98 research outputs found
The Burst-Like Behavior of Aseismic Slip on a Rough Fault: The Creeping Section of the Haiyuan Fault, China
Recent observations suggesting the influence of creep on earthquakes nucleation and arrest are strong incentives to investigate the physical mechanisms controlling how active faults slip. We focus here on deriving generic characteristics of shallow creep along the Haiyuan fault, a major strikeâslip fault in China, by investigating the relationship between fault slip and geometry. We use optical images and time series of Synthetic Aperture Radar data to map the surface fault trace and the spatiotemporal distribution of surface slip along the creeping section of the Haiyuan fault. The fault trace roughness shows a powerâlaw behavior similar to that of the aseismic slip distribution, with a 0.8 roughness exponent, typical of a selfâaffine regime. One possible interpretation is that fault geometry controls to some extent the distribution of aseismic slip, as it has been shown previously for coseismic slip along active faults. Creep is characterized by local fluctuations in rates that we define as creep bursts. The potency of creep bursts follows a powerâlaw behavior similar to the GutenbergâRichter earthquake distribution, whereas the distribution of bursts velocity is nonâGaussian, suggesting an avalancheâlike behavior of these slip events. Such similarities with earthquakes and lab experiments lead us to interpret the rich dynamics of creep bursts observed along the Haiyuan fault as resulting from longârange elastic interactions within the heterogeneous Earthâs crust
Modeling Deep Rooted Thrust Mechanism of Crustal Thickening in Eastern Tibet
To test Eastern Tibet crustal thickening modes, we compare 2-D numerical models of two emblematic end-member models, with either an obstacle in the low viscosity lower crust or a thrust embedded in the high viscosity one. We show that the obstacle halts the viscous lower crustal flow potentially initiated by the weight of the high Central Tibet, generating a smooth exhumation gradient at the edge of the plateau, not observed in Eastern Tibet. On the contrary, including a low viscosity discontinuity in the upper crust, mimicking a shallow steep listric fault as inferred in the region, reproduces a sharper exhumation profile, as constrained from thermo-kinematic inversions of thermochronological data, and the lack of foreland basin, as observed in the field. Moreover, such fault drives deformation throughout the entire crust, suggesting a deep crustal ductile shear zone limiting the more ductile deformation in the lower crust although no discontinuity is imposed
New Radar Interferometric Time Series Analysis Toolbox Released
Interferometric synthetic aperture radar (InSAR) has become an important geodetic
tool for measuring deformation of Earthâs surface due to various geophysical phenomena,
including slip on earthquake faults, subsurface migration of magma, slowâmoving
landslides, movement of shallow crustal fluids (e.g., water and oil), and glacier flow.
Airborne and spaceborne synthetic aperture radar (SAR) instruments transmit microwaves
toward Earthâs surface and detect the returning reflected waves. The phase of the
returned wave depends on the distance between the satellite and the surface, but it is
also altered by atmospheric and other effects. InSAR provides measurements of surface
deformation by combining amplitude and phase information from two SAR images of
the same location taken at different times to create an interferogram. Several existing
openâsource analysis tools [Rosen et al., 2004; Rosen et al., 2011; Kampes et al., 2003 ;
Sandwell et al., 2011] enable scientists to exploit observations from radar satellites
acquired at two different epochs to produce a surface displacement map
L-band Synthetic Aperture Radar: Current and future applications to Earth sciences
International audienc
Back-arc strain in subduction zones: Statistical observations versus numerical modeling
International audience1] Recent statistical analysis by Lallemand et al. (2008) of subduction zone parameters revealed that the back-arc deformation mode depends on the combination between the subducting (nu(sub)) and upper (nu(up)) plate velocities. No significant strain is recorded in the arc area if plate kinematics verifies nu(up) = 0.5 vsub - 2.3 (cm/a) in the HS3 reference frame. Arc spreading ( shortening) occurs if nu(up) is greater ( lower) than the preceding relationship. We test this statistical law with numerical models of subduction, by applying constant plate velocities far away from the subduction zone. The subducting lithosphere is free to deform at all depths. We quantify the force applied on the two converging plates to sustain constant surface velocities. The simulated rheology combined viscous (non-Newtonian) and brittle behaviors, and depends on water content. The influence of subduction rate vs is first studied