Strike-Slip Earthquakes at the Northern Edge of the Calabrian Arc Subduction Zone

2020 ◽  
Author(s):  
Giovanna Calderoni ◽  
Anna Gervasi ◽  
Mario La Rocca ◽  
Guido Ventura
Keyword(s):  
Subduction Zone ◽  
Shear Zones ◽  
Strike Slip ◽  
Corner Frequency ◽  
Tyrrhenian Sea ◽  
Northern Border ◽  
Source Directivity ◽  
Northern Edge ◽  
East West ◽  
Good Agreement

Abstract We analyzed earthquakes of a swarm started in October 2019 in the Tyrrhenian Sea, at the northern border of the Calabrian arc subduction zone. The swarm is located in the same area where a subduction-transform edge propagator (STEP) shear- zone -oriented east–west is recognized from ocean floor morphology and submarine volcanoes. We computed focal mechanism, relative location, stress drop, corner frequency, and source directivity of the mainshock Mw 4.4 and of some aftershocks in the local magnitude range 2.3–3.7. Results indicate clearly that the mainshock occurred on a northwest–southeast-oriented fault, with right-lateral strike-slip motion, and it was characterized by a strong directivity of the rupture propagation from northwest to southeast. On the contrary, most of aftershocks were located on another strike-slip fault oriented northeast–southwest and had left-lateral kinematics. The kinematic features of these earthquakes indicate a strain field with the P-axis oriented north–south and the T-axis oriented east–west. Fault directions and stress field are in good agreement with the theoretical fracture model of shear zones associated with a STEP.

Carboniferous magmatism related to progressive pull-apart opening in the western French Massif Central

2014 ◽  
Vol 185 (3) ◽  
pp. 171-189 ◽  
Author(s):  
Patrick Rolin ◽  
Didier Marquer ◽  
Charles Cartannaz ◽  
Philippe Rossi
Keyword(s):  
Shear Zones ◽  
Strike Slip ◽  
Fault System ◽  
Normal Faults ◽  
Variscan Belt ◽  
French Massif Central ◽  
Massif Central ◽  
Granite Emplacement ◽  
Regional Deformation ◽  
Northern Border

AbstractThe Variscan continental collision induced the development of large crustal melting in the western French Massif Central, accompanied by emplacement and deformation of syn- to post-tectonic granites spatially related to normal and strike slip faulting. Our study focuses on the regional deformation and shear zone patterns in the Millevaches massif, one of the largest magmatic area of the French Massif Central. In this massif, the syn-tectonic intrusions are related i) to the dextral wrenching along the Treignac-Pradines shear zones and the Creuse faults system, and ii) to the coeval extension along the N000°–N020° normal faults on the western edge of the Millevaches massif (Bourganeuf and Argentat faults). The analysis of deformation and kinematics correlated to new datations of granites allow us to propose a pull-apart model to explain the tectono-magmatic evolution of this part of the Variscan belt from 350 Ma to 325 Ma. At that time, these granites intruded a “pull-apart” system bounded by two major N140°–160° dextral strike-slip zones operating in the middle continental crust during a bulk N020° regional shortening.From 325 Ma to 320 Ma, a clockwise rotation of the regional shortening axis was responsible for the late reactivation of the N020° eastern Millevaches tectonic border as a dextral fault system (Felletin-Ambrugeat fault system). This NE-SW shortening displaced the N140°–160° Creuse fault system and induced a reverse motion along the northern border of the Millevaches massif (St-Michel-de-Veisse fault). This Visean tectono-magmatic event induced the late exhumation of the Millevaches massif with respect to surrounding units and favoured the widespread granite emplacement in this part of the Variscan belt.

Zircon geochronology and paleomagnetism of an Archean harzburgite intrusion, eastern Bighorn Mountains, Wyoming

2020 ◽  
Vol 57 (1) ◽  
pp. 21-40
Author(s):  
Alexandra Wallenberg ◽  
Michelle Dafov ◽  
David Malone ◽  
John Craddock
Keyword(s):  
Hanging Wall ◽  
Vertical Axis ◽  
Shear Zones ◽  
Strike Slip ◽  
Zircon Geochronology ◽  
Weighted Mean ◽  
Mafic Complex ◽  
Laramide Orogeny ◽  
Axis Rotation ◽  
Bighorn Mountains

