Earthquake slip vectors in the Himalayan thrust Zone and their tectonic implications

Slip vectors of thirty-nine thrust events occurring along the Himalayan collision zone have been compared with the velocity vectors between the Indian-Eurasian plates derived from the RM 2 and NUVEL 1 models, The observed deviations of the slip vector from the velocity vector have been interpreted in terms of a simple kinematic model according to which the eastern and western blocks of south Tibet are separating from each other, From the model it is estimated that the western and eastern blocks of Tibet are moving at the rate of 3.6 cm/year westwards at 76°Eand 2.6 cm/year eastwards at 94°E with respect to Eurasia respectively, resulting in an east-west extension, projected to the trend at 85°E, at the rate of 5, 5 cm/year. This would correspond to a strain rate of about 6.9 x 10-8year in central Tibetan region.

Reconfigurable Slip Vectoring Control in Four In-Wheel Drive Electric Vehicles

Controllability, maneuverability, fault-tolerance/isolation and safety are significantly enhanced in electric vehicles (EV) equipped with the redundant actuator configuration of four-in-wheel electric motors (4IWM). A highly reconfigurable architecture is proposed and illustrated for the adaptive, nonmodel-based control of 4IWM-EVs. Given the longitudinal force, yaw-moment requests and the reconfiguration matrix, each IWM is given a slip reference according to a Slip Vectoring (SV) allocation strategy, which minimizes the overall slip vector norm. The distributed electric propulsion and the slip vector reference allow for a decentralized online estimation of the four-wheel torque-loads, which are uncertain depending on loading and road conditions. This allows for the allocation of four different torques depending on individual wheel conditions and to determine in which region (linear/nonsaturated or nonlinear/saturated) of the torque/slip characteristics each wheel is operating. Consequently, the 4IWMs can be equalized or reconfigured, including actuator fault-isolation as a special case, so that they are enforced to operate within the linear tire region. The initial driving-mode selection can be automatically adjusted and restored among eighteen configurations to meet the safety requirements of linear torque/slip behavior. Three CarSim realistic simulations illustrate the equalization algorithm, the quick fault-isolation capabilities and the importance of a continuous differential action in a critical double-lane-change maneuver.

Fault2SHA Central Apennines database and structuring active fault data for seismic hazard assessment

We present a database of field data for active faults in the central Apennines, Italy, including trace, fault and main fault locations with activity and location certainties, and slip-rate, slip-vector and surface geometry data. As advances occur in our capability to create more detailed fault-based hazard models, depending on the availability of primary data and observations, it is desirable that such data can be organized in a way that is easily understood and incorporated into present and future models. The database structure presented herein aims to assist this process. We recommend stating what observations have led to different location and activity certainty and presenting slip-rate data with point location coordinates of where the data were collected with the time periods over which they were calculated. Such data reporting allows more complete uncertainty analyses in hazard and risk modelling. The data and maps are available as kmz, kml, and geopackage files with the data presented in spreadsheet files and the map coordinates as txt files. The files are available at: 10.1594/PANGAEA.922582.

Neogene rift tectonic activity in the West Somali Basin, offshore Tanzania: example of a segmented oblique rift structure.

<p>Little is still known about the structural fabric of a potential continuation of the East African Rift System (EARS) offshore Tanzania in the West Somali Basin. This continuation has been established mostly through sparse GPS measurements, earthquake slip vector data, spatial distribution of teleseismically detected earthquake focal mechanisms, and some recent seismic reflection data. West of the Davie Ridge (which part of a larger structure named the Davie Fracture Zone) and across its northern extension, regional seismic reflection profiles indicate the occurrence of continental - oceanic crust transition, which is characterized by early Cretaceous reverse faulting localized along deformation corridors. After the Aptian, the seafloor spreading ceased and the Tanzania margin evolved into a passive margin dominated by clastic deep-water deposition. In this contribution, we describe some results obtained from structural mapping of a 3D seismic dataset, calibrated by few explorations well, covering an area located between the Davie Ridge and the continent, south of Mafia Island.  The seismic data maps suggest a major structural style change across the Neogene that is still active today. The recent structures are represented by two main interacting fault trends: some NS boundary faults corridors and a NW-SE internal arcuate segmented fault, both depicting a widely and diffused distribution of normal fault (with an overall cumulative amount of horizontal brittle extension ranging between 5 to 10 km). Some of the largest faults appear to reactivate older extensional structures but the general absence of growth faults cutting across the Paleo-Neogene depositional units suggest very recent rift re-activation. The recent rift system appears to show a component of obliquity with respect to the orientation of the Davie Ridge, and to the onshore structure related to the EARS tectonics.</p>

