Dynamics of continental deformation in Asia

International audienceThe relevance of plate tectonics concepts to the description of deformation of large continental areas like Asia is subject to much debate. For some, the deformation of continents is better described by rigid motion of lithospheric blocks with strain concentrated along narrow fault zones. For others, it is better described by viscous flow of a continuously deforming solid in which faults play a minor role. Discriminating these end-member hypotheses requires spatially dense measurements of surface strain rates covering the whole deforming area. Here we revisit the issue of the forces and rheological structure that control present-day deformation in Asia. We use the ‘‘thin sheet'' theory, with deformation driven by the balance of boundary and buoyancy stresses acting on a faulted lithosphere with laterally varying strength. Models are validated against a recent, homogeneous, GPS velocity field that covers most of Asia. In the models, deformation in compressional areas (Himalayas, Tien Shan, Altay) is well reproduced with strong coupling at the India/Eurasia plate contact, which allows for boundary forces to transfer into Asia. Southeastward motions observed in north and south China, however, require tensional, oceanward directed stresses, possibly generated by gravitational potential energy gradients across the Indonesian and Pacific subductions. Model and observed strain rates show that a large part of Asia undergoes no resolvable strain, with a kinematics apparently consistent with block- or plate-like motions. Internal strain, possibly continuous, is limited to high-elevation, mechanically weaker areas. Lateral variations of lithospheric strength appear to control the style of deformation in Asia, with a dynamics consistent with the thin sheet physical framework

Continental deformation in Asia from a combined GPS solution

International audienceAfter decades of research on continental tectonics, there is still no consensus on the mode of deformation of continents or on the forces that drive their deformation. In Asia the debate opposes edge-driven block models, requiring a strong lithosphere with strain localized on faults, to buoyancy-driven continuous models, requiring a viscous lithosphere with pervasive strain. Discriminating between these models requires continent-wide estimates of lithospheric strain rates. Previous efforts have relied on the resampling of heterogeneous geodetic and Quaternary faulting data sets using interpolation techniques. We present a new velocity field based on the rigorous combination of geodetic solutions with relatively homogeneous station spacing, avoiding technique-dependend biases inherent to interpolation methods. We find (1) unresolvable strain rates (< 3×10923 /yr) over a large part of Asia, with current motions well-described by block or microplate rotations, and (2) internal strain, possibly continuous, limited to high-elevation areas

Joint Inversion of Coseismic and Early Postseismic Slip to Optimize the Information Content in Geodetic Data: Application to the 2009 M_w 6.3 L'Aquila Earthquake, Central Italy

When analyzing the rupture of a large earthquake, geodetic data are often critical. These data are generally characterized by either a good temporal or a good spatial resolution, but rarely both. As a consequence, many studies analyze the coseismic rupture with data that also include one or more days of early postseismic deformation. Here, we invert simultaneously for the coseismic and postseismic slip with the condition that the sum of the two models remains compatible with data covering the two slip episodes. We validate the benefits of this approach with a toy model and an application to the 2009 M_w 6.3 L'Aquila earthquake, using a Bayesian approach and accounting for epistemic uncertainties. For the L'Aquila earthquake, we find that if early postseismic deformation is not an explicitly acknowledged coseismic signal, coseismic slip models may overestimate the peak amplitude while long‐term postseismic models may largely underestimate the total postseismic slip amplitude. This example illustrates how the proposed approach could improve our comprehension of the seismic cycle, fault frictional properties, and the spatial and temporal relationship between seismic rupture, afterslip, and aftershocks

Rhéologie et déformation de la lithosphère continentale : apports de mesures GPS en Asie et de modèles numériques

