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Sample records for active strike-slip fault

  1. 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.

  2. Tectonics and Quaternary sequence development of basins along the active Vienna Basin strike-slip fault

    NASA Astrophysics Data System (ADS)

    Salcher, B.; Lomax, J.; Meurers, B.; Smit, J.; Preusser, F.; Decker, K.

    2012-04-01

    The Vienna Basin strike-slip fault is a continent scale active fault extending over a distance of some 300 km from the Eastern Alps through the Vienna Basin into the Western Carpathians. Sinistral movement causes the formation of several tight Pleistocene strike-slip basins within the older Miocene Vienna Basin. These sub-basins not only have a high relevance for groundwater exploitation but their fault activities depict serious seismic hazards. Basins are filled with fluvial sediments from the Danube and, closer to the Alpine front, with thick alluvial fan deposits. However, knowledge on the stratigraphy and tectonics is sparse and rather limited to the Miocene part of the Vienna Basin as it hosts giant hydrocarbon fields. This study tackles two major questions: (i) What is the effect of Quaternary climatic oscillations and subsidence on the sequence development of the alluvial fans and (ii) what is the deformation style of these basins? To answer (i) we present a series of new OSL ages and biotic data from both, surface and cores, to better constrain the timing of fan activity, fan abandonment but also to constrain the onset of Pleistocene basin formation. For (ii) we utilize information from unparalleled geophysical and geological data. Specifically we utilize industrial Bouguer gravity's derivatives to highlight shallow structures and to compensate for the lag of fault trace information. The integration of geological and geophysical data highlights textbook-like models of strike-slip basins, with typical features like Riedel shears with intervening relay ramps, en-echelon sidewall faults and a cross-basin fault zone delimiting opposite depocenters. The infill reflects a distinct cyclicity with thick sequences of coarse sediments deposited during colder periods and thin sequences of paleosol and flood sediments deposited during warmer periods. Ages indicate main activity around the short peak glacial periods and basin formation starting c. 300 ka ago. The

  3. 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.

  4. Faults paragenesis and paleostress state in the zone of actively propagating continental strike-slip on the example of North Khangai fault (Northern Mongolia)

    NASA Astrophysics Data System (ADS)

    Sankov, Vladimir; Parfeevets, Anna

    2014-05-01

    Sublatitudinal North Khangai fault extends from Ubsunuur basin to the eastern part of the Selenga corridor trough 800 km. It is the northern boundary of the massive Mongolian block and limits of the Baikal rift system structures propagation in the south (Logatchev, 2003). Late Cenozoic and present-day fault activity are expressed in the left-lateral displacements of a different order of river valleys and high seismicity. We have carried out studies of the kinematics of active faults and palaeostresses reconstruction in the zone of the dynamic influence of North Khangai fault, the width of which varies along the strike and can exceeds 100 km. The result shows that the fault zone has a longitudinal and a transverse zoning. Longitudinal zonation presented gradual change from west to east regions of compression and transpression regimes (Khan-Khukhey ridge) to strike-slip regime (Bolnay ridge) and strike-slip and transtensive regimes (west of Selenga corridor). Strike-slip zones are represented by linearly concentrated rupture deformations. In contrast, near the termination of the fault the cluster fault deformation formed. Here, from north to south, there are radical changes in the palaeostress state. In the north-western sector (east of Selenga corridor) strike-slip faults, strike-slip faults with normal components and normal faults are dominated. For this sector the stress tensors of extensive, transtension and strike-slip regimes are typical. South-western sector is separated from the north-eastern one by massive Buren Nuruu ridge within which the active faults are not identified. In the south-western sector between the Orkhon and Tola rivers the cluster of NW thrusts and N-S strike-slip faults with reverse component are discovered. The faults are perfectly expressed by NW and N-S scarps in the relief. The most structures dip to the east and north-east. Holocene fault activity is demonstrated by the hanging river valleys and horizontal displacements with amplitudes

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. 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

  10. 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.

  11. River Captures and Erosional Disequilibrium Along Strike-slip Faults

    NASA Astrophysics Data System (ADS)

    Brocard, G. Y.; Fayon, A. K.; Perg, L. A.; Paola, C.; Teyssier, C.; Whitney, D. L.; Mota, M.; Moran-Ical, S.

    2005-12-01

    very subdued topography are preserved on the highlands. The capture has been interpreted as the diversion of the former headwaters of a westward flowing river located south of the fault (Rio Selegua) into a northward flowing river located north of the fault (Rio Chixoy), based on drainage pattern and preserved conglomerates. The capture event, the dissection of the landscape, and the uplift of the summit paleosurface are closely related, and likely Miocene in age. Newly discovered conglomerates confirm that the captured basin was drained by the Selegua River before being drained into the Chixoy River. Other newly discovered paleovalleys and conglomerates further document the expansion of the dissected captured watershed at the expense of surrounding catchments. Since the capture event, both the captured stream paleovalley and the subdued topography have been displaced by large normal faults, many of them striking parallel to the Polochic strike-slip fault. Recent faulted sediments on the Polochic Fault trace also display a significant vertical component of slip. The inception of this tectonic activity after the abandonment of the paleovalleys suggests that the faults may have accommodated the isostatic uplift that followed unloading of the captured drainage basin by erosion.

  12. 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

  13. Strike-slip Faulting On Ganymede, Now And Then

    NASA Astrophysics Data System (ADS)

    Pappalardo, Robert T.; Smith-Konter, B. R.; Cameron, M. E.; DeRemer-Keeney, L. C.; Nimmo, F.

    2012-10-01

    Strike-slip tectonism is important to the structural development of Ganymede’s surface, and in the transition from dark to grooved terrain. Three distinct signatures of strike-slip faulting are recognized [1]: (1) en echelon structures, (2) strike-slip duplexes, and (3) laterally offset pre-existing features. As strike-slip faulting progressed, en echelon fractures (in both dark and grooved terrains) merged to define en echelon swaths, which can become distinct tectonic domains. Three morphological categories of strike-slip “duplexes” (spindle-shaped lensoid regions bounded by strike-slip faults) occur, suggesting an evolutionary sequence from discontinuous fractures in dark terrain, to lensoid bounding structures, to lensoid regions with subparallel internal structure in grooved terrain. Ganymede’s 24 measured duplexes have an average length/width ratio of 2.4, on the low end of the terrestrial range [2]. Lateral offsets of pre-existing features betray the existence of some major strike-slip faults: Dardanus Sulcus (13°W, 18°S) is displaced 45 km by a prominent NE-SW trending fault. We model Coulomb shear failure on Ganymede, considering nonsynchronous rotation (NSR), and diurnal stresses both for present (0.0013) and possible past high ( 0.05) eccentricity [3]. We adopt NSR period 0.14 Ma; Love numbers h2 = 1.52 and l2 = 0.38; Young’s modulus 9.3 GPa; Poisson’s ratio 0.33; and fault depth 2 km. NSR shear stress resolved along the Dardanus fault is 0.3 MPa, sufficient to induce failure to 1.4 km for friction coefficient 0.3. For past high eccentricity, diurnal stress would have modulated NSR stress by 100 kPa through Ganymede’s tidal cycle. This could have induced shear heating [4] and tidal walking [5], as modeled for Europa. References: [1] DeRemer and Pappalardo (2003), LPSC, 34, #2033; [2] Aydin and Nur (1982), Tectonics, 1, 91; [3] Showman and Malhotra (1997), Icarus, 127, 93; [4] Nimmo and Gaidos (2002), JGR, 107, 10.1029/2000JE001476; [5

  14. 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.

  15. Water accumulation below Europa's strike-slip faults

    NASA Astrophysics Data System (ADS)

    Kalousova, K.; Tobie, G.; Soucek, O.; Choblet, G.; Cadek, O.

    2015-10-01

    The onset of melting below Europa's recently active strike-slip faults and the gravitational/thermal stability of partially molten ice are investigated by solving the equations for a two-phase compressible mixture of water ice and liquid water in 2D geometry. As a first step, the relative motion between ice and water is neglected, i.e. the meltwater is transported by the flowing ice. Our preliminary results suggest that for sufficiently large shear heating rate of˜2×10-4W m-3 melting can occur at depths as shallow as˜3km below Europa's surface. Moreover, the reservoirs of partially molten ice with˜5-10% of liquid water can remain within the cold lid for a few hundreds of kiloyears if the underlying ice is sufficiently cold (vis-cous) and free of fractures.

  16. 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.

  17. Analysis of surface structures of major strike-slip faults

    NASA Astrophysics Data System (ADS)

    Hsieh, Shang Yu; Neubauer, Franz

    2013-04-01

    Strike-slip faults commonly appear with complex fractures and deformation structures on the surface, which also reveal the 3-D geometry with variable structures at depth. The aim of our study is finding the systematic features and correlations of various surface expressions including width, length, height and angle (to the main fault trace) of individual structures like pressure ridges, sag ponds, riedel and anti-riedel faults and oversteps, and also doing a classification with these data. The variation might by caused by distinct convergence angles along strike-slip fault. We study the above mentioned properties on Altyn Tagh fault (ATF), Kunlun, San Andrea and Greendale (Darfield earthquake) faults, which are large strike-slip tectonic structures accommodating major displacement along plate boundaries. Especially the recent events of 2001 Kunlun earthquake and 2010 Darfield earthquake allow a detailed study of structures formed by a single earthquake. Along the fault valley of a 610 km segment of ATF, many large-scale pressure ridges, few pressure basins and horizontal offsets of wadi channels were found; similarly, around 20 features with large scale pressure ridges and pressure basins are found in Carrizo Plain of San Andreas fault. Surface ruptures are uncommon, and dominated by anti-riedels in the case of the Altyn fault. Interpretations show the range of length, width and height in pressure ridges located between 150 and ~6400 m, 35 and ~800 m, and 1 to ~80 m, respectively, along ATF and 255 to ~5750 m, 33 to ~800 m, 2 to ~65 m in Carrizo plain of San Andreas fault. These parameters exhibit a good correlation among each other implying a common cause. Compared with these two strike-slip faults, fault valley portions of the Greendale and Kunlun faults show more surface ruptures for instance riedel shears and anti-riedel structures, which have been caused by the last major earthquake, and also the scale of deformations along the ATF and San Andreas fault is

  18. 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

  19. Along strike-slip faults, do fault segments exist and how long are they ? (Invited)

    NASA Astrophysics Data System (ADS)

    Klinger, Y.; Rockwell, T. K.; Cubas, N.; Souloumiac, P.

    2013-12-01

    The existence of relay zones and bends along strike-slip faults has long been recognized. The control of such geometrical asperities in initiation and arrest of seismic ruptures has been documented in many cases, suggesting they have a key role in the structure along strike of strike-slip faults. We produced dense slip distribution for two large strike-slip earthquakes, the 2001 Kunlun earthquake and the 1940 Imperial fault earthquake. In the Kunlun case we correlated satellite images acquired before and after the event to obtain a slip distribution of 1 point/km over 300 km. For the Imperial fault earthquake, we used a set of low altitude aerial photos that were flown just after the earthquake. The resolution of the photos is good enough to allow us to measure offsets of hundreds of plow lines along the trace of the rupture. In both cases the amplitude of the slip varies at a scale of several kilometers. In the case of Kunlun, the correlation between slip variations and jogs or side faults branching off the main rupture is straightforward. In the case of the Imperial fault, where long-term morphology is not preserved because of anthropic activities, still the slip distribution corresponds well with the slip patches determined independently by seismologists. These two examples strongly suggest that the segmentation of the fault controls the way seismic ruptures propagate along strike-slip faults. A more systematic exploration of slip maps derived from kinematic inversions of geophysical data shows that beyond variation due to different methodology and data, the lateral size of slip patches derived from such geophysical studies saturates around 20 km, independently of the earthquake magnitude. In parallel, using the available dataset of well documented ground ruptures maps for strike slip earthquakes, we designed an automatic procedure to quantify the minimum number of connected strait lines, approximating fault segment, needed to fit the rupture trace. The

  20. 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.

  1. Geomorphic analysis of the Sierra Cabrera, an active pop-up in the constriction domain of conjugate strike-slip faults: the Palomares and Polopos fault zones (eastern Betics, SE Spain)

    NASA Astrophysics Data System (ADS)

    Giaconia, F.; Booth-Rea, G.; Martínez-Martínez, J. M.; Pérez-Peña, V.; Azañón, J. M.

    2012-04-01

    Segments of the Quaternary sinistral Carboneras and Palomares fault zones, striking NE-SW and NNE-SSW, respectively, terminate in the Sierra Cabrera antiform together with the conjugate dextral WNW-ESE striking Polopos fault zone. In the constriction domain between these fault zones a pop-up structure occurs formed by the North and the South Cabrera reverse faults that bound the northern and the southern hillslopes, respectively. In order to test the Quaternary activity and relief control of these fault zones, here we present new qualitative and quantitative geomorphic analyses for the Sierra Cabrera using the following indices: mountain-front sinuosity, valley floor width-to-height ratio, drainage basin asymmetry factor, basin hypsometric curve and integral, and the SLk index. These analyses were performed with the aid of several maps such as the SLk and the minimum bulk erosion map. Qualitative observations carried out on the drainage network highlight the existence of a Late Miocene fold-related drainage network and a following late Miocene to Plio-Quaternary fault-related one. Integrating the mountain-front sinuosity and the valley floor width-to-height ratio for each mountain front we estimated the uplift rates associated to each of them. Fault-related mountain-fronts with a N50-60°E strike have reverse kinematics and uplift rates larger than 0.5 m ky-1 (e.g. North and South Cabrera reverse faults), whereas those with N20-30°E and N90-100°E strikes show oblique strike-slip kinematics and show lower uplift rates, between 0.05 and 0.5 m ky-1 (e.g. the Palomares and the Polopos fault segments). Furthermore, these faults produce knickpoints, complex basin hypsometric curves, high SLk anomalies and highly eroded basins above the fault traces. The estimated uplift rates are larger than those obtained from other authors for strike-slip faults in the eastern Betics that range between 0.1 and 0.05 m ky-1 (e.g. Palomares and southern Carboneras strike-slip fault

  2. 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.

  3. Actively evolving microplate formation by oblique collision and sideways motion along strike-slip faults: An example from the northeastern Caribbean plate margin

    NASA Astrophysics Data System (ADS)

    Mann, Paul; Taylor, F. W.; Edwards, R. Lawrence; Ku, Teh-Lung

    1995-06-01

    The pattern of folding, faulting, and late Quaternary coral-reef uplift rates in western and central Hispaniola (Haiti and Dominican Republic) suggest that the elongate Gonave microplate, a 190,000-km 2 area of the northeastern Caribbean plate, is in the process of shearing off the Caribbean plate and accreting to the North American plate. Late Cenozoic transpression between the southeastern Bahama Platform and the Caribbean plate in Hispaniola has inhibited the eastward motion of the northeastern corner of the plate. Transpression is manifested in western and central Hispaniola by the formation of regional scale folds that correspond to present-day, anticlinal topographic mountain chains continuous with offshore anticlinal ridges. Areas of most rapid Quaternary uplift determined from onland coral reefs 125 ka and younger, coincide with the axial traces of these folds. Offshore data suggest recent folding and faulting of the seafloor. Onshore reef data do not conclusively require late Quaternary folding, but demonstrate that tectonic uplift rates of the axial areas of the anticlines decrease from the Northwest Peninsula of Haiti (0.37 mm/yr) to to the central part of the coast of western Haiti (0.19 mm/yr) to the south-central part of western Haiti (0 mm/yr). Formation of the 1200-km-long Enriquillo-Plantain Garden-Walton fault zone as a 'bypass' strike-slip fault has isolated the southern edge of the Gonave microplate and is allowing continued, unimpeded eastward motion of a smaller Caribbean plate past the zone of late Neogene convergence and Quaternary uplift of coral reefs in Hispaniola. Offshore seismic reflection data from the Jamaica Passage, the marine strait separating Jamaica and Haiti, show that the Enriquillo-Plantain Garden fault zone forms a narrow but deep, active fault-bounded trough beneath the passage. The active fault is continuous with active faults mapped onshore in western Haiti and eastern Jamaica; the bathymetric deep is present because the

  4. 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

  5. Geomorphic analysis of the Sierra Cabrera, an active pop-up in the constrictional domain of conjugate strike-slip faults: The Palomares and Polopos fault zones (eastern Betics, SE Spain)

    NASA Astrophysics Data System (ADS)

    Giaconia, Flavio; Booth-Rea, G.; Martínez-Martínez, J. M.; Azañón, J. M.; Pérez-Peña, J. V.

    2012-12-01

    The NNE-SSW sinistral Palomares and the conjugate dextral WNW-ESE striking Polopos fault zones terminate in the Sierra Cabrera antiform. In order to test the Quaternary activity and topographic relief control in the termination of these fault zones, here we present new qualitative and quantitative geomorphic analyses supported by a new structural map of the region. The main mountain fronts of the Cabrera antiform are formed by the North and South Cabrera reverse faults that merge laterally into the Palomares and Polopos faults, respectively. These faults produce knickpoints, stream deflections, complex basin hypsometric curves, high SLk anomalies and highly eroded basins in their proximity. Furthermore, the drainage network shows an S-shaped pattern reflecting progressive anticlockwise rotation related to the sinistral Palomares fault zone. The estimated uplift rates determined by the integration between mountain front sinuosity index and valley floor width to height ratio are larger than those obtained for strike-slip faults in the eastern Betics. These larger uplift rates with our geomorphic and structural dataset indicate that the topographic relief of the Sierra Cabrera antiform is controlled by reverse faults that form a pop-up structure in the constrictional domain between the larger Palomares-Polopos conjugate strike-slip faults. Existing GPS geodetic data suggest that the North and South Cabrera reverse faults probably accommodate a large part of Africa-Iberia convergence in the region.

  6. 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

  7. 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

  8. 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

  9. 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.

  10. 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

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

    NASA Astrophysics Data System (ADS)

    Swanson, Mark T.

    2005-05-01

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

  12. Large-scale Geometry of Intra-continental Strike-slip Faults: Example of the Karakorum Fault, Western Tibet

    NASA Astrophysics Data System (ADS)

    Chevalier, M. L.; Leloup, P. H.; Li, H.

    2015-12-01

    How large-scale, active strike-slip fault systems are defined can sometimes be ambiguous, especially when viewed at different timescales (geodetic vs longer term measurements). Does every kilometer of the fault system need to be visible in the morphology (offset geomorphic features, fault trace, etc) to be considered as currently active? Does every segment of the fault need to have a unique and consistent kinematics along the entire fault system (normal, strike-slip, reverse)? Does all segments need to be physically connected at the surface to be considered part of the same fault system? To illustrate our arguments against such statements, we use the example of the right-lateral strike-slip Karakorum fault, located in western Tibet, along which lively debates have been taking place in the last ~20 years. These concern its initiation age, total geologic offsets, slip-rates, and more recently, even the location and current activity of the northern half of the fault. In particular, whether the active Kongur Shan extensional system, located in the Chinese Pamir, belongs to the Karakorum fault system remains controversial. Here, we argue that both systems are connected and that they both play a significant role in accommodating deformation at the western Himalayan syntaxis, under the form of extensional displacement in the Chinese Pamir.

  13. 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.

  14. 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.

  15. 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.

  16. 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.

  17. Paleofluid evolution of strike-slip compartmentalized extensional fault zones in the Jabal Qusaybah anticline, Salakh Arc, Oman

    NASA Astrophysics Data System (ADS)

    Balsamo, Fabrizio; Clemenzi, Luca; Storti, Fabrizio; Mozafari, Mahtab; Solum, John; Swennen, Rudy; Taberner, Conxita; Tueckmantel, Christian

    2015-04-01

    The E-W-trending Jabal Qusaybah anticline, developed in layered Cretaceous carbonates, is located at the western termination of the Salakh Arc, Oman Mountains. The anticline is 10 km long and is characterized by a complex fault pattern which mainly includes NE-SW left-lateral strike-slip and N-S extensional fault zones. The N-S striking extensional fault zones are best developed in the central sector of the anticlinal crest, likely due to along-strike outer-arc extension associated with positive fault inversion and salt migration. Extensional fault zones are perpendicular to the fold axis and geometrically confined within major NE-SW left-lateral strike-slip fault zones. They have trace lengths ranging from a few m up to ~800 m, and displacements ranging from a few dm up to ~60 m. Fault zones consist of cataclastic fault cores (~1-15 cm thick) surrounded by vein-dominated damage zones. Overall, fault zones show significant volumes of dilation breccia texture, m-thick infillings of calcite crystals, and cm- to m-thick veins localized at fault tip zones, areas of fault overlap, and zones of interaction between strike-slip and extensional fault segments. By analyzing fault abutting geometries, detailed vein relative chronology, delta13C and delta18O signatures and fluid inclusion data from calcite veins and calcite fault infillings, we propose a model where a deep seated left-lateral strike-slip fault system, active during the growth of the anticline, inhibited the lateral propagation of late-stage transversal extensional fault zones. Our findings show that, in this geological setting, the structural position, rather than fault throw, is the parameter controlling the location of the more dilatant fault segments.

  18. The width of fault zones in a brittle-viscous lithosphere: Strike-slip faults

    NASA Technical Reports Server (NTRS)

    Parmentier, E. M.

    1991-01-01

    A fault zone in an ideal brittle material overlying a very weak substrate could, in principle, consist of a single slip surface. Real fault zones have a finite width consisting of a number of nearly parallel slip surfaces on which deformation is distributed. The hypothesis that the finite width of fault zones reflects stresses due to quasistatic flow in the ductile substrate of a brittle surface layer is explored. Because of the simplicity of theory and observations, strike-slip faults are examined first, but the analysis can be extended to normal and thrust faulting.

  19. 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

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

    USGS Publications Warehouse

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

    1996-01-01

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

  1. 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

  2. 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

  3. Formation and evolution of strike-slip faults, rifts, and basins during the India-Asia collision - An experimental approach

    NASA Astrophysics Data System (ADS)

    Peltzer, Gilles; Tapponnier, Paul

    1988-12-01

    The processes which have governed the formation and evolution of large tertiary strike-slip faults during the penetration of India into eastern Asia are investigated by plane strain indentation experiments on layered plasticine models. The results show the influence of boundary conditions as well as that of the internal structure of the plasticine model on the faulting sequence. The ubiquity of strain softening in experimental deformation of a variety of rocks, as well as the widespread occurrence of shear zones in nature, suggest that long-term deformation of the continental lithosphere may also be primarily influenced by the geometry of large faults which rapidly develop with increasing strain. The deformation and faulting sequence observed in the plasticine indentation experiments may thus be compared to collision-induced strike-slip faulting in Asia, particularly to total offsets and rates of movements on the faults. The experiments also illustrate mechanisms for the formation of extension basins near active continental margins.

  4. An Inexpensive Device for Modelling Strike-Slip and Oblique-Slip Fault Zones.

    ERIC Educational Resources Information Center

    Larter, Richard C. L.; Allison, Iain

    1983-01-01

    Describes construction/use of a device to simulate structures produced in fault zones of dominantly strike-dip motion. Apparatus modifications allow simulation of transtension and transpression as well as pure strike-slip fault motion. Illustrates formation of several structures using the apparatus, comparing them with natural examples. Includes…

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

    USGS Publications Warehouse

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

    1989-01-01

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

  6. 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.

  7. 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

  8. Influence of erosion and sedimentation on strike-slip fault systems: insights from analogue models

    NASA Astrophysics Data System (ADS)

    Le Guerroué, Erwan; Cobbold, Peter Robert

    2006-03-01

    We describe 18 experiments on the formation of strike-slip fault systems in sand. All models were in a rectangular box. A piston imparted strike-slip motion along a basal cut. In some experiments, uplifted areas underwent erosion. In others, all areas were subject to sedimentation. In experiments without erosion or sedimentation, first to develop were R-faults, at 16° to the basal cut. At later stages, P-faults and Y-faults took over. In section, faults splayed upward, forming flower structures. The splays had reverse components of slip. This was due to dilation, which reached 7% within fault splays. In experiments with erosion but no sedimentation, faults were less steep and accumulated greater amounts of reverse slip. In experiments with erosion and sedimentation, some faults propagated through their syn-kinematic cover, others became buried and inactive, whilst yet others were exposed by erosion. Therefore the average fault dip increased significantly. In experiments with sedimentation but no erosion, early faults propagated, whereas others became buried. Flower structures in nature have similar features. In areas of sedimentation, fault splays with gentle dips die out at depth, whereas steeper faults penetrate higher. In areas of erosion, strike-slip systems exhibit large amounts of reverse slip on steep bounding faults.

  9. 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.

  10. 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.

  11. 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

  12. 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.

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

    USGS Publications Warehouse

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

    2010-01-01

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

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

    USGS Publications Warehouse

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

    2010-01-01

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

  15. 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.

  16. 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

  17. Asymmetric alluvial fans along strike-slip faults: A potential slip-rate record?

    NASA Astrophysics Data System (ADS)

    Morelan, A. E., III; Oskin, M. E.

    2014-12-01

    We investigate the phenomenon of asymmetric alluvial fan morphology along strike-slip faults. From analysis of high-resolution topographic data, we find that asymmetric alluvial fans are common along several strike-slip faults in the western United States. Affected fans are steeper in the direction of translation of the sediment source, often resulting in stream deflections counter to that expected from the sense of fault slip (e.g. left deflected streams along dextral faults). We hypothesize that fan asymmetry results from lateral translation of the sediment source relative to the depocenter. This relative motion changes the accommodation space in such a way that one side of the alluvial fan continuously progrades while the other is gradually abandoned. Therefore, lateral translation results in radial asymmetry of slopes about the fan apex. As a first approximation, we model this asymmetry as a result of diffusive sediment transport down fan. From this analysis, we predict that the degree of asymmetry of the alluvial fan is controlled by the ratio of sediment flux to fault slip rate. Qualitatively, more rapidly slipping faults should host more highly asymmetric fans; conversely, high sediment flux will obscure asymmetry. By measuring the sediment flux, through catchment-average concentration of cosmogenic isotopes or other means, we show that it is theoretically possible to quantify strike-slip fault slip-rates and alluvial-fan sediment transport rates using alluvial fan morphometry.

  18. The role of oblique strike-slip faulting in the tectonics of the Puget Lowlands and throughout the Pacific Northwest

    NASA Astrophysics Data System (ADS)

    Keranen, K. M.

    2015-12-01

    Upper-plate seismicity in the Puget Lowland, away from and oblique to known fault structures, challenges our understanding of active tectonics and seismic hazards of the region. The challenge arises in part from the thick glacial sediments and extensive water bodies that obscure active faults. Multichannel seismic reflection data in waterways, combined with aeromagnetic and gravity data, can effectively map fault structures throughout the Puget Lowland. Seismic reflection data indicate a NE-SW zone of recent high-angle faulting and shallow sediment deformation crossing the Seattle Uplift and the Seattle Basin, distinct from previously interpreted E-W fault systems including the main Seattle Fault. These NE-SW faults correlate with a zone of active seismicity, cut or deform sediments at the seafloor, and trend across the central Puget Lowland at an oblique angle to major regional structures. Aeromagnetic data show that the trend continues southeastward across the Seattle Uplift and connects deformation of shallow sediment in the Puget Sound with deformation of shallow sediment in Hood Canal. Two additional zones of faulting have NW-SE trend and cut through the Seattle Basin and Kingston Arch. Though strike-slip motion is a new interpretation for deformation along the southern edge of the Seattle Basin, it is not anomalous in the Puget Lowland; it is observed to the north along the southern Whidbey Island Fault (Sherrod et al., 2008) and Darrington-Devils Mountain Fault (Personius et al., 2014) and to the south along the Mount St. Helens seismic zone. Strike-slip motion accompanying regional compression and thrust-faulting occurs elsewhere in the Pacific Northwest including in south-central Washington (Blakely et al., 2014). Oblique strike-slip faults may contribute more significantly to deformation and seismicity within the Puget Lowland than previously recognized. Future work will evaluate the impact of deformation along these structures in tectonic models and

  19. 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

  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. On the Origin and Distribution of Fracture Damage Surrounding Strike-Slip Fault Zones

    NASA Astrophysics Data System (ADS)

    Mitchell, T. M.; Faulkner, D. R.

    2006-12-01

    Fault damage zones are represented by both microfracturing of the rock matrix and by macroscopic fracture networks. The spatial distribution and geometric characterization of fracture patterns at various scales help to predict fault growth processes, subsequent mechanics and bulk hydraulic properties of a fault zone. We studied strike-slip faults of various displacements that cut crystalline rock (granodiorite) within the excellently exposed and passively exhumed Atacama Fault Zone, Northern Chile. Micro- and macroscale fracture densities within the damage zones of faults with well-constrained displacements ranging over 3 orders of magnitude (~0.12 m 5000 m) have been characterized. These faults can be compared and contrasted as they all cut the same rock type. Multiple generations of microfractures indicating deformation at different crustal depths and times are represented by fluid inclusion planes (FIPs), partially healed, and open microfractures. The FIPs show a log- linear decrease in density with perpendicular distance from the fault plane on all faults studied. Recent work has shown that the damage zone surrounding faults is largely developed in the process zone that precedes the fault tip. As the fault tip propagates through the process zone, microfracture damage is left flanking either side of the fault. These FIPs are in a predominantly mode I orientation and we interpret them to record a snapshot of fault history related to the passage of a migrating fault tip process zone. Microfracture densities fall to background levels at ~150 m for the 5000 m offset fault, ~115 m for the 220 m offset fault, ~18 m for the 35 m fault, ~0.06 m for the 2 m offset fault, ~0.09 m for the 1.2 m offset fault and ~0.05mm for the 0.13 m offset fault. All faults appear to have a critical microfracture density independent of displacement. However, fault damage zone widths scale with displacement. Later microfractures do not show a clear relationship of microfracture density

  2. Investigating the crustal structure of a strike-slip ``step-over'' zone along the Great Glen fault

    NASA Astrophysics Data System (ADS)

    McBride, J. H.

    1994-10-01

    Strike-slip step-overs and bends are regions of anomalous deformation that may yield clues to the mechanical behavior of the Earth's crust. Experimental reprocessing of a marine deep seismic reflection profile cutting across an ˜35-km-wide right-stepping step-over developed on the Great Glen fault system north of the Inner Moray Firth basin (east of Northwest Highlands, Scotland) reveals a restricted zone of prominent reflections and diffractions beginning at 7-8 km depth, continuing as deep as the interpreted Moho discontinuity at 26-27 km. Geological interpretation of this zone suggests a concentration of possible diffractors marking sharp structural disruption underlain by a ˜12-km thick layer of subhorizontal and moderately dipping reflectors that dominates the lower crust in the step-over region. The known kinematic history of the Great Glen fault system, together with the observed direction of the step-over, implies that a zone of contraction would have formed within the step-over during early Caledonian sinistral strike slip. The seismic reflection structure can be interpreted as developing by deformation associated with contraction and possible block rotation between the two fault segments such that the diffractive zone represents steep structure in a near-vertical zone of strike slip which passes deeper into a layer of low-angle dipping thrusts or shear zones. The results of this study are consistent with a concept of mechanical detachment in the middle crust as documented for areas of contraction along active strike-slip faults.

  3. 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.

  4. Cenozoic geodynamics of the Ross Sea region, Antarctica: Crustal extension, intraplate strike-slip faulting, and tectonic inheritance

    NASA Astrophysics Data System (ADS)

    Salvini, Francesco; Brancolini, Giuliano; Busetti, Martina; Storti, Fabrizio; Mazzarini, Francesco; Coren, Franco

    1997-11-01

    An integrated study of onshore and offshore geology of the Ross Sea region (namely, Victoria Land, north of Ross Island, and the Ross Sea, Antarctica) has revealed a complex, post-Eocene tectonic framework. Regional NW-SE right-lateral, strike-slip faults are the outstanding feature of this framework and overprint an older Mesozoic extensional event, responsible for formation of N-S basins in the Ross Sea. The Cenozoic framework includes kinematic deformation and reactivation along the NW-SE faults, including formation of pull-apart basins, both positive and negative flower structures, and push-up ridges. N-S extensional faults are well developed between NW-SE faults and indicate E-W extension during the Cenozoic, produced by the NW-SE right-lateral strike-slip motion together with regional crustal extension. NNW-SSE compression, induced by the right-lateral, strike-slip kinematics, is indicated by locally inverted NE-SW faults and basins. The evolution, geometry, and location of the Rennick Graben and the Lanterman Range fit well into this model. Variations in the deformational style across the region can be linked to corresponding variations in the bulk crustal rheology, from brittle behavior in the west, to ductile deformation (at subseismic-scale resolution) near the Eastern Basin. A semibrittle region that favors N-S clustering of Cenozoic magmatic activity lies in between. In this region, Cenozoic volcanoes develop at the intersections of the NW-SE and the major N-S faults. The NW-SE faults cut almost continually from the Ross Sea to East Antarctica through lithospheric sectors with different rheology and thickness. At least two of the NW-SE faults correspond to older Paleozoic terrane boundaries in northern Victoria Land. The NW-SE faults link in the Southern Ocean with major transform faults related to the plate motions of Australia, New Zealand, and Antarctica.

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

    USGS Publications Warehouse

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

    2003-01-01

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

  6. 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.

