NNE SSW Research Articles

The role of crystallized magma and crustal fluids in intraplate seismic activity in Talala region (Saurashtra), Western India: An insight from local earthquake tomography

The Talala region in Saurashtra, Western India is one of the seismically active intraplate regions on the Earth. In recent past, this region has been site of moderate magnitude earthquakes as well as swarm-type earthquake activities. To understand the processes of earthquake generation in this intraplate setting, we constrained the earthquake distribution pattern along with the crustal seismic P-wave velocity (Vp) and Vp/Vs variations, using local earthquakes data. We inverted 2470 P- and 2230 S-wave arrival times from 550 earthquakes which were recorded over 11 seismic stations during 2007 to 2012. The earthquakes distribution shows that the seismicity is following ~NNE–SSW trend, extending for a distance of ~25km and up to 15km in depth. The seismic tomographic images show that the swarm-type earthquake activities at shallower depths are mostly in the zone of lower Vp and lower Vp/Vs. Whereas, the moderate magnitude earthquakes are occurring in a ~NW trending zone of higher Vp and higher Vp/Vs, possibly indicating a zone of crystallized mafic magma, which was transported from deeper Earth. This zone represents a pronounced heterogeneity and provides locale for stress accumulation in this region. After 2001 Bhuj earthquake (Mw 7.7), due to stress perturbation the ~NNE–SSW trending fault got activated and caused bigger earthquakes in this region. Moreover, the crystallized mafic magma is possibly feeding fluids at shallower depths for causing the swarm-type earthquake activities in this region.

Structural and litho-tectonic controls on Neoproterozoic base metal sulfide and gold mineralization in North Hamisana shear zone, South Eastern Desert, Egypt: The integrated field, structural, Landsat 7 ETM + and ASTER data approach

The Hamisana shear zone (HSZ), is an excellent example of high strain shear belt of the Neoproterozoic Arabian–Nubian Shield (ANS), situated in a position between three major Pan-African terranes (SE Desert, Gabgaba, and Gebeit terranes). The north Hamisana shear zone area (NHSZ), cuts across sequences of island arc-related metasediment-metavolcanic, which are structurally overlain by ophiolitic nappes and intruded by a number of granitoids and gabbroic rocks. Although it is interesting geological-tectonic setting for base metal sulfide and gold ores, there is a lack of detailed studies on structure, geology and mineralization in this area, which considered as poorly mapped remote region not only in Egypt but also in Sudan.For these reasons, we integrated image transformation methods include; Principal Components Analysis (PCA), Band Ratios (BR), False-Color Composite (FCC) and filtering on the spectral bands of two distinct datasets ETM+ and ASTER for detailed mapping of the NHSZ area. Spectral data fusion with structural data analysis and field observations provide a better understand of the temporal and spatial relationships between the litho-tectonic units and regional tectonic setting in the course of controls on base-metal sulfide and associated gold mineralization. Merging these different data sources in the study area suggests that, the base-metal sulfide and associated gold mineralization are restricted to quartzites, (member of island arc-related metasediments), and mostly controlled by D3 deformational event (main HSZ deformational event). This event characterized by transpressional stress regime, with σ1 trending E–W and σ3 trending N–S, activated conjugate NNW sinistral and NNE–SSW dextral strike-slip faulting, likely during syn-tectonic granodiorite emplacement.

Anisotropic Rayleigh wave tomography of Northeast China using ambient seismic noise

