En-echelon Pattern Research Articles

Potential domino effect of the 2023 Kahramanmaraş earthquake on the centuries-long seismic quiescence of the Dead Sea fault: inferences from the North Anatolian fault

Field observations conducted immediately following the February 6, 2023, Mw 7.8 Kahramanmaraş earthquake documented the southern surface rupture termination in the Amik Basin. The termination occurred in an en-echelon pattern, extending across the 3.5 km width of the approximately 10-km-wide stepover. This extension reached towards the northern tip of the Hacıpaşa Fault, which constitutes the main northern segment of the Dead Sea Fault Zone (DSFZ). Archaeoseismologic and paleoseismologic data show that the approximately 800-km-long DSFZ has been seismically quiet for more than 600 years in the north and 900 years in the south. A similar fault connection geometry at the western end of the 1939 Ms 7.9 Erzincan earthquake in the easternmost part of the North Anatolian Fault Zone and the subsequently triggered successive large magnitude earthquakes migrating westward within a few decades highlights an increased seismic hazard for the entire DSFZ. This heightened seismic hazard potential along the DSFZ, combined with historical population centers experiencing wars and migrations, puts millions of people at an unparalleled risk.

Episodic evolution of intracontinental orogenic deformation: Insight from the southern Bogda fold-and-thrust belt of the Tianshan Mountains, NW China

The Mesozoic-Cenozoic Tianshan orogenic belt, a key area for studying intracontinental orogenic deformation, experienced multiple uplift episodes due to the far-field effects from a series of collision events along the southern margin of Eurasia. Focusing on the fold-and-thwrust belt at the southern margin of the Bogda Mountain, a branch of the eastern Tianshan orogenic belt, we integrated 2D seismic data, borehole and outcrop data to construct a balanced and sequentially restored cross-section across the central part of this belt. The activities and mechanical evolution of the major faults were analyzed by using the discrete-element modeling (DEM) method, offering new insights into the tectonic transformation of the Turpan-Hami Basin influenced by episodic uplifts of the Bogda Mountain in an intracontinental setting. The studied fold-and-thrust belt can be divided into two deformation systems: (i) the piedmont deformation system, comprising a southward basement thrust system and a thin-skinned thrust system on Jurassic detachment, and (ii) the thrust front belt, exhibiting an en-echelon pattern in the basin center and featured by fault-propagation folds along the lower Jurassic coal unit. Stratigraphic and reported thermochronological analyses pinpoint four key contractional deformation periods: Late Jurassic, Late Cretaceous, Paleocene-Pliocene, and Pleistocene-present. The DEM numerical simulation results indicate a critical conical Coulomb wedge model governed by the episodic activities of the southern Bogda fold-and-thrust belts from the Mesozoic to the Cenozoic. Surface processes (syntectonic erosion/deposition) significantly impacted differential activities between the orogenic belt and the basin's thrust structures. We propose that periodic arid climates in the Tianshan Mountains reduced erosion rates, promoting the expansion of the southern Bogda fold-and-thrust belts toward the basin and the widening of the orogenic belt.

Extrapolation Paleostress Orientations Deduced from Joints Analyses at Spi Rais and West Part of Chai Gara Anticlines, Duhok Area, Kurdistan Region, Iraq

Spi Rais anticline (East part of major Bekhair anticline) and western part of Chia Gara anticline were chosen to study joint paths. They are located within the highly folded zone of the western zagros fold and thrust belt, Iraqi segment. These anticlines arranged in an en-echelon pattern and they expose rocks range in age from Late Cretaceous to Late Miocene. The Late Cretaceous (Campanian – Maastrichtian) succession represented by Bekhme and Shiranish Formations. The lithologies of these rocks are competent and consist of limestone, dolomitic limestone and marly limestone whichare favorable to joint development. Different types of joints were developed in such rocks due to stresses resulted from collision between Arabian and Eurasian (Turkish and Iranian) plates. The joint sets and systems are the most abundant fractures in the rocks of the study area. The chronological relationships of the joints refer that the area had witnessed multiple tectonic pulses in the form of compressional and extensional stresses. The stereonet and the Win – Tensor programs were used to plot the attitudes of joints and deduce their paleostresss orientations. Furthermore, the orientations of deduced paleostresses were plotted onto geological map of investigated area and simulated as paleo trajectories as well. The deduced paleostress direction responsible for folding in traverse 1 was (356° - 195°), in traverse 2 (330° - 168°) and in traverse 3 (353°- 163°).

