faults continue northwestwards beneath Phanerozoic rocks. The faults are regional tectonic structures. They seem to continue northwards below the Trans-Mexican Volcanic Belt. A major E-W to NE-SW discontinuity on the Oaxaca terrane is inferred to exist between profiles 1 and 2. The Tehuacan Valley posses a large groundwater potential.

Unravelling the Mysteries of Slip Histories, Validating Cosmogenic 36Cl Derived Slip Rates on Normal Faults

NASA Astrophysics Data System (ADS)

Goodall, H.; Gregory, L. C.; Wedmore, L.; Roberts, G.; Shanks, R. P.; McCaffrey, K. J. W.; Amey, R.; Hooper, A. J.

2017-12-01

The cosmogenic isotope chlorine-36 (36Cl) is increasingly used as a tool to investigate normal fault slip rates over the last 10-20 thousand years. These slip histories are being used to address complex questions, including investigating slip clustering and understanding local and large scale fault interaction. Measurements are time consuming and expensive, and as a result there has been little work done validating these 36Cl derived slip histories. This study aims to investigate if the results are repeatable and therefore reliable estimates of how normal faults have been moving in the past. Our approach is to test if slip histories derived from 36Cl are the same when measured at different points along the same fault. As normal fault planes are progressively exhumed from the surface they accumulate 36Cl. Modelling these 36Cl concentrations allows estimation of a slip history. In a previous study, samples were collected from four sites on the Magnola fault in the Italian Apennines. Remodelling of the 36Cl data using a Bayesian approach shows that the sites produced disparate slip histories, which we interpret as being due to variable site geomorphology. In this study, multiple sites have been sampled along the Campo Felice fault in the central Italian Apennines. Initial results show strong agreement between the sites we have processed so far and a previous study. This indicates that if sample sites are selected taking the geomorphology into account, then 36Cl derived slip histories will be highly similar when sampled at any point along the fault. Therefore our study suggests that 36Cl derived slip histories are a consistent record of fault activity in the past.

Geometric and thermal controls on normal fault seismicity from rate-and-state friction models

NASA Astrophysics Data System (ADS)

Mark, H. F.; Behn, M. D.; Olive, J. A. L.; Liu, Y.

2017-12-01

Seismic and geodetic observations from the last two decades have led to a growing realization that a significant amount of fault slip at plate boundaries occurs aseismically, and that the amount of aseismic displacement varies across settings. Here we investigate controls on the seismogenic behavior of crustal-scale normal faults that accommodate extensional strain at mid-ocean ridges and continental rifts. Seismic moment release rates measured along the fast-spreading East Pacific Rise suggest that the majority of fault growth occurs aseismically with almost no seismic slip. In contrast, at the slow-spreading Mid-Atlantic Ridge seismic slip may represent up to 60% of the total fault displacement. Potential explanations for these variations include heterogeneous distributions of frictional properties on fault surfaces, effects of variable magma supply associated with seafloor spreading, and/or differences in fault geometry and thermal structure. In this study, we use rate-and-state friction models to study the seismic coupling coefficient (the fraction of total fault slip that occurs seismically) for normal faults at divergent plate boundaries, and investigate controls on fault behavior that might produce the variations in the coupling coefficient observed in natural systems. We find that the seismic coupling coefficient scales with W/h*, where W is the downdip width of the seismogenic area of the fault and h* is the critical earthquake nucleation size. At mid-ocean ridges, W is expected to increase with decreasing spreading rate. Thus, the observed relationship between seismic coupling and W/h* explains to first order variations in seismic coupling coefficient as a function of spreading rate. Finally, we use catalog data from the Gulf of Corinth to show that this scaling relationship can be extended into the thicker lithosphere of continental rift systems.

Fault zone characterization using P- and S-waves

NASA Astrophysics Data System (ADS)

Wawerzinek, Britta; Buness, Hermann; Polom, Ulrich; Tanner, David C.; Thomas, Rüdiger

2014-05-01

Although deep fault zones have high potential for geothermal energy extraction, their real usability depends on complex lithological and tectonic factors. Therefore a detailed fault zone exploration using P- and S-wave reflection seismic data is required. P- and S-wave reflection seismic surveys were carried out along and across the eastern border of the Leinetal Graben in Lower Saxony, Germany, to analyse the structural setting, different reflection characteristics and possible anisotropic effects. In both directions the P-wave reflection seismic measurements show a detailed and complex structure. This structure was developed during several tectonic phases and comprises both steeply- and shallowly-dipping faults. In a profile perpendicular to the graben, a strong P-wave reflector is interpreted as shallowly west-dipping fault that is traceable from the surface down to 500 m depth. It is also detectable along the graben. In contrast, the S-waves show different reflection characteristics: There is no indication of the strong P-wave reflector in the S-wave reflection seismic measurements - neither across nor along the graben. Only diffuse S-wave reflections are observable in this region. Due to the higher resolution of S-waves in the near-surface area it is possible to map structures which cannot be detected in P-wave reflection seismic, e.g the thinning of the uppermost Jurassic layer towards the south. In the next step a petrophysical analysis will be conducted by using seismic FD modelling to a) determine the cause (lithological, structural, or a combination of both) of the different reflection characteristics of P- and S-waves, b) characterize the fault zone, as well as c) analyse the influence of different fault zone properties on the seismic wave field. This work is part of the gebo collaborative research programme which is funded by the 'Niedersächsisches Ministerium für Wissenschaft und Kultur' and Baker Hughes.

Three-dimensional fault framework of the 2014 South Napa Earthquake, San Francisco Bay region, California

NASA Astrophysics Data System (ADS)

Graymer, R. W.

2014-12-01

Assignment of the South Napa earthquake to a mapped fault is difficult, as it occurred where three large, northwest-trending faults converge and may interact in the subsurface. The surface rupture did not fall on the main trace of any of these faults, but instead between the Carneros and West Napa faults and northwest along strike from the northern mapped end of the Franklin Fault. The 2014 rupture plane appears to be nearly vertical, based on focal mechanisms of the mainshock and connection of the surface trace/rupture to the relocated hypocenter (J. Hardebeck, USGS). 3D surfaces constructed from published data show that the Carneros Fault is a steeply west-dipping fault that runs just west of the near-vertical 2014 rupture plane. The Carneros Fault does not appear to have been involved in the earthquake, although relocated aftershocks suggest possible minor triggered slip. The main West Napa Fault is also steeply west-dipping and that its projection intersects the 2014 rupture plane at around the depth of the mainshock hypocenter. UAVSAR data (A. Donnellan, JPL) and relocated aftershocks suggest that the main West Napa Fault experienced triggered slip/afterslip along a length of roughly 20 km. It is possible that the 2014 rupture took place along a largely unrecognized westerly strand of the West Napa Fault. The Franklin Fault is a steeply east-dipping fault (with a steeply west-dipping subordinate trace east of Mare Island) that has documented late Quaternary offset. Given the generally aligned orientation of the 3D fault surfaces, an alternative interpretation is that the South Napa earthquake occurred on the northernmost reach of the Franklin Fault within it's 3D junction with the West Napa Fault. This interpretation is supported, but not proven, by a short but prominent linear feature in the UAVSAR data at Slaughterhouse Point west of Vallejo, along trend south-southeast of the observed coseismic surface rupture.

Reexamination of the subsurface fault structure in the vicinity of the 1989 moment-magnitude-6.9 Loma Prieta earthquake, central California, using steep-reflection, earthquake, and magnetic data

USGS Publications Warehouse

Zhang, Edward; Fuis, Gary S.; Catchings, Rufus D.; Scheirer, Daniel S.; Goldman, Mark; Bauer, Klaus

2018-06-13

We reexamine the geometry of the causative fault structure of the 1989 moment-magnitude-6.9 Loma Prieta earthquake in central California, using seismic-reflection, earthquake-hypocenter, and magnetic data. Our study is prompted by recent interpretations of a two-part dip of the San Andreas Fault (SAF) accompanied by a flower-like structure in the Coachella Valley, in southern California. Initially, the prevailing interpretation of fault geometry in the vicinity of the Loma Prieta earthquake was that the mainshock did not rupture the SAF, but rather a secondary fault within the SAF system, because network locations of aftershocks defined neither a vertical plane nor a fault plane that projected to the surface trace of the SAF. Subsequent waveform cross-correlation and double-difference relocations of Loma Prieta aftershocks appear to have clarified the fault geometry somewhat, with steeply dipping faults in the upper crust possibly connecting to the more moderately southwest-dipping mainshock rupture in the middle crust. Examination of steep-reflection data, extracted from a 1991 seismic-refraction profile through the Loma Prieta area, reveals three robust fault-like features that agree approximately in geometry with the clusters of upper-crustal relocated aftershocks. The subsurface geometry of the San Andreas, Sargent, and Berrocal Faults can be mapped using these features and the aftershock clusters. The San Andreas and Sargent Faults appear to dip northeastward in the uppermost crust and change dip continuously toward the southwest with depth. Previous models of gravity and magnetic data on profiles through the aftershock region also define a steeply dipping SAF, with an initial northeastward dip in the uppermost crust that changes with depth. At a depth 6 to 9 km, upper-crustal faults appear to project into the moderately southwest-dipping, planar mainshock rupture. The change to a planar dipping rupture at 6–9 km is similar to fault geometry seen in the

Logs and Geologic Data from a Paleoseismic Investigation of the Susitna Glacier fault, Central Alaska Range, Alaska

USGS Publications Warehouse

Personius, Stephen F.; Crone, Anthony J.; Burns, Patricia A.C.; Beget, James E.; Seitz, Gordon G.; Bemis, Sean P.

