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Sample records for e-w striking faults

  1. E-W strike slip shearing of Kinwat granitoid at South East Deccan Volcanic Province, Kinwat, Maharashtra, India

    NASA Astrophysics Data System (ADS)

    Kaplay, R. D.; Kumar, T. Vijay; Mukherjee, Soumyajit; Wesanekar, P. R.; Babar, Md; Chavan, Sumeet

    2017-07-01

    We study the margin of South East Deccan Volcanic Province around Kinwat lineament, Maharashtra, India, which is NW extension of the Kaddam Fault. Structural field studies document ˜ E-W strike-slip mostly brittle faults from the basement granite. We designate this as `Western boundary East Dharwar Craton Strike-slip Zone' (WBEDCSZ). At local level, the deformation regime from Kinwat, Kaddam Fault, micro-seismically active Nanded and seismically active Killari corroborate with the nearby lineaments. Morphometric analyses suggest that the region is moderately tectonically active. The region of intense strike-slip deformation lies between seismically active fault along Tapi in NW and Bhadrachalam in the SE part of the Kaddam Fault/lineament. The WBEDCSZ with the surface evidences of faulting, presence of a major lineaments and intersection of faults could be a zone of intraplate earthquake.

  2. Constraints from Mesozoic siliciclastic cover rocks and satellite image analysis on the slip history of regional E-W faults in the southeast Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Tewksbury, Barbara J.; Mehrtens, Charlotte J.; Gohlke, Steven A.; Tarabees, Elhamy A.; Hogan, John P.

    2017-12-01

    In the southeast Western Desert of Egypt, a prominent set of E-W faults and co-located domes and basins involve sedimentary cover rock as young as the early Eocene. Although earlier Mesozoic slip on faults in southern Egypt has been widely mentioned in the literature and attributed to repeated reactivation of basement faults, evidence is indirect and based on the idea that regional stresses associated with tectonic events in the Syrian Arc would likely have reactivated basement faults in south Egypt in dextral strike slip during the Mesozoic as well as the Cenozoic. Here, we present direct evidence from the rock record for the sequence of development of features along these faults. Southwest of Aswan, a small structural dome in Mesozoic Nubia facies rocks occurs where the Seiyal Fault bends northward from west to east. The dome is cut by strands of the Seiyal Fault and a related set of cataclastic deformation bands showing dominantly right lateral strike slip, as well as by younger calcite veins with related patchy poikilotopic cement. High resolution satellite image analysis of the remote southwest Kharga Valley shows a similar sequence of events: older structural domes and basins located where E-W faults bend northward from west to east, right lateral offset of domes and basins along the E-W faults, and two sets of deformation band faults that lack co-located domes and basins. We suggest that field data, image analysis, and burial depth estimates are best explained by diachronous development of features along the E-W fault system. We propose that Late Mesozoic right lateral strike slip produced domes and basins in Nubia facies rocks in stepover regions above reactivated basement faults. We further suggest that the extensively linked segments of the E-W fault system in Nubia facies rocks, plus the deformation band systems, formed during the late Eocene when basement faults were again reactivated in dominantly right lateral strike slip.

  3. Active strike-slip faulting in El Salvador, Central America

    NASA Astrophysics Data System (ADS)

    Corti, Giacomo; Carminati, Eugenio; Mazzarini, Francesco; Oziel Garcia, Marvyn

    2005-12-01

    Several major earthquakes have affected El Salvador, Central America, during the Past 100 yr as a consequence of oblique subduction of the Cocos plate under the Caribbean plate, which is partitioned between trench-orthogonal compression and strike-slip deformation parallel to the volcanic arc. Focal mechanisms and the distribution of the most destructive earthquakes, together with geomorphologic evidence, suggest that this transcurrent component of motion may be accommodated by a major strike-slip fault (El Salvador fault zone). We present field geological, structural, and geomorphological data collected in central El Salvador that allow the constraint of the kinematics and the Quaternary activity of this major seismogenic strike-slip fault system. Data suggest that the El Salvador fault zone consists of at least two main ˜E-W fault segments (San Vicente and Berlin segments), with associated secondary synthetic (WNW-ESE) and antithetic (NNW-SSE) Riedel shears and NW-SE tensional structures. The two main fault segments overlap in a dextral en echelon style with the formation of an intervening pull-apart basin. Our original geological and geomorphologic data suggest a late Pleistocene Holocene slip rate of ˜11 mm/yr along the Berlin segment, in contrast with low historical seismicity. The kinematics and rates of deformation suggested by our new data are consistent with models involving slip partitioning during oblique subduction, and support the notion that a trench-parallel component of motion between the Caribbean and Cocos plates is concentrated along E-W dextral strike-slip faults parallel to the volcanic arc.

  4. 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.

  5. The role of E-W basement faults in the Mesozoic geodynamic evolution of the Gafsa and Chotts basins, south-central Tunisia

    NASA Astrophysics Data System (ADS)

    Amri, Dorra Tanfous; Dhahri, Ferid; Soussi, Mohamed; Gabtni, Hakim; Bédir, Mourad

    2017-10-01

    The Gafsa and Chotts intracratonic basins in south-central Tunisia are transitional zones between the Atlasic domain to the north and the Saharan platform to the south. The principal aim of this paper is to unravel the geodynamic evolution of these basins following an integrated approach including seismic, well log and gravity data. These data are used to highlight the tectonic control on the deposition of Jurassic and Lower Cretaceous series and to discuss the role of the main faults that controlled the basin architecture and Cretaceous-Tertiary inversion. The horizontal gravity gradient map of the study area highlights the pattern of discontinuities within the two basins and reveals the presence of deep E-W basement faults. Primary attention is given to the role played by the E-W faults system and that of the NW-SE Gafsa fault which was previously considered active since the Jurassic. Facies and thickness analyses based on new seismic interpretation and well data suggest that the E-W-oriented faults controlled the subsidence distribution especially during the Jurassic. The NW-SE faults seem to be key structures that controlled the basins paleogeography during Late Cretaceous-Cenozoic time. The upper Triassic evaporite bodies, which locally outline the main NW-SE Gafsa fault, are regarded as intrusive salt bodies rather than early diapiric extrusions as previously interpreted since they are rare and occurred only along main strike-slip faults. In addition, seismic lines show that Triassic rocks are deep and do not exhibit true diapiric features.

  6. 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

  7. Stress accumulated mechanisms on strike-slip faults

    NASA Technical Reports Server (NTRS)

    Turcotte, D. L.

    1980-01-01

    The tectonic framework causing seismicity on the San Andreas and North Anatolian faults can be understood in terms of plate tectonics. However, the mechanisms responsible for the distribution of seismicity in space and time on these faults are poorly understood. The upper part of the crust apparently behaves elastically in storing energy that is released during an earthquake. The relatively small distances from the fault in which stress is stored argue in favor of a plate with a thickness of 5-10 km. The interaction of this plate with a lower crust that is behaving as a fluid damps the seismic cycling in distances of the order of 10 km from the fault. Low measured heat flow also argues in favor of a thin plate with a low stress level on the fault. Future measurements of stress, strain, and heat flow should help to provide a better understanding of the basic mechanisms governing the behavior of strike-slip faults.

  8. Late Quaternary strike-slip along the Taohuala Shan-Ayouqi fault zone and its tectonic implications in the Hexi Corridor and the southern Gobi Alashan, China

    NASA Astrophysics Data System (ADS)

    Yu, Jing-xing; Zheng, Wen-jun; Zhang, Pei-zhen; Lei, Qi-yun; Wang, Xu-long; Wang, Wei-tao; Li, Xin-nan; Zhang, Ning

    2017-11-01

    The Hexi Corridor and the southern Gobi Alashan are composed of discontinuous a set of active faults with various strikes and slip motions that are located to the north of the northern Tibetan Plateau. Despite growing understanding of the geometry and kinematics of these active faults, the late Quaternary deformation pattern in the Hexi Corridor and the southern Gobi Alashan remains controversial. The active E-W trending Taohuala Shan-Ayouqi fault zone is located in the southern Gobi Alashan. Study of the geometry and nature of slip along this fault zone holds crucial value for better understanding the regional deformation pattern. Field investigations combined with high-resolution imagery show that the Taohuala Shan fault and the E-W trending faults within the Ayouqi fault zone (F2 and F5) are left-lateral strike-slip faults, whereas the NW or WNW-trending faults within the Ayouqi fault zone (F1 and F3) are reverse faults. We collected Optically Stimulated Luminescence (OSL) and cosmogenic exposure age dating samples from offset alluvial fan surfaces, and estimated a vertical slip rate of 0.1-0.3 mm/yr, and a strike-slip rate of 0.14-0.93 mm/yr for the Taohuala Shan fault. Strata revealed in a trench excavated across the major fault (F5) in the Ayouqi fault zone and OSL dating results indicate that the most recent earthquake occurred between ca. 11.05 ± 0.52 ka and ca. 4.06 ± 0.29 ka. The geometry and kinematics of the Taohuala Shan-Ayouqi fault zone enable us to build a deformation pattern for the entire Hexi Corridor and the southern Gobi Alashan, which suggest that this region experiences northeastward oblique extrusion of the northern Tibetan Plateau. These left-lateral strike-slip faults in the region are driven by oblique compression but not associated with the northeastward extension of the Altyn Tagh fault.

  9. Global strike-slip fault distribution on Enceladus reveals mostly left-lateral faults

    NASA Astrophysics Data System (ADS)

    Martin, E. S.; Kattenhorn, S. A.

    2013-12-01

    Within the outer solar system, normal faults are a dominant tectonic feature; however, strike-slip faults have played a role in modifying the surfaces of many icy bodies, including Europa, Ganymede, and Enceladus. Large-scale tectonic deformation in icy shells develops in response to stresses caused by a range of mechanisms including polar wander, despinning, volume changes, orbital recession/decay, diurnal tides, and nonsynchronous rotation (NSR). Icy shells often preserve this record of tectonic deformation as patterns of fractures that can be used to identify the source of stress responsible for creating the patterns. Previously published work on Jupiter's moon Europa found that right-lateral strike-slip faults predominantly formed in the southern hemisphere and left-lateral strike-slip faults in the northern hemisphere. This pattern suggested they were formed in the past by stresses induced by diurnal tidal forcing, and were then rotated into their current longitudinal positions by NSR. We mapped the distribution of strike-slip faults on Enceladus and used kinematic indicators, including tailcracks and en echelon fractures, to determine their sense of slip. Tailcracks are secondary fractures that form as a result of concentrations of stress at the tips of slipping faults with geometric patterns dictated by the slip sense. A total of 31 strike-slip faults were identified, nine of which were right-lateral faults, all distributed in a seemingly random pattern across Enceladus's surface, in contrast to Europa. Additionally, there is a dearth of strike-slip faults within the tectonized terrains centered at 90°W and within the polar regions north and south of 60°N and 60°S, respectively. The lack of strike-slip faults in the north polar region may be explained, in part, by limited data coverage. The south polar terrain (SPT), characterized by the prominent tiger stripes and south polar dichotomy, yielded no discrete strike-slip faults. This does not suggest that

  10. San Andreas-sized Strike-slip Fault on Europa

    NASA Technical Reports Server (NTRS)

    1998-01-01

    This mosaic of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, about the size of the California portion of the San Andreas fault, which runs from the California-Mexico border north to the San Francisco Bay.

    In a strike-slip fault, two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. Overall motion along the fault seems to have followed a continuous narrow crack along the feature's entire length, with a path resembling steps on a staircase crossing zones that have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. The fault's opposite sides can be reconstructed like a puzzle, matching the shape of the sides and older, individual cracks and ridges broken by its movements.

    [figure removed for brevity, see original site]

    The red line marks the once active central crack of the fault. The black line outlines the fault zone, including material accumulated in the regions which have been pulled apart.

    Bends in the fault have allowed the surface to be pulled apart. This process created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling-apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, in Death Valley and the Dead Sea. In those cases, the pulled-apart regions can include upwelled materials, but may be filled mostly by sedimentary and eroded material from above.

    One theory is that fault motion on Europa is induced by the pull of variable daily tides generated by Jupiter's gravitational tug on Europa. Tidal tension

  11. Deformation in Neogene sediments of the Sorbas and Vera Basins (SE Spain): constraints on simple-shear deformation and rigid body rotation along major strike-slip faults

    NASA Astrophysics Data System (ADS)

    Jonk, R.; Biermann, C.

    2002-05-01

    Detailed structural analyses are presented of the Neogene Sorbas Basin adjacent to the E-W striking Gafarillos fault zone and the Vera Basin adjacent to the 020° striking Palomares fault zone in southeastern Spain. A stress regime with an E-W oriented subhorizontal maximum principal stress ( σ1) existed in pre-Tortonian (>11.3 Ma) time. A strike-slip regime with NW-SE oriented compression during Tortonian and earliest Messinian time caused dextral displacement along the E-W trending Gafarillos fault of approximately 10 km. Structural analysis indicates that most displacement took place in the Early Tortonian. Deformational patterns within the adjacent pull-apart basin reflect a dextral simple shear-zone of at least 500 m width. Kinematical analysis of folds in the Sorbas Basin suggests, however, that rotational effects are largely caused by rigid-body rotation without much internal deformation. Sinistral strike-slip displacements occurred along the Palomares fault zone under the influence of the same stress-regime. An abrupt change in the orientation of the stress field to N-S directed compression in earliest Messinian time (6.5 Ma) caused the termination of displacements along the Gafarillos fault zone, whereas the 020° trending Palomares fault zone continued to accumulate sinistral strike-slip displacements of about 25 km. Volcanism occurred along splays of the fault zone. A wider shear-zone of a few kilometers width evolved, in which considerable anti-clockwise rotation of folds occurred. Kinematic analysis of these folds shows that these rotational effects are again dominantly rigid-body rotations. Assuming rotations are merely caused by simple-shear deformation overestimates the amounts of strain. A better way to deal with simple-shear deformation is to compare observed shortening caused by folding with the magnitude of rotation of fold-hinges.

  12. Quantifying Vertical Exhumation in Intracontinental Strike-Slip Faults: the Garlock fault zone, southern California

    NASA Astrophysics Data System (ADS)

    Chinn, L.; Blythe, A. E.; Fendick, A.

    2012-12-01

    New apatite fission-track ages show varying rates of vertical exhumation at the eastern terminus of the Garlock fault zone. The Garlock fault zone is a 260 km long east-northeast striking strike-slip fault with as much as 64 km of sinistral offset. The Garlock fault zone terminates in the east in the Avawatz Mountains, at the intersection with the dextral Southern Death Valley fault zone. Although motion along the Garlock fault west of the Avawatz Mountains is considered purely strike-slip, uplift and exhumation of bedrock in the Avawatz Mountains south of the Garlock fault, as recently as 5 Ma, indicates that transpression plays an important role at this location and is perhaps related to a restricting bend as the fault wraps around and terminates southeastward along the Avawatz Mountains. In this study we complement extant thermochronometric ages from within the Avawatz core with new low temperature fission-track ages from samples collected within the adjacent Garlock and Southern Death Valley fault zones. These thermochronometric data indicate that vertical exhumation rates vary within the fault zone. Two Miocene ages (10.2 (+5.0/-3.4) Ma, 9.0 (+2.2/-1.8) Ma) indicate at least ~3.3 km of vertical exhumation at ~0.35 mm/yr, assuming a 30°C/km geothermal gradient, along a 2 km transect parallel and adjacent to the Mule Spring fault. An older Eocene age (42.9 (+8.7/-7.3) Ma) indicates ~3.3 km of vertical exhumation at ~0.08 mm/yr. These results are consistent with published exhumation rates of 0.35 mm/yr between ~7 and ~4 Ma and 0.13 mm/yr between ~15 and ~9 Ma, as determined by apatite fission-track and U-Th/He thermochronometry in the hanging-wall of the Mule Spring fault. Similar exhumation rates on both sides of the Mule Spring fault support three separate models: 1) Thrusting is no longer active along the Mule Spring fault, 2) Faulting is dominantly strike-slip at the sample locations, or 3) Miocene-present uplift and exhumation is below detection levels

  13. Late Pleistocene, Holocene, and decadal constancy of slip-rate of the Doruneh strike-slip fault, Iran.

    NASA Astrophysics Data System (ADS)

    Walker, R. T.; Fattahi, M.; Mousavi, Z.; Pathier, E.; Sloan, R. A.; Talebian, M.; Thomas, A. L.; Walpersdorf, A.

    2014-12-01

    The Doruneh left-lateral strike-slip fault of NE Iran has a prominent expression in the landscape, showing that the fault is active in the late Quaternary. Existing estimates of its slip-rate vary, however, which has led to suggestions that it may exhibit temporal changes in activity. Using high-resolution optical satellite imagery we make reconstructions of displacement across four alluvial fans that cross the Doruneh fault, and determine the ages of these fans using luminescence dating, combined with U-series dating of pedogenic carbonates in one case. The four fans, which vary in age from 10-100 kyr, yield estimates of slip rate of ~2-3 mm/yr. We compare the average slip-rate measurements to the rate of accumulation of strain across the Doruneh fault using GPS and InSAR measurements, and find that the slip-rate is likely to have remained constant - within the uncertainty of our measurements - over the last ~100 ka. The slip-rate that we measure is consistent with the E-W left-lateral Doruneh fault accommodating N-S right-lateral faulting by 'bookshelf' faulting, with clockwise rotation about a vertical axis, in a similar manner to the Eastern California Shear Zone.

  14. New paleomagnetic constraints on middle Miocene strike-slip faulting along the middle Altyn Tagh Fault

    NASA Astrophysics Data System (ADS)

    Li, Bingshuai; Yan, Maodu; Zhang, Weilin; Fang, Xiaomin; Meng, Qingquan; Zan, Jinbo; Chen, Yi; Zhang, Dawen; Yang, Yongpeng; Guan, Chong

    2017-06-01

    Knowledge of the evolution of the Altyn Tagh Fault (ATF) has significant implications for our understanding of the tectonic deformation of the Tibetan Plateau. Controversy exists regarding the formation of the orocline-like arcuate structures or curved thrust faults south of the ATF. In this paper, we conducted a paleomagnetic rotation study of the Akatengnengshan (AK) and Youshashan (YSS) anticlines to determine whether the changes in the anticlines' axes were caused by frictional drag associated with sinistral strike-slip faulting along the ATF. No significant paleomagnetic rotations during the last 20 Ma were observed at the Xichagou and Laomangai localities, which are situated along the YSS anticline, whereas significant counterclockwise (CCW) rotations of 50° that occurred between 16.2 and 11.1 Ma were noted at the Yitunbulake locality, which lies along the western edge of the AK anticline. This amount of CCW rotation is consistent with the difference in axes between the AK and YSS anticlines. Combined with other geological evidence, we believe that the middle ATF was active between 16 and 11 Ma. Frictional drag associated with sinistral strike-slip motion likely resulted in the 50° CCW rotation of the AK anticline, which was originally straight or parallel to the YSS anticline. There was concentrated or insignificant strike-slip faulting along the middle ATF before 16 Ma, but rapid and distributed (< 40 km) strike-slip faulting occurred between 16 and 11 Ma at a rate of ≥10 mm/yr, and the minimum displacement was 50 km.

  15. Strike-slip faulting of ridged plains near Valles Marineris, Mars

    NASA Astrophysics Data System (ADS)

    Schultz, R. A.

    1989-10-01

    This paper identifies and documents several well-preserved examples of Martian strike-slip faults and examines their relationships to wrinkle-ridges. The strike-slip faulting predates or overlaps periods of wrinkle-ridge growth southeast of Valles Marineris, and some wrinkle ridges may have nucleated and grown as a result of strike-slip displacements along the echelon fault arrays. Lateral displacements of several km inferred along these arrays may be related to tectonism in Tharsis.

  16. Influence of fault steps on rupture termination of strike-slip earthquake faults

    NASA Astrophysics Data System (ADS)

    Li, Zhengfang; Zhou, Bengang

    2018-03-01

    A statistical analysis was completed on the rupture data of 29 historical strike-slip earthquakes across the world. The purpose of this study is to examine the effects of fault steps on the rupture termination of these events. The results show good correlations between the type and length of steps with the seismic rupture and a poor correlation between the step number and seismic rupture. For different magnitude intervals, the smallest widths of the fault steps (Lt) that can terminate the rupture propagation are variable: Lt = 3 km for Ms 6.5 6.9, Lt = 4 km for Ms 7.0 7.5, Lt = 6 km for Ms 7.5 8.0, and Lt = 8 km for Ms 8.0 8.5. The dilational fault step is easier to rupture through than the compression fault step. The smallest widths of the fault step for the rupture arrest can be used as an indicator to judge the scale of the rupture termination of seismic faults. This is helpful for research on fault segmentation, as well as estimating the magnitude of potential earthquakes, and is thus of significance for the assessment of seismic risks.

  17. 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.

  18. Kinematics of rotating panels of E-W faults in the San Andreas system: what can we tell from geodesy?

    NASA Astrophysics Data System (ADS)

    Platt, J. P.; Becker, T. W.

    2013-09-01

    Sets of E- to NE-trending sinistral and/or reverse faults occur within the San Andreas system, and are associated with palaeomagnetic evidence for clockwise vertical-axis rotations. These structures cut across the trend of active dextral faults, posing questions as to how displacement is transferred across them. Geodetic data show that they lie within an overall dextral shear field, but the data are commonly interpreted to indicate little or no slip, nor any significant rate of rotation. We model these structures as rotating by bookshelf slip in a dextral shear field, and show that a combination of sinistral slip and rotation can produce the observed velocity field. This allows prediction of rates of slip, rotation, fault-parallel extension and fault-normal shortening within the panel. We use this method to calculate the kinematics of the central segment of the Garlock Fault, which cuts across the eastern California shear zone at a high angle. We obtain a sinistral slip rate of 6.1 ± 1.1 mm yr-1, comparable to geological evidence, but higher than most previous geodetic estimates, and a rotation rate of 4.0 ± 0.7° Myr-1 clockwise. The western Transverse Ranges transect a similar shear zone in coastal and offshore California, but at an angle of only 40°. As a result, the faults, which were sinistral when they were at a higher angle to the shear zone, have been reactivated in a dextral sense at a low rate, and the rate of rotation of the panel has decreased from its long-term rate of ˜5° to 1.6° ± 0.2° Myr-1 clockwise. These results help to resolve some of the apparent discrepancies between geological and geodetic slip-rate estimates, and provide an enhanced understanding of the mechanics of intracontinental transform systems.

  19. Coulomb Fault Mechanics at Work in the Proterozoic: Strike-Slip Faults and Regional-Scale Veining in the Mt. Isa Inlier, Australia

    NASA Astrophysics Data System (ADS)

    Begbie, M. J.; Sibson, R. H.; Ghisetti, F. C.

    2005-12-01

    The Proterozoic Mt Isa inlier, comprising greenschist to amphibolite facies metamorphic assemblages intruded by granites during the Isan Orogeny (1590-1500 Ma), is disrupted by brittle, late- or post-orogenic strike-slip faults. The faults occur in two mutually cross-cutting sets; a set of NE-SW subvertical dextral strike-slip faults, and a conjugate set of NW-SE sinistral faults. These faults thus define a regional stress field with σ1 oriented approximately E-W and σ3 oriented approximately N-S. Locally, the faults outcrop as linear blade-like ridges of silicified microbreccias-cataclasites and quartz veining that extends for kilometres across the semi-arid terrain. The informally named Spinifex Fault is one of the dextral set of subvertical faults. This fault is a classic example of coulomb fault mechanics at work in the Proterozoic. The Spinifex Fault trends ~065° across an outcropping granitic pluton, the margins of which it offsets dextrally by ~0.75 km. Locally within the pluton, the fault refracts to ~075° across an amphibolite layer. In the surrounding granitic pluton the fault trace is comparatively inconspicuous and unmineralized but where it transects the amphibolite it is defined by an upstanding ridge of silicified microbreccia-cataclasite (~10 m thick). Associated with the Spinifex Fault is a swarm of predominantly extensional subvertical quartz veins (cm to m thick) trending 090-95° and a series of mineralised fault splays trending 070-080°. Extension veins define the σ1-σ2 plane, with the Spinifex fault lying at an angle of ~25-30° to the inferred σ1. These veins are composed of colloform and crustiform banded quartz, brecciated fragments of quartz vein and wallrock that are typically rimmed with cockade overgrowths and bladed quartz after calcite pseudomorphs. Mineralised fault splays are < 50 m or so wide with a composite brittle fabric comprising: (1) bounding subvertical cataclastic `walls' <10 m or so thick made up of silicified

  20. Geomorphic expression of strike-slip faults: field observations vs. analog experiments: preliminary results

    NASA Astrophysics Data System (ADS)

    Hsieh, S. Y.; Neubauer, F.; Genser, J.

    2012-04-01

    The aim of this project is to study the surface expression of strike-slip faults with main aim to find rules how these structures can be extrapolated to depth. In the first step, several basic properties of the fault architecture are in focus: (1) Is it possible to define the fault architecture by studying surface structures of the damage zone vs. the fault core, particularly the width of the damage zone? (2) Which second order structures define the damage zone of strike-slip faults, and how relate these to such reported in basement fault strike-slip analog experiments? (3) Beside classical fault bend structures, is there a systematic along-strike variation of the damage zone width and to which properties relates the variation of the damage zone width. We study the above mentioned properties on the dextral Altyn fault, which is one of the largest strike-slip on Earth with the advantage to have developed in a fully arid climate. The Altyn fault includes a ca. 250 to 600 m wide fault valley, usually with the trace of actual fault in its center. The fault valley is confined by basement highs, from which alluvial fans develop towards the center of the fault valley. The active fault trace is marked by small scale pressure ridges and offset of alluvial fans. The fault valley confining basement highs are several kilometer long and ca. 0.5 to 1 km wide and confined by rotated dextral anti-Riedel faults and internally structured by a regular fracture pattern. Dextral anti-Riedel faults are often cut by Riedel faults. Consequently, the Altyn fault comprises a several km wide damage zone. The fault core zone is a barrier to fluid flow, and the few springs of the region are located on the margin of the fault valley implying the fractured basement highs as the reservoir. Consequently, the southern Silk Road was using the Altyn fault valley. The preliminary data show that two or more orders of structures exist. Small-scale develop during a single earthquake. These finally

  1. The San Andreas Fault and a Strike-slip Fault on Europa

    NASA Technical Reports Server (NTRS)

    1998-01-01

    The mosaic on the right of the south polar region of Jupiter's moon Europa shows the northern 290 kilometers (180 miles) of a strike-slip fault named Astypalaea Linea. The entire fault is about 810 kilometers (500 miles) long, the size of the California portion of the San Andreas fault on Earth which runs from the California-Mexico border north to the San Francisco Bay.

    The left mosaic shows the portion of the San Andreas fault near California's san Francisco Bay that has been scaled to the same size and resolution as the Europa image. Each covers an area approximately 170 by 193 kilometers(105 by 120 miles). The red line marks the once active central crack of the Europan fault (right) and the line of the San Andreas fault (left).

    A strike-slip fault is one in which two crustal blocks move horizontally past one another, similar to two opposing lanes of traffic. The overall motion along the Europan fault seems to have followed a continuous narrow crack along the entire length of the feature, with a path resembling stepson a staircase crossing zones which have been pulled apart. The images show that about 50 kilometers (30 miles) of displacement have taken place along the fault. Opposite sides of the fault can be reconstructed like a puzzle, matching the shape of the sides as well as older individual cracks and ridges that had been broken by its movements.

    Bends in the Europan fault have allowed the surface to be pulled apart. This pulling-apart along the fault's bends created openings through which warmer, softer ice from below Europa's brittle ice shell surface, or frozen water from a possible subsurface ocean, could reach the surface. This upwelling of material formed large areas of new ice within the boundaries of the original fault. A similar pulling apart phenomenon can be observed in the geological trough surrounding California's Salton Sea, and in Death Valley and the Dead Sea. In those cases, the pulled apart regions can include upwelled

  2. Three-dimensional models of deformation near strike-slip faults

    USGS Publications Warehouse

    ten Brink, Uri S.; Katzman, Rafael; Lin, J.

    1996-01-01

    We use three-dimensional elastic models to help guide the kinematic interpretation of crustal deformation associated with strike-slip faults. Deformation of the brittle upper crust in the vicinity of strike-slip fault systems is modeled with the assumption that upper crustal deformation is driven by the relative plate motion in the upper mantle. The driving motion is represented by displacement that is specified on the bottom of a 15-km-thick elastic upper crust everywhere except in a zone of finite width in the vicinity of the faults, which we term the "shear zone." Stress-free basal boundary conditions are specified within the shear zone. The basal driving displacement is either pure strike slip or strike slip with a small oblique component, and the geometry of the fault system includes a single fault, several parallel faults, and overlapping en echelon faults. We examine the variations in deformation due to changes in the width of the shear zone and due to changes in the shear strength of the faults. In models with weak faults the width of the shear zone has a considerable effect on the surficial extent and amplitude of the vertical and horizontal deformation and on the amount of rotation around horizontal and vertical axes. Strong fault models have more localized deformation at the tip of the faults, and the deformation is partly distributed outside the fault zone. The dimensions of large basins along strike-slip faults, such as the Rukwa and Dead Sea basins, and the absence of uplift around pull-apart basins fit models with weak faults better than models with strong faults. Our models also suggest that the length-to-width ratio of pull-apart basins depends on the width of the shear zone and the shear strength of the faults and is not constant as previously suggested. We show that pure strike-slip motion can produce tectonic features, such as elongate half grabens along a single fault, rotated blocks at the ends of parallel faults, or extension perpendicular to

  3. Three-dimensional models of deformation near strike-slip faults

    USGS Publications Warehouse

    ten Brink, Uri S.; Katzman, Rafael; Lin, Jian

    1996-01-01

    We use three-dimensional elastic models to help guide the kinematic interpretation of crustal deformation associated with strike-slip faults. Deformation of the brittle upper crust in the vicinity of strike-slip fault systems is modeled with the assumption that upper crustal deformation is driven by the relative plate motion in the upper mantle. The driving motion is represented by displacement that is specified on the bottom of a 15-km-thick elastic upper crust everywhere except in a zone of finite width in the vicinity of the faults, which we term the “shear zone.” Stress-free basal boundary conditions are specified within the shear zone. The basal driving displacement is either pure strike slip or strike slip with a small oblique component, and the geometry of the fault system includes a single fault, several parallel faults, and overlapping en echelon faults. We examine the variations in deformation due to changes in the width of the shear zone and due to changes in the shear strength of the faults. In models with weak faults the width of the shear zone has a considerable effect on the surficial extent and amplitude of the vertical and horizontal deformation and on the amount of rotation around horizontal and vertical axes. Strong fault models have more localized deformation at the tip of the faults, and the deformation is partly distributed outside the fault zone. The dimensions of large basins along strike-slip faults, such as the Rukwa and Dead Sea basins, and the absence of uplift around pull-apart basins fit models with weak faults better than models with strong faults. Our models also suggest that the length-to-width ratio of pull-apart basins depends on the width of the shear zone and the shear strength of the faults and is not constant as previously suggested. We show that pure strike-slip motion can produce tectonic features, such as elongate half grabens along a single fault, rotated blocks at the ends of parallel faults, or extension

  4. Strike-slip faults in the Moroccan Rif: Their geophysical signatures and hydrocarbon potential

    SciTech Connect

    Jobidon, G.P.; Dakki, M.

    1994-12-31

    The Rif Domain in Northern Morocco includes major movements along left-lateral strike-slips faults that created various structures and influenced depositional systems. The major ones are the Jebha fault in the Rif`s northwest area, and the Nekkor fault that extends southwesterly from the Mediterranean sea toward the Meseta. Although identified by surface geology in the east, the western extent of the faults is ambiguous. Detail interpretation of gravity and magnetic maps provide a better definition of their locations and related structures. The Rif`s geology is a mirror image of the right-lateral strike-slip fault system of Venezuela and Trinidad. Most features associatedmore » with the Rif`s strike-slip faults have not been explored to data and hydrocarbon potential remains a good possibility.« less

  5. 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

  6. Mechanics of slip and fracture along small faults and simple strike-slip fault zones in granitic rock

    NASA Astrophysics Data System (ADS)

    Martel, Stephen J.; Pollard, David D.

    1989-07-01

    We exploit quasi-static fracture mechanics models for slip along pre-existing faults to account for the fracture structure observed along small exhumed faults and small segmented fault zones in the Mount Abbot quadrangle of California and to estimate stress drop and shear fracture energy from geological field measurements. Along small strike-slip faults, cracks that splay from the faults are common only near fault ends. In contrast, many cracks splay from the boundary faults at the edges of a simple fault zone. Except near segment ends, the cracks preferentially splay into a zone. We infer that shear displacement discontinuities (slip patches) along a small fault propagated to near the fault ends and caused fracturing there. Based on elastic stress analyses, we suggest that slip on one boundary fault triggered slip on the adjacent boundary fault, and that the subsequent interaction of the slip patches preferentially led to the generation of fractures that splayed into the zones away from segment ends and out of the zones near segment ends. We estimate the average stress drops for slip events along the fault zones as ˜1 MPa and the shear fracture energy release rate during slip as 5 × 102 - 2 × 104 J/m2. This estimate is similar to those obtained from shear fracture of laboratory samples, but orders of magnitude less than those for large fault zones. These results suggest that the shear fracture energy release rate increases as the structural complexity of fault zones increases.

  7. Long term fault system reorganization of convergent and strike-slip systems

    NASA Astrophysics Data System (ADS)

    Cooke, M. L.; McBeck, J.; Hatem, A. E.; Toeneboehn, K.; Beyer, J. L.

    2017-12-01

    Laboratory and numerical experiments representing deformation over many earthquake cycles demonstrate that fault evolution includes episodes of fault reorganization that optimize work on the fault system. Consequently, the mechanical and kinematic efficiencies of fault systems do not increase monotonically through their evolution. New fault configurations can optimize the external work required to accommodate deformation, suggesting that changes in system efficiency can drive fault reorganization. Laboratory evidence and numerical results show that fault reorganization within accretion, strike-slip and oblique convergent systems is associated with increasing efficiency due to increased fault slip (frictional work and seismic energy) and commensurate decreased off-fault deformation (internal work and work against gravity). Between episodes of fault reorganization, fault systems may become less efficient as they produce increasing off fault deformation. For example, laboratory and numerical experiments show that the interference and interaction between different fault segments may increase local internal work or that increasing convergence can increase work against gravity produced by a fault system. This accumulation of work triggers fault reorganization as stored work provides the energy required to grow new faults that reorganize the system to a more efficient configuration. The results of laboratory and numerical experiments reveal that we should expect crustal fault systems to reorganize following periods of increasing inefficiency, even in the absence of changes to the tectonic regime. In other words, fault reorganization doesn't require a change in tectonic loading. The time frame of fault reorganization depends on fault system configuration, strain rate and processes that relax stresses within the crust. For example, stress relaxation may keep pace with stress accumulation, which would limit the increase in the internal work and gravitational work so that

  8. Analytic Study of Three-Dimensional Rupture Propagation in Strike-Slip Faulting with Analogue Models

    NASA Astrophysics Data System (ADS)

    Chan, Pei-Chen; Chu, Sheng-Shin; Lin, Ming-Lang

    2014-05-01

    Strike-slip faults are high angle (or nearly vertical) fractures where the blocks have moved along strike way (nearly horizontal). Overburden soil profiles across main faults of Strike-slip faults have revealed the palm and tulip structure characteristics. McCalpin (2005) has trace rupture propagation on overburden soil surface. In this study, we used different offset of slip sandbox model profiles to study the evolution of three-dimensional rupture propagation by strike -slip faulting. In strike-slip faults model, type of rupture propagation and width of shear zone (W) are primary affecting by depth of overburden layer (H), distances of fault slip (Sy). There are few research to trace of three-dimensional rupture behavior and propagation. Therefore, in this simplified sandbox model, investigate rupture propagation and shear zone with profiles across main faults when formation are affecting by depth of overburden layer and distances of fault slip. The investigators at the model included width of shear zone, length of rupture (L), angle of rupture (θ) and space of rupture. The surface results was follow the literature that the evolution sequence of failure envelope was R-faults, P-faults and Y-faults which are parallel to the basement fault. Comparison surface and profiles structure which were curved faces and cross each other to define 3-D rupture and width of shear zone. We found that an increase in fault slip could result in a greater width of shear zone, and proposed a W/H versus Sy/H relationship. Deformation of shear zone showed a similar trend as in the literature that the increase of fault slip resulted in the increase of W, however, the increasing trend became opposite after a peak (when Sy/H was 1) value of W was reached (small than 1.5). The results showed that the W width is limited at a constant value in 3-D models by strike-slip faulting. In conclusion, this study helps evaluate the extensions of the shear zone influenced regions for strike

  9. Subsurface Resistivity Structures in and Around Strike-Slip Faults - Electromagnetic Surveys and Drillings Across Active Faults in Central Japan -

    NASA Astrophysics Data System (ADS)

    Omura, K.; Ikeda, R.; Iio, Y.; Matsuda, T.

    2005-12-01

    Electrical resistivity is important property to investigate the structure of active faults. Pore fluid affect seriously the electrical properties of rocks, subsurface electrical resistivity can be an indicator of the existence of fluid and distribution of pores. Fracture zone of fault is expected to have low resistivity due to high porosity and small gain size. Especially, strike-slip type fault has nearly vertical fracture zone and the fracture zone would be detected by an electrical survey across the fault. We performed electromagnetic survey across the strike-slip active faults in central Japan. At the same faults, we also drilled borehole into the fault and did downhole logging in the borehole. We applied MT or CSAMT methods onto 5 faults: Nojima fault which appeared on the surface by the 1995 Great Kobe earthquake (M=7.2), western Nagano Ohtaki area(1984 Nagano-ken seibu earthquake (M=6.8), the fault did not appeared on the surface), Neodani fault which appeared by the 1891 Nobi earthquake (M=8.0), Atera fault which seemed to be dislocated by the 1586 Tensyo earthquake (M=7.9), Gofukuji fault that is considered to have activated about 1200 years ago. The sampling frequencies of electrical and magnetic field were 2 - 1024Hz (10 frequencies) for CSAMT survey and 0.00055 - 384Hz (40 frequencies) for MT survey. The electromagnetic data were processed by standard method and inverted to 2-D resistivity structure along transects of the faults. Results of the survey were compared with downhole electrical logging data and observational descriptions of drilled cores. Fault plane of each fault were recognized as low resistivity region or boundary between relatively low and high resistivity region, except for Gofukuji fault. As for Gofukuji fault, fault was located in relatively high resistivity region. During very long elapsed time from the last earthquake, the properties of fracture zone of Gofukuji fault might changed from low resistivity properties as observed for

  10. Strike-slip faulting at Thebes Gap, Missouri and Illinois; implications for New Madrid tectonism

    USGS Publications Warehouse

    Harrison, Richard W.; Schultz, Art

    1994-01-01

    Numerous NNE and NE striking strike-slip faults and associated normal faults, folds, and transtensional grabens occur in the Thebes Gap area of Missouri and Illinois. These structures developed along the northwestern margin of the buried Reelfoot rift of Precambrian-Cambrian age at the northern edge of the Mississippi embayment. They have had a long-lived and complex structural history. This is an area of recent moderate seismicity, approximately 45 km north of the New Madrid seismic zone. Stratigraphic evidence suggests that these faults were active during the Middle Ordovician. They were subsequently reactivated between the Early Devonian and Late Cretaceous, probably in response to both the Acadian and Ouachita orogenies. Deformation during this period was characterized by strongly faulted and folded Ordovician through Devonian rocks. In places, these deformed rocks are overlain with angular unconformity by undeformed Cretaceous strata. Fault motion is interpreted as dominantly strike slip. A still younger period of reactivation involved Late Cretaceous and Cenozoic formations as young as the Miocene or Pliocene Mounds Gravel. These formations have experienced both minor high-angle normal faulting and subsequent major, right-lateral strike-slip faulting. En echelon north-south folds, ENE striking normal faults, regional fracture patterns, and drag folds indicate the right-lateral motion for this major episode of faulting which predates deposition of Quaternary loess. Several nondefinitive lines of evidence suggest Quaternary faulting. Similar fault orientations and kinematics, as well as recent seismicity and proximity, clearly suggest a structural relationship between deformation at Thebes Gap and tectonism associated with the New Madrid area.

  11. Large-scale splay faults on a strike-slip fault system: The Yakima Folds, Washington State

    USGS Publications Warehouse

    Pratt, Thomas L.

    2012-01-01

    The Yakima Folds (YF) comprise anticlines above reverse faults cutting flows of the Miocene Columbia River Basalt Group of central Washington State. The YF are bisected by the ~1100-km-long Olympic-Wallowa Lineament (OWL), which is an alignment of topographic features including known faults. There is considerable debate about the origin and earthquake potential of both the YF and OWL, which lie near six major dams and a large nuclear waste storage site. Here I show that the trends of the faults forming the YF relative to the OWL match remarkably well the trends of the principal stress directions at the end of a vertical strike-slip fault. This comparison and the termination of some YF against the OWL are consistent with the YF initially forming as splay faults caused by an along-strike decrease in the amount of strike-slip on the OWL. The hypothesis is that the YF faults initially developed as splay faults in the early to mid Miocene under NNW-oriented principal compressive stress, but the anticlines subsequently grew with thrust motion after the principal compressive stress direction rotated to N-S or NNE after the mid-Miocene. A seismic profile across one of the YF anticlines shows folding at about 7 km depth, indicating deformation of sub-basalt strata. The seismic profile and the hypothesized relationship between the YF and the OWL suggest that the structures are connected in the middle or lower crust, and that the faults forming the YF are large-scale splay faults associated with a major strike-slip fault system.

  12. The Role of Near-Fault Relief in Creating and Maintaining Strike-Slip Landscape Features

    NASA Astrophysics Data System (ADS)

    Harbert, S.; Duvall, A. R.; Tucker, G. E.

    2016-12-01

    Geomorphic landforms, such as shutter ridges, offset river terraces, and deflected stream channels, are often used to assess the activity and slip rates of strike-slip faults. However, in some systems, such as parts of the Marlborough Fault System (South Island, NZ), an active strike-slip fault does not leave a strong landscape signature. Here we explore the factors that dampen or enhance the landscape signature of strike-slip faulting using the Channel-Hillslope Integrated Landscape Development model (CHILD). We focus on variables affecting the length of channel offsets, which enhance the signature of strike-slip motion, and the frequency of stream captures, which eliminate offsets and reduce this signature. We model a strike-slip fault that passes through a mountain ridge, offsetting streams that drain across this fault. We use this setup to test the response of channel offset length and capture frequency to fault characteristics, such as slip rate and ratio of lateral to vertical motion, and to landscape characteristics, such as relief contrasts controlled by erodibility. Our experiments show that relief downhill of the fault, whether generated by differential uplift across the fault or by an erodibility contrast, has the strongest effect on offset length and capture frequency. This relief creates shutter ridges, which block and divert streams while being advected along a fault. Shutter ridges and the streams they divert have long been recognized as markers of strike-slip motion. Our results show specifically that the height of shutter ridges is most responsible for the degree to which they create long channel offsets by preventing stream captures. We compare these results to landscape metrics in the Marlborough Fault System, where shutter ridges are common and often lithologically controlled. We compare shutter ridge length and height to channel offset length in order to assess the influence of relief on offset channel features in a real landscape. Based on our

  13. Structures associated with strike-slip faults that bound landslide elements

    USGS Publications Warehouse

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

    1989-01-01

    Large landslides are bounded on their flanks and on elements within the landslides by structures analogous to strike-slip faults. We observed the formation of thwse strike-slip faults and associated structures at two large landslides in central Utah during 1983-1985. The strike-slip faults in landslides are nearly vertical but locally may dip a few degrees toward or away from the moving ground. Fault surfaces are slickensided, and striations are subparallel to the ground surface. Displacement along strike-slip faults commonly produces scarps; scarps occur where local relief of the failure surface or ground surface is displaced and becomes adjacent to higher or lower ground, or where the landslide is thickening or thinning as a result of internal deformation. Several types of structures are formed at the ground surface as a strike-slip fault, which is fully developed at some depth below the ground surface, propagates upward in response to displacement. The simplest structure is a tension crack oriented at 45?? clockwise or counterclockwise from the trend of an underlying right- or left-lateral strike-slip fault, respectively. The tension cracks are typically arranged en echelon with the row of cracks parallel to the trace of the underlying strike-slip fault. Another common structure that forms above a developing strike-slip fault is a fault segment. Fault segments are discontinuous strike-slip faults that contain the same sense of slip but are turned clockwise or counterclockwise from a few to perhaps 20?? from the underlying strike-slip fault. The fault segments are slickensided and striated a few centimeters below the ground surface; continued displacement of the landslide causes the fault segments to open and a short tension crack propagates out of one or both ends of the fault segments. These structures, open fault segments containing a short tension crack, are termed compound cracks; and the short tension crack that propagates from the tip of the fault segment

  14. Influence of fault trend, fault bends, and fault convergence on shallow structure, geomorphology, and hazards, Hosgri strike-slip fault, offshore central California

    NASA Astrophysics Data System (ADS)

    Johnson, S. Y.; Watt, J. T.; Hartwell, S. R.

    2012-12-01

    We mapped a ~94-km-long portion of the right-lateral Hosgri Fault Zone from Point Sal to Piedras Blancas in offshore central California using high-resolution seismic reflection profiles, marine magnetic data, and multibeam bathymetry. The database includes 121 seismic profiles across the fault zone and is perhaps the most comprehensive reported survey of the shallow structure of an active strike-slip fault. These data document the location, length, and near-surface continuity of multiple fault strands, highlight fault-zone heterogeneity, and demonstrate the importance of fault trend, fault bends, and fault convergences in the development of shallow structure and tectonic geomorphology. The Hosgri Fault Zone is continuous through the study area passing through a broad arc in which fault trend changes from about 338° to 328° from south to north. The southern ~40 km of the fault zone in this area is more extensional, resulting in accommodation space that is filled by deltaic sediments of the Santa Maria River. The central ~24 km of the fault zone is characterized by oblique convergence of the Hosgri Fault Zone with the more northwest-trending Los Osos and Shoreline Faults. Convergence between these faults has resulted in the formation of local restraining and releasing fault bends, transpressive uplifts, and transtensional basins of varying size and morphology. We present a hypothesis that links development of a paired fault bend to indenting and bulging of the Hosgri Fault by a strong crustal block translated to the northwest along the Shoreline Fault. Two diverging Hosgri Fault strands bounding a central uplifted block characterize the northern ~30 km of the Hosgri Fault in this area. The eastern Hosgri strand passes through releasing and restraining bends; the releasing bend is the primary control on development of an elongate, asymmetric, "Lazy Z" sedimentary basin. The western strand of the Hosgri Fault Zone passes through a significant restraining bend and

  15. Geometry and kinematics of adhesive wear in brittle strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Swanson, Mark T.

    2005-05-01

    Detailed outcrop surface mapping in Late Paleozoic cataclastic strike-slip faults of coastal Maine shows that asymmetric sidewall ripouts, 0.1-200 m in length, are a significant component of many mapped faults and an important wall rock deformation mechanism during faulting. The geometry of these structures ranges from simple lenses to elongate slabs cut out of the sidewalls of strike-slip faults by a lateral jump of the active zone of slip during adhesion along a section of the main fault. The new irregular trace of the active fault after this jump creates an indenting asperity that is forced to plow through the adjoining wall rock during continued adhesion or be cut off by renewed motion along the main section of the fault. Ripout translation during adhesion sets up the structural asymmetry with trailing extensional and leading contractional ends to the ripout block. The inactive section of the main fault trace at the trailing end can develop a 'sag' or 'half-graben' type geometry due to block movement along the scallop-shaped connecting ramp to the flanking ripout fault. Leading contractional ramps can develop 'thrust' type imbrication and forces the 'humpback' geometry to the ripout slab due to distortion of the inactive main fault surface by ripout translation. Similar asymmetric ripout geometries are recognized in many other major crustal scale strike-slip fault zones worldwide. Ripout structures in the 5-500 km length range can be found on the Atacama fault system of northern Chile, the Qujiang and Xiaojiang fault zones in western China, the Yalakom-Hozameen fault zone in British Columbia and the San Andreas fault system in southern California. For active crustal-scale faults the surface expression of ripout translation includes a coupled system of extensional trailing ramps as normal oblique-slip faults with pull-apart basin sedimentation and contractional leading ramps as oblique thrust or high angle reverse faults with associated uplift and erosion. The

  16. Astypalaea Linea: A Large-Scale Strike-Slip Fault on Europa

    NASA Astrophysics Data System (ADS)

    Tufts, B. Randall; Greenberg, Richard; Hoppa, Gregory; Geissler, Paul

    1999-09-01

    Astypalaea Linea is an 810-km strike-slip fault, located near the south pole of Europa. In length, it rivals the San Andreas Fault in California, and it is the largest strike-slip fault yet known on Europa. The fault was discovered using Voyager 2 images, based upon the presence of familiar strike-slip features including linearity, pull-aparts, and possible braids, and upon the offset of multiple piercing points. Fault displacement is 42 km, right-lateral, in the southern and central parts and probably throughout. Pull-aparts present along the fault trace probably are gaps in the lithosphere bounded by vertical cracks, and which opened due to fault motion and filled with material from below. Crosscutting relationships suggest the fault to be of intermediate relative age. The fault may have initiated as a crack due to tension from combined diurnal tides and nonsynchronous rotation, according to the tectonic model of R. Greenberg et al. (1998a, Icarus135, 64-78). Under the influence of varying diurnal tides, strike-slip offset may have occurred through a process called “walking,” which depends upon an inelastic lithospheric response to displacement. Alternatively, fault displacement may have been driven by currents in the theorized Europan ocean, which may have created simple shear structures such as braids. The discovery of Astypalaea Linea extends the geographical range of lateral motion on Europa. Such motion requires the presence of a decoupling zone of ductile ice or liquid water, a sufficiently rigid lithosphere, and a mechanism to consume surface area.

  17. Do mesoscale faults near the tip of an active strike-slip fault indicate regional or local stress?

    NASA Astrophysics Data System (ADS)

    Yamaji, Atsushi

    2017-04-01

    Fault-slip analysis is used in Japan after the Great Tohoku Earthquake (2011) to judge the stability of fractures in the foundations of nuclear power plants. In case a fault-slip datum from a fracture surface is explained by the present stress condition, the fracture is thought to have a risk to be activated as a fault. So, it is important to understand the relative significance of regional and local stresses. To answer the question whether mesoscale faults indicate regional or local stress, fault-slip data were collected from the walls of a trenching site of the Nojima Fault in central Japan—an active, dextral, strike-slip fault. The fault gave rise to the 1995 Kobe earthquake, which killed more than 6000 people. The trench was placed near the fault tip, which produced compressional and extensional local stress conditions on the sides of the fault near the tip. A segment of the fault, which ruptured the surface in 1995, bounded Cretaceous granite and latest Pliocene sediments in the trench. As a result, the stress inversion of the data from the mesoscale faults observed in the trench showed both the local stresses. The present WNW-ESE regional compression was found from the compressive side, but was not in the extensional side, probably because local extension surpassed the regional compression. Instead, the regional N-S compression of the Early Pleistocene was found from the extensional side. From this project, we got the lesson that fault-slip analysis reveals regional and local stresses, and that local stress sometimes masks regional one. This work was supported by a science project of "Drilling into Fault Damage Zone" (awarded to A. Lin) of the Secretariat of Nuclear Regulation Authority (Japan).

  18. Characterizing the Alpine Fault Strike Slip System Using a Novel Method for Analyzing GPS Data

    NASA Astrophysics Data System (ADS)

    Haines, A. J.; Dimitrova, L. L.; Wallace, L. M.; Williams, C. A.

    2013-12-01

    Plate motion across the South Island is dominated by right-lateral strike-slip (38-39 mm/yr total in the direction parallel to the Alpine Fault), with a small convergent component (8-10 mm/yr). The Alpine Fault is the most active fault in the region taking up 27×5 mm/yr in right-lateral strike-slip and ~10 mm/yr in dip-slip. It fails in large >=7 Mw earthquakes with recurrence time of 200-400 years and last ruptured around 1717. A significant component of the plate motion budget must occur on faults other than the Alpine Fault, but this is not fully accounted for in catalogues of known active faults. In the central part of the South Island, low slip rate active faults are not well-expressed due to the rapid erosion of the Southern Alps and deposition of these sediments onto the Canterbury plains; the devastating 2010 Darfield earthquake sequence occurred on such previously unknown faults. We apply a novel inversion technique (Dimitrova et al. 2012, 2013) to dense campaign GPS velocities in the region to solve for the vertical derivatives of horizontal stress (VDoHS) rates which are a substantially higher resolution expression of subsurface sources of ongoing deformation than the GPS velocities or GPS derived strain rates. Integrating the VDoHS rates gives us strain rates. Relationships between the VDoHS and strain rates allow us to calculate the variation in fault slip rate and locking depth for the identified faults; e.g., we estimate along fault variations for locking depth and slip rate for the Alpine Fault in the South Island in good agreement with previous estimates, and provide first estimates for those properties on the smaller, previously-uncharacterized faults which account for as much as 50% of the plate motion depending on location. For the first time, we note that the area between the Alpine Fault and the Main Divide of the Southern Alps is undergoing extensional areal strain, potentially indicative of gravitational collapse of the Southern Alps. The

  19. Strike-slip fault propagation and linkage via work optimization with application to the San Jacinto fault, California

    NASA Astrophysics Data System (ADS)

    Madden, E. H.; McBeck, J.; Cooke, M. L.

    2013-12-01

    Over multiple earthquake cycles, strike-slip faults link to form through-going structures, as demonstrated by the continuous nature of the mature San Andreas fault system in California relative to the younger and more segmented San Jacinto fault system nearby. Despite its immaturity, the San Jacinto system accommodates between one third and one half of the slip along the boundary between the North American and Pacific plates. It therefore poses a significant seismic threat to southern California. Better understanding of how the San Jacinto system has evolved over geologic time and of current interactions between faults within the system is critical to assessing this seismic hazard accurately. Numerical models are well suited to simulating kilometer-scale processes, but models of fault system development are challenged by the multiple physical mechanisms involved. For example, laboratory experiments on brittle materials show that faults propagate and eventually join (hard-linkage) by both opening-mode and shear failure. In addition, faults interact prior to linkage through stress transfer (soft-linkage). The new algorithm GROW (GRowth by Optimization of Work) accounts for this complex array of behaviors by taking a global approach to fault propagation while adhering to the principals of linear elastic fracture mechanics. This makes GROW a powerful tool for studying fault interactions and fault system development over geologic time. In GROW, faults evolve to minimize the work (or energy) expended during deformation, thereby maximizing the mechanical efficiency of the entire system. Furthermore, the incorporation of both static and dynamic friction allows GROW models to capture fault slip and fault propagation in single earthquakes as well as over consecutive earthquake cycles. GROW models with idealized faults reveal that the initial fault spacing and the applied stress orientation control fault linkage propensity and linkage patterns. These models allow the gains in

  20. 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

  1. Response to comment on "No late Quaternary strike-slip motion along the northern Karakoram fault"

    NASA Astrophysics Data System (ADS)

    Robinson, Alexander C.; Owen, Lewis A.; Chen, Jie; Schoenbohm, Lindsay M.; Hedrick, Kathryn A.; Blisniuk, Kimberly; Sharp, Warren D.; Imrecke, Daniel B.; Li, Wenqiao; Yuan, Zhaode; Caffee, Marc W.; Mertz-Kraus, Regina

    2016-06-01

    In their comment on ;No late Quaternary strike-slip motion along the northern Karakoram fault;, while Chevalier et al. (2016) do not dispute any of the results or interpretations regarding our observations along the main strand of the northern Karakoram fault, they make several arguments as to why they interpret the Kongur Shan Extensional System (KES) to be kinematically linked to the Karakoram fault. These arguments center around how an ;active; fault is defined, how slip on segments of the KES may be compatible with dextral shear related to continuation of the Karakoram fault, and suggestions as to how the two fault systems might still be connected. While we appreciate that there are still uncertainties in the regional geology, we address these comments and show that their arguments are inconsistent with all available data, known geologic relationships, and basic kinematics.

  2. Rheological structure of the lithosphere in plate boundary strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Chatzaras, Vasileios; Tikoff, Basil; Kruckenberg, Seth C.; Newman, Julie; Titus, Sarah J.; Withers, Anthony C.; Drury, Martyn R.

    2016-04-01

    How well constrained is the rheological structure of the lithosphere in plate boundary strike-slip fault systems? Further, how do lithospheric layers, with rheologically distinct behaviors, interact within the strike-slip fault zones? To address these questions, we present rheological observations from the mantle sections of two lithospheric-scale, strike-slip fault zones. Xenoliths from ˜40 km depth (970-1100 ° C) beneath the San Andreas fault system (SAF) provide critical constraints on the mechanical stratification of the lithosphere in this continental transform fault. Samples from the Bogota Peninsula shear zone (BPSZ, New Caledonia), which is an exhumed oceanic transform fault, provide insights on lateral variations in mantle strength and viscosity across the fault zone at a depth corresponding to deformation temperatures of ˜900 ° C. Olivine recrystallized grain size piezometry suggests that the shear stress in the SAF upper mantle is 5-9 MPa and in the BPSZ is 4-10 MPa. Thus, the mantle strength in both fault zones is comparable to the crustal strength (˜10 MPa) of seismogenic strike-slip faults in the SAF system. Across the BPSZ, shear stress increases from 4 MPa in the surrounding rocks to 10 MPa in the mylonites, which comprise the core of the shear zone. Further, the BPSZ is characterized by at least one order of magnitude difference in the viscosity between the mylonites (1018 Paṡs) and the surrounding rocks (1019 Paṡs). Mantle viscosity in both the BPSZ mylonites and the SAF (7.0ṡ1018-3.1ṡ1020 Paṡs) is relatively low. To explain our observations from these two strike-slip fault zones, we propose the "lithospheric feedback" model in which the upper crust and lithospheric mantle act together as an integrated system. Mantle flow controls displacement and the upper crust controls the stress magnitude in the system. Our stress data combined with data that are now available for the middle and lower crustal sections of other transcurrent fault

  3. The Trans-Rocky Mountain Fault System - A Fundamental Precambrian Strike-Slip System

    USGS Publications Warehouse

    Sims, P.K.

    2009-01-01

    Recognition of a major Precambrian continental-scale, two-stage conjugate strike-slip fault system - here designated as the Trans-Rocky Mountain fault system - provides new insights into the architecture of the North American continent. The fault system consists chiefly of steep linear to curvilinear, en echelon, braided and branching ductile-brittle shears and faults, and local coeval en echelon folds of northwest strike, that cut indiscriminately across both Proterozoic and Archean cratonic elements. The fault system formed during late stages of two distinct tectonic episodes: Neoarchean and Paleoproterozoic orogenies at about 2.70 and 1.70 billion years (Ga). In the Archean Superior province, the fault system formed (about 2.70-2.65 Ga) during a late stage of the main deformation that involved oblique shortening (dextral transpression) across the region and progressed from crystal-plastic to ductile-brittle deformation. In Paleoproterozoic terranes, the fault system formed about 1.70 Ga, shortly following amalgamation of Paleoproterozoic and Archean terranes and the main Paleoproterozoic plastic-fabric-producing events in the protocontinent, chiefly during sinistral transpression. The postulated driving force for the fault system is subcontinental mantle deformation, the bottom-driven deformation of previous investigators. This model, based on seismic anisotropy, invokes mechanical coupling and subsequent shear between the lithosphere and the asthenosphere such that a major driving force for plate motion is deep-mantle flow.

  4. Abrupt along-strike change in tectonic style: San Andreas fault zone, San Francisco Peninsula

    USGS Publications Warehouse

    Zoback, M.L.; Jachens, R.C.; Olson, J.A.

