Science.gov

Sample records for active right-lateral strike-slip

  1. A Newly Recognized, 460 km Long and Arcuate, Right-Lateral Strike-Slip Fault Traversing Puerto Rico and the Virgin Islands

    NASA Astrophysics Data System (ADS)

    Loureiro, P.; Mann, P.

    2014-12-01

    We use 830 km of seismic reflection lines and 94,000 km2 of high-resolution multibeam bathymetry to identify a 460-km-long and semi-arcuate strike-slip fault that can be traced to the southwest from the Mona rift west of Puerto, across the onland area of south-central Puerto Rico (Cerro Goden and Great Southern Puerto Rico fault zones), across the Whiting basin southeast of Puerto Rico, across the Virgin Islands basin and to the northeast along the Anegada Passage and Tortola ridge. On multibeam and seismic reflection data the fault is active based on a continuous seafloor scarp ranging in height from 10 to 40 m. Seismic profiles show that the fault is alternatively downthrown to the north and south typical of strike-slip faults. The sense of most recent strike-slip offset on the fault is right-lateral based on offsets at 4 localities that range from 1.5 to3.5 km. Shallow earthquake swarms are associated with the fault trace in the Virgin Islands area but large segments of the fault are aseismic and appear locked. We propose that this fault system forms the southern boundary of an actively CCW-rotating Puerto Rico microplate that is driven by oblique, left-lateral shear of the North America-Caribbean plate boundary. The northern edge of the microplate is inferred to follow left-lateral faults known in the Puerto Rico trench (Bunce and Bowin fault zones) that close the loop around the crudely circular microplate in the area of the Mona rift. We have modeled these boundaries of the rotating block using the Defnode method of finite elements constrained by GPS and earthquake slip vectors.

  2. Evidence for right-lateral strike-slip environment in the Kutch basin of northwestern India from moment tensor inversion studies

    NASA Astrophysics Data System (ADS)

    Rao, Ch. Nagabhushana; Rao, N. Purnachandra; Rastogi, B. K.

    2013-03-01

    The Kutch region located in northwestern part of India is an ancient rift basin that was active until Cretaceous period. The region falls close to the India-Arabia and the India-Eurasia plate boundaries and has experienced devastating earthquakes in the past, namely the 1819 Allah Bund earthquake, the 1956 Anjar earthquake and the 2001 Bhuj earthquake. To understand the tectonics of this region with respect to the adjacent plate boundaries, we invert seismic waveform data of 11 earthquakes in this region recorded by a network of the Institute of Seismological Research (ISR) during 2007-2009. The study yields focal mechanism solutions of reverse fault and strike-slip type mechanism. The inferred fault planes correlate well with the local trends of the known tectonic faults while the principal stress directions derived from stress inversion based on a linearized least squares approach, trend agreeably with the ambient stress field directions. A consistently right-lateral sense of shear is found on all the local faults as derived from each of the matching planes of the focal mechanism solutions computed in the present study. It is inferred that in the Kutch region a right-lateral strike-slip environment prevails along predominantly EW to NW-SE oriented deep-seated pre-existing faults in an otherwise compressive stress regime. This, in conjunction with the left-lateral movements along the Girnar mountain in southern Saurashtra, inferred from previous studies, indicates a westward escape of the Kutch-Saurashtra block as a consequence of the northward collision of the Indian plate with respect to the Eurasian landmass.

  3. Seismic evidence of active strike-slip faulting in the external Gulf of Cadiz (SW Iberian Margin)

    NASA Astrophysics Data System (ADS)

    Bartolome, R.; Gràcia, E.; Stich, D.; Martinez-Loriente, S.; Klaeschen, D.; Masana, E.; Diez, S.; Lo Iacono, C.; Moreno, X.; Zitellini, N.; Manuel, A.; Dañobeitia, J.

    2009-12-01

    with a deformation fault zone ranging from 2.5 to 6 km wide. Recent estimations of seismic moment tensors, obtained from time domain inversion of near-regional waveforms, show right-lateral strike-slip faulting solutions with some reverse component being consistent with the geometry identified in the structures of the SL area. We present an additional MCS and TOPAS profile, crossing perpendicular a newly identified WNW-ESE lineament located north of the SFZ, that we called the North Lineation. Seismic data show right-lateral faulting in an 8.7 km wide fault deformation zone up to 9 km depth. This structure evidence that strike-slip faulting is not only constrained to the SFZ but widespread across the GC area, thus, giving new lights on the geodynamics of the SW Iberian margin.

  4. Strike-slip fault geometry in Turkey and its influence on earthquake activity

    NASA Technical Reports Server (NTRS)

    Barka, A. A.; Kadinsky-Cade, K.

    1988-01-01

    The geometry of Turkish strike-slip faults is reviewed, showing that fault geometry plays an important role in controlling the location of large earthquake rupture segments along the fault zones. It is found that large earthquake ruptures generally do not propagate past individual stepovers that are wider than 5 km or bends that have angles greater than about 30 degrees. It is suggested that certain geometric patterns are responsible for strain accumulation along portions of the fault zone. It is shown that fault geometry plays a role in the characteristics of earthquake behavior and that aftershocks and swarm activity are often associated with releasing areas.

  5. Relative tectonic activity assessment along the East Anatolian strike-slip fault, Eastern Turkey

    NASA Astrophysics Data System (ADS)

    Khalifa, Abdelrahman

    2016-04-01

    The East Anatolian transform fault is a morphologically distinct and seismically active left-lateral strike-slip fault that extends for ~ 500 km from Karlıova to the Maraş defining the boundary between the Anatolian Block and Syrian Foreland. Deformed landforms along the East Anatolian fault provide important insights into the nature of landscape development within an intra-continental strike-slip fault system. Geomorphic analysis of the East Anatolian fault using geomorphic indices including mountain front sinuosity, stream length-gradient index, drainage density, hypsometric integral, and the valley-width to valley height ratio helped differentiate the faulting into segments of differing degrees of the tectonic and geomorphic activity. Watershed maps for the East Anatolian fault showing the relative relief, incision, and maturity of basins along the fault zone help define segments of the higher seismic risk and help evaluate the regional seismic hazard. The results of the geomorphic indices show a high degree of activity, reveal each segment along the fault is active and represent a higher seismic hazard along the entire fault.

  6. Slip sense inversion on active strike-slip faults in southwest Japan and its implications for Cenozoic tectonic evolution

    NASA Astrophysics Data System (ADS)

    Maruyama, Tadashi; Lin, Aiming

    2004-05-01

    Analyses of deflected river channels, offset of basement rocks, and fault rock structures reveal that slip sense inversion occurred on major active strike-slip faults in southwest Japan such as the Yamasaki and Mitoke fault zones and the Median Tectonic Line (MTL). Along the Yamasaki and Mitoke fault zones, small-size rivers cutting shallowly mountain slopes and Quaternary terraces have been deflected sinistrally, whereas large-size rivers which deeply incised into the Mio-Pliocene elevated peneplains show no systematically sinistral offset or complicated hairpin-shaped deflection. When the sinistral offsets accumulated on the small-size rivers are restored, the large-size rivers show residual dextral deflections. This dextral offset sense is consistent with that recorded in the pre-Cenozoic basement rocks. S-C fabrics of fault gouge and breccia zone developed in the active fault zones show sinistral shear sense compatible with earthquake focal mechanisms, whereas those of the foliated cataclasite indicate a dextral shear sense. These observations show that the sinistral strike-slip shear fabrics were overprinted on dextral ones which formed during a previous deformation phase. Similar topographic and geologic features are observed along the MTL in the central-eastern part of the Kii Peninsula. Based on these geomorphological and geological data, we infer that the slip sense inversion occurred in the period between the late Tertiary and mid-Quaternary period. This strike-slip inversion might result from the plate rearrangement consequent to the mid-Miocene Japan Sea opening event. This multidisciplinary study gives insight into how active strike-slip fault might evolves with time.

  7. Quantification of Both Normal and Right-Lateral Late Quaternary Activity Along the Kongur Shan Extensional System, Chinese Pamir

    NASA Astrophysics Data System (ADS)

    Chevalier, M. L.; Pan, J.; Liu, D.; Wang, M.; Lu, H.; Li, H.

    2014-12-01

    The Pamir Mountains, located at the western end of the Indo-Asian collision zone, are one of the most tectonically active regions in central Asia. The Kongur Shan extensional system (KES), located in the Chinese Pamir, accommodates EW extension due to the India/Asia collision and has been the focus on numerous Cenozoic studies, whereas there are very few late Quaternary studies. The KES is mostly normal, except towards its NW end, where it becomes right-lateral strike-slip, along the Muji segment. From Muji to Tashkorgan, we investigated 6 sites, where active normal and/or strike-slip faults cut and offset abandoned river channels or alluvial fans and terraces, which allows us to quantify both the normal and strike-slip motions at different locations along the KES. Our preliminary results yield vertical and right-lateral rates of ~1.8 and >3.2 mm/yr along the northern KES (Muji to Bulunkou) during the Holocene, and of ~1.9-2.7 and ~1 mm/yr along the southern KES (near Taheman) since ~30 ka. These preliminary rates, consistent with GPS data and Cenozoic rates, imply that the EW extension rate due to the northward indentation of the Pamir salient as well as due to the clockwise rotation of the rigid Tarim basin, is partly accommodated by the Muji-Tashkorgan pull-apart basin, and is faster in the north than in the south (from ~5 to ~2 mm/yr).

  8. Active interplay between strike-slip and extensional structures in a Back-Arc environment, Bay of Plenty, New Zealand

    NASA Astrophysics Data System (ADS)

    Barnes, P. M.; Lamarche, G.; Bull, J. M.

    2003-12-01

    Active continental back-arc tectonics associated with the oblique Hikurangi subduction zone, North Island, New Zealand, is characterized by (1) extensional deformation distributed across a 40-50 km-wide zone, but presently concentrated in the east within the 20 km-wide, NE-striking Taupo Fault Belt (TFB) and Whakatane Graben (WG); (2) c. 12mm/yr extension rate at the Bay of Plenty coast; (3) 1-3 mm/yr subsidence in the WG; and (4) a seismogenic zone estimated to be 6-9 km thick. A component of the oblique convergence within the plate boundary is partitioned to the east onto the adjacent North Island Dextral Fault Belt (NIDFB), a large NNE-trending strike-slip fault system traversing the entire North Island. At the Bay of Plenty coast, the NIDFB strikes north, with an estimated strike-slip rate of at least 1 mm/yr. Both normal and strike-slip fault systems extend beneath the continental shelf in the Bay of Plenty, and because of differences in their strike, they converge and interact. Detailed mapping of faults using marine seismic reflection profiles and multibeam bathymetric data reveals the structure of the WG. Tilted basement blocks are associated with large west-dipping faults, numerous antithetic secondary faults, and domino-style fault arrays. Eastward migration of the principal extension zone during the last c. 1 Myrs has resulted in the encroachment and oblique overprinting of the NIDFB by the WG. The structure and geometry of the White Island Fault (WIF), currently the principal fault along the eastern margin of the graben, results from interaction and linkage of the two fault systems. The displacement profile of this fault reveals relatively young NE-striking sections that obliquely link more northerly-striking, inherited components of the NIDFB. Understanding of the fault structure and evolution may have implications for the interpretation of earthquake potential close to urban centres.

  9. Walker Lake, Nevada: sedimentation in an active, strike-slip related basin

    SciTech Connect

    Link, M.H.; Roberts, M.T.

    1984-04-01

    Walker Lake, Nevada, is in an active fault-controlled basin related to the right-lateral, northwest-trending Walker Lane Shear Zone on the western side of the Basin and Range province. The lake occurs in a half graben bounded on its west side by a high-angle normal fault zone along the Wassuk Range front. This fault zone may merge to the north into the Walker Lane fault system, which forms the northeast boundary of the basin. To the south of Walker Lake, the Wassuk front fault merges with an east-northeast trending left-lateral fault. The Walker Lake basin is interpreted to be a pull-apart basin formed within the triangular zone bounded by the Wassuk front, the Walker Lane, and left-lateral faults. The Walker River drainage basin occupies about 10,000 km/sup 2/ (3800 mi/sup 2/) in western Nevada and parts of California and is essentially a closed hydrologic system that drains from the crest of the Sierra Nevada in California and terminates in Walker Lake. Walker Lake trends north-northwest and is 27.4 km (17 mi) long and 8 km (5 mi) wide with water depths exceeding 30 m (100 ft). Lake Lahontan (Wisconsinian) shorelines ring Walker Lake and suggest water depths of 150 m (500 ft) above the present lake level. The lake is situated in an asymmetric basin with steep alluvial fans flanking the western shoreline (Wassuk Range) and gentle, areally more extensive fans flanking the eastern shoreline (Gillis Range). The Walker River delta enters the lake from the north and is a major sediment point source for the basin. Older dissected shoreline, alluvial fan, Gilbert delta, and beach ridge deposits were built largely of coarse-grained, locally derived materials. Stromatolites, oncolites, and tufas formed along the shorelines, whereas mud and organic sediments accumulated in the lake on the west side of the basin. Extensive submerged sand flats and local sand dunes occur on the east side of the basin.

  10. Sag-ponding and its Significance in determining Paleo-seismic events along the active strike- slip fault

    NASA Astrophysics Data System (ADS)

    Li, C.; Zhang, P.; Yuan, D.

    2007-12-01

    During the development of one active fault, we really want to know how it behaves and what it will do next. This mostly depends on the record and preservation of the information showing the action of the fault. Sparse young sediments or sediments with coarse grain along most of big strike-slip faults make it hard record and preserve the vestige of the paleo-seismic events. This extremely restricts the development of the Paleo-seismic research. Sag-ponding as well as the deposits in ponds, which are formed by the movement of the fault, can help settling the difficulty. Periodic sag-ponding is a feature to which should be paid more attention along the strike-slip fault, it can develop a pond to capture plenty fine sediments which well record the action of the faults. Sag-ponding can easily be found on the main active strike-slip faults in northern and eastern Tibet. By disclosing the sag-ponding depositions with 3-D excavations, sediment distribution and characters of relevant sag-ponds, and the relation between the sag-ponding and faulting were discussed. 1. Mechanism of the formation of the sag-pond When the valleys and ridges intersecting with the fault are displaced, the fault scarps will block the flow of the streams cut by the fault, or make the gullies develop ancon-like bend. This would form a space for water-storage, and thus a sag-pond comes into being. If the fault behaves like this many times, multi-sag-ponding will occur. 2. Rhythmic sag-ponding deposition features and stratigraphic sequence (1) Vertical characteristics. Observed from the stratigraphic profiles disclosed by the excavation, stratigraphic sequence shows good rhythms. There are several rhythms in each pond, and one rhythm is composed of the lower coarse layers and the upper fine layers. That is, the grains are coarser below and finer upward. (2) Transverse variation. In the direction parallel to the fault, the deposition center of each sag-pond appears regular movement, or migration

  11. Tsunami Hazards From Strike-Slip Earthquakes

    NASA Astrophysics Data System (ADS)

    Legg, M. R.; Borrero, J. C.; Synolakis, C. E.

    2003-12-01

    Strike-slip faulting is often considered unfavorable for tsunami generation during large earthquakes. Although large strike-slip earthquakes triggering landslides and then generating substantial tsunamis are now recognized hazards, many continue to ignore the threat from submarine tectonic displacement during strike-slip earthquakes. Historical data record the occurrence of tsunamis from strike-slip earthquakes, for example, 1906 San Francisco, California, 1994 Mindoro, Philippines, and 1999 Izmit, Turkey. Recognizing that strike-slip fault zones are often curved and comprise numerous en echelon step-overs, we model tsunami generation from realistic strike-slip faulting scenarios. We find that tectonic seafloor uplift, at a restraining bend or"pop-up" structure, provides an efficient mechanism to generate destructive local tsunamis; likewise for subsidence at divergent pull-apart basin structures. Large earthquakes on complex strike-slip fault systems may involve both types of structures. The California Continental Borderland is a high-relief submarine part of the active Pacific-North America transform plate boundary. Natural harbors and bays created by long term vertical motion associated with strike-slip structural irregularities are now sites of burgeoning population and major coastal infrastructure. Significant local tsunamis generated by large strike-slip earthquakes pose a serious, and previously unrecognized threat. We model several restraining bend pop-up structures offshore southern California to quantify the local tsunami hazard. Maximum runup derived in our scenarios ranges from one to several meters, similar to runup observed from the 1994 Mindoro, Philippines, (M=7.1) earthquake. The runup pattern is highly variable, with local extremes along the coast. We only model the static displacement field for the strike-slip earthquake source; dynamic effects of moving large island or submerged banks laterally during strike-slip events remains to be examined

  12. Tectonic Geomorphology in the Laboratory: Evolution of landscape along an active thrust, normal and strike-slip fault

    NASA Astrophysics Data System (ADS)

    Graveleau, Fabien; Strak, Vincent; Dominguez, Stéphane; Malavieille, Jacques; Chatton, Marina; Manighetti, Isabelle; Petit, Carole

    2015-04-01

    Tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics. We present here results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes (erosion, transport and sedimentation), coupled with accurate model monitoring techniques. This approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end-member geological settings: compression, extension and strike-slip. Experimental results outline first that experimental morphologies evolve significantly at a short timescale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike-slip setting, the complex morphology of the wrench zone, composed of

  13. 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

  14. Earthquake cycle associated with active strike slip faults in central Panamá

    NASA Astrophysics Data System (ADS)

    Rick, Bennett; Spinler, Joshua C.; Compton, Kathleen; Rockwell, Thomas K.; Gath, Eldon

    2013-04-01

    The rigidity of the Panamá Isthmus is currently under debate, with important implications for seismic hazards to the Panamá Canal and Panamá City. Whereas Panamá has traditionally been described as a non-deforming microplate caught between a number of larger tectonic plates, new paleoseismic data collected at a limited number of trench sites in association with the ongoing expansion of the Panamá Canal may challenge the validity of the rigid microplate hypothesis. Crustal velocities from a new, ~100 km aperture, 5-station continuous GPS network constructed across the Rio Gatún, Limón, and Pedro Miguel fault zones confirm that these fault zones are active, forming a system of faults that traverse central Panamá in close proximity to the Panamá Canal and Panamá City. However, the slip rates inferred from these new geodetic data are lower than the geologic rates when using an elastic halfspace model. Differences among previous geodetic investigations, which concluded that Panamá is rigid, and the geological slip rate estimates are explained by earthquake cycle effects associated with long recurrence intervals relative to lower crust and upper mantle Maxwell relaxation times. Late in the earthquake cycle the geodetic strain field is broadly distributed, giving the false appearance of low seismic hazards.

  15. Ground Motion Polarization in the Damage Zone of the Active, Strike-Slip Mattinata Fault, Southern Italy

    NASA Astrophysics Data System (ADS)

    Pischiutta, M.; Cianfarra, P.; Anselmi, M.; Salvini, F.; Rovelli, A.

    2013-12-01

    We have recently observed the occurrence of directional amplification effects in fault zones using both earthquakes and ambient noise records. In several faults we have found that ground motion polarization tends to have a high angle to cleavages produced by the stress related to the kinematics in the fault damage zone. We thus interpret this effect as due to the higher compliance of the fractured rocks of the damage zone in a direction transversal to the cleavage strike. Here we have tested the technique of the wavefield polarization using ambient vibrations recorded across the seismically active Mattinata Fault, in the Gargano Promontory, Italy. This fault has been chosen for the high number of structural investigations led out so far. The Mattinata Fault outcrops for over 40 km and shows an ondulated trajectory that is characterized by a number of significant tectonic-related morphological features compatible with a general left-lateral strike-slip kinematics. These features include a pull-apart basin and a transpressional zone. The main associated cleavage consists of a marked array of disjunctive, spaced pressure-solution surfaces developed within the 200-300 m wide fault damage zone. In order to relate the orientation of cleavage to the ground motion polarization, we measured 20-50 min of ambient noise at about 30 sites chosen in the fault damage zone close to rock outcrops where also structural geological measurements were carried out. Ground motion polarization is assessed both in the frequency and time domain through the individual-station horizontal-to-vertical spectral ratio and covariance-matrix analysis, respectively. Two ambient noise measurements were performed close to permanent broadband stations of the Italian Seismic Telemetric Network. Results are consistent with those inferred on earthquake records at the two permanent stations, confirming that ambient noise yields results consistent with earthquake records as previously observed in other

  16. Late Quaternary Activity and Seismogenic Potential of the Gonave Microplate: Plantain Garden Strike-Slip Fault Zone of Eastern Jamaica

    NASA Astrophysics Data System (ADS)

    Mann, P.; Prentice, C.; King, W.; Demets, C.; Wiggins-Grandison, M.; Benford, B.

    2008-12-01

    At the longitude of Jamaica, Caribbean (Carib)-North America (Noam) plate motion of 19 ± 2 mm/a is carried by two parallel, left-lateral strike-slip faults, the Oriente fault zone, immediately south of Cuba, and the Enriquillo-Plantain Garden fault zone (EPGFZ), which lies 100-150 km further south. It has been postulated that the lithosphere between these faults constitutes an independent Gonave microplate that has formed in response to the ongoing collision between the leading edge of Carib in Hispaniola and the Bahama carbonate platform. GPS measurements in Jamaica and Hispanola is supportive of the microplate hypothesis and indicates that roughly half of Carib-Noam plate motion (8-14 mm/a) is carried by the EPGFZ of southern Hispaniola and eastern Jamaica. This study applies geomorphic and paleoseismic methods as a direct test of the activity and amount of microplate motion carried on the Plantain Garden fault segment of eastern Hispaniola and how this motion is distributed across a large restraining bend that has formed the island of Jamaica since the late Miocene. The EPFZ curves gently to the northeast and forming a steep mountain front to the Blue Mountains restraining bend with elevations up to 2200 m. Geomorphic fault-related features along the mountain front fault zone include left-laterally deflected rivers and streams, but no small scale features indicative of Holocene activity. River and stream deflections range from 0.1 to 0.5 km. We identified and trenched the most active trace of the mountain front fault at the Morant River where the fault is characterized by a 1.5-m-wide sub-vertical fault zone juxtaposing sheared alluvium and fault Cretaceous basement rocks This section is overlain by a 6-m-thick fluvial terrace. Trenching in the unfaulted terrace immediately overlying the fault trace revealed radiocarbon and OSL ages ranging from 20 to 21 ka that are consistent with a prominent unfaulted alluvial fan along the projection of this fault 1.5 km to

  17. Interaction between slip events, erosion and sedimentation along an active strike-slip fault: Insights from analog models

    NASA Astrophysics Data System (ADS)

    Chatton, M.; Malavieille, J.; Dominguez, S.; Manighetti, I.; Romano, C.; Beauprêtre, S.; Garembois, S.; Larroque, C.

    2012-04-01

    Recovering information on past (i.e., last 102-104 yrs) large earthquakes on faults is a challenge. The classical approach -especially used on strike-slip faults- consists in searching morphological markers such as river channels, streams, alluvial fans, ridges or terrace risers, etc, that would be offset by the fault, and measure these offsets by reconstructing the original position and shape of the markers. Combined with the dating of the offset markers, this morphotectonic paleoseismological approach may provide information on the slips and ages of the most recent earthquakes on the fault under study. Yet, the approach is complex as it depends on the recognition of unambiguous paired markers on either side of the fault. And our capability to recognize similar markers on either side of a fault in turn greatly depends on the 'evolution' that these markers may have sustained subsequently to their very first slip disruption. Did the repeating earthquake slip events modify their surface appearance? Did their morphology and position (ex: burying, destruction, modification, etc) evolve with the sedimentation and erosion that might have occurred during the fault history? Etc. These questions have rarely been approached for they are difficult to address in natural settings. And as we are unable to answer them in the natural cases that we study, the slip reconstructions that we provide are generally uncertain as they are likely based on an incomplete or biased record of the past fault slips. Therefore, the objective of our work is to contribute to better understand and document the nature and 'evolution' of the morphological markers that are commonly used in morphotectonic and paleoseismological analyses, especially along strike-slip faults. We approach these questions experimentally. We have developed an original experimental set-up made to simulate repeated slip events on a strike-slip fault placed in a wet environment sustaining sedimentation and erosion. The fault

  18. Hairpin river loops and slip-sense inversion on southeast Asian strike-slip faults

    NASA Astrophysics Data System (ADS)

    Lacassin, Robin; Replumaz, Anne; Hervé Leloup, P.

    1998-08-01

    In the Golden Triangle region of southeast Asia (northern Thailand, Laos and Burma, southern Yunnan), the Mekong, Salween, and neighboring rivers show hairpin geometries where they cross active strike-slip faults. Restoration of young, left-lateral offsets of these rivers leaves residual right-lateral bends of many kilometers. We interpret these hairpins as evidence of late Cenozoic slip-sense inversion on these faults, about 5 to 20 Ma. Near the Red River fault, stress field and slip-sense inversion occurred ca. 5 Ma. This implies that the present course of these large rivers has existed for at least several million years. Pliocene Quaternary slip rates, possibly on the order of 1 mm/yr, are inferred on each of the strike-slip faults of the Golden Triangle.

  19. Active strike-slip faulting history inferred from offsets of topographic features and basement rocks: a case study of the Arima Takatsuki Tectonic Line, southwest Japan

    NASA Astrophysics Data System (ADS)

    Maruyama, Tadashi; Lin, Aiming

    2002-01-01

    Geological, geomorphological and geophysical data have been used to determine the total displacement, slip rates and age of formation of the Arima-Takatsuki Tectonic Line (ATTL) in southwest Japan. The ATTL is an ENE-WSW-trending dextral strike-slip fault zone that extends for about 60 km from northwest of the Rokko Mountains to southwest of the Kyoto Basin. The ATTL marks a distinct topographic boundary between mountainous regions and basin regions. Tectonic landforms typically associated with active strike-slip faults, such as systematically-deflected stream channels, offset ridges and fault scarps, are recognized along the ATTL. The Quaternary drainage system shows progressive displacement along the fault traces: the greater the magnitude of stream channel, the larger the amount of offset. The maximum dextral deflection of stream channels is 600-700 m. The field data and detailed topographic analyses, however, show that pre-Neogene basement rocks on both sides of the ATTL are displaced by about 16-18 km dextrally and pre-Mio-Pliocene elevated peneplains are also offset 16-17 km in dextral along the ATTL. This suggests that the ATTL formed in the period between the development of the pre-Mio-Pliocene peneplains and deflection of the Quaternary stream channels. The geological, geomorphological and geophysical evidence presented in this study indicates that (1) the ATTL formed after the mid-Miocene, (2) the ATTL has moved as a dextral strike-slip fault with minor vertical component since its formation to late Holocene and (3) the ATTL is presently active with dextral slip rates of 1-3 mm/year and a vertical component of >0.3 mm/year. The formation of the ATTL was probably related to the opening of the Japan Sea, which is the dominant tectonic event around Japan since mid-Miocene. The case study of the ATTL provides insight into understanding the tectonic history and relationship between tectonic landforms and structures in active strike-slip faults.

  20. The geometry of the active strike-slip El Tigre Fault, Precordillera of San Juan, Central-Western Argentina: integrating resistivity surveys with structural and geomorphological data

    NASA Astrophysics Data System (ADS)

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

    2013-07-01

    The geometry and related geomorphological features of the right-lateral strike-slip El Tigre Fault, one of the main morphostructural discontinuities in the Central-Western Precordillera of Argentina, were investigated. Achievements of this survey include: recognition of structural and geometrical discontinuities along the fault trace, identification and classification of landforms associated with local transpressional and transtensional sectors, observation of significant changes in the fault strike and detection of right and left bends of different wavelength. In the Central Segment of the El Tigre Fault, 2D electrical resistivity tomography surveys were carried out across the fault zone. The resistivity imaging permitted to infer the orientation of the main fault surface, the presence of blind fault branches along the fault zone, tectonic tilting of the Quaternary sedimentary cover, subsurface structure of pressure ridges and depth to the water table. Based on this information, it is possible to characterize the El Tigre Fault also as an important hydro-geological barrier. Our survey shows that the main fault surface changes along different segments from a high-angle to a subvertical setting whilst the vertical-slip component is either reverse or normal, depending on the local transpressive or transtensive regime induced by major bends along the trace. These local variations are expressed as sections of a few kilometres in length with relatively homogeneous behaviour and frequently separated by oblique or transversal structures.

  1. Quaternary slip-rates of the Kazerun and the Main Recent Faults: active strike-slip partitioning in the Zagros fold-and-thrust belt

    NASA Astrophysics Data System (ADS)

    Authemayou, Christine; Bellier, Olivier; Chardon, Dominique; Benedetti, Lucilla; Malekzade, Zaman; Claude, Christelle; Angeletti, Bernard; Shabanian, Esmaeil; Abbassi, Mohammad Reza

    2009-07-01

    The aim of this work is to constrain the Late Quaternary activity of two major dextral strike-slip faults of the Zagros fold-and-thrust belt of Southern Iran, within the framework of right-oblique convergence between Arabia and Eurasia. The NW-trending Main Recent fault marks the rear of the belt along two thirds of its length. Its southeastern tip connects to the northern termination of the N-trending Kazerun Fault, which affects the entire width of the belt. Horizontal slip rates have been estimated on these two faults over the last 140 ka from lateral offsets of streams and fans and in situ cosmogenic 36Cl exposure dating of cobbles sampled on the surface of these geomorphic features. Compared to GPS data, the obtained minimum slip rate of 3.5-12.5 mm yr-1 on the Main Recent Fault implies strike-slip partitioning of the convergence along this fault. Minimum slip rate of the Kazerun Fault is 2.5-4 mm yr-1 for its northern strand, 1.5-3.5 mm yr-1 for its central segment and is negligible for its southern segment. These results are consistent with southward distribution of the slip from along the Main Recent Fault to the longitudinal thrusts and folds of the fold-and-thrust belt through the Kazerun Fault, with a decrease of slip from the southeastern tip of the Main Recent Fault towards the southern termination of the Kazerun Fault. The Kazerun and associated faults form the horsetail termination of the Main Recent fault and may be seen as the propagating southeastern front of the fault system that accommodates indentation of Eurasia by Arabia.

  2. Oligocene dextral strike-slip faulting in Anatolia: an early escape

    NASA Astrophysics Data System (ADS)

    Okay, A. I.; Satir, M.; Zattin, M.; Cavazza, W.; Topuz, G.

    2011-12-01

    The Early Eocene collision between the Eurasian and Anatolian plates in Turkey was followed by regional contraction, uplift, erosion and strike-slip faulting, which spanned the Late Eocene-Oligocene interval. This period ended abruptly in western Turkey in the Early Miocene by regional north-south extension and calc-alkaline magmatism. There are few rock records of the Late Eocene - Oligocene in western Anatolia, however, a major structure, active in this period between contraction and extension, was the NW-SE trending, right-lateral strike-slip Paleo-Eskisehir Fault with a length of over 225 km and a cumulative displacement of ca. 100 km. The ductile lower sections of the Paleo-Eskisehir Fault are exposed in the Uludag Massif, a NW-SE trending fault-bounded mountain range in northwest Turkey consisting of gneiss, amphibolite and marble. The Uludag Massif is characterized by NW-SE striking subvertical foliation and subhorizontal mineral stretching lineation with a dextral shear sense. The Rb/Sr muscovite and biotite ages from the Uludag Massif are Eocene (ca. 49 Ma) and Oligocene (36-30 Ma), respectively. The metamorphic rocks are intruded by a tectonically foliated subvertical Oligocene (ca. 33 Ma) granitic dyke, 17 km long and only 1.5 km wide, with subhorizontal mineral stretching lineation. A 27 Ma post-kinematic granite marks the termination of the shear zone activity. The apatite fission track (AFT) ages from the crystalline rocks are Early Miocene (ca. 20 Ma). Large gneiss clasts derived from the Uludag Massif are found in the adjacent Miocene basin. The 14 Ma AFT age from a gneiss clast from the Miocene basin show that the Uludag Massif was on the surface by the Middle Miocene. These data constrain the strike-slip faulting along the Paleo-Eskisehir Fault to the Late Eocene-Oligocene (38-27 Ma). The exhumation of the Uludag Massif occurred in the Early Miocene and post-dates the strike-slip activity. Although the Paleo-Eskisehir Fault is comparable in length

  3. Mesoscopic structure of the Punchbowl Fault, Southern California and the geologic and geophysical structure of active strike-slip faults

    NASA Astrophysics Data System (ADS)

    Schulz, Steven E.; Evans, James P.

    2000-07-01

    We examine the distribution, density, and orientation of outcrop-scale structures related to the Punchbowl Fault, an exhumed ancient trace of the San Andreas Fault, southern California, in order to determine the structure of the fault zone. The Punchbowl Fault has 44 km of right-lateral slip, and cuts the Cretaceous Pelona Schist in the study area. The mesoscopic structures examined include fractures, small faults, and veins; they were inventoried using scan lines at closely spaced stations along three strike-perpendicular traverses 200-250 m long across the fault. The fault zone thickness is a function of the type of structure measured. Slip along narrow (<2 m wide) ultracataclasite cores of the faults results in foliation reorientation over a distance of 50 m from the cores: fracture and fault densities appear to increase 50-80 m from the fault cores, and vein densities are highly variable across the fault zone. Fractures and faults in the damaged zone have a variety of orientations, but most are at high angles to the main fault zone. When coupled with previous geochemical and microstructural data, these data show that large-displacement faults of the San Andreas system, are up to 200-250 m thick, and enclose zones of mineralogic and geochemical alteration that are 20-30 m thick. Extreme slip localization occurs over zones 1-5 m thick. When reconciled with geophysical imaging, our data suggest that trapped headwaves travel in the damaged zone, and that some aftershock events produce slip on faults and fractures, which often have orientations very different from the principal slip surfaces.

  4. Distribution of strike-slip faults on Europa

    NASA Astrophysics Data System (ADS)

    Hoppa, Gregory; Greenberg, Richard; Tufts, B. Randall; Geissler, Paul; Phillips, Cynthia; Milazzo, Moses

    2000-09-01

    Study of four different regions on Europa imaged by the Galileo spacecraft during its first 15 orbits has revealed 117 strike-slip faults. Europa appears to form preferentially right-lateral faults in the southern hemisphere and left-lateral faults in the northern hemisphere. This observation is consistent with a model where diurnal tides due to orbital eccentricity drive strike-slip motion through a process of ``walking,'' in which faults open and close out of phase with alternating right-and left-lateral shear. Lineaments that record both left-and right-lateral motion (e.g., Agave Linea) may record the accommodation of compression in nearby chaotic zones. Nearly all identified strike-slip faults were associated with double ridges or bands, and few were detected along ridgeless cracks. Thus the depth of cracks without ridges does not appear to have penetrated to the low-viscosity decoupling layer, required for diurnal displacement, but cracks that have developed ridges do extend down to such a level. This result supports a model for ridge formation that requires cracks to penetrate to a decoupling layer, such as a liquid water ocean.

  5. Termination of major strike-slip faults against thrust faults in a syntaxis, as interpreted from landsat images

    SciTech Connect

    Iranpanah, A.

    1988-01-01

    The north to northeast-striking Minab fault (Zendan fault) in western Makran, Iran, is interpreted as an intracontinental transform structure that separates, along its length, the Zagros foldbelt from the Makran active trench-arc system. The 200-km long fault has a right-lateral strike-slip component and is terminated at its northern end by the north-northwest and northwest-striking Zagros main thrust. The Minab transform zone delimits the western margin of the Makran convergence zone where an oceanic part of the Afro-Arabian lithosphere is being subducted beneath the Lut and Afghan microplates. A northern extension of the Minab transform zone terminates at an internal convergence boundary within the Bandar Abbas-Minab syntaxis. The Minab transform fault consists of a zone of generally north-northwest-trending thombic conjugate strike-slip faults. The pattern of faulting for the Minab strike-slip fault zone, when traced over the entire area on the Landsat image, shows that areas with rhombic sets of conjugate strike-slip faults are separated by a few areas showing only extensional zones. This is compatible with the traditionally idealized reverse-S pattern for the strike-slip faults reported from the United States Basin and Range province. The mechanical explanation for the rhombic pattern of the fault system is consistent with the same pattern and motion as currently exists in the Makran accretionary belt. The origin of the Bandar Abbas-Minab syntaxis is believed to be related to convergence between the Afro-Arabian plate and the Lut and Afghan microplates. The convergence zone is a well-developed trench-arc gap. The western edge of this trench-arc system has been dragged to the north along the Minab dextral fault zone. This zone, which started developing in the Late Cretaceous-Paleocene, is directly responsible for the development of the Bandar Abbas-Minab syntaxis.

  6. Distribution and structure of active strike-slip faults in the Enshu forearc basin of the eastern Nankai subduction zone

    NASA Astrophysics Data System (ADS)

    Ojima, T.; Ashi, J.; Nakamura, Y.

    2010-12-01

    Accretionary prisms and forearc basins are developed in the Nankai Trough, SW Japan. Many active faults are recognized and classified into five fault systems in the eastern Nankai Trough. The Enshu Faults System, the most landward one, runs over 200 km along the northern edge of the Tokai, Enshu and Kumano forearc basins. Swath bathymetry and side-scan sonar surveys indicate a general fault trend of ENE-WSW and dextral displacement of submarine canyons across the landward-most fault. Seismic reflection profiles partly exhibit landward dipping fault planes and flower structures suggesting that the Enshu fault system is affected by oblique subduction of the Philippines Sea Plate. Structural investigation of this area is important for earthquake disaster mitigation as well as understanding of oblique subduction tectonics. However, activity of faults has not been clarified. Japan Oil, Gas and Metal National Corporation (JOGMEC) conducted dense seismic reflection survey at the Tokai-Kumano area in 2001. Seismic reflection profiles clearly show depositional sequences and deformation structures such as faults and folds. This study examined deformation styles and fault activities based on detailed interpretation of seismic reflection profiles. Sediment thickness mapped from seismic profiles clearly changes with age. Sediment thickness is almost homogeneous from the acoustic basement (probably Paleogene Shimanto Complex) to a Pliocene horizon in the survey area. In contrast, thickness between a Pliocene horizon and present seafloor shows large variations from east to west. It is suggested that sedimentary environments change drastically at this period. There are also small-scale variations in sediment thickness for all horizons. Some distinct changes are distributed along linear boundaries. It seems that they correspond to the faults recognized as lineaments on the sidescan sonar images. We estimated activities of faulting based on such sediment thickness changes and their

  7. Reactivated strike slip faults: examples from north Cornwall, UK

    NASA Astrophysics Data System (ADS)

    Kim, Young-Seog; Andrews, Jim R.; Sanderson, David J.

    2001-10-01

    Several strike-slip faults at Crackington Haven, UK show evidence of right-lateral movement with tip cracks and dilatational jogs, which have been reactivated by left-lateral strike-slip movement. Evidence for reactivation includes two slickenside striae on a single fault surface, two groups of tip cracks with different orientations and very low displacement gradients or negative (left-lateral) displacements at fault tips. Evidence for the relative age of the two strike-slip movements is (1) the first formed tip cracks associated with right-lateral slip are deformed, whereas the tip cracks formed during left-lateral slip show no deformation; (2) some of the tip cracks associated with right-lateral movement show left-lateral reactivation; and (3) left-lateral displacement is commonly recorded at the tips of dominantly right-lateral faults. The orientation of the tip cracks to the main fault is 30-70° clockwise for right-lateral slip, and 20-40° counter-clockwise for left-lateral slip. The structure formed by this process of strike-slip reactivation is termed a "tree structure" because it is similar to a tree with branches. The angular difference between these two groups of tip cracks could be interpreted as due to different stress distribution (e.g., transtensional/transpressional, near-field or far-field stress), different fracture modes or fractures utilizing pre-existing planes of weakness. Most of the d- x profiles have similar patterns, which show low or negative displacement at the segment fault tips. Although the d- x profiles are complicated by fault segments and reactivation, they provide clear evidence for reactivation. Profiles that experienced two opposite slip movements show various shapes depending on the amount of displacement and the slip sequence. For a larger slip followed by a smaller slip with opposite sense, the profile would be expected to record very low or reverse displacement at fault tips due to late-stage tip propagation. Whereas for a

  8. 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.

  9. Strike-slip movements and thrusting along a transpressive fault zone: The North Giudicarie line (Insubric line, northern Italy)

    NASA Astrophysics Data System (ADS)

    Prosser, Giacomo

    1998-12-01

    This paper analyzes the kinematic evolution and the deformation partitioning within an important transpressive fault zone located in the central part of the Alpine chain. The North Giudicarie line is a NNE trending fault which offsets the dextral Insubric line with an apparent left-lateral displacement of about 70 km. The main fault plane of the North Giudicarie line dips about 35°-45° to the NW. The footwall is characterized by N-S striking strike-slip faults, which reactivate extensional faults of Early Jurassic to Late Cretaceous age. The early deformation history of the North Giudicarie line is revealed by basement-and limestone-mylonites. Shear sense of mylonites indicates on average top-to-the-east thrusting. These movements took place during the late Oligocene-early Miocene, when the Insubric line was active as a right-lateral strike-slip fault. Therefore, in this time span the North Giudicarie line can be interpreted as a dextral transpressive bend of the Insubric line. Mylonites have later been overprinted by brittle faults related to top-to-the-SE thrusting of middle-late Miocene age. During this event the shape of the Insubric line was strongly modified by left-lateral transpression along the Giudicarie fault zone. Deformation was partitioned between prevailing compression along the Giudicarie line and left-lateral strike-slip movements along the N-S striking faults. These faults transferred the strike-slip component of the Giudicarie line into a wider area of the central southern Alps.

  10. Reworking of structural inheritance at strike-slip restraining-bends: templates from sandbox analogue models

    NASA Astrophysics Data System (ADS)

    Nestola, Yago; Storti, Fabrizio; Cavozzi, Cristian; Magistroni, Corrado; Meda, Marco; Piero Righetti, Fabrizio

    2016-04-01

    master strike-slip fault zone, antithetic shear zones form and enhance dextral escape of fault-bounded compartments. The intermediate case (30°) shows the interaction of both left-lateral synthetic and right-lateral antithetic shearing. Comparison with natural prototypes support the effectiveness of our experimental results.

  11. Pericollisional strike-slip basins in western Cordillera, Canada

    SciTech Connect

    Eisbacher, G.H.

    1984-04-01

    The late Mesozoic-Paleogene evolution of the Canadian Cordillera was dominated by accretion of elongate crustal blocks against the North American craton. Geologic and paleomagnetic evidence suggest that these exotic terranes dispersed from volcanic arcs and oceanic platforms and approached North America along anastomosing right-lateral faults with great cumulative displacement. Obduction of oceanic allochthons was followed by transpressive thickening and regional metamorphism of the cratonic margin in the mid-Jurassic. Strike-slip motion and emplacement of plutonic rocks continued near relict sutures and reactivated deep faults. Sedimentary basins related to strike-slip faults formed by elongation of accreted terranes (''Stikinia'' and ''Wrangellia'') and by shear within the deformed cratonic margin zone (''Rocky Mountain Trench''). Subsidence is reflected by northwest-southeast stretching along pull-apart structures, and by massive influx of turbidites from incipient collision zones and relict are relief. It was interrupted and outlived by rotation of blocks, folding of basin sediments, and vigorous progradation of deltaic-fluvial clastics from rising collision belts. Transition from predominant transtension to prevailing transpression is diachronous from basin to basin. Near the Stikine-Wrangellia collision zone (Bowser basin), it occurred in the Late Jurassic; along the Stikine-Wrangellia border it occurred in the mid to Late Cretaceous. Only small nonmarine basins developed in the Rocky Mountain Trench system, which, in its southern-most part, was closed completely during Paleogene thrust faulting. The strike-slip basins of the western Canadian Cordillera were subject to high regional heat flow and also suffered from widespread intrusion of paleogene granitoids. Therefore, they are generally poor oil and gas prospects.

  12. Strike-slip faulting and block rotation in the Lake Mead fault system

    NASA Astrophysics Data System (ADS)

    Ron, Hagai; Aydin, Atilla; Nur, Amos

    1986-12-01

    Strike-slip faults in the Basin and Range province have often been considered passive boundaries between differentially extended domains of tilted normal faults and are thus considered secondary in accommodating regional horizontal deformation. Paleomagnotic investigation of late Miocene age volcanic rocks, displaced by the left-lateral fault system of Lake Mead, Nevada, shows: (1) that these rocks have not been affected by significant structural tilt, the difference between observed and expected inclinations being only -0.6° ± 14.9° and (2) a significant horizontal counterclockwise rotation of -29.4° ± 8.5° about a vertical axis. This rotation was accommodated by slip on northwest-trending, right-lateral strike-slip faults; this implies significant west-northwest elongation. Results of the investigation indicate that strike-slip faulting is the primary process accommodating crustal deformation along the Lake Mead fault system and that tilting in response to normal faulting is secondary.

  13. 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 associated with the Rif`s strike-slip faults have not been explored to data and hydrocarbon potential remains a good possibility.

  14. Investigating The Role Of Non-synchronous Rotation In The Development Of Large Strike-slip Faults On Europa

    NASA Astrophysics Data System (ADS)

    Olgin, John G.; Smith-Konter, B. R.; Pappalardo, R. T.

    2010-10-01

    Much of Europa's surface is crosscut by a dense network of fractured lineaments, offering many candidate faults for studying both past and potentially present tectonic activity. Here we investigate the role of both diurnal and non-synchronous rotation (NSR) tidal stresses in the development of Agenor Linea, a major strike-slip fault in Europa's southern hemisphere with strong evidence of right-lateral offsets. Preliminary calculations suggest that diurnal tidal stresses alone may be insufficient to cause Coulomb failure at Agenor Linea, thus we consider the role of NSR as a secular stress source for strike-slip faulting. To investigate Europa's combined diurnal and NSR tidal stress field, we utilize the SatStress numerical code and assume a spherically symmetric ice shell of thickness 20 km, underlain by a global subsurface ocean. We also assume an NSR period of 104 - 105 yrs, ice shell viscosity of 1022 Pa s, a coefficient of friction of 0.2, and a fault depth of 6 km. Application of the Coulomb failure criterion reveals that a combination of NSR and diurnal tidal stresses are required for Agenor Linea to succumb to right-lateral shear failure at specific portions of the orbital cycle. We further explore the relationship of NSR to Agenor Linea's east-west orientation. Preliminary work suggests that if the fault were oriented in the north-south direction, NSR would generate only left-lateral shear and compressive normal stress, neither of which could constructively combine to produce right-lateral offsets. This research was supported by the NASA Outer Planets Research Program (NNG06GF44G, 07-OPR08-0088).

  15. Suppression of strike-slip fault systems

    NASA Astrophysics Data System (ADS)

    Curren, I. S.

    2012-12-01

    In orogens elongated parallel to a great circle about the Euler pole for the two bounding plates, theory requires simple-shear deformation in the form of distributed deformation or velocity discontinuities across strike-slip faults. This type of deformation, however, does not develop at all plate boundaries requiring toroidal motion. Using the global plate boundary model, PB2002 [Bird, 2003], as the basis for identifying areas where expected simple-shear deformation is absent or underdeveloped, it was also possible to identify two potential causes for this behavior: (1) the presence of extensive fracturing at right angles to the shear plane and (2) regional cover of flood basalts or andesites with columnar joints. To test this hypothesis, a new plane-stress finite-strain model was developed to study the effects of such pre-existing structures on the development of simple shear in a clay cake. A homogenous kaolinite-water mixture was poured into a deforming parallelogram box and partially dried to allow for brittle and plastic deformation at and below the surface of the clay, respectively. This was floated on a dense fluid foundation, effectively removing basal friction, and driven by a motor in a sinistral direction from the sides of the box. Control experiments produced classic Riedel model fault assemblages and discrete, through-going primary deformation zones (PDZs); experiments with pre-existing structures developed the same, though subdued and distributed, fault assemblages but did not develop through-going PDZs. Although formation of strike-slip faults was underdeveloped at the surface in clay with pre-existing structures, offset within the clay cake (measured, with respect to a fixed point, by markers on the clay surface) as a fraction of total offset of the box was consistently larger than that of the control experiments. This suggests that while the extent of surface faulting was lessened in clay with pre-existing structures, slip was still occurring at

  16. 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.

  17. Manifestations of Strike-Slip Faulting on Ganymede

    NASA Technical Reports Server (NTRS)

    DeRemer, Lindsay C.; Pappalardo, Robert T.

    2003-01-01

    Voyager images of Ganymede suggested that strike-slip faulting may have taken place [1, 2], but the role of this process in shaping grooved terrain was uncertain. In Galileo high-resolution images of Ganymede's surface, we recognize three signature features of strike-slip faulting: (1) en echelon structures, (2) strike-slip duplexes, and (3) offset preexisting features. We have undertaken a study to recognize and map these features, and identify any morphological progressions of strike-slip features. This will allow a better understanding of the structural history of Ganymede, and the formation and evolution of grooved terrain.

  18. Active Strike-Slip Faulting in the Inner Continental Borderland, Southern California: Results From New High-Resolution Seismic Reflection Data

    NASA Astrophysics Data System (ADS)

    Conrad, J. E.; Ryan, H. F.; Sliter, R. W.

    2008-12-01

    The inner Continental Borderland offshore of southern California accommodates about 7 mm/yr of slip between the North American and Pacific plates. Nearly half of this total has previously been thought to be taken up on the Palos Verdes (PV) and Coronado Bank (CB) fault zones, which have been modeled as a single, continuous fault zone in recent seismic hazard assessments for southern California. Although these faults lie roughly on strike with each other, a connection between these faults has not been clearly demonstrated. Newly acquired high-resolution seismic reflection data indicate that the PV fault terminates southwest of Lasuen Knoll in a horsetail splay that becomes progressively buried to the south. The lack of a connection between the PV and CB fault zones implies that a significant amount of slip must be taken up elsewhere in the inner Continental Borderland. Two other significant offshore faults, the San Diego Trough (SDT) and San Pedro Basin (SPB) fault zones, lie about 10-15 km southwest of and sub parallel to the trace of the PV and CB faults. The SDT fault zone extends from south of the Mexican border near Punta Santo Tomas for about 150 km northward to near Crespi Knoll. The SPB fault zone extends northward from off Santa Catalina Island to near Point Dume. The new seismic reflection data reveal a previously unmapped but apparently active fault zone along strike and in the area between the known strands of the SDT and the SPB fault zones. This newly recognized fault links the SDT and SPB faults, forming a continuous, active fault zone that extends about 250 km along the inner Continental Borderland. Although there are no slip rate data available for this fault zone, its overall length, continuity, and active character suggest that a significant portion of the plate motion that occurs offshore is accommodated along the SDT-SPB fault zone, which may pose a more significant seismic hazard than previously recognized.

  19. 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

  20. 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.

    2016-05-01

    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.

  1. Evaluating fault rupture hazard for strike-slip earthquakes

    USGS Publications Warehouse

    Petersen, M.; Cao, T.; Dawson, Tim; Frankel, A.; Wills, C.; Schwartz, D.

    2004-01-01

    We present fault displacement data, regressions, and a methodology to calculate in both a probabilistic and deterministic framework the fault rupture hazard for strike-slip faults. To assess this hazard we consider: (1) the size of the earthquake and probability that it will rupture to the surface, (2) the rate of all potential earthquakes on the fault (3) the distance of the site along and from the mapped fault, (4) the complexity of the fault and quality of the fault mapping, (5) the size of the structure that will be placed at the site, and (6) the potential and size of displacements along or near the fault. Probabilistic fault rupture hazard analysis should be an important consideration in design of structures or lifelines that are located within about 50m of well-mapped active faults.

  2. Exhumation and continental strike-slip fault systems: Introduction

    USGS Publications Warehouse

    Roeske, S.M.; Till, A.B.; Foster, D.A.; Sample, J.C.

    2007-01-01

    Metamorphic rocks adjacent to and within strike-slip faultsystems occur in a wide range of tectonic settings. Detailed studies show that for a number of these locales a significant part of the exhumation occurred during strike-slip fault motion, but the specific processes involved are often cryptic. Although some sites share characteristic features, such as metamorphic rocks exhumed in extensional step-overs within overall transtensional systems, no one common theme emerges from all of the studies. Our understanding of the variables that control continental strike-slip faults' interaction with mid- to lower-crustal structures is still primitive.

  3. Deformation pattern around the conjoining strike-slip fault systems in the Basin and Range, southeast Nevada: The role of strike-slip faulting in basin formation and inversion

    NASA Astrophysics Data System (ADS)

    Çakir, Mehmet; Aydin, Atilla; Campagna, David J.

    1998-06-01

    Within the extensional regime of the Basin and Range, strike-slip faults create a regional pattern of opposing sense of fault systems. The relationship between these faults and other deformational features nearby is enigmatic. This paper addresses a diverse assemblage of contractional and extensional structures reflecting local uplift and subsidence, respectively, at the junction of two large Neogene strike-slip faults in southeastern Nevada, the right-lateral Las Vegas Valley shear zone and the left-lateral Bitter Spring Valley fault of the Lake Mead fault system. First, a middle Miocene lacustrine carbonate basin, the Bitter Ridge-Lovell Wash carbonate basin, formed north of the strike-slip faults. Second, the lacustrine basin inverted locally, while sediments accumulated south of the strike-slip faults. Third, the study area was deformed by north-northeast trending, high-angle oblique faults with normal and left-slip components. The results, both from field observations and numerical modeling of the intersecting strike-slip faults, show that the Las Vegas Valley shear zone and the Bitter Spring Valley fault may have produced the basin in the north and its intense contractional deformation as well as the southward shift of deposition during the inversion event. We conclude that conjoining strike-slip fault systems can promote localized vertical tectonics and lead to basin formation and uplift right next to each other. Subsequent inversion of the earlier basinal deposits, however, requires a reversal in the sense of slip across the Las Vegas Valley shear zone and a change in the regional stress system.

  4. The September 27, 2012, ML 4.1, Benevento earthquake: A case of strike-slip faulting in Southern Apennines (Italy)

    NASA Astrophysics Data System (ADS)

    Adinolfi, Guido Maria; De Matteis, Raffaella; Orefice, Antonella; Festa, Gaetano; Zollo, Aldo; de Nardis, Rita; Lavecchia, Giusy

    2015-10-01

    On September 27, 2012 at 01:08 (UTC) a ML 4.1 earthquake started a seismic sequence approximately 10 km east of the city of Benevento, in Southern Apennines (Italy). During the following four days, about 40 events with ML ranging between 1.3 and 4.1 were detected in the same area, where the seismic hazard is one of the largest of the Italian Peninsula and where several historical and destructive events took place. In order to investigate the seismicity spatio-temporal pattern and to identify the seismogenic source geometry, a detailed analysis was performed integrating data recorded at three different seismic networks. The earthquakes were relocated using the double-difference technique and focal mechanism solutions were obtained by the moment tensor inversion. Also, to better understand the rupture process, seismic source parameters were estimated and apparent source time functions were inverted to retrieve the slip distribution for the largest magnitude event. Our results show the existence in the study area of roughly E-W striking fault plane with a right-lateral strike-slip kinematics, seated at mid-crustal depths (10-20 km), revealing a characteristic seismicity quite different from that typically associated to the outcropping NW-SE-striking active normal faults that are responsible of moderate to large earthquakes in the Southern Apennines axial sector. In this work, we address questions concerning i) the presence in the Benevento area of a mid-crust seismogenic strike-slip fault, previously unrecognized; ii) its link to the regional seismotectonic setting; and iii) the existence of a strike-slip tectonic regime that uniformly extends in the footwall of the Apennines thrust at relevant depth, not only in the Apulian foreland, as demonstrated to date, but also under the mountain chain axial zone.

  5. Transpressional segment boundaries in strike-slip fault systems offshore southern California: Implications for fluid expulsion and cold seep habitats

    NASA Astrophysics Data System (ADS)

    Maloney, Jillian M.; Grupe, Benjamin M.; Pasulka, Alexis L.; Dawson, Katherine S.; Case, David H.; Frieder, Christina A.; Levin, Lisa A.; Driscoll, Neal W.

    2015-05-01

    The importance of tectonics and fluid flow in controlling cold seep habitats has long been appreciated at convergent margins but remains poorly understood in strike-slip systems. Here we present geophysical, geochemical, and biological data from an active methane seep offshore from Del Mar, California, in the inner California borderlands (ICB). The location of this seep appears controlled by localized transpression associated with a step in the San Diego Trough fault zone and provides an opportunity to examine the interplay between fluid expulsion and restraining step overs along strike-slip fault systems. These segment boundaries may have important controls on seep locations in the ICB and other margins characterized by strike-slip faulting (e.g., Greece, Sea of Marmara, and Caribbean). The strike-slip fault systems offshore southern California appear to have a limited distribution of seep sites compared to a wider distribution at convergent plate boundaries, which may influence seep habitat diversity and connectivity.

  6. How Orogen-scale Exhumed Strike-slip Faults Initiate

    NASA Astrophysics Data System (ADS)

    Cao, S.; Neubauer, F.

    2015-12-01

    Orogen-scale strike-slip faults present one the most important geodynamic processes affecting the lithosphere-asthenosphere system. In specific subtypes, faulting is virtually initiated along hot-to-cool boundaries, e.g. at such of hot granite intrusions or metamorphic core complexes to cool country rocks. Such 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 and are stacked within each other ("telescoping"). Exhumation of rocks is, therefore, a common feature of such strike-slip faults implying major transtensive and/or transpressive processes accompanying pure strike-slip motion. The hot-to-cool thermal structure across the fault zone significantly influences the physical fault rock properties. One major question is how and where a major strike-slip initiates and further development. Here, we propose a model in which major continental exhumed strike-slip faults potentially evolve along rheologically weak zones such as plutons or margins of metamorphic complexes. As an example, we propose a model for the Ailao Shan-Red River (ASRR) fault, SE Asia, which initiated along the edge of a plutonic belt and evolved in response to India-Asia collision with four tectonic phases.

  7. 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

  8. New constraints from seismology and geodesy on the Mw = 6.4 2008 Movri (Greece) earthquake: evidence for a growing strike-slip fault system

    NASA Astrophysics Data System (ADS)

    Serpetsidaki, A.; Elias, P.; Ilieva, M.; Bernard, P.; Briole, P.; Deschamps, A.; Lambotte, S.; Lyon-Caen, H.; Sokos, E.; Tselentis, G.-A.

    2014-09-01

    The 2008 Mw = 6.4 Movri earthquake ruptured a NNE right lateral strike-slip fault about 30 km south of the city of Patras. Although some strike-slip activity on minor faults was known, there was no tectonic evidence of large scale NS striking fault and such a large event was not anticipated. Following the event, a network of six stations was installed for 4 months in the epicentral area in order to monitor aftershocks and in particular the northern part of the rupture area closest to the city of Patras. We combine these new aftershock observations with GPS measurements of an already existing geodetic network in the area performed just after the earthquake, as well as with SAR interferograms, together with already published source studies, in order to refine already proposed models of this event. The combined data set allows defining much more accurately the lateral and vertical limits of the rupture. Its length inferred from geodesy is ˜15 km and its modelled upper edge ˜17 km. The seismic moment then constrains the lower edge to coincide, within a few kilometres, with the Moho interface. The absence of seismicity in the shallow crust above the co-seismic fault is interpreted as a result of the decoupling effect of possible presence of salt layers above the rupture area, near 14 to 16 km in depth, which favours our interpretation of an immature strike-slip fault system, compatible with the absence of surface ruptures. The immature character of this large crustal fault is further suggested by the high variability of focal mechanisms and of fault geometries deduced from aftershock clusters, in the strike direction. Its geometry and mechanism is consistent with the crustal shear, striking NNE, revealed by GPS in this region. This shear and faulting activity might be generated by the differential slip rate on the subduction interface, 50 km to the south, leading to a north-northeastward propagating strike-slip fault zone. The wide extension of the aftershock

  9. Strike-slip faulting during the 2014 Bárðarbunga-Holuhraun dike intrusion, central Iceland

    NASA Astrophysics Data System (ADS)

    Ágústsdóttir, Thorbjörg; Woods, Jennifer; Greenfield, Tim; Green, Robert G.; White, Robert S.; Winder, Tom; Brandsdóttir, Bryndís.; Steinthórsson, Sveinbjörn; Soosalu, Heidi

    2016-02-01

    Over a 13 day period magma propagated laterally from the subglacial Bárðarbunga volcano in the northern rift zone, Iceland. It created > 30,000 earthquakes at 5-7 km depth along a 48 km path before erupting on 29 August 2014. The seismicity, which tracked the dike propagation, advanced in short bursts at 0.3-4.7 km/h separated by pauses of up to 81 h. During each surge forward, seismicity behind the dike tip dropped. Moment tensor solutions from the leading edge show exclusively left-lateral strike-slip faulting subparallel to the advancing dike tip, releasing accumulated strain deficit in the brittle layer of the rift zone. Behind the leading edge, both left- and right-lateral strike-slip earthquakes are observed. The lack of non-double-couple earthquakes implies that the dike opening was aseismic.

  10. Volcano instability induced by strike-slip faulting

    NASA Astrophysics Data System (ADS)

    Lagmay, A. M. F.; van Wyk de Vries, B.; Kerle, N.; Pyle, D. M.

    2000-09-01

    Analogue sand cone experiments were conducted to study instability generated on volcanic cones by basal strike-slip movement. The results of the analogue models demonstrate that edifice instability may be generated when strike-slip faults underlying a volcano move as a result of tectonic adjustment. This instability occurs on flanks of the volcano above the strike-slip shear. On the surface of the volcano this appears as a pair of sigmoids composed of one reverse and one normal fault. In the interior of the cone the faults form a flower structure. Two destabilised regions are created on the cone flanks between the traces of the sigmoidal faults. Bulging, intense fracturing and landsliding characterise these unstable flanks. Additional analogue experiments conducted to model magmatic intrusion show that fractures and faults developed within the volcanic cone due to basal strike-slip motions strongly control the path of the intruding magma. Intrusion is diverted towards the areas where previous development of reverse and normal faults have occurred, thus causing further instability. We compare our model results to two examples of volcanoes on strike-slip faults: Iriga volcano (Philippines), which underwent non-magmatic collapse, and Mount St. Helens (USA), where a cryptodome was emplaced prior to failure. In the analogue and natural examples, the direction of collapse takes place roughly parallel to the orientation of the underlying shear. The model presented proposes one mechanism for strike-parallel breaching of volcanoes, recently recognised as a common failure direction of volcanoes found in regions with transcurrent and transtensional deformation. The recognition of the effect of basal shearing on volcano stability enables prediction of the likely direction of eventual flank failure in volcanoes overlying strike-slip 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. Intra-arc strike-slip fault exposed at batholithic levels in the southern Sierra Nevada, California

    SciTech Connect

    Busby-Spera, C.J. ); Saleeby, J.B. )

    1990-03-01

    The Kern Canyon fault is a major north-trending fault that is continuous for a distance of 140 km in the southern Sierra Nevada, California. Previous geologic mapping and geochronological work along the northern third of the fault indicate that dextral offset occurred sometime after 80 Ma and before 3.5 Ma; this offset was interpreted to be the result of Cenozoic basin-and-range extension. Our new results from the central third of the fault (Kernville-Lake Isabella region) indicate an earlier right-lateral movement history, contemporaneous with emplacement of the largest plutons in the Sierra Nevada. The older structure is termed the proto-Kern Canyon fault zone. The Cenozoic fault trace is a narrow zone of brittle deformation, whereas the Cretaceous fault zone is a broad zone of ductile deformation. U-Pb zircon geochronology on plutonic and metavolcanic rocks involved int he ductile deformation, as well as a pluton that postdates ductile deformation, demonstrate that the proto-Kern Canyon fault zone was active at 85 Ma, and may have begun to move as early as 105 Ma. Longitudinal strike-slip faults are common in modern magmatic arcs where convergence is oblique. The proto-Kern Canyon fault zone may have originated in response to a moderate northward component in subduction of the Farallon plate or perhaps a strong northward component for the Kula plate.

  13. Formation and Suppression of Strike-Slip Fault Systems

    NASA Astrophysics Data System (ADS)

    Curren, Ivy S.; Bird, Peter

    2014-11-01

    Strike-slip faults are a defining feature of plate tectonics, yet many aspects of their development and evolution remain unresolved. For intact materials and/or regions, a standard sequence of shear development is predicted from physical models and field studies, commencing with the formation of Riedel shears and culminating with the development of a throughgoing fault. However, for materials and/or regions that contain crustal heterogeneities (normal and/or thrust faults, joints, etc.) that predate shear deformation, kinematic evolution of strike-slip faulting is poorly constrained. We present a new plane-stress finite-strain physical analog model developed to investigate primary deformation zone evolution in simple shear, pure strike-slip fault systems in which faults or joints are present before shear initiation. Experimental results suggest that preexisting mechanical discontinuities (faults and/or joints) have a marked effect on the geometry of such systems, causing deflection, lateral distribution, and suppression of shears. A lower limit is placed on shear offset necessary to produce a throughgoing fault in systems containing preexisting structures. Fault zone development observed in these experiments provides new insight for kinematic interpretation of structural data from strike-slip fault zones on Earth, Venus, and other terrestrial bodies.

  14. Dynamic Ridges and Valleys in a Strike-Slip Environment

    NASA Astrophysics Data System (ADS)

    Duvall, Alison R.; Tucker, Gregory E.

    2015-10-01

    Strike-slip faults have long been known for characteristic near-fault landforms such as offset rivers and strike-parallel valleys. In this study, we use a landscape evolution model to investigate the longer-term, catchment-wide landscape response to horizontal fault motion. Our results show that strike-slip faulting induces a persistent state of disequilibrium in the modeled landscapes brought about by river lengthening along the fault alternating with abrupt shortening due to stream capture. The models also predict that, in some cases, ridges oriented perpendicular to the fault migrate laterally in conjunction with fault motion. We find that ridge migration happens when slip rate is slow enough and/or soil creep and river incision are efficient enough that the landscape can respond to the disequilibrium brought about by strike-slip motion. Regional rock uplift relative to baselevel also plays a role, as topographic relief is required for ridge migration. In models with faster horizontal slip rates, stronger rocks, or less efficient hillslope transport, ridge mobility is limited or arrested despite the continuance of river lengthening and capture. In these cases, prominent steep, fault-facing facets form along well-developed fault valleys. Comparison of landscapes adjacent to fast-slipping (>30 mm/yr) and slower-slipping (≤1 mm/yr or less) strike-slip faults in California, USA, reveals features that are consistent with model predictions. Our results highlight a potential suite of geomorphic signatures that can be used as indicators of horizontal crustal motion and geomorphic processes in strike-slip settings even after river capture has diminished or erased apparent offset along the fault.

  15. Fault displacement hazard for strike-slip faults

    USGS Publications Warehouse

    Petersen, M.D.; Dawson, T.E.; Chen, R.; Cao, T.; Wills, C.J.; Schwartz, D.P.; Frankel, A.D.