2010-01-01

This report contains field and laboratory data from a paleoseismic study of the Susitna Glacier fault, Alaska. The initial M 7.2 subevent of the November 3, 2002, M 7.9 Denali fault earthquake sequence produced a 48-km-long set of complex fault scarps, folds, and aligned landslides on the previously unknown, north-dipping Susitna Glacier thrust fault along the southern margin of the Alaska Range in central Alaska. Most of the 2002 folds and fault scarps are 1-3 m high, implying dip-slip thrust offsets (assuming a near-surface fault dip of approximately 20 degrees)of 3-5 m. Locally, some of the 2002 ruptures were superimposed on preexisting scarps that have as much as 5-10 m of vertical separation and are evidence of previous surface-rupturing earthquakes on the Susitna Glacier fault. In 2003-2005, we focused follow-up studies on several of the large scarps at the 'Wet fan' site in the central part of the 2002 rupture to determine the pre-2002 history of large surface-rupturing earthquakes on the fault. We chose this site for several reasons: (1) the presence of pre-2002 thrust- and normal-fault scarps on a gently sloping, post-glacial alluvial fan; (2) nearby natural exposures of underlying fan sediments revealed fine-grained fluvial silts with peat layers and volcanic ash beds useful for chronological control; and (3) a lack of permafrost to a depth of more than 1 m. Our studies included detailed mapping, fault-scarp profiling, and logging of three hand-excavated trenches. We were forced to restrict our excavations to 1- to 2-m-high splay faults and folds because the primary 2002 ruptures mostly were superimposed on such large scarps that it was impossible to hand dig through the hanging wall to expose the fault plane. Additional complications are the pervasive effects of cryogenic processes (mainly solifluction) that can mask or mimic tectonic deformation. The purpose of this report is to present photomosaics, trench logs, scarp profiles, and fault slip

3D Model of the San Emidio Geothermal Area

DOE Data Explorer

James E. Faulds

2013-12-31

The San Emidio geothermal system is characterized by a left-step in a west-dipping normal fault system that bounds the western side of the Lake Range. The 3D geologic model consists of 5 geologic units and 55 faults. Overlying Jurrassic-Triassic metasedimentary basement is a ~500 m-1000 m thick section of the Miocene lower Pyramid sequence, pre- syn-extensional Quaternary sedimentary rocks and post-extensional Quaternary rocks. 15-30º eastward dip of the stratigraphy is controlled by the predominant west-dipping fault set. Both geothermal production and injection are concentrated north of the step over in an area of closely spaced west dipping normal faults.

Anatomy of a Plate Boundary at Shallow Crustal Levels: a Composite Section from the Alpine Fault, New Zealand

NASA Astrophysics Data System (ADS)

Barth, N. C.; Toy, V. G.; Boulton, C. J.; Carpenter, B. M.

2010-12-01

New Zealand's Alpine Fault is mostly a moderately SE-dipping dextral reverse plate boundary structure, but at its southern end, strike-slip-normal motion is indicated by offset of recent surfaces, juxtaposition of sediments, and both brittle and ductile shear sense indicators. At the location of uplift polarity reversal fault rocks exhumed from both the hangingwall Pacific and footwall Australian Plates are juxtaposed, offering a remarkably complete cross section of the plate boundary at shallow crustal levels. We describe Alpine Fault damage zone and fault core structures overprinted on Pacific and Australian plate mylonites of a variety of compositions, in a fault-strike perpendicular composite section spanning the reversal in dip-slip polarity. The damage zone is asymmetric; on the Australian Plate 160m of quartzose paragneiss-derived mylonites are overprinted by brittle faults and fractures that increase in density towards the principal slip surface (PSS). This damage zone fabric consists of 1-10m-spaced, moderately to steeply-dipping, 1-20cm-thick gouge-filled faults, overprinted on and sub-parallel to a mylonitic foliation sub-parallel to the PSS. On the Pacific Plate, only 40m of the 330m section of volcaniclastic-derived mylonites have brittle damage in the form of unhealed fractures and faults, as well as a pervasive greenschist facies hydrothermal alteration absent in the footwall. These damage-related structures comprise a network of small-offset faults and fractures with increasing density and intensity towards the PSS. The active Pacific Plate fault core is composed of ~1m of cataclasite grading into folded protocataclasite that is less folded and fractured with increasing distance from the PSS. The active Australian Plate fault core is <1.5m wide and consists of 3 distinct foliated clay gouges, as well as a 4cm thick brittle ultracataclasite immediately adjacent to the active PSS. The Australian Plate foliated clay gouge contains stringers of quartz

Crustal structure and fault geometry of the 2010 Haiti earthquake from temporary seismometer deployments

USGS Publications Warehouse

Douilly, Roby; Haase, Jennifer S.; Ellsworth, William L.; Bouin, Marie‐Paule; Calais, Eric; Symithe, Steeve J.; Armbruster, John G.; Mercier de Lépinay, Bernard; Deschamps, Anne; Mildor, Saint‐Louis; Meremonte, Mark E.; Hough, Susan E.

2013-01-01

Haiti has been the locus of a number of large and damaging historical earthquakes. The recent 12 January 2010 Mw 7.0 earthquake affected cities that were largely unprepared, which resulted in tremendous losses. It was initially assumed that the earthquake ruptured the Enriquillo Plantain Garden fault (EPGF), a major active structure in southern Haiti, known from geodetic measurements and its geomorphic expression to be capable of producing M 7 or larger earthquakes. Global Positioning Systems (GPS) and Interferometric Synthetic Aperture Radar (InSAR) data, however, showed that the event ruptured a previously unmapped fault, the Léogâne fault, a north‐dipping oblique transpressional fault located immediately north of the EPGF. Following the earthquake, several groups installed temporary seismic stations to record aftershocks, including ocean‐bottom seismometers on either side of the EPGF. We use data from the complete set of stations deployed after the event, on land and offshore, to relocate all aftershocks from 10 February to 24 June 2010, determine a 1D regional crustal velocity model, and calculate focal mechanisms. The aftershock locations from the combined dataset clearly delineate the Léogâne fault, with a geometry close to that inferred from geodetic data. Its strike and dip closely agree with the global centroid moment tensor solution of the mainshock but with a steeper dip than inferred from previous finite fault inversions. The aftershocks also delineate a structure with shallower southward dip offshore and to the west of the rupture zone, which could indicate triggered seismicity on the offshore Trois Baies reverse fault. We use first‐motion focal mechanisms to clarify the relationship of the fault geometry to the triggered aftershocks.

Pluton emplacement within an extensional transfer zone during dextral strike-slip faulting: an example from the late Archaean Abitibi Greenstone Belt

NASA Astrophysics Data System (ADS)

Lacroix, S.; Sawyer, E. W.; Chown, E. H.

1998-01-01

The Lake Abitibi area within the late Archaean Abitibi Greenstone Belt exhibits an interlinked plutonic, structural and metamorphic evolution that may characterize segmented strike-slip faults at upper-to-mid-crustal levels. Along the major, southeastward propagating Macamic D2 dextral strike-slip fault, Theological and preexisting D1 structural heterogeneities induced the development of NNW-trending dextral-oblique splays which evolved into an extensional trailing fan and created an extensional, NNW-dipping stepover. Magma flowing upwards from deeper parts of the Macamic Fault spread towards the southeast at upper crustal levels along both the oblique-slip and extensional D2 splays, and built several plutons in a pull-apart domain between 2696 and 2690 Ma. Different emplacement and material transfer mechanisms operated simultaneously in different parts of the system, including fault dilation and wedging, lateral expansion, wall-rock ductile flow and stoping. Transfer of movement between D2 splays occurred under ductile conditions during syn-emplacement, amphibolite-grade metamorphism (500-700 °C). During cooling (< 2690 Ma), narrower brittle-ductile zones of greenschist-grade shearing were concentrated along the pluton-wall rock contacts, but the extensional stepover locked since both normal and reverse movements occurred along NNW-dipping faults. Pluton emplacement, contact metamorphism and propagation of D2 faults appear to have been closely linked during the Superior Province-wide late transpressional event.

Work Optimization Predicts Accretionary Faulting: An Integration of Physical and Numerical Experiments

NASA Astrophysics Data System (ADS)

McBeck, Jessica A.; Cooke, Michele L.; Herbert, Justin W.; Maillot, Bertrand; Souloumiac, Pauline

2017-09-01

We employ work optimization to predict the geometry of frontal thrusts at two stages of an evolving physical accretion experiment. Faults that produce the largest gains in efficiency, or change in external work per new fault area, ΔWext/ΔA, are considered most likely to develop. The predicted thrust geometry matches within 1 mm of the observed position and within a few degrees of the observed fault dip, for both the first forethrust and backthrust when the observed forethrust is active. The positions of the second backthrust and forethrust that produce >90% of the maximum ΔWext/ΔA also overlap the observed thrusts. The work optimal fault dips are within a few degrees of the fault dips that maximize the average Coulomb stress. Slip gradients along the detachment produce local elevated shear stresses and high strain energy density regions that promote thrust initiation near the detachment. The mechanical efficiency (Wext) of the system decreases at each of the two simulated stages of faulting and resembles the evolution of experimental force. The higher ΔWext/ΔA due to the development of the first pair relative to the second pair indicates that the development of new thrusts may lead to diminishing efficiency gains as the wedge evolves. The numerical estimates of work consumed by fault propagation overlap the range calculated from experimental force data and crustal faults. The integration of numerical and physical experiments provides a powerful approach that demonstrates the utility of work optimization to predict the development of faults.

Geometry of the southern San Andreas fault and its implications for seismic hazard

NASA Astrophysics Data System (ADS)

Langenheim, V. E.; Dorsey, R. J.; Fuis, G. S.; Cooke, M. L.; Fattaruso, L.; Barak, S.

2015-12-01

The southern San Andreas fault (SSAF) provides rich opportunities for studying the geometry and connectivity of fault stepovers and intersections, including recently recognized NE tilting of the Salton block between the SSAF and San Jacinto fault (SJF) that likely results from slight obliquity of relative plate motion to the strike of the SSAF. Fault geometry and predictions of whether the SSAF will rupture through the restraining bend in San Gorgonio Pass (SGP) are controversial, with significant implications for seismic hazard. The evolution of faulting in SGP has led to various models of strain accommodation, including clockwise rotation of fault-bounded blocks east of the restraining bend, and generation of faults that siphon strike slip away from the restraining bend onto the SJF (also parallel to the SSAF). Complex deformation is not restricted to the upper crust but extends to mid- and lower-crustal depths according to magnetic data and ambient-noise surface-wave tomography. Initiation of the SJF ~1.2 Ma led to formation of the relatively intact Salton block, and end of extension on the West Salton detachment fault on the west side of Coachella Valley. Geologic and geomorphic data show asymmetry of the southern Santa Rosa Mountains, with a steep fault-bounded SW flank produced by active uplift, and gentler topographic gradients on the NE flank with tilted, inactive late Pleistocene fans that are incised by modern upper fan channels. Gravity data indicate the basin floor beneath Coachella Valley is also asymmetric, with a gently NE-dipping basin floor bound by a steep SSAF; seismic-reflection data suggest that NE tilting took place during Quaternary time. 3D numerical modeling predicts gentle NE dips in the Salton block that result from the slight clockwise orientation of relative motion across a NE-dipping SSAF. A NE dip of the SSAF, supported by various geophysical datasets, would reduce shaking in Coachella Valley compared to a vertical fault.