    1999-01-01

    Seismicity and high-resolution aeromagnetic data are used to define an abrupt change from compressional to extensional tectonism within a 10- to 15-km-wide zone along the San Andreas fault on the San Francisco Peninsula and offshore from the Golden Gate. This 100-km-long section of the San Andreas fault includes the hypocenter of the Mw = 7.8 1906 San Francisco earthquake as well as the highest level of persistent microseismicity along that ???470-km-long rupture. We define two distinct zones of deformation along this stretch of the fault using well-constrained relocations of all post-1969 earthquakes based a joint one-dimensional velocity/hypocenter inversion and a redetermination of focal mechanisms. The southern zone is characterized by thrust- and reverse-faulting focal mechanisms with NE trending P axes that indicate "fault-normal" compression in 7- to 10-km-wide zones of deformation on both sides of the San Andreas fault. A 1- to 2-km-wide vertical zone beneath the surface trace of the San Andreas is characterized by its almost complete lack of seismicity. The compressional deformation is consistent with the young, high topography of the Santa Cruz Mountains/Coast Ranges as the San Andreas fault makes a broad restraining left bend (???10??) through the southernmost peninsula. A zone of seismic quiescence ???15 km long separates this compressional zone to the south from a zone of combined normal-faulting and strike-slip-faulting focal mechanisms (including a ML = 5.3 earthquake in 1957) on the northernmost peninsula and offshore on the Golden Gate platform. Both linear pseudo-gravity gradients, calculated from the aeromagnetic data, and seismic reflection data indicate that the San Andreas fault makes an abrupt ???3-km right step less than 5 km offshore in this northern zone. A similar right-stepping (dilatational) geometry is also observed for the subparallel San Gregorio fault offshore. Persistent seismicity and extensional tectonism occur within the San

  5. High tsunami frequency as a result of combined strike-slip faulting and coastal landslides

    USGS Publications Warehouse

    Hornbach, Matthew J.; Braudy, Nicole; Briggs, Richard W.; Cormier, Marie-Helene; Davis, Marcy B.; Diebold, John B.; Dieudonne, Nicole; Douilly, Roby; Frohlich, Cliff; Gulick, Sean P.S.; Johnson, Harold E.; Mann, Paul; McHugh, Cecilia; Ryan-Mishkin, Katherine; Prentice, Carol S.; Seeber, Leonardo; Sorlien, Christopher C.; Steckler, Michael S.; Symithe, Steeve Julien; Taylor, Frederick W.; Templeton, John

    2010-01-01

    Earthquakes on strike-slip faults can produce devastating natural hazards. However, because they consist predominantly of lateral motion, these faults are rarely associated with significant uplift or tsunami generation. And although submarine slides can generate tsunami, only a few per cent of all tsunami are believed to be triggered in this way. The 12 January Mw 7.0 Haiti earthquake exhibited primarily strike-slip motion but nevertheless generated a tsunami. Here we present data from a comprehensive field survey that covered the onshore and offshore area around the epicentre to document that modest uplift together with slope failure caused tsunamigenesis. Submarine landslides caused the most severe tsunami locally. Our analysis suggests that slide-generated tsunami occur an order-of-magnitude more frequently along the Gonave microplate than global estimates predict. Uplift was generated because of the earthquake's location, where the Caribbean and Gonave microplates collide obliquely. The earthquake also caused liquefaction at several river deltas that prograde rapidly and are prone to failure. We conclude that coastal strike-slip fault systems such as the Enriquillo-Plantain Garden fault produce relief conducive to rapid sedimentation, erosion and slope failure, so that even modest predominantly strike-slip earthquakes can cause potentially catastrophic slide-generated tsunami - a risk that is underestimated at present.

  6. High tsunami frequency as a result of combined strike-slip faulting and coastal landslides

    USGS Publications Warehouse

    Hornbach, M.J.; Braudy, N.; Briggs, R.W.; Cormier, M.-H.; Davis, M.B.; Diebold, J.B.; Dieudonne, N.; Douilly, R.; Frohlich, C.; Gulick, S.P.S.; Johnson, H. E.; Mann, P.; McHugh, C.; Ryan-Mishkin, K.; Prentice, C.S.; Seeber, L.; Sorlien, C.C.; Steckler, M.S.; Symithe, S.J.; Taylor, F.W.; Templeton, J.

    2010-01-01

    Earthquakes on strike-slip faults can produce devastating natural hazards. However, because they consist predominantly of lateral motion, these faults are rarely associated with significant uplift or tsunami generation. And although submarine slides can generate tsunami, only a few per cent of all tsunami are believed to be triggered in this way. The 12 January Mw 7.0 Haiti earthquake exhibited primarily strike-slip motion but nevertheless generated a tsunami. Here we present data from a comprehensive field survey that covered the onshore and offshore area around the epicentre to document that modest uplift together with slope failure caused tsunamigenesis. Submarine landslides caused the most severe tsunami locally. Our analysis suggests that slide-generated tsunami occur an order-of-magnitude more frequently along the Gonave microplate than global estimates predict. Uplift was generated because of the earthquake?s location, where the Caribbean and Gonave microplates collide obliquely. The earthquake also caused liquefaction at several river deltas that prograde rapidly and are prone to failure. We conclude that coastal strike-slip fault systems such as the Enriquillog-Plantain Garden fault produce relief conducive to rapid sedimentation, erosion and slope failure, so that even modest predominantly strike-slip earthquakes can cause potentially catastrophic slide-generated tsunamig-a risk that is underestimated at present. ?? 2010 Macmillan Publishers Limited. All rights reserved.

  7. Crustal Strike-Slip Faulting along Small Circle Paths in the Northwestern United States

    NASA Astrophysics Data System (ADS)

    Brocher, T. M.; Wells, R. E.; Lamb, A. P.; Weaver, C. S.

    2015-12-01

    Late Cenozoic and Quaternary faults, seismicity lineaments, and focal mechanisms provide evidence that clockwise rotation of Washington and Oregon is accommodated by north-directed thrusting and strike-slip deformation in the Washington segment of the Cascadia forearc. Curvilinear NW- to NNW-trending high-angle strike-slip faults and seismicity lineaments define small circles around an Euler pole (117.7°W, 47.9°N) of rotation relative to North America that approximates GPS-derived poles for the rotation of eastern Washington and the Snake River Plain. Although the lengths of strike-slip faults that follow small circle paths suggest maximum earthquake magnitudes of M6.6 to M7.2, their slip rates calculated from the Euler pole are low (0.3 to 0.5 mm/yr). Many normal faults in the Lewis and Clark Zone in Montana, the Centennial fault system north of the Snake River Plain, west of the Wasatch Front, in the northern Basin and Range, and locally east of the Oregon Cascade arc are radial to this pole of rotation, suggesting that these normal faults help accommodate this crustal rotation. Regions undergoing contraction in western Washington and northwestern Oregon are separated from those to the east undergoing extension by lines radial to the Euler pole. In our regional kinematic model, dextral faults along small circles connect SW-directed crustal extension in the Intermountain Seismic Belt and E-directed extension in the Cascade arc south of Mount Hood to N-directed contraction in the Olympic Peninsula, Puget Lowland, and the Yakima Fold and Thrust Belt. The lack of Quaternary faulting and seismicity in the Oregon segment of the forearc is consistent with its clockwise rotation as a rigid block. Potential drivers of the crustal rotation include westward slab rollback and the Yellowstone geoid high, and the overall velocity field may integrate the response of rotating blocks and distributed deformation between them.

  8. Characterization of Aftershock Sequences from Large Strike-Slip Earthquakes Along Geometrically Complex Faults

    NASA Astrophysics Data System (ADS)

    Sexton, E.; Thomas, A.; Delbridge, B. G.

    2017-12-01

    Large earthquakes often exhibit complex slip distributions and occur along non-planar fault geometries, resulting in variable stress changes throughout the region of the fault hosting aftershocks. To better discern the role of geometric discontinuities on aftershock sequences, we compare areas of enhanced and reduced Coulomb failure stress and mean stress for systematic differences in the time dependence and productivity of these aftershock sequences. In strike-slip faults, releasing structures, including stepovers and bends, experience an increase in both Coulomb failure stress and mean stress during an earthquake, promoting fluid diffusion into the region and further failure. Conversely, Coulomb failure stress and mean stress decrease in restraining bends and stepovers in strike-slip faults, and fluids diffuse away from these areas, discouraging failure. We examine spatial differences in seismicity patterns along structurally complex strike-slip faults which have hosted large earthquakes, such as the 1992 Mw 7.3 Landers, the 2010 Mw 7.2 El-Mayor Cucapah, the 2014 Mw 6.0 South Napa, and the 2016 Mw 7.0 Kumamoto events. We characterize the behavior of these aftershock sequences with the Epidemic Type Aftershock-Sequence Model (ETAS). In this statistical model, the total occurrence rate of aftershocks induced by an earthquake is λ(t) = λ_0 + \\sum_{i:t_i

  9. Effects of Strike-Slip Fault Segmentation on Earthquake Energy and Seismic Hazard

    NASA Astrophysics Data System (ADS)

    Madden, E. H.; Cooke, M. L.; Savage, H. M.; McBeck, J.

    2014-12-01

    Many major strike-slip faults are segmented along strike, including those along plate boundaries in California and Turkey. Failure of distinct fault segments at depth may be the source of multiple pulses of seismic radiation observed for single earthquakes. However, how and when segmentation affects fault behavior and energy release is the basis of many outstanding questions related to the physics of faulting and seismic hazard. These include the probability for a single earthquake to rupture multiple fault segments and the effects of segmentation on earthquake magnitude, radiated seismic energy, and ground motions. Using numerical models, we quantify components of the earthquake energy budget, including the tectonic work acting externally on the system, the energy of internal rock strain, the energy required to overcome fault strength and initiate slip, the energy required to overcome frictional resistance during slip, and the radiated seismic energy. We compare the energy budgets of systems of two en echelon fault segments with various spacing that include both releasing and restraining steps. First, we allow the fault segments to fail simultaneously and capture the effects of segmentation geometry on the earthquake energy budget and on the efficiency with which applied displacement is accommodated. Assuming that higher efficiency correlates with higher probability for a single, larger earthquake, this approach has utility for assessing the seismic hazard of segmented faults. Second, we nucleate slip along a weak portion of one fault segment and let the quasi-static rupture propagate across the system. Allowing fractures to form near faults in these models shows that damage develops within releasing steps and promotes slip along the second fault, while damage develops outside of restraining steps and can prohibit slip along the second fault. Work is consumed in both the propagation of and frictional slip along these new fractures, impacting the energy available

  10. Strike-slip faulting in the Inner California Borderlands, offshore Southern California.

    NASA Astrophysics Data System (ADS)

    Bormann, J. M.; Kent, G. M.; Driscoll, N. W.; Harding, A. J.; Sahakian, V. J.; Holmes, J. J.; Klotsko, S.; Kell, A. M.; Wesnousky, S. G.

    2015-12-01

    In the Inner California Borderlands (ICB), offshore of Southern California, modern dextral strike-slip faulting overprints a prominent system of basins and ridges formed during plate boundary reorganization 30-15 Ma. Geodetic data indicate faults in the ICB accommodate 6-8 mm/yr of Pacific-North American plate boundary deformation; however, the hazard posed by the ICB faults is poorly understood due to unknown fault geometry and loosely constrained slip rates. We present observations from high-resolution and reprocessed legacy 2D multichannel seismic (MCS) reflection datasets and multibeam bathymetry to constrain the modern fault architecture and tectonic evolution of the ICB. We use a sequence stratigraphy approach to identify discrete episodes of deformation in the MCS data and present the results of our mapping in a regional fault model that distinguishes active faults from relict structures. Significant differences exist between our model of modern ICB deformation and existing models. From east to west, the major active faults are the Newport-Inglewood/Rose Canyon, Palos Verdes, San Diego Trough, and San Clemente fault zones. Localized deformation on the continental slope along the San Mateo, San Onofre, and Carlsbad trends results from geometrical complexities in the dextral fault system. Undeformed early to mid-Pleistocene age sediments onlap and overlie deformation associated with the northern Coronado Bank fault (CBF) and the breakaway zone of the purported Oceanside Blind Thrust. Therefore, we interpret the northern CBF to be inactive, and slip rate estimates based on linkage with the Holocene active Palos Verdes fault are unwarranted. In the western ICB, the San Diego Trough fault (SDTF) and San Clemente fault have robust linear geomorphic expression, which suggests that these faults may accommodate a significant portion of modern ICB slip in a westward temporal migration of slip. The SDTF offsets young sediments between the US/Mexico border and the

  11. The timing of strike-slip shear along the Ranong and Khlong Marui faults, Thailand

    NASA Astrophysics Data System (ADS)

    Watkinson, Ian; Elders, Chris; Batt, Geoff; Jourdan, Fred; Hall, Robert; McNaughton, Neal J.

    2011-09-01

    The timing of shear along many important strike-slip faults in Southeast Asia, such as the Ailao Shan-Red River, Mae Ping and Three Pagodas faults, is poorly understood. We present 40Ar/39Ar, U-Pb SHRIMP and microstructural data from the Ranong and Khlong Marui faults of Thailand to show that they experienced a major period of ductile dextral shear during the middle Eocene (48-40 Ma, centered on 44 Ma) which followed two phases of dextral shear along the Ranong Fault, before the Late Cretaceous (>81 Ma) and between the late Paleocene and early Eocene (59-49 Ma). Many of the sheared rocks were part of a pre-kinematic crystalline basement complex, which partially melted and was intruded by Late Cretaceous (81-71 Ma) and early Eocene (48 Ma) tin-bearing granites. Middle Eocene dextral shear at temperatures of ˜300-500°C formed extensive mylonite belts through these rocks and was synchronous with granitoid vein emplacement. Dextral shear along the Ranong and Khlong Marui faults occurred at the same time as sinistral shear along the Mae Ping and Three Pagodas faults of northern Thailand, a result of India-Burma coupling in advance of India-Asia collision. In the late Eocene (<37 Ma) the Ranong and Khlong Marui faults were reactivated as curved sinistral branches of the Mae Ping and Three Pagodas faults, which were accommodating lateral extrusion during India-Asia collision and Himalayan orogenesis.

  12. Dimensionality and regional strike analyses of the Cibeber segment, Cimandiri fault zone, West Jawa, Indonesia

    NASA Astrophysics Data System (ADS)

    Febriani, F.; Handayani, L.; Setyani, A.; Anggono, T.; Syuhada; Soedjatmiko, B.

    2018-03-01

    The dimensionality and regional strike analyses of the Cimandiri Fault, West Java, Indonesia have been investigated. The Cimandiri Fault consists of six segments. They are Loji, Cidadap, Nyalindung, Cibeber, Saguling and Padalarang segments. The magnetotelluric (MT) investigation was done in the Cibeber segment. There were 42 observation points of the magnetotelluric data, which were distributed along 2 lines. The magnetotelluric phase tensor has been applied to determine the dimensionality and regional strike of the Cibeber segment, Cimandiri Fault, West Java. The result of the dimensionality analysis shows that the range values of the skew angle value which indicate the dimensionality of the study area are -5 ≤ β ≥ 5. These values indicate if we would like to generate the subsurface model of the Cibeber segment by using the magnetotelluric data, it is safe to assume that the Cibeber segment has the 2-D. While the regional strike analysis presents that the regional strike of the Cibeber segment is about N70-80°E.

  13. Structural characteristics and implication on tectonic evolution of the Daerbute strike-slip fault in West Junggar area, NW China

    NASA Astrophysics Data System (ADS)

    Wu, Kongyou; Pei, Yangwen; Li, Tianran; Wang, Xulong; Liu, Yin; Liu, Bo; Ma, Chao; Hong, Mei

    2018-03-01

    The Daerbute fault zone, located in the northwestern margin of the Junggar basin, in the Central Asian Orogenic Belt, is a regional strike-slip fault with a length of 400 km. The NE-SW trending Daerbute fault zone presents a distinct linear trend in plain view, cutting through both the Zair Mountain and the Hala'alate Mountain. Because of the intense contraction and shearing, the rocks within the fault zone experienced high degree of cataclasis, schistosity, and mylonization, resulting in rocks that are easily eroded to form a valley with a width of 300-500 m and a depth of 50-100 m after weathering and erosion. The well-exposed outcrops along the Daerbute fault zone present sub-horizontal striations and sub-vertical fault steps, indicating sub-horizontal shearing along the observed fault planes. Flower structures and horizontal drag folds are also observed in both the well-exposed outcrops and high-resolution satellite images. The distribution of accommodating strike-slip splay faults, e.g., the 973-pluton fault and the Great Jurassic Trough fault, are in accordance with the Riedel model of simple shear. The seismic and time-frequency electromagnetic (TFEM) sections also demonstrate the typical strike-slip characteristics of the Daerbute fault zone. Based on detailed field observations of well-exposed outcrops and seismic sections, the Daerbute fault can be subdivided into two segments: the western segment presents multiple fault cores and damage zones, whereas the eastern segment only presents a single fault core, in which the rocks experienced a higher degree of rock cataclasis, schistosity, and mylonization. In the central overlapping portion between the two segments, the sediments within the fault zone are primarily reddish sandstones, conglomerates, and some mudstones, of which the palynological tests suggest middle Permian as the timing of deposition. The deformation timing of the Daerbute fault was estimated by integrating the depocenters' basinward

  14. Fault and fracture patterns around a strike-slip influenced salt wall

    NASA Astrophysics Data System (ADS)

    Alsop, G. I.; Weinberger, R.; Marco, S.; Levi, T.

    2018-01-01

    The trends of faults and fractures in overburden next to a salt diapir are generally considered to be either parallel to the salt margin to form concentric patterns, or at right angles to the salt contact to create an overall radial distribution around the diapir. However, these simple diapir-related patterns may become more complex if regional tectonics influences the siting and growth of a diapir. Using the Sedom salt wall in the Dead Sea Fault system as our case study, we examine the influence of regional strike-slip faulting on fracture patterns around a salt diapir. This type of influence is important in general as the distribution and orientation of fractures on all scales may influence permeability and hence control fluid and hydrocarbon flow. Fractures adjacent to the N-S trending salt wall contain fibrous gypsum veins and injected clastic dykes, attesting to high fluid pressures adjacent to the diapir. Next to the western flank of the salt wall, broad (∼1000 m) zones of upturn or 'drape folds' are associated with NW-SE striking conjugate extensional fractures within the overburden. Within 300 m of the salt contact, fracture patterns in map view display a progressive ∼30°-35° clockwise rotation with more NNW-SSE strikes immediately adjacent to the salt wall. While some extensional faults display growth geometries, indicating that they were syn-depositional and initiated prior to tilting of beds associated with drape folding, other fractures display increasing dips towards the salt, suggesting that they have formed during upturn of bedding near the diapir. These observations collectively suggest that many fractures developed to accommodate rotation of beds during drape folding. Extensional fractures in the overburden define a mean strike that is ∼45° anticlockwise (counter-clockwise) of the N-S trending salt wall, and are therefore consistent with sinistral transtension along the N-S trending Sedom Fault that underlies the salt wall. Our outcrop

  15. A preliminary study on surface ground deformation near shallow foundation induced by strike-slip faulting

    NASA Astrophysics Data System (ADS)

    Wong, Pei-Syuan; Lin, Ming-Lang

    2016-04-01

    According to investigation of recent earthquakes, ground deformation and surface rupture are used to map the influenced range of the active fault. The zones of horizontal and vertical surface displacements and different features of surface rupture are investigated in the field, for example, the Greendale Fault 2010, MW 7.1 Canterbury earthquake. The buildings near the fault rotated and displaced vertically and horizontally due to the ground deformation. Besides, the propagation of fault trace detoured them because of the higher rigidity. Consequently, it's necessary to explore the ground deformation and mechanism of the foundation induced by strike-slip faulting for the safety issue. Based on previous study from scaled analogue model of strike-slip faulting, the ground deformation is controlled by material properties, depth of soil, and boundary condition. On the condition controlled, the model shows the features of ground deformation in the field. This study presents results from shear box experiment on small-scale soft clay models subjected to strike-slip faulting and placed shallow foundations on it in a 1-g environment. The quantifiable data including sequence of surface rupture, topography and the position of foundation are recorded with increasing faulting. From the result of the experiment, first en echelon R shears appeared. The R shears rotated to a more parallel angle to the trace and cracks pulled apart along them with increasing displacements. Then the P shears crossed the basement fault in the opposite direction appears and linked R shears. Lastly the central shear was Y shears. On the other hand, the development of wider zones of rupture, higher rising surface and larger the crack area on surface developed, with deeper depth of soil. With the depth of 1 cm and half-box displacement 1.2 cm, en echelon R shears appeared and the surface above the fault trace elevated to 1.15 mm (Dv), causing a 1.16 cm-wide zone of ground-surface rupture and deformation

  16. The Damage and Geochemical Signature of a Crustal Scale Strike-Slip Fault Zone

    NASA Astrophysics Data System (ADS)

    Gomila, R.; Mitchell, T. M.; Arancibia, G.; Jensen Siles, E.; Rempe, M.; Cembrano, J. M.; Faulkner, D. R.

    2013-12-01

    Fluid-flow migration in the upper crust is strongly controlled by fracture network permeability and connectivity within fault zones, which can lead to fluid-rock chemical interaction represented as mineral precipitation in mesh veins and/or mineralogical changes (alteration) of the host rock. While the dimensions of fault damage zones defined by fracture intensity is beginning to be better understood, how such dimensions compare to the size of alteration zones is less well known. Here, we show quantitative structural and chemical analyses as a function of distance from a crustal-scale strike-slip fault in the Atacama Fault System, Northern Chile, to compare fault damage zone characteristics with its geochemical signature. The Jorgillo Fault (JF) is a ca. 18 km long NNW striking strike-slip fault cutting Mesozoic rocks with sinistral displacement of ca. 4 km. In the study area, the JF cuts through orthogranulitic and gabbroic rocks at the west (JFW) and the east side (JFE), respectively. A 200 m fault perpendicular transect was mapped and sampled for structural and XRF analyses of the core, damage zone and protolith. The core zone consists of a ca. 1 m wide cataclasite zone bounded by two fault gouge zones ca. 40 cm. The damage zone width defined by fracture density is ca. 50 m wide each side of the core. The damage zone in JFW is characterized by NW-striking subvertical 2 cm wide cataclastic rocks and NE-striking milimetric open fractures. In JFE, 1-20 mm wide chlorite, quartz-epidote and quartz-calcite veins, cut the gabbro. Microfracture analysis in JFW reveal mm-wide cataclasitic/ultracataclasitic bands with clasts of protolith and chlorite orientated subparallel to the JF in the matrix, calcite veins in a T-fractures orientation, and minor polidirectional chlorite veins. In JFE, chlorite filled conjugate fractures with syntaxial growth textures and evidence for dilational fracturing processes are seen. Closest to the core, calcite veins crosscut chlorite veins

  17. Statistical Correlation between Red Wood Ant Sites and Neotectonic Strike-Slip Faults

    NASA Astrophysics Data System (ADS)

    Berberich, G.; Klimetzek, D.; Wöhler, C.; Grumpe, A.

    2012-04-01

    Recent research in the West Eifel (West Germany) has demonstrated the correlation of soil gas anomalies and spatial distribution of red wood ant (RWA) mounds along strike-slip faults. RWA can be used as biological indicators for the identification of neotectonic fault systems (Berberich 2010, Schreiber & Berberich 2011). For myrmecologists, the causes and stringency of such a linkage are paramount, since linear patterns have been mostly associated with edge effects of forest stands and/or roads (Klimetzek 1970, Klimetzek & Kaiser 1995, Wellenstein 1990). Therefore, geostatistical techniques were applied in the West Eifel and the Bodanrück (South West Germany) to distribution data of approx. 3,000 resp. 2,300 mounds of RWA (Formica spp., Hymenoptera: Formicidae) in correlation with known neotectonic fault systems Both study areas are located in areas with a complex tectonic history. Commenced during the Neogene and persisted during the Quaternary, the uplift of both, the Rhenoherzynikum and the Black Forest, affects the dynamics of the study areas and reactivates pre-existing Palaeozoic crustal discontinuities. The West Eifel (Rhenoherzynikum) was tectonically sheared in Mesozoic and Cenozoic times. The current NW-SE-trending main stress direction opens pathways for geogenic gases. At the same time, Variscan faults as part of a conjugated shear system, are reactivated. At the Bodanrück, the compressional stress field (NNW-SSE) leads to a WSW-ENE extensional regime, in which faults cut through the entire crust (Ziegler & Dèzes 2007, Nagra 1992). The prominent large-scale neotectonic structure is the NW-SE to WNW-ESE trending "Freiburg-Bonndorf-Hegau-Bodensee-Graben" that consists of several sub-trenches (Müller et al. 2002). Field surveys indicate a possible existence of a NNE-SSW trending strike-slip fault extending east of Stein am Rhein (Büchi & Müller 2003) possibly reactivated in the Quaternary (Birkhäuser et al. 2001). Available focal mechanism solutions

  18. A multilayer model of time dependent deformation following an earthquake on a strike-slip fault

    NASA Technical Reports Server (NTRS)

    Cohen, S. C.

    1981-01-01

    A multilayer model of the Earth to calculate finite element of time dependent deformation and stress following an earthquake on a strike slip fault is discussed. The model involves shear properties of an elastic upper lithosphere, a standard viscoelastic linear solid lower lithosphere, a Maxwell viscoelastic asthenosphere and an elastic mesosphere. Systematic variations of fault and layer depths and comparisons with simpler elastic lithosphere over viscoelastic asthenosphere calculations are analyzed. Both the creep of the lower lithosphere and astenosphere contribute to the postseismic deformation. The magnitude of the deformation is enhanced by a short distance between the bottom of the fault (slip zone) and the top of the creep region but is less sensitive to the thickness of the creeping layer. Postseismic restressing is increased as the lower lithosphere becomes more viscoelastic, but the tendency for the width of the restressed zone to growth with time is retarded.

  19. Strike-Slip Fault Patterns on Europa: Obliquity or Polar Wander?

    NASA Technical Reports Server (NTRS)

    Rhoden, Alyssa Rose; Hurford, Terry A.; Manga, Michael

    2011-01-01

    Variations in diurnal tidal stress due to Europa's eccentric orbit have been considered as the driver of strike-slip motion along pre-existing faults, but obliquity and physical libration have not been taken into account. The first objective of this work is to examine the effects of obliquity on the predicted global pattern of fault slip directions based on a tidal-tectonic formation model. Our second objective is to test the hypothesis that incorporating obliquity can reconcile theory and observations without requiring polar wander, which was previously invoked to explain the mismatch found between the slip directions of 192 faults on Europa and the global pattern predicted using the eccentricity-only model. We compute predictions for individual, observed faults at their current latitude, longitude, and azimuth with four different tidal models: eccentricity only, eccentricity plus obliquity, eccentricity plus physical libration, and a combination of all three effects. We then determine whether longitude migration, presumably due to non-synchronous rotation, is indicated in observed faults by repeating the comparisons with and without obliquity, this time also allowing longitude translation. We find that a tidal model including an obliquity of 1.2?, along with longitude migration, can predict the slip directions of all observed features in the survey. However, all but four faults can be fit with only 1? of obliquity so the value we find may represent the maximum departure from a lower time-averaged obliquity value. Adding physical libration to the obliquity model improves the accuracy of predictions at the current locations of the faults, but fails to predict the slip directions of six faults and requires additional degrees of freedom. The obliquity model with longitude migration is therefore our preferred model. Although the polar wander interpretation cannot be ruled out from these results alone, the obliquity model accounts for all observations with a value

  20. The 2013, Mw 7.7 Balochistan earthquake, energetic strike-slip reactivation of a thrust fault

    NASA Astrophysics Data System (ADS)

    Avouac, Jean-Philippe; Ayoub, Francois; Wei, Shengji; Ampuero, Jean-Paul; Meng, Lingsen; Leprince, Sebastien; Jolivet, Romain; Duputel, Zacharie; Helmberger, Don

    2014-04-01

    We analyse the Mw 7.7 Balochistan earthquake of 09/24/2013 based on ground surface deformation measured from sub-pixel correlation of Landsat-8 images, combined with back-projection and finite source modeling of teleseismic waveforms. The earthquake nucleated south of the Chaman strike-slip fault and propagated southwestward along the Hoshab fault at the front of the Kech Band. The rupture was mostly unilateral, propagated at 3 km/s on average and produced a 200 km surface fault trace with purely strike-slip displacement peaking to 10 m and averaging around 6 m. The finite source model shows that slip was maximum near the surface. Although the Hoshab fault is dipping by 45° to the North, in accordance with its origin as a thrust fault within the Makran accretionary prism, slip was nearly purely strike-slip during that earthquake. Large seismic slip on such a non-optimally oriented fault was enhanced possibly due to the influence of the free surface on dynamic stresses or to particular properties of the fault zone allowing for strong dynamic weakening. Strike-slip faulting on thrust fault within the eastern Makran is interpreted as due to eastward extrusion of the accretionary prism as it bulges out over the Indian plate. Portions of the Makran megathrust, some thrust faults in the Kirthar range and strike-slip faults within the Chaman fault system have been brought closer to failure by this earthquake. Aftershocks cluster within the Chaman fault system north of the epicenter, opposite to the direction of rupture propagation. By contrast, few aftershocks were detected in the area of maximum moment release. In this example, aftershocks cannot be used to infer earthquake characteristics.

  1. Inelastic off-fault response and three-dimensional dynamics of earthquake rupture on a strike-slip fault

    USGS Publications Warehouse

    Andrews, D.J.; Ma, Shuo

    2010-01-01

    Large dynamic stress off the fault incurs an inelastic response and energy loss, which contributes to the fracture energy, limiting the rupture and slip velocity. Using an explicit finite element method, we model three-dimensional dynamic ruptures on a vertical strike-slip fault in a homogeneous half-space. The material is subjected to a pressure-dependent Drucker-Prager yield criterion. Initial stresses in the medium increase linearly with depth. Our simulations show that the inelastic response is confined narrowly to the fault at depth. There the inelastic strain is induced by large dynamic stresses associated with the rupture front that overcome the effect of the high confining pressure. The inelastic zone increases in size as it nears the surface. For material with low cohesion (~5 MPa) the inelastic zone broadens dramatically near the surface, forming a "flowerlike" structure. The near-surface inelastic strain occurs in both the extensional and the compressional regimes of the fault, induced by seismic waves ahead of the rupture front under a low confining pressure. When cohesion is large (~10 MPa), the inelastic strain is significantly reduced near the surface and confined mostly to depth. Cohesion, however, affects the inelastic zone at depth less significantly. The induced shear microcracks show diverse orientations near the surface, owing to the low confining pressure, but exhibit mostly horizontal slip at depth. The inferred rupture-induced anisotropy at depth has the fast wave direction along the direction of the maximum compressive stress.

  2. The stress shadow effect: a mechanical analysis of the evenly-spaced parallel strike-slip faults in the San Andreas fault system

    NASA Astrophysics Data System (ADS)

    Zuza, A. V.; Yin, A.; Lin, J. C.

    2015-12-01

    Parallel evenly-spaced strike-slip faults are prominent in the southern San Andreas fault system, as well as other settings along plate boundaries (e.g., the Alpine fault) and within continental interiors (e.g., the North Anatolian, central Asian, and northern Tibetan faults). In southern California, the parallel San Jacinto, Elsinore, Rose Canyon, and San Clemente faults to the west of the San Andreas are regularly spaced at ~40 km. In the Eastern California Shear Zone, east of the San Andreas, faults are spaced at ~15 km. These characteristic spacings provide unique mechanical constraints on how the faults interact. Despite the common occurrence of parallel strike-slip faults, the fundamental questions of how and why these fault systems form remain unanswered. We address this issue by using the stress shadow concept of Lachenbruch (1961)—developed to explain extensional joints by using the stress-free condition on the crack surface—to present a mechanical analysis of the formation of parallel strike-slip faults that relates fault spacing and brittle-crust thickness to fault strength, crustal strength, and the crustal stress state. We discuss three independent models: (1) a fracture mechanics model, (2) an empirical stress-rise function model embedded in a plastic medium, and (3) an elastic-plate model. The assumptions and predictions of these models are quantitatively tested using scaled analogue sandbox experiments that show that strike-slip fault spacing is linearly related to the brittle-crust thickness. We derive constraints on the mechanical properties of the southern San Andreas strike-slip faults and fault-bounded crust (e.g., local fault strength and crustal/regional stress) given the observed fault spacing and brittle-crust thickness, which is obtained by defining the base of the seismogenic zone with high-resolution earthquake data. Our models allow direct comparison of the parallel faults in the southern San Andreas system with other similar strike

  3. Searching for the buried memory of past strong earthquakes on strike-slip faults

    NASA Astrophysics Data System (ADS)

    Garambois, S.; Manighetti, I.; Malavieille, J.; Langridge, R. M.; Davies, T. R.

    2009-12-01

    On strike-slip faults, the effect of a large earthquake is to suddenly displace the ground surface laterally, often by up to several meters. A consequence is the lateral offset, hence lateral separation, of the preexisting ground features. In alluvial settings, the dominant surface features are the stream network and related sediments. Where ongoing sedimentation is significant, the surface imprints of an earthquake may be rapidly buried under fresh sediments so that, when the next seismic event occurs (if not too close in time from the previous one), it offsets and deforms a younger soil layer possibly holding new markers such as newly formed drainage channels. Hence as earthquakes repeat on a strike-slip fault under ongoing sedimentation, the subsurface should keep part of their memory more or less buried in the form of distinctly offset markers, lying at various depths (0-10 m) in the ground. To search for that buried memory, we need non-invasive investigation methods, allowing imaging the sub-surface down to depths of several meters to 10s of meters. Ground penetrating radar (GPR) has appropriate resolution and acquisition time, provided that the subsurface layers are not too electrically conductive. We have performed serial 2D GPR profiles using 100 MHz antennas along several major strike-slip faults in New Zealand. In particular, at the Mason river site on the Hope dextral fault, four 450 m-long profiles were recorded parallel to the fault, two on each northern and southern compartments of the fault, whose surfaces are made of the 14-26 ka-old Terako alluvial terrace. The processed GPR data show the ground architecture only down to 5 meters in such conductive sediments. The profiles however reveal a number of places along the fault where the reflector pile is deflected at depth to form concave-up patterns. Some of those buried features have their edges extending up to the ground surface, what suggests they may post-date the Terako terrace surface. Most of

  4. Dynamic rupture modeling of the transition from thrust to strike-slip motion in the 2002 Denali fault earthquake, Alaska

    USGS Publications Warehouse

    Aagaard, Brad T.; Anderson, G.; Hudnut, K.W.

    2004-01-01

    We use three-dimensional dynamic (spontaneous) rupture models to investigate the nearly simultaneous ruptures of the Susitna Glacier thrust fault and the Denali strike-slip fault. With the 1957 Mw 8.3 Gobi-Altay, Mongolia, earthquake as the only other well-documented case of significant, nearly simultaneous rupture of both thrust and strike-slip faults, this feature of the 2002 Denali fault earthquake provides a unique opportunity to investigate the mechanisms responsible for development of these large, complex events. We find that the geometry of the faults and the orientation of the regional stress field caused slip on the Susitna Glacier fault to load the Denali fault. Several different stress orientations with oblique right-lateral motion on the Susitna Glacier fault replicate the triggering of rupture on the Denali fault about 10 sec after the rupture nucleates on the Susitna Glacier fault. However, generating slip directions compatible with measured surface offsets and kinematic source inversions requires perturbing the stress orientation from that determined with focal mechanisms of regional events. Adjusting the vertical component of the principal stress tensor for the regional stress field so that it is more consistent with a mixture of strike-slip and reverse faulting significantly improves the fit of the slip-rake angles to the data. Rotating the maximum horizontal compressive stress direction westward appears to improve the fit even further.

  5. Effects of Arabia-Eurasia Collision on Strike-slip Faults in Central Anatolia?

    NASA Astrophysics Data System (ADS)

    Whitney, D. L.; Lefebvre, C.; Thomson, S. N.; Idleman, L.; Cosca, M. A.; Kaymakci, N.; Teyssier, C. P.; Umhoefer, P. J.

    2013-12-01

    The North and East Anatolian faults accommodate much of the tectonic escape of Anatolia in response to Arabia-Eurasia collision and building of the Turkish-Iranian plateau, but these structures formed <10 m.y. ago, at least 25 m.y. after the onset of collision at ~35 Ma. Some of the major strike-slip fault zones located between the North and East Anatolian faults have had long and complex histories of displacement. These faults have deformed, and in some cases exhumed, metamorphic massifs located between fault strands. One example is the Nigde Massif, which was initially exhumed in the Late Cretaceous, then reburied and reheated, along with its overlying sedimentary basin, to a depth of ~10 km at 30 × 5 Ma. Final exhumation and cooling occurred by ~15-17 Ma (massif margin) to ~12 Ma (structurally deepest levels). This depth-temperature-time-deformation history is tracked by a combination of thermobarometric methods, structural and stratigraphic analysis, and geo/thermochronometry (U-Pb zircon, monazite; 40Ar/39Ar hornblende, muscovite, biotite, K-feldspar; zircon and apatite fission-track in metamorphic rocks and basin deposits; and apatite (U-Th)/He). Recent mapping shows the presence of at least two oblique-thrust slices; the structurally higher one accounts for the resetting of detrital apatite fission track and AHe ages in the basin rocks as well as metamorphic apatite near the margin of the massif. The structurally deeper one cuts through the metamorphic basement and explains why mineral lineations and metamorphic assemblages are different along the eastern margin relative to those in the core of the massif. Although the timing of displacement has not been dated directly, low-T thermochronology age and modeling results document a perturbation at ~30 Ma, consistent with the idea that the Ecemis Fault of the Central Anatolian Fault Zone, and probably other pre-existing strike-slip faults in central Anatolia, experienced Late Eocene-Oligocene displacement in

  6. Ground Surface Deformation in Unconsolidated Sediments Caused by Bedrock Fault Movements: Dip-Slip and Strike-Slip Fault Model Test and Field Survey

    NASA Astrophysics Data System (ADS)

    Ueta, K.; Tani, K.

    2001-12-01

    Sandbox experiments were performed to investigate ground surface deformation in unconsolidated sediments caused by dip-slip and strike-slip motion on bedrock faults. A 332.5 cm long, 200 cm high, and 40 cm wide sandbox was used in a dip-slip fault model test. In the strike-slip fault test, a 600 cm long, 250 cm wide, and 60 cm high sandbox and a 170 cm long, 25 cm wide, 15 cm high sandbox were used. Computerized X-ray tomography applied to the sandbox experiments made it possible to analyze the kinematic evolution, as well as the three-dimensional geometry, of the faults. The fault type, fault dip, fault displacement, thickness and density of sandpack and grain size of the sand were varied for different experiments. Field survey of active faults in Japan and California were also made to investigate the deformation of unconsolidated sediments overlying bedrock faults. A comparison of the experimental results with natural cases of active faults reveals the following: (1) In the case of dip-slip faulting, the shear bands are not shown as one linear plane but as en echelon pattern. Thicker and finer unconsolidated sediments produce more shear bands and clearer en echelon shear band patterns. (2) In the case of left-lateral strike-slip faulting, the deformation of the sand pack with increasing basement displacement is observed as follows. a) In three dimensions, the right-stepping shears that have a "cirque" / "shell" / "ship body" shape develop on both sides of the basement fault. The shears on one side of the basement fault join those on the other side, resulting in helicoidal shaped shear surfaces. Shears reach the surface of the sand near or above the basement fault and en echelon Riedel shears are observed at the surface of the sand. b) Right-stepping pressure ridges develop within the zone defined by the Riedel shears. c) Lower-angle shears generally branch off from the first Riedel shears. d) Right-stepping helicoidal shaped lower-angle shears offset Riedel

  7. Enigmatic rift-parallel, strike-slip faults around Eyjafjörður, Northern Iceland

    NASA Astrophysics Data System (ADS)

    Proett, J. A.; Karson, J. A.

    2014-12-01

    Strike-slip faults along mid-ocean ridge spreading centers are generally thought to be restricted to transform boundaries connecting rift segments. Faults that are parallel to spreading centers are generally assumed to be normal faults associated with tectonic extension. However, clear evidence of north-south (rift-parallel), strike-slip displacements occur widely around the southern portion of Eyjafjörður, northern Iceland about 50 km west of the Northern Rift Zone. The area is south of the southernmost strand (Dalvík Lineament) of the NW-SE-trending, dextral-slip, Tjӧrnes Fracture Zone (where N-S, sinistral, strike-slip "bookshelf" faulting occurs). Faults in the Eyjafjörður area cut 8.5-10 m.y. basaltic crust and are parallel to spreading-related dikes and are commonly concentrated along dike margins. Fault rocks range from fault breccia to gouge. Riedel shears and other kinematic indicators provide unambiguous evidence of shear sense. Most faults show evidence of sinistral, strike-slip movement but smaller proportions of normal and oblique-slip faults also are present. Cross cutting relations among the different types of faults are inconsistent and appear to be related to a single deformation event. Fault slip-line kinematic analysis yields solutions indicating sinistral-normal oblique-slip overall. These results may be interpreted in terms of either previously unrecognized transform-fault bookshelf faulting or slip accommodating block rotation associated with northward propagation of the Northern Rift Zone.

  8. Role of strike-slip faulting in the evolution of allochthonous terranes in the Philippines

    SciTech Connect

    Karig, D.E.; Sarewitz, D.R.; Haeck, G.D.

    1986-10-01

    Concepts of allochthonous terrane transport and emplacement are dominated by the assumption that most terranes originate on the subducting plate, collide with the upper plate, and are emplaced there. Movement of terranes along the convergent margin is recognized but is generally attributed to postcollision slip. In the northern Philippines, allochthonous terranes originate primarily within the arc system, have been translated along it by strike-slip faults, and were emplaced by cessation of that slip. The authors suggest that in the Philippines some originally vertical strike-slip boundaries may have evolved into shallow-dipping sutures marked by fold and thrust systems. This mode ofmore » terrane evolution may be more common than generally appreciated, particularly in orogenic belts developed in response to oblique convergence.« less

  9. Aspects of Non-Newtonian Viscoelastic Deformation Produced by Slip on a Major Strike- slip Fault

    NASA Astrophysics Data System (ADS)

    Postek, E. W.; Houseman, G. A.; Jimack, P. K.

    2008-12-01

    Non-Newtonian flow occurs in crustal deformation processes on the long timescales associated with large- scale continental deformation, and also on the short time-scales associated with post-seismic deformation. The co-seismic displacement is determined by the instantaneous elastic response of the rocks on either side of the fault surface to the distribution of slip on the surface of the fault. The post-seismic deformation is determined by some combination of visco-elastic relaxation of the medium and post-seismic creep on the fault. The response of the crust may depend on elastic moduli, Poisson's ratio, temperature, pressure and creep function parameters including stress exponent, activation energy, activation volume and viscosity coefficient. We use the von Mises function in describing the non-linear Maxwell visco-elastic creep models. In this study we examine a model of a strike-slip fault crossing a 3D block. The fault slips at time zero, and we solve for the viscoelastic deformation field throughout the 3D volume using a 3D finite element method. We perform parametric studies on the constitutive equation by varying these parameters and the depth of the fault event. Our findings are focused on the fact that the system is very sensitive to the above mentioned parameters. In particular, the most important seems to be the temperature profiles and stress exponent. The activation energy and the pressure are of lower importance, however, they have their meaning. We investigated the relaxation times and the deformation patterns. We took the material properties as typical to dry quartzite and diabase. Depending on the parameters the surface can be deformed permanently or the deformation can decrease. We attempt to compare qualitatively the calculated post-seismic response in terms of the post-seismic displacement history of the earth's surface with InSAR patterns determined from recent major strike-slip earthquakes. Quantitative comparison of the observations with

  10. Earthquake swarms and local crustal spreading along major strike-slip faults in California

    USGS Publications Warehouse

    Weaver, C.S.; Hill, D.P.

    1978-01-01

    Earthquake swarms in California are often localized to areas within dextral offsets in the linear trend in active fault strands, suggesting a relation between earthquake swarms and local crustal spreading. Local crustal spereading is required by the geometry of dextral offsets when, as in the San Andreas system, faults have dominantly strike-slip motion with right-lateral displacement. Three clear examples of this relation occur in the Imperial Valley, Coso Hot Springs, and the Danville region, all in California. The first two of these areas are known for their Holocene volcanism and geothermal potential, which is consistent with crustal spreading and magmatic intrusion. The third example, however, shows no evidence for volcanism or geothermal activity at the surface. ?? 1978 Birkha??user Verlag.

  11. P-wave velocity structure offshore central Sumatra: implications for compressional and strike-slip faulting

    NASA Astrophysics Data System (ADS)

    Karplus, M.; Henstock, T.; McNeill, L. C.; Vermeesch, P. M. T.; Barton, P. J.

    2014-12-01

    The Sunda subduction zone features significant along-strike structural variability including changes in accretionary prism and forearc morphology. Some of these changes have been linked to changes in megathrust faulting styles, and some have been linked to other thrust and strike-slip fault systems across this obliquely convergent margin (~54-58 mm/yr convergence rate, 40-45 mm/yr subduction rate). We examine these structural changes in detail across central Sumatra, from Siberut to Nias Island, offshore Indonesia. In this area the Investigator Fracture Zone and the Wharton Fossil Ridge, features with significant topography, are being subducted, which may affect sediment thickness variation and margin morphology. We present new seismic refraction P-wave velocity models using marine seismic data collected during Sonne cruise SO198 in 2008. The experiment geometry consisted of 57 ocean bottom seismometers, 23 land seismometers, and over 10,000 air gun shots recorded along ~1750 km of profiles. About 130,000 P-wave first arrival refractions were picked, and the picks were inverted using FAST (First Arrivals Refraction Tomography) 3-D to give a velocity model, best-resolved in the top 25 km. Moho depths, crustal composition, prism geometry, slab dip, and upper and lower plate structures provide insight into the past and present tectonic processes at this plate boundary. We specifically examine the relationships between velocity structure and faulting locations/ styles. These observations have implications for strain-partitioning along the boundary. The Mentawai Fault, located west of the forearc basin in parts of Central Sumatra, has been interpreted variably as a backthrust, strike-slip, and normal fault. We integrate existing data to evaluate these hypotheses. Regional megathrust earthquake ruptures indicate plate boundary segmentation in our study area. The offshore forearc west of Siberut is almost aseismic, reflecting the locked state of the plate interface, which

  12. Finite element models of earthquake cycles in mature strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Lynch, John Charles

    The research presented in this dissertation is on the subject of strike-slip earthquakes and the stresses that build and release in the Earth's crust during earthquake cycles. Numerical models of these cycles in a layered elastic/viscoelastic crust are produced using the finite element method. A fault that alternately sticks and slips poses a particularly challenging problem for numerical implementation, and a new contact element dubbed the "Velcro" element was developed to address this problem (Appendix A). Additionally, the finite element code used in this study was bench-marked against analytical solutions for some simplified problems (Chapter 2), and the resolving power was tested for the fault region of the models (Appendix B). With the modeling method thus developed, there are two main questions posed. First, in Chapter 3, the effect of a finite-width shear zone is considered. By defining a viscoelastic shear zone beneath a periodically slipping fault, it is found that shear stress concentrates at the edges of the shear zone and thus causes the stress tensor to rotate into non-Andersonian orientations. Several methods are used to examine the stress patterns, including the plunge angles of the principal stresses and a new method that plots the stress tensor in a manner analogous to seismic focal mechanism diagrams. In Chapter 4, a simple San Andreas-like model is constructed, consisting of two great earthquake producing faults separated by a freely-slipping shorter fault. The model inputs of lower crustal viscosity, fault separation distance, and relative breaking strengths are examined for their effect on fault communication. It is found that with a lower crustal viscosity of 1018 Pa s (in the lower range of estimates for California), the two faults tend to synchronize their earthquake cycles, even in the cases where the faults have asymmetric breaking strengths. These models imply that postseismic stress transfer over hundreds of kilometers may play a

  13. Role of N-S strike-slip faulting in structuring of north-eastern Tunisia; geodynamic implications

    NASA Astrophysics Data System (ADS)

    Arfaoui, Aymen; Soumaya, Abdelkader; Ben Ayed, Noureddine; Delvaux, Damien; Ghanmi, Mohamed; Kadri, Ali; Zargouni, Fouad

    2017-05-01

    Three major compressional events characterized by folding, thrusting and strike-slip faulting occurred in the Eocene, Late Miocene and Quaternary along the NE Tunisian domain between Bou Kornine-Ressas-Msella and Cap Bon Peninsula. During the Plio-Quaternary, the Grombalia and Mornag grabens show a maximum of collapse in parallelism with the NNW-SSE SHmax direction and developed as 3rd order distensives zones within a global compressional regime. Using existing tectonic and geophysical data supplemented by new fault-kinematic observations, we show that Cenozoic deformation of the Mesozoic sedimentary sequences is dominated by first order N-S faults reactivation, this sinistral wrench system is responsible for the formation of strike-slip duplexes, thrusts, folds and grabens. Following our new structural interpretation, the major faults of N-S Axis, Bou Kornine-Ressas-Messella (MRB) and Hammamet-Korbous (HK) form an N-S first order compressive relay within a left lateral strike-slip duplex. The N-S master MRB fault is dominated by contractional imbricate fans, while the parallel HK fault is characterized by a trailing of extensional imbricate fans. The Eocene and Miocene compression phases in the study area caused sinistral strike-slip reactivation of pre-existing N-S faults, reverse reactivation of NE-SW trending faults and normal-oblique reactivation of NW-SE faults, creating a NE-SW to N-S trending system of east-verging folds and overlaps. Existing seismic tomography images suggest a key role for the lithospheric subvertical tear or STEP fault (Slab Transfer Edge Propagator) evidenced below this region on the development of the MRB and the HK relay zone. The presence of extensive syntectonic Pliocene on top of this crustal scale fault may be the result of a recent lithospheric vertical kinematic of this STEP fault, due to the rollback and lateral migration of the Calabrian slab eastward.

  14. 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

  15. Stress interaction between subduction earthquakes and forearc strike-slip faults: Modeling and application to the northern Caribbean plate boundary

    USGS Publications Warehouse

    ten Brink, Uri S.; Lin, J.

    2004-01-01

    Strike-slip faults in the forearc region of a subduction zone often present significant seismic hazard because of their proximity to population centers. We explore the interaction between thrust events on the subduction interface and strike-slip faults within the forearc region using three-dimensional models of static Coulomb stress change. Model results reveal that subduction earthquakes with slip vectors subparallel to the trench axis enhance the Coulomb stress on strike-slip faults adjacent to the trench but reduce the stress on faults farther back in the forearc region. In contrast, subduction events with slip vectors perpendicular to the trench axis enhance the Coulomb stress on strike-slip faults farther back in the forearc, while reducing the stress adjacent to the trench. A significant contribution to Coulomb stress increase on strike-slip faults in the back region of the forearc comes from "unclamping" of the fault, i.e., reduction in normal stress due to thrust motion on the subduction interface. We argue that although Coulomb stress changes from individual subduction earthquakes are ephemeral, their cumulative effects on the pattern of lithosphere deformation in the forearc region are significant. We use the Coulomb stress models to explain the contrasting deformation pattern between two adjacent segments of the Caribbean subduction zone. Subduction earthquakes with slip vectors nearly perpendicular to the Caribbean trench axis is dominant in the Hispaniola segment, where the strike-slip faults are more than 60 km inland from the trench. In contrast, subduction slip motion is nearly parallel to the Caribbean trench axis along the Puerto Rico segment, where the strike-slip fault is less than 15 km from the trench. This observed jump from a strike-slip fault close to the trench axis in the Puerto Rico segment to the inland faults in Hispaniola is explained by different distributions of Coulomb stress in the forearc region of the two segments, as a result

  16. Transition from strike-slip faulting to oblique subduction: active tectonics at the Puysegur Margin, South New Zealand

    NASA Astrophysics Data System (ADS)

    Lamarche, Geoffroy; Lebrun, Jean-Frédéric

    2000-01-01

    South of New Zealand the Pacific-Australia (PAC-AUS) plate boundary runs along the intracontinental Alpine Fault, the Puysegur subduction front and the intraoceanic Puysegur Fault. The Puysegur Fault is located along Puysegur Ridge, which terminates at ca. 47°S against the continental Puysegur Bank in a complex zone of deformation called the Snares Zone. At Puysegur Trench, the Australian Plate subducts beneath Puysegur Bank and the Fiordland Massif. East of Fiordland and Puysegur Bank, the Moonlight Fault System (MFS) represents the Eocene strike-slip plate boundary. Interpretation of seafloor morphology and seismic reflection profiles acquired over Puysegur Bank and the Snares Zone allows study of the transition from intraoceanic strike-slip faulting along the Puysegur Ridge to oblique subduction at the Puysegur Trench and to better understand the genetic link between the Puysegur Fault and the MFS. Seafloor morphology is interpreted from a bathymetric dataset compiled from swath bathymetry data acquired during the 1993 Geodynz survey, and single beam echo soundings acquired by the NZ Royal Navy. The Snares Zone is the key transition zone from strike-slip faulting to subduction. It divides into three sectors, namely East, NW and SW sectors. A conspicuous 3600 m-deep trough (the Snares Trough) separates the NW and East sectors. The East sector is characterised by the NE termination of Puysegur Ridge into right-stepping en echelon ridges that accommodate a change of strike from the Puysegur Fault to the MFS. Between 48°S and 47°S, in the NW sector and the Snares Trough, a series of transpressional faults splay northwards from the Puysegur Fault. Between 49°50'S and 48°S, thrusts develop progressively at Puysegur Trench into a decollement. North of 48°S the Snares Trough develops between two splays of the Puysegur Fault, indicating superficial extension associated with the subsidence of Puysegur Ridge. Seismic reflection profiles and bathymetric maps show a

  17. Strike-Slip Fault Deformation and Its Control in Hydrocarbon Trapping in Ketaling Area, Jambi Subbasin, Indonesia

    NASA Astrophysics Data System (ADS)

    Ramadhan, Aldis; Badai Samudra, Alexis; Jaenudin; Puji Lestari, Enik; Saputro, Julian; Sugiono; Hirosiadi, Yosi; Amrullah, Indi

    2018-03-01

    Geologically, Ketaling area consists of a local high considered as flexure margin of Tempino-Kenali Asam Deep in west part and graben in east part also known as East Ketaling Deep. Numerous proven plays were established in Ketaling area with reservoir in early Miocene carbonate and middle Miocene sand. This area underwent several major deformations. Faults are developed widely, yet their geometrical features and mechanisms of formation remained so far indistinct, which limited exploration activities. With new three-dimensional seismic data acquired in 2014, this area evidently interpreted as having strike-slip mechanism. The objective of this study is to examine characteristic of strike slip fault and its affect to hydrocarbon trapping in Ketaling Area. Structural pattern and characteristic of strike slip fault deformation was examined with integration of normal seismic with variance seismic attribute analysis and the mapping of Syn-rift to Post-rift horizon. Seismic flattening on 2D seismic cross section with NW-SE direction is done to see the structural pattern related to horst (paleohigh) and graben. Typical flower structure, branching strike-slip fault system and normal fault in synrift sediment clearly showed in section. An echelon pattern identified from map view as the result of strike slip mechanism. Detail structural geology analysis show the normal fault development which has main border fault in the southern of Ketaling area dipping to the Southeast-East with NE-SW lineament. These faults related to rift system in Ketaling area. NW-SE folds with reactive NE-SW fault which act as hydrocarbon trapping in the shallow zone. This polyphase tectonic formed local graben, horst and inverted structure developed a good kitchen area (graben) and traps (horst, inverted structure). Subsequently, hydrocarbon accumulation potentials such as basement fractures, inverted syn-rift deposit and shallow zone are very interesting to explore in this area.

  18. The role of large strike-slip faults in a convergent continental setting - first results from the Dzhungarian Fault in Eastern Kazakhstan

    NASA Astrophysics Data System (ADS)

    Grützner, Christoph; Campbell, Grace; Elliott, Austin; Walker, Richard; Abdrakhmatov, Kanatbek

    2016-04-01

    The Tien Shan and the Dzhungarian Ala-tau mountain ranges in Eastern Kazakhstan and China take up a significant portion of the total convergence between India and Eurasia, despite the fact that they are more than 1000 km away from the actual plate boundary. Shortening is accommodated by large thrust faults that strike more or less perpendicular to the convergence vector, and by a set of conjugate strike-slip faults. Some of these strike-slip faults are major features of several hundred kilometres length and have produced great historical earthquakes. In most cases, little is known about their slip-rates and earthquake history, and thus, about their role in the regional tectonic setting. This study deals with the NW-SE trending Dzhungarian Fault, a more than 350 km-long, right-lateral strike slip feature. It borders the Dzhungarian Ala-tau range and forms one edge of the so-called Dzhungarian Gate. The fault curves from a ~305° strike at its NW tip in Kazakhstan to a ~328° strike in China. No historical ruptures are known from the Kazakh part of the fault. A possible rupture in 1944 in the Chinese part remains discussed. We used remote sensing, Structure-from-Motion (SfM), differential GPS, field mapping, and Quaternary dating of offset geological markers in order to map the fault-related morphology and to measure the slip rate of the fault at several locations along strike. We also aimed to find out the age of the last surface rupturing earthquake and to determine earthquake recurrence intervals and magnitudes. We were further interested in the relation between horizontal and vertical motion along the fault and possible fault segmentation. Here we present first results from our 2015 survey. High-resolution digital elevation models of offset river terraces allowed us to determine the slip vector of the most recent earthquake. Preliminary dating results from abandoned fluvial terraces allow us to speculate on a late Holocene surface rupturing event. Morphological

  19. Fault Branching and Long-Term Earthquake Rupture Scenario for Strike-Slip Earthquake

    NASA Astrophysics Data System (ADS)

    Klinger, Y.; CHOI, J. H.; Vallage, A.

    2017-12-01

    Careful examination of surface rupture for large continental strike-slip earthquakes reveals that for the majority of earthquakes, at least one major branch is involved in the rupture pattern. Often, branching might be either related to the location of the epicenter or located toward the end of the rupture, and possibly related to the stopping of the rupture. In this work, we examine large continental earthquakes that show significant branches at different scales and for which ground surface rupture has been mapped in great details. In each case, rupture conditions are described, including dynamic parameters, past earthquakes history, and regional stress orientation, to see if the dynamic stress field would a priori favor branching. In one case we show that rupture propagation and branching are directly impacted by preexisting geological structures. These structures serve as pathways for the rupture attempting to propagate out of its shear plane. At larger scale, we show that in some cases, rupturing a branch might be systematic, hampering possibilities for the development of a larger seismic rupture. Long-term geomorphology hints at the existence of a strong asperity in the zone where the rupture branched off the main fault. There, no evidence of throughgoing rupture could be seen along the main fault, while the branch is well connected to the main fault. This set of observations suggests that for specific configurations, some rupture scenarios involving systematic branching are more likely than others.

  20. Development of the Elastic Rebound Strike-slip (ERS) Fault Model for Teaching Earthquake Science to Non-science Students

    NASA Astrophysics Data System (ADS)

    Glesener, G. B.; Peltzer, G.; Stubailo, I.; Cochran, E. S.; Lawrence, J. F.

    2009-12-01

    The Modeling and Educational Demonstrations Laboratory (MEDL) at the University of California, Los Angeles has developed a fourth version of the Elastic Rebound Strike-slip (ERS) Fault Model to be used to educate students and the general public about the process and mechanics of earthquakes from strike-slip faults. The ERS Fault Model is an interactive hands-on teaching tool which produces failure on a predefined fault embedded in an elastic medium, with adjustable normal stress. With the addition of an accelerometer sensor, called the Joy Warrior, the user can experience what it is like for a field geophysicist to collect and observe ground shaking data from an earthquake without having to experience a real earthquake. Two knobs on the ERS Fault Model control the normal and shear stress on the fault. Adjusting the normal stress knob will increase or decrease the friction on the fault. The shear stress knob displaces one side of the elastic medium parallel to the strike of the fault, resulting in changing shear stress on the fault surface. When the shear stress exceeds the threshold defined by the static friction of the fault, an earthquake on the model occurs. The accelerometer sensor then sends the data to a computer where the shaking of the model due to the sudden slip on the fault can be displayed and analyzed by the student. The experiment clearly illustrates the relationship between earthquakes and seismic waves. One of the major benefits to using the ERS Fault Model in undergraduate courses is that it helps to connect non-science students with the work of scientists. When students that are not accustomed to scientific thought are able to experience the scientific process first hand, a connection is made between the scientists and students. Connections like this might inspire a student to become a scientist, or promote the advancement of scientific research through public policy.

  1. Palaeopermeability structure within fault-damage zones: A snap-shot from microfracture analyses in a strike-slip system

    NASA Astrophysics Data System (ADS)

    Gomila, Rodrigo; Arancibia, Gloria; Mitchell, Thomas M.; Cembrano, Jose M.; Faulkner, Daniel R.

    2016-02-01

    Understanding fault zone permeability and its spatial distribution allows the assessment of fluid-migration leading to precipitation of hydrothermal minerals. This work is aimed at unraveling the conditions and distribution of fluid transport properties in fault zones based on hydrothermally filled microfractures, which reflect the ''frozen-in'' instantaneous advective hydrothermal activity and record palaeopermeability conditions of the fault-fracture system. We studied the Jorgillo Fault, an exposed 20 km long, left-lateral strike-slip fault, which juxtaposes Jurassic gabbro against metadiorite belonging to the Atacama Fault System in northern Chile. Tracings of microfracture networks of 19 oriented thin sections from a 400 m long transect across the main fault trace was carried out to estimate the hydraulic properties of the low-strain fault damagezone, adjacent to the high-strain fault core, by assuming penny-shaped microfractures of constant radius and aperture within an anisotropic fracture system. Palaeopermeability values of 9.1*10-11 to 3.2*10-13 m2 in the gabbro and of 5.0*10-10 to 1.2*10-13 m2 in the metadiorite were determined, both decreasing perpendicularly away from the fault core. Fracture porosity values range from 40.00% to 0.28%. The Jorgillo Fault has acted as a left-lateral dilational fault-bend, generating large-scale dilation sites north of the JF during co-seismic activity.

  2. Mountain building, strike-slip faulting, and landscape evolution in the Marlborough Fault System, NZ: Insights from new low-temperature thermochronology and modeling

    NASA Astrophysics Data System (ADS)

    Duvall, A. R.; Collett, C.; Flowers, R. M.; Tucker, G. E.; Upton, P.