    2011-01-01

    In this paper we present a methodology, data, and regression equations for calculating the fault rupture hazard at sites near steeply dipping, strike-slip faults. We collected and digitized on-fault and off-fault displacement data for 9 global strikeslip earthquakes ranging from moment magnitude M 6.5 to M 7.6 and supplemented these with displacements from 13 global earthquakes compiled byWesnousky (2008), who considers events up to M 7.9. Displacements on the primary fault fall off at the rupture ends and are often measured in meters, while displacements on secondary (offfault) or distributed faults may measure a few centimeters up to more than a meter and decay with distance from the rupture. Probability of earthquake rupture is less than 15% for cells 200 m??200 m and is less than 2% for 25 m??25 m cells at distances greater than 200mfrom the primary-fault rupture. Therefore, the hazard for off-fault ruptures is much lower than the hazard near the fault. Our data indicate that rupture displacements up to 35cm can be triggered on adjacent faults at distances out to 10kmor more from the primary-fault rupture. An example calculation shows that, for an active fault which has repeated large earthquakes every few hundred years, fault rupture hazard analysis should be an important consideration in the design of structures or lifelines that are located near the principal fault, within about 150 m of well-mapped active faults with a simple trace and within 300 m of faults with poorly defined or complex traces.

  16. Kinematically Coupled Strike-Slip and Normal Faults in the Lake Mead Strike-Slip Fault System, Southeast Nevada

    NASA Astrophysics Data System (ADS)

    Kattenhorn, S. A.; Marshall, S. T.; Cooke, M. L.

    2008-12-01

    The Lake Mead fault system consists of a ~95 km long, northeast-trending zone of strike-slip faults of Miocene age that accommodate a total left-lateral offset of 20-65 km. We use a combination of detailed field mapping and numerical modeling to show that a previously unnamed left-lateral strike-slip segment of the Lake Mead fault system and a dense cluster of dominantly west-dipping normal faults acted in concert to accommodate regional left-lateral offset. We suggest that the strike-slip fault that we refer to as the Pinto Ridge fault: (1) was kinematically related to other faults of the Lake Mead fault system; (2) was responsible for the creation of the normal fault cluster at Pinto Ridge; and (3) utilized these normal faults as linking structures between separate strike-slip fault segments to create a longer, through-going fault. Results from numerical models demonstrate that the observed location and curving strike patterns of the normal fault cluster is consistent with the faults having formed as secondary structures as the result of the perturbed stress field around the slipping Pinto Ridge fault. Comparison of mechanical efficiency of various normal fault geometries within extending terranes suggests that the observed west dip of normal faults reflects a west- dipping anisotropy at depth, such as a detachment. The apparent terminations of numerous strike-slip faults of the Lake Mead fault system into west-dipping normal faults suggest that a west-dipping detachment may be regionally coherent.

  17. Paleogene tectonics and forearc strike-slip faulting: southern Chile

    SciTech Connect

    Leslie, R.B.; Cande, S.C.

    1985-01-01

    Several lines of evidence suggest that highly oblique Nazca-South America convergence during the middle to late Paleogene resulted in the development of a dextral strike-slip fault landward of the Chile trench. The Linquine-Ofqui fault (LOF) is nearly 1000 km long and trends approximately N10/sup 0/E between 39/sup 0/S and 47/sup 0/S. It consists of several fault strands with the dominant strand represented by a mylonitic zone approximately 3 km wide. Preliminary field mapping (Herve, 1984) indicates seaward trending splay faults that can be projected offshore in the vicinity of two large embayments along the Chile margin. The Golfo de Guafo embayment occurs between 43/sup 0/S and 44/sup 0/S and is approx.40 km wide in the N-S direction. The Golfo de Penas embayment is approx.75 km wide in the N-S direction and occurs between 47/sup 0/S and 48/sup 0/S at the southern end of the LOF. The authors suggest that these embayments are a consequence of NE-SW extension due to movement on splay faults of the LOF system during the middle to late Paleogene. Convergence during this time was highly oblique. Movement decreased on the northern portion of the LOF prior to a decrease in movement on the southern end. Radiometric dates on rocks from the fault zone (Herve, 1984) provide constraints on the timing of movement along the fault. Marine geophysical data allow you to map the structures in these embayments which support the model of dextral shear along the LOF. Reactivation of the LOF may have occurred 6 Ma when a segment of the actively spreading Chile ridge was subducted at the Chile trench adjacent to the Golfo de Penas.

  18. Investigating Stress Seources and Fault Parameters Along Major Strike-Slip Lineae on Europa

    NASA Astrophysics Data System (ADS)

    Cameron, M. E.; Smith-Konter, B. R.; Pappalardo, R. T.

    2014-12-01

    The surface of Europa is crosscut by a dense network of structures, many of these representing a complex history of strike-slip tectonic activity, presumably arising from a combination of global and local stress sources. Several dominant (~1000 km) structures span geographically diverse locations of Europa, offering a unique opportunity to study strike-slip activity at the hemispheric scale. These structures also exhibit kilometer-scale geometric bends that can promote or discourage shear failure. To better understand the role of tidal stress sources and implications for strike-slip faulting on Europa, we investigate the relationship between shear and normal stresses at four major fault zones: Agenor Linea, Rhadamanthys Linea, Conamara Chaos (Agave and Asterius Lineae), and Astypalaea Linea. Assuming tidal diurnal and non-synchronous rotation (NSR) stresses as the primary mechanisms for strike-slip tectonism, here we investigate the mechanics of Coulomb shear failure on Europa. We consider a range of friction coefficients (µf = 0.2 - 0.6) and fault depths (0 - 6 km) to evaluate how the predicted failure varies as a function of depth and its dependency on ice friction, geographic location, and fault geometry. Our results indicate that the conditions for failure at depth are not met for any of the lineae if subject to diurnal stresses only. Alternatively, models that include both diurnal and NSR stresses readily generate stress magnitudes that could permit shear failure. Shear failure is easily activated and extends to depths ranging from 3 - 6 km on all four linea systems when a low coefficient of friction (µf = 0.2) is assumed, but is generally limited to depths < 3 km when a high coefficient of friction (µf = 0.6) is applied. Based on these results, we infer that the conditions for shear failure are potentially met along at least these four studied lineae, and possibly others, on Europa when NSR is adopted as a driving stress mechanism and the coefficient of

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

    USGS Publications Warehouse

    Aagaard, B.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.

  20. Right-lateral shear across Iran and kinematic change in the Arabia-Eurasia collision zone

    NASA Astrophysics Data System (ADS)

    Allen, Mark B.; Kheirkhah, Monireh; Emami, Mohammad H.; Jones, Stuart J.

    2011-02-01

    New offset determinations for right-lateral strike-slip faults in Iran revise the kinematics of the Arabia-Eurasia collision, by indicating along-strike lengthening of the collision zone before a change to the present kinematic regime at ˜5 Ma. A series of right-lateral strike-slip faults is present across the Turkish-Iranian plateau between 48°E and 57°E. Fault strikes vary between NW-SE and NNW-SSE. Several of the faults are seismically active and/or have geomorphic evidence for Holocene slip. None of the faults affects the GPS-derived regional velocity field, indicating active slip rates are ≤2 mm yr-1. We estimate total offsets for these faults from displaced geological and geomorphic markers, based on observations from satellite imagery, digital topography, geology maps and our own fieldwork observations, and combine these results with published estimates for fault displacement. Total right-lateral offset of the Dehu, Anar, Deh Shir, Kashan, Ab-Shirin-Shurab, Kousht Nousrat, Qom, Bid Hand, Indes, Soltanieh and Takab faults is ˜250 km. Other faults (North Zanjan, Saveh, Jorjafk, Rafsanjan, Kuh Banan and Behabad) have unknown or highly uncertain amounts of slip. Collectively, these faults are inferred to have accommodated part of the Arabia-Eurasia convergence. Three roles are possible, which are not mutually exclusive: (1) shortening via anticlockwise, vertical axis rotations; (2) northward movement of Iranian crust with respect to stable Afghanistan to the east; (3) combination with coeval NW-SE thrusts in the Turkish-Iranian plateau, to produce north-south plate convergence (`strain partitioning'). This strike-slip faulting across Iran requires along-strike lengthening of the collision zone. This was possible until the Pliocene (≤ 5 Ma), when the Afghan crust collided with the western margin of the Indian plate, thereby sealing off a free face at the eastern side of the Arabia-Eurasia collision zone. Continuing Arabia-Eurasia plate convergence had to

  1. Pattern of dynamic displacements in a strike-slip earthquake

    NASA Astrophysics Data System (ADS)

    Saltogianni, V.; Gianniou, M.; Moschas, F.; Stiros, S.

    2016-07-01

    High-rate (1 Hz) records from GPS stations uniformly distributed along the fault ruptures of the 2014 Samothraki-Gökçeada Mw6.9 earthquake in the North Aegean Trough, at the extension of the North Anatolian Fault Zone, were analyzed using the Precise Point Positioning (PPP) technique. Computed dynamic displacements shed light to the pattern of dynamic displacements during shallow strike-slip earthquakes. The area of near-field static seismic displacements bounds ramp-type, long-period dynamic displacements (fling steps) in the sense of static displacements. Along-fault and normal to fault components of dynamic displacement follow typical attenuation laws, but attenuation is higher in the fault-parallel component hence confined to the area of static dislocations. Forward directivity and local, especially topography-controlled amplification effects, consistent with accelerometer evidence, were also observed. The overall pattern seems to characterize shallow strike-slip earthquakes and is expected to prove useful to explain or even predict the near-field damaging potential of strike-slip earthquakes.

  2. Cenozoic right-lateral wrench tectonics in the Western Pyrenees (Spain): The Ubierna Fault System

    NASA Astrophysics Data System (ADS)

    Tavani, S.; Quintà, A.; Granado, P.

    2011-08-01

    A study of macro and mesostructural deformation patterns of the southern margin of the Cantabrian area (Western Pyrenees, Spain) has revealed a complex Cenozoic tectonic framework. Right-lateral tectonics reactivated inherited WNW-ESE striking faults, which developed during Late Paleozoic and Early Triassic events, and Late Jurassic to Early Cretaceous main rifting stage. The Ubierna Fault represents the southern boundary of the Mesozoic basin. During the Oligocene (even Eocene) to present day deformation, this fault and the Ventaniella Fault located to the south in the study area acted as right-lateral slightly transpressive elements forming a 120 km long and 15 km wide overstep area, here named Ubierna Fault System, where the cumulative right-lateral displacement exceeds 15 km. The Cenozoic tectonic framework of the Ubierna Fault System includes reactivation along the WNW-ESE faults, development of negative and, mostly, positive flower structures, branch faults, strike-slip duplexes, and releasing and restraining bends. NE-SW to ENE-WSW striking reverse faults and contractional horsetail terminations, and NNW-SSE striking normal faults and joints are produced by the WNW-ESE right-lateral strike-slip motion. The extensional elements are well developed and deformation progression implied their incorporation in the strike-slip system as right-lateral faults (forming part of strike-slip duplexes). The abundance of flower structures striking WNW-ESE and paralleling the main strike-slip faults, together with the overall uplift of the overstep area, testifies for a slight compressional component. At a regional scale, the Ubierna Fault System represents the most prominent element of a Cenozoic transpressional belt, which incorporates the western portion of the Basque-Cantabrian Basin and the Asturian Massif area. Lateral transition between this transpressive belt and the dip-slip belt located to the east, occurs across an area experiencing along strike-shortening, which

  3. Multiple strike slip faults sets: A case study from the Dead Sea transform

    NASA Technical Reports Server (NTRS)

    Ron, Hagai; Nur, Amos; Eyal, Y.

    1990-01-01

    In many strike slip tectonic settings, large rotations of crust blocks about vertical axes have been inferred from paleomagnetic data. These blocks are bounded by sets of parallel faults which presumably accommodate the relative motion between the blocks as regional deformation progress. A mechanical model by Nur et al., (1986) suggests that rotations greater than phi sub c equals 25 to 45 degrees must be accommodated by more than one set of faults, with angle phi sub c between their direction; consequently the sum of the angles between sets must be roughly equal to the total tectonic material rotation. To test this model, the authors investigated the fault geometry and field relation of fault sets in the Mt. Hermon area in northern Israel, where paleomagnetic declination implies data 69 degrees plus or minus 13 degrees counter-clockwise block rotation. The statistical and field relation analysis of over 315 faults shows that the faulting is predominantly right lateral strike slip consisting of three distinct sets. The oldest set strikes 253 degrees, the second oldest set strikes 293 degrees and the youngest strikes 339 degrees. This last direction is consistent also with the current north-south direction of the maximum principle stress axis. The angle phi sub c between the first and second sets is 39 degrees and between the second and third sets 46 degrees, in good agreement with the phi sub c angle predicted from mechanical considerations. The sum of the two angles is 85 degrees, in good agreement with the 69 degrees plus or minus 13 degrees CCW paleomagnetically derived rotation. The results suggest specifically that the sequential development of multiple intersecting fault sets is responsible for the faulting in the Mt. Hermon area; and generally that the model of block rotation with multiple faults provides very good simple rules for analyzing very complex fault patterns.

  4. 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

  5. Structure and evolution of the Sura-Kama strike-slip zone in the Cenozoic (the Volga-Ural anteclise of the East European Platform)

    NASA Astrophysics Data System (ADS)

    Kolodyazhnyi, S. Yu.

    2015-07-01

    The Sura-Kama zone (SKZ) complicates the central area of the Volga-Ural anteclise and extends sublaterally from the Sura River basin towards the Kama River at a distance of 700-750 km. Based on the analysis of geological-geophysical data and structural studies, a model for the tectonic structure and the evolution of the SKZ is developed. This is a deep tectonic fault that shows the features of long-term polystage development. During the latest Cimmerian-Alpine period of tectonic reactivation, the SKZ represented a zone of strike-slip and consecutive manifestation of early transpressional right-lateral strike-slip dislocations that changed to left-lateral strike-slip displacements under transtension settings as a result of kinematic inversion. Features of the heterogeneous structure of the SKZ are revealed. The segments formed by the system of strike-slip duplexes are alternated along the strike by the principle of rotation-fold and "domino" structures. The particular models of evolution of these segments are proposed by the examples of the widely known Karlin, Tetyushin, and Lower Kama dislocations. It is assumed that kinematic inversion and compression-decompression phenomena on the flanks of the SKZ, as well as the tectonic environments in the area of its dynamic influence were highly important for the development of the processes of migration and redistribution of hydrocarbon components.

  6. Fast rupture propagation for large strike-slip earthquakes

    NASA Astrophysics Data System (ADS)

    Wang, Dun; Mori, Jim; Koketsu, Kazuki

    2016-04-01

    Studying rupture speeds of shallow earthquakes is of broad interest because it has a large effect on the strong near-field shaking that causes damage during earthquakes, and it is an important parameter that reflects stress levels and energy on a slipping fault. However, resolving rupture speed is difficult in standard waveform inversion methods due to limited near-field observations and the tradeoff between rupture speed and fault size for teleseismic observations. Here we applied back-projection methods to estimate the rupture speeds of 15 Mw ≥ 7.8 dip-slip and 8 Mw ≥ 7.5 strike-slip earthquakes for which direct P waves are well recorded in Japan on Hi-net, or in North America on USArray. We found that all strike-slip events had very fast average rupture speeds of 3.0-5.0 km/s, which are near or greater than the local shear wave velocity (supershear). These values are faster than for thrust and normal faulting earthquakes that generally rupture with speeds of 1.0-3.0 km/s.

  7. 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

  8. The Mechanics, Geometry and Distribution of Strike Slip Faults in a Fold and Thrust Belt, County Clare, Ireland

    NASA Astrophysics Data System (ADS)

    Nenna, F. A.; Aydin, A.

    2010-12-01

    Fundamental structures such as opening mode joints and veins, and closing mode pressure solution seams (PSSs) can form dense orthogonal arrays in collisional deformation belts and play important roles in the initiation and development of larger scale faults. We describe the deformation processes and the evolution of fault architecture using systematic documentation of field observations from arrays of strike-slip faults in the Carboniferous Ross Sandstone. This unit is exposed on the Loop Head Peninsula, County Clare, Ireland and was subject to compressive stresses associated with the Variscan orogeny at the end of the Carboniferous producing broad regional east-west trending folds and also tight low-amplitude folds cored by thrust faults. Near these faults, orthogonal sets of PSSs and joints/veins form contemporaneous arrays with pressure solution seams that are sub-parallel to the thrust fault traces and fold axes. A stress or material rotation during the Variscan Orogeny (or perhaps a major second stage of deformation either in late phase of the orogeny or post-orogeny) has lead to left-lateral shear of the PSSs evidenced by pressure solution splays and pull-aparts between their sheared segments, and right-lateral shear on the joints/veins evidenced by splay fractures. The splays of the sheared joints are in the same orientation of the joints in the pull-aparts of the sheared PSSs with which they merge. This indicates that the shearing of the joints/veins and the PSSs was likely to have occurred simultaneously under the same remote loading conditions. With increased shear, extensive splay fractures and pull-apart networks form weak damage zones through which strike-slip faults systems develop with slip of up to 2km. As a higher proportion of the shear is resolved on the joint system than that of the PSS system, the more prominent strike-slip faults are sub-parallel to or slightly inclined to the pre-existing joint/vein set and have a right-lateral sense of slip

  9. 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.

  10. Vein attribute scaling in strike-slip and extensional fault damage zones affecting the platform carbonates in the Jabal Qusaybah anticline, Salakh Arc, Oman

    NASA Astrophysics Data System (ADS)

    Clemenzi, Luca; Balsamo, Fabrizio; Storti, Fabrizio; Solum, John; Taberner, Conxita; Tueckmantel, Christian

    2015-04-01

    Understanding factors that determine deformation intensity and vein attributes in fault damage zones is important to predict fracture patterns and fault system permeability in the subsurface. In this contribution we present a new dataset on vein attributes collected along 26 fault zones (extensional and strike-slip) developed in the Cretaceous platform carbonates of the Natih Formation during the growth of the Jabal Qusaybah anticline, in the foreland basin of the Oman Mountains. Extensional and strike slip fault zones accommodated comparable displacements (~0.1 up to ~100 m), but were active at different burial depths. Extensional fault zones developed at shallow burial depth (<1-2 km) during late-stage folding and strike-slip faulting, and are laterally restricted by sub-vertical strike-slip fault zones. Vein aperture (A), eight (H), and spacing (S) were measured in vertical sections by scanlines across 10 strike-slip and 16 extensional fault damage zones, and then statistically analyzed. In both strike-slip and extensional fault damage zones vein aperture and height generally increase approaching the master slip surfaces, while vein spacing decreases approaching them. Deformation intensity, calculated as vein H/S ratio per meter, exponentially increases moving from background host rock toward master slip surfaces. Furthermore, the mean vein H/S ratio calculated in each damage zone increases also with increasing fault displacement in extensional fault zones, whereas it remain almost constant in strike-slip fault zones. Different vein pattern evolutions in the two fault systems are due to the presence of sub-vertical strike-slip fault zones which provided mechanical barriers that hindered the lateral propagation of extensional fault zones. During extensional faulting, the vertical downthrown was not inhibited, thus resulting in a progressively higher deformation intensity in laterally-restricted, extensional fault damage zones.

  11. Internal Structure of a Strike-Slip Dilational Fault Jog: Overlander Fault, Mt Isa Inlier, Australia

    NASA Astrophysics Data System (ADS)

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

    2004-12-01

    The Overlander Fault is one of a set of NE-SW subvertical dextral strike-slip faults which, together with a NW-SE conjugate sinistral set, disrupt the Mt Isa Proterozoic orogen (1590-1500 Ma) in NW Queensland, Australia. These late- to post-orogenic faults thus define a regional stress field with σ 1 oriented approximately E-W and σ 3 oriented approximately N-S. The Overlander Fault trends ˜060° across the metamorphic assemblage except where it refracts to 070-074° across an outcropping granitic pluton, the margins of which it offsets dextrally by ˜1.5 km. The stepover width of this dilational fault jog approaches 1 km, comparable to dilational stepovers within active strike-slip faults (e.g. the San Andreas fault at Parkfield). In the surrounding amphibolite facies metamorphic assemblage the fault trace is comparatively inconspicuous and unmineralized but where it crosses the granite it is defined by upstanding ridges of silicified microbreccia and associated quartz veining. The stepover region provides opportunities for studying incremental and finite dilatation associated with slip transfer across the jog, and associated influx of hydrothermal fluids. Shearing across the stepover region is accommodated by a mesh structure with principal components that include: (1) a series of silicified microbreccia-cataclasite `walls' <10 m or so thick with associated quartz veins <1 m or so thick trending 070° and defining a `main zone' about 100±20 m wide; (2) parallel subsidiary strike-slip cataclastic shear zones occurring <200 m laterally from the main zone; (3) a set of subvertical <1-2 m thick extension veins oriented 090-100° , some with evidence of marginal shearing (both sinistral and dextral); (4) a conspicuous sinistral extensional-shear curving eastwards for ˜250 m from the main fault core on a trend of 100-115° ; and (5) a set of unmineralized faults with sinistral separations trending 120-130° . Slickenfibers and striations along the main fault

  12. Strike-slip structural styles and petroleum system evolution, northeast Sakhalin Island

    SciTech Connect

    Meisling, K.E.; Wagner, J.B.

    1996-12-31

    The primary petroleum system of northeast Sakhalin Island and adjacent shelfal areas is comprised of a system of Late Miocene to Quaternary faulted transpressional anticlines that trap oil and gas in Early Miocene to Pliocene deltaic reservoirs sourced from Late Oligocene to Early Miocene diatomaceous shales. Existing production has been limited to onshore anticlines, and offshore structural trends remain undeveloped, despite several discoveries. The regional tectonic evolution of Sakhalin Island can be divided into five major phases: (1) Late Cretaceous to Early Eocene subduction, (2) Middle-Eocene collision and uplift, (3) Late Eocene to Early Oligocene oblique rifting, (4) Late Oligocene to Middle Miocene thermal subsidence, and (5) Late Miocene to Quaternary transpression and inversion. Oil-prone source rocks were deposited during rapid post-rift thermal subsidence of transtensional rift basins and adjacent highs, which provided an ideal sediment-starved setting for source rock accumulation. Reservoir facies were supplied by prograding post-rift Miocene deltaics of the paleo-Amur river, which built a shelf across the thermally subsiding basin and intrabasin highs. Traps were formed when the basin was later inverted during Late Miocene to Pleistocene transpression, which reactivated both Paleogene normal faults and structural trends of the Mesozoic accretionary prism to create a broad zone of distributed shear. Strike-slip structural styles are evidenced by linear, en echelon alignments of doubly-plunging anticlines characterized by numerous small-displacement, transverse normal faults. Strike slip on individual structures is relatively small, however, based on a lack of thorough going faults. Strike-slip structures on Sakhalin Island are considered active, in light of the earthquake of May 27, 1995 (M=7.6) and uplift of Pleistocene marine terraces.

  13. Strike-slip structural styles and petroleum system evolution, northeast Sakhalin Island

    SciTech Connect

    Meisling, K.E.; Wagner, J.B. )

    1996-01-01

    The primary petroleum system of northeast Sakhalin Island and adjacent shelfal areas is comprised of a system of Late Miocene to Quaternary faulted transpressional anticlines that trap oil and gas in Early Miocene to Pliocene deltaic reservoirs sourced from Late Oligocene to Early Miocene diatomaceous shales. Existing production has been limited to onshore anticlines, and offshore structural trends remain undeveloped, despite several discoveries. The regional tectonic evolution of Sakhalin Island can be divided into five major phases: (1) Late Cretaceous to Early Eocene subduction, (2) Middle-Eocene collision and uplift, (3) Late Eocene to Early Oligocene oblique rifting, (4) Late Oligocene to Middle Miocene thermal subsidence, and (5) Late Miocene to Quaternary transpression and inversion. Oil-prone source rocks were deposited during rapid post-rift thermal subsidence of transtensional rift basins and adjacent highs, which provided an ideal sediment-starved setting for source rock accumulation. Reservoir facies were supplied by prograding post-rift Miocene deltaics of the paleo-Amur river, which built a shelf across the thermally subsiding basin and intrabasin highs. Traps were formed when the basin was later inverted during Late Miocene to Pleistocene transpression, which reactivated both Paleogene normal faults and structural trends of the Mesozoic accretionary prism to create a broad zone of distributed shear. Strike-slip structural styles are evidenced by linear, en echelon alignments of doubly-plunging anticlines characterized by numerous small-displacement, transverse normal faults. Strike slip on individual structures is relatively small, however, based on a lack of thorough going faults. Strike-slip structures on Sakhalin Island are considered active, in light of the earthquake of May 27, 1995 (M=7.6) and uplift of Pleistocene marine terraces.

  14. The Northern Caribbean Plate Boundary Offshore Hispaniola: Strike-slip and Compressive Tectonic Processes

    NASA Astrophysics Data System (ADS)

    Corbeau, J.; Rolandone, F.; Leroy, S. D.; Mercier De Lepinay, B. F.; Meyer, B.; Ellouz, N.

    2014-12-01

    The boundary between the Caribbean plate and the North American plate is transpressive due to the oblique collision between these two plates. The transpressive movement is partitioned and accommodated in the Hispaniola region along two left-lateral strike-slip structures surrounding a fold-and-thrust belt. New multibeam bathymetry data and multichannel seismic reflection profiles have been recently collected during the Haiti-SIS and Haiti-SIS 2 cruises, along part of the northern Caribbean plate boundary between Cuba, Jamaica and Hispaniola. From the north to the south, three types of deformations are observed. In the Windward Passage, the analysis of the data set reveals that the movement on the Oriente fault between Cuba and Hispaniola is purely left-lateral strike-slip according to the GPS measurements. In the Gonave basin, west of Hispaniola, the deformation is compressive. A series of folds is identified and moves toward the southwest. The Enriquillo-Plantain-Garden Fault (EPGF) is localized in the Jamaica Passage, between Jamaica and Hispaniola. The analysis of the data set reveals that the left-lateral EPGF recently intersects inherited basins from the eastern Cayman Trough margin. The study of the actual EPGF active trace shows that this fault moves with a pure strike-slip component, at least in its western part: the presence of a little push-up structure and a set of three en echelon folds is highlighting in the western part of the Jamaica Passage. The shortening rate in the inherited basins crossed by the EPGF increases from west to east (5.8% to 8.5%), indicating that a thrusting component is also accommodated around the EPGF.

  15. 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

  16. Dynamics of fault interaction - Parallel strike-slip faults

    NASA Astrophysics Data System (ADS)

    Harris, Ruth A.; Day, Steven M.

    1993-03-01

    We use a 2D finite difference computer program to study the effect of fault steps on dynamic ruptures. Our results indicate that a strike-slip earthquake is unlikely to jump a fault step wider than 5 km, in correlation with field observations of moderate to great-sized earthquakes. We also find that dynamically propagating ruptures can jump both compressional and dilational fault steps, although wider dilational fault steps can be jumped. Dilational steps tend to delay the rupture for a longer time than compressional steps do. This delay leads to a slower apparent rupture velocity in the vicinity of dilational steps. These 'dry' cases assumed hydrostatic or greater pore-pressures but did not include the effects of changing pore pressures. In an additional study, we simulated the dynamic effects of a fault rupture on 'undrained' pore fluids to test Sibson's (1985, 1986) suggestion that 'wet' dilational steps are a barrier to rupture propagation. Our numerical results validate Sibson's hypothesis.

  17. Magma storage in a strike-slip caldera

    NASA Astrophysics Data System (ADS)

    Saxby, J.; Gottsmann, J.; Cashman, K.; Gutiérrez, E.

    2016-07-01

    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.

  18. 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.

  19. Magma storage in a strike-slip caldera.

    PubMed

    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

  20. Provenance of alluvial fan deposits to constrain the mid-term offsets along a strike-slip active fault: the Elsinore fault in the Coyote Mountains, Imperial Valley, California.

    NASA Astrophysics Data System (ADS)

    Masana, Eulalia; Stepancikova, Petra; Rockwell, Thomas

    2013-04-01

    The lateral variation in rates along a fault and its constancy along time is a matter of discussion. To give light to this discussion, short, mid and long term offset distribution along a fault is needed. Many studies analyze the short-term offset distribution along a strike-slip fault that can be obtained by the analysis of offset features imprinted in the morphology of the near-fault area. We present an example on how to obtain the mid- to long-term offset values based on the composition of alluvial fans that are offset by the fault. The study area is on the southern tip of the Elsinore fault, which controls the mountain front of the Coyote Mountains (California). The Elsinore-Laguna Salada fault is part of the San Andreas fault (SAF) system, extending 250 km from the Los Angeles Basin southeastward into the Gulf of California, in Mexico. The slip-rate on the southern Elsinore fault is believed to be moderate based on recent InSAR observations, although a recent study near Fossil Canyon (southern Coyote Mountains) suggests a rate in the range of 1-2 mm/yr. For this study we processed the airborne LiDAR dataset (EarthScope Southern & Eastern California, SoCal) to map short to mid-term alluvial offsets. We reprocessed the point clouds to produce DEMs with 0.5m and 0.25m grids and we varied the insolation angles to illuminate the various fault strands and the offset features. We identified numerous offset features, such as rills, channel bars, channel walls, alluvial fans, beheaded channels and small erosional basins that varied in displacement from 1 to 350 m. For the mid- to long-term offsets of the alluvial fans we benefited from the diverse petrological composition of their sources. Moreover, we recognized that older alluvium, which is offset by greater amounts, is in some cases buried beneath younger alluvial fan deposits and separated by buried soils. To determine the source canyon of various alluvial elements, we quantified the clast assemblage of each source

  1. Ascension Submarine Canyon, California - Evolution of a multi-head canyon system along a strike-slip continental margin

    USGS Publications Warehouse

    Nagel, D.K.; Mullins, H.T.; Greene, H. Gary

    1986-01-01

    Ascension Submarine Canyon, which lies along the strike-slip (transform) dominated continental margin of central California, consists of two discrete northwestern heads and six less well defined southeastern heads. These eight heads coalesce to form a single submarine canyon near the 2700 m isobath. Detailed seismic stratigraphic data correlated with 19 rock dredge hauls from the walls of the canyon system, suggest that at least one of the two northwestern heads was initially eroded during a Pliocene lowstand of sea level ???3.8 m.y. B.P. Paleogeographic reconstructions indicate that at this time, northwestern Ascension Canyon formed the distal channel of nearby Monterey Canyon and has subsequently been offset by right-lateral, strike-slip faulting along the San Gregorio fault zone. Some of the six southwestern heads of Ascension Canyon may also have been initially eroded as the distal portions of Monterey Canyon during late Pliocene-early Pleistocene sea-level lowstands (???2.8 and 1.75 m.y. B.P.) and subsequently truncated and offset to the northwest. There have also been a minimum of two canyon-cutting episodes within the past 750,000 years, after the entire Ascension Canyon system migrated to the northwest past Monterey Canyon. We attribute these late Pleistocene erosional events to relative lowstands of sea level 750,000 and 18,000 yrs B.P. The late Pleistocene and Holocene evolution of the six southeastern heads also appears to have been controlled by structural uplift of the Ascension-Monterey basement high at the southeastern terminus of the Outer Santa Cruz Basin. We believe that uplift of this basement high sufficiently oversteepened submarine slopes to induce gravitational instability and generate mass movements that resulted in the erosion of the canyon heads. Most significantly, though, our results and interpretations support previous proposals that submarine canyons along strike-slip continental margins can originate by tectonic trunction and lateral

  2. 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

  3. Neotectonics, geodesy, and seismic hazard in the Northern Walker Lane of Western North America: Thirty kilometers of crustal shear and no strike-slip?

    NASA Astrophysics Data System (ADS)

    Wesnousky, Steven G.; Bormann, Jayne M.; Kreemer, Corné; Hammond, William C.; Brune, James N.

    2012-05-01

    Roughly 30 km of cumulative right-lateral crustal displacement and 5-6 mm/yr of the ongoing relative right-lateral motion between the Pacific and North American plates are observed in the northern Walker Lane. The right-lateral shear has been accommodated in large part by the development of a set of discontinuous, en echelon, normal fault-bounded basins and perhaps significant vertical axis rotations of the intervening crust. The observations provide an illustrative example of how large amounts of crustal shear may be accommodated in the absence of strike-slip faults and point to difficulties attendant to melding geologic and geodetic observations in the analysis of seismic hazard. In this particular case, the assumption that all geodetically observed shear across the area will be recorded by earthquake displacements may be flawed.

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

    NASA Technical Reports Server (NTRS)

    Schultz, Richard A.

    1989-01-01

    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.

  5. The distribution and characterization of strike-slip faults on Enceladus

    NASA Astrophysics Data System (ADS)

    Martin, Emily S.

    2016-03-01

    Strike-slip faulting is typically characterized by lateral offsets on icy satellites of the outer solar system. However, strike-slip faults on Enceladus lack these typical lateral offsets and instead are marked by the presence of tailcracks or en echelon cracks. These features are used here to develop the first near-global distribution of strike-slip faults on Enceladus. Strike-slip faults on Enceladus fall into three broad categories: tectonic terrain boundaries, reactivated linear features, and primary strike-slip faults. All three types of strike-slip faults are found predominantly, or within close proximity to, the antipodal cratered terrains on the Saturnian and anti-Saturnian hemispheres. Stress modeling suggests that strike-slip faulting on Enceladus is not controlled by nonsynchronous rotation, as on Europa, suggesting a fundamentally different process driving Enceladus's strike-slip faulting. The motion along strike-slip faults at tectonic terrain boundaries suggests large-scale northward migration of the ice shell on the leading hemisphere of Enceladus, occurring perpendicular to the opening direction of the tiger stripes in the south polar terrain.

  6. Evidence for Significant Aseismic Strike Slip During the 2007 Dike Intrusion Episode in Tanzania

    NASA Astrophysics Data System (ADS)

    Himematsu, Y.; Furuya, M.

    2014-12-01

    In July 2007, an earthquake swarm initiated Northern Tanzania near Lake Natron and lasted for about two months. Mt. Oldoinyo Lengai, which located near the seismicity, began to erupt effusively before about a month later, and increased eruption intensity on September when the swarm almost ceased. The explosive eruption continued until April 2008. Calais et al. (2008), Baer et al. (2008), and Biggs et al. (2009) have already reported the deformation associated with the swarm using InSAR. However, they mainly used ENVISAT/ASAR(C-band) images and only used images acquired from descending pass. We use both ascending and descending passes of ALOS/PALSAR (L-band) images. In addition to InSAR data, we also employ the offset-tracking technique to detect the signals along the azimuth direction. Using InSAR and offset-tracking, we could obtain the full 3D displacement field associated with the swarm. The inferred full 3D displacement indicates that the graben-like-subsiding zone was horizontally moving by ~48cm toward SSW. To our knowledge, the horizontal movement at the subsidence zone has never been identified. To explain the displacement, we performed the fault source modeling. The fault slip distribution indicates that the ratio of strike slip component is about 30% of total moment release. Aseismic strike-slip creep motion might have also been responsible for the horizontal motion area and the swarm activity.

  7. Northward growth of the Qimen Tagh Range: A new model accounting for the Late Neogene strike-slip deformation of the SW Qaidam Basin

    NASA Astrophysics Data System (ADS)

    Cheng, Feng; Jolivet, Marc; Fu, Suotang; Zhang, Qiquan; Guan, Shuwei; Yu, Xiangjiang; Guo, Zhaojie

    2014-09-01

    Situated along the western termination of the Eastern Kunlun Mountains, the Qimen Tagh Range represents a key area to understand the Cenozoic basin-range interactions between the northeastern Tibetan Plateau and the Qaidam Basin. Within that region, several huge bow-like fault systems such as the Kunbei and Qimen Tagh fault systems accommodate the transpressive deformation but their kinematic evolution is still highly debated. Newly acquired seismic profiles and isopach maps of the Late Eocene sediments strongly suggest that the Kunbei fault system (consisting of the Kunbei, Arlar and Hongliuquan faults) in the southwestern Qadaim Basin was initially a left-lateral strike-slip fault system rather than a thrusting system. Growth strata indicate an Early Miocene onset age for this strike-slip deformation. However, earthquake focal mechanisms show that the present-day tectonic pattern of this fault system is dominated by NE-SW transpression. As for the Qimen Tagh fault system, numerous linear geomorphic features and fault scarps indicate that it was again a strike-slip fault system. Deformed sediments within the Adatan Valley prove that strike-slip motion prevailed during the Pleistocene, yet the present day deformation is marked by NE-SW transpression. Collectively, the Kunbei and Qimen Tagh fault systems were initially left-lateral strike-slip fault systems that formed during Early Miocene and Pleistocene respectively. Colligating with these southward younging left-lateral strike-slip faulting ages and the fact that these convex-northward structures converge to the center segment of active Kunlun fault in the east, we thus considered the Kunbei and Qimen Tagh fault systems as former western segments of the Kunlun fault once located further south in the present-day location of that fault. These faults gradually migrated northward since the Early Miocene while their kinematics changed from left-lateral strike-slip motion to NE-SW transpression.

  8. Displacements and segment linkage in strike-slip fault zones

    NASA Astrophysics Data System (ADS)

    Peacock, D. C. P.

    Small-scale, well exposed strike-slip fault zones near Kirkcudbright, Scotland, cut sub-vertical bedding, so that mapped bed separations allow the displacements, linkage and evolution of fault segments to be assessed. Displacement variations along the segments can be related to lithologic variations, conjugate relationships, offsets, segment linkage and fault bends. High displacement gradients at the tips of conjugate and offset faults produce convex-upwards ( E-type) displacement-distance ( d-x) profiles. Contractional fault bends and linkage points are marked by a decrease in fault displacement, producing partially concave-upwards ( D-type) d-x profiles. Where fault displacement gradients are steep, wallrocks are marked by structures such as synthetic faults, normal drag folding, ductile strain and veining, which transfer displacement. The faults studied tend to have lower r/ dMAX ratios (where r = distance between the point of maximum displacement and the fault tip on a particular profile, and dMAX = maximum displacement on the profile) than are shown by normal faults in map view. This may be because r is measured parallel to the displacement direction and/or because of lithologic variations.

  9. Stress triggering of the great Indian Ocean strike-slip earthquakes in a diffuse plate boundary zone

    NASA Astrophysics Data System (ADS)

    Wiseman, Kelly; Bürgmann, Roland

    2012-11-01

    On April 11, 2012, two great magnitude 8+ earthquakes occurred within a two-hour period off the west coast of northern Sumatra, Indonesia, in the broadly distributed India-Australia plate boundary zone. The magnitude 8.6 mainshock holds the distinction of being both the largest instrumentally recorded strike-slip earthquake and the largest earthquake away from a recognized plate boundary fault. The mainshock involved sequential ruptures of multiple fault planes oriented nearly perpendicular to each other. The adjacent 2004 megathrust earthquake statically loaded the northern Wharton Basin oceanic lithosphere on both of the 2012 mainshock fault plane orientations, and greatly enhanced the rate of earthquake activity in the region for a year. Viscoelastic relaxation of the asthenosphere following the 2004 and 2005 megathrust earthquakes continued to positively stress the offshore region, correlating with the locations of later strike-slip earthquakes, including two magnitude 7+ and the 2012 magnitude 8+ earthquakes.

  10. 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

  11. Tectonics, magmatism and paleo-fluid distribution in a strike-slip setting: Insights from the northern termination of the Liquiñe-Ofqui fault System, Chile

    NASA Astrophysics Data System (ADS)

    Pérez-Flores, Pamela; Cembrano, José; Sánchez-Alfaro, Pablo; Veloso, Eugenio; Arancibia, Gloria; Roquer, Tomás

    2016-06-01

    This study addresses the interplay between strain/stress fields and paleo-fluid migration in the Southern Andean Volcanic Zone (SVZ). The SVZ coexists with the margin-parallel Liquiñe-Ofqui Fault System (LOFS) and with NW-striking Andean Transverse Faults (ATF). To tackle the role of different fault-fracture systems on deformation distribution and magma/fluid transport, we map the nature, geometry and kinematics of faults, veins and dikes at various scales. Fault-slip data analysis yields stress and strain fields from the full study area data base (regional scale) and fault zones representative of each fault system (local scale). Regional scale strain analysis shows kinematically heterogeneous faulting. Local strain analyses indicate homogeneous deformation with NE-trending shortening and NW-trending extension at NNE-striking Liquiñe-Ofqui master fault zones. Strain axes are clockwise rotated at second order fault zones, with ENE-trending shortening and NNW-trending stretching. The ATF record polyphasic deformation. Conversely, stress field analysis at regional scale indicates a strike-slip dominated transpressional regime with N64°E-trending σ1 and N30°W-trending σ3. Deformation is further partitioned within the arc through NNE-striking dextral-reverse faults, NE-striking dextral-normal faults and NW-striking sinistral-reverse faults with normal slip activation. The regional tectonic regime controls the geometry of NE-striking dikes and volcanic centers. NE-striking faults record local stress axes that are clockwise rotated with respect to the regional stress field. NNE- and NE-striking faults are favorably oriented for reactivation under the regional stress field and show poorly-developed damage zones. Conversely, NW-striking fault systems, misoriented under the regional stress field, show multiple fault cores, wider damage zones and dense vein networks. Deformation driven by oblique subduction is partially partitioned into strike-slip and shortening

  12. Late Pleistocene to Present - normal and strike slip - faulting in the western Gulf of Corinth; data from high resolution seismic reflection SISCOR surveys

    NASA Astrophysics Data System (ADS)

    Beckers, Arnaud; Bodeux, Sarah; Beck, Christian; Hubert-Ferrari, Aurélia; Tripsanas, Efthymios; Sakellariou, Dimitris; De Batist, Marc; De Rycker, Koen; Bascou, Pascale; Versteeg, Willem

    2013-04-01

    dipping faults, 4 to 6 km long, have been identified. These faults strike NE-SW. The northern one shows a clear strike-slip component. This fault system is not part to the Corinth Fault System. It could be part of a local transfer zone linking the Patras and the Corinth Basins, or of the NE-SW right-lateral slip fault system interconnecting the Gulf of Corinth to the Kephalonia transform Fault and the Hellenic subduction.

  13. Overview of cenozoic strike-slip displacement of the caribbean plate

    SciTech Connect

    Mann, P.

    1985-01-01

    Geologic and tectonic studies in the Caribbean region have traditionally focused on Cretaceous and Paleogene arc rocks which, for the most part, record a long period (approx. = 100 Ma) of plate convergence. Since the recognition of the plate structure of the Caribbean by Molnar and Sykes in 1969, there has been steadily increasing interest in mapping widespread ares of Neogene sedimentary and volcanic rocks that generally record a long period (65.-40 Ma) of eastward displacement of the Caribbean plate relative to the Americas. The purpose of this talk is to review different aspects of present knowledge on this strike-slip displacement, namely: 1) location of major strike-slip faults within the northern and southern plate boundary zones; 2) sense, offset, rate of slip of major strike-slip faults; 3) secondary deformational features related to strike-slip displacements; 4) intraplate deformational features related to interplate strike-slip movements; 5) relation of seismicity to major strike-slip faults; and 6) constraints imposed by strike-slip fault systems on plate motion models. Based on these observations, several critical problems which future studies might help resolve are pointed out.

  14. 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

  15. 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.

  16. Strike-slip faults in the southernmost Andes and the development of the Patagonian orocline

    NASA Astrophysics Data System (ADS)

    Cunningham, W. Dickson

    1993-02-01

    The Patagonian orocline is the 90° bend in the southernmost Andes between 50°S and 56°S. Paleomagnetic and structural data indicate that the orocline is, at least in part, the product of tectonic rotation. Recent field work in the Beagle Channel region of southernmost Chile provides evidence for widespread left-lateral strike-slip faulting in the internal zones of the mountain belt. Both arms of the Beagle Channel are interpreted to be left-lateral strike-slip faults based on detailed study of mesoscale strike-slip faults (Riedel shears) observed in coastal outcrops. Although much of the evidence indicates Cenozoic brittle strike-slip faulting, other fabric data, including vertical foliation zones containing horizontal quartz stretching lineations and ductile left-lateral kinematic indicators, suggest that Mesozoic ductile strike-slip or oblique-slip shearing also occurred. The implication is that the mid-Cretaceous Andean orogeny involved the transpressional inversion of the Rocas Verdes marginal basin and that transpression has been the dominant deformational regime in the region for the last 120 Ma. Regional left-lateral strike-slip faults are now recognized in all lithotectonic provinces of the southernmost Andes. A statistical study of regional lineament trends using aerial photographs and satellite imagery suggests that many unstudied lineaments are also strike-slip faults. A new model is proposed that integrates the development of strike-slip faulting and the structural evolution and uplift of the southernmost Andes with the rotational development of the orocline. The Patagonian orocline appears to be the product of broad interplate shearing accommodated by strike-slip faulting, block rotation, and contraction and is probably continuing to evolve today.

  17. 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

    2015-01-01

    Models that treat long-term evolution of the Tibetan orogen in terms of interactions between rigid blocks require the right-slip Karakoram fault that bounds the western margin of the Tibetan plateau to be a long-lived, stable, high slip-rate feature. While the southern portion of the fault clearly remains active, recent work has proposed that the northern half of the Karakoram fault is currently inactive. New field observations and geochronologic results from the northern end of the Karakoram fault system confirm this interpretation and provide the first quantitative data on the minimum age for the termination of slip. In the southeast Pamir, gravel that yields a U-series age of 198 ± 5 ka on secondary carbonate caps a non-deformed strath terrace that extends across the main strand of the Karakoram fault. The secondary Achiehkopai fault strand is overlain by undisturbed Hangdi glacial stage (24 ± 6 ka) deposits and Dabudar glacial stage (penultimate glacial cycle, ∼ 150 ka, or older) deposits, which lack observable lateral displacement or deformation. Together, these observations show that the northern portion of the Karakoram fault system has not accommodated any detectable strike-slip deformation since at least 24 ± 6 ka, and most likely since ∼ 200 ka or more. These results show that the Karakoram fault system no longer forms a continuous discrete kinematic boundary at the western margin of the Tibetan Plateau. This suggests that even long (> 500 km) strike-slip faults within orogenic belts are inherently unstable features, consistent with models of continental collision zones involving relatively weak crust and distributed deformation.

  18. 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

  19. Termination of major ductile strike-slip shear and differential cooling along the Insubric line (Central Alps): UPb, RbSr and 40Ar /39Ar ages of cross-cutting pegmatites

    NASA Astrophysics Data System (ADS)

    Schärer, Urs; Cosca, Michael; Steck, Albrecht; Hunziker, Johannes

    1996-08-01

    To constrain the age of strike-slip shear, related granitic magmatism, and cooling along the Insubric line, 29 size fractions of monazite and xenotime were dated by the UPb method, and a series of 25 RbSr and 40Ar /39Ar ages were measured on different size fractions of muscovite and biotite. The three pegmatitic intrusions analyzed truncate high-grade metamorphic mylonite gneisses of the Simplon shear zone, a major Alpine structure produced in association with dextral strike-slip movements along the southern edge of the European plate, after collision with its Adriatic indenter. Pegmatites and aplites were produced between 29 and 25 Ma in direct relation to right-lateral shear along the Insubric line, by melting of continental crust having 87Sr /86Sr between 0.7199 and 0.7244 at the time of melting. High-temperature dextral strike-slip shear was active at 29.2 ± 0.2 (2σ) Ma, and it terminated before 26.4 ± 0.1 Ma. During dike injection, temperatures in the country rocks of the Isorno-Orselina and Monte Rosa structural units did not exceed ≈ 500°C, leading to fast initial cooling, followed by slower cooling to ≈ 350°C within several million years. In one case, initial cooling to ≈ 500°C was significantly delayed by about 4 m.y., with final cooling to ≈ 300°C at 20-19 Ma in all units. For the period between 29 and 19 Ma, cooling of the three sample localities was non-uniform in space and time, with significant variations on the kilometre scale. These differences are most likely due to strongly varying heat flow and/or heterogeneous distribution of unroofing rates within the continuously deforming Insubric line. If entirely ascribed to differences in unroofing, corresponding rates would vary between 0.5 and 2.5 mm/y, for a thermal gradient of 30°/km.

  20. Strike-slip accommodated core complexes in the Najd fault system, Arabian-Nubian shield

    NASA Astrophysics Data System (ADS)

    Meyer, S. E.; Passchier, C. W.; Abu-Alam, T. S.; Stuewe, K.

    2013-12-01

    Metamorphic core complexes are usually developed as extensional features during crustal thinning in a continental collision zone, 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 dome 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 curves by more than 90 degrees eastwards 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 strike slip motion, which caused local exhumation of lower crustal rocks by 25 km along the detachment. The eastern shear zone branch formed late 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

  1. The geometries and development of late orogenic strike-slip faults

    NASA Astrophysics Data System (ADS)

    Anderson, M. W.; Peacock, D. C. P.

    2003-04-01

    Strike-slip faults are commonly the final phase of contraction in orogenic belts, occurring when the folds have locked-up and the thrusts have become too steep for further displacement to occur. Where the maximum stress axis (sigma1) is perpendicular to the orogenic belt (i.e. pure shear), the strike-slip faults are conjugate and represent strike-perpendicular shortening and necessary strike-parallel extension. An example of such behaviour occurs in the steeply dipping Silurian sandstones and shales in Kirkcudbrightshire, in the Southern Uplands of Scotland. If sigma1 is at ~ 70°; to the strike of the orogenic belt, the conjugate strike-slip faults become asymmetric. One set of strike-slip faults occurs at a high angle to the strike of bedding, and the conjugate set has a ramp-flat trajectory across steeply dipping beds. An example of this behaviour occurs in the steeply dipping Silurian turbidites at Ardglass, in the Longford-Down terrane of Northern Ireland. If sigma1 is at a lower angle to the orogenic belt (i.e. transpression), one set of strike-slip faults tends to dominate. In some cases, the dominant strike-slip fault set is parallel to the strike of the orogenic belt, the Caledonian-age Great Glen Fault of Scotland being such an example. In other cases, block rotation occurs on the set of strike-slip faults that are at a high angle to the orogenic belt, as in the Variscan Orogenic Belt of SW England. An annulus model is presented to illustrate the variations in geometries of late-orogenic strike-slip faults from pure shear to transpression.

  2. 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.

  3. Effect of inherited structures on strike-slip plate boundaries: insight from analogue modelling of the central Levant Fracture System, Lebanon

    NASA Astrophysics Data System (ADS)

    Ghalayini, Ramadan; Daniel, Jean-Marc; Homberg, Catherine; Nader, Fadi

    2015-04-01

    Analogue sandbox modeling is a tool to simulate deformation style and structural evolution of sedimentary basins. The initial goal is to test what is the effect of inherited and crustal structures on the propagation, evolution, and final geometry of major strike-slip faults at the boundary between two tectonic plates. For this purpose, we have undertaken a series of analogue models to validate and reproduce the structures of the Levant Fracture System, a major NNE-SSW sinistral strike-slip fault forming the boundary between the Arabian and African plates. Onshore observations and recent high quality 3D seismic data in the Levant Basin offshore Lebanon demonstrated that Mesozoic ENE striking normal faults were reactivated into dextral strike-slip faults during the Late Miocene till present day activity of the plate boundary which shows a major restraining bend in Lebanon with a ~ 30°clockwise rotation in its trend. Experimental parameters consisted of a silicone layer at the base simulating the ductile crust, overlain by intercalated quartz sand and glass sand layers. Pre-existing structures were simulated by creating a graben in the silicone below the sand at an oblique (>60°) angle to the main throughgoing strike-slip fault. The latter contains a small stepover at depth to create transpression during sinistral strike-slip movement and consequently result in mountain building similarly to modern day Lebanon. Strike-slip movement and compression were regulated by steady-speed computer-controlled engines and the model was scanned using a CT-scanner continuously while deforming to have a final 4D model of the system. Results showed that existing normal faults were reactivated into dextral strike-slip faults as the sinistral movement between the two plates accumulated. Notably, the resulting restraining bend is asymmetric and segmented into two different compartments with differing geometries. One compartment shows a box fold anticline, while the second shows an

  4. Application of terrestrial LiDAR topographic data to reconstruct offset geomorphic markers along the Fuyun strike-slip fault, Xinjiang, China

    NASA Astrophysics Data System (ADS)

    Etchebes, M.; Tapponnier, P.; Klinger, Y.; Van Der Woerd, J.; Xu, X.; Xinzhe, S.; Xibin, T.; Rizza, M.; Hang, T. Lok

    2012-04-01

    Tectonically offset geomorphic markers such as stream channels, terrace risers, alluvial fan surfaces and other types of ridges and troughs record the surface signature of successive earthquakes on active faults. Increasingly detailed 3D surface measurements, together with multiple age constraints, now yield a much-improved understanding of the long-term seismic behavior of such faults. Using sub-metric-resolution Quickbird optical satellite images, we obtained a dense horizontal offset dataset (553 measurements) along the right-lateral Fuyun fault. The most recent rupture along this fault, which is remarkably well preserved due to the arid climate, was generated by the Ms 7.9, august 11, 1931 Fuyun earthquake. For 5 successive earthquakes of similar size, the dataset is consistent with characteristic seismic behavior (≈ 6 ± 1 m of co-seismic slip). To complement and validate this dataset, we acquired terrestrial LiDAR topographic data over a total length of 7.5 km at 4 sites where multiples of the 1931 offsets were measured on Quickbird images. Using the new LiDAR DEMs obtained, we were able to map fault scarps more accurately, and the restoration of horizontal offset measurements was improved using apparent vertical offsets. The identification and definition of the markers with the 3D LiDAR data is unambiguous, and qualitative differences in the apparent ages of the markers may be assessed, increasing the confidence level in the reconstructions. On the thrust segments of the rupture, knickpoint retreat can be quantified, opening the way to a better understanding of the interaction between erosion and seismic surface deformation in shaping the landforms. Field observations, HR optical satellite images and LiDAR topographic data ideally complement one another to test the repeatability of offset measurements and constrain the densest possible vertical and horizontal slip distributions along active faults. By combining them, we are starting to build unique

  5. Controls on timing and amount of right-lateral offset on the East Bay fault system, San Francisco Bay region, California

    USGS Publications Warehouse

    Graymer, R.W.; Sarna-Wojcicki, A. M.; Walker, J.P.; McLaughlin, R.J.; Fleck, R.J.

    2002-01-01

    The distribution of offset, correlated rock units, relative position of northward- younging volcanic rocks, and distribution of units not offset together reveal the history of strike-slip deformation along the East Bay fault system. The system accumulated 175 km of right-lateral offset since 12 Ma, but of this amount, only ???25 km was accumulated between 12 and 10 Ma and only ???75 km between 12 and 6 Ma. The westernmost Hayward fault zone is responsible for more than half (100 km) of the total, and it, too, has undergone more offset (60 km) after 6 Ma than before. The activity on any single fault zone in the system has been sporadic, and alternating periods of activity and inactivity have been recorded on at least some of the fault zones.

  6. Offset of Latest Pleistocene Shoreface Reveals Slip Rate on the Hosgri Strike-Slip Fault, Offshore Central California

    NASA Astrophysics Data System (ADS)

    Johnson, S. Y.; Hartwell, S. R.; Dartnell, P.

    2014-12-01

    The Hosgri fault is the southern part of the regional Hosgri-San Gregorio dextral strike-slip fault system, which extends primarily in the offshore region for about 400 km in central California. Between Morro Bay and San Simeon, high-resolution multibeam bathymetry reveals that the eastern strand of the Hosgri fault is crossed by a ~265-m-wide slope interpreted as the shoreface of a relict sand spit that formed during a period of relatively slower sea-level rise (Younger Dryas stadial) in the latest Pleistocene. This sand spit crossed an embayment and connected a western fault-bounded bedrock peninsula and an eastern bedrock highland, a paleogeography similar to modern geomorphology along coastal segments of the San Andreas fault. Detailed analysis of the relict shoreface with slope profiles and slope maps indicates a lateral slip rate of 2.6 ± 0.9 mm/yr. Because the Hosgri fault locally includes an active western strand, and regionally converges with several other faults, this slip rate should be considered a minimum for the Hosgri fault in central California and should not be applied for the entire Hosgri-San Gregorio fault system. This slip rate indicates that the Hosgri system takes up the largest share of the strike-slip fault budget and is the most active strike-slip fault west of the San Andreas fault in central California. This result further demonstrates the value and potential of high-resolution bathymetry in earthquake-hazard characterization of active offshore faults.

  7. Transformations in shallow fault zones; evidence from fault rocks in young strike-slip systems.

    NASA Astrophysics Data System (ADS)

    van der Pluijm, B. A.; Schleicher, A. M.; Warr, L. N.

    2008-12-01

    Shallow fault rocks are typically interpreted in terms of brittle deformation features, such as fracture patterns, processes like cataclasis, and frictional properties from laboratory experiments. There is growing evidence from observations in natural rocks, however, that chemical and state transformations play an important, perhaps even a key role in shallow fault processes. Sheared mudrocks from a recent, active part of the San Andreas Fault (SAFOD) drillhole (3-3.3 km depth) show abundant, hydrous mixed-layer clay mineral phases. These hydrous phases formed during enhanced circulation of aqueous fluids along permeable fractures by low-temperature dissolution-precipitation reactions. Of particular significance is their occurrence as thin, nm- thick clay coatings on polished and striated fracture surfaces, similar in appearance to, but much smaller than slickensided surfaces commonly found in exhumed brittle fault rocks. These clay precipitates on secondary surfaces may be key to understanding creep and weak fault behavior, as they are restricted to displacement surfaces. Their occurrence also explains the low degree of preferred orientation, measured by X-ray texture goniometry, which is typical for clay gouges. Another area where transformations influence fault behavior at shallow crustal levels is by friction melting and associated neocrystallization. At seismic slip conditions, the formation of friction melts has been proposed from calculations and laboratory experiments. Few, unaltered natural laboratories are available, but the Alpine Fault of New Zealand provides opportunity for study in recent strike-slip activity. A suite of samples collected near a type locality show that brief melt generation occurred during a single period (with several pulses?) of displacement. Dating of these samples, in conjunction with thermal modeling, shows that pseudotachylyte formed at 3.5-5 km depth, which is just below SAFOD drilling depth. A general picture is emerging where

  8. Experimental modelling of tectonics-erosion-sedimentation interactions in compressional, extensional, and strike-slip settings

    NASA Astrophysics Data System (ADS)

    Graveleau, Fabien; Strak, Vincent; Dominguez, Stéphane; Malavieille, Jacques; Chatton, Marina; Manighetti, Isabelle; Petit, Carole

    2015-09-01

    Tectonically controlled landforms develop morphologic features that provide useful markers to investigate crustal deformation and relief growth dynamics. In this paper, we present results of morphotectonic experiments obtained with an innovative approach combining tectonic and surface processes (erosion, transport, and sedimentation), coupled with accurate model monitoring techniques. This approach allows for a qualitative and quantitative analysis of landscape evolution in response to active deformation in the three end-member geological settings: compression, extension, and strike-slip. Experimental results outline first that experimental morphologies evolve significantly at a short time scale. Numerous morphologic markers form continuously, but their lifetime is generally short because erosion and sedimentation processes tend to destroy or bury them. For the compressional setting, the formation of terraces above an active thrust appears mainly controlled by narrowing and incision of the main channel through the uplifting hanging-wall and by avulsion of deposits on fan-like bodies. Terrace formation is irregular even under steady tectonic rates and erosional conditions. Terrace deformation analysis allows retrieving the growth history of the structure and the fault slip rate evolution. For the extensional setting, the dynamics of hanging-wall sedimentary filling appears to control the position of the base level, which in turn controls footwall erosion. Two phases of relief evolution can be evidenced: the first is a phase of relief growth, and the second is a phase of upstream propagation of topographic equilibrium that is reached first in the sedimentary basin. During the phase of relief growth, the formation of triangular facets occurs by degradation of the fault scarp, and their geometry (height) becomes stationary during the phase of upstream propagation of the topographic equilibrium. For the strike-slip setting, the complex morphology of the wrench zone

  9. Complex Rift-Parallel, Strike-Slip Faulting in Iceland: Kinematic Analysis of the Gljúfurá Fault Zone

    NASA Astrophysics Data System (ADS)

    Nanfito, A.; Karson, J. A.

    2009-12-01

    The N-S striking Gljúfurá Fault Zone is an anomalous, dextral, strike-slip fault cutting Tertiary basaltic lavas in west-central Iceland. The fault zone is nearly parallel to structures formed at extinct spreading centers that were active from ~15 to 7 Ma ago in this region, suggesting ridge-parallel strike-slip faulting. The fault zone is well exposed in a river gorge for ~2 km along a well-defined regional lineament. The combined damage zone and fault core are about 50 m wide revealing an especially intense and complex style of deformation compared to other Icelandic fault zones. Basaltic lava flows on either side of the fault zone are cut by numerous closely spaced (10s of cm to m) Riedel shear fractures that grade into a fault core of progressively more intensely fractured lava and strongly altered and mineralized fault breccias, cataclasite and fault gouge. Riedel shears are frequently rotated or bend into the main fault zone. Distinctive bands of fault breccia derived from lava flow interiors, flow tops and dike rock are mapped for tens of meters along strike and reach thicknesses of several meters wide. Breccias contain angular basaltic fragments that range from few meters to millimeters. Fault breccias are typically clast supported with a matix of finely comminuted basalt clasts to clay gouge. 'Jigsaw' breccias are supported by a calcite matrix. Discrete faults and shear fractures show dominantly gently plunging slickenlines and abundant kinematic indicators showing dextral>normal oblique slip. Zeolite and calcite veins show multiple episodes of extension. Local left steps in fault zone are marked by extensional duplex structures with vertical separations of tens of meters bounded by major strike-slip fault strands. The overall architecture of the fault zone in interpreted as an exhumed flower structure. Numerous deformed and undeformed basaltic dikes sub-parallel the deformation structures, suggesting synkinematic intrusion. Some dikes deviate from the

  10. Shallow Hydrothermal Flow in a Strike-Slip Fault System, Mt Isa, Australia: A Proterozoic Analog for Modern Geothermal Systems Along Strike-Slip Faults

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Strong E-W shortening during the Isan Orogeny (1590-1500 Ma) led to crustal thickening and compressional inversion of former intracontinental rift basins. The resulting metamorphic/plutonic basement complex is disrupted by conjugate, mutually cross-cutting sets of brittle, late-orogenic strike-slip faults. Dextral strike-slip faults (separations < 25 km) strike NE-NNE, while conjugate sinistral faults strike SE-SSE, defining a wrench regime (σv = σ2) with horizontal maximum compression, σ1, trending c. 100°. The strike-slip faults are recessive except in dilational sites where upwelling hydrothermal fluids have silicified the cataclastic shear zones (CSZ) which protrude as blade-like ridges extending for kilometres across the semi-arid terrain. The mineralized fault segments include sinuous releasing bends where the fault trace is deflected <10° as well as more abrupt dilational stepovers with distributed extension fracturing linking en echelon fault segments. Other components of structural permeability include: (1) innumerable fault-parallel quartz-veins (cm to m thickness) within the CSZ; (2) irregular stringer veins; and (3) a regional set of predominantly extensional, subvertical planar quartz veins oriented 080-120° at moderate angles to the main faults. Broad contemporaneity is indicated by mutual cross-cutting relationships between all structural components. Measured strike separations along shear fractures are consistent with seismic slip increments which refreshed fracture permeability and promoted hydrothermal flow. Textures suggest the faults were exhumed from epithermal boiling environments (<1-2 km depth). Restoration of fault cohesive strength by hydrothermal cementation was critical in allowing continued vein formation by hydraulic extension fracturing. The distribution of hydrothermal quartz within the fault system provides a guide to structural localization of upflow zones in geothermal fields developed along strike-slip faults.

  11. Fault Population Analyses in the Eastern California Shear Zone: Insights into the Development of Young, Actively Evolving Plate Boundary Structures

    NASA Astrophysics Data System (ADS)

    Zhou, X.; Dawers, N. H.; Amer, R. M.

    2014-12-01

    Relationships between cumulative fault displacement, slip rate and length, along with fault population statistics are analyzed for faults located within the Eastern California Shear Zone (ECSZ), focusing on areas north of the Garlock fault. Here many faults are geologically young and in an early stage of evolution, while many older and larger faults are also still active. We analyze scaling relationships for both strike-slip and normal faults in order to determine whether the two fault populations share the same properties or not. Cumulative displacement, slip rate and length data are collected from published maps and literature sources. The dataset spans fault lengths from tens of meters to hundreds of kilometers. Results of fault scaling analyses indicate that displacement has a linear relationship with fault length for normal faults in this area over the entire length span, whereas strike-slip faults do not have a clear displacement-length scaling relation. For a given length, the subset of strike-slip faults typically exhibits a much larger displacement than that for the normal faults. The slip rate versus length trends are similar but are considerably more scattered. In addition, we define a subpopulation of normal faults that are kinematically related to the right-lateral strike-slip faults; these have a maximum length set by the spacing between the right-lateral faults. Fault size-frequency distributions also indicate differences between the normal and strike-slip fault populations. Overall, the normal faults have higher ratios of cumulative number to fault length than the strike-slip population does, which we relate to different patterns of localization of faulting. We interpret these trends as reflecting different tectonic histories, with the majority of normal faults being intraplate faults associated with Basin and Range extension and the strike-slip faults being kinematically connected with plate boundary.

  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. 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

  14. Miocene strike-slip and normal fault controls on Au-Ag mineralization in the Talapoosa district, Lyon County, Nevada

    SciTech Connect

    Dilles, P.A.; Carpenter, A.S.

    1993-04-01

    Structurally controlled epithermal stockwork Au-Ag mineralization formed at the intersection of three complexly interacting fault sets in intermediate Miocene volcanic rocks at the Talapoosa District (TD) on the western margin of the Walker Lane during the mid.-late Miocene. The TD lies at the intersection of the N 75[degree] W Talapoosa-Gooseberry (T-G) lineament with the N 70[degree] E Carson River fault system. Earliest high angle faults guided the dacite intrusive and early hydrothermal fluids. In response to increasing down to the south motion on these faults, first low angle then moderate angle striking, south dipping normal faults evolved. The Hematite fault separates argillized hanging wall from stockwork mineralized footwall in the Dyke zone, but is offset by the 40--65[degree] S dipping Talapoosa Fault (TF). The TF, traceable for over 1,500 m, is the primary conduit flooring tabular south dipping stockwork mineralization in the Bear Creek, Dyke and East Hill zones. The TF has accommodated at least 150 m of dip-slip motion, as well as repeated strike-slip and rare oblique-slip motions. High angle left-lateral and normal faults horsetail and flatten to moderate southerly dips creating mineralized brecciated zones where they merge with the TF in the Dyke zone. Significant post mineral faulting occurred on all fault sets as the core of the district was subsequently uplifted as a horst. Latest left-lateral and normal motions on faults displace the TF and Lousetown Fm. The authors preliminary interpretation of structural data is that low to moderate south dipping faults evolved above the intersection of right-lateral N 20-40[degree] W strike-slip faults of the Walker Lane bent toward (older ) N 75[degree] W faults of the T-G lineament. During and after mineralization left-lateral and normal faults of the Carson River system merged into and moved in concert with the Talapoosa fault, shattering hangingwall andesites and reacting older structures.

  15. 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., III; 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.

  16. 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., III; 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.

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

    NASA Astrophysics Data System (ADS)

    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., III; 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

    2010-11-01

    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.

  18. 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

  19. Multi-scale properties of strike-slip faults crosscutting the Pleistocene carbonate grainstones of Favignana Island (NW Sicily, Italy).