  7. 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

  8. Quantifying the Relationship between Strike-slip Fault Spacing and Brittle Crust Thickness in Continental Settings based on Sandbox Experiments

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    Parallel and evenly spaced strike-slip faults occur widely in continental settings. The fault spacing varies from 10s of km along transform fault systems (e.g., southern California and New Zealand) to 200-400 km in continental interiors (e.g., central Tibet, central Asia, and North China plains). In order to understand the role of the brittle crust rheology and thickness in controlling the fault spacing in continental settings, we performed a series of sandbox experiments using medium-grained dry sand under strike-slip simple-shear conditions. With a self-built sliding device, we determined the yield strength of the dry sand to follow a Coulomb fracture relationship: Tn = 0.5173Sn + 15.475(Pa), with R2 = 0.936, where Tn is the shear stress, Sn is the normal stress, R is the coefficient of linear correlation, and 15.475 Pa is the cohesive strength. In our experiments, we created parallel Riedel shears in a simple shear zone with sand layer thickness varying from 1 cm to 6 cm. The relationship between the fault spacing (S) and the sand layer thickness (T) fits a linear equation of S = 0.5528T + 4.765, with R2 = 0.975. Assuming that the cohesive strength of the continental crust is 1-5 MPa and neglecting the density difference between rock and sand, the scaling relationship between sand and crustal thickness can be approximated as 1:1 X 105 to 1:5 X 105, which means that our experiments simulate a range of crustal thicknesses from 1 km to 30 km. The relevance of the S-T relationship obtained from this study will be tested in areas of active strike-slip tectonics, where the thickness of the brittle crust can be determined by the thickness of the seismogenic zones.

  9. 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.

  10. 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.

  11. Orogeny and large-scale strike-slip faulting on Venus - Tectonic evolution of Maxwell Montes

    NASA Astrophysics Data System (ADS)

    Vorder Bruegge, R. W.; Head, J. W.; Campbell, D. B.

    1990-06-01

    Complementary data sets from the Arecibo and Venera 15/16 imaging radar systems are used here to produce geologic and structural maps of the Maxwell Montes, a region of large-scale strike-slip faulting on Venus. The maps are compared with the characteristics of other linear mountain belts. The tectonic deformation occurring in Maxwell Montes is assessed, identifying the structural elements, their tectonic origin, and their sequence. A geologic and tectonic chronology is developed and a model for the origin and evolution of Maxwell Montes is proposed.

  12. 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

  13. 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.

  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. 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

  16. 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

  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. 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.

  19. 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.

  20. Strain localization versus distributed deformation along strike-slip faults in eastern Tibet (Invited)

    NASA Astrophysics Data System (ADS)

    Kirby, E.; Harkins, N. W.

    2010-12-01

    Thirty-five years after the recognition of the tectonic significance of Eurasian strike-slip faults, the mechanical implications of these structures and how they accommodate ongoing Indo-Asian convergence continues to engender vigorous debate. Do the rules of plate tectonics, where strike-slip faults bound quasi-rigid blocks, govern intracontinental deformation? Or does strain localization simply occur along pre-existing heterogeneities in an otherwise continuously medium? Despite improved estimates of slip-rates along nearly all of the major fault systems over the past decade, we have not yet reached consensus on these questions. One possible reason is that most studies have been focused along portions of these fault systems adjacent to rigid blocks, where slip-rates are expected to be relatively high and spatially uniform, irrespective of mechanical behavior. In these regions, slip-rates alone may not be sufficient to distinguish between competing modes of deformation. In contrast, where these major fault systems are embedded within deforming regions, slip-rates, and how they vary along strike, may yield insight into the relationship between fault-slip and deformation of the surrounding crust. Within the Indo-Asian collision zone, such conditions exist in several places: at the eastern and western terminations of the Kunlun fault, along the western segments of the Yushu-Ganzi-Xianshuihe fault, and perhaps along much of the Karakorum fault. Here, we focus on recent results along the eastern Kunlun fault. In the region east of the Qaidam Basin, the Kunlun fault transects high topography in the Anyemaqen Shan for ~250 km along strike. Late Quaternary slip-rates determined at 9 localities reveal a systematic decrease along this section of the fault, from >10 mm/yr to <2 mm/yr, a result corroborated by existing geodetic data. Moreover, the high relief within the Anyemaqen Shan appears to reflect internal deformation of a broad region surrounding the fault tip

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

    NASA Astrophysics Data System (ADS)

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

    2011-09-01

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

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

    USGS Publications Warehouse

    Sims, P.K.

    2009-01-01

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

  3. Moderately-dipping California Strike-slip Faults With Bends in map View and Cross-section

    NASA Astrophysics Data System (ADS)

    Cormier, M. H.; Sorlien, C. C.; Nicholson, C.; Legg, M.; Behl, R. J.; Seeber, L.

    2015-12-01

    New faults in a strike-slip stress field are expected to be sub-vertical. However, continental strike-slip faults commonly reactivate arrays of pre-existing non-vertical faults with non-optimal strike. The systems of strike-slip faults that dissect the Inner California Continental Borderland , Santa Monica Bay, and south-Central California are imaged with multiple grids of closely spaced 2D multichannel seismic reflection profiles. From these and stratigraphic information, we constructed multiple digital 3D fault and fold interpretations. Quaternary strike-slip faults that dip moderately in their upper few km include the southern Hosgri fault, part of the Carlsbad fault, and the Santa Monica-Dume fault. These faults reactivate structures that developed in pre-19 Ma subduction and subsequent Miocene extension and transtension. Seismic reflection imaging reveal that they dip 40° to 55°. 3D seismic data image the Hosgri fault to locally dip less than 30° below 1 km depth. Where Pliocene-Quaternary sediment accumulated in basins, these faults tend to propagate upwards as sub-vertical faults, as expected. Thus, cross sectional fault geometry can be used together with other information to infer strike-slip motion. Imaged gently-dipping faults underlie and/or interact with the Santa Monica-Dume and Carlsbad faults. Seismicity and tectonic models suggest that the southern Hosgri fault and faults to its west do not affect the subducted oceanic lower crust. Thus, strike-slip motion there may occur on the former subduction megathrust. These moderately-dipping faults also describe bends and stepovers in map view, resulting in significant vertical deformation. Northwest of San Diego, the Carlsbad fault bends sharply as part of a 15 km right-stepover to the Descanso and Coronado Bank fault system. N-striking fault strands, a releasing orientation for the Pliocene to present strain orientation, connect between the Newport-Inglewood and Carlsbad faults and also between the Rose

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

    NASA Astrophysics Data System (ADS)

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

    2014-04-01

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

  5. 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

  6. 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.

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

    USGS Publications Warehouse

    Sharp, R.V.

    1981-01-01

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

  8. 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.

  9. 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

  10. Strike-slip fault patterns on Europa: Obliquity or polar wander?

    NASA Astrophysics Data System (ADS)

    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

  11. 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.

  12. 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

  13. Strike-Slip displacement along the Furnace Creek Fault Zone, southern Basins and Ranges, Death Valley, California

    NASA Astrophysics Data System (ADS)

    Baucke, W.; Cemen, I.

    2007-12-01

    The southern Basins and Ranges contain several strike-slip fault zones in addition to predominant normal faults. One of the strike-slip faults is the Furnace Creek fault zone (FCFZ) which extends from the Amor¬gosa Valley in eastern California northwestward continuously about 200 km and termi¬nates in the Fish Lake Valley in Nevada. The fault zone is a part of the Eastern California Shear Zone. Although the right-lateral sense of strike-slip movement along the FCFZ is undisputed, the magnitude of displacement has been controversial since the 1970s. Recently, we have mapped conglomerates exposed in the Travertine point area of the Furnace Creek Wash of the Death Valley region. The conglomerates are composed of Paleozoic clasts from the following formations: Bonanza King, Nopah, Pogonip, Eureka Quartzite, Hidden Valley, and Ely Springs Dolomite. Our analysis of these breccias showed that they are made out of clasts of one composition and a matrix that was slightly different. This observation and our microscopic analysis suggest to us that these breccias were formed as fault breccias along the Furnace Creek fault zone. We have also mapped breccias in the Desolation Canyon on the southwestern side of the FCFZ where the Bonanza King Formation is brought into structural contact over the Ely Spring Dolomite and Eureka Quartzite suggesting the presence of a thrust fault. We correlate this thrust fault with a similar structural setting along the Clery Thrust of the southern Funeral Mountains on northeastern sides of the FCFZ where the Clery thrust brings the Cambrian Bonanza King Formation over the Eureka Quartzite and Ely Spring Dolomite in the southern Funeral Mountains. These observations suggest to us that the thrust fault in the Desolation Canyon area is the continuation of the Clery Thrust of the southern Funeral Mountains. If this interpretation is correct, the strike-slip displacement along the FCFZ is about 30 km.

  14. 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

  15. Late-Cretaceous allochthons and post-Cretaceous strike-slip displacement along the Cuilco-Chixoy-Polochic Fault, Guatemala

    NASA Astrophysics Data System (ADS)

    Anderson, Thomas H.; Erdlac, Richard J., Jr.; Sandstrom, Melissa A.

    1985-08-01

    The disposition of allochthonous masses, emplaced in late Cretaceous to Early Tertiary time, along the Cuilco-Chixoy-Polochic strike-slip fault zone in western Guatemala, constrains the amount of Tertiary displacement. The absence of major disruption of the allochthons argues against lateral displacements of hundreds of kilometers during the Tertiary. In westernmost Guatemala, along the flank of the Cuilco-Chixoy-Polochic fault, granite, volcaniclastic and volcanic rocks, minor carbonate and phyllite comprise a sequence of south-dipping allochthons. These tilted slabs lie against almost horizontal Jurassic and Cretaceous beds to the north. Field relations indicate that the slides were emplaced across the Cuilco-Chixoy-Polochic fault from south to north probably during late Cretaceous or early Tertiary time. Other fault-bounded masses, which crop out tens of kilometers eastward, near San Sebastián Huehuetenango, probably were emplaced contemporaneously with those to the west. Locally, these allochthons lie astride the active trace of the Cuilco-Chixoy-Polochic fault along which offset streams record about 1 km of left-lateral motion. Total displacement recorded by the apparent offset of allochthonous sheets is no more than several kilometers. Farther east, along much of the Cuilco-Chixoy-Polochic fault zone, a throughgoing strike-slip trace has not been identified. We postulate that the pre-Tertiary tectonic record is obscured by an extensive series of allochthons composed of regional stratigraphic suites emplaced during late Cretaceous time. In western Guatemala stratigraphic relationships between serpentinized peridotite and carbonate beds of late Cretaceous age indicate Turonian as a maximum age for initial emplacement of allochthonous material. Regional relationships indicate that deformation culminated during latest Cretaceous - earliest Tertiary time. The emplacement of thrust sheets along the Cuilco-Chixoy-Polochic fault is a likely product of

  16. Structure of a continental strike-slip fault from deep seismic reflection: Walls Boundary fault, northern British Caledonides

    NASA Astrophysics Data System (ADS)

    McBride, John H.

    1994-12-01

    Reprocessing of four offshore deep reflection profiles across the Walls Boundary strike-slip fault, postulated as the northward continuation of the Great Glen fault over the Shetland platform, provides useful constraints on the lithospheric structure of a major continental transform and some insight into the manner in which strike-slip faults deform. The reprocessing was aimed at delineating complex structure and reducing noise contamination and consisted of analyses of diffractions and amplitude variations and experimentation with seismic migration. The results demonstrate a highly variable crustal and uppermost mantle structure for the Walls Boundary fault along more than 150 km of its length. Six key observations can be made from this study. A vertical or steeply dipping structure is deduced for the fault in much of the crust and perhaps parts of the uppermost mantle; however, more diverse reflecting structures and interpreted for the lower crust, such as the Moho deflection and steeply dipping reflectors directly beneath the fault that may have been related to a localized component of transpression and resultant crustal thickening. The presence of diffractions at the level of the Moho discontinuity where the downward projection of the fault intersects it suggests points of structural 'roughness' that may be related to deformation of the Moho by late motion along the fault. Integrating the interpretation of the reflection data with previous geological studies implies that the age of the Moho deflection is post Early Cretaceous but that the dipping structure adjacent to and cut off by the fault is probably Caledonian (Silurian-Early Devonian). Although the disparate structure of the crust on opposite sides of the fault supports geologic interpretations of large-scale displacement, a major step in the Moho discontinuity directly beneath the Walls Boundary fault cannot be substantiated from the seismic data.

  17. Dynamic Modeling of Coseismic Rupture on Partially-Creeping Strike-Slip Faults

    NASA Astrophysics Data System (ADS)

    Lozos, J.; Funning, G.; Oglesby, D. D.

    2013-12-01

    Partially creeping faults exhibit complex behavior in terms of which parts of the fault slip seismically versus aseismically; this complexity is both temporal and spatial. Several faults in California exhibit creep that is rapid enough to be detected geodetically using InSAR, GPS and near-field methods, such as theodolite measurements of alignment arrays. Such studies of the Hayward Fault in the San Francisco Bay Area suggest that it has a complex pattern of creeping and locked patches along strike and down dip. The spatial pattern of creeping versus locked zones may have as much of an effect on throughgoing rupture as the more general presence of creep does. We use the 3D finite element modeling code FaultMod to conduct single-cycle models of dynamic rupture on partially creeping strike slip faults, in order to determine whether coseismic rupture can propagate into creeping regions, and how the presence and distribution of creep affects the ability of rupture to propagate along strike. We implement a rate-state friction criterion, in which locked zones of the fault are represented by rate-weakening behavior, and creeping zones of the fault are assigned rate-strengthening properties. We model two simplified partial creep geometries: a locked patch at the base of a largely creeping fault (similar to what is inferred for the Hayward Fault), and a creeping patch at the surface of a predominantly locked fault (similar to what is inferred for the Rodgers Creek Fault). We find that, in the case of a locked patch within a creeping fault, rupture does not propagate more than a kilometer past the edges of the locked patch, regardless of the patch radius. The case of a creeping patch within a locked fault is more complicated. We find that the width of the locked areas around the creeping patch determine whether or not rupture is able to propagate around the creeping patch and along the full strike of the fault; if the width of locked zone between the edge of the creeping

  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. Intracontinental strike-slip faults, associated magmatism, mineral systems and mantle dynamics: examples from NW China and Altay-Sayan (Siberia)

    NASA Astrophysics Data System (ADS)

    Pirajno, Franco

    2010-09-01

    In the orogenic belts of the Central Asian Orogenic Belt (CAOB), many mafic and felsic plutons are temporally and spatially associated with orogen-scale strike-slip faults. The CAOB is a huge and complex orogenic collage of accreted terranes that was formed in the Early to Mid-Palaeozoic. In the CAOB, orogen-scale strike-slip faults extend for 100-1000 s of kilometres marking the boundaries of tectonic units and terranes. I use examples from southern Siberia and NW China to illustrate the important role that strike-slip faults have in localising intraplate magmatism and associated metallogeny. Cases from the Altay-Sayan in southern Siberia, the Altay and Tianshan orogens in NW China, are compelling for providing good evidence of the control that strike-slip structures exert for the emplacement of magmas and related mineral systems. These strike-slip faults controlled the emplacement of mafic-ultramafic intrusions, alkaline mafic and felsic magmatism in the period 280-240 Ma, which coincides with mantle plume(s) activity that led to the emplacement of the Tarim and Siberian large igneous provinces (LIPs). Mineral systems that are associated with these LIPs include magmatic Ni-Cu in sill-like intrusions, concentrically zoned mafic-ultramafic intrusions (e.g. Kalatongke, the second largest Ni-Cu sulphide deposit in China, after Jinchuan), epithermal systems, breccia pipes, polymetallic hydrothermal veins, granitoid-related greisen and rare earth pegmatites, as well as kimberlite fields. In the Altay-Sayan and NW China regions, orogen-scale translithospheric strike-slip faults provided the channels for the emplacement of magmas, resulting from lateral flow of mantle melts along the base of the lithosphere. This lateral flow is interpreted to have resulted from the impingement of mantle plumes to the base of the lithosphere of what was, to all intents and purposes, a stationary plate. Lateral flow from mantle plumes head was sustained or facilitated, during stages of

  20. 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

  1. 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.

  2. 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.

  3. 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.

  4. 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.

  5. 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

  6. 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

  7. 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

  8. 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.

  9. 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.

  10. 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

  11. 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

  12. 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.

  13. Middle proterozoic dextral strike-slip event in the central Appalachians: Evidence from the Reservoir fault, NJ

    NASA Astrophysics Data System (ADS)

    Gates, Alexander E.

    1995-07-01

    Unequivocal kinematic indicators in cataclasites and mylonites of the Reservoir fault zone, New Jersey, show consistent dextral strike-slip shear sense and provide evidence for an extensive strike-slip event subsequent to the peak of the Grenvillian (Ottawan) Orogeny. The fault zone occurs in layered granitic gneiss and minor amphibolite of Precambrian age in the New Jersey Highlands (northern Reading Prong). The fault rocks underwent extensive synkinematic hydrothermal retrogression that produced amphibole-rich assemblages from all previous phases. Retrogression of the protolith shows sequential reactions to assemblages dominated by F-magnesiohastingsite, Cl-magnesiohastingsite, ferro-actinolite, actinolite, and finally actinolite + chlorite. Although deformation was purely brittle within the granitic protolith (quartz shows marginal plasticity), reaction enhanced ductility and plasticity of some phases produced S-C mylonites in amphibole mineralized fault rocks. C planes are composed of fine aligned grains of ferro-actinolite and actinolite and define tails on σ-type amphibole porphyroclasts. The porphyroclast cores are composed of F-magnesiohastingsite and/or Cl-magnesiohastingsite and commonly define S-planes. Some porphyroclast cores show brittle pull-apart textures and SEM analysis shows that virtually all have micro-brecciated rims that are indurated with epitaxial amphibole overgrowths from a more retrograde assemblage. C' planes are locally developed and defined by fine-grained chlorite and actinolite. All kinematic indicators show a consistent dextral strike-slip shear sense. Because retrogression was facilitated by fluids that evolved from F-rich to Cl-rich, as recorded by the amphiboles, they are interpreted as Proterozoic which is characterized by F-rich metamorphic fluids. Conditions of retrogression were lower greenschist facies as indicated by both mineralogy and dynamic response of minerals. Therefore the strike-slip event postdates granulite

  14. 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

  15. 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

  16. 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.

  17. Development of a self-similar strike-slip duplex system in the Atacama Fault system, Chile

    NASA Astrophysics Data System (ADS)

    Jensen, E.; Cembrano, J.; Faulkner, D.; Veloso, E.; Arancibia, G.

    2011-11-01

    Fault development models are crucial to predict geometry and distribution of fractures at all scales. We present here structures related to the development of the Bolfín Fault in the Atacama Fault System (AFS), covering a range of scales of 7 orders of magnitude. The AFS is a 1000 km-long trench-parallel fault system located in the Andean Forearc. The Bolfín Fault is a first-order fault of the Caleta Coloso Duplex, has a trend ∼170° and length >45 km. It cuts mainly meta-diorites and exhibits a 100-200 m thick core of subvertical bands of altered fractured host rock and of foliated cataclasites. This foliation is made up of several trend-parallel cm-thick shear bands, composed of plagioclase fragments (>0.1 mm) surrounded by epidote. In the compressive quadrant around the tip point of Bolfín Fault, the lower strain faults exhibit an unusual internal structure consisting of fractures arranged in a multi-duplex pattern. This pattern can be observed from meters to millimeters scale. The fractures in the strike-slip duplex pattern can be separated into two types. Main Faults: trend-parallel, longer and with larger offsets; and Secondary Fractures: sigmoid-shape fractures distributed in the regions between Main Faults, all oriented between 15° and 75° with respect to the Main Faults, measured counterclockwise (i.e. in P-diedra). On the basis of the distribution of the two types of recognized fractures, the relative sequence of propagation can be inferred. Main Faults, the more widely distributed, propagated earlier. The Secondary Fractures, in turn, distributed in thinner areas between the larger Main Faults, were propagated later as linking fractures. The duplex pattern is self-similar: Multiple-Core Faults with internal structure of multiple-duplex are itself in turn secondary faults within a larger km-scale duplex (Caleta Coloso Duplex). The duplex width (W) and the length (L) of the Main Faults forming the duplex show an almost linear relationship, for

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

    USGS Publications Warehouse

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

    2004-01-01

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

  19. 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

  20. 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

  1. 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

  2. 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.

  3. 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.

  4. 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

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

    NASA Astrophysics Data System (ADS)

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

    2016-04-01

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

  6. Characteristics of Middle and Deep Crustal Expression of an Arc - Forearc Boundary Strike-Slip Fault System

    NASA Astrophysics Data System (ADS)

    Roeske, S.; Mulcahy, S. R.; McClelland, W.; Cain, J.

    2008-12-01

    Strike-slip faults below the seismogenic zone are commonly assumed to widen with depth into broad region of distributed strain or flatten into subhorizontal shear zones within the middle crust. While this may occur in some continental strike-slip systems, we propose that strike-slip faults at a major rheologic boundary, such as an arc-forearc transition, remain relatively narrow at depth, with localized high strain zones separating discrete packages of less-deformed metamorphic rock. Strain localization allows for greater displacements and explains the juxtaposition of significantly different crustal levels exposed in such strike-slip systems. We present metamorphic and geochronologic evidence for the initiation of one such strike slip system in western Argentina. The Valle Fertil, Desaguadero-Bermejo lineament is a prominent high angle lineament which currently accommodates significant shortening in the western Sierra Pampeanas of Argentina. The lineament is characterized geophysically as a high-angle to steeply east-dipping boundary with denser and more magnetic rocks on the east. The fault zone is bounded by the Cambrian-Ordovician Famatina arc, an intermediate composition batholith, to the east and an arc-forearc package of predominantly metasedimentary rocks intruded by Ordovician mafic to intermediate composition plutonic rocks to the west. The two packages currently expose markedly different crustal levels; those to the east expose rocks metamorphosed at 2-8 kbar, while those to the west expose rocks metamorphosed 11-14 kbar. Both units experienced high-grade metamorphism and granulite facies migmatization between ~470-450 Ma. Separate isolated packages within the fault/ shear zone record separate histories from those exposed to the east and west of the lineament. Low grade-limestone as well as 1.1 Ga and 845 Ma granitoids are overprinted by low-grade shear zones and show no significant thermal effect of the Ordovician magmatism and metamorphism. Regional

  7. 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

  8. Multi-mineral detrital geochronology applied to a glaciated strike-slip fault system: A case study along a ~250 km transect of the Denali Fault, Alaska

    NASA Astrophysics Data System (ADS)

    Benowitz, J.; Layer, P. W.; O Sullivan, P. B.; Fitzgerald, P. G.; Roeske, S.

    2013-12-01

    Many applications of detrital geochronology are hampered by issues of provenance leading to limited constraints on sediment source. In particular detrital geochronology investigations on glacial outwash sand from glacier ice fields can be handicapped by the inability to map a basin's sub-glacial geology. More generally, sub-basin scale non-unique magmatic and exhumation bedrock histories can be a factor. Issues can also arise due to lithological variations in bedrock mineral fertility. The use of multiple mineral phase (light e.g., biotite and heavy e.g.., zircon) geochronology approach can help overcome transport and fertility issues. Glaciated strike slip faults, with axial drainages, juxtaposed translated crustal blocks, and across strike asymmetrical rock cooling histories potentially provide a unique geological and hydrological environment to overcome some of the issues of provenance in detrital geochronology while addressing general process questions. The Denali Fault is a right-lateral strike-slip fault system, with up to ~400 km of slip in the Cenozoic. The Alaska Range formed along the Denali Fault and variations in magmatic and rock cooling (exhumation) histories exist across and along the Fault. Most of the sub-arctic fault zone is glaciated, hence is an ideal location to test a multi-mineral detrital geochronology approach on modern sediment from a glaciated strike-slip fault system. Specifically we are interested in constraining the sub-glacial exhumation record along the Denali Fault to evaluate if there is a positive feedback between highly efficient glacial erosion processes and an active fault zone leading to long-term sub-glacial exhumation at rates significantly higher than experienced by the exposed bedrock of the Alaska Range. Modern river and glacial outwash sands were collected at single sites along a ~250 km transect of the Denali Fault, to compare to an existing data set of over 150 bedrock 40Ar/39Ar muscovite, biotite, and K

  9. 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.

  10. Effect of source parameters on forward-directivity velocity pulse for vertical strike slip fault in half space

    NASA Astrophysics Data System (ADS)

    Liu, Qifang; Yuan, Yifan; Jin, Xing

    2006-06-01

    It has been found that the large velocity pulse is one of the most important characteristics of near-fault strong ground motions. Some statistical relationships between pulse period and the moment magnitude for near-fault strong ground motions have been established by Somerville (1998); Alavi and Krawinkler (2000); and Mavroeidis and Papageorgiou (2003), where no variety of rupture velocity, fault depth, and fault distance, etc. were considered. Since near-fault ground motions are significantly influenced by the rupture process and source parameters, the effects of some source parameters on the amplitude and the period of a forward-directivity velocity pulse in a half space are analyzed by the finite difference method combined with the kinematic source model in this paper. The study shows that the rupture velocity, fault depth, position of the initial rupture point and distribution of asperities are the most important parameters to the velocity pulse. Generally, the pulse period decreases and the pulse amplitude increases as the rupture velocity increases for shallow crustal earthquakes. In a definite region besides the fault trace, the pulse period increases as the fault depth increases. For a uniform strike slip fault, rupture initiating from one end of a fault and propagating to the other always generates a higher pulse amplitude and longer pulse period than in other cases.

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

    NASA Astrophysics Data System (ADS)

    Zhang, X.; Sagiya, T.

    2015-12-01

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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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.

  17. 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

  18. 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).

  19. 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

  20. 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

  1. 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

  2. Shear failure of icy satellites: Present-day implications along Enceladus's Tiger Stripes and indications of past strike-slip faulting on Ganymede's Dardanus Sulcus

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    The icy fractured surfaces of both Enceladus and Ganymede offer many candidate faults for studying both past and potentially present tectonic activity. Recent studies have suggested that Enceladus's "tiger stripe" fractures may be associated with tectonic strike-slip (shear) motions as a result of Coulomb failure, but low coefficients of friction were primarily considered in past stress models. Recent work suggests that friction is highly sensitive to the state of seismic fault slip; low friction (μf = 0.1-0.2) may be applicable in initial slip events and high friction (μf = 0.3-0.6) may be more appropriate for subsequent sliding velocities. On Ganymede, strike-slip tectonics is common, notably where a prominent fault offsets Dardanus Sulcus. We investigate the role of fault friction and orbital eccentricity in the development of Enceladus's tiger stripes and Ganymede's Dardanus Sulcus. We consider both tidal diurnal and non-synchronous rotation (NSR) stresses, as applicable, and compute Coulomb failure conditions for these target fractures. For the Enceladus tiger stripes, previous shear failure models showed that low coefficients of friction (μf = 0.1-0.2) and shallow fracture depths (2-4 km) provide a very active diurnal shear failure scenario. Our new simulations suggest that shear failure is also possible for friction coefficients as high as uf = 0.6 at depths of 2 km, but the lateral extent of failure is suppressed in comparison. For Ganymede's Dardanus Sulcus, we consider tidal stress scenarios for both present (0.0013) and possible past high (~0.05) eccentricity. We find that NSR shear stress resolved along the Dardanus fault is sufficient to induce failure to ~1.4 km depths for μf ~0.3. For past high eccentricity, diurnal stress would have modulated NSR stress by ~100 kPa through Ganymede's tidal cycle, which could have also induced shear heating and tidal walking mechanisms. Together, these tidally driven failure models for Enceladus and Ganymede are

  3. 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.

  4. 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.

  5. 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.

  6. 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

  7. 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.

  8. 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.

  9. Dynamic Rupture and Ground Motion Modeling on Realistically Complex Strike-Slip Faults

    NASA Astrophysics Data System (ADS)

    Lozos, Julian Charles

    Faults are complex structures: they are geometrically complex, and have variable stress conditions and frictional behaviors along their length. In addition, faults exist in heterogeneous settings, in terms of surrounding geology, and in terms of regional and local stresses. These individual types of heterogeneity all contribute to complex dynamic rupture behaviors and ground motion distributions, as inferred from observational data and supported by previous modeling studies. In this study, we investigate the effects of individual types of complexity, and we combine different types of heterogeneity in order to enhance the realism of models of real-world faults. We use the finite element method to conduct dynamic rupture models of earthquakes on faults with complex geometry, initial stresses, frictional parameters, and surrounding geology, and with combinations of these factors, in order to investigate the effects of this complexity on fault interactions, rupture extent, and ground motion. In particular, we investigate the effect of critical weakening distance on the ability of rupture to propagate through a discontinuity in the fault trace, the effect of a small fault between the larger strands of a stepover on the ability of rupture to jump the stepover, and how zones of aseismic creep affect rupture through locked portions of the same fault. We also construct realistically complex models of the northern San Jacinto Fault, California, incorporating realistic geometry, velocity structure, and combined regional and stochastic stress fields. We find that the distribution of complexity of any type on the fault, which leads to heterogeneous fault strength, has the primary controlling effect on rupture behavior. The relative strength or weakness of the fault, rather than the actual value, is most important. We also find that the balance of the energy budget is crucial; if too much energy is redirected into fracture, rupture stops. Lastly, we find that each type of

  10. 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.

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

    NASA Technical Reports Server (NTRS)

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

  12. On the absence of strike-slip faults from the planets and satellites

    NASA Astrophysics Data System (ADS)

    Golombek, M. P.

    1985-04-01

    Lunar grabens are bounded by two downward converging 60 deg dipping normal faults. These faults intersect below the surface at a major mechanical discontinuity in the shallow crust between the megaregolith (total ejecta built up by repeated cratering) and the underlying in situ fractured rock. The ymmetry and simplicity of lunar grabens demands that the bounding faults initiate at this mechanical discontinuity and propagate up. Wrinkle ridges are though to result from thrust faulting or compressional folding of mare basalts. Identification and analysis of a number of terrestrial analogs that are morphologically similar to lunar and martian examples indicates that wrinkle ridges results from thrust faulting. The location of wrinkle ridges above suggested subsurface basin structures indicates that the trend and location of many wrinkle ridges are inherited from these pre-existing basin structures. This implies that the thrust faults responsible for wrinkle ridges initiate at the ase of the basalt-basin floor contact. This contact almost certainly represents a mechanical discontinuity in the shallow lunar crust because mare basalts are undoubtedly stronger than the underlying fall-back ejecta of the basin floor.

  13. Fault modeling of the Mw 7.0 shallow intra-slab strike-slip earthquake occurred on 2011 July 10th using near-field tsunami record

    NASA Astrophysics Data System (ADS)

    Kubota, T.; Hino, R.; Iinuma, T.

    2014-12-01

    On 2011 July 10th, an earthquake of Mw 7.0 occurred in the shallow part of the Pacific slab beneath the large coseismic slip area of the 2011 Tohoku-Oki earthquake. This event has a strike-slip focal mechanism with steep dipping nodal planes. Near the epicenter, aftershocks determined by OBS deployment formed clear two orthogonal lineaments with identical strikes of the focal mechanism solution, suggesting that the aftershock activity occurred along the two conjugate faults. The strikes of these faults were almost parallel to the direction of the magnetic lineations and the fracture zones of the incoming Pacific plate, suggesting that the earthquake was the re-rupture of congenital fractures under the extensional stress induced by the Tohoku-Oki earthquake. It is of great interest to know the down-dip size of the source fault not only to understand the mechanical nature of the slab but also the post-2011 stress state. Coseismic seafloor deformation and tsunami associated with the earthquake were observed by ocean bottom pressure gauges deployed within ~ 100 km from the epicenter. We estimated the finite fault model of this event to discuss the rupture properties of the earthquake. We sought the source model assuming a rectangular fault with a uniform slip assuming the strike of the fault to be one of those of two nodal planes of the focal mechanism. The two preferable source models corresponding to the two nodal planes explained the observed data equally well. For either model, the depth of the downdip end exceeds 40 km below the plate boundary, meaning the fault widths (down-dip size) were much larger than the depth extent of the aftershock distribution (~ 15 km). We sought another source model assuming the simultaneous rupture of the conjugate faults and found that the width of the fault model was more consistent with the aftershock distribution than the single rupture plane models. The 2011 intraslab strike-slip earthquake might be a compound rupture of the

  14. 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.

  15. '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

  16. 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.

  17. 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.

  18. Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip shear zone. The case of the right-lateral Karakorum fault.

    NASA Astrophysics Data System (ADS)

    Leloup, P. H.; Boutonnet, E.; Arnaud, N.; Paquette, J. L.; Davis, W. J.; Hattori, K.