    2016-12-01

    The 150 km wide Marlborough Fault System (MFS) and adjacent dextral-reverse Alpine Fault accommodate oblique convergence of the Australian and Pacific plates in a broad transform boundary that extends for much of the South Island New Zealand. Understanding the deformation history of the Marlborough region offers the opportunity to study topographic evolution in a strike-slip setting and a fuller picture of the evolving New Zealand plate boundary as the MFS lies at the transition from oceanic Pacific plate subduction to oblique continental collision. Here we present low-temperature thermochronology from the MFS to place new limits on the timing and style of mountain building. We sampled a range of elevations spanning 2 km within and adjacent to the Kaikoura Mountains, which stand high as topographic anomalies above active strike-slip faults. Young apatite (U-Th)/He ages ( 2-5 Ma) on both sides of range-bounding faults are consistent with regional distributed deformation since the Pliocene initiation of strike-slip faulting. However, large differences in both zircon helium and apatite fission track ages, from Paleogene/Neogene ages within hanging walls to unreset >100 Ma ages in footwalls, indicate an early phase of fault-related vertical exhumation. Thermal modeling using the QTQt program reveals two phases of exhumation within the Kaikoura Ranges: rapid cooling at 15-12 Ma localized to hanging wall rocks and regional rapid cooling reflected in all samples starting at 4-5 Ma. These results and landscape evolution models suggest that, despite the presence of active mountain front faults, much of the topographic relief in this region may predate the onset of strike-slip faulting and that portions of the Marlborough Faults are re-activated thrusts that coincide with the early development of the transpressive plate boundary. Regional exhumation after 5 Ma likely reflects increased proximity to the migrating Pacific plate subduction zone and the buoyant Chatham Rise.

  3. Variable rates of late Quaternary strike slip on the San Jacinto fault zone, southern California.

    USGS Publications Warehouse

    Sharp, R.V.

    1981-01-01

    3 strike slip displacements of strata with known approximate ages have been measured at 2 locations on the San Jacinto fault zone. Minimum horizontal offset between 5.7 and 8.6km in no more than 0.73Myr NE of Anza indicates 8-12 mm/yr average slip rate since late Pleistocene time. Horizontal slip of 1.7m has been calculated for the youngest sediment of Lake Cahuilla since its deposition 271- 510 yr BP. The corresponding slip rate is 2.8-5.0 mm/yr. Right lateral offset of 10.9m measured on a buried stream channel older than 5060 yr BP but younger than 6820 yr BP yields average slip rates for the intermediate time periods, 400 to 6000 yr BP of 1-2 mm/yr. The rates of slip suggest a relatively quiescent period from about 4000 BC to about 1600 AD.-from Author

  4. The Ural-Herirud transcontinental postcollisional strike-slip fault and its role in the formation of the Earth's crust

    NASA Astrophysics Data System (ADS)

    Leonov, Yu. G.; Volozh, Yu. A.; Antipov, M. P.; Kheraskova, T. N.

    2015-11-01

    The paper considers the morphology, deep structure, and geodynamic features of the Ural-Herirud postorogenic strike-slip fault (UH fault), along which the Moho (the "M") shifts along the entire axial zone of the Ural Orogen, then further to the south across the Scythian-Turan Plate to the Herirud sublatitudinal fault in Afghanistan. The postcollisional character of dextral displacements along the Ural-Herirud fault and its Triassic-Jurassic age are proven. We have estimated the scale of displacements and made an attempt to make a paleoreconstruction, illustrating the relationship between the Variscides of the Urals and the Tien Shan before tectonic displacements. The analysis of new data includes the latest generation of 1: 200000 geological maps and the regional seismic profiling data obtained in the most elevated part of the Urals (from the seismic profile of the Middle Urals in the north to the Uralseis seismic profile in the south), as well as within the sedimentary cover of the Turan Plate, from Mugodzhary to the southern boundaries of the former water area of the Aral Sea. General typomorphic signs of transcontinental strike-slip fault systems are considered and the structural model of the Ural-Herirud postcollisional strike-slip fault is presented.

  5. Ductile shear zones beneath strike-slip faults: Implications for the thermomechanics of the San Andreas fault zone

    USGS Publications Warehouse

    Thatcher, W.; England, P.C.

    1998-01-01

    We have carried out two-dimensional (2-D) numerical experiments on the bulk flow of a layer of fluid that is driven in a strike-slip sense by constant velocities applied at its boundaries. The fluid has the (linearized) conventional rheology assumed to apply to lower crust/upper mantle rocks. The temperature dependence of the effective viscosity of the fluid and the shear heating that accompanies deformation have been incorporated into the calculations, as has thermal conduction in an overlying crustal layer. Two end-member boundary conditions have been considered, corresponding to a strong upper crust driving a weaker ductile substrate and a strong ductile layer driving a passive, weak crust. In many cases of practical interest, shear heating is concentrated close to the axial plane of the shear zone for either boundary condition. For these cases, the resulting steady state temperature field is well approximated by a cylindrical heat source embedded in a conductive half-space at a depth corresponding to the top of the fluid layer. This approximation, along with the application of a theoretical result for one-dimensional shear zones, permits us to obtain simple analytical approximations to the thermal effects of 2-D ductile shear zones for a range of assumed rheologies and crustal geotherms, making complex numerical calculations unnecessary. Results are compared with observable effects on heat flux near the San Andreas fault using constraints on the slip distribution across the entire fault system. Ductile shearing in the lower crust or upper mantle can explain the observed increase in surface heat flux southeast of the Mendocino triple junction and match the amplitude of the regional heat flux anomaly in the California Coast Ranges. Because ductile dissipation depends only weakly on slip rate, faults moving only a few millimeters per year can be important heat sources, and the superposition of effects of localized ductile shearing on both currently active and now

  6. Along-strike variations of geometry and kinematics on the border fault of Nanpu sag, Bohai Bay Basin

    NASA Astrophysics Data System (ADS)

    Zhang, C.; Ren, J.; Liu, X.; Sun, Z.; Su, M.

    2010-12-01

    Nanpu sag is located in the north-eastern portion of the Huanghua depression, covering an area of approximately 1900km2, and comprises one of the most important petroliferous basins of the Bohai Bay Basin. The Nanpu sag is bordered by two master faults with long-term activity: the Xi’nanzhuang (XNZ) and Bogezhuang (BGZ) fault. By analysis of horizontal slices, gravity anomaly map and seismic reflection sections, we found there is no cutting relationship, and thus considered the XNZ and BGZ fault as a same one. However it showed striking differences between the XNZ and BGZ segment in fault occurrence, fault throw and residual formation thickness and so on. The BGZ fault was NW trending fault with a steep inclination. Taken section across the northern region in Nanpu sag for example, its controlling depocenter is located in eastern subsag (Fig.1); the XNZ fault was a NE fault and displayed a Shovel-shaped to plate-like geometry, with its controlling depocenter located in western subsag. We qualitify the fault throw, showing that the XNZ fault strongly acted during the sedimentary period of Es3-Es2, while the BGZ fault presented weak activity, and especially during Es31 submember-Es2 member, the XNZ fault acted so strongly that the hanging wall of BGZ fault was tilt-lifted and suffered erosion (Fig.1), which created Es1 uncomformity; The BGZ fault acted strongly during the sedimentary period of Es1-Ed, which led the hanging wall of XNZ fault to be tilt-lifted. Controlled by such segmented activity of the whole border fault, which we suggested a "seesaw" model for its evolution, the northern part in the Nanpu sag experienced an alternative variation between a deposition center and an erosion region after tilt-lifting. Combination of the sediment stacking patterns, we further classified the history of "seesaw" activities into four stages: 1) Early double-break stage (Es35-Es31), both of the XNZ and BGZ fault acted; 2) Middle the XNZ segment throw and the BGZ tilting

  7. Late Cenozoic strike-slip faulting in the NE Mojave Block: Deformation at the southwest boundary of the Walker Lane belt

    SciTech Connect

    Schermer, E.R.

    1993-04-01

    New structural and stratigraphy data from the NE Mojave Block (NEMB) establish the timing and style of Cenozoic deformation south of the Garlock fault and west of the Avawatz Mts. Unlike adjacent areas, most of the NEMB did not undergo early-mid Miocene extension. Major fault zones strike EW; offset markers and small-scale shear criteria indicate left-lateral strike slip with a small reverse component. Lateral offsets average ca. 1--6 km and vertical offset is locally >200m. Pre-Tertiary markers indicate minimum cumulative sinistral shear of ca. 15 km in the area between the Garlock and Coyote Lake faults. Tertiary strata are deformedmore » together with the older rocks. Along the Ft. Irwin fault, alluvial fan deposits interpreted to be <11Ma appear to be displaced as much as Mesozoic igneous rocks. EW sinistral faults S. of the Garlock fault cut unconsolidated Quaternary deposits; geomorphologic features and trench exposures along segments of the McLean Lake fault and the Tiefort Mt. fault suggest Late Quaternary activity. The EW faults do not cut modern drainages and are not seismically active. NW-striking faults are largely absent within the NEMB; the largest faults bound the domain of EW-striking faults. Offset of Cretaceous and Miocene rocks suggests the W boundary (Goldstone Lake fault) has <2km right separation. Along the E boundary (Soda-Avawatz fault zone), the presence of distinctive clasts in mid-late Miocene conglomerates west of the Avawatz Mts. supports the suggestion of Brady (1984) of ca. 20 km dextral displacement. Other NW-striking faults are cut by EW faults, have unknown or minor dextral displacement (Desert King Spring Fault, Garlic Spring fault) or are low- to moderate-angle left-oblique thrust faults (Red Pass Lake fault zone).« less

  8. Slip rate and slip magnitudes of past earthquakes along the Bogd left-lateral strike-slip fault (Mongolia)

    USGS Publications Warehouse

    Rizza, M.; Ritz, J.-F.; Braucher, R.; Vassallo, R.; Prentice, C.; Mahan, S.; McGill, S.; Chauvet, A.; Marco, S.; Todbileg, M.; Demberel, S.; Bourles, D.

    2011-01-01

    We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans-particularly well preserved in the arid environment of the Gobi region-allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is ~1 mm yr-1 along the WIB and EIB segments and ~0.5 mm yr-1 along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault. Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at Mw 7.78-7.95. Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of ~2500-5200 yr for past

  9. Slip rate and slip magnitudes of past earthquakes along the Bogd left-lateral strike-slip fault (Mongolia)

    USGS Publications Warehouse

    Prentice, Carol S.; Rizza, M.; Ritz, J.F.; Baucher, R.; Vassallo, R.; Mahan, S.

    2011-01-01

    We carried out morphotectonic studies along the left-lateral strike-slip Bogd Fault, the principal structure involved in the Gobi-Altay earthquake of 1957 December 4 (published magnitudes range from 7.8 to 8.3). The Bogd Fault is 260 km long and can be subdivided into five main geometric segments, based on variation in strike direction. West to East these segments are, respectively: the West Ih Bogd (WIB), The North Ih Bogd (NIB), the West Ih Bogd (WIB), the West Baga Bogd (WBB) and the East Baga Bogd (EBB) segments. Morphological analysis of offset streams, ridges and alluvial fans—particularly well preserved in the arid environment of the Gobi region—allows evaluation of late Quaternary slip rates along the different faults segments. In this paper, we measure slip rates over the past 200 ka at four sites distributed across the three western segments of the Bogd Fault. Our results show that the left-lateral slip rate is∼1 mm yr–1 along the WIB and EIB segments and∼0.5 mm yr–1 along the NIB segment. These variations are consistent with the restraining bend geometry of the Bogd Fault. Our study also provides additional estimates of the horizontal offset associated with the 1957 earthquake along the western part of the Bogd rupture, complementing previously published studies. We show that the mean horizontal offset associated with the 1957 earthquake decreases progressively from 5.2 m in the west to 2.0 m in the east, reflecting the progressive change of kinematic style from pure left-lateral strike-slip faulting to left-lateral-reverse faulting. Along the three western segments, we measure cumulative displacements that are multiples of the 1957 coseismic offset, which may be consistent with a characteristic slip. Moreover, using these data, we re-estimate the moment magnitude of the Gobi-Altay earthquake at Mw 7.78–7.95. Combining our slip rate estimates and the slip distribution per event we also determined a mean recurrence interval of∼2500

  10. Strike-slip faulting, wrinkle ridges, and time variable stress states in the Coprates Region of Mars

    NASA Technical Reports Server (NTRS)

    Schultz, Richard A.

    1990-01-01

    The existence of strike-slip faults was recently documented in two locations on Mars. Two clear examples are reviewed located southeast of Valles Marineris and preliminary evidence is presented for more widespread strike-slip deformation elsewhere in Coprates. The first two examples show that strike-slip faulting occurred in a broad zone east of the Coprates Rise spanning approximately 400 km east-west by perhaps 1000 km north-south. The last example suggests that the growth of major wrinkle ridges throughout Coprates may have been influenced by horizontally directed shear stresses and that more than one generation of ridges was produced. Thus, 'compressional' deformation of ridged plains south of Valles Marineris was spatially heterogeneous and a temporal change in stress may have been involved.

  11. Analogue modelling of strike-slip fault propagation across a rheological/morphological crustal anisotropy: implications for the morphotectonic evolution of the Gloria Fault - Tore Madeira Rise area in NE Atlantic.

    NASA Astrophysics Data System (ADS)

    Tomás, Ricardo; Rosas, Filipe M.; Duarte, João C.; Terrinha, Pedro; Kullberg, Maria C.; Almeida, Jaime; Barata, Frederico; Carvalho, Bruno; Almeida, Pedro

    2015-04-01

    The Gloria Fault (GF) marks the E-W dextral transcurrent plate boundary between Eurasia and Africa in NE Atlantic, displaying complying high magnitude (historical and instrumental) seismic activity (e.g. M=7.1 in 1939 and M=8.4 in 1941, Bufforn et al., 1988), and cutting across a NNE-SSW 1000 km long bathymetric ridge: the so called Tore-Madeira Rise - TMR (rising in average 3km above the abyssal plain). The precise origin and tectono-magmatic evolution of the TMR is still not fully understood, although reported wide-angle refraction data points to a rheological configuration comprising an isostatically compensated thickened oceanic crust, possibly formed during a period of high accretion in the Mid-Atlantic Ridge (Pierce and Barton, 1991). Widespread evidence for volcanic activity has also been recognized, spanning from late Cretaceous to Present (Geldmacher et al. 2006, Merle et al. 2009), noticeably with the most recent volcanism (~500 Ky) occurring as tectonically aligned volcanic plugs, distributed along the E-W tectonic trend of the GF-related structures. To better understand the complex interference at play in this key area between the tectonic structures (essentially determined by the Gloria Fault system), the present and past magmatic activity and the resulting seafloor morphology, a series of dynamically scaled analogue modelling experiments have been conceived and carried out. The main focus of this experimental work was to decipher the potential influence of a rheological vs. morphological anisotropy (accounting for the TMR) on the lateral propagation of a major right-lateral strike-slip fault (representing the GF). The preliminary comparison of the obtained experimental results with the natural morphotectonic pattern in the study area reveals, not only a strong tectonic control of the ongoing volcanism, manifested by the observed preferred directions of aligned volcanic plugs, but also a so far unsuspected deflection/distributed pattern of several

  12. Strike-Slip Faulting Processes on Ganymede: Global Morphological Mapping and Structural Interpretation of Grooved and Transitional Terrains

    NASA Astrophysics Data System (ADS)

    Burkhard, L. M.; Cameron, M. E.; Smith-Konter, B. R.; Seifert, F.; Pappalardo, R. T.; Collins, G. C.

    2015-12-01

    Ganymede's fractured surface reveals many large-scale, morphologically distinct regions of inferred distributed shear and strike-slip faulting that may be important to the structural development of its surface and in the transition from dark to light (grooved) materials. To better understand the role of strike-slip tectonism in shaping Ganymede's complex icy surface, we perform a detailed mapping of key examples of strike-slip morphologies (i.e., en echelon structures, strike-slip duplexes, laterally offset pre-existing features, and possible strained craters) from Galileo and Voyager images. We focus on complex structures associated with grooved terrain (e.g. Nun Sulcus, Dardanus Sulcus, Tiamat Sulcus, and Arbela Sulcus) and terrains transitional from dark to light terrain (e.g. the boundary between Nippur Sulcus and Marius Regio, including Byblus Sulcus and Philus Sulcus). Detailed structural interpretations suggest strong evidence of strike-slip faulting in some regions (i.e., Nun and Dardanus Sulcus); however, further investigation of additional strike-slip structures is required of less convincing regions (i.e., Byblus Sulcus). Where applicable, these results are synthesized into a global database representing an inferred sense of shear for many of Ganymede's fractures. Moreover, when combined with existing observations of extensional features, these results help to narrow down the range of possible principal stress directions that could have acted at the regional or global scale to produce grooved terrain on Ganymede.

  13. Surface rupture of the 2002 Denali fault, Alaska, earthquake and comparison with other strike-slip ruptures

    USGS Publications Warehouse

    Haeussler, Peter J.; Schwartz, D.P.; Dawson, T.E.; Stenner, Heidi D.; Lienkaemper, J.J.; Cinti, F.; Montone, Paola; Sherrod, B.; Craw, P.

    2004-01-01

    On 3 November 2002, an M7.9 earthquake produced 340 km of surface rupture on the Denali and two related faults in Alaska. The rupture proceeded from west to east and began with a 40-km-long break on a previously unknown thrust fault. Estimates of surface slip on this thrust are 3-6 m. Next came the principal surface break along ???218 km of the Denali fault. Right-lateral offsets averaged around 5 m and increased eastward to a maximum of nearly 9 m. The fault also ruptured beneath the trans-Alaska oil pipeline, which withstood almost 6 m of lateral offset. Finally, slip turned southeastward onto the Totschunda fault. Right-lateral offsets are up to 3 m, and the surface rupture is about 76 km long. This three-part rupture ranks among the longest strike-slip events of the past two centuries. The earthquake is typical when compared to other large earthquakes on major intracontinental strike-slip faults. ?? 2004, Earthquake Engineering Research Institute.

  14. Modeling the evolution of the lower crust with laboratory derived rheological laws under an intraplate strike slip fault

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Sagiya, T.

    2015-12-01

    The earth's crust can be divided into the brittle upper crust and the ductile lower crust based on the deformation mechanism. Observations shows heterogeneities in the lower crust are associated with fault zones. One of the candidate mechanisms of strain concentration is shear heating in the lower crust, which is considered by theoretical studies for interplate faults [e.g. Thatcher & England 1998, Takeuchi & Fialko 2012]. On the other hand, almost no studies has been done for intraplate faults, which are generally much immature than interplate faults and characterized by their finite lengths and slow displacement rates. To understand the structural characteristics in the lower crust and its temporal evolution in a geological time scale, we conduct a 2-D numerical experiment on the intraplate strike slip fault. The lower crust is modeled as a 20km thick viscous layer overlain by rigid upper crust that has a steady relative motion across a vertical strike slip fault. Strain rate in the lower crust is assumed to be a sum of dislocation creep and diffusion creep components, each of which flows the experimental flow laws. The geothermal gradient is assumed to be 25K/km. We have tested different total velocity on the model. For intraplate fault, the total velocity is less than 1mm/yr, and for comparison, we use 30mm/yr for interplate faults. Results show that at a low slip rate condition, dislocation creep dominates in the shear zone near the intraplate fault's deeper extension while diffusion creep dominates outside the shear zone. This result is different from the case of interplate faults, where dislocation creep dominates the whole region. Because of the power law effect of dislocation creep, the effective viscosity in the shear zone under intraplate faults is much higher than that under the interplate fault, therefore, shear zone under intraplate faults will have a much higher viscosity and lower shear stress than the intraplate fault. Viscosity contract between

  15. Stress sensitivity of fault seismicity: A comparison between limited-offset oblique and major strike-slip faults

    USGS Publications Warehouse

    Parsons, T.; Stein, R.S.; Simpson, R.W.; Reasenberg, P.A.

    1999-01-01

    We present a new three-dimensional inventory of the southern San Francisco Bay area faults and use it to calculate stress applied principally by the 1989 M = 7.1 Loma Prieta earthquake and to compare fault seismicity rates before and after 1989. The major high-angle right-lateral faults exhibit a different response to the stress change than do minor oblique (right-lateral/thrust) faults. Seismicity on oblique-slip faults in the southern Santa Clara Valley thrust belt increased where the faults were unclamped. The strong dependence of seismicity change on normal stress change implies a high coefficient of static friction. In contrast, we observe that faults with significant offset (>50-100 km) behave differently; microseismicity on the Hayward fault diminished where right-lateral shear stress was reduced and where it was unclamped by the Loma Prieta earthquake. We observe a similar response on the San Andreas fault zone in southern California after the Landers earthquake sequence. Additionally, the offshore San Gregorio fault shows a seismicity rate increase where right-lateral/oblique shear stress was increased by the Loma Prieta earthquake despite also being clamped by it. These responses are consistent with either a low coefficient of static friction or high pore fluid pressures within the fault zones. We can explain the different behavior of the two styles of faults if those with large cumulative offset become impermeable through gouge buildup; coseismically pressurized pore fluids could be trapped and negate imposed normal stress changes, whereas in more limited offset faults, fluids could rapidly escape. The difference in behavior between minor and major faults may explain why frictional failure criteria that apply intermediate coefficients of static friction can be effective in describing the broad distributions of aftershocks that follow large earthquakes, since many of these events occur both inside and outside major fault zones.

  16. Interactions between Polygonal Normal Faults and Larger Normal Faults, Offshore Nova Scotia, Canada

    NASA Astrophysics Data System (ADS)

    Pham, T. Q. H.; Withjack, M. O.; Hanafi, B. R.

    2017-12-01

    Polygonal faults, small normal faults with polygonal arrangements that form in fine-grained sedimentary rocks, can influence ground-water flow and hydrocarbon migration. Using well and 3D seismic-reflection data, we have examined the interactions between polygonal faults and larger normal faults on the passive margin of offshore Nova Scotia, Canada. The larger normal faults strike approximately E-W to NE-SW. Growth strata indicate that the larger normal faults were active in the Late Cretaceous (i.e., during the deposition of the Wyandot Formation) and during the Cenozoic. The polygonal faults were also active during the Cenozoic because they affect the top of the Wyandot Formation, a fine-grained carbonate sedimentary rock, and the overlying Cenozoic strata. Thus, the larger normal faults and the polygonal faults were both active during the Cenozoic. The polygonal faults far from the larger normal faults have a wide range of orientations. Near the larger normal faults, however, most polygonal faults have preferred orientations, either striking parallel or perpendicular to the larger normal faults. Some polygonal faults nucleated at the tip of a larger normal fault, propagated outward, and linked with a second larger normal fault. The strike of these polygonal faults changed as they propagated outward, ranging from parallel to the strike of the original larger normal fault to orthogonal to the strike of the second larger normal fault. These polygonal faults hard-linked the larger normal faults at and above the level of the Wyandot Formation but not below it. We argue that the larger normal faults created stress-enhancement and stress-reorientation zones for the polygonal faults. Numerous small, polygonal faults formed in the stress-enhancement zones near the tips of larger normal faults. Stress-reorientation zones surrounded the larger normal faults far from their tips. Fewer polygonal faults are present in these zones, and, more importantly, most polygonal faults

  17. Relationships between sliding behavior and internal geometry of laboratory fault zones and some creeping and locked strike-slip faults of California

    USGS Publications Warehouse

    Moore, Diane E.; Byerlee, J.

    1992-01-01

    Moore, D.E. and Byerlee, J., 1992. Relationships between sliding behavior and internal geometry of laboratory fault zones and some creeping and locked strike-slip faults of California. In: T. Mikumo, K. Aki, M. Ohnaka, L.J. Ruff and P.K.P. Spudich (Editors), Earthquake Source Physics and Earthquake Precursors. Tectonophysics, 211: 305-316. In order to relate fault geometries to sliding behavior, maps of recently active breaks within the Hayward fault of central California, which is characterized by fault creep, have been examined and compared to maps of the San Andreas fault. The patterns of recent breaks of the Hayward fault are consistent with those found within the creeping section of the San Andreas, and they appear to have plausible physical explanations in the findings of laboratory experiments. The distinguishing geometric features of the examined locked and creeping faults are: (1) P-type second-order traces predominate over R(Riedel)-type traces in creeping sections; and (2) R-type second-order traces make smaller angles to the local fault strike in creeping sections than they do in locked sections. Two different maps of the Hayward fault gave similar results, supporting the inference that the patterns identified are basic characteristics of the fault rather than artifacts of a particular mapping procedure. P shears predominate over R shears under laboratory conditions that allow dilation within the fault zone. In our own experiments, P-shear development was favored by the generation of excess pore-fluid pressures. We propose that creep in California faults also is the result of fluid overpressures that are maintained in a low-permeability gouge zone and that significantly lower effective stresses, thus helping to stabilize slip and producing high values of the ratio P/R. Small R-trace angles may also be an indicator of low effective stresses, but the evidence for this is not conclusive because other factors can also affect the size of the angles. ?? 1992.

  18. A tectonic model for the Tertiary evolution of strike slip faults and rift basins in SE Asia

    NASA Astrophysics Data System (ADS)

    Morley, C. K.

    2002-04-01

    Models for the Tertiary evolution of SE Asia fall into two main types: a pure escape tectonics model with no proto-South China Sea, and subduction of proto-South China Sea oceanic crust beneath Borneo. A related problem is which, if any, of the main strike-slip faults (Mae Ping, Three Pagodas and Aliao Shan-Red River (ASRR)) cross Sundaland to the NW Borneo margin to facilitate continental extrusion? Recent results investigating strike-slip faults, rift basins, and metamorphic core complexes are reviewed and a revised tectonic model for SE Asia proposed. Key points of the new model include: (1) The ASRR shear zone was mainly active in the Eocene-Oligocene in order to link with extension in the South China Sea. The ASRR was less active during the Miocene (tens of kilometres of sinistral displacement), with minor amounts of South China Sea spreading centre extension transferred to the ASRR shear zone. (2) At least three important regions of metamorphic core complex development affected Indochina from the Oligocene-Miocene (Mogok gneiss belt; Doi Inthanon and Doi Suthep; around the ASRR shear zone). Hence, Paleogene crustal thickening, buoyancy-driven crustal collapse, and lower crustal flow are important elements of the Tertiary evolution of Indochina. (3) Subduction of a proto-South China Sea oceanic crust during the Eocene-Early Miocene is necessary to explain the geological evolution of NW Borneo and must be built into any model for the region. (4) The Eocene-Oligocene collision of NE India with Burma activated extrusion tectonics along the Three Pagodas, Mae Ping, Ranong and Klong Marui faults and right lateral motion along the Sumatran subduction zone. (5) The only strike-slip fault link to the NW Borneo margin occurred along the trend of the ASRR fault system, which passes along strike into a right lateral transform system including the Baram line.

  19. Along-strike variations of the partitioning of convergence across the Haiyuan fault system detected by InSAR

    NASA Astrophysics Data System (ADS)

    Daout, S.; Jolivet, R.; Lasserre, C.; Doin, M.-P.; Barbot, S.; Tapponnier, P.; Peltzer, G.; Socquet, A.; Sun, J.

    2016-04-01

    Oblique convergence across Tibet leads to slip partitioning with the coexistence of strike-slip, normal and thrust motion on major fault systems. A key point is to understand and model how faults interact and accumulate strain at depth. Here, we extract ground deformation across the Haiyuan Fault restraining bend, at the northeastern boundary of the Tibetan plateau, from Envisat radar data spanning the 2001-2011 period. We show that the complexity of the surface displacement field can be explained by the partitioning of a uniform deep-seated convergence. Mountains and sand dunes in the study area make the radar data processing challenging and require the latest developments in processing procedures for Synthetic Aperture Radar interferometry. The processing strategy is based on a small baseline approach. Before unwrapping, we correct for atmospheric phase delays from global atmospheric models and digital elevation model errors. A series of filtering steps is applied to improve the signal-to-noise ratio across high ranges of the Tibetan plateau and the phase unwrapping capability across the fault, required for reliable estimate of fault movement. We then jointly invert our InSAR time-series together with published GPS displacements to test a proposed long-term slip-partitioning model between the Haiyuan and Gulang left-lateral Faults and the Qilian Shan thrusts. We explore the geometry of the fault system at depth and associated slip rates using a Bayesian approach and test the consistency of present-day geodetic surface displacements with a long-term tectonic model. We determine a uniform convergence rate of 10 [8.6-11.5] mm yr-1 with an N89 [81-97]°E across the whole fault system, with a variable partitioning west and east of a major extensional fault-jog (the Tianzhu pull-apart basin). Our 2-D model of two profiles perpendicular to the fault system gives a quantitative understanding of how crustal deformation is accommodated by the various branches of this

  20. Late Pleistocene-Holocene Activity of the Strike-slip Xianshuihe Fault Zone, Tibetan Plateau, Inferred from Tectonic Landforms

    NASA Astrophysics Data System (ADS)

    Lin, A.; Yan, B.

    2017-12-01

    Knowledges on the activity of the strike-slip fault zones on the Tibetan Plateau have been promoted greatly by the interpretation of remote sensing images (Molnar and Tapponnier, 1975; Tapponnier and Molnar, 1977). The active strike-slip Xianshuihe-Xiaojiang Fault System (XXFS), with the geometry of an arc projecting northeastwards, plays an important role in the crustal deformation of the Tibetan Plateau caused by the continental collision between the Indian and Eurasian plates. The Xianshuihe Fault Zone (XFZ) is located in the central segment of the XXFS and extends for 370 km, with a maximum sinistral offset of 60 km since 13‒5 Ma. In this study, we investigated the tectonic landforms and slip rate along the central segment of the left-lateral strike-slip XFZ. Field investigations and analysis of ttectonic landforms show that horizontal offset has been accumulated on the topographical markers of different scales that developed since the Last Glacial Maximum (LGM). The central segment of the XFZ is composed of three major faults: Yalahe, Selaha, and Zheduotang faults showing a right-stepping echelon pattern, that is characterized by systematical offset of drainages, alluvial fans and terrace risers with typical scissoring structures, indicating a structural feature of left-lateral strike-slip fault. Based on the offset glacial morphology and radiocarbon dating ages, we estimate the Late Pleistocene-Holocene slip rate to be 10 mm/yr for the central segment of the XFZ, which is consistent with that estimated from the GPS observations and geological evidence as reported previously. Across the central segment of the XFZ, the major Selaha and Zheduotang faults participate a slip rate of 5.8 mm/yr and 3.4 mm/yr, respectively. Detailed investigations of tectonic landforms are essential for the understanding the activity of active faults. Our findings suggest that the left-lateral slipping of the XFZ partitions the deformation of eastward extrusion and northeastward

  1. Is there a "blind" strike-slip fault at the southern end of the San Jacinto Fault system?

    NASA Astrophysics Data System (ADS)

    Tymofyeyeva, E.; Fialko, Y. A.

    2015-12-01

    We have studied the interseismic deformation at the southern end of the San Jacinto fault system using Interferometric Synthetic Aperture Radar (InSAR) and Global Positioning System (GPS) data. To complement the continuous GPS measurements from the PBO network, we have conducted campaign-style GPS surveys of 19 benchmarks along Highway 78 in the years 2012, 2013, and 2014. We processed the campaign GPS data using GAMIT to obtain horizontal velocities. The data show high velocity gradients East of the surface trace of the Coyote Creek Fault. We also processed InSAR data from the ascending and descending tracks of the ENVISAT mission between the years 2003 and 2010. The InSAR data were corrected for atmospheric artifacts using an iterative common point stacking method. We combined average velocities from different look angles to isolate the fault-parallel velocity field, and used fault-parallel velocities to compute strain rate. We filtered the data over a range of wavelengths prior to numerical differentiation, to reduce the effects of noise and to investigate both shallow and deep sources of deformation. At spatial wavelengths less than 2km the strain rate data show prominent anomalies along the San Andreas and Superstition Hills faults, where shallow creep has been documented by previous studies. Similar anomalies are also observed along parts of the Coyote Creek Fault, San Felipe Fault, and an unmapped southern continuation of the Clark strand of the San Jacinto Fault. At wavelengths on the order of 20km, we observe elevated strain rates concentrated east of the Coyote Creek Fault. The long-wavelength strain anomaly east of the Coyote Creek Fault, and the localized shallow creep observed in the short-wavelength strain rate data over the same area suggest that there may be a "blind" segment of the Clark Fault that accommodates a significant portion of the deformation on the southern end of the San Jacinto Fault.

  2. Low-angle faulting in strike-slip dominated settings: Seismic evidence from the Maritimes Basin, Canada

    NASA Astrophysics Data System (ADS)

    Pinet, Nicolas; Dietrich, Jim; Duchesne, Mathieu J.; Hinds, Steve J.; Brake, Virginia

    2018-07-01

    The Maritimes Basin is an upper Paleozoic sedimentary basin centered in the Gulf of St. Lawrence (Canada). Early phases of basin formation included the development of partly connected sub-basins bounded by high-angle faults, in an overall strike-slip setting. Interpretation of reprocessed seismic reflection data indicates that a low-angle detachment contributed to the formation of a highly asymmetric sub-basin. This detachment was rotated toward a lower angle and succeeded by high-angle faults that sole into the detachment or cut it. This model bears similarities to other highly extended terranes and appears to be applicable to strike-slip and/or transtensional settings.

  3. Along strike variation of active fault arrays and their effect on landscape morphology of the northwestern Himalaya

    NASA Astrophysics Data System (ADS)

    Nennewitz, Markus; Thiede, Rasmus; Bookhagen, Bodo

    2017-04-01

    The location and magnitude of the active deformation of the Himalaya has been debated for decades, but several aspects remain unknown. For instance, the spatial distribution of the deformation and the shortening that ultimately sustains Himalayan topography and the activity of major fault zones are not well constrained neither for the present day and nor for Holocene and Quarternary timescales. Because of these weakly constrained factors, many previous studies have assumed that the structural setting and the fault geometry of the Himalaya is continuous along strike and similar to fault geometries of central Nepal. Thus, the sub-surface structural information from central Nepal have been projected along strike, but have not been verified at other locations. In this study we use digital topographic analysis of the NW Himalaya. We obtained catchment-averaged, normalized steepness indexes of longitudinal river profiles with drainage basins ranging between 5 and 250km2 and analyzed the relative change in their spatial distribution both along and across strike. More specific, we analyzed the relative changes of basins located in the footwall and in the hanging wall of major fault zones. Under the assumption that along strike changes in the normalized steepness index are primarily controlled by the activity of thrust segments, we revealed new insights in the tectonic deformation and uplift pattern. Our results show three different segments along the northwest Himalaya, which are located, from east to west, in Garwhal, Chamba and Kashmir Himalaya. These have formed independent orogenic segments characterized by significant changes in their structural architecture and fault geometry. Moreover, their topographic changes indicate strong variations on fault displacement rates across first-order fault zones. With the help of along- and across-strike profiles, we were able to identify fault segments of pronounced fault activity across MFT, MBT, and the PT2 and identify the

  4. Seismic images of the sliver strike-slip fault and back thrust in the Andaman-Nicobar region

    NASA Astrophysics Data System (ADS)

    Singh, Satish C.; Moeremans, Raphaele; McArdle, Jo; Johansen, Kjell

    2013-10-01

    sliver strike-slip Great Sumatra Fault (GSF) traverses mainland Sumatra from the Sunda Strait in the southeast to Banda Aceh in the northwest, and defines the present day plate boundary between the Sunda Plate in the north and the Burmese Sliver Plate in the south. It has been well studied on mainland Sumatra but poorly north of Banda Aceh in the Andaman Sea. Here we present deep seismic reflection images along the northward extension of the GSF over 700 km until it joins the Andaman Sea Spreading Centre, and we interpret these images in the light of earthquake, gravity, and bathymetry data. We find that the GSF has two strands between Banda Aceh and Nicobar Island: a transpression in the south and a deep narrow active rift system in the north, dotted with volcanoes in the center, suggesting that the volcanic arc is coincident with rifting. Farther north of Nicobar Island, an active strike-slip fault, the Andaman-Nicobar Fault, cuts through a rifted deep basin until its intersection with the Andaman Sea Spreading Centre. The volcanic arc lies just east of the rift basin. The western margin of this basin seems to be a rifted continental margin, tilted westward, and flooring the Andaman-Nicobar fore-arc basin. The Andaman-Nicobar fore-arc basin is bounded in the west by back thrusts similar to the West Andaman and Mentawai faults. The cluster of seismicity after the 2004 great Andaman-Sumatra earthquake just north of Nicobar Island coincides with the intersection of two strike-slip fault systems.

  5. Microstructural record of pressure solution and crystal plastic deformation in carbonate fault rocks from a shallow crustal strike-slip fault, Northern Calcareous Alps (Austria)

    NASA Astrophysics Data System (ADS)

    Bauer, Helene; Rogowitz, Anna; Grasemann, Benhard; Decker, Kurt

    2017-04-01

    This study presents microstructural investigations of natural carbonate fault rocks that formed by a suite of different deformation processes, involving hydro-fracturing, dissolution-precipitation creep and cataclasis. Some fault rocks show also clear indications of crystal plastic deformation, which is quite unexpected, as the fault rocks were formed in an upper crustal setting, raising the question of possible strongly localised, low temperature ductile deformation in carbonate rocks. The investigated carbonate fault rocks are from an exhumed, sinistral strike-slip fault at the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Northern Calcareous Alps (Austria). The SEMP fault system formed during eastward lateral extrusion of the Eastern Alps in the Oligocene to Lower Miocene. Based on vitrinite reflectance data form intramontane Teritary basins within the Northern Calcareous Alps, a maximum burial depth of 4 km for the investigated fault segment is estimated. The investigated fault accommodated sinistral slip of several hundreds of meters. Microstructural analysis of fault rocks includes scanning electron microscopy, optical microscopy and electron backscattered diffraction mapping. The data show that fault rocks underwent various stages of evolution including early intense veining (hydro-fracturing) and stylolite formation reworked by localised shear zones. Cross cutting relationship reveals that veins never cross cut clay seams accumulated along stylolites. We conclude that pressure solution processes occured after hydro-fracturing. Clay enriched zones localized further deformation, producing a network of small-scale clay-rich shear zones of up to 1 mm thickness anastomosing around carbonate microlithons, varying from several mm down to some µm in size. Clay seams consist of kaolinit, chlorite and illite matrix and form (sub) parallel zones in which calcite was dissolved. Beside pressure solution, calcite microlithons

  6. Uplifted Yellow river terraces across the Haiyuan fault, China and their implications to geometrical complexity of strike-slip fault system

    NASA Astrophysics Data System (ADS)

    Liu, J.; van der Woerd, J.; Li, Z.; Klinger, Y.; Matrau, R.; Shao, Y.; Zhang, J.; Wang, P.

    2016-12-01

    Geometrical complexities and discontinues, such as fault bends, splays and step-overs, are common along large strike-slip faults. Numerical and observational studies show that geometrical complexities above some threshold degree may inhibit thoroughgoing rupture, limiting rupture length and the size of the resulting earthquake. Studying the fine structure and long-term evolution of fault step-overs would help us better understand their effect on earthquake ruptures. In this study, we focus on a prominent geometrical "knot" on the left-lateral Haiyuan fault, where the fault curves with multi-strand splays bounding the Mijia Shan-Hasi Shan ranges. Incidentally, the Yellow river flows between the Mijia Shan and Hasi Shan and cuts a deep gorge when crossing the fault. On the western bank of the river, a series of at least twelve levels of fluvial strath terraces perch above river bed, and are capped with no more than 5 meters of alluvial deposits. We measured the terrace heights above river bed, using RTK and UAV surveys. We collected quartz-rich pebbles of yellow river gravel for cosmogenic radio nuclide (CRN), and silt layers within gravel and the overlying loess cap for optimally stimulated luminescence (OSL) dating to constrain the terrace formation ages. Quartz-rich pebbles were sampled both in hand-dug pit for depth-profile method and surface samples on terrace surfaces. The CRN age results were corrected in terms of inheritance and shielding by loess. The dates and heights of serial terraces yielded an average uplift rate of 2±0.34 mm/yr, which represents the late Quaternary uplifting rate of the Mijia Shan. The uplift of the Mijia Shan-Hasi Shan may result from the oblique shear of positive flower in the deep crust of the left-lateral Haiyuan fault. We further speculate that with progressively uplifted mountain ranges, the active fault trace shifts with time among the multi-strands of the fault system. In addition, the coincidence of prominent uplifted

  7. What causes an icy fault to slip? Investigating strike-slip failure conditions on Ganymede at Dardanus and Tiamat Sulcus.

    NASA Astrophysics Data System (ADS)

    Cameron, M. E.; Smith-Konter, B. R.; Burkhard, L. M.; Collins, G. C.; Seifert, F.; Pappalardo, R. T.

    2015-12-01

    Ganymede exhibits two geologically distinct terrains known as dark and light (grooved) terrain. The mechanism for a transition from dark to light terrain remains unclear; however, inferences of strike-slip faulting and distributed shear zones suggest that strike-slip tectonism may be important to the structural development of Ganymede's surface and in this transition. Here we investigate the role of tidal stresses on Ganymede in the formation and evolution of strike-slip structures in both dark and grooved terrains. Using numerical code SatStress, we calculate both diurnal and non-synchronous rotation (NSR) tidal stresses at Ganymede's surface. Specifically, we investigate the role of fault friction and orbital eccentricity in the development of ~45 km of right-lateral offset at Dardanus Sulcus and a possible case of <10 km of right-lateral offset at Tiamat Sulcus. We compute Coulomb failure conditions for these target fractures and consider tidal stress scenarios for both present eccentricity (0.0013) and possible past high (~0.05) eccentricity of Ganymede. We find that while diurnal stresses are not large enough to support strike-slip failure at present or past eccentricities, models that include both diurnal and NSR stress readily generate shear and normal stress magnitudes that could give rise to shear failure. Results for a past high eccentricity assuming a low coefficient of friction (μf = 0.2) suggest shear failure is possible down to depths of 1-2 km along both Dardanus and Tiamat. For a high coefficient of friction (μf = 0.6), failure is limited to about 1 km depth at Dardanus and Tiamat, although confined to small episodic slip windows for the latter. Moreover, our models predict a right-lateral sense of slip, in agreement with inferred offset observed at both regions. Based on these results, we infer that past shear failure on Ganymede is possible when NSR is a driving stress mechanism. We complement this study with a detailed morphological mapping of

  8. Along strike behavior of the Tizi n' Firest fault during the Lower Jurassic rifting (Central High Atlas Carbonate basin, Morocco)

    NASA Astrophysics Data System (ADS)

    Sarih, S.; Quiquerez, A.; Allemand, P.; Garcia, J. P.; El Hariri, K.

    2018-03-01

    The purpose of this study is to document the along-strike early syn-rift history of the Lower Jurassic Carbonate basin of the Central High Atlas (Morocco) by combining sedimentological observations and high-resolution biostratigraphy. Six sections, each from the Sinemurian to the Upper Pliensbachian, were investigated along a 75 km-long transect at the hanging wall of a major fault of the Lower Jurassic Basin (i.e. the Tizi n' Firest fault). Depositional geometries of the early syn-rift deposits were reconstructed from the correlation between eight main timelines dated by biochronological markers for a time span covering about 6 Ma. Depocentre migration was examined and accommodation rates were calculated at the sub-zone timescale to discuss the along-strike-fault behavior of the Lower Jurassic basin formation. The early stages of extension are marked by contrasted along-strike variations in depositional geometry thickness, depocentre migration and accommodation rates, leading to the growth of three independent sub-basins (i.e. western, central, and eastern), ranging in size from 30 to 50 km, and displaying three contrasted tectono-sedimentary histories. Our results suggest that, during the early rifting phase, tectonic activity was not a continuous and progressive process evolving towards a rift climax stage, but rather a series of acceleration periods that alternated with periods of much reduced activity. The length of active fault segments is estimated at about 15-20 km, with a lifespan of a few ammonite sub-zones (> 2-3 Ma).

  9. Modelling the role of basement block rotation and strike-slip faulting on structural pattern in the cover units of fold-and-thrust belts

    NASA Astrophysics Data System (ADS)

    Koyi, Hemin; Nilfouroushan, Faramarz; Hessami, Khaled

    2015-04-01

    A series of scaled analogue models are run to study the degree of coupling between basement block kinematics and cover deformation. In these models, rigid basal blocks were rotated about vertical axis in a "bookshelf" fashion, which caused strike-slip faulting along the blocks and, to some degrees, in the overlying cover units of loose sand. Three different combinations of cover basement deformations are modeled; cover shortening prior to basement fault movement; basement fault movement prior to shortening of cover units; and simultaneous cover shortening with basement fault movement. Model results show that the effect of basement strike-slip faults depends on the timing of their reactivation during the orogenic process. Pre- and syn-orogen basement strike-slip faults have a significant impact on the structural pattern of the cover units, whereas post-orogenic basement strike-slip faults have less influence on the thickened hinterland of the overlying fold-and-thrust belt. The interaction of basement faulting and cover shortening results in formation of rhomb features. In models with pre- and syn-orogen basement strike-slip faults, rhomb-shaped cover blocks develop as a result of shortening of the overlying cover during basement strike-slip faulting. These rhombic blocks, which have resemblance to flower structures, differ in kinematics, genesis and structural extent. They are bounded by strike-slip faults on two opposite sides and thrusts on the other two sides. In the models, rhomb-shaped cover blocks develop as a result of shortening of the overlying cover during basement strke-slip faulting. Such rhomb features are recognized in the Alborz and Zagros fold-and-thrust belts where cover units are shortened simultaneously with strike-slip faulting in the basement. Model results are also compared with geodetic results obtained from combination of all available GPS velocities in the Zagros and Alborz FTBs. Geodetic results indicate domains of clockwise and

  10. Combining Earthquake Focal Mechanism Inversion and Coulomb Friction Law to Yield Tectonic Stress Magnitudes in Strike-slip Faulting Regime

    NASA Astrophysics Data System (ADS)

    Soh, I.; Chang, C.

    2017-12-01

    The techniques for estimating present-day stress states by inverting multiple earthquake focal mechanism solutions (FMS) provide orientations of the three principal stresses and their relative magnitudes. In order to estimate absolute magnitudes of the stresses that are generally required to analyze faulting mechanics, we combine the relative stress magnitude parameter (R-value) derived from the inversion process and the concept of frictional equilibrium of stress state defined by Coulomb friction law. The stress inversion in Korean Peninsula using 152 FMS data (magnitude≥2.5) conducted at regularly spaced grid points yields a consistent strike-slip faulting regime in which the maximum (S1) and the minimum (S3) principal stresses act in horizontal planes (with an S1 azimuth in ENE-WSW) and the intermediate principal stress (S2) close to vertical. However, R-value varies from 0.28 to 0.75 depending on locations, systematically increasing eastward. Based on the assumptions that the vertical stress is lithostatic, pore pressure is hydrostatic, and the maximum differential stress (S1-S3) is limited by Byerlee's friction of optimally oriented faults for slip, we estimate absolute magnitudes of the two horizontal principal stresses using R-value. As R-value increases, so do the magnitudes of the horizontal stresses. Our estimation of the stress magnitudes shows that the maximum horizontal principal stress (S1) normalized by vertical stress tends to increase from 1.3 in the west to 1.8 in the east. The estimated variation of stress magnitudes is compatible with distinct clustering of faulting types in different regions. Normal faulting events are densely populated in the west region where the horizontal stress is relatively low, whereas numerous reverse faulting events prevail in the east offshore where the horizontal stress is relatively high. Such a characteristic distribution of distinct faulting types in different regions can only be explained in terms of stress

  11. The 2003 Bam (Iran) earthquake: Rupture of a blind strike-slip fault

    NASA Technical Reports Server (NTRS)

    Talebian, M.; Fielding, E. J.; Funning, G. J.; Ghorashi, M.; Jackson, J.; Nazari, H.; Parsons, B.; Priestley, K.; Rosen, P. A.; Walker, R.; hide

    2004-01-01

    A magnitude 6.5 earthquake devastated the town of Bam in southeast Iran on 26 December 2003. Surface displacements and decorrelation effects, mapped using Envisat radar data, reveal that over 2 m of slip occurred at depth on a fault that had not previously been identified. It is common for earthquakes to occur on blind faults which, despite their name, usually produce long-term surface effects by which their existence may be recognised. However, in this case there is a complete absence of morphological features associated with the seismogenic fault that destroyed Bam.

  12. Inland termination of the Weddell Sea Rift against a major Jurassic strike-slip fault zone between East and West Antarctica

    NASA Astrophysics Data System (ADS)

    Jordan, Tom; Ferraccioli, Fausto; Leat, Phil; Ross, Neil; Bingham, Rob; Rippin, David; LeBrocq, Anne; Corr, Hugh; Siegert, Martin

    2013-04-01

    within the newly identified Pagano Shear Zone, a major tectonic boundary between East and West Antarctica. We put forward two alternative kinematic tectonic models by analysing a compilation of our new data with previous magnetic and gravity datasets. In the simple shear model, ~E-W oriented Jurassic extension within the WSR was accommodated by left-lateral strike-slip motion on the Pagano Shear Zone. This would have facilitated eastward motion of the EWM block relative to East Antarctica, effectively transferring the block to West Antarctica. In a pure shear model, the left-lateral Pagano Shear Zone we identified and the dextral and normal fault systems, previously interpreted from aeromagnetic data further east at the the margins of the Dufek Intrusion, would represent conjugate fault systems. In the latter scenario, a more complex and potentially more distributed strike-slip boundary between the WSE and a mosaic of distinct East and West Antarctic crustal blocks may be possible. This tectonic model would resemble some geodynamic models for the opposite side of Antarctica, in the Ross Sea Embayment and Transantarctic Mountains, where more recent (Cenozoic) intraplate strike-slip fault systems have been proposed.

  13. A new finite element code for the study of strain-localization under strike-slip faults

    NASA Astrophysics Data System (ADS)

    Rodríguez-González, J.; Montesi, L.

    2016-12-01

    Shear localization under strike-slip faults in ductile conditions remains a matter of debate. The rheology of rocks in the ductile regime is fundamentally strain-rate hardening, which complicates the understanding of the formation of narrow shear zones. Localized shear zones are present in a variety of scales, including kilometric structures at plate boundaries. To compensate for strain-rate hardening, shear zones must be weaker than their surroundings thanks to some weakening mechanism that works at multiple length scales. Mechanisms as shear heating or grain size reduction have been invoked to explain localization of deformation, but none of these mechanisms can work in scales that range from 1 to 1000 km. Layered fabric development has been suggested as a candidate to develop localized shear zones at multiple scales. To test this hypothesis, we have developed a new software that uses the Finite Element Method library deal.II written in C++. We solve the elasticity equations for elastic and Maxwell visco-elastic mediums. A key component required to study strain localization is adaptive mesh refinement. The code automatically identifies those regions in which the deformation is being localized and will increase the resolution. We benchmark the code and test its accuracy using analytical solutions of strike-slip deformation with different boundary conditions. We simulate the instantaneous deformation caused by two kinds of dislocations: a free fault subject to a far field traction and fault with an imposed displacement. We also simulate the visco-elastic relaxation following a strike-slip dislocation. We show that deal.II is a flexible library, suitable for different problems, which will prove useful to study the mechanisms that can lead to strain localization.

  14. Microstructural, textural and thermal evolution of an exhumed strike-slip fault and insights into localization and rheological transition

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz; Liu, Junlai; Bernroider, Manfred; Genser, Johann

    2016-04-01

    The presence of deep exhumed crustal rocks with a dominant but contrasting mineralogy results in shear concentration in the rheological weakest layer, which exhibits contrasting patterns of fabrics and thermal conditions during their formation. We tested a combination of methodologies including microstructural and textural investigations, geochronology and geothermometry on deformed rocks from exhumed strike-slip fault, Ailao Shan-Red River, SE, Asian. Results indicate that the exhumed deep crustal rocks since late Oligocene (ca. 28 Ma) to Pliocene (ca. 4 Ma) typically involve dynamic microstructural, textural and thermal evolution processes, which typically record a progressive deformation and syn-kinematic reactions from ductile to semi-ductile and brittle behavior during exhumation. This transformation also resulted in dramatic strength reduction that promoted strain localization along the strike-slip and transtensional faults. Detailed analysis has revealed the co-existence of microfabrics ranging from high-temperatures (granulite facies conditions) to overprinting low-temperatures (lower greenschist facies conditions). The high-temperature microstructures and textures are in part or entirely altered by subsequent, overprinting low-temperature shearing. In quartz-rich rocks, quartz was deformed in the dislocation creep regime and records transition of microfabrics and slip systems during decreasing temperature, which lasted until retrogression related to final exhumation. As a result, grain-size reduction associated by fluids circulating within the strike-slip fault zone at brittle-ductile transition leads to rock softening, which resulted in strain localization, weak rock rheology and the overall hot thermal structure of the crust. Decompression occurred during shearing and as a result of tectonic exhumation. All these results demonstrate that the ductile to ductile-brittle transition involves a combination of different deformation mechanisms, rheological

  15. What are the control mechanisms of evenly-spaced parallel strike-slip faults? Insights from DEM modeling

    NASA Astrophysics Data System (ADS)

    Bonilla Sierra, V.; Donze, F. V.; Duriez, J.; Klinger, Y.; Scholtes, L.

    2016-12-01

    At the very early stages of a pure strike-slip fault zone formation, shear displacement along a deep buried parent fault produces a characteristic set of "evenly-spaced" strike-slip faults at the surface, e.g. Southern San Andreas, North Anatolian, Central Asian, and Northern Tibetan fault systems. This mode III fracture propagation is initiated by the rotation of the local principal stress at the tip of the parent discontinuity, generating twisted fractures with a helicoidal shape. In sandbox or clay-cake experiments used to reproduce these structures, it has been observed that the spacing and possibly the characteristic length of the fractures appearing at the surface are proportional to the overburden thickness of the deformed layer. Based on a Discrete Element Method (YADE DEM-Open Source), we have investigated the conditions controlling the linear relationships between the spacing of the surface "evenly-spaced" strike-slip discontinuities and the thickness of the deformed layer. Increasing the basement displacement of the model, a diffused shear zone appears first at the tip of the basal parent discontinuity. From this mist zone, localized and strongly interacting shear fractures start to propagate. This interaction process can generate complex internal structures: some fractures will propagate faster than their neighbors, modifying their close surrounding stress environment. Some propagating fractures can stop growing and asymmetrical fracture sets can be observed. This resulting hierarchical bifurcation process leads to a set of "en echelon" discontinuities appearing at the surface (Figure 1). In a pure strike-slip mode, fracture spacing is proportional to the thickness, with a ratio and a bifurcation mode controlled by the cohesion value at the first order. Depending on the Poisson's ratio value, which mainly controls the orientation of the discontinuities, this ratio can be affected at a lower degree. In presence of mixed-mode (transpression or

  16. 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

  17. Basement and regional structure along strike of the Queen Charlotte Fault in the context of modern and historical earthquake ruptures

    USGS Publications Warehouse

    Walton, Maureen A. L.; Gulick, Sean P. S.; Haeussler, Peter J.; Roland, Emily C.; Tréhu, Anne M.

    2015-01-01

    The Queen Charlotte fault (QCF) is a dextral transform system located offshore of southeastern Alaska and western Canada, accommodating ∼4.4  cm/yr of relative motion between the Pacific and North American plates. Oblique convergence along the fault increases southward, and how this convergence is accommodated is still debated. Using seismic reflection data, we interpret offshore basement structure, faulting, and stratigraphy to provide a geological context for two recent earthquakes, an Mw 7.5 strike‐slip event near Craig, Alaska, and an Mw 7.8 thrust event near Haida Gwaii, Canada. We map downwarped Pacific oceanic crust near 54° N, between the two rupture zones. Observed downwarping decreases north and south of 54° N, parallel to the strike of the QCF. Bending of the Pacific plate here may have initiated with increased convergence rates due to a plate motion change at ∼6  Ma. Tectonic reconstruction implies convergence‐driven Pacific plate flexure, beginning at 6 Ma south of a 10° bend the QCF (which is currently at 53.2° N) and lasting until the plate translated past the bend by ∼2  Ma. Normal‐faulted approximately late Miocene sediment above the deep flexural depression at 54° N, topped by relatively undeformed Pleistocene and younger sediment, supports this model. Aftershocks of the Haida Gwaii event indicate a normal‐faulting stress regime, suggesting present‐day plate flexure and underthrusting, which is also consistent with reconstruction of past conditions. We thus favor a Pacific plate underthrusting model to initiate flexure and accommodation space for sediment loading. In addition, mapped structures indicate two possible fault segment boundaries along the QCF at 53.2° N and at 56° N.

  18. Earthquake hypocenters and focal mechanisms in central Oklahoma reveal a complex system of reactivated subsurface strike-slip faulting

    USGS Publications Warehouse

    McNamara, Daniel E.; Benz, Harley M.; Herrmann, Robert B.; Bergman, Eric A.; Earle, Paul S.; Holland, Austin F.; Baldwin, Randy W.; Gassner, A.

    2015-01-01

    The sharp increase in seismicity over a broad region of central Oklahoma has raised concern regarding the source of the activity and its potential hazard to local communities and energy industry infrastructure. Since early 2010, numerous organizations have deployed temporary portable seismic stations in central Oklahoma in order to record the evolving seismicity. In this study, we apply a multiple-event relocation method to produce a catalog of 3,639 central Oklahoma earthquakes from late 2009 through 2014. RMT source parameters were determined for 195 of the largest and best-recorded earthquakes. Combining RMT results with relocated seismicity enabled us to determine the length, depth and style-of-faulting occurring on reactivated subsurface fault systems. Results show that the majority of earthquakes occur on near vertical, optimally oriented (NE-SW and NW-SE), strike-slip faults in the shallow crystalline basement. These are necessary first order observations required to assess the potential hazards of individual faults in Oklahoma.

  19. The geometry of pull-apart basins in the southern part of Sumatran strike-slip fault zone

    NASA Astrophysics Data System (ADS)

    Aribowo, Sonny

    2018-02-01

    Models of pull-apart basin geometry have been described by many previous studies in a variety tectonic setting. 2D geometry of Ranau Lake represents a pull-apart basin in the Sumatran Fault Zone. However, there are unclear geomorphic traces of two sub-parallel overlapping strike-slip faults in the boundary of the lake. Nonetheless, clear geomorphic traces that parallel to Kumering Segment of the Sumatran Fault are considered as inactive faults in the southern side of the lake. I demonstrate the angular characteristics of the Ranau Lake and Suoh complex pull-apart basins and compare with pull-apart basin examples from published studies. I use digital elevation model (DEM) image to sketch the shape of the depression of Ranau Lake and Suoh Valley and measure 2D geometry of pull-apart basins. This study shows that Ranau Lake is not a pull-apart basin, and the pull-apart basin is actually located in the eastern side of the lake. Since there is a clear connection between pull-apart basin and volcanic activity in Sumatra, I also predict that the unclear trace of the pull-apart basin near Ranau Lake may be covered by Ranau Caldera and Seminung volcanic products.

  20. The Iceland Plate Boundary Zone: Propagating Rifts, Migrating Transforms, and Rift-Parallel Strike-Slip Faults

    NASA Astrophysics Data System (ADS)

    Karson, J. A.

    2017-11-01

    Unlike most of the Mid-Atlantic Ridge, the North America/Eurasia plate boundary in Iceland lies above sea level where magmatic and tectonic processes can be directly investigated in subaerial exposures. Accordingly, geologic processes in Iceland have long been recognized as possible analogs for seafloor spreading in the submerged parts of the mid-ocean ridge system. Combining existing and new data from across Iceland provides an integrated view of this active, mostly subaerial plate boundary. The broad Iceland plate boundary zone includes segmented rift zones linked by transform fault zones. Rift propagation and transform fault migration away from the Iceland hotspot rearrange the plate boundary configuration resulting in widespread deformation of older crust and reactivation of spreading-related structures. Rift propagation results in block rotations that are accommodated by widespread, rift-parallel, strike-slip faulting. The geometry and kinematics of faulting in Iceland may have implications for spreading processes elsewhere on the mid-ocean ridge system where rift propagation and transform migration occur.

  1. Three-dimensional structure across the Tintina strike-slip fault, northern Canadian Cordillera, from seismic refraction and reflection tomography

    NASA Astrophysics Data System (ADS)

    Zelt, Colin A.; Ellis, Robert M.; Zelt, Barry C.

    2006-12-01

    The development of the northern Canadian Cordillera involved major strike-slip displacement of accreted terranes relative to North America along faults such as the Tintina, which has experienced ~425 km of dextral motion since the Palaeocene. The SNORE seismic refraction/wide-angle reflection experiment was carried out in 1997 as one component of Lithoprobe's Slave-Northern Cordillera Lithospheric Evolution (SNORCLE) transect. In addition to four 2-D profiles, two sets of broadside recordings were acquired to image the 3-D structure across the Tintina fault (TF) in areas centred at about 59.5°N and 62°N. Simultaneous and independent refraction and reflection traveltime tomography were applied to the combined inline and broadside data set for each region to establish the range of lower crustal velocity, Moho depth and upper mantle velocity structure consistent with the data. Our preferred models are the average of the simultaneous and independent models since they represent the robust features required by the data. The preferred 3-D models are generally consistent with the 2-D models obtained from the inline data in previous independent studies. There are along-strike variations across the TF, perhaps due to the change in strike direction or the amount of motion along the fault in the north compared to the south. In the lower crust, the only correlation with the TF that is required by the data is a 0.1 km s-1 drop in velocity to the southwest of the fault in the northern study area. The absence of a strong correlation with the TF in the lower crust is consistent with the interpreted continuity of lower crustal units across the fault in the SNORCLE reflection data. The Moho is relatively flat throughout the study area, 34-35 km depth, but there is broad crustal thickening of a few kilometres centred ~50 km southwest of the TF in the northern and southern study areas. This thickening may be the result of a period when there was a component of compression along the

  2. Spatial variations in focused exhumation along a continental-scale strike-slip fault: The Denali fault of the eastern Alaska Range

    USGS Publications Warehouse

    Benowitz, J.A.; Layer, P.W.; Armstrong, P.; Perry, S.E.; Haeussler, Peter J.; Fitzgerald, P.G.; VanLaningham, S.