    NASA Astrophysics Data System (ADS)

    Cilona, Antonino; Agosta, Fabrizio; Giunta, Giuseppe; Renda, Pietro; Tondi, Emanuele

    2010-05-01

    After detailed field (stratigraphic and structural) and laboratory analyses of intact and deformed rocky outcrops, we studied the multi-scale properties of strike-slip faults nucleated and developed in Pleistocene carbonate grainstones of Favignana Island (Sicily, Italy). This skeletal carbonate rocks ranging in thickness between 5 and 20 meters make up the whole eastern side of the Island, where they unconformably lie on silicoclastic deposits of the Upper Pliocene. The studied structures are very similar to those one affecting carbonate grainstones of San vito Lo Capo Peninsula (Sicily, Italy) and already documented in a recent paper. There strain localization into narrow bands encompass first compaction, shear, pressure solution formation, their subsequent shearing, and finally cataclasis. The transitions from one deformation process to another, which were likely controlled by changes in the material properties, are recorded by different ratios and dissimilar distributions of the fault dimensional attributes. In Favignana Island, the results of our study allow us to: (i) indentify two conjugate sets of faults trending NW and NNE, characterized by right-lateral and left-lateral kinematics, respectively; (ii) document the progression of the deformation from single compactive shear bands, with an offset ranging between mm's to cm's, to zones of compactive shear bands, characterized by a larger amount of offset with discontinuous cataclasis and slip surfaces, and finally to well developed faults, with an inner cataclastic core surrounded by wider damage zones made up of compactive shear bands, joints, and possible dilational bands; (iii) decipher that linkage processes, responsible for fault development, took place by mechanical interaction of adjacent individual structures at any deformation stage (single bands, zone of shear bands or well developed faults) with formation of characteristic ramp and eye structures. Based on their internal architecture and

  20. 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-slip

  1. Dynamics of a strike-slip fault analog model : Effects of the tectonic loading rate

    NASA Astrophysics Data System (ADS)

    Caniven, Y.; Dominguez, S.; Soliva, R.; Cattin, R.; Peyret, M.; Chéry, J.; Romano, C.

    2013-12-01

    The average seismic cycle duration extends from hundred to a few thousands years but geodetic measurements and seismological data extend over less than one century. This short time observation scale renders difficult to constrain the role of key parameters such as fault friction and geometry, crust rheology, stress and strain rate that control the kinematics and mechanics of active faults. To solve this time scale issue, we have developed a new experimental set-up that reproduces scaled micro-earthquakes and several hundreds of seismic cycles along a strike-slip fault. The model is constituted by two polyurethane foam plates laterally in contact, lying on a basal silicone layer, which simulate the mechanical behaviour of an elastoplastic upper crust over a ductile lower crust, respectively. To simulate the boundary conditions of a strike-slip fault, a computerized motoreductor system moves the two compartments on an opposite sens at a constant low velocity (a few μm/s). The model scaling, deduces from analog material physical parameters, implies that 1 cm in the model represents 2-3 km in the nature and 1 s is equivalent to 5-15 years. Surface-horizontal strain field is quantified by sub-pixel correlation of digital camera pictures recorded every 16 μm of displacement. We record about 2000 horizontal-velocity field measurements for each experiment. The analysis of model-interseismic and coseismic surface displacements and their comparison to seismogenic natural faults demonstrate that our analog model reproduces correctly both near and far-field surface strains. To compare the experiments, we have developed several algorithms that allow studying the main spatial and temporal evolution of the physical parameters and surface deformation processes that characterise the seismic cycle (magnitudes, stress, strain, friction coefficients, interseismic locking depth, recurrence time, ...). We also performed surface-velocity field inversions to assess the spatial

  2. The rupture process of the Manjil, Iran earthquake of 20 june 1990 and implications for intraplate strike-slip earthquakes

    USGS Publications Warehouse

    Choy, G.L.; Zednik, J.

    1997-01-01

    In terms of seismically radiated energy or moment release, the earthquake of 20 January 1990 in the Manjil Basin-Alborz Mountain region of Iran is the second largest strike-slip earthquake to have occurred in an intracontinental setting in the past decade. It caused enormous loss of life and the virtual destruction of several cities. Despite a very large meizoseismal area, the identification of the causative faults has been hampered by the lack of reliable earthquake locations and conflicting field reports of surface displacement. Using broadband data from global networks of digitally recording seismographs, we analyse broadband seismic waveforms to derive characteristics of the rupture process. Complexities in waveforms generated by the earthquake indicate that the main shock consisted of a tiny precursory subevent followed in the next 20 seconds by a series of four major subevents with depths ranging from 10 to 15 km. The focal mechanisms of the major subevents, which are predominantly strike-slip, have a common nodal plane striking about 285??-295??. Based on the coincidence of this strike with the dominant tectonic fabric of the region we presume that the EW striking planes are the fault planes. The first major subevent nucleated slightly south of the initial precursor. The second subevent occurred northwest of the initial precursor. The last two subevents moved progressively southeastward of the first subevent in a direction collinear with the predominant strike of the fault planes. The offsets in the relative locations and the temporal delays of the rupture subevents indicate heterogeneous distribution of fracture strength and the involvement of multiple faults. The spatial distribution of teleseismic aftershocks, which at first appears uncorrelated with meizoseismal contours, can be decomposed into stages. The initial activity, being within and on the periphery of the rupture zone, correlates in shape and length with meizoseismal lines. In the second stage

  3. 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

  4. 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

  5. A three-dimensional viscoelastic model of a strike slip fault

    NASA Technical Reports Server (NTRS)

    Rundle, J. B.; Jackson, D. D.

    1975-01-01

    An analytic approximation to the Green's function for the displacements due to a strike slip point source in an elastic layer over a viscoelastic half-space is developed. This approximate Green's function is useful because it can be analytically integrated over the fault surface. Comparison with a numerical integration of the exact solution integral indicates that the approximation is quite good. The approximate Green's function is integrated analytically to obtain the displacements due to a finite rectangular strike slip fault in an elastic layer over a viscoelastic half-space. Ground displacements and angle changes from a model survey net are computed to illustrate the viscoelastic relaxation which follows a fracture in the elastic region.

  6. Jurassic normal and strike-slip faults at Crater Island, northwestern Utah

    USGS Publications Warehouse

    Miller, D.M.; Allmendinger, R.W.

    1991-01-01

    At Crater Island, northern Silver Island Mountains, northwestern Utah, an unbroken Tertiary fault block within the Basin and Range province exhibits Jurassic or older structures that are virtually unmodified by subsequent tectonism. Widespread high-angle faults, mainly striking north and north-east, offset the moderately west-dipping strata down to the west, thereby extending the strata parallel to bedding by 10% to 20%. The normal faults merge with a north northwest dextral strike-slip fault system. The two fault systems are kinematically compatible, suggesting that they may have been contemporaneous. The data indicate that minor thrusting, probably during the Jurassic, was followed by extensional faulting within a strike-slip fault system, probably close in time to intrusion. -from Authors

  7. Tectonics of the Western Betics: the role of E-W strike slip fault corridors

    NASA Astrophysics Data System (ADS)

    Frasca, Gianluca; Gueydan, Frédéric; Brun, Jean-Pierre; Célérier, Bernard

    2014-05-01

    The tectonic origin of the arcuate Betic-Rif orogenic belt that surrounds the Alboran Sea at the western tip of the Mediterranean Sea remains debated. Here, we investigate the tectonic units cropping out in the Western Betics (Malaga region, Southern Spain) with the main goal of reconstructing the Oligo-Miocene evolution of the area. New structural data and geological mapping together with available data allow us to identify the main structural features of the area. Deformation is found to be extremely diffused but two E-W elongated tectonic blocks with different lithological composition are outlined by marked E-W dextral strike-slip corridors ending up in horse-tail splays. These E-W strike slip corridors are responsible for late Miocence tectonics of both the internal and external zones of the Betic Cordillera.

  8. Structural subprovinces of the Central Basin Platform, west Texas: Strike-slip bounded crustal blocks

    SciTech Connect

    Gardiner, W.B. )

    1990-05-01

    The Central Basin platform (CBP) of west Texas is composed of six structural blocks, which moved independently during the Ouachita orogeny. As the South American plate collided with North America the Wasson uplift on the northwestern shelf of the Permian basin acted as a buttress against which the CBP was compressed. Shear forces transmitted through the crust resulted in buckling, uplifting, and faulting of the greater CBP. Although the platform is dominated by vertical movement, it did not however, uplift as a single tectonic unit. Rather, it splintered into six megablocks, which moved simultaneously along oblique-slip fault systems. A tectonic model for formation of the CBP is useful for predicting the orientation and spacing of fault systems. The three structurally highest blocks on the CBP, the Eunice high, the Sand Hills high, and the Fort Stockton uplift, show three distinct positive gravity and magnetic anomalies. These county-sized blocks (35 x 80 km) share similar characteristics: (1) they are bounded by strike-slip faults that involve basement uplift; (2) they have maximum structural deformation along their margins where bends in the strike-slip fault system enhance compressions; and (3) their oil is trapped in high-angle fault structures (R-shears ) along the clock boundaries, but toward the center of the blocks, oil tends to accumulate at unconformity and fold traps. Strike-slip fault systems in west Texas are subtle, with only about 3-7 km of offset and commonly may be overlooked. However, detailed regional mapping indicates that these individual fault segments are parts of through-going systems, which are distributed in logical patterns based upon models for strike-slip tectonics.

  9. Lower Miocene coeval thrusting and strike-slip faulting in the Western Betics

    NASA Astrophysics Data System (ADS)

    Frasca, Gianluca; Gueydan, Frédéric; Brun, Jean-Pierre

    2015-04-01

    In the framework of the Africa-Europe convergence, the Mediterranean system presents a complex interaction between subduction rollback and upper subduction plate deformation since 30 Ma. The western end of the system shows an arcuate geometry across the Gibraltar arc, the Betico-Rifean belt, in which the relationship between slab dynamics and onshore tectonics is poorly constrained. The present study focuses on the Western Betics, which is characterized by two major thrusts: 1/ the Alboran Front limits the metamorphic domain (Alboran Domain) from the fold-and-thrust belts involving the Mesozoic cover of the Iberian margin (Subbetics Domain); 2/ the Alboran Internal Thrust allows the juxtaposition of a strongly attenuated lithosphere section, containing the large Ronda subcontinental mantle bodies, on top of crustal rocks. New structural data show that two major E-W strike-slip corridors controlled the deformation pattern of the Alboran Domain, in which E-W dextral strike-slip faults, N60° thrusts and N140° normal faults developed simultaneously during dextral strike-slip simple shear. The Alozaina piggy-back Basin, mainly formed by olistotromic deposits of Lower Miocene age, provides an age estimate for the continuous westward translation of the Alboran Domain, with reference to Iberia, that is accommodated mainly by an E-W lateral strike-slip ramp and a N60° frontal thrust ramp. In this context, a thrust sequence led to the piling up of thrust units in the Western Betics and to the crustal emplacement of the Ronda Peridotites bodies.

  10. The morphology of strike-slip faults - Examples from the San Andreas Fault, California

    NASA Technical Reports Server (NTRS)

    Bilham, Roger; King, Geoffrey

    1989-01-01

    The dilatational strains associated with vertical faults embedded in a horizontal plate are examined in the framework of fault kinematics and simple displacement boundary conditions. Using boundary element methods, a sequence of examples of dilatational strain fields associated with commonly occurring strike-slip fault zone features (bends, offsets, finite rupture lengths, and nonuniform slip distributions) is derived. The combinations of these strain fields are then used to examine the Parkfield region of the San Andreas fault system in central California.

  11. What causes an icy fault to slip? Investigating the depth and frictional conditions for tidally driven Coulomb failure along major strike-slip faults of Europa and Ganymede

    NASA Astrophysics Data System (ADS)

    Cameron, Marissa E.; Smith-Konter, Bridget R.; Pappalardo, Robert T.

    2014-11-01

    The surfaces of Europa and Ganymede display strike-slip fractures, presumably arising from a combination of global and local stress sources. To better understand the role of tidal stress sources and implications for strike-slip faulting on these icy bodies, we investigate the relationship between shear and normal stresses at several major fault zones: Agenor Linea, Rhadamanthys Linea, Agave/Asterius Lineae, and Astypalaea Linea (on Europa), and Dardanus Sulcus (on Ganymede). Assuming tidal diurnal and non-synchronous rotation (NSR) stresses as plausible mechanisms for strike-slip tectonism, here we investigate the mechanics of Coulomb shear failure. We consider a range of friction coefficients (µf = 0.2 - 0.6) and fault depths (0 - 6 km) to evaluate how failure predictions vary between the satellites and as a function of depth, ice friction, geographic location, and fault geometry. Assuming present-day orbital eccentricities, our results indicate that the conditions for failure at depth are not met for any of the fault systems if subject to diurnal stresses only. Alternatively, models that include both diurnal and NSR stresses readily generate stress magnitudes that could permit shear failure. On Europa, shear failure is easily activated and failure extends to depths ranging from 3 - 6 km when a low coefficient of friction (µf = 0.2) is assumed. On Ganymede, failure is limited to even shallower depths (< 2 km). A high coefficient of friction (µf = 0.6) limits failure depths to < 3 km on Europa faults and discourages strike-slip faulting completely on Ganymede. Based on these results, we infer that the conditions for shear failure are potentially met along at least these five studied systems, and possibly others in the outer solar system, if NSR is adopted as a driving stress mechanism and the coefficient of friction is low.

  12. Neotectonics of the Owen Fracture Zone (NW Indian Ocean): Structural evolution of an oceanic strike-slip plate boundary

    NASA Astrophysics Data System (ADS)

    Rodriguez, M.; Fournier, M.; Chamot-Rooke, N.; Huchon, P.; Bourget, J.; Sorbier, M.; Zaragosi, S.; Rabaute, A.

    2011-12-01

    The Owen Fracture Zone is a 800 km-long fault system that accommodates the dextral strike-slip motion between India and Arabia plates. Because of slow pelagic sedimentation rates that preserve the seafloor expression of the fault since the Early Pliocene, the fault is clearly observed on bathymetric data. It is made up of a series of fault segments separated by releasing and restraining bends, including a major pull-apart basin at latitude 20°N. Some distal turbiditic channels from the Indus deep-sea fan overlap the fault system and are disturbed by its activity, thus providing landmarks to date successive stages of fault activity and structural evolution of the Owen Fracture Zone from Pliocene to Present. We determine the durability of relay structures and the timing of their evolution along the principal displacement zone, from their inception to their extinction. We observe subsidence migration in the 20°N basin, and alternate activation of fault splays in the vicinity of the Qalhat seamount. The present-day Owen Fracture Zone is the latest stage of structural evolution of the 20-Myr-old strike-slip fault system buried under Indus turbiditic deposits whose activity started at the eastern foot of the Owen Ridge when the Gulf of Aden opened. The evolution of the Owen Fracture Zone since 3-6 Myr reflects a steady state plate motion between Arabia and India, such as inferred by kinematics for the last 20 Myr period. The structural evolution of the Owen Fracture Zone since 20 Myr, including fault segments propagation and migration, pull-apart basin opening and extinction, seems to be characterized by a progressive reorganization of the fault system, and does not require any major kinematics change.

  13. Impact of Cenozoic strike-slip tectonics on the evolution of the northern Levant Basin (offshore Lebanon)

    NASA Astrophysics Data System (ADS)

    Ghalayini, Ramadan; Daniel, Jean-Marc; Homberg, Catherine; Nader, Fadi H.; Comstock, John E.

    2014-11-01

    Sedimentary basins adjacent to plate boundaries contain key tectonic and stratigraphic elements to understand how stress is transmitted through plates. The Levant Basin is a place of choice to study such elements because it flanks the Levant Fracture System and the Africa/Anatolia boundary. This paper uses new high-quality 3-D seismic reflection data to unravel the tectonic evolution of the margin of this basin during the Cenozoic, the period corresponding to the formation of the Levant Fracture System, part of the Africa/Arabia plate boundary. Four major groups of structures are identified in the interpreted Cenozoic units: NW-SE striking normal faults, NNE-SSW striking thrust-faults, ENE-WSW striking dextral strike-slip faults, and NNE trending anticlines. We demonstrate that all structures, apart of the NW-SE striking normal faults, are inherited from Mesozoic faults. Their reactivation and associated folding started during the late Miocene prior to the Messinian salinity crisis due to a NW-SE compressional stress field. No clear evidence of shortening at present-day offshore Lebanon and no large NNE-SSW strike-slip faults parallel to the restraining bend are found indicating that the Levant Fracture System is mainly contained onshore at present day. The intermittent activity of the interpreted structures correlates with the two stages of Levant Fracture System movement during late Miocene and Pliocene. This paper provides a good example of the impact of the evolution of plate boundaries on adjacent basins and indicates that any changes in the stress field, as controlled by the plate boundary, will affect immediately the preexisting structures in adjacent basins.

  14. 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

  15. Pushing the Limits of Geological Mapping Outside the Earth: 3D Modeling of Strike-Slip and Extensional Fault Systems in Meridiani Planum Region, Mars.

    NASA Astrophysics Data System (ADS)

    Vidal Royo, O.

    2014-12-01

    GIS and geological modeling software have radically changed the means by which geological mapping is produced, published and visualized. This type of software environment normally requires a spatially aware reference system to position data and interpretation, often referred as georeferenced data (i.e. geographic data referenced on the Earth). However, for this study we coin the term areoreferenced data (i.e. Mars-referenced "geographic" data). Thanks to the wealth of areoreferenced data made available by the NASA and the HiRise at University of Arizona it is now possible to carry out 3D areographic and areologic (i.e. related to the topography and geology of Mars, respectively) reconstructions in great detail. The present work benefits from the availability of software and areographic data, and presents the results of an areologic map and 3D model of the fault systems in the Meridiani Planum of Mars. The work has been carried out in Move™ (developed by Midland Valley Exploration), a geological modeling toolkit that allows for easy data loading in a wide range of formats as well as straightforward 2D/3D model building tools of geological bodies. Initial data consisted of Digital Terrain Model and orthoimages (NASA/JPL/University of Arizona/USGS). From these we have interpreted several structural domains: right-lateral strike-slip systems with associated releasing bends, which gave room to an extensional event causing a horizontal-axis rotation of the bedding. Bedding ranges from subhorizontal in the southern domain where strike-slip prevails to nearly 40º in the central and northern domains, where a more complex interaction between strike-slip and extensional faults is described. The stratigraphic sequence is mainly composed by moderately rounded well laminated basaltic sandstones (Squyres et al., 2004) in which a high component of sulfurs (e.g. sulfate anhydrate, hexahydrite, epsomite, gypsum) and salts (e.g. halite) has been described (Squyres et al., 2004

  16. Basement-driven strike-slip deformation involving a salt-stock canopy system

    NASA Astrophysics Data System (ADS)

    Dooley, Tim; Jackson, Martin; Hudec, Mike

    2016-04-01

    NW-striking basement-involved strike-slip zones have been reported or inferred from the northern Gulf of Mexico (GoM). This interpretation is uncertain, because the effects of strike-slip deformation are commonly difficult to recognize in cross sections. Recognition is doubly difficult if the strike-slip zone passes through a diapir field that complicates deformation, and an associated salt canopy that partially decouples shallow deformation from deep deformation. We use physical models to explore the effects of strike-slip deformation above and below a salt-stock canopy system. Canopies of varying maturity grew from a series of 14 feeders/diapirs located on and off the axis of a dextral basement fault. Strike-slip deformation styles in the overburden vary significantly depending on: (1) the location of the diapirs with respect to the basement fault trace, and; (2) the continuity of the canopy system. On-axis diapirs (where the diapirs lie directly above the basement fault) are typically strongly deformed and pinched shut at depth to form sharp S-shapes, whereas their shallow deformation style is that of a open-S-shaped pop-up structure in a restraining bend. The narrow diapir stem acts as a shear zone at depth. Pull-apart structures form between diapirs that are arranged in a right-stepping array tangental to the basement fault trace. These grade along strike into narrow negative flower structures. Off-axis diapirs (diapirs laterally offset from the basement fault but close enough to participate in the deformation) form zones of distributed deformation in the form of arrays of oblique faults (R shears) that converge along strike onto the narrower deformation zones associated with on-axis diapirs. Above an immature, or patchy, canopy system the strike-slip structures closely match sub canopy structures, with the exception of wrench fold formation where the supracanopy roof is thin. In contrast, the surface structures above a mature canopy system consist of a broad

  17. 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.

  18. 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.

  19. Modeling Strike-Slip-Driven Stream Capture in Detachment- and Transport-Limited Fluvial Systems

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Rivers, especially those in mountainous settings, are known to respond to tectonic and climatic drivers through both gradual and abrupt changes in slope, hydraulic geometry, and planform. Modification of drainage network topology by stream capture, in which drainage area, and therefore water and sediment, is diverted suddenly from one catchment into another, represents the rapid end of the fluvial response spectrum. Such sudden drainage rearrangement affects the river's potential for incision and sediment transport, and thus has implications for the development of topography and for depositional histories in sedimentary basins. Despite recognition of the importance of this process in landscape evolution, the factors controlling the occurrence of stream capture are not well understood. Here we investigate the process of stream capture using strike-slip faults as a natural experiment. Lateral fault motion drives stream capture when offset is enough to juxtapose adjacent fault-perpendicular streams. In the simplest scenario, the capture events should occur regularly in space and time whenever two streams are juxtaposed, the frequency of capture depending only on drainage spacing and fault slip rate. However, in real-world settings such as the San Andreas Fault Zone of California and the Marlborough Fault System of New Zealand, such regularity is not always observed. We use the Channel-Hillslope Integrated Landscape Development Model (CHILD) to investigate the mechanisms and frequency of stream capture in a strike-slip setting. Models are designed to address the connection between the size (i.e. drainage area) of juxtaposed rivers and the likelihood that capture will occur between them. We also explore the role of sediment load in the capture process by modeling both detachment-limited and transport-limited systems. Comparison of these model results to case-study field sites will help us to interpret the landscape signature of strike-slip faulting, and to understand

  20. Aseismic strike-slip associated with the 2007 dike intrusion episode in Tanzania

    NASA Astrophysics Data System (ADS)

    Himematsu, Yuji; Furuya, Masato

    2015-08-01

    In July 2007, an earthquake swarm initiated in northern Tanzania near Lake Natron and lasted for about two months. Mt. Oldoinyo Lengai, located to the southwest of the swarm, began to erupt effusively about a month prior to the swarm, and increased its eruption intensity on September when the swarm almost ceased. Several previous studies have already reported the crustal deformation signals associated with the swarm using Interferometric Synthetic Aperture Radar (InSAR). However, nearly all the published data are based on the C-band ENVISAT/ASAR images acquired only from the descending path. We use the L-band ALOS/PALSAR images acquired from both ascending and descending paths, which allow us to examine the deformation signals in more detail. In addition to the InSAR data, we employ the offset-tracking technique to detect the signals along the azimuth direction. Using InSAR and offset-tracking data, we obtain the full 3D displacement fields associated with the episode. Besides the horizontal extension and subsidence signals due to the dike intrusion as already reported, the inferred full 3D displacements further indicate that the subsiding zone was horizontally moving by ~ 48 cm toward SSW. To explain the displacements, we performed fault source modeling, assuming an elastic half space. The fault slip distribution indicates that the contribution of the strike-slip component is about 20% of total moment release. Because almost all the focal mechanisms of earthquakes during the 2007 event indicate nearly pure normal faulting, aseismic strike-slip must have been responsible for the horizontal movement of the subsiding zone. The strike-slip at the shallowest depths suggests the presence of transtensive stress, which seems to be reasonable to generate the relay zones that are widely observed in the East African Rift. We also confirmed that the stress changes due to the dike intrusion were consistent with the inferred fault slip distributions.

  1. What can we learn from 20 years of interseismic GPS measurements across strike-slip faults?

    NASA Astrophysics Data System (ADS)

    Vernant, Philippe

    2015-03-01

    I use GPS interseismic velocities and classic 2D elastic half-space models with a screw dislocation to estimate the long-term fault slip rate, locking depth, and the offset between the surface fault trace and the location of the dislocation below the seismogenic zone for 13 segments along 8 major strike-slip faults. Using deduced strike-slip rates and the position of the dislocation to normalize the interseismic velocities to facilitate comparison of spatial patterns of deformation, I show that no substantial differences can be detected, ruling out a large asymmetry in interseismic velocities across the 8 faults used in this study. Only the Carrizo Plain segment of the San Andreas Fault shows a significant asymmetry that cannot be explained by shifting the position of the dislocation at depth relative to the fault trace. However, the resulting perturbation is less than 10% of total strike-slip rate. Fault traces are usually curved, defining a concave side. When the dislocation at depth is significantly offset from the fault trace, the shift is always toward the block on the concave side of the fault trace. This suggests that the fault zone in the lower crust may develop a simpler geometry more consistent with relative motion across the fault than its upper seismogenic part constrained by the structural complexity of the brittle crust. Since the faults used in this study are at different times in their interseismic period, comparing the interseismic velocity fields across them allows identification of possible variations of the interseismic velocities with time. When normalized by slip rate and dislocation location, all the faults show the same interseismic strain with no significant differences between deduced locking depths. These comparisons suggest that if temporal variations occur as suggested by some dynamic earthquake cycle models, they are small and below the accuracy of the available geodetic measurements.

  2. Coarse-grained deltaic sedimentation in the Miocene Cuyama strike-slip basin, California coast ranges

    SciTech Connect

    Bartow, J.A. )

    1990-05-01

    The Cuyama basin, located in the southern Coast Ranges southwest of the San Andreas fault developed early in the history of the San Andreas transform system. The Miocene marine basin formed in a transtensional setting along a dextral strike-slip fault of the transform system, the San Juan-Chimineas fault following Oligocene nonmarine basin formation in an extensional setting. The lower and middle Miocene Vaqueros Formation in the northwestern part of the basin, which represents the first of two transgressive-regressive cycles, consists of eight facies making up two depositional systems. The 400-m-thick Soda Lake Shale Member constitutes a basinal system consisting of deep-basin and starved-basin facies. The overlying 2,200-m-thick Painted Rock Sandstone Member consists mostly of coarse-grained, pebbly sandstone and constitutes a deltaic depositional system of prodelta, slope channel, delta front, tidal channel, interdistributary bay, and fluvial channel facies. The basinal depositional system consists of turbidite sand and mud, and hemipelagic and pelagic sediments that were deposited in a rapidly subsiding basin. The deltaic depositional system prograded into the deep basin and had a steep prodelta slope that extended to bathyal depths. The delta is inferred to be a river-dominated fan delta in which coarse sediment was transported down the prodelta slope into deep water by sediment gravity flows. The overall basin history and geometry of the northwestern Cuyama basin are typical of strike-slip basins. The initial rapid subsidence to bathyal depths at rates of more than 500 m/m.y. in the early Miocene is interpreted to be a result of extension at the releasing bend of a dextral strike-slip fault.

  3. 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.

  4. Block rotation by strike-slip faulting - Structural and paleomagnetic evidence

    NASA Technical Reports Server (NTRS)

    Ron, H.; Garfunkel, Z.; Nur, A.; Freund, R.

    1984-01-01

    The magnitude and sense of block rotations depicted from such structural data as fault spacing and slip are noted to agree with values obtained from independent paleomagnetic determinations. The agreement between paleomagnetic rotation data and those inferred from offset and spacing data in northern Israel is excellent, suggesting that the faults and intervening blocks were rotated with progressive deformation along the levant transform. It is suggested that the rotation of blocks and the strike-slip displacement are two qualitative and quantitative contemporaneous aspects of a single deformation process.

  5. Analogue modelling of the effect of topographic steps in the development of strike-slip faults

    NASA Astrophysics Data System (ADS)

    Tomás, Ricardo; Duarte, João C.; Rosas, Filipe M.; Schellart, Wouter; Strak, Vincent

    2016-04-01

    Strike-slip faults often cut across regions of overthickened crust, such as oceanic plateaus or islands. These morphological steps likely cause a local variation in the stress field that controls the geometry of these systems. Such variation in the stress field will likely play a role in strain localization and associated seismicity. This is of particular importance since wrench systems can produce very high magnitude earthquakes. However, such systems have been generally overlooked and are still poorly understood. In this work we will present a set of analogue models that were designed with the objective of understanding how a step in the morphology affects the development of a strike-slip fault system. The models consist of a sand-cake with two areas with different thicknesses connected by a gentle ramp perpendicular to a dextral strike-slip basal fault. The sand-cake lies above two basal plates to which the dextral relative motion was imposed using a stepping-motor. Our results show that a Riedel fault system develops across the two flat areas. However, a very asymmetric fault pattern develops across the morphological step. A deltoid constrictional bulge develops in the thinner part of the model, which progressively acquires a sigmoidal shape with increasing offset. In the thicker part of the domain, the deformation is mostly accommodated by Riedel faults and the one closer to the step acquires a relatively lower angle. Associated to this Riedel fault a collapse area develops and amplifies with increasing offset. For high topographic steps, the propagation of the main fault across the step area only occurs in the final stages of the experiments, contrary to what happens when the step is small or inexistent. These results strongly suggest a major impact of the variation of topography on the development of strike-slip fault systems. The step in the morphology causes variations in the potential energy that changes the local stress field (mainly the vertical

  6. Numerical model of formation of a 3-D strike-slip fault system

    NASA Astrophysics Data System (ADS)

    Chemenda, Alexandre I.; Cavalié, Olivier; Vergnolle, Mathilde; Bouissou, Stéphane; Delouis, Bertrand

    2016-01-01

    The initiation and the initial evolution of a strike-slip fault are modeled within an elastoplasticity constitutive framework taking into account the evolution of the hardening modulus with inelastic straining. The initial and boundary conditions are similar to those of the Riedel shear experiment. The models first deform purely elastically. Then damage (inelastic deformation) starts at the model surface. The damage zone propagates both normal to the forming fault zone and downwards. Finally, it affects the whole layer thickness, forming flower-like structure in cross-section. At a certain stage, a dense set of parallel Riedel shears forms at shallow depth. A few of these propagate both laterally and vertically, while others die. The faults first propagate in-plane, but then rapidly change direction to make a larger angle with the shear axis. New fault segments form as well, resulting in complex 3-D fault zone architecture. Different fault segments accommodate strike-slip and normal displacements, which results in the formation of valleys and rotations along the fault system.

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

    USGS Publications Warehouse

    ten Brink, U.; 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

  8. Oblique strike-slip faulting of the Cascadia submarine forearc: The Daisy Bank fault zone off central Oregon

    NASA Astrophysics Data System (ADS)

    Goldfinger, Chris; Kulm, LaVerne D.; Yeats, Robert S.; Hummon, Cheryl; Huftile, Gary J.; Niem, Alan R.; McNeill, Lisa C.

    The Cascadia submarine forearc off Oregon and Washington is deformed by numerous active WNW-trending, left-lateral strike-slip faults. The kinematics of this set of sub-parallel left-lateral faults suggests clockwise block rotation of the forearc driven by oblique subduction. One major left-lateral strike-slip fault, the 94 km-long Daisy Bank fault, located off central Oregon, was studied in detail using high-resolution AMS 150 kHz and SeaMARC-lA sidescan sonar, swath bathymetry, multichannel seismic reflection profiles and a submersible. The Daisy Bank fault zone cuts the sediments and basaltic basement of the subducting Juan de Fuca plate, and the overriding North American plate, extending from the abyssal plain to the upper slope-outer shelf region. The Daisy Bank fault, a near-vertical left-lateral fault striking 292°, is a wide structural zone with multiple scarps observed in high-resolution sidescan images. From a submersible, we observe that these scarps offset late Pleistocene gray clay and overlying olive green Holocene mud, dating fault activity as post-12 ka on the upper slope. Vertical separation along individual fault scarps ranges from a few centimeters to 130 meters. Using a retrodeformation technique with multichannel reflection records, we calculate a net slip of 2.2±0.5 km. Fault movement commenced at about 380±50 ka near the western fault tip, based upon an analysis of growth strata and correlation with deep-sea drill hole biostratigraphy. We calculate a slip rate of 5.7±2.0 mm/yr. for the Daisy Bank fault at its western end on the Juan de Fuca plate. The motion of the set of oblique faults, including the Daisy Bank fault, may accommodate a significant portion of the oblique component of plate motion along the central Cascadia margin. We propose a block rotation model by which the seawardmost part of the forearc rotates clockwise and translates northward.

  9. Tectonic Tremor Triggered along Major Strike-Slip Faults around the World

    NASA Astrophysics Data System (ADS)

    Aiken, C.; Peng, Z.; Shelly, D. R.; Hill, D. P.; Gonzalez-Huizar, H.; Chao, K.; Zimmerman, J. P.; Douilly, R.; Deschamps, A.; Haase, J. S.; Calais, E.

    2013-12-01

    Over the last decade, deep tectonic tremor has been observed at several major plate-bounding faults around the Pacific Rim. Observations in these regions show that ambient tremor occurs spontaneously in association with geodetically detectable slow-slip events and that triggered tremor occurs in response to small stress perturbations arising from solid earth tides as well as passing seismic waves of a distant earthquake. Tremor generally occurs in the lower crust, beneath the seismogenic zone where earthquakes occur. In order to investigate the potential link between tremor and earthquake nucleation, further study of when, where, and how tremor occurs is needed. Here, we present a review of remotely triggered tectonic tremor in four strike-slip regions: (1) the Queen Charlotte Fault near Haida Gwaii, Canada, (2) the Eastern Denali Fault in Yukon, Canada, (3) the Enriquillo-Plantain Garden Fault in the southern Haiti peninsula, and (4) the Parkfield-Cholame segment of the San Andreas Fault near Parkfield, California. In Haida Gwaii, Yukon and Parkfield, we first compute the estimated dynamic stress for all magnitude ≥ 5.5 earthquakes based on the magnitude listed in the Advanced National Seismograph System (ANSS) earthquake catalog and epicentral distance to the region where tremor is observed. We then retrieve seismic data from local networks for earthquakes that are estimated to generate ≥ 1 kPa dynamic stress, without regard to epicentral distance. We characterize tremor triggered by these distant earthquakes as broadband signals with long duration that are coincident with surface waves from a distant event or occur in a large cluster immediately following the teleseismic wavetrain. In Haiti, a temporary seismic network was deployed shortly after the 2010/01/12 Mw7.0 Haiti earthquake. Thus, we are only able to report on triggering by the 2010/02/27 Mw8.8 Maule, Chile earthquake that occurred shortly thereafter. In Parkfield, we use a low-frequency earthquake

  10. Coarse-grained deltaic sedimentation in the Miocene Cuyama strike-slip basin, California Coast Ranges

    USGS Publications Warehouse

    Alan, Bartow J.

    1990-01-01

    The Cuyama basin, located in the southern Coast Ranges of California southwest of the San Andreas fault, developed early in the history of the San Andreas transform system. The Miocene marine basin formed in a transtensional setting along a dextral strike-slip fault of the transform system following Oligocene non-marine basin formation in an extensional setting. The lower and middle Miocene Vaqueros Formation in the northwestern part of the basin, which represents the first of two transgressive-regressive cycles, is described here in terms of nine facies in two broad facies groups. The 400-m-thick Soda Lake Shale Member (of the Vaqueros) comprises deep-basin and starved-basin facies. A thin transgressive facies occurs locally at the base of the formation. The overlying Painted Rock Sandstone Member (of the Vaqueros), which is more than 2200 m thick and consists mostly of coarse-grained sandstone and pebbly sandstone, constitutes a delta complex of prodelta, slope channel, delta front, tide-influenced distributary channel, interdistributary bay, and fluvial channel facies. The basinal depositional system consisted of turbidite mud and sand, and hemipelagic and pelagic sediments of the basinal facies deposited in a rapidly subsiding basin. The delta depositional system consisted of the delta complex facies that prograded into the deep basin and had a steep prodelta slope that extended to bathyal depths. The delta is inferred to be a mixed fluvial-wave-dominated fan delta, analogous in its delta-front morphology and processes to a fjord delta, in which coarse sediment delivered to the delta front by braided streams was transported down the prodelta slope into deep water by sediment gravity flows. Transgression and rapid deepening of the basin in the early Miocene coincided with rapid tectonic subsidence. Deepening culminated with deposition of a starved-basin facies or condensed section at the time of maximum transgression, which was followed by the beginning of a

  11. Lineament Domain of Regional Strike-Slip Corridor: Insight from the Neogene Transtensional De Geer Transform Fault in NW Spitsbergen

    NASA Astrophysics Data System (ADS)

    Cianfarra, P.; Salvini, F.

    2015-05-01

    Lineaments on regional scale images represent controversial features in tectonic studies. Published models explain the presence of the lineament domains in most geodynamic environments as resulting from the enhanced erosion along strikes normal to the upper crustal regional extension. Despite their success in many tectonic frameworks, these models fail to explain the existing lineament domains in the regional strike-slip corridors that separate regional blocks, including the transform faults. The present paper investigates the lineament distribution in such environments, and specifically presents the results from a study along the shear corridor of the De Geer Transform Fault in the North Atlantic, responsible for the separation and drifting away between Northern Greenland and the Svalbard Archipelago since Oligocene times. The study spans from satellite image analysis and outcrop scale investigations to a more regional analysis on a digital bathymetric model of the North Atlantic-Arctic Ocean. Lineaments were automatically detected in the spectral band 8 (0.52-0.9 μm) of a Landsat 7 image (15 m/pixel resolution). A total of 320 image lineaments were extracted from both the regional and the local scale investigations and statistically analyzed. Results from the multi-scalar lineament analyses revealed the existence of a main N-S lineament domain regionally persistent from the De Geer corridor to the western margin of northern Spitsbergen where it relates to the youngest, post-Oligocene, tectonics observed onshore. This is confirmed by field observations showing that the N-S faults represent the youngest brittle deformation system and systematically cut the deformations associated with the building of the Tertiary West Spitsbergen fold and thrust belt. The N-S lineament domain is the result of the activity of a larger, regional scale tectonic feature, NW-SE oriented and responsible for the localized extension within its deformation corridor, the De Geer Transform

  12. A Physical Analog Model of Strike-Slip Faulting for Model-Based Inquiry in the Classroom

    NASA Astrophysics Data System (ADS)

    Curren, I. S.; Glesener, G.

    2013-12-01

    Geoscience educators often use qualitative physical analog models to demonstrate natural processes; while these are effective teaching tools, they often neglect the fundamental scientific practices that make up the core of scientific work. Physical analog models with dynamic properties that can be manipulated and measured quantitatively in real-time, on the other hand, can give students the opportunity to explore, observe and empirically test their own ideas and hypotheses about the relevant target concepts within a classroom setting. Providing classroom content for inquiry, such as a hands-on physical analog model, which fosters students' production and refinement of their mental models in participatory and discursive activities have been argued by many education researchers to help students build a deeper understanding of science and scientific reasoning. We present a physical analog model that was originally developed by UCLA's Modeling and Educational Demonstrations Laboratory (MEDL) for the purpose of engaging students in the study of elastic rebound on a strike-slip fault; it was later modified to accommodate research of complex tectonic processes associated with strike-slip faulting, which are currently debated by scientists in both the geology and geophysics disciplines. During experimentation, it became clear that this new design could be used as a relevant resource for inquiry from which students would be able to make and discuss real-time empirical measurements and observations to help them infer causal accounts of theoretical and/or unobservable dynamic processes within the Earth's crust. In our poster session, we will: 1) demonstrate the physical analog model; 2) describe various real-time data collection tools, as well as quantitative methods students can use to process their data; and 3) describe the surficial, structural and relational similarities between the physical analog model and the target concepts intended for students to explore in the

  13. 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

  14. 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.

  15. 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

  16. The role of an intracrustal asthenosphere on the behavior of major strike-slip faults

    NASA Technical Reports Server (NTRS)

    Turcotte, D. L.; Liu, J. Y.; Kulhawy, F. H.

    1984-01-01

    Strain accumulation measurements adjacent to the San Andreas fault have indicated that the strain accumulation zone extends only a few tens of kms away from the fault. While the restricted zone of cyclic accumulation and release of elastic energy adjacent to major strike-slip faults has been attributed to a viscoelastic asthenosphere's damping effect, the narrowness of the San Andreas zone implies a thickness of the lithosphere that, at 10-20 km, may not be consistent with the relatively low surface heat flow measurements obtained. It is presently proposed that an upper elastic plate extends to a depth of 15 km, and that beneath this upper elastic plate is a soft, intracrustal asthenosphere exhibiting a viscoelastic behavior. A second elastic layer lies under this, followed by the asthenosphere. It is shown that the damping due to the intracrustal asthenosphere can explain the observed narrow zone of cyclic strain accumulation and release.

  17. 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.

  18. Depth Localization of Seismicity on Strike-Slip Faults in California

    NASA Astrophysics Data System (ADS)

    Boutwell, C.; Powers, P. M.; Jordan, T. H.

    2008-12-01

    We investigate the distribution of earthquake ruptures in three separate dimensions along California strike- slip faults. Previous work by Powers and Jordan (in prep.) shows that the average rate of small earthquakes along California strike-slip faults obeys a power-law of the form R~(x2+d2)-γ/2, where the rate R is in events/km2, x is the distance from a fault, γ is the decay rate of seismicity, and d is the near-fault inner scale. However, they do not consider the depth variability of earthquake hypocenters. We therefore perform a reconnaissance of their fault-referenced data set to determine if there is significant on-fault versus off-fault variability in earthquake depths. For each fault segment, we compute the depth variance in 4d km wide fault-normal bins, centered on the fault. For particularly long fault segments, we take the average variance over several shorter fault-parallel sub-segments. Results show interesting regional variations. In southern California, on-fault earthquake hypocenters are strongly localized in depth, but become more distributed with distance from a fault. In contrast, variance of hypocenter depths in northern California is similar both on and off of faults. Similar regional variations are observed for γ and d, so depth variance likely correlates with fault properties such as seismic productivity, creep rate, and cumulative offset. These results have important implications for fault-based models of seismicity, which can be used to improve current earthquake forecasting methods such as ETAS.

  19. Continental strike slip fault zones in geologically complex lithosphere: the North Anatolian Fault, Turkey.

    NASA Astrophysics Data System (ADS)

    Cornwell, David; Thompson, David; Papaleo, Elvira; Rost, Sebastian; Houseman, Gregory; Kahraman, Metin; Turkelli, Niyazi; Teoman, Ugur; Altuncu Poyraz, Selda; Gulen, Levent; Utkucu, Murat

    2016-04-01

    As part of the multi-disciplinary Faultlab project, we present new detailed images in a geologically complex region where the crust and upper mantle is bisected by a major continental strike-slip fault system. Our study region samples the north Anatolian fault zone (NAFZ) near the epicentres of two large earthquakes that occurred in 1999 at Izmit (M7.5) and Düzce (M7.2) and where estimates of present day slip rate are 20-25 mm/yr. Using recordings of teleseismic earthquakes from a rectangular seismometer array spanning the NAFZ with 66 stations at a nominal inter-station spacing of 7 km and 7 additional stations further afield, we build a detailed 3-D image of structure and anisotropy using receiver functions, tomography and shear wave splitting and illuminate major changes in the architecture and properties of the upper crust, lower crust and upper mantle, both across and along the two branches of the NAFZ, at length scales of less than 20 km. We show that the northern NAFZ branch depth extent varies from the mid-crust to the upper mantle and it is likely to be less than 10 km wide. A high velocity lower crust and a region of crustal underthrusting appear to add strength to a heterogeneous crust and play a role in dictating the variation in faulting style and postseismic deformation. Sharp changes in lithospheric mantle velocity and anisotropy are constrained as the NAFZ is crossed, whereas crustal structure and anisotropy vary considerably both parallel and perpendicular to the faulting. We use our observations to test current models of the localisation of strike-slip deformation and develop new ideas to explain how narrow fault zones develop in extremely heterogeneous lithosphere.

  20. 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.

  1. A new multilayered visco-elasto-plastic experimental model to study strike-slip fault seismic cycle

    NASA Astrophysics Data System (ADS)

    Caniven, Y.; Dominguez, S.; Soliva, R.; Cattin, R.; Peyret, M.; Marchandon, M.; Romano, C.; Strak, V.

    2015-02-01

    Nowadays, technological advances in satellite imagery measurements as well as the development of dense geodetic and seismologic networks allow for a detailed analysis of surface deformation associated with active fault seismic cycle. However, the study of earthquake dynamics faces several limiting factors related to the difficulty to access the deep source of earthquake and to integrate the characteristic time scales of deformation processes that extend from seconds to thousands of years. To overcome part of these limitations and better constrain the role and couplings between kinematic and mechanical parameters, we have developed a new experimental approach allowing for the simulation of strike-slip fault earthquakes and analyze in detail hundreds of successive seismic cycle. Model rheology is made of multilayered visco-elasto-plastic analog materials to account for the mechanical behavior of the upper and lower crust and to allow simulating brittle/ductile coupling, postseismic deformation phase and far-field stress transfers. The kinematic evolution of the model surface is monitored using an optical system, based on subpixel spectral correlation of high-resolution digital images. First, results show that the model succeed in reproducing the deformation mechanisms and surface kinematics associated to the main phases of the seismic cycle indicating that model scaling is satisfactory. These results are comforted by using numerical algorithms to study the strain and stress distribution at the surface and at depth, along the fault plane. Our analog modeling approach appears, then, as an efficient complementary approach to investigate earthquake dynamics.

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

    NASA Astrophysics Data System (ADS)

    McNamara, D. E.; Benz, H. M.; Herrmann, R. B.; Bergman, E. A.; Earle, P.; Holland, A.; Baldwin, R.; Gassner, A.

    2015-04-01

    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 3639 central Oklahoma earthquakes from late 2009 through 2014. Regional moment tensor (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.

  3. 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; 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.

  4. The role of pressure solution seam and joint assemblages in the formation of strike-slip and thrust faults in a compressive tectonic setting; The Variscan of south-western Ireland

    NASA Astrophysics Data System (ADS)

    Nenna, Filippo; Aydin, Atilla

    2011-11-01

    The Ross Sandstone in County Clare, Ireland, was deformed by an approximately north-south compression during the end-Carboniferous Variscan orogeny. The initial assemblage consists of mutually abutting orthogonal arrays of 170° oriented set 1 joints/veins (JVs) and approximately 75° oriented set 1 pressure solution seams (PSSs) formed under the same stress conditions. Orientations of splay JVs and PSSs (set 2) suggest a clockwise remote stress rotation of about 35° responsible for the contemporaneous shearing of the set 1 arrays. Among these nearly orthogonal strike-slip faults, the prominent set is sub-parallel to set 1 JVs. These faults are formed by the linkage of en-echelon segments with broad damage zones responsible for right-lateral offsets of hundreds of meters. Thrust faults with up to 30 m of offset initiate within shale horizons and follow either the PSSs in the sandstones or high-angle shales within tilted sequences. Within the large thrust fault zones, compartmentalised blocks of rocks are bounded by thrust faults segments with various dip angles. Strike-slip and thrust faults are contemporaneous and owe their existence to initial weaknesses in the form of JVs and PSSs rather than by switching relative stress magnitudes and orientations associated with Andersonian models of faults and related stress orientations.

  5. Post-Late Jurassic, pre-late Eocene strike-slip faulting in west-central Utah

    SciTech Connect

    Robinson, J.P.

    1993-04-01

    Two events of strike-slip faulting interpreted to be of Late Mesozoic-Early Tertiary age are recorded in the northern Deep Creek Mountains. These fault systems display principal detachment zones that strike N50W and N84E. Both fault systems are manifested as fault mosaics, locally anastomosing with local duplex formation. They are interpreted to represent first-order structures that operated independently of other strain regimes. A quartz monzonite stock dated 38 Ma displays strong control of the intrusion by the NW-striking faults. That, in addition to cross-cutting relationships between the NW-striking faults and a granodiorite dated 152 Ma place age constraints on the strike-slip faulting. The ENE-striking faults are younger than the NW-striking faults and are interpreted to be older than the quartz monzonite, although this relationship is ambiguous. Strike-separation on the major NW-striking faults is on the order of 3 km. Offsets of similar magnitude or greater are interpreted for the ENE-striking faults, although this remains unquantified. Despite the small area of influence, relatively minor displacements, and broad time frame of occurrence, these faults have some regional significance. If Cretaceous-aged, the strike-slip faults are markedly different than the extensional structures that formed in the internal zone' of the Cordilleran thrust belt. If Tertiary-aged, the strike-slip faults represent an age of structure with few documented examples in the eastern Basin and Range.

  6. Evidence and dynamics for the change of strike-slip direction of the Changle Nanao ductile shear zone, southeastern China

    NASA Astrophysics Data System (ADS)

    Zhihong, Wang; Huafu, Lu

    1997-12-01

    The Changle-Nanao ductile shear zone was developed from a suture zone. The evidence from the ductile fabrics and mylonitic microstructures indicates that the strike-slip was sinistral during pre-collision. It became dominantly dextral in the syn-collision stage in late Early Cretaceous. The dextral strike-slip movement continued in the post-collision stage with extension as the dominant process. The strike-slip movement of the zone was strictly controlled by dynamics of collision between the Fujian (Min)-Taiwan (Tai) microcontinent and the Fujian (Min)-Zhejiang (Zhe) Mesozoic volcanic arc during the time interval of 100-120 Ma. The Min-Tai microcontinent in which the ductile shear zone developed might have been located originally to the south of its present position. The northward migration of the microcontinent had contributed to a few hundred kilometers of drift rather than a shear displacement. The real shear displacement is small due to the change of strike-slip direction from sinistral to dextral.

  7. Stress interaction of strike-slip and thrust faults associated with the 2010 M=7.0 Haiti earthquake

    NASA Astrophysics Data System (ADS)

    Lin, J.; Stein, R. S.; Sevilgen, V.; Toda, S.

    2010-12-01

    Recent investigations from combined seismological and space geodetic constraints suggest that the mainshock source faults of the 12 January 2010 Haiti earthquake might be complex and consist of both strike-slip and thrust faults. We calculate Coulomb stress changes on adjacent strike-slip and thrust faults caused by the 2010 M=7.0 rupture by considering a range of mainshock and receiver fault models. We find that for all of the mainshock source models examined, including Hayes et al. (submitted to Nature Geoscience), the Coulomb stress is calculated to have increased on sections of the Enriquillo Fault to both the east and west of the January ruptures. We assume the Enriquillo is dominantly strike-slip. While the magnitude of the calculated stress increase depends on the complexity of the proposed mainshock models, the Enriquillo Fault segment immediately south of Port-au-Prince is calculated to be within a zone of stress increases regardless if the Enriquillo Fault is assumed south dipping or vertical. We further calculate that 60-70% of the nodal planes of the aftershocks determined by Nettles & Hjorleifsdottir (GJI, 2010) were brought closer to failure by the mainshock. Relocating these aftershock locations north by 10 km would bring additional 10% of the aftershock nodal planes into Coulomb stress increases. Overall the 2010 Haiti earthquake illustrates the complex stress interaction between strike-slip and thrust motion on various segments of a larger compressional fault system.

  8. Late Paleozoic strike-slip faults and related vein arrays of Cape Elizabeth, Maine

    NASA Astrophysics Data System (ADS)

    Swanson, Mark T.

    2006-03-01

    Strike-slip faults and related quartz vein arrays of Late Paleozoic-age cut gently-dipping metasedimentary rocks at Cape Elizabeth in southern coastal Maine and formed in response to regional dextral shearing along the Norumbega fault system. Vertical quartz veins up to 20 m wide and 10s of meters long were emplaced orthogonal to the local shear zone-parallel elongation fabric, reflecting strain partitioning during transpression. Earlier veins were reoriented by clockwise rotation toward this NE-trending regional shear direction. The later brittle strike-slip faults are oblique to the regional shear direction and interpreted as a 10-km-scale R-shear array on the southeast flank of the Norumbega fault system. These left-stepping en échelon fault zones consist of the three Two Lights fault zones (˜200 m lengths and up to ˜5 m displacements) and the Richmond Island fault zone (˜1.6 km length and ˜40 m displacement). Displacements on these fault zones have developed fine-grained silicified, obliquely-foliated and laminated cataclasites and locally, millimeter-thin pseudotachylyte fault and injection veins. Individual fault core zones are up to 10s of centimeters thick as part of several complex anastamosing zones of faulting 10s of meters wide. Initial segments within each fault zone are typically terminated with oblique extension fractures in horsetail configurations. The left-stepping en échelon relationships between these segments led to dominantly contractional step-over zones where P-shear linkages created a through-going fault that truncated the ends of the earlier-formed terminated segments. This linkage-growth model for fault zone evolution works toward larger scales and longer fault lengths as displacement accumulates, within a limiting maximum displacement/length ratio characteristic of the host lithologies. Length-frequency data for fault segments within these zones suggest a transition to linkage-dominated growth once fault segments were longer than

  9. 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

  10. Tectonics, magmatism and fluid flow in a transtensional strike-slip setting: The northern termination of the dextral strike-slip Liquiñe-Ofqui Fault System, Chile

    NASA Astrophysics Data System (ADS)

    Perez Flores, P.; Sanchez, P.; Sielfeld, G.; Cembrano, J. M.

    2013-05-01

    One fundamental problem in continental margin tectonics is the nature of the interplay between tectonics and magma/fluid transport through the lithosphere. Deformation-driven fault-fracture networks have been regarded as efficient pathways through which magma and/or hydrothermal fluids are transported, stored and eventually connected to the earth surface. Thus, the state of stress of the lithosphere at the time of fluid transport should somehow control the first and second-order spatial distribution of dikes swarms, volcanic centers and geothermal reservoirs. We conducted a detailed structural mapping of the geometry, kinematics and relative timing of first and second-order fault systems and their spatially associated fault-vein networks at regional and local scales at the northern termination of the Liquiñe-Ofqui Fault System (LOFS). This is characterized by a transtensional imbricate fan (horsetail structure). Stratovolcanoes, minor eruptive centers, and hydrothermal vein systems are spatially and temporally associated with NNE master and ENE subsidiary faults of the LOFS and with NW-striking long-lived basement faults. The overprinted geothermal system is documented by NNE and ENE striking calcite-quartz hybrid and extensional vein systems, which appear to be associated with dextral strike-slip displacement on the LOFS. Fault-vein and vein microstructure varies from mineral fibers indicative of creeping faults to typical ridge-and-groove striae. Bladed calcite occurs in dilational jogs along the main LOFS master faults; they are interpreted to represent boiling episodes. Thicker and more pervasive NW sinistral-reverse fault-vein systems and breccias bodies suggest that the fault-valve mechanism was active during fluid transport and mineral precipitation. In some sites the NW-striking system cuts and displaces the active LOFS, suggesting that their active has extended to at least the Pleistocene.

  11. Detectability of slow slip beneath the seismogenic zone of strike-slip faults using borehole tiltmeters

    NASA Astrophysics Data System (ADS)

    Chery, J.

    2015-12-01

    During the last decades, geodetic tools like C-GPS allowed the detection of slow slip events associated with transient motion below the seismogenic zone. This new class of fault motion lead us to revise the standard version of the seismic cycle simply including coseismic, postseismic and interseismic phases. Most of these discoveries occurred on subduction margins in various places like Japan, Cascadia, Chile and Indonesia. By contrast, GPS and strainmeters have provided little evidence of slow slip beneath the seismogenic zone of large continental faults like the San Andreas fault or the North Anatolian fault. Because the detectability of such motions is mostly tributary from instrumental precision, we examine the theoretical capability of tiltmeter arrays for detecting horizontal motion of a buried vertical fault. We define the slipping part of the strike-slip fault like a buried rectangular patch submitted to horizontal motion. This motion provides horizontal and vertical surface deformation as a function of both patch geometry (length, width, depth) and motion amplitude. Using a dislocation buried at 15km depth, we compute the maximum motion and tilt as a function of seismic moment. Assuming yields of detectability of 1mm for GPS horizontal motion and 10 nrad for a tiltmeter, we show that small slip events could be better detected using high resolution and stability tiltmeters. We then examine how tiltmeters arrays could be used for such a purpose. In particular, we discuss how to deal with usual problems often plaguing tiltmeters data like instrumental drift, borehole coupling and hydrological strain.

  12. Models of recurrent strike-slip earthquake cycles and the state of crustal stress

    NASA Technical Reports Server (NTRS)

    Lyzenga, Gregory A.; Raefsky, Arthur; Mulligan, Stephanie G.

    1991-01-01

    Numerical models of the strike-slip earthquake cycle, assuming a viscoelastic asthenosphere coupling model, are examined. The time-dependent simulations incorporate a stress-driven fault, which leads to tectonic stress fields and earthquake recurrence histories that are mutually consistent. Single-fault simulations with constant far-field plate motion lead to a nearly periodic earthquake cycle and a distinctive spatial distribution of crustal shear stress. The predicted stress distribution includes a local minimum in stress at depths less than typical seismogenic depths. The width of this stress 'trough' depends on the magnitude of crustal stress relative to asthenospheric drag stresses. The models further predict a local near-fault stress maximum at greater depths, sustained by the cyclic transfer of strain from the elastic crust to the ductile asthenosphere. Models incorporating both low-stress and high-stress fault strength assumptions are examined, under Newtonian and non-Newtonian rheology assumptions. Model results suggest a preference for low-stress (a shear stress level of about 10 MPa) fault models, in agreement with previous estimates based on heat flow measurements and other stress indicators.

  13. The influence of fault geometry on small strike-slip fault mechanics

    NASA Astrophysics Data System (ADS)

    Ritz, Elizabeth; Pollard, David D.; Ferris, Michael

    2015-04-01

    Meter-scale subvertical strike-slip fault traces in the central Californian Sierra Nevada exhibit geometric complexities that significantly contribute to their mechanical behavior. Sections of faults that opened at depth channelized fluid flow, as evidenced by hydrothermal mineral infillings and alteration haloes. Thin sections show a variation in the style of ductile deformation of infill along the fault, with greater intensities of deformation along restraining bends. Orthorectified photomosaics of outcrops provide model geometries and parameter constraints used in a two-dimensional displacement discontinuity model incorporating a complementarity algorithm. Model results show that fault shape influences the distribution of opening, and consequently the spatial distribution of fluid conduits. Geometric irregularities are present at many scales, and sections of opening occur along both releasing and restraining bends. Model sensitivity tests focus on boundary conditions along the fault: frictional properties on closed sections and fluid pressure within sections of opening. The influence of the remote stress state varies along a non-planar fault, complicating the relationships between remote stresses, frictional properties, slip, and opening. Discontinuous sections of opening along model faults are similar in spatial distribution and aperture to the epidote infill assemblages observed in the field.

  14. Analysis of the growth of strike-slip faults using effective medium theory

    SciTech Connect

    Aydin, A.; Berryman, J.G.

    2009-10-15

    Increases in the dimensions of strike-slip faults including fault length, thickness of fault rock and the surrounding damage zone collectively provide quantitative definition of fault growth and are commonly measured in terms of the maximum fault slip. The field observations indicate that a common mechanism for fault growth in the brittle upper crust is fault lengthening by linkage and coalescence of neighboring fault segments or strands, and fault rock-zone widening into highly fractured inner damage zone via cataclastic deformation. The most important underlying mechanical reason in both cases is prior weakening of the rocks surrounding a fault's core and between neighboring fault segments by faulting-related fractures. In this paper, using field observations together with effective medium models, we analyze the reduction in the effective elastic properties of rock in terms of density of the fault-related brittle fractures and fracture intersection angles controlled primarily by the splay angles. Fracture densities or equivalent fracture spacing values corresponding to the vanishing Young's, shear, and quasi-pure shear moduli were obtained by extrapolation from the calculated range of these parameters. The fracture densities or the equivalent spacing values obtained using this method compare well with the field data measured along scan lines across the faults in the study area. These findings should be helpful for a better understanding of the fracture density/spacing distribution around faults and the transition from discrete fracturing to cataclastic deformation associated with fault growth and the related instabilities.

  15. Simulation of Tremor and Slow Slip Earthquakes Along a Strike-Slip Fault

    NASA Astrophysics Data System (ADS)

    Payton, K. A.; Cochran, E. S.; Richards-Dinger, K. B.; Dieterich, J. H.; Harrington, R. M.; Kroll, K.

    2014-12-01

    We use an earthquake simulator to investigate the conditions that may result in tectonic tremor. Tremor comprises small seismic events often associated with slow slip earthquakes (SSEs) that were initially discovered in subduction zones, but have subsequently been observed along transform faults such as the San Andreas Fault. For this study, our primary region of interest is the Parkfield-Cholame segment of the San Andreas, which is located between the locked segment to the south and the creeping segment to the north. Due to Parkfield's unique history of successive earthquakes at quasi-regular intervals, deep borehole seismometers were installed in this region, enabling the discovery of low-amplitude tectonic tremor. To better understand the fault properties that result in SSEs and tremor, we utilize the earthquake simulator RSQSim to simulate multi-cycle SSEs and tremor along a planar strike-slip fault. RSQSim is a computationally efficient method that uses rate- and state- dependent friction to simulate a wide range of event sizes for long time histories of slip [Dieterich and Richards-Dinger, 2010; Richards-Dinger and Dieterich, 2012]. RSQSim has been previously used to investigate slow slip events in Cascadia [Colella et al., 2011; 2012]. Here, we examine a suite of parameters to understand the influence of normal stress, rate-and-state constants a and b, and slip speed as well as the distribution of tremor patches on tremor and SSE occurrence. We compare the simulation results to previous tremor observations.

  16. Geodetic evidence for continuing tectonic activity of the Carboneras fault (SE Spain)

    NASA Astrophysics Data System (ADS)

    Echeverria, Anna; Khazaradze, Giorgi; Asensio, Eva; Masana, Eulalia

    2015-11-01

    The Carboneras fault zone (CFZ) is a prominent onshore-offshore strike-slip fault that forms part of the Eastern Betic Shear Zone (EBSZ), located in SE Spain. In this work, we show for the first time, the continuing tectonic activity of the CFZ and quantify its geodetic slip-rates using continuous and campaign GPS observations conducted during the last decade. We find that the left-lateral motion dominates the kinematics of the CFZ, with a strike-slip rate of 1.3 ± 0.2 mm/yr along the N48° direction. The shortening component is significantly lower and poorly constrained. Recent onshore and offshore paleoseismic and geomorphic results across the CFZ suggest a minimum Late Pleistocene to present-day strike-slip rate of 1.1 mm/yr. Considering the similarity of the geologic and geodetic slip rates measured at different points along the fault, the northern segment of the CFZ must have been slipping approximately at a constant rate during the Quaternary. Regarding the eastern Alpujarras fault zone corridor (AFZ), located to the north of the CFZ, our GPS measurements corroborate that this zone is active and exhibits a right-lateral motion. These opposite type strike-slip motion across the AFZ and CFZ is a result of a push-type force due to Nubia and Eurasia plate convergence, which, in turn, causes the westward escape of the block bounded by these two fault zones.

  17. Cenozoic strike-slip faults in the northern Wassuk Range, Walker Lane

    SciTech Connect

    Dilles, J.H. . Geosciences Dept.)

    1993-04-01

    The N. Wassuk Ra. yields estimates of right-lateral Cenozoic strain in a portion of the northwest-trending Walker Lane, which has a total estimated right-lateral strain of 48--60 km (Ekren et al., 1984). The net right-lateral strain is < 10 km within an east-west 50 km-long segment extending from the N. Wassuk Ra. west to the Pine Nut Mts on the basis of continuous Jurassic plutonic units: Yerington batholith and quartz monzodiorite porphyry dikes. One of two dikes in the N. Wassuk Ra. may correlate easterly to Gillis Ra., suggesting [approximately]10 or 25 km right-lateral offset (Diles and R. Hardyman, unpub). In the N. Wassuk Ra. there are several ages of northwesterly striking faults. The oldest are [approximately]N45[degree]W striking, steeply dipping faults including the White Mt. and Wassuk Spur faults that step left to the northwest. Associated moderately dipping faults have tilted Oligocene tuffs to the W or SW to the SW of the fault zone, and both E and W on the NW; based on offset of the Jurassic porphyry dike and slickensides, these faults were dominantly oblique-slip normal faults with WNW-ESE slip. No lateral offsets can be directly measured across the steeply dipping faults; however, they juxtapose different Mesozoic metamorphic rocks and different thicknesses of Oligocene ignimbrites, suggesting significant lateral offset. Bingler's (1978) proposal that the White Mt. fault had left-laterally offset the White Mt. granite (WMG) from granite of Black Mountain (BMG) is unreasonable because the BMG intrudes the Wassuk Range diorite and contain biotite aplites, whereas the WMG intrudes metavolcanic rocks and contains tourmaline-muscovite aplites.

  18. 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

  19. Evidence for Right-lateral Shear Along the Northwest Margin of the Eastern Snake River Plain, Idaho

    NASA Astrophysics Data System (ADS)

    Payne, S. J.; McCaffrey, R.; King, R. W.

    2007-12-01

    Previous investigators have proposed that extension within the eastern Snake River Plain (ESRP) is accommodated by intrusion of dikes at a rate similar to the rate of extension in the surrounding Basin and Range. This hypothesis is primarily based on the lack of strike-slip offset along the northwest physiographic boundary of the ESRP, the lack of seismicity within the ESRP relative to the surrounding active Basin and Range, and the presence of NW-trending volcanic rift zones within the ESRP. The ESRP is a 400-km long region within the track of the Yellowstone Hotspot that extends from southern Idaho northeast into northwestern Wyoming. GPS data compiled for this study are used to test this hypothesis. Several institutions including the Idaho National Laboratory, National Geodetic Survey, Rensselaer Polytechnic Institute, and University of Utah observed GPS stations from 1994 to 2007 within the ESRP and surrounding region. The GPS velocities show the average orientation of horizontal GPS velocities in the adjacent northwest Basin and Range region is similar to the average orientation for the ESRP (N113°W vs N91°W, respectively), but the average magnitude of horizontal GPS velocities in the Basin and Range (1.4 ± 0.3 mm/yr) is less than that for the ESRP (2.2 ± 0.3 mm/yr). Additionally, the adjacent northwest Basin and Range extends at about 9 x 10-9 /yr with most of the deformation localized along three NW-trending normal faults (Lost River, Lemhi, and Beaverhead). In contrast, the ESRP extends at a rate that is an order of magnitude lower than the adjacent northwest Basin and Range and we see little indication of extension along the Great Rift or other volcanic rift zones over the 400 km length. The GPS differential motion along the region of the ESRP adjacent to the northwest Basin and Range indicates a NE-trending zone of right-lateral shear. Preliminary inversions of GPS velocities, earthquakes, faults, and volcanic features indicate this zone of right-lateral

  20. 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

  1. Dynamic response to strike-slip tectonic control on the deposition and evolution of the Baranof Fan, Gulf of Alaska

    USGS Publications Warehouse

    Walton, Maureen A. L.; Gulick, Sean P. S.; Reece, Robert S.; Barth, Ginger A.; Christeson, Gail L.; VanAvendonk, Harm J.