Structural setting and kinematics of Nubian fault system, SE Western Desert, Egypt: An example of multi-reactivated intraplate strike-slip faults

NASA Astrophysics Data System (ADS)

Sakran, Shawky; Said, Said Mohamed

2018-02-01

Detailed surface geological mapping and subsurface seismic interpretation have been integrated to unravel the structural style and kinematic history of the Nubian Fault System (NFS). The NFS consists of several E-W Principal Deformation Zones (PDZs) (e.g. Kalabsha fault). Each PDZ is defined by spectacular E-W, WNW and ENE dextral strike-slip faults, NNE sinistral strike-slip faults, NE to ENE folds, and NNW normal faults. Each fault zone has typical self-similar strike-slip architecture comprising multi-scale fault segments. Several multi-scale uplifts and basins were developed at the step-over zones between parallel strike-slip fault segments as a result of local extension or contraction. The NNE faults consist of right-stepping sinistral strike-slip fault segments (e.g. Sin El Kiddab fault). The NNE sinistral faults extend for long distances ranging from 30 to 100 kms and cut one or two E-W PDZs. Two nearly perpendicular strike-slip tectonic regimes are recognized in the NFS; an inactive E-W Late Cretaceous - Early Cenozoic dextral transpression and an active NNE sinistral shear.

Extensional tectonics and collapse structures in the Suez Rift (Egypt)

NASA Technical Reports Server (NTRS)

Chenet, P. Y.; Colletta, B.; Desforges, G.; Ousset, E.; Zaghloul, E. A.

1985-01-01

The Suez Rift is a 300 km long and 50 to 80 km wide basin which cuts a granitic and metamorphic shield of Precambrian age, covered by sediments of Paleozoic to Paleogene age. The rift structure is dominated by tilted blocks bounded by NW-SE normal faults. The reconstruction of the paleostresses indicates a N 050 extension during the whole stage of rifting. Rifting began 24 My ago with dikes intrusions; main faulting and subsidence occurred during Early Miocene producing a 80 km wide basin (Clysmic Gulf). During Pliocene and Quaternary times, faulting is still active but subsidence is restricted to a narrower area (Present Gulf). On the Eastern margin of the gulf, two sets of fault trends are predominant: (1) N 140 to 150 E faults parallel to the gulf trend with pure dip-slip displacement; and (2) cross faults, oriented NOO to N 30 E that have a strike-slip component consistent with the N 050 E distensive stress regime. The mean dip cross fault is steeper (70 to 80 deg) than the dip of the faults parallel to the Gulf (30 to 70 deg). These two sets of fault define diamond shaped tilted block. The difference of mechanical behavior between the basement rocks and the overlying sedimentary cover caused structural disharmony and distinct fault geometries.

Influence of low-angle normal faulting on radial fracture pattern associated to pluton emplacement in Tuscany, Italy

NASA Astrophysics Data System (ADS)

Balsamo, F.; Rossetti, F.; Salvini, F.

2003-04-01

Fault-related fracture distribution significantly influences fluid flow in the sub-surface. Fault zone can act either as barriers or conduits to fluid migration, or as mixed conduit/barrier systems, depending on several factors that include the enviromental condition of deformation (pore fluid pressure, regional stress fields, overburden etc.), the kinematics of the fault and its geometry, and the rock type. The aim of this study is to estimate the boundary conditions of deformation along the Boccheggiano Fault, in the central Appennines. Seismic and deep well data are avaible for the Boccheggiano area, where a fossil geothermal system is exposed. The dominant structural feature of the studied area is a NW-SE trending low-angle detachment fault (Boccheggiano fault, active since the upper Miocene times), separating non-metamorphic sedimentary sequences of the Tuscan meso-cenozoic pelagiac succession and oceanic-derived Ligurids in the hangingwall, from green-schists facies metamorphic rocks of Paleozoic age in the footwall. Gouge-bearing mineralized damage zone (about 100 m thick) is present along the fault. The deep geometry of the Boccheggiano Fault is well imaged in the seismic profiles. The fault is shallow-dipping toward NE and flattens at the top of a magmatic intrusion, which lies at about 1000 m below the ground-level. Geometrical relationships indicate syn-tectonic pluton emplacement at the footwall of the Boccheggiano fault. Statistical analysis of fracture distribution pointed out a strong control of both azimuth and frequency by their position with respect to the Boccheggiano Fault: (i) a NW-SE trending fracture set within the fault zone, (ii) a radial pattern associated away from fault zone. Interpretation of structural and seismic data suggest an interplay between the near-field deformation associated with the rising intrusion during its emplacement (radial fracturing) and the NE-SW far-field extensional tectonic regime (NW-SE fractures) recognized in

Is low-angle normal fault slip aided by local stress rotations?: Assessment of paleostress inversion methods

NASA Astrophysics Data System (ADS)

Luther, A. L.; Axen, G. J.; Selverstone, J.; Khalsa, N.

2009-12-01

Classical fault mechanic theory does not adequately explain slip on “weak” faults oriented at high angles to the regional maximum stress direction, such as the San Andreas Fault and low-angle normal faults. One hypothesis is that stress rotation due to fault-weakening mechanisms allows slip, which may be testable using detailed paleostress analyses of minor faults and tensile fractures. Preliminary data from the footwalls of the Whipple detachment (WD) and the West Salton detachment (WSD) suggest lateral and/or vertical stress rotations. Three inversion programs that use different fault-slip datasets are compared. 1) FaultKin (Marrett and Allmendinger ‘90; Cladouhos and Allmendinger ‘93) determines the principal strain directions using only faults with striae and known slip senses; principal stress orientations are determined assuming coaxiality. To date, FaultKin results appear to be the most reproducible, but it is difficult to find enough faults with striae and slip sense in the small outcrop areas of our study. 2) Slick.bas (Ramsey and Lisle ‘00) uses a grid search to find the best-fit stress tensor from fault and striae orientations, but does not accept slip sense. This program can yield erroneous stress fields that predict slip senses opposite those known for some faults (particularly faults at a high angle to sigma 1). 3) T-TECTO 2.0 (Zalohar and Vrabec ‘07) applies a Gaussian approach, using orientations of faults and striae, the slip senses of any faults for which it is known, plus tensile fractures. We expect that this flexibility of input data types will be best, but testing is preliminary. Paleostress analyses assume that minor faults slipped in response to constant, homogeneous stress fields. We use shear and tensile fractures and cross-cutting relationships from the upper ~25 m of both footwalls to test for spatial and temporal changes to the paleostress field. Paleostress analysis of fractures ~0.3 - 2 m below the WSD on the N limb of an

Layered Fault Rocks Below the West Salton Detachment Fault (WSDF), CA Record Multiple Seismogenic? Slip Events and Transfer of Material to a Fault Core

NASA Astrophysics Data System (ADS)

Axen, G. J.; Luther, A. L.; Selverstone, J.; Mozley, P.

2011-12-01

Unique layered cataclasites (LCs) occur locally along footwall splays, S of the ~N-dipping, top-E WSDF. They are well exposed in a NW-plunging antiform that folds the LCs and their upper and lower bounding faults. Layers range from very fine-grained granular shear zones 1-2 mm thick and cm's to m's long, to medium- to coarse-grained isotropic granular cataclasite with floating clasts up to 4-5 cm diameter in layers up to ~30 cm thick and 3 to >10 m long. The top, N-flank contact is ~5 m structurally below the main WSDF. Maximum thickness of the LCs is ~5 m on the S flank of the antiform, where the upper 10-50 cm of LCs are composed of relatively planar layers that are subparallel to the upper fault, which locally displays ultracataclasite. Deeper layers are folded into open to isoclinal folds and are faulted. Most shear-sense indicators show N-side-to-E or -SE slip, and include: (1) aligned biotite flakes and mm-scale shear bands that locally define a weak foliation dipping ~ESE, (2) sharp to granular shears, many of which merge up or down into fine-grained layers and, in the base of the overlying granodiorite, (3) primary reidel shears and (4) folded pegmatite dikes. Biotite is unaltered and feldspars are weakly to strongly altered to clays and zeolites. Zeolites also grew in pores between clasts. XRF analyses suggest minimal chemical alteration. The upper fault is sharp and relatively planar, carries granular to foliated cataclasitic granodiorite that grades up over ~2-4 m into punky, microcracked but plutonic-textured rock with much of the feldspar alteration seen in LC clasts. Some upper-plate reidels bend into parallelism with the top fault and bound newly formed LC layers. The basal fault truncates contorted layers and lacks evidence of layers being added there. We infer that the deeper, contorted layers are older and that the LC package grew upward by transfer of cataclasized slices from the overlying granodiorite while folding was ongoing. Particle

Coseismic fault zone deformation caused by the 2014 Mw=6.2 Nagano-ken-hokubu, Japan, earthquake on the Itoigawa-Shizuoka Tectonic Line revealed with differential LiDAR

NASA Astrophysics Data System (ADS)

Toda, S.; Ishimura, D.; Homma, S.; Mukoyama, S.; Niwa, Y.

2015-12-01

The Mw = 6.2 Nagano-ken-hokubu earthquake struck northern Nagano, central Japan, on November 22, 2014, and accompanied a 9-km-long surface rupture mostly along the previously mapped N-NW trending Kamishiro fault, one of the segments of the 150-km-long Itoigawa-Shizuoka Tectonic Line active fault system. While we mapped the rupture and measured vertical displacement of up to 80 cm at the field, interferometric synthetic aperture radar (InSAR) shows densely spaced fringes on the hanging wall side, suggesting westward or uplift movement associated with thrust faulting. The mainshock focal mechanism and aftershock hypocenters indicate the source fault dips to the east but the InSAR images cannot exactly differentiate between horizontal and vertical movements and also lose coherence within and near the fault zone itself. To reveal near-field deformation and shallow fault slip, here we demonstrate a differential LiDAR analysis using a pair of 1 m-resolution pre-event and post-event bare Earth digital terrain models (DTMs) obtained from commercial LiDAR provider. We applied particle image velocity (PIV) method incorporating elevation change to obtain 3-D vectors of coseismic displacements (Mukoyama, 2011, J. Mt. Sci). Despite sporadic noises mostly due to local landslides, we detected up to 1.5 m net movement at the tip of the hanging wall, more than the field measurement of 80 cm. Our result implies that a 9-km-long rupture zone is not a single continuous fault but composed of two bow-shaped fault strands, suggesting a combination of shallow fault dip and modest amount (< 1.5 m) of slip. Eastward movement without notable subsidence on the footwall also supports the low angle fault dip near the surface, and significant fault normal contraction, observed as buckled cultural features across the fault zone. Secondary features, such as subsidiary back-thrust faults confirmed at the field, are also visible as a significant contrast of vector directions and slip amounts.