    2012-04-01

    The Pangong range is an 8km wide shear zone corresponding to the exhumed root of the central Karakorum fault zone (KFZ), one of the great continental strike-slip faults of the India-Asia collision zone. Ductile deformation is the most intense in the Tangtse and Muglib strands which bracket the shear zone to the SW and NE respectively. Structural and microstructural data show that deformation was at least partly synchronous with partial melting and the intrusion of granitic bodies and dykes. New U/Pb SHRIMPII and LA-ICP-MS ages for 24 zircons populations, from 5 gneiss and mylonites as well as 10 leucocratic dykes, span in age from 105.1±1.1 Ma to 14.2±0.1 Ma. Old ages are inherited from the surrounding Cretaceous Ladakh and Karakorum batholiths, while 13 ages are younger than 25.6 Ma and reflect Miocene partial melting. The oldest dyke that can be shown to be syntectonic to the KFZ is 18.8±0.4 Ma old, suggesting that strike slip deformation started in the Tangtse strand at least at ~19 Ma. Other published U/Pb ages imply that deformation lasted until at least ~13.5 Ma. The absolute ages of dykes that are deformed or crosscut the foliation demonstrate that deformation was heterogeneous in space and time. 24 new Ar/Ar ages, together with published ones, allow reconstructing the shear zone cooling history. Cooling was diachronic across strike and ductile deformation (~300°C) stopped earlier in the SW than in the NE: at ~16 Ma in the south Tangtse granite, ~11 Ma in the Tangtse strand, ~9Ma in the Pangong range, and ~ 8Ma in the Muglib Strand. Deformation thus appears to have migrated / localized from the whole shear zone to the Muglib strand, the only locus showing evidence for brittle deformation and active faulting. Taking into account data previously collected along the KFZ, and a finite offset of 200 to 240 km, it appears that the fault has been active for at least 22 Ma, with a slip rate of 0.84 to 1.3 cm/yr in its central section. Stain rates measured in

  19. 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

  20. Origin and structure of major orogen-scale exhumed strike-slip

    NASA Astrophysics Data System (ADS)

    Cao, Shuyun; Neubauer, Franz

    2016-04-01

    The formation of major exhumed strike-slip faults represents one of the most important dynamic processes affecting the evolution of the Earth's lithosphere and surface. Detailed models of the potential initiation and properties and architecture of orogen-scale exhumed strike-slip faults and how these relate to exhumation are rare. In this study, we deal with key properties controlling the development of major exhumed strike-slip fault systems, which are equivalent to the deep crustal sections of active across fault zones. We also propose two dominant processes for the initiation of orogen-scale exhumed strike-slip faults: (1) pluton-controlled and (2) metamorphic core complex-controlled strike-slip faults. In these tectonic settings, the initiation of faults occurs by rheological weakening along hot-to-cool contacts and guides the overall displacement and ultimate exhumation. These processes result in a specific thermal and structural architecture of such faults. These types of strike-slip dominated fault zones are often subparallel to mountain ranges and expose a wide variety of mylonitic, cataclastic and non-cohesive fault rocks, which were formed at different structural levels of the crust during various stages of faulting. The high variety of distinctive fault rocks is a potential evidence for recognition of these types of strike-slip faults. Exhumation of mylonitic rocks is, therefore, a common feature of such reverse oblique-slip strike-slip faults, implying major transtensive and/or transpressive processes accompanying pure strike-slip motion during exhumation. Some orogen-scale strike-slip faults nucleate and initiate along rheologically weak zones, e.g. at granite intrusions, zones of low-strength minerals, thermally weakened crust due to ascending fluids, and lateral borders of hot metamorphic core complexes. A further mechanism is the juxtaposition of mechanically strong mantle lithosphere to hot asthenosphere in continental transform faults (e.g., San

  1. 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

  2. Mesozoic fault systems, deformation and fault block rotation in the Andean forearc: a crustal scale strike-slip duplex in the Coastal Cordillera of northern Chile

    NASA Astrophysics Data System (ADS)

    Taylor, G. K.; Grocott, J.; Pope, A.; Randall, D. E.

    1998-12-01

    In this paper we discuss the evolution and tectonic significance of the Mesozoic trench-parallel fault systems which affected the Coastal Cordillera and their relation to magmatism and crustal rotation. The oldest, extensional, fault system separates basement from rift-related Late Triassic and younger sedimentary units. This system [I] subsequently developed into a wider extensional fault system which acted as the locus of magma ascent and emplacement of the Coastal Batholith during much of the Jurassic to earliest Cretaceous period. This extensional fault system defined the forearc sliver during this period and was the consequence of a retreating subduction boundary. During the Early Cretaceous (c. 132-125 Ma) the kinematics of this fault system changed to transtension [II] and accommodated a major component of left-lateral strike-slip motion, the principal fault being the Atacama Fault Zone along which plutons continued to be emplaced. The final phase of pluton emplacement within the Coastal Cordillera appears to be c. 106 Ma, after which this magmatic arc and fault system was abandoned. An Late Cretaceous arc and fault system [III] developed some 20 Ma later and located some 50 km to the east in what is now the Central Valley of northern Chile. This paper seeks to show that the Coastal Cordillera was deformed as a whole by this Late Cretaceous fault system [III] which formed a crustal-scale left-lateral transpressional duplex. During this deformation the thermally weakened crust was dissected into a series of large-scale blocks bounded by NW-trending left-lateral strike-slip faults which merge into a NNE-SSW fault zone which forms the eastern boundary to the duplex. We term this eastern boundary zone the Central Valley Fault Zone (CVFZ) and this together with the NW-trending faults defines the duplex system which we refer to as a whole as the Coastal Cordillera Fault System (CCFS) [III]. We have traced the CCFS duplex between 25°S and 29°S and suspect that it

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

    NASA Astrophysics Data System (ADS)

    Hsieh, Shang Yu; Neubauer, Franz

    2015-04-01

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

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

    NASA Astrophysics Data System (ADS)

    Parsons, Tom; Stein, Ross S.; Simpson, Robert W.; Reasenberg, Paul A.

    1999-09-01

    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 undamped. 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 undamped 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.

  7. 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.

  8. 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.

  9. Synkinematic magmatism, heterogeneous deformation, and progressive strain localization in a strike-slip shear zone: The case of the right-lateral Karakorum fault

    NASA Astrophysics Data System (ADS)

    Boutonnet, Emmanuelle; Leloup, P. H.; Arnaud, N.; Paquette, J.-L.; Davis, W. J.; Hattori, K.

    2012-08-01

    New structural observations coupled with 15 U/Pb and 24 Ar/Ar new ages from the Karakorum shear zone (KSZ) constrain the timing and slip rate of the right-lateral Karakorum fault zone (KFZ), one of the great continental Asian strike-slip faults. In the Tangtse-Darbuk area, the Tangtse (SW) and Muglib (NE) mylonitic strands of the KSZ frame the less deformed Pangong Range. Inherited U/Pb ages show that granitic protoliths are mostly from the Karakorum and Ladakh batoliths, with a major Miocene melting event lasting from ≥21.5 to 13.5 Ma. Some of the Miocene granitic bodies show structural evidence for intrusion synkinematic to the KSZ. The oldest of these granitoids is 18.8 ± 0.4 Ma old, implying that deformation started prior to ˜19 Ma. Microstructural data show that right-lateral deformation pursued during cooling. Ar/Ar data show that ductile deformation stopped earlier in the Tangtse (˜11 Ma) than in the Muglib strand (˜7 Ma). Deformation ended at ˜11 Ma in the Tangtse strand while it is still active in the Muglib strand, suggesting a progressive localization of deformation. When merged with published observations along the KFZ, these data suggest that the KFZ nucleated in the North Ayilari range at least ˜22 Ma ago. The long-term fault rate is 0.84 to 1.3 cm/yr, considering a total offset of 200 to 240 km. The KSZ collected magma produced within the shear zone and/or deeper in crust for which the producing mechanism stays unclear but was not the lower crustal channel flow.

  10. 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.

  11. 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.

  12. 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.

  13. 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.

  14. Stress fields during the evolution of large-scale strike-slip systems and tectonic slivers, Atacama Fault Zone, northern Chile

    NASA Astrophysics Data System (ADS)

    Veloso, E. E.; Gomila, R.

    2009-12-01

    Tectonic evolution of crustal slivers generated during oblique subduction involves a series of translations and rotations. Slivers are defined by large-scale strike-slip faults, whereas internal blocks are by the faulting pattern related to the fault system. Translations and rotations are then likely to accommodate the internal deformation caused by external forces. The Atacama Fault System (AFS), a crustal-scale strike-slip fault in northern Chile, can be divided into three concave, oceanward segments, that show sinestral (Mesozoic) and normal (Cenozoic) displacements. Clockwise rotations of ca. 50° have been suggested for the AFS, mostly for the northernmost segment. The Paposo segment defines a sliver of 160 km long and 25 km wide. In the northern part, it exhibits intense internal faulting, duplexes, single- and multiple-core faults. To determine the stress field responsible for the development and evolution of the sliver, we measured 162 brittle fault planes on which we determined the sense and direction of maximum shear. Fault planes show a main NW-SE trend and subvertical dip-angles (Fig. 1). Brittle kinematic indicators indicate subhorizontal (sinestral) and subvertical (normal) movements. Fault-slip data was processed with the multiple inverse method. Input parameters were k=5 (grouping), e=9 (enhance) and d=1 (dispersion). Calculations show that σ1 axes are distributed on a NW-SE trending great-circle whereas σ3 axes are clustered near the horizontal in NE and SW orientations. Stress ratios average 0.55±0.20. In the horizontal, σ1 axes cover an arc of about 30° and σ3 axes cover about 60° (Fig. 1), suggesting a strike-slip stress field. On the contrary, the subvertical cluster of σ1 axes suggests a normal stress field. These analyses indicate that the Paposo Sliver developed during a period of NW-SE compression and NE-SW tension. The wide distribution of the tensile axes may denote rotation of the internal blocks to accommodate the deformation or

  15. 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

  16. 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.

  17. 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

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

    NASA Astrophysics Data System (ADS)

    Guarnieri, P.

    2012-04-01

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

  19. 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.

  20. Microstructural investigations of principal slip zones in carbonates, examples from shallow crustal strike-slip faults in the Northern Calcareous Alps (Austria)

    NASA Astrophysics Data System (ADS)

    Bauer, Helene; Grasemann, Bernhard; Decker, Kurt

    2014-05-01

    Faults in the upper crust can move episodically by seismic deformation (individual earthquake ruptures) and/or continuously by aseismic creep deformation. In carbonate fault zones, several studies have shown that seismic deformation produces very narrow principal slip zones (cm to mm wide) that accommodate most of the fault displacement during an individual earthquake. Within these principal slip zones, ultracataclasites containing the principal slip surface, fluidization of ultracataclastic sub-layers and clast cortex grains have been proposed to be characteristic for seismic slip. In contrast, pressure solution has been proposed as a mechanism of aseismic sliding along a fault. Spaced cleavage solution planes and associated veins indicate diffusive mass transfer and precipitation in pervasive vein networks. At micro-scale, calcite CPO in fine-grained matrix of principal slip zones has been suggested to result from post-seismic pressure solution creep. Here, we present field data from the Salzchtal-Ennstal-Mariazell-Puchberg (SEMP) fault system (Austria) to interpret the principal slip zones with regard to possible indicators of seismic or aseismic deformation. We investigated exhumed, ancient sinistral strike-slip faults in dolomite and limestone that formed during eastward lateral extrusion of the Eastern Alps during Oligocene to Lower Miocene. The faults belong to a system of convergent strike-slip duplexes that developed at a restraining bend on an eastern segment of the SEMP-fault system. Distinct fault cores contain cataclastic fault rocks differing in textural complexity. Microstructural analysis of cataclastic fault rocks was done using both, optical and electron microscopy. Microstructures reveal several cataclastic types that can be interpreted in terms of different stages of cataclastic evolution. Coarser grained, well cemented cataclasites underlie fine grained ultracataclastic layers. For at least two of the faults, cataclasites containing clast

  1. 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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

  7. 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

  8. Magnetic and magmatic structures of the Emas granodioritic pluton (Cachoeirinha belt, NE Brazil). relationships with Pan-African strike-slip fault systems

    NASA Astrophysics Data System (ADS)

    Olivier, Ph.; Archanjo, C. J.

    1994-01-01

    The Emas granodiorite was intruded during the Brasiliano (Pan-African) orogeny into the metapelites of the Cachoeirinha belt (NE Brazil). This pluton was chosen for a petrofabric study of magmatic emplacement structures using magnetic anisotropy, because of its conspicuous position in the junction area between the large E-W-trending Patos shear zone and the NE-SW-trending Cachoeira da Mina strike-slip fault. The magnetic behavior of this calc-alkaline granite is dominated by paramagnetic minerals which is optimal for the application of the Anisotropy of Magnetic Susceptibility technique used for this study. Almost all microstructures correspond to the magmatic state, so the measured magnetic lineations and foliations may be interpreted, respectively, as directions and planes of magmatic flow. These magnetic/magmatic lineations and foliations are dominantly N-S and NE-SW oriented, and are gently to moderately dipping. The anisotropy of magnetic susceptibility ratios range from 1 to 5.4%, most of these values corresponding to magmatic alignment. The lowest ratios are located chiefly in the centre of the pluton and the highest on the northern and western margins. From these data we propose that the emplacement of the Emas pluton was controlled by a NE-SW-trending left-lateral strike-slip zone, parallel to the Cachoeira da Mina fault, giving rise to openings in the metapelitic country rocks infilled by two succesive magmas. The principal result of this study is the unexpected independence between the emplacement of the Emas pluton and the functioning of the Patos dextral shear zone.

  9. 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

  10. Kinematics of a Strike-Slip Fault Segment at Various Time Scales, Determined From GPS and Geomorphic Measurements: the Example of the Wadi Araba Fault, Dead Sea Transform.

    NASA Astrophysics Data System (ADS)

    Le Beon, M.; Klinger, Y.; Amrat, A.; Agnon, A.; Meriaux, A.; Dorbath, L.; Baer, G.; Finkel, R. C.; Ruegg, J.; Charade, O.; Elias, A.; Mayyas, O.; Ryerson, F. J.; Tapponnier, P.

    2008-12-01

    This work investigates slip rate evolution over time along one large strike-slip fault, the Dead Sea Transform (DST), which is the 1000-km long plate boundary between the Arabia plate and the Sinai sub-plate. We focus on the Wadi Araba fault, the southernmost segment of the DST. No agreement has been reached yet about the slip rate of the DST. Proposed values vary from 2 to 10 mm/yr. Here, we present results from GPS profiles and measurements of offset geomorphologic features, which ages are comprised between 10 ka and ~300 ka. We installed 17 campaign-style GPS sites distributed along three profiles perpendicular to the fault, with far-field points up to 90 km away from the fault. The sites have been measured twice, in 1999 and 2005, during 48h-long sessions. Campaign data are complemented by data from permanent stations in Israel. Using a locked-fault model, we estimate the present-day slip rate to be 4.9 ± 1.4 mm/yr over 6 years. To estimate the slip rate over longer periods of time, we targeted abandoned alluvial fans offset by the fault at four sites. We mapped and sampled these sites for 10Be cosmogenic dating. At one site, best offset of 48 ± 7 m of a surface dated at 12.1 ± 3.6 ka yields a slip rate of 4.6 ± 2 mm/yr, in very good agreement with the present-day slip rate. Moreover, our morphologic analysis at this site invalidates previous study that suggested a value of 10 mm/yr. At a second site, an offset of 137 ± 7 m of a surface younger than ~50 ka provides a minimum slip rate of 2.6 mm/yr and a larger offset of 598 ± 30 of a surface interpreted to be 93.7 ± 35.4 ka old leads to a slip rate of 7.4 ± 3 mm/yr. The offsets determined at the two other sites, where we obtained ages comprised between 50 to ~300 ka, turned out not to be precise enough to bring new constraints on a Middle to Late Pleistocene time scale. Yet, these results are not inconsistent with previous intervals. Although variations in fault slip rate at the time scale of a few ten

  11. 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.

  12. Recent mantle degassing recorded by carbonic spring deposits along sinistral strike-slip faults, south-central Australia

    NASA Astrophysics Data System (ADS)

    Ring, Uwe; Tonguç Uysal, I.; Yüce, Galip; Ünal-İmer, Ezgi; Italiano, Francesco; İmer, Ali; Zhao, Jian-xin

    2016-11-01

    The interior of the Australian continent shows evidence for late Quaternary to Recent fault-controlled mantle 3He and CO2 degassing. A series of interconnected NW-striking sinistral faults, the Norwest fault zone (NFZ), in south-central Australia are associated with travertine mounds, the latter show a regular spacing of 50-70 km. U-series ages on 26 samples range from 354 ± 7 to 1.19 ± 0.02ka (2σ errors) and suggest a clustering every ∼3-4 ka since ∼26 ka. Geochemical data demonstrate a remarkable mantle-to-groundwater connection. Isotopic data indicate that the groundwater is circulating to depths >3 km and interacting with Neoproterozoic/Cambrian basement and mantle volatiles. 3He/4He isotope ratios show that the He comes in part from the mantle. This demonstrates that the NFZ cuts through the entire crust and provides pathways for mantle degassing. Scaling relationships suggest that the series of sinistral faults that make up the NFZ are interconnected at depths and have a significant strike length of 60-70 km or more. The NFZ occurs where a major compositional boundary and a significant heat flow anomaly occurs, and a major step in lithospheric thickness has been mapped. We discuss a tectonic model in which recent stress field, heat flow and lithospheric structure in central Australia reactivated a set of steeply dipping Neoproterozoic faults, which may now be growing into a crustal/lithospheric-scale structure.

  13. 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.

  14. Various paleoseismological records of M~7 earthquakes rupturing strike-slip fault in a semi closed marine basin: examples from the Sea of Marmara

    NASA Astrophysics Data System (ADS)

    Hubert-Ferrari, Aurélia; Drab, Laureen; Schmidt, Sabine; Martinez, Philippe; Carlut, Julie; El Ouahabi, Meriam

    2016-04-01

    The North Anatolian fault (NAF) in the Marmara Sea is a major strike slip fault that ruptures in large magnitude earthquakes. It crosses the Marmara Sea, which borders Istanbul and its 12 million inhabitants. The presented paleoseimological record rests upon sedimentary cores sampling the different basins. The turbidites identified at the different sites are earthquake generated, based on their particular sedimentological and geochemical signatures; the correlation of turbidites at different sites; and the match of the most recent turbidite with a nineteenth century historical earthquake. The studied earthquake induced sedimentary deposits have different origins: (1) classical thick turbidites and homegenites, (2) very thin silt-rich sedimentary layers linked to the settling of the sedimentary cloud induced by the seismic waves, (3) thin turbiditic deposits linked to reworking of sediment veneer covering slopes. In the eastern Cinarcik Basin, an accurate earthquake record was obtained using two cores that were correlated using long-term geochemical variations in the sediment. To date turbidites, we used carbon 14 and paleomagnetic data to build an OxCal model with a local reservoir correction of 400±50 yr. The Çınarcık segment is found to have ruptured in 1509 C.E., sometime in the fourteenth century, in 989 C.E., and in 740 C.E., with a mean recurrence interval in the range of 256-321 years. Finally, we used the earthquake record obtained to review the rupture history of the adjacent segments over the past 1500 years.

  15. 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.

  16. 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.

  17. 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).

  18. 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

  19. The Hills are Alive: Dynamic Ridges and Valleys in a Strike-Slip Environment

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Strike-slip fault zones have long been known for characteristic landforms such as offset and deflected rivers, linear strike-parallel valleys, and shutter ridges. Despite their common presence, questions remain about the mechanics of how these landforms arise or how their form varies as a function of slip rate, geomorphic process, or material properties. We know even less about what happens far from the fault, in drainage basin headwaters, as a result of strike-slip motion. Here we explore the effects of horizontal fault slip rate, bedrock erodibility, and hillslope diffusivity on river catchments that drain across an active strike-slip fault using the CHILD landscape evolution model. Model calculations demonstrate that lateral fault motion induces a permanent state of landscape disequilibrium brought about by fault offset-generated river lengthening alternating with abrupt shortening due to stream capture. This cycle of shifting drainage patterns and base level change continues until fault motion ceases thus creating a perpetual state of transience unique to strike-slip systems. Our models also make the surprising prediction that, in some cases, hillslope ridges oriented perpendicular to the fault migrate laterally in conjunction with fault motion. Ridge migration happens when slip rate is slow enough and/or diffusion and river incision are fast enough that the hillslopes can respond to the disequilibrium brought about by strike-slip motion. In models with faster slip rates, stronger rocks or less-diffusive hillslopes, ridge mobility is limited or arrested despite the fact that the process of river lengthening and capture continues. Fast-slip cases also develop prominent steep fault-facing hillslope facets proximal to the fault valley and along-strike topographic profiles with reduced local relief between ridges and valleys. Our results demonstrate the dynamic nature of strike-slip landscapes that vary systematically with a ratio of bedrock erodibility (K) and

  20. Neotectonics of a subduction/strike-slip transition: the northeastern Dominican Republic

    SciTech Connect

    Winslow, M.A.; McCann, W.R.

    1985-01-01

    The Septentrional fault system in the northeastern Dominican Republic marks the zone where the North American-Carribean plate boundary is evolving from subduction to strike-slip motion, and where terranes appear to be forming and migrating laterally in a subduction complex/forearc region. On the Island of Hispaniola, slip vectors are oblique to the strike of the Puerto Rico trench, and oblique subduction thrusts the upper plate over normal seafloor. The offshore geology and seismicity of the northern Caribbean suggest that uplift, broad crustal warping, thrusting, and strike-slip faulting (ie. collisional tectonics) should be present in the northern part of the Dominican Republic. The high topography (>1000m), high levels of seismicity, and large earthquakes support the hypothesis of contemporary deformation in Hispaniola. In this region, the subduction regime dies out toward the west, and deformation is transferred to onshore, oblique-slip faults. As this change in tectonic style has occurred in Neogene to Recent times, we are investigating the modern evolution of a plate boundary. We have already documented: (1) the presence of a strike-slip faulting in the northeastern Dominican Republic; (2) an anomalous push-up structure; and (3) a region of numerous splay faults. In conclusion, recent seismicity suggest a wide zone of deformation and variations in interplate motions near Hispaniola. This island lies at the western limit of active underthrusting and at the eastern limit of onshore faulting, i.e., at an important transition from a subduction to strike-slip regime.

  1. The nature and origin of off-fault damage surrounding strike-slip fault zones with a wide range of displacements: A field study from the Atacama fault system, northern Chile

    NASA Astrophysics Data System (ADS)

    Mitchell, T. M.; Faulkner, D. R.

    2009-08-01

    Damage surrounding the core of faults is represented by deformation on a range of scales from microfracturing of the rock matrix to macroscopic fracture networks. The spatial distribution and geometric characterization of damage at various scales can help to predict fault growth processes, subsequent mechanics, bulk hydraulic and seismological properties of a fault zone. Within the excellently exposed Atacama fault system, northern Chile, micro- and macroscale fracture densities and orientation surrounding strike-slip faults with well-constrained displacements ranging over nearly 5 orders of magnitude (˜0.12 m-5000 m) have been analyzed. Faults have been studied that cut granodiorite and have been passively exhumed from 6 to 10 km depth. This allows direct comparison of the damage surrounding faults of different displacements. The faults consist of a fault core and associated damage zone. Macrofractures in the damage zone are predominantly shear fractures orientated at high angles to the faults studied. They have a reasonably well-defined exponential decrease with distance from the fault core. Microfractures are a combination of open, healed, partially healed and fluid inclusion planes (FIPs). FIPs are the earliest set of fractures and show an exponential decrease in fracture density with perpendicular distance from the fault core. Later microfractures do not show a clear relationship of microfracture density with perpendicular distance from the fault core. Damage zone widths defined by the density of FIPs scale with fault displacement but appear to reach a maximum at a few km displacement. One fault, where damage was characterized on both sides of the fault core shows no damage asymmetry. All faults appear to have a critical microfracture density at the fault core/damage zone boundary that is independent of displacement. An empirical relationship for microfracture density distribution with displacement is presented. Preferred FIP orientations have a high angle to

  2. 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

  3. 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

  4. Deformation patters above intrusive complexes in strike-slip settings

    NASA Astrophysics Data System (ADS)

    Girard, G.; van Wyk de Vries, B.

    2003-04-01

    Long-lived intrusions below volcanic complexes are weak, ductile zones in the crust. In volcanic areas with strike-slip deformation pull-apart complexes are often associated with volcanoes, especially calderas. The Masaya-Las Sierras volcano in Nicaragua is a basaltic caldera complex situated in a developing pull-apart (Managua Graben). The pull-apart faults are responsible for highly damaging earthquakes (Managua 1931, 68, 72). We raise the hypothesis that pull-apart and caldera intrusive system are interrelated and that joint surveillance of faults and volcano could provide the best monitoring strategy. To test relationships between intrusive complex and tectonics we have run a series of ‘sand-box’ analogue models. Displacement is created by a motor on a basal discontinuity and computer-controlled. The models have a lower ductile crust (silicone layer), an upper brittle crust (sand and plaster), and an intrusion made of silicone or varying density and viscosity. Experiments show that a pull apart always forms around a ductile intrusion, irrespective of its density, however that a non-ductile intrusive complex has no significant influence. Whatever the shape of the intrusion, the fault pattern forms a typical rhombohedral pull-apart shape. Fault patterns spaying out from the models resemble closely the Managua fault pattern. With large displacements two zones of thrusting were observed in the system. Such deformation is not present at Masaya, but may be at other calderas with more active strike-slip activity. We provide one possible example in the Atacama, N Chile.

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

    USGS Publications Warehouse

    Johnson, Samuel Y.; Watt, Janet T.

    2012-01-01

    Earthquake hazard assessments should incorporate a minimum rupture length of 110 km based on continuity of the Hosgri fault zone through this area. Lateral slip rates may vary along the fault (both to the north and south) as different structures converge and diverge but are probably in the geodetically estimated range of 2–4 mm/yr.

  6. No evidence for shallow shear motion on the Mat Fault, a prominent strike slip fault in the Indo-Burmese wedge

    NASA Astrophysics Data System (ADS)

    Tiwari, R. P.; Gahalaut, V. K.; Rao, Ch U. B.; Lalsawta, C.; Kundu, B.; Malsawmtluanga

    2015-07-01

    The motion between India and Sunda plates is accommodated along the Churachandpur Mao Fault (CMF) in the Indo-Burmese Wedge (IBW) and Sagaing Fault in the Myanmar region. Within the IBW, the Mat Fault is the most prominent transverse structure with prominent topographic and geomorphic expressions. We undertook Global Positioning System (GPS) measurements across this fault to investigate the current deformation across it. Modelling of these observations using locking depth of up to 4 km yields no resolvable slip (dextral slip rate as 0 ±5 mm/year) across the fault. Due to limited spatial extent of the GPS measurements, it is not possible to comment on the status of deeper slip, if any.

  7. 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.

  8. Radiometric and kinematic evidence for Middle Jurassic strike-slip faulting in southern Mexico related to the opening of the Gulf of Mexico

    NASA Astrophysics Data System (ADS)

    Alaniz-Alvarez, Susana A.; van der Heyden, Peter; Nieto Samaniego, Angel F.; Ortega-Gutiérrez, Fernando

    1996-05-01

    One of the least-known aspects of the evolution of the Gulf of Mexico is the nature and location of shear zones along which the relevant continental fragments were displaced. The Sierra de Juárez mylonitic complex, located in southern Mexico, is a polyorogenic north-northwest trending structure. Here we report U-Pb mylonitization dates of 165 ± 20 Ma for igneous zircon from the syntectonic San Felipe granite, and an integrated 40Ar/39Ar age of 169.3 ± 1.7 Ma from synkinematic muscovite, both of which indicate a Middle Jurassic age for the strike-slip event along the Sierra de Juárez mylonitic complex. This event therefore occurred during the opening of the Gulf of Mexico, and we propose that the shear zone was kinematically related to the southeast displacement of the Yucatan block.

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

    USGS Publications Warehouse

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

    2011-01-01

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

  10. Weak ductile shear zone beneath a major strike-slip fault: Inferences from earthquake cycle model constrained by geodetic observations of the western North Anatolian Fault Zone

    NASA Astrophysics Data System (ADS)

    Yamasaki, Tadashi; Wright, Tim J.; Houseman, Gregory A.

    2014-04-01

    GPS data before and after the 1999 İzmit/Düzce earthquakes on the North Anatolian Fault Zone (Turkey) reveal a preseismic strain localization within about 25 km of the fault and a rapid postseismic transient. Using 3-D finite element calculations of the earthquake cycle in an idealized model of the crust, comprising elastic above Maxwell viscoelastic layers, we show that spatially varying viscosity in the crust can explain these observations. Depth-dependent viscosity without lateral variations can reproduce some of the observations but cannot explain the proximity to the fault of maximum postseismic velocities. A localized weak zone beneath the faulted elastic lid satisfactorily explains the observations if the weak zone extends down to midcrustal depths, and the ratio of relaxation time to earthquake repeat time ranges from ~0.005 to ~0.01 (for weak-zone widths of ~24 and 40 km, respectively) in the weakened domain and greater than ~1.0 elsewhere, corresponding to viscosities of ~1018 ± 0.3 Pa s and greater than ~1020 Pa s. Models with sharp weak-zone boundaries fit the data better than those with a smooth viscosity increase away from the fault, implying that the weak zone may be bounded by a relatively abrupt change in material properties. Such a change might result from lithological contrast, grain size reduction, fabric development, or water content, in addition to any effects from shear heating. Our models also imply that viscosities inferred from postseismic studies primarily reflect the rheology of the weak zone and should not be used to infer the mechanical properties of normal crust.

  11. Global Morphological Mapping of Strike-Slip Structures on Ganymede

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Many inferences of strike-slip faulting and distributed shear zones on Ganymede suggest that strike-slip tectonism 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 multifaceted surface, we identify and map key examples of strike-slip morphologies (en echelon structures, strike-slip duplexes, laterally offset pre-existing features, and possible strained craters) from Galileo and Voyager images. Here we present the current state of these global mapping efforts, with particular emphasis given to complex structures associated with grooved terrain (e.g. Nun Sulci) and terrains transitional from dark to light terrain (e.g. the boundary between Nippur Sulcus and Marius Regio). These results are being synthesized into a global database representing an inferred sense of shear for fractures on Ganymede. This, combined with existing observations of extensional features, is helping to narrow down the range of possible principal stress directions that could have acted at the regional or global scale to produce grooved terrain. Moreover, these data sets, combined with mechanical models of shear failure and global stress sources, are providing constraints for testing possible mechanisms for grooved terrain formation on Ganymede.

  12. 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

  13. 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.

    2014-12-01

    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

  14. 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

  15. Spatial slip behavior of large strike-slip fault belts: Implications for the Holocene slip rates of the eastern termination of the North Anatolian Fault, Turkey

    NASA Astrophysics Data System (ADS)

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

    2015-12-01

    We present new data on Holocene slip rates for the eastern end of the North Anatolian Fault (NAF) by using the optically stimulated luminescence ages of the offset terrace deposits at two sites, where a total of four displaced landforms was studied. Each offset feature was analyzed independently, and three different assumptions were made for all the offsets, depending on whether the age of the upper tread (upper tread reconstruction), the lower tread (lower tread reconstruction), or all bounding surfaces (intermediate solution) were used in dating of the terrace risers. The deflected geometry of the risers strongly suggests the use of either the intermediate solution or the upper tread reconstruction. The joint slip rate distributions for the upper tread reconstructions and the intermediate solutions were modeled as 13.0 + 1.8 / -1.4 and 14.3 + 5.8 / -2.4 mm/yr (2σ), respectively. Although the intermediate solution covers the full range of ages for the measured displacements, the curved geometry of the terrace risers suggests that the initiations of the riser offsets are most probably close to the abandonment ages of the upper terrace treads. Therefore, we accepted the joint slip rate of the intermediate solution but suggested that the average rate for the main displacement zone of the eastern NAF should be close to its lower limits. This slower rate with respect to previous estimates suggests that the total deformation is not only accommodated on the main displacement zone but is also distributed along the secondary faults to the south of the easternmost segments of the NAF.

  16. 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.

  17. 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

    Structural inheritance plays a fundamental role during crustal deformation because pre-existing fault and shear zones typically provide weakness zone suitable to fail again when affected by a new regional stress field. Re-activation of structural inheritance is expected to unavoidably increase the complexity of structural architectures, whose geometric and kinematic patterns can significantly deviate from what expected in newly deformed crustal sectors. Availability of templates from analogue models can provide a very effective tool to help unraveling such a structural complexity. For this purpose, we simulated the reworking of a set of basement hosted pre-existing fault zones at strike-slip restraining fault bends. In the models, the mechanical stratigraphy consists of a basement, made of a mixture of dry kaolin and sand to slightly increase cohesion, and a sedimentary cover made by pure dry sand. Inherited fault zones are confined to the basement and coated by a thin veneer of silicone putty. In the experimental programme, the geometry of the left-lateral restraining bend is maintained the same, with a bending angle of 30° of the restraining fault segment. The strike of the inherited fault zones, measured counterclockwise with respect to that of the master strike-slip fault zone outside the restraining bend, was 0°, 30°, and 60° in different experiments, respectively. An end member experiment without inheritance was also run for comparison. Our experimental results show that the angle that the inherited fault zones make with the restraining bend plays a fundamental role in governing the deformation pattern. When structural inheritance is near parallel to the master strike-slip fault zone, synthetic shears form and severely compartmentalize the transpressional pop-up anticline growing on top of the restraining bend. Fault-bounded blocks undergo sinistral escape during transpression. On the other hand, when structural inheritance makes a high angle to the

  18. 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.

  19. 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

  20. 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.