The ambient noise data recorded by 249 seismic stations in the permanent and temporary networks in Northeast China are used to invert for the isotropic phase velocity and azimuthal anisotropy of Rayleigh waves in the period band 5–50s. The inversion results reflect the structure from the shallow crust to upper mantle up to approximately 120km depth. Beneath the Songliao basin, both the fast direction in shallow crust and strike of a low-velocity anomaly in the middle crust are NNE–SSW, which is coincident with the main tectonic trend of the (Paleo) Pacific tectonic domain. This indicates that the rifting of the Songliao basin is influenced by the subduction of (Paleo) Pacific plate. The upper mantle of Songliao block (except the central area of Songliao basin) to the west of Mudanjiang fault, and the east of the North–South Gravity Lineament, is characterized by high-velocity and weak anisotropy up to approximately ​120km depth. We infer that there is delamination of lithospheric mantle beneath the Songliao block. Obvious N–S, NE–SW, and E–W trending fast directions are found in the lithospheric mantles of the east, west, and south sides of Songliao block, respectively, which coincide with the strikes of the Paleozoic tectonic in these areas. This suggests that the frozen-in anisotropic fabric in the lithospheric mantle can be used to indicate the historical deformation of the lithosphere. In the northern margin of the North China Craton, the spatial variations of phase velocity and azimuthal anisotropy are more dramatic than those in Northeast China blocks, which indicates that the lithosphere of the North China Craton has experienced more complicated tectonic evolution than that of the Northeast China blocks.

Rapid dike intrusion into Sakurajima volcano on August 15, 2015, as detected by multi-parameter ground deformation observations

We present observations of ground deformation at Sakurajima in August 2015 and model the deformation using a combination of GNSS, tilt and strain data in order to interpret a rapid deformation event on August 15, 2015. The pattern of horizontal displacement during the period from August 14 to 16, 2015, shows a WNW–ESE extension, which suggests the opening of a dike. Using a genetic algorithm, we obtained the position, dip, strike length, width and opening of a dislocation source based on the combined data. A nearly vertical dike with a NNE–SSW strike was found at a depth of 1.0 km below sea level beneath the Showa crater. The length and width are 2.3 and 0.6 km, respectively, and a dike opening of 1.97 m yields a volume increase of 2.7 × 106 m3. 887 volcano-tectonic (VT) earthquakes beside the dike suggest that the rapid opening of the dike caused an accumulation of strain in the surrounding rocks, and the VT earthquakes were generated to release this strain. Half of the total amount of deformation was concentrated between 10:27 and 11:54 on August 15. It is estimated that the magma intrusion rate was 1 × 106 m3/h during this period. This is 200 times larger than the magma intrusion rate prior to one of the biggest eruptions at the summit crater of Minami-dake on July 24, 2012, and 2200 times larger than the average magma intrusion rate during the period from October 2011 to March 2012. The previous Mogi-type ground deformation is considered to be a process of magma accumulation in preexisting spherical reservoirs. Conversely, the August 2015 event was a dike intrusion and occurred in a different location to the preexisting reservoirs. The direction of the opening of the dike coincides with the T-axes and direction of faults creating a graben structure.

Lithology and characteristics of the Messinian evaporite sequence of the deep Levant Basin, eastern Mediterranean

As the lithological composition of the Messinian salt sequence of the Levant Basin is still controversial and unconstrained, we reveal for the first time the lithology of the entire evaporite sequence from deep basin depth migrated seismic and borehole data. The data presented here shows that the seismic transparent layers are composed of pure and uniform halite while the reflective layers are bundles of thin clay layers interbedded in the halite background. The thin clay layers inside the deep basin evaporites have a cumulative thickness of 25–40m. High amplitude fan structures are observed on the deepest internal reflector which may suggest clay transportation. Among all the internal reflectors, the upper units are more deformed while the deeper units are more coherent and flat. Two sets of folds/faults are shown on the shallower intra-units: folds with NNE–SSW trending axes and thrust faults strike NW–SE. On a regional scale, the top salt reflector is generally horizontal while the other internal reflectors dip toward the NW. The shallowest intra-unit is the only one that has a wedge shape thickening to the NW, while the other intra-units generally have uniform thicknesses.