3D seismic detection of shallow faults and fluid migration pathways offshore Southern Costa Rica: Application of neural-network meta-attributes

NASA Astrophysics Data System (ADS)

Kluesner, J. W.; Silver, E. A.; Nale, S. M.; Bangs, N. L.; McIntosh, K. D.

2013-12-01

We employ a seismic meta-attribute workflow to detect and analyze probable faults and fluid-pathways in 3D within the sedimentary section offshore Southern Costa Rica. During the CRISP seismic survey in 2011 we collected an 11 x 55 km grid of 3D seismic reflection data and high-resolvability EM122 multibeam data, with coverage extending from the incoming plate to the outer-shelf. We mapped numerous seafloor seep indicators, with distributions ranging from the lower-slope to ~15 km landward of the shelf break [Kluesner et al., 2013, G3, doi:10.1002/ggge.20058; Silver et al., this meeting]. We used the OpendTect software package to calculate meta-attribute volumes from the 3D seismic data in order to detect and visualize seismic discontinuities in 3D. This methodology consists of dip-steered filtering to pre-condition the data, followed by combining a set of advanced dip-steered seismic attributes into a single object probability attribute using a user-trained neural-network pattern-recognition algorithm. The parameters of the advanced seismic attributes are set for optimal detection of the desired geologic discontinuity (e.g. faults or fluid-pathways). The product is a measure of probability for the desired target that ranges between 0 and 1, with 1 representing the highest probability. Within the sedimentary section of the CRISP survey the results indicate focused fluid-migration pathways along dense networks of intersecting normal faults with approximately N-S and E-W trends. This pattern extends from the middle slope to the outer-shelf region. Dense clusters of fluid-migration pathways are located above basement highs and deeply rooted reverse faults [see Bangs et al., this meeting], including a dense zone of fluid-pathways imaged below IODP Site U1413. In addition, fault intersections frequently show an increased signal of fluid-migration and these zones may act as major conduits for fluid-flow through the sedimentary cover. Imaged fluid pathways root into high

Constraining the fault slip rate using morphology of normal fault footwalls: insights from analog and numerical models (Invited)

NASA Astrophysics Data System (ADS)

Strak, V.; Dominguez, S.; Petit, C.; Meyer, B.; Loget, N.

2013-12-01

Relief evolution in active tectonic areas is controlled by the interactions between tectonics and surface processes (erosion, transport and sedimentation). These interactions lead to the formation of geomorphologic markers that remain stable during the equilibrium reached in the long-term between tectonics and erosion. In regions experiencing active extension, drainage basins and faceted spurs (triangular facets) are such long-lived morphologic markers and they can help in quantifying the competing effects between tectonics, erosion and sedimentation. We performed analog and numerical models simulating the morphologic evolution of a mountain range bounded by a normal fault. In each approach we imposed identical initial conditions. We carried out several models by varying the fault slip rate (V) and keeping a constant rainfall rate allowing us to study the effect of V on morphology. Both approaches highlight the main control of V on the topographic evolution of the footwall. The experimental approach shows that V controls erosion rates (incision rate, erosion rate of slopes and regressive erosion rate) and possibly the height of triangular facets. This approach indicates likewise that the parameter K of the stream power law depends on V even for non-equilibrium topography. The numerical approach corroborates the control of V on erosion rates and facet height. It also shows a correlation between the shape of drainage basins and V (slope-area relationship) and it suggests the same for the parameters of the stream power law. Therefore both approaches suggest the possibility of using the height of triangular facets and the slope-area relationship to infer the fault slip rate of normal faults situated in a given climatic context.

Fluid pathways from mantle wedge up to forearc seafloor in the coseismic slip area of the 2011 Tohoku earthquake

NASA Astrophysics Data System (ADS)

Park, J. O.; Tsuru, T.; Fujie, G.; Kagoshima, T.; Sano, Y.

2017-12-01

A lot of fluids at subduction zones are exchanged between the solid Earth and ocean, affecting the earthquake and tsunami generation. New multi-channel seismic reflection and sub-bottom profiling data reveal normal and reverse faults as the fluid pathways in the coseismic slip area of the 2011 Tohoku earthquake (M9.0). Based on seismic reflection characteristics and helium isotope anomalies, we recognize variations in fluid pathways (i.e., faults) from the mantle wedge up to forearc seafloor in the Japan Trench margin. Some fluids are migrated from the mantle wedge along plate interface and then normal or reverse faults cutting through the overriding plate. Others from the mantle wedge are migrated directly up to seafloor along normal faults, without passing through the plate interface. Locations of the normal faults are roughly consistent with aftershocks of the 2011 Tohoku earthquake, which show focal mechanism of normal faulting. It is noticeable that landward-dipping normal faults developing down into Unit C (Cretaceous basement) from seafloor are dominant in the middle slope region where basal erosion is inferred to be most active. A high-amplitude, reverse-polarity reflection of the normal faults within Unit C suggests that the fluids are locally trapped along the faults in high pore pressures. The 2011 Tohoku mainshock and subsequent aftershocks could lead the pre-existing normal faults to be reactive and more porous so that the trapped fluids are easily transported up to seafloor through the faults. Elevated fluid pressures can decrease the effective normal stress for the fault plane, allowing easier slip of the landward-dipping normal fault and also enhancing its tsunamigenic potential.

Three-Dimensional Structural and Hydrologic Evolution of Sant Corneli Anticline, a Fault-Cored Fold in the Central Spanish Pyrenees

NASA Astrophysics Data System (ADS)

Shackleton, J. R.; Cooke, M. L.

2005-12-01

The Sant Corneli Anticline is a well-exposed example of a fault-cored fold whose hydrologic evolution and structural development are directly linked. The E-W striking anticline is ~ 5 km wide with abrupt westerly plunge, and formed in response to thrusting associated with the upper Cretaceous to Miocene collision of Iberia with Europe. The fold's core of fractured carbonates contains a variety of west dipping normal faults with meter to decameter scale displacement and abundant calcite fill. This carbonate unit is capped by a marl unit with low angle, calcite filled normal faults. The marl unit is overlain by clastic syn-tectonic strata whose sedimentary architecture records limb rotation during the evolution of the fold. The syn-tectonic strata contain a variety of joint sets that record the stresses before, during, and possibly after fold growth. Faulting in the marl and calcite-filled joints in the syn-tectonic strata suggest that normal faults within the carbonate core of the fold eventually breached the overlying marl unit. This breach may have connected the joints of the syn-tectonic strata to the underlying carbonate reservoir and eliminated previous compartmentalization of fluids. Furthermore, breaching of the marl units probably enhanced joint formation in the overlying syn-tectonic strata. Future geochemical studies of calcite compositions in the three units will address this hypothesis. Preliminary mapping of joint sets in the syn-tectonic strata reveal a multistage history of jointing. Early bed-perpendicular joints healed by calcite strike NE-SW, parallel to normal faults in the underlying carbonates, and may be related to an early regional extensional event. Younger healed bed-perpendicular joints cross cut the NE-SW striking set, and are closer to N-S in strike: these joints are interpreted to represent the initial stages of folding. Decameter scale, bed perpendicular, unfilled fractures that are sub-parallel to strike probably represent small joints

A Controllable Earthquake Rupture Experiment on the Homestake Fault

NASA Astrophysics Data System (ADS)

Germanovich, L. N.; Murdoch, L. C.; Garagash, D.; Reches, Z.; Martel, S. J.; Gwaba, D.; Elsworth, D.; Lowell, R. P.; Onstott, T. C.

2010-12-01

Fault-slip is typically simulated in the laboratory at the cm-to-dm scale. Laboratory results are then up-scaled by orders of magnitude to understand faulting and earthquakes processes. We suggest an experimental approach to reactivate faults in-situ at scales ~10-100 m using thermal techniques and fluid injection to modify in situ stresses and the fault strength to the point where the rock fails. Mines where the modified in-situ stresses are sufficient to drive faulting, present an opportunity to conduct such experiments. During our recent field work in the former Homestake gold mine in the northern Black Hills, South Dakota, we found a large fault present on multiple mine levels. The fault is subparallel to the local foliation in the Poorman formation, a Proterozoic metamorphic rock deformed into regional-scale folds with axes plunging ~40° to the SSE. The fault extends at least 1.5 km along strike and dip, with a center ~1.5 km deep. It strikes ~320-340° N, dips ~45-70° NE, and is recognized by a ~0.3-0.5 m thick distinct gouge that contains crushed host rock and black material that appears to be graphite. Although we could not find clear evidence for fault displacement, secondary features suggest that it is a normal fault. The size and distinct structure of this fault make it a promising target for in-situ experimentation of fault strength, hydrological properties, and slip nucleation processes. Most earthquakes are thought to be the result of unstable slip on existing faults, Activation of the Homestake fault in response to the controlled fluid injection and thermally changing background stresses is likely to be localized on a crack-like patch. Slow patch propagation, moderated by the injection rate and the rate of change of the background stresses, may become unstable, leading to the nucleation of a small earthquake (dynamic) rupture. This controlled instability is intimately related to the dependence of the fault strength on the slip process and has been

Earthquake Nucleation on Faults With Heterogeneous Frictional Properties, Normal Stress

NASA Astrophysics Data System (ADS)

Ray, Sohom; Viesca, Robert C.

2017-10-01

We examine the development of an instability of fault slip rate. We consider a slip rate and state dependence of fault frictional strength, in which frictional properties and normal stress are functions of position. We pose the problem for a slip rate distribution that diverges quasi-statically within finite time in a self-similar fashion. Scenarios of property variations are considered and the corresponding self-similar solutions found. We focus on variations of coefficients, a and b, respectively, controlling the magnitude of a direct effect on strength due to instantaneous changes in slip rate and of strength evolution due to changes in a state variable. These results readily extend to variations in fault-normal stress, σ, or the characteristic slip distance for state evolution, Dc. We find that heterogeneous properties lead to a finite number of self-similar solutions, located about critical points of the distributions: maxima, minima, and between them. We examine the stability of these solutions and find that only a subset is asymptotically stable, occurring at just one of the critical point types. Such stability implies that during instability development, slip rate and state evolution can be attracted to develop in the manner of the self-similar solution, which is also confirmed by solutions to initial value problems for slip rate and state. A quasi-static slip rate divergence is ultimately limited by inertia, leading to the nucleation of an outward expanding dynamic rupture: asymptotic stability of self-similar solutions then implies preferential sites for earthquake nucleation, which are determined by distribution of frictional properties.

A model for the geomorphic development of normal-fault facets

NASA Astrophysics Data System (ADS)

Tucker, G. E.; Hobley, D. E. J.; McCoy, S. W.