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

    USGS Publications Warehouse

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

    2007-01-01

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

  2. Structural deformation and evolution of right-lateral strike-slip tectonics of the Liaohe western depression during the early Cenozoic

    NASA Astrophysics Data System (ADS)

    Li, Zhigang; Jia, Dong; Chen, Wei; Zhang, Yikun; Wang, Maomao; Li, Yiquan; Li, Haibin; Li, Shiqin; Zhou, Xiaojun; Wu, Long; Zhang, Meng; Shen, Li; Sun, Chuang; Jin, Ke

    2013-11-01

    The Tan-Lu fault zone (TLFZ) traverses the Liaohe western depression (LHWD), affords an exceptional opportunity to reveal the structural deformation and evolution of a major strike-slip fault of the LHWD using three dimensional seismic data and well data. In this paper, based on structural interpretations of the 3-D seismic data of the LHWD, combined with depth slice and seismic coherency, a variety of structural features in relation to right-lateral strike-slip fault (the western branch of the Tan-Lu fault) have been revealed presence in the depression, such as thrust faults (Xinlongtai, Taian-Dawa, and Chenjia faults), structural wedges, positive flower structures, and en echelon normal faults. Fault cutoffs, growth strata and the Neogene unconformity developed in the LHWD verify that the activity of right-lateral strike-slip from the late Eocene to Neogene (ca. 43-23 Ma). The study indicates that the right-lateral strike-slip played an important role in controlling the structural deformation and evolution of the LHWD in the early Cenozoic. Moreover, the front structural wedge generated the gross morphology of the Xinlongtai anticline and developed the Lengdong faulted anticline during the late Eocene, and the back structural wedge refolded the Lengdong faulted anticline zone in the late Eocene to the early Oligocene. Wrench-related structures (the Chenjia thrust fault and the en echelon normal faults) were developed during the late Oligocene. Uniform subsidence in the Neogene to Quaternary. Furthermore, the driving force of the right-lateral strike-slip deformation was originated from N-S extension stress related to the opening of the Japan Sea and NE-SW compression, as the far-field effect of India-Eurasia convergence.

  3. 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.

  4. 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

  5. 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.

  6. 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.

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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

  12. 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

  13. Magma storage in a strike-slip caldera.

    PubMed

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

    2016-07-22

    Silicic calderas form during explosive volcanic eruptions when magma withdrawal triggers collapse along bounding faults. The nature of specific interactions between magmatism and tectonism in caldera-forming systems is, however, unclear. Regional stress patterns may control the location and geometry of magma reservoirs, which in turn may control the spatial and temporal development of faults. Here we provide new insight into strike-slip volcano-tectonic relations by analysing Bouguer gravity data from Ilopango caldera, El Salvador, which has a long history of catastrophic explosive eruptions. The observed low gravity beneath the caldera is aligned along the principal horizontal stress orientations of the El Salvador Fault Zone. Data inversion shows that the causative low-density structure extends to ca. 6 km depth, which we interpret as a shallow plumbing system comprising a fractured hydrothermal reservoir overlying a magmatic reservoir with vol% exsolved vapour. Fault-controlled localization of magma constrains potential vent locations for future eruptions.

  14. 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

  15. 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.

  16. 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.

  17. Dextral strike-slip tectonism and arc processes in the Sierra Nevada and Idaho batholiths

    NASA Astrophysics Data System (ADS)

    Tikoff, B.; Byerly, A.; Gaschnig, R. M.; Vervoort, J. D.; Kelso, P. R.

    2014-12-01

    Both the Sierra Nevada (CA) and Idaho batholiths display clear evidence for magmatism simultaneous with dextral strike-slip movement during the Cretaceous. There is, however, a significant difference between both the style and the timing of the deformation and magmatism in these two magmatic arcs. The Sierra Nevada displays dextral strike-slip tectonism active from 92-80 Ma, as evidenced by a series of dextral shear zones associated with the axis of active magmatism. The concept of the plutons intruding en echelon pull-apart structures in a dextral system has been supported by the recognition of widespread, syn-tectonic shear zones along the axis of the arc. Further, a modern analog can be found in El Salvador, where dextral translation of the forearc has resulted in en echelon dextral shearing in a magmatic arc dominated by arc-perpendicular normal faulting. In contrast, dextral tectonism in Idaho both starts (~103 Ma) and ceases earlier (~90 Ma) than strike-slip motion in the Sierra Nevada batholith. Further, the deformation is better developed, as recorded by the ~5 km thick, dextral transpressional western Idaho shear zone (WISZ). The WISZ deformation affects I-type magmas that are not typically considered part of the Idaho batholith. The main phase of the 85-70 Ma, peraluminous Idaho batholith (Atlanta lobe) only contains local evidence for dextral shearing, such as the NS-oriented Johnson Creek-Profile Gap shear zone. The reasons for this along-strike variation in deformation for Cretaceous magmatic arcs in North America may relate to the collisional and translation histories of offshore terranes.

  18. Finite Element Stress Model of a Strike-Slip Duplex: A Case Study from Southern Chile

    NASA Astrophysics Data System (ADS)

    Iturrieta, P. C.; Hurtado, D.; Cembrano, J. M.; Valderrama, C.; Stanton-Yonge, A.

    2015-12-01

    The Liquiñe-Ofqui Fault System (LOFS) is spatially and genetically related to seismic activity, volcanic hazard and hydrothermal resources in southern Chile. The LOFS is a regional-scale shear zone, which accommodates part of the oblique component of the convergence vector. In the LOFS southern end, an extensional strike-slip duplex arises from the connection between two NNE-striking master faults, where two damaging earthquakes (6.1-6.2 Mw) occurred in 2007. In order to understand the nature and origin of the stress field within the duplex area, we calculate the ellipticity of the stress tensor field by means of a 3D finite element model. The model represents the brittle-plastic transition in the mid crust, within which the fault zone is mechanically distinguished from the host rock in a continuum fashion. The fault zone is modeled by using an elastic-plastic constitutive relation, which is built on the basis of a range of width and orientation of mylonitic bands, representing the fault zone as seen in the field. Boundary conditions reproduce the convergence velocity between Nazca and South-America plates. Results are broadly consistent with structural data and seismicity recorded in the region. Extensional-to-transtensional stress regimes match spatially with a seismic swarm recorded in the region in 2007, and with the spatial distribution of quaternary volcanic centers. The model also shows a transpressive state of stress in the western branch of the LOFS, whereas in the eastern branch, pure strike-slip is obtained. We propose that the current duplex kinematics can be explained by convergence obliquity, duplex geometry and the occurrence of plastic deformation, which are sufficient enough to deliver the current stress configuration. Sources of discrepancy between structural data and model results might be explained by other factors not considered by the model, such as the timing of deformation or the current activity of blind faults.

  19. 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.

  20. 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.

  1. Subduction-to-Strike-Slip-Transition in the Southeastern Caribbean Imaged Using Deeply-Penetrating Seismic Reflection Lines and Tomography

    NASA Astrophysics Data System (ADS)

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

    2010-12-01

    The subduction-to-strike-slip transition (SSST) zone of the southeastern Caribbean is one of thirty identified locations where active subduction and strike-slip tectonic styles transition along strongly curved and seismogenic plate boundaries. This SSST zone provides a field laboratory for understanding how sedimentary basins, faults, basement areas and subducted slabs change from an area of dominantly westward-directed subduction beneath the Lesser Antilles arc to an area of dominantly east-west strike-slip faulting along northern South America. We use two geophysical data types to image the lithosphere and study the relationships between lithospheric scale deformation and basin scale response to the transitional tectonic configuration. Interpretation of deeply-penetrating seismic reflection lines recorded down to 16 seconds two-way time, or depths of about 18 km, is combined with tomographic slices of the upper mantle and lower crust which were constructed using the coda method on ~ 700 earthquakes in the depth range of 70-250 km. Results from the tomographic study are compared with nine seismogenic zones in the southeast Caribbean SSST zone which are defined based on the depth, and focal mechanism of earthquake events. These zones include: (1) the Paria slab tear region; (2) Caribbean/South American strike-slip zone; (3) Hinge area separating continental margin in Trinidad from Tobago forearc basin; (4) Central Range -strike-slip fault zone, onshore Trinidad; (5) Underthrust zone of South American beneath southern onshore and offshore eastern Trinidad, including the prolific hydrocarbon-bearing Columbus Basin; (6) Venezuela foreland and fold-thrust belt; (7) flexural bulge area of oceanic crust located east of Barbados accretionary prism (BAP); (8) Subducted slab beneath the stabilized and supracomplex zones of the BAP; (9) Inner accretionary prism of the BAP. Primary controls on the seismogenic character of each curving tectonic belt include the strike of the

  2. 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

  3. Complicated rupture process of the Mw 7.0 intraslab strike-slip earthquake in the Tohoku region on 10 July 2011 revealed by near-field pressure records

    NASA Astrophysics Data System (ADS)

    Kubota, Tatsuya; Hino, Ryota; Inazu, Daisuke; Ito, Yoshihiro; Iinuma, Takeshi

    2015-11-01

    We examined fault models of the Tohoku strike-slip intraslab earthquake (Mw 7.0) on 10 July 2011 using near-field tsunami data. After constraining the strike and location of the fault from tsunami source distribution, we investigated fault models assuming simple rupture of one fault, and simultaneous rupture of two conjugate faults. The estimated single fault reached >30 km down into the slab from the plate interface, suggesting bending stress enhancement after the 2011 Tohoku-Oki earthquake, but the depth extent was inconsistent with the aftershock activity. The model involving conjugate faults extended ~20 km below the slab surface and was more consistent with the aftershocks. We concluded that it is more plausible that this earthquake involved two conjugate strike-slip faults, and the enhancement of the downdip extensional stress after Tohoku-Oki earthquake was not large enough to allow rupture to propagate deeply into the slab beneath the landward slope of the Japan Trench.

  4. 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.

  5. Neotectonics in the foothills of the southernmost central Andes (37°-38°S): Evidence of strike-slip displacement along the Antiñir-Copahue fault zone

    NASA Astrophysics Data System (ADS)

    Folguera, AndréS.; Ramos, VíCtor A.; Hermanns, Reginald L.; Naranjo, José

    2004-10-01

    The Antiñir-Copahue fault zone (ACFZ) is the eastern orogenic front of the Andes between 38° and 37°S. It is formed by an east vergent fan of high-angle dextral transpressive and transtensive faults, which invert a Paleogene intra-arc rift system in an out of sequence order with respect to the Cretaceous to Miocene fold and thrust belt. 3.1-1.7 Ma volcanic rocks are folded and fractured through this belt, and recent indicators of fault activity in unconsolidated deposits suggest an ongoing deformation. In spite of the absence of substantial shallow seismicity associated with the orogenic front, neotectonic studies show the existence of active faults in the present mountain front. The low shallow seismicity could be linked to the high volumes of retroarc-derived volcanic rocks erupted through this fault system during Pliocene and Quaternary times. This thermally weakened basement accommodates the strain of the Antiñir-Copahue fault zone, absorbing the present convergence between the South America and Nazca plates.

  6. 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.

  7. 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

  8. Packaged Fault Model for Geometric Segmentation of Active Faults Into Earthquake Source Faults

    NASA Astrophysics Data System (ADS)

    Nakata, T.; Kumamoto, T.

    2004-12-01

    In Japan, the empirical formula proposed by Matsuda (1975) mainly based on the length of the historical surface fault ruptures and magnitude, is generally applied to estimate the size of future earthquakes from the extent of existing active faults for seismic hazard assessment. Therefore validity of the active fault length and defining individual segment boundaries where propagating ruptures terminate are essential and crucial to the reliability for the accurate assessments. It is, however, not likely for us to clearly identify the behavioral earthquake segments from observation of surface faulting during the historical period, because most of the active faults have longer recurrence intervals than 1000 years in Japan. Besides uncertainties of the datasets obtained mainly from fault trenching studies are quite large for fault grouping/segmentation. This is why new methods or criteria should be applied for active fault grouping/segmentation, and one of the candidates may be geometric criterion of active faults. Matsuda (1990) used _gfive kilometer_h as a critical distance for grouping and separation of neighboring active faults. On the other hand, Nakata and Goto (1998) proposed the geometric criteria such as (1) branching features of active fault traces and (2) characteristic pattern of vertical-slip distribution along the fault traces as tools to predict rupture length of future earthquakes. The branching during the fault rupture propagation is regarded as an effective energy dissipation process and could result in final rupture termination. With respect to the characteristic pattern of vertical-slip distribution, especially with strike-slip components, the up-thrown sides along the faults are, in general, located on the fault blocks in the direction of relative strike-slip. Applying these new geometric criteria to the high-resolution active fault distribution maps, the fault grouping/segmentation could be more practically conducted. We tested this model

  9. 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

  10. The M8.1 Intraplate, Strike-Slip Macquarie Earthquake of 23 December 2004

    NASA Astrophysics Data System (ADS)

    Murphy, K.; Abercrombie, R. E.; Antolik, M.; Yamada, T.

    2006-12-01

    The M8.1, strike-slip earthquake on 23 December 2004 was ~150 km from the Macquarie Ridge plate boundary. This large intraplate earthquake provides an opportunity to investigate both the source processes of oceanic strike-slip earthquakes, which are controversial and poorly known, and to constrain the tectonics of the complex region surrounding the Macquarie Ridge. We model teleseismic P and SH waves from 29 stations using a point source moment tensor inversion. Our preferred model has two subevents, both strike-slip with strike and dip within about 15 degrees of one another; the first is tightly constrained by the first motions. The sources overlap by 17 s and have a combined duration of ~50 s. The centroid depths are 30 -- 35 km. There is no evidence for directivity in the waveforms, so our result is consistent with bilateral rupture along a slightly curved or bent fault. The lack of directivity means that we cannot unambiguously identify the fault plane. We prefer the NNW-SSE plane as it aligns with the aftershocks and the fossil transform faults in the region. We are performing a slip inversion to constrain further the fault plane and slip distribution. The apparent stress of the earthquake is ~5 MPa, higher than continental strike-slip earthquakes, but similar to previous intraplate oceanic earthquakes, e.g. 1998 M8.1 Antarctica. The stress drop (based on the 200 km aftershock extent, and the depth of 35 km) is ~3 MPa, consistent with previous oceanic and also continental strike-slip earthquakes. The tectonics of the region around the Macquarie Ridge are poorly known. Cande and Stock (2004) proposed that the SE part of the Australian plate is actually a separate plate (the Macquarie plate) separated by a diffuse plate boundary. Their model predicts NNE-SSW extension in the region of the 2004 M8.1 earthquake, which is at the northerly extent of a group of previous, smaller, earthquakes. They all have T axis orientations that fit this plate model. The age of the

  11. 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.

  12. Strike-slip earthquakes can also be detected in the ionosphere

    NASA Astrophysics Data System (ADS)

    Astafyeva, Elvira; Rolland, Lucie M.; Sladen, Anthony

    2014-11-01

    It is generally assumed that co-seismic ionospheric disturbances are generated by large vertical static displacements of the ground during an earthquake. Consequently, it is expected that co-seismic ionospheric disturbances are only observable after earthquakes with a significant dip-slip component. Therefore, earthquakes dominated by strike-slip motion, i.e. with very little vertical co-seismic component, are not expected to generate ionospheric perturbations. In this work, we use total electron content (TEC) measurements from ground-based GNSS-receivers to study ionospheric response to six recent largest strike-slip earthquakes: the Mw7.8 Kunlun earthquake of 14 November 2001, the Mw8.1 Macquarie earthquake of 23 December 2004, the Sumatra earthquake doublet, Mw8.6 and Mw8.2, of 11 April 2012, the Mw7.7 Balochistan earthquake of 24 September 2013 and the Mw 7.7 Scotia Sea earthquake of 17 November 2013. We show that large strike-slip earthquakes generate large ionospheric perturbations of amplitude comparable with those induced by dip-slip earthquakes of equivalent magnitude. We consider that in the absence of significant vertical static co-seismic displacements of the ground, other seismological parameters (primarily the magnitude of co-seismic horizontal displacements, seismic fault dimensions, seismic slip) may contribute in generation of large-amplitude ionospheric perturbations.

  13. Influence of the Convergence and Stepover Angles in the Structural Style of Strike-Slip Systems: Analogue Models

    NASA Astrophysics Data System (ADS)

    Gonzalez, D.; Pinto, L.

    2008-12-01

    The presented results of analogue models analyze the influence of the relation between the convergence angle and the stepover angle on strike-slip systems. The experiments include 2 stepovers arrays to generate both transpressional and transtensional zones. These experiments were prepared using 5 cm thick sandpack (sand diameter <500 μm, internal friction angle 30°, density 1,400 kg/m3) to simulate brittle deformation; the base of the model was formed by thin zinc base plates, one of them mobile, cut in such a way so as to produce restraining and releasing strike-slip stepovers; the rate convergence was constant. We carried out 3 series of experiments in which the convergence angles (0°-60°) and stepover angles (30°-60°) were varied systematically. Preliminary results indicate that by increasing the angle between the stepover and the convergence vector: a) the restraining area generated a positive flower structure that is progressively wider; b) progressively more reverse faults which absorb more shortening were generated. Locally, strike-slip faults in the positive flowers were accommodated by the geometry of the stepover base. Areas most complex involved the development of normal faults, which subsequently were inverted. In conclusion, the relation between the convergence and stepover angles is a main factor that determines the structural style of flowers structures on strike-slip systems. This work was done through the ACT-18 PBCT project.

  14. Tracing the Geomorphic Signature of Lateral Faulting

    NASA Astrophysics Data System (ADS)

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

    2012-12-01

    Active strike-slip faults are among the most dangerous geologic features on Earth. Unfortunately, it is challenging to estimate their slip rates, seismic hazard, and evolution over a range of timescales. An under-exploited tool in strike-slip fault characterization is quantitative analysis of the geomorphic response to lateral fault motion to extract tectonic information directly from the landscape. Past geomorphic work of this kind has focused almost exclusively on vertical motion, despite the ubiquity of horizontal motion in crustal deformation and mountain building. We seek to address this problem by investigating the landscape response to strike-slip faulting in two ways: 1) examining the geomorphology of the Marlborough Fault System (MFS), a suite of parallel strike-slip faults within the actively deforming South Island of New Zealand, and 2) conducting controlled experiments in strike-slip landscape evolution using the CHILD landscape evolution model. The MFS offers an excellent natural experiment site because fault initiation ages and cumulative displacements decrease from north to south, whereas slip rates increase over four fold across a region underlain by a single bedrock unit (Torlesse Greywacke). Comparison of planform and longitudinal profiles of rivers draining the MFS reveals strong disequilibrium within tributaries that drain to active fault strands, and suggests that river capture related to fault activity may be a regular process in strike-slip fault zones. Simple model experiments support this view. Model calculations that include horizontal motion as well as vertical uplift demonstrate river lengthening and shortening due to stream capture in response to shutter ridges sliding in front of stream outlets. These results suggest that systematic variability in fluvial knickpoint location, drainage area, and incision rates along different faults or fault segments may be expected in catchments upstream of strike-slip faults and could act as useful

  15. 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.

  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 and extrusion tectonics of the Greater Caucasus-Kopetdagh region

    NASA Astrophysics Data System (ADS)

    Kopp, M. L.

    2012-04-01

    In the Paleogene-Early Miocene, the areas of the modern Greater Caucasus and Kopetdagh were occupied by marginal seas (parts of the Paratethys intracontinental sea) inheriting the Cretaceous back-arc basins. In the Early Miocene, a collisional compression of the seas began at the time when the Arabian plate detached from Africa to move northward. The compression proceeded in a good accordance with the Arabia movement that was manifested in a general synchroneity of the Late Alpine orogenies in the Caucasus and Kopetdagh with the rifting and spreading phases in the Aden Gulf and the Red Sea. The earliest orogeny was the Styrian one of the terminal Early Miocene. It corresponds to the initial stage of the rift opening and was mostly pronounced in the east, in Kopetdagh and East Iran, where a recent structure has been formed by the initial Middle Miocene. In the Greater Caucasus, the Styrian deformations occurred in its central part only (i.e., in front of the Arabian plate northern tip) where the main Caucasian thrusts and conjugate asymmetrical megaanticline of the Central Caucasus were formed. An essential feature of the earliest, Styrian, structure of the whole Caucasus-Kopetdagh region was a series of regional right-lateral strike-slip faults. In the Kopetdagh, the strike-slips have no submeridional but northwestern direction although they occurred in the northern continuation of the submeridional right-lateral strike-slip faults framing the Lut block. In the Caucasus, they became even sublatitudinal, in parallel with the North Anatolian fault, thus constituting a single domain with the latter. So, the right-lateral strike-slip faults of East Iran, Kopetdagh, and the Caucasus compose an extensive arc convex to the north and appeared probably as a result of the right-lateral shear caused by the known counterclockwise rotation of the Arabian lithospheric plate. The Middle Miocene was characterized by a tectonic pause both in the Red Sea-Aden rift system and in the

  18. 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

  19. Central Asia Active Fault Database

    NASA Astrophysics Data System (ADS)

    Mohadjer, Solmaz; Ehlers, Todd A.; Kakar, Najibullah

    2014-05-01

    The ongoing collision of the Indian subcontinent with Asia controls active tectonics and seismicity in Central Asia. This motion is accommodated by faults that have historically caused devastating earthquakes and continue to pose serious threats to the population at risk. Despite international and regional efforts to assess seismic hazards in Central Asia, little attention has been given to development of a comprehensive database for active faults in the region. To address this issue and to better understand the distribution and level of seismic hazard in Central Asia, we are developing a publically available database for active faults of Central Asia (including but not limited to Afghanistan, Tajikistan, Kyrgyzstan, northern Pakistan and western China) using ArcGIS. The database is designed to allow users to store, map and query important fault parameters such as fault location, displacement history, rate of movement, and other data relevant to seismic hazard studies including fault trench locations, geochronology constraints, and seismic studies. Data sources integrated into the database include previously published maps and scientific investigations as well as strain rate measurements and historic and recent seismicity. In addition, high resolution Quickbird, Spot, and Aster imagery are used for selected features to locate and measure offset of landforms associated with Quaternary faulting. These features are individually digitized and linked to attribute tables that provide a description for each feature. Preliminary observations include inconsistent and sometimes inaccurate information for faults documented in different studies. For example, the Darvaz-Karakul fault which roughly defines the western margin of the Pamir, has been mapped with differences in location of up to 12 kilometers. The sense of motion for this fault ranges from unknown to thrust and strike-slip in three different studies despite documented left-lateral displacements of Holocene and late

  20. 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.

  1. Strike-slip tectonics, related basin formation, and sedimentology in zones of continental escape: Turkey as a case study

    SciTech Connect

    Sengor, A.M.C.; Gorur, N.

    1984-04-01

    Since the Tortonian (11 Ma), the tectonics of Turkey has been dominated by its escape westward from the east Anatolian collision zone onto the oceanic lithosphere of the eastern Mediterranean, mainly along the north and east Anatolian transform faults (NAT and EAT), and at least two other southeast-concave strike-slip faults that branch off the NAT near Erzincan and Resadiye. The Aegean graben system is a broad shear zone between the latter of these and the Grecian shear zone. At triple junctions involving the NAT/EAT and EAT/Dead Sea transform fault, space problems arise, giving rise to the Karliova and Adana/Cilicia basins, respectively. In Thrace, where the NAT takes a southwesterly bend, part of the resulting constraint is released by rifting in a northwest orientation that formed the Ergene basin. In addition, various pull-apart structures and leaky strike-slip faults contribute to the richness of strike-slip-related negative structures in Turkey. Some of these are of lithospheric dimensions and contain thousands of meters of sediment, whereas others formed within thinner crustal flakes above decollement horizons. Because escape tectonics necessarily involves subduction, arc-related strike-slip deformation may interfere with that indigenous to collision tectonics, as in south Turkey. Continental convergence eventually eliminates all subductable areas along the collision front and the structures generated by escape regimes may fall prey to compressional obliteration. In zones of complex and multiple continental collision such as Turkey, several episodes of escape tectonics may alternate with intracontinental compressional deformation, whereby the products of the older escape regimes would be very difficult to recognize. The present tectonics of Turkey constitutes an excellent guide to earlier episodes of escape tectonics in and around Turkey.

  2. 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

  3. Stress history controls the spatial pattern of aftershocks: case studies from strike-slip earthquakes

    NASA Astrophysics Data System (ADS)

    Utkucu, Murat; Durmuş, Hatice; Nalbant, Süleyman

    2016-09-01

    Earthquake ruptures perturb stress within the surrounding crustal volume and as it is widely accepted now these stress perturbations strongly correlates with the following seismicity. Here we have documented five cases of the mainshock-aftershock sequences generated by the strike-slip faults from different tectonic environments of world in order to demonstrate that the stress changes resulting from large preceding earthquakes decades before effect spatial distribution of the aftershocks of the current mainshocks. The studied mainshock-aftershock sequences are the 15 October 1979 Imperial Valley earthquake (Mw = 6.4) in southern California, the 27 November 1979 Khuli-Boniabad (Mw = 7.1), the 10 May 1997 Qa'enat (Mw = 7.2) and the 31 March 2006 Silakhor (Mw = 6.1) earthquakes in Iran and the 13 March 1992 Erzincan earthquake (Mw = 6.7) in Turkey. In the literature, we have been able to find only these mainshocks that are mainly characterized by dense and strong aftershock activities along and beyond the one end of their ruptures while rare aftershock occurrences with relatively lower magnitude reported for the other end of their ruptures. It is shown that the stress changes resulted from earlier mainshock(s) that are close in both time and space might be the reason behind the observed aftershock patterns. The largest aftershocks of the mainshocks studied tend to occur inside the stress-increased lobes that were also stressed by the background earthquakes and not to occur inside the stress-increased lobes that fall into the stress shadow of the background earthquakes. We suggest that the stress shadows of the previous mainshocks may persist in the crust for decades to suppress aftershock distribution of the current mainshocks. Considering active researches about use of the Coulomb stress change maps as a practical tool to forecast spatial distribution of the upcoming aftershocks for earthquake risk mitigation purposes in near-real time, it is further suggested that

  4. 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.

  5. 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.

  6. Viscoelastic shear zone model of a strike-slip earthquake cycle

    USGS Publications Warehouse

    Pollitz, F.F.

    2001-01-01

    I examine the behavior of a two-dimensional (2-D) strike-slip fault system embedded in a 1-D elastic layer (schizosphere) overlying a uniform viscoelastic half-space (plastosphere) and within the boundaries of a finite width shear zone. The viscoelastic coupling model of Savage and Prescott [1978] considers the viscoelastic response of this system, in the absence of the shear zone boundaries, to an earthquake occurring within the upper elastic layer, steady slip beneath a prescribed depth, and the superposition of the responses of multiple earthquakes with characteristic slip occurring at regular intervals. So formulated, the viscoelastic coupling model predicts that sufficiently long after initiation of the system, (1) average fault-parallel velocity at any point is the average slip rate of that side of the fault and (2) far-field velocities equal the same constant rate. Because of the sensitivity to the mechanical properties of the schizosphere-plastosphere system (i.e., elastic layer thickness, plastosphere viscosity), this model has been used to infer such properties from measurements of interseismic velocity. Such inferences exploit the predicted behavior at a known time within the earthquake cycle. By modifying the viscoelastic coupling model to satisfy the additional constraint that the absolute velocity at prescribed shear zone boundaries is constant, I find that even though the time-averaged behavior remains the same, the spatiotemporal pattern of surface deformation (particularly its temporal variation within an earthquake cycle) is markedly different from that predicted by the conventional viscoelastic coupling model. These differences are magnified as plastosphere viscosity is reduced or as the recurrence interval of periodic earthquakes is lengthened. Application to the interseismic velocity field along the Mojave section of the San Andreas fault suggests that the region behaves mechanically like a ???600-km-wide shear zone accommodating 50 mm/yr fault

  7. 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

  8. 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.

  9. 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.

  10. 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.

    2016-10-01

    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.

  11. 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.

  12. 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.

  13. Further Investigation into the Seismic Nucleation Phase of Large Earthquakes with a Focus on Strike-Slip Events

    NASA Astrophysics Data System (ADS)

    Burkhart, E.; Ji, C.

    2012-12-01

    The dynamic motion of an earthquake begins abruptly, but is often initiated by a small interval of weak motion called the seismic nucleation phase (SNP), first named by Ellsworth and Beroza (1995). In their study, Ellsworth and Beroza (1995, 1996) concluded that the SNP was detectable in near-source records of all of the 41 M 1 to M 8 earthquakes they investigated, with the SNP accounting for ~0.5% of the total moment and lasting ~1/6 of the total duration. Concentrating on large earthquakes, Ji et al (2010) investigated the SNP of 19 M 8.0 earthquakes since 1994 using a new approach applied to teleseismic broadband data. They found that ~50% of the earthquakes had a detectable SNP. Burkhart and Ji (2011) found that, in 68 M 7.5 to M 8.0 since 1994, the SNP is clearly detectable in 31 events, with 27 events showing no nucleation phase and 10 having too much noise or not enough stations to tell. After making modifications to the stacking code allowing for more specific station choice, these earthquakes have all been re-examined, and a consistent finding is that strike-slip earthquakes are more likely to exhibit a clear SNP than normal or thrust earthquakes. Continuing to investigate these events, this study finds further conclusive evidence that large shallow, continental, and strike-slip earthquakes show a clear SNP. We find that 11 of the 15 strike-slip earthquakes investigated show a clear SNP, with three having none (including the 2002 Mw 7.8 Denali Fault earthquake, which initiated as a thrust subevent), and one with not enough stations to perform stacking.

  14. 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

    2016-10-01

    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

  15. 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.

  16. Triggering of tsunamigenic aftershocks from large strike-slip earthquakes: Analysis of the November 2000 New Ireland earthquake sequence

    NASA Astrophysics Data System (ADS)

    Geist, Eric L.; Parsons, Tom

    2005-10-01

    The November 2000 New Ireland earthquake sequence started with a Mw = 8.0 left-lateral main shock on 16 November and was followed by a series of aftershocks with primarily thrust mechanisms. The earthquake sequence was associated with a locally damaging tsunami on the islands of New Ireland and nearby New Britain, Bougainville, and Buka. Results from numerical tsunami-propagation models of the main shock and two of the largest thrust aftershocks (Mw > 7.0) indicate that the largest tsunami was caused by an aftershock located near the southeastern termination of the main shock, off the southern tip of New Ireland (Aftershock 1). Numerical modeling and tide gauge records at regional and far-field distances indicate that the main shock also generated tsunami waves. Large horizontal displacements associated with the main shock in regions of steep bathymetry accentuated tsunami generation for this event. Most of the damage on Bougainville and Buka Islands was caused by focusing and amplification of tsunami energy from a ridge wave between the source region and these islands. Modeling of changes in the Coulomb failure stress field caused by the main shock indicate that Aftershock 1 was likely triggered by static stress changes, provided the fault was on or synthetic to the New Britain interplate thrust as specified by the Harvard CMT mechanism. For other possible focal mechanisms of Aftershock 1 and the regional occurrence of thrust aftershocks in general, evidence for static stress change triggering is not as clear. Other triggering mechanisms such as changes in dynamic stress may also have been important. The 2000 New Ireland earthquake sequence provides evidence that tsunamis caused by thrust aftershocks can be triggered by large strike-slip earthquakes. Similar tectonic regimes that include offshore accommodation structures near large strike-slip faults are found in southern California, the Sea of Marmara, Turkey, along the Queen Charlotte fault in British Columbia

  17. The Maritsa strike-slip shear zone between Kostenets and Krichim towns, South Bulgaria — Structural, petrographic and isotope geochronology study

    NASA Astrophysics Data System (ADS)

    Naydenov, Kalin; Peytcheva, Irena; von Quadt, Albrecht; Sarov, Stoyan; Kolcheva, Krastina; Dimov, Dimo

    2013-06-01

    The present study describes the characteristics of the Maritsa Shear Zone (MSZ), a major tectonic element in the Balkanides in South Central Bulgaria. Metamorphic rocks of four lithotectonic units — Madan, Chepinska, Asenitsa and Thrace units crop out in the study area. Strike-slip ductile deformation in MSZ affects the Thrace Lithotectonic Unit (TLU) for up to 15 km. The stratigraphy of this unit is divided in two: Parvenets succession and variegated succession. U-Pb zircon dating reveals Late Jurassic protolith age for metagranitoids and metagabbros of the variegated succession. For its metasedimentary part Triassic to Upper Jurassic age is suggested based on the strontium isotope signature of the marbles. The Parvenets succession affiliates to the Variscan metamorphic basement of Europe. The metamorphic evolution of the zone is subdivided into synmetamorphic strike-slip deformations and annealing stages. The ductile shearing occurred in greenschist to lower amphibolite facies between 130 Ma (discordant U-Pb ages) and 82-78 Ma (late-syntectonic granites). This stage is connected with the oblique collision of the Rhodope Late Jurassic arc with the European platform. With the docking of the arc and the triggering of the strike-slip movements, MSZ represents an orogen-scale border between the Rhodope south-vergent thrust complex and the north-vergent deformations in the Srednogorie and Sakar-Strandzha zones. During the Late Cretaceous MSZ is the contact between the Srednogorie magmatic arc (part of the Apuseni-Banat-Timok-Srednogorie Belt) and the Rhodopean metamorphic core complexes. NW-SE dextral faulting characterized the brittle tectonics along the zone. Strike-slip faults of the southern border of the TLU are transferred into reverse faults, along which the TLU overthrusted Oligocene sediments. MSZ is an orogen-scale transpressional shear zone and an important border in the structure of the Balkanides. This multidisciplinary research emphasizes its role as a

  18. Active Tectonics along the Carboneras Fault (SE Iberian Margin): Onshore-Offshore Paleoseismological Approach

    NASA Astrophysics Data System (ADS)

    Moreno, X.; Masana, E.; Gràcia, E.; Pallàs, R.; Santanach, P.; Dañobeitia, J. J.; Party, I.