In this work we study the current kinematic of Mongolia in the northern part of Asia and the dynamics of the deformation in Mongolia and Asia First we present the 1994-2002 Mongolia-Baikal GPS velocity field ( 50 sites) with respect to Eurasia Velocities show that 15% of the IN/EU convergence is accommodated north of the Tien Shan by N-S shortening and dextral shear in the Altay mountain and by E-SEward displacement of central and eastern Mongolia at 3-6 mm/yr Our results suggest that the Eward motion in Asia could be controlled by other processes than the IN/EU convergence such as the dynamic of the oceanic subduction zone or the gravitational potential energy gradient Then starting with the large mongolian EQ of the last century and the GPS velocities we model the postseismic deformation (current viscoelastic relaxation < 2mm/an) and estimate the lithosphere rheology under Mongolia (weak upper mantle and lower crust) Next with a study on viscoelastic and static stress transfer we suggest that significant stress transfer is possible among continental faults separated by 100s of km and on time scales of decades Finally we validate dynamic deformation models of Asia with a GPS velocity field covering most of Asia We estimate the average lithosphere rheology and quantify the different mechanisms of deforma- tion We show that the IN/EU collision is the major contribution to the asian deformation However the deformation in north and east Asia is also controlled by the body forces and the dynamic of the oceanic subduction zone Our results suggest that the deformation is mostly continuous but this last point should be confirmed by further measurementsCe travail s intéresse à la cinématique et à la dynamique des déformations continentales Nous présentons le champ de vitesse 1994-2002 mesuré par GPS dans la région Mongolie-Baïkal (située au nord de l Asie) par rapport à l Eurasie Il montre que 15% de la convergence IN/EU est accommodé au nord du Tien Shan par du raccourcissement N-S et du cisaillement dextre dans l Altaï et par du déplacement vers l E-SE (3-6 mm/an) en Mongolie centrale et orientale Nos résultats suggèrent que le mouvement vers l est pourrait être contrôlé par d autres processus que la convergence IN/EU seule A partir des grands séismes de Mongolie au 20ème siècle et de l inversion des vitesses obtenues nous modélisons la déformation postsismique (relaxation viscoélastique actuelle <2 mm/an) et estimons la rhéologie de la lithosphère sous la Mongolie (manteau supérieur et croûte inférieure peu visqueux) Par une étude de redistribution des contraintes à la suite de séismes nous montrons le possible transfert de contrainte entre failles continentales séparées de centaines de kilomètres et sur des dizaines d années Enfin à partir de modèles dynamiques de la déformation en Asie validés par les données GPS en Chine Mongolie et Sibérie nous estimons la rhéologie moyenne de la lithosphère et quantifions les mécanismes de la déformation Nous montrons que bien que la collision IN/EU soit la contribution majeure à la déformation les forces de volume et la dynamique des zones de subduction sont d une importance équivalente dans les zones septentrionales et orientales de l Asie D après nos résultats l accommodation de la déformation actuelle se ferait essentiellement de manière continue mais ceci reste à confirmer

Fault Interactions and Synchronization: Insight from the 1936-1997 NE Lut, Iran, Earthquake Sequence

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Rhéologie et déformation de la lithosphère continentale (apports de mesures GPS en Asie et de modèles numériques)

Ce travail s intéresse à la cinématique et à la dynamique des déformations continentales. Nous présentons le champ de vitesse 1994-2002 mesuré par GPS dans la région Mongolie-Baïkal (située au nord de l Asie) par rapporte à l Eurasie. Il montre que 15% de la convergence IN/EU est accommodé au nord du Tien Shan par raccourcissement NS et cisaillement dextre dans l Altaï et par déplacement vers l E-SE (3-9 mm/an) en Mongolie centrale et orientale. Nos résultats suggèrent que le mouvement vers l est pourrait être contrôlé par d autres processus que la convergence IN/EU seule. A partir des grands séismes de Mongolie au 20e siècle et de l inversion des vitesses obtenues, nous modélisons la déformation postsismique (relaxation viscoélastique actuelle <2 mm/an) et estimons la rhéologie de la lithosphère sous la Mongolie (manteau supérieur et croûte inférieure peu visqueux). Par une étude de redistribution des contraintes à la suite de séismes, nous montrons le possible transfert de contrainte entre failles continentales séparées de centaines de kilomètres et sur des dizaines d années. Enfin, à partir de modèles dynamiques de la déformation en Asie validés par les données GPS en Chine, Mongolie et Sibérie, nous estimons la rhéologie moyenne de la lithosphère et quantifions les mécanismes de déformation. Nous montrons que bien que la collision IN/EU soit la contribution majeure à la déformation, les forces de volume et la dynamique des zones de subduction sont d une importance équivalente dans les zones septentrionales et orientales de l Asie. D après nos résultats, l accommodation de la déformation actuelle se ferait essentiellement de manière continue mais ceci reste à confirmer.In this work, we study the current kinematic of Mongolia, in the northern part of Asia and the dynamics of the deformation in Mongolia and Asia. First, we present the 1994-2002 Mongolia-Baikal GPS velocity fields (-50 sites) with respect to Eurasia. Velocities show that 15% of th IN/EU convergence is accommodated north of the Tien Shan by NS shortening and dextral shear in the Altay mountains and by E-SE displacement of central and eastern Mongolia at 3-6mm/yr. Our results suggest that the Eward motion in Asia could be controlled by other processes then the IN/EU convergence such as the dynamic of the oceanic subduction zone of the gravitational potential energy gradient. Then starting with the large Mongolian EQ of the last century and the GPS velocities, we model the postseismic deformation (current viscoelastic relaxation < 2 mm/an) and estimate he lithosphere rheology under Mongolia (weak upper mantle and lower crust). Next, with a study on viscoelastic and static stress transfer, we suggest that significant stress transfer is possible among continental faults separated by 100s of km and on time scales of decades. Finally, we validate dynamic deformation models of Asia With a GPS velocity field covering most of Asia. We estimate the average lithosphere rheology and quantify the different mechanisms of deformation. We show that the IN/EU collision is the major contribution to the Asian deformation. However, the deformation in north and East Asia is also controlled by the body forces and the dynamic of the oceanic subduction zone. In the first part, we define a new programming language with a functional core and generalized recursion, by using Boudol s type system with degrees to rule out unsafe recursions. The language is extended first with recursive records, then with mixins, allowing the programmer to fully mix functional and object-oriented paradigms. We also present an implementation, MlObj, and an abstract machine for execution. In a second part, we design a new inference algorithm for intersection type systems, on an extension of the lambda-calculus. After proving its correctness, we study its generalisation to references and recursion, we compare it with existing inference algorithms, mainly System l, and we show that its finite rank version becomes decidable. Our results suggest that the current deformation is mostly continuous but this last point should be confirmed by further measurements.NICE-BU Sciences (060882101) / SudocSudocFranceF