    2011-01-01

    40Ar/39Ar, apatite fission-track, and apatite (U-Th)/He thermochronological techniques were used to determine the Neogene exhumation history of the topographically asymmetric eastern Alaska Range. Exhumation cooling ages range from ~33 Ma to ~18 Ma for 40Ar/39Ar biotite, ~18 Ma to ~6 Ma for K-feldspar minimum closure ages, and ~15 Ma to ~1 Ma for apatite fission-track ages, and apatite (U-Th)/He cooling ages range from ~4 Ma to ~1 Ma. There has been at least ~11 km of exhumation adjacent to the north side of Denali fault during the Neogene inferred from biotite 40Ar/39Ar thermochronology. Variations in exhumation history along and across the strike of the fault are influenced by both far-field effects and local structural irregularities. We infer deformation and rapid exhumation have been occurring in the eastern Alaska Range since at least ~22 Ma most likely related to the continued collision of the Yakutat microplate with the North American plate. The Nenana Mountain region is the late Pleistocene to Holocene (~past 1 Ma) primary locus of tectonically driven exhumation in the eastern Alaska Range, possibly related to variations in fault geometry. During the Pliocene, a marked increase in climatic instability and related global cooling is temporally correlated with an increase in exhumation rates in the eastern Alaska Range north of the Denali fault system.

  3. Along-strike variations in fault frictional properties along the San Andreas Fault near Cholame, California from joint earthquake and low-frequency earthquake relocations

    USGS Publications Warehouse

    Harrington, Rebecca M.; Cochran, Elizabeth S.; Griffiths, Emily M.; Zeng, Xiangfang; Thurber, Clifford H.

    2016-01-01

    Recent observations of low‐frequency earthquakes (LFEs) and tectonic tremor along the Parkfield–Cholame segment of the San Andreas fault suggest slow‐slip earthquakes occur in a transition zone between the shallow fault, which accommodates slip by a combination of aseismic creep and earthquakes (<15  km depth), and the deep fault, which accommodates slip by stable sliding (>35  km depth). However, the spatial relationship between shallow earthquakes and LFEs remains unclear. Here, we present precise relocations of 34 earthquakes and 34 LFEs recorded during a temporary deployment of 13 broadband seismic stations from May 2010 to July 2011. We use the temporary array waveform data, along with data from permanent seismic stations and a new high‐resolution 3D velocity model, to illuminate the fine‐scale details of the seismicity distribution near Cholame and the relation to the distribution of LFEs. The depth of the boundary between earthquakes and LFE hypocenters changes along strike and roughly follows the 350°C isotherm, suggesting frictional behavior may be, in part, thermally controlled. We observe no overlap in the depth of earthquakes and LFEs, with an ∼5  km separation between the deepest earthquakes and shallowest LFEs. In addition, clustering in the relocated seismicity near the 2004 Mw 6.0 Parkfield earthquake hypocenter and near the northern boundary of the 1857 Mw 7.8 Fort Tejon rupture may highlight areas of frictional heterogeneities on the fault where earthquakes tend to nucleate.

  4. Hematite (U-Th)/He thermochronometry constrains intraplate strike-slip faulting on the Kuh-e-Faghan Fault, central Iran

    NASA Astrophysics Data System (ADS)

    Calzolari, Gabriele; Rossetti, Federico; Ault, Alexis K.; Lucci, Federico; Olivetti, Valerio; Nozaem, Reza

    2018-03-01

    The Kuh-e-Faghan strike-slip fault system (KFF), located to the northern edge of the Lut Block in central Iran, developed through a Neogene-Quaternary pulsed history of eastward fault propagation and fault-related exhumation. This system is a consequence of the residual stresses transmitted from the Arabia-Eurasia convergent plate boundary. Here we integrate structural and textural analysis with new and previously published apatite fission-track (AFT) and apatite (U-Th)/He (apatite He) results, chlorite thermomentry, and hematite (U-Th)/He data from hematite-coated brittle fault surfaces to constrain the timing of tectonic activity and refine patterns of late Miocene-Pliocene burial and exhumation associated with the propagation of the KFF. Twenty-nine hematite (U-Th)/He (hematite He) dates from three striated hematite coated slip surfaces from the KFF fault core and damage zone yield individual dates from 12-2 Ma. Petrographic analysis and chlorite thermometry of a polyphase, fossil fluid system in the KFF fault core document that fluid circulation and mineralization transitioned from a closed system characterized by pressure solution and calcite growth to an open system characterized by hot hydrothermal (T = 239 ± 10 °C) fluids and hematite formation. Hematite microtextures and grain size analysis reveal primary and secondary syntectonic hematite fabrics, no evidence of hematite comminution and similar hematite He closure temperatures ( 60-85 °C) in each sample. Integration of these results with thermal history modeling of AFT and apatite He data shows that KFF activity in the late Miocene is characterized by an early stage of fault nucleation, fluid circulation, hematite mineralization, and eastward propagation not associated with vertical movement that lasted from 12 to 7 Ma. Hematite He, AFT, and apatite He data track a second phase of fault system activity involving fault-related exhumation initiating at 7 Ma and continuing until present time. Our new data

  5. Phanerozoic strike-slip faulting in the continental interior platform of the United States: Examples from the Laramide Orogen, midcontinent, and Ancestral Rocky Mountains

    USGS Publications Warehouse

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

    2003-01-01

    The continental interior platform of the United States is that part of the North American craton where a thin veneer of Phanerozoic strata covers Precambrian crystalline basement. N- to NE-trending and W- to NW-trending fault zones, formed initially by Proterozoic/Cambrian rifting, break the crust of the platform into rectilinear blocks. These zones were reactivated during the Phanerozoic, most notably in the late Palaeozoic Ancestral Rockies event and the Mesozoic-Cenozoic Laramide orogeny - some remain active today. Dip-slip reactivation can be readily recognized in cross section by offset stratigraphic horizons and monoclinal fault-propagation folds. Strike-slip displacement is hard to document because of poor exposure. Through offset palaeochannels, horizontal slip lineations, and strain at fault bends locally demonstrate strike-slip offset, most reports of strike-slip movements for interior-platform faults are based on occurrence of map-view belts of en echelon faults and anticlines. Each belt overlies a basement-penetrating master fault, which typically splays upwards into a flower structure. In general, both strike-slip and dip-slip components of displacement occur in the same fault zone, so some belts of en echelon structures occur on the flanks of monoclinal folds. Thus, strike-slip displacement represents the lateral components of oblique fault reactivation: dip-slip and strike-slip components are the same order of magnitude (tens of metres to tens of kilometres). Effectively, faults with strike-slip components of displacement act as transfers accommodating jostling of rectilinear crustal blocks. In this context, the sense of slip on an individual strike-slip fault depends on block geometry, not necessarily on the trajectory of regional ??1. Strike-slip faulting in the North American interior differs markedly from that of southern and central Eurasia, possibly because of a contrast in lithosphere strength. Weak Eurasia strained significantly during the

  6. Dislocation pileup as a representation of strain accumulation on a strike-slip fault

    USGS Publications Warehouse

    Savage, J.C.

    2006-01-01

    The conventional model of strain accumulation on a vertical transform fault is a discrete screw dislocation in an elastic half-space with the Burgers vector of the dislocation increasing at the rate of relative plate motion. It would be more realistic to replace that discrete dislocation by a dislocation distribution, presumably a pileup in which the individual dislocations are in equilibrium. The length of the pileup depends upon the applied stress and the amount of slip that has occurred at depth. I argue here that the dislocation pileup (the transition on the fault from no slip to slip at the full plate rate) occupies a substantial portion of the lithosphere thickness. A discrete dislocation at an adjustable depth can reproduce the surface deformation profile predicted by a pileup so closely that it will be difficult to distinguish between the two models. The locking depth (dislocation depth) of that discrete dislocation approximation is substantially (???30%) larger than that (depth to top of the pileup) in the pileup model. Thus, in inverting surface deformation data using the discrete dislocation model, the locking depth in the model should not be interpreted as the true locking depth. Although dislocation pileup models should provide a good explanation of the surface deformation near the fault trace, that explanation may not be adequate at greater distances from the fault trace because approximating the expected horizontally distributed deformation at subcrustal depths by uniform slip concentrated on the fault is not justified.

  7. The influence of fault geometry and frictional contact properties on slip surface behavior and off-fault damage: insights from quasi-static modeling of small strike-slip faults from the Sierra Nevada, CA

    NASA Astrophysics Data System (ADS)

    Ritz, E.; Pollard, D. D.

    2011-12-01

    Geological and geophysical investigations demonstrate that faults are geometrically complex structures, and that the nature and intensity of off-fault damage is spatially correlated with geometric irregularities of the slip surfaces. Geologic observations of exhumed meter-scale strike-slip faults in the Bear Creek drainage, central Sierra Nevada, CA, provide insight into the relationship between non-planar fault geometry and frictional slip at depth. We investigate natural fault geometries in an otherwise homogeneous and isotropic elastic material with a two-dimensional displacement discontinuity method (DDM). Although the DDM is a powerful tool, frictional contact problems are beyond the scope of the elementary implementation because it allows interpenetration of the crack surfaces. By incorporating a complementarity algorithm, we are able to enforce appropriate contact boundary conditions along the model faults and include variable friction and frictional strength. This tool allows us to model quasi-static slip on non-planar faults and the resulting deformation of the surrounding rock. Both field observations and numerical investigations indicate that sliding along geometrically discontinuous or irregular faults may lead to opening of the fault and the formation of new fractures, affecting permeability in the nearby rock mass and consequently impacting pore fluid pressure. Numerical simulations of natural fault geometries provide local stress fields that are correlated to the style and spatial distribution of off-fault damage. We also show how varying the friction and frictional strength along the model faults affects slip surface behavior and consequently influences the stress distributions in the adjacent material.

  8. Recent, slow normal and strike-slip faulting in the Pasto Ventura region of the southern Puna Plateau, NW Argentina

    USGS Publications Warehouse

    Zhou, Renjie; Schoenbohm, Lindsay M.; Cosca, Michael

    2013-01-01

    Recent normal and strike-slip faulting on the Puna Plateau of NW Argentina has been linked to lithospheric foundering, gravitational spreading, plate boundary forces and a decrease in crustal shortening from north to south. However, the timing, kinematics and rate of extension remain poorly constrained. We focus on the Pasto Ventura region (NW Argentina) located on the southern Puna Plateau and recent deformation (<1 Ma). Field mapping and kinematic analysis across offset volcanic cinder cones show that the overall extension direction is subhorizontal, is oriented NE-SW to NNE-SSW, and occurs at a slow, time-integrated rate of 0.02 to 0.08 mm/yr since at least 0.8–0.5 Ma. A regional compilation from this study and existing data shows that recent extension across the Puna Plateau is subhorizontal but varies in azimuthal orientation dramatically. Data from the Pasto Ventura region are consistent with a number of models to explain normal and strike-slip faulting on the Puna Plateau, all of which likely influence the region. Some role for lower lithospheric foundering through dripping appears to be seen based on the regional extension directions and ages of mafic volcanism in the southern Puna Plateau.

  9. Late Cretaceous-Paleocene strike-slip faults along the East Greenland margin (63°N to 75°N): constraints for the North East Atlantic opening

    NASA Astrophysics Data System (ADS)

    Guarnieri, P.

    2012-04-01

    The East Greenland margin is a long stretch starting from 60°N up to 81°N in a distance of almost 3000 km. It represents the conjugate of the European margin now separated by the North East Atlantic (NEA). After a long period of E-W extension and almost N-S oriented rift basins since Early Cretaceous, separation between Greenland and Europe began at 55 Ma following a NE-SW oriented line of breakup and the emplacement of the North Atlantic Igneous Province (NAIP). Post-breakup thermal subsidence followed in the Eocene, and the Oligocene initiated a period of plate re-organization together with the initial separation of Jan Mayen microcontinent, a complex tectonic history with inversion structures and uplifts along both the East Greenland and European margins. The effect of this history is represented by exhumed sedimentary basins, dyke swarms, fault systems, intrusive centers, shield volcanoes and plateau lavas constituting highest mountain of Greenland with some peaks up to 3700 m (e.g. Watkins Bjerge). During expeditions for fieldwork in East Greenland (2009 to 2011) to collect new geological and structural data related to the North East Atlantic tectonics, four areas were visited: Skjoldungen 63°N, Kangerlussuaq 68°N, Traill Ø 72°N and Wollaston Forland 75°N. More than 1000 measurement of fault-slip data for structural analysis along major faults were collected and helicopter flights to collect oblique pictures for 3D-photogeology and 3D-mapping were taken. Kinematic analysis of brittle deformation associated with Late Cretaceous-Paleocene rift shows strike-slip movements. Palaeo-stress tensors reconstructed from fault-slip data highlight a NE-SW maximum horizontal stress in a strike-slip tectonic setting along the entire East Greenland margin (Guarnieri 2011a; Guarnieri 2011b; Guarnieri et al. 2011). Structural data show clear evidence for oblique rifting that corresponds in time to the "volcanic rift" (61-55 Ma) with in some cases the magmatic

  10. Structural evolution of Cenozoic basins in northeastern Tunisia, in response to sinistral strike-slip movement on the El Alia-Teboursouk Fault

    NASA Astrophysics Data System (ADS)

    Bejaoui, Hamida; Aïfa, Tahar; Melki, Fetheddine; Zargouni, Fouad

    2017-10-01

    This paper resolves the structural complexity of Cenozoic sedimentary basins in northeastern Tunisia. These basins trend NE-SW to ∼ E-W, and are bordered by old fracture networks. Detailed descriptions of the structural features in outcrop and in subsurface data suggest that the El Alia-Teboursouk Fault zone in the Bizerte area evolved through a series of tectonic events. Cross sections, lithostratigraphic correlations, and interpretation of seismic profiles through the basins show evidence for: (i) a Triassic until Jurassic-Early Cretaceous rifting phase that induced lateral variations of facies and strata thicknesses; (ii) a set of faults oriented NE-SW, NW-SE, N-S, and E-W that guided sediment accumulation in pull-apart basins, which were subject to compressive and transpressive deformation during Eocene (Lutetian-Priabonian), Miocene (Tortonian), and Pliocene-Quaternary; and (iii) NNW-SSE to NS contractional events that occurred during the Late Pliocene. Part of the latest phase has been the formation of different synsedimentary folded structures with significant subsidence inversion. Such events have been responsible for the reactivation of inherited faults, and the intrusion of Triassic evaporites, ensuring the role of a slip layer. The combined effects of the different paleoconstraints and halokinetic movements are at the origin of the evolution of these pull-apart basins. The subsurface data suggest that an important fault displacement occurred during the Mesozoic-Cenozoic. The patterns of sediment accumulation in the different basins reflect a high activity of deep ancient faults.

  11. Structure of the Melajo clay near Arima, Trinidad and strike-slip motion in the El Pilar fault zone

    NASA Technical Reports Server (NTRS)

    Robertson, P.; Burke, K.; Wadge, G.

    1985-01-01

    No consensus has yet emerged on the sense, timing and amount of motion in the El Pilar fault zone. As a contribution to the study of this problem, a critical area within the zone in North Central Trinidad has been mapped. On the basis of the mapping, it is concluded that the El Pilar zone has been active in right-lateral strike-slip motion during the Pleistocene. Recognition of structural styles akin to those of the mapped area leads to the suggestion that the El Pilar zone is part of a 300 km wide plate boundary zone extending from the Orinoco delta northward to Grenada. Lateral motion of the Caribbean plate with respect to South America has been suggested to amount to 1900 km in the last 38 Ma. Part of this displacement since the Miocene can be readily accommodated within the broad zone identified here. No one fault system need account for more than a fraction of the total motion and all faults need not be active simultaneously.

  12. Structural analysis of S-wave seismics around an urban sinkhole: evidence of enhanced dissolution in a strike-slip fault zone

    NASA Astrophysics Data System (ADS)

    Wadas, Sonja H.; Tanner, David C.; Polom, Ulrich; Krawczyk, Charlotte M.

    2017-12-01

    In November 2010, a large sinkhole opened up in the urban area of Schmalkalden, Germany. To determine the key factors which benefited the development of this collapse structure and therefore the dissolution, we carried out several shear-wave reflection-seismic profiles around the sinkhole. In the seismic sections we see evidence of the Mesozoic tectonic movement in the form of a NW-SE striking, dextral strike-slip fault, known as the Heßleser Fault, which faulted and fractured the subsurface below the town. The strike-slip faulting created a zone of small blocks ( < 100 m in size), around which steep-dipping normal faults, reverse faults and a dense fracture network serve as fluid pathways for the artesian-confined groundwater. The faults also acted as barriers for horizontal groundwater flow perpendicular to the fault planes. Instead groundwater flows along the faults which serve as conduits and forms cavities in the Permian deposits below ca. 60 m depth. Mass movements and the resulting cavities lead to the formation of sinkholes and dissolution-induced depressions. Since the processes are still ongoing, the occurrence of a new sinkhole cannot be ruled out. This case study demonstrates how S-wave seismics can characterize a sinkhole and, together with geological information, can be used to study the processes that result in sinkhole formation, such as a near-surface fault zone located in soluble rocks. The more complex the fault geometry and interaction between faults, the more prone an area is to sinkhole occurrence.

  13. The 3D fault and vein architecture of strike-slip releasing- and restraining bends: Evidence from volcanic-centre-relatedmineral deposits

    USGS Publications Warehouse

    Berger, B.R.; ,

    2007-01-01

    High-temperature, volcanic-centre-related hydrothermal systems involve large fluid-flow volumes and are observed to have high discharge rates in the order of 100-400 kg/s. The flows and discharge occur predominantly on networks of critically stressed fractures. The coupling of hydrothermal fluid flow with deformation produces the volumes of veins found in epithermal mineral deposits. Owing to this coupling, veins provide information on the fault-fracture architecture in existence at the time of mineralization. They therefore provide information on the nature of deformation within fault zones, and the relations between different fault sets. The Virginia City and Goldfield mining districts, Nevada, were localized in zones of strike-slip transtension in an Early to Mid-Miocene volcanic belt along the western margin of North America. The Camp Douglas mining area occurs within the same belt, but is localized in a zone of strike-slip transpression. The vein systems in these districts record the spatial evolution of strike-slip extensional and contractional stepovers, as well as geometry of faulting in and adjacent to points along strike-slip faults where displacement has been interrupted and transferred into releasing and restraining stepovers. ?? The Geological Society of London 2007.

  14. Microstructural record of cataclastic and dissolution-precipitation processes from shallow crustal carbonate strike-slip faults, Northern Calcareous Alps (Austria)

    NASA Astrophysics Data System (ADS)

    Bauer, Helene; Grasemann, Bernhard; Decker, Kurt

    2015-04-01

    The concept of coseismic slip and aseismic creep deformation along faults is supported by the variability of natural fault rocks and their microstructures. Faults in carbonate rocks are characterized by very narrow principal slip zones (cm to mm wide) containing (ultra)cataclastic fault rocks that accommodate most of the fault displacement. Fluidization of ultracataclastic sub layers and thermal decomposition of calcite due to frictional heating have been proposed as possible indicators for seismic slip. Dissolution-precipitation (DP) processes are possible mechanism of aseismic sliding, resulting in spaced cleavage solution planes and associated veins, indicating diffusive mass transfer and precipitation in pervasive vein networks. We investigated exhumed, sinistral strike-slip faults in carbonates of the Northern Calcareous Alps. The study presents microstructural investigations of natural carbonate fault rocks that formed by cataclastic and dissolution-precipitation related deformation processes. Faults belong to the eastern segment of the Salzachtal-Ennstal-Mariazell-Puchberg (SEMP) fault system that was formed during eastward lateral extrusion of the Eastern Alps in Oligocene to Lower Miocene. The investigated faults accommodated sinistral slip between several tens and few hundreds of meters. Microstructural analysis of fault rocks was done with scanning electron microscopy and optical microscopy. Deformation experiments of natural fault rocks are planned to be conducted at the Sapienza University of Roma and should be available at the meeting. The investigated fault rocks give record of alternating cataclastic deformation and DP creep. DP fault rocks reveal various stages of evolution including early stylolites, pervasive pressure solution seams and cleavage, localized shear zones with syn-kinematic calcite fibre growth and mixed DP/cataclastic microstructures, involving pseudo sc- and scc'-fabrics. Pressure solution seams host fine grained kaolinit, chlorite

  15. Extrapolating subsurface geometry by surface expressions in transpressional strike slip fault, deduced from analogue experiments with settings of rheology and convergence angle

    NASA Astrophysics Data System (ADS)

    Hsieh, Shang Yu; Neubauer, Franz

    2015-04-01

    The internal structure of major strike-slip faults is still poorly understood, particularly how to extrapolate subsurface structures by surface expressions. Series of brittle analogue experiments by Leever et al., 2011 resulted the convergence angle is the most influential factor for surface structures. Further analogue models with different ductile settings allow a better understanding in extrapolating surface structures to the subsurface geometry of strike-slip faults. Fifteen analogue experiments were constructed to represent strike-slip faults in nature in different geological settings. As key parameters investigated in this study include: (a) the angle of convergence, (b) the thickness of brittle layer, (c) the influence of a rheological weak layer within the crust, and (d) influence of a thick and rheologically weak layer at the base of the crust. The experiments are aimed to explain first order structures along major transcurrent strike-slip faults such as the Altyn, Kunlun, San Andrea and Greendale (Darfield earthquake 2010) faults. The preliminary results show that convergence angle significantly influences the overall geometry of the transpressional system with greater convergence angles resulting in wider fault zones and higher elevation. Different positions, densities and viscosities of weak rheological layers have not only different surface expressions but also affect the fault geometry in the subsurface. For instance, rheological weak material in the bottom layer results in stretching when experiment reaches a certain displacement and a buildup of a less segmented, wide positive flower structure. At the surface, a wide fault valley in the middle of the fault zone is the reflection of stretching along the velocity discontinuity at depth. In models with a thin and rheologically weaker layer in the middle of the brittle layer, deformation is distributed over more faults and the geometry of the fault zone below and above the weak zone shows significant

  16. Role of the offshore Pedro Banks left-lateral strike-slip fault zone in the plate tectonic evolution of the northern Caribbean

    NASA Astrophysics Data System (ADS)

    Ott, B.; Mann, P.; Saunders, M.

    2013-12-01

    Previous workers, mainly mapping onland active faults on Caribbean islands, defined the northern Caribbean plate boundary zone as a 200-km-wide bounded by two active and parallel strike-slip faults: the Oriente fault along the northern edge of the Cayman trough with a GPS rate of 14 mm/yr, and and the Enriquillo-Plaintain Garden fault zone (EPGFZ) with a rate of 5-7 mm/yr. In this study we use 5,000 km of industry and academic data from the Nicaraguan Rise south and southwest of the EPGFZ in the maritime areas of Jamaica, Honduras, and Colombia to define an offshore, 700-km-long, active, left-lateral strike-slip fault in what has previously been considered the stable interior of the Caribbean plate as determined from plate-wide GPS studies. The fault was named by previous workers as the Pedro Banks fault zone because a 100-km-long segment of the fault forms an escarpment along the Pedro carbonate bank of the Nicaraguan Rise. Two fault segments of the PBFZ are defined: the 400-km-long eastern segment that exhibits large negative flower structures 10-50 km in width, with faults segments rupturing the sea floor as defined by high resolution 2D seismic data, and a 300-km-long western segment that is defined by a narrow zone of anomalous seismicity first observed by previous workers. The western end of the PBFZ terminates on a Quaternary rift structure, the San Andres rift, associated with Plio-Pleistocene volcanism and thickening trends indicating initial rifting in the Late Miocene. The southern end of the San Andreas rift terminates on the western Hess fault which also exhibits active strands consistent with left-lateral, strike-slip faults. The total length of the PBFZ-San Andres rift-Southern Hess escarpment fault is 1,200 km and traverses the entire western end of the Caribbean plate. Our interpretation is similar to previous models that have proposed the "stable" western Caribbean plate is broken by this fault whose rate of displacement is less than the threshold

  17. Tectonic geomorphology and paleoseismology of strike-slip faults in Jamaica: Implications for distribution of strain and seismic hazard along the southern edge of the Gonave microplate

    NASA Astrophysics Data System (ADS)

    Koehler, R. D.; Mann, P.; Brown, L. A.

    2009-12-01

    The east-west, left lateral strike-slip fault system forming the southern edge of the Gonave microplate crosses the110-km-long and 70-km-wide island of Jamaica. GPS measurements in the northeastern Caribbean are supportive of the microplate interpretation and indicate that ~ half of the Caribbean-North America left-lateral plate motion (8-14 mm/yr) is carried by the Plantain Garden (PGFZ) and associated faults in Jamaica. We performed Neotectonic mapping of the Plantain Garden fault along the southern rangefront of the Blue Mountains and conducted a paleoseismic study of the fault at Morant River. Between Holland Bay and Morant River, the fault is characterized by a steep, faceted, linear mountain front, prominent linear valleys and depressions, shutter ridges, and springs. At the eastern end of the island, the PGFZ is characterized by a left-stepping fault geometry that includes a major, active hot spring. The river cut exposure at Morant River exposes a 1.5-m-wide, sub-vertical fault zone juxtaposing sheared alluvium and faulted Cretaceous basement rocks. This section is overlain by an, unfaulted 3-m-thick fluvial terrace inset into a late Pleistocene terrace that is culturally modified. Upward fault terminations indicate the occurrence of three paleoearthquakes that occurred prior to deposition of the flat lying inset terrace around 341-628 cal yr BP. At this time, our radiocarbon results suggest that we can rule out the PGFZ as the source of the 1907 Kingston earthquake 102 years ago, as well as, the 1692 event that destroyed Port Royal 317 years ago and produced a major landslide at Yallahs. Pending OSL ages will constrain the age of the penultimate and most recent ruptures. Gently to steeply dipping rocks as young as Pliocene exposed in roadcuts within the low coastal hills south of and parallel to the Plantain Garden fault may indicate active folding and blind thrust faulting. These structures are poorly characterized and may accommodate an unknown amount of

  18. 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.

  19. Cenozoic structural inversion from transtension to transpression in Yingxiong Range, western Qaidam Basin: New insights into strike-slip superimposition controlled by Altyn Tagh and Eastern Kunlun Faults

    NASA Astrophysics Data System (ADS)

    Cheng, Xiang; Zhang, Daowei; Jolivet, Marc; Yu, Xiangjiang; Du, Wei; Liu, Runchao; Guo, Zhaojie

    2018-01-01

    A Cenozoic structural inversion event from transtension to transpression involving salt tectonics has been uncovered in the Yingxiong Range, the western Qaidam Basin. Seismic reflection data show that there are two common structural styles in the Yingxiong Range: (1) the positive flower structure; (2) the thrust-controlled fold at shallow depth and the positive inverted flower structure at deep levels, which are separated by a salt layer in the upper Xiaganchaigou Formation. The Yingxiong Range experienced a first stage of transtension in the Eocene, induced by the Altyn Tagh Fault, and a second stage of transpression from the early Miocene to present, jointly controlled by the Altyn Tagh and Eastern Kunlun Faults. The Eocene transtension produced numerous NW-striking right-stepping en-échelon transtensional normal faults or fractures in the Yingxiong Range. At the same time, evaporites and mudstone were deposited in the vicinity of these faults. In the early Miocene, the Eocene transtensional normal faults were reactivated in a reverse sense, and the thrust-controlled folds at shallow depth started to form simultaneously. With transpression enhanced in the late Cenozoic, positive flower structures directly formed in places without evaporites. The Cenozoic transtension to transpression inversion of the Yingxiong Range is the result of strike-slip superimposition controlled by the Altyn Tagh and Eastern Kunlun Faults in time and space.

  20. Stress triggering in thrust and subduction earthquakes and stress interaction between the southern San Andreas and nearby thrust and strike-slip faults

    USGS Publications Warehouse

    Lin, J.; Stein, R.S.

    2004-01-01

    We argue that key features of thrust earthquake triggering, inhibition, and clustering can be explained by Coulomb stress changes, which we illustrate by a suite of representative models and by detailed examples. Whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust, slip on blind thrust faults increases the stress on some nearby zones, particularly above the source fault. Blind thrusts can thus trigger slip on secondary faults at shallow depth and typically produce broadly distributed aftershocks. Short thrust ruptures are particularly efficient at triggering earthquakes of similar size on adjacent thrust faults. We calculate that during a progressive thrust sequence in central California the 1983 Mw = 6.7 Coalinga earthquake brought the subsequent 1983 Mw = 6.0 Nunez and 1985 Mw = 6.0 Kettleman Hills ruptures 10 bars and 1 bar closer to Coulomb failure. The idealized stress change calculations also reconcile the distribution of seismicity accompanying large subduction events, in agreement with findings of prior investigations. Subduction zone ruptures are calculated to promote normal faulting events in the outer rise and to promote thrust-faulting events on the periphery of the seismic rupture and its downdip extension. These features are evident in aftershocks of the 1957 Mw = 9.1 Aleutian and other large subduction earthquakes. We further examine stress changes on the rupture surface imparted by the 1960 Mw = 9.5 and 1995 Mw = 8.1 Chile earthquakes, for which detailed slip models are available. Calculated Coulomb stress increases of 2-20 bars correspond closely to sites of aftershocks and postseismic slip, whereas aftershocks are absent where the stress drops by more than 10 bars. We also argue that slip on major strike-slip systems modulates the stress acting on nearby thrust and strike-slip faults. We calculate that the 1857 Mw = 7.9 Fort Tejon earthquake on the San Andreas fault and subsequent interseismic slip brought

  1. Palaeopermeability anisotropies of a strike-slip fault damage zone: 3D Insights of quantitative fluid flow from µCT analysis.

    NASA Astrophysics Data System (ADS)

    Gomila, R.; Arancibia, G.; Nehler, M.; Bracke, R.; Morata, D.

    2017-12-01

    Fault zones and their related structural permeability are a key aspect in the migration of fluids through the continental crust. Therefore, the estimation of the hydraulic properties (palaeopermeability conditions; k) and the spatial distribution of the fracture mesh within the damage zone (DZ) are critical in the assessment of fault zones behavior for fluids. The study of the real spatial distribution of the veinlets of the fracture mesh (3D), feasible with the use of µCT analyses, is a first order factor to unravel both, the real structural permeability conditions of a fault-zone, and the validation of previous (and classical) estimations made in 2D analyses in thin-sections. This work shows the results of a fault-related fracture mesh and its 3D spatial distribution in the damage-zone of the Jorgillo Fault (JF), an ancient subvertical left-lateral strike-slip fault exposed in the Atacama Fault System in northern Chile. The JF is a ca. 20 km long NNW-striking strike-slip fault with sinistral displacement of ca. 4 km. The methodology consisted of drilling 5 mm vertically oriented plugs at several locations within the JF damage zone. Each specimen was scanned with an X-Ray µCT scanner, to assess the fracture mesh, with a voxel resolution of ca. 4.5 µm in the 3D reconstructed data. Tensor permeability modeling, using Lattice-Boltzmann Method, through the segmented microfracture mesh show GMkmin (geometric mean values) of 2.1x10-12 and 9.8x10-13 m2, and GMkmax of 6.4x10-12 and 2.1x10-12 m2. A high degree of anisotropy of the DZ permeability tensor both sides of the JF (eastern and western side, respectively) is observed, where the k values in the kmax plane are 2.4 and 1.9 times higher than the kmin direction at the time of fracture sealing. This style of anisotropy is consistent with the obtained for bedded sandstones supporting the idea that damage zones have an analogous effect - but vertically orientated - on bulk permeability (in low porosity rocks) as

  2. Secondary Fracturing of Europa's Crust in Response to Combined Slip and Dilation Along Strike-Slip Faults

    NASA Technical Reports Server (NTRS)

    Kattenhorn, S. A.

    2003-01-01

    A commonly observed feature in faulted terrestrial rocks is the occurrence of secondary fractures alongside faults. Depending on exact morphology, such fractures have been termed tail cracks, wing cracks, kinks, or horsetail fractures, and typically form at the tip of a slipping fault or around small jogs or steps along a fault surface. The location and orientation of secondary fracturing with respect to the fault plane or the fault tip can be used to determine if fault motion is left-lateral or right-lateral.

  3. The Border Ranges fault system in Glacier Bay National Park, Alaska: Evidence for major early Cenozoic dextral strike-slip motion

    USGS Publications Warehouse

    Smart, K.J.; Pavlis, T.L.; Sisson, V.B.; Roeske, S.M.; Snee, L.W.

    1996-01-01

    The Border Ranges fault system of southern Alaska, the fundamental break between the arc basement and the forearc accretionary complex, is the boundary between the Peninsular-Alexander-Wrangellia terrane and the Chugach terrane. The fault system separates crystalline rocks of the Alexander terrane from metamorphic rocks of the Chugach terrane in Glacier Bay National Park. Mylonitic rocks in the zone record abundant evidence for dextral strike-slip motion along north-northwest-striking subvertical surfaces. Geochronologic data together with regional correlations of Chugach terrane rocks involved in the deformation constrain this movement between latest Cretaceous and Early Eocene (???50 Ma). These findings are in agreement with studies to the northwest and southeast along the Border Ranges fault system which show dextral strike-slip motion occurring between 58 and 50 Ma. Correlations between Glacier Bay plutons and rocks of similar ages elsewhere along the Border Ranges fault system suggest that as much as 700 km of dextral motion may have been accommodated by this structure. These observations are consistent with oblique convergence of the Kula plate during early Cenozoic and forearc slivering above an ancient subduction zone following late Mesozoic accretion of the Peninsular-Alexander-Wrangellia terrane to North America.

  4. Major strike-slip faulting along the tectonic boundary between East and West Antarctica: implications for early Gondwana break-up and Jurassic granitic magma emplacement

    NASA Astrophysics Data System (ADS)

    Jordan, T. A.; Ferraccioli, F.; Anderson, L.; Ross, N.; Corr, H.; Leat, P. T.; Bingham, R.; Rippin, D. M.; Le Brocq, A. M.; Siegert, M. J.

    2013-12-01

    The fragmentation of the Gondwana supercontinent began with continental rifting between the Weddell Sea region of Antarctica and South Africa during the Jurassic. This initial Jurassic phase of continental rifting is critical for understanding the process that initiated supercontinent breakup and dispersal, including the role of mantle plumes and major intracrustal tectonic structures. However, due to the remote location and blanketing ice sheets, the tectonic and magmatic evolution of the Weddell Sea Sector of Antarctica has remained relatively poorly understood. Our recent aeromagnetic and airborne gravity investigations have revealed the inland extent of the Weddell Sea Rift system beneath the West Antarctic Ice Sheet, and indicate the presence of a major left-lateral strike slip fault system separating the Ellsworth Whitmore block (a possible exotic microcontinent derived from the Natal Embayment, or the Shackleton Range region of East Antarctica) from East Antarctica (Jordan et al., 2013 Tectonophysics). In this study we use GPlates plate-tectonic reconstruction software to start evaluating the influence of strike-slip faulting between East and West Antarctica on Gondwana breakup models. Specifically, we investigate the possibility of poly-phase motion along the fault system and explore scenarios involving more diffuse strike slip faulting extending into the interior of East Antarctica in the hinterland of the Transantarctic Mountains. Our preliminary models suggest that there may be a link between the prominent step in the flank of the later Cretaceous-Cenozoic West Antarctic Rift System (at the southern end of Ellsworth-Whitmore Block) and the earlier Jurassic Weddell Sea rift system. Additionally, we present preliminary joint 3D magnetic and gravity models to investigate the crustal architecture of the proposed strike-slip fault system and assess its influence on the emplacement of voluminous Jurassic granitic magmatism along the boundary of the Ellsworth

  5. A recent Mw 4.3 earthquake proving activity of a shallow strike-slip fault in the northern part of the Western Desert, Egypt

    NASA Astrophysics Data System (ADS)

    Ezzelarab, Mohamed; Ebraheem, Mohamed O.; Zahradník, Jiří

    2018-03-01

    The Mw 4.3 earthquake of September 2015 is the first felt earthquake since 1900 A.D in the northern part of the Western Desert, Egypt, south of the El-Alamein City. The available waveform data observed at epicentral distances 52-391 km was collected and carefully evaluated. Nine broad-band stations were selected to invert full waveforms for the centroid position (horizontal and vertical) and for the focal mechanism solution. The first-arrival travel times, polarities and low-frequency full waveforms (0.03-0.08 Hz) are consistently explained in this paper as caused by a shallow source of the strike-slip mechanism. This finding indicates causal relation of this earthquake to the W-E trending South El-Alamein fault, which developed in Late Cretaceous as dextral strike slip fault. Recent activity of this fault, proven by the studied rare earthquake, is of fundamental importance for future seismic hazard evaluations, underlined by proximity (∼65 km) of the source zone to the first nuclear power plant planned site in Egypt. Safe exploration and possible future exploitation of hydrocarbon reserves, reported around El-Alamein fault in the last decade, cannot be made without considering the seismic potential of this fault.

  6. Mesozoic strike-slip movement of the Dunhua-Mishan Fault Zone in NE China: A response to oceanic plate subduction

    NASA Astrophysics Data System (ADS)

    Liu, Cheng; Zhu, Guang; Zhang, Shuai; Gu, Chengchuan; Li, Yunjian; Su, Nan; Xiao, Shiye

    2018-01-01

    The NE-striking Dunhua-Mishan Fault Zone (DMFZ) is one of two branches of the continental-scale sinistral Tan-Lu Fault Zone in NE China. The field data presented here indicate that the ca. 1000 km long DMFZ records two phases of sinistral faulting. The structures produced by these two phases of faulting include NE-SW-striking ductile shear belts and brittle faults, respectively. Mylonite-hosted microstructures and quartz c-axis fabrics suggest deformation temperatures of 450 °C-500 °C for the ductile shear belts. Combining new zircon U-Pb dates for 14 igneous rock samples analyzed during this study with the geology of this region indicates these shear belts formed during the earliest Early Cretaceous. This phase of sinistral displacement represents the initial formation of the DMFZ in response to the northward propagation of the Tan-Lu Fault Zone into NE China. A phase of Early Cretaceous rifting was followed by a second phase of sinistral faulting at 102-96 Ma, as evidenced by our new U-Pb ages for associated igneous rocks. Combining our new data with the results of previous research indicates that the DFMZ records a four-stage Cretaceous evolutionary history, where initial sinistral faulting at the beginning of the Early Cretaceous gave way to rifting during the rest of the Early Cretaceous. This was followed by a second phase of sinistral faulting at the beginning of the Late Cretaceous and a second phase of local rifting during the rest of the Late Cretaceous. The Cretaceous evolution of the DMFZ records the synchronous tectonic evolution of the NE China continent bordering the Pacific Ocean. Two phases of regional N-S compression generated the two phases of sinistral faulting within the DMFZ, whereas two-stage regional extension generated the two phases of rifting. The two compressive events were the result of the rapid low-angle subduction of the Izanagi and Pacific plates, whereas the two-stage extension was caused by the roll-back of these respective

  7. The Sorong Fault Zone, Indonesia: Mapping a Fault Zone Offshore

    NASA Astrophysics Data System (ADS)

    Melia, S.; Hall, R.

    2017-12-01

    The Sorong Fault Zone is a left-lateral strike-slip fault zone in eastern Indonesia, extending westwards from the Bird's Head peninsula of West Papua towards Sulawesi. It is the result of interactions between the Pacific, Caroline, Philippine Sea, and Australian Plates and much of it is offshore. Previous research on the fault zone has been limited by the low resolution of available data offshore, leading to debates over the extent, location, and timing of movements, and the tectonic evolution of eastern Indonesia. Different studies have shown it north of the Sula Islands, truncated south of Halmahera, continuing to Sulawesi, or splaying into a horsetail fan of smaller faults. Recently acquired high resolution multibeam bathymetry of the seafloor (with a resolution of 15-25 meters), and 2D seismic lines, provide the opportunity to trace the fault offshore. The position of different strands can be identified. On land, SRTM topography shows that in the northern Bird's Head the fault zone is characterised by closely spaced E-W trending faults. NW of the Bird's Head offshore there is a fold and thrust belt which terminates some strands. To the west of the Bird's Head offshore the fault zone diverges into multiple strands trending ENE-WSW. Regions of Riedel shearing are evident west of the Bird's Head, indicating sinistral strike-slip motion. Further west, the ENE-WSW trending faults turn to an E-W trend and there are at least three fault zones situated immediately south of Halmahera, north of the Sula Islands, and between the islands of Sanana and Mangole where the fault system terminates in horsetail strands. South of the Sula islands some former normal faults at the continent-ocean boundary with the North Banda Sea are being reactivated as strike-slip faults. The fault zone does not currently reach Sulawesi. The new fault map differs from previous interpretations concerning the location, age and significance of different parts of the Sorong Fault Zone. Kinematic

  8. 'Extra-regional' strike-slip fault systems in Chile and Alaska: the North Pacific Rim orogenic Stream vs. Beck's Buttress

    NASA Astrophysics Data System (ADS)

    Redfield, T. F.; Scholl, D. W.; Fitzgerald, P. G.

    2010-12-01

    The ~2000 km long Denali Fault System (DFS) of Alaska is an example of an extra-regional strike-slip fault system that terminates in a zone of widely-distributed deformation. The ~1200 km long Liquiñe-Ofqui Fault Zone (LOFZ) of Patagonia (southern Chile) is another. Both systems are active, having undergone large-magnitude seismic rupture is 2002 (DFS) and 2007 (LOFZ). Both systems appear to be long-lived: the DFS juxtaposes terranes that docked in at least early Tertiary time, whilst the central LOFZ appears to also record early Tertiary or Mesozoic deformation. Both fault systems comprise a relatively well-defined central zone where individual fault traces can be identified from topographic features or zones of deformed rock. In both cases the proximal and distal traces are much more diffuse tributary and distributary systems of individual, branching fault traces. However, since their inception the DFS and LOFZ have followed very different evolutionary paths. Copious Alaskan paleomagnetic data are consistent with vertical axis small block rotation, long-distance latitudinal translation, and a recently-postulated tectonic extrusion towards a distributary of subordinate faults that branch outward towards the Aleution subduction zone (the North Pacific Rim orogenic Stream; see Redfield et al., 2007). Paleomagnetic data from the LOFZ region are consistent with small block rotation but preclude statistically-significant latitudinal transport. Limited field data from the southernmost LOFZ suggest that high-angle normal and reverse faults dominate over oblique to strike-slip structures. Rather than the high-angle oblique 'slivering regime' of the southeasternmost DFS, the initiation of the LOFZ appears to occur across a 50 to 100 km wide zone of brittly-deformed granitic and gneissic rock characterized by bulk compression and vertical pathways of exhumation. In both cases, relative plate motions are consistent with the hypothetical style, and degree, of offset, leading

  9. Vertical-axis rotations and deformation along the active strike-slip El Tigre Fault (Precordillera of San Juan, Argentina) assessed through palaeomagnetism and anisotropy of magnetic susceptibility

    NASA Astrophysics Data System (ADS)

    Fazzito, Sabrina Y.; Rapalini, Augusto E.; Cortés, José M.; Terrizzano, Carla M.

    2017-03-01

    Palaeomagnetic data from poorly consolidated to non-consolidated late Cenozoic sediments along the central segment of the active El Tigre Fault (Central-Western Precordillera of the San Juan Province, Argentina) demonstrate broad cumulative deformation up to 450 m from the fault trace and reveal clockwise and anticlockwise vertical-axis rotations of variable magnitude. This deformation has affected in different amounts Miocene to late Pleistocene samples and indicates a complex kinematic pattern. Several inherited linear structures in the shear zone that are oblique to the El Tigre Fault may have acted as block boundary faults. Displacement along these faults may have resulted in a complex pattern of rotations. The maximum magnitude of rotation is a function of the age of the sediments sampled, with largest values corresponding to middle Miocene-lower Pliocene deposits and minimum values obtained from late Pleistocene deposits. The kinematic study is complemented by low-field anisotropy of magnetic susceptibility data to show that the local strain regime suggests a N-S stretching direction, subparallel to the strike of the main fault.

  10. Strike-slip linked core complexes: A new kinematic model of basement rock exhumation in a crustal-scale fault system

    NASA Astrophysics Data System (ADS)

    Meyer, Sven Erik; Passchier, Cees; Abu-Alam, Tamer; Stüwe, Kurt

    2014-05-01

    Metamorphic core complexes usually develop as extensional features during continental crustal thinning, such as the Basin and Range and the Aegean Terrane. The Najd fault system in Saudi Arabia is a 2000 km-long and 400 km-wide complex network of crustal-scale strike-slip shear zones in a Neoproterozoic collision zone. Locally, the anastomosing shear zones lead to exhumation of lower crustal segments and represent a new kinematic model for the development of core complexes. We report on two such structures: the Qazaz complex in Saudi Arabia and the Hafafit complex in Egypt. The 15 km-wide Qazaz complex is a triangular dome of gently dipping mylonitic foliations within the 140 km-long sinistral strike-slip Qazaz mylonite zone. The gneissic dome consists of high-grade rocks, surrounded by low-grade metasediments and metavolcanics. The main SE-trending strike-slip Qazaz shear zone splits southwards into two branches around the gneiss dome: the western branch is continuous with the shallow dipping mylonites of the dome core, without overprinting, and changes by more than 90 degrees from a NS-trending strike-slip zone to an EW-trending 40 degree south-dipping detachment that bounds the gneiss dome to the south. The eastern SE-trending sinistral strike-slip shear zone branch is slightly younger and transects the central dome fabrics. The gneiss dome appears to have formed along a jog in the strike-slip shear zone during 40 km of horizontal strike-slip motion, which caused local exhumation of lower crustal rocks by 25 km along the detachment. The eastern shear zone branch formed later during exhumation, transacted the gneiss dome and offset the two parts by another 70 km. The Hafafit core complex in Egypt is of similar shape and size to the Qazaz structure, but forms the northern termination of a sinistral strike-slip zone that is at least 100 km in length. This zone may continue into Saudi Arabia as the Ajjaj shear zone for another 100 km. The NW trending strike slip

  11. Strike-slip deformation reflects complex partitioning of strain in the Nankai Accretionary Prism (SE Japan)

    NASA Astrophysics Data System (ADS)

    Azevedo, Marco C.; Alves, Tiago M.; Fonseca, Paulo E.; Moore, Gregory F.

    2018-01-01

    Previous studies have suggested predominant extensional tectonics acting, at present, on the Nankai Accretionary Prism (NAP), and following a parallel direction to the convergence vector between the Philippine Sea and Amur Plates. However, a complex set of thrusts, pop-up structures, thrust anticlines and strike-slip faults is observed on seismic data in the outer wedge of the NAP, hinting at a complex strain distribution across SE Japan. Three-dimensional (3D) seismic data reveal three main families of faults: (1) NE-trending thrusts and back-thrusts; (2) NNW- to N-trending left-lateral strike-slip faults; and (3) WNW-trending to E-W right-lateral strike-slip faults. Such a fault pattern suggests that lateral slip, together with thrusting, are the two major styles of deformation operating in the outer wedge of the NAP. Both styles of deformation reflect a transpressional tectonic regime in which the maximum horizontal stress is geometrically close to the convergence vector. This work is relevant because it shows a progressive change from faults trending perpendicularly to the convergence vector, to a broader partitioning of strain in the form of thrusts and conjugate strike-slip faults. We suggest that similar families of faults exist within the inner wedge of the NAP, below the Kumano Basin, and control stress accumulation and strain accommodation in this latter region.

  12. Timing of metamorphism of the Lansang gneiss and implications for left-lateral motion along the Mae Ping (Wang Chao) strike-slip fault, Thailand

    NASA Astrophysics Data System (ADS)

    Palin, R. M.; Searle, M. P.; Morley, C. K.; Charusiri, P.; Horstwood, M. S. A.; Roberts, N. M. W.

    2013-10-01

    The Mae Ping fault (MPF), western Thailand, exhibits dominantly left-lateral strike-slip motion and stretches for >600 km, reportedly branching off the right-lateral Sagaing fault in Myanmar and extending southeast towards Cambodia. Previous studies have suggested that the fault assisted the large-scale extrusion of Sundaland that occurred during the Late Eocene-Early Oligocene, with a geological offset of ˜120-150 km estimated from displaced high-grade gneisses and granites of the Chiang Mai-Lincang belt. Exposures of high-grade orthogneiss in the Lansang National Park, part of this belt, locally contain strong mylonitic textures and are bounded by strike-slip ductile shear zones and brittle faults. Geochronological analysis of monazite from a sample of sheared biotite-K-feldspar orthogneiss suggests two episodes of crystallization, with core regions documenting Th-Pb ages between c. 123 and c. 114 Ma and rim regions documenting a significantly younger age range between c. 45-37 Ma. These data are interpreted to represent possible magmatic protolith emplacement for the Lansang orthogneiss during the Early Cretaceous, with a later episode of metamorphism occurring during the Eocene. Textural relationships provided by in situ analysis suggest that ductile shearing along the MPF occurred during the latter stages of, or after, this metamorphic event. In addition, monazite analyzed from an undeformed garnet-two-mica granite dyke intruding metamorphic units at Bhumipol Lake outside of the Mae Ping shear zone produced a Th-Pb age of 66.2 ± 1.6 Ma. This age is interpreted to date the timing of dyke emplacement, implying that the MPF cuts through earlier formed magmatic and high-grade metamorphic rocks. These new data, when combined with regional mapping and earlier geochronological work, show that neither metamorphism, nor regional cooling, was directly related to strike-slip motion.

  13. An L-band interferometric synthetic aperture radar study on the Ganos section of the north Anatolian fault zone between 2007 and 2011: Evidence for along strike segmentation and creep in a shallow fault patch.

    PubMed

    de Michele, Marcello; Ergintav, Semih; Aochi, Hideo; Raucoules, Daniel

    2017-01-01

    We utilize L-band interferometric synthetic aperture radar (InSAR) data in this study to retrieve a ground velocity map for the near field of the Ganos section of the north Anatolian fault (NAF) zone. The segmentation and creep distribution of this section, which last ruptured in 1912 to generate a moment magnitude (Mw)7.3 earthquake, remains incompletely understood. Because InSAR processing removes the mean orbital plane, we do not investigate large scale displacements due to regional tectonics in this study as these can be determined using global positioning system (GPS) data, instead concentrating on the close-to-the-fault displacement field. Our aim is to determine whether, or not, it is possible to retrieve robust near field velocity maps from stacking L-band interferograms, combining both single and dual polarization SAR data. In addition, we discuss whether a crustal velocity map can be used to complement GPS observations in an attempt to discriminate the present-day surface displacement of the Ganos fault (GF) across multiple segments. Finally, we characterize the spatial distribution of creep on shallow patches along multiple along-strike segments at shallow depths. Our results suggest the presence of fault segmentation along strike as well as creep on the shallow part of the fault (i.e. the existence of a shallow creeping patch) or the presence of a smoother section on the fault plane. Data imply a heterogeneous fault plane with more complex mechanics than previously thought. Because this study improves our knowledge of the mechanisms underlying the GF, our results have implications for local seismic hazard assessment.

  14. An L-band interferometric synthetic aperture radar study on the Ganos section of the north Anatolian fault zone between 2007 and 2011: Evidence for along strike segmentation and creep in a shallow fault patch

    PubMed Central

    Ergintav, Semih; Aochi, Hideo; Raucoules, Daniel

    2017-01-01

    We utilize L-band interferometric synthetic aperture radar (InSAR) data in this study to retrieve a ground velocity map for the near field of the Ganos section of the north Anatolian fault (NAF) zone. The segmentation and creep distribution of this section, which last ruptured in 1912 to generate a moment magnitude (Mw)7.3 earthquake, remains incompletely understood. Because InSAR processing removes the mean orbital plane, we do not investigate large scale displacements due to regional tectonics in this study as these can be determined using global positioning system (GPS) data, instead concentrating on the close-to-the-fault displacement field. Our aim is to determine whether, or not, it is possible to retrieve robust near field velocity maps from stacking L-band interferograms, combining both single and dual polarization SAR data. In addition, we discuss whether a crustal velocity map can be used to complement GPS observations in an attempt to discriminate the present-day surface displacement of the Ganos fault (GF) across multiple segments. Finally, we characterize the spatial distribution of creep on shallow patches along multiple along-strike segments at shallow depths. Our results suggest the presence of fault segmentation along strike as well as creep on the shallow part of the fault (i.e. the existence of a shallow creeping patch) or the presence of a smoother section on the fault plane. Data imply a heterogeneous fault plane with more complex mechanics than previously thought. Because this study improves our knowledge of the mechanisms underlying the GF, our results have implications for local seismic hazard assessment. PMID:28961264

  15. Comment on "No late Quaternary strike-slip motion along the northern Karakoram fault" published by Robinson et al. in EPSL, 2015

    NASA Astrophysics Data System (ADS)

    Chevalier, Marie-Luce; Leloup, Philippe Hervé; Li, Haibing

    2016-06-01

    The northern part of the already highly debated Karakorum fault (KF) in western Tibet (regarding its initiation age, total geological offset and slip-rate) has been argued by Robinson (2009a) and Robinson et al. (2015) to be inactive. This is based on field investigation and satellite images interpretation showing a few km of Quaternary deposits from the southern Tashkorgan basin in the Chinese Pamir, that appear undisturbed by the main branch of the KF. In particular, Robinson et al. (2015) suggested that the Kongur Shan extensional system (KES) is not kinematically related to the KF, and that the latter is only a local fault. Here, we use basic definitions of what is an active strike-slip fault system, as well as re-emphasize the importance of the timescale of observation to discuss whether a fault is active, to demonstrate that the KF and the KES are part of the same fault system. We argue that they together play a significant role in accommodating deformation at the western Himalayan syntaxis, under the form of extensional displacement in the Chinese Pamir.

  16. The 2014 Mw6.9 Gokceada and 2017 Mw6.3 Lesvos Earthquakes in the Northern Aegean Sea: The Transition from Right-Lateral Strike-Slip Faulting on the North Anatolian Fault to Extension in the Central Aegean

    NASA Astrophysics Data System (ADS)

    Cetin, S.; Konca, A. O.; Dogan, U.; Floyd, M.; Karabulut, H.; Ergintav, S.; Ganas, A.; Paradisis, D.; King, R. W.; Reilinger, R. E.

    2017-12-01

    The 2014 Mw6.9 Gokceada (strike-slip) and 2017 Mw6.3 Lesvos (normal) earthquakes represent two of the set of faults that accommodate the transition from right-lateral strike-slip faulting on the North Anatolian Fault (NAF) to normal faulting along the Gulf of Corinth. The Gokceada earthquake was a purely strike-slip event on the western extension of the NAF where it enters the northern Aegean Sea. The Lesvos earthquake, located roughly 200 km south of Gokceada, occurred on a WNW-ESE-striking normal fault. Both earthquakes respond to the same regional stress field, as indicated by their sub-parallel seismic tension axis and far-field coseismic GPS displacements. Interpretation of GPS-derived velocities, active faults, crustal seismicity, and earthquake focal mechanisms in the northern Aegean indicates that this pattern of complementary faulting, involving WNW-ESE-striking normal faults (e.g. Lesvos earthquake) and SW-NE-striking strike-slip faults (e.g. Gokceada earthquake), persists across the full extent of the northern Aegean Sea. The combination of these two "families" of faults, combined with some systems of conjugate left-lateral strike-slip faults, complement one another and culminate in the purely extensional rift structures that form the large Gulfs of Evvia and Corinth. In addition to being consistent with seismic and geodetic observations, these fault geometries explain the increasing velocity of the southern Aegean and Peloponnese regions towards the Hellenic subduction zone. Alignment of geodetic extension and seismic tension axes with motion of the southern Aegean towards the Hellenic subduction zone suggests a direct association of Aegean extension with subduction, possibly by trench retreat, as has been suggested by prior investigators.

  17. From 2012 HAITI-SIS Survey: thick-skin versus thin-skin tectonics partitioned along offshore strike-slip Faults-Haïti

    NASA Astrophysics Data System (ADS)

    Ellouz, N.; Leroy, S. D.; Momplaisir, R.; Mercier de Lepinay, B.

    2013-12-01

    The characterization of the deformation along large strike-slip fault-systems like transpressive boundaries between N. Caribbean/N America is a challenging topic, which requires a multi-scale approach. Thanks to Haiti-sis new data, the precise description of the fault segmentation pattern, the sedimentogical distribution, the uplift/subsidence rates, the along-fault and intra-basin fluids circulations, allows to actualize the evolution of the deformation history up to present-day . All the co-seismic surface to near-surface events, have to be also identified in order to integrate geophysical solutions for the earthquake, within the present-day geological and structural pattern. These two approaches, ranging from geological to instantaneous time-scales have been used during multi-tools Haiti-Sis oceanographic survey, allowing to document and image these different aspects at a large scale. The complex strike-slip North Caribbean boundary registered significative stress partitioning. Oblique convergence is expressed by along-strike evolution; from rifted segments (Cayman Through) to transpressive ones (Haiti, Dominican Rep.), to subduction (Porto Rico). In the Haiti-Sis survey, we acquired new offshore data surrounding the active fault areas, in the Gonâve Bay, the Jamaica Channel and along Southern Peninsula. Mapping the sea-floor, and HR seismic acquisition were our main objectives, in order to characterize the fault and fold architecture, with a new delineation of active segments. Offshore piston cores, have been used as representative of the modern basin sedimentation, and to document the catastrophic events (earthquakes, massive flood or sudden destabilization of the platform ) represented by turbiditic or mass-flow sequences, with the objective to track the time recurrence of seismic events by dating some of these catastrophic sediment deposition. At surface, the other markers of the fault activity are linked with along-fault permeability and fluid circulation

  18. Seismically-triggered soft-sediment deformation structures close to a major strike-slip fault system in the Eastern Alps (Hirlatz cave, Austria)

    NASA Astrophysics Data System (ADS)

    Salomon, Martina Lan; Grasemann, Bernhard; Plan, Lukas; Gier, Susanne; Schöpfer, Martin P. J.

    2018-05-01

    We investigate episodic soft-sediment deformation structures cross-cut by normal faults preserved in unlithified finely laminated calcite rich sediments in the Hirlatz cave in the Northern Calcareous Alps (Austria). These sediments comprise varve-like alternations of brighter carbonate/quartz rich layers, and darker clay mineral rich layers. The deformed sediments contain abundant millimeter to centimeter-scale soft-sediment structures (load casts, ball-and-pillow structures), sheet slumps (thrust faults and folds), erosive channels filled with slides and chaotic slumps. After deposition and soft-sediment deformation normal faults developed within the entire sedimentary succession, an event that probably correlates with an offset of c. 10 cm of the passage wall above the outcrop. Our major conclusions are: (i) The sediments have a glacial origin and were deposited in the Hirlatz cave under phreatic fluvio-lacustrine conditions. The deposition and the soft-sediment deformation occurred most likely during the last glaciation (i.e. around 25 ka ago); (ii) The liquefaction and formation of the soft-sediment structures in water-saturated stratified layers was triggered by episodic seismic events; (iii) The internally deformed sediments were later displaced by normal faults; (iv) A possible source for the seismic events is the active sinistral Salzach-Ennstal-Mariazeller-Puchberger (SEMP) strike-slip fault which is located about 10 km south of the outcrop and plays a major role in accommodating the extrusion of the Eastern Alps towards the Pannonian Basin. To our knowledge, the described structures are the first report of liquefaction and seismically induced soft-sediment deformations in Quaternary sediments in the Eastern Alps.

  19. Empirical Relationships Among Magnitude and Surface Rupture Characteristics of Strike-Slip Faults: Effect of Fault (System) Geometry and Observation Location, Dervided From Numerical Modeling

    NASA Astrophysics Data System (ADS)

    Zielke, O.; Arrowsmith, J.

    2007-12-01

    In order to determine the magnitude of pre-historic earthquakes, surface rupture length, average and maximum surface displacement are utilized, assuming that an earthquake of a specific size will cause surface features of correlated size. The well known Wells and Coppersmith (1994) paper and other studies defined empirical relationships between these and other parameters, based on historic events with independently known magnitude and rupture characteristics. However, these relationships show relatively large standard deviations and they are based only on a small number of events. To improve these first-order empirical relationships, the observation location relative to the rupture extent within the regional tectonic framework should be accounted for. This however cannot be done based on natural seismicity because of the limited size of datasets on large earthquakes. We have developed the numerical model FIMozFric, based on derivations by Okada (1992) to create synthetic seismic records for a given fault or fault system under the influence of either slip- or stress boundary conditions. Our model features A) the introduction of an upper and lower aseismic zone, B) a simple Coulomb friction law, C) bulk parameters simulating fault heterogeneity, and D) a fault interaction algorithm handling the large number of fault patches (typically 5,000-10,000). The joint implementation of these features produces well behaved synthetic seismic catalogs and realistic relationships among magnitude and surface rupture characteristics which are well within the error of the results by Wells and Coppersmith (1994). Furthermore, we use the synthetic seismic records to show that the relationships between magntiude and rupture characteristics are a function of the observation location within the regional tectonic framework. The model presented here can to provide paleoseismologists with a tool to improve magnitude estimates from surface rupture characteristics, by incorporating the

  20. A reality check on the timing of initiation, geological offsets, slip rates and geodetic rates on the Karakoram strike-slip fault.