    2006-12-01

    The southern margin of the Iberian Peninsula hosts the convergent boundary between the European and African Plates. At the eastern Betic Cordillera, the Neogene and Quaternary shortening has mainly been absorbed by left-lateral strike-slip faults, which in the Iberian Peninsula is represented by the Eastern Betics Shear Zone (EBSZ). One of the longest structures in the EBSZ is the Carboneras Fault, with almost 50 km onshore and more than 100 km offshore. The low record seismicity along its trace, suggest either non seismic behaviour or long recurrence intervals (104 years). The aim of this work is an integrated onshore-offshore neotectonic and paleoseismological study of the Carboneras Fault Zone to characterize its seismic potential. The onshore study was made through regional geological and geomorphological analysis, geophysical prospecting, microtopography, trenching, and dating (14 C, U/Th, TL). Onshore macro and microstructures as beheaded and offset alluvial fans and S-C microstructures in the fault zone reveals a Quaternary left-lateral strike-slip motion combined with a vertical component along the fault. Trenching reveals this fault is seismogenic, with at least four late Quaternary events. The oldest occurred between 54.9 and 32.2 ka BP, the second one between 40.9 and 27.1 ka BP, and the two most recent events occurred between 30.8 and 0.875 ka BP. The thickness of the colluvial wedges suggest a Mw=7 for the first and Mw=6.6 for the second event. The mean recurrence rate is 14 ka, and the minimum elapsed time is 875 years. The offshore portion, studied by high-resolution marine geophysical methods, shows very similar strike-slip structures. The marine paleoseismic data will be integrated with the onland results in order to accurately determine the recent activity and seismic parameters of the entire Carboneras Fault.

  19. 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).

  20. Fault Rock Variation as a Function of Host Rock Lithology

    NASA Astrophysics Data System (ADS)

    Fagereng, A.; Diener, J.

    2013-12-01

    Fault rocks contain an integrated record of the slip history of a fault, and thereby reflect the deformation processes associated with fault slip. Within the Aus Granulite Terrane, Namibia, a number of Jurassic to Cretaceous age strike-slip faults cross-cut Precambrian high grade metamorphic rocks. These strike-slip faults were active at subgreenschist conditions and occur in a variety of host rock lithologies. Where the host rock contains significant amounts of hydrous minerals, representing granulites that have undergone retrogressive metamorphism, the fault rock is dominated by hydrothermal breccias. In anhydrous, foliated rocks interlayered with minor layers containing hydrous phyllosilicates, the fault rock is a cataclasite partially cemented by jasper and quartz. Where the host rock is an isotropic granitic rock the fault rock is predominantly a fine grained black fault rock. Cataclasites and breccias show evidence for multiple deformation events, whereas the fine grained black fault rocks appear to only record a single slip increment. The strike-slip faults observed all formed in the same general orientation and at a similar time, and it is unlikely that regional stress, strain rate, pressure and temperature varied between the different faults. We therefore conclude that the type of fault rock here depended on the host rock lithology, and that lithology alone accounts for why some faults developed a hydrothermal breccia, some cataclasite, and some a fine grained black fault rock. Consequently, based on the assumption that fault rocks reflect specific slip styles, lithology was also the main control on different fault slip styles in this area at the time of strike-slip fault activity. Whereas fine grained black fault rock is inferred to represent high stress events, hydrothermal breccia is rather related to events involving fluid pressure in excess of the least stress. Jasper-bearing cataclasites may represent faults that experienced dynamic weakening as seen

  1. 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

  2. Strike-Slip Tectonics in Northwestern Ireland? Evidence From the 2012 January Seismic Sequence in Co. Donegal, Ireland

    NASA Astrophysics Data System (ADS)

    Lebedev, S.; Agius, M. R.; Schaeffer, A. J.; Horan, C.; Piccinini, D.; Piana Agostinetti, N.

    2012-12-01

    main shock which suggests strike-slip faulting along a near-vertical fault-plane that strikes from north-northeast to south-southwest. This observation is in agreement with previously inferred regional stress and may be related to compression induced by the Mid-Ocean Ridge. We discuss the implications of the new data for the current stress field and tectonics of the British Isles and northeastern Atlantic margins.

  3. Active faulting and tectonics of the Ningxia-Hui Autonomous Region, China

    NASA Astrophysics Data System (ADS)

    Qidong, Deng; Sung, Fengmin; Zhu, Shilong; Li, Mengluan; Wang, Tielin; Zhang, Weiqi; Burchfiel, B. C.; Molnar, Peter; Zhang, Peizhen

    1984-06-01

    Strike-slip, thrust, and normal faulting all seem to play an active role in the tectonics of Ningxia. In the southernmost part of the region a major left-lateral strike-slip fault enters the region from the neighboring Gansu province to the west and trends about S65°E. This fault is very clear on Landsat imagery and on aerial photos, and the portion in eastern Gansu and Ningxia broke in the Haiyuan earthquake of December 16, 1920. Displacements of 5-10 m caused by that earthquake are clear in numerous localities and accord with a revised value of the seismic moment of 1.2×1021N m. The eastern end of the Haiyuan fault terminates in a narrow south trending fold and thrust zone. Several other similar, north to northwest trending fold and thrust belts are present in the area about 50-200 km northeast of the Haiyuan fault and divide it into small, apparently relatively undeformed blocks 10-40 km in dimensions. The geometry of the structures in the fold and thrust zones and the apparently shallow depths at the time of deformation suggest that current deformation is similar to that that occurred in the fold and thrust belt of the Idaho-Wyoming Rocky Mountains. North of this area, both the Helan Shan (a horst) and the Yinchuan graben are bounded by clear, active northerly trending normal faults, in some cases with right-lateral strike-slip components. The overall deformation, hence, seems to include dominant components of east-west left-lateral strike-slip movement, northeast-southwest crustal shortening, and northwest-southeast extension. We interpret the extension as a response to a northeast directed force applied to the Ordos block and both this northeast directed force and the left-lateral slip on the Haiyuan fault to the eastward displacement of material on the northeast edge of the Tibetan plateau with respect to Eurasia north of it.

  4. Sinistral strike-slip dominated inclined transpression along the Pai-Khoi fold-and-thrust belt, Russian Arctic

    NASA Astrophysics Data System (ADS)

    Curtis, Michael

    2014-05-01

    The Arctic Uralides comprise Pai-Khoi, Novaya Zemlya and the Taimyr Peninsula. Together they form a margin controlled salient in the former Baltica margin of Laurussia. This arcuate orogen forms a fundamental tectonic boundary between major hydrocarbon provinces; Timan-Pechora and Barents Sea to the southwest and west, respectively, and the South Kara Sea to the east. To understand the complex regional tectonic relationship between the Arctic Uralides and the South Kara Sea, it is essential to establish the structural and kinematic style of the various sectors of this remote orogen. This contribution focuses on the southern limb of the salient, the NW-SE trending, Pai-Khoi fold-and-thrust belt (PKFB), which links the Polar Urals with Novaya Zemlya approximately 600 km to the northwest. The PKFB comprises a highly deformed, Late Cambrian to Mississippian age, passive margin succession, with allochthonous deep-water and continental slope facies rocks thrust over a shallow-water carbonate platform succession along the Main Pai-Khoi Thrust. Deformation is interpreted to have occurred between the Late Palaeozoic and end Triassic resulting in the formation of an apparent southwesterly verging fold-and-thrust belt with an associated foreland basin. Analysis of regional scale geological maps reveals the presence of large scale en-echelon folds, together with late stage, orogen-parallel faults, indicating that the evolution of PKFB has been influenced by a component of sinistral strike-slip. Detailed field data from a transect across the largest structure in the orogen, the Main Pai-Khoi Thrust, confirms the obliquity of both planar structures and finite stretching lineations to this major allochthon bounding thrust. Subtle but consistent variations in the orientation of finite stretching directions within zones of qualitatively differing finite strain were identified. Comparison of these variations with theoretical models of inclined transpression suggests that deformation

  5. Strain localization across main continental strike-slip shear zones

    NASA Astrophysics Data System (ADS)

    Boutonnet, E.; Leloup, P.; Rozel, A.

    2011-12-01

    across the 8 km-large shear zone. The local strain rates measured inside the two mylonitic strands of the fault zone are higher than the reference value (6.7 x10-14 s-1 to 11.3 x10-14 s-1). Contrary to that, the local strain rates measured in the exhumed core of the shear zone where deformation is weak are lower than de reference value (6.5 x10-15 s-1). We made 1-D numerical models of the Ksz with the Tangtse (India) region geometry, in order to understand the causes of the strain localization. We calculated the temperature and the strain rates profiles across the 8-km width shear zone during shearing. Two main parameters were tested: (1) the heat created by shear heating and advected by granites emplacement, and (2) the rheology contrast in a heterogeneous crust. The first conclusions are that deformation localized in zones where the rocks are less viscous, and that granites emplacement does not modify the local strain rates for a long-standing.

  6. Variations in the geometry and amount of slip on the Haiyuan (Nanxihaushan) fault zone, China and the surface rupture of the 1920 Haiyuan earthquake

    NASA Astrophysics Data System (ADS)

    Qidong, Deng; Shefa, Chen; Fangnin, Song; Shilong, Zhu; Yipeng, Wang; Weiqi, Zhang; Decheng, Jiao; Burchfiel, B. C.; Molnar, P.; Royden, L.; Peizhen, Zhang

    The Haiyuan earthquake (M = 8.7) of December 16, 1920, in China caused strike-slip displacement along 220 km of the Haiyuan (or Nanxihaushan) Fault Zone, which lies on the northeastern margin of the Qinghai-Xizang (Tibetan) plateau. The Haiyuan fault zone, which strikes 285°-295°, apparently became an active sinistral strike-slip during Pleistocene time. The fault zone is composed of at least eight major subparallel shear fractures, most of which are arranged in a left-stepping pattern, and as many as six pull-apart basins have formed in the central segment of the fault zone. River systems of different ages have been sinistrally offset different amounts. Variations in the sense of vertical motion have occurred along segments of the fault, and pull-apart basins are commonly associated with the areas where normal components on subparallel segments prevail. Relatively young faults with oblique normal slip strike parallel to the overall trend of the fault zone and intersect the major subparallel shear faults with acute angles (10 to 15°). The earthquake fault of 1920 caused slip along the major strike-slip fault segments and along oblique normal faults within pull-apart basins. Thus segments with pure strike-slip and with oblique normal slip, were activated in 1920, each with different surficial features and with different amounts of slip.

  7. 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.

  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. Neotectonics of the Western Nepal Fault System: Implications for Himalayan strain partitioning

    NASA Astrophysics Data System (ADS)

    Silver, Calvin R. P.; Murphy, Michael A.; Taylor, Michael H.; Gosse, John; Baltz, Thomas

    2015-12-01

    Oblique convergence at the Himalayan margin is hypothesized to be partitioned by orogen-normal thrusting and orogen-parallel strike-slip faulting. We conducted field mapping and remote sensing in the Dhaulagiri Range of Nepal, and the results reveal an active regional fault system termed the Western Nepal Fault System (WNFS). Right and normally offset Quaternary deposits and brittly deformed bedrock demarcate dextral slip along two strike-slip faults striking N40-50°W linked via an extensional right step over striking N10-20°E. The strike-slip attitudes subparallel bedrock foliation, while the step over cuts at a high angle (~70°). Fault slip data along the strike-slip segments trend N70°W with minor dip component, top to north. Fault slip data and observed kinematics along the WNFS support our interpretation that the WNFS formed via arc-parallel stress. On the basis of geometry, kinematics, and structural position we correlate the WNFS to active faults between the Karakoram and Bari Gad faults. This suggests an ~350 km long dextral fault system extending obliquely across the Western Nepal Himalaya which appears to intersect the Main Frontal Thrust (MFT) near 83°30'E, coinciding with a large gradient in the arc-parallel component of GPS velocities. We interpret the WNFS to represent a class of orogen-parallel strike-slip faults working with subduction to accommodate obliquely convergent plate motion. Our observations support the hypothesis that the region lying between the MFT and the WNFS is a continental version of a fore-arc sliver bounded at its base by the Main Himalayan Thrust.

  10. The Lawanopo Fault, central Sulawesi, East Indonesia

    NASA Astrophysics Data System (ADS)

    Natawidjaja, Danny Hilman; Daryono, Mudrik R.

    2015-04-01

    The dominant tectonic-force factor in the Sulawesi Island is the westward Bangga-Sula microplate tectonic intrusion, driven by the 12 mm/year westward motion of the Pacific Plate relative to Eurasia. This tectonic intrusion are accommodated by a series of major left-lateral strike-slip fault zones including Sorong Fault, Sula-Sorong Fault, Matano Fault, Palukoro Fault, and Lawanopo Fault zones. The Lawanopo fault has been considered as an active left-lateral strike-slip fault. The natural exposures of the Lawanopo Fault are clear, marked by the breaks and liniemants of topography along the fault line, and also it serves as a tectonic boundary between the different rock assemblages. Inpections of IFSAR 5m-grid DEM and field checks show that the fault traces are visible by lineaments of topographical slope breaks, linear ridges and stream valleys, ridge neckings, and they are also associated with hydrothermal deposits and hot springs. These are characteristics of young fault, so their morphological expressions can be seen still. However, fault scarps and other morpho-tectonic features appear to have been diffused by erosions and young sediment depositions. No fresh fault scarps, stream deflections or offsets, or any influences of fault movements on recent landscapes are observed associated with fault traces. Hence, the faults do not show any evidence of recent activity. This is consistent with lack of seismicity on the fault.

  11. 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

  12. 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

  13. 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.

  14. 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.

  15. Upper Pleistocene - Holocene activity of the Carrascoy Fault (Murcia, SE Spain): preliminary results from paleoseismological research.

    NASA Astrophysics Data System (ADS)

    Martin-Banda, Raquel; Garcia-Mayordomo, Julian; Insua-Arevalo, Juan M.; Salazar, Angel; Rodriguez-Escudero, Emilio; Alvarez-Gomez, Jose A.; Martinez-Diaz, Jose J.; Herrero, Maria J.; Medialdea, Alicia

    2014-05-01

    The Carrascoy Fault is located in the Internal Zones of the Betic Cordillera (Southern Spain). In particular, the Carrascoy Fault is one of the major faults forming the Eastern Betic Shear Zone, the main structure accommodating the convergence between Nubian and Eurasian plates in the westernmost Mediterranean. So far, the Carrascoy Fault has been defined as a left-lateral strike-slip fault. It extends for at least 31 km in a NE-SW trend from the village of Zeneta (Murcia) at its northeastern tip, to the Cañaricos village, controlling the northern edge of the Carrascoy Range and its linkage to the Guadalentin Depression towards the southwest. This is an area of moderate seismic activity, but densely populated, the capital of the region, Murcia, being settled very close to the fault. Hence, the knowledge of the structure and kinematics of the Carrascoy Fault is essential for assessing reliably the seismic hazard of the region. We present a detailed-scale geological and geomorphological map along the fault zone created from a LIDAR DEM combined with fieldwork, and geological and geophysical information. Furthermore, a number of trenches have been dug across the fault at different locations providing insights in the fault most recent activity as well as paleoseismic data. Preliminary results suggest that the Cararscoy Fault has recently changed its kinematic showing a near pure reverse motion. According to this, the fault can be divided into two distinct segments, the eastern one: Zeneta - Fuensanta, and the western one: Fuensanta - Cañaricos, each one having its own characteristic style and geodynamics. Some new active strands of the fault locate at the foot of the very first relief towards the North of the older strand, forming the current southern border of the Guadalentin Depression. These new faults show an increasingly reverse component westwards, so that the Fuensanta - Cañaricos segment is constituted by thrusts, which are blind at its western end

  16. Structural Evidence for Fault Reactivation: the Active Priene-Sazli Fault Zone, Söke-Milet Basin, Western Anatolia

    NASA Astrophysics Data System (ADS)

    Sümer, Ö.; Inci, U.; Sözbilir, H.; Uzel, B.

    2009-04-01

    Western Anatolia is located at tha eastern part of the Aegean region that forms one of the most seismically active and rapidly extending regions in the world. One of the most prominent structural component of the Western Anatolia is E-W trending grabens. One of them is the Büyük Menderes Graben (BMG) showing a major change in strike ranging from E-W to NE-SW in its western end. This NE-SW oriented part of the graben is known as the Söke-Milet basin (SMB). The depression is 35 km long and 16 km wide. NW border of the basin is characterized by a morphotectonic structure namely Priene-Sazlı fault zone (PSFZ). The 16 July 1955 Söke-Balat earthquake (M=6.8) was atributed to this fault (Eyidogan and Jackson, 1985; Sengör, 1987; Altunel, 1998). However, field based kinematic studies on the PSFZ are lacking except for Gürer et. al. (2001). In this paper, we studied several reactivated fault segments of the PSFZ that are repeatedly formed under changing stress fields in order to evaluate the kinematic and stress history of the region by using structural relationships between striations and fault-plane related structures. The PSFZ consists of 5 fault segments which are en échelon arranged on the basis of mapping geological structures. The northern segments that strikes NE in the north and bends into an approximately E-W direction around Doganbey to the SW. Each segment is identified as steep opographic scarps ranging in height from a few meters to several hundred meters. Fault segments become to linkage and show breaching of the relay ramps between them. We interpret that such fault patterns have been formed in a region where extension has reactivated on pre-existing structures in an oblique sense. Evidence for this is the presence of three sets of striations each with different orientations on the same slip surface of the studied fault segments. Here, two differently oriented strike-slip slickenlines are postdated by dip-slip striations. Based on our structural

  17. 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

  18. Active tectonics of the Seattle fault and central Puget sound, Washington - Implications for earthquake hazards

    USGS Publications Warehouse

    Johnson, S.Y.; Dadisman, S.V.; Childs, J. R.; Stanley, W.D.

    1999-01-01

    We use an extensive network of marine high-resolution and conventional industry seismic-reflection data to constrain the location, shallow structure, and displacement rates of the Seattle fault zone and crosscutting high-angle faults in the Puget Lowland of western Washington. Analysis of seismic profiles extending 50 km across the Puget Lowland from Lake Washington to Hood Canal indicates that the west-trending Seattle fault comprises a broad (4-6 km) zone of three or more south-dipping reverse faults. Quaternary sediment has been folded and faulted along all faults in the zone but is clearly most pronounced along fault A, the northernmost fault, which forms the boundary between the Seattle uplift and Seattle basin. Analysis of growth strata deposited across fault A indicate minimum Quaternary slip rates of about 0.6 mm/yr. Slip rates across the entire zone are estimated to be 0.7-1.1 mm/yr. The Seattle fault is cut into two main segments by an active, north-trending, high-angle, strike-slip fault zone with cumulative dextral displacement of about 2.4 km. Faults in this zone truncate and warp reflections in Tertiary and Quaternary strata and locally coincide with bathymetric lineaments. Cumulative slip rates on these faults may exceed 0.2 mm/yr. Assuming no other crosscutting faults, this north-trending fault zone divides the Seattle fault into 30-40-km-long western and eastern segments. Although this geometry could limit the area ruptured in some Seattle fault earthquakes, a large event ca. A.D. 900 appears to have involved both segments. Regional seismic-hazard assessments must (1) incorporate new information on fault length, geometry, and displacement rates on the Seattle fault, and (2) consider the hazard presented by the previously unrecognized, north-trending fault zone.

  19. Characterization of Appalachian faults

    SciTech Connect

    Hatcher, R.D. Jr.; Odom, A.L.; Engelder, T.; Dunn, D.E.; Wise, D.U.; Geiser, P.A.; Schamel, S.; Kish, S.A.

    1988-02-01

    This study presents a classification/characterization of Appalachian faults. Characterization factors include timing of movement relative to folding, metamorphism, and plutonism; tectonic position in the orogen; relations to existing anisotropies in the rock masses; involvement of particular rock units and their ages, as well as the standard Andersonian distinctions. Categories include faults with demonstrable Cenozoic activity, wildflysch-associated thrusts, foreland bedding-plane thrusts, premetamorphic to synmetamorphic thrusts in medium- to high-grade terranes, postmetamorphic thrusts in medium- to high-grade terranes, thrusts rooted in Precambrian basement, reverse faults, strike-slip faults, normal (block) faults, compound faults, structural lineaments, faults associated with local centers of disturbance, and geomorphic (nontectonic) faults.

  20. 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.

  1. Ductile duplexing at a bend of a continental-scale strike-slip shear zone: example from NE Brazil

    NASA Astrophysics Data System (ADS)

    Corsini, Michel; Vauchez, Alain; Caby, Renaud

    1996-04-01

    During the Pan-African orogeny, the Borborema Province in NE Brazil developed a continental-scale shear-zone system that comprises NE- and EW-trending ductile strike-slip shear zones. Remote sensing and structural mapping has revealed a pattern of arcuate anastomosing strike-slip shear zones separating sigmoidal lenses of less deformed material, located at the western end of the EW-trending Patos shear zone, which is one of the largest shear zones of the Province. This structure of imbricate shear zones was initiated under high-temperature deformation conditions. It is interpreted as a ductile strike-slip duplex and may represent a kinematic pattern for strain accommodation in response to a bend of a ductile mega-shear zone.

  2. Strain localization across main continental strike-slip shear zones : a multi-methods approach for the case of the Karakorum shear zone

    NASA Astrophysics Data System (ADS)

    Boutonnet, E.; Leloup, P. H.; Rozel, A.; Arnaud, N.; Paquette, J. L.

    2012-04-01

    Whether deformation within the deep continental crust is fundamentally concentrated in narrow shear zones or distributed in wide zones stays a major controversy of the earth sciences. This is in part because direct measurements of ductile shear or strain rate are difficult, especially when deformation is intense, as it is the case in ductile shear zones. The Pangong range (India) is an 8km-wide shear zone, corresponding to the exhumed root of the central Karakorum fault zone (KFZ), one of the great continental strike-slip faults of the India-Asia collision zone. Ductile deformation is most intense in the Tangtse and Muglib mylonitic strands, which bracket the shear zone to the SW and NE, respectively. The relationships between dykes emplacement ages (U/Pb dating) and deformation indicate that deformation was not synchronous across the shear zone. Ar/Ar dating document that cooling was diachronic across strike and ductile deformation (~ 300°C) stopped earlier in the SW than in the NE. Deformation thus appears to have migrated / localized from the whole shear zone to the Muglib strand, the only locus showing evidence for brittle deformation and active faulting. We compared the strain rates measured at different spatial scales: (1) a global scale investigated by the geological fault rate estimation and (2) a local scale, investigated with the QSR (Quartz strain rate metry) method. The total offset (200-240 km) and the KFZ life span (18 to 25 Ma) yield an average fault rate of 1.1 ±0.2 cm/yr. this corresponds to a global shear rate of 4.4 x10-14 s-1, assuming an homogenous deformation in space and time within a 8 km wide shear zone. Five quartz samples provided deformation temperatures between 348 and 428°C and corresponding paleo-stresses between 24 and 65 MPa. The local strain rates measured within the two mylonitic strands of the fault zone (> 1 x10-13 s-1), are higher than those measured outside of these strands (≤ 1 x10-14 s-1), where deformation is weaker

  3. Tectonic geomorphology and neotectonics of the Kyaukkyan Fault, Myanmar

    NASA Astrophysics Data System (ADS)

    Crosetto, Silvia; Watkinson, Ian; Gori, Stefano; Falcucci, Emanuela; Min, Soe

    2016-04-01

    The Kyaukkyan Fault is a dextral strike-slip fault, part of a complex zone of active dextral transpression that absorbs most of the northward motion of India relative to Sundaland. While much of the strike-slip displacement is localised in western Myanmar and along the prominent Sagaing Fault, significant dextral shear also occurs across the Kyaukkyan Fault, on the Shan Plateau in the east. The largest recorded earthquake in Myanmar occurred on the Kyaukkyan Fault in 1912, near Maymyo (Mw 7.7), but the fault has generated little significant seismicity since then. Despite its demonstrated seismic potential and remarkable topographic expression, the fault's neotectonic history remains poorly known. Interpretation of ≤30 m Landsat TM/ETM+ images, together with field investigations, reveals deformation features developed along the Kyaukkyan Fault system, mostly indicative of Quaternary dextral strike-slip faulting. Well-marked fault scarps and valleys locate the fault especially in its northernmost and southernmost part; geomorphic features related with Kyaukkyan Fault activity are sag ponds, shutter ridges, offset and beheaded streams, triangular facets and low-sinuosity mountain fronts. Geomorphic markers of young fault activity such as offset and deformed alluvial fans, wind-gaps were also identified during field observation. The fault's central section is characterised by a complex pull-apart system, whose normal border faults show signals of relatively slow neotectonic activity. In the central part of the basin, deformation of Quaternary sediments by a locally-buried cross-basin fault system includes dip-slip faulting, where subsidence adjacent to linear ridges is suggested by notably active mountain fronts, dextral strike-slip faulting and local transpression. Although no direct evidence of a 1912 surface rupture has been detected, the fresh geomorphic expression of the cross-basin fault system indicates that it is likely to have been the focus of that event

  4. Determining the Through-Going Active Fault Geometry of the Western North Anatolian Fault Through Stress Modeling

    NASA Astrophysics Data System (ADS)

    Karimi, B.; McQuarrie, N.

    2015-12-01

    The North Anatolian Fault (NAF) is a seismically active 1200 km long dextral strike-slip fault part of an east-west trending dextral shear zone (NAF system) between the Anatolian and Eurasian plates. This shear zone widens to the west, complicating potential earthquake rupture paths and highlighting the importance of understanding the geometry of active fault systems. West of the town of Bolu - the NAF bifurcates into the northern and southern strands, which converge and are linked through the Mudurnu Valley, then diverge to border the Marmara Sea. The westward continuation of these two fault traces is marked by further complexities in potential active fault geometry, particularly in the Marmara Sea (northern strand), and the Biga Peninsula (southern strand). We evaluate potential active fault geometries for both strands by comparing stress models of various fault geometries in these regions to a record of focal mechanisms and inferred paleostress from a lineament analysis. For the Marmara region, two of the three possible geometries matched the maximum horizontal stress (σH) orientations determined from a record of focal mechanisms; however, only one represented the northern and southern sidewalls associated with the principal zone of deformation of the developing Marmara basin. This suggests that it is the most likely representation of the active through-going fault geometry in the region. In the Biga Peninsula region, the active geometry of the southern strand has the southern component approaching and intersecting the northern component through a linking feature in a narrow topographic valley. This geometry was selected over two others as it overlaps the σH orientation determined from focal mechanism data and a lineament analysis. Additionally, this geometry does not develop a prominent mis-oriented NE-SW stress feature observed in the model results of the other two geometries, otherwise absent in the focal mechanism data or inferred from a lineament analysis.

  5. Contradicting Estimates of Location, Geometry, and Rupture History of Highly Active Faults in Central Japan

    NASA Astrophysics Data System (ADS)

    Okumura, K.

    2011-12-01

    Accurate location and geometry of seismic sources are critical to estimate strong ground motion. Complete and precise rupture history is also critical to estimate the probability of the future events. In order to better forecast future earthquakes and to reduce seismic hazards, we should consider over all options and choose the most likely parameter. Multiple options for logic trees are acceptable only after thorough examination of contradicting estimates and should not be a result from easy compromise or epoche. In the process of preparation and revisions of Japanese probabilistic and deterministic earthquake hazard maps by Headquarters for Earthquake Research Promotion since 1996, many decisions were made to select plausible parameters, but many contradicting estimates have been left without thorough examinations. There are several highly-active faults in central Japan such as Itoigawa-Shizuoka Tectonic Line active fault system (ISTL), West Nagano Basin fault system (WNBF), Inadani fault system (INFS), and Atera fault system (ATFS). The highest slip rate and the shortest recurrence interval are respectively ~1 cm/yr and 500 to 800 years, and estimated maximum magnitude is 7.5 to 8.5. Those faults are very hazardous because almost entire population and industries are located above the fault within tectonic depressions. As to the fault location, most uncertainties arises from interpretation of geomorphic features. Geomorphological interpretation without geological and structural insight often leads to wrong mapping. Though non-existent longer fault may be a safer estimate, incorrectness harm reliability of the forecast. Also this does not greatly affect strong motion estimates, but misleading to surface displacement issues. Fault geometry, on the other hand, is very important to estimate intensity distribution. For the middle portion of the ISTL, fast-moving left-lateral strike-slip up to 1 cm/yr is obvious. Recent seismicity possibly induced by 2011 Tohoku

  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. Left-lateral active deformation along the Mosha-North Tehran fault system (Iran): Morphotectonics and paleoseismological investigations

    NASA Astrophysics Data System (ADS)

    Solaymani Azad, Shahryar; Ritz, Jean-François; Abbassi, Mohammad Reza

    2011-01-01

    The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip-slip thrusting movements. The recent faulting mainly occurs on new traces trending E-W to ENE-WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike-slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike-slip motion is transferred along the ENE-WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.

  8. Transform fault earthquakes in the North Atlantic: Source mechanisms and depth of faulting

    NASA Technical Reports Server (NTRS)

    Bergman, Eric A.; Solomon, Sean C.

    1987-01-01

    The centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern Mid-Atlantic Ridge were determined from an inversion of long-period body waveforms. The earthquakes occurred on the Gibbs, Oceanographer, Hayes, Kane, 15 deg 20 min, and Vema transforms. The depth extent of faulting during each earthquake was estimated from the centroid depth and the fault width. The source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes; slip vector azimuths agree to 2 to 3 deg of the local strike of the zone of active faulting. The only anomalies in mechanism were for two earthquakes near the western end of the Vema transform which occurred on significantly nonvertical fault planes. Secondary faulting, occurring either precursory to or near the end of the main episode of strike-slip rupture, was observed for 5 of the 12 earthquakes. For three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform. In all three cases, the site of secondary reverse faulting is near a compression jog in the current trace of the active transform fault zone. No evidence was found to support the conclusions of Engeln, Wiens, and Stein that oceanic transform faults in general are either hotter than expected from current thermal models or weaker than normal oceanic lithosphere.

  9. Transform fault earthquakes in the North Atlantic - Source mechanisms and depth of faulting

    NASA Technical Reports Server (NTRS)

    Bergman, Eric A.; Solomon, Sean C.

    1988-01-01

    The centroid depths and source mechanisms of 12 large earthquakes on transform faults of the northern Mid-Atlantic Ridge were determined from an inversion of long-period body waveforms. The earthquakes occurred on the Gibbs, Oceanographer, Hayes, Kane, 15 deg 20 min, and Vema transforms. The depth extent of faulting during each earthquake was estimated from the centroid depth and the fault width. The source mechanisms for all events in this study display the strike slip motion expected for transform fault earthquakes; slip vector azimuths agree to 2 to 3 deg of the local strike of the zone of active faulting. The only anomalies in mechanism were for two earthquakes near the western end of the Vema transform which occurred on significantly nonvertical fault planes. Secondary faulting, occurring either precursory to or near the end of the main episode of strike-slip rupture, was observed for 5 of the 12 earthquakes. For three events the secondary faulting was characterized by reverse motion on fault planes striking oblique to the trend of the transform. In all three cases, the site of secondary reverse faulting is near a compression jog in the current trace of the active transform fault zone. No evidence was found to support the conclusions of Engeln, Wiens, and Stein that oceanic transform faults in general are either hotter than expected from current thermal models or weaker than normal oceanic lithosphere.

  10. 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

  11. The Eastern Lower Tagus Valley Fault Zone in central Portugal: Active faulting in a low-deformation region within a major river environment

    NASA Astrophysics Data System (ADS)

    Canora, Carolina; Vilanova, Susana P.; Besana-Ostman, Glenda M.; Carvalho, João; Heleno, Sandra; Fonseca, Joao

    2015-10-01

    Active faulting in the Lower Tagus Valley, Central Portugal, poses a significant seismic hazard that is not well understood. Although the area has been affected by damaging earthquakes during historical times, only recently has definitive evidence of Quaternary surface faulting been found along the western side of the Tagus River. The location, geometry and kinematics of active faults along the eastern side of the Tagus valley have not been previously studied. We present the first results of mapping and paleoseismic analysis of the eastern strand of the Lower Tagus Valley Fault Zone (LTVFZ). Geomorphological, paleoseismological, and seismic reflection studies indicate that the Eastern LTVFZ is a left-lateral strike-slip fault. The detailed mapping of geomorphic features and studies in two paleoseismic trenches show that surface fault rupture has occurred at least six times during the past 10 ka. The river offsets indicate a minimum slip rate on the order of 0.14-0.24 mm/yr for the fault zone. Fault trace mapping, geomorphic analysis, and paleoseismic studies suggest a maximum magnitude for the Eastern LTVFZ of Mw ~ 7.3 with a recurrence interval for surface ruptures ~ 1.7 ka. At least two events occurred after 1175 ± 95 cal yr BP. Single-event displacements are unlikely to be resolved in the paleoseismic trenches, thus our observations most probably represent the minimum number of events identified in the trenches.

  12. Map and Database of Probable and Possible Quaternary Faults in Afghanistan

    USGS Publications Warehouse

    Ruleman, C.A.; Crone, A.J.; Machette, M.N.; Haller, K.M.; Rukstales, K.S.

