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  • 1
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    Geodetic exploration of strain along the El Pilar Fault in northeastern Venezuela (2015)
    Wiley
    Details
    Publication Date: 2015-02-18
    Description: We use GNSS observations in northeastern Venezuela to constrain the El Pilar Fault (EPF) kinematics and to explore the effects of the variable elastic properties of the surrounding medium and of the fault geometry on inferred slip rates and locking depth. The velocity field exhibits an asymmetric velocity gradient on either side of the EPF. We use five different approaches to explore possible models to explain this asymmetry. First, we infer a 1.6-km locking depth using a classic elastic half-space dislocation model. Second, we infer a 1.5-km locking depth and a 0.33 asymmetry coefficient using a heterogeneous asymmetric model, including contrasting material properties on either side of a vertical fault, suggesting that the igneous-metamorphic terranes on the northern side are ~2 times more rigid than the sedimentary southern side. Third, we use a three-dimensional elasto-static model to evaluate the presence of a compliant zone (CZ), suggesting a 30% reduction of rigidity in the upper 3 km at the depth of a 1- to 5-km wide fault zone. Fourth, we evaluate the distribution of fault slip, revealing a widespread partial-creep pattern in the eastern upper segment, while the upper western segment exhibits a partially locked area, which coincides with the rupture surface of the 1797 and 1929 earthquakes. To supplement these models, we upgrade the previously published displacement simulation method using non-vertical dislocations with data acquired between 2003 and 2013. The localized aseismic displacement pattern associated with creeping or partially creeping fault segments could explain the low level of historic seismicity.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 2
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    Estimating present-day displacement fields and tectonic deformation in active mountain belts: an example from the Chartreuse Massif and the southern Jura Mountains, western Alps (1999)
    In:  Tectonophysics, (submitted), Icelandic Meteorological Office, Ministry for the Environment University of Iceland, vol. 296, no. 3, pp. 403-419, pp. TC1011, (ISSN 0016-8548, ISBN 3-510-50045-8)
    Details
    Publication Date: 1999
    Keywords: Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Tectonics ; Geol. aspects ; Stress ; Structural geology
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    BIBLIOGRAPHY SEISMOLOGY
  • 3
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    Seismic risk at the rift-transform junction in north Iceland (1999)
    In:  Geophys. Res. Lett., (submitted), Icelandic Meteorological Office, Ministry for the Environment University of Iceland, vol. 26, no. 24, pp. 3689-3692, pp. TC1011, (ISSN 0016-8548, ISBN 3-510-50045-8)
    Details
    Publication Date: 1999
    Keywords: Earthquake risk ; Tjoernes ; Fault zone ; 1206 ; Geodesy ; and ; gravity ; Crustal ; movements ; interplate ; (8155) ; 1243 ; Space ; geodetic ; surveys ; 7230 ; Seismology ; Seismicity ; and ; seismotectonics ; GRL
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    BIBLIOGRAPHY SEISMOLOGY
  • 4
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    Present-day deformation of the French northwestern Alps/southern Jura mountains: Comparison between historical triangulations (1994)
    In:  Geophys. J. Int., (submitted), Icelandic Meteorological Office, Ministry for the Environment University of Iceland, vol. 119, no. 1, pp. 151-165, pp. TC1011, (ISSN 0016-8548, ISBN 3-510-50045-8)
    Details
    Publication Date: 1994
    Keywords: Tectonics ; Crustal deformation (cf. Earthquake precursor: deformation or strain) ; Geodesy ; GJI
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    BIBLIOGRAPHY SEISMOLOGY
  • 5
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    Postseismic relaxation in Kashmir shows lateral variations in crustal architecture and materials (2015)
    Wiley
    Details
    Publication Date: 2015-05-29
    Description: Thirty horizontal displacement time series from GPS sites in the area around the 2005 Kashmir earthquake show lateral spatial variations in displacement magnitude and relaxation time for the postseismic interval from 2005–2012. The observed spatial pattern of surface displacements can only be reproduced by finite element models of postseismic deformation in elastic over viscoelastic crust that include lateral differences both in the thickness of the elastic layer and viscosity of the viscoelastic layer. Solutions reproducing the sign of horizontal displacements everywhere in the epicentral region also require afterslip on the portion of the fault dislocation in the viscoelastic layer, but not in the elastic lid. Although there are substantial tradeoffs among contributions to postseismic displacements of the surface, the observations preclude both crustal homogeneity and shallow afterslip. In the best family of solutions, the thickness of the elastic upper crust differs by a factor of five and the viscosity of the middle and lower crust by an order of magnitude between domains north and south of a suture zone containing the Main Boundary Thrust and Main Mantle Thrust.