Imaging active faulting in a region of distributed deformation from the joint clustering of focal mechanisms and hypocentres: Application to the Azores–western Mediterranean region

The matching between linear trends of hypocentres and fault planes indicated by focal mechanisms (FMs) is frequently used to infer the location and geometry of active faults. This practice works well in regions of fast lithospheric deformation, where earthquake patterns are clear and major structures accommodate the bulk of deformation, but typically fails in regions of slow and distributed deformation. We present a new joint FM and hypocentre cluster algorithm that is able to detect systematically the consistency between hypocentre lineations and FMs, even in regions of distributed deformation. We apply the method to the Azores–western Mediterranean region, with particular emphasis on western Iberia. The analysis relies on a compilation of hypocentres and FMs taken from regional and global earthquake catalogues, academic theses and technical reports, complemented by new FMs for western Iberia. The joint clustering algorithm images both well-known and new seismo-tectonic features. The Azores triple junction is characterised by FMs with vertical pressure (P) axes, in good agreement with the divergent setting, and the Iberian domain is characterised by NW–SE oriented P axes, indicating a response of the lithosphere to the ongoing oblique convergence between Nubia and Eurasia. Several earthquakes remain unclustered in the western Mediterranean domain, which may indicate a response to local stresses. The major regions of consistent faulting that we identify are the mid-Atlantic ridge, the Terceira rift, the Trans-Alboran shear zone and the north coast of Algeria. In addition, other smaller earthquake clusters present a good match between epicentre lineations and FM fault planes. These clusters may signal single active faults or wide zones of distributed but consistent faulting. Mainland Portugal is dominated by strike–slip earthquakes with fault planes coincident with the predominant NNE–SSW and WNW–ESE oriented earthquake lineations. Clusters offshore SW Iberia are predominantly strike–slip or reverse, confirming previous suggestions of slip partitioning.

Carbonate karst and its relationship with geodynamic conditions of the Odessa city (Ukraine)

A connection between karst and geodynamic features in the area of the city of Odessa (Black Sea karst region) was considered. The geodetic, geological and hydrogeological researches showed divergent vertical and horizontal movements of the individual units of the Neogene–Quaternary structural stage. It was found that the main orientations of passages in the caves in the Moldavansky and Kryvobalkovsky sites are NNW–SSE, WNW–ESE and NNE–SSW. This agrees well with the direction of the diagonal lineament network disclosed in recent years. The main directions of cave passages in the Bugaevsky site coincide with the main directions of the lineaments WNW–ESE, NNW–SSE located in the immediate vicinity of the zones of influence of the lineaments of the orthogonal networks N–S, SSW–NNE, and W–E. These findings suggest that caves developed along the directions of the lineaments of two tectonic networks of Neogene structural stage—diagonal and orthogonal. These networks of tectonic fractures were mapped and analyzed previously by applying the geological and hydrogeological methods and analyzing digital maps of the Neogene surfaces. Results of the research were compared to a map of isolines of long-term average velocity of vertical deformations of ground surface, and of zones of influence of lineaments identified in the surface topography of Upper Miocene clay, limestone and Pliocene red-brown clay. They show that the karst areas are mainly located in the gradient zones of vertical deformation of ground surface, and zones where Upper Miocene limestone is compartmentalized by diagonal and orthogonal lines of fracture. These areas could be considered as tectonically weakened.

Seismotectonics of the Antalya Basin and surrounding regions in eastern Mediterranean from 8 to 28 December 2013 Mw 5.0–5.8 earthquake sequence