    NASA Astrophysics Data System (ADS)

    Searle, M. P.; Phillips, R. J.

    2003-12-01

    Total geological offset of 1000 km along the dextral Karakoram fault (Peltzer & Tapponnier 1989) were based on incorrect correlation of granite belts from the Pamir to S. Tibet and active slip rates of 30mm/yr-1 were based on an assumption of the age of offset post-glacial features (10 +/- 2 ka; Liu et al. 1992). Detailed mapping and U-Pb and 40Ar/39Ar geochronology has confirmed that total dextral offsets are less than 120 km, the timing of initiation of the fault must have been younger than 15 Ma and that exhumation of sheared leucogranites and migmatites occurred between 15-11 Ma (Searle et al., 1997; Dunlap et al., 1998). We stress that: 1. All Tibetan fault slip rates published prior to 1996 are invalid as no precise timing constraints on the post-glacial Quaternary features were used. The common assumption was that all glacial features were formed 10 +/- 2 ka, without any absolute dating. The glacial and fluvial features used to constrain offsets could have been awry by a factor of 3 or 4 (from 3.5 Ma - 20,000 ka). 2. Recent slip rates derived from cosmogenic isotope dating of offset Quaternary features should be treated with immense caution because during the continual recycling process of glacial moraine or alluvial fan burial, exposure and re-deposition, it cannot be known precisely which phase of exhumation is being dated. 3. Long-term geological slip rates on offset granites, precisely constrained by U-Pb geochronology remain the best estimates of timing of initiation, total finite offset and slip rates on Tibetan strike-slip faults. 4. The Karakoram fault is unlikely to be a lithospheric scale fault, because (a) temperatures beneath the southern part of the Tibetan plateau and beneath the faults are high enough to induce melting (>700° C at only 20 km depth), and (b) the lower crust beneath these faults must be underplated cold, old granulite facies crust of the Indian shield. 5. There appears to be a distinct lack of seismicity located along the

  1. Aeromagnetic evidence for a major strike-slip fault zone along the boundary between the Weddell Sea Rift and East Antarctica

    NASA Astrophysics Data System (ADS)

    Jordan, T. A.; Ferraccioli, F.; Ross, N.; Siegert, M. J.; Corr, H.; Leat, P. T.; Bingham, R. G.; Rippin, D. M.; le Brocq, A.

    2012-04-01

    The >500 km wide Weddell Sea Rift was a major focus for Jurassic extension and magmatism during the early stages of Gondwana break-up, and underlies the Weddell Sea Embayment, which separates East Antarctica from a collage of crustal blocks in West Antarctica. Here we present new aeromagnetic data combined with airborne radar and gravity data collected during the 2010-11 field season over the Institute and Moeller ice stream in West Antarctica. Our interpretations identify the major tectonic boundaries between the Weddell Sea Rift, the Ellsworth-Whitmore Mountains block and East Antarctica. Digitally enhanced aeromagnetic data and gravity anomalies indicate the extent of Proterozoic basement, Middle Cambrian rift-related volcanic rocks, Jurassic granites, and post Jurassic sedimentary infill. Two new joint magnetic and gravity models were constructed, constrained by 2D and 3D magnetic depth-to-source estimates to assess the extent of Proterozoic basement and the thickness of major Jurassic intrusions and post-Jurassic sedimentary infill. The Jurassic granites are modelled as 5-8 km thick and emplaced at the transition between the thicker crust of the Ellsworth-Whitmore Mountains block and the thinner crust of the Weddell Sea Rift, and within the Pagano Fault Zone, a newly identified ~75 km wide left-lateral strike-slip fault system that we interpret as a major tectonic boundary between East and West Antarctica. We also suggest a possible analogy between the Pagano Fault Zone and the Dead Sea transform. In this scenario the Jurassic Pagano Fault Zone is the kinematic link between extension in the Weddell Sea Rift and convergence across the Pacific margin of West Antarctica, as the Dead Sea transform links Red Sea extension to compression within the Zagros Mountains.

  2. Sculpting the Philippine archipelago since the Cretaceous through rifting, oceanic spreading, subduction, obduction, collision and strike-slip faulting: Contribution to IGMA5000

    NASA Astrophysics Data System (ADS)

    Aurelio, Mario A.; Peña, Rolando E.; Taguibao, Kristine Joy L.

    2013-08-01

    The Philippine archipelago resulted from a complex series of geologic events that involved continental rifting, oceanic spreading, subduction, ophiolite obduction, arc-continent collision, intra-arc basin formation and strike-slip faulting. It can be divided into two tectono-stratigraphic blocks, namely; the Palawan-Mindoro Continental Block (PCB) and the Philippine Mobile Belt (PMB). The PCB was originally a part of the Asian mainland that was rifted away during the Mesozoic and drifted in the course of the opening of the South China Sea (SCS) during Late Paleogene. On the other hand, the PMB developed mainly from island arcs and ophiolite terranes that started to form during the Cretaceous. At present, the PMB collides with the PCB in the Visayas in the central-western Philippines. This paper discusses recent updates on Philippine geology and tectonics as contribution to the establishment of the International Geologic Map of Asia at 1:5 M scale (IGMA5000).

  3. Reconciling postseismic and interseismic surface deformation around strike-slip faults: Earthquake-cycle models with finite ruptures and viscous shear zones

    NASA Astrophysics Data System (ADS)

    Hearn, E. H.

    2013-12-01

    Geodetic surface velocity data show that after an energetic but brief phase of postseismic deformation, surface deformation around most major strike-slip faults tends to be localized and stationary, and can be modeled with a buried elastic dislocation creeping at or near the Holocene slip rate. Earthquake-cycle models incorporating an elastic layer over a Maxwell viscoelastic halfspace cannot explain this, even when the earliest postseismic deformation is ignored or modeled (e.g., as frictional afterslip). Models with heterogeneously distributed low-viscosity materials or power-law rheologies perform better, but to explain all phases of earthquake-cycle deformation, Burgers viscoelastic materials with extreme differences between their Maxwell and Kelvin element viscosities seem to be required. I present a suite of earthquake-cycle models to show that postseismic and interseismic deformation may be reconciled for a range of lithosphere architectures and rheologies if finite rupture length is taken into account. These models incorporate high-viscosity lithosphere optionally cut by a viscous shear zone, and a lower-viscosity mantle asthenosphere (all with a range of viscoelastic rheologies and parameters). Characteristic earthquakes with Mw = 7.0 - 7.9 are investigated, with interseismic intervals adjusted to maintain the same slip rate (10, 20 or 40 mm/yr). I find that a high-viscosity lower crust/uppermost mantle (or a high viscosity per unit width viscous shear zone at these depths) is required for localized and stationary interseismic deformation. For Mw = 7.9 characteristic earthquakes, the shear zone viscosity per unit width in the lower crust and uppermost mantle must exceed about 10^16 Pa s /m. For a layered viscoelastic model the lower crust and uppermost mantle effective viscosity must exceed about 10^20 Pa s. The range of admissible shear zone and lower lithosphere rheologies broadens considerably for faults producing more frequent but smaller

  4. Breaching of strike-slip faults and flooding of pull-apart basins to form the southern Gulf of California seaway from 8 to 6 Ma

    NASA Astrophysics Data System (ADS)

    Umhoefer, P. J.; Skinner, L. A.; Oskin, M. E.; Dorsey, R. J.; Bennett, S. E. K.; Darin, M. H.

    2017-12-01

    Studies from multiple disciplines delineate the development of the oblique-divergent Pacific - North America plate boundary in the southern Gulf of California. Integration of onshore data from the Loreto - Santa Rosalia margin with offshore data from the Pescadero, Farallon, and Guaymas basins provides a detailed geologic history. Our GIS-based paleotectonic maps of the plate boundary from 9 to 6 Ma show that evolution of pull-apart basins led to the episodic northwestward encroachment of the Gulf of California seaway. Because adjacent pull-apart basins commonly have highlands between them, juxtaposition of adjacent basin lows during translation and pull apart lengthening played a critical role in seaway flooding. Microfossils and volcanic units date the earliest marine deposits at 9(?) - 8 Ma at the mouth of the Gulf. By ca. 8 Ma, the seaway had flooded north to the Pescadero basin, while the Loreto fault and the related fault-termination basin was proposed to have formed along strike at the plate margin. East of Loreto basin, a short topographic barrier between the Pescadero and Farallon pull-apart basins suggests that the Farallon basin was either a terrestrial basin, or if breaching occurred, it may contain 8 Ma salt or marine deposits. This early southern seaway formed along a series of pull-apart basins within a narrow belt of transtension structurally similar to the modern Walker Lane in NV and CA. At ca. 7 Ma, a series of marine incursions breached a 75-100 km long transtensional fault barrier between the Farallon and Guaymas basins offshore Bahía Concepción. Repeated breaching events and the isolation of the Guaymas basin in a subtropical setting formed a 2 km-thick salt deposit imaged in offshore seismic data, and thin evaporite deposits in the onshore Santa Rosalia basin. Lengthening of the Guaymas, Yaqui, and Tiburon basins caused breaches of the intervening Guaymas and Tiburón transforms by 6.5-6.3 Ma, forming a permanent 1500 km-long marine seaway

  5. Analogue modelling on the interaction between shallow magma intrusion and a strike-slip fault: Application on the Middle Triassic Monzoni Intrusive Complex (Dolomites, Italy)

    NASA Astrophysics Data System (ADS)

    Michail, Maria; Coltorti, Massimo; Gianolla, Piero; Riva, Alberto; Rosenau, Matthias; Bonadiman, Costanza; Galland, Olivier; Guldstrand, Frank; Thordén Haug, Øystein; Rudolf, Michael; Schmiedel, Tobias

    2017-04-01

    The southwestern part of the Dolomites in Northern Italy has undergone a short-lived Ladinian (Middle Triassic) tectono-magmatic event, forming a series of significant magmatic features. These intrusive bodies deformed and metamorphosed the Permo-Triassic carbonate sedimentary framework. In this study we focus on the tectono-magmatic evolution of the shallow shoshonitic Monzoni Intrusive Complex of this Ladinian event (ca 237 Ma), covering an area of 20 km^2. This NW-SE elongated intrusive structure (5 km length) shows an orogenic magmatic affinity which is in contrast to the tectonic regime at the time of intrusion. Strain analysis shows anorogenic transtensional displacement in accordance with the ENE-WSW extensional pattern in the central Dolomites during the Ladinian. Field interpretations led to a detailed description of the regional stratigraphic sequence and the structural features of the study area. However, the geodynamic context of this magmatism and the influence of the inherited strike-slip fault on the intrusion, are still in question. To better understand the specific natural prototype and the general mechanisms of magma emplacement in tectonically active areas, we performed analogue experiments defined by, but not limited to, first order field observations. We have conducted a systematic series of experiments in different tectonic regimes (static conditions, strike-slip, transtension). We varied the ratio of viscous to brittle stresses between magma and country rock, by injecting Newtonian fluids both of high and low viscosity (i.e. silicone oil/vegetable oil) into granular materials of varying cohesion (sand, silica flour, glass beads). The evolving surface and side view of the experiments were monitored by photogrammetric techniques for strain analyses and topographic evolution. In our case, the combination of the results from field and analogue experiments brings new insights regarding the tectonic regime, the geometry of the intrusive body, and

  6. The 2012 Strike-slip Earthquake Sequence in Black Sea and its Link to the Caucasus Collision Zone

    NASA Astrophysics Data System (ADS)

    Tseng, T. L.; Hsu, C. H.; Legendre, C. P.; Jian, P. R.; Huang, B. S.; Karakhanian, A.; Chen, C. W.

    2016-12-01

    The Black Sea formed as a back-arc basin in Late Cretaceous to Paleogene with lots of extensional features. However, the Black Sea is now tectonically stable and absent of notable earthquakes except for the coastal region. In this study we invert regional waveforms of a new seismic array to constrain the focal mechanisms and depths of the 2012/12/23 earthquake sequence occurred in northeastern Black Sea basin that can provide unique estimates on the stress field in the region. The results show that the focal mechanisms for the main shock and 5 larger aftershocks are all strike-slip faulting and resembling with each other. The main rupture fall along the vertical dipping, NW-SE trending sinistral fault indicated by the lineation of most aftershocks. The fault strike and aftershock distribution are both consistent with the Shatsky Ridge, which is continental in nature but large normal faults was created by previous subsidence. The occurrence of 2012 earthquakes can be re-activated, as strike-slip, on one of the pre-existing normal fault cutting at depth nearly 20-30 km in the extended crust. Some of the aftershocks, including a larger one occurred 5 days later, are distributed toward NE direction 20 km away from main fault zone. Those events might be triggered by the main shock along a conjugate fault, which is surprisingly at the extension of proposed transform fault perpendicular to the rift axis of eastern Black Sea Basin. The focal mechanisms also indicate that the maximum compression in northeast Black Sea is at E-W direction, completely different from the N-S compression in the Caucasus and East Turkey controlled by Arabia-Eurasia collision. The origin of E-W maximum compression is probably the same as the secondary stress inferred from earthquakes in Racha region of the Greater Caucasus.

  7. Seismogenic faulting in the Meruoca granite, NE Brazil, consistent with a local weak fracture zone.

    PubMed

    Moura, Ana Catarina A; De Oliveira, Paulo H S; Ferreira, Joaquim M; Bezerra, Francisco H R; Fuck, Reinhardt A; Do Nascimento, Aderson F

    2014-12-01

    A sequence of earthquakes occurred in 2008 in the Meruoca granitic pluton, located in the northwestern part of the Borborema Province, NE Brazil. A seismological study defined the seismic activity occurring along the seismically-defined Riacho Fundo fault, a 081° striking, 8 km deep structure. The objective of this study was to analyze the correlation between this seismic activity and geological structures in the Meruoca granite. We carried out geological mapping in the epicentral area, analyzed the mineralogy of fault rocks, and compared the seismically-defined Riacho Fundo fault with geological data. We concluded that the seismically-defined fault coincides with ∼E-W-striking faults observed at outcrop scale and a swarm of Mesozoic basalt dikes. We propose that seismicity reactivated brittle structures in the Meruoca granite. Our study highlights the importance of geological mapping and mineralogical analysis in order to establish the relationships between geological structures and seismicity at a given area.

  8. Seismogenic faulting in the Meruoca granite, NE Brazil, consistent with a local weak fracture zone.

    PubMed

    Moura, Ana Catarina A; Oliveira, Paulo H S DE; Ferreira, Joaquim M; Bezerra, Francisco H R; Fuck, Reinhardt A; Nascimento, Aderson F DO

    2014-10-24

    A sequence of earthquakes occurred in 2008 in the Meruoca granitic pluton, located in the northwestern part of the Borborema Province, NE Brazil. A seismological study defined the seismic activity occurring along the seismically-defined Riacho Fundo fault, a 081° striking, 8 km deep structure. The objective of this study was to analyze the correlation between this seismic activity and geological structures in the Meruoca granite. We carried out geological mapping in the epicentral area, analyzed the mineralogy of fault rocks, and compared the seismically-defined Riacho Fundo fault with geological data. We concluded that the seismically-defined fault coincides with ∼E-W-striking faults observed at outcrop scale and a swarm of Mesozoic basalt dikes. We propose that seismicity reactivated brittle structures in the Meruoca granite. Our study highlights the importance of geological mapping and mineralogical analysis in order to establish the relationships between geological structures and seismicity at a given area.

  9. Strike-slip Fault Structure in the Salton Trough and Deformation During and After the 2010 M7.2 El Mayor-Cucapah Earthquake from Geodetic and Seismic Data

    NASA Astrophysics Data System (ADS)

    Fielding, E. J.; Sun, J.; Gonzalez-Ortega, A.; González-Escobar, M.; Freed, A. M.; Burgmann, R.; Samsonov, S. V.; Gonzalez-Garcia, J.; Fletcher, J. M.; Hinojosa, A.

    2013-12-01

    The Pacific-North America plate boundary character changes southward from the strike-slip and transpressional configuration along most of California to oblique rifting in the Gulf of California, with a transitional zone of transtension beneath the Salton Trough in southernmost California and northern Mexico. The Salton Trough is characterized by extremely high heat flow and thin lithosphere with a thick fill of sedimentary material delivered by the Colorado River during the past 5-6 million years. Because of the rapid sedimentation, most of the faults in Salton Trough are buried and reveal themselves when they slip either seismically or aseismically. They can also be located by refraction and reflection of seismic waves. The 4 April 2010 El Mayor-Cucapah earthquake (Mw 7.2) in Baja California and Sonora, Mexico is probably the largest earthquake in the Salton Trough for at least 120 years, and had primarily right-lateral strike-slip motion. The earthquake ruptured a complex set of faults that lie to the west of the main plate boundary fault, the Cerro Prieto Fault, and shows that the strike-slip fault system in the southern Salton Trough has multiple sub-parallel active faults, similar to southern California. The Cerro Prieto Fault is still likely absorbing the majority of strain in the plate boundary. We study the coseismic and postseismic deformation of the 2010 earthquake with interferometric analysis of synthetic aperture radar (SAR) images (InSAR) and pixel tracking by subpixel correlation of SAR and optical images. We combine sampled InSAR and subpixel correlation results with GPS (Global Positioning System) offsets at PBO (Plate Boundary Observatory) stations to estimate the likely subsurface geometry of the major faults that slipped during the earthquake and to derive a static coseismic slip model. We constrained the surface locations of the fault segments to mapped locations in the Sierra Cucapah to the northwest of the epicenter. SAR along-track offsets

  10. Aerogeophysical evidence for strike-slip faulting at the boundary between East and West Antarctica: implications for Jurassic magma emplacement and Gondwana breakup models

    NASA Astrophysics Data System (ADS)

    Jordan, Tom; Ferraccioli, Fausto

    2014-05-01

    Fragmentation of the Gondwana supercontinent began in the Jurassic and was the most significant reconfiguration of the continents of the southern hemisphere in the last 500 Ma. Jurassic continental rifting began adjacent to South Africa in the Weddell Sea region of Antarctica. This region is therefore critical for understanding the process that initiated supercontinent breakup, including the role of mantle plumes, magmatism, and major plate and microplate re-configurations. However, due to the remote location and blanketing ice sheets, the magmatic and tectonic evolution of the Weddell Sea sector of Antarctica has remained poorly understood and controversial. Our recent aeromagnetic and airborne gravity investigations reveal the inland extent of the Weddell Sea Rift system beneath the West Antarctic Ice Sheet, and indicate the presence of a major left-lateral strike slip fault system, separating the Ellsworth Whitmore block from East Antarctica (Jordan et al., 2013 Tectonophysics). In this study we use 3D inversion of magnetic data to investigate the geometry and emplacement mechanism of Jurassic granites both along the boundary and within the Ellsworth-Whitmore block. Our models demonstrate a high degree of structural control on Jurassic granite emplacement along the newly identified left-lateral Pagano Shear Zone that flanks the Ellsworth-Whitmore block. Other granitoids emplaced further west within the Ellsworth-Whtimore block itself do not appear to have the same structural control, suggesting that this possible microplate or block was relatively more rigid. Extensive and likely more rigid Precambrian basement of Grenvillian-age is clearly delineated from aeromagnetic signatures at the northern edge of the Ellsworth-Whitmore block, lending support to this interpretation. Most intriguing, it that the high amplitude anomalies over the northern margin of the Ellsworth-Whitmore block are remarkably similar to those previously mapped over the Shackleton Range in

  11. Middle Pleistocene infill of Hinkley Valley by Mojave River sediment and associated lake sediment: Depositional architecture and deformation by strike-slip faults

    USGS Publications Warehouse

    Miller, David; Haddon, Elizabeth; Langenheim, Victoria; Cyr, Andrew J.; Wan, Elmira; Walkup, Laura; Starratt, Scott W.

    2018-01-01

    avulsed through the valley, rather than continuing toward Lake Manix, during the late Pleistocene. Two dextral strike-slip fault zones, the Lockhart and the Mt. General, fold and displace the distinctive stratigraphic units, as well as surficial late Pleistocene and Holocene deposits. The sedimentary architecture and the two fault zones provide a framework for evaluating groundwater flow in Hinkley Valley.

  12. 4. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. Historic American Buildings Survey E. W. Russell, Photographer, August 4, 1936 REFLECTED VIEW OF PORTICO CEILING - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  13. 1. Historic American Buildings Survey E. W. Russell, Photographer, November ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, November 5, 1936 FRONT ELEVATION (SOUTH) - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  14. Tertiary and Quaternary tectonic faulting in southernmost Illinois

    USGS Publications Warehouse

    Nelson, W.J.; Denny, F.B.; Devera, J.A.; Follmer, L.R.; Masters, J.M.

    1997-01-01

    Tertiary and/or Quaternary tectonic faulting is documented in three areas of southernmost Illinois: the Fluorspar Area Fault Complex (FAFC) in Pope and Massac Counties, the Ste. Genevieve Fault Zone (SGFZ) in Alexander and Union Counties, and the Commerce Fault Zone (CFZ) in Alexander County. In the FAFC, faults that strike NE and NNE displace Mounds Gravel (late Miocene to early Pleistocene) and, locally, the Metropolis terrace gravel (Pleistocene; pre-Woodfordian). No Woodfordian or younger deposits are deformed. Faults typically outline narrow, linear grabens that formed under tension with a component of strike slip. North-south to NW-trending vertical faults near the southeast end of the SGFZ displace Eocene sediments. Again, faults outline narrow grabens and show indications of strike slip. Deformed Quaternary sediments have not been observed. The CFZ, which trends northeast, displaces Mounds Gravel in Illinois and units as young as Peoria Silt (Woodfordian) in Missouri. Quaternary movement has been interpreted as right-lateral strike-slip. The CFZ coincides with a subtle gravity and magnetic lineament and seems to reflect a major feature in the basement. Surface expression in Illinois is subtle, but mafic and ultramafic intrusions, hydrothermal alteration and small faults align with the Commerce geophysical lineament. Earthquake foci in Missouri and Illinois lie on or close to the CFZ; some focal mechanisms fit the fault trend. Among these structures, only the CFZ exhibits slip that conforms to the current stress field (principal compressive stress axis E-W to ENE-WSW). Possibly, the stress field changed during Neogene time. Alternatively, high fluid pressures or local stress concentrations may have induced slip on less favorably oriented fractures. Tighter constraints are needed on timing, magnitude, and direction of Neogene displacement. ?? 1997 Elsevier Science B.V.

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

    SciTech Connect

    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

  16. Characteristics of newly found Quaternary fault, southern Korea, and its tectonic implication

    NASA Astrophysics Data System (ADS)

    Lee, Y.; Kim, M. C.; Cheon, Y.; Ha, S.; Kang, H. C.; Choi, J. H.; Son, M.

    2017-12-01

    This study introduces the detailed geometry and kinematics of recently found Quaternary fault in southern Korea, named Seooe Fault, and discusses its tectonic implication through a synthetic analysis with previous studies. The N-S striking Seooe Fault shows a top-to-the-east thrust geometry and cuts the Cretaceous Goseong Formation and overlying Quaternary deposits, and its slip senses and associated minor folds in the hanging wall indicate an E-W compressional stress. The age of the lower part of the Quaternary deposits obtained by OSL dating indicates that the last movement of the fault occurred after 61 60 ka. Arcuate geometry of the main fault showing an upward decreasing dip-angle, reverse offset of the fault breccias, and reverse-sense indicators observed on neighboring N-S striking high-angle fractures indicate that this Quaternary fault was produced by the reactivation of pre-existing fault under E-W compressional stress field. Using the apparent vertical displacement of the fault and the attitudes of cutting slope and main fault surface, its minimum net displacement is calculated as 2.17 m. When the value is applied to the empirical equation of maximum displacement - moment earthquake magnitude (Mw), the magnitude is estimated to reach about 6.7, assuming that this displacement was due to one seismic event. Most of the Quaternary faults in southern Korea are observed along major inherited fault zones, and their geometry and kinematics indicate that they were reactivated under ENE-WSW or E-W compressional stress field, which is concordant with the characteristics of the Seooe Fault. In addition, focal mechanism solutions and geotechnical in-situ stress data in and around the Korean peninsula also support the current ENE-WSW or E-W regional compression. On the basis of the regional stress trajectories in and around East Asia, the current stress field in Korean peninsula is interpreted to have resulted from the cooperation of westward shallow subduction of

  17. 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

  18. Evidence of extensional and strike-slip deformation in the offshore Gökova-Kos area affected by the July 2017 Mw6.6 Bodrum-Kos earthquake, eastern Aegean Sea

    NASA Astrophysics Data System (ADS)

    Ocakoğlu, Neslihan; Nomikou, Paraskevi; İşcan, Yeliz; Loreto, Maria Filomena; Lampridou, Danai

    2018-06-01

    The interpretation of new multichannel seismic profiles and previously published high-resolution swath and seismic reflection data from the Gökova Gulf and southeast of Kos Island in the eastern Aegean Sea revealed new morphotectonic features related to the July 20, 2017 Mw6.6 Bodrum-Kos earthquake offshore between Kos Island and the Bodrum Peninsula. The seafloor morphology in the northern part of the gulf is characterized by south-dipping E-W-oriented listric normal faults. These faults bend to a ENE-WSW direction towards Kos Island, and then extend parallel to the southern coastline. A left-lateral SW-NE strike-slip fault zone is mapped with segments crossing the Gökova Gulf from its northern part to south of Kos Island. This fault zone intersects and displaces the deep basins in the gulf. The basins are thus interpreted as the youngest deformed features in the study area. The strike-slip faults also produce E-W-oriented ridges between the basin segments, and the ridge-related vertical faults are interpreted as reverse faults. This offshore study reveals that the normal and strike-slip faults are well correlated with the focal mechanism solutions of the recent earthquake and general seismicity of the Gökova Gulf. Although the complex morphotectonic features could suggest that the area is under a transtensional regime, kinematic elements normally associated with a transtensional system are missing. At present, the Gökova Gulf is experiencing strike-slip motion with dominant extensional deformation, rather than transtensional deformation.

  19. 25. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    25. Historic American Buildings Survey E. W. Russell, Photographer, June 13, 1935 HALL, S. SECTION OF BUILDING, THIRD FLOOR, SHOWING SKYLIGHT IN ROOF - Southern Hotel, 53-65 Water Street, Mobile, Mobile County, AL

  20. 1. Historic American Buildings Survey E. W. Russell, Photographer, March ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, March 14, 1936 REAR VIEW, NORTH OF SLAVE QUARTERS - Waring House, Slave Quarters, 351 Government Street (now South Claiborne Street), Mobile, Mobile County, AL

  1. 2. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, April 7, 1936 GATE IN FRONT OF U. S. MARINE HOSPITAL TO E. OF MAIN ENTRANCE STEPS - U. S. Marine Hospital & Gates, 800 Saint Anthony Street, Mobile, Mobile County, AL

  2. 4. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. Historic American Buildings Survey E. W. Russell, Photographer, April 7, 1936 IRON GATE IN WALL (REAR) SURROUNDING U. S. MARINE HOSPITAL, CONGRESS STREET - U. S. Marine Hospital & Gates, 800 Saint Anthony Street, Mobile, Mobile County, AL

  3. 12. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    12. Historic American Buildings Survey E. W. Russell, Photographer, June 7, 1935 PANELED WINDOW BASES, FRONT ROOM MAIN FLOOR - Oakleigh, House & Slave Quarters, 350 Oakleigh Place, Mobile, Mobile County, AL

  4. 11. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    11. Historic American Buildings Survey E. W. Russell, Photographer, June 17, 1937 FIREPLACE, NORTH WALL OF NORTH SIDE FRONT ROOM OF MAIN HOUSE. - Wewoka, Riser Mill Road, Sylacauga, Talladega County, AL

  5. 5. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey E. W. Russell, Photographer, June 17, 1937 CLOSEUP OF THE LOWER SECTION OF FIRST STORY WINDOW ON FRONT, SHOWING SHUTTER AND HINGE. - Wewoka, Riser Mill Road, Sylacauga, Talladega County, AL

  6. 14. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    14. Historic American Buildings Survey E. W. Russell, Photographer, June 17, 1937 OLD WATER POWER GRIST MILL, NORTHEAST OF MAIN HOUSE, LOOKING EAST. - Wewoka, Riser Mill Road, Sylacauga, Talladega County, AL

  7. 10. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    10. Historic American Buildings Survey E. W. Russell, Photographer, June 17, 1937 FIREPLACE AND MANTEL. SOUTH WALL OF SOUTH FRONT ROOM, FIRST STORY. - Wewoka, Riser Mill Road, Sylacauga, Talladega County, AL

  8. 12. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    12. Historic American Buildings Survey E. W. Russell, Photographer, June 17, 1937 FIREPLACE AND MANTEL, SOUTH WALL OF SOUTH SIDE ROOM, SECOND STORY. - Wewoka, Riser Mill Road, Sylacauga, Talladega County, AL

  9. 2. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 STANDARD AND BRACKETS, P. J. LYONS HOME - 300 STATE STREET - Patrick Lyons House (Ironwork), 300 State Street, Mobile, Mobile County, AL

  10. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 FRONT ELEVATION, P. J. LYONS HOME - 300 STATE STREET - Patrick Lyons House (Ironwork), 300 State Street, Mobile, Mobile County, AL

  11. 3. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 STEPS AND RAILINGS, LYONS HOME - 300 STATE STREET - Patrick Lyons House (Ironwork), 300 State Street, Mobile, Mobile County, AL

  12. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 FRONT ELEVATION, R. H. REDWOOD HOME - 260 ST. LOUIS STREET - R. H. Redwood House (Ironwork), 260 Saint Louis Street, Mobile, Mobile County, AL

  13. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 4, 1936 FRONT ELEVATION, M. S. BROWN - 108 S. CONCEPTION STREET - Milton S. Brown House, 108 South Conception Street, Mobile, Mobile County, AL

  14. 2. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, September 4, 1936 BALUSTRADE ON FRONT, M. S. BROWN HOME - 108 SOUTH CONCEPTION STREET - Milton S. Brown House, 108 South Conception Street, Mobile, Mobile County, AL

  15. 8. Historic American Buildings Survey E. W. Russell, Photographer, January ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Historic American Buildings Survey E. W. Russell, Photographer, January 15, 1937 OLD SMOKE HOUSE - FRONT (WEST), SOUTH SIDE - Vogtner Farm (House & Smokehouse), Jeff Hamilton Road vicinity, Dawes, Mobile County, AL

  16. 8. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Historic American Buildings Survey E. W. Russell, Photographer, August 4 1936. GENERAL VIEW OF CEILING IN MAIN AUDITORIUM. - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  17. 4. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    4. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 EAST HALF OF REAR, WILLIAM H. KETCHUM - 400 GOVERNMENT STREET - William H. Ketchum House & Gates (Ironwork), 400 Government Street, Mobile, Mobile County, AL

  18. 1. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, August 23, 1936 FRONT ELEVATION, MRS. ALBERT QUIGLEY - 751 GOVERNMENT STREET - Gilmore-Gaines-Quigley House, 751 Government Street, Mobile, Mobile County, AL

  19. 6. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 SOUTH (GOV. ST.) ENTRANCE GATE, WILLIAM H. KETCHUM - 400 GOVERNMENT STREET - William H. Ketchum House & Gates (Ironwork), 400 Government Street, Mobile, Mobile County, AL

  20. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 4, 1936 EAST END OF PORCH, OWEN FINNIGAN PLACE - 752 GOVERNMENT STREET - Captain Owen Finnigan House (Ironwork), 752 Government Street, Mobile, Mobile County, AL

  1. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 15, 1936 GATE IN FRONT OF 201 GOVERNMENT STREET - 201 Government Street (Iron Gate), Moved to Spring Hill Avenue & Riviere du Chin Road, Mobile, Mobile County, AL

  2. 3. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, August 23, 1936 CLOSE- UP BRACKETS AND FRIEZE, MRS. ALBERT QUIGLEY - 751 GOVERNMENT STREET - Gilmore-Gaines-Quigley House, 751 Government Street, Mobile, Mobile County, AL

  3. 12. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    12. Historic American Buildings Survey E. W. Russell, Photographer, August 4, 1936 EAST SIDE STAIR HEAD (BALCONY FLOOR) - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  4. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 2, 1936 UPPER PORTION OF SOUTH FRONT. W. H. ROSS HOME - 602 GOVERNMENT STREET - Ross House, 602 Government Street, Mobile, Mobile County, AL

  5. 10. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    10. Historic American Buildings Survey E. W. Russell, Photographer, August 4, 1936 INTERIOR VIEW OF WINDOW AND COLUMN UNDER SIDE BALCONY - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  6. 5. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey E. W. Russell, Photographer, August 4, 1936 CLOSE-UP OF MAIN ENTRANCE (FRONT) - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  7. 9. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    9. Historic American Buildings Survey E. W. Russell, Photographer, August 4, 1936 CEILING AND CORNICE IN MAIN AUDITORIUM - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  8. 1. Historic American Buildings Survey E. W. Russell, Photographer, February ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, February 6, 1936 WROUGHT IRON GATE WITH CAST IRON ORNAMENTS, FRONT OF 605 GOVERNMENT STREET - 605 Government Street (Iron Gate), Mobile, Mobile County, AL

  9. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 15, 1936 SIDNEY SMITH PLACE - 203 GOVERNMENT ST., FRONT ELEVATION - Sidney Smith House (Iron Gate & Balcony), 203 Government Street, Mobile, Mobile County, AL

  10. 2. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, September 3, 1936 FENCE IN FRONT, GOLDSBY HOME - 452 GOVERNMENT STREET - J. W. Goldsby House & Iron Fence, 452 Government Street, Mobile, Mobile County, AL

  11. 2. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, September 2, 1936 B. P. BESTER - 208 GOVERNMENT STREET, FRONT OF EAST SIDE WING - Daniel Perrin Bestor, Jr., House (Ironwork), 208 Government Street, Mobile, Mobile County, AL

  12. 11. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    11. Historic American Buildings Survey E. W. Russell, Photographer, August 4, 1936 STAIR ON WEST SIDE, VIEW THROUGH DOOR ON W. END OF FRONT PORTICO - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  13. 2. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 CLOSE- UP OF SECTION ON FRONT OF PORCH, WILLIAM H. KETCHUM - 400 GOVERNMENT STREET - William H. Ketchum House & Gates (Ironwork), 400 Government Street, Mobile, Mobile County, AL

  14. 13. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    13. Historic American Buildings Survey E. W. Russell, Photographer, September 15, 1936 STAIR ON E. WALL OF BASEMENT - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  15. 3. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 EAST VIEW OF HOUSE, ENTRANCE ON FRANKLIN STREET, WILLIAM H. KETCHUM - 400 GOVERNMENT STREET - William H. Ketchum House & Gates (Ironwork), 400 Government Street, Mobile, Mobile County, AL

  16. 3. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, August 4, 1936 DENTIL, COLUMN AND PILASTER CAPS, SOUTH ELEVATION (FRONT) - Government Street Presbyterian Church, Government & Jackson Streets, Mobile, Mobile County, AL

  17. 7. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Historic American Buildings Survey E. W. Russell, Photographer, September 2, 1936 GATE TO DRIVE ON FRANKLIN STREET (EAST SIDE), WILLIAM H. KETCHUM - 400 GOVERNMENT STREET - William H. Ketchum House & Gates (Ironwork), 400 Government Street, Mobile, Mobile County, AL

  18. 5. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 STEP RAILINGS TO SOUTH FRONT, WILLIAM H. KETCHUM - 400 GOVERNMENT STREET - William H. Ketchum House & Gates (Ironwork), 400 Government Street, Mobile, Mobile County, AL

  19. 1. Historic American Buildings Survey E. W. Russell, Photographer, November ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, November 5, 1936 GATE AT EAST SIDE MINGE FLORAL CO. BUILDING, 453 GOVERNMENT STREET - 453 Government Street (Iron Gate & Fence), Mobile, Mobile County, AL

  20. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 1, 1936 EAST SIDE AND SOUTH FRONT, 400 GOVERNMENT STREET - William H. Ketchum House & Gates (Ironwork), 400 Government Street, Mobile, Mobile County, AL

  1. 1. Historic American Buildings Survey E. W. Russell, Photographer, Sept. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, Sept. 2, 1936 B.P. Bester-- 208 Government Street, Front (side) and West Side - Daniel Perrin Bestor, Jr., House (Ironwork), 208 Government Street, Mobile, Mobile County, AL

  2. 1. Historic American Buildings Survey E. W. Russell, Photographer, September ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, September 2, 1936 WINDOWS ON FRONT (SOUTH), J. W. GOLDSBY HOME - 452 GOVERNMENT STREET - J. W. Goldsby House & Iron Fence, 452 Government Street, Mobile, Mobile County, AL

  3. 13. Historic American Buildings Survey E. W. Russell, Photographer, October ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    13. Historic American Buildings Survey E. W. Russell, Photographer, October 5, 1936 DOORS BETWEEN FRONT AND REAR ROOMS, EAST SIDE OF HOUSE - J. J. McMahon House, 456 Saint Francis Street, Mobile, Mobile County, AL

  4. 5. Historic American Buildings Survey E. W. Russell, Photographer, October ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey E. W. Russell, Photographer, October 5, 1936 VIEW IN FRONT PORCH, TOWARDS EAST, SHOWING FRONT ENTRANCE - J. J. McMahon House, 456 Saint Francis Street, Mobile, Mobile County, AL

  5. 15. Historic American Buildings Survey E. W. Russell, Photographer, October ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    15. Historic American Buildings Survey E. W. Russell, Photographer, October 5, 1936 NORTH WALL OF ATTIC ROOM ON EAST SIDE OF HOUSE, SHOWING REAR DORMER RECESS - J. J. McMahon House, 456 Saint Francis Street, Mobile, Mobile County, AL

  6. 16. Historic American Buildings Survey E. W. Russell, Photographer, October ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    16. Historic American Buildings Survey E. W. Russell, Photographer, October 6, 1936 FIREPLACE WITH RAISED BRICK HEARTH, W. WALL OF ATTIC ROOM - J. J. McMahon House, 456 Saint Francis Street, Mobile, Mobile County, AL

  7. 11. Historic American Buildings Survey E. W. Russell, Photographer, October ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    11. Historic American Buildings Survey E. W. Russell, Photographer, October 5, 1936 INTERIOR OF FRENCH WINDOW, W. FRONT ROOM, SOUTH WALL - J. J. McMahon House, 456 Saint Francis Street, Mobile, Mobile County, AL

  8. 12. Historic American Buildings Survey E. W. Russell, Photographer, October ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    12. Historic American Buildings Survey E. W. Russell, Photographer, October 5, 1936 SLIDING DOUBLE DOOR BETWEEN FRONT AND REAR ROOMS, WEST SIDE OF HOUSE - J. J. McMahon House, 456 Saint Francis Street, Mobile, Mobile County, AL

  9. 33. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    33. Historic American Buildings Survey E. W. Russell, Photographer, May 26, 1936 E. FRONT ROOM OF W. APARTMENT SHOWING MANTEL AND N. WALL, 4th FLOOR - 67-69 Government Street (Commercial Building), Mobile, Mobile County, AL

  10. 19. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    19. Historic American Buildings Survey E. W. Russell, Photographer, May 26, 1936 VIEW IN ATTIC (S. ROOM) SHOWING E. WALL, 4th FLOOR, W. SIDE APARTMENT - 67-69 Government Street (Commercial Building), Mobile, Mobile County, AL

  11. 20. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    20. Historic American Buildings Survey E. W. Russell, Photographer, May 26, 1936 MANTEL AND SOAPSTONE HEARTH, E. WALL OF S. ROOM, 4th FLOOR - 67-69 Government Street (Commercial Building), Mobile, Mobile County, AL

  12. 28. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    28. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 INTERIOR VIEW OF MAIN ENTRANCE TO MAIN HALL, 1st FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  13. 35. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    35. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 ROTUNDA, THIRD FLOOR, LOOKING W. FROM E. HALLWAY - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  14. 9. Historic American Buildings Survey E. W. Russell, Photographer, February ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    9. Historic American Buildings Survey E. W. Russell, Photographer, February 28, 1935 MAIN BUILDING (ADMINISTRATION) WEST - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  15. 41. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    41. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 CORNICE AROUND ROTUNDA WALL, THIRD FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  16. 25. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    25. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 FRONT ENTRANCE DOOR TO WEST OF MAIN ENTRANCE - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  17. 37. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    37. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 ROTUNDA, 3rd FLOOR, SHOWING E. HALL BETWEEN ROOMS ON N. AND E. - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  18. 39. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    39. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 CLOSE-UP OF ROTUNDA BALUSTRADE, THIRD FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  19. 30. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    30. Historic American Buildings Survey E. W. Russell, Photographer, May 8, 1936 STAIR IN HALL TOWARDS REAR, W. EXTENSION, 1st FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  20. 1. Historic American Buildings Survey COPIED E. W. Russell, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey COPIED - E. W. Russell, Photographer, August 31, 1936 75TH ANNIVERSARY YEARBOOK (NOT COPYRIGHT) - VIEW OF ORIGINAL BUILDING - Spring Hill College, Original Building, Old Shell Road, Spring Hill, Mobile County, AL

  1. 20. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    20. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 CLOSE-UP OF STUCCO PORTICO COLUMN (SOUTH) FIRST FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  2. 21. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    21. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 CLOSE-UP OF IRON COLUMN CAP, SOUTH PORTICO - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  3. 23. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    23. Historic American Buildings Survey E. W. Russell, Photographer, May 8, 1936 EXTERIOR VIEW OF DOOR IN N. WALL (FRONT) 1st FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  4. 22. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    22. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 BASE OF IRON COLUMN TO PORTICO (SOUTH) FIRST FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  5. 27. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    27. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 EXTERIOR VIEW OF REAR DOOR TO MAIN HALLWAY, 1st FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  6. 18. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    18. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 VIEW OF PORTICO COLUMNS LOOKING N. E., 1st FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  7. 33. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    33. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 VIEW OF STAIR FROM 2nd STORY HALL, W. END OF BUILDING - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  8. 3. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 NORTH ELEVATION (FRONT) LOOKING SOUTH EAST - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  9. 19. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    19. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 SOUTH ELEVATION (REAR) SHOWING ROUND IRON COLUMN AND SQUARE STUCCO COLUMN - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  10. 5. Historic American Buildings Survey E. W. Russell, Photographer, February ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey E. W. Russell, Photographer, February 28, 1935 REAR VIEW OF MAIN BLDG. S.W. (REAR FACES S.) - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  11. 15. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    15. Historic American Buildings Survey E. W. Russell, Photographer, May 8, 1936 CLOSE-UP OF CORNICE ON REAR OF BUILDING - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  12. 26. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    26. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 EXTERIOR VIEW OF WINDOW IN REAR S. WALL, 1st FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  13. 14. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    14. Historic American Buildings Survey E. W. Russell, Photographer, May 8, 1936 GENERAL VIEW OF S. ELEVATION (REAR) FROM 3rd STORY REAR PORCH - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  14. 17. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    17. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 GENERAL VIEW OF PORTICO (OR ARCADE) LOOKING WEST, 1st FLOOR OF ADMINISTRATION BUILDING - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  15. 36. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    36. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 ROTUNDA, 3rd FLOOR, SHOWING N. HALL - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  16. 24. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    24. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 N. DOOR OPENING ON PORTICO (OR ARCADE) - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  17. 34. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    34. Historic American Buildings Survey E. W. Russell, Photographer, May 8, 1936 VIEW OF STAIR FROM REAR (SOUTH) OF HALL, 2nd FLOOR - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  18. 6. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Historic American Buildings Survey E. W. Russell, Photographer, May 8, 1936 SOUTH ELEVATION OF W END WING (REAR) - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  19. 2. Historic American Buildings Survey E. W. Russell, Photographer, January ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, January 8, 1937 REAR VIEW SHOWING RECENT ADDITION - Nelias Fall House, County Road 96 (Old Saint Stephens Road), Mount Vernon, Mobile County, AL

  20. 5. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1937 FIREPLACE, NORTH WALL OF NORTH SIDE. FRONT ROOM OR DINING ROOM. - Jenkins-Carlton-Autry House, County Road 52, Alpine, Talladega County, AL

  1. 6. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1937 NORTH WALL & FIREPLACE, NORTH SIDE ROOM, SECOND STORY. - Jenkins-Carlton-Autry House, County Road 52, Alpine, Talladega County, AL

  2. 8. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    8. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1937 OLD KITCHEN & DINING ROOM (EAST OF AND TO THE REAR OF MAIN HOUSE) LOOKING EAST. - Jenkins-Carlton-Autry House, County Road 52, Alpine, Talladega County, AL

  3. 9. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    9. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1937 OLD SMOKEHOUSE (CONVERTED INTO GARAGE) LOOKING SLIGHTLY NORTHEAST. - Jenkins-Carlton-Autry House, County Road 52, Alpine, Talladega County, AL

  4. 7. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1937 FIREPLACE, SOUTH WALL OF SOUTH SIDE ROOM, SECOND STORY. - Jenkins-Carlton-Autry House, County Road 52, Alpine, Talladega County, AL

  5. 3. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1937 CLOSE-UP OF FRONT ENTRANCE FROM SOUTH SIDE. - Jenkins-Carlton-Autry House, County Road 52, Alpine, Talladega County, AL

  6. 2. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1936 CLOSE-UP OF GEAR WHEEL FROM OPPOSITE SIDE - Cotton Gin & Well Sweep, Cliatt Plantation, State Route 165, Cottonton, Russell County, AL

  7. 7. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1936 OLD WELL SWEEP (LEVER IN UPRIGHT POSITION) - Cotton Gin & Well Sweep, Cliatt Plantation, State Route 165, Cottonton, Russell County, AL

  8. 6. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1936 OLD WELL SWEEP (LEVER IN OPERATION) - Cotton Gin & Well Sweep, Cliatt Plantation, State Route 165, Cottonton, Russell County, AL

  9. 5. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    5. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1936 CLOSE-UP OF GEAR SHAFT AND SPOKES - Cotton Gin & Well Sweep, Cliatt Plantation, State Route 165, Cottonton, Russell County, AL

  10. 3. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1936 OLD MULE GIN HOUSE LOOKING S. E. - Cotton Gin & Well Sweep, Cliatt Plantation, State Route 165, Cottonton, Russell County, AL

  11. 1. Historic American Buildings Survey E. W. Russell, Photographer, June ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, June 19, 1936 OLD MULE GIN HOUSE LOOKING N. W. - Cotton Gin & Well Sweep, Cliatt Plantation, State Route 165, Cottonton, Russell County, AL

  12. 7. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    7. Historic American Buildings Survey E. W. Russell, Photographer, April 19, 1937 REPRODUCTION OF INTERIOR OF CHRIST CHURCH INTERIOR PRIOR TO STORM OF 1909 - Christ Episcopal Church, Church & Saint Emanuel Streets, Mobile, Mobile County, AL

  13. Pleistocene Brawley and Ocotillo Formations: Evidence for initial strike-slip deformation along the San Felipe and San Jacinto fault zonez, Southern California

    USGS Publications Warehouse

    Kirby, S.M.; Janecke, S.U.; Dorsey, R.J.; Housen, B.A.; Langenheim, V.E.; McDougall, K.A.; Steeley, A.N.

    2007-01-01

    We examine the Pleistocene tectonic reorganization of the Pacific-North American plate boundary in the Salton Trough of southern California with an integrated approach that includes basin analysis, magnetostratigraphy, and geologic mapping of upper Pliocene to Pleistocene sedimentary rocks in the San Felipe Hills. These deposits preserve the earliest sedimentary record of movement on the San Felipe and San Jacinto fault zones that replaced and deactivated the late Cenozoic West Salton detachment fault. Sandstone and mudstone of the Brawley Formation accumulated between ???1.1 and ???0.6-0.5 Ma in a delta on the margin of an arid Pleistocene lake, which received sediment from alluvial fans of the Ocotillo Formation to the west-southwest. Our analysis indicates that the Ocotillo and Brawley formations prograded abruptly to the east-northeast across a former mud-dominated perennial lake (Borrego Formation) at ???1.1 Ma in response to initiation of the dextral-oblique San Felipe fault zone. The ???25-km-long San Felipe anticline initiated at about the same time and produced an intrabasinal basement-cored high within the San Felipe-Borrego basin that is recorded by progressive unconformities on its north and south limbs. A disconformity at the base of the Brawley Formation in the eastern San Felipe Hills probably records initiation and early blind slip at the southeast tip of the Clark strand of the San Jacinto fault zone. Our data are consistent with abrupt and nearly synchronous inception of the San Jacinto and San Felipe fault zones southwest of the southern San Andreas fault in the early Pleistocene during a pronounced southwestward broadening of the San Andreas fault zone. The current contractional geometry of the San Jacinto fault zone developed after ???0.5-0.6 Ma during a second, less significant change in structural style. ?? 2007 by The University of Chicago. All rights reserved.

  14. Striking Clepsydras

    NASA Astrophysics Data System (ADS)

    Nam, Moon-Hyon

    The term "Striking Clepsydra" is a shortened translation of the Korean name Jagyeongnu (自擊漏, tzu-chi lou in Chinese, literally "automatic-striking water-clock"). It was given to the two monumental time-keeping installations built by chief court engineer Yeong-sil Jang in AD 1432-38 under King Sejong (r. AD 1418-50) of the Joseon dynasty (1392-1910) in Seoul. These were housed separately in the Gyeongbok palace complex as major installations of the Royal Observatory Ganuidae equipped during 1432-38. One was the Striking Palace Clepsydra Borugangnu that was employed as the standard time-keeper from 1434, and the other was the Striking Heavenly Clepsydra Heumgyeonggangnu that was put into use not only as the symbol of Neo-Confucian ideology from 1438, but also as a demonstrational orrery and time-keeper. These were restored several times through the dynasty after loss by fires and warfare, and clepsydra-making technologies were succeeded by the development of armillary clocks in 1669. The National Palace Museum of Korea recreated the 1434 Striking Palace Clepsydra of King Sejong, and the replica was installed for permanent exhibition from November 2007.

  15. Along-Strike Variation in Geometry and Kinematics of a Major, Active Intracontinental Thrust System: the Pred-Terskey Fault Zone, Kyrgyz Tien Shan, Central Asia

    NASA Astrophysics Data System (ADS)

    Burgette, R. J.; Weldon, R. J.; Abdrakhmatov, K. Y.; Ormukov, C.

    2004-12-01

    The Pred-Terskey fault zone defines the southern margin of the Issyk-Kul basin, extending eastward over 250 km from at least the Chu River to the Kazakhstan border, and appears to be one of the most active zones in the Kyrgyz Tien Shan. Despite a diversity of structural styles and changes of vergence at the surface, the lateral continuity and overall geometry of the zone is consistent with a single north vergent thrust at depth, which uplifts the Terskey Range and generally tilts the south margin of the basin to the north. This northward tilting of the margin is probably due to a flattening of the fault as it approaches the surface. In spite of historical quiescence, it is likely capable of producing great earthquakes. We have conducted detailed field mapping coupled with terrace profiling and dating at seven representative, well-exposed areas of the fault zone. Based on these field observations and satellite image and air photo interpretation along the entire zone, we identify three major divisions in structural style expressed at the surface. The western segment is typified by the Tura-Su, Ak-Terek and Ton areas. A series of left-stepping, south-vergent, basement-involved reverse faults and folds are uplifting the southern margin of the Issyk-Kul basin in this area. The resulting uphill-facing scarps have trapped and diverted many of the rivers flowing north from the Terskey Range. Tertiary strata and Quaternary geomorphic surfaces show consistent, progressive northward tilting across the entire zone. The west-central segment is represented by the Kajy-Say area. South-vergent reverse faults and a north-vergent backthrust have uplifted an arcuate granite block. Offshore of this area, the lake floor descends to a sharp break in slope with a low relief area at a depth of about 650 m. Late Quaternary geomorphic features do not show evidence of tilting. In contrast to the areas east and west, the major north-dipping thrust is likely planar over this segment and

  16. Rifting and subduction in the papuan peninsula, papua new guinea: The significance of the trobriand tough, the nubara strike-slip fault, and the woodlark rift to the present configuration of papua new guinea

    NASA Astrophysics Data System (ADS)

    Cameron, Milo Louis

    The calculated extension (~111 km) across the Woodlark rift is incompatible with the > 130 km needed to exhume the Metamorphic Core Complexes on shallow angle faults (< 30°) using N-S extension in the Woodlark Basin. High resolution bathymetry, seismicity, and seismic reflection data indicate that the Nubara Fault continues west of the Trobriand Trough, intersects the Woodlark spreading center, and forms the northern boundary of the Woodlark plate and the southern boundary of the Trobriand plate. The newly defined Trobriand plate, to the north of this boundary, has moved SW-NE along the right lateral Nubara Fault, creating SW-NE extension in the region bounded by the MCC's of the D'Entrecasteaux Islands and Moresby Seamount. Gravity and bathymetry data extracted along four transect lines were used to model the gravity and flexure across the Nubara Fault boundary. Differences exist in the elastic thickness between the northern and southern parts of the lines at the Metamorphic Core Complexes of Goodenough Island (Te_south = 5.7 x 103 m; Te_north = 6.1 x 103 m) and Fergusson Island (Te_south = 1.2 x 103 m; Te_north = 5.5 x 103 m). Differences in the elastic strength of the lithosphere also exist at Moresby Seamount (Te_south = 4.2 x 103 m; Te_north = 4.7 x 103 m) and Egum Atoll (Te_south =7.5 x 103 m; Te_north = 1.3 x 104 m). The differences between the northern and southern parts of each transect line imply an east-west boundary that is interpreted to be the Nubara Fault. The opening of the Woodlark Basin resulted in the rotation of the Papuan Peninsula and the Woodlark Rise, strike slip motion between the Solomon Sea and the Woodlark Basin at the Nubara Fault, and the formation of the PAC-SOL-WLK; SOL-WLK-TRB triple junctions. The intersection of the Woodlark Spreading Center with the Nubara Fault added the AUS-WLK-TRB triple junction and established the Nubara Fault as the northern boundary of the Woodlark plate.

  17. Fault trends on the seaward slope of the Aleutian Trench: Implications for a laterally changing stress field tied to a westward increase in oblique convergence

    USGS Publications Warehouse

    Mortera-Gutierrez, C. A.; Scholl, D. W.; Carlson, R.L.

    2003-01-01

    Normal faults along the seaward trench slope (STS) commonly strike parallel to the trench in response to bending of the oceanic plate into the subduction zone. This is not the circumstance for the Aleutian Trench, where the direction of convergence gradually changes westward, from normal to transform motion. GLORIA side-scan sonar images document that the Aleutian STS is dominated by faults striking oblique to the trench, west of 179??E and east of 172??W. These images also show a pattern of east-west trending seafloor faults that are aligned parallel to the spreading fabric defined by magnetic anomalies. The stress-strain field along the STS is divided into two domains west and east, respectively, of 179??E. Over the western domain, STS faults and nodal planes of earthquakes are oriented oblique (9??-46??) to the trench axis and (69??-90??) to the magnetic fabric. West of 179??E, STS fault strikes change by 36?? from the E-W trend of STS where the trench-parallel slip gets larger than its orthogonal component of convergence. This rotation indicates that horizontal stresses along the western domain of the STS are deflected by the increasing obliquity in convergence. An analytical model supports the idea that strikes of STS faults result from a superposition of stresses associated with the dextral shear couple of the oblique convergence and stresses caused by plate bending. For the eastern domain, most nodal planes of earthquakes strike parallel to the outer rise, indicating bending as the prevailing mechanism causing normal faulting. East of 172??W, STS faults strike parallel to the magnetic fabric but oblique (10??-26??) to the axis of the trench. On the basis of a Coulomb failure criterion the trench-oblique strikes probably result from reactivation of crustal faults generated by spreading. Copyright 2003 by the American Geophysical Union.

  18. 1. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, April 2, 1935 N. AND W. SIDE OF BLDG. USED AS MESS HALL E. OF BARRACK BLDG. - Mount Vernon Arsenal, Old Mess Hall, Old Saint Stephens Road (County Road 96), Mount Vernon, Mobile County, AL

  19. 1. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, April 7, 1936 BALUSTRADE ON 2nd FLOOR PORTICO, U. S. MARINE HOSPITAL, ST. ANTHONY ST. BETWEEN BAYOU AND JEFFERSON STREETS - U. S. Marine Hospital & Gates, 800 Saint Anthony Street, Mobile, Mobile County, AL

  20. 3. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, April 7, 1936 SECTION OF IRON FENCE IN FRONT OF U. S. MARINE HOSPITAL, N. SIDE OF ST. ANTHONY ST. - U. S. Marine Hospital & Gates, 800 Saint Anthony Street, Mobile, Mobile County, AL

  1. 2. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, April 2, 1935 OLD MESS HALL AND BARRACKS E. SIDE OF BOTH BLDGS. N. END OF MESS HALL - Mount Vernon Arsenal, Old Barracks Building, Old Saint Stephens Road (County Road 96), Mount Vernon, Mobile County, AL

  2. 1. Historic American Buildings Survey E. W. Russell, Photographer, October ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey E. W. Russell, Photographer, October 17, 1935 51-69 Government St. BLOCK OF BUILDINGS ON GOVERNMENT ST. (S. SIDE) BETWEEN WATER AND ROYAL STREETS - 51-69 Government Street (Commercial Building), Mobile, Mobile County, AL

  3. 2. Historic American Buildings Survey E. W. Russell, Photographer, August ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey E. W. Russell, Photographer, August 23, 1936 CLOSE- UP BALUSTRADE SHOWING LOWER PART CORNER STANDARD E. END, FIRST FLOOR. MRS. ALBERT QUIGLEY - 751 GOVERNMENT ST. - Gilmore-Gaines-Quigley House, 751 Government Street, Mobile, Mobile County, AL

  4. 2. Historic American Buildings Survey Copied by E. W. Russell, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey Copied by E. W. Russell, Photographer, August 31, 1936 75TH ANNIVERSARY YEARBOOK (NOT COPYRIGHT) - REAR OF BUILDING BEFORE REINFORCED CONCRETE BALCONIES WERE ADDED - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  5. 2. Historic American Buildings Survey Copied by E. W. Russell, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    2. Historic American Buildings Survey Copied by E. W. Russell, Photographer, August 31, 1936 75TH ANNIVERSARY YEARBOOK (NOT COPYRIGHT) - RUINS OF OLD COLLEGE AFTER FIRE OF 1869 - Spring Hill College, Original Building, Old Shell Road, Spring Hill, Mobile County, AL

  6. 6. Historic American Buildings Survey E. W. Russell, Photographer, Feb. ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    6. Historic American Buildings Survey E. W. Russell, Photographer, Feb. 12, 1937 VIEW LOOKING UP MAIN DRIVEWAY SHOWING SO. E. (UPPER PORTION) OF BLDG. ALSO WEST ELEV. OF CHURCH. - Convent of the Visitation, 2300 Spring Hill Avenue, Mobile, Mobile County, AL

  7. 38. Historic American Buildings Survey E. W. Russell, Photographer, May ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    38. Historic American Buildings Survey E. W. Russell, Photographer, May 7, 1936 N. W. SIDE OF ROTUNDA, 3rd FLOOR, SHOWING W. AND N. HALLS AND STAIR OPENING - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  8. 1. Historic American Buildings Survey Copied by E. W. Russell, ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    1. Historic American Buildings Survey Copied by E. W. Russell, Photographer, August 31, 1936 75TH ANNIVERSARY YEARBOOK (NOT COPYRIGHT) - FRONT OF MAIN BUILDING BEFORE CLOISTER ARCADE WAS ADDED - Spring Hill College, Main Building, Old Shell Road, Spring Hill, Mobile County, AL

  9. 3. Historic American Buildings Survey E. W. Russell, Photographer, April ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    3. Historic American Buildings Survey E. W. Russell, Photographer, April 2, 1937 VIEW LOOKING S.W. SHOWING N.W. CORNER OF SECTION 'D' & 'E' ON THE RIGHT & NORTH ELEV. OF SMALL BUILDING WITH HALF OCTAGONAL BAYS ON LEFT. - Convent of the Visitation, 2300 Spring Hill Avenue, Mobile, Mobile County, AL

  10. 15. Historic American Buildings Survey E. W. Russell, Photographer, March ...