The Impact of Pre-Existing Faults on Fault Geometry during Multiphase Rifts: The Jiyang Depression, Eastern China

The combination of multi-phase extension and pre-existing fault reactivation results in a complex fault pattern within hydrocarbon-bearing basins, affecting hydrocarbon exploration at different stages. We used high-resolution 3D seismic data and well data to reveal the impact of multi-phase extension and pre-existing fault reactivation on Cenozoic fault pattern changes over time in the Jiyang Depression of eastern China. The results show that during the Paleocene, a portion of NW-striking pre-existing faults reactivated under NS extension and controlled the basin structure (type 1). Other parts of the NW-striking pre-existing faults stopped activity and served as weak surfaces, and a series of NNE-striking faults were distributed in an en-echelon pattern along the NW direction at shallow depths (type 2). In areas unaffected by pre-existing faults, NE-striking faults formed perpendicular to regional stresses. During the Eocene, the regional stresses shifted clockwise to near-NS extension, and many EW-striking faults developed within the basin. The NE-striking faults and the EW-striking faults were hard-linked, forming the ENE-striking curved faults that controlled the structure in the basin (type 3). The NNE-striking faults were distinctly strike-slip at this time, with the ENE-striking faults forming a horsetail pattern at their tails. Many ENE-striking faults perpendicular to the extension direction were formed in areas where the basement was more stable and pre-existing faults were not developed (type 4). There were also developing NS-striking faults that were small in scale and appeared in positions overlapping different main faults (type 5). Additionally, different fault patterns can guide different phases of hydrocarbon exploration. Type 1, type 2, and type 3 faults are particularly suitable for early-stage exploration. In contrast, type 4 and type 5 faults are more appropriate for mature exploration areas, where they may reveal smaller hydrocarbon reservoirs.

UAS-Derived Surficial Deformation around the Epicenter of the 2016 Mw 5.8 Pawnee, Oklahoma, USA, Earthquake

ABSTRACT Unmanned aerial systems (UAS) provide a framework for recording perishable surficial data or information. Open fractures exhibiting regular en-echelon patterns were captured by a 12-megapixel, FL-9 mm camera attached to a Phantom IV UAS over the epicenter of the magnitude (Mw) 5.8 earthquake of September 3, 2016, 15 months later. The Digital Surface Models (DSMs) and orthoimagery offered a spatial resolution (∼1 cm) sufficient to identify small-scale plastic deformations that appear to be controlled by en-echelon joint sets developed in the underlying formation. The fissure boundaries and intersections are remarkably linear and sharp. They appeared to have been recently formed, presumably by seismic swarms believed to have been associated with wastewater injection. The DSMs revealed a series of conjugate patterns suggestive of regional systematic joints with apparent subsidence of infilling up to 50 cm. The earthquakes emanated from the Precambrian metamorphic basement, with epicentral clusters at ∼5- and 8-km depths. Low energy release from depths >1.5 km appears to be locally attenuated by an unconsolidated “soil cap,” which likely formed an impedance contrast. The maximum deformation direction from the cumulative energy of earthquakes correlates with a wrench fault tectonics model that could conceivably produce the observed en-echelon joint sets observed in the orthoimagery and DSMs. These features were observed within 275 m of the reported Mw 5.8 epicenter. The remarkably linear repeating pattern of deformation appears to express fissures that preserve the wrench fault fractures generated by the Mw 5.8 earthquake emanating from discontinuity suites within marine sandstone, shale, and limestone of Pennsylvanian to Permian age.