The 8–28 December 2013 Mw 5.0–5.8 Antalya Basin earthquake sequence in eastern Mediterranean is examined. Centroid moment tensors for 16 earthquakes with moment magnitudes (Mw) between 3.6 and 5.8 are determined by applying a waveform inversion method. All earthquakes are shallow focus thrust events at a depth of 40–45km. The seismic moments (Mo) of the earthquakes are estimated as 4.10×1016–5.54×1017Nm and rupture durations of the mainshocks are 20–22s. The focal mechanisms of the aftershocks are mainly thrust faulting with a strike-slip component and reveal NW–SE trending direction of T-axis in the entire activated region. According to high-resolution hypocenter relocation of the Antalya earthquake sequence, seven main clusters are revealed. The aftershock activity in the observation period between 1 December 2013 and 23 January 2015 extends in an N to S direction. A seismic cross-section indicates that a complex pattern of the hypocenter distribution with the activation of seven segments. The westernmost cluster (cluster 1) is associated with a fault plane trending mainly WNW–ESE and dipping vertical, while the cluster 5 is related to a fault plane trending NNE–SSW and dipping towards SSE. The best constrained focal depths indicate that the aftershock sequence is mainly confined in the crust (depth<40km) and are operating in the approximate depth range from 3 to 110km. A stress tensor inversion of focal mechanism data is performed to obtain a more precise picture of the Antalya Basin stress field. The stress tensor inversion results indicate a predominant thrust stress regime with a NE–SW oriented maximum horizontal compressive stress (SH). According to variance of the stress tensor inversion, to first order, the Antalya Basin is characterized by a homogeneous interplate stress field. The Coulomb stress change associated with two mainshocks are also investigated to evaluate any significant enhancement of stresses along the Antalya Basin and surrounding regions. Positive lobes with stress of more than 0.4 bars are obtained for two mainshocks, indicating that these values are large enough to increase the Coulomb stress failure towards NE–SW and NW–SE directions, respectively.

Tectonic forcing of drainages and geomorphic features developed across Himalayan mountain frontal part of western limb of Siang Antiform, Arunachal Himalaya

Drainages display tectonic forcing of their channels on the frontal region of the Arunachal Himalaya due to structural control. Dikari, a transverse river flowing along the N–S trending western limb of the major Siang Antiform, exhibits structurally controlled nature of its drainage on its downstream flow towards south, through a network of NE–SW and NW–SE trending conjugate faults. The river shows compressed meandering as the regional structural trend of ENE–WSW seems to be reactivated by the transverse NW–SE trend of neotectonic fault activity. The Himalayan frontal thrust (HFT) tracing along the Himalaya mountain front has been displaced sinisterly for a distance of ~7 km by a WNW–ESE trending fault running along the Sileng stream. Development of parallel drainages in the southern part of the Sub-Himalaya is interpreted to have formed as a result of uplifting related to the above-mentioned strike-slip movement. Along the HFT zone, the frontal streams and rivers exhibit deflection of their channels from NE–SW to ENE–WSW directions. Channel of the transverse Siang river has been deflected for a length of 3 km along the NNE–SSW direction across the Himalayan frontal part. In this part of the Himalaya, previous workers did not give much emphasis on the role of Siang Antiform as far as neotectonic with respect to the tectonics related to the HFT is concerned. There is a syntectonic relationship between the active NE–SW-oriented compression direction and the tectonic forcing of the drainages including development of the tectonic geomorphology.

Demarcating saline water intrusion pathways using remote sensing, GIS and geophysical techniques in structurally controlled coastal aquifers in Southern India

Application of remote sensing and geographical information system (GIS) with the help of ground truth studies like vertical electrical soundings (VES) and water quality measurements gave a comprehensive picture on saline water intrusion pathways in the structural controlled aquifers of Uppanar and Cauvery River systems located in Sirkazhi and Mannanpandal coastal areas of Southern India. The detailed geomorphic units and lineaments were mapped using IRS LISS-III (1:50,000 Scale) and SRTM Elevation Digital data under GIS environment. The area is mainly alluvial deposits of Holocene Age and classified into three major geomorphic units (i.e., fluvial, fluviomarine, and marine geomorphic units). The identified lineaments are mostly trending North-northeast (NNE)–South-southwest (SSW), Northeast (NE)–Southwest (SW), Northwest (NW)–Southeast (SE), East–West (EW) and East-Northeast (ENE)–West-Southwest (WSW) directions. Some of them are potential for fresh groundwater occurrence and movement. The lineaments trending NE–SW, NNE–SSW, and ENE–WSW act as pathways for saline water intrusion to the inland. The lineament L1 (NNE–SSW trending) conformed as a sinisterly shifted fault played a significant role in saline water intrusion. The area within the parallel lineaments L2 and L3 oriented ENE–WSW direction indicates low topography, beach ridges, paleo-channel sinuosity, large aerial extent of tidal flats, and backwater inundation. All the above geomorphic units gave indirect evidence of land subsidence, which was confirmed with the help of sub-surface geo-electrical signals obtained through VES and in situ groundwater quality measurements. Integrating all the above results, the saline water spread and fresh water pockets were identified.