    Print ISSN: 0094-8276
    Electronic ISSN: 1944-8007
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 6
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    Present-day deformation of northern Pakistan from Salt Ranges to Karakorum Ranges (2014)
    Wiley
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    Publication Date: 2014-02-27
    Description: [1]  Episodic GPS measurements are used to quantify the present-day velocity field in the northwestern Himalaya from the southern Pamir to the Himalayan foreland. We report large postseismic displacements following the 2005 Kashmir earthquake and several mm/year thrusting of the central segment of the Salt Ranges and Potwar plateau over the foreland, westward thrusting of Nanga Parbat above the Kohistan plateau, and ~ 12 mm/yr SSE velocities of the Karakorum Ranges and of the Deosai and Kohistan plateaus relative to the Indian plate. Numerical simulations allow to determine a first approximation of slip along active faults : (1) substantial creep of ~87 mm/year between 2006 and 2012 along the flat northeast of the Balakot-Bagh thrust affected by the 2005 earthquake; (2) ~ 5 mm/year slip of the central segment of the Salt Ranges and Potwar plateau whereas their western boundaries are clearly inactive over the time span covered by our measurements; (3) 13 mm/year ductile slip along the MHT modeled by a dislocation dipping 7° northward, locked at a depth of 15 km; and (4) ~20 mm/year slip along the shear zone forming the western boundary of Nanga Parbat, between depths of 1.6 and 6.5 km. Residuals velocities suggest the existence of left-lateral strike-slip along the Jhelum fault.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 7
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    Postseismic deformation in Pakistan after the 8 October 2005 earthquake: Evidence of afterslip along a flat north of the Balakot-Bagh thrust (2011)
    Wiley
    Details
    Publication Date: 2011-07-07
    Description: The 8 October 2005 Kashmir earthquake ruptured an out-of-sequence Himalayan thrust known as the Balakot-Bagh thrust. The earthquake's hypocenter was located at a depth of 15 km on the ramp close to a possible ramp/flat transition. In the weeks following the earthquake a GPS network was installed to measure postseismic displacement. The initial measurements in November 2005 were followed by other campaigns in January and August 2006, in March and December 2007, and in August 2008 and 2009. Two hypotheses were tested: post-seismic displacements controlled by viscous relaxation of the lower crust or by afterslip along a flat north of the ramp affected by the main shock. A single Newtonian viscosity for the different periods cannot be determined by numerical simulations of viscous relaxation, which may indicate that the viscosity of the lower crust is non-Newtonian or that viscous relaxation does not control postseismic displacements. Numerical simulations using dislocations in a uniform elastic half-space indicate afterslip north of the ramp of the earthquake along a flat connected to the ramp. Slip along the northwestern portion of the flat accrued to about 285 mm between November 2005 and August 2006, while slip along the southeastern portion accrued to 130 mm over the same time period. Residual misfit of the observed and predicted displacements clearly indicated that afterslip is a better explanation for the observations than the hypothesis of viscous relaxation. The time evolution of the afterslip was found to be consistent with that predicted from rate-strengthening frictional sliding.
    Print ISSN: 0148-0227
    Topics: Geosciences , Physics
    Published by Wiley on behalf of American Geophysical Union (AGU).
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  • 8
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    Micro-granulometry of sedimentary dykes, Kathmandu basin, Nepal (2011)
    PANGAEA
    In:  Supplement to: Mugnier, Jean-Louis; Huyghe, Pascale; Gajurel, Anata; Upreti, B N; Jouanne, F (2011): Seismites in the Kathmandu basin and seismic hazard in central Himalaya. Tectonophysics, 509(1-2), 33-49, https://doi.org/10.1016/j.tecto.2011.05.012
    Details
    Publication Date: 2023-07-11
    Description: Soft-sediment deformation structures have been analyzed at six sites of the Kathmandu valley. Microgranulometric study (this Supplement and Fig. 3B of Mugnier et al., Tectonophysics, 2011) reveals that silty levels (60 to 80% silt) favor the development of soft-sediment deformation structures, while sandy levels (60 to 80% sand) are passively deformed. Nonetheless well sorted sand levels (more than 80% sand) generate over-fluid pressure during compaction if located beneath a silty cap, leading to fluidization and dike development. 3-D geometry of seismites indicates a very strong horizontal shearing during their development. Using a physical approach based on soil liquefaction during horizontal acceleration, we show that the fluidization zone progressively grows down-section during the shaking, but does not exactly begin at the surface. The comparison of bed-thickness and strength/depth evolution indicates three cases: i) no soft-sediment deformation occurs for thin (few centimeters) silty beds; ii) the thickness of soft-sediment deformation above sandy beds is controlled by the lithological contrast; iii) the thickness of soft-sediment deformation depends on the shaking intensity for very thick silty beds. These 3 cases are evidenced in the Kathmandu basin. We use the 30 cm-thick soft-sediment deformation level formed during the 1833 earthquake as a reference: the 1833 earthquake rupture zone extended very close to Kathmandu, inducing there MMI IX-X damages. A 90 cm-thick sediment deformation has therefore to be induced by an event greater than MMI X. From a compilation of paleo and historic seismology studies, it is found that the great (M ~ 8.1) historical earthquakes are not characteristic of the greatest earthquakes of Himalaya; hence earthquakes greater than M ~ 8.6 occurred. Kathmandu is located above one of the asperities that laterally limits the extent of mega-earthquake ruptures and two successive catastrophic events already affected Kathmandu, in 1255 located to the west of this asperity and in ~ 1100 to the east.