Extension Related Magmatism and Basin Evolution in Northwestern Part of the Cuddapah Rift, India

Spatial distribution and field relationship of igneous intrusives viz. basic dykes, pink granite-leucogranite-tourmaline pegmatites and quartz reefs across interface between the Neoarchean Gadwal schist belt (Basement) and the Proterozoic Cuddapah basin have been documented. The Cuddapah basin is a half graben (rift) developed at right angle to the basement and displays two sets of faults: (1) NE-SW longitudinal and (2) NW-SE transverse. The longitudinal faults oriented parallel to basin margin have controlled sedimentation, subsidence and uplift. The transverse faults extending from rift shoulder (basement) right into central part of the basin are post depositional faults and imparted en-echelon pattern to the basement-basin interface. Sedimentary facies, depositional environments and basin setting indicate that the basin fill was deposited in a rift setting over the northwestern part of the epeiric sea embayment that flooded on to the Dharwar batholith of the Eastern Dharwar craton. Basin evolution stages have been outlined. Basin uplift/inversion is controlled by reverse faults and is viewed as a cause and effect to the post Cuddapah extension related magmatism which is attributed to magma underplating in the environs of the northwestern part of the Cuddapah rift at crustal levels.

Structural analysis of the Aghajari and Pazanan anticlines, Dezful Embayment, SW Iran

In the present study, seismic profiles and well data were used to provide detailed deformational patterns through the Aghajari and Pazanan anticlines located in the Zagros fold and thrust belt. A suite of 32 and 26 seismic profiles obtained from the Aghajari and Pazanan anticlines, respectively were examined. Furthermore, some 50 well data upon top of drilled formations were applied to prepare depth contour map of the relevant formations in these two anticlines. These asymmetric anticlines with a northwest-southeast trend and en-echelon pattern host considerable oil reserve in the Dezful Embayment. The fold axis of these anticlines are not identical above and below the upper detachment level (the Middle Miocene Gachsaran Formation). Progressive deformation caused thinning and escape of incompetent layers of the Gachsaran Formation from the crest of the anticlines toward adjacent synclines. A main deep-rooted fore-thrust within middle detachment level (the Lower Cretaceous Garu Formation) also cuts up-section toward the foreland and flattens in the Gachsaran detachment. Furthermore, a back-thrust cuts up from the main thrust into the hinterland. The shortening percentage was estimated in 58 seismic profiles across the Pazanan and Aghajari anticlines, by averaging of the Asmari, Sarvak and Fahlian Formations’ top restoration. The maximum and minimum amount of shortening is about 11.1 and 8.5 percent, respectively which is slightly less than those reported along the Dezful Embayment. The Hendijan High is the most important structure between the Aghajari and Pazanan anticlines which imparted considerable changes in basin fill facies. These changes presumably affected the folding geometry of the area, since it is similar to the fault bend folding geometry through the Hendijan High wherein exhibit fault propagation folding geometry on its both flanks. There is an anomaly and discontinuity in the depth contour maps of the Asmari and Fahlian formations which separated the northwest termination of the Pazanan anticline from the rest of the structure. Reasonably, it is better to consider it as southeast continuation of the Aghajari anticline, which is similar to the most anticlines with en-echelon pattern.

Active tectonic and palaeoseismological features of the western section of Mustafakemalpaşa Fault; Bursa, NW Anatolia

The Mustafakemalpaşa Fault (MF), located among Manyas, Ulubat and Orhaneli faults, is a right lateral strike-slip and 47 km in length. The MF begins with a pressure ridge at the west and exhibits complex jog terminations at east ends in restraining left stepovers. The western section of the fault bounds Miocene and Quaternary units and continues towards İlyasçılar. The central segment of the fault, starts with approximately 750-m leftward stepover, exhibits a sinusoidal geometry between Kapaklıoluk and Kabulbaba. In this section, MF traverses mountainous terrain and cuts Ophiolite, Jurassic limestones and Miocene detritals, forming dextral faulting features and gaining reverse component. The eastern section exhibits left stepping en-echelon pattern and consists 2.5-km offset on the Orhaneli River. In this study, palaeoseismological findings related to the Holocene activity and active tectonic properties of the MF are presented. The trenches exposed mismatched stratigraphy, demonstrating evidence of events across the fault. We identified three events (before BC 2190, later AD 1425 and 1850) that have occurred during the past 4000 years. We suggest a long non-characteristic recurrence interval and ~0.7 mm/y slip-rate for MF, based on trench data and offset of the Late Pliocene drainage of Orhaneli River.