Application of high-pass filtering techniques on gravity and magnetic data of the eastern Qattara Depression area, Western Desert, Egypt

In this work, a reconnaissance study is presented to delineate the subsurface tectonics and lithological inferences of the eastern area of Qattara Depression using the Bouguer gravity and aeromagnetic data. To achieve this goal, several transformation techniques and filtering processes are accomplished on these maps. At first, the total intensity aeromagnetic map is processed through the application of reduction to the magnetic north pole technique. The fast Fourier transform is carried out on the gravity and RTP magnetic data for establishing and defining the residual (shallow) sources. The frequency high-pass filtering is used to enhance the anomaly wavelengths associated with the shallow sources. The used processing techniques are the polynomial surface fitting enhancement, Laplacian, Strike Filtering, Enhancement Utilization, Suppression Utilization, Butterworth Filtering Utilization, Butterworth high-pass filter, Euler’s deconvolution and forward modeling. The equivalent depths of the isolated short wavelength anomalies are 0.759 and 0.340km below the flight surface, and the depths of the intermediate wavelength anomalies are 1.28 and 2.00km for the gravity and magnetic data, respectively. Finally, the quantitative interpretations of the Bouguer gravity and RTP magnetic maps of the study area, reflect the occurrence of the various types of structures and their components. The main tectonic deformations of the study area have NNW–SSE, NNE–SSW, NE–SW, NW–SE and E–W trends.

The St. Gallen Fault Zone: a long-lived, multiphase structure in the North Alpine Foreland Basin revealed by 3D seismic data

The St. Gallen Fault Zone (SFZ) is a system of major NNE–SSW striking normal faults within the North Alpine Foreland Basin (NAFB), just west of the city of St. Gallen. It used to be only roughly known from 2D seismic data, locally displaying offsets of up to 300 m at the level of the Mesozoic strata. We present a detailed structural interpretation of a recently acquired 3D seismic dataset that reveals the occurrence of multiphase tectonic activity along the SFZ from at least the Late Paleozoic to the early Oligocene, and possibly even later. We can show that the SFZ roots in extensional basement structures that bound small Permo-Carboniferous grabens. Thickness changes in the younger sediments above these Paleozoic grabens indicate several phases of tectonic subsidence during the Triassic and the Jurassic. The Lower Cenozoic units in the northernmost part of the 3D seismic area are also offset by the SFZ. No offsets can be identified in the overlying, shallower part of the Cenozoic units. Most faults constituting the SFZ are favourably oriented in the present-day stress field (SHmax NNW–SSE) to be reactivated in strike-slip mode. The seismic events induced by testing operations at the geothermal exploration borehole “St. Gallen GT-1” (SG GT-1) in July 2013 revealed that, even though the seismicity of northeastern Switzerland is considered to be low and diffuse, parts of the SFZ have to be regarded as critically stressed. Combining the interpretation of geological and seismic data, we conclude that the SFZ represents a reactivated basement-rooted normal fault, which was active during several phases in Permo-Carboniferous and Mesozoic times and that is still active today in strike-slip mode.