    2014-01-01

    The Baranof Fan is one of three large deep-sea fans in the Gulf of Alaska, and is a key component in understanding large-scale erosion and sedimentation patterns for southeast Alaska and western Canada. We integrate new and existing seismic reflection profiles to provide new constraints on the Baranof Fan area, geometry, volume, and channel development. We estimate the fan’s area and total sediment volume to be ∼323,000 km2 and ∼301,000 km3, respectively, making it among the largest deep-sea fans in the world. We show that the Baranof Fan consists of channel-levee deposits from at least three distinct aggradational channel systems: the currently active Horizon and Mukluk channels, and the waning system we call the Baranof channel. The oldest sedimentary deposits are in the northern fan, and the youngest deposits at the fan’s southern extent; in addition, the channels seem to avulse southward consistently through time. We suggest that Baranof Fan sediment is sourced from the Coast Mountains in southeastern Alaska, transported offshore most recently via fjord to glacial sea valley conduits. Because of the translation of the Pacific plate northwest past sediment sources on the North American plate along the Queen Charlotte strike-slip fault, we suggest that new channel formation, channel beheadings, and southward-migrating channel avulsions have been influenced by regional tectonics. Using a simplified tectonic reconstruction assuming a constant Pacific plate motion of 4.4 cm/yr, we estimate that Baranof Fan deposition initiated ca. 7 Ma.

  2. Changes of static stress and aftershocks distribution for the strike-slip earthquakes in the West Pilippine Sea Plate

    NASA Astrophysics Data System (ADS)

    Lin, Y.; Lin, J.

    2013-12-01

    Over the last few decades, several strike-slip type earthquakes have been observed within the West Philippine Sea Plate (WPSP), to the east of the Gagua Ridge area. Nearly all of these earthquakes possessed a similar focal mechanism pattern with one fault plane sub-parallel to approximately N35°E. Based on bathymetric and magnetic anomaly data, several obvious NE-SW ancient fracture zones have been identified in the WPSP and considered to be the main rupture plane of these strike-slip earthquakes. However, the aftershocks distributions of these strike-slip earthquakes show NW-SE trending pattern, which is almost in orthogonal with the fracture zones orientation. Thus, the real rupture plane of these events is still undetermined. Otherwise, many researches have provided evidence that stress increase promotes seismicity: the increase of static Coulomb stress is generally correlated to the high occurrence of aftershocks. In our study, we chose three large earthquakes occurred in the WPSP to analyze the relationship between static Coulomb stress changes and seismicity rate changes, in the aim of determining an appropriate rupture plane for these strike-slip events. In our analysis, two fault planes have been used to estimate the static Coulomb stress change. Then, we compared the aftershocks distribution with the Coulomb stress distribution pattern. Our results shows that when the fault plane is trending NW-SE direction, the aftershocks occurred in the region with positive Coulomb stress changes, while the seismicity was decreased in the region of negative Coulomb stress changes. Otherwise, the other fault plane could not at all explain the observed aftershocks distribution. Consequently, the NW-SE fault plane is the preferred rupture plane for the strike-slip events occurred in the WPSP. The 11 April 2012, Mw 8.6 and Mw 8.2 earthquakes occurred off the west coast of northern Sumatra, Indonesia, are also strike-slip fault events within the Indo-Australia plate. These

  3. Strike-slip fault Kinematics and mechanics at the seismic cycle time-scale : Results from new analogue model experiments.

    NASA Astrophysics Data System (ADS)

    Caniven, Yannick; Dominguez, Stéphane; Soliva, Roger; Cattin, Rodolphe; Peyret, Michel; Chéry, Jean; Romano, Christian

    2013-04-01

    The average seismic cycle duration extends from hundred to a few thousands years but geodetic measurements, including trilateration, GPS, Insar and seismological data extend over less than one century. This short time observation scale renders difficult, then, to constrain the role of key parameters such as fault friction and geometry, crust rheology, stress and strain rate that control the kinematics and mechanics of active faults. To solve this time scale issue, we have developed a new experimental set-up that reproduces scaled micro-earthquakes and several hundreds of seismic cycles along a strike-slip fault. The model is constituted by two polyurethane foam plates laterally in contact, lying on a basal silicone layer, which simulate the mechanical behaviour of an elastoplastic upper crust over a ductile lower crust, respectively. To simulate the boundary conditions of a strike-slip fault, a computerized motoreductor system moves the two compartments on an opposite sens and at a constant very low velocity (a few µm/s). The model spatial and temporal scaling, deduces from analog material physical and mechanical parameters, implies that 1 cm in the model represents 2-3 km in the nature and 1 s is equivalent to 5-15 years. Surface-horizontal strain field is quantified by sub-pixel correlation of digital camera pictures recorded every 16 µm of displacement. For each experience about 2000 horizontal-velocity field measurements are recorded. The analysis of model-interseismic and coseismic surface displacements and their comparison to seismogenic natural faults demonstrate that our analog model reproduces correctly both near and far-field surface strains. To compare the experiences, we have developed several algorithms that allow studying the main spatial and temporal evolution of the physical parameters and surface deformation processes that characterise the seismic cycle (magnitudes, stress, strain, friction coefficients, interseismic locking depth, recurrence

  4. 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

  5. Strike-slip faults imaging from galleries with seismic waveform imaging methods

    NASA Astrophysics Data System (ADS)

    Bretaudeau, F.; Gélis, C.; Leparoux, D.; Cabrera, J.; Côte, P.

    2011-12-01

    Deep argillaceous formations are potential host media for radioactive waste due to their physical properties such as low intrinsic permeability and radionuclide retention (Boisson et al 2001). The experimental station of Tournemire is composed of an old tunnel excavated in 1885 in a 250m thick Toarcien argilitte layer, and of several galleries excavated more recently in directions perpendicular and parallel to the tunnel. This station is operated by the French Institute for Radiological protection and Nuclear Safety (IRSN) in order to expertise possible projects of radioactive waste disposal in a geological clay formation. The presence of secondary strike-slip faults in argillaceous formations must be well assessed since they could change any rock properties such as permeability. The ones with small vertical offsets as observed in the station cannot be seen from the surface, indeed we investigate on new approaches to image them directly from the underground works. We investigate here on the potential of new imaging methods that take advantage of the full seismic waveforms in order to optimise the imaging performances: Full Waveform Inversion (FWI) and Reverse Time Migration (RTM). We try to assess the capacities and limits of those methods in this specific context, and to determine the optimum acquisition and processing parameters. The subvertical fault in the nearly homogeneous subhorizontal structure of the clay layer allows us to consider a 2D imaging problem with no anisotropy where the fault is surrounded by three galleries. The waveform inversion strategy used is based on the frequency domain formulation proposed by Pratt et al. (1990). Non linearity is mitigated by introducing sequentially information from 50Hz to 1000Hz and starting from an homogeneous medium as initial model. Preliminary tests on synthetic data (fig. 1) show the ability of FWI to quantitatively image the fault zone and illustrate the impact of the illumniation configuration. RTM suceeds to

  6. Subsurface architecture of a strike-slip collapse structure: insights from Ilopango caldera, El Salvador

    NASA Astrophysics Data System (ADS)

    Saxby, Jennifer; Gottsmann, Joachim; Cashman, Katherine; Gutierrez, Eduardo

    2016-04-01

    While most calderas are created by roof collapse along ring-like faults into an emptying magma reservoir during a large and violent explosive eruption, an additional condition for caldera formation may be tectonically induced extensional stresses. Here we provide geophysical insights into the shallow sub-volcanic plumbing system of a collapse caldera in a major strike-slip tectonic setting by inverting Bouguer gravity data from the Ilopango caldera in El Salvador. Despite a long history of catastrophic eruptions with the most recent in 500 A.D., the internal architecture of the caldera has not been investigated, although studies of the most recent eruption have not identified the ring faults commonly associated with caldera collapse. The gravity data show that low-density material aligned along the principal stress orientations of the El Salvador Fault Zone (ESFZ) forms a pronounced gravity low beneath the caldera. Extending to around 6 km depth, the low density structure likely maps a complex stacked shallow plumbing system composed of magmatic and fractured hydrothermal reservoirs. A substantial volume of the plumbing system must be composed of a vapour phase to explain the modeled negative density contrasts. We use these constraints to map the possible multi-phase parameter space contributing to the subsurface architecture of the caldera and propose that the local extension along the complex ESFZ controls accumulation, ascent and eruption of magma at Ilopango. The data further suggest that future eruptions at Ilopango could be facilitated by rapid rise of magma along conjugate fault damage zones through a mechanically weak crust under tension. This may explain the absence of clear ring fault structures at the caldera.

  7. 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

  8. Abrupt strike-slip fault to subduction transition: The Alpine Fault-Puysegur Trench connection, New Zealand

    NASA Astrophysics Data System (ADS)

    Lebrun, Jean-FréDéRic; Lamarche, Geoffroy; Collot, Jean-Yves; Delteil, Jean

    2000-08-01

    Swath bathymetry and other geophysical data collected over the Fiordland Margin, southwest of New Zealand are used to investigate the mechanism of transform-subduction transition between the Alpine Fault and the Puysegur Trench, two segments of the Pacific-Australian plate boundary. In this region the Cenozoic Southeast Tasman Basin, which obliquely underthrusts Fiordland at the Puysegur Trench, is separated from the Cretaceous Tasman Basin by the Resolution Ridge System, a major lithospheric discontinuity of the downgoing plate. Interpretation of seafloor morphology shows that the Alpine Fault extends offshore along the Fiordland coast and splits into West and East Branches. The West Branch cuts obliquely across the margin and connects sharply to the Puysegur subduction front at the northeastern tip of the Resolution Ridge System. Earthquake and seismic reflection data indicate that the West Branch is genetically controlled by downgoing plate structures associated with the Resolution Ridge System. Hence the West Branch is interpreted as the surface trace of the plate boundary segment extending between the Alpine Fault and the Puysegur Trench. We conclude that the development of the strike-slip segment of the plate boundary and its sharp transition to the Puysegur subduction are controlled by inherited structures of the Australian plate. Furthermore, according to geophysical data presented here, a tearing of the downgoing plate can be interpreted beneath the West Branch. A review of geophysical data along the region of the Alpine Fault-Hikurangi Trough, northeast New Zealand, shows a progressive transform-subduction transition that is accommodated by motion partitioning between the subduction interface and strike-slip faults. This transition is accounted for by an interplate coupling that progressively increases toward the Alpine Fault in relation with a gradual thickening of the downgoing crust. The comparison between the Fiordland and the Hikurangi strike-slip

  9. 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.

  10. Procedure of evaluating parameters of inland earthquakes caused by long strike-slip faults for ground motion prediction

    NASA Astrophysics Data System (ADS)

    Ju, Dianshu; Dan, Kazuo; Fujiwara, Hiroyuki; Morikawa, Nobuyuki

    2016-04-01

    We proposed a procedure of evaluating fault parameters of asperity models for predicting strong ground motions from inland earthquakes caused by long strike-slip faults. In order to obtain averaged dynamic stress drops, we adopted the formula obtained by dynamic fault rupturing simulations for surface faults of the length from 15 to 100 km, because the formula of the averaged static stress drops for circular cracks, commonly adopted in existing procedures, cannot be applied to surface faults or long faults. The averaged dynamic stress drops were estimated to be 3.4 MPa over the entire fault and 12.2 MPa on the asperities, from the data of 10 earthquakes in Japan and 13 earthquakes in other countries. The procedure has a significant feature that the average slip on the seismic faults longer than about 80 km is constant, about 300 cm. In order to validate our proposed procedure, we made a model for a 141 km long strike-slip fault by our proposed procedure for strike-slip faults, predicted ground motions, and showed that the resultant motions agreed well with the records of the 1999 Kocaeli, Turkey, earthquake (Mw 7.6) and with the peak ground accelerations and peak ground velocities by the GMPE of Si and Midorikawa (1999).

  11. Microstructural and Rheological Constraints on the Mantle Strength of Strike-Slip Fault Systems: Evidence from the Bogota Peninsula Shear Zone, New Caledonia

    NASA Astrophysics Data System (ADS)

    Chatzaras, V.; Titus, S.; Tikoff, B.; Drury, M. R.

    2014-12-01

    Crust-mantle coupling along major strike-slip fault zones suggests that these two lithospheric layers act as an integrated system. In such a system, the spatial and temporal evolution of mantle strength across strike-slip shear zones has proven a key component in understanding lithospheric deformation and rheology. The Bogota Peninsula shear zone is exposed in the mantle section of the New Caledonia ophiolite. It contains a unique microstructural and textural record across a 4-km wide mylonitic zone bordered by a wider zone of weaker deformation. The shear zone is interpreted as a paleotransform fault, based on the orientations of fabrics and dikes inside and outside the zone. No ultramylonites or pseudotachylites were observed within the shear zone. Olivine grain size paleopiezometers suggest variation of the shear zone stresses, with the highest values recorded in the center of the shear zone, coincident with increasing olivine CPO strength toward the shear zone center. By estimating the finite strain in the zone, and assuming that all portions of the shear zone were active synchronously, we can correlate the increased stresses to increased strain rates. We compare the mantle strength in the Bogota Peninsula shear zone to other transform faults, such as the San Andreas fault (SAF) system. The differential stresses in the upper mantle of the SAF system, determined from xenoliths, is similar to those observed in the New Caledonia. Further, the width of shearing deformation in Bogota Peninsula shear zone is similar to that inferred for other transform zones, in both the upper crust and lithospheric mantle. These similarities suggest that viscous flow in the lithospheric mantle is in mechanical communication to brittle deformation in the upper crust. We propose a "Lithospheric Feedback" model, in which displacement due to mantle flow loads the crust during interseismic cycles, while the upper crust effectively limits the strength of the lithosphere.

  12. Ductile shear zones beneath strike-slip faults: Implications for the thermomechanics of the San Andreas Fault Zone

    NASA Astrophysics Data System (ADS)

    Thatcher, Wayne; England, Philip 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

  13. 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

  14. The influence of volcanism on fluvial depositional systems in a Cenozoic strike-slip basin, Denali fault system, Yukon Territory, Canada

    SciTech Connect

    Cole, R.B.; Ridgway, K.D. )

    1993-01-01

    The depositional history of the Eocene-Oligocene Burwash strike-slip basin is characterized by a transition from non-volcanic clastic sedimentation of the Amphitheater Formation to deposition of lavas and volcaniclastic rocks of the overlying lower Wrangell volcanic sequence. The purpose of this paper is twofold: (1) to document the contemporaneous fluvial and volcanic depositional history of a nonmarine strike-slip basin, and (2) to discuss the transition from non-volcanic to volcanic deposition in the context of strike-slip basin evolution. The authors indicate that the onset of volcanism within strike-slip basins can result in major reorganizations of drainage systems as well as changes in sediment sources.

  15. 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

  16. Structure of the la VELA Offshore Basin, Western Venezuela: AN Obliquely-Opening Rift Basin Within the South America-Caribbean Strike-Slip Plate Boundary

    NASA Astrophysics Data System (ADS)

    Blanco, J. M.; Mann, P.

    2015-12-01

    Bathymetric, gravity and magnetic maps show that the east-west trend of the Cretaceous Great Arc of the Caribbean in the Leeward Antilles islands is transected by an en echelon series of obliquely-sheared rift basins that show right-lateral offsets ranging from 20 to 40 km. The basins are 75-100 km in length and 20-30 km in width and are composed of sub-parallel, oblique slip normal faults that define deep, bathymetric channels that bound the larger islands of the Leeward Antilles including Aruba, Curacao and Bonaire. A single basin of similar orientation and structure, the Urumaco basin, is present to the southwest in the Gulf of Venezuela. We mapped structures and sedimentation in the La Vela rift basin using a 3D seismic data volume recorded down to 6 seconds TWT. The basin can be mapped from the Falcon coast where it is correlative with the right-lateral Adicora fault mapped onshore, and its submarine extension. To the southeast of the 3D survey area, previous workers have mapped a 70-km-wide zone of northeast-striking, oblique, right-lateral faults, some with apparent right-lateral offsets of the coastline. On seismic data, the faults vary in dip from 45 to 60 degrees and exhibit maximum vertical offsets of 600 m. The La Vela and other obliquely-opening rifts accommodate right-lateral shear with linkages to intervening, east-west-striking right-lateral faults like the Adicora. The zone of oblique rifts is restricted to the trend of the Great Arc of the Caribbean and may reflect the susceptiblity of this granitic basement to active shearing. The age of onset for the basins known from previous studies on the Leeward Antilles is early Miocene. As most of these faults occur offshore their potential to generate damaging earthquakes in the densely populated Leeward Antilles is not known.

  17. Modelling a strike-slip fault system affecting porous carbonates in Favignana Island (Sicily, southern Italy)

    NASA Astrophysics Data System (ADS)

    Cilona, A.; Tondi, E.; Agosta, F.; Johnson, G.; Shackleton, R.

    2012-12-01

    Investigating the deformation processes as well as the characteristics and distribution of their end-products is a crucial issue to improve geo-fluid exploitation in carbonate reservoirs (≈50% of natural geo-fluids). Indeed, besides the primary controls on the petrophysical properties of limestones, which are due to nature and organization/shape of the constituent elements (i.e. grains, pores, cement, clay minerals), both containment and migration of fluids in these rocks are influenced by fault zones and fractures. In this contribution we integrate quantitative structural analysis and numerical modelling approaches aiming at testing a new workflow useful to create a 3D discrete fracture network (DFN) model of a reservoir starting from outcrop data collected in Favignana Island (Sicily, southern Italy). The presence of several quarries in the Island provides 3D exposures of ≈25 m-thick Lower-Pleistocene high-porosity grainstones crosscut by two conjugate sets of strike-slip faults. This fault system, documented by Tondi et al. (2012), is comprised of three types of structure: single compactive shear bands (CSB); zones of bands (ZB); and, faults. CSBs are narrow tabular features with porosity less than the surrounding host rocks, and have thicknesses and displacements on the order of a few mm. The growth process for these structures involves localizing further deformation within zones of closely-spaced CSBs and, possibly, along continuous slip surfaces within fault rocks overprinting older ZBs. The transitions from one growth step to another are recorded by different values of the dimensional parameters (i.e. length, thickness and displacement) for the structures. These transitions are also reflected by the ratios and distributions of the dimensional parameters. The DFN model was built by means of the Fracture Modelling module of the commercial software package Move from Midland Valley©. The analysis of an aerial photo was performed firstly to delimit the

  18. Strike-slip earthquakes in the oceanic lithosphere: Observations of exceptionally high apparent stress

    USGS Publications Warehouse

    Choy, G.L.; McGarr, A.

    2002-01-01

    The radiated energies, Es, and seismic moments, Mo, for 942 globally distributed earthquakes that occurred between 1987 to 1998 are examined to find the earthquakes with the highest apparent stresses (??a = ?? Es/Mo, where ?? is the modulus of rigidity). The globally averaged ??a for shallow earthquakes in all tectonic environments and seismic regions is 0.3 MPa. However, the subset of 49 earthquakes with the highest apparent stresses (??a greater than about 5.0 MPa) is dominated almost exclusively by strike-slip earthquakes that occur in oceanic environments. These earthquakes are all located in the depth range 7-29 km in the upper mantle of the young oceanic lithosphere. Many of these events occur near plate-boundary triple junctions where there appear to be high rates of intraplate deformation. Indeed, the small rapidly deforming Gorda Plate accounts for 10 of the 49 high-??a events. The depth distribution of ??a, which shows peak values somewhat greater than 25 MPa in the depth range 20-25 km, suggests that upper bounds on this parameter are a result of the strength of the oceanic lithosphere. A recently proposed envelope for apparent stress, derived by taking 6 per cent of the strength inferred from laboratory experiments for young (less than 30 Ma) deforming oceanic lithosphere, agrees well with the upper-bound envelope of apparent stresses over the depth range 5-30 km. The corresponding depth-dependent shear strength for young oceanic lithosphere attains a peak value of about 575 MPa at a depth of 21 km and then diminishes rapidly as the depth increases. In addition to their high apparent stresses, which suggest that the strength of the young oceanic lithosphere is highest in the depth range 10-30 km, our set of high-??a earthquakes show other features that constrain the nature of the forces that cause interplate motion. First, our set of events is divided roughly equally between intraplate and transform faulting with similar depth distributions of ??a for

  19. Strike-slip fault bridge fluid pumping mechanism: insights from field-based palaeostress analysis and numerical modelling

    NASA Astrophysics Data System (ADS)

    Nemčok, Michal; Henk, Andreas; Gayer, Rodney A.; Vandycke, Sara; Hathaway, Tanya M.

    2002-12-01

    We present a finite-element study of stress perturbation in evolving compressive and extensional strike-slip fault bridges. The results are compared with a fracture study of a compressive bridge at St Donats, UK. Horizontally interbedded calcareous mudstone and bioclastic calcilutite at St Donats have a distinct vertical permeability anisotropy. This sedimentary sequence behaves as a set of horizontal aquifers. The fluid flow in these aquifers is sensitive to mean stress gradients. Paleostress analysis of field fracture data, verified by finite-element modelling, indicates a rotation of σ1 towards parallelism with boundary faults inside the growing compressive bridge. Boundary faults and bridge faults recorded numerous fluid flow events. The modelled mean stress pattern shows a regional maximum within the bridge and local maxima/minima pairs at boundary fault tips. Finite-element modelling of an extensional bridge indicates that σ3 rotates towards parallelism with boundary faults. The mean stress pattern is similar to the pattern in compressive bridge but with maxima and minima locations interchanged. The stress patterns are reestablished by each stress build-up preceding the rupturation of the boundary faults throughout the development stages of strike-slip fault bridges. Mean stress gradients developed pre-failure control the fluid flow in fractures of the strike-slip fault system at and after the end of each stress build-up and the fluid flow in boundary faults post-failure. Fracture reactivation and new fracture generation within an evolving bridge is a process consisting of multiple successive events that retain the storage capacity of the bridge. Rupture and sealing of the main bounding-faults is a step-wise process that opens and closes fluid conduits between areas with different pressures.

  20. Rupture and frequency-dependent seismic radiation of the 2012 Mw 8.6 Sumatra strike-slip earthquake

    NASA Astrophysics Data System (ADS)

    Yin, Jiuxun; Yao, Huajian

    2016-06-01

    On 2012 April 11, a great strike-slip earthquake (moment magnitude of Mw 8.6) occurred off the west coast of northern Sumatra area followed by an Mw 8.2 aftershock 2 hr later. Different geophysical data and methods have been used to investigate the mechanism, faulting, seismic radiation and slip propagation of this event, but frequency-dependent features of its rupture process have not been discussed much. In this study, we use a compressive sensing method based on sparsity inversion in the frequency domain to study the frequency-dependent seismic radiation and rupture process of this event. Our results indicate a very complex rupture process concerning at least three different rupture stages on multiple subfaults with nearly conjugate geometries. The main shock has triggered seismicity on a series of ridge-perpendicular or ridge-parallel conjugate strike-slip faults around the Nighty East Ridge. Obvious frequency-dependent rupture process has been presented and discussed. Combining results from slip inversion based on the finite-fault model, we observe that in the beginning stage of the rupture lower frequency radiation appears to originate from the areas with large slip, while the high-frequency radiation is located at the boundary of large-slip region or rupture front. Some radiation probably originates from the repeating slip on the main faults or triggered events on some nearby faults in the rupture area. The complex frequency-dependent seismic radiation patterns observed in this study provide important information for future investigation of rupture physics of this complex strike-slip event.

  1. Jelly Quakes - Characteristics of periodic slip events in an analog model of strike slip seismotectonics using ballistic gelatin.

    NASA Astrophysics Data System (ADS)

    Rudolf, Michael; Rosenau, Matthias; Oncken, Onno

    2016-04-01

    Large lithospheric strike-slip faults, such as the San-Andreas Fault, North-Anatolian Fault, or the Tancheng-Lujiang Faultzone, are major sources of seismic hazard. The interplay of complex 3D-geometry and displacement style along the fault, coupled with a varying rheological layering makes it very difficult to model these faults on all relevant timescales. Here we present a novel experimental approach to model intra- and interplate strike-slip faults using a physical/ analog model. We model earthquakes as a stick-slip process, following a rate-and-state frictional law, with glass beads as granular material within a molded fault zone. Crustal elasticity is introduced by using ballistic gelatin (30 w%, pig skin) as analog material. Furthermore, the low-strength and viscous deep crust below 15 km depth, is modeled using a viscoelastic silicone oil (PDMS-G30M). The layered model crust floats on sugar syrup and is compressed in pure shear vice configuration. We monitor the compressive force along with surface kinematics from optical image correlation. The fault is oriented at 45° to the compression direction imposing ideal strike-slip kinematics onto it. After an initial loading phase the model shows periodic slip events occurring alongside with creep on the fault. Using digital image correlation, surface displacement maps are obtained which are similar to those of natural earthquakes. Coseismic displacement along strike is showing a similar bell-shaped distribution as for natural faults. Furthermore, the recurrence intervals and stress drops are scalable to the natural prototype. The modeling results are combined with numerical rate-and-state models using physical parameters from the experiment. This enables us to explore a wide range of parameters and to draw connections between the parameters that control the behavior of seismic and aseismic fault systems.

  2. Tectonic controls on late Cenozoic strike-slip faulting, volcanism, and landscape development in the Mojave Desert, California

    SciTech Connect

    Dokka, R.K.; Travis, C.J.; Ross, T.M. )

    1990-06-01

    Recent studies of the late Cenozoic tectonics of the Mojave Desert Block suggest that strain is regionally heterogeneous and has been partitioned into six domains that are separated by major strike-slip faults and extensional zones. Tectonic rotation of these domains as well as their internal deformation by strike-slip faulting have occurred as the result of broadly distributed regional right shear. Sixty-five kilometers of total right slip is reckoned to have occurred along faults of the southern half of the province (between the Helendale and Granite Mountains faults). The broad network of faults of the Mojave, along with kinematically and temporally similar strike-slip faults of the Death Valley region (Furnace Creek and Southern Death Valley fault zones), constitute a regional, through going zone of right shear named the Eastern California shear zone (ECSZ). This zone of intracontinental shear also likely includes the Walker Lane belt of western Nevada. Because of its physical connection to faults the southern portion of the San Andreas fault system, the ECSZ must have also accommodated a portion of Pacific-North American transform motion. In addition to imparting the strong NW structural grain to the region, the tectonic regime has had a profound effect on Neogene paleogeography and has apparently facilitated local magmatism. Faulting and block rotations have created a series of structurally controlled basins and uplifts of many geometries. Extension in several basins has also been accompanied by young basaltic magmatism. These include surface flows such as at Mt. Pisgah (shield volcano) and subsurface dike emplacement beneath Troy Lake.

  3. A numerical study of strike-slip bend formation with application to the Salton Sea pull-apart basin

    NASA Astrophysics Data System (ADS)

    Ye, Jiyang; Liu, Mian; Wang, Hui

    2015-03-01

    How stepovers of strike-slip faults connect to form bends is a question important for understanding the formation of push-up ranges (restraining bends) and pull-apart basins (releasing bends). We investigated the basic mechanics of this process in a simple three-dimensional viscoelastoplastic finite element model. Our model predicts localized plastic strain within stepovers that may eventually lead to the formation of strike-slip bends. Major parameters controlling strain localization include the relative fault strength, geometry of the fault system, and the plasticity model assumed. Using the Drucker-Prager plasticity model, in which the plastic yield strength of the crust depends on both shear and normal stresses, our results show that a releasing bend is easier to develop than a restraining bend under similar conditions. These results may help explain the formation of the Salton Sea pull-apart basin in Southern California 0.5-0.1 Ma ago, when the stepover between the Imperial Fault and the San Andreas Fault was connected by the Brawley seismic zone.

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

    NASA Astrophysics Data System (ADS)

    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.

  5. 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.

  6. STRIKE SLIP ON REACTIVATED TRIASSIC(? ) BASIN BOUNDARY FAULT ZONES AS SOURCES OF EARTHQUAKES NEAR CHARLESTON, S. C.

    USGS Publications Warehouse

    Behrendt, John C.; Yuan, Annette

    1986-01-01

    Interpretation of several thousand kilometers of multifold seismic reflection data supports the old theory that earthquakes in the Charleston, S. C. area are associated with reactivated Triassic(? ) basin boundary extensional fault zones. The Gants-Cooke fault zone associated with the Jedburg basin in the 1886 meizoseismal area, an unnamed fault along the margin of the Branchville basin in the Bowman earthquake area and the offshore Helena Banks fault zone (no observed seismicity) along the margin of the Kiawah basin show evidence of reactivation of Triassic(? ) normal faults zones in a compressional, probably strike slip sense. The previously reported reverse separation of these faults observed on the seismic profiles in the late Cretaceous-Cenozoic Coastal Plain sediments is possibly produced by oblique slip with the horizontal component possibly 10 to 100 times the vertical. Earthquake recurrence intervals of several thousand years reported in the Charleston area appear consistent with ranges of magnitude of strike slip displacement inferred from the seismic reflection data, and are constrained by aeromagnetic data.

  7. Transition from Subduction to Strike-Slip in the Southeast Caribbean: Effects on Lithospheric Structures and Overlying Basin Evolution

    NASA Astrophysics Data System (ADS)

    Alvarez, T.; Mann, P.; Wood, L. J.; Vargas, C. A.; Latchman, J. L.

    2013-12-01

    Topography, basin structures and geomorphology of the southeast Caribbean-northeast South American margin are controlled by a 200-km-long transition from westward-directed subduction of South American lithosphere beneath the Caribbean plate, to east-west strike-slip motion of the Caribbean and South American plates. Our study of structures and basins present in the transitional area integrates a tomographic study of the lithospheric structures associated with lateral variations in the subduction of the South American lithosphere and orientation of the slab beneath the Caribbean plate as well as the evolution of overlying sedimentary basins imaged with deep-penetration seismic data kindly provided by the oil industry and Trinidad & Tobago government agencies. We use an earthquake dataset containing more than 700 events recorded by the eastern Caribbean regional seismograph network to build travel-time and attenuation tomography models used to image the mantle to depths of 100 km beneath transition zone. Approximately 10,000 km of 2D seismic reflection lines which are recorded to depths > 12 seconds TWT are used to interpret basin scale structures including tectono-stratigraphic sequences and structures which deform and displace sedimentary sequences. We use the observed satellite gravity to generate a gravity model for key sections traversing the tectonic transitional zone and to determine depth to basement in basins with sedimentary fill > 12 km. Within the study area, the dip of subducted South American oceanic lithosphere imaged on tomographic images is variable from ~44 to ~24 degrees. There is a distinct low gravity, low velocity, high attenuation, northwest - southeast trending lineation located east of Trinidad which defines the location of a Mesozoic oceanic fracture zone which accommodated the opening of the Central Atlantic during the Jurassic to Middle Cretaceous. This feature is also coincident with the present-day continent-ocean boundary and acts as a

  8. The Deep Structurs which are Transformed From Strike-slip ones into extending ones and Their Composite evolution of The Southern Segment of Tanlu Fault Belt During Yanshanian stage

    NASA Astrophysics Data System (ADS)

    Zhang, J.; Chen, X.; Zhou, Q.; SinoProbe

    2011-12-01

    The Tan-Lu fault is a well-known active fault belt in eastern Asia. After 40 years of study, a series of important scientific results have been achieved. However, its deep structure, activity history and mechanism still remains in debate. A large quantity of geophysical exploration work has been conducted since late 1990's. This paper focuses on the Jiashan- Lujiang section based on the geophysical exploration, magnetotelluric and magnetic sounding and seismic survey. We find the southern part of the Tan-Lu fault belt can be separated into two parts with different characteristics along the Chihe-Taihu sub-fault. In the east, the Tan-Lu fault belt is composed of several sub-faults with a positive flower structure, characterized by strike-slip in the late Middle Jurassic to early Late Jurassic. In the west, the Tan-Lu fault belt is represented by extensional fracture, made of 3 sub-faults near Dingyuan county. Among them, two sub-faults stretch to the south disappearing in the Hefei basin, one sub-fault, i.e., the Chihe-Taihu sub-fault stretches to the east edge of the Hefei basin, showing a half-graben structure with fault depression occurred in the Early Cretaceous. we establish the evolution model in the Jiashan-Lujiang section with active transforming from strike-slip to extension as well as its relationship between adjacent regions.Our study can be better integration of geological phenomena, interpreting the different views.Our model presents more reasonable explanation for the proposed different points of view on "rift valley hypothesis" and "strike-slip hypothesis". It provides new concept for the further study of the Tan-Lu fault belt.

  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. Crustal thickening in Gansu-Qinghai, lithospheric mantle subduction, and oblique, strike-slip controlled growth of the Tibet plateau

    NASA Astrophysics Data System (ADS)

    Meyer, B.; Tapponnier, P.; Bourjot, L.; Métivier, F.; Gaudemer, Y.; Peltzer, G.; Shunmin, Guo; Zhitai, Chen

    1998-10-01

    Late-Cenozoic crustal shortening on NE sections between the Kunlun fault and the Hexi corridor are estimated to range between 100 and 200 km. In keeping with the inference of a deep crustal décollement and with the existence of Mid-Miocene to Pliocene plutonism and volcanism south of the Kunlun range, such values suggest that the lithospheric mantle of the Qaidam plunged obliquely into the asthenosphere south of that range to minimum depths of the order of 200-300 km. A minimum of ~150 km of shortening in the last ~10 Ma, consistent with the average age of the earliest volcanic-plutonic rocks just south of the Kunlun (~10.8 Ma) would imply average Late-Cenozoic rates of shortening and regional uplift in NE Tibet of at least ~15 mm yr-1 and ~0.2 mm yr-1, respectively. Such numbers are consistent with a cumulative sinistral offset and slip rate of at least ~200 km and ~2 cm yr-1, respectively, on the Altyn Tagh fault east of 88°E. The fault may have propagated more than 1000 km, to 102°E, in the last 10 Ma. Our study of ongoing tectonics in northeast Tibet is consistent with a scenario in which, while the Himalayas-Gangdese essentially `stagnated' above India's subducting mantle, much of Tibet grew by thickening of the Asian crust, as propagation of large, lithospheric, strike-slip shear zones caused the opposite edge of the plateau to migrate far into Asia. The Asian lithospheric mantle, decoupled from the crust, appears to have subducted southwards along the two Mesozoic sutures that cut Tibet north of the Gangdese, rather than to have thickened. The Bangong-Nujiang suture was probably reactivated earlier than the Jinsha-Kunlun suture, located farther north. Overall, the large-scale deformation bears a resemblance to plate tectonics at obliquely convergent margins, including slip-partioning along large strike-slip faults such as the Altyn Tagh and Kunlun faults. Simple mechanisms at the level of the lithospheric mantle are merely hidden by the broader distribution

  11. Relationships between Variscan strike-slip faults in the Paleozoic basement and oil-gas deposits in its Mesozoic-Cenozoic cover: West Siberian sedimentary basin as example

    SciTech Connect

    Clauzon, G.; Rubino, J.L.

    1995-08-01

    The West-Siberian Sedimentary Basin was filled during Mesozoic and Cenozoic. Polychronous compressive and extensional deformations and strike-slip faulting occurred at the time of sedimentary basin formation. Late Variscan (Late Permian-Early Triassic) strike-slips in the basement took place as a result of N-S compression of the Central Asian Fold Belt. Strike-slips form wide and continuous shear zones which coincide with large oil and gas fields in the cover. Some strike-slips controlled distribution and formation of Permian and Triassic-Jurassic compressional and extensional local structures in the lower stage of the cover and anticlines in the upper stage of the cover. All these structures reveal potential oil and gas resources. In the Triassic, some of the N-S and SW-NE trending strike-slip faults in the axial part of the West Siberian Sedimentary Basin were transformed into graben-rift structures of the Koltogorsk-Urengoy Rift Belt. These transtension structures occurred as a result of N-S compression and reactivation of the Late Variscan faults. The largest oil and gas fields have been formed in the cover above the Koltogorsk-Urengoy Rift Belt of the West Siberian Sedimentary Basin.

  12. '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

  13. The tsunami-like sea level disturbance in Crotone harbor, Italy, after the Mw6.5 strike-slip earthquake of 17 November 2015 in Lefkada Isl., Ionian Sea, Greece

    NASA Astrophysics Data System (ADS)

    Novikova, Tatyana; Annunziato, Alessandro; Charalampakis, Marinos; Romano, Fabrizio; Volpe, Manuela; Tonini, Roberto; Gerardinger, Andrea; Papadopoulos, Gerassimos A.

    2016-04-01

    On 17 November 2015 an Mw6.5 earthquake ruptured offshore Lefkada Isl. in Ionian Sea, Greece, causing two human victims, minor damage and several ground failures including coastal landslides. Fault plane solutions released by CMT/Harvard, NOA and other institutes have indicated that the faulting style was strike-slip right-lateral, which is quite typical for the area, as for example, the Mw6.3 event that occurred on August 14, 2003, in exactly the same fault zone. In spite of the very low tsunami potential commonly associated to this faulting mechanism, a tsunami-like sea level change was recorded after the earthquake by one tide-gauge in the Crotone harbor, Italy. Preliminary tsunami numerical simulations were performed to reproduce the observed signal. The spectral analysis of the synthetic mareograms close to the entrance of the harbor shows the presence of some peaks that could justify the relation between the natural port resonance and the observed wave amplification. Of particular interest is the coupling between the tsunami energy and the natural modes of basin oscillation enhancing tsunami wave amplitude in harbors through resonance, as shown in some historical events in the Mediterranean Sea and elsewhere. This research is a contribution to the EU-FP7 tsunami research project ASTARTE (Assessment, Strategy And Risk Reduction for Tsunamis in Europe), grant agreement no: 603839, 2013-10-30.

  14. Late Neogene structural inversion around the northern Gulf of Tonkin, Vietnam: Effects from right-lateral displacement across the Red River fault zone

    NASA Astrophysics Data System (ADS)

    Fyhn, Michael B. W.; Phach, Phung V.

    2015-02-01

    Continental extrusion may take up much of the deformation involved in continental collisions. Major strike-slip zones accommodate the relative extrusion displacement and transfer deformation away from the collision front. The Red River fault zone (RRFZ) accommodated left- and right-lateral displacements when Indochina and South China were extruded during the Indian-Eurasian collision. The northern Song Hong basin onshore and offshore in the Gulf of Tonkin delineates the direct extension of the RRFZ and thus records detailed information on the collision-induced continental extrusion. We assess the rapidly evolving kinematics of the fault zone buried within the basin based on seismic analysis. Contrary to previous studies, we do not identify indications for latest Miocene left-lateral motion across the RRFZ. We tentatively consider the shift from left- to right-lateral motion to have occurred already during the middle Late Miocene as indicated by inversion of NE-SW-striking faults in the Bach Long Vi area. Right-lateral displacement terminated around the end of the Miocene in the Song Hong basin. However, continued inversion in the Bach Long Vi area and NNW-SSE-striking normal faulting suggests a stress regime compatible with right-lateral motion across the onshore part of the RRFZ continuing to the present. Inversion around the Bach Long Vi Island may have accommodated up to a few kilometers of right-lateral displacement between the Indochina and South China blocks. Comparable NE-SW-striking fault zones onshore may have accommodated a larger fraction of the right-lateral slip across the RRFZ, thus accounting for the restricted transfer of lateral displacement to the offshore basins.

  15. Dextral strike-slip along the Kapıdağ shear zone (NW Turkey): evidence for Eocene westward translation of the Anatolian plate

    NASA Astrophysics Data System (ADS)

    Türkoğlu, Ercan; Zulauf, Gernold; Linckens, Jolien; Ustaömer, Timur

    2016-07-01

    The northern part of the Kapıdağ Peninsula (Marmara Sea, NW Turkey) is affected by the E-W trending Kapıdağ shear zone, which cuts through calc-alkaline granitoids of the Ocaklar pluton resulting in mylonitic orthogneiss. Macroscopic and microscopic shear-sense indicators, such as SC fabrics, shear bands, σ-clasts and mica fish, unequivocally suggest dextral strike-slip for the Kapıdağ shear zone. Based on petrographic data, deformation microfabrics of quartz and feldspar, and the slip systems in quartz, the dextral shearing should have been active at T = 500-300 °C and P < 5 kbar. Published K-Ar and 39Ar-40Ar cooling ages of hornblende and biotite suggest that cooling below 500-300 °C occurred during the Eocene (ca. 45-ca. 35 Ma), meaning that the Kapıdağ shear zone should have been active during Middle to Late Eocene times. The differential stress related to the shearing was <50 MPa as is indicated by the size of recrystallized quartz grains. Based on the new and published data, it is concluded that the westward movement of the Anatolian plate might have been active almost continuously from the Middle Eocene until recent times.

  16. A PHYSICAL MODEL OF THE EFFECT OF A SHALLOW WEAK LAYER ON STRONG GROUND MOTION FOR STRIKE-SLIP RUPTURES

    SciTech Connect

    JAMES N. BRUNE AND ABDOLRASOOL ANOOSHEHPOOR

    1998-02-23

    We report results of foam-rubber modeling of the effect of a shallow weak layer on ground motion from strike-slip ruptures. Computer modeling of strong ground motion from strike-slip earthquakes has involved somewhat arbitrary assumptions about the nature of slip along the shallow part of the fault (e.g., fixing the slip to be zero along the upper 2 kilometers of the fault plane) in order to match certain strong motion accelerograms. Most modeling studies of earthquake strong ground motion have used what is termed kinematic dislocation modeling. In kinematic modeling the time function for slip on the fault is prescribed, and the response of the layered medium is calculated. Unfortunately, there is no guarantee that the model and the prescribed slip are physically reasonable unless the true nature of the medium and its motions are known ahead of time. There is good reason to believe that in many cases faults are weak along the upper few kilometers of the fault zone and may not be able to maintain high levels of shear strain required for high dynamic energy release during earthquakes. Physical models of faulting, as distinct from numerical or mathematical models, are guaranteed to obey static and dynamic mechanical laws. Foam-rubber modeling studies have been reported in a number of publications. The object of this paper is to present results of physical modeling using a shallow weak layer, in order to verify the physical basis for assuming a long rise time and a reduced high frequency pulse for the slip on the shallow part of faults. It appears a 2-kilometer deep, weak zone along strike-slip faults could indeed reduce the high frequency energy radiated from shallow slip, and that this effect can best be represented by superimposing a small amplitude, short rise-time pulse at the onset of a much longer rise-time slip. A weak zone was modeled by inserting weak plastic layers of a few inches in thickness into the foam rubber model. For the 15 cm weak zone the average

  17. Silicification Strengthening and Non-Localization of Slip in Dilational Sites Along Strike-Slip Faults, Mt Isa Inlier, Australia

    NASA Astrophysics Data System (ADS)

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

    2006-12-01

    Sets of late- or post-orogenic brittle strike-slip faults disrupt the complex of subgreenschist to amphibolite facies metasediments and metavolcanics intruded by granites that make up the Proterozoic Mt Isa inlier of NW Queensland, Australia. Subvertical dextral faults with offsets <25 km generally strike NE-SW to NNE- SSW and mutually cross-cut a conjugate set of sinistral faults striking NW-SE to NNW-SSE. Together, they define a regional stress field with horizontal maximum compression, σ1, at an azimuth of ~100° and horizontal σ3 trending ~010°. The strike-slip faults are recessive except in dilational sites where upwelling hydrothermal fluids have led to silicification of the cataclastic shear zones which then form prominent blade-like ridges sometimes extending for kilometres across the semi-arid terrain. Silicification textures suggest the faults have been exhumed from epizonal boiling environments (<1-2 km depth). The mineralized fault segments include sinuous releasing bends where the fault trace is deflected <10° as well as more abrupt dilational stepovers linking en echelon fault segments. Particularly noticeable is the change from recessive to upstanding wall-like character of the faults as they approach dilational stepovers linking en echelon fault segments. Where recessive, limited outcrop is consistent with standard models of brittle infrastructure with a fault core localized in a damage zone tens of metres in width. By contrast, along the dilational segments the faults are defined by one or more subvertical cataclastic shear zones (CSZ), commonly ranging up to 10 m or so in thickness, made up of silicified microbreccia-cataclasite containing a mixture of protolith and hydrothermal vein fragments. The composite fabric of the CSZ includes: (1) local grain-size banding developed subparallel to margins; (2) irregular quartz-cemented breccias of varying dilation; (3) innumerable subvertical, cm - dm quartz-veins of variable planarity lying

  18. The transpressional strain model applied to strike-slip, oblique-convergent and oblique-divergent deformation

    NASA Astrophysics Data System (ADS)

    Krantz, R. W.

    1995-08-01

    Zones of distributed shear deformation associated with strike-slip and oblique-convergent or oblique-divergent systems accommodate complex three-dimensional strains. Current models suggest that structural orientations within the zones depend on not only the magnitude of shear strain but also the degree of convergence or divergence. The transpressional strain model of Sanderson and Marchini is further developed here, and this study also focuses on relating structural orientations in map view to the magnitude of shear and the degree of convergence or divergence, and to the magnitudes of horizontal and vertical strains. Results include both the mathematical derivation and a set of nomograms relating the model parameters. Applications of the model to field examples and laboratory analogs show how the model can be used to determine the degree of convergence or divergence, and to calculate strain parameters. The model provides geologists with a method to evaluate and predict structural orientations, and to test map and cross-section interpretations.

  19. A nonlinear least-squares inverse analysis of strike-slip faulting with application to the San Andreas fault

    NASA Technical Reports Server (NTRS)

    Williams, Charles A.; Richardson, Randall M.

    1988-01-01

    A nonlinear weighted least-squares analysis was performed for a synthetic elastic layer over a viscoelastic half-space model of strike-slip faulting. Also, an inversion of strain rate data was attempted for the locked portions of the San Andreas fault in California. Based on an eigenvector analysis of synthetic data, it is found that the only parameter which can be resolved is the average shear modulus of the elastic layer and viscoelastic half-space. The other parameters were obtained by performing a suite of inversions for the fault. The inversions on data from the northern San Andreas resulted in predicted parameter ranges similar to those produced by inversions on data from the whole fault.

  20. Stress near geometrically complex strike-slip faults - Application to the San Andreas fault at Cajon Pass, southern California

    NASA Technical Reports Server (NTRS)

    Saucier, Francois; Humphreys, Eugene; Weldon, Ray, II

    1992-01-01

    A model is presented to rationalize the state of stress near a geometrically complex major strike-slip fault. Slip on such a fault creates residual stresses that, with the occurrence of several slip events, can dominate the stress field near the fault. The model is applied to the San Andreas fault near Cajon Pass. The results are consistent with the geological features, seismicity, the existence of left-lateral stress on the Cleghorn fault, and the in situ stress orientation in the scientific well, found to be sinistral when resolved on a plane parallel to the San Andreas fault. It is suggested that the creation of residual stresses caused by slip on a wiggle San Andreas fault is the dominating process there.

  1. 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.

  2. Coseismic strike slip at a point during the last four earthquakes on the Wellington fault near Wellington, New Zealand

    NASA Astrophysics Data System (ADS)

    Little, Timothy A.; van Dissen, Russ; Rieser, Uwe; Smith, Euan G. C.; Langridge, Rob M.

    2010-05-01

    We analyze progressively displaced late Quaternary (<12 ka) fluvial terraces along the Wellington fault, near Wellington, New Zealand. Optically stimulated luminescence dating indicates that degradational terraces were produced at a rate of about one terrace per 1000 years, similar to the rate of earthquake surface rupturing. Along the Hutt River near Te Marua, we measured the strike slip of 15 terrace risers and paleochannels on the lowest 8 of these terraces, of Holocene age. The river, after earthquakes, was generally capable of smoothing its faulted riverbanks. The dextral offsets appear to fall into several groupings that record slip accumulation during the last four earthquakes. We calculate a mean single-event slip of 5.0 ± 0.24 m (95% confidence) with an RMS scatter (1σ) of slips about the mean of ±1.5 m. The coefficient of variation (CV) of single-event slip is thus 0.30. This CV is slightly less than a recently compiled global average for point measurements on strike-slip faults, suggesting that the southernmost Wellington fault has behaved in a more nearly characteristic way. We speculate that recent large earthquake ruptures have been bounded on their southern end by the Wellington fault's offshore fault termination and perhaps on their northern end by a ˜2 km wide releasing step over. Such persistent sources of rupture arrest might have led to a relative uniformity of rupture dimensions and slip amounts. We infer a late Holocene dextral slip rate of ≥4.5 ± 0.4 mm/yr (1σ) and <8.2 mm/yr, and a mean earthquake recurrence interval of ˜610-1100 years.

  3. Dextral Strike-Slip Faulting Along the Early Permian Margin of Pangaea (Eastern Australia) and Implications for Oroclinal Bending

    NASA Astrophysics Data System (ADS)

    Rosenbaum, G.; Uysal, I. T.; Babaahmadi, A.

    2014-12-01

    The breakup of the Pangaean supercontinent was one of the most significant events that affected Phanerozoic global tectonics. Heralding this process, and following the Carboniferous maximum stage of continental assembly, was a period in which the southern part of Pangaea (Gondwana) was subjected to a counterclockwise rotation relative to Laurasia. According to tectonic reconstructions, dextral wrench faulting and oroclinal bending in Varsican Europe and eastern Gondwana accompanied this rotation, but direct evidence for dextral strike-slip faulting in the eastern Gondwanan margin has hitherto not been reported. Here we show evidence from a well-preserved fault zone in eastern Australia (Red Rock fault zone), which occurs along the eastern limb of the Z-shaped Texas/Coffs Harbour orocline. Structural observations show evidence for dextral strike-slip faulting, with a reverse kinematic component, along a sub-vertical fault plane oriented NNE-SSW. Direct geochronological data (Rb-Sr and Ar-Ar) from fault gouge samples associated with this fault zone indicate that brittle faulting occurred in the early-mid Permian (288-264 Ma). In addition, oxygen and hydrogen stable isotope geochemistry indicates that the origin of fluids that circulated in the fault zone was associated with a deep crustal source. These results are consistent with independent constraints on the timing of oroclinal bending, supporting the idea that dextral wrench faulting has directly contributed to the formation of the oroclines. We propose a kinematic model for the formation of the oroclines, attributing the early stage of oroclinal bending to subduction rollback and slab segmentation (at ~300-288 Ma) followed by a period of dextral wrench faulting at 288-264 Ma. In the context of Pangaea, our model suggests that the origin of oroclines along the rim of Gondwana was likely associated with bending in response to migrating plate boundaries, and a subsequent tightening of pre-existing curvatures by

  4. 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

    segmentation of macro-dyke complexes or the activation of major shear zones with strike-slip movements. Oblique rifting and strike-slip deformation along the East Greenland margin reflect the progressive clockwise shift, from W-E to NW-SE, of the separation trend between Greenland and Europe probably in response to the opening of the Labrador Sea.

  5. 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.

  6. Interplay of thrust, back-thrust, strike-slip and salt tectonics in a fold and thrust belt system: an example from Zakynthos Island, Greece

    NASA Astrophysics Data System (ADS)

    Zelilidis, A.; Papatheodorou, G.; Maravelis, A. G.; Christodoulou, D.; Tserolas, P.; Fakiris, E.; Dimas, X.; Georgiou, N.; Ferentinos, G.

    2016-01-01

    The southwestern flank of the Hellenic fold and thrust belt, situated along the southern edge of the Dinarides-Albanides-Hellenides continental convergent zone, was examined for reconstructing the tectonic deformation. This investigation presents an integrated study of onshore sedimentological and structural analyses, as well as offshore seismic lines, across the Pliocene-Pleistocene sedimentary succession in Zakynthos Island. Back-thrust faults, using the Triassic evaporites as decollement surface, during the Pliocene, and coeval diapiric intrusions formed three sub-basins on the hangingwall of the Kalamaki back-thrust fault. This interaction is responsible for the growth of the Skopos Mountain and the soft sediment deformation that formed synclines and slumps, respectively. Back-thrust and strike-slip faults were active during the early Pleistocene, and diapiric intrusions modified the bathymetry on the sea floor, giving rise to slumps and recumbent folds. At least five events of synsedimentary diapiric intrusions have been recognized and are marked by five slump horizons. During the Holocene, the diapiric intrusions between the Kalamaki back-thrust and the Vrachionas anticline could be either related to normal faults or gravitationally driven.

  7. 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.

  8. Surface deformation due to a strike-slip fault in an elastic gravitational layer overlying a viscoelastic gravitational half-space

    SciTech Connect

    Yu, T.T.; Rundle, J.B.; Fernandez, J.

    1996-02-10

    This report discusses crustal surface displacements following a dipping strike-slip faulting using a green function model. The solutions for the elastic-gravitational problem are computed also. A comparison between calculated results and the global positioning system measurement of the Landers earthquake is made.

  9. Links between long-term and short-term rheology of the lithosphere: insights from strike-slip fault modelling

    NASA Astrophysics Data System (ADS)

    Le Pourhiet, Laetitia

    2014-05-01

    The study of geodetic data across strike-slip fault zones is believed to play a key role in our understanding of the lithosphere mechanical behaviour. InSAR and GPS measurements permits to determine more and more accurately both large and rapid co-seismic displacements and the slower deformation associated with the inter-seismic and post-seismic phases of the earthquake cycle on continents. However, no modern geodetic observation spans a complete earthquake cycle for any single fault in the world. Understanding this time variability through modelling is therefore crucial to reconstruct a global pattern. It is non trivial to compare the effective parameters retrieved from the different simple models are used to extract effective parameters from the geodetic data. Using the popular visco-elastic relaxation model reaches two paradoxes: - the lower crust must be very strong in order to fit the data long after the earthquake and very weak to fit the data during the early post-seismic period. - the retrieved a mantle lithosphere viscosity is as weak as 10^17 - 10^20 Pa.s and differ significantly from those deduced from post glacial rebound models and long term geodynamic models requirements in order to generate self consistent plate tectonics. Rather than assuming that the rheology of the lithosphere changes with time scale, it would be preferable to go on quest for an Earth's lithosphere rheological model based on some simple physics, which would be equally valid at all time scale from inter-seismic to orogeny. 3D models of long term strain localisation in wrenching context show that localisation of strain across strike slip faults modifies locally the rheological architecture of the lithosphere and lead to some sort of structural weakening. That weakening occurs because as strain localises the "jelly sandwich" type lithosphere evolves self-consistently into a "banana split" type rheological structure. This strain localisation process is very efficient when the lower

  10. 2D Seismic interpretation of strike-slip faulting, salt tectonics, and Cretaceous unconformities, Atlas Mountains, central Tunisia

    NASA Astrophysics Data System (ADS)

    Zouaghi, Taher; Bédir, Mourad; Inoubli, Mohamed Hédi

    2005-11-01

    The Cretaceous deposits in central Tunisia blocks were studied by sequence stratigraphy, 2D seismic interpretation calibrated to the well and associated outcrop data. The constructing and comparing histories of the northern and southern blocks of the Gafsa master fault was the establishment of platform to basin stratigraphic configuration based on the major unconformity surfaces. Three important basin zones mark subsurface structures: Gafsa to the south, Souinia-Majoura to the northeast and Sidi Aïch-Mèjel Bel Abbès to the northwest. Basin depocenters and upthrown blocks are bounded by the N120° Gafsa and Majoura and N180° Sidi Ali Ben Aoun wrench fault salt-intruded tectonic corridors and subdivided by the associated N60° and N90° trending second-order fault corridors. The Mèjel Bel Abbès block is characterized by brittle structures associated with a deep asymmetric geometry that is organized into depressions and uplifts. Halokinesis of Triassic salt began in the Jurassic and continued during the Cretaceous periods. During extensional deformations, salt movement controlled sedimentation distribution and location of pre-compressional structures. During compressional deformations, salt remobilization accentuated the folded uplifts. The Triassic salt facies constitutes a level of decollement at the base of the Mesozoic deposits during the later displacements. The coeval dextral strike-slip motion along the three northwest-southeast bounding master faults (Gafsa, Sehib-Alima and Majoura-Mech) suggests a pull-apart opening of the Gafsa basin. Synchronous movements of the Gafsa first-order dextral strike-slip fault with the Sidi Ali Ben Aoun sinistral wrench fault caused formation of tectonic obstacles that are shown first by the sealed structures, then by development of the local compressive stress that caused formation of the south overturned folds and the syncline depressions. The transcurrent fault systems caused formation of Turonian and Senonian

  11. Lidar reveals paleoseismic sites and recent strike-slip and thrust faulting along the central Alpine Fault, New Zealand

    NASA Astrophysics Data System (ADS)

    De Pascale, G. P.; Langridge, R. M.; Davies, T. R.

    2013-12-01

    In the South Island of New Zealand, the dextral-reverse Alpine fault forms the major plate boundary structure between the Pacific and Australian plates and is thought to fail in large to great earthquakes approximately every 100 to 400 years, with the most recent major surface rupture event occurring in 1717 AD. We used a recently collected lidar dataset to evaluate the central section of the fault to both measure recent slip along the fault, recent co-seismic uplift, and to find new paleoseismic sites. The new high-resolution topography in the dense temperate rainforest allowed insight into the fault that was previously unavailable. Lidar mapping, combined with field mapping facilitated the discovery of a multi-event thrust fault scarp of the Alpine Fault that was later trenched at Gaunt Creek. C-14 dating of units in the trench and mapping there, show that the last earthquake was probably the 1717 event. Along the length of the lidar survey, small (< 25 m) dextral offsets were also mapped along the fault, which were rated for quality, and then visited in the field. The lidar itself was a guide to locate these offsets, and the offset measurements in the field have lower uncertainties than the lidar resolution; dextral slip in the 1717 earthquake here was c. 7 m × 1 m. Additional sites with evidence for cumulative slip were also mapped in the field which showing repetitive slip of ~ 7 to 8 m per event for the past three surface ruptures on the fault. Sag ponds discovered during field mapping are important new targets for investigation and will likely yield slip-rate information here for the correlation of slip with events. Additional field mapping near the Whataroa River and Mint Creek demonstrates that between debris flow fans that cross the Alpine Fault at the rangefront of the Southern Alps, preservation of strike-slip scarps is rare due to post-earthquake deposition and erosion. However, one likely scarp was found in a post-earthquake aggradation surface

  12. Progressive Development of Riedel-Shear on Overburden Soil by Strike-Slip Faulting: Insights from Analogue Model

    NASA Astrophysics Data System (ADS)

    Chan, Pei-Chen; Wong, Pei-Syuan; Lin, Ming-Lang

    2015-04-01

    According to the investigations of well-known disastrous earthquakes in recent years, ground deformation (ground strain and surface rupture) induced by faulting is one of the causes for engineering structure damages in addition to strong ground motion. However, development and propagation of shear zone were effect of increasing amounts of basal slip faulting. Therefore, mechanisms of near ground deformation due to faulting, and its effect on engineering structures within the influenced zone are worthy of further study. In strike-slip faults model, type of rupture propagation and width of shear zone (W) are primary affecting by material properties (M) and depth (H) of overburden layer, distances of fault slip (Sy) (Lin, A., and Nishikawa, M.,2011, Narges K. et al, 2014). There are few research on trace of development and propagation of trace tip, trace length, and rupture spacing. In this research, we used sandbox model to study the progressive development of riedel-shear on overburden soil by strike-slip faulting. The model can be used to investigate the control factors of the deformation characteristics (such as the evolution of surface rupture). To understand the deformation characteristics (including development and propagation of trace tip(Tt), trace length(Tl), rupture spacing(Ts)) during the early stages of deformation by faulting. We found that an increase in fault slip Sy could result in a greater W, trace length, rupture density and proposed a Tl/H versus Sy/H relationship. Progressive development of riedel-shear showed a similar trend as in the literature that the increase of fault slip resulted in the reduction of Ts, however, the increasing trend became opposite after a peak value of W was reached. The above approaches benefit us in enhancing our understanding on how propagation of fault-tip affects the width of deformation zone near the ground of the soil/rock mass, the spatial distribution of strain and stress within the influenced zone, and the

  13. 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

  14. 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

  15. Stress fields recorded on large-scale strike-slip fault systems: Effects on the tectonic evolution of crustal slivers during oblique subduction

    NASA Astrophysics Data System (ADS)

    Veloso, Eugenio E.; Gomila, Rodrigo; Cembrano, José; González, Rodrigo; Jensen, Erik; Arancibia, Gloria

    2015-11-01

    In continental margins, large-scale, strike-slip fault-systems resulted from oblique subduction commonly exhibit a complex pattern of faulting where major faults define the inland boundary of tectonic slivers that can be detached from the margin. In turn, subsidiary faults bound and define internal tectonic blocks within the sliver which are expected to rotate, translate and/or internally disrupt in order to accommodate the internal deformation. The geometrical and spatial arrangement of faults and tectonic blocks thus determines the evolution of the sliver given a particular stress field regime. The Paposo segment of the Atacama Fault System in northern Chile displays a series of brittle faults whose orientations are hierarchically arranged: low-order faults splay off higher-order faults forming Riedel-type and strike-slip duplexes geometries at several scales. The master (1st- and highest-order) Paposo Fault defines the inland boundary of a tectonic sliver whereas subsidiary faults bound and disrupt internal tectonic blocks. By using newly collected brittle fault-slip data we estimated the orientations and regimes of the stress fields that acted upon the entire sliver, the different fault-orders and the tectonic blocks. Results indicate that an overall transtensional - with NW-compressional and NE-tensional principal axes - strike-slip regime affected the sliver and triggered the development of left-lateral strike-slip structures. An incomplete split of the stress field imposed by the subduction process resulted in the generation of a nested pattern of R-type faults as well as in a combined strike-slip/normal faulting disruption of the tectonic blocks within the sliver.

  16. The block structure and Quaternary strike-slip block rotation of central Japan

    NASA Astrophysics Data System (ADS)

    Kanaori, Yuji; Kawakami, Shin-Ichi; Yairi, Kenji

    1992-02-01

    Central Japan is situated on the inflection point of the bow-shaped Japanese islands. Numerous NW-SE trending active faults, arranged in parallel at intervals of 20 to 80 km are found in this area. These active faults are more than 30 km long with shattered zones from 30 to 300 m wide. Several active faults constitute a given block boundary, which serves as the dividing line for one of the four blocks that make up central Japan. The block boundaries require careful study since numerous historical earth-quakes have occurred along these lines. Offset measurements of basement rocks, created during the Quaternary period due to left-lateral faulting, amount to 1 to 7 km. Gravity lineaments, which link points of sudden change and saddles of Bouguer anomalies, are clearly found along the block boundaries. The NW-SE trending active faults appearing on the ground surface are associated with motions of the block boundaries. Block rotational movement, caused by left-lateral faulting, plays an important role in the crustal deformation of central Japan. Rotational angles of the blocks calculated from the amount of displacement of basement rocks, initiated during the Quaternary period, are estimated to be 3° to 7° in a clockwise manner.

  17. Formation of flower structures in a geological layer at a strike-slip displacement in the basement

    NASA Astrophysics Data System (ADS)

    Stefanov, Yu. P.; Bakeev, R. A.

    2015-07-01

    Formation of dislocations in a geological layer at a strike-slip displacement in its basement is studied by three-dimensional (3D) numerical modeling. It is shown that the pattern of strain localization is determined by the initial stress state or thickness of the deformed layer as well as by the Poisson ratio and strength of the medium. Three types of fracture zones are observed. Shear bands of the first type are dominated by the propeller-like surfaces of Riedel R-shears, which merge into a single main fault with feathering structures. In the second type of dislocation zones, the primary role is played by the surfaces oriented at an angle of ˜40° to the shear axis in the horizontal projections. After reaching the free surface, these discontinuities are cut by a V-shaped fault. In this case, the pattern of dislocations most closely corresponds to the flower structures. The third type is a trough, which may accommodate the formation of yet another strain localization zone along its axial part—a vertical fault.

  18. Architectural characteristics and petrophysical properties evolution of a strike-slip fault zone in a fractured porous carbonate reservoir

    NASA Astrophysics Data System (ADS)

    Jeanne, Pierre; Guglielmi, Yves; Lamarche, Juliette; Cappa, Frédéric; Marié, Lionel

    2012-11-01

    This paper describes the structural, petrophysical and hydromechanical properties relationships between a small fault zone and the porous layered carbonate series which host it. In a gallery located at 250-m depth, the deformation of a 22-m thick section of layered carbonates-, affected by a strike slip-fault have been characterized by means of structural (Q-value), acoustic velocities (Vp), porosity and uniaxial compressive strength (σc) measurements conducted in situ at the meter scale, and on laboratory samples at the infra-centimeter scale. A clear influence of the layers initial properties on fault architecture and properties evolution is underlined. In the porous layers with a low σc, there is an important accommodation of the deformation by micro-mechanisms resulting in a progressive decrease in the porosity toward the fault core. In the low-porosity layers with a high σc, deformations are accommodated toward the fault core by: an increase in the fracture porosity, in the micro-cracks porosity, and by displacements along pre-existing fractures resulting from a joint roughness decrease. The fault zone appears as relatively stiff and low permeable zones intercalated with low stiffness and high fracture permeability zones that extend one to tens of meters from the fault following the initial properties contrasts and geometry of the sedimentary layers.

  19. 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.

  20. 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.

  1. Architecture and Segmentation of Strike-Slip Faults in Southern California

    NASA Astrophysics Data System (ADS)

    Sahakian, Valerie Jean

    This dissertation investigates the architecture and segmentation of fault structures in Southern California, using marine active-source seismic data. Onshore or marine fault geometry is often poorly constrained due to their location. This study employs marine active-source seismic data to image these structures, and further the current understanding of the hazards they pose to the region. With these data, this dissertation first improves the existing framework of knowledge of fault architecture in the Salton pull-apart basin, near the terminus of the Southern San Andreas Fault (SSAF). It investigates the evolution of the pull-apart basin in the Imperial-San Andreas fault system with reflection and refraction data, and provides important constraints regarding the interplay of faults and strain partitioning in this region. New data suggest the existence of a previously unknown fault in the Salton Sea, the Salton Trough Fault (STF). This transtensional fault is located just to the west of the eastern Salton Sea shoreline, and strikes approximately parallel to the SSAF terminus. Finally, this dissertation investigates the architecture and segmentation of the Newport-Inglewood/Rose Canyon (NIRC) fault zone offshore Southern California, using seismic data sets with unprecedented density and resolution. It identifies four main fault strands, with three main stepover boundaries, and presents possible rupture scenarios based on quantitative and qualitative assessments of throughgoing rupture at stepovers or segment boundaries.

  2. 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.

  3. Estimating Fault Slip Rates and Deformation at Complex Strike-Slip Plate Boundaries

    NASA Astrophysics Data System (ADS)

    Thatcher, Wayne; Murray-Moraleda, Jessica

    2010-05-01

    Modeling GPS velocity fields in seismically active regions worldwide indicates deformation can be efficiently and usefully described as relative motions among elastic, fault-bounded crustal blocks. These models are providing hundreds of new decadal fault slip rate estimates that can be compared with the (much smaller) independent Holocene (<10 ka) to late Quaternary (<125 ka) rates obtained by geological methods. Updated comparisons show general agreement but a subset of apparently significant outliers. Some of these outliers have been discussed previously and attributed either to a temporal change in slip rate or systematic error in one of the estimates. Here we focus particularly on recent GPS and geologic results from southern California and discuss criteria for assessing the differing rates. In southern California (and elsewhere), subjective choices of block geometry are unavoidable and introduce significant uncertainties in model formulation and in the resultant GPS fault slip rate estimates. To facilitate comparison between GPS and geologic results in southern California we use the SCEC Community Fault Model (CFM) and geologic slip rates tabulated in the 2008 Uniform California Earthquake Rupture Forecast (UCERF2) report as starting points for identifying the most important faults and specifying the block geometry. We then apply this geometry in an inversion of the SCEC Crustal Motion Model (CMM4) GPS velocity field to estimate block motions and intra-block fault slip rates and compare our results with previous work. Here we use 4 criteria to evaluate GPS/geologic slip rate differences. First: Is there even-handed evaluation of random and systematic errors? ‘Random error' is sometimes subjectively estimated and its statistical properties are unknown or idealized. Differences between ~equally likely block models introduces a systematic error into GPS rate estimates that is difficult to assess and seldom discussed. Difficulties in constraining the true

  4. Tectonics, magmatism and fluid flow in a transtensional strike-slip setting: The northern termination of the Liquiñe-Ofqui fault System, Chile

    NASA Astrophysics Data System (ADS)

    Cembrano, J. M.; Perez-Flores, P.; Sánchez, P.; Sielfeld, G.