    2007-01-01

    The U.S. Geological Survey (USGS) with support from the U.S. Agency for International Development (USAID) mission in Afghanistan, has prepared a digital map showing the distribution of probable and suspected Quaternary faults in Afghanistan. This map is a key component of a broader effort to assess and map the country's seismic hazards. Our analyses of remote-sensing imagery reveal a complex array of tectonic features that we interpret to be probable and possible active faults within the country and in the surrounding border region. In our compilation, we have mapped previously recognized active faults in greater detail, and have categorized individual features based on their geomorphic expression. We assigned mapped features to eight newly defined domains, each of which contains features that appear to have similar styles of deformation. The styles of deformation associated with each domain provide insight into the kinematics of the modern tectonism, and define a tectonic framework that helps constrain deformational models of the Alpine-Himalayan orogenic belt. The modern fault movements, deformation, and earthquakes in Afghanistan are driven by the collision between the northward-moving Indian subcontinent and Eurasia. The patterns of probable and possible Quaternary faults generally show that much of the modern tectonic activity is related to transfer of plate-boundary deformation across the country. The left-lateral, strike-slip Chaman fault in southeastern Afghanistan probably has the highest slip rate of any fault in the country; to the north, this slip is distributed onto several fault systems. At the southern margin of the Kabul block, the style of faulting changes from mainly strike-slip motion associated with the boundary between the Indian and Eurasian plates, to transpressional and transtensional faulting. North and northeast of the Kabul block, we recognized a complex pattern of potentially active strike-slip, thrust, and normal faults that form a

  13. Active faults, stress field and plate motion along the Indo-Eurasian plate boundary

    NASA Astrophysics Data System (ADS)

    Nakata, Takashi; Otsuki, Kenshiro; Khan, S. H.

    1990-09-01

    The active faults of the Himalayas and neighboring areas are direct indicators of Recent and sub-Recent crustal movements due to continental collision between the Indian and Eurasian plates. The direction of the maximum horizontal shortening or horizontal compressive stress axes deduced from the strike and type of active faulting reveals a characteristic regional stress field along the colliding boundary. The trajectories of the stress axes along the transcurrent faults and the Eastern Himalayan Front, are approximately N-S, parallel to the relative motion of the two plates. However, along the southern margin of the Eurasian plate, they are NE-SW in the Western Himalayan Front and NW-SE to E-W in the Kirthar-Sulaiman Front, which is not consistent with the direction of relative plate motion. A simple model is proposed in order to explain the regional stress pattern. In this model, the tectonic sliver between the transcurrent faults and the plate margin, is dragged northward by the oblique convergence of the Indian plate. Thus, the direction of relative motion between the tectonic sliver and the Indian plate changes regionally, causing local compressive stress fields. Judging from the long-term slip rates along the active faults, the relative motion between the Indian and Eurasian plates absorbed in the colliding zone is about one fourth of its total amount; the rest may be consumed along the extensive strike-slip faults in Tibet and China.

  14. Felsic Intrusion in a Strike-slip Dilational Overstepping Linkage in the Upper Crust: An Example of Palgongsan Granite in SE Korea

    NASA Astrophysics Data System (ADS)

    Gwon, S.; Jang, Y.; Kim, Y. S.

    2014-12-01

    The Palgongsan Granite which intruded into the Cretaceous Gyengsang Basin in SE Korea is elongated in NW-SE direction (ca. 2.4 aspect ratio of long axis to short in exposure) and is generally thought as being emplaced along the WNW-ESE trending Palgongsan Fault which is the boundary between the Uiseong sub-basin (north) and Miryang sub-basin (south) within the basin. It is widely believed that emplacement of the pluton along the sub-basin boundary removed all evidence associated with the faulting. Recent studies of gravity and aeromagnetic anomalies in the vicinity of the granite imply that the emplacement of this pluton was controlled by the geometry of WNW-ESE trending right-lateral overstepping lineaments. It gives us an opportunity to examine the controlling factors for emplacement such as the internal structural characteristics of the pluton, thermal cooling history, residual magmatic fluid pressure, and external regional stress regime. Within the granite, pegmatitic dykes and hydrothermal deposits related to the late stages of intrusion are frequently observed and penetrative joints and faults are also well developed. The study of orientation, distribution, relative cross-cutting relationships and kinematics based on the indicators of each structural element coupled with geochronological and geophysical data provides information of the prevailing stress regime at the time of dyke intrusions and the controlling structures, such as strike-slip overstepping and dilational linkage. The results of 3-D mohr-circle analysis for NW-SE trending dykes show they intruded under vertical σ1 and NE-SW horizontal σ3 in low differential stress and relatively high residual pressure of magmatic fluid. This coincided with regional NW-SE horizontal σ1 and NE-SW horizontal σ3 direction based on other structural analysis. Although these results imply the possibility that the pluton was emplaced in a dilational overstep along a WNW-ESE reactivated dextral strike-slip fault

  15. Imaging active faults in a region of distributed deformation from joint focal mechanism and hypocenter clustering: Application to western Iberia

    NASA Astrophysics Data System (ADS)

    Custodio, S.; Lima, V.; Vales, D.; Carrilho, F.; Cesca, S.

    2015-12-01

    Mainland Portugal, on the SW edge of the European continent, is located directly north of the boundary between the Eurasian and Nubian plates. It lies in a region of slow lithospheric deformation, which has generated some of the largest earthquakes in Europe, both intraplate (mainland) and interplate (offshore). The seismicity of mainland Portugal and its adjacent offshore has been repeatedly classified as diffuse. We analyse the instrumental earthquake catalog for western Iberia, enriched with data from recent dense broadband deployments. We show that although the plate boundary south of Portugal is diffuse, in that deformation is accommodated along several distributed faults rather than along one long linear plate boundary, the seismicity itself is not diffuse. Rather, when located using high quality data, earthquakes collapse into well-defined clusters and lineations. We then present a new joint focal mechanism and hypocenter cluster algorithm that is able to extract coherent information between hypocenter locations and focal mechanisms. We apply the method to the Azores-western Mediterranean region, with emphasis on western Iberia. In addition to identifying well-known seismo-tectonic features, the joint clustering algorithm identifies eight new clusters of earthquakes with a good match between the directions of epicentre lineations and focal mechanism fault planes. These clusters may signal single active faults or wider fault zones accommodating a consistent type of faulting. Mainland Portugal is dominated by strike-slip faulting, consistent with the NNE-SSW and WNW-ESE oriented lineations. The region offshore SW Iberia displays clusters that are either predominantly strike-slip or reverse, indicating slip partitioning. This work shows that the study of low-magnitude earthquakes using dense seismic deployments is a powerful tool to study lithospheric deformation in slowly deforming regions, where high-magnitude earthquakes occur with long recurrence intervals.

  16. Active faulting in the Inner California Borderlands: new constraints from high-resolution multichannel seismic and multibeam bathymetric data.

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

    Geodetic data indicate that faults offshore of Southern California accommodate 6-8 mm/yr of dextral Pacific-North American relative plate motion. In the Inner California Borderlands (ICB), modern strike-slip deformation is overprinted on topography formed during plate boundary reorganization 30-15 Ma. Despite its proximity to urban Southern California, the hazard posed by active faults in the ICB remains poorly understood. We acquired a 4000-line-km regional grid of high-resolution, 2D multichannel seismic (MCS) reflection data and multibeam bathymetry to examine the fault architecture and tectonic evolution of the ICB. We interpret the MCS data using a sequence stratigraphic approach to establish a chronostratigraphy and identify discrete episodes of deformation. We present our results in a regional fault model that distinguishes active deformation from older structures. Significant differences exist between our model of ICB deformation and existing models. Mounting evidence suggests a westward temporal migration of slip between faults in the ICB. In the eastern ICB, slip on the Newport-Inglewood/Rose Canyon fault and the neighboring Coronado Bank fault (CBF) diminishes to the north and appears to decrease over time. Undeformed Late Pliocene sediments overlie the northern extent of the CBF and the breakaway zone of the purported Oceanside Blind Thrust. Therefore, CBF slip rate estimates based on linkage with the Palos Verdes fault to the north are unwarranted. Deformation along the San Mateo, San Onofre, and Carlsbad trends is best explained as localized deformation resulting from geometrical complexities in a dextral strike-slip fault system. In the western ICB, the San Diego Trough fault (SDTF) offsets young sediments between the US/Mexico border and the eastern margin of Avalon Knoll, where the fault is spatially coincident with the San Pedro Basin fault (SPBF). Farther west, the San Clemente fault (SCF) has a strong linear bathymetric expression. The length

  17. Paleoseismic activity at the southern termination of Alhama de Murcia fault (Southeastern Betics, Spain): geomporphic and trenching evidence along a slow moving fault

    NASA Astrophysics Data System (ADS)

    Ortuño, M. C.; Masana, E.; Buylaert, J. P.; Canora, C.; Cunha, P.; García-Meléndez, E.; Martínez-Díaz, J.; Murrey, A.; Sohbati, R.; Štěpančíková, P.

    2009-12-01

    The Alhama de Murcia fault (FAM) is part of the Eastern Betics Shear Zone (EBSZ), one of the most seismically active regions of the Iberian Peninsula. The fault, of NE-SW strike, is prominent along an almost 100 km trace and constitutes the geomorphologic southeastern boundary between a train of ranges situated in the NW block (Eg. Las Estancias and La Tercia ranges) and the Plioquaternary basins in the SE block (Eg. Huercal-Overa and Guadalentin-Segura basins). Its activity as a senestral strike-slip fault with local reverse component has been well documented in its central and north-eastern segments in previous works. In this study, we have focused on its south-western termination, that has a special interest for the risk assessment since no historical damaging earthquake has been associated to it. At this part, the FAM has generated a splay-like structure composed of three main branches referred as septentrional, medium and meridional tips. Owing to a more E-W orientation of this fault arrangement compared to the northernmost segment, the faults are expected to have a greater reverse component. This assumption is corroborated by the geomorphological and geological survey, which has shown that the area is compartmentalized in tectonic highs that result from the folding and faulting of Plioquaternary units. The paleosismological survey and OSL dating of sediments in 5 trenches along the medium and meridional fault branches have permitted to better understand the most recent tectonic activity of the area: Alluvial fans draining from Las Estancias range have been blocked, strongly folded and faulted repeatedly in a complex manner during the Middle-Late Pliestocene. The occurrence of, at least, two paleoearthquakes during the last 150 ka has been recognized in each of the trenches, and a third event, in one of them. The structures observed suggest that the strike-slip component decreases gradually towards the western end, while the vertical component increases. A ~ 0

  18. Late Cenozoic intraplate faulting in eastern Australia

    NASA Astrophysics Data System (ADS)

    Babaahmadi, Abbas; Rosenbaum, Gideon

    2014-12-01

    The intensity and tectonic origin of late Cenozoic intraplate deformation in eastern Australia is relatively poorly understood. Here we show that Cenozoic volcanic rocks in southeast Queensland have been deformed by numerous faults. Using gridded aeromagnetic data and field observations, structural investigations were conducted on these faults. Results show that faults have mainly undergone strike-slip movement with a reverse component, displacing Cenozoic volcanic rocks ranging in ages from ˜31 to ˜21 Ma. These ages imply that faulting must have occurred after the late Oligocene. Late Cenozoic deformation has mostly occurred due to the reactivation of major faults, which were active during episodes of basin formation in the Jurassic-Early Cretaceous and later during the opening of the Tasman and Coral Seas from the Late Cretaceous to the early Eocene. The wrench reactivation of major faults in the late Cenozoic also gave rise to the occurrence of brittle subsidiary reverse strike-slip faults that affected Cenozoic volcanic rocks. Intraplate transpressional deformation possibly resulted from far-field stresses transmitted from the collisional zones at the northeast and southeast boundaries of the Australian plate during the late Oligocene-early Miocene and from the late Miocene to the Pliocene. These events have resulted in the hitherto unrecognized reactivation of faults in eastern Australia.

  19. Imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres: Application to the Azores-western Mediterranean region

    NASA Astrophysics Data System (ADS)

    Custódio, Susana; Lima, Vânia; Vales, Dina; Cesca, Simone; Carrilho, Fernando

    2016-04-01

    The matching between linear trends of hypocentres and fault planes indicated by focal mechanisms (FMs) is frequently used to infer the location and geometry of active faults. This practice works well in regions of fast lithospheric deformation, where earthquake patterns are clear and major structures accommodate the bulk of deformation, but typically fails in regions of slow and distributed deformation. We present a new joint FM and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and FMs, even in regions of distributed deformation. We apply the method to the Azores-western Mediterranean region, with particular emphasis on western Iberia. The analysis relies on a compilation of hypocentres and FMs taken from regional and global earthquake catalogues, academic theses and technical reports, complemented by new FMs for western Iberia. The joint clustering algorithm images both well-known and new seismo-tectonic features. The Azores triple junction is characterised by FMs with vertical pressure (P) axes, in good agreement with the divergent setting, and the Iberian domain is characterised by NW-SE oriented P axes, indicating a response of the lithosphere to the ongoing oblique convergence between Nubia and Eurasia. Several earthquakes remain unclustered in the western Mediterranean domain, which may indicate a response to local stresses. The major regions of consistent faulting that we identify are the mid-Atlantic ridge, the Terceira rift, the Trans-Alboran shear zone and the north coast of Algeria. In addition, other smaller earthquake clusters present a good match between epicentre lineations and FM fault planes. These clusters may signal single active faults or wide zones of distributed but consistent faulting. Mainland Portugal is dominated by strike-slip earthquakes with fault planes coincident with the predominant NNE-SSW and WNW-ESE oriented earthquake lineations. Clusters offshore SW Iberia are

  20. Probable slow slips in the mid-crust of Hsinchu, northwestern Taiwan: Temporal correlation between normal faulting earthquakes and relative uplift

    NASA Astrophysics Data System (ADS)

    Pu, H. C.; Lin, C. H.

    2016-05-01

    To investigate the seismic behavior of crustal deformation, we deployed a dense seismic network at the Hsinchu area of northwestern Taiwan during the period between 2004 and 2006. Based on abundant local micro-earthquakes recorded at this seismic network, we have successfully determined 274 focal mechanisms among ∼1300 seismic events. It is very interesting to see that the dominant energy of both seismic strike-slip and normal faulting mechanisms repeatedly alternated with each other within two years. Also, the strike-slip and normal faulting earthquakes were largely accompanied with the surface slipping along N60°E and uplifting obtained from the continuous GPS data, individually. Those phenomena were probably resulted by the slow uplifts at the mid-crust beneath the northwestern Taiwan area. As the deep slow uplift was active below 10 km in depth along either the boundary fault or blind fault, the push of the uplifting material would simultaneously produce both of the normal faulting earthquakes in the shallow depths (0-10 km) and the slight surface uplifting. As the deep slow uplift was stop, instead, the strike-slip faulting earthquakes would be dominated as usual due to strongly horizontal plate convergence in the Taiwan. Since the normal faulting earthquakes repeatedly dominated in every 6 or 7 months between 2004 and 2006, it may conclude that slow slip events in the mid crust were frequent to release accumulated tectonic stress in the Hsinchu area.

  1. 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.

  2. 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.

  3. Four-Dimensional Transform Fault Processes: Evolution of Step-Overs and Bends at Different Scales

    NASA Astrophysics Data System (ADS)

    Wakabayashi, J.; Hengesh, J. V.; Sawyer, T. L.

    2002-12-01

    Many bends or step-overs along strike-slip faults may evolve by propagation of the strike-slip fault on one side of the structure and progressive shut off of the strike-slip fault on the other side. In such a process, new transverse structures form, old ones become inactive, and the bend or step-over region migrates with respect to materials that were once affected by it. This process is the progressive asymmetric development of a strike-slip duplex. Consequences of this type of step-over evolution include the following: 1. the amount of vertical structural relief in restraining step-over or bend regions is less than expected (apatite fission track ages associated with these step-over regions predate the strike-slip faulting); 2. pull-apart basin deposits are left outside of the active basin and commonly subjected to contractional deformation and uplift; and 3. local basin inversion occurs that is not linked to regional plate motion changes. This type of evolution of step-overs and bends may be common along the dextral San Andreas fault system of California. Examples of pull-apart basin deposits related to migrating releasing () bends or step-overs are the Plio-Pleistocene Merced Formation (tens of km along strike), the Pleistocene Olema Creek Formation (several km along strike) along the San Andreas fault in the San Francisco Bay area, and an inverted colluvial graben exposed in a paleoseismic trench across the Miller Creek fault (meters to tens of meters along strike) in the eastern San Francisco Bay area. Examples of migrating restraining bends or step-overs include the transfer of slip from the Calaveras to Hayward fault in the Mission Peak area, and the Greenville to the Concord fault at Mount Diablo (10 km or more along strike), the offshore San Gregorio fold and thrust belt (40 km along strike), and the progressive transfer of slip from the eastern faults of the San Andreas system to the migrating Mendocino triple junction (over 150 km along strike). Another

  4. Delineation of Active Basement Faults in the Eastern Tennessee and Charlevoix Intraplate Seismic Zones

    NASA Astrophysics Data System (ADS)

    Powell, C. A.; Langston, C. A.; Cooley, M.

    2013-12-01

    Recognition of distinct, seismogenic basement faults within the eastern Tennessee seismic zone (ETSZ) and the Charlevoix seismic zone (CSZ) is now possible using local earthquake tomography and datasets containing a sufficiently large number of earthquakes. Unlike the New Madrid seismic zone where seismicity clearly defines active fault segments, earthquake activity in the ETSZ and CSZ appears diffuse. New arrival time inversions for hypocenter relocations and 3-D velocity variations using datasets in excess of 1000 earthquakes suggest the presence of distinct basement faults in both seismic zones. In the ETSZ, relocated hypocenters align in near-vertical segments trending NE-SW, parallel to the long dimension of the seismic zone. Earthquakes in the most seismogenic portion of the ETSZ delineate another set of near-vertical faults trending roughly E-ESE. These apparent trends and steep dips are compatible with ETSZ focal mechanism solutions. The solutions are remarkably consistent and indicate strike-slip motion along the entire length of the seismic zone. Relocated hypocenter clusters in the CSZ define planes that trend and dip in directions that are compatible with known Iapitan rift faults. Seismicity defining the planes becomes disrupted where the rift faults encounter a major zone of deformation produced by a Devonian meteor impact. We will perform a joint statistical analysis of hypocenter alignments and focal mechanism nodal plane orientations in the ETSZ and the CSZ to determine the spatial orientations of dominant seismogenic basement faults. Quantifying the locations and dimensions of active basement faults will be important for seismic hazard assessment and for models addressing the driving mechanisms for these intraplate zones.

  5. GPR measurements to assess the Emeelt active fault's characteristics in a highly smooth topographic context, Mongolia

    NASA Astrophysics Data System (ADS)

    Dujardin, Jean-Rémi; Bano, Maksim; Schlupp, Antoine; Ferry, Matthieu; Munkhuu, Ulziibat; Tsend-Ayush, Nyambayar; Enkhee, Bayarsaikhan

    2014-07-01

    To estimate the seismic hazard, the geometry (dip, length and orientation) and the dynamics (type of displacements and amplitude) of the faults in the area of interest need to be understood. In this paper, in addition to geomorphologic observations, we present the results of two ground penetrating radar (GPR) campaigns conducted in 2010 and 2011 along the Emeelt fault in the vicinity of Ulaanbaatar, capital of Mongolia, located in an intracontinental region with low deformation rate that induces long recurrence time between large earthquakes. As the geomorphology induced by the fault activity has been highly smoothed by erosion processes since the last event, the fault location and geometry is difficult to determine precisely. However, by using GPR first, a non-destructive and fast investigation, the fault and the sedimentary deposits near the surface can be characterized and the results can be used for the choice of trench location. GPR was performed with a 50 MHz antenna over 2-D lines and with a 500 MHz antenna for pseudo-3-D surveys. The 500 MHz GPR profiles show a good consistency with the trench observations, dug next to the pseudo-3-D surveys. The 3-D 500 MHz GPR imaging of a palaeochannel crossed by the fault allowed us to estimate its lateral displacement to be about 2 m. This is consistent with a right lateral strike-slip displacement induced by an earthquake around magnitude 7 or several around magnitude 6. The 2-D 50 MHz profiles, recorded perpendicular to the fault, show a strong reflection dipping to the NE, which corresponds to the fault plane. Those profiles provided complementary information on the fault such as its location at shallow depth, its dip angle (from 23° to 35°) and define its lateral extension.

  6. Late Proterozoic transpression on the Nabitah fault system-implications for the assembly of the Arabian Shield

    USGS Publications Warehouse

    Quick, J.E.

    1991-01-01

    The longest proposed suture zone in Saudi Arabia, the Nabitah suture, can be traced as a string of ophiolite complexes for 1200 km along the north-south axis of the Arabian Shield. Results of a field study in the north-central shield between 23?? and 26??N indicate that the Nabitah suture is indeed a major crustal discontinuity across which hundreds of kilometers of displacement may have occurred on north-south trending, subvertical faults of the Nabitah fault system. Although not a unique solution, many structures within and near these faults can be reconciled with transpression, i.e., convergent strike-slip, and syntectonic emplacement of calc-alkaline plutonic rocks. Transcurrent motion on the Nabitah fault system appears to have began prior to 710 Ma, was active circa 680 Ma, and terminated prior to significant left-lateral, strike slip on the Najd fault system, which began sometime after 650 Ma. Northwest-directed subduction in the eastern shield could have produced the observed association of calc-alkaline magmatism and left-lateral transpressive strike slip, and is consistent with interpretation of the Abt schist and sedimentary rocks of the Murdama group as relics of the associated accretionary wedge and fore-arc basin. ?? 1991.

  7. Active faulting and natural hazards in Armenia, eastern Turkey and northwestern Iran

    NASA Astrophysics Data System (ADS)

    Karakhanian, Arkady S.; Trifonov, Vladimir G.; Philip, Herve; Avagyan, Ara; Hessami, Khaled; Jamali, Farshad; Salih Bayraktutan, M.; Bagdassarian, H.; Arakelian, S.; Davtian, V.; Adilkhanyan, A.

    2004-03-01

    Active fault zones of Armenia, SE Turkey and NW Iran present a diverse set of interrelated natural hazards. Three regional case studies in this cross-border zone are examined to show how earthquakes interact with other hazards to increase the risk of natural disaster. In northern Armenia, a combination of several natural and man-made phenomena (earthquakes, landslides and unstable dams with toxic wastes) along the Pambak-Sevan-Sunik fault (PSSF) zone lowers from 0.4 to 0.2-0.3 g the maximum permissible level (MPL) of seismic hazard that may induce disastrous destruction and loss of life in the adjacent Vanadzor depression. In the Ararat depression, a large active fault-bounded pull-apart basin at the junction of borders of Armenia, Turkey, Iran and Azerbaijan, an earthquake in 1840 was accompanied by an eruption of Ararat Volcano, lahars, landslides, floods, soil subsidence and liquefaction. The case study demonstrates that natural hazards that are secondary with respect to earthquakes may considerably increase the damage and the casualties and increase the risk associated with the seismic impact. The North Tabriz-Gailatu fault system poses a high seismic hazard to the border areas of NW Iran, eastern Turkey, Nakhichevan (Azerbaijan) and southern Armenia. Right-lateral strike-slip motions along the North Tabriz fault have given rise to strong earthquakes, which threaten the city of Tabriz with its population of 1.2 million. The examples illustrate how the concentration of natural hazards in active fault zones increases the risk associated with strong earthquakes in Armenia, eastern Turkey and NW Iran. This generally occurs across the junctions of international borders. Hence, the transboundary character of active faults requires transboundary cooperation in the study and mitigation of the natural risk.

  8. Identification of recently active faults and folds in Java, Indonesia

    NASA Astrophysics Data System (ADS)

    Marliyani, G. I.; Arrowsmith, R.; Helmi, H.

    2013-12-01

    We analyze the spatial pattern of active deformation in Java, Indonesia with the aim of characterizing the deformation of the upper plate of the subduction zone in this region. The lack of detailed neotectonic studies in Java is mostly because of its relatively low rate of deformation in spite of significant historical seismic activity. In addition, the abundance of young volcanic materials as well as the region's high precipitation rate and vegetation cover obscure structural relationships and prevent reliable estimates of offset along active faults as well as exhumed intra-arc faults. Detailed maps of active faults derived from satellite and field-based neotectonic mapping, paleoseismic data, as well as new data on the fault kinematics and estimates of orientation of principal stresses from volcano morphology characterize recently active faults and folds. The structures in West Java are dominated by strike-slip faulting, while Central and northern part of East Java are dominated by folds and thrusting with minor normal faulting. The structures vary in length from hundreds meters to tens of kilometers and mainly trend N75°E, N8°E with some minor N45°W. Our preliminary mapping indicates that there are no large scale continuous structures in Java, and that instead deformation is distributed over wide areas along small structures. We established several paleoseismic sites along some of the identified structures. We excavated two shallow trenches along the Pasuruan fault, a normal fault striking NW-SE that forms a straight 13 km scarp cutting Pleistocene deltaic deposits of the north shore of East Java. The trenches exposed faulted and folded fluvial, alluvial and colluvial strata that record at least four ground-rupturing earthquakes since the Pleistocene. The Pasuruan site proves its potential to provide a paleoseismic record rarely found in Java. Abundant Quaternary volcanoes are emplaced throughout Java; most of the volcanoes show elongation in N100°E and N20

  9. GeoBioScience: Red Wood Ants as Bioindicators for Active Tectonic Fault Systems in the West Eifel (Germany).

    PubMed

    Berberich, Gabriele; Schreiber, Ulrich

    2013-01-01

    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.

  10. Contemporary fault mechanics in southern Alaska

    NASA Astrophysics Data System (ADS)

    Kalbas, James L.; Freed, Andrew M.; Ridgway, Kenneth D.

    Thin-shell finite-element models, constrained by a limited set of geologic slip rates, provide a tool for evaluating the organization of contemporary faulting in southeastern Alaska. The primary structural features considered in our analysis are the Denali, Duke River, Totschunda, Fairweather, Queen Charlotte, and Transition faults. The combination of fault configurations and rheological properties that best explains observed geologic slip rates predicts that the Fairweather and Totschunda faults are joined by an inferred southeast-trending strike-slip fault that crosses the St. Elias Mountains. From a regional perspective, this structure, which our models suggest slips at a rate of ˜8 mm/a, transfers shear from the Queen Charlotte fault in southeastern Alaska and British Columbia northward to the Denali fault in central Alaska. This result supports previous hypotheses that the Fairweather-Totschunda connecting fault constitutes a newly established northward extension of the Queen Charlotte-Fairweather transform system and helps accommodate right-lateral motion (˜49 mm/a) of the Pacific plate and Yakutat microplate relative to stable North America. Model results also imply that the Transition fault separating the Yakutat microplate from the Pacific plate is favorably oriented to accommodate significant thrusting (23 mm/a). Rapid dip-slip displacement on the Transition fault does not, however, draw shear off of the Queen Charlotte-Fairweather transform fault system. Our new modeling results suggest that the Totschunda fault, the proposed Fairweather-Totschunda connecting fault, and the Fairweather fault may represent the youngest stage of southwestward migration of the active strike-slip deformation front in the long-term evolution of this convergent margin.

  11. Earthquake recurrence on the southern San Andreas modulated by fault-normal stress

    NASA Technical Reports Server (NTRS)

    Palmer, Randy; Weldon, Ray; Humphreys, Eugene; Saucier, Francois

    1995-01-01

    Earthquake recurrence data from the Pallett Creek and Wrightwood paleoseismic sites on the San Andreas fault appear to show temporal variations in repeat interval. We investigate the interaction between strike-slip faults and auxiliary reverse and normal faults as a physical mechanism capable of producing such variations. Under the assumption that fault strength is a function of fault-normal stress (e.g. Byerlee's Law), failure of an auxiliary fault modifies the strength of the strike-slip fault, thereby modulating the recurrence interval for earthquakes. In our finite element model, auxiliary faults are driven by stress accumulation near restraining and releasing bends of a strike-slip fault. Earthquakes occur when fault strength is exceeded and are incorporated as a stress drop which is dependent on fault-normal stress. The model is driven by a velocity boundary condition over many earthquake cycles. Resulting synthetic strike-slip earthquake recurrence data display temporal variations similar to observed paleoseismic data within time windows surrounding auxiliary fault failures. Our simple model supports the idea that interaction between a strike-slip fault and auxiliary reverse or normal faults can modulate the recurrence interval of events on the strike-slip fault, possibly producing short term variations in earthquake recurrence interval.

  12. High-resolution relocation of aftershocks of the Mw 7.1 Darfield, New Zealand, earthquake and implications for fault activity

    NASA Astrophysics Data System (ADS)

    Syracuse, E. M.; Thurber, C. H.; Rawles, C. J.; Savage, M. K.; Bannister, S.

    2013-08-01

    Low-slip-rate regions often represent under-recognized hazards, and understanding the progression of seismicity when faults in such areas rupture will help us to better understand earthquake rupture patterns. The 3 September 2010 (UTC) Mw 7.1 Darfield earthquake revealed a formerly unrecognized set of faults in the Canterbury region of New Zealand, an area that had previously been mapped as one of the lower-hazard areas in the country. In this study, we analyze the first four months of its aftershock sequence to identify active faults and temporal changes in seismicity along them. We jointly invert for three-dimensional P wave and S wave velocities and hypocentral locations, using data for 2840 aftershocks recorded at 36 temporary and permanent seismic stations within 70 km of the main shock epicenter. These relocations delineate eight individual faults active prior to the 22 February 2011 Mw 6.3 Christchurch earthquake, the largest aftershock of the Darfield earthquake. Two of these faults are in the Christchurch region, one of which corresponds to geodetically determined rupture planes of the Christchurch earthquake. Using focal mechanisms calculated from first-motion polarities, we find mainly strike-slip faulting events, with some reverse and normal faulting events as well. We compare the orientations of these faults to the prevailing regional stress directions to identify which faults may have been active prior to the Darfield earthquake and which may be newly developed.

  13. Geodetic Network Design and Optimization on the Active Tuzla Fault (Izmir, Turkey) for Disaster Management

    PubMed Central

    Halicioglu, Kerem; Ozener, Haluk

    2008-01-01

    Both seismological and geodynamic research emphasize that the Aegean Region, which comprises the Hellenic Arc, the Greek mainland and Western Turkey is the most seismically active region in Western Eurasia. The convergence of the Eurasian and African lithospheric plates forces a westward motion on the Anatolian plate relative to the Eurasian one. Western Anatolia is a valuable laboratory for Earth Science research because of its complex geological structure. Izmir is a large city in Turkey with a population of about 2.5 million that is at great risk from big earthquakes. Unfortunately, previous geodynamics studies performed in this region are insufficient or cover large areas instead of specific faults. The Tuzla Fault, which is aligned trending NE–SW between the town of Menderes and Cape Doganbey, is an important fault in terms of seismic activity and its proximity to the city of Izmir. This study aims to perform a large scale investigation focusing on the Tuzla Fault and its vicinity for better understanding of the region's tectonics. In order to investigate the crustal deformation along the Tuzla Fault and Izmir Bay, a geodetic network has been designed and optimizations were performed. This paper suggests a schedule for a crustal deformation monitoring study which includes research on the tectonics of the region, network design and optimization strategies, theory and practice of processing. The study is also open for extension in terms of monitoring different types of fault characteristics. A one-dimensional fault model with two parameters – standard strike-slip model of dislocation theory in an elastic half-space – is formulated in order to determine which sites are suitable for the campaign based geodetic GPS measurements. Geodetic results can be used as a background data for disaster management systems.

  14. Active fault segments as potential earthquake sources: Inferences from integrated geophysical mapping of the Magadi fault system, southern Kenya Rift

    NASA Astrophysics Data System (ADS)

    Kuria, Z. N.; Woldai, T.; van der Meer, F. D.; Barongo, J. O.

    2010-06-01

    Southern Kenya Rift has been known as a region of high geodynamic activity expressed by recent volcanism, geothermal activity and high rate of seismicity. The active faults that host these activities have not been investigated to determine their subsurface geometry, faulting intensity and constituents (fluids, sediments) for proper characterization of tectonic rift extension. Two different models of extension direction (E-W to ESE-WNW and NW-SE) have been proposed. However, they were based on limited field data and lacked subsurface investigations. In this research, we delineated active fault zones from ASTER image draped on ASTER DEM, together with relocated earthquakes. Subsequently, we combined field geologic mapping, electrical resistivity, ground magnetic traverses and aeromagnetic data to investigate the subsurface character of the active faults. Our results from structural studies identified four fault sets of different age and deformational styles, namely: normal N-S; dextral NW-SE; strike slip ENE-WSW; and sinistral NE-SW. The previous studies did not recognize the existence of the sinistral oblique slip NE-SW trending faults which were created under an E-W extension to counterbalance the NW-SE faults. The E-W extension has also been confirmed from focal mechanism solutions of the swarm earthquakes, which are located where all the four fault sets intersect. Our findings therefore, bridge the existing gap in opinion on neo-tectonic extension of the rift suggested by the earlier authors. Our results from resistivity survey show that the southern faults are in filled with fluid (0.05 and 0.2 Ωm), whereas fault zones to the north contain high resistivity (55-75 Ωm) material. The ground magnetic survey results have revealed faulting activity within active fault zones that do not contain fluids. In addition, the 2D inversion of the four aero-magnetic profiles (209 km long) revealed: major vertical to sub vertical faults (dipping 75-85° east or west); an

  15. 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.