Detailed fault structure of the Tarutung Pull-Apart Basin in Sumatra, Indonesia, derived from local earthquake data

The Tarutung Basin is located at a right step-over in the northern central segment of the dextral strike-slip Sumatran Fault System (SFS). Details of the fault structure along the Tarutung Basin are derived from the relocations of seismicity as well as from focal mechanism and structural geology. The seismicity distribution derived by a 3D inversion for hypocenter relocation is clustered according to a fault-like seismicity distribution. The seismicity is relocated with a double-difference technique (HYPODD) involving the waveform cross-correlations. We used 46,904 and 3191 arrival differences obtained from catalogue data and cross-correlation analysis, respectively. Focal mechanisms of events were analyzed by applying a grid search method (HASH code). Although there is no significant shift of the hypocenters (10.8m in average) and centroids (167m in average), the application of the double difference relocation sharpens the earthquake distribution. The earthquake lineation reflects the fault system, the extensional duplex fault system, and the negative flower structure within the Tarutung Basin. The focal mechanisms of events at the edge of the basin are dominantly of strike-slip type representing the dextral strike-slip Sumatran Fault System. The almost north–south striking normal fault events along extensional zones beneath the basin correlate with the maximum principal stress direction which is the direction of the Indo-Australian plate motion. The extensional zones form an en-echelon pattern indicated by the presence of strike-slip faults striking NE–SW to NW–SE events. The detailed characteristics of the fault system derived from the seismological study are also corroborated by structural geology at the surface.

The role of structural inheritance in oblique rifting: Insights from analogue models and application to the Gulf of Aden

The geometry and kinematics of rifts are strongly controlled by pre-existing structures that may be present in both the crust and the mantle lithosphere. In the Gulf of Aden, the Tertiary oblique rift developed through inherited Mesozoic extensional basins that trend orthogonal to the direction of Oligo-Miocene divergence. Such inheritance may produce lateral variations in crustal thickness and thus in rheology of the crust and mantle lithosphere. How can such variations influence the present-day geometry of oblique rifts? May they locally overcome the impact of the oblique rheological weaknesses that in certain cases control the overall trend of the rift system? Moreover, we observe that major fracture zones systematically crosscut the inherited basins: may such inheritance influence the localization of major fracture zones by shifting the initial spreading centers? The brittle-ductile multilayer analogue models presented in this contribution reproduce oblique rifts. We tested the effect of an initial oblique weakness in the lithospheric mantle (i.e. structural or thermal inheritance) by introducing an oblique rheological weakness, which is alternatively initially imposed or dismissed. We tested the effect of the orthogonal Mesozoic inheritance by adding an elongated thicker brittle mantle, orthogonal to the direction of extension, in two models. These models mainly show en-echelon patterns with orthogonal faults and few rift-parallel faults (parallel to the rift obliquity), suggesting that the inherited orthogonal discontinuity is more influential than the oblique weakness in the lithospheric mantle. These results suggest that the presence in the lithosphere of an inherited basin could constitute a barrier to the deformation and sufficiently offset the spreading centers to lead to independent rift systems separated by major fracture faults. Moreover, the genetic nature of the obliquity (boundaries-driven or inherited) could control the length of the transform offset between two spreading centers and thus, the length of the future transform margin (continental domain affected by a transform fault).

Initiation and growth of strike-slip faults within intact metagranitoid (Neves area, eastern Alps, Italy)