for a fixed upper plate. After 950 km of convergence ( steady state slab pull), the transition from extensional to compressive stresses in the upper plate occurs for vs similar to 1.4 cm/a. The effect of upper plate velocity is then tested at constant subduction rate. Upper plate retreat ( advance) with respect to the trench increases extension ( compression) in the arc lithosphere and increases ( decreases) the subducting plate dip. Our modeling confirms the statistical kinematic relationship between vsub and nu(up) that describes the transition from extensional to compressive stresses in the arc lithosphere, even if the modeled law is shifted toward higher rates of upper plate retreat, using our set of physical parameters ( e. g., 100 km thick subducting oceanic plate) and short- term simulations. Our results make valid the choice of the HS3 reference frame for assessing plate velocity influence on arc tectonic regime. The subduction model suggests that friction along the interplate contact and the mantle Stokes reaction could be the two main forces competing against slab pull for upper mantle subductions. Besides, our simulations show that the arc deformation mode is strongly time dependent
Constant slipârate on the Doruneh strikeâslip fault, Iran, averaged over Late Pleistocene, Holocene, and decadal timescales
Varying estimates of both presentâday strain accumulation and longâterm slipârate on the Doruneh leftâlateral strikeâslip fault, NE Iran, have led to suggestions that it exhibits large alongâstrike and/or temporal changes in activity. In this paper, we make and compare estimates of slipârate measured using both geodesy and geomorphology, and spanning time periods ranging from decadal to 100 ka. To image the presentâday accumulation of strain we process seven years (2003â2010) of data from six ENVISAT tracks covering the fault, with interferograms produced for 400 kmâlong strips of data in order to image the longâwavelength signals associated with interseismic strain accumulation across the locked fault. Our analysis shows that less than 4 mm/yr â and likely only 1â3 mm/yr â of slip accumulates across the fault. Using highâresolution optical satellite imagery we make reconstructions of displacement across six alluvial fans whose surfaces cross the fault, in four separate river catchments. We determine the ages of these fans using infraâredâstimulated luminescence dating combined with Uâseries dating of pedogenic carbonates. The six fans vary in age from âŒ10â100 kyr, and a regression line fitted to four of these yields a slip rate of 2.5 ± 0.3 mm/yr. We conclude that within the uncertainty of our measurements the slipârate has remained constant over the last âŒ100 ka and is representative of the strain accumulation at the presentâday. The slipârate that we measure is consistent with the EâW leftâlateral Doruneh fault accommodating NâS rightâlateral faulting by 'bookshelf' faulting, with clockwise rotation about a vertical axis
First recorded eruption of Nabro volcano, Eritrea, 2011
We present a synthesis of diverse observations of the first recorded eruption of Nabro volcano, Eritrea, which began on 12 June 2011. While no monitoring of the volcano was in effect at the time, it has been possible to reconstruct the nature and evolution of the eruption through analysis of re- gional seismological and infrasound data and satellite remote sensing data, supplemented by petrological analysis of erupted products and brief field surveys. The event is notable for the comparative rarity of recorded historical eruptions in the region and of caldera systems in general, for the prodi- gious quantity of SO2 emitted into the atmosphere and the significant human impacts that ensued notwithstanding the low population density of the Afar region. It is also relevant in understanding the broader magmatic and tectonic signifi- cance of the volcanic massif of which Nabro forms a part and which strikes obliquely to the principal rifting directions in the Red Sea and northern Afar. The whole-rock compositions of
Editorial responsibility: G. Giordano
the erupted lavas and tephra range from trachybasaltic to trachybasaltic andesite, and crystal-hosted melt inclusions contain up to 3,000 ppm of sulphur by weight. The eruption was preceded by significant seismicity, detected by regional networks of sensors and accompanied by sustained tremor. Substantial infrasound was recorded at distances of hundreds to thousands of kilometres from the vent, beginning at the onset of the eruption and continuing for weeks. Analysis of ground deformation suggests the eruption was fed by a shal- low, NWâSE-trending dike, which is consistent with field and satellite observations of vent distributions. Despite lack of prior planning and preparedness for volcanic events in the country, rapid coordination of the emergency response miti- gated the human costs of the eruption
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