    2013-12-01

    vein systems, which appear to be associated with dextral strike-slip displacement on the LOFS. Fault-vein and vein structure varies from mineral fibers to typical ridge-and-groove striae. Bladed calcite occurs in dilational jogs along the main LOFS master faults; they are interpreted to represent boiling episodes. Thicker and more pervasive WNW sinistral-reverse fault-vein systems and breccias bodies suggest that the fault-valve mechanism was active during fluid transport and mineral precipitation. In some sites the WNW-striking system cuts and displaces the active LOFS, suggesting that their active has extended to at least the Pleistocene. Internally consistent structural and kinematic data from fault-fracture systems spatially and temporally associated with volcanoes and hydrothermal systems suggest that the same processes that drive the interplay between volcanism and tectonics may also control the nature, geometry and composition of geothermal reservoirs in the southern Andes.

  5. 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

  6. 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. . Geology Dept.)

    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 deformed 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).

  7. Tectonic burial and exhumation cycles tracked by muscovite and K-feldspar 40Ar/39Ar thermochronology in a strike-slip fault zone, central Turkey

    NASA Astrophysics Data System (ADS)

    Idleman, Lauren; Cosca, Michael A.; Heizler, Matthew T.; Thomson, Stuart N.; Teyssier, Christian; Whitney, Donna L.

    2014-02-01

    Muscovite and K-feldspar 40Ar/39Ar ages from the eastern margin of the Niğde massif in central Anatolia track the timing of initial exhumation, reburial, and final exhumation and cooling of metamorphic rocks deformed within a strike-slip fault zone. Although the ages of initial and final cooling were known from previous studies, our new results document the timing of the reheating/reburial event. Muscovite from four of eight gneiss samples have Late Cretaceous 40Ar/39Ar ages that date initial cooling at ~ 75 Ma. The remaining samples have perturbed spectra that climb to Late Cretaceous ages with increasing extraction temperatures during analysis. These perturbed samples are located beneath a faulted unconformity overlain by Paleogene sedimentary deposits that were derived in part from the metamorphic rocks, then buried, metamorphosed, and deformed under greenschist facies conditions. Samples close to the faulted unconformity are more perturbed than structurally deeper samples. The age of the thermal perturbation is determined at 30 ± 5 Ma using multi-diffusion domain modeling of K-feldspar 40Ar/39Ar data from two gneiss samples, one located close to the unconformity and one at a structurally deeper level. Muscovite 40Ar/39Ar results and modeled K-feldspar temperature-time histories show that the eastern margin of the Niğde massif experienced a reheating event that peaked at ~ 30 Ma. The thermal pulse has been attributed to reburial associated with transpression in the Ecemiş segment of the Central Anatolian Fault Zone along the eastern margin of the Niğde massif. Activity of this fault zone may represent a far-field expression of the onset of collision of Arabia with Eurasia in SE Anatolia.

  8. Kinematics of the Tengchong Terrane in SE Tibet from the late Eocene to early Miocene: Insights from coeval mid-crustal detachments and strike-slip shear zones

    NASA Astrophysics Data System (ADS)

    Xu, Zhiqin; Wang, Qin; Cai, Zhihui; Dong, Hanwen; Li, Huaqi; Chen, Xijie; Duan, Xiangdong; Cao, Hui; Li, Jing; Burg, Jean-Pierre

    2015-12-01

    It is generally believed that the extrusion of SE Tibet was bounded by the dextral Gaoligong and the sinistral Ailaoshan-Red River strike-slip shear zones from the Oligocene to early Miocene. This study integrates field mapping, structural analysis and geochronology in western Yunnan (China), where foliated Precambrian basement rocks and late Cretaceous to early Eocene plutons are exposed to the west of the Gaoligong shear zone. We found that late Eocene to early Miocene flat-lying ductile shear zones were kinematically related to steeply dipping strike-slip shear zones. Four elongated gneiss domes (Donghe, Guyong, Yingjiang and Sudian) are cored by high-grade metamorphic rocks and pre-kinematic granite plutons, and bounded by top-to-NE detachments and NE-trending dextral strike-slip shear zones. Zircon U-Pb ages from LA-ICP-MS analysis and 40Ar/39Ar ages of micas and hornblende demonstrate that the flat-lying Donghe Detachment (> 35-15 Ma) and the Nabang dextral strike-slip shear zone (41-19 Ma) were sites of prolonged, mostly coeval ductile deformation from amphibolite to greenschist facies metamorphism. The Gaoligong shear zone experienced dextral shearing under similar metamorphic conditions between 32 and 10 Ma. Consistent 40Ar/39Ar ages of hornblende from the three shear zones indicate their contemporaneity at mid-crustal depth, causing the rapid exhumation and SW-ward extrusion of the Tengchong Terrane. The strain geometry and shear zone kinematics in the Tengchong Terrane are interpreted with folding of the anisotropic lithosphere around a vertical axis, i.e., the northeast corner of the Indian Plate since 41 Ma. The newly discovered NE-trending Sudian, Yingjiang, and Lianghe strike-slip shear zones are subordinate ductile faults accommodating the initially rapid clockwise rotation of the Tengchong Terrane. The detachments caused mid-crustal decoupling and faster SW-ward extrusion below the sedimentary cover, whereas the strike-slip shear zones accommodated

  9. 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-slip

  10. Heterogeneity within a deep crustal strike-slip shear zone with implications for lower crustal flow, Athabasca granulite terrane, western Canadian Shield

    NASA Astrophysics Data System (ADS)

    Leslie, S. R.; Mahan, K. H.; Regan, S.; Williams, M. L.

    2011-12-01

    Deep crustal strike-slip shear zones play a fundamental role in lower crustal flow. Although commonly modeled in two-dimensions, regional considerations suggest that large-scale crustal flow is a heterogeneous, three-dimensional process. The Athabasca granulite terrane, western Canadian Shield, exposes a large region of high-pressure tectonite (>20,000 km2) that provides a natural example of ancient lower crustal flow and an analog for similar processes active today in other regions. Regional heterogeneous deformation permits preservation of Neoarchean deformation fabrics and metamorphic textures. The Cora Lake shear zone (CLsz) is a NW-dipping km-scale mylonite to ultramylonite zone that forms a discrete tectonic discontinuity between two rheologically distinct Neoarchean lower-crustal domains. Northwest of the CLsz, the domain is primarily underlain by ~2.6 Ga felsic to mafic metaplutonic gneisses and interlayered ~2.55 Ga felsic granulite. Lithologies here preserve Neoarchean granulite-facies metamorphism coupled with partial melting and synkinematic melt-enhanced ESE-directed subhorizontal flow at ~0.9 GPa (~30 km paleodepths). Southeast of the CLsz, the Chipman domain is underlain by ~3.2 Ga metatonalite gneiss, an extensive ~1.9 Ga mafic dike swarm, and generally minor ~2.55 Ga mafic and felsic granulite. In contrast to the northwest, lithologies of the western Chipman domain document higher pressures at ~1.3 GPa (~40 km paleodepths) synchronous with development of a gently dipping Neoarchean gneissic fabric. Strong, anhydrous Chipman domain lithologies and melt-weakened lithologies to the northwest are juxtaposed by sinistral to sinistral-normal oblique shear along the CLsz, consistent with higher pressures (deeper paleodepths) documented in the footwall Chipman domain. A notable and pervasive feature along strike of the CLsz in the western Chipman domain is the marked increase in abundance of m-scale layers of mafic and felsic granulite westward with

  11. Precursory surface deformation expected from a strike-slip fault model into which rheological properties of the lithosphere are incorporated

    NASA Astrophysics Data System (ADS)

    Yamashita, Teruo; Ohnaka, Mitiyasu

    1992-09-01

    Yamashita, T. and Ohnaka, M., 1992. Precursory surface deformation expected from a strike-slip fault model into which rheological properties of the lithosphere are incorporated. In: T. Mikumo, K. Aki, M. Ohnaka, L.J. Ruff and P.K.P. Spudich (Editors), Earthquake Source Physics and Earthquake Precursors. Tectonophysics, 211: 179-199. Earthquake prediction is one of the important problems with which seismologists are confronted. Much observational effort has been made to detect precursory surface deformation before earthquake occurrence. However, the physical mechanism to generate such precursory deformation is not fully understood. We, in this paper, theoretically study the growth process of strike-slip fault from nucleation to instability and a possibility to detect precursory surface deformation. Analyses are made on the basis of a breakdown zone crack model, which has been successfully applied in many aspects of earthquake rupture. We specifically attempt to simulate earthquake occurrence at the San Andreas fault, California, taking account of geological and geophysical conditions there. The most important parameters of the breakdown zone crack model will be the peak shear stress σ p near the crack tip, the sliding frictional stress σ f, and the critical slip displacement Dc. For the depth variation of these parameters we assume a three-layer model, which is composed of a brittle upper layer, a plastic lower layer and an intervening semibrittle layer. We model the depth variations of σ p and σ f, modifying the shear resistance profile appropriate for the San Andreas fault obtained by Sibson. The depth distribution of Dc is assumed to be constant D0 in the brittle layer and to increase exponentially with depth in the semibrittle and plastic layers on the basis of the study of Ohnaka; the depth distribution of Dc is described by two parameters, D0 and S, the latter standing for the increase rate of Dc in the lower two layers. Since there appears to exist much

  12. Contrasting strike-slip motions on thrust and normal faults: Implications for space-geodetic monitoring of surface deformation

    NASA Astrophysics Data System (ADS)

    Hampel, Andrea; Li, Tao; Maniatis, Georgios

    2013-04-01

    Recent GPS records of surface deformation caused by earthquakes on intra-continental dip-slip faults revealed in unprecedented detail a significant strike-slip component near the fault tips, which is markedly different for thrust and normal faults. In the hanging wall of the thrust fault ruptured during the 2003 Chengkung (Taiwan) earthquake, a divergent displacement pattern was recorded (Hsu et al., 2009). In contrast, a convergent slip pattern was observed in the hanging wall of the normal fault that produced the 2009 L'Aquila (Italy) earthquake (Cheloni et al., 2010; Serpelloni et al., 2012). Remarkably, such convergent slip patterns are also evident in field records of cumulative fault slip (e.g., Jackson et al., 1982; Roberts & Koukouvelas 1996), which underlines the coseismic origin of the cumulative slip pattern. Here we use three-dimensional numerical modeling to demonstrate that the observed fault-parallel motions are a characteristic feature of the coseismic slip pattern on normal and thrust faults (Hampel et al., in press). Modeled slip vectors converge toward the center of normal faults whereas they diverge for thrust faults, which causes contrasting fault-parallel displacements at the model surface. Our model also predicts divergent movements in normal fault footwalls, which were recorded for the first time during the L'Aquila earthquake. During the postseismic phase, viscous flow in the lower crust induces fault-parallel surface displacements, which have the same direction as the coseismic displacements but are distributed over a larger area that extends far beyond the fault tips. Hence, detecting this signal requires GPS stations in the prolongation of the fault's strike. Postseismic velocities vary over several orders of magnitude depending on the lower-crustal viscosity and may reach tens of millimeters per year for low viscosities. Our study establishes the link between coseismic and cumulative slip patterns on normal and thrust faults and

  13. Sedimentologic evidence for structural and topographic evolution following the onset of strike slip, E San Francisco Bay area, CA

    SciTech Connect

    Buising, A.V. )

    1992-01-01

    Mid- to Upper Miocene continental (Orinda and Mulholland Fms.) and shallow marine (Neroly Fm.) strata in the Upper San Leandro Reservoir watershed (SLR) area east of San Francisco Bay preserve important information on structural and landscape evolution during the early phases of strike slip along the Pacific-North American plate boundary. The SLR area lies between the Hayward and Calaveras Faults, major strands of the San Andreas Fault system, and is bisected by the NW-striking Cull Creek Fault (CCF). Geologic mapping delineates five completely intercalated lithofacies in the Mulholland Fm. at SLR. The conglomerate-dominated, sandstone-dominated, and interbedded conglomerate, sandstone, and siltstone facies represent fluvial channel and floodplain deposits; the sandstone + mudstone facies represent lacustrine-deltaic and shallow lacustrine deposits; the shale facies records open lacustrine deposition. Sparse unidirectional paleocurrent indicators show southerly and easterly transport west of the CCF and both westerly and easterly transport east of the CCF. Conglomerate-rich and sand-rich facies tracts are juxtaposed along the CCF. Clast assemblages in Mulholland conglomerates include abundant chart, graywacke, blueschist, and vein quartz, suggesting derivation from a Franciscan-dominated source terrane. Clast assemblages in the gradationally underlying and interfingering Neroly Fm. suggest that it shared the same source terrane; this is atypical for the primarily andesitic (Sierra-derived) Neroly. Fluvial deposits are volumetrically dominant in the Mulholland Fm. at SLR; open-lacustrine shales occur in stratigraphically isolated lenses ranging from > 1 km to < 100 m along strike. This suggests numerous small lakes on a broad drainage plain rather than the single large lake envisioned by previous workers.

  14. Photogeologic and kinematic analysis of lineaments at Yucca Mountain, Nevada: Implications for strike-slip faulting and oroclinal bending

    SciTech Connect

    O`Neill, J.M.; Whitney, J.W.; Hudson, M.R.

    1992-12-31

    The main structural grain at Yucca Mountain, as seen from aerial photographs, is a pronounced north-trending linear fabric defined by parallel east-tilted fault-block ridges. The ridges are bounded on the west by normal faults that are easily recognizable on aerial photographs, mainly as isolated, colinear scarps in alluvium and as offset bedrock units. AH ridge-bounding to adjacent faults, most commonly by short northwest-trending fault splays. The generally north-trending high-angle faults primarily display down-to-the-west normal offset, but also have an auxiliary component of left-lateral slip. Left-lateral slip is indicated by offset stream channels, slickenlines, and en echelon fault splays that are structurally linked, commonly by pull-apart grabens. These grabens, best seen on low-sun angle aerial photographs, rangefrom tens of meters to more than 3 kilometers wide. The smallest pull-apart zones are well developed along the Windy Wash and Solitario Canyon faults on the west side of Yucca Mountain; the largest of these features is interpreted to structurally link the Bow Ridge and Solitario Canyon faults in the north-central part of Yucca Mountain; the pronounced northwest-trending drainage system in this part of Yucca Mountain appears to be controlled by tension fractures related to left-lateral strike-slip movement on these north-trending faults. Midway Valley, directly east of this pull-apart graben, may also owe its origin, in part, to a pull-apart mechanism.

  15. 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.

  16. An old question revisited: the mechanics of shallow creep events on strike-slip faults and their triggering by nearby earthquakes

    NASA Astrophysics Data System (ADS)

    Wei, M.; Liu, Y.; McGuire, J. J.

    2012-12-01

    Tectonic displacement on faults can occur as seismic slip, continuous aseismic creep, or transient creep events. Shallow creep events on strike-slip faults can take place in a coupled process with earthquake afterslip, spontaneously, or be triggered by nearby earthquakes. Despite more than five decades of observations, the mechanics of shallow creep events and their implications for seismic hazard are still not fully understood. To understand the mechanics and triggering of creep events, we developed a physics-based model to simulate shallow creep events on a strike-slip fault with rate-and-state frictional properties that vary both in depth and along strike. Our 1D simulation shows that a simple 2-layer model as proposed by Bilham and Behr [1992] cannot explain both the rapid afterslip and shallow creep events that were observed on the Superstition Hills Fault following the 1987 earthquake. Therefore, we propose a 3-layer model that can reproduce all the known surface deformation observations, including the co-seismic slip, afterslip, and the creep events. Using the strike-slip fault model, we also study the triggering process of creep events, by a static, a dynamic or a combined stress perturbation induced on the fault by a nearby earthquake. Preliminary results show that the magnitude of the perturbation relative to the ambient stress level and the timing of perturbation are the important parameters. By developing state-of-the-art models and constraining parameters with rich datasets from the Salton Trough, we aim to transition from a conceptual understanding of fault creep towards a quantitative and predictive understanding of the physical mechanism of creep events on strike-slip faults.

  17. 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

  18. The Deese and Collings ranch conglomerates of the Arbuckle Mountains, Oklahoma: Evidence of strike-slip movement during the deformation stage of the southern Oklahoma Aulacogen

    SciTech Connect

    Cemen, I.; Pybas, K.; Stafford, C.; Al-Shaieb, Z. . School of Geology)

    1993-02-01

    It has been widely recognized that the Pennsylvanian conglomerates of the Arbuckle Mountains, Oklahoma, record the deformation stage of the Southern Oklahoma Aulacogen. Two of these units are the Desmoinesian Deese Conglomerate, exposed in the Mill Creek Syncline area between the Reagan and Mill Creek fault zones, and the Middle Virgilian Collings Ranch Conglomerate, exposed along the Washita Valley fault zone in the Turner Falls area. The authors investigated clast size, geometry, and content, primary sedimentary structures, petrography, petrology, and diagenesis of the two conglomerate units, as well as the geometric relationship of their basins with nearby faults. Their evidence suggests that the two conglomerates were deposited as alluvial fans in basins formed by strike-slip movements. The Collings Ranch Conglomerate was deposited in a basin formed as the result of left-stepping along the nearby Washita Valley strike-slip fault zone. The Deese Conglomerate was deposited in a basin formed due to the combined effect of strike-slip and dip-slip movements along the Reagan and Mill Creek fault zones. In the Collings Ranch basin, the deposition was accomplished primarily by channel-fill and sieve deposits in the proximal region of the fan. The Deese Conglomerate was deposited as an alluvial fan or fans which included several channel deposits while, in the deeper parts of the basin, fine-grained materials and limestones were deposited. These observations and their possible interpretations suggest that the Washita Valley, Mill Creek, and Reagan fault zones have experienced substantial strike-slip movement during the deformation stage of the Southern Oklahoma Aulacogen.

  19. The role of thrust faulting in the formation of the eastern Alaska Range: Thermochronological constraints from the Susitna Glacier Thrust Fault region of the intracontinental strike-slip Denali Fault system

    NASA Astrophysics Data System (ADS)

    Riccio, Steven J.; Fitzgerald, Paul G.; Benowitz, Jeff A.; Roeske, Sarah M.

    2014-11-01

    Horizontal-slip along restraining bends of strike-slip faults is often partitioned into a vertical component via splay faults. The active Susitna Glacier Thrust Fault (SGTF), as shown by its initiation of the 2002 M7.9 Denali Fault earthquake, lies south of, and intersects the dextral strike-slip Denali Fault. Geochronology and thermochronology data from samples across the SGTF constrain the region's tectonic history and the role of thrusting in the formation of the eastern Alaska Range south of the Denali fault. U-Pb zircon ages indicate intrusion of plutons in the footwall (~57 Ma) and hanging wall (~98 Ma). These U-Pb zircon ages correlate to those from the Ruby Batholith/Kluane Terrane ~400 km east along the Denali Fault, supporting geologic correlations and hence constraints on long-term slip rates. 40Ar/39Ar mica and K-feldspar data from footwall and hanging wall samples (~54 to ~46 Ma) reflect cooling following magmatism and/or regional Eocene metamorphism related to ridge subduction. Combined with apatite fission track data (ages 43-28 Ma) and thermal models, both sides of the SGTF acted as a coherent block during the Eocene and early Oligocene. Contrasting apatite (U-Th)/He ages across the Susitna Glacier (~25 Ma footwall, ~15 Ma hanging wall) suggest initiation of faulting during the middle Miocene. Episodic cooling and exhumation is related to thrusting on known or hypothesized faults that progressively activate due to varying partition of strain along the Denali Fault associated with changing kinematics and plate interaction (Yakutat microplate collision, flat-slab subduction and relative plate motion change) at the southern Alaskan plate margin.

  20. Kane Basin, Nares-Strait: Strike-slip induced sediment deformation along the coastline of Ellesmere Island

    NASA Astrophysics Data System (ADS)

    Ehrhardt, A.; Schnabel, M.; Damm, V.

    2015-12-01

    fault pattern, a pull-apart development of the Kane Basin can't be supported. However, the steepening of the sedimentary beds towards Ellesmere Island and anticlinal deformation parallel to the NS point to the presence of a strike-slip fault that runs parallel to the Ellesmere Island coastline.

  1. 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

  2. Fault valve action and vein development during strike slip faulting: An example from the Ribeira Shear Zone, Southeastern Brazil

    NASA Astrophysics Data System (ADS)

    Faleiros, Frederico Meira; Campanha, Ginaldo Ademar da Cruz; Bello, Rosa Maria da Silveira; Fuzikawa, Kazuo

    2007-06-01

    Fluid inclusion microthermometry and structural data are presented for quartz vein systems of a major dextral transcurrent shear zone of Neoproterozoic-Cambrian age in the Ribeira River Valley area, southeastern Brazil. Geometric and microstructural constraints indicate that foliation-parallel and extensional veins were formed during dextral strike-slip faulting. Both vein systems are formed essentially by quartz and lesser contents of sulfides and carbonates, and were crystallized in the presence of CO 2-CH 4 and H 2O-CO 2-CH 4-NaCl immiscible fluids following unmixing from a homogeneous parental fluid. Contrasting fluid entrapment conditions indicate that the two vein systems were formed in different structural levels. Foliation-parallel veins were precipitated beneath the seismogenic zone under pressure fluctuating from moderately sublithostatic to moderately subhydrostatic values (319-397 °C and 47-215 MPa), which is compatible with predicted fluid pressure cycle curves derived from fault-valve action. Growth of extensional veins occurred in shallower structural levels, under pressure fluctuating from near hydrostatic to moderately subhydrostatic values (207-218 °C and 18-74 MPa), which indicate that precipitation occurred within the near surface hydrostatically pressured seismogenic zone. Fluid immiscibility and precipitation of quartz in foliation-parallel veins resulted from fluid pressure drop immediately after earthquake rupture. Fluid immiscibility following a local pressure drop during extensional veining occurred in pre-seismic stages in response to the development of fracture porosity in the dilatant zone. Late stages of fluid circulation within the fault zone are represented dominantly by low to high salinity (0.2 to 44 wt.% equivalent NaCl) H 2O-NaCl-CaCl 2 fluid inclusions trapped in healed fractures mainly in foliation-parallel veins, which also exhibit subordinate H 2O-NaCl-CaCl 2, CO 2-(CH 4) and H 2O-CO 2-(CH 4)-NaCl fluid inclusions trapped

  3. Modelling the interplay between magmatic intrusions and strike-slip faults: application to Miyakejima (Japan) and Mt. Etna (Italy)

    NASA Astrophysics Data System (ADS)

    Maccaferri, Francesco; Rivalta, Eleonora; Aoki, Yosuke

    2014-05-01

    Magma is often transported in the brittle crust by means of diking, which are magma-filled lenses propagating by fracturing rock at their tip and pinching themselves closed at their back. One of the main unanswered question revolving around diking is how dikes are arrested. Several mechanisms have been suggested that may concur in stopping a dike: magma freezing; magma volume loss in the dike tail; dikes reaching a level of buoyancy inversion; stress heterogeneities exerting compression around the propagating tip; structural discontinuities such as layering, or co-diking slip on pre-existing fractures or faults. The interaction of dikes with faults and fractures has been investigated through crustal deformation and seismic studies, theoretically, numerically and experimentally. Most of studies assume static dikes, that generate seismicity or react to the presence of fractures. In this work we use a boundary element approach to study the interplay between a propagating dike and pre-stressed fault. While the stresses induced by a propagating dike may favor slippage on a fault, also slip occurring on a large structure will change the stress state in the medium and influence the dynamics of the dike. We use a 2D boundary element plain strain model for fluid-filled fracture propagation based on the Displacement Discontinuity Method. For the present applications, we implemented the full coupling between a strike-slip lubricated fault (a friction free shear crack) and a mixed-mode dike (accounting for both tensile and shear displacement components). The dike is propagated by adding an element at the tip. By computing the energy released during dike propagation for a range of virtual elongations in different directions, our code indicates the energetically favored trajectory for the dike and whether the dike will accelerate, decelerate or stop in a given location. We apply our model to the 2000 dike intrusion at Miyakejima, Izu arc, Japan, and to the interaction between

  4. 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

  5. Evolution of the Rodgers Creek–Maacama right-lateral fault system and associated basins east of the northward-migrating Mendocino Triple Junction, northern California

    USGS Publications Warehouse

    McLaughlin, Robert J.; Sarna-Wojcicki, Andrei M.; Wagner, David L.; Fleck, Robert J.; Langenheim, V.E.; Jachens, Robert C.; Clahan, Kevin; Allen, James R.

    2012-01-01

    The Rodgers Creek–Maacama fault system in the northern California Coast Ranges (United States) takes up substantial right-lateral motion within the wide transform boundary between the Pacific and North American plates, over a slab window that has opened northward beneath the Coast Ranges. The fault system evolved in several right steps and splays preceded and accompanied by extension, volcanism, and strike-slip basin development. Fault and basin geometries have changed with time, in places with younger basins and faults overprinting older structures. Along-strike and successional changes in fault and basin geometry at the southern end of the fault system probably are adjustments to frequent fault zone reorganizations in response to Mendocino Triple Junction migration and northward transit of a major releasing bend in the northern San Andreas fault. The earliest Rodgers Creek fault zone displacement is interpreted to have occurred ca. 7 Ma along extensional basin-forming faults that splayed northwest from a west-northwest proto-Hayward fault zone, opening a transtensional basin west of Santa Rosa. After ca. 5 Ma, the early transtensional basin was compressed and extensional faults were reactivated as thrusts that uplifted the northeast side of the basin. After ca. 2.78 Ma, the Rodgers Creek fault zone again splayed from the earlier extensional and thrust faults to steeper dipping faults with more north-northwest orientations. In conjunction with the changes in orientation and slip mode, the Rodgers Creek fault zone dextral slip rate increased from ∼2–4 mm/yr 7–3 Ma, to 5–8 mm/yr after 3 Ma. The Maacama fault zone is shown from several data sets to have initiated ca. 3.2 Ma and has slipped right-laterally at ∼5–8 mm/yr since its initiation. The initial Maacama fault zone splayed northeastward from the south end of the Rodgers Creek fault zone, accompanied by the opening of several strike-slip basins, some of which were later uplifted and compressed

  6. Active faulting in the Walker Lane

    NASA Astrophysics Data System (ADS)

    Wesnousky, Steven G.

    2005-06-01

    Deformation across the San Andreas and Walker Lane fault systems accounts for most relative Pacific-North American transform plate motion. The Walker Lane is composed of discontinuous sets of right-slip faults that are located to the east and strike approximately parallel to the San Andreas fault system. Mapping of active faults in the central Walker Lane shows that right-lateral shear is locally accommodated by rotation of crustal blocks bounded by steep-dipping east striking left-slip faults. The left slip and clockwise rotation of crustal blocks bounded by the east striking faults has produced major basins in the area, including Rattlesnake and Garfield flats; Teels, Columbus and Rhodes salt marshes; and Queen Valley. The Benton Springs and Petrified Springs faults are the major northwest striking structures currently accommodating transform motion in the central Walker Lane. Right-lateral offsets of late Pleistocene surfaces along the two faults point to slip rates of at least 1 mm/yr. The northern limit of northwest trending strike-slip faults in the central Walker Lane is abrupt and reflects transfer of strike-slip to dip-slip deformation in the western Basin and Range and transformation of right slip into rotation of crustal blocks to the north. The transfer of strike slip in the central Walker Lane to dip slip in the western Basin and Range correlates to a northward broadening of the modern strain field suggested by geodesy and appears to be a long-lived feature of the deformation field. The complexity of faulting and apparent rotation of crustal blocks within the Walker Lane is consistent with the concept of a partially detached and elastic-brittle crust that is being transported on a continuously deforming layer below. The regional pattern of faulting within the Walker Lane is more complex than observed along the San Andreas fault system to the west. The difference is attributed to the relatively less cumulative slip that has occurred across the Walker

  7. Refined Views of Strike-slip Fault Zones, Seismicity, and State of Stress Associated With the Pacific-North America Plate Boundary in Southern California

    NASA Astrophysics Data System (ADS)

    Hauksson, E.; Nicholson, C.; Shaw, J. H.; Plesch, A.; Shearer, P. M.; Sandwell, D. T.; Yang, W.

    2013-12-01

    The mostly strike-slip plate boundary in southern California is expressed as a system of late Quaternary faults or principal slip zones (PSZs), with numerous adjacent smaller slip surfaces. It is complex, even after large cumulative displacements, and consists of major fault systems with multi-stranded, non-planar fault geometry, including some in close proximity to each other. There are also secondary cross faults and low-angle detachments that interact with the PSZs accommodating main plate boundary motion. The loading of plate-tectonic strain causes the largest earthquakes along PSZs, moderate-sized events in their immediate vicinity, and small earthquakes across the whole region. We apply relocated earthquake and refined focal mechanism (1981-2013) catalogs, as well as other geophysical datasets to provide refined views of the 3D fault geometry of these active fault systems. To determine properties of individual fault zones, we measure the Euclidian distance from every hypocenter to the nearest PSZ. In addition, we assign crustal geophysical parameters such as heat flow value and shear or dilatation strain rates to each epicenter. We investigate seismogenic thickness and fault zone width as well as earthquake source processes. We find that the seismicity rate is a function of location, with the rate dying off exponentially with distance from the PSZ. About 80% of small earthquakes are located within 5 km of a PSZ. For small earthquakes, stress drops increase in size with distance away from the PSZs. The magnitude distribution near the PSZs suggests that large earthquakes are more common close to PSZs, and they are more likely to occur at greater depth than small earthquakes. In contrast, small quakes can occur at any geographical location. An optimal combination of heat flow and strain rate is required to concentrate the strain along rheologically weak fault zones, which accommodate the crustal deformation processes, causing seismicity. The regional trend of

  8. Analysis of the Shallow Slip Deficit Using Sub-Pixel Image Correlation:examples from various large continental strike-slip earthquakes

    NASA Astrophysics Data System (ADS)

    Milliner, C. W.; Hollingsworth, J.; Dolan, J. F.; Leprince, S.; Ayoub, F.; Avouac, J.

    2012-12-01

    We use the optical image correlation technique to analyze the near-field displacement field for a variety of large (Mw 7+) continental strike-slip earthquakes, to better determine the contribution of distributed deformation to coseismic surface ruptures. Various satellite datasets are correlated using the COSI-Corr software package, including WorldView, Quickbird, SPOT and Landsat7 imagery, along with de-classified KH-9 spy satellite imagery and aerial photos, allowing us to investigate earthquakes as far back as 1976. The variety of datasets used highlights the versatility of COSI-Corr for measuring displacements at the Earth's surface. The following earthquakes are investigated: 1976 Guatemala (Mw 7.5), 1990 Luzon (Mw 7.4), 1992 Landers (Mw 7.3), 1995 Sakhalin (Mw 7.0), 1997 Zirkuh (Mw 7.2), 1999 Izmit (Mw 7.6), 1999 Hector Mine (Mw 7.1), 1999 Duzce (Mw 7.1), 2001 Kokoxilli (Mw 7.1) and 2002 Denali (Mw 7.8). For each event we examine the surface displacement field produced by COSI-Corr, and compare them with published field measurements to assess the component of distributed deformation that may be routinely missed by geologists when collecting data in the field. These results also complement surface displacements determined using InSAR, which commonly de-correlates at distances of 1-2 km from the fault rupture. Fault displacements are extracted from the displacement maps using a new tool written for MATLAB, which extracts the maximum and minimum values on either side of the fault, as well as the distance between these points, thus giving a potential measure of the total width of the deforming zone. Where possible, we determine the total geological displacements for each fault through analysis of satellite data, geological maps and published results, thus allowing an assessment of the structural maturity for each fault. The difference between field measurements and COSI-Corr-derived measurements of the coseismic displacement field are compared with geological

  9. Onset and Mechanisms of Surface Creep on Strike Slip Faults: Clues from the North Anatolian Fault and Comparisons with the San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Cakir, Z.; Ergintav, S.; Akoglu, A. M.; Cetin, E.; Meghraoui, M.; Reilinger, R. E.

    2014-12-01

    Aseismic fault slip was first reported over forty years ago along some major strike slip faults including the San Andreas (SAF) and North Anatolian faults (NAF). Yet both their origin and timing on active faults and underlying physical processes remain subjects of debate. The presence of weak minerals and/or trapped fluid overpressures within fault zones have been proposed as mechanics for aseismic fault creep. Our InSAR observations together with GPS measurements and geology along the NAF provide new evidence for the mechanism, characteristics, and initiation of fault surface creep. We have used the persistent scatterer InSAR (PS-InSAR) technique to investigate both the creeping section of the NAF at Ismetpaşa that had ruptured during the 1944 and 1951 earthquakes, and the postseismic era of the 1999 İzmit Earthquake. The results reveal that the central segment of the 1999 Izmit Earthquake rupture has been creeping for over for the past 15 years since the event, becoming the longest lasting afterslip ever recorded. The slip pattern of ongoing surface creep on the İzmit rupture supports the idea that stable fault creep can be initiated as postseismic afterslip, a mechanism we proposed previously but could not have confirmed due to the lack of pre- and post-earthquake observations on creeping faults such as the Ismetpaşa segment of the NAF and the segments of the SAF in the San Francisco Bay area. Geological maps along the Ismetpaşa and Izmit creeping segments show that both fault zones run through ophiolitic and calcareous rocks with phyllosilicates that probably result in fault weakening. Earthquake rupture maps and PS-InSAR velocity fields for these regions also reveal that the creeping faults have simple geometry being fairly rectilinear and continuous along their strike. These common features suggest that following a large earthquake, a stable surface creep can be triggered on a section of a mature fault if it has evolved in to simple geometry and is

  10. 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.

  11. The Teisseyre-Tornquist Zone - early Palaeozoic strike-slip plate boundary or Ediacaran rifted margin of Baltica?

    NASA Astrophysics Data System (ADS)

    Mazur, Stanislaw; Krzywiec, Piotr; Malinowski, Michal; Lewandowski, Marek; Buffenmeyer, Vinton; Green, Christopher

    2016-04-01

    The Teisseyre-Tornquist Zone (TTZ) is the longest European tectonic and geophysical lineament extending from the Baltic Sea in the northwest to the Black Sea in the southeast. This tectonic feature defines a transition between the thick crust of the East European Craton (EEC) and the thinner crust of the Palaeozoic Platform to the southwest. Being a profound zone of crustal and lithospheric thickness perturbation, the TTZ has usually been considered a Caledonian tectonic suture formed due to the closure of the Tornquist Ocean. The suture was hypothesised to originate from the collision between Baltica and Avalonia or large-scale strike-slip displacement along strike of the Caledonian Orogen. However, some minority views postulated the continuation of Baltica crystalline basement farther to the southwest up to the Elbe Lineament and the margin of the Variscan Belt. We studied the ION Geophysical PolandSPAN survey that consists of 10 regional, seismic depth profiles covering the SW margin of the EEC and the TTZ in Poland. Since the PolandSPAN profiles image to ~30 km depth their interpretation was integrated with the potential fields data and earlier results of refraction sounding to better image the deep structure of the TTZ. Our data show that the NW and central sections of the TTZ correspond, at the Moho level, to a relatively narrow crustal keel and a significant Moho step at the transition from the EEC to the Palaeozoic Platform. However, top of basement above the TTZ is smooth and moderately sloping towards the southwest. In the central part of the TTZ, top of Precambrian is covered by undisturbed lower Palaeozoic sediments. In contrast, the lower Palaeozoic sediments are involved in a latest Silurian, thin-skinned fold-and-thrust belt along the NW section of the TTZ, where the sharply defined Caledonian Deformation Front adjoins a rigid basement buttress above the TTZ. Finally, the crustal keel is mostly missing from the SE section of the TTZ. Instead, this

  12. Strain partitioning at orogenic contacts during rotation, strike-slip and oblique convergence: Paleogene-Early Miocene evolution of the contact between the South Carpathians and Moesia

    NASA Astrophysics Data System (ADS)

    Krézsek, Csaba; Lăpădat, Alexandru; Maţenco, Liviu; Arnberger, Klaus; Barbu, Victor; Olaru, Radu

    2013-04-01

    Oblique convergence accompanied by large-scale strike-slip deformation taking place between orogenic units is an inherent feature of highly bended mountain chains. Strain partitioning during subduction and collision takes place between differently oriented orogenic segments and creates contrasting styles of deformation that may include coeval extension, strike-slip and shortening, in particular when large amounts of rotations are recorded. A typical area is the one connecting the Balkans with East Carpathians along the highly bended South Carpathians Mountains that were affected by large scale Paleogene-Miocene strain partitioning at the contact with their lower Moesia unit in what is commonly known as the Getic Depression. We analyse this contact by the means of a number of seismic transects calibrated by exploration wells. The kinematic restoration of these transects is correlated with connecting depth information and with previously published studies. This has allowed the definition of a novel kinematic evolution of the deformation observed in the Getic Depression. This evolution is compatible with the definition of a Paleogene-Early Miocene period of transtensional opening by using strike-slip faults that terminate along horsetail geometries. This transtensional deformation migrates in space and time across the basin and is kinematically connected with the oblique shortening taking place in the eastern part of the Getic Depression and SE/East Carpathians. In particular interesting is the mechanism of transtensional migration E-wards and contractional migration W-wards that took place coevally during the rotation and E-ward translation of the upper Carpathians units along the strike of the Getic Depression. This has been subsequently followed by shortening and transpression during Middle Miocene-Quaternary times that was recorded at the scale of the entire studied area.

  13. The 2003 M=6.9 Zemmouri, Algeria, Earthquake Brought Thrust and Strike-Slip Faults Near Algiers Closer to Coulomb Failure

    NASA Astrophysics Data System (ADS)

    Lin, J.; Stein, R. S.; Toda, S.; Meghraoui, M.; Dorbath, C.

    2007-12-01

    We investigate key features of thrust earthquake triggering, inhibition, and clustering associated with the stress transferred by the 2003 M=6.9 Zemmouri quake on an offshore hidden thrust fault in coastal Algeria. A crucial question is whether the seismic hazard increased on the Boumerdes and Thenia faults, which lie just west of the Zemmouri rupture and only 10-20 km from the city of Algiers. The capital city suffered large damaging quakes in A.D. 1365 and 1716, and is today home to 3 million people. Slip on blind thrust faults tend to increase the stress above the source fault and in much of the surrounding crust, whereas slip on surface-cutting thrust faults drops the stress in most of the adjacent crust. We examined the sensitivity of the imparted stress to different published source models of the 2003 Zemmouri event inferred from geodetic and seismic inversions, and focus here on the robust results. We calculate that the 2003 M=6.9 Zemmouri quake brought the Coulomb stress 1.0 bars closer to failure on the reverse Boumerdes and 0.5 bars closer on the right-lateral Thenia faults that bound the populated Mitidja basin, although the Thenia fault may not be tectonically active. The calculated pattern of the stress increase appears consistent with aftershock distribution determined from double difference earthquake tomography by Ayadi et al. (submitted); both of these faults were illuminated by aftershocks during the first three months of the sequence. The East Sahel and Larbaa faults, which lie further to the west, are calculated to have sustained a weak 0.1-bar stress increase and show no associated aftershocks. We also calculate a 1.0-bar stress increase on the NNW-SSE trending vertical right-lateral Kabyle fault located south of the Zemmouri fault, although there is no evidence of recent Quaternary tectonic movement, no geomorphology typical of active zones, and little seismicity along the Kabyle fault.

  14. Fault zone development and strain partitioning in an extensional strike-slip duplex: A case study from the Mesozoic Atacama fault system, Northern Chile

    NASA Astrophysics Data System (ADS)

    Cembrano, J.; González, G.; Arancibia, G.; Ahumada, I.; Olivares, V.; Herrera, V.

    2005-05-01

    Upper crustal strike-slip duplexes provide an excellent opportunity to address the fundamental question of fault zone development and strain partitioning in an evolving system. Detailed field mapping of the Mesozoic Atacama fault system in the Coastal Cordillera of Northern Chile documents the progressive development of second- and third-order faults forming a duplex at a dilational jog between two overstepping master faults: the sinistral strike-slip, NNW-striking, Jorgillo and Bolfin faults. These are constituted by a meter-wide core of foliated S-C ultracataclasite and cataclasite, flanked by a damage zone of protocataclasite, splay faults and veins. Lateral separation of markers along master faults is on the order of a few kilometers. Second-order, NW-striking, oblique-slip subsidiary fault zones do not show foliated ultracataclasite; lateral sinistral separations are in the range of ˜ 10 to 200 m with a relatively minor normal dip-slip component. In turn, third-order, east-west striking normal faults exhibit centimetric displacement. Oblique-slip (sinistral-normal) fault zones located at the southern termination of the Bolfin fault form a well-developed imbricate fan structure. They exhibit a relatively simple architecture of extensional and extensional-shear fractures bound by low displacement shear fractures. Kinematic analysis of fault slip data from mesoscopic faults within the duplex area, document that the NW-striking and the EW-striking faults accommodate transtension and extension, respectively. Examination of master and subsidiary faults of the duplex indicates a strong correlation between total displacement and internal fault structure. Faults started from arrays of en echelon extensional/extensional-shear fractures that then coalesced into throughgoing strike-slip faults. Further displacement leads to the formation of discrete bands of cataclasite and ultracataclasite that take up a significant part of the total displacement. We interpret that the

  15. UAVSAR Indication of Right-Lateral Faults in Southern California

    NASA Astrophysics Data System (ADS)

    Donnellan, A.; Parker, J. W.

    2011-12-01

    UAVSAR data have been collected in southern California since spring of 2009. Data started being routinely collected in fall of 2009. Repeat pass interferometry (RPI) products show multiple lineations that strike SE parallel to the main strike of the San Andreas fault (outside of the Big bend). Aside from slip associated with the 2010 M 7.2 El Mayor Cucapah earthquake the lineations, while prominent in the data products, do not indicate large or any offsets on the faults. Faults that are indicated in the data include the Rialto-Colton fault, and the Superstition Hills fault. The RPI products indicate line of site changes between the ground and the instrument, which in this case is on an airborne platform. The flight lines were designed to be generally perpendicular to strike slip motions in southern California, and as a result should show the maximum component of motion toward the instrument. However, it is not possible to decompose horizontal versus vertical motions. Cross sections across these lineations show no offset, except near the 2010 El Mayor-Cucapah rupture, but show substantial differences in range change near the fault as compared to further from the fault. It is likely that different material properties within the fault zone, coupled with either ground-water migration or shaking from the El Mayor-Cucapah earthquake are the cause of these range change differences. We also discuss conjugate faulting associated with the 2010 earthquake and other crustal deformation observed in the Salton Trough.

  16. A tectonic interpretation of NW-SE strike-slip faulting during the 2004 off the Kii peninsula earthquakes, Japan: Probable tear of the Philippine Sea plate

    NASA Astrophysics Data System (ADS)

    Miyoshi, T.; Ishibashi, K.

    2005-11-01

    The 2004 off the Kii peninsula earthquakes (Mw 7.5 for the main shock) occurred within the subducting Philippine Sea (PHS) plate near its boundary, the Nankai trough, southwest Japan. The rupture mode of the foreshock-main shock-aftershock sequence was complicated, a combination of ENE-WSW striking (almost trough parallel) reverse faulting beneath the trough and NW-SE trending (almost trough normal) strike-slip faulting mostly on the landward side of the former. In this paper, we discuss the tectonic meaning of this NW-SE running strike-slip fault. We examined hypocenter distribution and focal mechanisms of slab earthquakes from October 1997 through September 2004 and confirmed a NW-SE striking tear of the PHS slab beneath the middle part of the Kii Peninsula pointed out by Miyoshi and Ishibashi (2004). According to the Earthquake Research Committee (2004) there is a NW-SE trending structural discontinuity in the PHS crust to the southeast of the main shock epicenter. Putting all features together, we interpret that there is a NW-SE striking fracture within the PHS plate continuously from the Nankai trough region to the slab beneath the Kii Peninsula, and that a partial rupture of this fracture occurred during the off the Kii peninsula earthquakes together with trough-parallel reverse faulting. It should be noted that two disastrous M 7-class slab earthquakes seem to have occurred along this tear beneath the peninsula in 1899 and 1952.

  17. 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.

  18. Mechanics of evenly spaced strike-slip faults and its implications for the formation of tiger-stripe fractures on Saturn's moon Enceladus

    NASA Astrophysics Data System (ADS)

    Yin, An; Zuza, Andrew V.; Pappalardo, Robert T.

    2016-03-01

    We present the first mechanical analysis based on realistic rheology and boundary conditions on the formation of evenly spaced strike-slip faults. Two quantitative models employing the stress-shadow concept, widely used for explaining extensional-joint spacing, are proposed in this study: (1) an empirically based stress-rise-function model that simulates the brittle-deformation process during the formation of evenly spaced parallel strike-slip faults, and (2) an elastic plate model that relates fault spacing to the thickness of the fault-hosting elastic medium. When applying the models for the initiation and development of the tiger-stripe fractures (TSF) in the South Polar Terrain (SPT) of Enceladus, the mutually consistent solutions of the two models, as constrained by the mean spacing of the TSF at ∼35 km, requires that the brittle ice-shell thickness be ∼30 km, the elastic thickness be ∼0.7 km, and the cohesive strength of the SPT ice shell be ∼30 kPa. However, if the brittle and elastic models are decoupled and if the ice-shell cohesive strength is on the order of ∼1 MPa, the brittle ice shell would be on the order of ∼10 km.

  19. Strike-slip accomodation during the development of the Cantabrian and Central-Iberian oroclines: 40Ar*/39Ar geochronological ages of major shear zones.

    NASA Astrophysics Data System (ADS)

    Gutierrez-Alonso, Gabriel; Pastor-Galán, Daniel; Collins, Alan S.

    2013-04-01

    One of the most striking features found in the West European Variscan Belt is a large strikeslip shear zone/fault system, characterized as "Late-Variscan", that runs parallel to the broad structural trends around the Iberian Armorican Arc. 40Ar*-39Ar ages of micas grown during fabric development in five shear zones of this system (Traguntia-Juzbado; Porto-Tomar; Malpica-Tuy, Punta Langosteira and Ricobayo, both dextral and left lateral, have yielded ages that, within error, cluster at 307 Ma, suggesting that their development took place within the time frame of oroclinal bending constrained by paleomagnetism and structural data, that is to say, coeval with the formation of the Ibero-Armorican Arc. According to our new data and other data from the literature, we interpret the development of the strike-slip shear zone system and the origin of the magmatic pulse at ca 307 Ma as being related to the initiation of the orocline development. These new ages constrain deformation in the outer arc to be penecontemporaneous with thrust-sheet rotations in the inner arc Cantabrian Zone. The 307 Ma strike-slip shear-zones are inferred to have accommodated the vertical axis crustal or lithospheric-block rotations needed to accommodate oroclinal bending. Coeval granitoid ages, clustering at 307 Ma and located in Cantabrian orocline outer arc represent decompressive melting during the mechanical thinning of the mantle lithosphere below the outer arc during bending.

  20. 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.

  1. Secondary Normal Faulting Near the Terminus of a Strike-Slip Fault Segment in the Lake Mead Fault System, SE Nevada

    NASA Astrophysics Data System (ADS)

    Marshall, S. T.; Kattenhorn, S. A.

    2003-12-01

    The 95 km long Lake Mead Fault System (LMFS), located about 50 km east of Las Vegas and about 100 km west of the relatively undeformed Colorado Plateau, consists of a group of NE/SW-trending Miocene left-lateral strike-slip faults with a total offset of 65-110 km. Previous work suggests that the LMFS acted as a transform zone to accommodate differential extension between the southern Basin and Range to the north and the metamorphic core complexes of the Colorado River extensional corridor to the south. Studies of individual faults of the LMFS have shown that strike-slip faulting was the dominant mode of deformation while normal faulting, pull-apart basins, and push up structures formed as localized secondary structures related to strike-slip faults. This study focuses on the portion of the LMFS west of the Overton Arm of Lake Mead, which consists of the Bitter Spring Valley Fault (BSVF) and the Hamblin Bay Fault (HBF). Both faults have estimated offsets of 20-60 km, but past mapping efforts have been inconsistent with respect to the BSVF trace locations and degree of fault complexity. In order to demonstrate that the apparent complexity of the BSVF is the result of segmentation and secondary normal faults associated with individual segments, we focused field mapping efforts on an apparent segment of the BSVF near Pinto Ridge, located southwest of the Echo Hills and about 5 km NW of the more prominent HBF. We have identified nine normal faults that initiate near the SW tip of a segment of the BSVF and die out to the south before reaching the HBF. The offset on all these faults is a maximum at their northern intersection with the BSVF, then steadily decreases to zero away from the BSVF. These normal faults range from 0.6 km-2.25 km in length and have variable fault trace patterns. The normal fault originating closest to the SW tip of the BSVF segment curves with increasing distance away towards parallelism with the BSVF. The eight other normal faults are all oriented

  2. Reconstruction of Sea/Lake-Level Changes in an Active Strike-Slip Basin (Gulf of Cariaco, NE Venezuela)

    NASA Astrophysics Data System (ADS)

    van Daele, M.; Audemard, F.; Beck, C.; de Batist, M.; van Welden, A.; Moernaut, J.; 2006 Shipboard Party, G.

    2008-05-01

    In January 2006, 76 high-resolution reflection seismic profiles were acquired in the Gulf of Cariaco, Northeast Venezuela. In the upper 100 m of sedimentary infill, 17 unconformity-bounded sequences were identified and mapped throughout the basin. Up to now, no core or borehole information is available to provide age constraints on these units. The sedimentary infill is cut by several faults, Riedel faults in the central part and the El Pilar fault (one of the main faults of the South American-Caribbean plate boundary) in the southern part of the gulf. The connection of the Gulf of Cariaco with the adjacent Cariaco Basin occurs at a present-day water depth of ~ 55 m. This implies that the gulf was disconnected from the world ocean and functioned as a lake during a large part of the last glacial. The main rivers entering the gulf drain the coastal mountain ranges and tend to form pronounced deltas at their inlet. During times when the gulf was a lake, periods with a dry climate resulted in dramatic lake-level lowstands and even complete desiccation/evaporation. The present-day depths of delta offlap breaks and the presence of lowstand/evaporite deposits can thus be used to estimate sea/lake level at the time of their formation. Detailed analysis of these stratigraphic sea/lake-level indicators allowed reconstructing the sea/lake-level history for the period encompassed by the 17 identified sequences. This sea/lake-level reconstruction also needed to be corrected for tectonic subsidence, affecting different parts of the gulf with different intensity. The reconstructed sea/lake-level curve of the Gulf of Cariaco was compared with the eustatic sea-level curve and with results of previous paleoclimate studies in Venezuela. The striking coherence between the eustatic curve and the amplitudes and absolute heights of successive reconstructed lowstands and highstands compelled us to tune our record to the eustatic curve in order to achieve a rough age estimate for our units. According to this age model, our seismic stratigraphy reaches back to MIS6, and the average sedimentation rate in the central parts of the gulf since MIS5e is 0.92 mm/y. Our data show that reconstructed lake levels in the Gulf of Cariaco, which represent a proxy for climate in NE- Venezuela, are very strongly coupled to the global stadials and interstadials of the last glacial period. Also the Younger Dryas is recognised in the sedimentary record of the Gulf of Cariaco as lowstand deposit resulting from an (almost) complete desiccation. Our data reveal that the stratigraphy of the Gulf of Cariaco holds a very accurate, complete and promising record of eustasy and climate change, at least since the penultimate glacial maximum. The quality of this record and the vicinity to the iconic Cariaco Basin make the Gulf of Cariaco an ideal target for future ocean drilling (or long coring).

  3. Width of late Quaternary deformation of the Enriquillo-Plantain Garden strike-slip fault zone in Haiti and the Jamaica Passage and implications for accumulated stress

    NASA Astrophysics Data System (ADS)

    Mann, P.; Bachhuber, J. L.

    2010-12-01

    The devastating Haiti earthquake of January 12, 2010, is now known to have occurred on multiple rupture planes with most of the seismic energy release along a north-dipping thrust fault located from 0.5 to 15 km north of the main late Quaternary trace of the EPGFZ. Two alternative views of this rupture are that this north-dipping thrust is unrelated to the main trace of the fault - which showed no rupture during the event - or this north-dipping thrust is part of its larger, subsurface “flower zone” of deformation poorly understood because we have no seismic reflection images crossing the EGPFZ in epicentral area of the 2010 earthquake. The significance of distinguishing these two views of fault behavior relates to whether centuries of accumulated stress were not released on the main trace of the EPGFZ (first model) or whether some accumulated stress was released on the low-angle thrust as part of a broad and linked “flower zone” of deformation parallel to the EPGFZ (second model). In this talk we review observations on the width of the EPGFZ deformation to support the latter view that the EPGFZ is in fact a broad zone of deformation commensurate with its tectonic role as a major, active plate boundary fault. Three areas of broad late Quaternary tectonic deformation varying from transpressional to transtensional in structural style are examined using DEM, imagery, surface geologic maps, and aftershock locations. The Cul-de-Sac basin of Haiti is the xx-km-wide, fault bounded alluvial plain upon which the city of Port-au-Prince was constructed in the early 18th century. Merged DEM and geologic map data from the Cul-de-Sac plain show that an en echelon array of large, open folds deforming uplifted and deeply dissected Plio-Pleistocene fans can be traced 3 to 7 km north of the main trace of the EPGFZ. Map studies show that west-northwest-striking, sub-parallel reverse-oblique/strike-slip faults can be mapped transecting the folds at distances of 3 to 5 km north

  4. Right-lateralized alpha desynchronization during regularity discrimination: Hemispheric specialization or directed spatial attention?

    PubMed Central

    Wright, Damien; Makin, Alexis D J; Bertamini, Marco

    2015-01-01

    When actively classifying abstract patterns according to their regularity, alpha desynchronization (ERD) becomes right lateralized over posterior brain areas. This could reflect temporary enhancement of contralateral visual inputs and specifically a shift of attention to the left, or right hemisphere specialization for regularity discrimination. This study tested these competing hypotheses. Twenty-four participants discriminated between dot patterns containing a reflection or a translation. The direction of the transformation, which matched one half onto the other half, was either vertical or horizontal. The strategy of shifting attention to one side of the patterns would not produce lateralized ERD in the horizontal condition. However, right-lateralized ERD was found in all conditions, regardless of orientation. We conclude that right hemisphere networks that incorporate the early posterior regions are specialized for regularity discrimination. PMID:25532558

  5. Oroclinal bending, distributed thrust and strike-slip faulting, and the accommodation of Arabia-Eurasia convergence in NE Iran since the Oligocene

    NASA Astrophysics Data System (ADS)

    Hollingsworth, James; Fattahi, Morteza; Walker, Richard; Talebian, Morteza; Bahroudi, Abbas; Bolourchi, Mohammad Javad; Jackson, James; Copley, Alex

    2010-06-01

    Regional shortening is accommodated across NE Iran in response to the collision of Arabia with Eurasia. We examine how N-S shortening is achieved on major thrust systems bounding the eastern branch of the Alborz (east of 57°E), Sabzevar and Kuh-e-Sorkh mountain ranges, which lie south of the Kopeh Dagh mountains in NE Iran. Although these ranges have experienced relatively few large earthquakes over the last 50 yr, they have been subject to a number of devastating historical events at Neyshabur, Esfarayen and Sabzevar. A significant change in the tectonics of the eastern Alborz occurs directly south of the Central Kopeh Dagh, near 57°E. To the east, shortening occurs on major thrust faults which bound the southern margin of the range, resulting in significant crustal thickening, and forming peaks up to 3000 m high. Active shortening dies out eastward into Afghanistan, which is thought to belong to stable Eurasia. The rate of shortening across thrust faults bounding the south side of the eastern Alborz north of Neyshabur is determined using optically stimulated luminescence dating of displaced river deposits, and is likely to be 0.4-1.7 mm yr-1. Shortening across the Sabzevar range 150 km west of Neyshabur has previously been determined at 0.4-0.6 mm yr-1, although reassessment of the rate here suggests it may be as high as 1 mm yr-1. Migration of thrust faulting into foreland basins is common across NE Iran, especially in the Esfarayen region near 57°E, where the northward deflection of the East Alborz range reaches a maximum of 200 +/- 20 km (from its presumed linear E-W strike at the beginning of the Oligocene). West of 57°E, the tectonics of the Alborz are affected by the westward motion of the South Caspian region, which results in the partitioning of shortening onto separate thrust and left-lateral strike-slip faults north and south of the range. At the longitude of 59°E, published GPS velocities indicate that 50 per cent of the overall shortening across

  6. The late Quaternary slip history of the North Anatolian Fault, Turkey: Implications for the spatial and temporal behaviour of large strike-slip fault belts

    NASA Astrophysics Data System (ADS)

    Zabcı, Cengiz; Akyüz, H. Serdar; Sançar, Taylan; Güneç Kıyak, Nafiye

    2015-04-01

    The study of the spatial and temporal behaviour of active faults by estimating the geologic and geodetic slip rates is critical not only for assessing the seismic potential of these tectonic structures, but also for understanding their geodynamics. Geodetic data can provide detailed spatial coverage but represent a short time interval of a single earthquake cycle, while geologic rates are derived as average values for multiple events at spatially limited sites. In the complex tectonic setting of the eastern Mediterranean, the westward extrusion of the Anatolian scholle is mainly accommodated by two major tectonic structures, the North Anatolian (NASZ) and the East Anatolian (EASZ) shear zones, respectively forming the northern and eastern boundaries. The rate of deformation all along the North Anatolian Fault (NAF) is spatially well documented mainly by GPS and InSAR based geodetic studies during the last two decades. Furthermore, the number of the morphochronology-based geologic slip rate studies significantly increased, covering the different sections of this large strike slip fault for various time intervals. In this study, we do not only compile all previous geologic slip rate estimates, but we also present data for three new and two revised sites from central to the most eastern parts of the NAF in order to understand the spatial and temporal behaviour of this important fault system. The integrated dataset of geologic studies were classified into two groups to represent the central to eastern sections (Model I) and the western part (Model II). The geographical diversion between two models is about at the 31° E longitude, where the NAF bifurcates into two branches from this point toward west into the Marmara Region. To test any secular variation in fault's slip history, we used the Monte Carlo approach of Gold and Cowgill (2011). After the removal of rates, which do not account the near fault deformation or the existing parallel/sub-parallel faults, the Model

  7. Coordinated strike-slip and normal faulting in the Southern Ozark dome of Northern Arkansas: Deformation in a late Paleozoic foreland

    USGS Publications Warehouse

    Hudson, M.R.

    2000-01-01

    Structures that formed on the southern flank of the Ozark dome, in the foreland of the late Paleozoic Ouachita orogeny, have received little modern study. New mapping of the western Buffalo River region of northern Arkansas identifies diversely oriented faults and monoclinal folds that displace the generally flat lying Mississippian Boone Formation over a 180 m elevation range. Kinematic measurements and spatial relations reveal the presence of both east-striking normal faults and broader northeast-striking dextral strike-slip fault zones that acted in a coordinated fashion to accommodate constrictional strain, in which north-south extension was balanced by vertical and east-directed shortening. North-south extension in the Buffalo River region probably reflects Pennsylvanian-Early Permian deformation within the flexural forebulge of the developing Ouachita orogeny, which closed progressively westward along the southern margin of the craton.

  8. The last interglacial period at Guantanamo Bay, Cuba and an estimate of late Quaternary tectonic uplift rate in a strike-slip regime

    NASA Astrophysics Data System (ADS)

    Schweig, E. S.; Muhs, D. R.; Simmons, K. R.; Halley, R. B.

    2015-12-01

    Guantanamo Bay, Cuba is an area dominated by a strike-slip tectonic regime and is therefore expected to have very low Quaternary uplift rates. We tested this hypothesis by study of an unusually well preserved emergent reef terrace around the bay. Up to 12 m of unaltered, growth-position reef corals are exposed at about 40 sections examined around ˜40 km of coastline. Maximum reef elevations in the protected, inner part of the bay are ˜11-12 m, whereas outer-coast shoreline angles of wave-cut benches are as high as ˜14 m. Fifty uranium-series analyses of unrecrystallized corals from six localities yield ages ranging from ˜134 ka to ˜115 ka, when adjusted for small biases due to slightly elevated initial 234U/238U values. Thus, ages of corals correlate this reef to the peak of the last interglacial period, marine isotope stage (MIS) 5.5. Previously, we dated the Key Largo Limestone to the same high-sea stand in the tectonically stable Florida Keys. Estimates of paleo-sea level during MIS 5.5 in the Florida Keys are ~6.6 to 8.3 m above present. Assuming a similar paleo-sea level in Cuba, this yields a long-term tectonic uplift rate of 0.04-0.06 m/ka over the past ~120 ka. This estimate supports the hypothesis that the tectonic uplift rate should be low in this strike-slip regime. Nevertheless, on the southeast coast of Cuba, east of our study area, we have observed flights of multiple marine terraces, suggesting either (1) a higher uplift rate or (2) an unusually well-preserved record of pre-MIS 5.5 terraces not observed at Guantanamo Bay.

  9. Is There any Relationship Between Active Tabriz Fault Zone and Bozkush Fault Zones, NW Iran?

    NASA Astrophysics Data System (ADS)

    ISIK, V.; Saber, R.; Caglayan, A.

    2012-12-01

    Tectonic plate motions and consequent earthquakes can be actively observed along the northwestern Iran. The Tabriz fault zone (TFZ), also called the North Tabriz fault, active right-lateral strike-slip fault zone with slip rates estimated as ~8 mm/yr, has been vigorously deforming much of northwestern Iran for over the past several million years. Historical earthquakes on the TFZ consist of large magnitude, complimentary rupture length and changed the landscape of regions surrounding the fault zone. The TFZ in the city of Bostanabad is more segmented with several strands and joined by a series of WNW-ESE trending faults, called the Bozkush fault zones. The Bozkush fault zones (BFZ's) (south and north), bounding arch-shaped Bozkush mountains, generates not only hundreds of small earthquakes each year but also has provided significant earthquakes that have been historically documented. The rock units deformed within the BFZ's include Eocene-Oligocene volcanic rocks with intercalation limestone, Oligo-Miocene clastic rocks with intercalation gypsiferous marl and Plio-Quaternary volcano-sedimentary rocks, travertine and alluvium. The North and South Bozkush fault zones are characterized by development of structures typically associated with transpression. These include right-lateral strike-slip faults, thrust faults and foldings. Our field studies indicate that these zones include step to sub-vertical fault surfaces trending NW and NE with slickenlines. Slickensides preserve brittle kinematic indicators (e.g., Riedel shear patterns, slickenside marks) suggesting both dextral displacements and top-to-the-NE/NW and-SE/SW sense of shearing. Besides, mesoscopic and microscopic ductile kinematic indicators (e.g., asymmetric porphyroclasts, C/S fabrics) within Miocene gypsum marl show dextral displacements. Fault rocks along most of these faults consist of incohesive fault breccia and gauge. Adjacent to the fault contact evidence of bedding in Oligo-Miocene and Plio

  10. 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

  11. 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.

  12. Response to the commentary by Shah, A. A. (2015) and further evidence supporting the dextral strike-slip pull-apart evolution of the Kashmir basin along the central Kashmir fault (CKF)

    NASA Astrophysics Data System (ADS)

    Alam, Akhtar; Ahmad, Shabir; Sultan Bhat, M.; Ahmad, Bashir

    2016-01-01

    This research article provides added evidence in support of the already presented tectonic evolution model of the Kashmir basin by Alam et al. (2015), which states that the local dextral strike-slip structure, embedded with the southern forefront thrust system (MBT/MCT), resulted in the development of the NNW-SSE-oriented elliptical pull-apart sedimentary trough (Kashmir basin). Simultaneously, we respond to the argument of Shah (2015), wherein the author expresses his concern about the tectonic evolution model proposed by Alam et al. (2015). The commentator (Shah, 2015)-merely based on assumptions (1: perfectly planar geometry of the central Kashmir fault-CKF; 2: pure strike-slip along the CKF) and misinterpretations of the data (tectonic, geologic, structural, seismic, geodetic, and geomorphic)-makes extraneous criticism throughout the length of his commentary by referring copied text/figures. However, Alam et al. (2015) projected the CKF as noticeably curvilinear major exhibiting complex strike-slip tectonics (dextral, lateral, and vertical motion). Moreover, contradictory to the claim of Shah (2015), the tectonic, geologic, structural, seismic, geodetic, and geomorphic data is in complete agreement with the model proposed by Alam et al. (2015). Hence, in addition to complimentary evidence for the dextral strike-slip, pull-apart evolution of the Kashmir basin, a detailed response is provided to the commentary of Shah (2015).