Exhumed strike-slip faults exposed in the Neves area of the Tauern Window (eastern Alps, Italy) formed in the lower brittle crust under hydrous conditions within intact metagranitoids, where any precursor fractures were already healed due to earlier amphibolite-facies metamorphism. Faults initiated as newly formed en-echelon fractures delineating shear bands, with segmentation occurring over scales of 10 –3 to 10 2 m. Due to the initial en-echelon pattern, stepovers between fault segments were almost invariably contractional during subsequent slip accumulation. In initial low-slip (centimeter to decimeter) stages, synthetic slip on the segments was associated with the development of a set of antithetic faults in the contractional stepovers, oriented at an angle of 30°–45° to the bounding faults. Slip on this antithetic set did not fully compensate for the decrease in slip on the main faults, implying an additional deformation mechanism within the stepovers (e.g., block rotation and/or out-of-plane movement). In larger faults with slip on the order of a few meters, the antithetic faults within the stepover were crosscut by synthetic sigmoidal faults that connected the overstepped fault segments and accommodated most of the subsequent displacement transfer. This second stage of evolution involving fault linkage is well documented in the Mesule fault, which has a current maximum offset of ∼10 m. In the Mesule fault, the total horizontal slip summed along all secondary faults within the stepover accounts almost entirely for the net slip decrease toward the tips of the overstepping faults. However, the boundary faults remain nearly straight in spite of the sigmoidal ramp-like geometry of the connecting faults. Since the adjacent blocks are little deformed and there is no evidence for appreciable volume loss or block rotation in the stepover, significant out-of-plane movement is implied, although it is difficult to quantify. The Neves area provides unusually detailed field constraints on fault initiation, linkage, and displacement accumulation within nonbedded and relatively isotropic granitoid rocks at the base of the brittle crust, where neither a free upper surface nor substantial volume change (e.g., by veining and pressure solution) was a controlling factor in accommodating fault linkage and displacement transfer.

Fault-trapped waves depict continuity of the fault system responsible for the 6 April 2009 MW 6.3 L'Aquila earthquake, central Italy

We investigate fault-trapped waves observed at a permanent broad-band station (FAGN) installed on the San Demetrio Fault, about 20km southeast of L'Aquila. This fault has the same strike of the Paganica Fault which was responsible for the MW 6.3, 6 April 2009 earthquake. The two faults display an en-echelon pattern with a few km offset. We have found that events causing efficient trapped waves are clustered at the northwestern and southeastern bottom ends of the ruptured Paganica fault plane. The efficiency of trapped waves at FAGN, which is located about 5km far from the ruptured fault plane, indicates that the two faults are linked at depth. This suggests that fault segments in the study area can be part of a longer and continuous fault system which controls the seismic hazard of the region. Moreover, we have found that the two earthquake clusters generating the most efficient trapped waves occur in portions of the fault system with the highest fluid pressure.

Identification of Loriya Fault, Its Reactivation Due to 2001 Bhuj Earthquake, (Using Remote Sensing Data) and Its Bearing on the Kachchh Mainland Fault, Kachchh District, Gujarat

The 2001 Bhuj earthquake (Mw 7.7), one of the most severe earthquakes in the recent history of India, reactivated various existing active faults. It is manifested in the form of coseismic ground fissures/cracks and upheaval of land in the form of bumps. Identification and reactivation of Loriya Fault is established by 1—Geomorphic changes with the help of digital imagery (LISS III images). 2—Coseismic changes through ground checks and 3—Geophysical signatures through magnetic and gravity survey. A lineament cutting the north-western part of the Pur River alluvial fan has been revealed by satellite imagery. The streams flowing along the lineament add to the evidences of a weak plane, while the occurrence of coseismic ground fissures confirms the existence of an active fault. No dip slip movement is recorded in the trenches made across the Loriya active fault while the en-echelon pattern of ground fissures suggest strike slip movement along the fault due to 2001 earthquake.

Left-lateral active deformation along the Mosha–North Tehran fault system (Iran): Morphotectonics and paleoseismological investigations

The Mosha and North Tehran faults correspond to the nearest seismic sources for the northern part of the Tehran megacity. The present-day structural relationships and the kinematics of these two faults, especially at their junction in Lavasanat region, is still a matter of debate. In this paper, we present the results of a morphotectonic analysis (aerial photos and field investigations) within the central part of the Mosha and eastern part of the North Tehran faults between the Mosha valley and Tehran City. Our investigations show that, generally, the traces of activity do not follow the older traces corresponding to previous long-term dip–slip thrusting movements. The recent faulting mainly occurs on new traces trending E–W to ENE–WSW affecting Quaternary features (streams, ridges, risers, and young glacial markers) and cutting straight through the topography. Often defining en-echelon patterns (right- and left-stepping), these new traces correspond to steep faults with either north- or south-dipping directions, along which clear evidences for left-lateral strike–slip motion are found. At their junction zone, the two sinistral faults display a left-stepping en-echelon pattern defining a positive flower structure system clearly visible near Ira village. Further west, the left-lateral strike–slip motion is transferred along the ENE–WSW trending Niavaran fault and other faults. The cumulative offsets associated with this left-lateral deformation is small compared with the topography associated with the previous Late Tertiary thrusting motion, showing that it corresponds to a recent change of kinematics.