Cenozoic structural evolution of the southwestern Bükk Mts. and the southern part of the Darnó Deformation Belt (NE Hungary)

Abstract Extensive structural field observations and seismic interpretation allowed us to delineate 7 deformation phases in the study area for the Cenozoic period. Phase D1 indicates NW–SE compression and perpendicular extension in the Late Oligocene–early Eggenburgian and it was responsible for the development of a wedge-shaped Paleogene sequence in front of north-westward propagating blind reverse faults. D2 is represented by E–W compression and perpendicular extension in the middle Eggenburgian–early Ottnangian. The D1 and D2 phases resulted in the erosion of Paleogene suites on elevated highs. Phase D2 was followed by a counterclockwise rotation, described in earlier publications. When considering the age of sediments deformed by the syn-sedimentary D3 deformation and preliminary geochronological ages of deformed volcanites the time of the first CCW rotation can be shifted slightly younger (~17–16.5 Ma) than previously thought (18.5–17.5 Ma). Another consequence of our new timing is that the extrusional tectonics of the ALCAPA unit, the D2 local phase, could also terminate somewhat later by 1 Myr. D4 shows NE–SW extension in the late Karpatian–Early Badenian creating NW–SE trending normal faults which connected the major NNE–SSW trending sinistral faults. The D5 and D6 phases are late syn-rift deformations indicating E–W extension and NW–SE extension, respectively. D5 indicates syn-sedimentary deformation in the Middle Badenian–early Sarmatian and caused the synsedimentary thickening of mid-Miocene suites along NNE–SSW trending transtensional faults. D5 postdates the second CCW rotation which can be bracketed between ~16–15 Ma. This timing is somewhat older than previously considered and is based on new geochronological dates of pyroclastite rocks which were not deformed by this phase. D6 was responsible for further deepening of half-grabens during the Sarmatian. D7 is post-tilt NNW–SSE extension and induced the deposition of the 700 m thick Pannonian wedge between 11.6–8.92 Ma in the southern part of the study area.

Transpressional granite-emplacement model: Structural and magnetic study of the Pan-African Bandja granitic pluton (West Cameroon)

The Pan-African NE–SW elongated Bandja granitic pluton, located at the western part of the Pan-African belt in Cameroon, is a K-feldspar megacryst granite. It is emplaced in banded gneiss and its NW border underwent mylonitization. The magmatic foliation shows NE–SW and NNE–SSW strike directions with moderate to strong dip respectively in its northern and central parts. This mostly, ferromagnetic granite displays magnetic fabrics carried by magnetite and characterized by (i) magnetic foliation with best poles at 295/34, 283/33 and 35/59 respectively in its northern, central and southern parts and (ii) a subhorizontal magnetic lineation with best line at 37/8, 191/9 and 267/22 respectively in the northern, central and southern parts. Magnetic lineation shows an ‘S’ shape trend that allows to (1) consider the complete emplacement and deformation of the pluton during the Pan-African D 2 and D 3 events which occurred in the Pan-African belt in Cameroon and (2) reorganize Pan-African ages from Nguiessi Tchakam et al. (1997) compared with those of the other granitic plutons in the belt as: 686 ±17 Ma (Rb/Sr) for D 1 age of metamorphism recorded in gneiss; and the period between 604–557 Ma for D 2–D 3 emplacement and deformation age of the granitic pluton in a dextral ENE–WSW shear movement.

Metamorphic record of the NW Himalayan orogeny between the Indian plate-Kohistan Ladakh Arc and Asia: Revelations from foliation intersection axis (FIA) controlled P–T–t–d paths