  16. 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.

  17. 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

    2016-10-01

    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.

  18. Block-like motion of Tibetan Plateau: Evidences from active faults , GPS velocities and recent earthquake slips

    NASA Astrophysics Data System (ADS)

    Xu, X.; Cheng, J.

    2012-12-01

    Collision of India with Eurasia during the past ~ 55 million years has created the high Tibetan Plateau with a flat interior at an average altitude of ~ 5000 m (Matte et al., 1996; Tapponnier et al., 1986, 2001). Two alternative end-member models of how the Tibetan Plateau formed have been proposed: (1) continuous thickening and widespread viscous channel flow of the crust and mantle of the entire plateau (e. g. Bai et al., 2011; Beaumont et al., 2001; Bendick and Flesch, 2007; Clark and Royden, 2000; Houseman and England, 1996; Royden et al., 1997; Shen F. et al., 2001; Zhang et al., 2004; Bai et al., 2010), and (2) time-dependent, localized shear between coherent lithospheric blocks (e. g. Avouac and Tapponnier, 1993; Peltzer and Saucier, 1996; Replumaz and Tapponnier, 2003; Ryerson et al., 2006; Tapponnier et al., 2001; Thatcher, 2007). A new 3-D mechanical model, in which the underthrust India and Tibet are strongly coupled, seems to explain spatial variation in faulting style, and to be inconsistent with channel-flow model for the southern Tibet (Copley et al., 2011). This 3-D model has placed important new constraints on mechanical behavior of the Tibetan lithosphere in its most extreme environment and forced a critical evaluation of the Tibetan channel flow models (Freymueller, 2011), but does not match details of the GPS velocity field, and underestimates the EW extension rate across the southern Tibet. More important is that the model approximates Tibet as a continuous medium, and cannot include localized slip on the mega-strike-slip fault systems, and thus cannot further discuss relationship among the eastward block-like motion, mega-strike-slip faults, normal faults and thrust faults in and around the Tibetan Plateau. It has been recognized for many years that GPS data are likely to be ultimately decisive in distinguishing between block-like and continuous models, at least for describing present-day deformation. Nonetheless, both block-like models and

  19. Complex Faulting within the New Madrid Seismic Zone

    NASA Astrophysics Data System (ADS)

    Deshon, H. R.; Powell, C. A.; Magnani, M.; Bisrat, S. T.

    2010-12-01

    Relative relocations derived using double-difference tomography techniques reveal a complex sequence of faulting within the New Madrid Seismic Zone (NMSZ) and upper Mississippi Embayment. The majority of NMSZ seismicity recorded over the last 30 years occurs along four limbs: 1) a NE-SW trending dextral strike-slip fault, termed the Axial fault, coincident with the central valley of the Cambrian Reelfoot Rift system; 2) the SE-NW trending Reelfoot thrust fault; 3) a E-W trending left lateral strike-slip fault extending off of the northern terminus of the Reelfoot fault, here termed New Madrid west; and 4) a NE-SW dextral strike-slip fault also extending off of the northern terminus of the Reelfoot fault, here termed New Madrid north. Each of these segments is thought to have ruptured during the 1811-1812 large earthquake sequence. A fifth segment, the Bootheel lineament, is marked by 1811-1812 related liquefaction features but appears largely aseismic, though we suggest there are at least five events in the catalog associated with this feature. Geological and geophysical evidence across the embayment suggests that the region is crossed by additional faults at shallow depths (<1-2 km), while seismicity is generally confined to the 3-20 km depth range. Here we present relative relocations derived using catalog and waveform cross-correlation differential times of the 1989-1992 local PANDA network and the 1995-2010 Cooperative New Madrid Seismic Network. We show that the four known seismic lineations exhibit internal complexity. For example, New Madrid north is composed of two parallel faults rather then a single fault, and seismicity associated with the Axial lineation exhibits temporal changes along strike and becomes spatially more diffuse south of the Axial fault/Bootheel lineament intersection. Seismicity along the southern Reelfoot fault does not define a dipping plane consistent with thrust faulting, unlike the northern Reelfoot fault, and is associated with

  20. Style of deformation along the Death Valley-Furnace Creek fault zone and other faults in the southern Walker Lane, Nevada and California

    SciTech Connect

    Noller, J.S. ); Reheis, M.C. )

    1993-04-01

    Quaternary normal and right-lateral faults and associated lineaments in the southern part of the Walker Lane are anomalous with respect to the north-striking normal faults in most of the central Great Basin. The authors identify and characterize many faults and lineaments that were previously unmapped, with the exception of faults in the Death Valley-Furnace Creek fault zone (DVFCFZ) and some faults in and near the Nevada Test Site. Faults and associated lineaments in deposits of late Cenozoic age are distinguished on the basis of age of most recent activity and orientation, and are grouped into two domains. One domain is characterized by northwest-striking faults and lineaments and associated north-striking en echelon structures within the DVFCFZ and the Pahrump fault zone; the other domain is characterized by north- to northeast-striking faults and linearments within a broad region east of the DVFCFZ that narrows southward toward the Pahrump fault zone. Preliminary observations of faults and linearments suggest dominantly right-oblique slip in the first domain and dominantly dip-slip in the second domain. The DVFCFZ is a regional right-lateral strike-slip system that shows changes in style of deformation along strike. Numerous normal faults at the northern end of the DVFCFZ in northern fish Lake Valley and the Volcanic Hills form an extensional right step that links the DVFCFZ with northwest-striking right-lateral faults of the northern part of the Walker Lane. South of this extensional step, the DVFCFZ trends southeast along strike-slip faults from central Fish Lake Valley to the latitude of Furnace Creek. From Furnace Creek, the fault zone apparently steps left to the Pahrump fault zone in the area of Ash Meadows where a complex zone of folds and faults of diverse orientation suggest local compression. This stepover coincides with east-northeast-striking faults that appear to be an extension of the left-lateral Rock Valley fault zone.

  1. Review of active faults in the Borborema Province, Intraplate South America — Integration of seismological and paleoseismological data

    NASA Astrophysics Data System (ADS)

    Bezerra, Francisco H. R.; do Nascimento, Aderson F.; Ferreira, Joaquim M.; Nogueira, Francisco C.; Fuck, Reinhardt A.; Neves, Benjamim B. Brito; Sousa, Maria O. L.

    2011-10-01

    In this paper, we provide a review of the properties and behavior of active faults in the Borborema Province, northeastern Brazil, using instrumental, historical and paleoseismological records. The Borborema Province is one of the most seismically active parts of the South American stable continental region (the South American Platform). The Province encompasses an area ~ 900 km long and ~ 600 km wide. It is composed of a branching system of Neoproterozoic orogens, encompassing Archean and Proterozoic inliers deformed during the Brasiliano orogeny at ~ 750-500 Ma. Active faults reactivate shear zones or regional foliation and quartz veins or cut across the preexisting fabric. Active faults are usually strike-slip and generate events ≤ 5.2 m b, which we interpret as the lower limit for maximum possible earthquakes. Seismicity is concentrated in the upper crust down to a depth of 12 km. Earthquake sequences illuminated naturally occurring faults up to 40 km long and segments in the order of 0.5-2.6 km in faults related to induced seismicity. Earthquakes have a recurrence interval of ~ 15 years for M s = 4. Paleoseismological data indicate that although earthquakes associated with surface ruptures have not occurred in the last 200 years, they struck the region in the last ~ 100 ka. Paleoearthquakes have a recurrence interval of ~ 15.8 ka for magnitudes of ~ 5.5 M w in individual faults. Moreover, earthquake-induced soft-sediment deformation caused by events of at least 5.5-6.0 M s have occurred at least six times in the last 400-10 ka in one alluvial valley. Seismically defined faults are concentrated along the continental margin at the border of sedimentary basins as far as 250-300 km inland in areas of extended crust; faults in the paleoseismic record are also found in rift basins along this margin. Both records also reveal that active faults tend to be hydraulically conductive.

  2. Paleostress inversion of fault-slip data from the Jurassic to Cretaceous Huangshan Basin and implications for the tectonic evolution of southeastern China

    NASA Astrophysics Data System (ADS)

    Xu, Xianbing; Tang, Shuai; Lin, Shoufa

    2016-08-01

    Eight paleostress stages are established in the Jurassic-Cretaceous Huangshan Basin based on fault-slip analysis and age estimation. The first six stages correspond to the subduction of the Paleo-Pacific Plate or the northward motion of the Philippine Block along the southeastern active margin of the South China Block: (1) the 169-162 Ma strike-slip regime was caused by westward low-angle subduction of the Paleo-Pacific Plate, which resulted in NNE-striking folds and top-to-the west thrusting along the southeastern margin of the Huangshan Basin; (2) the 156-125 Ma NW-SE extensional regime was triggered by slab break-off of the Paleo-Pacific Plate. This extension led to Early Cretaceous magmatism, deposition of Early Cretaceous sediments and development of normal faults along the northern boundary of the Huangshan Basin; (3) the 125-107 Ma strike-slip regime was induced by the N-S collision between the Philippine and South China blocks. This tectonic event caused the angular unconformity between the Upper and Lower Cretaceous and the inversion of the Early Cretaceous extensional basin; (4) the 105-86 Ma WNW-ESE extensional regime resulted from an off-shore arc jump of the subducted Paleo-Pacific Plate. This extension triggered the deposition of the Late Cretaceous Qiyunshan Formation; (5) the 86-80 Ma strike-slip regime was induced by high-angle subduction of the Pacific Plate after the off-shore arc jump. This event led to regional uplift and an unconformity at the base of the Late Cretaceous Xiaoyan Formation; (6) the 80-36 Ma N-S extensional regime was caused by the extension following the collision between the Philippine and South China blocks, corresponding to the deposition of the Late Cretaceous Xiaoyan Formation. The last two paleostress stages were the consequences of the far-field effect of the India-Asia continent-continent collision to the southwest of the South China Block: (7) the 36-30 Ma strike-slip regime was caused by the India-Asia collision. It

  3. Hanging canyons of Haida Gwaii, British Columbia, Canada: Fault-control on submarine canyon geomorphology along active continental margins

    NASA Astrophysics Data System (ADS)

    Harris, Peter T.; Barrie, J. Vaughn; Conway, Kim W.; Greene, H. Gary

    2014-06-01

    Faulting commonly influences the geomorphology of submarine canyons that occur on active continental margins. Here, we examine the geomorphology of canyons located on the continental margin off Haida Gwaii, British Columbia, that are truncated on the mid-slope (1200-1400 m water depth) by the Queen Charlotte Fault Zone (QCFZ). The QCFZ is an oblique strike-slip fault zone that has rates of lateral motion of around 50-60 mm/yr and a small convergent component equal to about 3 mm/yr. Slow subduction along the Cascadia Subduction Zone has accreted a prism of marine sediment against the lower slope (1500-3500 m water depth), forming the Queen Charlotte Terrace, which blocks the mouths of submarine canyons formed on the upper slope (200-1400 m water depth). Consequently, canyons along this margin are short (4-8 km in length), closely spaced (around 800 m), and terminate uniformly along the 1400 m isobath, coinciding with the primary fault trend of the QCFZ. Vertical displacement along the fault has resulted in hanging canyons occurring locally. The Haida Gwaii canyons are compared and contrasted with the Sur Canyon system, located to the south of Monterey Bay, California, on a transform margin, which is not blocked by any accretionary prism, and where canyons thus extend to 4000 m depth, across the full breadth of the slope.

  4. The Cottage Grove fault system (Illinois Basin): Late Paleozoic transpression along a Precambrian crustal boundary

    USGS Publications Warehouse

    Duchek, A.B.; McBride, J.H.; Nelson, W.J.; Leetaru, H.E.

    2004-01-01

    The Cottage Grove fault system in southern Illinois has long been interpreted as an intracratonic dextral strike-slip fault system. We investigated its structural geometry and kinematics in detail using (1) outcrop data, (2) extensive exposures in underground coal mines, (3) abundant borehole data, and (4) a network of industry seismic reflection profiles, including data reprocessed by us. Structural contour mapping delineates distinct monoclines, broad anticlines, and synclines that express Paleozoic-age deformation associated with strike slip along the fault system. As shown on seismic reflection profiles, prominent near-vertical faults that cut the entire Paleozoic section and basement-cover contact branch upward into outward-splaying, high-angle reverse faults. The master fault, sinuous along strike, is characterized along its length by an elongate anticline, ???3 km wide, that parallels the southern side of the master fault. These features signify that the overall kinematic regime was transpressional. Due to the absence of suitable piercing points, the amount of slip cannot be measured, but is constrained at less than 300 m near the ground surface. The Cottage Grove fault system apparently follows a Precambrian terrane boundary, as suggested by magnetic intensity data, the distribution of ultramafic igneous intrusions, and patterns of earthquake activity. The fault system was primarily active during the Alleghanian orogeny of Late Pennsylvanian and Early Permian time, when ultramatic igneous magma intruded along en echelon tensional fractures. ?? 2004 Geological Society of America.

  5. Sequence stratigraphic interpretations in a continental strike-slip Basin - Southern Dead Sea, Israel

    SciTech Connect

    Csato, I.; Kendall, C.

    1996-12-31

    Sequence stratigraphic interpretations of subsurface data from the Southern Dead Sea have been integrated with computer modeling of the stratigraphy, demonstrating that the sedimentary fill was controlled by extremely high rates of subsidence (1000 m/MY), salt tectonics, multiple sediment sources, and lake-level fluctuations. The southern part of the basin is underlain by half-grabens and full-grabens. A northwest-southeast directed shear zone (5-6 km wide) closes the basin to the north, while the large Amaziahu growth fault, developed by gravity sliding and salt-withdrawal, separates the basin into two segments. Fan deltas entered the basin at its southern and northern ends, while salt and lacustrine offshore sediments accumulated in its interior. The southern and northern lacustrine systems interfinger in a mixing zone which changed position as a function of lake-level variations. The advance of the northern system was accompanied by lake level falls, while lake-level rises favored an influx from the southern system. The northern sedimentary system gradually became more dominant. The stratigraphic simulation revealed that the lake-level falls paralleled those of the Mediterranean sea, but with a slight (0.3-0.4 MY) delay. Combined stratigraphic and thermal maturation modeling suggests that sediments in the deepest part of the basin are currently within the oil generation window. Significant pinch-out zones flanking the Mount Sedom diapir, buried fan delta complexes, and the peculiar interfingering, zones may be important exploration targets.

  6. Arc-oblique fault systems: their role in the Cenozoic structural evolution and metallogenesis of the Andes of central Chile

    NASA Astrophysics Data System (ADS)

    Piquer, Jose; Berry, Ron F.; Scott, Robert J.; Cooke, David R.

    2016-08-01

    The evolution of the Main Cordillera of Central Chile is characterized by the formation and subsequent inversion of an intra-arc volcano-tectonic basin. The world's largest porphyry Cu-Mo deposits were emplaced during basin inversion. Statistically, the area is dominated by NE- and NW-striking faults, oblique to the N-striking inverted basin-margin faults and to the axis of Cenozoic magmatism. This structural pattern is interpreted to reflect the architecture of the pre-Andean basement. Stratigraphic correlations, syn-extensional deposits and kinematic criteria on fault surfaces show several arc-oblique structures were active as normal faults at different stages of basin evolution. The geometry of syn-tectonic hydrothermal mineral fibers, in turn, demonstrates that most of these structures were reactivated as strike-slip ± reverse faults during the middle Miocene - early Pliocene. Fault reactivation age is constrained by 40Ar/39Ar dating of hydrothermal minerals deposited during fault slip. The abundance and distribution of these minerals indicates fault-controlled hydrothermal fluid flow was widespread during basin inversion. Fault reactivation occurred under a transpressive regime with E- to ENE-directed shortening, and was concentrated around major plutons and hydrothermal centers. At the margins of the former intra-arc basin, deformation was largely accommodated by reverse faulting, whereas in its central part strike-slip faulting was predominant.

  7. Deformation history of the Ballik travertine (Denizli, SW Turkey): a matter of normal faulting and fault reactivation

    NASA Astrophysics Data System (ADS)

    Van Noten, Koen; Topal, Savaş; Oruç Baykara, M.; Özkul, Mehmet; Swennen, Rudy

    2015-04-01

    The Ballık travertine mass is the largest Pleistocene travertine precipitation site in the world. It developed along the basin margin faults of the eastern part of the NW-SE oriented Denizli Graben-Horst System (DGHS), one of the large extensional basins in SW Turkey. Travertine formed from hot basinal carbonate-precipitating fluids that resurfaced along an already existing fault-fracture network affecting the uplifted margin. Analysis of faults affecting a 2 km-long, complex travertine domal structure at the base of this margin revealed that many of the normal faults affecting the travertine are reactivated as sinistral strike-slip faults during the Pleistocene. Remarkably, except for the Ballık area, Quaternary strike-slip faulting has nowhere else been observed in the Denizli Basin and is rather exceptional in extensional basins. With the aim of understanding the consistency of fault reactivation, we present a new tectonic analysis of the NE Denizli margin flank to derive a new reactivation kinematic model. Fault-slip data and paleostress inversion shows that a WNW-ESE oriented, graben-facing fault network was installed during a long-lived phase of NNE-SSW extension in the Pleistocene. Normal faulting was hereby accompanied by blocktilting, backtilting of the hanging walls, fault infill, secondary cement infill and extensional fracturing. Whereas the travertine in the upper part of the margin is only affected by extension, normal faults in the middle and lower parts of the margin show numerous overprinting strike-slip reactivation kinematics. Inversion of fault-slip data suggests that after the initiation of the normal fault network, reactivation was related to NW-SE extension, i.e. an opening direction oriented more or less perpendicular to the opening of this part of the Denizli Basin. This extension is related to the activity of nearby NE-SW-trending basin-bounding margin faults adjacent to the Ballık travertine. The travertine fault network in the middle

  8. 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.

  9. 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.

  10. Holocene activity of the Rose Canyon fault zone in San Diego, California

    NASA Astrophysics Data System (ADS)

    Lindvall, Scott C.; Rockwell, Thomas K.

    1995-12-01

    The Rose Canyon fault zone in San Diego, California, has many well-expressed geomorphic characteristics of an active strike-slip fault, including scarps, offset and deflected drainages and channel walls, pressure ridges, a closed depression, and vegetation lineaments. Geomorphic expression of the fault zone from Mount Soledad south to Mission Bay indicates that the Mount Soledad strand is the most active. A network of trenches excavated across the Mount Soledad strand in Rose Creek demonstrate a minimum of 8.7 m of dextral slip in a distinctive early to middle Holocene gravel-filled channel that crosses the fault zone. The gravel-filled channel was preserved within and east of the fault but was removed west of the fault zone by erosion or possibly grading during development. Consequently, the actual displacement of the channel could be greater than 8.7 m. Radiocarbon dates on detrital charcoal recovered from the sediments beneath the channel yield a maximum calibrated age of about 8.1±0.2 kyr. The minimum amount of slip along with the maximum age yield a minimum slip rate of 1.07±0.03 mm/yr on this strand of the Rose Canyon fault zone for much of Holocene time. Other strands of the Rose Canyon fault zone, which are east and west of our site, may also have Holocene activity. Based on an analysis of the geomorphology of fault traces within the Rose Canyon fault zone, along with the results of our trenching study, we estimate the maximum likely slip rate at about 2 mm/yr and a best estimate of about 1.5 mm/yr. Stratigraphie evidence of at least three events is present during the past 8.1 kyr. The most recent surface rupture displaces the modern A horizon (topsoil), suggesting that this event probably occurred within the past 500 years. Stratigraphie and structural relationships also indicate the occurrence of a scarp-forming event at about 8.1 kyr, prior to deposition of the gravel-filled channel that was used as a piercing line. A third event is indicated by the

  11. 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

  12. Geological features of Subduction Transfer Edge Propagator (STEP) faults, examples from the Betics and Rif

    NASA Astrophysics Data System (ADS)

    Booth-Rea, Guillermo; Pérez-Peña, Vicente; Azañón, José Miguel; de Lis Mancilla, Flor; Morales, Jose; Stich, Daniel; Giaconia, Flavio

    2014-05-01

    Most of the geological features of the Betics and Rif have resulted from slab tearing, edge delamination and punctual slab breakoff events between offset STEP faults. New P-reciever function data of the deep structure under the Betics and Rif have helped to map the deep boundaries of slab tearing and rupture in the area. Linking surface geological features with the deep structure shows that STEP faulting under the Betics occurred along ENE-WSW segments offset towards the south, probably do to the westward narrowing of the Tethys slab. The surface expression of STEP faulting at the Betics consists of ENE-WSW dextral strike-slip fault segments like the Crevillente, Alpujarras or Torcal faults that are interrupted by basins and elongated extensional domes were exhumed HP middle crust occurs. Exhumation of deep crust erases the effects of strike-slip faulting in the overlying brittle crust. Slab tearing affected the eastern Betics during the Tortonian to Messinian, producing the Fortuna and Lorca basins, and later propagated westward generating the end-Messinian to Pleistocene Guadix-Baza basins and the Granada Pliocene-Pleistocene depocentre. At present slab tearing is occurring beneath the Málaga depression, where the Torcal dextral strike-slip fault ends in a region of active distributed shortening and where intermediate depth seismicity occurs. STEP fault migration has occurred at average rates between 2 and 4 cm/yr since the late Miocene, producing a wave of alternating uplift-subsidence pulses. These initiate with uplift related to slab flexure, subsidence related to slab-pull, followed by uplift after rupture and ending with thermal subsidence. This "yo-yo" type tectonic evolution leads to the generation of endorheic basins that later evolve to exhorheic when they are uplifted and captured above the region where asthenospheric upwelling occurs.

  13. Preliminary results on the tectonic activity of the Ovacık Fault (Malatya-Ovacık Fault Zone, Turkey): Implications of the morphometric analyses

    NASA Astrophysics Data System (ADS)

    Yazıcı, Müge; Zabci, Cengiz; Sançar, Taylan; Sunal, Gürsel; Natalin, Boris A.

    2016-04-01

    The Anatolian 'plate' is being extruded westward relative to the Eurasia along two major tectonic structures, the North Anatolian and the East Anatolian shear zones, respectively making its northern and eastern boundaries. Although the main deformation is localized along these two structures, there is remarkable intra-plate deformation within Anatolia, especially which are characterized by NE-striking sinistral and NW-striking dextral strike-slip faults (Şengör et al. 1985). The Malatya-Ovacık Fault Zone (MOFZ) and its northeastern member, the Ovacık Fault (OF), is a one of the NE-striking sinistral strike slip faults in the central 'ova' neotectonic province of Anatolia, located close to its eastern boundary. Although this fault zone is claimed to be an inactive structure in some studies, the recent GPS measurements (Aktuǧ et al., 2013) and microseismic activity (AFAD, 2013) strongly suggest the opposite. In order to understand rates and patterns of vertical ground motions along the OF, we studied the certain morphometric analyses such as hypsometric curves and integrals, longitudinal channel profiles, and asymmetry of drainage basins. The Karasu (Euphrates) and Munzur rivers form the main drainage systems of the study area. We extracted all drainage network from SRTM-based Digital Elevation Model with 30 m ground pixel resolution and totally identified 40 sub-drainage basins, which are inhomogeneously distributed to the north and to the south of the OF. Most of these basins show strong asymmetry, which are mainly tilted to SW. The asymmetry relatively decreases from NE to SW in general. The only exception is at the margins of the Ovacık Basin (OB), where almost the highest asymmetry values were calculated. On the other hand, the characteristics of hypsometric curves and the calculated hypsometric integrals do not show the similar systematic spatial pattern. The hypsometric curves with convex-shaped geometry, naturally indicating relatively young morphology

  14. Deformation partitioning at the junction between the Enriquillo fault and the Trans-Haitian belt

    NASA Astrophysics Data System (ADS)

    Leroy, S.; Pubellier, M.; Ellouz, N.; Momplaisir, R.; Boisson, D.; Amilcar, H.

    2010-12-01

    The recent Haiti earthquake, although it ruptured dramatically the strike-slip Enriquillo Plantain Garden Fault Zone (EPGFZ), is actually located where this fault cross-cut or is overlapped by the frontal part of the Trans-Haitian belt accretionary wedge. This belt started accreting flysch series in the North of Hispaniola during the late Palaeogene and propagated onto the carbonate platform during the Miocene and the Pliocene. Well dated flexural basins filled with clastics attest for this migration. The recent Matheux and the latest Gonave anticline are still currently uplifting as shown by marine terraces, so that the wedge has at present reached the active flower structure of the Presqu’île-du-Sud of Haiti, which is dissected by the EPGFZ. Therefore the structures and possible recent expression associated with their compression must be carefully investigated at surface as well as the strike-slip structure itself, recent ground destabilization and fluid escape. In fact, fault propagation is controlled mainly by, tectonic regime, physical/mechanical properties of the host-rocks and fluid/gas circulation within fault planes. Fluid and gas composition changes, flow increase or decrease, noble gas isotopic evolution can be used as indicators and evenly precursors of stress regime and mechanical variation along faults. We are now initiating onshore field observation on the strike-slip and compressional faults connection, coupled with fluid/gas sampling along both active and locked segments of the Haiti active fault system, similarly with methods tested in the Colorado plateau and along the South Atlas front (Morocco). Some investigations will be realized offshore, especially the mapping of the junction between Haïti and Jamaïca, in order to precise (1) newly and/or past destabilized segments, (2) the wavelength of the segmentation, (3) relationships with the oblique ridges, inherited segments, cross-cut by the EPGFZ.

  15. 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.

  16. Tectonic evolution of the El Salvador Fault Zone. Insights from analogue experiments.

    NASA Astrophysics Data System (ADS)

    Alonso-Henar, Jorge; Schreurs, Guido; Jesús Martínez-Díaz, José; Álvarez-Gómez, José Antonio

    2014-05-01

    The El Salvador Fault Zone (ESFZ) is an active, c. 150 km long and 20 km wide segmented, dextral strike-slip fault zone within the El Salvador Volcanic Arc striking N90°-100°E. Although several studies have investigated the surface expression of the ESFZ, little is known about its structure at depth and its kinematic evolution. Our analysis of structural field data, remote sensing images and morphometric indices reveals a trenchward migration of the volcanic arc and furthermore suggests that not all structures within the ESFZ can be explained within the current tectonic context, but require a phase of extension or an extensional component of deformation at some stage in the evolution of the ESFZ. Such an extension and trenchward migration of the volcanic arc could be related to subduction roll-back of the Cocos Plate beneath the Chortis Block in Mio-Pliocene times. Such a possible evolution leads to open questions that we address in our research: Is the ESFZ a neo-formed fault zone, i.e. did it form during one phase of strike-slip or transtensional deformation, or do the structures in the ESFZ reflect a two-phase evolution, i.e. an early phase of extension overprinted by a later phase of strike-slip or transtension? Did subduction roll-back occur beneath El Salvador? We carried out analogue model experiments to test whether or not an early phase of extension is required to form the present-day fault pattern in the ESFZ. Analogue modeling is an effective tool in testing various hypotheses, as it allows the experimenter to control specific parameters and to test their influence on the resulting structures. Our experiments suggest that a two-phase tectonic evolution best explains the ESFZ: an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures of the ESFZ and can explain the shallow geometry of the fault zone. This extensional phase is followed by a strike-slip dominated regime, which results in inter

  17. 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.

  18. Potential earthquake faults offshore Southern California, from the eastern Santa Barbara Channel south to Dana Point

    USGS Publications Warehouse

    Fisher, M.A.; Sorlien, C.C.; Sliter, R.W.

    2009-01-01

    Urban areas in Southern California are at risk from major earthquakes, not only quakes generated by long-recognized onshore faults but also ones that occur along poorly understood offshore faults. We summarize recent research findings concerning these lesser known faults. Research by the U.S. Geological Survey during the past five years indicates that these faults from the eastern Santa Barbara Channel south to Dana Point pose a potential earthquake threat. Historical seismicity in this area indicates that, in general, offshore faults can unleash earthquakes having at least moderate (M 5-6) magnitude. Estimating the earthquake hazard in Southern California is complicated by strain partitioning and by inheritance of structures from early tectonic episodes. The three main episodes are Mesozoic through early Miocene subduction, early Miocene crustal extension coeval with rotation of the Western Transverse Ranges, and Pliocene and younger transpression related to plate-boundary motion along the San Andreas Fault. Additional complication in the analysis of earthquake hazards derives from the partitioning of tectonic strain into strike-slip and thrust components along separate but kinematically related faults. The eastern Santa Barbara Basin is deformed by large active reverse and thrust faults, and this area appears to be underlain regionally by the north-dipping Channel Islands thrust fault. These faults could produce moderate to strong earthquakes and destructive tsunamis. On the Malibu coast, earthquakes along offshore faults could have left-lateral-oblique focal mechanisms, and the Santa Monica Mountains thrust fault, which underlies the oblique faults, could give rise to large (M ??7) earthquakes. Offshore faults near Santa Monica Bay and the San Pedro shelf are likely to produce both strike-slip and thrust earthquakes along northwest-striking faults. In all areas, transverse structures, such as lateral ramps and tear faults, which crosscut the main faults, could

  19. Recurrent late Quaternary surface faulting along the southern Mohawk Valley fault zone, NE California

    SciTech Connect

    Sawyer, T.L.; Hemphill-Haley, M.A. ); Page, W.D. )

    1993-04-01

    The Mohawk Valley fault zone comprises NW- to NNW-striking, normal and strike-slip( ) faults that form the western edge of the Plumas province, a diffuse transitional zone between the Basin and Range and the northern Sierra Nevada. The authors detailed evaluation of the southern part of the fault zone reveals evidence for recurrent late Pleistocene to possibly Holocene, moderate to large surface-faulting events. The southern Mohawk fault zone is a complex, 6-km-wide zone of faults and related features that extends from near the crest of the Sierra Nevada to the middle of southern Sierra Valley. The fault zone has two distinct and generally parallel subzones, 3 km apart, that are delineated by markedly different geomorphic characteristics and apparently different styles of faulting. Paleoseismic activity of the western subzone was evaluated in two trenches: one across a fault antithetic to the main range-bounding fault, and the other across a splay fault delineated by a 3.7-m-high scarp in alluvium. Stratigraphic relations, soil development, and radiocarbon dates indicate that at least four mid- to late-Pleistocene surface-faulting events, having single-event displacements in excess of 1.6 to 2.6 m, occurred along the splay fault prior to 12 ka. The antithetic fault has evidence of three late Pleistocene events that may correspond to event documented on the splay fault, and a Holocene event that is inferred from youthful scarplets and small closed depressions.

  20. 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

  1. Four-dimensional transform fault processes: progressive evolution of step-overs and bends

    NASA Astrophysics Data System (ADS)

    Wakabayashi, John; Hengesh, James V.; Sawyer, Thomas L.

    2004-11-01

    Many bends or step-overs along strike-slip faults may evolve by propagation of the strike-slip fault on one side of the structure and progressive shut-off of the strike-slip fault on the other side. In such a process, new transverse structures form, and the bend or step-over region migrates with respect to materials that were once affected by it. This process is the progressive asymmetric development of a strike-slip duplex. Consequences of this type of step-over evolution include: (1) the amount of structural relief in the restraining step-over or bend region is less than expected; (2) pull-apart basin deposits are left outside of the active basin; and (3) local tectonic inversion occurs that is not linked to regional plate boundary kinematic changes. This type of evolution of step-overs and bends may be common along the dextral San Andreas fault system of California; we present evidence at different scales for the evolution of bends and step-overs along this fault system. Examples of pull-apart basin deposits related to migrating releasing (right) bends or step-overs are the Plio-Pleistocene Merced Formation (tens of km along strike), the Pleistocene Olema Creek Formation (several km along strike) along the San Andreas fault in the San Francisco Bay area, and an inverted colluvial graben exposed in a paleoseismic trench across the Miller Creek fault (meters to tens of meters along strike) in the eastern San Francisco Bay area. Examples of migrating restraining bends or step-overs include the transfer of slip from the Calaveras to Hayward fault, and the Greenville to the Concord fault (ten km or more along strike), the offshore San Gregorio fold and thrust belt (40 km along strike), and the progressive transfer of slip from the eastern faults of the San Andreas system to the migrating Mendocino triple junction (over 150 km along strike). Similar 4D evolution may characterize the evolution of other regions in the world, including the Dead Sea pull-apart, the Gulf

  2. Neotectonic development of the El Salvador Fault Zone and implications for deformation in the Central America Volcanic Arc: Insights from 4-D analog modeling experiments

    NASA Astrophysics Data System (ADS)

    Alonso-Henar, Jorge; Schreurs, Guido; Martinez-Díaz, José Jesús; Álvarez-Gómez, José Antonio; Villamor, Pilar

    2015-01-01

    The El Salvador Fault Zone (ESFZ) is an active, approximately 150 km long and 20 km wide, segmented, dextral strike-slip fault zone within the Central American Volcanic Arc striking N100°E. Although several studies have investigated the surface expression of the ESFZ, little is known about its structure at depth and its kinematic evolution. Structural field data and mapping suggest a phase of extension, at some stage during the evolution of the ESFZ. This phase would explain dip-slip movements on structures that are currently associated with the active, dominantly strike slip and that do not fit with the current tectonic regime. Field observations suggest trenchward migration of the arc. Such an extension and trenchward migration of the volcanic arc could be related to slab rollback of the Cocos plate beneath the Chortis Block during the Miocene/Pliocene. We carried out 4-D analog model experiments to test whether an early phase of extension is required to form the present-day fault pattern in the ESFZ. Our experiments suggest that a two-phase tectonic evolution best explains the ESFZ: an early pure extensional phase linked to a segmented volcanic arc is necessary to form the main structures. This extensional phase is followed by a strike-slip dominated regime, which results in intersegment areas with local transtension and segments with almost pure strike-slip motion. The results of our experiments combined with field data along the Central American Volcanic Arc indicate that the slab rollback intensity beneath the Chortis Block is greater in Nicaragua and decreases westward to Guatemala.