Field evidences from northern Dead Sea Fault Zone (South Turkey): New findings for the initiation age and slip rate

The left-lateral strike–slip Dead Sea Fault Zone (DSFZ) extends from the Red Sea in the south to the East Anatolian Fault Zone (EAFZ) in the north. This study examines the northern part of the DSFZ around Amik Basin and presents surface and subsurface geological evidence for the Quaternary activity and initiation age of the northernmost DSFZ. The DSFZ extends N–S in the south of the Amik Basin where clear geological and morphological evidence exists for faulting. Geological observations around Amik Basin, analyses of borehole data and electrical resistivity profiles within the Amik Basin indicate that the activity of the northern DSFZ started after Pliocene in the Amik Basin. Subsurface data in the basin suggest that the DSFZ offsets a pre-Quaternary basin sinistrally by about 7.9 km. The offset pre-Quaternary basin suggests at least 4.94 ± 0.13 mm/year slip rate for the northern part of the DSFZ. The Karasu Fault Zone (KFZ) extends in an en-echelon pattern along the western margin of the Karasu Valley and it transfers the significant amount of slip from DSFZ to the EAFZ.

Finite deformation model of simple shear of fault with microrotations: apparent strain localisation and en-echelon fracture pattern

Strain localisation is a widespread phenomenon often observed in shear and compressive loading of geomaterials, for example, the fault gouge. It is believed that the main mechanisms of strain localisation are strain softening and mismatch between dilatancy and pressure sensitivity. Observations show that gouge deformation is accompanied by considerable rotations of grains. In our previous work as a model for gouge material, we proposed a continuum description for an assembly of particles of equal radius in which the particle rotation is treated as an independent degree of freedom. We showed that there exist critical values of the model parameters for which the displacement gradient exhibits a pronounced localisation at the mid-surface layers of the fault, even in the absence of inelasticity. Here, we generalise the model to the case of finite deformations characteristic for the gouge deformation. We derive objective constitutive relationships relating the Jaumann rates of stress and moment stress to the relative strain and curvature rates, respectively. The model suggests that the pattern of localisation remains the same as in the linear case. However, the presence of the Jaumann terms leads to the emergence of non-zero normal stresses acting along and perpendicular to the shear layer (with zero hydrostatic pressure), and localised along the mid-line of the gouge; these stress components are absent in the linear model of simple shear. These additional normal stresses, albeit small, cause a change in the direction in which the maximal normal stresses act and in which en-echelon fracturing is formed.

Structure and tectonics of the Achankovil Shear Zone, southern India

An integrated approach to resolve the kinematics of the controversial Achankovil Shear Zone (AKSZ) has been attempted involving remote sensing data, shaded relief topo-maps, ground details of lithology and mesoscopic structures. An excellent correlation of structural trends exists on all scales of observation. The AKSZ is distinctly defined by NW–SE trending foliation fabrics with steep dips to southwest. The adjacent Madurai block and Trivandrum block show contrasting lithological and structural characteristics as shown in structural cross-sections. The mesoscopic structural studies reveal the presence of sub-horizontal stretching lineations, asymmetric structures like S–C′ fabrics, porphyroclasts, ‘S’ shaped folds and shear bands confirming the strike-slip component of shear along AKSZ. The deformation undergone by the AKSZ could be described in terms of an initial dextral deformation — D 1, reactivated and superimposed by sinistral kinematics — D 2, which is also supported by megascopic structural interpretation of remote sensing data. The megascopic structural interpretation of AKSZ displays en-echelon pattern of lineaments with right overstepping arrangement, which can be interpreted as an evidence of the latest sinistral transpressional deformation.