Analysis of deformation features using integrated field methods and aerial drone imaging on the Bach Long Vy island, Gulf of Tonkin, Vietnam

<p>Situated in the junction between the Song Hong Basin and the Beibuwan Basin, the Bach Long Vy island exposes Paleogene syn-rift rocks not seen elsewhere in the Gulf of Tonkin. The island underwent a complex geological history related to the Cenozoic SE-ward tectonic escape of Indochina, recorded as deformation features along the outstanding, continuous coastal exposure. To analyze these deformation features in detail and relate them to the regional events, we acquired a high-resolution Unmanned Aerial Vehicle (UAV) dataset covering about 635,000m<sup>2</sup> of the 3.5 km long coastal outcrop. In addition, 656 strike and dip measurements were made and 390 photos were taken using smart phone apps, thus on-the-ground data were rapidly acquired and georeferenced. Strike and dip measurements from smart phone apps were periodically checked against traditional Brunton compasses for their reliability. The ground photos were correlated with the UAV image during interpretation. QGIS allows both datasets to be overlain on one another for detailed analysis and interpretation.</p><p>We interpreted 2236 deformation features from the dataset, which can be divided into three major types: sand injectites, NW-SE faults, and NE-SW faults. Sand injectites can be divided into three main types: linear dikes, irregular dikes, and massive remobilized sands. Linear dikes trend dominantly N80-100E.</p><p>NW-SE faults are closely spaced and have high dip with N110-130E trend. They consistently left-laterally offset sand dikes while most of the time left-laterally offset the gently dipping beds. Apparent right-lateral separation of beddings probably resulted from variation of the slip vector from horizontal pure strike-slip. Occasionally, sand dikes fill in these NW-SE faults. The offsets are small, mostly less than 1 m.</p><p>NE-SW faults are larger scale than the NW-SE faults, and are associated with drag folding of the strata. No fault surface kinematic indicators were found, probably due to wave erosion. The drag folds are consistently right-lateral, while the bedding separation can be either left-lateral or right lateral. Left-lateral separation is inferred to indicate a second phase of movement along the same fault. Sand dikes cross-cut the drag folds, thus sand dikes formed after the drag folds and the right-lateral motion on NE-SW faults.</p><p>The orientations of these deformation features are consistent with the regional stress field associated with the End-Oligocene inversion, which affected the northern Song Hong Basin and the western Beibuwan Basin due to transpression along the junction between the two basins. The inversion caused regional tilting and NE-SW right-lateral faulting, followed by the main phase of sand injection, and finally the left-lateral NW-SE faults that offset sand dikes. Previously the inversion event was characterized at large scale using industrial seismic and well data. This study provides further evidence of the inversion at the outcrop scale, well below the resolution of the seismic data.</p>

The opening of the Tyrrhenian basin and the Apennine chain formation in the kinematic context of Africa - Europe collision

<p>The Africa Europe collision, which produces the formation of the Alpine arc, in the Mediterranean area is accompanied by passive subduction processes, resulting from the sinking of the remnant Alpine Tethys and the Ionian lithosphere, and from the fragmentation of the Adriatic plate. In this complex deformation, back-arc basins (Alboran, Balearic, Tyrrhenian and Hellenic) and circum - Mediterranean mountain ranges are formed.</p><p>In this work we focus our attention on the opening of the Tyrrhenian basin and the contemporary formation of the Apennine chain.</p><p>In order to describe the evolution of the geodynamic processes that guided the formation of the Tyrrhenian basin and the Apennine chain we used the plate kinematics technique. Through careful observation of the regional structures we have divided the area of the Apennine Chain and the Tyrrhenian basin into polygons (crustal blocks or microplates) distinguished on the basis of the direction of the Tyrrhenian extension. The boundary between the polygons has been placed coinciding with the large structures that characterize the Tyrrhenian-Apennine area. The rotation poles of the individual polygons, in the frame of reference of the Sardo-Corso block, are based on the Tyrrhenian extension directions that characterize them. The velocity ratio between the polygons was determined by the slip vector of the structure (plate boundary) that separates them. To determine the rotation time of the polygons we used the stratigraphic records of the syn-rift sequences, while the rotation angle of the polygons is obtained comparing the crustal balance with the speed ratios.</p><p>Finally, the kinematic framework obtained, included in the global rotation model, allowed us to reconstruct the tectonic evolution of the central Mediterranean during the opening of the Tyrrhenian basin.</p><p><strong>Key Words</strong>: Tyrrhenian-Apennine System, Non-rigid plate kinematics.</p>