  3. 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

  4. Imaging the Alpine Fault, South Island, New Zealand, using local earthquake coda

    NASA Astrophysics Data System (ADS)

    Bannister, S.; Louie, J.; Henrys, S.

    2004-12-01

    The major strike-slip Alpine fault marks the boundary between the obliquely converging Pacific and Australian plates in South Island, New Zealand. Previous studies have inferred a total strike-slip displacement of c. 450 km along this transpressional section of the plate boundary, and an estimated c. 100 km of shortening, which has resulted in the uplift of the Southern Alps mountain range. Active-source seismic reflection imaging suggests that the Alpine fault dips southeast at c. 40 degrees, to a depth of around 22 km (Davey et al., 1998). Here, we attempt to directly image the Alpine fault zone using back-projection migration of local-earthquake coda. We specifically use records from aftershocks of the Mw 6.7 Arthur's Pass earthquake, the largest earthquake in the region for 65 years, which occurred about 25 km southeast of the Alpine fault. The aftershocks of this earthquake were well recorded by a 6-station portable array (Abercrombie et al., 2000). Pre-processing involved relocation of these aftershocks with the double difference technique, utilising cross-correlation differences between the waveforms. This relocation substantially improved relative event locations, and highlighted the Bruce fault and other secondary faults in the region. Subsequent back-projection imaging, using station gathers of the seismograms of the relocated events, results in reflectivity images of the mid-crust near the Alpine fault and beneath the aftershock sequence.

  5. Multiscale seismic imaging of active fault zones for hazard assessment: A case study of the Santa Monica fault zone, Los Angeles, California

    USGS Publications Warehouse

    Pratt, T.L.; Dolan, J.F.; Odum, J.K.; Stephenson, W.J.; Williams, R.A.; Templeton, M.E.

    1998-01-01

    High-resolution seismic reflection profiles at two different scales were acquired across the transpressional Santa Monica Fault of north Los Angeles as part of an integrated hazard assessment of the fault. The seismic data confirm the location of the fault and related shallow faulting seen in a trench to deeper structures known from regional studies. The trench shows a series of near-vertical strike-slip faults beneath a topographic scarp inferred to be caused by thrusting on the Santa Monica fault. Analysis of the disruption of soil horizons in the trench indicates multiple earthquakes have occurred on these strike-slip faults within the past 50 000 years, with the latest being 1000 to 3000 years ago. A 3.8-km-long, high-resolution seismic reflection profile shows reflector truncations that constrain the shallow portion of the Santa Monica Fault (upper 300 m) to dip northward between 30?? and 55??, most likely 30?? to 35??, in contrast to the 60?? to 70?? dip interpreted for the deeper portion of the fault. Prominent, nearly continuous reflectors on the profile are interpreted to be the erosional unconformity between the 1.2 Ma and older Pico Formation and the base of alluvial fan deposits. The unconformity lies at depths of 30-60 m north of the fault and 110-130 m south of the fault, with about 100 m of vertical displacement (180 m of dip-slip motion on a 30??-35?? dipping fault) across the fault since deposition of the upper Pico Formation. The continuity of the unconformity on the seismic profile constrains the fault to lie in a relatively narrow (50 m) zone, and to project to the surface beneath Ohio Avenue immediately south of the trench. A very high-resolution seismic profile adjacent to the trench images reflectors in the 15 to 60 m depth range that are arched slightly by folding just north of the fault. A disrupted zone on the profile beneath the south end of the trench is interpreted as being caused by the deeper portions of the trenched strike-slip

  6. 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.

  7. Kinematics of the oblique faults in the east central Gulf of Suez Rift, Wadi Araba, Sinai Peninsula, Egypt

    NASA Astrophysics Data System (ADS)

    Abdeen, Mamdouh; Abdelmaksoud, Ashraf

    2014-05-01

    The Oligo-Miocene Gulf of Suez rift is characterized by four fault trends; a rift-parallel trend, two trends oblique to the rift trend and a cross trend. The rift-parallel trend strikes 310o to 340o and is referred to as the Clysmic trend. The two trends, which are oblique to the Clysmic trend, strike 350o to 030o and 280o to 310o; the first has been referred to as the north-oblique (N-oblique), and the second as the northwest-oblique (NW-oblique). The cross trend includes faults nearly orthogonal to the Clysmic trend i.e. they strike between 050o and 075o. Image interpretation and detailed field mapping and structural studies at a scale of 1: 20,000 of the Wadi Araba area in southwest Sinai Peninsula indicate e Clysmic faults are mostly normal showing major dip-slip movements. The oblique faults were found to be younger than the Clysmic faults and that the N-oblique faults are characterized by major sinistral strike-slip movement, while the NW-oblique faults are characterized by major dextral strike-slip movement. Cross cutting relationship, geometry and palaeostress analysis indicate that the oblique faults are conjugate Riedel shears originated due to NE to NNE extension related to the Aqaba-Levant transform that has been active since the Middle Miocene.

  8. The 1995 Mw 7.2 Gulf of Aqaba Earthquake revisited: Identifying active fault segments by joint inversion of geodetic and teleseismic data

    NASA Astrophysics Data System (ADS)

    Bathke, H.; Feng, G.; Heimann, S.; Jonsson, S.; Mai, P. M.; Nikkhoo, M.

    2015-12-01

    The largest earthquakes in Saudi Arabia occur at the northwestern boundary of the Arabian plate on a system of left-lateral transform faults extending from the Red Sea in the South and North through the Gulf of Aqaba. The last major earthquake along this boundary occurred in November 1995 and in a complex tectonic setting offshore in the Gulf of Aqaba, consisting of several transform faults and pull-apart basins. Various authors have studied this earthquake in the past, either by using geodetic radar (InSAR) or teleseismic (P and S waves) data, and several source models of the earthquake rupture and the active fault segments have been proposed. However, these source models differ significantly from each other and it still remains unclear which fault segments within the Gulf were activated during the event. There are various reasons for these differences. Teleseismic data alone cannot locate the event well, whereas the lack of near field co-seismic displacement data (due to the event's offshore location) and the quasi north-south oriented strike-slip faulting of the earthquake result in a low SNR in the radar data. Consequently, the uncertainties of inferred model parameters are large and have not been properly estimated so far. In this work, we use radar data from two additional tracks that have not been used before, which provides a more complete displacement field of the earthquake. By using multiple aperture radar interferometry it is possible to better constrain the south-north oriented strike-slip component. In addition, we include both the geodetic data and the teleseismic data in a joint inversion setup allowing combining the strengths of each dataset to constrain the model parameters. By including the full data-variance covariance-matrixes in Bayesian inference sampling, we estimate the model-uncertainties and the related range of likely source models. Consequently, we re-evaluate, which fault segments were activated during the earthquake in the Gulf of

  9. Kinematic analysis of recent and active faults of the southern Umbria-Marche domain, Northern Apennines, Italy: geological constraints to geodynamic models

    NASA Astrophysics Data System (ADS)

    Pasqui, Valeria; Viti, Marcello; Mantovani, Enzo

    2013-04-01

    The recent and active deformation that affects the crest zone of the Umbria-Marche belt (Northern Apennines, Italy) displays a remarkable extensional character, outlined by development of normal fault sets that overprint pre-existing folds and thrusts of Late Miocene-Early Pliocene age. The main extensional fault systems often bound intermontane depressions hosting recent, mainly continental, i.e. fluvial or lacustrine deposits, separating the latter from Triassic-Miocene, mainly carbonatic and siliciclastic marine rocks that belong to the Romagna-Umbria-Marche stratigraphic succession. Stratigraphic data indicate that the extensional strain responsible for the development of normal fault-bounded continental basins in the outer zones of the Northern Apennines was active until Middle Pleistocene time. Since Middle Pleistocene time onwards a major geodynamic change has affected the Central Mediterranean region, with local reorganization of the kinematics in the Adria domain and adjacent Apennine belt. A wide literature illustrates that the overall deformation field of the Central Mediterranean area is presently governed by the relative movements between the Eurasia and Africa plates. The complex interaction of the Africa-Adria and the Anatolian-Aegean-Balkan domains has led the Adria microplate to migrate NW-ward and to collide against Eurasia along the Eastern Southern Alps. As a consequence Adria is presently moving with a general left-lateral displacement with respect to the Apennine mountain belt. The sinistral component of active deformations is also supported by analysis of earthquake focal mechanisms. A comparison between geophysical and geological evidence outlines an apparent discrepancy: most recognized recent and active faults display a remarkable extensional character, as shown by the geometry of continental basin-bounding structutes, whereas geodetic and seismologic evidence indicates the persistency of an active strike-slip, left-lateral dominated

  10. Armenia-To Trans-Boundary Fault: AN Example of International Cooperation in the Caucasus

    NASA Astrophysics Data System (ADS)

    Karakhanyan, A.; Avagyan, A.; Avanesyan, M.; Elashvili, M.; Godoladze, T.; Javakishvili, Z.; Korzhenkov, A.; Philip, S.; Vergino, E. S.

    2012-12-01

    Studies of a trans-boundary active fault that cuts through the border of Armenia to Georgia in the area of the Javakheti volcanic highland have been conducted since 2007. The studies have been implemented based on the ISTC 1418 and NATO SfP 983284 Projects. The Javakheti Fault is oriented to the north-northwest and consists of individual segments displaying clear left-stepping trend. Fault mechanism is represented by right-lateral strike-slip with normal-fault component. The fault formed distinct scarps, deforming young volcanic and glacial sediments. The maximum-size displacements are recorded in the central part of the fault and range up to 150-200 m by normal fault and 700-900 m by right-lateral strike-slip fault. On both flanks, fault scarps have younger appearance, and displacement size there decreases to tens of meters. Fault length is 80 km, suggesting that maximum fault magnitude is estimated at 7.3 according to the Wells and Coppersmith (1994) relation. Many minor earthquakes and a few stronger events (1088, Mw=6.4, 1899 Mw=6.4, 1912, Mw=6.4 and 1925, Mw=5.6) are associated with the fault. In 2011/2012, we conducted paleoseismological and archeoseismological studies of the fault. By two paleoseismological trenches were excavated in the central part of the fault, and on its northern and southern flanks. The trenches enabled recording at least three strong ancient earthquakes. Presently, results of radiocarbon age estimations of those events are expected. The Javakheti Fault may pose considerable seismic hazard for trans-boundary areas of Armenia and Georgia as its northern flank is located at the distance of 15 km from the Baku-Ceyhan pipeline.

  11. The southern Whidbey Island fault: An active structure in the Puget Lowland, Washington

    USGS Publications Warehouse

    Johnson, S.Y.; Potter, C.J.; Armentrout, J.M.; Miller, J.J.; Finn, C.; Weaver, C.S.

    1996-01-01

    Information from seismic-reflection profiles, outcrops, boreholes, and potential field surveys is used to interpret the structure and history of the southern Whidbey Island fault in the Puget Lowland of western Washington. This northwest-trending fault comprises a broad (as wide as 6-11 km), steep, northeast-dipping zone that includes several splays with inferred strike-slip, reverse, and thrust displacement. Transpressional deformation along the southern Whidbey Island fault is indicated by alongstrike variations in structural style and geometry, positive flower structure, local unconformities, out-of-plane displacements, and juxtaposition of correlative sedimentary units with different histories. The southern Whidbey Island fault represents a segment of a boundary between two major crustal blocks. The Cascade block to the northeast is floored by diverse assemblages of pre-Tertiary rocks; the Coast Range block to the southwest is floored by lower Eocene marine basaltic rocks of the Crescent Formation. The fault probably originated during the early Eocene as a dextral strike-slip fault along the eastern side of a continental-margin rift. Bending of the fault and transpressional deformation began during the late middle Eocene and continues to the present. Oblique convergence and clockwise rotation along the continental margin are the inferred driving forces for ongoing deformation. Evidence for Quaternary movement on the southern Whidbey Island fault includes (1) offset and disrupted upper Quaternary strata imaged on seismic-reflection profiles; (2) borehole data that suggests as much as 420 m of structural relief on the Tertiary-Quaternary boundary in the fault zone; (3) several meters of displacement along exposed faults in upper Quaternary sediments; (4) late Quaternary folds with limb dips of as much as ???9??; (5) large-scale liquefaction features in upper Quaternary sediments within the fault zone; and (6) minor historical seismicity. The southern Whidbey

  12. Geomechanical Risk Assessment on Shear Activation of Faults in the CO2 Storage Test Site, Offshore Pohang, South Korea

    NASA Astrophysics Data System (ADS)

    Jo, Y.; Chang, C.; Shinn, Y. J.; Song, I.; Kwon, Y. K.

    2015-12-01

    A pilot CO2 sequestration test project is underway in offshore Pohang, South Korea. The target brine aquifer for CO2 storage is 100 m-thick sandstone/conglomerate formations at a depth range between 750 and 850 mbsf (meter below seafloor), which were verified by a 3D seismic survey and a cored borehole (980 m deep). We also found that a family of steep-dip, NE-striking faults cross the target aquifer. In order to analyze potential risk of shear activation along the faults, we characterize in situ stress state at the site. Borehole image logs, generated by an acoustic televiewer tool showed borehole breakouts along the whole logged section to ~705 mbsf, which consistently indicate an average maximum horizontal principal stress (SHmax) direction of N135°±15°E. A leak-off test conducted at the bottom of a casing shoe (700 mbsf) yielded the magnitude of the minimum horizontal principal stress (Shmin) of 12.1 MPa, which is lower than the vertical stress (Sv =14.8 MPa). For the given Shmin and Sv conditions, we used the logged breakout widths and laboratory determined rock compressive strength to constrain possible SHmax magnitudes that could create the observed breakouts. Our stress estimation indicates that the stress regime in the CO2 injection test site is in favor of strike-slip faulting (Shmin < Sv < SHmax). We utilized our estimated stress conditions to analyze slip tendency of the faults. All regional-scale faults turn out to have relatively low slip tendency under the given stress condition, suggesting a low risk of triggering shear activation of faults during CO2 injection.

  13. GPS constraints on active deformation in the Isparta Angle region of SW Turkey

    NASA Astrophysics Data System (ADS)

    Tiryakioğlu, İbrahim; Floyd, Michael; Erdoğan, Saffet; Gülal, Engin; Ergintav, Semih; McClusky, Simon; Reilinger, Robert

    2013-12-01

    We use survey and continuous GPS observations during the period 1997-2010 to investigate active deformation in the Isparta Angle region of SW Anatolia, Turkey. This region, bordered by the Fethiye Burdur Fault Zone (FBFZ) in the west and the SE extension of the Aksehir Simav Fault Zone (AKSFZ) in the east, accommodates a part of the active deformation of W Turkey. Our results show that the Isparta Angle region rotates counter-clockwise (CCW) with respect to Anatolia. Both the FBFZ and the AKSFZ are predominantly transtensional boundaries that accommodate southward motion of the Isparta region with respect to Anatolia. The FBFZ has left-lateral strike-slip behaviour along its SW segment that changes to right-lateral strike-slip along its NE extension. This change in the sense of strike-slip motion is accommodated by extension on a NW-SE striking normal fault system that is associated with the Menderes Graben system. Transtensional fault systems along the boundaries of the Isparta Angle with Anatolia are inconsistent with extrusion models for present-day southward motion. An increase in motion rates towards the Hellenic and Cyprus arc subduction systems, and CCW of the Isparta region, supports dynamic models involving active rollback of the subducting African Plate, toroidal mantle flow around the eastern edge of the subducting African slab near the Hellenic arc/Florence Rise junction, and/or gravitational collapse of the overriding Anatolia Plate.

  14. Neogene extension and volcanism in the Kunlun fault zone Northern Tibet

    NASA Astrophysics Data System (ADS)

    Jolivet, M.; Brunel, M.; Seward, D.; Malavieille, J.; Roger, F.; Leyreloup, A.; Arnaud, N.

    2003-04-01

    Significant extensional features have been described in Tibet, especially in the southern part of the plateau. The data presented here have been gathered in the Jingyu basin and describe transtensional features affecting the Tibetan plateau on its northern margin. West of 91^o E, the lithospheric strike-slip Kunlun Fault is divided into several segments in a complex pattern involving large relay zones. Some of those segments join at the edge of small-scale, E-W elongated pull-apart basins filled with Quaternary sediments. Magmatic activity, shown by large basaltic lava flows and small basaltic volcanic cones is often associated with the basins. There are no clear relationships between the rifts described further to the south (Yin et al., 1999) and this new type of extensional structures. The Jingyu basin started to form during the Miocene when SW-NE compression and E-W strike-slip faulting were replaced by localised E-W extension and strike-slip faulting. We propose that this change in the deformation pattern corresponds in age with the onset of continental subduction underneath the Kunlun Ranges. We suggest that initiation of this subduction could be responsible for the relaxation of the SW-NE directed constraints in the Bayan Har -- Songpan Garze terrane, allowing localised extension along the Kunlun Fault. Thermochronologic, sedimentary and tectonic data imply that E-W strike-slip movements in the western Kunlun Ranges started at least in Late Eocene times. This in turn might indicate that the Kunlun Fault, which was though to be younger than 10 Ma, is much older (Kidd and Molnar, 1988; Yin et al., 1999). Finally we show for the first time the relation between faulting and extrusive magmatism in North Tibet. If the shoshonites found in North Tibet were associated with the intracontinental subduction underneath the Kunlun Range, then the age of initiation of this subduction would probably have to be revised to account for the 15 Ma old lava flows in the Jingyu

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

    NASA Astrophysics Data System (ADS)

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

    2014-12-01

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

  16. Identifying active interplate and intraplate fault zones in the western Caribbean plate from seismic reflection data and the significance of the Pedro Bank fault zone in the tectonic history of the Nicaraguan Rise

    NASA Astrophysics Data System (ADS)

    Ott, B.; Mann, P.

    2015-12-01

    The offshore Nicaraguan Rise in the western Caribbean Sea is an approximately 500,000 km2 area of Precambrian to Late Cretaceous tectonic terranes that have been assembled during the Late Cretaceous formation of the Caribbean plate and include: 1) the Chortis block, a continental fragment; 2) the Great Arc of the Caribbean, a deformed Cretaceous arc, and 3) the Caribbean large igneous province formed in late Cretaceous time. Middle Eocene to Recent eastward motion of the Caribbean plate has been largely controlled by strike-slip faulting along the northern Caribbean plate boundary zone that bounds the northern margin of the Nicaraguan Rise. These faults reactivate older rift structures near the island of Jamaica and form the transtensional basins of the Honduran Borderlands near Honduras. Recent GPS studies suggest that small amount of intraplate motion within the current margin of error of GPS measurements (1-3 mm/yr) may occur within the center of the western Caribbean plate at the Pedro Bank fault zone and Hess Escarpment. This study uses a database of over 54,000 km of modern and vintage 2D seismic data, combined with earthquake data and results from previous GPS studies to define the active areas of inter- and intraplate fault zones in the western Caribbean. Intraplate deformation occurs along the 700-km-long Pedro Bank fault zone that traverses the center of the Nicaraguan Rise and reactivates the paleo suture zone between the Great Arc of the Caribbean and the Caribbean large igneous province. The Pedro Bank fault zone also drives active extension at the 200-km-long San Andres rift along the southwest margin of the Nicaraguan Rise. Influence of the Cocos Ridge indentor may be contributing to reactivation of faulting along the southwesternmost, active segment of the Hess Escarpment.

  17. Late Cenozoic transpressional mountain building directly north of the Altyn Tagh Fault in the Sanweishan and Nanjieshan, North Tibetan Foreland, China

    NASA Astrophysics Data System (ADS)

    Cunningham, Dickson; Zhang, Jin; Li, Yanfeng

    2016-09-01

    For many tectonicists, the structural development of the northern Tibetan Plateau stops at the Altyn Tagh Fault (ATF). This study challenges that assumption. Structural field observations and remote sensing analysis indicate that the Sanweishan and Nanjieshan basement cored ridges of the Archean Dunhuang Block, which interrupt the north Tibetan foreland directly north of the ATF, are bound and cut by an array of strike-slip, thrust and oblique-slip faults that have been active in the Quaternary and remain potentially active. The Sanweishan is a SE-tilted block that is bound on its NW margin by a steep south-dipping thrust fault that has also accommodated sinistral strike-slip displacements. The Nanjieshan consists of parallel, but offset basement ridges that record NNW and SSE thrust displacements and sinistral strike-slip. Regional folds characterize the extreme eastern Nanjieshan and appear to have formed above blind thrust faults which break the surface further west. Previously published magnetotelluric data suggest that the major faults of the Sanweishan and Nanjieshan ultimately root to the south within conductive zones that are inferred to merge into the ATF. Therefore, although the southern margin of the Dunhuang Block focuses significant deformation along the ATF, the adjacent cratonic basement to the north is also affected. Collectively, the ATF and structurally linked Sanweishan and Nanjieshan fault array represent a regional asymmetric half-flower structure that is dominated by non-strain partitioned sinistral transpression. The NW-trending Dengdengshan thrust fault system near Yumen City appears to define the northeastern limit of the Sanweishan-Nanjieshan block, which may be regionally viewed as the most northern, but early-stage expression of Tibetan Plateau growth into a slowly deforming, mechanically stiff Archean craton.

  18. New evidence on the state of stress of the san andreas fault system.

    PubMed

    Zoback, M D; Zoback, M L; Mount, V S; Suppe, J; Eaton, J P; Healy, J H; Oppenheimer, D; Reasenberg, P; Jones, L; Raleigh, C B; Wong, I G; Scotti, O; Wentworth, C

    1987-11-20

    Contemporary in situ tectonic stress indicators along the San Andreas fault system in central California show northeast-directed horizontal compression that is nearly perpendicular to the strike of the fault. Such compression explains recent uplift of the Coast Ranges and the numerous active reverse faults and folds that trend nearly parallel to the San Andreas and that are otherwise unexplainable in terms of strike-slip deformation. Fault-normal crustal compression in central California is proposed to result from the extremely low shear strength of the San Andreas and the slightly convergent relative motion between the Pacific and North American plates. Preliminary in situ stress data from the Cajon Pass scientific drill hole (located 3.6 kilometers northeast of the San Andreas in southern California near San Bernardino, California) are also consistent with a weak fault, as they show no right-lateral shear stress at approximately 2-kilometer depth on planes parallel to the San Andreas fault. PMID:17839366

  19. Preliminary results on the tectonic activity of the Ovacık Fault (Malatya-Ovacık Fault Zone, Turkey): Implications of the morphometric analyses

    NASA Astrophysics Data System (ADS)

    Yazıcı, Müge; Zabci, Cengiz; Sançar, Taylan; Sunal, Gürsel; Natalin, Boris A.

    2016-04-01

    The Anatolian 'plate' is being extruded westward relative to the Eurasia along two major tectonic structures, the North Anatolian and the East Anatolian shear zones, respectively making its northern and eastern boundaries. Although the main deformation is localized along these two structures, there is remarkable intra-plate deformation within Anatolia, especially which are characterized by NE-striking sinistral and NW-striking dextral strike-slip faults (Şengör et al. 1985). The Malatya-Ovacık Fault Zone (MOFZ) and its northeastern member, the Ovacık Fault (OF), is a one of the NE-striking sinistral strike slip faults in the central 'ova' neotectonic province of Anatolia, located close to its eastern boundary. Although this fault zone is claimed to be an inactive structure in some studies, the recent GPS measurements (Aktuǧ et al., 2013) and microseismic activity (AFAD, 2013) strongly suggest the opposite. In order to understand rates and patterns of vertical ground motions along the OF, we studied the certain morphometric analyses such as hypsometric curves and integrals, longitudinal channel profiles, and asymmetry of drainage basins. The Karasu (Euphrates) and Munzur rivers form the main drainage systems of the study area. We extracted all drainage network from SRTM-based Digital Elevation Model with 30 m ground pixel resolution and totally identified 40 sub-drainage basins, which are inhomogeneously distributed to the north and to the south of the OF. Most of these basins show strong asymmetry, which are mainly tilted to SW. The asymmetry relatively decreases from NE to SW in general. The only exception is at the margins of the Ovacık Basin (OB), where almost the highest asymmetry values were calculated. On the other hand, the characteristics of hypsometric curves and the calculated hypsometric integrals do not show the similar systematic spatial pattern. The hypsometric curves with convex-shaped geometry, naturally indicating relatively young morphology

  20. 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

  1. Comparative study of two active faults in different stages of the earthquake cycle in central Japan -The Atera fault (with 1586 Tensho earthquake) and the Nojima fault (with 1995 Kobe earthquake)-

    NASA Astrophysics Data System (ADS)

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

    2003-12-01

    National Research Institute for Earth Science and Disaster Prevention (NIED) has been conducting _gFault zone drilling_h. Fault zone drilling is especially important in understanding the structure, composition, and physical properties of an active fault. In the Chubu district of central Japan, large active faults such as the Atotsugawa (with 1858 Hietsu earthquake) and the Atera (with 1586 Tensho earthquake) faults exist. After the occurrence of the 1995 Kobe earthquake, it has been widely recognized that direct measurements in fault zones by drilling. This time, we describe about the Atera fault and the Nojima fault. Because, these two faults are similar in geological situation (mostly composed of granitic rocks), so it is easy to do comparative study of drilling investigation. The features of the Atera fault, which have been dislocated by the 1586 Tensho earthquake, are as follows. Total length is about 70 km. That general trend is NW45 degree with a left-lateral strike slip. Slip rate is estimated as 3-5 m / 1000 years. Seismicity is very low at present and lithologies around the fault are basically granitic rocks and rhyolite. Six boreholes have been drilled from the depth of 400 m to 630 m. Four of these boreholes (Hatajiri, Fukuoka, Ueno and Kawaue) are located on a line crossing in a direction perpendicular to the Atera fault. In the Kawaue well, mostly fractured and alternating granitic rock continued from the surface to the bottom at 630 m. X-ray fluorescence analysis (XRF) is conducted to estimate the amount of major chemical elements using the glass bead method for core samples. The amounts of H20+ are about from 0.5 to 2.5 weight percent. This fractured zone is also characterized by the logging data such as low resistivity, low P-wave velocity, low density and high neutron porosity. The 1995 Kobe (Hyogo-ken Nanbu) earthquake occurred along the NE-SW-trending Rokko-Awaji fault system, and the Nojima fault appeared on the surface on Awaji Island when this

  2. High-resolution seismic reflection imaging of growth folding and shallow faults beneath the Southern Puget Lowland, Washington State

    USGS Publications Warehouse

    Clement, C.R.; Pratt, T.L.; Holmes, M.L.; Sherrod, B.L.

    2010-01-01

    Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ???350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ???2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ???3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

  3. High-resolution seismic reflection imaging of growth folding and shallow faults beneath the Southern Puget Lowland, Washington State

    USGS Publications Warehouse

    Odum, Jackson K.; Stephenson, William J.; Pratt, Thomas L.; Blakely, Richard J.

    2016-01-01

    Marine seismic reflection data from southern Puget Sound, Washington, were collected to investigate the nature of shallow structures associated with the Tacoma fault zone and the Olympia structure. Growth folding and probable Holocene surface deformation were imaged within the Tacoma fault zone beneath Case and Carr Inlets. Shallow faults near potential field anomalies associated with the Olympia structure were imaged beneath Budd and Eld Inlets. Beneath Case Inlet, the Tacoma fault zone includes an ∼350-m wide section of south-dipping strata forming the upper part of a fold (kink band) coincident with the southern edge of an uplifted shoreline terrace. An ∼2 m change in the depth of the water bottom, onlapping postglacial sediments, and increasing stratal dips with increasing depth are consistent with late Pleistocene to Holocene postglacial growth folding above a blind fault. Geologic data across a topographic lineament on nearby land indicate recent uplift of late Holocene age. Profiles acquired in Carr Inlet 10 km to the east of Case Inlet showed late Pleistocene or Holocene faulting at one location with ∼3 to 4 m of vertical displacement, south side up. North of this fault the data show several other disruptions and reflector terminations that could mark faults within the broad Tacoma fault zone. Seismic reflection profiles across part of the Olympia structure beneath southern Puget Sound show two apparent faults about 160 m apart having 1 to 2 m of displacement of subhorizontal bedding. Directly beneath one of these faults, a dipping reflector that may mark the base of a glacial channel shows the opposite sense of throw, suggesting strike-slip motion. Deeper seismic reflection profiles show disrupted strata beneath these faults but little apparent vertical offset, consistent with strike-slip faulting. These faults and folds indicate that the Tacoma fault and Olympia structure include active structures with probable postglacial motion.

  4. Deep-fault connection characterization from combined field and geochemical methodology; examples from Green River and Haiti fault systems

    NASA Astrophysics Data System (ADS)

    Nadine, E. Z.; Frery, E.; Leroy, S.; Mercier De Lepinay, B. F.; Momplaisir, R.

    2011-12-01

    widening of the impacted zones indicating a strong partitioning of the deformation. The resulting stress re-location is well expressed by (1) the dispersion of the aftershocks, essentially North of the strike-slip fault, (2) a progressive local uplift on the hanging wall, and (3) by along-fault fluid flow variation (leaking segments) either along the EPGF recently active segments but also around the Cul-de-Sac plain. As a first approach, we focus our attention on fault-related fluid leakage distribution, located at intersection points between strike-slip and compressive faults. Using this combined approach, mixing structural and geochemical analytical work, we will hopefully be able (i) to identify the transient and permanent fault activity, and (ii) to characterize the time recurrence (if any) and (iii) the location of the seismic activity during the Quaternary in this two natural analogues.

  5. Fracturing and rock pulverization along an exhumed seismogenic fault zone in dolostones: The Foiana Fault Zone (Southern Alps, Italy)

    NASA Astrophysics Data System (ADS)

    Fondriest, Michele; Aretusini, Stefano; Di Toro, Giulio; Smith, Steven A. F.

    2015-07-01

    The Foiana Fault Zone (FFZ) is a major sinistral transpressive fault zone exhumed from < 2 km depth in the Italian Southern Alps. The fault zone crosscuts thick sequences of sedimentary dolostones and shows increasing cumulative throw (0.3-1.8 km) moving from south to north along fault strike. The FFZ consists of variably fractured and fragmented dolostones locally cut by small-displacement (< 0.5 m) faults containing discrete, highly-reflective (so-called "mirror-like") slip surfaces. The mirror-like slip surfaces are typically embedded within fine-grained cataclasite layers up to a few centimeters thick. Preservation of bedding planes in the fragmented dolostones indicates a lack of significant shear strain. Instead, the fragmented dolostones are affected by in-situ shattering from the centimeter down to the micrometer scale, resembling pulverized rocks in crystalline lithologies. Detailed field and aerial structural mapping reveals significant changes in the structure of the FFZ along strike. In particular, the fault zone exhibits large variations in thickness (from c. 100 m in the north to more than 300 m in the south) and changes in mean fault orientation and fault kinematics (from dominant oblique- and strike-slip in the north to dip-slip reverse in the south), together with the reactivation of preexisting anisotropies (i.e. bedding). Overall, the structure of the FFZ, when considered together with possible variable exhumation levels along strike, compares favorably to the predicted damage distribution in three-dimensional earthquake rupture simulations on strike-slip faults, as well as to the characteristics of active seismic sources hosted in carbonate rocks as illuminated by recent seismological studies.

  6. North East Atlantic Tsunamis Related with Gloria Fault

    NASA Astrophysics Data System (ADS)

    Baptista, M.; Miranda, J. M.; Batllo, J.; Macia, R.

    2011-12-01

    Gloria fault is one segment of the Eurasia-Nubia plate boundary. It is a large strike slip fault, located between 24W and 19W, with scarce seismic activity but which was the location of several large events during the XX Century, in particular the 25 November 1941 earthquake, a submarine strike-slip event of magnitude 8.3-8.4 and the 26 May 1975 with magnitude 7.9. Since the installation of the tide-gauge networks in several countries of the North East Atlantic area a significant amount of mareograms were obtained, concerning these events, in a number of coastal stations located along the European coasts. The most impacted areas were the north coast of Portugal where the sea overtopped some beaches, in November 1941, and the harbors of Azores, in 1975, where it was observed the fast withdraw of the sea followed by a strong influx over the highest water mark. We present here a systematic view of the tsunami potential of the Gloria Fault and using results of hydrodynamic simulations we compare model results against observations and tide records and we discuss the corresponding implications in the design of the NEAMTWS decision matrix. To properly constrain the source characteristics of the tsunamigenic earthquakes, relocation and scalar moment calculation of the 1941 earthquake from digitized seismograms have been performed. This work is a funded by project s TAGUSDELTA. Ref. PTDC/MAR/113888/2009 and PTDC/CTE-GIX/110205/2009

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