2014-12-01

Triangular facets are among the most striking landforms associated with normal faulting. The genesis of facets is of great interest both for the information facets contain about tectonic motion, and because the progressive emergence of facets makes them potential recorders of both geomorphic and tectonic history. In this report, we present observations of triangular facets in the western United States and in the Italian Central Apennines. Facets in these regions typically form quasi-planar surfaces that are aligned in series along and above the trace of an active fault. Some facet surfaces consist mainly of exposed bedrock, with a thin and highly discontinuous cover of loose regolith. Other facets are mantled by a several-decimeter-thick regolith cover. Over the course of its morphologic development, a facet slope segment may evolve from a steep (~60 degree) bedrock fault scarp, well above the angle of repose for soil, to a gentler (~20-40 degree) slope that can potentially sustain a coherent regolith cover. This evolutionary trajectory across the angle of repose renders nonlinear diffusion theory inapplicable. To formulate an alternative process-based theory for facet evolution, we use a particle-based approach that acknowledges the possibility for both short- and long-range sediment-grain motions, depending on the topography. The processes of rock weathering, grain entrainment, and grain motion are represented as stochastic state-pair transitions with specified transition rates. The model predicts that facet behavior can range smoothly along the spectrum from a weathering-limited mode to a transport-limited mode, depending on the ratio of fault-slip rate to bare-bedrock regolith production rate. The model also implies that facets formed along a fault with pinned tips should show systematic variation in slope angle that correlates with along-fault position and slip rate. Preliminary observations from central Italy and the eastern Basin and Range are consistent

Winnetka deformation zone: Surface expression of coactive slip on a blind fault during the Northridge earthquake sequence, California. Evidence that coactive faulting occurred in the Canoga Park, Winnetka, and Northridge areas during the 17 January 1994, Northridge, California earthquake

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cruikshank, K.M.; Johnson, A.M.; Fleming, R.W.

1996-12-31

Measurements of normalized length changes of streets over an area of 9 km{sup 2} in San Fernando Valley of Los Angeles, California, define a distinctive strain pattern that may well reflect blind faulting during the 1994 Northridge earthquake. Strain magnitudes are about 3 {times} 10{sup {minus}4}, locally 10{sup {minus}3}. They define a deformation zone trending diagonally from near Canoga Park in the southwest, through Winnetka, to near Northridge in the northeast. The deformation zone is about 4.5 km long and 1 km wide. The northwestern two-thirds of the zone is a belt of extension of streets, and the southeastern one-thirdmore » is a belt of shortening of streets. On the northwest and southeast sides of the deformation zone the magnitude of the strains is too small to measure, less than 10{sup {minus}4}. Complete states of strain measured in the northeastern half of the deformation zone show that the directions of principal strains are parallel and normal to the walls of the zone, so the zone is not a strike-slip zone. The magnitudes of strains measured in the northeastern part of the Winnetka area were large enough to fracture concrete and soils, and the area of larger strains correlates with the area of greater damage to such roads and sidewalks. All parts of the pattern suggest a blind fault at depth, most likely a reverse fault dipping northwest but possibly a normal fault dipping southeast. The magnitudes of the strains in the Winnetka area are consistent with the strains produced at the ground surface by a blind fault plane extending to depth on the order of 2 km and a net slip on the order of 1 m, within a distance of about 100 to 500 m of the ground surface. The pattern of damage in the San Fernando Valley suggests a fault segment much longer than the 4.5 km defined by survey data in the Winnetka area. The blind fault segment may extend several kilometers in both directions beyond the Winnetka area. This study of the Winnetka area further supports

Fault-slip directions in central and southern Greece measured from striated and corrugated fault planes: Comparison with focal mechanism and geodetic data

NASA Astrophysics Data System (ADS)

Roberts, Gerald P.; Ganas, Athanassios

2000-10-01

Fault-slip directions recorded by outcropping striated and corrugated fault planes in central and southern Greece have been measured for comparison with extension directions derived from focal mechanism and Global Positioning System (GPS) data for the last ˜100 years to test how far back in time velocity fields and deformation dynamics derived from the latter data sets can be extrapolated. The fault-slip data have been collected from the basin-bounding faults to Plio-Pleistocene to recent extensional basins and include data from arrays of footwall faults formed during the early stages of fault growth. We show that the orientation of the inferred stress field varies along faults and earthquake ruptures, so we use only slip-directions from the centers of faults, where dip-slip motion occurs, to constrain regionally significant extension directions. The fault-slip directions for the Peloponnese and Gulfs of Evia and Corinth are statistically different at the 99% confidence level but statistically the same as those implied by earthquake focal mechanisms for each region at the 99% confidence level; they are also qualitatively similar to the principal strain axes derived from GPS studies. Extension directions derived from fault-slip data are 043-047° for the southern Peloponnese, 353° for the Gulf of Corinth, and 015-014° for the Gulf of Evia. Extension on active normal faults in the two latter areas appears to grade into strike-slip along the North Anatolian Fault through a gradual change in fault-slip directions and fault strikes. To reconcile the above with 5° Myr-1 clockwise rotations suggested for the area, we suggest that the faults considered formed during a single phase of extension. The deformation and formation of the normal fault systems examined must have been sufficiently rapid and recent for rotations about vertical axes to have been unable to disperse the fault-slip directions from the extension directions implied by focal mechanisms and GPS data

3D Model of the Tuscarora Geothermal Area

DOE Data Explorer

Faulds, James E.

2013-12-31

The Tuscarora geothermal system sits within a ~15 km wide left-step in a major west-dipping range-bounding normal fault system. The step over is defined by the Independence Mountains fault zone and the Bull Runs Mountains fault zone which overlap along strike. Strain is transferred between these major fault segments via and array of northerly striking normal faults with offsets of 10s to 100s of meters and strike lengths of less than 5 km. These faults within the step over are one to two orders of magnitude smaller than the range-bounding fault zones between which they reside. Faults within the broad step define an anticlinal accommodation zone wherein east-dipping faults mainly occupy western half of the accommodation zone and west-dipping faults lie in the eastern half of the accommodation zone. The 3D model of Tuscarora encompasses 70 small-offset normal faults that define the accommodation zone and a portion of the Independence Mountains fault zone, which dips beneath the geothermal field. The geothermal system resides in the axial part of the accommodation, straddling the two fault dip domains. The Tuscarora 3D geologic model consists of 10 stratigraphic units. Unconsolidated Quaternary alluvium has eroded down into bedrock units, the youngest and stratigraphically highest bedrock units are middle Miocene rhyolite and dacite flows regionally correlated with the Jarbidge Rhyolite and modeled with uniform cumulative thickness of ~350 m. Underlying these lava flows are Eocene volcanic rocks of the Big Cottonwood Canyon caldera. These units are modeled as intracaldera deposits, including domes, flows, and thick ash deposits that change in thickness and locally pinch out. The Paleozoic basement of consists metasedimenary and metavolcanic rocks, dominated by argillite, siltstone, limestone, quartzite, and metabasalt of the Schoonover and Snow Canyon Formations. Paleozoic formations are lumped in a single basement unit in the model. Fault blocks in the eastern

Various Slip Behaviors in the Frictionally Heterogeneous Fault Model

NASA Astrophysics Data System (ADS)

Yabe, S.; Ide, S.

2017-12-01

Diverse slip behaviors have been observed on the fault, including regular earthquakes followed by afterslip, and slow earthquakes. In Southwest Japan and Cascadia, hypocenters of slow earthquakes seem to be separated from the locked region of megathrust earthquakes (e.g., Liu et al., 2010). In contrary, M7 earthquakes and their afterslips and repeating occurrences of slow slip events were reported in the coseismic slip area of 2011 M9 earthquake in Tohoku region (Ohta et al., 2012; Ito et al., 2013). Understanding the physical mechanism of diverse slip behavior is important to understand the strain accumulation and release cycle in a whole subduction zone. Among various candidates to explain the slip diversity, including dynamic weakening (e.g., Noda and Lapusta, 2013), fluid-slip interactions (e.g., Segall, 2010), and along-dip variation of frictional property (e.g., Tse and Rice, 1986), we consider in this study frictional heterogeneity on the fault (e.g., Ando et al., 2010, 2012; Nakata et al., 2011; Skarbek et al., 2012; Dublanchet et al., 2013; Yabe and Ide, 2017). We have considered the finite linear fault governed by rate and state friction law on which velocity-weakening zone and velocity-strengthening zone are alternately distributed. The fault outside the model space slips stably, which loads stress to the model space. Such frictionally heterogeneous fault shows diverse slip behavior which cannot be observed in the frictionally homogeneous fault. In some parameter space, the entire faults including velocity-strengthening zones slips seismically (Skarbek et al., 2012; Dublanchet et al., 2013; Yabe and Ide, 2017). We have sometimes observed foreshocks and aftershocks within the mainshock slip area. We have also sometimes observed repeating slow slip events during the inter-seismic period around the rupture initiation point of the mainshock. We will report parameter studies to clarify the relation between diverse slip behavior and frictional heterogeneity.

Factors affecting the recognition of faults exposed in exploratory trenches

USGS Publications Warehouse

Bonilla, Manuel G.; Lienkaemper, James J.

1991-01-01

generally decreases with depth of dieout up. Length of obscure segments and depth of dieout up are typically less than the effective thickness of associated beds. On the basis of few data, obscure segments seem to be more common on faults with younger, rather than older, ages of latest displacement. Our study revealed additional relations not directly related to nonvisibility. For example, the median widths of faults crossed by the trenches vary by fault type, strike-slip faults being narrower than dip-slip faults. In the shallow and mostly unconsolidated materials cut by the trenches, fault widths show only an erratic and, at best, weak relationship to fault displacements. Hanging walls are deformed more frequently than footwalls in dip-slip faults, but both walls are deformed at more than 30 percent of the exposures. We tabulated several phenomena that may indicate faulting or provide evidence of prehistorical earthquakes. Rotation of pebbles was identified in 41 percent of the exposures having gravel in the fault zone; type of fault has no strong influence on the incidence of pebble rotation. Fissures were recorded at 52 percent of the exposures and were more common in strike-slip and normal faults than in reverse fau Its. Gouge was reported at 1 5 percent of the exposures; fault type has no significant influence on its frequency. Slickensides were noted at 10 percent of the exposures, and fault type has an unknown influence on their incidence. Slickensides in unconsolidated materials were restricted to clay, silt, and gouge. Other mechanical or hydrologic effects related to faulting or earthquakesrubble, breccia, mixing, crushing, polishing, water barriers, c;ind probable liquefaction effects-were reported at fewer than 1 0 percent of the exposures.

Dip-slope and Dip-slope Failures in Taiwan - a Review

NASA Astrophysics Data System (ADS)

Lee, C.