Monitoring of the 2018 Pu’u ‘Ō’ō, Hawaii, volcanic eruption using high-rate GNSS data

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Fault Geometry and Slip Distribution at Depth of the 1997 Mw 7.2 Zirkuh Earthquake: Contribution of Near-Field Displacement Data

International audienceIn this study, we reestimate the source model of the 1997 Mw 7.2 Zirkuh earthquake (northeastern Iran) by jointly optimizing intermediate‐field Interferometry Synthetic Aperture Radar data and near‐field optical correlation data using a two‐step fault modeling procedure. First, we estimate the geometry of the multisegmented Abiz fault using a genetic algorithm. Then, we discretize the fault segments into subfaults and invert the data to image the slip distribution on the fault. Our joint‐data model, although similar to the Interferometry Synthetic Aperture Radar‐based model to the first order, highlights differences in the fault dip and slip distribution. Our preferred model is ∼80° west dipping in the northern part of the fault, ∼75° east dipping in the southern part and shows three disconnected high slip zones separated by low slip zones. The low slip zones are located where the Abiz fault shows geometric complexities and where the aftershocks are located. We interpret this rough slip distribution as three asperities separated by geometrical barriers that impede the rupture propagation. Finally, no shallow slip deficit is found for the overall rupture except on the central segment where it could be due to off‐fault deformation in quaternary deposits

Mechanical deformation model of the western United States instantaneous strain-rate field

International audienceWe present a relationship between the long-term fault slip rates and instantaneous velocities as measured by Global Positioning System (GPS) or other geodetic measurements over a short time span. The main elements are the secularly increasing forces imposed by the bounding Pacific and Juan de Fuca (JdF) plates on the North American plate, viscoelastic relaxation following selected large earthquakes occurring on faults that are locked during their respective interseismic periods, and steady slip along creeping portions of faults in the context of a thin-plate system. In detail, the physical model allows separate treatments of faults with known geometry and slip history, faults with incomplete characterization (i.e. fault geometry but not necessarily slip history is available), creeping faults, and dislocation sources distributed between the faults. We model the western United States strain-rate field, derived from 746 GPS velocity vectors, in order to test the importance of the relaxation from historic events and characterize the tectonic forces imposed by the bounding Pacific and JdF plates. Relaxation following major earthquakes (Mγ 8.0) strongly shapes the present strain-rate field over most of the plate boundary zone. Equally important are lateral shear transmitted across the Pacific-North America plate boundary along ∼1000 km of the continental shelf, downdip forces distributed along the Cascadia subduction interface, and distributed slip in the lower lithosphere. Post-earthquake relaxation and tectonic forcing, combined with distributed deep slip, constructively interfere near the western margin of the plate boundary zone, producing locally large strain accumulation along the San Andreas fault (SAF) system. However, they destructively interfere further into the plate interior, resulting in smaller and more variable strain accumulation patterns in the eastern part of the plate boundary zone. Much of the right-lateral strain accumulation along the SAF system is systematically underpredicted by models which account only for relaxation from known large earthquakes. This strongly suggests that in addition to viscoelastic-cycle effects, steady deep slip in the lower lithosphere is needed to explain the observed strain-rate field

Le portail européen de données Epos-GNSS

National audienceLe système de distribution Epos-GNSS est une e-infrastructure conçue pour diffuser des données et produits GNSS. Le portail de données Epos-GNSS est le point d'accès central du système à ces données