    Library of Congress Historic Buildings Survey, Historic Engineering Record, Historic Landscapes Survey

    15. Historic American Buildings Survey E. W. Russell, Photographer, March 15, 1936 BLINDS ON FRENCH TYPE DOOR OPENING ON W. REAR PORCH, 2nd STORY, N. SIDE APARTMENT - Augustine Ottenstein House, 207-209 North Jackson Street, Mobile, Mobile County, AL

  11. Strike-slip brittle shear zone from coastal Deccan in and around Mumbai, India: Evidence for N-S extension

    NASA Astrophysics Data System (ADS)

    Bhattacharya, Gourab; Ayan Misra, Achyuta; Bose, Narayan; Mukherjee, Soumyajit

    2013-04-01

    An E-W extension separated India from the Seychelles micro-continent at ~ 62 Ma. This post-dated the Deccan volcanic eruptions. However, the structures attributed to this extension lack geometrical quantification, especially in the western Indian coast. The Narmada-Tapi region, ~ 400 Km north of Mumbai, experienced a ~ N-S extension prior to and/or concurrent with the volcanism. Normal faults dip towards W. Sub-horizontal lava flows, slickensides, N-S shear zones etc. have been reported from the western part of the Deccan Large Igneous Province (DLIP). This work, for the first time, identifies and investigates a ~ 20°N strike-slip brittle shear zone, traced for ~ 100 Km along the west coast of India from Mumbai to Murud by fieldworks. The W-block moved north through a dextral-slip. Deformation is more enhanced in the south (near Murud). Field observations reveal Y-planes (~ N20°E; abundant), Riedels (~ 0-N30°E; abundant), anti-Riedels (~ N30-50°W; less abundant), asymmetric elevations (~ N15°E; locally abundant), extension and en-echelon fractures (2 sets: ~N-S and ~E-W) with a single miniature pull-apart basin (~ N-S extension). The E-W fractures reactivated locally and around Murud slipped/faulted ~ N-S dykes. Average directions of paleostress tensors were computed for the regime yielding σ1 (trend = 99°; plunge = 0°), σ2 (trend = 196°; plunge = 90°) and σ3 (trend = 10°; plunge = 0°). Associated strain results convincingly display a dominant N-S extension. It was not possible to establish which set of extensions (i.e. between N-S and E-W) occurred earlier. Alongside E-W extension, structurally weak shear zones might have channelized late-stage intrusions of ~ N-S dykes. The DLIP was not subject to any post-rifting deformations regionally, except isostatic adjustments. Hence, based on available data, we postulate that these two extensions were coevally operating in the late phases of the Deccan eruptions. As the Indian plate drifted NE, the strike

  12. The role of major rift faults in the evolution of deformation bands in the Rio do Peixe Basin, Brazil

    NASA Astrophysics Data System (ADS)

    Hilario Bezerra, Francisco; Araujo, Renata; Maciel, Ingrid; Cezar Nogueira, Francisco; Balsamo, Fabrizio; Storti, Fabrizio; Souza, Jorge Andre; Carvalho, Bruno

    2017-04-01

    Many studies have investigated on the evolution and properties of deformation bands, but their occurrence and relationships with basin-boundary faults remain elusive when the latter form by brittle reactivation of structural inheritance in crystalline basements. The main objective of our study was to systematically record the location, kinematics, geometry, and density of deformation bands in the early Cretaceous Rio do Peixe basin, NE Brazil, and analyze their relationship with major syn-rift fault zones. Reactivation in early Cretaceous times of continental-scale ductile shear zones led to the development of rift basins in NE Brazil. These shear zones form a network of NE- and E-W-trending structures hundreds of kilometers long and 3-10 km wide. They were active in the Brasiliano orogeny at 540-740 Ma. Brittle reactivation of these structures occurred in Neocomian times ( 140-120 Ma) prior the breakup between the South American and African plates in the late Cretaceous. The Rio do Peixe basin formed at the intersection between the NE-SW-striking Portalegre shear zone and the E-W-striking Patos shear zone. The brittle fault systems developed by the shear zone reactivation are the Portalegre Fault and the Malta Fault, respectively. In this research we used field structural investigations and drone imagery with centimetric resolution. Our results indicate that deformation bands occur in poorly sorted, medium to coarse grain size sandstones and localize in 3-4 km wide belts in the hanging wall of the two main syn-rifts fault systems. Deformation bands formed when sandstones were not completely lithified. They strike NE along the Portalegre Fault and E-W along the Malta Fault and have slip lineations with rake values ranging from 40 to 90. The kinematics recorded in deformation bands is consistent with that characterizing major rift fault systems, i.e. major extension with a strike-slip component. Since deformations bands are typical sub-seismic features, our findings

  13. Geologic Inheritance and Earthquake Rupture Processes: The 1905 M ≥ 8 Tsetserleg-Bulnay Strike-Slip Earthquake Sequence, Mongolia

    NASA Astrophysics Data System (ADS)

    Choi, Jin-Hyuck; Klinger, Yann; Ferry, Matthieu; Ritz, Jean-François; Kurtz, Robin; Rizza, Magali; Bollinger, Laurent; Davaasambuu, Battogtokh; Tsend-Ayush, Nyambayar; Demberel, Sodnomsambuu

    2018-02-01

    In 1905, 14 days apart, two M 8 continental strike-slip earthquakes, the Tsetserleg and Bulnay earthquakes, occurred on the Bulnay fault system, in Mongolia. Together, they ruptured four individual faults, with a total length of 676 km. Using submetric optical satellite images "Pleiades" with ground resolution of 0.5 m, complemented by field observation, we mapped in detail the entire surface rupture associated with this earthquake sequence. Surface rupture along the main Bulnay fault is 388 km in length, striking nearly E-W. The rupture is formed by a series of fault segments that are 29 km long on average, separated by geometric discontinuities. Although there is a difference of about 2 m in the average slip between the western and eastern parts of the Bulnay rupture, along-fault slip variations are overall limited, resulting in a smooth slip distribution, except for local slip deficit at segment boundaries. We show that damage, including short branches and secondary faulting, associated with the rupture propagation, occurred significantly more often along the western part of the Bulnay rupture, while the eastern part of the rupture appears more localized and thus possibly structurally simpler. Eventually, the difference of slip between the western and eastern parts of the rupture is attributed to this difference of rupture localization, associated at first order with a lateral change in the local geology. Damage associated to rupture branching appears to be located asymmetrically along the extensional side of the strike-slip rupture and shows a strong dependence on structural geologic inheritance.

  14. 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.

  15. Seismogeodesy of the 2014 Mw6.1 Napa earthquake, California: Rapid response and modeling of fast rupture on a dipping strike-slip fault

    NASA Astrophysics Data System (ADS)

    Melgar, Diego; Geng, Jianghui; Crowell, Brendan W.; Haase, Jennifer S.; Bock, Yehuda; Hammond, William C.; Allen, Richard M.

    2015-07-01

    Real-time high-rate geodetic data have been shown to be useful for rapid earthquake response systems during medium to large events. The 2014 Mw6.1 Napa, California earthquake is important because it provides an opportunity to study an event at the lower threshold of what can be detected with GPS. We show the results of GPS-only earthquake source products such as peak ground displacement magnitude scaling, centroid moment tensor (CMT) solution, and static slip inversion. We also highlight the retrospective real-time combination of GPS and strong motion data to produce seismogeodetic waveforms that have higher precision and longer period information than GPS-only or seismic-only measurements of ground motion. We show their utility for rapid kinematic slip inversion and conclude that it would have been possible, with current real-time infrastructure, to determine the basic features of the earthquake source. We supplement the analysis with strong motion data collected close to the source to obtain an improved postevent image of the source process. The model reveals unilateral fast propagation of slip to the north of the hypocenter with a delayed onset of shallow slip. The source model suggests that the multiple strands of observed surface rupture are controlled by the shallow soft sediments of Napa Valley and do not necessarily represent the intersection of the main faulting surface and the free surface. We conclude that the main dislocation plane is westward dipping and should intersect the surface to the east, either where the easternmost strand of surface rupture is observed or at the location where the West Napa fault has been mapped in the past.

  16. 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

  17. Strike-slip Tectonics in the Schouten Basin: Western Branch of the Bismarck Sea Seismic Lineation

    NASA Astrophysics Data System (ADS)

    Llanes Estrada, P.; Hoffmann, G.; Silver, E.; Day, S.; Olaiz Campos, A.

    2007-12-01

    The Schouten Basin is located offshore the north-western coast of Papua New Guinea, approximately between longitudes 144° and 145°. The major tectonic feature in the area is the Bismarck Sea Seismic Lineation (BSSL), a sinistral strike-slip fault that bounds the north side of the basin and separates the North and South Bismarck Sea Plates. We collected bathymetry and backscatter data in the Schouten Basin and elsewhere in the Bismarck volcanic arc in 2004 aboard the research vessel Kilo Moana. In the area of the Schouten Islands, the BSSL changes its orientation from WNW east of Wei Island (144°21.5) to ENE west of Wei. The predominant structural geometry is a pattern of in-line structures, where several faults are parallel to the strike- slip zone. This geometry could be a result of strain partitioning to accommodate oblique shortening. The fault zone crosses less than 2 km off Wei's south coast and has probably affected the island itself. Our data reveals a major contrast offshore north and south of Wei, with a well developed insular slope and apron on the north side, eroded by a radial system of submarine canyons, and an extremely steep and uncommon insular slope on the south side, that also lacks the presence of an insular apron. We suggest that this south part of the island has been cut off and displaced left-laterally by the BSSL a distance of 45 km. In addition to the main structural direction, approximately E-W, the other predominant direction is given by a set of NE-SW faults. The latter are controlling the orientation of a set of submarine canyons off-shore from the Sepik and the Ramu rivers. These faults may also control local volcanism through the alignment of seamounts.

  18. 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.

  19. Extensional tectonics, graben development and fault terminations in the eastern Rif (Bokoya-Ras Afraou area)

    NASA Astrophysics Data System (ADS)

    Galindo-Zaldívar, Jesús; Azzouz, Omar; Chalouan, Ahmed; Pedrera, Antonio; Ruano, Patricia; Ruiz-Constán, Ana; Sanz de Galdeano, Carlos; Marín-Lechado, Carlos; López-Garrido, Angel Carlos; Anahnah, Farida; Benmakhlouf, Mohamed

    2015-11-01

    Westward motion of the Alboran Domain between the Eurasian and African plate boundaries determined crustal thickening along the southern border of the Gibraltar Arc, forming the Rif Cordillera. This process developed major sinistral NE-SW to ENE-WSW faults (such as the Nekor Fault), inactive since the Late Miocene. However, the Neogene-Quaternary Boudinar and Nekor basins underwent very intense recent tectonic and seismic activity related to N-S faults. Kinematics of this fault set changes with depth. While at ~ 10 km faults have a sinistral strike-slip kinematics, they become normal to normal-oblique at surface (Sfeha, Trougout and Boudinar faults). Their different kinematics could be explained by the existence of a crustal detachment separating two differently pre-structured domains. Shallow transtensive N-S faults trend orthogonal to the coastline, decreasing their slip southwards until disappearing. Paleostress analysis shows a progressive change from E-W extension near the coastline up to radial extension in southern areas of major fault terminations. The behavior of each fault-bounded block is conditioned by its inherited rheological features. The sequence of horsts (Bokoya, Ras Tarf, Ras Afraou) corresponds mainly to resistant rocks (volcanics or limestones), whereas the grabens (Nekor and Boudinar basins) are generally floored by weak metapelites and flysch. The presence of liquefaction structures, interpreted as seismites, underlines the continued recent seismic activity of the region. The recent structures deforming the two Alboran Sea margins come to support the continuity, at present, of orogenic processes undergone by the eastern internal regions of the Gibraltar Arc, involving regional E-W extension in the framework of NW-SE to N-S Eurasian-African convergence.

  20. The May 29 2008 earthquake aftershock sequence within the South Iceland Seismic Zone: Fault locations and source parameters of aftershocks

    NASA Astrophysics Data System (ADS)

    Brandsdottir, B.; Parsons, M.; White, R. S.; Gudmundsson, O.; Drew, J.

    2010-12-01

    The mid-Atlantic plate boundary breaks up into a series of segments across Iceland. The South Iceland Seismic Zone (SISZ) is a complex transform zone where left-lateral E-W shear between the Reykjanes Peninsula Rift Zone and the Eastern Volcanic Zone is accommodated by bookshelf faulting along N-S lateral strike-slip faults. The SISZ is also a transient feature, migrating sideways in response to the southward propagation of the Eastern Volcanic Zone. Sequences of large earthquakes (M > 6) lasting from days to years and affecting most of the seismic zone have occurred repeatedly in historical time (last 1100 years), separated by intervals of relative quiescence lasting decades to more than a century. On May 29 2008, a Mw 6.1 earthquake struck the western part of the South Iceland Seismic Zone, followed within seconds by a slightly smaller event on a second fault ~5 km further west. Aftershocks, detected by a temporal array of 11 seismometers and three permanent Icelandic Meteorological Office stations were located using an automated Coalescence Microseismic Mapping technique. The epicenters delineate two major and several smaller N-S faults as well as an E-W zone of activity stretching further west into the Reykjanes Peninsula Rift Zone. Fault plane solutions show both right lateral and oblique strike slip mechanisms along the two major N-S faults. The aftershocks deepen from 3-5 km in the north to 8-9 km in the south, suggesting that the main faults dip southwards. The faulting is interpreted to be driven by the local stress due to transform motion between two parallel segments of the divergent plate boundary crossing Iceland.

  1. Magmatic control along a strike-slip volcanic arc: The central Aeolian arc (Italy)

    NASA Astrophysics Data System (ADS)

    Ruch, J.; Vezzoli, L.; De Rosa, R.; Di Lorenzo, R.; Acocella, V.

    2016-02-01

    The regional stress field in volcanic areas may be overprinted by that produced by magmatic activity, promoting volcanism and faulting. In particular, in strike-slip settings, the definition of the relationships between the regional stress field and magmatic activity remains elusive. To better understand these relationships, we collected stratigraphic, volcanic, and structural field data along the strike-slip central Aeolian arc (Italy): here the islands of Lipari and Vulcano separate the extensional portion of the arc (to the east) from the contractional one (to the west). We collected >500 measurements of faults, extension fractures, and dikes at 40 sites. Most structures are NNE-SSW to NNW-SSE oriented, eastward dipping, and show almost pure dip-slip motion, consistent with an E-W extension direction, with minor dextral and sinistral shear. Our data highlight six eruptive periods during the last 55 ka, which allow considering both islands as a single magmatic system, in which tectonic and magmatic activities steadily migrated eastward and currently focus on a 10 km long × 2 km wide active segment. Faulting appears to mostly occur in temporal and spatial relation with magmatic events, supporting that most of the observable deformation derives from transient magmatic activity (shorter term, days to months), rather than from steady longer-term regional tectonics (102-104 years). More in general, the central Aeolian case shows how magmatic activity may affect the structure and evolution of volcanic arcs, overprinting any strike-slip motion with magma-induced extension at the surface.

  2. Fault kinematics and depocenter evolution of oil-bearing, continental successions of the Mina del Carmen Formation (Albian) in the Golfo San Jorge basin, Argentina

    NASA Astrophysics Data System (ADS)

    Paredes, José Matildo; Plazibat, Silvana; Crovetto, Carolina; Stein, Julián; Cayo, Eric; Schiuma, Ariel

    2013-10-01

    Up to 10% of the liquid hydrocarbons of the Golfo San Jorge basin come from the Mina del Carmen Formation (Albian), an ash-dominated fluvial succession preserved in a variably integrated channel network that evolved coeval to an extensional tectonic event, poorly analyzed up to date. Fault orientation, throw distribution and kinematics of fault populations affecting the Mina del Carmen Formation were investigated using a 3D seismic dataset in the Cerro Dragón field (Eastern Sector of the Golfo San Jorge basin). Thickness maps of the seismic sub-units that integrate the Mina del Carmen Formation, named MEC-A-MEC-C in ascending order, and mapping of fluvial channels performed applying geophysical tools of visualization were integrated to the kinematical analysis of 20 main normal faults of the field. The study provides examples of changes in fault throw patterns with time, associated with faults of different orientations. The "main synrift phase" is characterized by NE-SW striking (mean Az = 49°), basement-involved normal faults that attains its maximum throw on top of the volcanic basement; this set of faults was active during deposition of the Las Heras Group and Pozo D-129 formation. A "second synrift phase" is recognized by E-W striking normal faults (mean Az = 91°) that nucleated and propagated from the Albian Mina del Carmen Formation. Fault activity was localized during deposition of the MEC-A sub-unit, but generalized during deposition of MEC-B sub-unit, producing centripetal and partially isolated depocenters. Upward decreasing in fault activity is inferred by more gradual thickness variation of MEC-C and the overlying Lower Member of Bajo Barreal Formation, evidencing passive infilling of relief associated to fault boundaries, and conformation of wider depocenters with well integrated networks of channels of larger dimensions but random orientation. Lately, the Mina del Carmen Formation was affected by the downward propagation of E-W to ESE-WNW striking

  3. Structural and microstructural evolution of fault zones in Cretaceous poorly lithified sandstones of the Rio do Peixe basin, Paraiba, NE Brazil

    NASA Astrophysics Data System (ADS)

    Balsamo, Fabrizio; Nogueira, Francisco; Storti, Fabrizio; Bezerra, Francisco H. R.; De Carvalho, Bruno R.; André De Souza, Jorge

    2017-04-01

    In this contribution we describe the structural architecture and microstructural features of fault zones developed in Cretaceous, poorly lithified sandstones of the Rio do Peixe basin, NE Brazil. The Rio do Peixe basin is an E-W-trending, intracontinental half-graben basin developed along the Precambrian Patos shear zone where it is abutted by the Porto Alegre shear zone. The basin formed during rifting between South America and Africa plates and was reactivated and inverted in a strike-slip setting during the Cenozoic. Sediments filling the basin consist of an heterolithic sequence of alternating sandstones, conglomerates, siltstone and clay-rich layers. These lithologies are generally poorly lithified far from the major fault zones. Deformational structures in the basin mostly consist of deformation band-dominated fault zones. Extensional and strike-slip fault zones, clusters of deformation bands, and single deformation bands are commonly well developed in the proximity of the basin-boundary fault systems. All deformation structures are generally in positive relief with respect to the host rocks. Extensional fault zones locally have growth strata in their hangingwall blocks and have displacement generally <10 m. In map view, they are organized in anastomosed segments with high connectivity. They strike E-W to NE-SW, and typically consist of wide fault cores (< 1 m in width) surrounded by up to few-meter wide damage zones. Fault cores are characterized by distributed deformation without pervasive strain localization in narrow shear bands, in which bedding is transposed into foliation imparted by grain preferred orientation. Microstructural observations show negligible cataclasis and dominant non-destructive particulate flow, suggesting that extensional fault zones developed in soft-sediment conditions in a water-saturated environment. Strike-slip fault zones commonly overprint the extensional ones and have displacement values typically lower than about 2 m. They

  4. Neotectonic reactivation of shear zones and implications for faulting style and geometry in the continental margin of NE Brazil

    NASA Astrophysics Data System (ADS)

    Bezerra, F. H. R.; Rossetti, D. F.; Oliveira, R. G.; Medeiros, W. E.; Neves, B. B. Brito; Balsamo, F.; Nogueira, F. C. C.; Dantas, E. L.; Andrades Filho, C.; Góes, A. M.

    2014-02-01

    The eastern continental margin of South America comprises a series of rift basins developed during the breakup of Pangea in the Jurassic-Cretaceous. We integrated high resolution aeromagnetic, structural and stratigraphic data in order to evaluate the role of reactivation of ductile, Neoproterozoic shear zones in the deposition and deformation of post-rift sedimentary deposits in one of these basins, the Paraíba Basin in northeastern Brazil. This basin corresponds to the last part of the South American continent to be separated from Africa during the Pangea breakup. Sediment deposition in this basin occurred in the Albian-Maastrichtian, Eocene-Miocene, and in the late Quaternary. However, our investigation concentrates on the Miocene-Quaternary, which we consider the neotectonic period because it encompasses the last stress field. This consisted of an E-W-oriented compression and a N-S-oriented extension. The basement of the basin forms a slightly seaward-tilted ramp capped by a late Cretaceous to Quaternary sedimentary cover ~ 100-400 m thick. Aeromagnetic lineaments mark the major steeply-dipping, ductile E-W- to NE-striking shear zones in this basement. The ductile shear zones mainly reactivated as strike-slip, normal and oblique-slip faults, resulting in a series of Miocene-Quaternary depocenters controlled by NE-, E-W-, and a few NW-striking faults. Faulting produced subsidence and uplift that are largely responsible for the present-day morphology of the valleys and tablelands in this margin. We conclude that Precambrian shear zone reactivation controlled geometry and orientation, as well as deformation of sedimentary deposits, until the Neogene-Quaternary.

  5. Characterizing the potential for fault reactivation related to CO2 injection through subsurface structural mapping and stress field analysis, Wellington Field, Sumner County, KS

    NASA Astrophysics Data System (ADS)

    Schwab, D.; Bidgoli, T.; Taylor, M. H.

    2015-12-01

    South-central Kansas has experienced an unprecedented increase in seismic activity since 2013. The spatial and temporal relationship of the seismicity with brine disposal operations has renewed interest in the role of fluids in fault reactivation. This study focuses on determining the suitability of CO2 injection into a Cambro-Ordovician reservoir for long-term storage and a Mississippian reservoir for enhanced oil recovery in Wellington Field, Sumner County, Kansas. Our approach for determining the potential for induced seismicity has been to (1) map subsurface faults and estimate in-situ stresses, (2) perform slip and dilation tendency analysis to identify optimally-oriented faults relative to the estimated stress field, and (3) monitor surface deformation through cGPS data and InSAR imaging. Through the use of 3D seismic reflection data, 60 near vertical, NNE-striking faults have been identified. The faults range in length from 140-410 m and have vertical separations of 3-32m. A number of faults appear to be restricted to shallow intervals, while others clearly cut the top basement reflector. Drilling-induced tensile fractures (N=78) identified from image logs and inversion of earthquake focal mechanism solutions (N=54) are consistent with the maximum horizontal stress (SHmax) oriented ~E-W. Both strike-slip and normal-slip fault plane solutions for earthquakes near the study area suggest that SHmax and Sv may be similar in magnitude. Estimates of stress magnitudes using step rate tests (Shmin = 2666 psi), density logs (Sv = 5308 psi), and calculations from wells with drilling induced tensile fractures (SHmax = 4547-6655 psi) are determined at the gauge depth of 4869ft. Preliminary slip and dilation tendency analysis indicates that faults striking 0°-20° are stable, whereas faults striking 26°-44° may have a moderate risk for reactivation with increasing pore-fluid pressure.

  6. Crestal fault geometries reveal late halokinesis and collapse of the Samson Dome, Northern Norway: Implications for petroleum systems in the Barents Sea

    NASA Astrophysics Data System (ADS)

    Mattos, Nathalia H.; Alves, Tiago M.; Omosanya, Kamaldeen O.

    2016-10-01

    This paper uses 2D and high-quality 3D seismic reflection data to assess the geometry and kinematics of the Samson Dome, offshore Norway, revising the implications of the new data to hydrocarbon exploration in the Barents Sea. The study area was divided into three (3) zones in terms of fault geometries and predominant strikes. Displacement-length (D-x) and Throw-depth (T-z) plots showed faults to consist of several segments that were later dip-linked. Interpreted faults were categorised into three families, with Type A comprising crestal faults, Type B representing large E-W faults, and Type C consisting of polygonal faults. The Samson Dome was formed in three major stages: a) a first stage recording buckling of the post-salt overburden and generation of radial faults; b) a second stage involving dissolution and collapse of the dome, causing subsidence of the overburden and linkage of initially isolated fault segments; and c) a final stage in which large fault segments were developed. Late Cretaceous faults strike predominantly to the NW, whereas NE-trending faults comprise Triassic structures that were reactivated in a later stage. Our work provides scarce evidence for the escape of hydrocarbons in the Samson Dome. In addition, fault analyses based on present-day stress distributions indicate a tendency for 'locking' of faults at depth, with the largest leakage factors occurring close to the surface. The Samson Dome is an analogue to salt structures in the Barents Sea where oil and gas exploration has occurred with varied degrees of success.

  7. 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.

  8. Effect of basement structure and salt tectonics on deformation styles along strike: An example from the Kuqa fold-thrust belt, West China

    NASA Astrophysics Data System (ADS)

    Neng, Yuan; Xie, Huiwen; Yin, Hongwei; Li, Yong; Wang, Wei

    2018-04-01

    The Kuqa fold-thrust belt (KFTB) has a complex thrust-system geometry and comprises basement-involved thrusts, décollement thrusts, triangle zones, strike-slip faults, transpressional faults, and pop-up structures. These structures, combined with the effects of Paleogene salt tectonics and Paleozoic basement uplift form a complex structural zone trending E-W. Interpretation and comprehensive analysis of recent high-quality seismic data, field observations, boreholes, and gravity data covering the KFTB has been performed to understand the characteristics and mechanisms of the deformation styles along strike. Regional sections, fold-thrust system maps of the surface and the sub-salt layer, salt and basement structure distribution maps have been created, and a comprehensive analysis of thrust systems performed. The results indicate that the thrust-fold system in Paleogene salt range can be divided into five segments from east to west: the Kela-3, Keshen, Dabei, Bozi, and Awate segments. In the easternmost and westernmost parts of the Paleogene salt range, strike-slip faulting and basement-involved thrusting are the dominant deformation styles, as basement uplift and the limits of the Cenozoic evaporite deposit are the main controls on deformation. Salt-core detachment fold-thrust systems coincide with areas of salt tectonics, and pop-up, imbricate, and duplex structures are associated with the main thrust faults in the sub-salt layer. Distribution maps of thrust systems, basement structures, and salt tectonics show that Paleozoic basement uplift controlled the Paleozoic foreland basin morphology and the distribution of Cenozoic salt in the KFTB, and thus had a strong influence on the segmented structural deformation and evolution of the fold-thrust belt. Three types of transfer zone are identified, based on the characteristics of the salt layer and basement uplift, and the effects of these zones on the fault systems are evaluated. Basement uplift and the boundary of

  9. 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

  10. Origin and structure of major orogen-scale exhumed strike-slip

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz

    2016-04-01

    The formation of major exhumed strike-slip faults represents one of the most important dynamic processes affecting the evolution of the Earth's lithosphere and surface. Detailed models of the potential initiation and properties and architecture of orogen-scale exhumed strike-slip faults and how these relate to exhumation are rare. In this study, we deal with key properties controlling the development of major exhumed strike-slip fault systems, which are equivalent to the deep crustal sections of active across fault zones. We also propose two dominant processes for the initiation of orogen-scale exhumed strike-slip faults: (1) pluton-controlled and (2) metamorphic core complex-controlled strike-slip faults. In these tectonic settings, the initiation of faults occurs by rheological weakening along hot-to-cool contacts and guides the overall displacement and ultimate exhumation. These processes result in a specific thermal and structural architecture of such faults. These types of strike-slip dominated fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust during various stages of faulting. The high variety of distinctive fault rocks is a potential evidence for recognition of these types of strike-slip faults. Exhumation of mylonitic rocks is, therefore, a common feature of such reverse oblique-slip strike-slip faults, implying major transtensive and/or transpressive processes accompanying pure strike-slip motion during exhumation. Some orogen-scale strike-slip faults nucleate and initiate along rheologically weak zones, e.g. at granite intrusions, zones of low-strength minerals, thermally weakened crust due to ascending fluids, and lateral borders of hot metamorphic core complexes. A further mechanism is the juxtaposition of mechanically strong mantle lithosphere to hot asthenosphere in continental transform faults (e.g., San

  11. Lepton Number Violating e-W+ → e+W- → W-W- Processes in the Left-Right Gauge Model

    NASA Astrophysics Data System (ADS)

    Doi, M.

    1999-03-01

    As new tests of the nature of neutrinos, lepton number violating e-W+a → e+W-b and e-e- → W-a W-b processes are studied within the SU(2)L × SU(2)R × U(1)B-L gauge model. They take place via exchange of a Majorana neutrino and a doubly charged Higgs particle. Differential cross sections are derived in the most general form. The angular distribution of the former process becomes resonant at cos θj= -1+2(Ma2Mb2 -mj2s)/ (s-Ma2) (s-Mb2), from which the neutrino mass mj can be deduced. Differential cross sections are estimated by using present bounds on the parameters. The cross section of the former process is about 102 times larger than the latter. Another process, e-p → e+W-n, which includes e-W+ → e+ W- as a sub-process, is also discussed, and orders of magnitude of the cross section are estimated.

  12. 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.

  13. 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.

  14. 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

  15. The Seismic Stratigraphic Record of Quaternary Deformation Across the North Anatolian Fault System in Southern Marmara Sea, Turkey

    NASA Astrophysics Data System (ADS)

    Sorlien, C. C.; Seeber, L.; Diebold, J.; Shillington, D.; Steckler, M. S.; Gurcay, S.; Kucuk, H. M.; Akhun, S. D.; Timur, D.; Dondurur, D.; Kurt, H.; Perincek, E.; Ozer, P.; Imren, C.; Coskun, S.; Buyukasik, E.; Cevatoglu, M.; Cifci, G.; Demirbag, E.

    2008-12-01

    be ~320 ka (MIS10). Alternatively, it corresponds to the pronounced 420 ka glacial (MIS12). Younger deltas did not form in this area, at least not with prograding geometries, because the water depth became too great. Possibly, outer shelf anticlinal growth may have diverted the river westward, where younger deltas are preserved on the shelf. The slope between the 400 m platform and the lower flank of the NE-trending Central Marmara Ridge is dominated by north-trending and northeast-trending 1 km-wavelength folds. These folds grew through the late Quaternary interval of deposition of the imaged deltas, and they deform the seafloor. They could be secondary shortening structures, forced folds above blind normal faults, or both. Farther east along the same slope, low-angle normal faults also grew through much of late Quaternary time. These faults root above unfaulted strata, and represent a slow collapse of the escarpment into the deep basin. NE-trending thrust- folds, NW-striking normal faults, WNW-striking transtensional faults, and ENE-striking transpressional faults are all consistent with the E-W right-lateral continental transform fault system.

  16. Radial arm strike rail

    DOEpatents

    McKeown, Mark H.; Beason, Steven C.

    1991-01-01

    The radial arm strike rail assembly is a system for measurement of bearings, directions, and stereophotography for geologic mapping, particularly where magnetic compasses are not appropriate. The radial arm, pivoting around a shaft axis, provides a reference direction determination for geologic mapping and bearing or direction determination. The centerable and levelable pedestal provide a base for the radial arm strike rail and the telescoping camera pedestal. The telescoping feature of the radial arm strike rail allows positioning the end of the rail for strike direction or bearing measurement with a goniometer.

  17. Neotectonics in the foothills of the southernmost central Andes (37°-38°S): Evidence of strike-slip displacement along the Antiñir-Copahue fault zone

    NASA Astrophysics Data System (ADS)

    Folguera, AndréS.; Ramos, VíCtor A.; Hermanns, Reginald L.; Naranjo, José

    2004-10-01

    The Antiñir-Copahue fault zone (ACFZ) is the eastern orogenic front of the Andes between 38° and 37°S. It is formed by an east vergent fan of high-angle dextral transpressive and transtensive faults, which invert a Paleogene intra-arc rift system in an out of sequence order with respect to the Cretaceous to Miocene fold and thrust belt. 3.1-1.7 Ma volcanic rocks are folded and fractured through this belt, and recent indicators of fault activity in unconsolidated deposits suggest an ongoing deformation. In spite of the absence of substantial shallow seismicity associated with the orogenic front, neotectonic studies show the existence of active faults in the present mountain front. The low shallow seismicity could be linked to the high volumes of retroarc-derived volcanic rocks erupted through this fault system during Pliocene and Quaternary times. This thermally weakened basement accommodates the strain of the Antiñir-Copahue fault zone, absorbing the present convergence between the South America and Nazca plates.

  18. 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

  19. Numerical Elasto-Plastic Models on the Faulting development in Southwest Taiwan

    NASA Astrophysics Data System (ADS)

    Lee, F. Y.; Tan, E.; Chang, E. T. Y.

    2016-12-01

    We use 3D numerical elasto-plastic model to simulate the development of faults and the surface deformation in Southwest Taiwan, which is under oblique collision between Eurasian plate and Philippine Sea plate. The study area is bounded by the Central Range and the Peikang basement high, comprising the southernmost part of the fold-and-thrust belt joint with the coastal plain (mainly the Pingtung Plain). Our goal is to model the deformation mechanism under oblique collision of plates in and around the Taiwan Island. The Cenozoic sediment isopach is taken to form our experimental domain. The Chaochou fault locates at the eastern boundary, serving as a bulldozer moving westward in a velocity of 5 cm/yr. The Peikang high is the backstop at western boundary with material in various friction angle attached to supply friction. The northern boundary striking in E-W direction is at the northern end of the Chaochou fault as a frictional boundary. The southern boundary is in the offshore area of the Pingtung Plain with an open boundary, which allows material free to flow out. A thin layer with variable frictions is at the bottom. Our results show a significant correlation with the tectonic structures observed in the SW Taiwan. The motion velocity increases from north to south, which is similar to the GPS observation. Additionally, two longitudinal thrusts are generated at east. They correspond to the Chaochou fault and Koaping fault, the latter of which is reported as a thrust with sinistral motion. Furthermore, several sinistral strike-slip faults are emergent in the southeast in our experiment. In fact, the bathymetry in the SW offshore Taiwan reveals a lateral motion within the strata in the accretionary prism.

  20. A new Triassic shortening-extrusion tectonic model for Central-Eastern Asia: Structural, geochronological and paleomagnetic investigations in the Xilamulun Fault (North China)

    NASA Astrophysics Data System (ADS)

    Zhao, Pan; Faure, Michel; Chen, Yan; Shi, Guanzhong; Xu, Bei

    2015-09-01

    At the northern margin of the North China Block (NCB), the Xilamulun Fault (XMF) is a key belt to decipher the tectonic evolution of Central-Eastern Asia, as it records the Paleozoic final closure of the Paleo-Asian Ocean, and localizes a Late Triassic intracontinental deformation. In this study, structural analysis, 40Ar-39Ar dating, and paleomagnetic studies were performed to investigate the kinematics of the XMF and to further discuss its Triassic geodynamic significance in the Central-Eastern Asia framework after the Paleozoic Central Asian Orogenic evolution. The structural analyses reveal two phases of ductile deformation. The first one (D1), which displays N-verging and E-W trending folds, is related to the Early Paleozoic collisional event between the NCB and the Songliao-Hunshandake Block (SHB). The second phase (D2) displays a high-angle foliation and a pervasive sub-horizontal E-W stretching lineation with kinematic criteria indicative of dextral strike-slip shearing. The 40Ar-39Ar dating on mylonitic granite places the main shearing event around 227-209 Ma. This D2 shearing is coeval with that of the dextral strike-slip Bayan Obo-Chifeng Fault (BCF) and the Chicheng-Fengning-Longhua Fault to the south, which together constitute a dextral shearing fault system on the northern margin of the NCB during the Late Triassic. The paleomagnetic study performed on the Middle Permian Guangxingyuan pluton, located between the XMF and BCF, documents a local clockwise rotation of this pluton with respect to the NCB and SHB. Our multidisciplinary study suggests an NNW-SSE shortening and strike-slip shearing dominated tectonic setting on the northern margin of the NCB during the Late Triassic. Combining the contemporaneous dextral strike-slip movements of the XMF and BCF in northern China and the sinistral strike-slip movement of East Gobi Fault (EGF) in southeastern Mongolia with the large-scale tectonic framework, a Late Triassic NNW-SSE shortening-eastward extrusion

  1. 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

  2. Near N-S paleo-extension in the western Deccan region, India: Does it link strike-slip tectonics with India-Seychelles rifting?

    NASA Astrophysics Data System (ADS)

    Misra, Achyuta Ayan; Bhattacharya, Gourab; Mukherjee, Soumyajit; Bose, Narayan

    2014-09-01

    This is the first detailed report and analyses of deformation from the W part of the Deccan large igneous province (DLIP), Maharashtra, India. This deformation, related to the India-Seychelles rifting during Late Cretaceous-Early Paleocene, was studied, and the paleostress tensors were deduced. Near N-S trending shear zones, lineaments, and faults were already reported without significant detail. An E-W extension was envisaged by the previous workers to explain the India-Seychelles rift at ~64 Ma. The direction of extension, however, does not match with their N-S brittle shear zones and also those faults (sub-vertical, ~NE-SW/~NW-SE, and few ~N-S) we report and emphasize in this work. Slickenside-bearing fault planes, brittle shear zones, and extension fractures in meso-scale enabled us to estimate the paleostress tensors (directions and relative magnitudes). The field study was complemented by remote sensing lineament analyses to map dykes and shear zones. Dykes emplaced along pre-existing ~N-S to ~NE-SW/~NW-SE shears/fractures. This information was used to derive regional paleostress trends. A ~NW-SE/NE-SW minimum compressive stress in the oldest Kalsubai Subgroup and a ~N-S direction for the younger Lonavala, Wai, and Salsette Subgroups were deciphered. Thus, a ~NW/NE to ~N-S extension is put forward that refutes the popular view of E-W India-Seychelles extension. Paleostress analyses indicate that this is an oblique rifted margin. Field criteria suggest only ~NE-SW and ~NW-SE, with some ~N-S strike-slip faults/brittle shear zones. We refer this deformation zone as the "Western Deccan Strike-slip Zone" (WDSZ). The observed deformation was matched with offshore tectonics deciphered mainly from faults interpreted on seismic profiles and from magnetic seafloor spreading anomalies. These geophysical findings too indicate oblique rifting in this part of the W Indian passive margin. We argue that the Seychelles microcontinent separated from India only after much of

  3. The analysis and study of fault systems in the Southernmost Part of Okinawa Trough

    NASA Astrophysics Data System (ADS)

    Huang, Y.; Tsai, C.; Lee, C.

    2004-12-01

    Taiwan is located in the boundary between the Eurasian and Philippine Sea plates. Due to different subduction, two arc-trench systems in different direction were happened. One is Luzon arc-trench system in N-S direction; the other one is called Ryukyu arc-trench system in E-W direction. The Okinawa Trough is a back-arc basin which was formed by extension of Eurasian plate, and the tectonic setting in this area has a series of normal-faults and igneous bodies. According to previous studies, we know that Southernmost Part of Okinawa Trough (SPOT) have evolved at least two main tensional phases of Okinawa Trough, the first phase probably came up in early Pleistocene and struck in NE-SW direction; and the second phases occurred during late Pleistocene and Holocene changed the direction to E-W. In this study, we have used seismic data collected by R/V Chiu-Lien, Ocean Research I, and R/V L'Atalante to explain the normal-fault systems in the SPOT area. We integrate seismic profiles with corrected bathymetry to relocate these normal faults. Our results show these normal fault systems has two main strikes, respectively N60° E and N80° E. We find that most of N60° E faults are located in the northern slope of SPOT and landward to Taiwan. The N80° E faults are found in the southern slop and center area of SPOT. Compare with the faults and a new topographic map, we find there were a lot of faults around the canyon, such as North-Mienhua Canyon. We suggest that the origin of the canyon is probably due to these tectonic forces. The canyon is a weak area, and is eroded much fast than the surrounding continental shelf. Passing through a series of erosional processes, the canyon becomes what looks like today. We find a lot of graben structure located in the center of SPOT. This area is the extension axis of SPOT right now. We also find many possible igneous rocks in the seismic profiles, some of them are intrusions and the others penetrate the seabed along the weak zone and

  4. Deformation ages within the Klong Marui continental wrench fault, southern Thailand

    NASA Astrophysics Data System (ADS)

    Kanjanapayont, P.; Grasemann, B.; Edwards, M. A.

    2009-04-01

    The Klong Marui Fault is a ductile to brittle dextral strike-slip shear zone characterized by strong NNE-SSW geomorphic ridges trending up to 150 km. from Thai Gulf to Andaman Sea. At it southern part in the Phung Nga region, the ductile core forms a 40km long ridge. The geology within this wrench zone consisted of steep strongly deformed layers of migmatitic gneisses, mylonitic granites/pegmatites and phyllonitic metapelites. Brittle cataclasitc zones were localized in the eastern and western margin of this ductile core zone. The first deformation stage was dextral ductile strike-slip movement at mid to upper crustal levels and formed the main mylonitic foliation (c), secondary synthetic foliations (c'), and lineation in the migmatitic gneisses, mylonitic granites and metapelites. Locally sillimanite-clasts in high-temperature recrystallization quartz fabric fabric suggest deformation at amphibolite facies condition. More typically, quartz dynamically recrystallize by subgrain rotation and grain boundary migration under greenschist facies conditions. Microstructure of myrmekite and "V"-pull-apart clearly indicates dextral sense of shear. Pegmatites cross-cut the main mylonitic foliation but were sheared at the rims indicating syn-kinematic emplacement. Dynamically recrystallizing quartz mainly by basal gliding, bulging and low-temperature subgrain rotation record the latest stage of ductile dextral strike-slip deformation during decreasing temperature conditions. The NNE-SSW trending dextral strike-slip deformation accommodated the E-W transpression as a result of the differential movement of the northward drifting Indian craton and Asia. The brittle/ductile deformation produced cataclasites and minor faults which overprint the higher temperature fabric causing exhumation and juxtaposition of fault rocks developed under different metamorphic conditions in a positive flower structure.

  5. Strike Manual: Related to Potential School Employee Strike Action.

    ERIC Educational Resources Information Center

    Loftus, Richard J., Jr., Ed.; And Others

    Strikes and threats of strikes have become one of the realities of public education. School districts must be prepared to deal with strikes and the problems that they present. This manual is designed to provide a brief overview of the law relating to public employee strikes and to assist districts in adopting their own strike plans. It offers…

  6. A N-S fossil transform fault reactivated by the March 2, 2016 Mw7.8 southwest of Sumatra, Indonesia earthquake

    NASA Astrophysics Data System (ADS)

    Zhang, H.; van der Lee, S.

    2016-12-01

    Warton Basin (WB) is characterized by N-S striking fossil transform faults and E-W trending extinct ridges. The 2016 Mw7.8 southwest of Sumatra earthquake, nearby the WB's center, was first imaged by back-projecting P-waves from three regional seismic networks in Europn, Japan, and Australia. Next, the rupture direction of the earthquake was further determined using the rupture directivity analysis to P-waves from the global seismic network (GSN). Finally, we inverting these GSN waveforms on a defined N-S striking vertical fault for a kinematic source model. The results show that the earthquake reactivates a 190 degree N-S striking vertical fossil transform fault and asymmetrically bilaterally ruptures a 65 km by 30 km asperity over 35 s. Specifically, the earthquake first bilaterally ruptures northward and southward at a speed of 1.0 km/s over the first 12 s, and then mainly rupture northward at a speed of 1.6 km/s. Compared with two previous M≥7.8 WB earthquakes, including the 2000 southern WB earthquake and 2012 Mw8.6 Sumatra earthquake, the lower seismic energy radiation efficiency and slower rupture velicity of the 2016 earthquake indicate the rupture of the earthquake is probably controlled by the warmer ambient slab and tectonic stress regime.

  7. Assessment of the geodynamical setting around the main active faults at Aswan area, Egypt

    NASA Astrophysics Data System (ADS)

    Ali, Radwan; Hosny, Ahmed; Kotb, Ahmed; Khalil, Ahmed; Azza, Abed; Rayan, Ali

    2013-04-01

    The proper evaluation of crustal deformations in the Aswan region especially around the main active faults is crucial due to the existence of one major artificial structure: the Aswan High Dam. This construction created one of the major artificial lakes: Lake Nasser. The Aswan area is considered as an active seismic area in Egypt since many recent and historical felted earthquakes occurred such as the impressive earthquake occurred on November 14, 1981 at Kalabsha fault with a local magnitude ML=5.7. Lately, on 26 December 2011, a moderate earthquake with a local magnitude Ml=4.1 occurred at Kalabsha area too. The main target of this study is to evaluate the active geological structures that can potentially affect the Aswan High Dam and that are being monitored in detail. For implementing this objective, two different geophysical tools (magnetic, seismic) in addition to the Global Positioning System (GPS) have been utilized. Detailed land magnetic survey was carried out for the total component of geomagnetic field using two proton magnetometers. The obtained magnetic results reveal that there are three major faults parallel {F1 (Kalabsha), F2 (Seiyal) and F3} affecting the area. The most dominant magnetic trend strikes those faults in the WNW-ESE direction. The seismicity and fault plain solutions of the 26 December 2011 earthquake and its two aftershocks have been investigated. The source mechanisms of those events delineate two nodal plains. The trending ENE-WSW to E-W is consistent with the direction of Kalabsha fault and its extension towards east for the events located over it. The trending NNW-SSE to N-S is consistent with the N-S fault trending. The movement along the ENE-WSW plain is right lateral, but it is left lateral along the NNW-SSE plain. Based on the estimated relative motions using GPS, dextral strike-slip motion at the Kalabsha and Seiyal fault systems is clearly identified by changing in the velocity gradient between south and north stations

  8. Testing Pixel Translation Digital Elevation Models to Reconstruct Slip Histories: An Example from the Agua Blanca Fault, Baja California, Mexico

    NASA Astrophysics Data System (ADS)

    Wilson, J.; Wetmore, P. H.; Malservisi, R.; Ferwerda, B. P.; Teran, O.

    2012-12-01

    approximately equal to that to the east. The ABF has varying kinematics along strike due to changes in trend of the fault with respect to the nearly east-trending displacement vector of the Ensenada Block to the north of the fault relative to a stable Baja Microplate to the south. These kinematics include nearly pure strike slip in the central portion of the ABF where the fault trends nearly E-W, and minor components of normal dip-slip motion on the NABF and eastern sections of the fault where the trends become more northerly. A pixel translation vector parallel to the trend of the ABF in the central segment (290 deg, 10.5 km) produces kinematics consistent with those described above. The block between the NABF and STF has a pixel translation vector parallel the STF (291 deg, 3.5 km). We find these vectors are consistent with the kinematic variability of the fault system and realign several major drainages and ridges across the fault. This suggests these features formed prior to faulting, and they yield preferred values of offset: 10.5 km on the ABF, 7 km on the NABF and 3.5 km on the STF. This model is consistent with the kinematic model proposed by Hamilton (1971) in which the ABF is a transform fault, linking extensional regions of Valle San Felipe and the Continental Borderlands.

  9. Physical inter-relationships between hydrothermal activity, faulting and magmatic processes at the center of a slow-spreading, magma-rich mid-ocean ridge segment: A case study of the Lucky Strike segment (MAR, 37°03'-37‧N)

    NASA Astrophysics Data System (ADS)

    Fontaine, F. J.; Cannat, M.; Escartin, J.; Crawford, W. C.; Singh, S. C.

    2012-12-01

    The modalities and efficiency of hydrothermal heat evacuation at mid-ocean ridges (25% of the global heat loss) are controlled by the lithosphere thermal and permeability structures for which we had robust constraints only for fast/intermediate spreading axis until the last past few years during which integrated geophysical, geological and geochemical studies focused on some hydrothermal sites at slow-spreading ridges. At the Lucky Strike vent field of the mid-atlantic ridge - a hydrothermal complex composed of high-temperature (maximum T=340°C), smoker-like vents and associated diffuse flow and extracting a few hundreds MW from the oceanic lithosphere - a seafloor observatory which installation started in 2005 highlights local interactions between hydrothermal, tectonic and magmatic processes. Detailed geophysical and geological investigations stress the role of the local axial fault system on localizing high- and low-temperature ventings around the faulted rim of a paleo lava lake. Microseismic studies bring constraints on the subseafloor hydrology and suggest an along-axis flow pattern, with a privileged recharge area located about a kilometer north off the active discharges. Seismic reflection studies image a central magma chamber fueling the hydrothermal sites and also reveal its along-axis depth variations likely influencing hydrothermal cell organization and flow focusing. Such linkages among hydrothermal dynamics, heat source and crustal permeability geometries usually lack quantitative constraints at mid-ocean ridges in general, and the Lucky Strike segment settings offers a unique opportunity to couple high-resolution geophysical data to hydrodynamic model. Here we develop a series of original two- and three-dimensional numerical and physical models of hydrothermal activity, tailored to this slow-spreading environment. Our results highlight physical linkages among magmatism, tectonics and crustal hydrology stressing the key role of faulting and magma

  10. New type of kinematic indicator in bed-parallel veins, Late Jurassic-Early Cretaceous Vaca Muerta Formation, Argentina: E-W shortening during Late Cretaceous vein opening

    NASA Astrophysics Data System (ADS)

    Ukar, Estibalitz; Lopez, Ramiro G.; Gale, Julia F. W.; Laubach, Stephen E.; Manceda, Rene

    2017-11-01

    In the Late Jurassic-Early Cretaceous Vaca Muerta Formation, previously unrecognized yet abundant structures constituting a new category of kinematic indicator occur within bed-parallel fibrous calcite veins (BPVs) in shale. Domal shapes result from localized shortening and thickening of BPVs and the intercalation of centimeter-thick, host-rock shale inclusions within fibrous calcite beef, forming thrust fault-bounded pop-up structures. Ellipsoidal and rounded structures show consistent orientations, lineaments of interlayered shale and fibrous calcite, and local centimeter-scale offset thrust faults that at least in some cases cut across the median line of the BPV and indicate E-W shortening. Continuity of crystal fibers shows the domal structures are contemporaneous with BPV formation and help establish timing of fibrous vein growth in the Late Cretaceous, when shortening directions were oriented E-W. Differences in the number of opening stages and the deformational style of the different BPVs indicate they may have opened at different times. The new domal kinematic indicators described in this study are small enough to be captured in core. When present in the subsurface, domal structures can be used to either infer paleostress orientation during the formation of BPVs or to orient core in cases where the paleostress is independently known.

  11. Modeling along-axis variations in fault architecture in the Main Ethiopian Rift: Implications for Nubia-Somalia kinematics

    NASA Astrophysics Data System (ADS)

    Erbello, Asfaw; Corti, Giacomo; Agostini, Andrea; Sani, Federico; Kidane, Tesfaye; Buccianti, Antonella

    2016-12-01

    In this contribution, analogue modeling is used to provide new insights into the Nubia-Somalia kinematics responsible for development and evolution of the Main Ethiopian Rift (MER), at the northern termination of the East African Rift system. In particular, we performed new crustal-scale, brittle models to analyze the along-strike variations in fault architecture in the MER and their relations with the rift trend, plate motion and the resulting Miocene-recent kinematics of rifting. The models reproduced the overall geometry of the ∼600 km-long MER with its along-strike variation in orientation to test different hypothesis proposed to explain rift evolution. Analysis of model results in terms of statistics of fault length and orientation, as well as deformation architecture, and its comparison with the MER suggest that models of two-phase rifting (with a first phase of NW-SE extension followed by E-W rifting) or constant NW-SE extension, as well as models of constant ENE-WSW rifting are not able to reproduce the fault architecture observed in nature. Model results suggest instead that the rift has likely developed under a constant, post-11 Ma extension oriented roughly ESE-WNW (N97.5°E), consistent with recent plate kinematics models.

  12. Men, Not Money: E. W. Scripps and the Penny Newspapers of the Pacific Northwest.

    ERIC Educational Resources Information Center

    Jordan, Mike

    E.W. Scripps's penny newspapers brought a new style of public service journalism to the Pacific Northwest's four largest cities--Seattle, Spokane, Tacoma, and Portland--in the turbulent years of the Progressive movement from 1899 to 1912. Minimal investment, tight cost controls, and the idea that a small, condensed newspaper could be more popular…

  13. 75 FR 14437 - North Eastern Wisconsin Hydro Inc. (N.E.W. Hydro); Notice of Intent To File License Application...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2010-03-25

    ... Wisconsin Hydro Inc. (N.E.W. Hydro); Notice of Intent To File License Application, Filing of Pre-Application..., Inc. (N.E.W. Hydro) e. Name of Project: Menominee/Park Mill Hydroelectric Project. f. Location: The..., (202) 502-6156 or by e-mail at [email protected] . j. N.E.W. Hydro filed its request to use the...

  14. Shallow properties of faults in carbonate rocks - The Jandaíra Formation, Potiguar Basin, Brazil

    NASA Astrophysics Data System (ADS)

    Bezerra, F. H.; Bertotti, G.; Rabelo, J.; Silva, A. T.; Carneiro, M. A.; Cazarin, C. L.; Silva, C. C.; Vieira, M. M.; Bisdom, K.; Moraes, A.

    2014-12-01

    We studied the development of shallow faults in the Jandaíra Formation, a Turonian-Campanian carbonate platform in the Potiguar Basin, northeastern Brazil. Our main goal was to characterize fault geometry and properties such as porosity and permeability, and associate these results with fluid flow in shallow conditions. We used an integrated multidisciplinary approach, which combined Quickbird satellite and an unmanned aerial vehicle (UAV, drone) imagery, structural and sedimentary-facies mapping, and petrographic and petrophysical analyses. The Jandaíra Formation presents a variety of carbonate facies, which include mudstones to bioclastic, peloidal, intraclastic, and oolitic grainstones. We modeled our remote sensing and structural data using a finite element analysis system for 2D deformation modeling. We applied the magnitudes and directions of the present-day stress field to simulate depths as deep as 500 m. These stress data were derived from borehole breakout data and drilling-induced tensile fractures observed in resistivity image logs. Our results indicate the occurrence of dilation processes along three sets of joints that were reactivated as faults in the upper crust: N-S, NE-, and E-W-striking faults. These faults provided preferential leaching pathways to fresh water percolation, contributing to localized dissolution and increased secondary porosity and permeability. The results also indicate that the tectonic stresses are concentrated in preferred structural zones such as fault intersection and termination, which are sites of increased fracturing and dissolution. Dissolution by fluids increased permeability in carbonate rocks from primary values of 0.0-0.94 mD to as much as 1370.11 mD. This process is mostly Cenozoic.

  15. Hunger strike for science

    NASA Astrophysics Data System (ADS)

    Carlowicz, Michael

    Lamenting the degenerating working conditions for scientists in Russia, geophysicist Vladimir Strakhov and physicist Igor Naumenko-Bondarenko of the United Institute of Physics of the Earth (UIPE) at the Russian Academy of Sciences (RAS) have begun a hunger strike. Strakhov is General Director of UIPE, and Naumenko-Bondarenko is chairman of the Trade Union Committee of UIPE.In a press statement released on September 30 in Moscow, the geophysicists stated that they are striking to “protest the policy of the Government of the Russian Federation with regard to Russian science in general and to the Russian Academy of Sciences in particular.” They blame governmental neglect and, specifically, “the non-payment of funds that were in the 1996 budget” for the “virtual collapse of Russian science.”

  16. The Pietra Grande thrust (Brenta Dolomites, Italy): looking for co-seismic indicators along a main fault in carbonate sequences

    NASA Astrophysics Data System (ADS)

    Viganò, Alfio; Tumiati, Simone; Martin, Silvana; Rigo, Manuel

    2013-04-01

    /or breccias of the fault zone. Host and fault rocks are locally folded, with fold axes having a rough E-W direction compatible with simultaneous thrust activation, suggesting deformation under brittle-ductile conditions. A late brittle deformation is testified by near-vertical fractures and strike-slip faults (WNW-directed) intersecting the whole thrust system. Field structure, microtextures, chemical and mineralogical compositions of host rocks, cataclasites and breccias are analysed. In particular, red veins are carefully compared with the very similar Grigne carbonate pseudotachylytes (Viganò et al. 2011, Terra Nova, vol. 23, pp.187-194), in order to evaluate if they could represent a certain geological record of seismic faulting of the Pietra Grande thrust.

  17. The origin of strike-slip tectonics in continental rifts

    NASA Astrophysics Data System (ADS)

    Ebinger, C. J.; Pagli, C.; Yun, S. H.; Keir, D.; Wang, H.

    2016-12-01

    Although continental rifts are zones of lithospheric extension, strike-slip tectonics is also accommodated within rifts and its origin remains controversial. Here we present a combined analysis of recent seismicity, InSAR and GPS derived strain maps to reveal that the plate motion in Afar is accommodated primarily by extensional tectonics in all rift arms and lacks evidences of regional scale bookshelf tectonics. However in the rifts of central Afar we identify crustal extension and normal faulting in the central part of the rifts but strike-slip earthquakes at the rift tips. We investigate if strike-slip can be the result of Coulomb stress changes induced by recent dyking but models do not explain these earthquakes. Instead we explain strike-slips as shearing at the tips of a broad zone of spreading where extension terminates against unstretched lithosphere. Our results demonstrate that plate spreading can develop both strike-slip and extensional tectonics in the same rifts.

  18. Tsunamigenic potential of a newly discovered active fault zone in the outer Messina Strait, Southern Italy

    NASA Astrophysics Data System (ADS)

    Fu, Lili; Heidarzadeh, Mohammad; Cukur, Deniz; Chiocci, Francesco L.; Ridente, Domenico; Gross, Felix; Bialas, Jörg; Krastel, Sebastian

    2017-03-01

    The 1908 Messina tsunami was the most catastrophic tsunami hitting the coastline of Southern Italy in the younger past. The source of this tsunami, however, is still heavily debated, and both rupture along a fault and a slope failure have been postulated as potential origin of the tsunami. Here we report a newly discovered active Fiumefreddo-Melito di Porto Salvo Fault Zone (F-MPS_FZ), which is located in the outer Messina Strait in a proposed landslide source area of the 1908 Messina tsunami. Tsunami modeling showed that this fault zone would produce devastating tsunamis by assuming slip amounts of ≥5 m. An assumed slip of up to 17 m could even generate a tsunami comparable to the 1908 Messina tsunami, but we do not consider the F-MPS_FZ as a source for the 1908 Messina tsunami because its E-W strike contradicts seismological observations of the 1908 Messina earthquake. Future researches on the F-MPS_FZ, however, may contribute to the tsunami risk assessment in the Messina Strait.

  19. Transform fault earthquakes in the North Atlantic: Source mechanisms and depth of faulting

    NASA Technical Reports Server (NTRS)

    Bergman, Eric A.; Solomon, Sean C.

    1987-01-01

    The centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern Mid-Atlantic Ridge were determined from an inversion of long-period body waveforms. The earthquakes occurred on the Gibbs, Oceanographer, Hayes, Kane, 15 deg 20 min, and Vema transforms. The depth extent of faulting during each earthquake was estimated from the centroid depth and the fault width. The source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes; slip vector azimuths agree to 2 to 3 deg of the local strike of the zone of active faulting. The only anomalies in mechanism were for two earthquakes near the western end of the Vema transform which occurred on significantly nonvertical fault planes. Secondary faulting, occurring either precursory to or near the end of the main episode of strike-slip rupture, was observed for 5 of the 12 earthquakes. For three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform. In all three cases, the site of secondary reverse faulting is near a compression jog in the current trace of the active transform fault zone. No evidence was found to support the conclusions of Engeln, Wiens, and Stein that oceanic transform faults in general are either hotter than expected from current thermal models or weaker than normal oceanic lithosphere.

  20. Fault fluid evolution at the outermost edges of the southern Apennines fold-and-thrust belt, Italy

    NASA Astrophysics Data System (ADS)

    Agosta, Fabrizio; Belviso, Claudia; Cavalcante, Francesco; Vita Petrullo, Angela

    2017-04-01

    This work focuses on the structural architecture and mineralization of a high-angle, extensional fault zone that crosscuts the Middle Pleistocene tuffs and pyroclastites of the Vulture Volcano, southern Italy. This fault zone is topped by a few m-thick travertine deposit formed by precipitation, in a typical lacustrine depositional environment, from a fault fluid that included a mixed, biogenic- and mantle-derived CO2. The detailed analysis of its different mineralization can shed new lights into the shallow crustal fluid flow that took place during deformation of the outer edge of the southern Apennines fold-and-thrust belt. In fact, the study fault zone is interpreted as a shallow-seated, tear fault associated with a shallow thrust fault displacing the most inner portion of the Bradano foredeep basin infill, and was thus active during the latest stages of contractional deformation. Far from the fault zone, the fracture network is made up of three high-angle joint sets striking N-S, E-W and NW-SE, respectively. The former two sets can be interpreted as the older structural elements that pre-dated the latter one, which is likely due to the current stress state that affects the whole Italian peninsula. In the vicinity of the fault zone, a fourth joint high-angle set striking NE-SW is also present, which becomes the most dominant fracture set within the study footwall fault damage zone. Detailed X-ray diffraction analysis of the powder obtained from hand specimens representative of the multiple mineralization present within the fault zone, and in the surrounding volcanites, are consistent with circulation of a fault fluid that modified its composition with time during the latest stages of volcanic activity and contractional deformation. Specifically, veins infilled with and slickenside coated by jarosite, Opal A and/or goethite are found in the footwall fault damage zone. Based upon the relative timing of formation of the aforementioned joint sets, deciphered after

  1. Should junior doctors strike?

    PubMed

    Toynbee, Mark; Al-Diwani, Adam Aj; Clacey, Joe; Broome, Matthew R

    2016-03-01

    An impasse in negotiations between the Department of Health (DoH) and the British Medical Association in November this year led to an overwhelming vote for industrial action (IA) by junior doctors. At the time of writing, a last minute concession by DoH led to a deferment of IA to allow further negotiations mediated by the Advisory, Conciliation and Arbitration Service. However, IA by junior doctors remains a possibility if these negotiations stall again. Would the proposed action be ethically justifiable? Furthermore, is IA by doctors ever ethically defendable? Building on previous work, we explore important ethical considerations for doctors considering IA. The primary moral objection to doctors striking is often claimed to be risk of harm to patients. Other common arguments against IA by doctors include breaching their vocational responsibilities and possible damage to their relationship with patients and the public in general. These positions are in turn countered by claims of a greater long-term good and the legal and moral rights of employees to strike. Absolute restrictions appear to be hard to justify in the modern context, as does an unrestricted right to IA. We review these arguments, find that some common moral objections to doctors striking may be less relevant to the current situation, that a stronger contemporary objection to IA might be from a position of social justice and suggest criteria for ethically permissible doctor IA. Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://www.bmj.com/company/products-services/rights-and-licensing/

  2. 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

    region may be an accommodation zone between two linking faults, possibly an active fold that accommodates N-S shortening at a large-scale left step in the range front fault system. We collected ~200 paleomagnetic samples from the Late Miocene Eureka Valley Tuff of the Stanislaus Group at 21 sites over a 125-km-long, E-W transect (from the Sierra Nevada foothills to east of Mono Basin). Stepwise AF demagnetization reveals a stable characteristic remnant magnetization. Our preliminary data suggest 20-40 degrees of clockwise rotation adjacent to faults of the SNFFZ. An expanded dataset aims to identify specific structural domains, quantify differential vertical axis block rotations, and test geometric models of transrotation (i.e. block-specific versus gradational) during transtensional lithospheric deformation.