2011-12-01

Taiwan is famous for dip-slope and dip-slope slides. Dip-slopes exist at many places in the fold-and-thrust belt of Taiwan. Under active cutting of stream channels and man-made excavations, a dip-slope may become unstable and susceptible for mass sliding. Daylight of a bedding parallel clay seam is the most dangerous type for dip-slope sliding. Buckling or shear-off features may also happen at toe of a long dip-slope. Besides, a dip-slope is also dangerous for shallow debris slides, if the slope angle is between 25 to 45 degrees and the debris (colluvium or slope wash) is thick (>1m). These unstable slopes may slide during a triggering event, earthquake or typhoon storm; or even slide without a triggering event, like the 2010 Tapu case. Initial buckling feature had been found in the dip-slope of the Feitsui arch dam abutment after detailed explorations. Shear-off feature have also been found in dip-slope located in right bank of the Nahua reservoir after field investigation and drilling. The Chiufengerhshan slide may also be shear-off type. On the other hand, the Tapu, the Tsaoling slides and others are of direct slide type. The Neihoo Bishan slide is a shallow debris slide on dip-slope. All these cases demonstrate the four different types of dip-slope slide. The hazard of a dip-slope should be investigated to cover these possible types of failure. The existence of bedding parallel clay seams is critical for the stability of a dip-slope, either for direct slide or buckling or shear-off type of failure, and is a hot point during investigation. Because, the stability of a dip-slope is changing with time, therefore, detailed explorations to including weathering and erosion rates are also very necessary to ensure the long-term stability of a dip-slope.

Internal structure, fault rocks, and inferences regarding deformation, fluid flow, and mineralization in the seismogenic Stillwater normal fault, Dixie Valley, Nevada

USGS Publications Warehouse

Caine, Jonathan S.; Bruhn, R.L.; Forster, C.B.

2010-01-01

Outcrop mapping and fault-rock characterization of the Stillwater normal fault zone in Dixie Valley, Nevada are used to document and interpret ancient hydrothermal fluid flow and its possible relationship to seismic deformation. The fault zone is composed of distinct structural and hydrogeological components. Previous work on the fault rocks is extended to the map scale where a distinctive fault core shows a spectrum of different fault-related breccias. These include predominantly clast-supported breccias with angular clasts that are cut by zones containing breccias with rounded clasts that are also clast supported. These are further cut by breccias that are predominantly matrix supported with angular and rounded clasts. The fault-core breccias are surrounded by a heterogeneously fractured damage zone. Breccias are bounded between major, silicified slip surfaces, forming large pod-like structures, systematically oriented with long axes parallel to slip. Matrix-supported breccias have multiply brecciated, angular and rounded clasts revealing episodic deformation and fluid flow. These breccias have a quartz-rich matrix with microcrystalline anhedral, equant, and pervasively conformable mosaic texture. The breccia pods are interpreted to have formed by decompression boiling and rapid precipitation of hydrothermal fluids whose flow was induced by coseismic, hybrid dilatant-shear deformation and hydraulic connection to a geothermal reservoir. The addition of hydrothermal silica cement localized in the core at the map scale causes fault-zone widening, local sealing, and mechanical heterogeneities that impact the evolution of the fault zone throughout the seismic cycle. ?? 2010.

Evidence for large-magnitude, post-Eocene extension in the northern Shoshone Range, Nevada, and its implications for Carlin-type gold deposits in the lower plate of the Roberts Mountains allochthon

USGS Publications Warehouse

Colgan, Joseph P.; Henry, Christopher D.; John, David A.

2014-01-01

The northern Shoshone and Toiyabe Ranges in north-central Nevada expose numerous areas of mineralized Paleozoic rock, including major Carlin-type gold deposits at Pipeline and Cortez. Paleozoic rocks in these areas were previously interpreted to have undergone negligible postmineralization extension and tilting, but here we present new data that suggest major post-Eocene extension along west-dipping normal faults. Tertiary rocks in the northern Shoshone Range crop out in two W-NW–trending belts that locally overlie and intrude highly deformed Lower Paleozoic rocks of the Roberts Mountains allochthon. Tertiary exposures in the more extensive, northern belt were interpreted as subvertical breccia pipes (intrusions), but new field data indicate that these “pipes” consist of a 35.8 Ma densely welded dacitic ash flow tuff (informally named the tuff of Mount Lewis) interbedded with sandstones and coarse volcaniclastic deposits. Both tuff and sedimentary rocks strike N-S and dip 30° to 70° E; the steeply dipping compaction foliation in the tuffs was interpreted as subvertical flow foliation in breccia pipes. The southern belt along Mill Creek, previously mapped as undivided welded tuff, includes the tuff of Cove mine (34.4 Ma) and unit B of the Bates Mountain Tuff (30.6 Ma). These tuffs dip 30° to 50° east, suggesting that their west-dipping contacts with underlying Paleozoic rocks (previously mapped as depositional) are normal faults. Tertiary rocks in both belts were deposited on Paleozoic basement and none appear to be breccia pipes. We infer that their present east tilt is due to extension on west-dipping normal faults. Some of these faults may be the northern strands of middle Miocene (ca. 16 Ma) faults that cut and tilted the 34.0 Ma Caetano caldera ~40° east in the central Shoshone Range (

An imbalance fault detection method based on data normalization and EMD for marine current turbines.

PubMed

Zhang, Milu; Wang, Tianzhen; Tang, Tianhao; Benbouzid, Mohamed; Diallo, Demba

2017-05-01

This paper proposes an imbalance fault detection method based on data normalization and Empirical Mode Decomposition (EMD) for variable speed direct-drive Marine Current Turbine (MCT) system. The method is based on the MCT stator current under the condition of wave and turbulence. The goal of this method is to extract blade imbalance fault feature, which is concealed by the supply frequency and the environment noise. First, a Generalized Likelihood Ratio Test (GLRT) detector is developed and the monitoring variable is selected by analyzing the relationship between the variables. Then, the selected monitoring variable is converted into a time series through data normalization, which makes the imbalance fault characteristic frequency into a constant. At the end, the monitoring variable is filtered out by EMD method to eliminate the effect of turbulence. The experiments show that the proposed method is robust against turbulence through comparing the different fault severities and the different turbulence intensities. Comparison with other methods, the experimental results indicate the feasibility and efficacy of the proposed method. Copyright © 2017 ISA. Published by Elsevier Ltd. All rights reserved.

The influence of a reverse-reactivated normal fault on natural fracture geometries and relative chronologies at Castle Cove, Otway Basin

NASA Astrophysics Data System (ADS)

Debenham, Natalie; King, Rosalind C.; Holford, Simon P.

2018-07-01

Despite the ubiquity of normal faults that have undergone compressional inversion, documentation of the structural history of natural fractures around these structures is limited. In this paper, we investigate the geometries and relative chronologies of natural fractures adjacent to a reverse-reactivated normal fault, the Castle Cove Fault in the Otway Basin, southeast Australia. Local variations in strain resulted in greater deformation within the fault damage zone closer to the fault. Structural mapping within the damage zone reveals a complex tectonic history recording both regional and local perturbations in stress and a total of 11 fracture sets were identified, with three sets geometrically related to the Castle Cove Fault. The remaining fracture sets formed in response to local stresses at Castle Cove. Rifting in the late Cretaceous resulted in normal movement of the Castle Cove Fault and associated rollover folding, and the formation of the largest fracture set. Reverse-reactivation of the fault and associated anticlinal folding occurred during late Miocene to Pliocene compression. Rollover folding may have provided structural traps if seals were not breached by fractures, however anticlinal folding likely post-dated the main episodes of hydrocarbon generation and migration in the region. This study highlights the need to conduct careful reconstruction of the structural histories of fault zones that experienced complex reactivation histories when attempting to define off-fault fluid flow properties.

Fault Slip Distribution of the 2016 Fukushima Earthquake Estimated from Tsunami Waveforms

NASA Astrophysics Data System (ADS)

Gusman, Aditya Riadi; Satake, Kenji; Shinohara, Masanao; Sakai, Shin'ichi; Tanioka, Yuichiro

2017-08-01

The 2016 Fukushima normal-faulting earthquake (Mjma 7.4) occurred 40 km off the coast of Fukushima within the upper crust. The earthquake generated a moderate tsunami which was recorded by coastal tide gauges and offshore pressure gauges. First, the sensitivity of tsunami waveforms to fault dimensions and depths was examined and the best size and depth were determined. Tsunami waveforms computed based on four available focal mechanisms showed that a simple fault striking northeast-southwest and dipping southeast (strike = 45°, dip = 41°, rake = -95°) yielded the best fit to the observed waveforms. This fault geometry was then used in a tsunami waveform inversion to estimate the fault slip distribution. A large slip of 3.5 m was located near the surface and the major slip region covered an area of 20 km × 20 km. The seismic moment, calculated assuming a rigidity of 2.7 × 1010 N/m2 was 3.70 × 1019 Nm, equivalent to Mw = 7.0. This is slightly larger than the moments from the moment tensor solutions (Mw 6.9). Large secondary tsunami peaks arrived approximately an hour after clear initial peaks were recorded by the offshore pressure gauges and the Sendai and Ofunato tide gauges. Our tsunami propagation model suggests that the large secondary tsunami signals were from tsunami waves reflected off the Fukushima coast. A rather large tsunami amplitude of 75 cm at Kuji, about 300 km north of the source, was comparable to those recorded at stations located much closer to the epicenter, such as Soma and Onahama. Tsunami simulations and ray tracing for both real and artificial bathymetry indicate that a significant portion of the tsunami wave was refracted to the coast located around Kuji and Miyako due to bathymetry effects.

Slip Inversion Along Inner Fore-Arc Faults, Eastern Tohoku, Japan

NASA Astrophysics Data System (ADS)

Regalla, Christine; Fisher, Donald M.; Kirby, Eric; Oakley, David; Taylor, Stephanie

2017-11-01

The kinematics of deformation in the overriding plate of convergent margins may vary across timescales ranging from a single seismic cycle to many millions of years. In Northeast Japan, a network of active faults has accommodated contraction across the arc since the Pliocene, but several faults located along the inner fore arc experienced extensional aftershocks following the 2011 Tohoku-oki earthquake, opposite that predicted from the geologic record. This observation suggests that fore-arc faults may be favorable for stress triggering and slip inversion, but the geometry and deformation history of these fault systems are poorly constrained. Here we document the Neogene kinematics and subsurface geometry of three prominent fore-arc faults in Tohoku, Japan. Geologic mapping and dating of growth strata provide evidence for a 5.6-2.2 Ma initiation of Plio-Quaternary contraction along the Oritsume, Noheji, and Futaba Faults and an earlier phase of Miocene extension from 25 to 15 Ma along the Oritsume and Futaba Faults associated with the opening of the Sea of Japan. Kinematic modeling indicates that these faults have listric geometries, with ramps that dip 40-65°W and sole into subhorizontal detachments at 6-10 km depth. These fault systems can experience both normal and thrust sense slip if they are mechanically weak relative to the surrounding crust. We suggest that the inversion history of Northeast Japan primed the fore arc with a network of weak faults mechanically and geometrically favorable for slip inversion over geologic timescales and in response to secular variations in stress state associated with the megathrust seismic cycle.