  13. Cyclical Stress Field Switching and (Total?) Relief of Fault Shear Stress Recorded in Quartz Vein Systems Hosted by Proterozoic Strike-Slip Faults, Mt Isa, Australia

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    The Proterozoic Mt Isa inlier ( ˜50,000 km2) in NW Queensland, Australia, underwent a complex tectonothermal history involving multiple episodes of intracontinental rifting, sedimentation, and magmatism that culminated in the Isan Orogeny (1590-1500 Ma) where strong E-W shortening led to compressional inversion of former rift basins. The resulting metamorphic complex of subgreenschist to amphibolite facies assemblages is disrupted by brittle, late-orogenic (1500-1450 Ma?) strike-slip faults. The faults occur in two mutually cross-cutting sets; a set of dextral strike-slip faults striking NE-SW to NNE-SSW with offsets <20 km, and a conjugate set of sinistral faults striking NW-SE to NNW-SSE. The two contemporaneous fault sets therefore lie at +/-45-60° to inferred E-W maximum compression, approaching the expected lock-up angle for 'Byerlee' friction coefficients. The faults commonly outcrop as linear blade-like ridges extending for many kilometres across the semi-arid terrain. Transects across the NE-SW Fountain Range and Overlander Faults which crosscut Corella Formation amphibolite facies assemblages and granites have shown that the fault zones are about 100 m in width with a composite brittle fabric comprising: (1) subvertical silicified cataclastic shear zones (cataclasites plus microbreccias containing vein fragments); (2) innumerable subvertical quartz-veins (cm to m thickness) lying subparallel to the principal shear zones (some retain purely dilational textures; others are multiply recemented fault-breccias with wallrock fragments); (3) highly irregular non-systematic veins; and (4) a systematic set of predominantly extensional, steep planar quartz veins oriented 080-120° at moderate angles to the main faults. Mutual cross-cutting relationships occur between all structural components, indicating broad contemporaneity. Recorded dextral separations along shear fracture components are commonly of the order of 1-10 cm, consistent with small-moderate seismic

  14. 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

  15. Fluid-flow model of high-porosity carbonates crosscut by a strike-slip fault system, Favignana Island (southern Italy)

    NASA Astrophysics Data System (ADS)

    Cilona, Antonino; Antonellini, Marco; Tondi, Emanuele; Agosta, Fabrizio; Johnson, Gareth; Shackleton, Ryan

    2013-04-01

    This contribution integrates structural analysis and numerical modelling to build up, from outcrop data, a 3D Discrete Fracture Network (DFN) model, and then to run fluid flow simulations of a porous carbonate reservoir. A semi-automated process of lineament analysis, followed by the use of power law distributions to model sub-seismic scale features, is here proposed as a workflow for reservoir-scale assessment of the control exerted by structural features on the bulk permeability in porous carbonate reservoirs. In Favignana Island (southern Italy), several quarries provide an excellent 3D view of Lower-Pleistocene grainstones crosscut by a strike-slip fault system. This fault system is made up of two main conjugate sets of strike-slip structural features such as Compactive Shear Bands (CSB), Zones of compactive shear Bands (ZB) and faults. The multi-scale properties of the aforementioned elements, distinguished for individual sets, have been previously assessed by mean of detailed scan-line and scan-area measurements. The DFN model was built using the Fracture Modelling module within the MOVE software package from Midland Valley. Analysis of an aerial photo was performed to identify the major faults. The intensity of CSBs and ZBs was computed after a preliminary outcrop analysis. We used the variation in intensity to build a DFN that reflects a pattern of deformation similar to the natural structural framework. It is well known that both CSBs and ZBs reduce permeability, whilst slip surfaces present within faults enhance fault-parallel fluid flow. The obtained DFN was used, hence, to model the effect of deformation on host rock permeability by imposing a reduced porosity of the CSBs and ZBs relative to both host rock and slip surfaces. By taking advantage of the computed distribution of both porosity and permeability within the modelled rock volume, fluid flow simulations have been carried out by solving the flow and transport equations with finite elements. In

  16. Strain partitioning and timing of strike-slip faulting in the central Mojave Desert, CA, indicated by newly dated Pliocene and lower Pleistocene deposits

    NASA Astrophysics Data System (ADS)

    Miller, D. M.; Nuriel, P.; Oster, J. L.; Schmidt, K. M.; Reheis, M. C.; Cox, B. F.; Maher, K.

    2014-12-01

    New insights into ages for sinistral-slip faults and how they operate in simple slip mode even after 60 degrees of vertical axis rotation are revealed by study of coarse gravels in the area within ~40 km of Barstow, CA. Using 31 new U-Pb dates of opaline soil precipitates and crosscutting veins in faults, we demonstrate that many deposits are in the 1-4 Ma age range. Clast provenance and transport direction from sedimentary structures indicate that in the Pliocene a line of uplifts lay from western Fort Irwin to the Daggett Ridge area SE of Barstow, forming an irregular north-trending divide. East of the divide, deposition occurred in broad east-flowing (in modern coordinates) stream valleys coincident with sinistral faults. This relation is best demonstrated from the Manix fault northward into Fort Irwin, and is also suggested for the Cady fault. West of the divide, data are limited but consistent with the interpretation that north-and south-flowing streams met in a central, W- or WSW-flowing system in an axial valley near the modern Mojave River. Folded Pliocene deposits and the paleogeography indicate that strain was partitioned into sinistral fault slip and folds parallel to faults, with synclines forming valleys 7-10 km wide. Folds associated with the dextral faults west of the divide are much broader, with wavelengths of ~50 km and ~westerly trends. Pliocene uplifts that formed the divide have mostly persisted as topographic highs that lie roughly along the boundary between sinistral and dextral domains. The uplifts may reflect block interactions along the boundary including differential vertical-axis rotation of blocks in the sinistral domain. Partitioning of strain into folds and faults helps resolve the conundrum of why sinistral faults that rotated ~60 degrees out of Coulomb failure orientation, and have little resolved shear stress, persist as simple strike-slip faults. It may also explain why the central Mojave Desert is more mountainous than the

  17. 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

  18. Right-lateral displacements and the Holocene slip rate associated with prehistoric earthquakes along the southern Panamint Valley fault zone: Implications for southern Basin and Range tectonics and coastal California deformation

    SciTech Connect

    Peizhen Zhang; Ellis, M.; Slemmons, D.B.; Fengying Mao )

    1990-04-10

    The N 20{degree}W-trending Panamint Valley fault zone is linked to the N 60{degree}W-trending Hunter Mountain strike-slip fault and the Saline Valley fault system, which represents on of the three major fault systems accommodating active crustal extension in the southern Great Basin. The displacement associated with the most recent event, determined through six detailed topographic maps of offset features, is 3.2 {plus minus} 0.5 m, and a number of larger offsets, in range of 6-7 m and 12 m, are also observed. If the larger displacements represent, respectively, two and three events, each of {approximately} 3 m, then the fault zone appears to be associated with a characteristic earthquake, which the authors estimate from the length of the rupture zone and the displacement to be between (Ms) 6.5 and 7.2. The Holocene slip rate is 2.36 {plus minus} 0.79 mm/yr, is determined from the displacement of two alluvial features whose maximum age is estimated from pluvial shorelines. Assuming a characterisitc earthquake model, the recurrence interval is between 860 and 2,360 years. The total slip vector of the southern Panamint Valley fault system is oriented toward {approximately} N 35{degree}W, making this a predominately strike-slip fault. In conjunction with the N 60{degree}W orientation of the Hunter mountain strike-slip fault, the authors suggest that the displacement vector for the southern Great Basin is toward the NW, consistent with results from VLBI data, rather than WNW as determined by combining VLBI and geological data. This is turn suggests that the coastal California deformation component involves, respectively, less shortening and more strike-slip displacement perpendicular and parallel to the San Andreas fault than is currently proposed.

  19. Evolution and dynamics of active faults in southeastern Egyptian Western Desert

    NASA Astrophysics Data System (ADS)

    Abdeen, Mamdouh

    2016-07-01

    Remote sensing data processing and analysis together with interpretation of earthquake data that are followed by extensive field studies on some of the prevailing NS and EW striking faults indicate that these faults have an intimate relationship and were formed synchronously as a conjugate Riedel shears. Parallel to the NS and the EW faults open fractures filled with blown sand dominate the area of study. The Quaternary terraces adjacent to these faults are offset by the faults. Kinematic indicators on the NS striking faults indicate major sinistral (left-lateral) strike slip and minor dip-slip (normal) movement. On the other hand, kinematic indicators on the EW striking faults indicate major dextral (right-lateral) strike slip and minor dip-slip (normal) movement. Paleo-stress analysis of the fault striae measured on the NS and EW faults indicate that these faults were formed under NNE-SSW oriented extension. Instrumental earthquake data analysis shows a comparable extension direction to that derived from field measurements of slickenlineation. These observations indicate that the NS- and EW-striking faults are contemporaneous and are related to the Red Sea rifting that is currently active.

  20. Offset of latest pleistocene shoreface reveals slip rate on the Hosgri strike-slip fault, offshore central California

    USGS Publications Warehouse

    Johnson, Samuel Y.; Hartwell, Stephen R.; Dartnell, Peter

    2014-01-01

    The Hosgri fault is the southern part of the regional Hosgri–San Gregorio dextral strike‐slip fault system, which extends primarily in the offshore for about 400 km in central California. Between Morro Bay and San Simeon, high‐resolution multibeam bathymetry reveals that the eastern strand of the Hosgri fault is crossed by an ∼265  m wide slope interpreted as the shoreface of a latest Pleistocene sand spit. This sand spit crossed an embayment and connected a western fault‐bounded bedrock peninsula and an eastern bedrock highland, a paleogeography resembling modern coastal geomorphology along the San Andreas fault. Detailed analysis of the relict shoreface with slope profiles and slope maps indicates a lateral slip rate of 2.6±0.9  mm/yr, considered a minimum rate for the Hosgri given the presence of an active western strand. This slip rate indicates that the Hosgri system takes up the largest share of the strike‐slip fault budget and is the most active strike‐slip fault west of the San Andreas fault in central California. This result further demonstrates the value and potential of high‐resolution bathymetry in characterization of active offshore faults.

  1. Rock pulverization and localization of a strike-slip fault zone in dolomite rocks (Salzach-Ennstal-Mariazell-Puchberg fault, Austria)

    NASA Astrophysics Data System (ADS)

    Schröckenfuchs, Theresa; Bauer, Helene; Grasemann, Bernhard; Decker, Kurt

    2015-09-01

    Detailed investigations of dolomite fault rocks, formed at shallow crustal depths along the Salzach-Ennstal-Mariazell-Puchberg (SEMP) fault system in the Northern Calcareous Alps, revealed new insights into cataclasite formation. The examined Miocene, sinistral strike-slip faults reveal grain size reduction of dolomite host rocks by tensile microfracturing at a large range of scales, producing rock fragments of centimetre to micrometre sizes. In situ fracturing leads to grain size reduction down to grain sizes <25 μm, producing mosaic breccias and fault rocks which have previously been described as "initial/embryonic" and "intermediate" cataclasites. At all scales, grain fragments display little to no rotation and no or minor evidence of shear deformation. The observed microstructures are similar to those previously described in studies on pulverized rocks. Microstructural investigations of cataclasites and mosaic breccias revealed aggregations of small dolomite grains (<50 μm) that accumulated on top of large fragments or as infillings of V-shaped voids between larger grains and show constant polarity throughout the investigated samples. Fabrics indicate deposition in formerly open pore space and subsequent polyphase cementation. The newly described tectonic geopetal fabrics (geopetal-particle-aggregates, GPA) prove that these faults temporarily passed through a stage of extremely high porosity/permeability prior to partial cementation.

  2. Rheologic evolution of low-grade metasedimentary rocks and granite across a large strike-slip fault zone: A case study of the Kellyland fault zone, Maine, USA

    NASA Astrophysics Data System (ADS)

    Sullivan, W. A.; Monz, M. E.

    2016-05-01

    We examine a large strike-slip fault zone that juxtaposes low-grade clastic metasedimentary rocks with coarse-grained granite near the brittle-ductile transition. The load-bearing matrixes in granite-derived ultramylonites and pelite and wacke metasedimentary intervals are texturally similar, and all deformed by diffusion-assisted granular flow. Granite underwent rapid strengthening as the pluton cooled followed by rapid weakening driven by brittle grain-size reduction and mixing that catalyzed ultramylonite formation. The textural and mineralogical similarity of pelitic intervals across the zone indicates they experienced little textural and reaction weakening. Wacke intervals record progressive textural and reaction weakening in an open system. Quartz recrystallized grain sizes in granite-derived ultramylonites record ∼2-times more differential stress than those in metasedimentary rocks in the interior of the zone. The relative weakness of metasedimentary rocks is correlated with fluid influx that likely enhanced diffusion and grain-boundary sliding in pelitic and wacke intervals and catalyzed textural and reaction weakening in wacke intervals. The lack of evidence for fluid and ionic communication with granitic rocks indicates that fluid movement was restricted to foliation-parallel pathways within single rock units. This localized fluid influx is the best explanation for the strength contrasts between texturally similar fault rocks deformed by similar mechanisms.

  3. Calcite veins as an indicator of fracture dilatancy and connectivity during strike-slip faulting in Toarcian shale (Tournemire tunnel, Southern France)

    NASA Astrophysics Data System (ADS)

    Lefèvre, Mélody; Guglielmi, Yves; Henry, Pierre; Dick, Pierre; Gout, Claude

    2016-02-01

    The reactivation of faults induced by natural/human induced fluid pressure increases is a major concern to explain subsurface fluid migration and to estimate the risk of losing the integrity of reservoir/seal systems. This study focusses on paleo-fluid migration in a strike slip fault with >100 m long, affecting a Toarcian shale (Causses Basin, France). A high calcite concentration is observed in a 5 cm thick zone at the boundary between the fault core and damage zone. Cumulated displacements in this zone are of millimeter-to-centimeter-scale offsets and different dilatant deformation textures are observed. The zone is affected by thin slip planes containing gouge. Cathodo-luminescence observations indicate that two phases of vein formation occurred. The first phase coincides with the fluid migration along this centimeter thick dilatant zone. The second one is associated to re-shear along the millimeter thick slip planes that results in more localized mineralization, but also in a better hydrologic connection through the shale formation. These results show that in shales fluids may migrate off a slipping surface in centimeter scale dilatant volumes, at first controlled by the intact shale anisotropy related to bedding and then favored by brecciating, structures re-orientation and strengthening processes induced by calcite sealing effects.

  4. Fold and thrust belt structures and strike-slip faulting at the SE margin of the Salar de Atacama basin, Chilean Andes

    NASA Astrophysics Data System (ADS)

    Kuhn, Dirk

    2002-07-01

    A tectonic reinterpretation is reported for the southeastern margin of the Salar de Atacama basin of northern Chile. Detailed structural mapping revealed the presence of an east vergent thin-skinned fold and thrust belt affecting Oligocene-Miocene Paciencia Group rocks and the overlying Plio-Pleistocene volcanic rocks. Along-strike segmentation of the main fold implies local foreland influence on footwall ramp geometry leading to local thrust sheet rotation. To the east the adjacent western slope of the Western Cordillera displays two different structural domains, probably controlled by preexisting basement structures. The southern domain comprises two N-S oriented sigmoidal belts of linear arranged pressure ridges, indicating left-lateral transpression. In contrast, the northern domain is characterized by east vergent fold and thrust belt structures and reactivated NW-SE striking sinistral strike-slip faults, governing clockwise block rotations. An indenter-driven deformation model is proposed to explain sinistral transpression and clockwise block rotations around vertical axes. This variant of a small-block rotation mechanism is discussed in the context of oroclinal bending of the central Andes, emphasizing the significance of ancient structures in controlling rotations.

  5. E-W extension and mid-crustal extrusion governed by strike-slip faulting in southern Tibet

    NASA Astrophysics Data System (ADS)

    Edwards, M. A.

    2004-05-01

    Unfortunately Tibet is flat and high and far away. The enduring models (e.g. England et Houseman 1989) of the India-Asia plate convergence zone require no fieldwork and typically consider the gravitational potential and low hypsometric variation to infer a viscous "weak" middle and or lower crust - there is no linear transduction of crustal failure stresses to the surface and no crustal scale localisation. It is thought that Tibet is currently flowing "downhill" to the east (e.g. Clark et Royden 2000) and it is generally accepted that a key temporal-spatial switch is the plateau reaching some critical elevation after which the upper brittle plateau cracks up, riding on the eastward flow. Locally high heat flow and geophysical data from project INDEPTH (Nelson et al. 1996) seem to corroborate, imaging possible melts or fluids in a N-S trending graben adjacent to a granitic-gneiss cored range (the NQTL) suggested to have been extruded (core-complex style) from a molten middle crust initiating at ca. 8 Ma and thereby timing initiation of eastward flow. This study presents mapping, structural surveying, palaeostress and geochronologic data from a hitherto largely unrecognised >200 km long, presently active, sinistral wrench fault (the DJSZ) that cuts the continental lithosphere. Gradual southwards migration (<15 km) has exhumed palaeostrands of the fault (to upper greenschist facies) allowing spectacular access to the deep interior of the fault zone (historic portions). The DJSZ was active pre-, syn and post-plutonism to the NQTL and was shearing at greenschist facies at ca. 8 Ma, suggesting the DJSZ has played a major role in the melt influx, growth and emergence of the NQTL. Moreover, extensive evidence for historic DJSZ fluid flow (range of T's) and sub-surface imaging of the present fault architecture suggests that much of the partial melt evidence in southern Tibet is engendered from fluids in shear splays from the DJSZ. This suggests that the tectonic setting in

  6. Properties of Ductile Shear Zones Below Strike-Slip Faults: Insights From Numerical Experiments Incorporating Laboratory-Derived Rheologies (Invited)

    NASA Astrophysics Data System (ADS)

    Fialko, Y. A.; Takeuchi, C. S.

    2013-12-01

    We investigate the long-term evolution of stress and strain in a ductile substrate driven by far-field plate motion and slip on a vertical transform fault cutting through the brittle crust. Numerical models that incorporate laboratory-derived power-law rheologies with Arrhenius temperature dependence, viscous dissipation, and conductive heat transfer give rise to long-lived fault "roots" that localize deformation below the brittle-ductile transition. Strain localization in the viscoelastic medium in this case results from thermomechanical coupling and power law dependence of strain rate on stress. For conditions corresponding to the San Jacinto and San Andreas Faults in Southern California, the predicted width of the shear zone in the lower crust is a few kilometers; this shear zone accommodates more than 50% of the far-field plate motion. Coupled thermomechanical models predict a single-layer lithosphere in case of "dry" composition of the lower crust and upper mantle, and a "jelly sandwich" lithosphere in case of "wet" composition. Deviatoric stress in the lithosphere in our models is relatively insensitive to the water content, the far-field loading rate, and the fault strength, and is of the order of 102 MPa. Furthermore, stress in the lithosphere is found to inversely correlate with the velocity of relative plate motion. Somewhat surprisingly, we find that the thermally-activated shear zones have little effect on postseismic relaxation. In particular, the presence of such zones does not change the polarity of vertical displacements in cases of rheologies that are able to generate robust postseismic transients. We conclude that additional (to thermomechanical coupling) mechanisms of strain localization are required for a viscoelastic model to produce a vertical deformation pattern similar to that due to afterslip on a deep extension of a fault. Possible candidates include dynamic grain re-crystallization, and fabric development (mylonitization).

  7. 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.

  8. Resolving Rupture Directivity of Moderate Strike-Slip Earthquakes in Sparse Network with Ambient Noise Location: A Case Study with the 2011 M5.6 Oklahoma Earthquake

    NASA Astrophysics Data System (ADS)

    He, X.; Ni, S.

    2015-12-01

    Earthquake rupture directivity is essential for improving reliability of shakemap and understanding seismogenic processes by resolving the ruptured fault. Compared with field geological survey and InSAR technique, rupture directivity analysis based on seismological data provides rapid characterization of the rupture finiteness parameters or is almost the only way for resolving ruptured fault for earthquakes weaker than M5. In recent years, ambient seismic noise has been widely used in tomography and as well as earthquake location. Barmin et al. (2011) and Levshin et al. (2012) proposed to locate the epicenter by interpolating the estimated Green's functions (EGFs) determined by cross-correlation of ambient noise to arbitrary hypothetical event locations. This method does not rely on an earth model, but it requires a dense local array. Zhan et al. (2011) and Zeng et al. (2014) used the EGFs between a nearby station and remote stations as calibration for 3D velocity structure and then obtained the centroid location. In contrast, the hypocenter can be determined by P wave onsets. When assuming unilateral rupture, we can resolve the rupture directivity with relative location of the centroid location and hypocenter. We apply this method to the 2011 M5.6 Oklahoma earthquake. One M4.8 foreshock and one M4+ aftershock are chosen as reference event to calibrate the systematic bias of ambient noise location. The resolved rupture plane strikes southwest-northeast, consistent with the spatial distribution of aftershocks (McNamara et al., 2015) and finite fault inversion result (Sun et al., 2014). This method works for unilaterally ruptured strike-slip earthquakes, and more case studies are needed to test its effectiveness.

  9. 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

  10. Segmentation and kinematics of the Kazerun fault system (southern Iran): Implications for active deformation partitioning within the Zagros fold-and-thrust belt

    NASA Astrophysics Data System (ADS)

    Authemayou, C. A.; Bellier, O. B.; Chardon, D. C.; Malekzade, Z. M.; Abbassi, M. A.

    2003-04-01

    Iran is located within the interaction zone between the Arabian and Eurasian plates that currently converge at 30 mm/yr. Since the Miocene, continental collision resulted in the formation of the NW-trending Zagros fold-and-thrust belt that accommodates c.a. 10 mm/yr of NNE-trending shortening. The southeastern part of the thrust belt is affected by the north-trending, right lateral Kazerun Fault System (KFS) stretching from the Main Reverse Fault (i.e., the back-stop of the fold-and-thrust belt) in the vicinity of Borujen, in the North, to the Persian Gulf coast near Kormuj, in the south. Reconnaissance tectonic and geomorphic observations, combined with SPOT satellite image analyses allows characterising the KFS active trace geometry and kinematics as well as its relations with the folds and the thrust faults. This further allows evaluating the transfer process from right-lateral slip along the KSF to the fold-and-thrust system. The KFS consists in three North-trending fault zones of equivalent lengths (100 km) that show evidence for a northward increasing activity. The southern terminations of the fault zones are bent towards SE strikes and are generally connected westward with WNW-trending thrusts and ramp anticlines. Those terminations display a horsetail splay fault geometry associated with an eastward decrease of both the strike-slip and dip-slip component of finite offsets. Fault slip-vectors analyses indicate a consistent right-lateral strike-slip tectonic regime all along the KFS associated with a regionally homogeneous NNE-trending 1 direction. The central and northern fault zones show evidence for systematic Quaternary right-lateral offsets of geomorphic features such as stream beds and alluvial fans, as well as shutter ridges and faceted spurs. The northern termination of the KFS shows the most obvious criteria for active slip and the highest geomorphic offsets. This fault zone connects the southeastern tip of the Main Recent Fault, the major active

  11. Seismogenic Cycles, Quartz Microstructures and Localization at the Frictional to Viscous Transition in an Exhumed, Large-Displacement, Seismogenic Strike-Slip Fault

    NASA Astrophysics Data System (ADS)

    Song, W. J.; Johnson, S. E.; Price, N.; Song, B. R.; Gerbi, C. C.; West, D. P., Jr.

    2014-12-01

    The frictional-to-viscous transition (FVT) in the vicinity of seismogenic faults experiences coseismic fracturing/frictional sliding followed by viscous creep during postseismic relaxation. A more complete understanding of these processes at the FVT is important owing to its control over the mechanical decoupling between crustal levels. However, well-preserved microstructural records from this depth are rarely preserved in exhumed faults because of progressive deformation and metamorphism in exhumation. We investigate quartz deformation microstructures from traverses across the Sandhill Corner shear zone, a strand of the Norumbega fault system (an ancient large-displacement, subvertical strike-slip fault system in the northeastern Appalachians) exhumed from FVT depths in order to characterize in greater detail the previously proposed architecture that divides the shear zone into an outer zone, inner zone and core. Trends in quantitative crystallographic preferred orientation (CPO) and misorientation data from electron backscatter diffraction and 2D grain-size distributions confirm finer grain sizes within the inner zone and core, a weak CPO pattern and randomization in the misorientation of randomly selected grain pairs. Additional analyses with finer sample spacing and using fabric intensity indices (J- & M-Index), we show a progressive weakening of the CPO from the outer edges to the core and a decrease in grain size down to an average of 8 μm at the core, an average finer than previously reported. Within the inner zone and core (ca. 30m width), the microstructural parameters are unusual: a weak CPO but a pattern clearly indicative of basal slip. New deformation mechanism maps for different parts of the shear zone suggest deformation near the transition to grain size-sensitive creep. Our data confirms and builds new evidence for the model that during the seismic cycle, quartz grains within the core and inner zone experienced cycles of coseismic microfracture

  12. Hydrothermal alteration related to a deep mantle source controlled by a Cambrian intracontinental strike-slip fault: Evidence for the Meruoca felsic intrusion associated with the Transbraziliano Lineament, Northeastern Brazil

    NASA Astrophysics Data System (ADS)

    Santos, Roberto Ventura; Oliveira, Claudinei Gouveia de; Parente, Clóvis Vaz; Garcia, Maria da Glória Motta; Dantas, Elton Luis

    2013-04-01

    One of the most prominent geological structures in Borborema Province, northeast Brazil, is the Transbraziliano Lineament that crosscuts most of the South American Platform and was active at least until the Devonian. This continental structure is responsible for the formation of rift and pull-apart basins in Northeastern Brazil, most of which filled with volcanic and continental sedimentary rocks (Parente et al., 2004). In the region of Sobral, Ceará State, this same continental structure controlled the intrusion of the Meruoca pluton and the formation of the Jaibaras Basin, which is bounded by strike-slip shear zones. Hydrothermal alterations seem to have been pervasive in Meruoca, as indicated by disturbances in both the Rb-Sr and U-Pb systems (Sial et al., 1981; Fetter, 1999) and by the large dispersion of anisotropic magnetic susceptibility (AMS) (Archanjo et al., 2009). In this paper, we address the origin of the hydrothermal fluids that affected the borders of the Meruoca batholith and their relationship with the activity of the Transbraziliano Lineament. These fluids were responsible for carbonate veins and Fe-Cu mineral concentrations that are commonly found associated with hydrothermally altered breccias. The carbon and oxygen isotope composition of these carbonate veins suggest that they may be related to CO2-bearing mantle-derived fluids that were channelized by the Transbraziliano Lineament. Based on oxygen isotopes, we argue that Fe-Cu concentrations may have formed in isotope equilibrium with the rhyolitic rocks at temperatures between 500 and 560 °C. This scenario points to magmatism as the main process in the formation of these rocks. We also report a K-Ar age of 530 ± 12 Ma for muscovite associated with the last ductile event that affected the Sobral-Pedro II Shear Zone and a U-Pb age of 540.8 ± 5.1 Ma for the Meruoca pluton. We further suggest that this granite is a late-kinematic intrusion that is most likely associated with the Parapu

  13. Field study and three-dimensional reconstruction of thrusts and strike-slip faults in the Central Andes: implications for deep-seated geothermal circulation and ore deposits exploration

    NASA Astrophysics Data System (ADS)

    Norini, Gianluca; Groppelli, Gianluca; Giordano, Guido; Baez, Walter; Becchio, Raul; Viramonte, Jose; Arnosio, Marcelo

    2014-05-01

    The Puna plateau (NW Argentina), located in the back-arc of the Central Andes, is a plateau characterized by both orogen-parallel and orogen-oblique deformation styles, extensive magmatic and geothermal activity, and the broad occurrence of igneous and hydrothermal ore-forming minerals. In this area, like in other convergent margins, the behaviour of the magma-tectonics interplay can affect the circulation of hydrothermal fluids, so that the full comprehension of the tectonic control on the magmas and fluids paths in the continental crust is crucial to plan the geothermal and ore exploration. In this study, we present a structural analysis of the back-arc portion of the orogen-oblique Calama-Olacapato-El Toro fault system and the surrounding orogen-parallel thrust faults in the central-eastern Puna Plateau, comprising the Cerro Tuzgle-Tocomar geothermal volcanic area, with high geothermal potential, and silicic calderas and domes associated with epithermal ore deposits. We also focused on the tectonic and volcanotectonic structures of the Chimpa and Tuzgle stratovolcanoes, two of the most important polygenetic volcanic centres of the plateau. Morphostructural analysis and field mapping reveal the geometry, kinematics and dynamics of the tectonic structures of the studied area. These data and the available stratigraphic and geophysical data have been integrated with the software MOVE and PETREL in a three-dimensional reconstruction of the main fault planes, showing their attitude and intersections at depth. As a result of our study, we show that despite different geometry and kinematics of the Calama-Olacapato-El Toro fault system and the thrust faults, they formed and evolved under the same progressive evolving dynamic state, forming a single tectonic system and accommodating crustal shortening of a thickened crust. In this frame, the crust underwent simultaneous deformation along both the low-angle thrust faults and the vertical transcurrent strike-slip faults

  14. Geochemistry and fluid inclusions across a crustal strike-slip Mesozoic fault: insights of fluid-flow / rock interaction in the Atacama Fault System

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Faults architecture and their permeability related fractures play a first order role in fluid-flow migration throughout the upper crust. Commonly, the interaction between fluid-flow migration and host rock is reflected as mineral precipitation in a vein mesh and/or as mineralogical changes (alteration) of the host rock. Often, however, the relationship between a fault zone and the fluid-flow passing through it is poorly understood. In order to improve our understanding of this process we have chosen, as a case study, the Jorgillo Fault (JF), which lies within the Atacama Fault System, a trench-parallel large-scale structure developed within Mesozoic rocks of the present-day Coastal Cordillera in northern Chile. The JF is represented as a ca. 18 km long NNW-SSE, in its southern end, to NW-SE, in its northern part, west-ward concave-shape sinistral strike-slip fault showing a maximum left-lateral displacement of about 4 km and a subvertical dip. The fault cuts through crystalline rocks of gabbric, dioritic and granodioritic composition. The JF core is composed by a ca. 1 m wide cataclasite zone bounded by two fault gouge zones ca. 40 cm in average while its minimum damage zone extension, based in field observations, is ca. 2 m wide each side of the core zone. A fault perpendicular transect was mapped and sampled in order to run XRF and XRD analyses of the fault core, damage zone and undeformed protolith. XRF analyses of the rocks revealed that contents of Al and Ca decrease with increasing Si, while Na increases towards the fault core. Fujita et al. (2012) interpreted similar behavior in analysis of rocks belonging to the Coloso Fault, which is genetically and spatially related to the JF, as compositional changes of plagioclase to albite-rich ones due to chloritic-propilitic alteration processes. In the damage zone, L.O.I. data increase towards the fault core but decrease inside the core in its cataclastic zone. This behavior of L.O.I. data is explained by the

  15. Coeval folding, extensional and strike-slip faulting at the eastern end of an axial culmination in the Tauern Window (Eastern Alps)

    NASA Astrophysics Data System (ADS)

    Scharf, Andreas; Schmid, Stefan; Handy, Mark

    2010-05-01

    We seek to understand how folding and extensional faulting accommodated lateral motion of orogenic crust at the eastern end of the Tauern Window in the Eastern Alps. This is key to determining how the Tauern Window evolved during Miocene indentation of the Adriatic microplate. The Katschberg normal fault zone (KNFZ) at the eastern end of the Tauern Window (Genser & Neubauer 1989) comprises a thick (1-2 km) belt of retrograde, amphibolite-to-greenschist facies mylonites (the Katschberg shear zone, KSZ) capped along its central part by a narrow (10-100 m) zone of cataclasites (the Katschberg Brittle Normal Fault, KBF). The KNFZ accommodated top-E to -SE motion of the hangingwall, indicative of normal faulting. This is consistent with the observation from a newly compiled tectonic map that the Katschberg normal fault zone thinned and locally excised the folded Early Tertiary nappe stack of the eastern TW. The KBF capping the moderately (30°) SE-dipping central part of the KSZ coincides with the greatest amount of tectonic omission of the Early Tertiary nappe stack. New measurements of the main foliation (S2) and stretching lineation (Ls2) associated with the KSZ indicate that the northern and southern continuations of the KSZ are curved and affect primarily Mesozoic calc-schists (Bündnerschiefer) around the perimeter of the eastern TW. The northern continuation of the KSZ reveals dextral shear sense along moderately N- to NE-dipping S2 surfaces, whereas its southern continuation shows sinistral shear sense on subvertical, NE-SW striking S2 surfaces. These S2 surfaces accommodate sinistral strike-slip movement and bend into an orientation subparallel to the Mölltal fault, a major fault that has been interpreted as a stretching fault (Kurz & Neubauer 1996) that produced both dextral displacement and NE-side up vertical displacement. The relative ages of the KSZ and Mölltal Fault are not yet known, but we tentatively explain the opposite shear senses along the

  16. Insights into Surface Manifestation of Aseismic vs. Coseismic Strike-Slip Faulting from UAV Imagery of Creep-Induced Surface Fracturing Along the Central San Andreas Fault

    NASA Astrophysics Data System (ADS)

    Bunds, M. P.; Toke, N. A.; Lawrence, A.; Arrowsmith, R.; Salisbury, J. B.

    2015-12-01

    Left-stepping en echelon fractures formed at the Dry Lake Valley paleoseismic site (DLV, 36.470N, 121.057W) on the central creeping segment of the San Andreas Fault (SAF) during the 2012-14 drought. The fractures were investigated using high resolution DEMs and orthophotos made by applying Structure from Motion processing to photos taken using a UAV and handheld cameras on 9/20/2014. At DLV the SAF is marked by a distinctive 2-7 m high west-facing scarp that extends northwestward from a dilational step-over. The orthophotos and DEMs were used to measure 110 fractures along a 37 m section of scarp and 15 additional fracture sets along a further 79 m of scarp. The fractures averaged 54 cm long by 1.8 cm wide with 22% overlap, and were mode 1 opening fractures that on average trended 184o, nearly perpendicular to the maximum extension direction for right-lateral slip along the 144o - trending SAF. The fractures occurred in ~5 m long sets that were themselves left-stepping, on average trended 159o, and were confined to a 3-4 m wide zone along the fault scarp. We interpret the fracture sets to be incipient Riedel shears with a component of extension across them based on the orientation of the sets relative to the SAF, the obliquity of the individual fractures to the trend of the sets, and the presence of topographic lows along them. We conservatively estimate 2.5 ± 1 cm of right-lateral creep on the SAF was recorded in the opening of the fractures, which probably began forming at most 21 months before the photographic survey based on precipitation records and prior site inspection. From these results and the 2.5-3.2 cm/yr creep rate for the SAF, we infer that at least ~30%, and probably 50-80% or more of creep occurs along the narrow 5-50 m wide primary geomorphic expression of the fault, and that the same amount of creep can be accommodated by brittle fracturing in a narrow 3-4 m wide zone along the fault scarp during drought periods. In comparison to seismically

  17. Moment tensor inversion of the January 8, 2013 (Mw=5.7) and May 24, 2014 (Mw 6.8) North Aegean Earthquakes: seismicity and active tectonics of the North Aegean Region

    NASA Astrophysics Data System (ADS)

    Kalafat, Dogan; Kekovali, Kivanc; Pinar, Ali

    2015-04-01

    The North Aegean Sea is one of the most seismically active and deforming region between the Eurasia and Anatolia tectonic plates. On 8th January 2013 at 14:16 UTC (16:16 local time) a moderate earthquake (Mw= 5.7) occurred between the south of Gökçeada and southwest of Bozcaada Islands. The earthquake was felt at a wide area. Especially felt in the NE Greece south of Lemnos Island and NW Turkey surrounding areas, such as Çanakkale, Marmara Region and Northern Aegean coast as well as to Athens. The area is defined as the continuation of the branch of North Anatolian Fault (NAF) inside the Aegean Sea. Fault plane solution determined by this study shows that the earthquake occurred on NE-SW oriented strike slip fault segment. The aftershocks distribution also supported the rupture of the NE-SW oriented fault. Approximately 17 months later, another big earthquake occurred in the same area. On 24th May 2014, at 09:25 UTC (12:25 local time), a powerful Ml=6.7 (Mw=6.8) earthquake hit Greece and Turkey, 87 km west of Çanakkale, and totally 350 people injured in Greece and Turkey. This earthquake has been strongly felt in Greece, Turkey, Bulgaria, Romania. The main-shock occurred on a fault with a NE-SW strike, where the largest portion of the energy was released towards these directions. Therefore the earthquake was felt strongly in Çanakkale, Istanbul and Marmara region. In this study we calculated CMT solutions for main-shock and important aftershocks (M>4.0). CMT analyses were done for 50 important earthquakes. Moment tensor solutions show generally strike-slip faulting. The fault which caused earthquake, is thought to be a branch of North Anatolian Fault Zone in the North Aegean Sea. Generally, the location of the earthquakes and orientation of the NE-SW nodal planes are consistent with right-lateral faulting within the North Aegean Trough (NAT). The Aegean Sea is characterized by dextral strike-slip faulting along NE-SW striking faults, along fault zones formed

  18. Helena banks strike-slip(. ) fault and the relation to other Cenozoic faults along reactivated Triassic(. ) basin boundary fault zones in the Charleston, South Carolina, earthquake area - results from a marine high-resolution multichannel seismic-reflection survey

    SciTech Connect

    Behrendt, J.C.; Yuan, A.

    1985-01-01

    In 1981, the USGS conducted a high-resolution multichannel seismic (MCS) survey offshore of Charleston, South Carolina, to study the relation of Cenozoic faulting to future earthquake hazard. High-angle reverse displacement of Coastal Plain sedimentary rock indicating a linear increase with depth of 51 +/- 12 m/km is observed on the reflection profiles. This is similar to the Gants and Cooke faults in the meizoseismal area of the 1886 Charleston earthquake. The authors interpret these results to indicate that the stress field cannot have varied significantly in direction or in magnitude from Late Cretaceous time to Miocene or Pliocene time in the region. The HBF zone trends N 66/sup 0/ E; it comprises several 15- to 40-km-long segments that trend from N 68/sup 0/ E to N 77/sup 0/ E. The en-echelon pattern of the segments is compatible with left-lateral strike-slip and is thus consistent with the present northeast-trending maximum compressional stress field. The HBF zone appears to be an obliquely compressional reactivation of a tensional Triassic(.) fault zone bounding the Triassic(.) Kiawah Basin that has been identified on several MCS profiles. Similarly, the northeast-trending Gants reverse or strike-slip fault was probably reactivated from an old tensional fault bounding the Jedburg Triassic(.) basin in the 1886 meizoseismal area.

  19. Structural Analysis of Active North Bozgush Fault Zone (NW Iran)

    NASA Astrophysics Data System (ADS)

    Saber, R.; Isik, V.; Caglayan, A.

    2013-12-01

    NW Iran is one of the seismically active regions between Zagros Thrust Belt at the south and Caucasus at the north. Not only large magnitude historical earthquakes (Ms>7), but also 1987 Bozgush, 1997 Ardebil (Mw 6.1) and 2012 Ahar-Varzagan (Mw 6.4) earthquakes reveal that the region is seismically active. The North Bozgush Fault Zone (NBFZ) in this region has tens of kilometers in length and hundreds of meters in width. The zone has produced some large and destructive earthquakes (1593 M:6.1 and 1883 M:6.2). The NBFZ affects the Cenozoic units and along this zone Eocene units thrusted over Miocene and/or Plio-Quaternary sedimentary units. Together with morphologic features (stream offsets and alluvial fan movements) affecting the young unites reveal that the zone is active. The zone is mainly characterized by strike-slip faults with reverse component and reverse faults. Reverse faults striking N55°-85°E and dip of 40°-50° to the SW while strike-slip faults show right lateral slip with N60°-85°W and N60°-80°E directions. Our structural data analysis in NBFZ indicates that the axis direction of σ2 principal stress is vertical and the stress ratio (R) is 0.12. These results suggest that the tectonic regime along the North Bozgush Fault Zone is transpressive. Obtained other principal stresses (σ1, σ3) results are compatible with stress directions and GPS velocity suggested for NW Iran.

  20. How crustal-scale strike-slip faults initiate and further develop: The Red River fault and the East Himalaya Syntaxis as a result of the two-stage

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz

    2014-05-01

    One major question of tectonics is how and where major intracontinental transcurrent strike-slip faults initiate. Models assume an important rheological contrast between rheologically weak and strong lithologies, e.g. at margins of a stiff craton and juxtaposed mobile belts (Molnar & Dayem, 2010 and references therein). Several models assume weakening of the lithosphere by uprise of magma, e.g., formed by subduction or break off of the previously subducted lithosphere or as K-granites at the bases of a metasomatized lithosphere. In the case of slab break-off following oblique convergence, orogen-parallel strike-slip accommodation has been documented. Especially, the spatiotemporal relationships between synkinematic plutons and crustal-scale strike-slip faults have been documented worldwide. It is a matter of continuous debate whether strike-slip faults nucleate where melts have previously weakened the crust/lithosphere or whether pre-existing faults represent the preferred pathways for the ascending melt. A few further models document the role of lateral boundaries of metamorphic core complexes. The significance of some of these processes could be studied along the Red River (RR) fault, SE, Asia. Here we propose a model, how the development of RR fault evolved in response to the two-stage India-Asia collision that recently was proposed by van Hinsbergen et al., (2012 and references therein) and the interaction of the northeastern corner of the East Himalayan Syntaxis with Himalayan-Burman/Indochina collision belt. We propose a four-phase tectonic evolution for the RR fault. During the Eocene accretion of the Tethyan block to Asia, the Sichuan foreland subducted and Eocene K-granites evolved, which started to vertically extrude and introduced, causing a zone of weakness within the crust (Phase 1) along the future RR fault. Another consequence of continuing shortening after the Tethyan block-Asia collision (Stage 1 collision) is lateral extrusion of blocks, and the

  1. Geomorphic features of active faults around the Kathmandu Valley, Nepal, and no evidence of surface rupture associated with the 2015 Gorkha earthquake along the faults

    NASA Astrophysics Data System (ADS)

    Kumahara, Yasuhiro; Chamlagain, Deepak; Upreti, Bishal Nath

    2016-04-01

    The M7.8 April 25, 2015, Gorkha earthquake in Nepal was produced by a slip on the low-angle Main Himalayan Thrust, a décollement below the Himalaya that emerges at the surface in the south as the Himalayan Frontal Thrust (HFT). The analysis of the SAR interferograms led to the interpretations that the event was a blind thrust and did not produce surface ruptures associated with the seismogenic fault. We conducted a quick field survey along four active faults near the epicentral area around the Kathmandu Valley (the Jhiku Khola fault, Chitlang fault, Kulekhani fault, Malagiri fault and Kolphu Khola fault) from July 18-22, 2015. Those faults are located in the Lesser Himalaya on the hanging side of the HFT. Based on our field survey carried out in the area where most typical tectonic landforms are developed, we confirmed with local inhabitants the lack of any new surface ruptures along these faults. Our observations along the Jhiku Khola fault showed that the fault had some definite activities during the Holocene times. Though in the past it was recognized as a low-activity thrust fault, our present survey has revealed that it has been active with a predominantly right-lateral strike-slip with thrust component. A stream dissecting a talus surface shows approximately 7-m right-lateral offset, and a charcoal sample collected from the upper part of the talus deposit yielded an age of 870 ± 30 y.B.P, implying that the talus surface formed close to 870 y.B.P. Accordingly, a single or multiple events of the fault must have occurred during the last 900 years, and the slip rate we estimate roughly is around 8 mm/year. The fault may play a role to recent right-lateral strike-slip tectonic zone across the Himalayan range. Since none of the above faults showed any relationship corresponding to the April 25 Gorkha earthquake, it is possibility that a potential risk of occurrence of large earthquakes does exist close to the Kathmandu Valley due to movements of these active

  2. Verbal suppression and strategy use: a role for the right lateral prefrontal cortex?

    PubMed

    Robinson, Gail A; Cipolotti, Lisa; Walker, David G; Biggs, Vivien; Bozzali, Marco; Shallice, Tim

    2015-04-01

    Verbal initiation, suppression and strategy generation/use are cognitive processes widely held to be supported by the frontal cortex. The Hayling Test was designed to tap these cognitive processes within the same sentence completion task. There are few studies specifically investigating the neural correlates of the Hayling Test but it has been primarily used to detect frontal lobe damage. This study investigates the components of the Hayling Test in a large sample of patients with unselected focal frontal (n = 60) and posterior (n = 30) lesions. Patients and controls (n = 40) matched for education, age and sex were administered the Hayling Test as well as background cognitive tests. The standard Hayling Test clinical measures (initiation response time, suppression response time, suppression errors and overall score), composite errors scores and strategy-based responses were calculated. Lesions were analysed by classical frontal/posterior subdivisions as well as a finer-grained frontal localization method and a specific contrast method that is somewhat analogous to voxel-based lesion mapping methods. Thus, patients with right lateral, left lateral and superior medial lesions were compared to controls and patients with right lateral lesions were compared to all other patients. The results show that all four standard Hayling Test clinical measures are sensitive to frontal lobe damage although only the suppression error and overall scores were specific to the frontal region. Although all frontal patients produced blatant suppression errors, a specific right lateral frontal effect was revealed for producing errors that were subtly wrong. In addition, frontal patients overall produced fewer correct responses indicative of developing an appropriate strategy but only the right lateral group showed a significant deficit. This problem in strategy attainment and implementation could explain, at least in part, the suppression error impairment. Contrary to previous studies

  3. The relationship between normal and strike-slip faults in Valley of Fire State Park, Nevada, and its implications for stress rotation and partitioning of deformation in the east-central Basin and Range

    NASA Astrophysics Data System (ADS)

    Aydin, Atilla; de Joussineau, Ghislain

    2014-06-01

    This study expands on our earlier studies of the evolution of fracturing and faulting in the Jurassic aeolian Aztec Sandstone exposed over a large area in the Valley of Fire State Park, southeastern Nevada. Based on a nearly three-dimensional data set collected from 200-m-high cliff-face exposures with stair-case morphology composed of steep and flat parts, we find that a series of inclined, relatively low-angle normal faults and their splay fractures are precursors of the strike-slip fault network that we previously documented. We discuss the significance of this finding in terms of the tectonics of the broader area, stress rotation, partitioning of deformation, and the development of fracture clusters with compartmentalization of the structures as a function of spatial, depositional and deformational domains.

  4. 300-km-long co-seismic surface rupture produced by the 2008 Mw 7.9 Wenchuan earthquake along the active Longmen Shan Thrust Belt, China

    NASA Astrophysics Data System (ADS)

    Lin, A.; Rao, G.; Yan, B.

    2012-12-01

    evidence that the Qingchuan Fault was ruptured by the 2008 Wenchuan earthquake and that the total length of the co-seismic surface rupture zone is up to 285-300 km. Field investigations reveal that the earthquake produced a ≥60-km-long surface rupture zone along the pre-existing Qingchuan Fault, northeastern segment of the LSTB, with the offset being mainly right-lateral strike-slip and a distinct component of vertical slip. Co-seismic surface ruptures are characterized by faults and extensional cracks. Field measurements indicate co-seismic right-lateral strike-slip displacements along the Qingchuan Fault of 0.3-0.6 m and vertical offsets of 0.2-0.5 m, which differs to the displacements observed along the central and southwestern segments of the Wenchuan surface rupture zone in the displacement amount and sense. The change in slip sense from thrust-dominated slip in the central and southwestern segments of the LSTB to right-lateral strike-slip-dominated displacement along the Qingchuan Fault reflects a change in the orientation of compressive stress along the LSTB, associated with eastward extrusion of the Tibetan Plateau as it accommodates the ongoing penetration of the Indian Plate into the Eurasian Plate.

  5. Cenozoic to active deformation in Western Yunnan (Myanmar China border)

    NASA Astrophysics Data System (ADS)

    Socquet, A.; Pubellier, M.

    2003-04-01

    The northward movement of India induces a right-lateral shear band from the Sunda trench to the easternmost Himalaya, where wrenching between India and Sunda plates, interfere with a clockwise flow of material around the Eastern Himalayan Syntaxis. We describe brittle and ductile deformation styles in Western Yunnan and Northern Myanmar, using field data and Landsat 7 imagery for Cenozoic structures as well as GPS and seismicity for active structures to unravel the Neogene to Present evolution. Western Yunnan is crossed by three continental-size ductile shear zones characterized by high mountain belts mainly composed of high-grade metamorphics and mylonitic rocks, and affected by active faulting. The easternmost metamorphic range, the Gaoligong Shan composed of verticalized foliated granites and mylonites is flattened westward and joins the Mogok metamorphic belt in Myanmar. East of the Gaoligong Shan, lie the Chong Shan and the Ailao / Diangcan Shan metamorphic ranges, which presents a vertical shistosity and a left-lateral motion. These three shear zones are separated by sedimentary fold-and-thrust-belts in the East, and , West of the Gaoligong, by Quaternary basins and volcanics. Preliminary results indicate that the Shan Scarp constituted the major strike-slip boundary between Indochina and India during Eocene to Miocene time, and accommodated deformation in right-lateral wrench. At the same time, the Ailao / Diangcan Shan and the Chong Shan zones were sheared left-laterally allowing the displacement toward the SE of Indochina block relative to south China. In the Miocene, ductile deformation migrated north along the Shan Scarp to the Mogok / Ruili metamorphic belt and the Gaoligong belt, dragging the Chong Shan right-laterally and superimposing a late right-lateral ductile deformation on its metamorphic rocks. The present-day relative motion between India and Sundaland, inferred from GPS processing, reaches 35 mm / yr in the Myanmar area. It is classically

  6. Active Structure Evolutions Deduced from Geomorphic and Geodetic Evidence, from Hsinchu to Taoyuan, Northwestern Taiwan

    NASA Astrophysics Data System (ADS)

    Chen, Y.; Wang, Y.; Hou, C.; Chen, W.

    2003-12-01

    accomplished dataset derived from geodetic network shows that except for the Hsincheng fault nearly no detectable contraction occurs across the major structures in the study area. The most surprising phenomenon is that the Fengshan river geodetically plays a major boundary. The northern crust (Taoyuan) is moving due east relatively to the southern crust (Hsinchu) in a rate of ca. 2 cm/yr. This represents that the Fengshan river is currently a right-lateral strike-slip fault, confirming the former strike-slip suggested by geomorphic features. To probe the other details, more stations and precise measurements are needed in the future.

  7. World's largest coseismic strike-slip offset: The 1855 rupture of the Wairarapa Fault, New Zealand, and implications for displacement/length scaling of continental earthquakes

    NASA Astrophysics Data System (ADS)

    Rodgers, D. W.; Little, T. A.

    2006-12-01

    We used detailed microtopographic surveys to measure fault offset along the southern trace of the Wairarapa fault, near Wellington, New Zealand, which most recently experienced a Mw > 8.1 earthquake in 1855. Our measurements at 16 localities support the inference that dextral slip in 1855 reached 18.7 m and averaged ˜16 m over the 16 km length that we studied. Five measurements were made where a single active strand comprises the fault zone, yielding "smallest" dextral offsets of 13.0-18.7 m. At Pigeon Bush, sequential beheading of a stream and new 14C dating support the interpretation that its 18.7 ± 1.0 m of offset accumulated in 1855. We also measured three "next-smallest" offsets on single-strand faults of 26.3-32.7 m, evidence that dextral slip during the previous event was ˜14 m. Eight measurements were made where the Wairarapa fault includes two closely spaced strands, yielding smallest dextral offsets of 12.9-16.0 m. At Tauherenikau River, 14C dating of postoffset mud yielded ages indistinguishable from A.D. 1855. Combining all single-strand and two-strand (minimum) estimates yields an average dextral slip of 15.5 ± 1.4 m in the study area. Historical observations and our data indicate that vertical slip reached ˜2.5 m. The large displacement and short (˜145 km) strike length yield an unusually high displacement/length ratio for the rupture. As suggested by previous dislocation modeling, we propose that the rupture extended tens of kilometers downdip (W) to merge with the underlying subduction interface. Alternatively, the rupture may have been strongly segmented at depth, yielding an earthquake with an unusually large static stress drop.

  8. Westward extension of the Levantine Basin to the Eratosthenes Seamount and the Cyprus Arc - no evidence for strike-slip motion

    NASA Astrophysics Data System (ADS)

    Klimke, Jennifer; Ehrhardt, Axel

    2013-04-01

    The Eastern Mediterranean represents a complex pattern of micro plates. A side by side distribution of diverse tectonic situations like collision, subduction, obduction and shear makes this area a very interesting spot on earth. Whereas subduction of Neo-Tethys oceanic crust is still ongoing at the Hellenic Arc, a collision occurred eastward when the Eratosthenes Seamount (ESM) entered the Cyprus Arc. If subduction is still active further east towards the Syrian coast remains unclear. The collision related deformation of the ESM and the adjacent Levantine Basin will be discussed in this paper. We present a new set of 2D multichannel seismic data, acquired in 2010 with the RV Maria S Merian, which is a dense line grid with NW-SE and NE-SW trending profiles crossing the ESM and the western part of the Levantine Basin south of Cyprus. We show first results of the profiles that were processed up to Pre-Stack Depth Migration. Based on the dense line grid with distances of not more than 5 nautical miles, we picked the key horizons in the Levantine Basin and generated reliable 3D-grids of the horizons. With this dense line grid, it was possible to trace the western extension of the Levantine Basin sometimes also referred to as Baltim Hecataeus Line (BHL), which is a fault lineament of Mesozoic age separating the Levantine Basin from the ESM. This extension is observed on every NW-SE and NE-SW trending profile and we were able to trace it even further north and south of the ESM. The BHL is believed to be reactivated as a linear sinistral transform fault that compensates the northward motion of the African-Arabian plate with respect to the blocked ESM. With our data we can show that the western extension of the Levantine Basin does not coincide with a sinistral transform fault and that it is rather a normal fault with a meandering NNE-SSW trending strike.

  9. Alternating asymmetric topography of the Alaska range along the strike-slip Denali fault: Strain partitioning and lithospheric control across a terrane suture zone

    NASA Astrophysics Data System (ADS)

    Fitzgerald, Paul G.; Roeske, Sarah M.; Benowitz, Jeffery A.; Riccio, Steven J.; Perry, Stephanie E.; Armstrong, Phillip A.

    2014-08-01

    Contrasting lithospheric strength between terranes often results in the concentration of strain and deformation within the weaker material. Dramatic alternating asymmetric topography of the central and eastern Alaska Range along the active Denali fault is due to contrasting lithospheric strength between terranes and a suture zone, controlled by fault location with respect to the irregular boundary of a relatively stronger terrane backstop. Highest topography and greatest Neogene exhumation in the central Alaska Range occur on the concave side of the arcuate Denali fault, yet to the north and on the convex side of the fault in the eastern Alaska Range. The Denali fault largely lies along a Mesozoic suture zone between two large composite terranes (Yukon and Wrangellia composite terranes: YCT and WCT), but the McKinley strand of the fault cuts across an embayment of weaker suture-zone rocks (Alaska Range suture-zone, ARSZ) within the irregular southern boundary of the YCT (Hines Creek fault). Deformation (and uplift of the Alaska Range) is driven by slip and partitioning of strain along the Denali fault, occurring preferentially in weaker rocks of the ARSZ against the stronger YCT. Where the YCT lies well north of the McKinley strand, deformation is primarily to the north of the fault (eastern Alaska Range). Where the YCT is close to the fault, deformation is primarily to the south (central Alaska Range). While the trace of the McKinley strand approximates a small circle, two restraining bends (McKinley and Hayes) pinned equidistant from the ends of this strand localize uplift and exhumation.

  10. Revealing a strike-slip plate boundary: Drill-bit seismic imaging of the San Andreas Fault at the SAFOD site

    NASA Astrophysics Data System (ADS)

    Taylor, Stewart Thomas

    2006-12-01

    The San Andreas Fault at the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, CA forms the contact between the Pacific and North American tectonic plates. The hypotheses tested in this dissertation are that this boundary (1) is not located beneath the currently recognized surface trace of the SAF, (2) is not composed of a single active strand, but at least two overlapping, positive and negative flower structures, and (3) has juxtaposed, severely folded, and then buried Tertiary to pre-Cretaceous strata not previously known to exist in the Parkfield area. These hypotheses were tested through the construction, analysis, and interpretation of a new type of drill-bit seismic reflection imaging at the SAFOD drill site. Drill-bit seismic (DBS) imaging uses the drill bit as a seismic source. Previous DBS experiments have used geophone receiver arrays laid on the earth's surface. At SAFOD, a vertical receiver array supplemented a surface receiver array, to record the Stage 1 drilling of SAFOD well which was completed in 2004. This dissertation expands the DBS method by utilizing both the vertical and surface arrays to record the drill bit vibrations and produce two types of reverse vertical seismic profiles. A major portion of this dissertation includes research and development of DBS data signal processing techniques for industrial applications and the special case of the SAFOD observations. These observations include downhole geophone recordings which represent a new approach not previously reported in the seismic reflection literature. The application of algorithms produced by these studies has resulted in improved methods for estimating the drill bit seismic source signature. These methods also determine optimal deconvolution operators for DBS signals which produce estimates of the "pilot signal". It is shown that processing of DBS data is possible without drill string pilot accelerometers. This allows more economic deployment of equipment at the drill

  11. Rule violation errors are associated with right lateral prefrontal cortex atrophy in neurodegenerative disease.

    PubMed

    Possin, Katherine L; Brambati, Simona M; Rosen, Howard J; Johnson, Julene K; Pa, Judy; Weiner, Michael W; Miller, Bruce L; Kramer, Joel H

    2009-05-01

    Good cognitive performance requires adherence to rules specific to the task at hand. Patients with neurological disease often make rule violation (RV) errors, but the anatomical basis for RV during cognitive testing remains debated. The present study examined the neuroanatomical correlates of RV errors made on tests of executive functioning in 166 subjects diagnosed with neurodegenerative disease or as neurologically healthy. Specifically, RV errors were voxel-wisely correlated with gray matter volume derived from high-definition magnetic resonance images using voxel-based morphometry implemented in SPM2. Latent variable analysis showed that RV errors tapped a unitary construct separate from repetition errors. This analysis was used to generate factor scores to represent what is common among RV errors across tests. The extracted RV factor scores correlated with tissue loss in the lateral middle and inferior frontal gyri and the caudate nucleus bilaterally. When a more stringent control for global cognitive functioning was applied using Mini Mental State Exam scores, only the correlations with the right lateral prefrontal cortex (PFC) remained significant. These data underscore the importance of right lateral PFC in behavioral monitoring and highlight the potential of RV error assessment for identifying patients with damage to this region. PMID:19402921

  12. Cenozoic right-lateral slip on the Great Glen Fault, Scotland: Additional Evidence and Possible Causes

    NASA Astrophysics Data System (ADS)

    Le Breton, E.; Cobbold, P. R.; Zanella, A.

    2012-04-01

    The Great Glen Fault (GGF) trends NNE-SSW across all of Northern Scotland, separating two Neoproterozoic supergroups (Moine and Dalradian). The GGF developed as a left-lateral fault during the Caledonian Orogeny (Ordovician to Early Devonian). However, according to previous studies (involving seismic data from the Moray Firth and analyses of Tertiary dyke swarms in NW Scotland), the GGF reactivated right-laterally in the Tertiary. Here we present additional evidence for this later phase, from a study of Jurassic outcrops along the GGF and the nearby Helmsdale Fault. At Eathie and Shandwick, on the NE coast of Scotland, Jurassic strata of marine origin (mostly shale) crop out along the GGF, in contact with Neoproterozoic basement or Devonian Old Red Sandstone. Minor folds and faults in these outcrops indicate post-depositional right-lateral slip, under transpression. In the shale, we have also found bedding-parallel calcite veins ('beef' and 'cone-in-cone'). If these veins provide evidence for overpressure development and maturation of organic matter at significant depth (as they do in other basins), the host sediment must have accumulated deeper offshore in the Moray Firth. Therefore, the Jurassic strata at Eathie and Shandwick must have been subject to Cenozoic exhumation during right-lateral displacement along the GGF. At Helmsdale, according to previous studies, the Jurassic 'Boulder Beds' accumulated during a period of normal faulting on the Helmsdale Fault. There the sedimentary facies are more proximal than those at Eathie and Shandwick and abundant conglomerate contains Devonian clasts but no 'beef'. However we have found steep calcite veins, which cut the entire Jurassic sequence. Their sigmoidal shapes indicate left-lateral slip along the Helmsdale fault zone. Such a motion is compatible with right-lateral displacement on the GGF. Indeed, according to previous studies, folds between the Helmsdale Fault and the GGF may have developed as a result of opposing

  13. 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.

  14. The 1998 March 14 Fandoqa earthquake (Mw 6.6) in Kerman province, southeast Iran: re-rupture of the 1981 Sirch earthquake fault, triggering of slip on adjacent thrusts and the active tectonics of the Gowk fault zone

    NASA Astrophysics Data System (ADS)

    Berberian, M.; Jackson, J. A.; Fielding, E.; Parsons, B. E.; Priestley, K.; Qorashi, M.; Talebian, M.; Walker, R.; Wright, T. J.; Baker, C.

    2001-08-01

    The 1998 March 14 Fandoqa earthquake (Ms6.6) was the penultimate in a series of five substantial earthquakes on the Gowk fault system of southeast Iran since 1981, all of which were associated with co-seismic surface ruptures. We use observations of surface faulting, analysis of P and SH body waves, SAR interferometry and geomorphology to investigate the ruptures in these earthquakes and how they are related both to each other and to the regional active tectonics. The 1998 Fandoqa earthquake produced 23km of surface faulting with up to 3m right-lateral strike-slip and 1m vertical offsets. SAR interferometry and seismic waveforms show that the main rupture plane dipped west at ~50° and had a normal component, although the surface ruptures were more complicated, being downthrown to both the east and the west on steep faults in near-surface sediments. In addition, SAR interferometry shows that a nearby thrust with a similar strike but dipping at ~6°W moved about 8cm in a time interval and in a position that makes it likely that its slip was triggered by the Fandoqa earthquake. The 1998 surface ruptures in the Gowk valley followed part of a much longer (~80km) set of co-seismic ruptures with smaller offsets that were observed after larger earthquakes in 1981 (Mw6.6 and 7.1). The main ruptures in these 1981 earthquakes probably occurred on different, deeper parts of the same fault system, producing only minor reactivation of the shallower faults at the surface. Although the 1981-1998 earthquake sequence apparently ruptured parts of the same fault system repeatedly, these earthquakes had very different rupture characteristics: an important lesson for the interpretation of both palaeoseismological trenching investigations and historical accounts of earthquakes. The regional kinematics, which involve oblique right-lateral and convergent motion, are evidently achieved by a complex configuration of faults with normal, reverse and strike-slip components. Some of the

  15. Earthquake relocations, crustal rheology, and active deformation in the central-eastern Alps (N Italy)

    NASA Astrophysics Data System (ADS)

    Viganò, Alfio; Scafidi, Davide; Ranalli, Giorgio; Martin, Silvana; Della Vedova, Bruno; Spallarossa, Daniele

    2015-10-01

    A revised seismic catalogue (1994-2007) for the central-eastern Alps (N Italy) is presented. 396 earthquake relocations, for local magnitudes in the 1.2-5.3 range, are performed using a 3D crustal velocity structure and probabilistic locations. The location procedure is validated by computing a set of 41 quarry shot solutions and all the results, both about shots and seismic events, are compared with those obtained using the routine location procedure. Results are shown for five contiguous seismotectonic domains, as supported by geological and geophysical evidence (e.g., fault systems, crustal tomography, focal mechanisms types). Earthquake hypocentres are mostly located in the upper crust (0-15 km of depth), in good agreement with thermo-rheological models about the brittle-ductile transitions (8-9 km of depth) and total crustal strengths (1.0-2.0 TN m- 1). Epicentres are clustered and/or aligned along present-day active geological structures. The proposed seismotectonic model shows dominant compression along the Giudicarie and Belluno-Bassano-Montello thrusts, with strain partitioning along the dominant right-lateral strike-slip faults of the Schio-Vicenza domain. The present-day deformation of the Southern Alps and the internal Alpine chain is compatible with Adria indentation and the related crustal stress distribution.

  16. Active tectonics of the Ganzi-Yushu fault in the southeastern Tibetan Plateau

    NASA Astrophysics Data System (ADS)

    Shi, Feng; He, Honglin; Densmore, Alexander L.; Li, An; Yang, Xiaoping; Xu, Xiwei

    2016-04-01

    The ongoing convergence between India and Eurasia apparently is accommodated not merely by crustal shortening in Tibet, instead also by motions along strike slip faults which are usually boundaries between tectonic blocks, especially in the Tibetan Plateau. Quantification of this strike slip faulting is fundamental for understanding the collision between India and Eurasia. Here, we use a variety of geomorphic observations to place constraints on the late Quaternary kinematics and slip rates of the Ganzi-Yushu fault, one of the significant strike-slip faults in eastern Tibet. The Ganzi-Yushu fault is an active, dominantly left-lateral strike-slip structure that can be traced continuously for up to 500 km along the northern boundary of the clockwise-rotating southeastern block of the Tibetan Plateau. We analyse geomorphic evidence for deformation, and calculate the late Quaternary slip rates at four sites along the eastern portion of the fault trace. The latest Quaternary apparent throw rates are variable along strike but are typically ~ 1 mm/a. Rates of strike-slip displacement are likely to be an order of magnitude higher, 8-11 mm/a. Trenching at two locations suggests that the active fault behaviour is dominated by strike-slip faulting and reveals several earthquake events with refined information of timing. The 2010 Mw 6.9 Yushu earthquake, which occurred on the northwestern segment of the Ganzi-Yushu fault zone, provides additional evidence for fault activity. These observations agree with GPS-derived estimates, and show that late Quaternary slip rates on the Ganzi-Yushu fault are comparable to those on other major active strike-slip faults in the eastern Tibetan Plateau.

  17. Ground-penetrating radar investigations along the North Anatolian fault near Izmit, Turkey: Constraints on the right-lateral movement and slip history

    NASA Astrophysics Data System (ADS)

    Ferry, Matthieu; Meghraoui, Mustapha; Girard, Jean-François; Rockwell, Thomas K.; Kozaci, Özgur; Akyuz, Serdar; Barka, Aykut

    2004-01-01

    We analyze ground-penetrating radar (GPR) profiles made across and parallel to the August 1999 earthquake ruptures of the North Anatolian fault in Turkey. The profiles document cumulative right-lateral offset of stream channels and the successive faulting of a medieval (Ottoman) canal. The dominance of fine sand to coarse gravel in the sections imaged allows for reasonably deep penetration, and processed radar signals clearly image visible reflectors within the uppermost 5 m. Near Köseköy, buried fluvial-channel deposits, exposed in some trenches dug to determine paleoseismicity, are also visible on profiles and show a maximum 6.7 7.4 m of lateral displacement. Younger channel units display 4.5 4.9 m of right-lateral displacement at 2 3 m depth and show that the penultimate rupture along the Izmit segment produced a similar amount of displacement as in 1999. At the Ottoman canal site, GPR profiles complement a trench study and provide consistent results showing the occurrence of three faulting events after A.D. 1591, the date of canal construction. This study demonstrates that the use of GPR method in paleoseismology contributes to better identification of cumulative slip along active faults.

  18. The Tripoli, Libya, Earthquake of September 4, 1974: Implications for the active tectonics of the central Mediterranean

    NASA Astrophysics Data System (ADS)

    Westaway, Rob

    1990-04-01

    Source parameters have been determined for the earthquake (Ms 5.6) that occurred offshore of Tripoli, Libya, on September 4, 1974. One nodal plane of its focal mechanism has dip 37°, strike 297°, and rake -141°, indicating oblique normal faulting. This nodal plane is subparallel to many west-northwest striking normal faults in the epicentral area and is most likely the fault plane, indicating a component of right-lateral strike-slip with slip vector azimuth N84°E. Inversion of long-period teleseismic body waves indicates 12-km centroid depth and 0.4 × 1018 N m seismic moment. A much larger earthquake (Ms 7.0) on April 19, 1935, that occurred in the same zone of active oblique normal faults ˜400 km farther southeast near Sirte probably involved similar slip sense. This zone, for which the name "Tunisia-Libya seismic zone" appears appropriate, has overall northwest-southeast extent ˜1000 km from northern Libya to between Tunisia and Sicily. It takes up a change in motion direction relative to stable Europe from west of north inside the African plate to between N30°E and N50°E in the Ionian Sea between Sicily, southernmost peninsular Italy, southwest Greece, and Libya. This suggested motion direction of Sicily relative to stable Europe agrees with independent estimates from fault slip rates and senses elsewhere in Italy.