    Keywords: Density; Godawari; Grain size, mean; Kurtosis; Median, grain size; Mode, grain size; Nepal; Number; Obscuration; Residual, fractional; Sample code/label; Sample comment; Silt; Size fraction; Size fraction 〈 0.002 mm, clay; Size fraction 〈 0.0039 mm; Size fraction 0.125-0.063 mm, 3.0-4.0 phi, very fine sand; Size fraction 0.200-0.063 mm, fine sand; Size fraction 0.630-0.200 mm, medium sand; Size fraction 1.000-0.500 mm, 0.0-1.0 phi, coarse sand; Size fraction 2.000-1.000 mm, (-1.0)-0.0 phi, very coarse sand; Skewness; Sorting; Specific surface area
    Type: Dataset
    Format: text/tab-separated-values, 1978 data points
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    DATA PANGAEA
  • 9
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    Coseismic displacement field and slip distribution of the 2005 Kashmir earthquake from SAR amplitude image correlation and differential interferometry (2013)
    Oxford University Press
    Details
    Publication Date: 2013-03-12
    Description: The coseismic surface displacement field and slip distribution at depth due to the Kashmir earthquake (M w = 7.6, 2005) have been analysed by different authors using subpixel correlation of synthetic aperture radar (SAR) images and optical images, teleseismic analysis, GPS measurements, as well as in situ field measurements. In this paper, first, we use 23 sets of measurement from subpixel correlation of SAR images and differential interferometry to retrieve the 3-D coseismic surface displacement field. The obtained horizontal and vertical components along the fault trace are then compared, respectively, to equivalent measurements obtained from subpixel correlation of two optical ASTER images and in situ field measurements. Second, the coseismic fault geometry parameters and slip distribution at depth are estimated. In addition to the one segment slip model as reported in previous work, a two segments slip model that better fits the surface fault break is proposed. The improvement of the two segments slip model in interpreting the measured displacement field is highlighted through comparison of residuals of both slip models. Taking advantage of differential interferometry measurements that provide precise and continuous information in the far field of the fault, firstly, a wedge thrust according to Bendick et al. to the Northwest of the main rupture built on our two segments model is tested. According to the obtained results, the residual of the two segments main rupture plus wedge thrust model is slightly smaller than the residual of the two segments model to the Northwest of the Balakot–Bagh fault. Secondly, we test the sensitivity of our slip model to the presence of slip along a décollement as evidenced by Jouanne et al. through post-seismic analysis. The results indicate that the estimations of the coseismic displacement field and slip distribution in this paper are not significantly biased by such post-seismic displacement and that most coseismic displacement is located on a ~40° NE-dipping fault, as previously reported.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 10
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    Present kinematics of the Tjornes Fracture Zone, North Iceland, from campaign and continuous GPS measurements (2013)
    Oxford University Press
    Details
    Publication Date: 2013-01-11
    Description: The Tjörnes Fracture Zone (TFZ), North Iceland, is a 120 km transform offset of the Mid-Atlantic-Ridge that accommodates 18 mm yr –1 plate motion on two parallel transform structures and connects the offshore Kolbeinsey Ridge in the north to the on-shore Northern Volcanic Zone (NVZ) in the south. This transform zone is offshore except for a part of the right-lateral strike-slip Húsavík-Flatey fault (HFF) system that lies close to the coastal town of Húsavík, inducing a significant seismic risk to its inhabitants. In our previous work we constrained the locking depth and slip-rate of the HFF using 4 yr of continuous GPS measurements and found that the accumulated slip-deficit on the fault is equivalent to a M w 6.8 ± 0.1 earthquake, assuming a complete stress release in the last major earthquakes in 1872 and a steady accumulation since then. In this paper we improve our previous analysis by adding 44 campaign GPS (EGPS) data points, which have been regularly observed since 1997. We extract the steady-state interseismic velocities within the TFZ by correcting the GPS data for volcanic inflation of Theistareykir—the westernmost volcano of the NVZ—using a model with a magma volume increase of 25  x 10 6  m 3 , constrained by InSAR time-series analysis results. The improved velocity field based on 58 GPS stations confirms the robustness of our previous model and allows to better constrain the free model parameters. For the HFF we find a slightly shallower locking depth of ~6.2 km and a slightly higher slip-rate of ~6.8 mm yr –1 that again result in the same seismic potential equivalent to a M w 6.8 earthquake. The much larger number of GPS velocities improves the statistically estimated model parameter uncertainties by a factor of two, when compared to our previous study, a result that we validate using Bayesian estimation.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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