A harzburgite intrusion, which is part of the trailside mafic complex) intrudes ~2900-2950 Ma gneisses in the hanging wall of the Laramide Bighorn uplift west of Buffalo, Wyoming. The harzburgite is composed of pristine orthopyroxene (bronzite), clinopyroxene, serpentine after olivine and accessory magnetite-serpentinite seams, and strike-slip striated shear zones. The harzburgite is crosscut by a hydrothermally altered wehrlite dike (N20°E, 90°, 1 meter wide) with no zircons recovered. Zircons from the harzburgite reveal two ages: 1) a younger set that has a concordia upper intercept age of 2908±6 Ma and a weighted mean age of 2909.5±6.1 Ma; and 2) an older set that has a concordia upper intercept age of 2934.1±8.9 Ma and a weighted mean age 2940.5±5.8 Ma. Anisotropy of magnetic susceptibility (AMS) was used as a proxy for magmatic intrusion and the harzburgite preserves a sub-horizontal Kmax fabric (n=18) suggesting lateral intrusion. Alternating Field (AF) demagnetization for the harzburgite yielded a paleopole of 177.7 longitude, -14.4 latitude. The AF paleopole for the wehrlite dike has a vertical (90°) inclination suggesting intrusion at high latitude. The wehrlite dike preserves a Kmax fabric (n=19) that plots along the great circle of the dike and is difficult to interpret. The harzburgite has a two-component magnetization preserved that indicates a younger Cretaceous chemical overprint that may indicate a 90° clockwise vertical axis rotation of the Clear Creek thrust hanging wall, a range-bounding east-directed thrust fault that accommodated uplift of Bighorn Mountains during the Eocene Laramide Orogeny.

scholarly journals Mapping and classifying large deformation from digital imagery: application to analogue models of lithosphere deformation

2021 ◽  
Author(s):  
Taco Broerse ◽  
Nemanja Krstekanić ◽  
Cor Kasbergen ◽  
Ernst Willingshofer
Keyword(s):  
Large Deformation ◽  
Finite Deformation ◽  
Large Strain ◽  
Shear Zones ◽  
Strike Slip ◽  
Strain Measure ◽  
Lithospheric Deformation ◽  
Analogue Models ◽  
Strain Tensors ◽  
Shape Changes

Summary Particle Image Velocimetry (PIV), a method based on image cross-correlation, is widely used for obtaining velocity fields from time series of images of deforming objects. Rather than instantaneous velocities, we are interested in reconstructing cumulative deformation, and use PIV-derived incremental displacements for this purpose. Our focus is on analogue models of tectonic processes, which can accumulate large deformation. Importantly, PIV provides incremental displacements during analogue model evolution in a spatial reference (Eulerian) frame, without the need for explicit markers in a model. We integrate the displacements in a material reference (Lagrangian) frame, such that displacements can be integrated to track the spatial accumulative deformation field as a function of time. To describe cumulative, finite deformation, various strain tensors have been developed, and we discuss what strain measure best describes large shape changes, as standard infinitesimal strain tensors no longer apply for large deformation. PIV or comparable techniques have become a common method to determine strain in analogue models. However, the qualitative interpretation of observed strain has remained problematic for complex settings. Hence, PIV-derived displacements have not been fully exploited before, as methods to qualitatively characterize cumulative, large strain have been lacking. Notably, in tectonic settings, different types of deformation - extension, shortening, strike-slip - can be superimposed. We demonstrate that when shape changes are described in terms of Hencky strains, a logarithmic strain measure, finite deformation can be qualitatively described based on the relative magnitude of the two principal Hencky strains. Thereby, our method introduces a physically meaningful classification of large 2D strains. We show that our strain type classification method allows for accurate mapping of tectonic structures in analogue models of lithospheric deformation, and complements visual inspection of fault geometries. Our method can easily discern complex strike-slip shear zones, thrust faults and extensional structures and its evolution in time. Our newly developed software to compute deformation is freely available and can be used to post-process incremental displacements from PIV or similar autocorrelation methods.

A theoretical study of the radiation from small strikeslip earthquakes at close distances

1983 ◽  
Vol 73 (1) ◽  
pp. 83-96 ◽  
Author(s):  
Michel Campillo ◽  
Michel Bouchon
Keyword(s):  
Ground Motion ◽  
Epicentral Distance ◽  
Homogeneous Medium ◽  
Source Model ◽  
Strike Slip ◽  
Peak Ground Velocity ◽  
Corner Frequency ◽  
Crack Model ◽  
Sharp Change ◽  
S Wave

abstract We present a study of the seismic radiation of a physically realistic source model—the circular crack model of Madariaga—at close distance range and for vertically heterogeneous crustal structures. We use this model to represent the source of small strike-slip earthquakes. We show that the characteristics of the radiated seismic spectra, like the corner frequency, are strongly affected by the presence of the free surface and by crustal layering, and that they can be considerably different from the ones of the homogeneous-medium far-field solution. The vertical and radial displacement spectra are the most strongly affected. We use this source model to calculate the decay of peak ground velocity with epicentral distance and source depth for small strike-slip earthquakes in California. For distances between 10 and 80 km, the peak horizontal velocity decay is of the form r−1.25 for a 4-km hypocentral depth and r−1.65 for deeper sources. The predominance of supercritically reflected arrivals beyond epicentral distances of 70 to 80 km produces a sharp change in the rate of decay of the ground motion. For most of the cases considered, the peak ground velocity increases between 80 and 100 km. We also show that the S-wave velocity in the source layer is the lower limit of phase velocities associated with significant ground motion.

scholarly journals Midcrustal shear zones in postorogenic extension: Example from the northern Tyrrhenian Sea