Our recent Foliation Intersection Axes (FIAs) data from porphyroblasts in a metapelitic sequence, exposed south of the Indus suture of the NW Himalaya, revealed a fascinating relationship between the trends of three FIA sets versus the plate motion of India since its collision with the Kohistan–Ladakh Arc. The established FIA trend sequence, ESE–WNW (set 1), E–W (set 2) and NNE–SSW (set 3), matches successive vectors of relative India–Asia plate movement between magnetic anomalies 25–22 (55–50Ma), 21–20 (48–44Ma) and 13–8 (36–29Ma), on the premise that FIAs develop normal to the direction of bulk crustal shortening. The correlation allows us to precisely model the pressure (P)–temperature (T) path followed by this portion of the NW Himalayan orogen from 55 to 29Ma. Representative samples preserving FIA sets in garnet porphyroblasts are modeled in the chemical system MnNCKFMASH using THERMOCALC. A steep continuous P–T path is obtained from garnet porphyroblasts for sample preserving FIA set 1 that brackets metamorphic conditions during early NNE–SSW shortening (anomalies 25–22) between 0.4–0.87GPa and 495–535°C (M1 metamorphism). Garnets preserving FIA set 2 revealed 0.46–0.8GPa and 507–565°C (M2 metamorphism) during N–S (anomalies 21–20) shortening. Subsequent ESE–WNW shortening parallel to the orogenic arc (anomalies 13–8) peaked at 0.9 to 1GPa and 595±19 to 618±28°C (M3 metamorphism) and was followed by high-temperature/low-pressure conditions of 0.8±0.2GPa at 747±32°C that accompanied north-side-down decompression (M4 metamorphism) after 29Ma. The M3 and M4 P–T estimates are based on average P–T conditions of garnet inner rim with the matrix mineral phases, which we suspect may not be in equilibrium due to later reactivation of the matrix foliation. The orthogonal orientation of FIA 1 and the NNE movement of India between anomalies 25 and 22 (55–50Ma) suggest that the Indian plate collided with the Kohistan–Ladakh Arc around this time.

Crevasse-squeeze ridge corridors: Diagnostic features of late-stage palaeo-ice stream activity

A 200-km-long and 10-km-wide linear assemblage of till-filled geometrical ridges on the bed of the Maskwa palaeo-ice stream of the late Wisconsinan southwest Laurentide Ice Sheet are interpreted as crevasse-squeeze ridges (CSR) developed during internal flow unit reorganization, immediately prior to ice stream shutdown. Ridge orientations are predominantly orientated WNW–ESE, with a subordinate WSW–ENE alignment, both indicative of ice fracture development transverse to former ice stream flow, as indicated by NNE–SSW aligned MSGL. Subglacial till injection into basal and/or full depth, mode I and II crevasses occurred at the approximate centreline of the ice stream, in response to extension and fracturing. Landform preservation indicates that this took place during the final stages of ice streaming, immediately prior to ice stream shutdown. This linear zone of ice fracturing therefore likely represents the narrowing of the fast-flowing trunk, similar to the plug flow identified in some surging valley glaciers. Lateral drag between the final active flow unit and the slower moving ice on either side is likely recorded by the up-ice bending of the CSR limbs. The resulting CSR corridor, here related to an individual ice stream flow unit, constitutes a previously unreported style of crevasse infilling and contrasts with two existing CSR patterns: (1) wide arcuate zones of CSRs related to widespread fracturing within glacier surge lobes; and (2) narrow concentric arcs of CSRs and recessional push moraines related to submarginal till deformation at active temperate glacier lobes.

Remote detection of geological structures: an application to the Aravalli region, western India

Optical and microwave remote sensing data are used in conjunction with a digital elevation model to map lineaments in the central parts of the Aravalli region, Rajasthan, western India. Lineament maps interpreted from each data-set are subsequently combined to derive a composite lineament map of the area. Rose plots are used to identify the prominent trends of the lineaments and compared with published structural map of the study area. Three major trends are identified, namely, the NE–SW, NNE–SSW and EW, which are interpreted to be, related to the DF1, DF2 and DF4 deformation phases identified by the previous workers through field studies. The lineaments are classified as fold axes or faults, and a total of 10-fold axes and 30 faults mapped in the area.

ANIZOTROPIE MAGNETICKÉ SUSCEPTIBILITY HORNIN NA KONTAKTU METABAZITOVÉ A DIORITOVÉ ZÓNY BRNĚNSKÉHO MASIVU V OKOLÍ VELKÉ BABY U JINAČOVIC