  3. [Neurological diseases after lightning strike : Lightning strikes twice].

    PubMed

    Gruhn, K M; Knossalla, Frauke; Schwenkreis, Peter; Hamsen, Uwe; Schildhauer, Thomas A; Tegenthoff, Martin; Sczesny-Kaiser, Matthias

    2016-06-01

    Lightning strikes rarely occur but 85 % of patients have lightning-related neurological complications. This report provides an overview about different modes of energy transfer and neurological conditions related to lightning strikes. Moreover, two case reports demonstrate the importance of interdisciplinary treatment and the spectrum of neurological complications after lightning strikes.

  4. Late Cretaceous through Cenozoic strike-slip tectonics of southwestern Alaska

    USGS Publications Warehouse

    Miller, M.L.; Bradley, D.C.; Bundtzen, T.K.; McClelland, W.

    2002-01-01

    New geologic mapping and geochronology show that margin-parallel strike-slip faults on the western limb of the southern Alaska orocline have experienced multiple episodes of dextral motion since ~100 Ma. These faults are on the upper plate of a subduction zone ~350-450 km inboard of the paleotrench. In southwestern Alaska, dextral displacement is 134 km on the Denali fault, at least 88-94 km on the Iditarod-Nixon Fork fault, and perhaps tens of kilometers on the Dishna River fault. The strike-slip regime coincided with Late Cretaceous sedimentation and then folding in the Kuskokwim basin, and with episodes of magmatism and mineralization at ~70, ~60, and ~30 Ma. No single driving mechanism can explain all of the ~95 million-year history of strike-slip faulting. Since ~40 Ma, the observed dextral sense of strike slip has run contrary to the sense of subduction obliquity. This may be explained by northward motion of the Pacific plate driving continental margin slivers into and/or around the oroclinal bend. From 44 to 66 Ma, oroclinal rotation, perhaps involving large-scale flexural slip, may have been accompanied by westward escape of crustal blocks along strike-slip faults. However, reconstructions of this period involve unproven assumptions about the identity of the subducting plate, the position of subducting ridges, and the exact timing of oroclinal bending, thus obscuring the driving mechanisms of strike slip. Prior to 66 Ma, oblique subduction is the most plausible driving mechanism for dextral strike slip. Cumulative displacement on all faults of the western limb of the orocline is at least 400 km, about half that on the eastern limb; this discrepancy might be explained by a combination of thrusting and unrecognized strike-slip faulting.

  5. Philosophical methodology and strikes.

    PubMed

    Thomasma, David C

    1991-01-01

    ...how do we train residents to employ ethical reasoning? This is a good question, not only for the problem of strikes, but also for all medical training. The best method is inductive, since that most closely parallels the clinical reasoning processes that define the reality of medical practice. The strengths of inductive reasoning are that it most closely matches the realities of practice, it arises from the particular circumstances of the case, and it leads to a casuistic conclusion that applies more directly than abstract reasoning models to the problem at hand. The weaknesses, though, require that inductive models include a check and balance.

  6. Global strike hypersonic weapons

    NASA Astrophysics Data System (ADS)

    Lewis, Mark J.

    2017-11-01

    Beginning in the 1940's, the United States has pursued the development of hypersonic technologies, enabling atmospheric flight in excess of five times the speed of sound. Hypersonic flight has application to a range of military and civilian applications, including commercial transport, space access, and various weapons and sensing platforms. A number of flight tests of hypersonic vehicles have been conducted by countries around the world, including the United States, Russia, and China, that could lead the way to future hypersonic global strike weapon systems. These weapons would be especially effective at penetrating conventional defenses, and could pose a significant risk to national security.

  7. Founding the "Spokane Press": E. W. Scripps and an Ambitious New Publisher Debated the Issues of Newspaper Journalism.

    ERIC Educational Resources Information Center

    Jordan, Mike

    In the early 1900s, the small, penny newspapers of E. W. Scripps were aimed primarily at working class readers, had a policy of limited advertising, and relied upon circulation to provide the bulk of revenues. The "Spokane Press" was conceived in 1902 with E. W. Scripps, his sister Ellen Browning Scripps, and George Putnam as copartners.…

  8. Study on the Evaluation Method for Fault Displacement: Probabilistic Approach Based on Japanese Earthquake Rupture Data - Principal fault displacements -

    NASA Astrophysics Data System (ADS)

    Kitada, N.; Inoue, N.; Tonagi, M.

    2016-12-01

    The purpose of Probabilistic Fault Displacement Hazard Analysis (PFDHA) is estimate fault displacement values and its extent of the impact. There are two types of fault displacement related to the earthquake fault: principal fault displacement and distributed fault displacement. Distributed fault displacement should be evaluated in important facilities, such as Nuclear Installations. PFDHA estimates principal fault and distributed fault displacement. For estimation, PFDHA uses distance-displacement functions, which are constructed from field measurement data. We constructed slip distance relation of principal fault displacement based on Japanese strike and reverse slip earthquakes in order to apply to Japan area that of subduction field. However, observed displacement data are sparse, especially reverse faults. Takao et al. (2013) tried to estimate the relation using all type fault systems (reverse fault and strike slip fault). After Takao et al. (2013), several inland earthquakes were occurred in Japan, so in this time, we try to estimate distance-displacement functions each strike slip fault type and reverse fault type especially add new fault displacement data set. To normalized slip function data, several criteria were provided by several researchers. We normalized principal fault displacement data based on several methods and compared slip-distance functions. The normalized by total length of Japanese reverse fault data did not show particular trend slip distance relation. In the case of segmented data, the slip-distance relationship indicated similar trend as strike slip faults. We will also discuss the relation between principal fault displacement distributions with source fault character. According to slip distribution function (Petersen et al., 2011), strike slip fault type shows the ratio of normalized displacement are decreased toward to the edge of fault. However, the data set of Japanese strike slip fault data not so decrease in the end of the fault

  9. Strike-slip tectonics during rift linkage

    NASA Astrophysics Data System (ADS)

    Pagli, C.; Yun, S. H.; Ebinger, C.; Keir, D.; Wang, H.

    2017-12-01

    The kinematics of triple junction linkage and the initiation of transforms in magmatic rifts remain debated. Strain patterns from the Afar triple junction provide tests of current models of how rifts grow to link in area of incipient oceanic spreading. Here we present a combined analysis of seismicity, InSAR and GPS derived strain rate maps to reveal that the plate boundary deformation in Afar is accommodated primarily by extensional tectonics in the Red Sea and Gulf of Aden rifts, and does not require large rotations about vertical axes (bookshelf faulting). Additionally, models of stress changes and seismicity induced by recent dykes in one sector of the Afar triple junction provide poor fit to the observed strike-slip earthquakes. Instead we explain these patterns as rift-perpendicular shearing at the tips of spreading rifts where extensional strains terminate against less stretched lithosphere. Our results demonstrate that rift-perpendicular strike-slip faulting between rift segments achieves plate boundary linkage during incipient seafloor spreading.

  10. Mechanics of distributed fault and block rotation

    NASA Technical Reports Server (NTRS)

    Nur, A.; Scotti, O.; Ron, H.

    1989-01-01

    Paleomagnetic data, structural geology, and rock mechanics are used to explore the validity and significance of the block rotation concept. The analysis is based on data from Northern Israel, where fault slip and spacing are used to predict block rotation; the Mojave Desert, with well documented strike-slip sets; the Lake Mead, Nevada fault system with well-defined sets of strike-slip faults; and the San Gabriel Mountains domain with a multiple set of strike-slip faults. The results of the analysis indicate that block rotations can have a profound influence on the interpretation of geodetic measurments and the inversion of geodetic data. Furthermore, the block rotations and domain boundaries may be involved in creating the heterogeneities along active fault systems which may be responsible for the initiation and termination of earthquake rupture.

  11. Fault compaction and overpressured faults: results from a 3-D model of a ductile fault zone

    NASA Astrophysics Data System (ADS)

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

    2003-10-01

    investigated. Significant leakage perpendicular to the fault strike (in the case of a young fault), or cracks hydraulically linking the fault core to the damaged zone (for a mature fault) are probable mechanisms for keeping the faults strong and might play a significant role in modulating fault pore pressures. Therefore, fault-normal hydraulic properties of fault zones should be a future focus of field and numerical experiments.

  12. The Dauki Thrust Fault and the Shillong Anticline: An incipient plate boundary in NE India?

    NASA Astrophysics Data System (ADS)

    Ferguson, E. K.; Seeber, L.; Steckler, M. S.; Akhter, S. H.; Mondal, D.; Lenhart, A.

    2012-12-01

    The Shillong Massif is a regional contractional structure developing across the Assam sliver of the Indian plate near the Eastern Syntaxis between the Himalaya and Burma arcs. Faulting associated with the Shillong Massif is a major source of earthquake hazard. The massif is a composite basement-cored asymmetric anticline and is 100km wide, >350km long and 1.8km high. The high relief southern limb preserves a Cretaceous-Paleocene passive margin sequence despite extreme rainfall while the gentler northern limb is devoid of sedimentary cover. This asymmetry suggests southward growth of the structure. The Dauki fault along the south limb builds this relief. From the south-verging structure, we infer a regional deeply-rooted north-dipping blind thrust fault. It strikes E-W and obliquely intersects the NE-SW margin of India, thus displaying three segments: Western, within continental India; Central, along the former passive margin; and Eastern, overridden by the west-verging Burma accretion system. We present findings from recent geologic fieldwork on the western and central segments. The broadly warped erosional surface of the massif defines a single anticline in the central segment, east of the intersection with the hinge zone of the continental margin buried by the Ganges-Brahmaputra Delta. The south limb of the anticline forms a steep topographic front, but is even steeper structurally as defined by the Cretaceous-Eocene cover. Below it, Sylhet Trap Basalts intrude and cover Precambrian basement. Dikes, presumably parallel to the rifted margin, are also parallel to the front, suggesting thrust reactivation of rift-related faults. Less competent Neogene clastics are preserved only near the base of the mountain front. Drag folds in these rocks suggest north-vergence and a roof thrust above a blind thrust wedge floored by the Dauki thrust fault. West of the hinge zone, the contractional structure penetrates the Indian continent and bifurcates. After branching into the

  13. Quantifying Anderson's fault types

    USGS Publications Warehouse

    Simpson, R.W.

    1997-01-01

    Anderson [1905] explained three basic types of faulting (normal, strike-slip, and reverse) in terms of the shape of the causative stress tensor and its orientation relative to the Earth's surface. Quantitative parameters can be defined which contain information about both shape and orientation [Ce??le??rier, 1995], thereby offering a way to distinguish fault-type domains on plots of regional stress fields and to quantify, for example, the degree of normal-faulting tendencies within strike-slip domains. This paper offers a geometrically motivated generalization of Angelier's [1979, 1984, 1990] shape parameters ?? and ?? to new quantities named A?? and A??. In their simple forms, A?? varies from 0 to 1 for normal, 1 to 2 for strike-slip, and 2 to 3 for reverse faulting, and A?? ranges from 0?? to 60??, 60?? to 120??, and 120?? to 180??, respectively. After scaling, A?? and A?? agree to within 2% (or 1??), a difference of little practical significance, although A?? has smoother analytical properties. A formulation distinguishing horizontal axes as well as the vertical axis is also possible, yielding an A?? ranging from -3 to +3 and A?? from -180?? to +180??. The geometrically motivated derivation in three-dimensional stress space presented here may aid intuition and offers a natural link with traditional ways of plotting yield and failure criteria. Examples are given, based on models of Bird [1996] and Bird and Kong [1994], of the use of Anderson fault parameters A?? and A?? for visualizing tectonic regimes defined by regional stress fields. Copyright 1997 by the American Geophysical Union.

  14. Interacting faults

    NASA Astrophysics Data System (ADS)

    Peacock, D. C. P.; Nixon, C. W.; Rotevatn, A.; Sanderson, D. J.; Zuluaga, L. F.

    2017-04-01

    The way that faults interact with each other controls fault geometries, displacements and strains. Faults rarely occur individually but as sets or networks, with the arrangement of these faults producing a variety of different fault interactions. Fault interactions are characterised in terms of the following: 1) Geometry - the spatial arrangement of the faults. Interacting faults may or may not be geometrically linked (i.e. physically connected), when fault planes share an intersection line. 2) Kinematics - the displacement distributions of the interacting faults and whether the displacement directions are parallel, perpendicular or oblique to the intersection line. Interacting faults may or may not be kinematically linked, where the displacements, stresses and strains of one fault influences those of the other. 3) Displacement and strain in the interaction zone - whether the faults have the same or opposite displacement directions, and if extension or contraction dominates in the acute bisector between the faults. 4) Chronology - the relative ages of the faults. This characterisation scheme is used to suggest a classification for interacting faults. Different types of interaction are illustrated using metre-scale faults from the Mesozoic rocks of Somerset and examples from the literature.

  15. The Hills are Alive: Dynamic Ridges and Valleys in a Strike-Slip Environment

    NASA Astrophysics Data System (ADS)

    Duvall, A. R.; Tucker, G. E.

    2014-12-01

    Strike-slip fault zones have long been known for characteristic landforms such as offset and deflected rivers, linear strike-parallel valleys, and shutter ridges. Despite their common presence, questions remain about the mechanics of how these landforms arise or how their form varies as a function of slip rate, geomorphic process, or material properties. We know even less about what happens far from the fault, in drainage basin headwaters, as a result of strike-slip motion. Here we explore the effects of horizontal fault slip rate, bedrock erodibility, and hillslope diffusivity on river catchments that drain across an active strike-slip fault using the CHILD landscape evolution model. Model calculations demonstrate that lateral fault motion induces a permanent state of landscape disequilibrium brought about by fault offset-generated river lengthening alternating with abrupt shortening due to stream capture. This cycle of shifting drainage patterns and base level change continues until fault motion ceases thus creating a perpetual state of transience unique to strike-slip systems. Our models also make the surprising prediction that, in some cases, hillslope ridges oriented perpendicular to the fault migrate laterally in conjunction with fault motion. Ridge migration happens when slip rate is slow enough and/or diffusion and river incision are fast enough that the hillslopes can respond to the disequilibrium brought about by strike-slip motion. In models with faster slip rates, stronger rocks or less-diffusive hillslopes, ridge mobility is limited or arrested despite the fact that the process of river lengthening and capture continues. Fast-slip cases also develop prominent steep fault-facing hillslope facets proximal to the fault valley and along-strike topographic profiles with reduced local relief between ridges and valleys. Our results demonstrate the dynamic nature of strike-slip landscapes that vary systematically with a ratio of bedrock erodibility (K) and

  16. Volcanic facies architecture of an intra-arc strike-slip basin, Santa Rita Mountains, Southern Arizona

    NASA Astrophysics Data System (ADS)

    Busby, Cathy J.; Bassett, Kari N.

    2007-09-01

    The three-dimensional arrangement of volcanic deposits in strike-slip basins is not only the product of volcanic processes, but also of tectonic processes. We use a strike-slip basin within the Jurassic arc of southern Arizona (Santa Rita Glance Conglomerate) to construct a facies model for a strike-slip basin dominated by volcanism. This model is applicable to releasing-bend strike-slip basins, bounded on one side by a curved and dipping strike-slip fault, and on the other by curved normal faults. Numerous, very deep unconformities are formed during localized uplift in the basin as it passes through smaller restraining bends along the strike-slip fault. In our facies model, the basin fill thins and volcanism decreases markedly away from the master strike-slip fault (“deep” end), where subsidence is greatest, toward the basin-bounding normal faults (“shallow” end). Talus cone-alluvial fan deposits are largely restricted to the master fault-proximal (deep) end of the basin. Volcanic centers are sited along the master fault and along splays of it within the master fault-proximal (deep) end of the basin. To a lesser degree, volcanic centers also form along the curved faults that form structural highs between sub-basins and those that bound the distal ends of the basin. Abundant volcanism along the master fault and its splays kept the deep (master fault-proximal) end of the basin overfilled, so that it could not provide accommodation for reworked tuffs and extrabasinally-sourced ignimbrites that dominate the shallow (underfilled) end of the basin. This pattern of basin fill contrasts markedly with that of nonvolcanic strike-slip basins on transform margins, where clastic sedimentation commonly cannot keep pace with subsidence in the master fault-proximal end. Volcanic and subvolcanic rocks in the strike-slip basin largely record polygenetic (explosive and effusive) small-volume eruptions from many vents in the complexly faulted basin, referred to here as multi

  17. Shell Tectonics: A Mechanical Model for Strike-slip Displacement on Europa

    NASA Technical Reports Server (NTRS)

    Rhoden, Alyssa Rose; Wurman, Gilead; Huff, Eric M.; Manga, Michael; Hurford, Terry A.

    2012-01-01

    We introduce a new mechanical model for producing tidally-driven strike-slip displacement along preexisting faults on Europa, which we call shell tectonics. This model differs from previous models of strike-slip on icy satellites by incorporating a Coulomb failure criterion, approximating a viscoelastic rheology, determining the slip direction based on the gradient of the tidal shear stress rather than its sign, and quantitatively determining the net offset over many orbits. This model allows us to predict the direction of net displacement along faults and determine relative accumulation rate of displacement. To test the shell tectonics model, we generate global predictions of slip direction and compare them with the observed global pattern of strike-slip displacement on Europa in which left-lateral faults dominate far north of the equator, right-lateral faults dominate in the far south, and near-equatorial regions display a mixture of both types of faults. The shell tectonics model reproduces this global pattern. Incorporating a small obliquity into calculations of tidal stresses, which are used as inputs to the shell tectonics model, can also explain regional differences in strike-slip fault populations. We also discuss implications for fault azimuths, fault depth, and Europa's tectonic history.

  18. Magma storage in a strike-slip caldera

    PubMed Central

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-01-01

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions. PMID:27447932

  19. Magma storage in a strike-slip caldera.

    PubMed

    Saxby, J; Gottsmann, J; Cashman, K; Gutiérrez, E

    2016-07-22

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

  20. 77 FR 20622 - N.E.W. Hydro LLC; Notice of Application for Amendment of License and Soliciting Comments, Motions...

    Federal Register 2010, 2011, 2012, 2013, 2014

    2012-04-05

    ... DEPARTMENT OF ENERGY Federal Energy Regulatory Commission [Project No. 2744-041; 2744-042] N.E.W....: 2744-041 & 042. c. Date Filed: March 14, 2012. d. Applicant: N.E.W. Hydro LLC. e. Name of Project..., 16 U.S.C. 791(a)-825(r). h. Applicant Contact: Mr. Scott Klabunde, P.O. Box 167, 116 N. State Street...

  1. Physicians' strikes--a rejoinder.

    PubMed Central

    Glick, S M

    1985-01-01

    The author, a physician, rejects a previous defence of a doctors' strike. There is little justification for strikes in general, still less for doctors' strikes, he claims. Should not doctors rather 'stand above the common herd' and set an example, he asks. Furthermore the whole idea of strikes in which a third and innocent party is deliberately punished in order to apply pressure on someone else is a 'a bizarre ethic indeed' and not to his knowledge justified under any ethical theory. PMID:4078858

  2. Evolving transpressional strain fields along the San Andreas fault in southern California: implications for fault branching, fault dip segmentation and strain partitioning

    NASA Astrophysics Data System (ADS)

    Bergh, Steffen; Sylvester, Arthur; Damte, Alula; Indrevær, Kjetil

    2014-05-01

    The San Andreas fault in southern California records only few large-magnitude earthquakes in historic time, and the recent activity is confined primarily on irregular and discontinuous strike-slip and thrust fault strands at shallow depths of ~5-20 km. Despite this fact, slip along the San Andreas fault is calculated to c. 35 mm/yr based on c.160 km total right lateral displacement for the southern segment of the fault in the last c. 8 Ma. Field observations also reveal complex fault strands and multiple events of deformation. The presently diffuse high-magnitude crustal movements may be explained by the deformation being largely distributed along more gently dipping reverse faults in fold-thrust belts, in contrast to regions to the north where deformation is less partitioned and localized to narrow strike-slip fault zones. In the Mecca Hills of the Salton trough transpressional deformation of an uplifted segment of the San Andreas fault in the last ca. 4.0 My is expressed by very complex fault-oblique and fault-parallel (en echelon) folding, and zones of uplift (fold-thrust belts), basement-involved reverse and strike-slip faults and accompanying multiple and pervasive cataclasis and conjugate fracturing of Miocene to Pleistocene sedimentary strata. Our structural analysis of the Mecca Hills addresses the kinematic nature of the San Andreas fault and mechanisms of uplift and strain-stress distribution along bent fault strands. The San Andreas fault and subsidiary faults define a wide spectrum of kinematic styles, from steep localized strike-slip faults, to moderate dipping faults related to oblique en echelon folds, and gently dipping faults distributed in fold-thrust belt domains. Therefore, the San Andreas fault is not a through-going, steep strike-slip crustal structure, which is commonly the basis for crustal modeling and earthquake rupture models. The fault trace was steep initially, but was later multiphase deformed/modified by oblique en echelon folding

  3. Seven big strike-slip earthquakes

    NASA Astrophysics Data System (ADS)

    Lohman, R. B.; Simons, M.; Pritchard, M. E.

    2003-12-01

    We examine seven large (Mw > 7) strike-slip earthquakes that occurred since the beginning of ERS 1 and 2 missions. We invert GPS observations and InSAR interferograms and azimuth offsets for coseismic slip distributions. We explore two refinements to the traditional least-squares inversion technique with roughness constraints. First, we diverge from the usual definition of ``roughness'' as the average roughness over the entire fault plane, and allow ``variable smoothing'' constraints. Variable smoothing allows our inversion to select models that are more complex in regions that are well-resolved by the data, while still damping regions that are poorly resolved. Second, we choose our smoothing parameters using the jR_i criterion. The jR_i criterion draws on the theory behind cross-validation and the bootstrap method. We examine the theoretical basis behind such methods and use an analytical approximation technique for linear problems. We provide maps of model variance and spatial averaging scale over the fault plane, to explicitly show which features in our slip models are robust. We examine the 1992 Landers (CA), 1995 Sakhalin (Russia), 1995 Kobe (Japan), 1997 Ardekul (Iran), 1997 Manyi (Tibet), 1999 Hector Mine (CA), and 2001 Kunlun (Tibet) earthquakes. We compare features of the slip distributions such as the depth distribution of slip, the inferred magnitude and the degree of heterogeneity of slip over the fault plane, as resolved by the available InSAR and GPS data. We end with a brief description of the data coverage required for future earthquakes of similar size if we want to infer some of the above quantities to within a given confidence interval. We describe both the number of InSAR scenes and the distribution of GPS points that would be required, based on theoretical treatments of the fault plane/data point geometry using the jR_i method.

  4. The Dauki Fault and its Shillong-Sylhet Thrust Anticline-Foredeep Pair: A Footwall Reactivation along the Progressive Burma-India Collision

    NASA Astrophysics Data System (ADS)

    Seeber, L.; Ferguson, E. K.; Grall, C.; Steckler, M. S.; Betka, P. M.; Akhter, S. H.

    2016-12-01

    The Shillong Massif and the Sylhet basin form a south-verging anticline-foredeep pair associated with the E-W striking Dauki fault. Fold geometry and receiver-functions identify it as a blind thrust fault dipping north into the craton. This contractional structure may represent an incipient forward jump of the Himalayan front to the trailing margin of India. The Shillong Massif is one of the largest known basement-cored anticlines and is delineated by a relict erosional surface and folded strata. Where best exposed in the central segment, it has a steep southern limb and a gentle northern limb. This asymmetry is mirrored in the Sylhet foredeep, with a steep north flank and low dip south flank. The combined structure has 5 km of relief, most of which developed during the Quaternary. This foredeep overprints a thicker sequence that records the progradation of the Brahmaputra delta. These older strata thicken southward as expected at a passive margin. The Sylhet Traps, which are coeval with India-Antarctica rifting, outcrop along the southern limb of the anticline. Associated basalt dikes are also parallel to the E-W Dauki structure. The basal Cretaceous-Paleogene shallow marine strata onlap northward the regional unconformity above the cratonic and trap rocks. This suggests that the Dauki thrust front traces an E-W segment of the passive margin and former rift. The IndoBurma forearc overrides the Dauki structure 200 km farther west on the foredeep (south) side than on the massif (north) side of the Dauki fault. Much of this differential advance of the Burma deformation front predates the Dauki foredeep and was a response to the shape of the passive margin of India. This deformation front, known locally as the Haflong Fault, crosses obliquely the Dauki thrust front. Evidence includes contractional structures verging up-dip onto the forelimb of the Shillong anticline. The Shillong Massif-Sylhet Foredeep pair has a strong gravity signature that can be traced eastward

  5. Strike-parallel and strike-normal coordinate system around geometrically complicated rupture traces: use by NGA-West2 and further improvements

    USGS Publications Warehouse

    Spudich, Paul A.; Chiou, Brian

    2015-01-01

    We present a two-dimensional system of generalized coordinates for use with geometrically complex fault ruptures that are neither straight nor continuous. The coordinates are a generalization of the conventional strike-normal and strike-parallel coordinates of a single straight fault. The presented conventions and formulations are applicable to a single curved trace, as well as multiple traces representing the rupture of branching faults or noncontiguous faults. An early application of our generalized system is in the second round of the Next Generation of Ground-Motion Attenuation Model project for the Western United States (NGA-West2), where they were used in the characterization of the hanging-wall effects. We further improve the NGA-West2 strike-parallel formulation for multiple rupture traces with a more intuitive definition of the nominal strike direction. We also derive an analytical expression for the gradient of the generalized strike-normal coordinate. The direction of this gradient may be used as the strike-normal direction in the study of polarization effects on ground motions.

  6. Seismic Hazard and Fault Length

    NASA Astrophysics Data System (ADS)

    Black, N. M.; Jackson, D. D.; Mualchin, L.

    2005-12-01

    If mx is the largest earthquake magnitude that can occur on a fault, then what is mp, the largest magnitude that should be expected during the planned lifetime of a particular structure? Most approaches to these questions rely on an estimate of the Maximum Credible Earthquake, obtained by regression (e.g. Wells and Coppersmith, 1994) of fault length (or area) and magnitude. Our work differs in two ways. First, we modify the traditional approach to measuring fault length, to allow for hidden fault complexity and multi-fault rupture. Second, we use a magnitude-frequency relationship to calculate the largest magnitude expected to occur within a given time interval. Often fault length is poorly defined and multiple faults rupture together in a single event. Therefore, we need to expand the definition of a mapped fault length to obtain a more accurate estimate of the maximum magnitude. In previous work, we compared fault length vs. rupture length for post-1975 earthquakes in Southern California. In this study, we found that mapped fault length and rupture length are often unequal, and in several cases rupture broke beyond the previously mapped fault traces. To expand the geologic definition of fault length we outlined several guidelines: 1) if a fault truncates at young Quaternary alluvium, the fault line should be inferred underneath the younger sediments 2) faults striking within 45° of one another should be treated as a continuous fault line and 3) a step-over can link together faults at least 5 km apart. These definitions were applied to fault lines in Southern California. For example, many of the along-strike faults lines in the Mojave Desert are treated as a single fault trending from the Pinto Mountain to the Garlock fault. In addition, the Rose Canyon and Newport-Inglewood faults are treated as a single fault line. We used these more generous fault lengths, and the Wells and Coppersmith regression, to estimate the maximum magnitude (mx) for the major faults in

  7. 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.

  8. Reports on block rotations, fault domains and crustal deformation

    NASA Technical Reports Server (NTRS)

    Nur, Amos

    1990-01-01

    Studies of block rotations, fault domains and crustal deformation in the western United States, Israel, and China are discussed. Topics include a three-dimensional model of crustal fracture by distributed fault sets, distributed deformation and block rotation in 3D, stress field rotation, and multiple strike slip fault sets.

  9. Fault linkage and continental breakup

    NASA Astrophysics Data System (ADS)

    Cresswell, Derren; Lymer, Gaël; Reston, Tim; Stevenson, Carl; Bull, Jonathan; Sawyer, Dale; Morgan, Julia

    2017-04-01

    The magma-poor rifted margin off the west coast of Galicia (NW Spain) has provided some of the key observations in the development of models describing the final stages of rifting and continental breakup. In 2013, we collected a 68 x 20 km 3D seismic survey across the Galicia margin, NE Atlantic. Processing through to 3D Pre-stack Time Migration (12.5 m bin-size) and 3D depth conversion reveals the key structures, including an underlying detachment fault (the S detachment), and the intra-block and inter-block faults. These data reveal multiple phases of faulting, which overlap spatially and temporally, have thinned the crust to between zero and a few km thickness, producing 'basement windows' where crustal basement has been completely pulled apart and sediments lie directly on the mantle. Two approximately N-S trending fault systems are observed: 1) a margin proximal system of two linked faults that are the upward extension (breakaway faults) of the S; in the south they form one surface that splays northward to form two faults with an intervening fault block. These faults were thus demonstrably active at one time rather than sequentially. 2) An oceanward relay structure that shows clear along strike linkage. Faults within the relay trend NE-SW and heavily dissect the basement. The main block bounding faults can be traced from the S detachment through the basement into, and heavily deforming, the syn-rift sediments where they die out, suggesting that the faults propagated up from the S detachment surface. Analysis of the fault heaves and associated maps at different structural levels show complementary fault systems. The pattern of faulting suggests a variation in main tectonic transport direction moving oceanward. This might be interpreted as a temporal change during sequential faulting, however the transfer of extension between faults and the lateral variability of fault blocks suggests that many of the faults across the 3D volume were active at least in part

  10. 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

  11. Structural styles of Paleozoic intracratonic fault reactivation: A case study of the Grays Point fault zone in southeastern Missouri, USA

    USGS Publications Warehouse

    Clendenin, C.W.; Diehl, S.F.

    1999-01-01

    A pronounced, subparallel set of northeast-striking faults occurs in southeastern Missouri, but little is known about these faults because of poor exposure. The Commerce fault system is the southernmost exposed fault system in this set and has an ancestry related to Reelfoot rift extension. Recent published work indicates that this fault system has a long history of reactivation. The northeast-striking Grays Point fault zone is a segment of the Commerce fault system and is well exposed along the southeast rim of an inactive quarry. Our mapping shows that the Grays Point fault zone also has a complex history of polyphase reactivation, involving three periods of Paleozoic reactivation that occurred in Late Ordovician, Devonian, and post-Mississippian. Each period is characterized by divergent, right-lateral oblique-slip faulting. Petrographic examination of sidwall rip-out clasts in calcite-filled faults associated with the Grays Point fault zone supports a minimum of three periods of right-lateral oblique-slip. The reported observations imply that a genetic link exists between intracratonic fault reactivation and strain produced by Paleozoic orogenies affecting the eastern margin of Laurentia (North America). Interpretation of this link indicate that right-lateral oblique-slip has occurred on all of the northeast-striking faults in southeastern Missouri as a result of strain influenced by the convergence directions of the different Paleozoic orogenies.

  12. Modern Protection Against Lightning Strikes

    NASA Astrophysics Data System (ADS)

    Moore, C.

    2005-05-01

    The application of science to provide protection against lightning strikes began around 1750 when Benjamin Franklin who invented the lightning rod in an effort to discharge thunderclouds. Instead of preventing lightning as he expected, his rods have been quite successful as strike receptors, intercepting cloud-to ground discharges and conducting them to Earth without damage to the structures on which they are mounted. In the years since Franklin's invention there has been little attention paid to the rod configuration that best serves as a strike receptor but Franklin's original ideas continue to be rediscovered and promoted. Recent measurements of the responses of variously configured rods to nearby strikes indicate that sharp-tipped rods are not the optimum configuration to serve as strike receptors since the ionization of the air around their tips limits the strength of the local electric fields created by an approaching lightning leader. In these experiments, fourteen blunt-tipped rods exposed in strike-reception competitions with nearby sharp-tipped rods were struck by lightning but none of the sharp-tipped rods were struck.

  13. Evolving geometrical heterogeneities of fault trace data

    NASA Astrophysics Data System (ADS)

    Wechsler, Neta; Ben-Zion, Yehuda; Christofferson, Shari

    2010-08-01

    We perform a systematic comparative analysis of geometrical fault zone heterogeneities using derived measures from digitized fault maps that are not very sensitive to mapping resolution. We employ the digital GIS map of California faults (version 2.0) and analyse the surface traces of active strike-slip fault zones with evidence of Quaternary and historic movements. Each fault zone is broken into segments that are defined as a continuous length of fault bounded by changes of angle larger than 1°. Measurements of the orientations and lengths of fault zone segments are used to calculate the mean direction and misalignment of each fault zone from the local plate motion direction, and to define several quantities that represent the fault zone disorder. These include circular standard deviation and circular standard error of segments, orientation of long and short segments with respect to the mean direction, and normal separation distances of fault segments. We examine the correlations between various calculated parameters of fault zone disorder and the following three potential controlling variables: cumulative slip, slip rate and fault zone misalignment from the plate motion direction. The analysis indicates that the circular standard deviation and circular standard error of segments decrease overall with increasing cumulative slip and increasing slip rate of the fault zones. The results imply that the circular standard deviation and error, quantifying the range or dispersion in the data, provide effective measures of the fault zone disorder, and that the cumulative slip and slip rate (or more generally slip rate normalized by healing rate) represent the fault zone maturity. The fault zone misalignment from plate motion direction does not seem to play a major role in controlling the fault trace heterogeneities. The frequency-size statistics of fault segment lengths can be fitted well by an exponential function over the entire range of observations.

  14. Fault finder

    DOEpatents

    Bunch, Richard H.

    1986-01-01

    A fault finder for locating faults along a high voltage electrical transmission line. Real time monitoring of background noise and improved filtering of input signals is used to identify the occurrence of a fault. A fault is detected at both a master and remote unit spaced along the line. A master clock synchronizes operation of a similar clock at the remote unit. Both units include modulator and demodulator circuits for transmission of clock signals and data. All data is received at the master unit for processing to determine an accurate fault distance calculation.

  15. A new Triassic shortening-extrusion tectonic model for Central-EasternAsia: Structural, geochronological and paleomagnetic investigations in the Xilamulun Fault (North China)

    NASA Astrophysics Data System (ADS)

    Zhao, Pan; Faure, Michel; Chen, Yan; Xu, Bei

    2017-04-01

    At the northern margin of the North China Block (NCB), the Xilamulun Fault (XMF) is a key belt to decipher the tectonic evolution of Central-Eastern Asia, as it records the Paleozoic final closure of the Paleo-Asian Ocean, and localizes a Late Triassic intracontinental deformation. In this study, structural analysis, 40Ar-39Ar dating, and paleomagnetic studies were performed to investigate the kinematics of the XMF and to further discuss its Triassic geodynamic significance in the Central-Eastern Asia framework after the Paleozoic Central Asian Orogenic evolution. The structural analyses reveal two phases of ductile deformation. The first one (D1), which displays N-verging and E-W trending folds, is related to the Early Paleozoic collisional event between the NCB and the Songliao-Hunshandake Block (SHB). The second phase (D2) displays a high-angle foliation and a pervasive sub-horizontalE-W stretching lineation with kinematic criteria indicative of dextral strike-slip shearing. The 40Ar-39Ar dating on mylonitic granite places the main shearing event around 227-209 Ma. This D2 shearing is coeval with that of the dextral strike-slip Bayan Obo-Chifeng Fault (BCF) and the Chicheng-Fengning-Longhua Fault to the south, which together constitute a dextral shearing fault system on the northern margin of the NCB during the Late Triassic. The paleomagnetic study performed on the Middle Permian Guangxingyuan pluton, located between the XMF and BCF, documents a local clockwise rotation of this pluton with respect to the NCB and SHB. Our multidisciplinary study suggests anNNW-SSE shortening and strike-slip shearing dominated tectonic setting on the northern margin of the NCB during the Late Triassic. Combining the contemporaneous dextral strike-slip movements of the XMF and BCF in northern China and the sinistral strike-slip movement of East Gobi Fault (EGF) in southeastern Mongolia with the large-scale tectonic framework, a Late Triassic NNW-SSE shortening-eastward extrusion

  16. Modeling along-axis variations in fault architecture in the Main Ethiopian Rift: implications for Nubia-Somalia kinematics

    NASA Astrophysics Data System (ADS)

    Erbello, Asfaw; Corti, Giacomo; Sani, Federico; Kidane, Tesfaye

    2016-04-01

    The Main Ethiopian Rift (MER), at the northern termination of the East African Rift, is an ideal locale where to get insights into the long-term motion between Nubia and Somalia. The rift is indeed one of the few places along the plate boundary where the deformation is narrow: its evolution is thus strictly related to the kinematics of the two major plates, whereas south of the Turkana depression a two-plate model for the EARS is too simplistic as extension occurs both along the Western and Eastern branches and different microplates are present between the two major plates. Despite its importance, the kinematics responsible for development and evolution of the MER is still a matter of debate: indeed, whereas the Quaternary-present kinematics of rifting is rather well constrained, the plate kinematics driving the initial, Mio-Pliocene stages of extension is still not clear, and different hypothesis have been put forward, including: polyphase rifting, with a change in direction of extension from NW-SE extension to E-W extension; constant Miocene-recent NW-SE extension; constant Miocene-recent NE-SW extension; constant, post-11 Ma extension consistent with the GPS-derived kinematics (i.e., roughly E-W to ESE-WNW). To shed additional light on this controversy and to test these different hypothesis, in this contribution we use new crustal-scale analogue models to analyze the along-strike variations in fault architecture in the MER and their relations with the rift trend, plate motion and the resulting Miocene-recent kinematics of rifting. The extension direction is indeed one of the most important parameters controlling the architecture of continental rifts and the relative abundance and orientation of different fault sets that develop during oblique rifting is typically a function of the angle between the extension direction and the orthogonal to the rift trend (i.e., the obliquity angle). Since the trend of the MER varies along strike, and consequently it is

  17. 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.

  18. Lightning strike protection of composites

    NASA Astrophysics Data System (ADS)

    Gagné, Martin; Therriault, Daniel

    2014-01-01

    Aircraft structures are being redesigned to use fiber-reinforced composites mainly due to their high specific stiffness and strength. One of the main drawbacks from changing from electrically conductive metals to insulating or semi-conducting composites is the higher vulnerability of the aircraft to lightning strike damage. The current protection approach consists of bonding a metal mesh to the surface of the composite structure, but this weight increase negatively impact the fuel efficiency. This review paper presents an overview of the lightning strike problematic, the regulations, the lightning damage to composite, the current protection solutions and other material or technology alternatives. Advanced materials such as polymer-based nanocomposites and carbon nanotube buckypapers are promising candidates for lightweight lightning strike protection technology.

  19. Fatal lightning strikes in Malaysia.

    PubMed

    Murty, O P; Kian, Chong Kah; Ari Husin, Mohammed Husrul; Nanta Kumar, Ranjeev Kumar; Mohammed Yusuf, Wan Yuhana W

    2009-09-01

    Lightning strike is a natural phenomenon with potentially devastating effects and represents one of the important causes of deaths from environmental phenomena. Almost every organ system may be affected as lightning current passes through the human body taking the shortest pathways between the contact points. A 10 years retrospective study (1996-2005) was conducted at University Hospital Kuala Lumpur (20 cases) also including cases during last 3 years from Hospital Tengku Ampuan Rahimah, Klang (7 cases) from the autopsy reports at Forensic Pathology Units of these 2 hospitals. Both these hospitals are attached to University of Malaya. There were 27 fatal cases of lightning strike with male preponderance(92.59%) and male to female ratio of 12.5:1. Majority of victims of lightning strike were from the age group between 30 and 39 years old. Most of the victims were foreign workers. Indonesians workers contributed to 59.26% of overall cases. Majority of them were construction workers who attributed i.e.11 of 27 cases (40.74%). Most of the victims were brought in dead (37.04%). In majority of the cases the lightning incidence occurred in the evenings, with the frequency of 15 of 27 cases (62.5%). The month of December represented with the highest number of cases (5 cases of 23 cases); 2004 had the highest incidence of lightning strike which was 5 (19.23%). Lightning strike incidence occurred when victims had taken shelter (25.9%) under trees or shades. Lightning strike in open areas occurred in 10 of 27 cases (37.0%). Head and neck were the most commonly affected sites with the incidence of 77.78% and 74% respectively in all the victims. Only 29.63% of the cases presented with ear bleeding.

  20. Cardiac Effects of Lightning Strikes

    PubMed Central

    Khan, Sarosh; Ahmad, Mahmood; Fayed, Hossam; Bogle, Richard

    2017-01-01

    Lightning strikes are a common and leading cause of morbidity and mortality. Multiple organ systems can be involved, though the effects of the electrical current on the cardiovascular system are one of the main modes leading to cardiorespiratory arrest in these patients. Cardiac effects of lightning strikes can be transient or persistent, and include benign or life-threatening arrhythmias, inappropriate therapies from cardiac implantable electronic devices, cardiac ischaemia, myocardial contusion, pericardial disease, aortic injury, as well as cardiomyopathy with associated ventricular failure. Prolonged resuscitation can lead to favourable outcomes especially in young and previously healthy victims. PMID:29018518

  1. Air traffic controller lightning strike.

    PubMed Central

    Spieth, M. E.; Kimura, R. L.; Schryer, T. D.

    1994-01-01

    Andersen Air Force Base in Guam boasts the tallest control tower in the Air Force. In 1986, an air traffic controller was struck by lightning as the bolt proceeded through the tower. Although he received only a backache, the lightning left a hole with surrounding scorch marks on his fatigue shirt and his undershirt. The lightning strike also ignited a portion of the field lighting panel, which caused the runway lights to go out immediately. Lack of a lightning rod is the most likely reason the controller was struck. Proper precautions against lightning strikes can prevent such occupational safety hazards. PMID:7966436

  2. Fluid involvement in normal faulting

    NASA Astrophysics Data System (ADS)

    Sibson, Richard H.

    2000-04-01

    fluid overpressures are localised within the fault zone and the surrounding rock retains significant tensile strength. Migrating pore fluids interact both statically and dynamically with normal faults. Static effects include consideration of the relative permeability of the faults with respect to the country rock, and juxtaposition effects which determine whether a fault is transmissive to flow or acts as an impermeable barrier. Strong directional permeability is expected in the subhorizontal σ2 direction parallel to intersections between minor faults, extension fractures, and stylolites. Three dynamic mechanisms tied to the seismic stress cycle may contribute to fluid redistribution: (i) cycling of mean stress coupled to shear stress, sometimes leading to postfailure expulsion of fluid from vertical fractures; (ii) suction pump action at dilational fault jogs; and, (iii) fault-valve action when a normal fault transects a seal capping either uniformly overpressured crust or overpressures localised to the immediate vicinity of the fault zone at depth. The combination of σ2 directional permeability with fluid redistribution from mean stress cycling may lead to hydraulic communication along strike, contributing to the protracted earthquake sequences that characterise normal fault systems.

  3. 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

  4. Eyeing New York's Newspaper Strike.

    ERIC Educational Resources Information Center

    Fishleder, Paul

    The New York newspaper strike of 1978 was the direct result of a series of events that started in 1923 when the pressmen's union established a system that provided a minimum fixed number of pressmen per press unit and legitimized a loose labor pool. From that time, the number of pressmen increased through family-dominated union management that…

  5. The Mentawai forearc sliver off Sumatra: A model for a strike-slip duplex at a regional scale

    NASA Astrophysics Data System (ADS)

    Berglar, Kai; Gaedicke, Christoph; Ladage, Stefan; Thöle, Hauke

    2017-07-01

    At the Sumatran oblique convergent margin the Mentawai Fault and Sumatran Fault zones accommodate most of the trench parallel component of strain. These faults bound the Mentawai forearc sliver that extends from the Sunda Strait to the Nicobar Islands. Based on multi-channel reflection seismic data, swath bathymetry and high resolution sub-bottom profiling we identified a set of wrench faults obliquely connecting the two major fault zones. These wrench faults separate at least four horses of a regional strike-slip duplex forming the forearc sliver. Each horse comprises an individual basin of the forearc with differing subsidence and sedimentary history. Duplex formation started in Mid/Late Miocene southwest of the Sunda Strait. Initiation of new horses propagated northwards along the Sumatran margin over 2000 km until Early Pliocene. These results directly link strike-slip tectonics to forearc evolution and may serve as a model for basin evolution in other oblique subduction settings.

  6. Normal-Faulting in Madagascar: Another Round of Continental Rifting?

    NASA Astrophysics Data System (ADS)

    Wysession, M. E.; Pratt, M. J.; Tsiriandrimanana, R.; Andriampenomanana Ny Ony, F. S. T.; Nyblade, A.; Durrheim, R. J.; Tilmann, F. J.; Rumpker, G.; Rambolamanana, G.; Aleqabi, G. I.; Shore, P.

    2017-12-01

    Analyses of seismicity and seismic structure within Madagascar suggest the current occurrence of crustal extension, which may be related to continental rifting associated with a diffuse boundary between the Somalia and Lwandle tectonic plates. Madagascar has participated in two major rifting events as part of the break-up of Gondwana: the break-away of Greater India (Madagascar, India, the Seychelles) away from mainland Africa during the Jurassic and the break-away of India from Madagascar during the Cretaceous. Seismic activity and the structures obtained from it, using data from the 2-year (2011-2013) MACOMO project, suggest that this break-up may not be finished, and that continental rifts may be developing again. There are fairly high levels of intraplate seismicity within Madagascar: over 800 events located during the 22 months of the deployment. For comparison, a 2-year deployment of seismometers within the upper Midwest of the U.S. yielded just 12 intraplate earthquakes. While the Madagascar seismicity occurs across the island, it is strongly concentrated in the central region, where Cenozoic volcanism has occurred through the Holocene, and earthquakes align along N-S-trending lineations associated with N-S-trending pull-apart graben structures. The thickness of the crust is still >40 km in this region, but it is underlain by a large low-velocity structure within the lithosphere and asthenosphere that is observed in our studies of surface-wave, body-wave, and Pn-phase tomography. Normal faulting is not observed everywhere on the island, however; seismicity in the north is largely strike-slip, and seismicity in the south appears to be largely reverse faulting. Several studies have suggested that the diffuse boundary between the Somalia and Lwandle plates runs roughly E-W across Madagascar. Extensional faulting seems to predominate only within central Madagascar, likely associated with the current volcanic activity, which also appears to be associated with the

  7. Faulting along the southern margin of Reelfoot Lake, Tennessee

    USGS Publications Warehouse

    Van Arsdale, R.; Purser, J.; Stephenson, W.; Odum, J.

    1998-01-01

    The Reelfoot Lake basin, Tennessee, is structurally complex and of great interest seismologically because it is located at the junction of two seismicity trends of the New Madrid seismic zone. To better understand the structure at this location, a 7.5-km-long seismic reflection profile was acquired on roads along the southern margin of Reelfoot Lake. The seismic line reveals a westerly dipping basin bounded on the west by the Reelfoot reverse fault zone, the Ridgely right-lateral transpressive fault zone on the east, and the Cottonwood Grove right-lateral strike-slip fault in the middle of the basin. The displacement history of the Reelfoot fault zone appears to be the same as the Ridgely fault zone, thus suggesting that movement on these fault zones has been synchronous, perhaps since the Cretaceous. Since the Reelfoot and Ridgely fault systems are believed responsible for two of the mainshocks of 1811-1812, the fault history revealed in the Reelfoot Lake profile suggests that multiple mainshocks may be typical of the New Madrid seismic zone. The Ridgely fault zone consists of two northeast-striking faults that lie at the base of and within the Mississippi Valley bluff line. This fault zone has 15 m of post-Eocene, up-to-the-east displacement and appears to locally control the eastern limit of Mississippi River migration. The Cottonwood Grove fault zone passes through the center of the seismic line and has approximately 5 m up-to-the-east displacement. Correlation of the Cottonwood Grove fault with a possible fault scarp on the floor of Reelfoot Lake and the New Markham fault north of the lake suggests the Cottonwood Grove fault may change to a northerly strike at Reelfoot Lake, thereby linking the northeast-trending zones of seismicity in the New Madrid seismic zone.

  8. Characterization of Fluid Transfer Properties in a Transpressive Fault System: Chaîne des Matheux Fold-and-Thrust Belt and Enriquillo-Plantain Garden Fault Zone - Haiti

    NASA Astrophysics Data System (ADS)

    Wessels, R.; Ellouz-Zimmermann, N.; Rosenberg, C.; Hamon, Y.; Battani, A.; Bellahsen, N.; Deschamps, R.; Leroy, S. D.; Momplaisir, R.

    2016-12-01

    The NW - SE trending Chaîne des Matheux (CdM) comprises the onshore frontal thrust sheet of the SW-verging Haitian fold-and-thrust belt (HFTB). The HFTB's active deformation front is covered by sediments of the Cul-de-Sac plain and is bounded on the south by the E - W trending left-lateral Enriquillo-Plantain Garden fault zone (EPGFZ). Seismicity down to the junction between the two systems has been recorded during the 12 January 2010 Mw 7.0 Léogâne earthquake. Stratigraphic, structural and kinematic field data on a transect from the CdM to the EPGFZ indicate (N)NE - (S)SW oriented shortening, which is partitioned over 1) (N)NE-dipping oblique thrusts rooted in Cretaceous basement, 2) decollement levels in both latest Cretaceous and Paleogene limestones, and 3) by strike-slip and positive flower structures along the EPGFZ. We investigated the geometry and kinematics of both fault and fracture systems, which was coupled with sampling and analysis of fluid-derived mineralizations to constrain the timing and geological evolution. C & O isotope and whole-rock analyses have been performed to characterize the geochemistry of the source of these fluids. Raman spectroscopy and fluid-inclusion analyses has been applied to selected samples to comprehend the local burial history. Fluid and gas seepages along fault planes are qualitative indicators for transfer properties between different fault segments and their connectivity with deeper crustal or mantle reservoirs. Relative timing of structures in the CdM coupled with cathodoluminescence (CL) microscopy reveals three deformation phases, characterized by associated calcite veins that precipitated from oxidizing meteoric fluids. The deeply rooted frontal CdM thrust lacks mineralization, but fluids expelled from along-strike natural springs registered He and Ne isotope ratios suggesting a strong mantle-derived component. CL microscopy results on calcite veins from the EPGFZ's fault core imply fluid circulation in an

  9. Mountain front migration and drainage captures related to fault segment linkage and growth: The Polopos transpressive fault zone (southeastern Betics, SE Spain)

    NASA Astrophysics Data System (ADS)

    Giaconia, Flavio; Booth-Rea, Guillermo; Martínez-Martínez, José Miguel; Azañón, José Miguel; Pérez-Romero, Joaquín; Villegas, Irene

    2013-01-01

    The Polopos E-W- to ESE-WNW-oriented dextral-reverse fault zone is formed by the North Alhamilla reverse fault and the North and South Gafarillos dextral faults. It is a conjugate fault system of the sinistral NNE-SSW Palomares fault zone, active from the late most Tortonian (≈7 Ma) up to the late Pleistocene (≥70 ky) in the southeastern Betics. The helicoidal geometry of the fault zone permits to shift SE-directed movement along the South Cabrera reverse fault to NW-directed shortening along the North Alhamilla reverse fault via vertical Gafarillos fault segments, in between. Since the Messinian, fault activity migrated southwards forming the South Gafarillos fault and displacing the active fault-related mountain-front from the north to the south of Sierra de Polopos; whilst recent activity of the North Alhamilla reverse fault migrated westwards. The Polopos fault zone determined the differential uplift between the Sierra Alhamilla and the Tabernas-Sorbas basin promoting the middle Pleistocene capture that occurred in the southern margin of the Sorbas basin. Continued tectonic uplift of the Sierra Alhamilla-Polopos and Cabrera anticlinoria and local subsidence associated to the Palomares fault zone in the Vera basin promoted the headward erosion of the Aguas river drainage that captured the Sorbas basin during the late Pleistocene.

  10. 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

  11. Previously unrecognized now-inactive strand of the North Anatolian fault in the Thrace basin

    SciTech Connect

    Perincek, D.

    1988-08-01

    The North Anatolian fault is a major 1,200 km-long transform fault bounding the Anatolian plate to the north. It formed in late middle Miocene time as a broad shear zone with a number of strands splaying westward in a horsetail fashion. Later, movement became localized along the stem, and the southerly and northerly splays became inactive. One such right-lateral, now-inactive splay is the west-northwest-striking Thrace strike-slip fault system, consisting of three subparallel strike-slip faults. From north to south these are the Kirklareli, Lueleburgaz, and Babaeski fault zones, extending {plus minus} 130 km along the strike. The Thrace fault zone probablymore » connected with the presently active northern strand of the North Anatolian fault in the Sea of Marmara in the southeast and may have joined the Plovdiv graben zone in Bulgaria in the northwest. The Thrace basin in which the Thrace fault system is located, is Cenozoic with a sedimentary basin fill from middle Eocene to Pliocene. The Thrace fault system formed in pre-Pliocene time and had become inactive by the Pliocene. Strike-slip fault zones with normal and reverse separation are detected by seismic reflection profiles and subsurface data. Releasing bend extensional structures (e.g., near the town of Lueleburgaz) and restraining bend compressional structures (near Vakiflar-1 well) are abundant on the fault zones. Umurca and Hamitabad fields are en echelon structures on the Lueleburgaz fault zone. The Thrace strike-slip fault system has itself a horsetail shape, the various strands of which become younger southward. The entire system died before the Pliocene, and motion on the North Anatolian fault zone began to be accommodated in the Sea of Marmara region. Thus the Thrace fault system represents the oldest strand of the North Anatolian fault in the west.« less

  12. Fault diagnosis

    NASA Technical Reports Server (NTRS)

    Abbott, Kathy

    1990-01-01

    The objective of the research in this area of fault management is to develop and implement a decision aiding concept for diagnosing faults, especially faults which are difficult for pilots to identify, and to develop methods for presenting the diagnosis information to the flight crew in a timely and comprehensible manner. The requirements for the diagnosis concept were identified by interviewing pilots, analyzing actual incident and accident cases, and examining psychology literature on how humans perform diagnosis. The diagnosis decision aiding concept developed based on those requirements takes abnormal sensor readings as input, as identified by a fault monitor. Based on these abnormal sensor readings, the diagnosis concept identifies the cause or source of the fault and all components affected by the fault. This concept was implemented for diagnosis of aircraft propulsion and hydraulic subsystems in a computer program called Draphys (Diagnostic Reasoning About Physical Systems). Draphys is unique in two important ways. First, it uses models of both functional and physical relationships in the subsystems. Using both models enables the diagnostic reasoning to identify the fault propagation as the faulted system continues to operate, and to diagnose physical damage. Draphys also reasons about behavior of the faulted system over time, to eliminate possibilities as more information becomes available, and to update the system status as more components are affected by the fault. The crew interface research is examining display issues associated with presenting diagnosis information to the flight crew. One study examined issues for presenting system status information. One lesson learned from that study was that pilots found fault situations to be more complex if they involved multiple subsystems. Another was pilots could identify the faulted systems more quickly if the system status was presented in pictorial or text format. Another study is currently under way to

  13. Aftershocks of the 2014 South Napa, California, Earthquake: Complex faulting on secondary faults

    USGS Publications Warehouse

    Hardebeck, Jeanne L.; Shelly, David R.

    2016-01-01

    We investigate the aftershock sequence of the 2014 MW6.0 South Napa, California, earthquake. Low-magnitude aftershocks missing from the network catalog are detected by applying a matched-filter approach to continuous seismic data, with the catalog earthquakes serving as the waveform templates. We measure precise differential arrival times between events, which we use for double-difference event relocation in a 3D seismic velocity model. Most aftershocks are deeper than the mainshock slip, and most occur west of the mapped surface rupture. While the mainshock coseismic and postseismic slip appears to have occurred on the near-vertical, strike-slip West Napa fault, many of the aftershocks occur in a complex zone of secondary faulting. Earthquake locations in the main aftershock zone, near the mainshock hypocenter, delineate multiple dipping secondary faults. Composite focal mechanisms indicate strike-slip and oblique-reverse faulting on the secondary features. The secondary faults were moved towards failure by Coulomb stress changes from the mainshock slip. Clusters of aftershocks north and south of the main aftershock zone exhibit vertical strike-slip faulting more consistent with the West Napa Fault. The northern aftershocks correspond to the area of largest mainshock coseismic slip, while the main aftershock zone is adjacent to the fault area that has primarily slipped postseismically. Unlike most creeping faults, the zone of postseismic slip does not appear to contain embedded stick-slip patches that would have produced on-fault aftershocks. The lack of stick-slip patches along this portion of the fault may contribute to the low productivity of the South Napa aftershock sequence.

  14. 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

  15. Volcanism in slab tear faults is larger than in island-arcs and back-arcs.

    PubMed

    Cocchi, Luca; Passaro, Salvatore; Tontini, Fabio Caratori; Ventura, Guido

    2017-11-13

    Subduction-transform edge propagators are lithospheric tears bounding slabs and back-arc basins. The volcanism at these edges is enigmatic because it is lacking comprehensive geological and geophysical data. Here we present bathymetric, potential-field data, and direct observations of the seafloor on the 90 km long Palinuro volcanic chain overlapping the E-W striking tear of the roll-backing Ionian slab in Southern Tyrrhenian Sea. The volcanic chain includes arc-type central volcanoes and fissural, spreading-type centers emplaced along second-order shears. The volume of the volcanic chain is larger than that of the neighbor island-arc edifices and back-arc spreading center. Such large volume of magma is associated to an upwelling of the isotherms due to mantle melts upraising from the rear of the slab along the tear fault. The subduction-transform edge volcanism focuses localized spreading processes and its magnitude is underestimated. This volcanism characterizes the subduction settings associated to volcanic arcs and back-arc spreading centers.

  16. 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

  17. Borjomi-Kazbegi Fault: Does it Exist?

    NASA Astrophysics Data System (ADS)

    Martin, R. J.; O, Connor, T.; Adamia, S.; Szymanski, E.; Krasovec, M.

    2012-12-01

    The Caucasus region has long been considered to be an example of indenture tectonics. The proposed Borjomi-Kazbegi sinistral fault is considered the western boundary of the actively indenting wedge. However, an improved seismic network density has led to recent unpublished observations noting a lack of seismicity on the proposed Borjomi-Kazbegi fault. These new observations call into question the existence of the fault, and with it, the tectonic model of the region. To clarify this anomaly, geologic and geophysical field research was carried out on the proposed Borjomi-Kazbegi fault during the summers of 2005 and 2006. Since the Borjomi-Kazbegi fault is also proposed to be a major crustal structure, a multi-disciplinary approach was utilized for this investigation. Precise GPS instrumentation was used to map multiple local geologic marker beds across the proposed line of the fault, and gravimetric and magnetic surveys were used to map deeper structures. The results showed no evidence of a strike slip fault. Localized marker beds, which included lithologic contacts, structural folds, quaternary lava deposits and several sills, continue uninterrupted across the proposed fault zone. Data from the gravimetric and magnetic surveys also show no discontinuity across the proposed fault line. In addition, the newly collected geophysical data agrees with the results of gravity and magnetic surveys carried out during the Soviet period. The Soviet data has more extensive areal coverage, and also shows no evidence of a major strike slip fault in the region. Currently, the field observations support a model that suggests active shortening in the Borjomi region is accommodated predominantly by thrust faulting.

  18. A study of buried pipeline response to fault movement

    SciTech Connect

    Chiou, Y.J.; Chi, S.Y.; Chang, H.Y.

    1994-02-01

    This study investigates the buried pipeline response to strike slip fault movement. The large deflection pipe crossing the fault zone is modeled as an elastica, while the remaining portion of small deflection pipe is modeled as a semi-infinite beam on elastic foundation. The finite difference method is applied for the numerical solution and the results agree qualitatively with the earlier works.

  19. Geo-electrical and geological strikes of the Mount Lamongan geothermal area, East Java, Indonesia – preliminary results

    NASA Astrophysics Data System (ADS)

    Nugraheni, L. R.; Niasari, S. W.; Nukman, M.

    2018-04-01

    Geothermal manifestations located in the Tiris, Mount Lamongan, Probolinggo, consist of warm springs. These warm springs have temperature from 35° until 45°C. Tiris fault has NW-SE dominant orientation, similar to some lineaments of maars and cinder cones around Mount Lamongan. The Mount Lamongan geothermal area is situated between Bromo and Argapura volcanoes. This study aims to map the geo-electrical and geological strikes in the study area. Phase tensor analysis has been performed in this study to determine geo-electrical strike of study area. Geological field campaign has been conducted to measure geological strikes. Then, orientation of geo-electrical strike was compared to geological strike. The result presents that the regional geological strike of study area is NW-SE while the orientation of geo-electrical strike is N-S.

  20. Along-strike complex geometry of subduction zones - an experimental approach

    NASA Astrophysics Data System (ADS)

    Midtkandal, I.; Gabrielsen, R. H.; Brun, J.-P.; Huismans, R.