Mapping 3D fault geometry in earthquakes using high-resolution topography: Examples from the 2010 El Mayor-Cucapah (Mexico) and 2013 Balochistan (Pakistan) earthquakes

NASA Astrophysics Data System (ADS)

Zhou, Yu; Walker, Richard T.; Elliott, John R.; Parsons, Barry

2016-04-01

Fault dips are usually measured from outcrops in the field or inferred through geodetic or seismological modeling. Here we apply the classic structural geology approach of calculating dip from a fault's 3-D surface trace using recent, high-resolution topography. A test study applied to the 2010 El Mayor-Cucapah earthquake shows very good agreement between our results and those previously determined from field measurements. To obtain a reliable estimate, a fault segment ≥120 m long with a topographic variation ≥15 m is suggested. We then applied this method to the 2013 Balochistan earthquake, getting dips similar to previous estimates. Our dip estimates show a switch from north to south dipping at the southern end of the main trace, which appears to be a response to local extension within a stepover. We suggest that this previously unidentified geometrical complexity may act as the endpoint of earthquake ruptures for the southern end of the Hoshab fault.

Kanda fault: A major seismogenic element west of the Rukwa Rift (Tanzania, East Africa)

NASA Astrophysics Data System (ADS)

Vittori, Eutizio; Delvaux, Damien; Kervyn, François

1997-09-01

The NW-SE trending Rukwa Rift, part of the East African Rift System, links the approximately N-S oriented Tanganyika and Nyassa (Malawi) depressions. The rift has a complex half-graben structure, generally interpreted as the result of normal and strike-slip faulting. Morphological and structural data (e.g. fault scarps, faceted spurs, tilting of Quaternary continental deposits, volcanism, seismicity) indicate Late Quaternary activity within the rift. In 1910 an earthquake of M = 7.4 (historically the largest felt in Africa) struck the Rukwa region. The epicentre was located near the Kanda fault, which affects the Ufipa plateau, separating the Rukwa depression from the south-Tanganyika basin. The geomorphic expression of the Kanda fault is a prominent fresh-looking scarp more than 180 km long, from Tunduma to north of Sumbawanga, that strikes roughly NW-SE, and dips constantly northeast. No evidence for horizontal slip was observed. Generally, the active faulting affects a very narrow zone, and is only locally distributed over several subparallel scarps. The height of the scarp progressively decreases towards the northwest, from about 40-50 m to a few metres north of Sumbawanga. Faulted lacustrine deposits exposed in a road cut near Kaengesa were dated as 8340 ± 700 and 13 600 ± 1240 radiocarbon years. These low-energy deposits now hang more than 15 m above the present-day valley floor, suggesting rapid uplift during the Holocene. Due to its high rate of activity in very recent times, the Kanda Fault could have produced the 1910 earthquake. Detailed paleoseismological studies are used to characterize its recent history. In addition, the seismic hazard posed by this fault, which crosses the fast growing town of Sumbawanga, must be seriously considered in urban planning.

High Resolution Seismic Imaging of the Trench Canyon Fault Zone, Mono Lake, Northeastern California

NASA Astrophysics Data System (ADS)

Novick, M. W.; Jayko, A. S.; Roeske, S.; McClain, J. S.; Hart, P. E.; Boyle, M.

2009-12-01

High resolution seismic imaging of Mono Lake, located in northeastern California, has revealed an approximately northwest striking fault in the area to the west of aerially exposed Negit Volcano. This fault, henceforth referred to as the Trench Canyon Fault (TCF), has also been mapped onshore along a correlating strike as far north as Cedar Hill Volcano, located to the northeast of the lake on the California/Nevada border. Onshore, the TCF was mapped for approximately 10 kilometers using air photos, DEM images, and standard geologic pace and compass mapping techniques. The TCF post- dates the last glacial maximum, evidenced by the cutting of wave cut benches along Cedar Hill Volcano. Relict, non-historic shorelines, left by the steady evaporation of Mono Lake beginning approximately 13k, are also repeatedly cut by the fault. Additional evidence of fault presence includes sag ponds, pressure ridges, tectonically fractured rocks, and normal fault scarps found along strike. Offshore, DEM images show a northeast striking structure to the northwest of Negit Volcano, which is co-linear with the onshore TCF. High resolution seismic imaging of the structure, using an applied acoustic/SIG mini-sparker system, reveals steeply dipping Holocene sediments, as well as volcanic deposits from active vents which have erupted in the last 1000 years, offset by the fault. Detailed structural analysis of the previously unstudied Trench Canyon Fault (TFC) and faults in the Cedar Hill region of northern California, along with seismic studies of sediments beneath Mono Lake not only allow for a better comprehension of this minor fault system, but provide greater understanding of the larger and more complex Walker Lane Shear Zone. Fault analyses, combined and correlated with those from CHV, give a better understanding of how slip is transferred into the complicated Mina defection to the east, from the dextral and normal faults along the Sierra Nevada Range front.

Seismic interpretation of the deep structure of the Wabash Valley Fault System

USGS Publications Warehouse

Bear, G.W.; Rupp, J.A.; Rudman, A.J.

1997-01-01

Interpretations of newly available seismic reflection profiles near the center of the Illinois Basin indicate that the Wabash Valley Fault System is rooted in a series of basement-penetrating faults. The fault system is composed predominantly of north-northeast-trending high-angle normal faults. The largest faults in the system bound the 22-km wide 40-km long Grayville Graben. Structure contour maps drawn on the base of the Mount Simon Sandstone (Cambrian System) and a deeper pre-Mount Simon horizon show dip-slip displacements totaling at least 600 meters across the New Harmony fault. In contrast to previous interpretations, the N-S extent of significant fault offsets is restricted to a region north of 38?? latitude and south of 38.35?? latitude. This suggests that the graben is not a NE extension of the structural complex composed of the Rough Creek Fault System and the Reelfoot Rift as previously interpreted. Structural complexity on the graben floor also decreases to the south. Structural trends north of 38?? latitude are offset laterally across several large faults, indicating strike-slip motions of 2 to 4 km. Some of the major faults are interpreted to penetrate to depths of 7 km or more. Correlation of these faults with steep potential field gradients suggests that the fault positions are controlled by major lithologic contacts within the basement and that the faults may extend into the depth range where earthquakes are generated, revealing a potential link between specific faults and recently observed low-level seismicity in the area.

Late Quaternary Surface Displacement Across a Normal-Fault Structural Boundary on the Northern Lost River Fault Zone (Idaho, USA)

NASA Astrophysics Data System (ADS)

DuRoss, C. B.; Bunds, M. P.; Reitman, N. G.; Gold, R. D.; Personius, S. F.; Briggs, R. W.; Toke, N. A.; Johnson, K. L.; Lajoie, L. J.

2017-12-01

In 1983, about 36 km of the 130-km-long multisegment Lost River fault zone (LRFZ) (Idaho, USA) ruptured in the M 6.9 Borah Peak earthquake. Normal-faulting surface rupture propagated along the entire 24-km-long Thousand Springs section, then branched to the northwest along a 4-km-long fault (western section) that continues into the Willow Creek Hills, a prominent bedrock ridge that forms a structural boundary between the Thousand Springs section and Warms Springs section to the north. North of the Willow Creek Hills, the 1983 rupture continued onto the southern 8 km of the 16-km-long Warm Springs section. To improve our understanding of the Borah Peak earthquake and the role of structural boundaries in normal-fault rupture propagation, we acquired low-altitude aerial imagery of the southern 8 km of the Warm Springs section and northern 6 km of the Thousand Springs section, including the western section branch fault. Using 5-10-cm-pixel digital surface models generated from this dataset, we measured vertical surface offsets across both 1983 and prehistoric scarps. On the Warm Springs section, 1983 displacement is minor (mean of 0.3 m) compared to at least two prehistoric events having mean displacements of 1.1 m and 1.7 m inferred from displacement difference curves. Prehistoric scarps on the western section indicate rupture of this branch fault prior to 1983. Correcting for 1983 displacement, mean prehistoric displacement on the western section is 0.9 m compared to a mean of 0.7 m in 1983. Using these data and previous paleoseismic displacements, we evaluate the spatial distribution of cumulative and per-earthquake displacement. Our results suggest that at least one prehistoric rupture of the Thousand Springs section occurred with a similar length and displacement to that in 1983. Further, the 1983 spillover rupture from the Thousand Springs section to the southernmost Warm Springs section appears unique from larger displacement, prehistoric ruptures that may have

Geometry and earthquake potential of the shoreline fault, central California

USGS Publications Warehouse

Hardebeck, Jeanne L.

2013-01-01

The Shoreline fault is a vertical strike‐slip fault running along the coastline near San Luis Obispo, California. Much is unknown about the Shoreline fault, including its slip rate and the details of its geometry. Here, I study the geometry of the Shoreline fault at seismogenic depth, as well as the adjacent section of the offshore Hosgri fault, using seismicity relocations and earthquake focal mechanisms. The Optimal Anisotropic Dynamic Clustering (OADC) algorithm (Ouillon et al., 2008) is used to objectively identify the simplest planar fault geometry that fits all of the earthquakes to within their location uncertainty. The OADC results show that the Shoreline fault is a single continuous structure that connects to the Hosgri fault. Discontinuities smaller than about 1 km may be undetected, but would be too small to be barriers to earthquake rupture. The Hosgri fault dips steeply to the east, while the Shoreline fault is essentially vertical, so the Hosgri fault dips towards and under the Shoreline fault as the two faults approach their intersection. The focal mechanisms generally agree with pure right‐lateral strike‐slip on the OADC planes, but suggest a non‐planar Hosgri fault or another structure underlying the northern Shoreline fault. The Shoreline fault most likely transfers strike‐slip motion between the Hosgri fault and other faults of the Pacific–North America plate boundary system to the east. A hypothetical earthquake rupturing the entire known length of the Shoreline fault would have a moment magnitude of 6.4–6.8. A hypothetical earthquake rupturing the Shoreline fault and the section of the Hosgri fault north of the Hosgri–Shoreline junction would have a moment magnitude of 7.2–7.5.