1998 ◽  
Vol 103 (B6) ◽  
pp. 12123-12160 ◽  
Author(s):  
Laurent Jolivet ◽  
Claudio Faccenna ◽  
Bruno Goffé ◽  
Massimo Mattei ◽  
Federico Rossetti ◽  
...  
Keyword(s):  
Shear Zones ◽  
Tyrrhenian Sea

scholarly journals Structural analysis of the Rio Preto fold belt (northwestern Bahia / southern Piauí), a doubly-vergent asymmetric fan developed during the Brasiliano Orogeny

2014 ◽  
Vol 86 (3) ◽  
pp. 1101-1113 ◽  
Author(s):  
FABRÍCIO A. CAXITO ◽  
ALEXANDRE UHLEIN ◽  
LUIZ F.G. MORALES ◽  
MARCOS EGYDIO-SILVA ◽  
JULIO C.D. SANGLARD ◽  
...  
Keyword(s):  
Structural Analysis ◽  
Structural Evolution ◽  
Shear Zones ◽  
Central Compartment ◽  
Strike Slip ◽  
Fold Belt ◽  
Main Structure ◽  
The North ◽  
Brasiliano Orogeny ◽  
Analog Models

The Rio Preto fold belt borders the northwestern São Francisco craton and shows an exquisite kilometric doubly-vergent asymmetric fan structure, of polyphasic structural evolution attributed exclusively to the Brasiliano Orogeny (∼600-540 Ma). The fold belt can be subdivided into three structural compartments: The Northern and Southern compartments showing a general NE-SW trend, separated by the Central Compartment which shows a roughly E-W trend. The change of dip of S2, a tight crenulation foliation which is the main structure of the fold belt, between the three compartments, characterizes the fan structure. The Central Compartment is characterized by sub-vertical mylonitic quartzites, which materialize a system of low-T strike slip shear zones (Malhadinha – Rio Preto Shear Zone) crosscutting the central portion of the fold belt. In comparison to published analog models, we consider that the unique structure of the Rio Preto fold belt was generated by the oblique, dextral-sense interaction between the Cristalândia do Piauí block to the north and the São Francisco craton to the south.

scholarly journals Correction to: Early uranium mobilization in late Variscan strike-slip shear zones affecting leucogranites of central western Spain

2018 ◽  
Vol 45 (1) ◽  
pp. 245-245
Author(s):  
F. J. López-Moro ◽  
R. L. Romer ◽  
D. Rhede ◽  
A. Fernández ◽  
S. M. Timón-Sánchez ◽  
...  
Keyword(s):  
Shear Zones ◽  
Strike Slip ◽  
Western Spain

scholarly journals Looking beyond kinematics: 3D thermo-mechanical modelling reveals the dynamic of transform margins

2021 ◽  
Author(s):  
Anthony Jourdon ◽  
Charlie Kergaravat ◽  
Guillaume Duclaux ◽  
Caroline Huguen
Keyword(s):  
Boundary Conditions ◽  
Strain Localization ◽  
Numerical Models ◽  
Local Stress ◽  
Shear Zones ◽  
Strike Slip ◽  
Convergent Margins ◽  
Mechanical Modelling ◽  
Kinematic Models ◽  
Extension Direction

Abstract. Transform margins represent ~30 % of the non-convergent margins worldwide. Their formation and evolution have long been addressed through kinematic models that do not account for the mechanical behaviour of the lithosphere. In this study, we use high resolution 3D numerical thermo-mechanical modelling to simulate and investigate the evolution of the intra-continental strain localization under oblique extension. The obliquity is set through velocity boundary conditions that range from 15° (high obliquity) to 75° (low obliquity) every 15° for strong and weak lower continental crust rheologies. Numerical models show that the formation of localized strike-slip shear zones leading to transform continental margins always follows a thinning phase during which the lithosphere is thermally and mechanically weakened. For low (75°) to intermediate (45°) obliquity cases, the strike-slip faults are not parallel to the extension direction but form an angle of 20° to 40° with the plates' motion while for higher obliquities (30° to 15°) the strike-slip faults develop parallel to the extension direction. Numerical models also show that during the thinning of the lithosphere, the stress and strain re-orient while boundary conditions are kept constant. This evolution, due to the weakening of the lithosphere, leads to a strain localization process in three major phases: (1) strain initiates in a rigid plate where structures are sub-perpendicular to the extension direction; (2) distributed deformation with local stress field variations and formation of transtensional and strike-slip structures; (3) formation of highly localized plates boundaries stopping the intra-continental deformation. Our results call for a thorough re-evaluation of the kinematic approach to studying transform margins.

scholarly journals New Volcanic Complex Found Below the Southern Tyrrhenian Sea

Eos ◽  
2019 ◽  
Vol 100 ◽  
Author(s):  
Terri Cook
Keyword(s):  
Volcanic Complex ◽  
Tyrrhenian Sea ◽  
Intrusive Complex ◽  
Mantle Material ◽  
Northern Edge ◽  
Southern Tyrrhenian Sea

Researchers have identified a previously unknown volcanic-intrusive complex that originated through the melting of mantle material at the northern edge of the Ionian slab.

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