  19. Neogene Structural Basins Beneath Santa Rosa Plain: Strike-Slip Basins Formed in Wake of the Mendocino Triple Junction During Initiation of the Rodgers Creek-Healdsburg Fault Zone

    NASA Astrophysics Data System (ADS)

    McLaughlin, R. J.; Sarna-Wojcicki, A. M.; Fleck, R. J.; Langenheim, V. E.; McPhee, D. K.; Jachens, R. C.; Wagner, D. L.; McCabe, C. A.

    2006-12-01

    Located on the Humboldt Plate, just N of the San Francisco Bay block, the Santa Rosa Plain (SRP) is a NW- oriented dissected lowland ~60 km long by 12 km wide, underlain by fault bounded Neogene basins containing syntectonic sedimentary and volcanic fills up to 2.5 km-thick. In response to lengthening of the transform margin ~7 to 5 Ma, Neogene strata now beneath the plain were dropped into extensional basins in a SE-tapered wedge-shaped block bounded on the SW by ~N 50° W-oriented faults of a proto-Hayward fault zone, and on the NE by newly initiated ~N 35°- 40°W-oriented faults of the Rodgers Creek-Healdsburg fault zone. Comparisons of the geologic, chronostratigraphic and geophysical frameworks of SRP with well constrained datasets used for Neogene reconstructions of the northern San Andreas Fault system indicates to us that the SRP and its buried basins are firmly tied to a strike-slip basin formational setting in the wake of the Mendocino triple junction (MTJ). Onshore and offshore datasets that integrate the geology and chronostratigraphy with geophysical data show that the MTJ at ~7 to 5 Ma was situated between the present latitudes of ~38.5° and ~39° N, opposite SRP. The SRP formed the delta of a large river that flowed toward the WNW, around a proto-Hayward fault-bounded bedrock promontory, into an estuary that adjoined the adjacent near shore and shelf of the margin. The modern Eel River basin, a deformed and uplifted remnant of the Cascadia Forearc margin just north of the present position of the MTJ, lies in a setting similar to the paleogeographic setting of the SRP. Closer examination, however, reveals two important differences between the SRP and MTJ settings. First, the ~6 to 9 Ma fluvial system that flowed NW across the Hayward fault from the east San Francisco Bay region onto SRP, also flowed across the San Andreas fault into submarine canyons of the Delgada Fan on the Pacific Plate, south of the MTJ. In contrast, sediment transported by the

  20. A right-lateral structural model for Poui Field, offshore Trinidad, from 3D seismic interpretation and subsurface well control

    SciTech Connect

    Wolfe, J.E.; Sobol, F.T. )

    1993-02-01

    A new wrench fault structural model is developed for Poui Field, in the Colombus Basin, offshore Trinidad. A strain ellipse for a right-lateral simple shear stress field is demonstrated from observed fault patterns on recent seismic mapping of deep hydrocarbon-bearing sands at Poui Field. The seismic interpretation is calibrated by 20 points of well control which penetrated the best, continuous, mappable reflector at these deep sand levels. Seismic cross-sections taken over the Poui structure, which are perpendicular to the structural axis of the feature, and constrained by well control, demonstrate geometries typical of wrench faulting observed along the Los Bajos fault complex, onshore Trinidad, and along the San Andreas wrench fault systems of southern California. Variable dip rate along the fault, flower structures with associated sag features, asymmetry of the structure, an extensional duplex, and a possible horsetail splay appear on the maps and cross-sections, and support the wrench fault model. Various pieces of subsurface information, observed in the Field from well control, support the wrench hypothesis: isolated, pressure separated compartments, abrupt facies changes across faults and hydrocarbon migration anomalies. Subsequent extensional faulting created an overprinting of rotated, normal faulting that followed fracture planes created by the right-lateral simple shear stress field. Regional mapping indicates that this wrench fault is a stress field. Regional mapping indicates that this wrench fault is a continuation of the right-lateral fault system mapped onshore Trinidad as the Marcel Main fault system.

  1. Geomorphic signal of active faulting at the northern edge of Lut Block: Insights on the kinematic scenario of Central Iran

    NASA Astrophysics Data System (ADS)

    Calzolari, Gabriele; Della Seta, Marta; Rossetti, Federico; Nozaem, Reza; Vignaroli, Gianluca; Cosentino, Domenico; Faccenna, Claudio

    2016-01-01

    Recent works documented Neogene to Quaternary dextral strike-slip tectonics along the Kuh-e-Sarhangi and Kuh-e-Faghan intraplate strike-slip faults at the northern edge of the Lut Block of Central Iran, previously thought to be dominated by sinistral strike-slip deformation. This work focuses on the evidence of Quaternary activity of one of these fault systems, in order to provide new spatiotemporal constraints on their role in the active regional kinematic scenario. Through geomorphological and structural investigation, integrated with optically stimulated luminescence dating of three generations of alluvial fans and fluvial terraces (at ~53, ~25, and ~6 ka), this study documents (i) the topographic inheritance of the long-term (Myr) punctuated history of fault nucleation, propagation, and exhumation along the northern edge of Lut Block; (ii) the tectonic control on drainage network evolution, pediment formation, fluvial terraces, and alluvial fan architecture; (iii) the minimum Holocene age of Quaternary dextral strike-slip faulting; and (iv) the evidence of Late Quaternary fault-related uplift localized along the different fault strands. The documented spatial and temporal constraints on the active dextral strike-slip tectonics at the northern edge of Lut Block provide new insights on the kinematic model for active faulting in Central Iran, which has been reinterpreted in an escape tectonic scenario.

  2. Evidence of active tectonics on a Roman aqueduct system (II-III century A.D.) near Rome, Italy

    NASA Astrophysics Data System (ADS)

    Marra, Fabrizio; Montone, Paola; Pirro, Mario; Boschi, Enzo

    2004-04-01

    In this paper we describe evidence of strong tectonic deformation affecting two aqueducts of Roman age (II-III century A.D.). The channels are located approximately 20 km northeast of Rome along the ancient Via Tiburtina. Brittle and ductile deformation affects these two structures, including extensional joint systems, NE-oriented faults, and horizontal distortion. This deformation is consistent with right-lateral movement on major N-striking faults, and represents the first evidence that tectonic deformation took place in historical times in the vicinity of Rome, with local strike-slip movement superimposed on a regional extensional fault system.

  3. Active tectonics of the Binalud Mountains, a key puzzle segment to describe Quaternary deformations at the northeastern boundary of the Arabia-Eurasia collision

    NASA Astrophysics Data System (ADS)

    Shabanian, Esmaeil; Bellier, Olivier; Siame, Lionel L.; Abbassi, Mohammad R.; Leanni, Laetitia; Braucher, Régis; Farbod, Yassaman; Bourlès, Didier L.

    2010-05-01

    In northeast Iran, the Binalud Mountains accommodate part of active convergence between the Arabian and Eurasian plates. This fault-bounded mountain range has been considered a key region to describe Quaternary deformations at the northeastern boundary of the Arabia-Eurasia collision. But, the lack of knowledge on active faulting hampered evaluating the geological reliability of tectonic models describing the kinematics of deformation in northeast Iran. Morphotectonic investigations along both sides of the Binalud Mountains allowed us to characterize the structural and active faulting patterns along the Neyshabur and Mashhad fault systems on the southwest and northeast sides of the mountain range, respectively. We applied combined approaches of morphotectonic analyses based on satellite imageries (SPOT5 and Landsat ETM+), STRM and site-scale digital topographic data, and field surveys complemented with in situ-produced 10Be exposure dating to determine the kinematics and rate of active faulting. Three regional episodes of alluvial surface abandonments were dated at 5.3±1.1 kyr (Q1), 94±5 kyr (Q3), and 200±14 kyr (S3). The geomorphic reconstruction of both vertical and right-lateral fault offsets postdating these surface abandonment episodes yielded Quaternary fault slip rates on both sides of the Binalud Mountains. On the Neyshabur Fault System, thanks to geomorphic reconstructions of cumulative offsets recorded by Q3 fan surfaces, slip rates of 2.7±0.8 mm/yr and 2.4±0.2 mm/yr are estimated for right-lateral and reverse components of active faulting, respectively. Those indicate a total slip rate of 3.6±1.2 mm/yr for the late Quaternary deformation on the southwest flank of the Binalud Mountains. Reconstructing the cumulative right-lateral offset recorded by S3 surfaces, a middle-late Quaternary slip rate of 1.6±0.1 mm/yr is determined for the Mashhad Fault System. Altogether, our geomorphic observations reveal that, on both sides of the Binalud Mountains

  4. GPR investigations along the North Anatolian Fault near Izmit (Turkey): Constraints on the right-lateral movement and slip history

    NASA Astrophysics Data System (ADS)

    Ferry, M.; Meghraoui, M.; Rockwell, T. K.; Kozaci, Ö.; Akyuz, S.; Girard, J.-F.; Barka, A.

    2003-04-01

    The 1999 Ms 7.4 Izmit earthquake produced more than 110 km of surface rupture along the North Anatolian fault. We present here ground-penetrating radar (GPR) profiles surveyed across and parallel to the 1999 Izmit earthquake ruptures at two sites along the Izmit-Sapanca segment. Fine sandy and coarse gravels favor the penetration depth and processed radar profiles image clearly visible reflectors within the uppermost 10 m. In Köseköy, they document cumulative right-lateral offset of a stream channel by the fault. Old fluvial channel deposits also visible in trenches show a maximum 13.5 to 14 m lateral displacement. Younger channel units display 4 m of right-lateral displacement at 2.5 m depth and correlation with dated trench units yields an average slip rate of 15 mm/yr. At site 2, GPR profiles display the successive faulting of a medieval Ottoman Canal which excavation probably took place in 1591 A.D.. GPR profiles image the corresponding surface as well as numerous faults that affect it. A following trench study confirmed these results as they provide consistent results with the occurrence of three faulting events post-1591 A.D., one of which probably as large as the 1999 Izmit earthquake.

  5. UAV's for active tectonics : case example from the Longitudinal Valley and the Chishan Faults (Southern Taiwan)

    NASA Astrophysics Data System (ADS)

    Deffontaines, Benoit; Chang, Kuo-Jen; Chan, Yu-Chang; Chen, Rou-Fei; Hsieh, Yu-Chung

    2015-04-01

    Taiwan is a case example to study active tectonics due to the active NW-SE collision of the Philippine and Eurasian Sea Plates as the whole convergence reaches 10cm/y. In order to decipher the structural active tectonics geometry, we used herein UAV's to get high resolution Digital Terrain Model (DTM) in local active tectonics key areas. Classical photo-interpretation where then developped in order to structurally interprete these data, confirmed by field studies. Two location had first been choosen in order to highlight the contribution of such high resolution DTM in SW Taiwan on the Longitudinal Valley Fault (SE Taiwan) on its southern branch from Pinting to Luyeh terraces (Pinanshan) where UAV's lead to better interprete the location of the outcropping active deformations. Combined with available GPS data and PALSAR interferometry (Deffontaines et Champenois et al., submitted) it is then possible to reconstruct the way of the present deformation in this local area. In the Pinting terraces, If the western branch of the fault correspond to an outcroping thrust fault, the eastern branch act as a a growing active anticline that may be characterized and quantified independantly. The interpretation of the UAV's high resolution DTM data on the Chishan Fault (SW Taiwan) reveals also the geometry of the outcropping active faults complex structural behaviour. If the Chishan Fault act as a thrusting in its northern tip (close to Chishan city), it acts as a right lateral strike-slip fault north of Chaoshan (Kaohsiung city) as described by Deffontaines et al. 2014. Therefore UAV's are a so useful tool to get very high resolution topographic data in Taiwan that are of great help to get the geometry of the active neotectonic structures in Taiwan.

  6. Deformation Monitoring of AN Active Fault

    NASA Astrophysics Data System (ADS)

    Ostapchuk, A.

    2015-12-01

    The discovery of low frequency earthquakes, slow slip events and other deformation phenomena, new for geophysics, change our understanding of how the energy accumulated in the Earth's crust do release. The new geophysical data make one revise the underlying mechanism of geomechanical processes taking place in fault zones. Conditions for generating different slip modes are still unclear. The most vital question is whether a certain slip mode is intrinsic for a fault or may be controlled by external factors. This work presents the results of two and a half year deformation monitoring of a discontinuity in the zone of the Main Sayanskiy Fault. Main Sayanskiy Fault is right-lateral strike-slip fault. Observations were performed in the tunnel of Talaya seismic station (TLY), Irkutsk region, Russia. Measurements were carried out 70 m away from the entrance of the tunnel, the thickness of overlying rock was about 30 m. Inductive sensors of displacement were mounted at the both sides of a discontinuity, which recorded three components of relative fault side displacement with the accuracy of 0.2 mcm. Temperature variation inside the tunnel didn't exceed 0.5oC during the all period of observations. Important information about deformation properties of an active fault was obtained. A pronounced seasonality of deformation characteristics of discontinuity is observed in the investigated segment of rock. A great number of slow slip events with durations from several hours to several weeks were registered. Besides that alterations of fault deformation characteristics before the megathrust earthquake M9.0 Tohoku Oki 11 March 2011 and reaction to the event itself were detected. The work was supported by the Russian Science Foundation (grant no. 14-17-00719).

  7. The 1994 Sefidabeh earthquakes in eastern Iran: blind thrusting and bedding-plane slip on a growing anticline, and active tectonics of the Sistan suture zone

    NASA Astrophysics Data System (ADS)

    Berberian, M.; Jackson, J. A.; Qorashi, M.; Talebian, M.; Khatib, M.; Priestley, K.

    2000-08-01

    In 1994 a sequence of five earthquakes with Mw 5.5-6.2 occurred in the Sistan belt of eastern Iran, all of them involving motion on blind thrusts with centroid depths of 5-10km. Coseismic ruptures at the surface involved bedding-plane slip on a growing hanging-wall anticline displaying geomorphological evidence of uplift and lateral propagation. The 1994 earthquakes were associated with a NW-trending thrust system that splays off the northern termination of a major N-S right-lateral strike-slip fault. Elevation changes along the anticline ridge suggest that displacement on the underlying thrust dies out to the NW, away from its intersection with the strike-slip fault. This is a common fault configuration in eastern Iran and accommodates oblique NE-SW shortening across the N-S deforming zone, probably by anticlockwise rotations about a vertical axis. This style of fault kinematics may be transitional to a more evolved state that involves partitioning of the strike-slip and convergent motion onto separate subparallel faults.

  8. Paleoseismic and geomorphologic evidence of recent tectonic activity of the Pozohondo Fault (Betic Cordillera, SE Spain)

    USGS Publications Warehouse

    Rodríguez-Pascua, M.A.; Pérez-López, R.; Garduño-Monroy, V.H.; Giner-Robles, J.L.; Silva, P.G.; Perucha-Atienza, M.A.; Hernández-Madrigal, V.M.; Bischoff, J.

    2012-01-01

    Instrumental and historical seismicity in the Albacete province (External Prebetic Zone) has been scarcely recorded. However, major strike-slip faults showing NW-SE trending provide geomorphologic and paleoseismic evidence of recent tectonic activity (Late Pleistocene to Present). Moreover, these faults are consistently well oriented under the present stress tensor and therefore, they can trigger earthquakes of magnitude greater than M6, according to the lengths of surface ruptures and active segments recognized in fieldwork. Present landscape nearby the village of Hellin (SE of Albacete) is determined by the recent activity of the Pozohondo Fault (FPH), a NW-SE right-lateral fault with 90 km in length. In this study, we have calculated the Late Quaternary tectonic sliprate of the FPH from geomorphological, sedimentological, archaeoseimological, and paleoseismological approaches. All of these data suggest that the FPH runs with a minimum slip-rate of 0.1 mm/yr during the last 100 kyrs (Upper Pleistocene-Holocene). In addition, we have recognized the last two major paleoearthquakes associated to this fault. Magnitudes of these paleoearthquakes were gretarer than M6 and their recurrence intervals ranged from 6600 to 8600 yrs for the seismic cycle of FPH. The last earthquake was dated between the 1st and 6th centuries, though two earthquakes could be interpreted in this wide time interval, one at the FPH and other from a far field source. Results obtained here, suggest an increasing of the tectonic activity of the Pozohondo Fault during the last 10,000 yrs.

  9. Tectonic and gravity-induced deformation along the active Talas-Fergana Fault, Tien Shan, Kyrgyzstan

    NASA Astrophysics Data System (ADS)

    Tibaldi, A.; Corazzato, C.; Rust, D.; Bonali, F. L.; Pasquarè Mariotto, F. A.; Korzhenkov, A. M.; Oppizzi, P.; Bonzanigo, L.

    2015-08-01

    This paper shows, by field palaeoseismological data, the Holocene activity of the central segment of the intracontinental Talas-Fergana Fault (TFF), and the relevance of possible future seismic shaking on slope stability around a large water reservoir. The fault, striking NW-SE, is marked by a continuous series of scarps, deflected streams and water divides, and prehistoric earthquakes that offset substrate and Holocene deposits. Fault movements are characterised by right-lateral strike-slip kinematics with a subordinate component of uplift of the NE block. Structural, geological and geomorphological field data indicate that shallow and deep landslides are aligned along the TFF, and some of them are active. Where the TFF runs close to the reservoir, the fault trace is obscured by a series of landslides, affecting rock and soil materials and ranging in size from small slope instabilities to deep-seated gravity-induced slope deformations (DGSDs). The largest of these, which does not show clear evidence of present-day activity, involves a volume of about 1 km3 and is associated with smaller but active landslides in its lower part, with volumes in the order of 2.5 × 104 m3 to 1 × 106 m3. Based on the spatial and temporal relations between landslides and faults, we argue that at least some of these slope failures may have a coseismic character. Stability analyses by means of limit equilibrium methods (LEMs), and stress-strain analysis by finite difference numerical modelling (FDM), were carried out to evaluate different hazard scenarios linked to these slope instabilities. The results indicate concern for the different threats posed, ranging from the possible disruption of the M-41 highway, the main transportation route in central Asia, to the possible collapse of huge rock masses into the reservoir, possibly generating a tsunami.

  10. The stress state of the region around Inönü-Eskişehir. Active Fault System; interpretations derived from kinematic analysis accompanied with the TUTGA data

    NASA Astrophysics Data System (ADS)

    SaäžLam Selćuk, Azad; Gökten, Ergun; Aktuäž, Bahadır.

    2010-05-01

    The Central parts of the Anatolian block plays role of stress transferring zone between East Anatolian contractional province and Aegean extensional region in the west during its driven towards west along North and East Anatolian Fault systems. Because of this, various stress regimes characterize and control the different subregions of the Central Anatolia and this situation is reflected by the seismicity of subregions. However the much of the subregions are characterized by strike-slip faultings, the orientations and the trends of the stess tensors are apart from each other. The northwestern part of the Central Anatolia is experienced by İnönü-Eskişehir Fault System which creates a complex stress region with the interactions of the North Anatolian Fault System situated in close north. The İnönü-Eskişehir Fault System is a WNW-ESE striking right-lateral strike-slip deformational area with a normal component that extends from Uludağ in the west to Sivrihisar in the east and separates the western Anatolia extensional region from the central Anatolia to the northeast. This fault system consists of E-W- and NW-SE-trending fault sets and segments which have potential to produce earthquakes in a wide range of magnitutes. Different aged and typed strike-slip basins appear around the Inonu-Eskisehir fault system. One of them is Mahmudiye-Cifteler-Emirdag basin. The Mahmudiye-Cifteler-Emirdag basin is a fault-controlled pull-apart basin in 85 km length and 25 km average width, extending in northwest-southeast trend from Yürükkaracaören village in the North to Emirdag in the South. Because of the recorded GPS data are inadequate for determining characters of the the low velocity deformation in the studied area, the strain rates are computed by using the velocity vectors from TUTGA data. TUTGA network has been established between 1997 and 1999 as covering the Anatolian block, and considering the deformation acquired by means of active tectonic movements of Turkey

  11. Quaternary estimates of average slip-rates for active faults in the Mongolian Altay Mountains: the advantages and assumptions of multiple dating techniques

    NASA Astrophysics Data System (ADS)

    Gregory, L. C.; Walker, R. T.; Thomas, A. L.; Amgaa, T.; Bayasgalan, G.; Amgalan, B.; West, A.

    2010-12-01

    Active faults in the Altay Mountains, western Mongolia, produce surface expressions that are generally well-preserved due to the arid central-Asian climate. Motion along the right-lateral strike-slip and oblique-reverse faults has displaced major river systems by kilometres over millions of years and there are clear scarps and linear features in the landscape along the surface traces of active fault strands. With combined remote sensing and field work, we have identified sites with surface features that have been displaced by tens of metres as a result of cumulative motion along faults. In an effort to accurately quantify an average slip-rate for the faults, we used multiple dating techniques to provide an age constraint for the displaced landscapes. At one site on the Olgiy fault, we applied 10Be terrestrial cosmogenic nuclides (TCN) and uranium-series geochronology on boulder tops and in-situ formed carbonate rinds, respectively. Based on a displacement of approximately 17m, and geochronology results that range from 20-60ky, we resolve a slip-rate of less than 1 mm/yr. We have also applied optically stimulated luminescence (OSL), 10Be TCN, and U-series methods on the Ar Hotol fault. Each of these dating techniques provides unique constraints on the relationship between the ‘age’ of a displaced surface and the actual amount of displacement, and each has inherent assumptions. We will consider the advantages and assumptions made in utilising these techniques in western Mongolia- e.g. U-series dating of carbonate rinds can provide a minimum age for alluvial fan deposition, and inheritance must be considered when using TCN techniques on boulder tops. This will be put into the context of estimating accurate and geologically relevant slip-rates, and improving our understanding of the active deformation of the Mongolian Altay.

  12. The River Network, Active Tectonics and the Mexican Subduction Zone, Southwest Mexico

    NASA Astrophysics Data System (ADS)

    Gaidzik, K.; Ramirez-Herrera, M. T.; Kostoglodov, V.; Basili, R.

    2014-12-01

    Rivers, their profiles and network reflect the integration of multiple processes and forces that are part of the fundamental controls on the relief structure of mountain belts. The motivation of this study is to understand active tectonic processes in the forearc region of subduction zones, by distinguishing evidence of active deformation using the river network and topography. To this end, morphotectonic and structural studies have been conducted on fifteen drainage basins on the mountain front, parallel to the Mexican subduction zone, where the Cocos plate underthrusts the North American plate. The southwest - northeast Cocos plate subduction stress regime initiated ca. 20 MA. NE-SW to NNE-SSW normal faults as well as sub-latitudinal to NW-SE strike-slip faults (both dextral and sinistral) constitute the majority of mesofaults recorded in the field within the studied drainage basins. Occasionally dextral N-S strike-slip faults also occur. The stress tensor reconstruction suggests two main evolution stages of these faults: 1) the older is dominated by a NW-SE to WNW-ESE extensional regime and 2) the younger is a transcurrent regime, with NNE-SSW σ1 axis. The drainage pattern is strongly controlled by tectonic features, whereas lithology is only a subordinate factor, with only one exception (Petatlán river). Generally, major rivers flow from north to south mainly through NE-SW and NNE-SSW normal faults, and/or sub-longitudinal dextral (also locally sinistral) strike-slip faults. In the central and eastern part of the studied area, rivers also follow NW-SE structures, which are generally normal or sinistral strike-slip faults (rarely reverse). In most cases, local deflections of the river main courses are related to sub-latitudinal strike-slip faults, both dextral and sinistral. Within the current stress field related to the active Cocos subduction, both normal and strike-slip fault sets could be reactivated. Our analysis suggests that strike-slip faults, mainly

  13. Active fault kinematics and crustal stresses along the Ionian margin of southeastern Sicily

    NASA Astrophysics Data System (ADS)

    Adam, J.; Reuther, C.-D.; Grasso, M.; Torelli, L.

    2000-11-01

    Since the late Cretaceous onset of plate convergence between Africa and Europe, the Malta Escarpment has been converted from a Mesozoic passive margin into a mega-hinge fault system with an additional sinistral strike-slip component. The modern tectonic stress regime with NW-SE-directed maximum horizontal stresses has been established since Late Messinian times. Since the Pleistocene, sinistral strike-slip deformation and contemporaneous normal faulting along the Malta Escarpment have induced the opening of oblique trending onshore grabens at the eastern margin of the Hyblean Plateau. In this study, we focus on the kinematics, the controlling state of stress, and the temporal variation of the neotectonic to active strike-slip and normal fault structures. The stress-tensor calculations reveals that the widespread map-scaled to meso-scaled normal fault structures are governed by the long-term extensional state of stress during the Quaternary. This long-term stress tensor is predominantly controlled by gravitational induced stresses due to vertical load ( σ1= SV) and lateral extension due to the topographic gradient of the Malta Escarpment ( σ3= Sh=NE-SW). In this case, the average tectonic stresses ( σ2= SH=NW-SE) transmitted by the regional to plate-tectonic stress field are significantly smaller than the gravitational induced stresses. In contrast, the clear localization of conjugate sets of meso-scaled strike-slip fault structures and shear zones without accompanying normal fault structures give strong indications for episodic seismotectonic strike-slip faulting under critical stress conditions. In this state, tectonically induced maximum horizontal stresses are successively increased by ongoing plate convergence from low-level stress magnitudes ( σ1= SV, σ2= SH=NW-SE) up to critical stress magnitudes ( σ1= SH=NW-SE, σ2= SV), which are significantly larger than gravitational stresses. At the critical state, seismotectonic stress release occurs by active

  14. Active Tectonics of Southern California Revealed by Cluster Analysis of GPS Velocities

    NASA Astrophysics Data System (ADS)

    Thatcher, W. R.; Savage, J. C.; Simpson, R. W.

    2013-12-01

    We use cluster analysis of the USGS National Seismic Hazard Map GPS velocity field for southern California with standard deviations < 1 mm/yr to determine velocity gradients that locate the most important faults, the elastic strain associated with them, and regions of possible block-like behavior. Seven to ten well resolved clusters are statistically significant and spatially distinct with small overlap. In map view (see figure), the 7 clusters solution shows bands of relatively constant velocity sub-parallel to the San Andreas (SAF) and San Jacinto (SJF) faults and the major faults of the eastern Mojave shear zone (EMSZ). These bands are due both to elastic strain accumulation on the SAF and relative motion across lower slip rate faults in the EMSZ and Los Angeles and Ventura basins. At the largest scale, the 7-cluster map shows two main trends. The blue dots define the SJ and SA faults from northwest of the Salton Sea (SS) to Parkfield (P); the grey/magenta boundary suggests that the defined Eastern California Shear Zone could be extended farther south to the Salton Sea. The short ~80-km-long San Gorgonio Pass-San Bernardino Mountains (SGP) segment of the SAF has a much lower slip rate, ~7 mm/yr of right-lateral oblique convergence. As generally shown by previous GPS studies, right-lateral strike-slip movement rates vary considerably along the SAF. In the Imperial Valley (IV) the rate is ~40 mm/yr; east of the Salton Sea it drops to ~20 mm/yr, with 10-15 mm/yr having been shunted westward to the SJF; north of the Salton Sea ~10-15 mm/yr of strike-slip is transferred to the faults of the eastern Mojave; therefore the east-trending faults of San Gorgonio Pass (SGP) take up only ~5 mm/yr of strike slip and ~equal amounts of north-south shortening; on the Mojave (M) segment of the SAF the slip rate increases to ~15-20 mm/yr in the vicinity of Cajon Pass (CP) because of transfer of SJF slip back onto the San Andreas; northwest of Tejon Pass the rate increases again to

  15. Nucleation, linkage and active propagation of a segmented Quaternary normal-dextral fault: the Loma del Viento fault (Campo de Dalías, Eastern Betic Cordillera, SE Spain)

    NASA Astrophysics Data System (ADS)

    Pedrera, Antonio; Marín-Lechado, Carlos; Stich, Daniel; Ruiz-Constán, Ana; Galindo-Zaldívar, Jesús; Rey-Moral, Carmen; de Lis Mancilla, Flor

    2012-02-01

    Active faults from the Campo de Dalías (SE Betic Cordillera) allow us to constrain the deformation styles involved in the development of segmented oblique-slip faults. This sector constitutes the widest outcrop of Plio-Quaternary sediments in the northern boundary of the Alboran Sea. It has emerged since the Late Pliocene, and therefore provides recent deformation markers that are not disturbed by erosive processes. The faults started to grow during the Pleistocene, reactivating previous hybrid joints, with a normal-dextral slip. We present a detailed map of the largest fault in the area, the Loma del Viento fault, comprising six onshore segments. Based on field work and aerial photography, the distributions of the contiguous joints have been mapped, and the joints reactivated as faults are identified. Some of these fault segments are hard-linked, and fault slip enhances toward the linkage sectors between them with associated sedimentary depocenters. An electrical tomography profile reveals the wedge geometry of a unit of Pleistocene conglomerates and red silts that were coevally deposited during the fault movement. Long-term slip rate in the central part of the fault is estimated at 0.07 ± 0.03 mm/y. In addition, a seismic crisis nucleated close to the Loma del Viento fault during November 2010 was recorded. Moment tensor analysis of the two mainshocks (Mw 3.5 and 4.2) provides a focal solution indicating a N120°E striking right-lateral strike-slip fault. The corrugated morphology of the Loma del Viento fault may have influenced its seismic behavior. Some of the fault segments are oblique to the general motion of the fault. These oblique segments would provide higher resistance against the general fault motion and could lock the fault, leading to accumulate elastic energy.

  16. Holocene earthquakes and right-lateral slip on the left-lateral Darrington-Devils Mountain fault zone, northern Puget Sound, Washington

    USGS Publications Warehouse

    Personius, Stephen F.; Briggs, Richard W.; Nelson, Alan R.; Schermer, Elizabeth R; Maharrey, J. Zebulon; Sherrod, Brian; Spaulding, Sarah A.; Bradley, Lee-Ann

    2014-01-01

    Sources of seismic hazard in the Puget Sound region of northwestern Washington include deep earthquakes associated with the Cascadia subduction zone, and shallow earthquakes associated with some of the numerous crustal (upper-plate) faults that crisscross the region. Our paleoseismic investigations on one of the more prominent crustal faults, the Darrington–Devils Mountain fault zone, included trenching of fault scarps developed on latest Pleistocene glacial sediments and analysis of cores from an adjacent wetland near Lake Creek, 14 km southeast of Mount Vernon, Washington. Trench excavations revealed evidence of a single earthquake, radiocarbon dated to ca. 2 ka, but extensive burrowing and root mixing of sediments within 50–100 cm of the ground surface may have destroyed evidence of other earthquakes. Cores in a small wetland adjacent to our trench site provided stratigraphic evidence (formation of a laterally extensive, prograding wedge of hillslope colluvium) of an earthquake ca. 2 ka, which we interpret to be the same earthquake documented in the trenches. A similar colluvial wedge lower in the wetland section provides possible evidence for a second earthquake dated to ca. 8 ka. Three-dimensional trenching techniques revealed evidence for 2.2 ± 1.1 m of right-lateral offset of a glacial outwash channel margin, and 45–70 cm of north-side-up vertical separation across the fault zone. These offsets indicate a net slip vector of 2.3 ± 1.1 m, plunging 14° west on a 286°-striking, 90°-dipping fault plane. The dominant right-lateral sense of slip is supported by the presence of numerous Riedel R shears preserved in two of our trenches, and probable right-lateral offset of a distinctive bedrock fault zone in a third trench. Holocene north-side-up, right-lateral oblique slip is opposite the south-side-up, left-lateral oblique sense of slip inferred from geologic mapping of Eocene and older rocks along the fault zone. The cause of this slip reversal is

  17. New insights into the active deformation of accretionary prisms: examples from the Western Makran, Iran

    NASA Astrophysics Data System (ADS)

    Penney, Camilla; Copley, Alex; Oveisi, Benham

    2016-04-01

    The Makran subduction zone, along the southern coasts of Iran and Pakistan, hosts one of the largest exposed accretionary wedges in the world. The western Makran has been characterised by a lack of shallow and thrust seismicity in both the instrumental and historical periods. The Mw 6.1 2013 Minab earthquake thus provides a rare opportunity to study the deformation of the accretionary wedge in the transition region between continent-continent collision, in the Zagros, and oceanic subduction, in the Makran. We study the source parameters and slip distribution of this earthquake using seismology, geodesy and field observations. We observe left-lateral strike-slip motion on a fault striking ENE-WSW; approximately perpendicular to the faults of the Minab-Zendan-Palami fault zone, the main structure previously thought to accommodate the right-lateral shear between the Zagros and the Makran. The fault that ruptured in 2013 is one of a series of approximately E-W striking left-lateral faults visible in the geology and geomorphology. These accommodate a velocity field equivalent to right-lateral shear on N-S striking planes by clockwise rotations about vertical axes. The longitudinal range of shear in the western Makran is likely to be controlled by the distance over which the underthrusting Arabian lithosphere deepens in the transition from continent-continent collision to oceanic subduction. The lack of observed megathrust seismicity in the western Makran has led to assertions that the convergence in this region may be aseismic, in contrast to the eastern Makran, which experienced an Mw8.1 earthquake in 1945. The right-lateral Sistan Suture Zone, which runs ~N-S along the Iran-Afghanistan border to the north of the Makran, appears to separate these regimes. However, right-lateral faulting is not observed south of ~27°N, within the wedge. The Minab earthquake and the 2013 Balochistan earthquake show that the Makran accretionary wedge is dominated by strike-slip faulting

  18. Distributed extensional deformation in a zone of right-lateral shear: Implications for geodetic versus geologic rates of deformation in the eastern California shear zone-Walker Lane

    NASA Astrophysics Data System (ADS)

    Foy, T. Andrew; Frankel, Kurt L.; Lifton, Zachery M.; Johnson, Christopher W.; Caffee, Marc W.

    2012-08-01

    The eastern California shear zone (ECSZ)-Walker Lane belt represents an important, evolving component of the Pacific-North America plate boundary. Geodetic data suggest the northern ECSZ is accumulating dextral shear at a rate of ˜9.3 mm/a, more than double the total measured late Pleistocene rate at ˜37.5°N. At this latitude, the Silver Peak-Lone Mountain (SPLM) extensional complex plays an important role in accommodating and transferring slip among the strike-slip and normal faults of the ECSZ and Walker Lane. To better understand the recent geodynamic evolution of this region, we determined late Pleistocene extension rates for the Clayton Valley fault zone, one of a series of down-to-the-northwest normal faults comprising the SPLM, using geologic mapping, differential GPS fault scarp surveys, and cosmogenic nuclide geochronology. Extension rates along the Clayton Valley fault zone are time-invariant at 0.1 ± 0.1 to 0.3 ± 0.1 mm/a (depending on fault dip) since ˜137 ka. When combined with other published fault slip rates at this latitude, the cumulative late Pleistocene geologic slip rate is ˜3.3 to 5.2 mm/a. This rate is lower than both the geodetic rate of dextral shear and other long-term slip rate budgets in the northern ECSZ. Our results suggest that deformation in Clayton Valley is spread across a diffuse set of normal faults and that not all of the deformation is recorded in the surficial geology. We suggest that the low cumulative geologic slip rate in the northern ECSZ may be a result of this distributed extension, which can cause long-term rates of deformation to be significantly underestimated.

  19. Late Pleistocene to Historical Activity of the Hovd Fault (Mongolian Altay) from Tectonic Geomorphology and Paleoseismology

    NASA Astrophysics Data System (ADS)

    Ferry, M. A.; Battogtokh, D.; Ritz, J. F.; Kurtz, R.; Braucher, R.; Klinger, Y.; Ulzibat, M.; Chimed, O.; Demberel, S.

    2015-12-01

    Active tectonics of western Mongolia is dominated by large strike-slip fault systems that produced great historical earthquakes: the Bulnay fault (Mw 8.1 and 8.4 in 1905), the Fu-Yun fault (Mw 8.0 in 1931) and the Bogd fault (Mw 8.1 in 1957). Central to these faults is the Altay Range that accommodates ~4 mm/yr of right-lateral motion. An earthquake of similar magnitude occurred in 1761 and has been attributed to the Hovd fault were seemingly fresh surface rupture was reported in 1985. Here, we study the Ar-Hötöl section of the Hovd fault where surface rupture was described over a length of ~200 km. Detailed mapping of stream gullies from high-resolution Pleiades satellite images show a consistent pattern of right-lateral offsets from a few meters to ~500 m. At Climbing Rock, we surveyed a gully offset by 75 ± 5 m. The associated surface was sampled for 10Be profile which yields an exposure age of 154 ± 20 ka. The resulting minimal right-lateral slip rate ranges 0.4-0.6 mm/yr. However, drainage reconstruction suggests this surface may have recorded as much as 400 ± 20 m of cumulative offset. This implies the Hovd fault may accommodate as much as 2.6 ± 0.4 mm/yr, which would make it the main active fault of the Altay. At a smaller scale, TLS topography documents offsets in the order of 2.5-5 m that likely correspond to the most recent surface-rupturing event with Mw ~8. A value of 2.8-3.0 m is reconstructed from a Uiger grave dated AD 750-840. At Marmot Creek and Small Creek, short drainages flow across the fault and form ponds against the main scarp. Two paleoseimic trenches reveal similar stratigraphy with numerous peat layers that developed over alluvial sands. The fault exhibits near vertical strands affecting pre-ponding units as well as a well-developed peat unit radiocarbon-dated AD 1465-1635. This unit likely corresponds to the ground surface at the time of the last rupture. It is overlain with a sandy pond unit on top of which a second continuous peat

  20. Neural Signals Evoked by Stimuli of Increasing Social Scene Complexity Are Detectable at the Single-Trial Level and Right Lateralized

    PubMed Central

    Amaral, Carlos P.; Simões, Marco A.; Castelo-Branco, Miguel S.

    2015-01-01

    Classification of neural signals at the single-trial level and the study of their relevance in affective and cognitive neuroscience are still in their infancy. Here we investigated the neurophysiological correlates of conditions of increasing social scene complexity using 3D human models as targets of attention, which may also be important in autism research. Challenging single-trial statistical classification of EEG neural signals was attempted for detection of oddball stimuli with increasing social scene complexity. Stimuli had an oddball structure and were as follows: 1) flashed schematic eyes, 2) simple 3D faces flashed between averted and non-averted gaze (only eye position changing), 3) simple 3D faces flashed between averted and non-averted gaze (head and eye position changing), 4) animated avatar alternated its gaze direction to the left and to the right (head and eye position), 5) environment with 4 animated avatars all of which change gaze and one of which is the target of attention. We found a late (> 300 ms) neurophysiological oddball correlate for all conditions irrespective of their complexity as assessed by repeated measures ANOVA. We attempted single-trial detection of this signal with automatic classifiers and obtained a significant balanced accuracy classification of around 79%, which is noteworthy given the amount of scene complexity. Lateralization analysis showed a specific right lateralization only for more complex realistic social scenes. In sum, complex ecological animations with social content elicit neurophysiological events which can be characterized even at the single-trial level. These signals are right lateralized. These finding paves the way for neuroscientific studies in affective neuroscience based on complex social scenes, and given the detectability at the single trial level this suggests the feasibility of brain computer interfaces that can be applied to social cognition disorders such as autism. PMID:25807525

  1. Recognition on space photographs of structural elements of Baja California

    NASA Technical Reports Server (NTRS)

    Hamilton, W.

    1971-01-01

    Gemini and Apollo photographs provide illustrations of known structural features of the peninsula and some structures not recognized previously. An apparent transform relationship between strike-slip and normal faulting is illustrated by the overlapping vertical photographs of northern Baja California. The active Agua Blanca right-lateral strike-slip fault trends east-southeastward to end at the north end of the Valle San Felipe and Valle Chico. The uplands of the high Sierra San Pedro Martir are a low-relief surface deformed by young faults, monoclines, and warps, which mostly produce west-facing steps and slopes; the topography is basically structural. The Sierra Cucapas of northeasternmost Baja California and the Colorado River delta of northwesternmost Sonora are broken by northwest-trending strike-slip faults. A strike-slip fault is inferred to trend northward obliquely from near Cabo San Lucas to La Paz, thence offshore until it comes ashore again as the Bahia Concepcion strike-slip fault.

  2. 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

  3. Active faulting in northern Chile: ramp stacking and lateral decoupling along a subduction plate boundary?

    NASA Astrophysics Data System (ADS)

    Armijo, Rolando; Thiele, Ricardo

    1990-04-01

    Two large features parallel to the coastline of northern Chile have long been suspected to be the sites of young or active deformation: (1) The 700-km long Coastal Scarp, with average height (above sea level) of about 1000 m; (2) The Atacama Fault zone, that stretches linearly for about 1100 km at an average distance of 30-50 km from the coastline. New field observations combined with extensive analysis of aerial photographs demonstrate that both the Coastal Scarp and the Atacama Fault are zones of Quaternary and current fault activity. Little-degraded surface breaks observed in the field indicate that these fault zones have recently generated large earthquakes ( M = 7-8). Normal fault offsets observed in marine terraces in the Coastal Scarp (at Mejillones Peninsula) require tectonic extension roughly orthogonal to the compressional plate boundary. Strike-slip offsets of drainage observed along the Salar del Carmen and Cerro Moreno faults (Atacama Fault system) imply left-lateral displacements nearly parallel to the plate boundary. The left-lateral movement observed along the Atacama Fault zone may be a local consequence of E-W extension along the Coastal Scarp. But if also found everywhere along strike, left-lateral decoupling along the Atacama Fault zone would be in contradiction with the right lateral component of Nazca-South America motion predicted by models of present plate kinematics. Clockwise rotation with left-lateral slicing of the Andean orogen south of the Arica bend is one way to resolve this contradiction. The Coastal Scarp and the Atacama Fault zone are the most prominent features with clear traces of activity within the leading edge of continental South America. The great length and parallelism of these features with the subduction zone suggest that they may interact with the subduction interface at depth. We interpret the Coastal Scarp to be a west-dipping normal fault or flexure and propose that it is located over an east-dipping ramp stack at

  4. The 2006 Bahía Asunción Earthquake Swarm: Seismic Evidence of Active Deformation Along the Western Margin of Baja California Sur, Mexico

    NASA Astrophysics Data System (ADS)

    Munguía, Luis; Mayer, Sergio; Aguirre, Alfredo; Méndez, Ignacio; González-Escobar, Mario; Luna, Manuel

    2015-10-01

    The study of the Bahía Asunción earthquake swarm is important for two reasons. First, the earthquakes are clear evidence of present activity along the zone of deformation on the Pacific margin of Baja California. The swarm, with earthquakes of magnitude M w of up to 5.0, occurred on the coastline of the peninsula, showing that the Tosco-Abreojos zone of deformation is wider than previously thought. Second, the larger earthquakes in the swarm caused some damage and much concern in Bahía Asunción, a small town located in the zone of epicenters. We relocated the larger earthquakes with regional and/or local seismic data. Our results put the earthquake sources below the urban area of Bahía Asunción, at 40-50 km to the north of the teleseismically determined epicenters. In addition, these new locations are in the area of epicenters of many smaller events that were located with data from local temporary stations. This area trends in an E-W direction and has dimensions of approximately 15 km by 10 km. Most earthquakes had sources at depths that are between 4 and 9 km. A composite focal mechanism for the smaller earthquakes indicated right-lateral strike-slip motion and pure-normal faulting occurred during this swarm. Interestingly, the ANSS earthquake catalog of the United States Geological Survey (USGS) reported each one of these faulting styles for two large events of the swarm, with one of these earthquakes occurring 2 days before the other one. We associate the earthquake with strike-slip mechanism with the San Roque Fault, and the earthquake with the normal faulting style with the Asunción Fault. However, there is need of further study to verify this possible relation between the faults and the earthquakes. In addition, we recorded peak accelerations of up to 0.63g with an accelerometer installed in Bahía Asunción. At this site, an earthquake of M w 4.9 produced those high values at a distance of 4.1 km. We also used the acceleration dataset from this site

  5. Influences of archwire size and ligation method on the force magnitude delivered by nickel-titanium alloy archwires in a simulation of mandibular right lateral incisor linguoversion.

    PubMed

    Tochigi, Keisuke; Oda, Souichiro; Arai, Kazuhito

    2015-01-01

    The present study investigated the influence of archwire size and ligation method on the force magnitude delivered by nickel-titanium alloy archwires to 4 incisor brackets (42, 41, 31, and 32) in a simulation of mandibular right lateral incisor linguoversion. The force delivered by 0.014 and 0.016 inch nickel-titanium alloy archwires was measured using a newly developed multi-sensor measuring system and the mean force magnitudes were compared between different archwire sizes when using conventional ligation (CL) with elastic modules or self-ligating (SL) brackets by three-way ANOVA and post-hoc Bonferroni's tests. The mean force magnitudes for the brackets were significantly decreased in the order of 42, 41, 31, and 32 (p<0.01). The force magnitude was significantly larger in CL than SL at 42, 31, and 32 (p<0.05). In conclusion, the ligation method affected the force magnitude at 4 incisor brackets. Despite the ligation method, archwire size affected the force magnitude from 42 to 31. PMID:25948144

  6. Use of a Right Lateral Sector Graft in Living Donor Liver Transplantation Is Feasible, but Special Caution Is Needed With Respect to Liver Anatomy.

    PubMed

    Kokudo, T; Hasegawa, K; Arita, J; Yamamoto, S; Kaneko, J; Akamatsu, N; Sakamoto, Y; Makuuchi, M; Sugawara, Y; Kokudo, N

    2016-04-01

    Right lateral sector (RLS) grafting has been introduced to enlarge the potential donor pool for living donor liver transplantation (LDLT); however, evidence of its feasibility is limited. Data from 437 LDLTs carried out between 2000 and 2013 were analyzed retrospectively. LDLTs using a right liver graft (n = 251) were compared with those using a RLS graft (RLSG; n = 28). No donor mortality occurred, and the major complication rates were similar between the two groups. Postoperative liver function preservation was better in the RLSG donors. Concerning the recipients, the mortality and overall survival rates were similar between the two groups. The complication rate for the recipients was higher when more than two arterial or biliary anastomoses were necessary. A systematic literature search identified four reports on LDLT using RLSGs. Among 66 LDLTs, including the present series, there were no cases of donor death, and the rates of major and minor complications in the donors were 6% and 29%, respectively. The major complication and overall mortality rates in the recipients were 29% and 6%, respectively. LDLT using an RLSG is feasible, with an acceptable survival rate among the recipients. PMID:26602536

  7. Active tectonics along the Nebrodi-Peloritani boundary in northeastern Sicily (Southern Italy)

    NASA Astrophysics Data System (ADS)

    Pavano, F.; Romagnoli, G.; Tortorici, G.; Catalano, S.

    2015-09-01

    In the epicentral area of the seismic swarm of the June-September 2011, at southern edge of the Calabrian arc in NE Sicily, very recent extensional motions remobilised two main NW-SE dextral faults. The extensional reactivation of strike-slip faults responded to a new regional dynamic, also evidenced by GPS and seismological data. The inverted structures are aligned at the margin of a wide crustal block that is moving apart from the rest of the island and is uplifting faster than the adjacent regions. The active faults terminate to the northwest at the intersection with a prominent NNE trending fault that represents the western boundary of the mobile block. The vertical displacement along this border exactly matches the difference in elevation of the marine terraces resting inside and outside the block, respectively. On the contrary, only part of differential displacement of the marine terraces was actually accommodated as cumulative motion along the two NW oriented inverted faults, across the southwestern boundary of the block. Amounts of the vertical displacement were distributed on distinct fault planes of the previous dextral shear belts. The widespread fracturing is also the best explanation for the seismic swarm of the 2011, whose epicenters spread on a discrete rock volume rather than concentrated along a single fault plane. The diffuse fracturing seems to represent a peculiar style of deformation, connected to the tectonic inversion of previous strike-slip shear zones. Seismic swarm also affects the northern termination of the Calabrian arc where active extensional deformation reactivated previous strike-slip faults. The similarity of the two regions suggests that seismic swarm can be peculiar of extensional belts developed on previous strike-slip shear zones, along which the pre-existing geometry favours the dispersion of the tectonic motion on a network of small linked fault planes.

  8. Evidence of left-lateral active motion at the North America-Caribbean plate boundary

    NASA Astrophysics Data System (ADS)

    Leroy, S. D.; Ellouz, N.; Corbeau, J.; Rolandone, F.; Mercier De Lepinay, B. F.; Meyer, B.; Momplaisir, R.; Granja, J. L.; Battani, A.; Burov, E. B.; Clouard, V.; Deschamps, R.; Gorini, C.; Hamon, Y.; LE Pourhiet, L.; Loget, N.; Lucazeau, F.; Pillot, D.; Poort, J.; Tankoo, K.; Cuevas, J. L.; Alcaide, J.; Poix, C. J.; Mitton, S.; Rodriguez, Y.; Schmitz, J.; Munoz Martin, A.

    2014-12-01

    The North America-Caribbean plate boundary is one of the least-known among large plate boundaries. Although it was identified early on as an example of a strike-slip fault in the north of Hispaniola, its structure and rate of motion remains poorly constrained. We present the first direct evidence for active sinistral strike-slip motion along this fault, based on swath seafloor mapping of the northern Haiti area. There is evidence for ~16.5 km of apparent strike-slip motion along the mapped segment of the Septentrional fault zone off Cap Haitien town which is terminated to the east onland Dominican republic and in the west to southern Cuban margin. By evaluating these new constraints within the context of geodetic models of global plate motions, we estimate an activity of the fault since 2 Ma with an angular velocity for the Caribbean plate relative to the North America predicted 6-12 mmyr-1 sinistral motion along the Septentrional fault zone. This transform fault was initiated around 20 million years ago in its western segment and since 2 Ma in its eastern segment in response to a regional reorganization of plate velocities and directions, which induced a change in configuration of plate boundaries.

  9. Separation of the Guajira-Bonaire pair in the southern margin of the Caribbean: 65-50 Ma exhumation followed by 300 km right-lateral transtensional deformation

    NASA Astrophysics Data System (ADS)

    Zapata Henao, S.; Cardona, A.; Montes, C.; Valencia, V.; Vervoort, J. D.; Reiners, P. W.

    2012-12-01

    Middle to upper Eocene fluvial strata in the island of Bonaire contains detrital components that were tracked to the basement massifs of the Guajira Peninsula in northern Colombia. These detrital components confirm previous hypothesis that the Guajira-Bonaire pair constitute a tectonic piercing point along the southern Caribbean plate margin that was right-laterally displaced approximately 300 km after middle Eocene times. Other possible sources, the nearby Curacao and the far away Santa Marta massif, did not pass statistical similarity and overlap tests. U-Pb LA-ICP-MS from the metamorphic boulders of the Soebi Blanco Formation in Bonaire yield Grenvillian ages (1084 Ma, 1130 Ma and 1184 Ma), while the detrital zircons recovered from the sandy matrix of the conglomerates contains populations with peaks of 1000 Ma - 1200 Ma, 750 Ma - 950 Ma, and 200 Ma - 300 Ma. Overlap and Similarity tests run between these populations and published data from Guajira yield values of 0.750 and 0.680, which are significantly higher than the same comparison against the Santa Marta Massif (0.637 and 0.522), and the Curacao island (0.629 and 0.467). Thermochronological results from the metamorphic clasts yield Paleocene-middle Eocene ages (65 - 50 Ma) that confirm not only a regional-scale cooling event in this time period, but also help constrain the maximum depositional age (50 Ma) of the poorly dated Soebi Blanco Formation. Figure 6. U-Pb results from analyzed samples and other Caribbean provinces. (A), Detrital zircons from Soebi Blanco conglomerate matrix; (B), Zircon ages from metamorphic clasts (C), detrital zircons from late Cretaceous Etpana Formation in Guajira Peninsula (Weber et al., 2010); (D), detrital zircons from late Cretaceous Santa Marta San Lorenzo schists (Cardona et al., 2010a); (E), detrital zircons from late Cretaceous Knip Group (Wrigth and Wyld, 2010); (F), overlap and similarity values.

  10. Tectonique active du Nord-Est de Sulawesi(Indonésie) et contrôle structural de la caldeira de Tondano

    NASA Astrophysics Data System (ADS)

    Lécuyer, Frédéric; Bellier, Olivier; Gourgaud, Alain; Vincent, Pierre M.

    1997-10-01

    Field study and SPOT image analyses on the Tondano caldera region permit us to show a distributed active sinistral strike-slip fault zone which trends ENE- WSW This faulting accommodates the N-S movement of the Celebes Sea plate and represents a transfer fault zone between the Celebes sea subduetion end and the Moluccas sea subduetion zone. Furthermore, this study permits us to provide evidence for a tectonic control of the Tondano caldera collapse and evolution.

  11. Fault kinematics and active tectonics at the southeastern boundary of the eastern Alborz (Abr and Khij fault zones): Geodynamic implications for NNE Iran

    NASA Astrophysics Data System (ADS)

    Javidfakhr, Bita; Bellier, Olivier; Shabanian, Esmaeil; Siame, Lionel; Léanni, Laëtitia; Bourlès, Didier; Ahmadian, Seiran

    2011-10-01

    The Alborz is a region of active deformation within the Arabia-Eurasia collision zone. The Abr and the Khij Faults are two NE-trending left-lateral strike-slip faults in the eastern Alborz that correspond to the Shahrud fault system extended through an area of about 95 km × 55 km. Tectonic landforms typically associated with active strike-slip faults, such as deflected stream channels, offset ridges and fault scarps are documented along the mentioned faults. Detailed analyses of satellite images and digital topographic data accompanied by field surveys allowed us to measure horizontal offsets of about 420 ± 50 m and 400 ± 50 m for the Abr and Khij Faults, respectively. A total of 8 quartz-rich samples were sampled and dated from two different fan surfaces using in situ-produced 10Be cosmogenic dating method. Minimum exposure ages for the abandonment of the alluvial fan surfaces of 115 ± 14 kyr along the Abr Fault and of 230 ± 16 kyr along the Khij Fault imply that both faults are active with slip rates of about 3-4 mm yr -1 and 1-3 mm yr -1, respectively. The results of our study provide the first direct quantitative geological estimates of slip rate along these two active faults and place a new constraint on slip distribution between the faults in the eastern Alborz. Fault kinematic studies (from fault slip data) indicate a N35°E-trending maximum stress axis comprising a dominant strike-slip regime in agreement with the geomorphological analyses. The left-lateral strike-slip faulting along the Abr and Khij Faults and their associated fault zones in the eastern Alborz can be due to the westward component of motion of the South Caspian Basin with respect to Eurasia and Central Iran.

  12. The Beni-Ilmane (Algeria) seismic sequence of May 2010: Seismic sources and stress tensor calculations

    NASA Astrophysics Data System (ADS)

    Beldjoudi, H.; Delouis, B.; Djellit, H.; Yelles-Chaouche, A.; Gharbi, S.; Abacha, I.

    2016-02-01

    A moderate earthquake with a moment magnitude of Mw 5.5 struck the Sub-Bibanique region of eastern Algeria on 14 May 2010, killing three people, injuring hundreds of others, and causing moderate damages in the epicentral area, mainly in the villages of Beni-Ilmane and Samma. The focal mechanism of the seismic source for the first shock, obtained by near-field waveform modelling, exhibits left-lateral strike-slip faulting with the first nodal plane oriented at N345°, and right-lateral strike-slip faulting with the second nodal plane oriented at N254°. A second earthquake that struck the region on 16 May 2010, with a moment magnitude of Mw 5.1, was located 9 km SW of the first earthquake. The focal mechanism obtained by waveform modelling showed reverse faulting with nodal planes oriented NE-SW (N25° and N250°). A third earthquake that struck the region on 23 May 2010, with a moment magnitude of Mw 5.2, was located 7 km S of the first shock. The obtained focal mechanism showed a left-lateral strike-slip plane oriented at N12° and a right-lateral strike-slip plane oriented at N257°. Field investigations combined with geological and seismotectonic analyses indicate that the three earthquake shocks were generated by activity on three distinct faults. The second and third shocks were generated on faults oriented WSW-ENE and NNE-SSW, respectively. The regional stress tensor calculated in the region gives an orientation of N340° for the maximum compressive stress direction (σ1) which is close to the horizontal, with a stress shape factor indicating either a compressional or a strike-slip regime.

  13. New 40Ar/39Ar Ages Support The Dominant Right-Lateral Transform Motion Within The CARIB-SOAM PBZ Since Middle Eocene

    NASA Astrophysics Data System (ADS)

    Altamira, A.; Burke, K.; Copeland, P.; Foster, D.

    2006-12-01

    New 40Ar/3939Ar ages in amphiboles (84±2 to 95±2 Ma) and in white micas (86±3 to 95±2 Ma) from the Villa de Cura Blue Schist Belt (VdC) in Central Venezuela are in agreement with those ages reported by Smith et al., 1999 (96-80 Ma). We found that amphiboles and white micas reached their closure temperature at approximately the same time, suggesting a rapid cooling from 500°C to 300°C. The ages are very similar throughout the VdC, with no evident trend variations in any particular direction. We also report 40Ar/3939Ar amphibole ages from different localities along the Caribbean South America Plate Boundary Zone (CARIB-SOAM PBZ): 1) Batholithic granite in Aruba (88±9 Ma); 2) Ultramafic sliver in the northern coast of the Araya Peninsula, near San Juan de las Galdonas (145±14 Ma); 3) Dragon gneiss, in the extreme eastern tip of the Paria Peninsula (91±5 Ma); 4) Ultramafic rock from the Chacao Complex (122±17 Ma); 5) Three samples from Las Hermanas Formation, North of San Sebastian and South of VdC (134±4, 129±6 and 97±4 Ma). The igneous and high P/T metamorphic ages reported above were sampled in the thrust belts of Venezuela and are older than 70 Ma, when the Great Arc of the Caribbean struck the west coast of SOAM. The Venezuelan island of Los Testigos gave an 40Ar/3939Ar age for amphibole from a diorite of 41±2 Ma; this younger igneous age is located in the northern part of the PBZ; we interpret Los Testigos as a fragment of the southern end of the Lesser Antillean arc dragged into the PBZ as the arc slid by. All the ages are consistent with the predictions made by Burke et al., 2005, in which they proposed dominant right-lateral transform motion with limited flower structural strain-partitioning involving shortening (in thrusts) and extension (in pull-aparts) within the CARIB- SOAM PBZ and do not require a component of oblique convergence for the Caribbean-South America margin.

  14. The application of active-source seismic imaging techniques to transtensional problems the Walker Lane and Salton Trough

    NASA Astrophysics Data System (ADS)

    Kell, Anna Marie

    The plate margin in the western United States is an active tectonic region that contains the integrated deformation between the North American and Pacific plates. Nearly focused plate motion between the North American and Pacific plates within the northern Gulf of California gives way north of the Salton Trough to more diffuse deformation. In particular a large fraction of the slip along the southernmost San Andreas fault ultimately bleeds eastward, including about 20% of the total plate motion budget that finds its way through the transtensional Walker Lane Deformation Belt just east of the Sierra Nevada mountain range. Fault-bounded ranges combined with intervening low-lying basins characterize this region; the down-dropped features are often filled with water, which present opportunities for seismic imaging at unprecedented scales. Here I present active-source seismic imaging from the Salton Sea and Walker Lane Deformation Belt, including both marine applications in lakes and shallow seas, and more conventional land-based techniques along the Carson range front. The complex fault network beneath the Salton Trough in eastern California is the on-land continuation of the Gulf of California rift system, where North American-Pacific plate motion is accommodated by a series of long transform faults, separated by small pull-apart, transtensional basins; the right-lateral San Andreas fault bounds this system to the north where it carries, on average, about 50% of total plate motion. The Salton Sea resides within the most youthful and northerly "spreading center" in this several thousand-kilometer-long rift system. The Sea provides an ideal environment for the use of high-data-density marine seismic techniques. Two active-source seismic campaigns in 2010 and 2011 show progression of the development of the Salton pull-apart sub-basin and the northerly propagation of the Imperial-San Andreas system through time at varying resolutions. High fidelity seismic imagery

  15. Multistage evolution and variable motion history of Agenor Linea, Europa

    NASA Astrophysics Data System (ADS)

    Hoyer, Lauren; Kattenhorn, Simon A.; Watkeys, Michael K.

    2014-04-01

    Europa, the second Galilean moon of Jupiter, is composed of a silicate mantle and an ice shell which overlies a supposed subsurface ocean. The surface of Europa is scarred with fractures varying in morphology, dimensions, and geometry. We focus on Agenor Linea: a ∼1500 km bright band that extends across Europa’s antijovian to trailing southern hemisphere. Agenor Linea is morphologically a band-like strike-slip fault; however, it experienced at least three evolutionary growth phases marked by three zones of varying albedo, each with a different geological history. Structures within the band material and kinematic indicators are consistent with formation through oblique left-lateral dilation, followed by normal dilation and right-lateral strike-slip movement, or combinations thereof. These motions produced a cumulative maximum right-lateral offset of 29.5 km and a maximum band width of 34 km. We interpret Agenor Linea to have formed primarily in response to the combined effects of nonsynchronous rotation stress and diurnal tidal flexing. If so, its orientation is optimal for right-lateral oblique opening in the current global stress field, consistent with its most recent kinematic behavior. A small amount of offset of relatively young tension fractures that postdate cryospheric disruption by lenticulae suggest the possibility of ongoing activity along Agenor. In contrast to a previously published model in which strike-slip duplexing was the primary process of band formation, this study shows that initial dilation of three distinct morphological zones under disparate stress orientations preceded strike-slip motion that resulted in both localized and distributed deformation features within the zones across the width of the band.

  16. Reduced Activation in Right Lateral Prefrontal Cortex and Anterior Cingulate Gyrus in Medication-Naive Adolescents with Attention Deficit Hyperactivity Disorder during Time Discrimination

    ERIC Educational Resources Information Center

    Smith, Anna B.; Taylor, Eric; Brammer, Michael; Halari, Rozmin; Rubia, Katya

    2008-01-01

    Background: Patients with attention deficit hyperactivity disorder (ADHD) under-perform when discriminating between durations differing by several hundred milliseconds. This function involves right prefrontal and anterior cingulate (AC) brain regions, which are structurally and functionally compromised in this patient group during executive tasks.…

  17. Geodynamic implications of paleomagnetic data from Tertiary sediments in Sakhalin, Russia (NW Pacific)

    NASA Astrophysics Data System (ADS)

    Weaver, Richard; Roberts, Andrew P.; Flecker, Rachel; MacDonald, David I. M.; Fot'yanova, Lidiya M.

    2003-02-01

    N-S trending right-lateral strike-slip faults, which were active in the Tertiary, transect Sakhalin, Russia, while Mesozoic forearc and accretionary rocks testify to an earlier period of subduction. Several kinematic models have been proposed for the region, but the details required to constrain these models, such as the timing of the transition from subduction to strike-slip tectonics in Sakhalin, are still unknown. Even first-order tectonic features, such as the boundaries of the plates with which Sakhalin evolved during the Tertiary, are poorly known. Paleomagnetic results from around Sakhalin were obtained to constrain the geodynamic evolution of the region. Comparison of paleomagnetic inclination data with the apparent polar wander paths for the Eurasian, Pacific, and North American Plates suggests that Sakhalin probably evolved with the North American Plate, although a history including the Eurasian Plate cannot be ruled out. Paleomagnetic declination data suggest that significant clockwise vertical axis rotation has occurred in Sakhalin since the mid-Paleocene. It is likely that this rotational deformation was accommodated by Tertiary activity on right-lateral strike-slip faults, which may be associated with the opening of the Japan Sea, Tatar Strait, and Kuril Basin. These data contradict a published kinematic model for eastern Sakhalin, where counterclockwise vertical axis rotations were predicted for Neogene basins in the East Sakhalin Mountains. Agreement is better, however, with published paleomagnetic data from southern Sakhalin, where clockwise vertical axis rotations were documented.

  18. Cumulative right-lateral fault slip rate across the Zagros-Makran transfer zone: role of the Minab-Zendan fault system in accommodating Arabia-Eurasia convergence in southeast Iran

    NASA Astrophysics Data System (ADS)

    Regard, V.; Bellier, O.; Thomas, J.-C.; Bourlès, D.; Bonnet, S.; Abbassi, M. R.; Braucher, R.; Mercier, J.; Shabanian, E.; Soleymani, Sh.; Feghhi, Kh.

    2005-07-01

    The Zendan-Minab zone is the transition zone between the Zagros collision to the west and Makran subduction to the east. It is also linked to the north with the Nayband-Gowk fault system that bounds the Lut Block to the east. The total convergence rate between Arabia and Eurasia is estimated to range between 23 and 35 mm yr-1 in a NNE-trending direction. The deformation through the Minab-Zendan system is accommodated within two fault systems, the western N160°E-trending Minab-Zendan fault system and the eastern north-south Sabzevaran-Jiroft fault system. The study area is characterized by a well-defined succession of Quaternary deposit levels. The age of these deposits was estimated by archaeological data, regional palaeoclimate correlations and constrained by additional in situ10Be dating in another paper in this study. These deposits exhibit offsets, both lateral and vertical, that are evaluated by satellite image analysis and GPS profiles. Thanks to offsets and ages the strike-slip rates associated with the Minab-Zendan and the Sabzevaran-Jiroft fault systems are calculated to be 5.1 +/- 1.3 or 6.6 +/- 1.5, and 6.2 +/- 0.7 mm yr-1, respectively. These results allow an evaluation of the velocity vector of the Musandam Peninsula (Oman) with respect to the Lut Block of 11.4 +/- 2.0 or 12.9 +/- 2.2 mm yr-1 in a N10 +/- 15°E direction, close to the GPS estimates. This study also constrains the in-plane slip rates for each fault. Previous works indicate that the Zagros accommodates only 10 mm yr-1 of shortening, while 10 mm yr-1 should be accommodated by the Alborz mountains in northern Iran. This last 10 mm yr-1 may be accommodated through the Nayband-Gowk system and the East Iranian ranges, implying that the two fault systems constituting the Zagros-Makran transfer zone have different geodynamic roles. The western Minab-Zendan fault system links the Makran and Zagros deforming zones, whereas the northwestern Jiroft-Sabzevaran fault system is transmitting the

  19. Structure of the Hat Creek graben region: Implications for the structure of the Hat Creek graben and transfer of right-lateral shear from the Walker Lane north of Lassen Peak, northern California, from gravity and magnetic anomalies

    USGS Publications Warehouse

    Langenheim, Victoria; Jachens, Robert C.; Clynne, Michael A.; Muffler, L. J. Patrick

    2016-01-01

    Interpretation of magnetic and new gravity data provides constraints on the geometry of the Hat Creek Fault, the amount of right-lateral offset in the area between Mt. Shasta and Lassen Peak, and confirmation of the influence of pre-existing structure on Quaternary faulting. Neogene volcanic rocks coincide with short-wavelength magnetic anomalies of both normal and reversed polarity, whereas a markedly smoother magnetic field occurs over the Klamath Mountains and its Paleogene cover. Although the magnetic field over the Neogene volcanic rocks is complex, the Hat Creek Fault, which is one of the most prominent normal faults in the region and forms the eastern margin of the Hat Creek Valley, is marked by the eastern edge of a north-trending magnetic and gravity high 20-30 km long. Modeling of these anomalies indicates that the fault is a steeply dipping (~75-85°) structure. The spatial relationship of the fault as modeled by the potential-field data, the youngest strand of the fault, and relocated seismicity suggests that deformation continues to step westward across the valley, consistent with a component of right-lateral slip in an extensional environment. Filtered aeromagnetic data highlight a concealed magnetic body of Mesozoic or older age north of Hat Creek Valley. The body’s northwest margin strikes northeast and is linear over a distance of ~40 km. Within the resolution of the aeromagnetic data (1-2 km), we discern no right-lateral offset of this body. Furthermore, Quaternary faults change strike or appear to end, as if to avoid this concealed magnetic body and to pass along its southeast edge, suggesting that pre-existing crustal structure influenced younger faulting, as previously proposed based on gravity data.