    2012-04-01

    triangle zones. In the "ocean crust" domain, stage 1 was characterized by the growth of a fault-propagation anticline with an E-W-oriented fold axis, ending with the surfacing of a north-vergent thrust. In stage 2, the contraction was concentrated to the south in the oceanic domain, again ending with the surfacing of a thrust, here with top-south transport. By continued movement (stage 3), the thrust fault propagated towards the east, crossing into the "continental" domain and linking with the fault systems of the segment CC. The structure of domain T is dominated by the interference of faults propagating westwards from the domain CC and eastwards from the domain OC, respectively. The zone of overlap in the experiment was significant, and its central part had the geometry of a double "crocodile structure" (sensuMeissner 1989), separating the two areas of northerly and southerly subduction. Hence, its development is less easily subdivided into stages. Reference: Meissner,R., 1989: Rupture, creep lamellae and crocodiles: happenings in the continental crust. Terra Nova, 1, 17-28.

  1. 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.

  2. 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

  3. 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

  4. Estimating slip deficit of the North Anatolian Fault beneath the Sea of Marmara, Turkey, using on- and off-shore geodetic data

    NASA Astrophysics Data System (ADS)

    Yamamoto, R.; Kido, M.; Ohta, Y.; Takahashi, N.; Yamamoto, Y.; Kalafat, D.; Pinar, A.; Ozener, H.; Ozeren, M. S.; Yoshiyuki, K.

    2016-12-01

    The North Anatolian Fault (NAF) in the northern Turkey regionally has right-lateral strike-slip motion. In the last decade, seismic activities have been migrating from east to west along the fault. In 1999, Izmit and Duzce Earthquakes were respectively occurred at 100 km and 200 km east of Istanbul, while it remains un-ruptured in the vicinity of Istanbul beneath the Sea of Marmara. In this region, onshore geodetic tools cannot be used and we instead used "seafloor acoustic extensometers" to detect slip deficit rate across the western part of the NAF (around 27.7 °E). A pair of extensometers can periodically measure precise range (about 3-4 mm precision per 1 km baseline) by observing round-trip time of acoustic signal between the two. We installed four instruments in September 2014 and an additional one in March 2015 across the NAF. We have recovered data for about 600-days through acoustic modem. By correcting travel-times for sound velocity using concurrently measured temperature, pressure and tilt change of instruments, we obtained 8-10 ±1 mm/yr of right-lateral movement at the site. Combing the result with on-shore GNSS data across the Sea of Marmara, we constructed a possible fault model. According to the model in Kaneko et al. (2013), we simply assume a bimodal slip condition on the fault plane that infinitely continues to the E-W direction; full-creep (25 mm/yr as is given at infinite distant from the fault plane) deeper than 15 km and applied an overriding partially locked layer (17 mm/yr slip deficit as is obtained by extensometers). We calculated 2-D displacement field in a homogeneous elastic half-space medium. With this model, N-S variation of on-shore GNSS data across the Sea of Marmara can be reasonably explained. However, due to the lack of GNSS site near the fault plane, constraint on the depth of the partially locked layer is not sufficient. We have newly installed GNSS sites, one of which is closer to the fault plane ( 10 km) than before and

  5. The 2002 Denali fault earthquake, Alaska: A large magnitude, slip-partitioned event

    USGS Publications Warehouse

    Eberhart-Phillips, D.; Haeussler, Peter J.; Freymueller, J.T.; Frankel, A.D.; Rubin, C.M.; Craw, P.; Ratchkovski, N.A.; Anderson, G.; Carver, G.A.; Crone, A.J.; Dawson, T.E.; Fletcher, H.; Hansen, R.; Harp, E.L.; Harris, R.A.; Hill, D.P.; Hreinsdottir, S.; Jibson, R.W.; Jones, L.M.; Kayen, R.; Keefer, D.K.; Larsen, C.F.; Moran, S.C.; Personius, S.F.; Plafker, G.; Sherrod, B.; Sieh, K.; Sitar, N.; Wallace, W.K.

    2003-01-01

    The MW (moment magnitude) 7.9 Denali fault earthquake on 3 November 2002 was associated with 340 kilometers of surface rupture and was the largest strike-slip earthquake in North America in almost 150 years. It illuminates earthquake mechanics and hazards of large strike-slip faults. It began with thrusting on the previously unrecognized Susitna Glacier fault, continued with right-slip on the Denali fault, then took a right step and continued with right-slip on the Totschunda fault. There is good correlation between geologically observed and geophysically inferred moment release. The earthquake produced unusually strong distal effects in the rupture propagation direction, including triggered seismicity.

  6. Cascadia subduction tremor muted by crustal faults

    USGS Publications Warehouse

    Wells, Ray; Blakely, Richard J.; Wech, Aaron G.; McCrory, Patricia A.; Michael, Andrew

    2017-01-01

    Deep, episodic slow slip on the Cascadia subduction megathrust of western North America is accompanied by low-frequency tremor in a zone of high fluid pressure between 30 and 40 km depth. Tremor density (tremor epicenters per square kilometer) varies along strike, and lower tremor density statistically correlates with upper plate faults that accommodate northward motion and rotation of forearc blocks. Upper plate earthquakes occur to 35 km depth beneath the faults. We suggest that the faults extend to the overpressured megathrust, where they provide fracture pathways for fluid escape into the upper plate. This locally reduces megathrust fluid pressure and tremor occurrence beneath the faults. Damping of tremor and related slow slip caused by fluid escape could affect fault properties of the megathrust, possibly influencing the behavior of great earthquakes.

  7. Fault Slip Partitioning in the Eastern California Shear Zone-Walker Lane Belt: Pliocene to Late Pleistocene Contraction Across the Mina Deflection

    NASA Astrophysics Data System (ADS)

    Lee, J.; Stockli, D.; Gosse, J.

    2007-12-01

    Two different mechanisms have been proposed for fault slip transfer between the subparallel NW-striking dextral- slip faults that dominant the Eastern California Shear Zone (ECSZ)-Walker Lane Belt (WLB). In the northern WLB, domains of sinistral-slip along NE-striking faults and clockwise block rotation within a zone of distributed deformation accommodated NW-dextral shear. A somewhat modified version of this mechanism was also proposed for the Mina deflection, southern WLB, whereby NE-striking sinistral faults formed as conjugate faults to the primary zone of NW-dextral shear; clockwise rotation of the blocks bounding the sinistral faults accommodated dextral slip. In contrast, in the northern ECSZ and Mina deflection, domains of NE-striking pure dip-slip normal faults, bounded by NW-striking dextral-slip faults, exhibited no rotation; the proposed mechanism of slip transfer was one of right-stepping, high angle normal faults in which the magnitude of extension was proportional to the amount of strike-slip motion transferred. New geologic mapping, tectonic geomorphologic, and geochronologic data from the Queen Valley area, southern Mina deflection constrain Pliocene to late Quaternary fault geometries, slip orientations, slip magnitudes, and slip rates that bear on the mechanism of fault slip transfer from the relatively narrow northern ECSZ to the broad deformation zone that defines the Mina deflection. Four different fault types and orientations cut across the Queen Valley area: (1) The NE-striking normal-slip Queen Valley fault; (2) NE-striking sinistral faults; (3) the NW-striking dextral Coyote Springs fault, which merges into (4) a set of EW-striking thrust faults. (U-Th)/He apatite and cosmogenic radionuclide data, combined with magnitude of fault offset measurements, indicate a Pliocene to late Pleistocene horizontal extension rate of 0.2-0.3 mm/yr across the Queen Valley fault. Our results, combined with published slip rates for the dextral White Mountain

  8. Fethiye-Burdur Fault Zone (SW Turkey): a myth?

    NASA Astrophysics Data System (ADS)

    Kaymakci, Nuretdin; Langereis, Cornelis; Özkaptan, Murat; Özacar, Arda A.; Gülyüz, Erhan; Uzel, Bora; Sözbilir, Hasan

    2017-04-01

    Fethiye Burdur Fault Zone (FBFZ) is first proposed by Dumont et al. (1979) as a sinistral strike-slip fault zone as the NE continuation of Pliny-Strabo trench in to the Anatolian Block. The fault zone supposed to accommodate at least 100 km sinistral displacement between the Menderes Massif and the Beydaǧları platform during the exhumation of the Menderes Massif, mainly during the late Miocene. Based on GPS velocities Barka and Reilinger (1997) proposed that the fault zone is still active and accommodates sinistral displacement. In order to test the presence and to unravel its kinematics we have conducted a rigorous paleomagnetic study containing more than 3000 paleomagnetic samples collected from 88 locations and 11700 fault slip data collected from 198 locations distributed evenly all over SW Anatolia spanning from Middle Miocene to Late Pliocene. The obtained rotation senses and amounts indicate slight (around 20°) counter-clockwise rotations distributed uniformly almost whole SW Anatolia and there is no change in the rotation senses and amounts on either side of the FBFZ implying no differential rotation within the zone. Additionally, the slickenside pitches and constructed paleostress configurations, along the so called FBFZ and also within the 300 km diameter of the proposed fault zone, indicated that almost all the faults, oriented parallel to subparallel to the zone, are normal in character. The fault slip measurements are also consistent with earthquake focal mechanisms suggesting active extension in the region. We have not encountered any significant strike-slip motion in the region to support presence and transcurrent nature of the FBFZ. On the contrary, the region is dominated by extensional deformation and strike-slip components are observed only on the NW-SE striking faults which are transfer faults that accommodated extension and normal motion. Therefore, we claim that the sinistral Fethiye Burdur Fault (Zone) is a myth and there is no tangible

  9. Research on Distribution Characteristics of Lunar Faults

    NASA Astrophysics Data System (ADS)

    Lu, T.; Chen, S.; Lu, P.

    2017-12-01

    Circular and linear tectonics are two major types of tectonics on lunar surface. Tectonic characteristics are of significance for researching about lunar geological evolution. Linear tectonics refers to those structures extending linearly on a lunar surface. Their distribution are closely related to the internal geological actions of the moon. Linear tectonics can integrally or locally express the structural feature and the stress status as well as showing the geological information of the interior of the moon. Faults are of the largest number and are of a certain distribution regularity among the linear tectonics, and are always the focus of domestic and overseas lunar tectonic research. Based on remote sensing geology and theory of traditional tectonic geology, We use a variety of remote sensing data processing to establish lunar linear tectonic interpretation keys with lunar spectral, terrain and gravity data. On this basis, interpretation of faults of the whole moon was primarily conducted from Chang'e-2 CCD image data and reference to wide-angle camera data of LROC, laser altimeter data of LOLA and gravity data of GRAIL. Statistical analysis of the number and distribution characteristics of whole lunar faults are counted from three latitude ranges of low, middle and high latitudes, then analyze the azimuth characteristics of the faults at different latitudes. We concluded that S-N direction is a relatively developed orientation at low latitudes. Middle latitudes reveal six preferred orientations of N-E, N-W, NN-E, NN-W, N-EE and N-WW directions. There are sparse faults of E-W direction distribution at low and middle latitudes. Meanwhile, the largest number of faults of E-W direction on lunar surface are mainly distributed along high latitudes with continuity and regularity. Analyzing faults of Mare Imbrium by the method of Euler deconvolution. The result show that there are two different properties of faults in Mare Imbrium. In conclusion, we suggest that the

  10. Misbheaving Faults: The Expanding Role of Geodetic Imaging in Unraveling Unexpected Fault Slip Behavior

    NASA Astrophysics Data System (ADS)

    Barnhart, W. D.; Briggs, R.

    2015-12-01

    Geodetic imaging techniques enable researchers to "see" details of fault rupture that cannot be captured by complementary tools such as seismology and field studies, thus providing increasingly detailed information about surface strain, slip kinematics, and how an earthquake may be transcribed into the geological record. For example, the recent Haiti, Sierra El Mayor, and Nepal earthquakes illustrate the fundamental role of geodetic observations in recording blind ruptures where purely geological and seismological studies provided incomplete views of rupture kinematics. Traditional earthquake hazard analyses typically rely on sparse paleoseismic observations and incomplete mapping, simple assumptions of slip kinematics from Andersonian faulting, and earthquake analogs to characterize the probabilities of forthcoming ruptures and the severity of ground accelerations. Spatially dense geodetic observations in turn help to identify where these prevailing assumptions regarding fault behavior break down and highlight new and unexpected kinematic slip behavior. Here, we focus on three key contributions of space geodetic observations to the analysis of co-seismic deformation: identifying near-surface co-seismic slip where no easily recognized fault rupture exists; discerning non-Andersonian faulting styles; and quantifying distributed, off-fault deformation. The 2013 Balochistan strike slip earthquake in Pakistan illuminates how space geodesy precisely images non-Andersonian behavior and off-fault deformation. Through analysis of high-resolution optical imagery and DEMs, evidence emerges that a single fault map slip as both a strike slip and dip slip fault across multiple seismic cycles. These observations likewise enable us to quantify on-fault deformation, which account for ~72% of the displacements in this earthquake. Nonetheless, the spatial distribution of on- and off-fault deformation in this event is highly spatially variable- a complicating factor for comparisons

  11. Study on conditional probability of surface rupture: effect of fault dip and width of seismogenic layer

    NASA Astrophysics Data System (ADS)

    Inoue, N.

    2017-12-01

    The conditional probability of surface ruptures is affected by various factors, such as shallow material properties, process of earthquakes, ground motions and so on. Toda (2013) pointed out difference of the conditional probability of strike and reverse fault by considering the fault dip and width of seismogenic layer. This study evaluated conditional probability of surface rupture based on following procedures. Fault geometry was determined from the randomly generated magnitude based on The Headquarters for Earthquake Research Promotion (2017) method. If the defined fault plane was not saturated in the assumed width of the seismogenic layer, the fault plane depth was randomly provided within the seismogenic layer. The logistic analysis was performed to two data sets: surface displacement calculated by dislocation methods (Wang et al., 2003) from the defined source fault, the depth of top of the defined source fault. The estimated conditional probability from surface displacement indicated higher probability of reverse faults than that of strike faults, and this result coincides to previous similar studies (i.e. Kagawa et al., 2004; Kataoka and Kusakabe, 2005). On the contrary, the probability estimated from the depth of the source fault indicated higher probability of thrust faults than that of strike and reverse faults, and this trend is similar to the conditional probability of PFDHA results (Youngs et al., 2003; Moss and Ross, 2011). The probability of combined simulated results of thrust and reverse also shows low probability. The worldwide compiled reverse fault data include low fault dip angle earthquake. On the other hand, in the case of Japanese reverse fault, there is possibility that the conditional probability of reverse faults with less low dip angle earthquake shows low probability and indicates similar probability of strike fault (i.e. Takao et al., 2013). In the future, numerical simulation by considering failure condition of surface by the source

  12. Character and Significance of Surface Rupture Near the Intersection of the Denali and Totschunda Faults, M7.9 Denali Fault Earthquake, Alaska, November 3, 2002

    NASA Astrophysics Data System (ADS)

    Wallace, W. K.; Sherrod, B. L.; Dawson, T. E.

    2002-12-01

    Preliminary observations suggest that right-lateral strike-slip on the Denali fault is transferred to the Totschunda fault via an extensional bend in the Little Tok River valley. Most of the surface rupture during the Denali fault earthquake was along an east- to east-southeast striking, gently curved segment of the Denali fault. However, in the Little Tok River valley, rupture transferred to the southeast-striking Totschunda fault and continued to the southeast for another 75 km. West of the Little Tok River valley, 5-7 m of right-lateral slip and up to 2 m of vertical offset occurred on the main strand of the Denali fault, but no apparent displacement occurred on the Denali fault east of the valley. Rupture west of the intersection also occurred on multiple discontinuous strands parallel to and south of the main strand of the Denali fault. In the Little Tok River valley, the northern part of the Totschunda fault system consists of multiple discontinuous southeast-striking strands that are connected locally by south-striking stepover faults. Faults of the northern Totschunda system display 0-2.5 m of right-lateral slip and 0-2.75 m of vertical offset, with the largest vertical offset on a dominantly extensional stepover fault. The strands of the Totschunda system converge southeastward to a single strand that had up to 2 m of slip. Complex and discontinuous faulting may reflect in part the immaturity of the northern Totschunda system, which is known to be younger and have much less total slip than the Denali. The Totschunda fault forms an extensional bend relative to the dominantly right-lateral Denali fault to the west. The fault geometry and displacements at the intersection suggest that slip on the Denali fault during the earthquake was accommodated largely by extension in the northern Totschunda fault system, allowing a significant decrease in strike-slip relative to the Denali fault. Strands to the southwest in the area of the bend may represent shortcut

  13. Factors affecting the recognition of faults exposed in exploratory trenches

    USGS Publications Warehouse

    Bonilla, Manuel G.; Lienkaemper, James J.

    1991-01-01

    Trenching-a widely used method for evaluating fault activity-has limitations that can mislead investigators. Some segments of fault strands in trench walls may not be visible, and this nonvisibility can lead to incorrect interpretations of time of most recent displacement and recurrence intervals on a fault. We examined the logs of 163 trench exposures and tabulated data on more than 1,200 fault strands to investigate three categories of nonvisibility: (1) strands with obscure (invisible or poorly visible) segments, (2) strands that die out upward, and (3) strands that die out downward. About 14 percent of all the strands have obscure segments. Of the 143 strands on which it is possible to recognize dieout up (limited to strands for which position of ground surface at time of faulting is known), 45 percent do die out upward, and the fraction exceeds 70 percent for strike-slip and reverse faults. Thus a fault strand overlain by an apparently undisturbed deposit is not necessarily older than the deposit. More than 30 percent of all the strands die out downward, providing more evidence that fault strands can end for reasons other than being covered by deposits younger than the fault. Analysis of trench-log data revealed various relations between geologic factors and nonvisibility of fault strands. For example, fault type affects the incidence of nonvisibility, which is generally most common on strike-slip faults, less common on reverse faults, and least common on normal fau Its. The type of material penetrated by the fault also influences nonvisibility, which tends to be more common in soil horizons and sand, and less common in gravel. Dieout down is weakly influenced by fault displacement, decreasing in frequency with increase in displacement; the frequencies of obscure segments and dieout up do not vary consistently with fault displacement. Frequency of obscure segments generally decreases with increase in length of obscure segments, and frequency of dieout up

  14. Active faulting in apparently stable peninsular India: Rift inversion and a Holocene-age great earthquake on the Tapti Fault

    NASA Astrophysics Data System (ADS)

    Copley, Alex; Mitra, Supriyo; Sloan, R. Alastair; Gaonkar, Sharad; Reynolds, Kirsty

    2014-08-01

    We present observations of active faulting within peninsular India, far from the surrounding plate boundaries. Offset alluvial fan surfaces indicate one or more magnitude 7.6-8.4 thrust-faulting earthquakes on the Tapti Fault (Maharashtra, western India) during the Holocene. The high ratio of fault displacement to length on the alluvial fan offsets implies high stress-drop faulting, as has been observed elsewhere in the peninsula. The along-strike extent of the fan offsets is similar to the thickness of the seismogenic layer, suggesting a roughly equidimensional fault rupture. The subsiding footwall of the fault is likely to have been responsible for altering the continental-scale drainage pattern in central India and creating the large west flowing catchment of the Tapti river. A preexisting sedimentary basin in the uplifting hanging wall implies that the Tapti Fault was active as a normal fault during the Mesozoic and has been reactivated as a thrust, highlighting the role of preexisting structures in determining the rheology and deformation of the lithosphere. The slip sense of faults and earthquakes in India suggests that deformation south of the Ganges foreland basin is driven by the compressive force transmitted between India and the Tibetan Plateau. The along-strike continuation of faulting to the east of the Holocene ruptures we have studied represents a significant seismic hazard in central India.

  15. 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.

  16. Constraining slip rates and spacings for active normal faults

    NASA Astrophysics Data System (ADS)

    Cowie, Patience A.; Roberts, Gerald P.

    2001-12-01

    Numerous observations of extensional provinces indicate that neighbouring faults commonly slip at different rates and, moreover, may be active over different time intervals. These published observations include variations in slip rate measured along-strike of a fault array or fault zone, as well as significant across-strike differences in the timing and rates of movement on faults that have a similar orientation with respect to the regional stress field. Here we review published examples from the western USA, the North Sea, and central Greece, and present new data from the Italian Apennines that support the idea that such variations are systematic and thus to some extent predictable. The basis for the prediction is that: (1) the way in which a fault grows is fundamentally controlled by the ratio of maximum displacement to length, and (2) the regional strain rate must remain approximately constant through time. We show how data on fault lengths and displacements can be used to model the observed patterns of long-term slip rate where measured values are sparse. Specifically, we estimate the magnitude of spatial variation in slip rate along-strike and relate it to the across-strike spacing between active faults.

  17. 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

  18. Paleoseismic Investigation of the Ranong and Khlong Marui faults, Chumphon Province, Southern Thailand

    NASA Astrophysics Data System (ADS)

    Fenton, C. H.; Sutiwanich, C.

    2005-12-01

    The Ranong and Khlong Marui faults are northeast-southwest trending structures in the Isthmus of Kra, southern Thailand, that apparently link the extensional regimes of the Mergui Basin in the Andaman Sea and the Gulf of Thailand. These faults are depicted commonly as strike-slip faults, acting as conjugate structures to the dominant northwest-southeast trending strike-slip faults, in Southeast Asia. These faults are parallel to the predominant structural grain in the Carboniferous rocks of peninsular Thailand. In addition, they appear to be bounding structures for several Tertiary basins, including the onshore parts of the Surat Thani basin and the offshore Chumphon basin. Initial remote sensing studies showed that both faults have relatively subdued geomorphic expressions. Field reconnaissance investigations indicated a lack of youthful tectonic geomorphology along the Khlong Marui fault and ambiguous evidence for recent movement along the Ranong fault. Fault exposures along both fault trends and on minor parallel faults in the region indicated that, rather than predominantly strike-slip motion, these faults have experienced up-to-the-west reverse movement. Because of its more youthful geomorphic expression, several sites along the Ranong fault were chosen for paleoseismic trenching. Initial trench exposures indicate an absence of Holocene movement. Some exposures indicate the possibility of Late Tertiary-Early Holocene vertical movement. These investigations are currently ongoing and we hope to report our conclusions at the Fall Meeting.

  19. A New Kinematic Model for Polymodal Faulting: Implications for Fault Connectivity

    NASA Astrophysics Data System (ADS)

    Healy, D.; Rizzo, R. E.

    2015-12-01

    Conjugate, or bimodal, fault patterns dominate the geological literature on shear failure. Based on Anderson's (1905) application of the Mohr-Coulomb failure criterion, these patterns have been interpreted from all tectonic regimes, including normal, strike-slip and thrust (reverse) faulting. However, a fundamental limitation of the Mohr-Coulomb failure criterion - and others that assume faults form parallel to the intermediate principal stress - is that only plane strain can result from slip on the conjugate faults. However, deformation in the Earth is widely accepted as being three-dimensional, with truly triaxial stresses and strains. Polymodal faulting, with three or more sets of faults forming and slipping simultaneously, can generate three-dimensional strains from truly triaxial stresses. Laboratory experiments and outcrop studies have verified the occurrence of the polymodal fault patterns in nature. The connectivity of polymodal fault networks differs significantly from conjugate fault networks, and this presents challenges to our understanding of faulting and an opportunity to improve our understanding of seismic hazards and fluid flow. Polymodal fault patterns will, in general, have more connected nodes in 2D (and more branch lines in 3D) than comparable conjugate (bimodal) patterns. The anisotropy of permeability is therefore expected to be very different in rocks with polymodal fault patterns in comparison to conjugate fault patterns, and this has implications for the development of hydrocarbon reservoirs, the genesis of ore deposits and the management of aquifers. In this contribution, I assess the published evidence and models for polymodal faulting before presenting a novel kinematic model for general triaxial strain in the brittle field.

  20. The San Andreas Fault System, California

    USGS Publications Warehouse

    Wallace, Robert E.

    1990-01-01

    .; J.G. Vedder, offshore reglor south of lat 35° N.; and D.G. Herd, southern San Francisco Bay region. The Fault Evaluation Program of the California Division of Mines and Geology under the direction of E.W. Hart, provided much data about many faults. Unpublished material about the Bartlett Springs fault zone that was gathered by Geomatrix Consultants for the Pacific Gas and Electric Co. was very useful. In addition, selected publications that provided invaluable data include Bortugno (1982), Herd (1977), Herd and Helley (1977), Pampeyan and others (1981), and Yerkes and others (1980). 

  1. Preemptive strikes: Fear, hope, and defensive aggression.

    PubMed

    Halevy, Nir

    2017-02-01

    Preemptive strikes are costly and harmful. Existing models of defensive aggression focus narrowly on the role fear plays in motivating preemptive strikes. Theoretically integrating the literatures on conflict, decision making, and emotion, the current research investigated how specific emotions associated with certainty or uncertainty, including fear, anger, disgust, hope, and happiness, influence preemptive strikes. Study 1 demonstrated that hope negatively predicts defensive exits from relationships in choice dilemmas. Studies 2 and 3 experimentally manipulated risk of being attacked in an incentivized, interactive decision making task-the Preemptive Strike Game. Risk of being attacked fueled preemptive strikes; reduced feelings of hope partially mediated this effect in Study 3. Studies 4 and 5 investigated preemptive strikes under uncertainty (rather than risk). In Study 4, reasoning about the factors that make one trustful of others curbed preemptive strikes; cogitating about the factors that underlie discrete emotions, however, did not influence defensive aggression. Study 5 demonstrated that the valence and uncertainty appraisals of incidental emotions interact in shaping preemptive strikes. Specifically, recalling an autobiographical emotional experience that produced hope significantly decreased attack rates relative to fear, happiness, and a control condition. Fear, anger, disgust, and happiness were either unrelated to preemptive strikes or showed inconsistent relationships with preemptive strikes across the 5 studies. These findings shed light on how emotions shape defensive aggression, advance knowledge on strategic choice under risk and uncertainty, and demonstrate hope's positive effects on social interactions and relationships. (PsycINFO Database Record (c) 2017 APA, all rights reserved).

  2. Stress before and after the 2002 Denali fault earthquake

    USGS Publications Warehouse

    Wesson, R.L.; Boyd, O.S.

    2007-01-01

    Spatially averaged, absolute deviatoric stress tensors along the faults ruptured during the 2002 Denali fault earthquake, both before and after the event, are derived, using a new method, from estimates of the orientations of the principal stresses and the stress change associated with the earthquake. Stresses are estimated in three regions along the Denali fault, one of which also includes the Susitna Glacier fault, and one region along the Totschunda fault. Estimates of the spatially averaged shear stress before the earthquake resolved onto the faults that ruptured during the event range from near 1 MPa to near 4 MPa. Shear stresses estimated along the faults in all these regions after the event are near zero (0 ?? 1 MPa). These results suggest that deviatoric stresses averaged over a few tens of km along strike are low, and that the stress drop during the earthquake was complete or nearly so.

  3. Dynamical Instability Produces Transform Faults at Mid-Ocean Ridges

    NASA Astrophysics Data System (ADS)

    Gerya, Taras

    2010-08-01

    Transform faults at mid-ocean ridges—one of the most striking, yet enigmatic features of terrestrial plate tectonics—are considered to be the inherited product of preexisting fault structures. Ridge offsets along these faults therefore should remain constant with time. Here, numerical models suggest that transform faults are actively developing and result from dynamical instability of constructive plate boundaries, irrespective of previous structure. Boundary instability from asymmetric plate growth can spontaneously start in alternate directions along successive ridge sections; the resultant curved ridges become transform faults within a few million years. Fracture-related rheological weakening stabilizes ridge-parallel detachment faults. Offsets along the transform faults change continuously with time by asymmetric plate growth and discontinuously by ridge jumps.

  4. Missing link between the Hayward and Rodgers Creek faults

    PubMed Central

    Watt, Janet; Ponce, David; Parsons, Tom; Hart, Patrick

    2016-01-01

    The next major earthquake to strike the ~7 million residents of the San Francisco Bay Area will most likely result from rupture of the Hayward or Rodgers Creek faults. Until now, the relationship between these two faults beneath San Pablo Bay has been a mystery. Detailed subsurface imaging provides definitive evidence of active faulting along the Hayward fault as it traverses San Pablo Bay and bends ~10° to the right toward the Rodgers Creek fault. Integrated geophysical interpretation and kinematic modeling show that the Hayward and Rodgers Creek faults are directly connected at the surface—a geometric relationship that has significant implications for earthquake dynamics and seismic hazard. A direct link enables simultaneous rupture of the Hayward and Rodgers Creek faults, a scenario that could result in a major earthquake (M = 7.4) that would cause extensive damage and loss of life with global economic impact. PMID:27774514

  5. Missing link between the Hayward and Rodgers Creek faults

    USGS Publications Warehouse

    Watt, Janet; Ponce, David A.; Parsons, Thomas E.; Hart, Patrick E.

    2016-01-01

    The next major earthquake to strike the ~7 million residents of the San Francisco Bay Area will most likely result from rupture of the Hayward or Rodgers Creek faults. Until now, the relationship between these two faults beneath San Pablo Bay has been a mystery. Detailed subsurface imaging provides definitive evidence of active faulting along the Hayward fault as it traverses San Pablo Bay and bends ~10° to the right toward the Rodgers Creek fault. Integrated geophysical interpretation and kinematic modeling show that the Hayward and Rodgers Creek faults are directly connected at the surface—a geometric relationship that has significant implications for earthquake dynamics and seismic hazard. A direct link enables simultaneous rupture of the Hayward and Rodgers Creek faults, a scenario that could result in a major earthquake (M = 7.4) that would cause extensive damage and loss of life with global economic impact.

  6. Loading of the San Andreas fault by flood-induced rupture of faults beneath the Salton Sea

    USGS Publications Warehouse

    Brothers, Daniel; Kilb, Debi; Luttrell, Karen; Driscoll, Neal W.; Kent, Graham

    2011-01-01

    The southern San Andreas fault has not experienced a large earthquake for approximately 300 years, yet the previous five earthquakes occurred at ~180-year intervals. Large strike-slip faults are often segmented by lateral stepover zones. Movement on smaller faults within a stepover zone could perturb the main fault segments and potentially trigger a large earthquake. The southern San Andreas fault terminates in an extensional stepover zone beneath the Salton Sea—a lake that has experienced periodic flooding and desiccation since the late Holocene. Here we reconstruct the magnitude and timing of fault activity beneath the Salton Sea over several earthquake cycles. We observe coincident timing between flooding events, stepover fault displacement and ruptures on the San Andreas fault. Using Coulomb stress models, we show that the combined effect of lake loading, stepover fault movement and increased pore pressure could increase stress on the southern San Andreas fault to levels sufficient to induce failure. We conclude that rupture of the stepover faults, caused by periodic flooding of the palaeo-Salton Sea and by tectonic forcing, had the potential to trigger earthquake rupture on the southern San Andreas fault. Extensional stepover zones are highly susceptible to rapid stress loading and thus the Salton Sea may be a nucleation point for large ruptures on the southern San Andreas fault.

  7. 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.

  8. Kinematic vicissitudes and the spatial distribution of the alteration zone related to the Byobuyama fault, central Japan. (Implication; Influence of another faults.)

    NASA Astrophysics Data System (ADS)

    Katori, T.; Kobayashi, K.

    2015-12-01

    The central Japan is one of the most concentrated area of active faults (Quaternary fault). These are roughly classified into two orthogonally-oriented fault sets of NE-SW and NW-SE strikes. The study area is located in Gifu prefecture, central Japan. In there, the basement rocks are composed mainly of Triassic-Jurassic accretionary prism (Mino belt), Cretaceous Nohi Rhyolite and Cretaceous granitic rocks. Miocene Mizunami G. and Pliocene-Pleistocene Toki Sand and Gravel F. unconformably cover the basement rocks. The Byobuyama fault, 32 km in length, is NE-SW strike and displaces perpendicularly the Toki Sand and Gravel F. by 500 m. The northeastern terminal of the fault has contact with the southern terminal of the Atera fault of NW-SE strike and offset their displacements each other. It is clear that the activity of the Byobuyama fault plays a role of the development of the complicated fault geometry system in the central Japan. In this study, we performed a broad-based investigation along the Byobuyama fault and collected samples. Actually, we observed 400 faults and analyzed 200 fault rocks. Based on these results, we obtained the following new opinion. 1. The Byobuyama fault has experienced following activities that can be divided to 3 stages at least under different stress field. 1) Movement with the sinisterly sense (preserved in cataclasite zone). 2) Dextral movement (preserved in fault gouge zone). 3) Reverse fault movement (due to the aggressive rise of mountains). In addition, the change from Stage 2 to Stage 3 is a continuous. 2. There is a relationship between the distance from the trace of the Byobuyama fault and the combination of alteration minerals included in the fault rocks. 3. In the central part of the Byobuyama fault (CPBF), fault plane trend and combination of alteration minerals shows specific features. The continuous change is considered to mean the presence of factors that interfere with the dextral movement of the Byobuyama fault. What is

  9. Seismotectonics and fault structure of the California Central Coast

    USGS Publications Warehouse

    Hardebeck, Jeanne L.

    2010-01-01

    I present and interpret new earthquake relocations and focal mechanisms for the California Central Coast. The relocations improve upon catalog locations by using 3D seismic velocity models to account for lateral variations in structure and by using relative arrival times from waveform cross-correlation and double-difference methods to image seismicity features more sharply. Focal mechanisms are computed using ray tracing in the 3D velocity models. Seismicity alignments on the Hosgri fault confirm that it is vertical down to at least 12 km depth, and the focal mechanisms are consistent with right-lateral strike-slip motion on a vertical fault. A prominent, newly observed feature is an ~25 km long linear trend of seismicity running just offshore and parallel to the coastline in the region of Point Buchon, informally named the Shoreline fault. This seismicity trend is accompanied by a linear magnetic anomaly, and both the seismicity and the magnetic anomaly end where they obliquely meet the Hosgri fault. Focal mechanisms indicate that the Shoreline fault is a vertical strike-slip fault. Several seismicity lineations with vertical strike-slip mechanisms are observed in Estero Bay. Events greater than about 10 km depth in Estero Bay, however, exhibit reverse-faulting mechanisms, perhaps reflecting slip at the top of the remnant subducted slab. Strike-slip mechanisms are observed offshore along the Hosgri–San Simeon fault system and onshore along the West Huasna and Rinconada faults, while reverse mechanisms are generally confined to the region between these two systems. This suggests a model in which the reverse faulting is primarily due to restraining left-transfer of right-lateral slip.

  10. 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

  11. 2005 Precision Strike Annual Programs Review

    DTIC Science & Technology

    2005-04-20

    Control Canards (4) Polyurethane Foam Support DPICM (404 M101 Grenades) Warhead Fuze: Electronic Safe & Arm Device (ESAD) UNCLASSIFIED UNCLASSIFIED PF...SYSTEMS: • JASSM: Colonel James Geurts, USAF JASSM PM • ATACMS : Colonel Earnest Harris, USA PM, Precision Fires Rockets & Missiles, PEO Space and...UNCLASSIFIED UNCLASSIFIED Viper Strike Lineage ATACMS Delivered Base BATs Viper Strike SAL Seeker Proof of Principle Demos I & II Hunter-Viper Strike

  12. Equivalent strike-slip earthquake cycles in half-space and lithosphere-asthenosphere earth models

    USGS Publications Warehouse

    Savage, J.C.

    1990-01-01

    By virtue of the images used in the dislocation solution, the deformation at the free surface produced throughout the earthquake cycle by slippage on a long strike-slip fault in an Earth model consisting of an elastic plate (lithosphere) overlying a viscoelastic half-space (asthenosphere) can be duplicated by prescribed slip on a vertical fault embedded in an elastic half-space. Inversion of 1973-1988 geodetic measurements of deformation across the segment of the San Andreas fault in the Transverse Ranges north of Los Angeles for the half-space equivalent slip distribution suggests no significant slip on the fault above 30 km and a uniform slip rate of 36 mm/yr below 30 km. One equivalent lithosphere-asthenosphere model would have a 30-km thick lithosphere and an asthenosphere relaxation time greater than 33 years, but other models are possible. -from Author

  13. The continuation of the Kazerun fault system across the Sanandaj-Sirjan zone (Iran)

    NASA Astrophysics Data System (ADS)

    Safaei, Homayon

    2009-08-01

    The Kazerun (or Kazerun-Qatar) fault system is a north-trending dextral strike-slip fault zone in the Zagros mountain belt of Iran. It probably originated as a structure in the Panafrican basement. This fault system played an important role in the sedimentation and deformation of the Phanerozoic cover sequence and is still seismically active. No previous studies have reported the continuation of this important and ancient fault system northward across the Sanandaj-Sirjan zone. The Isfahan fault system is a north-trending dextral strike-slip fault across the Sanandaj-Sirjan zone that passes west of Isfahan city and is here recognized for the first time. This important fault system is about 220 km long and is seismically active in the basement as well as the sedimentary cover sequence. This fault system terminates to the south near the Main Zagros Thrust and to the north at the southern boundary of the Urumieh-Dokhtar zone. The Isfahan fault system is the boundary between the northern and southern parts of Sanandaj-Sirjan zone, which have fundamentally different stratigraphy, petrology, geomorphology, and geodynamic histories. Similarities in the orientations, kinematics, and geologic histories of the Isfahan and Kazerun faults and the way they affect the magnetic basement suggest that they are related. In fact, the Isfahan fault is a continuation of the Kazerun fault across the Sanandaj-Sirjan zone that has been offset by about 50 km of dextral strike-slip displacement along the Main Zagros Thrust.

  14. Fault connectivity, distributed shortening, and impacts on geologic- geodetic slip rate discrepancies in the central Mojave Desert, California

    NASA Astrophysics Data System (ADS)

    Selander, J.; Oskin, M. E.; Cooke, M. L.; Grette, K.

    2015-12-01

    Understanding off-fault deformation and distribution of displacement rates associated with disconnected strike-slip faults requires a three-dimensional view of fault geometries. We address problems associated with distributed faulting by studying the Mojave segment of the East California Shear Zone (ECSZ), a region dominated by northwest-directed dextral shear along disconnected northwest- southeast striking faults. We use a combination of cross-sectional interpretations, 3D Boundary Element Method (BEM) models, and slip-rate measurements to test new hypothesized fault connections. We find that reverse faulting acts as an important means of slip transfer between strike-slip faults, and show that the impacts of these structural connections on shortening, uplift, strike-slip rates, and off-fault deformation, help to reconcile the overall strain budget across this portion of the ECSZ. In detail, we focus on the Calico and Blackwater faults, which are hypothesized to together represent the longest linked fault system in the Mojave ECSZ, connected by a restraining step at 35°N. Across this restraining step the system displays a pronounced displacement gradient, where dextral offset decreases from ~11.5 to <2 km from south to north. Cross-section interpretations show that ~40% of this displacement is transferred from the Calico fault to the Harper Lake and Blackwater faults via a set of north-dipping thrust ramps. Late Quaternary dextral slip rates follow a similar pattern, where 1.4 +0.8/-0.4 mm/yr of slip along the Calico fault south of 35°N is distributed to the Harper Lake, Blackwater, and Tin Can Alley faults. BEM model results using revised fault geometries for the Mojave ECSZ show areas of uplift consistent with contractional structures, and fault slip-rates that more closely match geologic data. Overall, revised fault connections and addition of off-fault deformation greatly reduces the discrepancy between geodetic and geologic slip rates.

  15. The Quaternary Silver Creek Fault Beneath the Santa Clara Valley, California

    USGS Publications Warehouse

    Wentworth, Carl M.; Williams, Robert A.; Jachens, Robert C.; Graymer, Russell W.; Stephenson, William J.

    2010-01-01

    The northwest-trending Silver Creek Fault is a 40-km-long strike-slip fault in the eastern Santa Clara Valley, California, that has exhibited different behaviors within a changing San Andreas Fault system over the past 10-15 Ma. Quaternary alluvium several hundred meters thick that buries the northern half of the Silver Creek Fault, and that has been sampled by drilling and imaged in a detailed seismic reflection profile, provides a record of the Quaternary history of the fault. We assemble evidence from areal geology, stratigraphy, paleomagnetics, ground-water hydrology, potential-field geophysics, and reflection and earthquake seismology to determine the long history of the fault in order to evaluate its current behavior. The fault formed in the Miocene more than 100 km to the southeast, as the southwestern fault in a 5-km-wide right step to the Hayward Fault, within which the 40-km-long Evergreen pull-apart basin formed. Later, this basin was obliquely cut by the newly recognized Mt. Misery Fault to form a more direct connection to the Hayward Fault, although continued growth of the basin was sufficient to accommodate at least some late Pliocene alluvium. Large offset along the San Andreas-Calaveras-Mt Misery-Hayward Faults carried the basin northwestward almost to its present position when, about 2 Ma, the fault system was reorganized. This led to near abandonment of the faults bounding the pull-apart basin in favor of right slip extending the Calaveras Fault farther north before stepping west to the Hayward Fault, as it does today. Despite these changes, the Silver Creek Fault experienced a further 200 m of dip slip in the early Quaternary, from which we infer an associated 1.6 km or so of right slip, based on the ratio of the 40-km length of the strike-slip fault to a 5-km depth of the Evergreen Basin. This dip slip ends at a mid-Quaternary unconformity, above which the upper 300 m of alluvial cover exhibits a structural sag at the fault that we interpret as

  16. Tsunamis and splay fault dynamics

    USGS Publications Warehouse

    Wendt, J.; Oglesby, D.D.; Geist, E.L.

    2009-01-01

    The geometry of a fault system can have significant effects on tsunami generation, but most tsunami models to date have not investigated the dynamic processes that determine which path rupture will take in a complex fault system. To gain insight into this problem, we use the 3D finite element method to model the dynamics of a plate boundary/splay fault system. We use the resulting ground deformation as a time-dependent boundary condition for a 2D shallow-water hydrodynamic tsunami calculation. We find that if me stress distribution is homogeneous, rupture remains on the plate boundary thrust. When a barrier is introduced along the strike of the plate boundary thrust, rupture propagates to the splay faults, and produces a significantly larger tsunami man in the homogeneous case. The results have implications for the dynamics of megathrust earthquakes, and also suggest mat dynamic earthquake modeling may be a useful tool in tsunami researcn. Copyright 2009 by the American Geophysical Union.

  17. The Mw6.5 earthquake of 17 November 2015 in Lefkada Island and the seismotectonics in the Cephalonia Transform Fault (Ionian Sea, Greece)

    NASA Astrophysics Data System (ADS)

    Papadopoulos, Gerassimos A.; Agalos, Apostolos; Bocchini, Gian Maria; Chousianitis, Konstantinos; Karastathis, Vassilis; Triantafyllou, Ioanna; Kontoes, Charis; Papoutsis, Ioannis; Svigkas, Nikos; Koukouvelas, Ioannis; Zygouri, Vasiliki; Tselentis, Akis

    2016-04-01

    On 17 November 2015 a Mw6.5 earthquake ruptured offshore Lefkada Isl. in Ionian Sea, Greece, causing two victims, damage and ground failures particularly in the SW part of the island, which is consistent with the ground deformation pattern shown by InSAR analysis. Fault plane solutions released by CMT, NOA and other institutes are consistent indicating strike-slip right-lateral faulting, which is typical for the area, e.g. 2003 earthquake in the same fault zone. The analysis of 30-s daily observations of the permanent GPS stations operated by NOA showed displacement vectors with a motion pattern which is in agreement with the right-lateral kinematics of the rupture. The seismic plane was striking/dipping about N24E/W75.The seismic sequence for the period from 17 Nov. to 8 Dec. 2015 was relocated, with and without the use of time residuals, applying the NNLoc algorithm on a slightly modified 9-layer seismic velocity model (Haslinger et al., 1999) and by using only phases at stations closer than 120 km from the mainshock in order to avoid the use of Pn phases. The relocation procedure obtained without the use of residuals was repeated with the HypoDD algorithm. All relocations showed that the aftershock cloud follows the fault plane strike and consists of one north and one south clusters distributed in the seismogenic layer of 4-12 km. The south cluster started to develop a few hours after the mainshock, while it presents different statistical properties as compared to the north one. These results indicate that the south cluster was likely the result of triggering effect. Digital broadband P-wave teleseismic records, selected from GDSN stations to achieve the best possible azimuthal coverage, were used to invert for the mainshock rupture history. The teleseismic waveforms were corrected for instrument response, integrated to displacement, band-pass filtered from 0.01 to 1 Hz using a Butterworth filter and finally re-sampled to 0.2 samples/s. The finite fault

  18. Paleoseismology of Sinistral-Slip Fault System, Focusing on the Mae Chan Fault, on the Shan Plateau, SE Asia.

    NASA Astrophysics Data System (ADS)

    Curtiss, E. R.; Weldon, R. J.; Wiwegwin, W.; Weldon, E. M.

    2017-12-01

    The Shan Plateau, which includes portions of Myanmar, China, Thailand, Laos, and Vietnam lies between the dextral NS-trending Sagaing and SE-trending Red River faults and contains 14 active E-W sinistral-slip faults, including the Mae Chan Fault (MCF) in northern Thailand. The last ground-rupturing earthquake to occur on the broader sinistral fault system was the M6.8 Tarlay earthquake in Myanmar in March 2011 on the Nam Ma fault immediately north of the MCF the last earthquake to occur on the MCF was a M4.0 in the 5th century that destroyed the entire city of Wiang Yonok (Morley et al., 2011). We report on a trenching study of the MCF, which is part of a broader study to create a regional seismic hazard map of the entire Shan Plateau. By studying the MCF, which appears to be representative of the sinistral faults, and easy to work on, we hope to characterize both it and the other unstudied faults in the system. As part of a paleoseismology training course we dug two trenches at the Pa Tueng site on the MCF, within an offset river channel and the trenches exposed young sediment with abundant charcoal (in process of dating), cultural artifacts, and evidence for the last two (or three) ground-rupturing earthquakes on the fault. We hope to use the data from this site to narrow the recurrence interval, which is currently to be 2,000-4,000 years and the slip rate of 1-2 mm/year, being developed at other sites on the fault. By extrapolating the data of the MCF to the other faults we will have a better understanding of the whole fault system. Once we have characterized the MCF, we plan to use geomorphic offsets and strain rates from regional GPS to relatively estimate the activity of the other faults in this sinistral system.

  19. 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.

  20. Structural superposition in fault systems bounding Santa Clara Valley, California

    USGS Publications Warehouse

    Graymer, Russell W.; Stanley, Richard G.; Ponce, David A.; Jachens, Robert C.; Simpson, Robert W.; Wentworth, Carl M.

    2015-01-01

    Santa Clara Valley is bounded on the southwest and northeast by active strike-slip and reverse-oblique faults of the San Andreas fault system. On both sides of the valley, these faults are superposed on older normal and/or right-lateral normal oblique faults. The older faults comprised early components of the San Andreas fault system as it formed in the wake of the northward passage of the Mendocino Triple Junction. On the east side of the valley, the great majority of fault displacement was accommodated by the older faults, which were almost entirely abandoned when the presently active faults became active after ca. 2.5 Ma. On the west side of the valley, the older faults were abandoned earlier, before ca. 8 Ma and probably accumulated only a small amount, if any, of the total right-lateral offset accommodated by the fault zone as a whole. Apparent contradictions in observations of fault offset and the relation of the gravity field to the distribution of dense rocks at the surface are explained by recognition of superposed structures in the Santa Clara Valley region.

  1. The characteristics of the western extension of the Karakax fault in NW Tibet and its tectonic implications

    NASA Astrophysics Data System (ADS)

    Ge, C.; Liu, D.; Li, H.; Zheng, Y.; Pan, J.

    2017-12-01

    The Karakax strike-slip fault, located in northwest Tibet, is a mature deformation belt with a long-time evolutionary history, which is also active at present and plays an important role in the tectonic deformation of the northwestern Tibetan Plateau. Nowadays, most geologists consider that the Karakax fault is generally east-west striking along the Karakax river valley, and northwest striking until to the Tashkorgan in the Mazar area. However, an ENE-WSW fault was identified at the Mazar area, which sited at the bend of the Karakax fault, we named this fault as the Matar fault. Via the detailed geological survey, the similar geometry and kinematic characteristics were identified between the Karakax and Matar faults: (1) The similar fault zone scale(Karakax:90 300m; Matar:100 220m); (2) The similar preferred orientation (nearly EW) of the stretching lineations and foliations; (3) All the fault planes of the both faults have a high dip angle and is nearly EW striking; (4) Lots of ductile deformations, such as σ-type quartz rotational mortar, S-C fabric, symmetric drag fold and so on, indicated that the Matar fault is a right-lateral strike-slip and thrust fault during the early ductile deformation stage; (5) the deluvium, sheared by Matar fault, indicated that the Matar fault has already transformed into a left-lateral strike-slip fault during the later brittle deformation stage. All the above showed that the Matar fault has a similar geometry and kinematic characteristics with the Karakax fault, and the former is the probable the western extension of the latter. Moreover, the form of the Karakax-Matar fault may had an impact to the geomorphology of the west Kunlun-Pamir area, such as the strike of the moutains and faults. considering the age of west Kunlun mountains uplifting and Karakax fault activating, we regard that the Matar fault (the westward extension of Karakax fault) may contributes much in forming the modern geomorphology features of the west Kunlun

  2. 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.

  3. Illite authigenesis during faulting and fluid flow - a microstructural study of fault rocks

    NASA Astrophysics Data System (ADS)

    Scheiber, Thomas; Viola, Giulio; van der Lelij, Roelant; Margreth, Annina

    2017-04-01

    Authigenic illite can form synkinematically during slip events along brittle faults. In addition it can also crystallize as a result of fluid flow and associated mineral alteration processes in hydrothermal environments. K-Ar dating of illite-bearing fault rocks has recently become a common tool to constrain the timing of fault activity. However, to fully interpret the derived age spectra in terms of deformation ages, a careful investigation of the fault deformation history and architecture at the outcrop-scale, ideally followed by a detailed mineralogical analysis of the illite-forming processes at the micro-scale, are indispensable. Here we integrate this methodological approach by presenting microstructural observations from the host rock immediately adjacent to dated fault gouges from two sites located in the Rolvsnes granodiorite (Bømlo, western Norway). This granodiorite experienced multiple episodes of brittle faulting and fluid-induced alteration, starting in the Mid Ordovician (Scheiber et al., 2016). Fault gouges are predominantly associated with normal faults accommodating mainly E-W extension. K-Ar dating of illites separated from representative fault gouges constrains deformation and alteration due to fluid ingress from the Permian to the Cretaceous, with a cluster of ages for the finest (<0.1 µm) fraction in the early to middle Jurassic. At site one, high-resolution thin section structural mapping reveals a complex deformation history characterized by several coexisting types of calcite veins and seven different generations of cataclasite, two of which contain a significant amount of authigenic and undoubtedly deformation-related illite. At site two, fluid ingress along and adjoining the fault core induced pervasive alteration of the host granodiorite. Quartz is crosscut by calcite veinlets whereas plagioclase, K-feldspar and biotite are almost completely replaced by the main alteration products kaolin, quartz and illite. Illite-bearing micro

  4. Fault pattern at the northern end of the Death Valley - Furnace Creek fault zone, California and Nevada

    NASA Technical Reports Server (NTRS)

    Liggett, M. A. (Principal Investigator); Childs, J. F.

    1974-01-01

    The author has identified the following significant results. The pattern of faulting associated with the termination of the Death Valley-Furnace Creek Fault Zone in northern Fish Lake Valley, Nevada was studied in ERTS-1 MSS color composite imagery and color IR U-2 photography. Imagery analysis was supported by field reconnaissance and low altitude aerial photography. The northwest-trending right-lateral Death Valley-Furnace Creek Fault Zone changes northward to a complex pattern of discontinuous dip slip and strike slip faults. This fault pattern terminates to the north against an east-northeast trending zone herein called the Montgomery Fault Zone. No evidence for continuation of the Death Valley-Furnace Creek Fault Zone is recognized north of the Montgomery Fault Zone. Penecontemporaneous displacement in the Death Valley-Furnace Creek Fault Zone, the complex transitional zone, and the Montgomery Fault Zone suggests that the systems are genetically related. Mercury mineralization appears to have been localized along faults recognizable in ERTS-1 imagery within the transitional zone and the Montgomery Fault Zone.

  5. Potential earthquake faults offshore Southern California, from the eastern Santa Barbara Channel south to Dana Point

    USGS Publications Warehouse

    Fisher, M.A.; Sorlien, C.C.; Sliter, R.W.

    2009-01-01

    Urban areas in Southern California are at risk from major earthquakes, not only quakes generated by long-recognized onshore faults but also ones that occur along poorly understood offshore faults. We summarize recent research findings concerning these lesser known faults. Research by the U.S. Geological Survey during the past five years indicates that these faults from the eastern Santa Barbara Channel south to Dana Point pose a potential earthquake threat. Historical seismicity in this area indicates that, in general, offshore faults can unleash earthquakes having at least moderate (M 5-6) magnitude. Estimating the earthquake hazard in Southern California is complicated by strain partitioning and by inheritance of structures from early tectonic episodes. The three main episodes are Mesozoic through early Miocene subduction, early Miocene crustal extension coeval with rotation of the Western Transverse Ranges, and Pliocene and younger transpression related to plate-boundary motion along the San Andreas Fault. Additional complication in the analysis of earthquake hazards derives from the partitioning of tectonic strain into strike-slip and thrust components along separate but kinematically related faults. The eastern Santa Barbara Basin is deformed by large active reverse and thrust faults, and this area appears to be underlain regionally by the north-dipping Channel Islands thrust fault. These faults could produce moderate to strong earthquakes and destructive tsunamis. On the Malibu coast, earthquakes along offshore faults could have left-lateral-oblique focal mechanisms, and the Santa Monica Mountains thrust fault, which underlies the oblique faults, could give rise to large (M ??7) earthquakes. Offshore faults near Santa Monica Bay and the San Pedro shelf are likely to produce both strike-slip and thrust earthquakes along northwest-striking faults. In all areas, transverse structures, such as lateral ramps and tear faults, which crosscut the main faults, could

  6. 14 CFR 35.38 - Lightning strike.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... STANDARDS: PROPELLERS Tests and Inspections § 35.38 Lightning strike. The applicant must demonstrate, by tests, analysis based on tests, or experience on similar designs, that the propeller can withstand a lightning strike without causing a major or hazardous propeller effect. The limit to which the propeller has...

  7. 14 CFR 35.38 - Lightning strike.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... STANDARDS: PROPELLERS Tests and Inspections § 35.38 Lightning strike. The applicant must demonstrate, by tests, analysis based on tests, or experience on similar designs, that the propeller can withstand a lightning strike without causing a major or hazardous propeller effect. The limit to which the propeller has...

  8. 14 CFR 35.38 - Lightning strike.

    Code of Federal Regulations, 2013 CFR

    2013-01-01

    ... STANDARDS: PROPELLERS Tests and Inspections § 35.38 Lightning strike. The applicant must demonstrate, by tests, analysis based on tests, or experience on similar designs, that the propeller can withstand a lightning strike without causing a major or hazardous propeller effect. The limit to which the propeller has...

  9. 14 CFR 35.38 - Lightning strike.

    Code of Federal Regulations, 2012 CFR

    2012-01-01

    ... STANDARDS: PROPELLERS Tests and Inspections § 35.38 Lightning strike. The applicant must demonstrate, by tests, analysis based on tests, or experience on similar designs, that the propeller can withstand a lightning strike without causing a major or hazardous propeller effect. The limit to which the propeller has...

  10. 14 CFR 35.38 - Lightning strike.

    Code of Federal Regulations, 2014 CFR

    2014-01-01

    ... STANDARDS: PROPELLERS Tests and Inspections § 35.38 Lightning strike. The applicant must demonstrate, by tests, analysis based on tests, or experience on similar designs, that the propeller can withstand a lightning strike without causing a major or hazardous propeller effect. The limit to which the propeller has...

  11. 14 CFR 29.631 - Bird strike.

    Code of Federal Regulations, 2011 CFR

    2011-01-01

    ... 14 Aeronautics and Space 1 2011-01-01 2011-01-01 false Bird strike. 29.631 Section 29.631... STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Design and Construction General § 29.631 Bird strike. The... safe landing (for Category B) after impact with a 2.2-lb (1.0 kg) bird when the velocity of the...

  12. 14 CFR 29.631 - Bird strike.

    Code of Federal Regulations, 2010 CFR

    2010-01-01

    ... 14 Aeronautics and Space 1 2010-01-01 2010-01-01 false Bird strike. 29.631 Section 29.631... STANDARDS: TRANSPORT CATEGORY ROTORCRAFT Design and Construction General § 29.631 Bird strike. The... safe landing (for Category B) after impact with a 2.2-lb (1.0 kg) bird when the velocity of the...

  13. Collective Bargaining Laws and Teacher Strikes

    ERIC Educational Resources Information Center

    Colton, David L.

    1978-01-01

    Several methodological flaws were found in a Public Service Research Council study relating increases in public employee strikes with the adoption of bargaining statutes. A replication, using teachers, suggests some nonstatutory factors that may strongly affect the incidence of teacher strikes. (Author/IRT)

  14. Viscoelastic Postseismic Rebound to Strike-Slip Earthquakes in Regions of Oblique Plate Convergence

    NASA Technical Reports Server (NTRS)

    Cohen, Steven C.

    1999-01-01

    According to the slip partitioning concept, the trench parallel component of relative plate motion in regions of oblique convergence is accommodated by strike-slip faulting in the overriding continental lithosphere. The pattern of postseismic surface deformation due to viscoelastic flow in the lower crust and asthenosphere following a major earthquake on such a fault is modified from that predicted from the conventual elastic layer over viscoelastic halfspace model by the presence of the subducting slab. The predicted effects, such as a partial suppression of the postseismic velocities by 1 cm/yr or more immediately following a moderate to great earthquake, are potentially detectable using contemporary geodetic techniques.

  15. High Frequency Near-Field Ground Motion Excited by Strike-Slip Step Overs

    NASA Astrophysics Data System (ADS)

    Hu, Feng; Wen, Jian; Chen, Xiaofei

    2018-03-01

    We performed dynamic rupture simulations on step overs with 1-2 km step widths and present their corresponding horizontal peak ground velocity distributions in the near field within different frequency ranges. The rupture speeds on fault segments are determinant in controlling the near-field ground motion. A Mach wave impact area at the free surface, which can be inferred from the distribution of the ratio of the maximum fault-strike particle velocity to the maximum fault-normal particle velocity, is generated in the near field with sustained supershear ruptures on fault segments, and the Mach wave impact area cannot be detected with unsustained supershear ruptures alone. Sub-Rayleigh ruptures produce stronger ground motions beyond the end of fault segments. The existence of a low-velocity layer close to the free surface generates large amounts of high-frequency seismic radiation at step over discontinuities. For near-vertical step overs, normal stress perturbations on the primary fault caused by dipping structures affect the rupture speed transition, which further determines the distribution of the near-field ground motion. The presence of an extensional linking fault enhances the near-field ground motion in the extensional regime. This work helps us understand the characteristics of high-frequency seismic radiation in the vicinities of step overs and provides useful insights for interpreting the rupture speed distributions derived from the characteristics of near-field ground motion.

  16. 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.

  17. Geometrical and Structural Asperities on Fault Surfaces

    NASA Astrophysics Data System (ADS)

    Sagy, A.; Brodsky, E. E.; van der Elst, N.; Agosta, F.; di Toro, G.; Collettini, C.

    2007-12-01

    Earthquake dynamics are strongly affected by fault zone structure and geometry. Fault surface irregularities and the nearby structure control the rupture nucleation and propagation, the fault strength, the near-field stress orientations and the hydraulic properties. New field observations demonstrate the existence of asperities in faults as displayed by topographical bumps on the fault surface and hardening of the internal structure near them. Ground-based LIDAR measurements on more than 30 normal and strike slip faults in different lithologies demonstrate that faults are not planar surfaces and roughness is strongly dependent on fault displacement. In addition to the well-understood roughness exemplified by abrasive striations and fracture segmentation, we found semi-elliptical topographical bumps with wavelengths of a few meters. In many faults the bumps are not spread equally on the surface and zones can be bumpier than others. The bumps are most easily identified on faults with total displacement of dozens to hundreds of meters. Smaller scale roughness on these faults is smoothed by abrasive processes. A key site in southern Oregon shows that the topographic bumps are closely tied to the internal structure of the fault zone. At this location, we combine LiDAR data with detailed structural analysis of the fault zone embedded in volcanic rocks. Here the bumps correlate with an abrupt change in the width of the cohesive cataclasite layer that is exposed under a thin ultracataclasite zone. In most of the exposures the cohesive layer thickness is 10-20 cm. However, under protruding bumps the layer is always thickened and the width can locally exceed one meter. Field and microscopic analyses show that the layer contains grains with dimensions ranging from less than 10 μ up to a few centimeters. There is clear evidence of internal flow, rotation and fracturing of the grains in the layer. X-Ray diffraction measurements of samples from the layer show that the bulk

  18. The Intersection between the Gloria Transform Fault and the Tore-Madeira Rise in the NE Atlantic: New Tectonic Insights from Analog Modeling Results

    NASA Astrophysics Data System (ADS)

    Rosas, F. M.; Tomas, R.; Duarte, J. C.; Schellart, W. P.; Terrinha, P.

    2014-12-01

    The intersection between the Gloria Fault (GF) and the Tore-Madeira rise (TMR) in NE Atlantic marks a transition from a discrete to a diffuse nature along a critical segment of the Eurasia/Africa plate boundary. To the West of such intersection, approximately since the Azores triple junction, this plate boundary is mostly characterized by a set of closely aligned and continuous strike-slip faults that make up the narrow active dextral transcurrent system of the GF (with high magnitude M>7 historical earthquakes). Wh