Activity of crustal faults and the Xolapa sliver motion in Guerrero–Oaxaca forearc of Mexico, from seismic data

Oblique convergent margins often host forearc slivers separated by the subduction interface and a trench parallel strike-slip fault system in the overriding plate. Mexican oblique subduction setting led to the formation of a forearc sliver and accomodation of part of the slip at the bounding system of strike-slip faults. The Xolapa sliver is, on average, a $$\sim 105$$ ∼ 105 -km-wide crustal block located along the coast of Guerrero and Oaxaca states of Mexico, and is limited by a $$\sim 650$$ ∼ 650 -km-long La Venta-Chacalapa fault zone. Two types of datasets, local catalog and Global CMT compilation, are used to estimate the motion of the Xolapa sliver using the rigid block model that describes the phenomenon of slip partitioning. According to the results obtained from local and Global CMT catalogs for selected subduction thrust earthquakes, the forearc sliver moves southeastwards with respect to the fixed North America plate at the rate of 10 ± 1 mm/year and 5.6 ± 0.8 mm/year, respectively. These velocities in general agree with the values obtained from long-term GPS observations (5–6 mm/year). The origin of the inconsistency between local and teleseismic estimates is attributed to a difference in the double couple focal mechanism parameters for two types of datasets. Convergence obliquity changes from $$10.42{^\circ }$$ 10.42 ∘ and the rate of 58 mm/year to $$13.29{^\circ }$$ 13.29 ∘ at the rate of 68 mm/year along the Guerrero and Oaxaca coast increasing from northwest to southeast; therefore, the Xolapa sliver is supposed to be stretched. However, the slip vector azimuths of thrust subduction earthquakes tend to approach plate convergence vectors southeastwards along the coast; so, we assume that this may produce the forearc block compression.

The 10 June 2012 MW 6.0 earthquake sequence in the easternmost end of the Hellenic arc.

The 10 June 2012 (UTC 12:44:17.3; lat. 36.441°N, long. 28.904°E, Mw6.0) earthquake sequence, 60 km to the west of Rodos Island, is studied, in an attempt to shed light to the obscure deformation pattern at the easternmost end of the Hellenic Arc. Moment tensor solutions for the mainshock and the strongest aftershocks revealed the operation of WNW-ESE dextral strike-slip faulting, with slip vector at~N295°E, approximately orthogonal to the GPS velocity vectors. The strike of the activated structure generally aligns with bathymetric linear escarpments observed in the region, bordering the eastern section of the Rodos basin. The best constrained focal depths are in the range 10 to 25 km, with the mainshock at the depth of 24 km.The slip model for the mainshock, obtained through a finite-fault inversion scheme, showed that slip was mainly concentrated in a single patch, with the locus of peak slip (~125 cm) located ~ 4km to the NW of the hypocenter. The sequence which lies in the western continuation of the Fethiye – Burdur sinistral strike-slip zone into theAegean Sea and Rodos basin, is not connected with activation of this zone. Its characteristics comply with the activation of a dextral strike-slip structure, oblique to this zone, which accommodates along – arc NE-SW extension.

Rake rotation introduces ambiguity in the formulation of slip-dependent constitutive models: slip modulus or slip path?

<p>The linear slip–weakening (SW) law, predicting that the traction decreases for increasing fault slip, is one of the most widely adopted governing models to describe the traction evolution and the stress release processes occurring during coseismic slip failures. We will show that, contrary to other constitutive models, the SW law inherently poses the problem of considering the Euclidean norm of the slip vector or its cumulative value along its path. In other words, it has the intrinsic problem of its analytical formulation, which does not have a solution a priori. By considering a fully dynamic, spontaneous, 3–D rupture problem, with rake rotation allowed, in this paper we explore whether these two formulations can lead to different results. We prove that, for homogeneous configurations, the two formulations give the same results, with a normalized difference less than 1%, which is comparable to the numerical error due to grid dispersion. In particular, we show that the total slip, the resulting seismic moment, the fracture energy density, the slip–weakening curve and the energy flux at the rupture front are practically identical in the two formulations. These findings contribute to reconcile the results presented in previous papers, where the two formulations have been differently employed. However, this coincidence is not the rule. Indeed, by considering models with a highly heterogeneous initial shear stress distribution, where the rake variation is significant, we have also demonstrated that the overall rupture history is quite different by assuming the two formulations, as well as the fault striations, the traction evolution and the scalar seismic moment. In this case the choice of the analytical formulation of the governing law does really matter.</p>