An anisotropy of magnetic susceptibility and temperature dependence on magnetic susceptibility were used to reveal an evolution history along the contact of the Metabasite and Diorite zones of Brno massif north of Brno-Řečkovice. The analysis of temperature dependence of magnetic susceptibility indicated that magnetic properties of all rocks in this area are essentially controlled by magnetite with a very small contribution of pyrhotite and hematite. These minerals were formed later than the primary magmatic minerals. Therefore we assume that magnetic fabrics in studied rocks reflect deformational processes which affected these rocks. There are three patterns in anisotropy of magnetic susceptibility (AMS) in studied rocks. In the first pattern detected in diorites, the magnetic foliation is striking NE–SW, dipping to the NW and there is subvertical magnetic lineation. The second planar magnetic indicates a rotational movement of microgranite rocks along the contact of the Metabasite and Diorite zones. The last pattern found in rocks of the Metabasite zone is magnetic foliation striking NNE–SSW dipping on the NWW and magnetic lineation trending to the SW with plunge of 42° and it shows normal faulting of studied area.

The Beni-Ilmane (Algeria) seismic sequence of May 2010: Seismic sources and stress tensor calculations

A moderate earthquake with a moment magnitude of Mw 5.5 struck the Sub-Bibanique region of eastern Algeria on 14 May 2010, killing three people, injuring hundreds of others, and causing moderate damages in the epicentral area, mainly in the villages of Beni-Ilmane and Samma. The focal mechanism of the seismic source for the first shock, obtained by near-field waveform modelling, exhibits left-lateral strike-slip faulting with the first nodal plane oriented at N345°, and right-lateral strike-slip faulting with the second nodal plane oriented at N254°. A second earthquake that struck the region on 16 May 2010, with a moment magnitude of Mw 5.1, was located 9km SW of the first earthquake. The focal mechanism obtained by waveform modelling showed reverse faulting with nodal planes oriented NE–SW (N25° and N250°). A third earthquake that struck the region on 23 May 2010, with a moment magnitude of Mw 5.2, was located 7km S of the first shock. The obtained focal mechanism showed a left-lateral strike-slip plane oriented at N12° and a right-lateral strike-slip plane oriented at N257°. Field investigations combined with geological and seismotectonic analyses indicate that the three earthquake shocks were generated by activity on three distinct faults. The second and third shocks were generated on faults oriented WSW–ENE and NNE–SSW, respectively. The regional stress tensor calculated in the region gives an orientation of N340° for the maximum compressive stress direction (σ1) which is close to the horizontal, with a stress shape factor indicating either a compressional or a strike-slip regime.

Structural analysis of hanging wall and footwall blocks within the Río Guanajibo fold-and-thrust belt in Southwest Puerto Rico

The Rio Guanajibo fold-and-thrust belt (RGFT), composed of Cretaceous serpentinite and volcano-sedimentary rocks, represents the deformation front of a contractional event in SW Puerto Rico during the Paleogene. Previous studies inferred structural and stratigraphic relationships from poorly exposed outcrops. New road cuts exposed the Yauco (YF) and El Rayo Formations (ERF) providing insights on the deformation of the hanging wall and footwall. We described the nature and orientation of faults and folds and analyzed the kinematic indicators to characterize the deformation. The YF occurs in the hanging wall and shows a sequence of folded, medium-bedded mudstone and thinly bedded shale and sandstone. Major folds strike NW–SE and are gentle with steeply inclined axial planes and sub-horizontal fold axes. Minor folds are open with moderately inclined axial planes and gently to moderately inclined SE-plunging fold axes. NW–SE striking reverse and thrust faults cut layers and show movement to the SW. Steep left-lateral faults strike NW–SE and NE–SW, and smaller right-lateral strike-slip faults strike NNE–SSW. At the footwall, the ERF consists of bioclastic limestone and polymictic orthoconglomerates and paraconglomerates. Reverse and strike-slip faults cut along lithological contacts. Results suggest that the hanging wall and footwall accommodated strain along preexisting weaknesses, which are dependent on lithology and sedimentary structures. The kinematic analysis suggests that shortening in the NE–SW direction was partitioned between folding and interlayer shortening, accommodated by flexural slip, and reverse and left-lateral faults that resulted from contraction. The RGFT represents the Paleogene back arc deformation of a bivergent thrust system.