  20. New GPS constraints on active deformation along the Africa-Iberia plate boundary

    NASA Astrophysics Data System (ADS)

    Koulali, A.; Ouazar, D.; Tahayt, A.; King, R. W.; Vernant, P.; Reilinger, R. E.; McClusky, S.; Mourabit, T.; Davila, J. M.; Amraoui, N.

    2011-08-01

    We use velocities from 65 continuous stations and 31 survey-mode GPS sites as well as kinematic modeling to investigate present day deformation along the Africa-Iberia plate boundary zone in the western Mediterranean region. The GPS velocity field shows southwestward motion of the central part of the Rif Mountains in northern Morocco with respect to Africa varying between 3.5 and 4.0 mm/yr, consistent with prior published results. Stations in the southwestern part of the Betic Mountains of southern Spain move west-southwest with respect to Eurasia (˜ 2-3 mm/yr). The western component of Betics motion is consistent with partial transfer of Nubia-Eurasia plate motion into the southern Betics. The southward component of Betics motion with respect to Iberia is kinematically consistent with south to southwest motion of the Rif Mountains with respect to Africa. We use block modeling, constrained by mapped surface faults and seismicity to estimate the geometry and rates of strain accumulation on plate boundary structures. Our preferred plate boundary geometry includes one block between Iberia and Africa including the SW Betics, Alboran Sea, and central Rif. This geometry provides a good fit to the observed motions, suggesting a wide transpressive boundary in the westernmost Mediterranean, with deformation mainly accommodated by the Gloria-Azores fault system to the West and the Rif-Tell lineament to the East. Block boundaries encompass aspects of earlier interpretations suggesting three main deformation styles: (i) extension along the NE-SW trending Trans-Alboran shear zone, (ii) dextral strike-slip in the Betics corresponding to a well defined E-W seismic lineament, and (iii) right lateral strike-slip motion extending West to the Azores and right-lateral motion with compression extending East along the Algerian Tell. We interpret differential motion in the Rif-Alboran-Betic system to be driven both by surface processes related the Africa-Eurasia oblique convergence and

  1. Inhibitory Control of Memory Retrieval and Motor Processing Associated with the Right Lateral Prefrontal Cortex: Evidence from Deficits in Individuals with ADHD

    ERIC Educational Resources Information Center

    Depue, B. E.; Burgess, G. C.; Willcutt, E. G.; Ruzic, L.; Banich, M. T.

    2010-01-01

    Studies of inhibitory control have focused on inhibition of motor responses. Individuals with ADHD consistently show reductions in inhibitory control and exhibit reduced activity of rLPFC activity compared to controls when performing such tasks. Recently these same brain regions have been implicated in the inhibition of memory retrieval. The…

  2. 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.

  3. Quasi-static propagator matrices: Creep on strike-slip faults

    NASA Astrophysics Data System (ADS)

    Ward, Steven N.

    1985-11-01

    This paper presents a method for computing viscoelastic flow in a layered Earth by means of quasi-static propagator matrices. The method has advantages over approximate or purely numerical attacks in that exact, semi-analytical solutions are obtained. The procedure enables a more rapid calculation than is possible with finite elements, yet it does not sacrifice exactness as do analytical approximations. To illustrate the technique, I constructed a plausible model of the San Andreas fault and investigated the time and space behavior of displacement, displacement rate, shear-stress and shear-strain rate at depth as well as at the surface. Viscoelastic relaxation speeds the restressing of the fault. For events of magnitude 6.2 and 6.9, viscoelasticity reduces recharge time relative to the base strain rate by 15% and 50% respectively. For events of magnitude 6.2 and less, viscoelasticity has only a small influence and a linear extrapolation of stress accumulation will predict the time of recharge reasonably well. Relative plate velocities measured within 400 km of the fault are highly variable in space and time. Direct plate velocity measurements made as far as 100 km from a major fault could differ by a factor of two from the average rate. Features of the fault model at depth include: stresses and strain rates which exceed surface values by a factor of three; sign reversals in strain rates; and positive coseismic stress drops induced for limited periods in narrow thin zones. The latter feature could initiate and terminate aftershock sequences. Stress recharge does not occur simultaneously at all depths on the fault for all magnitude events. Recurrence times of earthquakes estimated from surface observations may thus be biased.

  4. 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.; Wright, T. J.

    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.

  5. Fault weakening and onset of aseismic creep on mature strike-slip faults

    NASA Astrophysics Data System (ADS)

    Çakir, Z.; Ergintav, S.; Ozener, H.; Dogan, U.; Akoglu, A. M.; Meghraoui, M.; Reilinger, R.

    2012-04-01

    Persistent Scatterer InSAR time series analysis of the radar images of the Envisat satellite of the European Space Agency, GPS measurements and field observations reveal that central section of the Izmit fault is now creeping at a steady-state rate reaching to its full speed of up to ~2 cm/yr, that is, its geodetically determined pre-earthquake slip rate. GPS measurements and InSAR time series west of Lake Sapanca show that rapid postseismic afterslip started immediately after the earthquake following the coseismic movement of ~3 m. As expected, it decays logarithmically with time and appears to be in a steady-state stage over the last 5-6 years, implying that it will likely continue for decades and possibly until late in the earthquake cycle. In other words, postseismic afterslip turns into surface creep with time, which is what might also have happened along the Hayward segment of the San Andreas fault and Ismetpasa segment of the North Anatolian fault following the large earthquakes in 1857 and 1944, respectively. Therefore, the 1999 Izmit earthquake demonstrates for the first time how postseismic afterslip evolves in to stable surface creep. We attribute the triggering of surface creep to trapped pore-fluid overpressures induced by the supershear rupture propagation during the Izmit earthquake, and to the oceanic and metamorphic rocks outcropping in the earthquake region as they are largely made up of weak phyllosilicates. The aseismic slip explains the relative seismic quiescence along supershear rupture segments observed after the 1999 Izmit and possibly various other large earthquakes elsewhere in the world, suggesting that supershear fault segments might be potential sites for aseismic surface creep.

  6. North-South contraction of the mojave block and strike-slip tectonics in southern california.

    PubMed

    Bartley, J M; Glazner, A F; Schermer, E R

    1990-06-15

    The Mojave block of southern California has undergone significant late Cenozoic north-south contraction. This previously unappreciated deformation may account for part of the discrepancy between neotectonic and plate-tectonic estimates of Pacific-North American plate motion, and for part of the Big Bend in the San Andreas fault. In the eastern Mojave block, contraction is superimposed on early Miocene crustal extension. In the western Mojave block, contractional folds and reverse faults have been mistaken for extensional structures. The three-dimensional complexity of the contractional structures may mean that rigid-block tectonic models of the region based primarily on paleomagnetic data are unreliable. PMID:17747526

  7. New aeromagnetic data reveal large strike-slip (?) faults inthe Northern Willamette Valley, Oregon

    USGS Publications Warehouse

    Blakely, R.J.; Wells, R.E.; Tolan, T.L.; Beeson, M.H.; Trehu, A.M.; Liberty, L.M.

    2000-01-01

    High-resolution aeromagnetic data from the northern Willamette Valley, Oregon, reveal large, northwest-striking faults buried beneath Quaternary basin sediments. Several faults known from geologic mapping are well defined by the data and appear to extend far beyond their mapped surface traces. The Mount Angel fault, the likely source of the Richter magnitude (M1) 5.6 earthquake in 1993, is at least 55 km long and may be connected in the subsurface with the Gales Creek fault 25 km farther northwest. Northeast of the Mount Angel fault, a 60-km-long, northwest-striking anomaly may represent a previously unrecognized dextral-slip fault beneath the towns of Canby and Molalla. Vertical offsets along the Mount Angel fault increase with depth, indicating a long history of movement for the fault. Dominantly northwest- trending, relatively straight faults, consistent stepover geometries, offset magnetic anomalies and earthquake focal mechanisms suggest that these faults collectively accommodate significant dextral slip. The 1993 earthquake may have occured on a left-stepping restraining bend along the Mount Angel-Gales Creek fault zone.

  8. Active Crustal Faults in the Forearc Region, Guerrero Sector of the Mexican Subduction Zone

    NASA Astrophysics Data System (ADS)

    Gaidzik, Krzysztof; Ramírez-Herrera, Maria Teresa; Kostoglodov, Vladimir

    2016-01-01

    This work explores the characteristics and the seismogenic potential of crustal faults on the overriding plate in an area of high seismic hazard associated with the occurrence of subduction earthquakes and shallow earthquakes of the overriding plate. We present the results of geomorphic, structural, and fault kinematic analyses conducted on the convergent margin between the Cocos plate and the forearc region of the overriding North American plate, within the Guerrero sector of the Mexican subduction zone. We aim to determine the active tectonic processes in the forearc region of the subduction zone, using the river network pattern, topography, and structural data. We suggest that in the studied forearc region, both strike-slip and normal crustal faults sub-parallel to the subduction zone show evidence of activity. The left-lateral offsets of the main stream courses of the largest river basins, GPS measurements, and obliquity of plate convergence along the Cocos subduction zone in the Guerrero sector suggest the activity of sub-latitudinal left-lateral strike-slip faults. Notably, the regional left-lateral strike-slip fault that offsets the Papagayo River near the town of La Venta named "La Venta Fault" shows evidence of recent activity, corroborated also by GPS measurements (4-5 mm/year of sinistral motion). Assuming that during a probable earthquake the whole mapped length of this fault would rupture, it would produce an event of maximum moment magnitude Mw = 7.7. Even though only a few focal mechanism solutions indicate a stress regime relevant for reactivation of these strike-slip structures, we hypothesize that these faults are active and suggest two probable explanations: (1) these faults are characterized by long recurrence period, i.e., beyond the instrumental record, or (2) they experience slow slip events and/or associated fault creep. The analysis of focal mechanism solutions of small magnitude earthquakes in the upper plate, for the period between 1995

  9. LiDAR-Assisted identification of an active fault near Truckee, California

    USGS Publications Warehouse

    Hunter, L.E.; Howle, J.F.; Rose, R.S.; Bawden, G.W.

    2011-01-01

    We use high-resolution (1.5-2.4 points/m2) bare-earth airborne Light Detection and Ranging (LiDAR) imagery to identify, map, constrain, and visualize fault-related geomorphology in densely vegetated terrain surrounding Martis Creek Dam near Truckee, California. Bare-earth LiDAR imagery reveals a previously unrecognized and apparently youthful right-lateral strike-slip fault that exhibits laterally continuous tectonic geomorphic features over a 35-km-long zone. If these interpretations are correct, the fault, herein named the Polaris fault, may represent a significant seismic hazard to the greater Truckee-Lake Tahoe and Reno-Carson City regions. Three-dimensional modeling of an offset late Quaternary terrace riser indicates a minimum tectonic slip rate of 0.4 ?? 0.1 mm/yr.Mapped fault patterns are fairly typical of regional patterns elsewhere in the northern Walker Lane and are in strong coherence with moderate magnitude historical seismicity of the immediate area, as well as the current regional stress regime. Based on a range of surface-rupture lengths and depths to the base of the seismogenic zone, we estimate a maximum earthquake magnitude (M) for the Polaris fault to be between 6.4 and 6.9.

  10. Results from NICLAKES Survey of Active Faulting Beneath Lake Managua,Central American Volcanic arc

    NASA Astrophysics Data System (ADS)

    McIntosh, K.; Funk, J.; Mann, P.; Perez, P.; Strauch, W.

    2006-12-01

    Lake Managua covers an area of 1,035 km2 of the Central American volcanic arc and is enclosed by three major stratovolcanoes: Momotombo to the northwest was last active in AD 1905, Apoyeque in the center on the Chiltepe Peninsula was last active ca. 4600 years BP, and Masaya to the southeast was last active in AD 2003. A much smaller volcano in the lake (Momotombito) is thought to have been active <4500 yrs B.P. In May of 2006, we used a chartered barge to collect 330 km of 3.5 kHz profiler data along with coincident 274 km of sidescan sonar and 27 km of seismic reflection data. These data identify three zones of faulting on the lake floor: 1) A zone of north-northeast-striking faults in the shallow (2.5-7.5 m deep) eastern part of the lake that extends from the capital city of Managua, which was severely damaged by shallow, left-lateral strike-slip displacements on two of these faults in 1931 (M 5.6) and 1972 (M 6.2): these faults exhibit a horst and graben character and include possible offsets on drowned river valleys 2) a semicircular rift zone that is 1 km wide and can be traced over a distance of 30 km in the central part of the lake; the rift structure defines the deepest parts of the lake ranging from 12 to 18 m deep and is concentric about the Apoyeque stratocone/Chiltepe Peninsula; and 3) a zone of fault scarps defining the northwestern lake shore that may correlate to the northwestern extension of the Mateare fault zone, a major scarp-forming fault that separates the Managua lowlands from the highlands south and west of the city. Following previous workers, we interpret the northeast- trending group of faults in the eastern part of the lake as part of a 15-km-long discontinuity where the trend of the volcanic arc is offset in a right-lateral sense. The semi-circular pattern of the rift zone that is centered on Chiltepe Peninsula appears to have formed as a distal effect of either magma intrusion or withdrawal from beneath this volcanic complex. The

  11. Foreland segmentation along an active convergent margin: New constraints in southeastern Sicily (Italy) from seismic and geodetic observations

    NASA Astrophysics Data System (ADS)

    Musumeci, Carla; Scarfì, Luciano; Palano, Mimmo; Patanè, Domenico

    2014-09-01

    We performed an in-depth analysis of the ongoing tectonics of a large sector of southern Sicily, including the Hyblean Foreland and the front of the Maghrebian Chain, as well as the Ionian Sea offshore, through the integration of seismic and GPS observations collected in the nearly two decades. In particular, a dataset consisting of more than 1100 small-to moderate-magnitude earthquakes (1.0 ≤ ML ≤ 4.6) has been used for local earthquake tomography in order to trace the characteristics of the faulting systems, and for focal mechanisms computation to resolve the current local stress field and to characterise the faulting regime of the investigated area. In addition, GPS measurements, carried out on both episodic and continuous stations, allowed us to infer the main features of the current crustal deformation pattern. Main results evidence that the Hyblean Plateau is subject to a general strike-slip faulting regime, with a maximum horizontal stress axis NW-SE to NNW-SSE oriented, in agreement with the Eurasia-Nubia direction of convergence. The Plateau is separated into two different tectonic crustal blocks by the left-lateral strike-slip Scicli-Ragusa Fault System. The western block moves in agreement with central Sicily while the eastern one accommodates part of the contraction arising from the main Eurasia-Nubia convergence. Furthermore, we provided evidences leading to consider the Hyblean-Maltese Escarpment Fault System as an active boundary characterised by a left-lateral strike-slip motion, separating the eastern block of the Plateau from the Ionian basin. All these evidences lend credit to a crustal segmentation of the southeastern Sicily.

  12. The interpretation of crustal dynamics data in terms of plate interactions and active tectonics of the Anatolian Plate and surrounding regions in the Middle East

    NASA Technical Reports Server (NTRS)

    Toksoz, M. Nafi

    1987-01-01

    The primary effort in this study during the past year has been directed along two separate lines: (1) expanding finite element models to include the entire Anatolian plate, the Aegean Sea and the Northeastern Mediterranean Sea, and (2) investigating the relationship between fault geometry and earthquake activity for the North Anatolian and similar strike-slip faults (e.g., San Andreas Fault). Both efforts are designed to provide an improved basis for interpreting the Crustal Dynamics measurements NASA has planned for this region. The initial phases of both investigations have been completed and the results are being prepared for publication. These investigations are described briefly.

  13. Spatial heterogeneities of deviatoric stress and pore-pressure in Kyushu, Japan, and their implication for seismic activity

    NASA Astrophysics Data System (ADS)

    Matsumoto, Satoshi; Chikura, Hiromi; Ohkura, Takahiro; Miyazaki, Masahiro; Shimizu, Hiroshi; Abe, Yuki; Inoue, Hiroyuki; Yoshikawa, Shin; Yamashita, Yusuke

    2013-04-01

    We investigated the spatial variation in stress fields and pore fluid pressures on Kyushu Island, southwestern Japan. High seismic activity is found not only along active faults in Kyushu Island (southwestern Japan) but also in the central area of the island where there are active volcanoes. We consider the focal mechanisms of the shallow earthquakes on Kyushu Island to determine the relative deviatoric stress field and pore fluid factor. Generally, the stress field corresponds to a strike slip regime in this area. A decline in the maximum principal compressional stress is found in the western part of the high seismicity area, in the middle of Kyushu Island; this may be caused by a thickening of the seismogenic zone, as estimated from D90 analysis. At thin seismogenic layer, strike slip faulting dominates and strain rate from GPS study is high. In the active fault zone, seismic activity along the fault is high, and the pore pressure within the zone is higher than the values observed elsewhere, suggesting a mechanism explained by the fault valve model of Sibson [1992]. The pore pressure in the high seismic area with scattered hypocenter distribution in the middle part is lower than that in the active fault zones.

  14. Multifaulting in a tectonic syntaxis revealed by InSAR: The case of the Ziarat earthquake sequence (Pakistan)

    NASA Astrophysics Data System (ADS)

    Pinel-Puysségur, B.; Grandin, R.; Bollinger, L.; Baudry, C.

    2014-07-01

    On 28-29 October 2008, within 12 h, two similar Mw = 6.4 strike-slip earthquakes struck Baluchistan (Pakistan), as part of a complex seismic sequence. Interferometric Synthetic Aperture Radar (InSAR) data reveal that the peak of surface displacement is near the Ziarat anticline, a large active fold affected by Quaternary strike-slip faulting. All coseismic interferograms integrate the deformation due to both earthquakes. As their causative faults ruptured close to each other, the individual signals cannot be separated. According to their focal mechanisms, each earthquake may have activated a NE-SW sinistral or a NW-SE dextral fault segment, which leads to four possible scenarios of fault orientations. A nonlinear inversion of the InSAR data set allows rejecting two scenarios. The best slip distributions on the two fault segments for the two remaining scenarios are determined by linear inversion. Stress-change modeling favors a scenario involving two abutting conjugate strike-slip faults. Two other fault segments accommodated left-lateral strike slip during the seismic sequence. The activated fault system includes multiple fault segments with different orientations and little surface expression. This may highlight, at a smaller scale, the distributed, possibly transient character of deformation within a broader right-lateral shear zone. It suggests that the activated faults delineate a small tectonic block extruding and subtly rotating within the shear zone. It occurs in the vicinity of the local tectonic syntaxis where orogenic structures sharply turn around a vertical axis. These mechanisms could participate in the long-term migration of active tectonic structures within this kinematically unstable tectonic syntaxis.

  15. First paleoseismological assessment of active deformation along the eastern front of the southern Alps (NE Italy, Friuli). Insights on the 1511 earthquake causative fault.

    NASA Astrophysics Data System (ADS)

    Falcucci, Emanuela; Eliana Poli, Maria; Galadini, Fabrizio; Paiero, Giovanni; Scardia, Giancarlo; Zanferrari, Adriano

    2014-05-01

    The study area belongs to the Julian Prealps that represent the easternmost portion of the Plio-Quaternary front of the eastern Southalpine Chain (ESC), a south-verging polyphase fold and thrust belt, in evolution from the Middle Miocene to the Present. Here, the WSW-ENE trending, SW- verging thrusts of the ESC join the NW-SE trending, right-lateral strike slip Idrija fault system, which develops along the Italian-Slovenian boundary. The area is characterized by medium/high seismicity testified by both large historical and instrumental earthquakes. The DBMI11 (Locati et al., 2011) records the 1348 Carinzia earthquake (Mw= 7.02), the 1511 Idrija earthquake (Mw=6.98), and the 1976 Friuli earthquakes on May (Mw=6.46) and September (Mw=5.98) We studied a segment of the Susans-Tricesimo thrust system, namely the Colle Villano (CV) thrust, identified by means of geological and geophysical investigations (Galadini et al., 2005). New geological and geomorphological analyses allowed identifying the surficial geomorphic evidence of recent blind thrusting along the structure, represented by gentle scarps and surface warping. In order to characterise the Late Pleistocene-Holocene activity of this blind thrust, paleoseismological investigations were performed along one of CV thrust-related fault scarps. We dug three trenches ~1 km to the north of the Magredis village. The analysis of the trench walls allowed identifying deformation events induced by the fault activity. Two subsequent episodes of deformation are distinguished by localised warping (few metres in wave length) of the sedimentary sequences exposed by the excavations and secondary extrados faulting. One event occurred between 544-646 AD (radiocarbon cal. age, 2σ) and 526-624 AD the other - probably the last one - occurred close to 1485-1604 AD. The last displacement event is consistent with the aforementioned 1511 earthquake both in terms of chronology of the deformation and location of the causative fault. This

  16. Locked and loading megathrust linked to active subduction beneath the Indo-Burman Ranges

    NASA Astrophysics Data System (ADS)

    Steckler, Michael S.; Mondal, Dhiman Ranjan; Akhter, Syed Humayun; Seeber, Leonardo; Feng, Lujia; Gale, Jonathan; Hill, Emma M.; Howe, Michael

    2016-08-01

    The Indo-Burman mountain ranges mark the boundary between the Indian and Eurasian plates, north of the Sumatra-Andaman subduction zone. Whether subduction still occurs along this subaerial section of the plate boundary, with 46 mm yr-1 of highly oblique motion, is contentious. About 21 mm yr-1 of shear motion is taken up along the Sagaing Fault, on the eastern margin of the deformation zone. It has been suggested that the remainder of the relative motion is taken up largely or entirely by horizontal strike-slip faulting and that subduction has stopped. Here we present GPS measurements of plate motions in Bangladesh, combined with measurements from Myanmar and northeast India, taking advantage of a more than 300 km subaerial accretionary prism spanning the Indo-Burman Ranges to the Ganges-Brahmaputra Delta. They reveal 13-17 mm yr-1 of plate convergence on an active, shallowly dipping and locked megathrust fault. Most of the strike-slip motion occurs on a few steep faults, consistent with patterns of strain partitioning in subduction zones. Our results strongly suggest that subduction in this region is active, despite the highly oblique plate motion and thick sediments. We suggest that the presence of a locked megathrust plate boundary represents an underappreciated hazard in one of the most densely populated regions of the world.

  17. Surface displacements in the 1906 san francisco and 1989 loma prieta earthquakes.

    PubMed

    Segall, P; Lisowski, M

    1990-11-30

    The horizontal displacements accompanying the 1906 San Francisco earthquake and the 1989 Loma Prieta earthquake are computed from geodetic survey measurements. The 1906 earthquake displacement field is entirely consistent with right-lateral strike slip on the San Andreas fault. In contrast, the 1989 Loma Prieta earthquake exhibited subequal components of strike slip and reverse faulting. This result, together with other seismic and geologic data, may indicate that the two earthquakes occurred on two different fault planes. PMID:17829210

  18. Surface displacements in the 1906 San Francisco and 1989 Loma Prieta earthquakes

    USGS Publications Warehouse

    Segall, P.; Lisowski, M.

    1990-01-01

    The horizontal displacements accompanying the 1906 San Francisco earthquake and the 1989 Loma Prieta earthquake are computed from geodetic survey measurements. The 1906 earthquake displacement field is entirely consistent with right-lateral strike slip on the San Andreas fault. In contrast, the 1989 Loma Prieta earthquake exhibited subequal components of strike slip and reverse faulting. This result, together with other seismic and geologic data, may indicate that the two earthquakes occurred on two different fault planes.

  19. Present-day Block Motions and Strain Accumulation on Active Faults in the Caribbean

    NASA Astrophysics Data System (ADS)

    Symithe, S. J.; Calais, E.; Freed, A. M.

    2014-12-01

    The quasi-frontal subduction of the north and south American plates under the Lesser Antilles and the left and right lateral strike-slip along the northern and southern margins of the Caribbean plate offer the opportunity to study the transition from subduction to strike-slip between major plates. In addition, the segmentation and degree of interplate coupling at the Lesser Antilles subduction is key to our understanding of the earthquake potential of a subduction whose length is similar to the rupture area of the Mw9.0, 2011, Tohoku earthquake in Japan. We used the block modeling approach described in Meade and Loveless (2009) to test the optimal block geometry for the northern, eastern and southern boundaries of the Caribbean plate. We solved for angular velocities for each block/plate and strain accumulation rates for all major faults in the region. Then we calculated the variations in interplate coupling along the subduction plate boundaries using the accumulated strain rates. We tested 11 different block geometries; they are all based on geological evidences unless they are suggested by discrepancies within the GPS and seismological data or by previously published results. We confirm the existence of the micro Gonave plate. The boundary between the Micro-Gonave plate and the Hispaniola crustal block is better suited along the Haitian-Thrust-Belt instead of the Neiba-Matheux fault. The interseismic GPS velocities do not show evidence for a distinct North Lesser Antilles block. We found a totally uncoupled section of the subduction starting from the Puerto-Rico trench to the end of the Lesser Antilles section. All the relative motion of the Caribbean block is lost aseismically along the boundary of that portion of the subduction. While we found strong coupling along the northern Hispaniola section, most of the deformation on this region is being accumulated along intrablock faults with very low strain (~2mm/yr) along the intraplate subduction interface. We also

  20. Role of Transtension in Rifting at the Pacific-North America Plate Boundary

    NASA Astrophysics Data System (ADS)

    Stock, J. M.

    2011-12-01

    Transtensional plate motion can be accommodated either in a localized zone of transtensional rifting or over a broader region. Broader zones of deformation can be classified either as diffuse deformation or strain partitioning (one or more major strike-slip shear zones geographically offset from a region of a extensional faulting). The Pacific-North America plate boundary in southwestern North America was transtensional during much of its history and has exhibited the full range of these behaviors at different spatial scales and in different locations, as recorded by fault motions and paleomagnetic rotations. Here we focus on the northern Gulf of California part of the plate boundary (Upper and Lower Delfin basin segments), which has been in a zone of transtensional Pacific-North America plate boundary motion ever since the middle Miocene demise of adjacent Farallon-derived microplates. Prior to the middle Miocene, during the time of microplate activity, this sector of North America experienced basin-and-range normal faults (core complexes) in Sonora. However there is no evidence of continued extensional faulting nor of a Gulf-related topographic depression until after ca 12 Ma when a major ignimbrite (Tuff of San Felipe/ Ignimbrite of Hermosillo) was deposited across the entire region of the future Gulf of California rift in this sector. After 12 Ma, faults disrupted this marker bed in eastern Baja California and western Sonora, and some major NNW-striking right-lateral faults are inferred to have developed near the Sonoran coast causing offset of some of the volcanic facies. However, there are major tectonic rotations of the volcanic rocks in NE Baja California between 12 and 6 Ma, suggesting that the plate boundary motion was still occurring over a broad region. By contrast, after about 6 Ma, diminished rotations in latest Miocene and Pliocene volcanic rocks, as well as fault slip histories, show that plate boundary deformation became localized to a narrower

  1. Tectonic evolution of the La González pull-apart basin in the Mérida Andes: combination of geological data and satellite radar interferometry (InSAR)

    NASA Astrophysics Data System (ADS)

    Javadi, Hamid Reza; Dehghani, Maryam; Foroutan, Mohammad; Naeimi, Amir; Roustaei, Mahasa; Saidi, Abdollah; Urbina, Josef Angel

    2016-07-01

    The 500-km-long Boconó strike-slip fault runs as a major active fault along the backbone of the Mérida Andes fold-and-thrust belt. The recent right-lateral motion on the fault led to formation of numerous structures such as pull-apart basins which have formed in releasing bends and/or right-step offsets along the fault strands. The La González pull-apart is the biggest basin generated as an extensional strike-slip duplex in the central part of the fault. This duplex is made up of two strands of the Boconó fault as master/first-order faults, while normal right-lateral faults which formed during evolution of the basin are second-order faults. The extension of the basin is associated with seismic activities and surface offsets along the Boconó fault. InSAR investigations over a 31-month period also support active deformation within the basin. These data indicate that the La González basin is continuously being extended as a result of motion along the Boconó fault and formation of subsequent normal faults. In addition, the basin is being transversely shortened in NW-SE direction due to regional shortening across the Mérida Andes range followed by convergence between the Maracaibo microplate and the Guyana shield.

  2. 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 probably 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.

  3. Intraplate termination of transform faulting within the Antarctic continent

    NASA Astrophysics Data System (ADS)

    Storti, F.; Salvini, F.; Rossetti, F.; Phipps Morgan, J.

    2007-08-01

    The sector of Antarctica facing Australia east of 139 °E is characterized by the abundance of exceptionally long oceanic fracture zones that are collinear to post-rift right-lateral strike-slip fault systems developed at the northeastern edge of the Antarctic continent. High-resolution reflection seismic profiles indicate recent strike-slip activity at the southeastern edge of the Balleny Fracture Zone, similar to what is observed onshore in North Victoria Land. The architecture, kinematics, and timing of this intraplate deformation at the northeastern edge of Antarctica cannot be reconciled with typical plate tectonic kinematics, in particular, with a classical divergent plate boundary environment. Here we show that combined geological and geophysical data in northeastern Antarctica support the post-rift southeastward reactivation of the passive margin east of 139 °E along intraplate right-lateral strike-slip deformation belts. These deformation belts include oceanic transform faults and their collinear oceanic fracture zone and continental shear zone extensions. A striking consequence is that there is intraplate accommodation of transform fault slip in this region of Earth's surface along fracture zones and a long-active region of intracontinental deformation that is 'reusing' prior plate boundary fault zones. As the intraplate termination of plate boundary transform faulting is not predicted by classical plate tectonic theory; this region is one of the most clear examples of the transition from rigid to semi-rigid plate tectonic deformation during the formation and long-lived incubation of a potential new plate boundary.

  4. Seismicity of the Earth 1900–2010 Himalaya and vicinity

    USGS Publications Warehouse

    Turner, Bethan; Jenkins, Jennifer; Turner, Rebecca; Parker, Amy; Sinclair, Alison; Davies, Sian; Hayes, Gavin P.; Villaseñor, Antonio; Dart, Rirchard L.; Tarr, Arthur C.; Furlong, Kevin P.; Benz, Harley M.

    2013-01-01

    Seismicity in the Himalaya region predominantly results from the collision of the India and Eurasia continental plates, which are converging at a relative rate of 40–50 mm/yr. Northward underthrusting of India beneath Eurasia generates numerous earthquakes and consequently makes this area one of the most seismically hazardous regions on Earth. The surface expression of the plate boundary is marked by the foothills of the north-south trending Sulaiman Range in the west, the Indo-Burmese Arc in the east, and the east-west trending Himalaya Front in the north of India. Along the western margin of the India plate, relative motions between India and Eurasia are accommodated by strike-slip, reverse, and oblique-slip faulting resulting in the complex Sulaiman Range fold and thrust belt, and the major translational Chaman Fault in Afghanistan. Beneath the Pamir‒Hindu Kush Mountains of northern Afghanistan, earthquakes occur to depths as great as 200 km as a result of remnant lithospheric subduction. Further north again, the Tian Shan is a seismically active intra-continental mountain belt defined by a series of east-west trending thrust faults thought to be related to the broad footprint of the India-Eurasia collision. Tectonics in northern India are dominated by motion along the Main Frontal Thrust and associated thrust faults of the India-Eurasia plate boundary, which have resulted in a series of large and devastating earthquakes in (and prior to) the 20th century. The Tibetan Plateau to the north of the main plate boundary is a broad region of uplift associated with the India-Eurasia collision, and is cut by a series of generally east-west trending strike-slip faults. These include the Kunlun, Haiyuan, and the Altyn Tagh faults, all of which are left-lateral structures, and the Kara-Koram right-lateral fault. Throughout the plateau, thrust faults accommodate the north-south compressional component of crustal shortening associated with the ongoing collision of India

  5. Geological interpretation of combined Seabeam, Gloria and seismic data from Anegada Passage (Virgin Islands, north Caribbean)

    USGS Publications Warehouse

    Jany, I.; Scanlon, K.M.; Mauffret, A.

    1990-01-01

    The Anegada Passage (sensu lato) includes several basins and ridges from Southeast of Puerto Rico to the corner of the Virgin Islands Platform. Seabeam (Seacarib I) and Gloria long-range sidescan sonar surveys were carried out in this area. These new data allow us to propose an interpretation of the Anegada Passage. Most of the features described are related to wrench faulting: (a) St Croix and Virgin Islands Basins are pull-apart basins created in a right-lateral strike-slip environment based on their rhomboidal shape and seismic data (e.g. the flower structure). These two pull-aparts are divided into two sub-basins by a curvilinear normal fault in the Virgin Islands Basin and a right-lateral strike-slip fault in the St Croix Basin. (b) Tortola Ridge and a 'dog's leg' shaped structure are inferred to be restraining bends between two right-lateral strike-slip faults. (c) We identified two ENE-WSW volcanic lineaments in the eastern area and one volcano lying between Virgin Islands and St Croix Basins. (d) As shown by the seismic activity main wrench motion occurs along the north slope of Virgin Islands Basin and through Anegada Passage. A branching of this main fault transmits the transtensional motion to St Croix Basin. A two-stage story is proposed for the creation of the basins. A first extensional event during Eocene(?)-Oligocene-lower Miocene time created Virgin Islands, St Croix Basins and the tilted blocks of St Croix Ridge. A second transtensional event from Pliocene to Recent gave the present day pattern to this area. However, the displacement along the strike-slip faults is no more than 15 km long. The proposed geodynamic model is based on the separation of the northeastern Caribbean boundary into two blocks. In the West, the indenter of Beata Ridge gives a northeastern motion to Hispaniola Block. In the East, as a result of Hispaniola Block's motion, the Puerto Rico-Virgin Islands Block could escape in an east-northeast direction. ?? 1990 Kluwer Academic

  6. The March 11, 2002 Masafi, United Arab Emirates Earthquake: Insights into the Seismotectonics of the Northern Oman Mountains

    SciTech Connect

    Rodgers, A; Fowler, A; Al-Amri, A; Al-Enezi, A

    2005-04-26

    A moderate (M{approx}5) earthquake struck the northeastern United Arab Emirates (UAE) and northern Oman on March 11, 2002. The event was felt over a wide area of the northern Emirates and was accompanied by smaller (felt) events before and after the March 11 main shock. The event was large enough to be detected and located by global networks at teleseismic distances. We estimated focal mechanism and depth from broadband complete regional waveform modeling. We report a normal mechanism with a slight right-lateral strike-slip component consistent with the large-scale tectonics. The normal component suggests relaxation of obducted crust of the Semail Ophilite (specifically, the Khor Fakkan Block) while the right-lateral strike-slip component of the mechanism is consistent with shear across the Oman Line. Felt earthquakes are rare in the region, however no regional seismic network exists in the UAE to determine local seismicity. This event offers a unique opportunity to study the active tectonics of the region as well as inform future studies of seismic hazard in the UAE and northern Oman.

  7. Study on the Late Quaternary Activity of Niyang River Fault

    NASA Astrophysics Data System (ADS)

    Fangtou, T.

    2015-12-01

    Niyang River fault with north-west trending is located on the west side of the Eastern Himalayan Syntaxis. It dislocated the eastern segment of Brahmaputra fault zone. We study the late Quaternary activity of the Niyang River fault by the high-resolution image data in combination with detailed field investigation, GPS observation, trenching and radiocarbon dating of charcoal samples. The GPS observation data shows that the movement characteristics of Niyang River fault is dextral strike-slip with extrusion at present, its strike-slip rate is 3~4mm/a and its extrusion rate is 2~3mm/a. The trench at Bayi town revealed that the first terraces of Niyang River was dislocated 50cm by the fault and it is dated to be 1220±40cal.a BP.. We found that third Lake terraces of the Linzhi ancient lakes was dislocated about 1.5m at Mirui town and it is dated to be 18060±60cal.a BP.. By the fault influence, there are different elevations at the same level terraces of Niyang river and the Linzhi ancient lakes both sides of Niyang river near Bayi town. The altitude of the second terraces of Niyang River is about 20 meters at eastern side higher than western side and it is dated to be between 8860±40cal.a BP. and 9870±50cal.a BP., the altitude of the third lake terraces of the Linzhi ancient lakes is about 60 meters at eastern side higher than western side. So, the average vertical slip rate of Niyang River fault was about 2mm/a since Holocene and its average vertical slip rate was about 3mm/a since late period of the late Pleistocene. This is consistent with GPS observation data. All these data suggest that Niyang River fault is active since Holocene. So further detailed research will be necessary to determine the range of the latest activity of this fault, movement characteristics and velocity and recurrence intervals of major earthquakes. These data will be a great significance for earthquake zonation and assessment of seismic risk in this region. Keywords:Niyang River fault

  8. Tectonic expression of an active slab tear from high-resolution seismic and bathymetric data offshore Sicily (Ionian Sea)

    NASA Astrophysics Data System (ADS)

    Gutscher, Marc-André; Dominguez, Stephane; Lepinay, Bernard Mercier; Pinheiro, Luis; Gallais, Flora; Babonneau, Nathalie; Cattaneo, Antonio; Le Faou, Yann; Barreca, Giovanni; Micallef, Aaron; Rovere, Marzia

    2016-01-01

    Subduction of a narrow slab of oceanic lithosphere beneath a tightly curved orogenic arc requires the presence of at least one lithospheric scale tear fault. While the Calabrian subduction beneath southern Italy is considered to be the type example of this geodynamic setting, the geometry, kinematics and surface expression of the associated lateral, slab tear fault offshore eastern Sicily remain controversial. Results from a new marine geophysical survey conducted in the Ionian Sea, using high-resolution bathymetry and seismic profiling reveal active faulting at the seafloor within a 140 km long, two-branched fault system near Alfeo Seamount. The previously unidentified 60 km long NW trending North Alfeo Fault system shows primarily strike-slip kinematics as indicated by the morphology and steep-dipping transpressional and transtensional faults. Available earthquake focal mechanisms indicate dextral strike-slip motion along this fault segment. The 80 km long SSE trending South Alfeo fault system is expressed by one or two steeply dipping normal faults, bounding the western side of a 500+ m thick, 5 km wide, elongate, syntectonic Plio-Quaternary sedimentary basin. Both branches of the fault system are mechanically capable of generating magnitude 6-7 earthquakes like those that struck eastern Sicily in 1169, 1542, and 1693.

  9. A neotectonic tour of the Death Valley fault zone, Inyo County

    SciTech Connect

    Wills, C.J.

    1989-09-01

    The Death Valley fault zone has recently been evaluated by the Division of Mines and Geology for zoning under the Alquist-Priolo Special Studies Zones Act of 1972. This act requires the State Geologist to zone for special studies those faults that are sufficiently active and well defined as to constitute a potential hazard to structures from surface faulting or fault creep. The Death Valley fault zone is part of a system of faults that extends over 180 miles (300 km) from Fish Lake Valley in Nevada to the Garlock fault. The northern part of this system, the Northern Death Valley-Furnace Creek fault zone, is an active right-lateral fault zone. The southern part of the system, the Death Valley fault zone, is a right-lateral oblique-slip fault between Furnace Creek and Shoreline Butte. From Shoreline Butte to the Garlock fault, it is a right-lateral strike-slip fault. Landforms along this fault indicate that it is the source of many earthquakes and that it has been active in Holocene time. The heights of the scarps and magnitude of the smallest right-lateral offsets (4 feet; 1.2 m) suggest that the most recent of these events was M 6.5 or larger. The freshness of the geomorphic features and the youth of the offset materials suggest that event occurred late in the Holocene, and that multiple Holocene earthquakes have occurred.

  10. Tectonic interpretation of the 13 february 2001, mw 6.6, El Salvador Earthquake: New evidences of coseismic surface rupture and paleoseismic activity.

    NASA Astrophysics Data System (ADS)

    Martinez-Diaz, J. J.; Canora, C.; Villamor, P.; Capote, R.; Alvarez-Gomez, J. A.; Berryman, K.; Bejar, M.; Tsige, M.

    2009-04-01

    In February 2001 a major strike slip earthquake stroke the central part of El Salvador causing hundreds of people killed, thousands injured and extensive damage. After this event the scientific effort was mainly focused on the study of the enormous and catastrophic landslides triggered by this event and no evidences of surface faulting were detected. This earthquake was produced by the reactivation of the Ilopango-San Vicente segment of the El Salvador Fault Zone. Recently, a surface rupture displacement on the ground was identified. The analysis of aerial and field photographs taken few hours after the event and the mapping of the conserved ground structures shows a pure strike-slip displacement ranging from 20 to 50 cm, with secondary features indicating dextral shearing. The paleoseismic analysis made through the excavation of six trenches and Radiocarbon dating indicate a minimum slip rate of 2.0 mm/yr and a recurrence of major ruptures (Mw > 6.5) lower than 500 yr. These evidences give interesting local data to increase our understanding about the tectonic behavior and the way how active deformation develops along the northern limit of the forearc sliver related to the Centroamerican subduction area.

  11. Seismic Activity in the Gulf of Mexico: a Preliminary Analysis

    NASA Astrophysics Data System (ADS)

    Franco, S. I.; Canet, C.; Iglesias, A.; Valdes-Gonzales, C. M.

    2013-05-01

    The southwestern corner of Gulf of Mexico (around the northern Isthmus of Tehuantepec) is exposed to an intense deep (> 100 km) seismic activity caused by the subduction of the Cocos plate. Aside from this, the gulf has been considered as a zone of low or no-seismicity. However, a sparse shallow seismic activity is observed across the Gulf of Mexico; some of these earthquakes have been strongly felt (e.g. 23/05/2007 and 10/09/2006), and the Jaltipan, 1959 earthquake caused fatalities and severe destruction in central and southern Veracruz. In this work we analyze 5 relevant earthquakes that occurred since 2001. At the central Gulf of Mexico focal mechanisms show inverse faults oriented approximately NW-SE with dip near 45 degrees, suggesting a link to sediment loading and/or to salt tectonics. On the other hand, in the southwestern corner of the gulf we analyzed some clear examples of strike-slip faults and activity probably related to the Veracruz Fault. One anomalous earthquake, recorded in 2007 in the western margin of the gulf, shows a strike-slip mechanism indicating a transform regime probably related with the East Mexican Fault. The recent improvement of the Mexican Seismological broadband network have allowed to record small earthquakes distributed in and around the Gulf of Mexico. Although the intermediate and large earthquakes in the region are infrequent, the historic evidence indicates that the magnitudes could reach Mw~6.4. This fact could be taken in consideration to reassess the seismic hazard for oil and industrial infrastructure in the region.

  12. Microearthquake seismicity at the intersection between the Kazerun fault and the Main Recent Fault (Zagros, Iran)

    NASA Astrophysics Data System (ADS)

    Yamini-Fard, Farzam; Hatzfeld, Denis; Tatar, Mohammad; Mokhtari, Mohammad

    2006-07-01

    Seismicity and fault plane solutions of earthquakes at the intersection between the Main Recent Fault (a right-lateral strike-slip fault that bounds the Zagros to the NE) and the Kazerun Fault system (another right-lateral zone that crosses the Zagros) show slip to be partitioned into nearly pure strike-slip at shallow depths and nearly pure thrust slip below 12 km. Such slip partitioning is commonly observed where oblique convergence occurs, but in general faults of different styles lie adjacent to one another, not at different depths with one below the other. We provide evidence for this partitioning in a microearthquake study in which we deployed a temporary network of 29 seismographs for 7 weeks. We located no activity north of the Main Zagros Reverse Fault (MZRF), which separates the Zagros fold belt from Central Iran. Most earthquakes occurred between the northern termination of the Kazerun Fault and the MZRF, but not near to known major faults. Activity is limited to the upper crust, between 2 and 16 km. Most of the focal mechanisms show strike-slip faulting, dextral if the NS striking plane is the active plane, but a few for the deepest events show reverse faulting, distributed between the Kazerun Fault and the MZRF, with P-axis trending consistently ~NS. This partitioning of the deformation with depth suggests that the brittle upper crust deforms by slip on pre-existing faults that strike obliquely but that the lower crust accommodates the shortening by reverse faulting. We infer that the deformation in the upper part of the crust reflects a stiffer medium in which pre-existing faults localize the deformation. The largest event recorded during this experiment, located at the same place as the destructive 1977 Naghan earthquake (Mw ~5.9, 348 victims), shows reverse faulting, likely related to the Dopolan High Zagros Fault. The crustal thickness deduced from receiver function analysis does not show a marked difference across the Kazerun fault, which suggests

  13. 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.

  14. Fault slip and earthquake recurrence along strike-slip faults - Contributions of high-resolution geomorphic data

    NASA Astrophysics Data System (ADS)

    Zielke, Olaf; Klinger, Yann; Arrowsmith, J. Ramon

    2015-01-01

    Understanding earthquake (EQ) recurrence relies on information about the timing and size of past EQ ruptures along a given fault. Knowledge of a fault's rupture history provides valuable information on its potential future behavior, enabling seismic hazard estimates and loss mitigation. Stratigraphic and geomorphic evidence of faulting is used to constrain the recurrence of surface rupturing EQs. Analysis of the latter data sets culminated during the mid-1980s in the formulation of now classical EQ recurrence models, now routinely used to assess seismic hazard. Within the last decade, Light Detection and Ranging (lidar) surveying technology and other high-resolution data sets became increasingly available to tectono-geomorphic studies, promising to contribute to better-informed models of EQ recurrence and slip-accumulation patterns. After reviewing motivation and background, we outline requirements to successfully reconstruct a fault's offset accumulation pattern from geomorphic evidence. We address sources of uncertainty affecting offset measurement and advocate approaches to minimize them. A number of recent studies focus on single-EQ slip distributions and along-fault slip accumulation patterns. We put them in context with paleoseismic studies along the respective faults by comparing coefficients of variation CV for EQ inter-event time and slip-per-event and find that a) single-event offsets vary over a wide range of length-scales and the sources for offset variability differ with length-scale, b) at fault-segment length-scales, single-event offsets are essentially constant, c) along-fault offset accumulation as resolved in the geomorphic record is dominated by essentially same-size, large offset increments, and d) there is generally no one-to-one correlation between the offset accumulation pattern constrained in the geomorphic record and EQ occurrence as identified in the stratigraphic record, revealing the higher resolution and preservation potential of the latter. While slip accumulation along a fault segment may be dominated by repetition of large, nearly constant offset increments, timing of surface-rupture is less regular.

  15. Mantle flow beneath a continental strike-slip fault: postseismic deformation after the 1999 Hector Mine earthquake.

    PubMed

    Pollitz, F F; Wicks, C; Thatcher, W

    2001-09-01

    Two recent large earthquakes in the Mojave Desert, California-the magnitude 7.3 1992 Landers and magnitude 7.1 1999 Hector Mine earthquakes-have each been followed by elevated crustal strain rates over periods of months and years. Geodetic data collected after the Hector Mine earthquake exhibit a temporally decaying horizontal velocity field and a quadrant uplift pattern opposite to that expected for localized shear beneath the earthquake rupture. We interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake. Our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the lower crust is a coherent stress guide coupling the upper crust with the upper mantle. PMID:11546869

  16. Earthquake depths and the relation to strain accumulation and stress near strike-slip faults in southern California

    SciTech Connect

    Sanders, C.O. )

    1990-04-10

    Earthquakes in the major fault zones are predominantly deep. Earthquakes in the crustal blocks bounding the fault zones are predominantly shallow. In the San Jacinto fault zone, maximum earthquake depths correlate with surface heat flow. These relations together with focal mechanisms, geodetic strain measurements, and fault zone models are consistent with the following ideas: (1) Interseismic plate motion is accommodated by aseismic slip along an extension of the major fault zone below a brittle zone that is locked between large earthquakes. (2) The aseismic slip in a narrow fault zone in the brittle-plastic transition region concentrates strain at the base of the brittle fault zone. (3) Deep earthquakes occur in thelower part of the brittle fault zone due to stick-slip failure of highly stressed patches. (4) Background earhtquakes and aftershocks that occur several kilometers deeper than large earthquake hypocenters suggest that a zone of mixed slip behavior may exist between the stable sliding (deep) and stick-slip (shallow) regions of the fault zone. Furthermore, the difference in seismicity between the San Jacinto and southern San Andreas faults suggests that the nature of this mixed zone may evolve as total displacement in the fault zone increases. (5) Shear stress may be less in the crustal blocks than in the deep brittle fault zones and generally at a level sufficient to cause brittle failure only shallow in the crustal blocks. (6) In the stress field produced by plate motion and slip in the deep fault zone, the upper brittle fault zone is not oriented favorably for shear failure. Lack of shallow earthquakes in the fault zones and the predominance of shallow earthquakes on favorably oriented fractures in the adjacent crustal blocks suggest that either stress in the upper brittle fault zone is relatively low or the upper fault zone is effectively strong due to its orientation.

  17. Mantle flow beneath a continental strike-slip fault: Postseismic deformation after the 1999 Hector Mine earthquake

    USGS Publications Warehouse

    Pollitz, F.F.; Wicks, C.; Thatcher, W.

    2001-01-01

    Two recent large earthquakes in the Mojave Desert, California - the magnitude 7.3 1992 Landers and magnitude 7.1 1999 Hector Mine earthquakes - have each been fog[owed by elevated crustal strain rates over periods of months and years. Geodetic data collected after the Hector Mine earthquake exhibit a temporaLLy decaying horizOntaL velocity field and a quadrant uplift pattern opposite to that expected for LocaLized shear beneath the earthquake rupture. We interpret the origin of this accelerated crustal deformation to be vigorous flow in the upper mantle in response to the stress changes generated by the earthquake. Our results suggest that transient flow in the upper mantle is a fundamental component of the earthquake cycle and that the Lower crust is a coherent stress guide coupling the upper crust with the upper mantle.

  18. Global Positioning System constraints on the active tectonics of NE Iran and the South Caspian region

    NASA Astrophysics Data System (ADS)

    Mousavi, Z.; Walpersdorf, A.; Walker, R. T.; Tavakoli, F.; Pathier, E.; Nankali, H.; Nilfouroushan, F.; Djamour, Y.

    2013-09-01

    We present a velocity field compiled from a network of 27 permanent and 20 campaign GPS stations across NE Iran. This new GPS velocity field helps to investigate how Arabia-Eurasia collision deformation is accommodated at the northern boundary of the deforming zone. The present-day northward motion decreases eastward from 11 mm/yr at Tehran (˜52°E) to 1.5 mm/yr at Mashhad (˜60°E). N-S shortening across the Kopeh Dagh, Binalud and Koh-e-Sorkh ranges sums to 4.5±0.5 mm/yr at longitude 59°E. The available GPS velocities allow us to describe the rigid-body rotation of the South Caspian about an Euler pole that is located further away than previously thought. We suggest that two new stations (MAVT and MAR2), which are sited far from the block boundaries, are most likely to indicate the full motion of the South Caspian basin. These stations suggest that NW motion is accommodated by right-lateral slip on the Ashkabad fault (at a rate of up to 7 mm/yr) and by up to 4-6 mm/yr of summed left-lateral slip across the Shahroud left-lateral strike-slip system. Our new GPS results are important for assessing seismic hazard in NE Iran, which contains numerous large population centers and possesses an abundant historical earthquake record. Our results suggest that the fault zones along the eastern Alborz and western Kopeh Dagh may accommodate slip at much faster rates than previously thought. Fully assessing the role of these faults, and the hazard that they represent, requires independent verification of their slip-rates through additional GPS measurements and geological fieldwork.

  19. Seismic images of the active fault system in the Yunlin and Chiayi area of Taiwan.

    NASA Astrophysics Data System (ADS)

    Sun, Wei-Hsiang; Shih, Ruey-Chyuan

    2015-04-01

    The Yunlin and Chiayi area in western Taiwan are well known of having a higher risk of earthquake disaster. The main fault system that controls the structure deformation in this area consists of the Chiuchiungkeng fault, the Meishan fault, and the Gukeng fault. According to historical records, the 1906 Meishan earthquake, magnitude 7.1, was triggered by the right-lateral strike-slip fault Meishan fault. Previous Seismic surveys showed that the Meishan fault is a high angle fault with flower structure. The Chiuchiungkeng fault is a thrust fault, located at front of the western foothills. Formations on the hanging wall and foot wall of the fault, both dipping to the east with different angles, can be identified from seismic images. The Gukeng fault was never been studied before. From the recent study of GPS monitoring, we may found that the velocity field near the Gukeng fault had a significant difference at both side of the fault. In addition, there is other information showed that there exists an aseismic gap around the fault. The above phenomena could be considered as a stress accumulation along the Gukeng fault. In the other words, the Gukeng fault could be playing an important role of controlling the regional surface deformation and seismicity distribution in this area. In this case, it will be worthwhile of knowing where the Gukeng fault is, and its subsurface structure. In this presentation, we will show our study of the subsurface structure of the Gukeng fault by using the seismic exploration method. The data consist of the shallow seismic reflection images those conducted by ourselves and the deeper seismic profiles acquired by CPC. Three dimensional relationships between the Gukeng fault, the Meishan fault, the Chiuchiungkeng fault, and other structures such as the Hsiaomei anticline will be illustrated as well.

  20. The role of block rotations and oroclinal bending in Iran during the Cenozoic Arabia-Eurasia shortening

    NASA Astrophysics Data System (ADS)

    Cifelli, F.; Mattei, M.; Alimohammadian, H.; Sabouri, J.; Rashid, H.; Ghassemi, M.

    2012-04-01

    Shortening related to the Arabia-Eurasia convergence in the Cenozoic has been - and is at present being - taken up mainly by displacements in the Zagros, Alborz, and Kopeh Dag thrust-and-fold belts of Iran, whereas the intervening, fault-bounded crustal blocks of Central Iran (Yazd, Tabas and Lut blocks) show little internal deformation. Central Iran is separated from the Alborz belt by NE-SW left-lateral strike-slip and thrust faults (e.g., the Great Kavir fault), whereas N-S right-lateral strike-slip faults define the boundary between the Tabas and Lut blocks within Central Iran (e.g., the Neyband fault). Based on structural and seismological data, it has been proposed that NE-SW left-lateral and N-S right-lateral faults can accommodate the NNE-SSW Arabia-Eurasia convergence if they are allowed to rotate clockwise (CW) and counterclockwise (CCW), respectively. A rotating-fault deformation model predicts that the intervening fault-bounded rigid blocks should rotate accordingly. To test this hypothesis, paleomagnetic sampling was carried out on Oligocene-Miocene sediments from different areas of Central Iran (Torud, Jandaq, Anarak, Tabas, Yazd, Bafq, Ferdows), dominated by right-lateral and left-lateral strike slip faults activity, and along the southeastern margin of the Alborz Mts. (Bastam, Tall, Gardaneye-Ahovan, Momenabad Abdolabad), where left lateral and thrust faults prevail. Large counterclockwise (CCW) rotations (20°-35°) have been measured in the Tabas and Yazd blocks, characterized by the presence of N-S to NNW-SSE trending, right-lateral strike-slip faults. This structural domain is bounded to the north by the ENE-WSW oriented Great Kavir-Doruneh left-lateral strike-slip fault system. North of this fault paleomagnetic data show a different behaviour, with no or small CW rotation about vertical axis during the late Tertiary. In particular a small amount of CW rotation has been measured in the Jandaq and Torud area, to the north of the Great Kavir fault

  1. The April 2007 earthquake swarm near Lake Trichonis and implications for active tectonics in western Greece

    NASA Astrophysics Data System (ADS)

    Kiratzi, A.; Sokos, E.; Ganas, A.; Tselentis, A.; Benetatos, C.; Roumelioti, Z.; Serpetsidaki, A.; Andriopoulos, G.; Galanis, O.; Petrou, P.

    2008-06-01

    We investigate the properties of the April 2007 earthquake swarm (Mw 5.2) which occurred at the vicinity of Lake Trichonis (western Greece). First we relocated the earthquakes, using P- and S-wave arrivals to the stations of the Hellenic Unified Seismic Network (HUSN), and then we applied moment tensor inversion to regional broad-band waveforms to obtain the focal mechanisms of the strongest events of the 2007 swarm. The relocated epicentres, cluster along the eastern banks of the lake, and follow a distinct NNW-ESE trend. The previous strong sequence close to Lake Trichonis occurred in June-December 1975. We applied teleseismic body waveform inversion, to obtain the focal mechanism solution of the strongest earthquake of this sequence, i.e. the 31 December 1975 (Mw 6.0) event. Our results indicate that: a) the 31 December 1975 Mw 6.0 event was produced by a NW-SE normal fault, dipping to the NE, with considerable sinistral strike-slip component; we relocated its epicentre: i) using phase data reported to ISC and its coordinates are 38.486°N, 21.661°E; ii) using the available macroseismic data, and the coordinates of the macroseismic epicentre are 38.49°N, 21.63°E, close to the strongly affected village of Kato Makrinou; b) the earthquakes of the 2007 swarm indicate a NNW-SSE strike for the activated main structure, parallel to the eastern banks of Lake Trichonis, dipping to the NE and characterized by mainly normal faulting, occasionally combined with sinistral strike-slip component. The 2007 earthquake swarm did not rupture the well documented E-W striking Trichonis normal fault that bounds the southern flank of the lake, but on the contrary it is due to rupture of a NW-SE normal fault that strikes at a ˜ 45° angle to the Trichonis fault. The left-lateral component of faulting is mapped for the first time to the north of the Gulf of Patras which was previously regarded as the boundary for strike-slip motions in western Greece. This result signifies the

  2. Active Tectonics In The Rukwa Rift (sw Tanzania): A Study of The Potential For Large Earthquakes In A Continental Rift.

    NASA Astrophysics Data System (ADS)

    Kervyn, F.

    The Rukwa rift is a deep sedimentary basin that is considered as a tectonic trans- fer zone between the Tanganyika and the Malawi troughs. The tectonic evolution of the depression is controlled by the reactivation of proterozoic structures and started with the deposition of the permo-triasic Karoo sediments. In the southeast, the rift is divided into two facing half graben separated by a Precambrian horst, whereas its northwestern part has a more symmetrical graben structure. Although most of the vertical displacement is accommodated by the Lupa eastern boundary fault, onshore shallow seismic profiles have confirmed the co-occurrence of intrabasin synthetic- and strike-slip faults within the sub surface sediments. Both normal and dextral strike-slip movement are indeed observed in the basin in response to the E-W to WNW-SSE ex- tension. The region has a moderate seismic activity and the earthquakes magnitude is generally below M 6.5. However, a M 7.4 earthquake occurred in the Rukwa region in 1910 but its exact location remains uncertain. The current research aimed at the identi- fication of active faults within the recent deposits of the basin by the combination in a GIS of radar interferometric data with topographical and geological maps, geophysical data, and field observations. Radar interferometry (InSAR) was found to be especially suitable for DEM computation in low relief areas where available topographic data are limited in accuracy. Numerous topographic lineaments were observed on InSAR DEM, and follow two main directions, both oblique to the main NW-SE trend of the rift. On the one hand, the GIS analysis confirms that the observed lineaments corre- spond to real natural alignment such like the drainage for example, and are therefore not related to atmospheric artefacts. On the other hand, the field observations revealed that in most cases, the topographic lineaments are very subtle and difficult to identify. However, direct correlations with tectonic

  3. Structural Analog from the 1967 Mogod Earthquake: an examination of the southern Bulgan Province, Mongolia

    NASA Astrophysics Data System (ADS)

    Sauermann, R. K.; Kelty, T. K.; Dash, B.

    2012-12-01

    Several seismological and field reports documenting the 1967 Mogod earthquake (Mw 7.1) in Mongolia have been conducted, but concentrated efforts to map the regional structure are limited. Due to the remote nature of the site, field observations have been generally constrained to the incredibly well exposed surface ruptures correlated to the 1967 earthquake. While not as spectacular as these 1967 scarps, substantial evidence suggesting additional active faulting in the region was found ~ 10 km to the east of the 1967 Mogod earthquake epicenter. At this location a 50-m stream offset indicative of right-lateral, strike-slip faulting was found. This ~10-m high fault scarp striking approximately N-S was traced for ~5km, found to offset additional streams, and indicated relatively recent tectonic activity. With help from local eyewitness accounts and previous research on the area, the 1967 surface ruptures were confirmed to be traceable for ~ 40 km and separable into three distinct components: (1) a ~15-km-long, right-lateral, strike-slip fault that strikes N-S through the town of Mogod, (2) a ~20 km long, right-lateral, strike-slip fault that strikes N-S south of Mogod along the Burdiin Hyar Ridge, and (3) a ~12 km long, thrust fault that strikes NW along the Tuleet Uul Ridge. The most substantial surface ruptures were found on the southern edge of the Burdiin Hyar sub-event and along the Tuleet Uul Ridge. At the southern end of the Burdiin Hyar Ridge, slickened sides on a truncated boulder confirmed right-lateral displacement and constrained the dip of the fault to be ~ N 40° - 50° E. In addition, syenite dikes striking N-S appear to be pervasively intruding basalt along the fault contact at the Burdiin Hyar Ridge, indicating development of a fracture system parallel to the active fault traces. Thrust faulting like that observed at the southern end of the surface ruptures associated with the 1967 Mogod Earthquake is not confined to this location. The majority of

  4. Why does the Size of the Laacher See Magma Chamber and its Caldera Size not go together? - New Findings with regard to Active Tectonics in the East Eifel Volcanic Field

    NASA Astrophysics Data System (ADS)

    Schreiber, Ulrich; Berberich, Gabriele

    2013-04-01

    The East Eifel's early Cenozoic tectonic development is characterized by a main stress field trending in NW-SE direction, causing a re-organisation of postvariscan dextral strike-slip faults in approximately 105° direction, the formation of the tectonic depression of the Neuwieder Basin and small-scale transtension zones. The 105° trending strike-slip faults are staggered in equidistant intervals of several kilometers. This system continues from the Eifel to the North into the Ruhr Carboniferous, where it has been recognized due to the extensive underground coal mining first (Loos et al. 1999). Our recent research on analyses of tectonics in quarries, quartz/ore-dykes, mapping of minerals springs and gas analyses, has revealed a prominent 105° trending strike-slip fault cutting the South of Laacher See ("Laacher See Strike-slip Fault"). Within the Laacher See caldera, the "Laacher See Strike-slip Fault" can be tracked by a wide mofette zone that was mapped with a self-propelled submarine. At present, the "Laacher See Strike-slip Fault" can be tracked from Holzmühlheim in the West, Spessart, Wehrer Kessel, Laacher See, Plaidt to Bad Ems and furthermore to the South-East. Along this direction five intersections points of the "Laacher See Strike-slip Fault" with the Lahn River are documented, creating small-scale mofette fields in the Lahn River. In the Neuwied Basin, near Plaidt, the "Laacher See Strike-slip Fault" is intersected by the NW-SE-trending Ochtendung Fault. Regional strike-slip faults in combination with block rotation and uplift could have provided the voids for the magma chambers of the Wehrer Kessel and the Laacher See Caldera. Holohan et al. (2005) showed in analogue models that regional strike-slip regimes (including Riedel shears, chamber-localised graben fault, and a partial Y-shear) play a decisive role for caldera formation. In the East Eifel tectonic movement rates of active faults are approx. 1 mm/year (Meyer & Stets 2002, Cambell et al

  5. Discovery of sublacustrine hydrothermal activity and associated massive sulfides and hydrocarbons in the north Tanganyika trough, East African Rift

    NASA Astrophysics Data System (ADS)

    Tiercelin, Jean-Jacques; Thouin, Catherine; Kalala, Tchibangu; Mondeguer, André

    1989-11-01

    Massive sulfides and carbonate mineral deposits associated with sublacustrine thermal springs were recently discovered along the Zaire side of the north Tanganyika trough, western branch of the East African Rift. This hydrothermal activity, investigated by scuba diving at a maximum depth of 20 m, is located at the intersection of major north-south normal faults and northwest-southeast faults belonging to the Tanganyika-Rukwa-Malawi (TRM) strike-slip fault zone. The preliminary results presented here come from analyses of sulfide deposits, hydrothermal fluids, and associated hydrocarbons that result from geothermal activity in this part of the East African Rift filled by a thick pile of sediment, the north Tanganyika trough.

  6. GeoBioScience: Red Wood Ants as Bioindicators for Active Tectonic Fault Systems in the West Eifel (Germany)

    PubMed Central

    Berberich, Gabriele; Schreiber, Ulrich

    2013-01-01

    Simple Summary In a 1.140 km² study area of the volcanic West Eifel, approx. 3,000 Red Wood Ant (RWA; Formica rufa-group) mounds had been identified and correlated with tectonically active gas-permeable faults, mostly strike-slip faults. Linear alignment of RWA mounds and soil gas anomalies distinctly indicate the course of these faults, while clusters of mounds indicate crosscut zones of fault systems, which can be correlated with voids caused by crustal block rotation. This demonstrates that RWA are bioindicators for identifying active fault systems and useful where information on the active regime is incomplete or the resolution by technical means is insufficient. Abstract In a 1.140 km² study area of the volcanic West Eifel, a comprehensive investigation established the correlation between red wood ant mound (RWA; Formica rufa-group) sites and active tectonic faults. The current stress field with a NW-SE-trending main stress direction opens pathways for geogenic gases and potential magmas following the same orientation. At the same time, Variscan and Mesozoic fault zones are reactivated. The results showed linear alignments and clusters of approx. 3,000 RWA mounds. While linear mound distribution correlate with strike-slip fault systems documented by quartz and ore veins and fault planes with slickensides, the clusters represent crosscut zones of dominant fault systems. Latter can be correlated with voids caused by crustal block rotation. Gas analyses from soil air, mineral springs and mofettes (CO2, Helium, Radon and H2S) reveal limiting concentrations for the spatial distribution of mounds and colonization. Striking is further the almost complete absence of RWA mounds in the core area of the Quaternary volcanic field. A possible cause can be found in occasionally occurring H2S in the fault systems, which is toxic at miniscule concentrations to the ants. Viewed overall, there is a strong relationship between RWA mounds and active tectonics in the West Eifel

  7. Crustal Extension and Rotation in the Isparta Angle Region of South-West Anatolia from a new GPS Velocity Solution

    NASA Astrophysics Data System (ADS)

    Floyd, M.; Tiryakioğlu, I.; Erdogan, S.; Gulal, E.; Ergintav, S.; McClusky, S.; Reilinger, R. E.

    2013-12-01

    We present a model of crustal kinematics for the south-west region of Anatolia (Turkey) using a new, expanded and updated GPS velocity solution, focusing on the motion of the Isparta Angle. This region, bordered by the Fethiye Burdur Fault Zone (FBFZ) in the west and the Aksehir Simav Fault Zone (AKSFZ) in the east, accommodates a part of the active deformation of south-western Anatolia. We use survey and continuous GPS observations during the period 1997-2010, combined with the published results of Reilinger et al. (2006) and Aktug et al. (2009). Our results show that the Isparta region rotates couterclockwise relative to Anatolia. Both the FBFZ and the AKSFZ a