Provenance and anatomy of Genyodectes serus, a large-toothed ceratosaur (Dinosauria: Theropoda) from Patagonia

ABSTRACT The type material of Genyodectes serus, the first unquestionable non-avian theropod dinosaur to be described from South America, is redescribed in detail and its provenance and systematic position are discussed. Although no detailed information about the provenance of the specimen exists, it is probably derived from the lower part of the Cerro Barcino Formation (Chubut Group; Aptian-Albian) at Canadón Grande, central Chubut Province, Argentina. Genyodectes is characterized by closely-spaced premaxillary teeth that are arranged in an overlapping en-echelon pattern and extremely transversely compressed maxillary teeth, the longest of which exceed the minimal height of the dentary in apicobasal length. Although systematic information is limited by the fragmentary nature of the material, the combination of fused interdental plates, maxillary and dentary teeth with a pronounced flat or even slightly concave area adjacent to the serrated carinae, premaxillary teeth that are considerably shorter than the maxillary teeth and strongly compressed and very long maxillary teeth indicates neoceratosaurian and, more specifically, ceratosaurid affinities for Genyodectes. Thus, this taxon adds a further lineage of neoceratosaurs to the already diverse South American record of this group.

InSAR-DEM analyses integrated with geologic field methods for the study of long-term seismogenic fault behavior: Applications in the axial zone of the central Apennines (Italy)

The integration of terrain computer modeling with field methods may provide a powerful mechanism for understanding active faults geometry, kinematics and long-term fault behavior. Radar interferometry was used on ERS tandem images to create a geocoded DEM (InSAR-DEM) with a nominal 20-m spatial-resolution of the central Apennines axial zone, a seismically active area characterized by historical destructive earthquakes with M ≤ 7. The potential was tested of InSAR-DEM application to the Fucino and Sulmona basin boundary faults, which have well-defined seismological, paleoseismological and/or geological evidence for their having seismogenic sources. In particular, slope maps extracted from the InSAR-DEM were used for fault scarps detection, whether on carbonate bedrock (“fault scarp type 2”) or affecting continental deposits within the basin (“fault scarp type 1”), and compared with the available geological and new field data. In order to assess the DEM accuracy and to evaluate morphometric parameters related to the long-term slip-rates of the faults, a set of topographic profiles was extracted from the InSAR-DEM and compared with analogous profiles derived from the available topographic map (i.e., 1/25,000, with 25 m contour interval). In particular, the use of InSAR-DEM analyses showed its better results, with respect to the standard topography, for urban/agricultural gently sloped areas where fault scarps affected unconsolidated and particularly soft sediments (e.g., Fucino basin fault systems), while in severely sloped carbonate ridge and forested areas low coherences and layover effects made InSAR-DEM application problematic. A maximum value of 1.1 ± 0.2 mm yr−1 slip-rate was obtained for the Fucino boundary fault. Finally, the recognized en-echelon pattern of the Sulmona basin boundary fault, provided a segmentation model for this structure corroborated by geological-structural field data.

The southern Rhine graben: A new view of the initial phase

One of the puzzling features of the southern end of the Rhine graben is the Dinkelberg-Tabular Jura block on the eastern shoulder of the graben. It is dissected by a large number of faults, the most notable ones forming a field of narrow little grabens and half-grabens whose bordering faults converge at the level of the Middle Triassic evaporites, which points to decollement at that horizon. The little grabens were traditionally considered to be of Oligocene age, coeval with the main taphrogenesis of the Rhine graben. Two hypotheses were offered for their formation, one ascribing them to extension on the extrados of large basement folds, the other to gravity sliding on paleoslopes. Recent field work uncovered overwhelming evidence for an Eocene age of the little grabens, the time of the initial phase of Rhine graben formation. At that time there were neither large basement folds nor paleoslopes of any significance, and therefore the two hypotheses offered until now do not work. However, the map-view pattern of the field of faults offers a somewhat unusual way out of the dilemma. This pattern is most prominently displayed in the Dinkelberg area north of the Rhine. There a lane of narrow decollement grabens with a mean NNE strike is confined within the NW- striking Dinkelberg graben, which is much wider and rooted in the basement. It is also very shallow, with a subsidence on the order of 100 m. The lane of decollement grabens forms a dextral en-echelon pattern with respect to the Dinkelberg graben, suggesting stretching of the post-evaporite sequence above a basement essentially extended by strike slip. This model, though not as clearly expressed, is also compatible with the data in the rest of the Dinkelberg-Tabular Jura block. It also fits surprisingly well a theoretical model by Withjack and Scheiner (1982) that predicts a dominance of strike-slip in the marginal area of a system consisting of extension superimposed on doming.