Surface faults on Montague Island associated with the 1964 Alaska earthquake: Chapter G in The Alaska earthquake, March 27, 1964: regional effects

USGS Publications Warehouse

Plafter, George

1967-01-01

Two reverse faults on southwestern Montague Island in Prince William Sound were reactivated during the earthquake of March 27, 1964. New fault scarps, fissures, cracks, and flexures appeared in bedrock and unconsolidated surficial deposits along or near the fault traces. Average strike of the faults is between N. 37° E. and N. 47° E.; they dip northwest at angles ranging from 50° to 85°. The dominant motion was dip slip; the blocks northwest of the reactivated faults were relatively upthrown, and both blocks were upthrown relative to sea level. No other earthquake faults have been found on land. The Patton Bay fault on land is a complex system of en echelon strands marked by a series of spectacular landslides along the scarp and (or) by a zone of fissures and flexures on the upthrown block that locally is as much as 3,000 feet wide. The fault can be traced on land for 22 miles, and it has been mapped on the sea floor to the southwest of Montague Island an additional 17 miles. The maximum measured vertical component of slip is 20 to 23 feet and the maximum indicated dip slip is about 26 feet. A left-lateral strike-slip component of less than 2 feet occurs near the southern end of the fault on land where its strike changes from northeast to north. Indirect evidence from the seismic sea waves and aftershocks associated with the earthquake, and from the distribution of submarine scarps, suggests that the faulting on and near Montague Island occurred at the northeastern end of a reactivated submarine fault system that may extend discontinuously for more than 300 miles from Montague Island to the area offshore of the southeast coast of Kodiak Island. The Hanning Bay fault is a minor rupture only 4 miles long that is marked by an exceptionally well defined almost continuous scarp. The maximum measured vertical component of slip is 16⅓ feet near the midpoint, and the indicated dip slip is about 20 feet. There is a maximum left-lateral strike-slip component of one

Relationship between displacement and gravity change of Uemachi faults and surrounding faults of Osaka basin, Southwest Japan

NASA Astrophysics Data System (ADS)

Inoue, N.; Kitada, N.; Kusumoto, S.; Itoh, Y.; Takemura, K.

2011-12-01

The Osaka basin surrounded by the Rokko and Ikoma Ranges is one of the typical Quaternary sedimentary basins in Japan. The Osaka basin has been filled by the Pleistocene Osaka group and the later sediments. Several large cities and metropolitan areas, such as Osaka and Kobe are located in the Osaka basin. The basin is surrounded by E-W trending strike slip faults and N-S trending reverse faults. The N-S trending 42-km-long Uemachi faults traverse in the central part of the Osaka city. The Uemachi faults have been investigated for countermeasures against earthquake disaster. It is important to reveal the detailed fault parameters, such as length, dip and recurrence interval, so on for strong ground motion simulation and disaster prevention. For strong ground motion simulation, the fault model of the Uemachi faults consist of the two parts, the north and south parts, because of the no basement displacement in the central part of the faults. The Ministry of Education, Culture, Sports, Science and Technology started the project to survey of the Uemachi faults. The Disaster Prevention Institute of Kyoto University is carried out various surveys from 2009 to 2012 for 3 years. The result of the last year revealed the higher fault activity of the branch fault than main faults in the central part (see poster of "Subsurface Flexure of Uemachi Fault, Japan" by Kitada et al., in this meeting). Kusumoto et al. (2001) reported that surrounding faults enable to form the similar basement relief without the Uemachi faults model based on a dislocation model. We performed various parameter studies for dislocation model and gravity changes based on simplified faults model, which were designed based on the distribution of the real faults. The model was consisted 7 faults including the Uemachi faults. The dislocation and gravity change were calculated based on the Okada et al. (1985) and Okubo et al. (1993) respectively. The results show the similar basement displacement pattern to the

Resolving the fault systems with the magnetotelluric method in the western Ilan plain of NE Taiwan

NASA Astrophysics Data System (ADS)

Chang, P. Y.; Chen, C. S.

2017-12-01

In the study we attempt to use the magnetotelluric (MT) surveys to delineate the basement topography of the western part of the Ilan plain. The triangular plain is located on the extension part of the Okinawa Trough, and is thought to be a subsidence basin bounded by the Hsueshan Range in the north and the Central Range in the south. The basement of the basin is composed of Tertiary metamorphic rocks such as argillites and slates. The recent extension of the Okinawa Trough started from approximately 0.1 Ma and involved ENE- and WSW-trending normal faults that may extended into the Ilan plain area. However, high sedimentation rates as well as the frequent human activities have resulted in unconsolidated sediments with a thickness of over 100 meters, and caused the difficulties in observing the surface traces of the active faults in the area. Hence we deployed about 70 MT stations across the southwestern tip of the triangular plain. We also tried to resolve the subsurface faults the relief variations of the basement with the inverted resistivity images, since the saturated sediments are relatively conductive and the consolidated rocks are resistive. With the inverted MT images, we found that there are a series of N-S trending horsts and grabens in addition to the ENE-WSW normal fault systems. The ENE-WSW trending faults are dipping mainly toward the north in our study area in the western tip of the Ilan plain. The preliminary results suggest that a younger N-S trending normal fault system may modify the relief of the basement in the recent stage after the activation of the ENE-WSW normal faults. The findings of the MT resistivity images provide new information to further review the tectonic explanations of the region in the future.

Flexure and faulting of sedimentary host rocks during growth of igneous domes, Henry Mountains, Utah

USGS Publications Warehouse

Jackson, M.D.; Pollard, D.D.

1990-01-01

A sequence of sedimentary rocks about 4 km thick was bent, stretched and uplifted during the growth of three igneous domes in the southern Henry Mountains. Mount Holmes, Mount Ellsworth and Mount Hillers are all about 12 km in diameter, but the amplitudes of their domes are about 1.2, 1.85 and 3.0 km, respectively. These mountains record successive stages in the inflation of near-surface diorite intrusions that are probably laccolithic in origin. The host rocks deformed along networks of outcrop-scale faults, or deformation bands, marked by crushed grains, consolidation of the porous sandstone and small displacements of sedimentary beds. Zones of deformation bands oriented parallel to the beds and formation contacts subdivided the overburden into thin mechanical layers that slipped over one another during doming. Measurements of outcrop-scale fault populations at the three mountains reveal a network of faults that strikes at high angles to sedimentary beds which themselves strike tangentially about the domes. These faults have normal and reverse components of slip that accommodated bending and stretching strains within the strata. An early stage of this deformation is displayed at Mount Holmes, where states of stress computed from three fault samples correlate with the theoretical distribution of stresses resulting from bending of thin, circular, elastic plates. Field observations and analysis of frictional driving stresses acting on horizontal planes above an opening-mode dislocation, as well as the paleostress analysis of faulting, indicate that bedding-plane slip and layer flexure were important components of the early deformation. As the amplitude of doming increased, radial and circumferential stretching of the strata and rotation of the older faults in the steepening limbs of the domes increased the complexity of the fault patterns. Steeply-dipping, map-scale faults with dip-slip displacements indicate a late-stage jostling of major blocks over the central

Recent deformation along the offshore Malibu Coast, Dume, and related faults west of Point Dume, southern California

USGS Publications Warehouse

Fisher, M.A.; Langenheim, V.E.; Sorlien, C.C.; Dartnell, P.; Sliter, R.W.; Cochrane, G.R.; Wong, F.L.

2005-01-01

Offshore faults west of Point Dume, southern California, are part of an important regional fault system that extends for about 206 km, from near the city of Los Angeles westward along the south flank of the Santa Monica Mountains and through the northern Channel Islands. This boundary fault system separates the western Transverse Ranges, on the north, from the California Continental Borderland, on the south. Previous research showed that the fault system includes many active fault strands; consequently, the entire system is considered a serious potential earthquake hazard to nearby Los Angeles. We present an integrated analysis of multichannel seismic- and high-resolution seismic-reflection data and multibeam-bathymetric information to focus on the central part of the fault system that lies west of Point Dume. We show that some of the main offshore faults have cumulative displacements of 3-5 km, and many faults are currently active because they deform the seafloor or very shallow sediment layers. The main offshore fault is the Dume fault, a large north-dipping reverse fault. In the eastern part of the study area, this fault offsets the seafloor, showing Holocene displacement. Onshore, the Malibu Coast fault dips steeply north, is active, and shows left-oblique slip. The probable offshore extension of this fault is a large fault that dips steeply in its upper part but flattens at depth. High-resolution seismic data show that this fault deforms shallow sediment making up the Hueneme fan complex, indicating Holocene activity. A structure near Sycamore knoll strikes transversely to the main faults and could be important to the analysis of the regional earthquake hazard because the structure might form a boundary between earthquake-rupture segments.

Near-surface location, geometry, and velocities of the Santa Monica Fault Zone, Los Angeles, California

USGS Publications Warehouse

Catchings, R.D.; Gandhok, G.; Goldman, M.R.; Okaya, D.; Rymer, M.J.; Bawden, G.W.

2008-01-01

High-resolution seismic-reflection and seismic-refraction imaging, combined with existing borehole, earthquake, and paleoseismic trenching data, suggest that the Santa Monica fault zone in Los Angeles consists of multiple strands from several kilometers depth to the near surface. We interpret our seismic data as showing two shallow-depth low-angle fault strands and multiple near-vertical (???85??) faults in the upper 100 m. One of the low-angle faults dips northward at about 28?? and approaches the surface at the base of a topographic scarp on the grounds of the Wadsworth VA Hospital (WVAH). The other principal low-angle fault dips northward at about 20?? and projects toward the surface about 200 m south of the topographic scarp, near the northernmost areas of the Los Angeles Basin that experienced strong shaking during the 1994 Northridge earthquake. The 20?? north-dipping low-angle fault is also apparent on a previously published seismic-reflection image by Pratt et al. (1998) and appears to extend northward to at least Wilshire Boulevard, where the fault may be about 450 m below the surface. Slip rates determined at the WVAH site could be significantly underestimated if it is assumed that slip occurs only on a single strand of the Santa Monica fault or if it is assumed that the near-surface faults dip at angles greater than 20-28??. At the WVAH, tomographic velocity modeling shows a significant decrease in velocity across near-surface strands of the Santa Monica fault. P-wave velocities range from about 500 m/sec at the surface to about 4500 m/sec within the upper 50 m on the north side of the fault zone at WVAH, but maximum measured velocities on the south side of the low-angle fault zone at WVAH are about 3500 m/sec. These refraction velocities compare favorably with velocities measured in nearby boreholes by Gibbs et al. (2000). This study illustrates the utility of com- bined seismic-reflection and seismic-refraction methods, which allow more accurate