Active Normal Faults Research Articles

Pore pressure assessment from well data and overpressure mechanism: Case study in Eastern Tunisia basins

Independent and complementary methods were used for pore pressure assessment in the eastern Tunisian basins. Drilling data and surveys allow settling the pore pressure profile in these basins. The main used parameters are mud weights, formation pressure surveys, drilling parameters, well logs, fluids exchange with formation and borehole issues. In the eastern Tunisia platform, the pore pressure profiles show changes in overpressure magnitude in all the three dimensions of the basin (location and depth/stratigraphy). We highlighted two overpressure intervals form bottom to top: The late Cretaceous in the North-eastern part, and the Tertiary overpressure interval hosted in the Palaeocene to Miocene series. The structural analysis of overpressure location shows that the Tertiary interval is likely to have originated in a disequilibrium compaction in Cenozoic grabens. Pore pressure cross sections and maps confirm the link between active normal faults that segmented the basin to grabens and highs and pore pressure anomalous area. In the Senonian interval, we noted mature source-rocks that can explain the overpressure in the late Cretaceous interval. In addition, the recent to active compressive tectonics may have contributed to both pore pressure anomaly generations. The fluid overpressures characterization in the eastern Tunisian sedimentary basins helps in hydrocarbons exploration. Indeed, the overpressure interval in the reservoir levels stimulates and improves the production in the oilfields and contributes to hydrocarbon trapping. Moreover, the adequate prediction of pore pressure profile contributes to reduce drilling cost and enhance the drilling operations safety.

Strain variations in a seismogenic normal fault (Baza Sub-basin, Betic Chain): Insights from magnetic fabrics (AMS)

AMS and structural analysis are here applied to study the deformed zone associated with a large-scale, active normal fault in the central Betic Cordillera (Spain), namely the Baza fault system, to determine: i) the kinematics of structures and their relation with fault zone architecture and segmentation degree, ii) the correlation between deformational structures and the different types of magnetic fabrics and iii) the evolution of magnetic fabrics patterns, from sedimentary to shear-related, associated with normal faults. Five outcrops (969 samples) were analysed along the fault trace, which shows different degrees of segmentation along strike and strong localization of deformation along narrow fault zones. A first, main set of magnetic fabric data corroborates the normal kinematics of the Baza fault, showing magnetic lineations parallel to the dip-slip, transport direction. A second, secondary set of magnetic lineations, is parallel to the intersection lineation, and can be related to less intense deformation in the fault rocks. Furthermore, a detailed study (523 samples) of a trench excavated across the fault zone, where two fault splays tend to coalesce in a linkage relay zone indicates that i) lithology and distance to fault planes are two factors that control the development of extension-related magnetic fabrics in weakly deformed sediments, ii) the development of shear-related fabrics in fault zones entails the mechanical rotation of minerals, iii) different orientation of magnetic lineations are related to different intensity of bulk deformation and iv) magnetic lineation is useful to define local deviations of deformation axes produced by changes in the local extension direction (from fault-perpendicular to fault-parallel extension) in the linkage zone between adjacent fault splays.

Linking CO2 degassing in active fault zones to long-term changes in water balance and surface water circulation, an example from SW Turkey

Calcite veins are commonly found at shallow depth (a few metres below the surface) in damage zones of active normal fault systems in southwest Turkey. Although earlier studies demonstrated the link between the vein formation and seismicity, the association of near-surface carbonate precipitation with climate-driven hydrological conditions (water table, amount of precipitation and evaporation, and water discharge) is poorly understood. In this study, using the U/Th dating method we investigate the timing of vein formation and the interrelationship between tectonic and climatic-related hydrological processes. Carbonate precipitation is interpreted to occur as a result of sudden pressure drops and CO2 release after earthquake-induced fracturing. Vein formation mostly occurred during glacial periods, which coincide with slow growth rates and higher oxygen isotope values of speleothems from the Eastern Mediterranean region. We relate these episodes to reduced winter rainfall due to the decrease in westerly flow in SW Turkey. These somewhat drier conditions influenced the chemical composition of circulating water, creating conditions conducive to carbonate precipitation and sealing of damage zones. These conditions also facilitated CO2 accumulation and overpressure build-up in the rupture zones. Failure of the faults resulted in the release of large volumes of CO2-rich fluids and the generation of shallow carbonate veins. It is proposed that during phases of increased winter rainfall CO2 is advected to the surface and discharged as passive degassing when meteoric water circulation is enhanced. While regional tectonics is the ultimate driver of fault activity and fracture formation, climate-driven near-surface hydrological changes may have played an important role in modulating CO2-rich fluid circulation and surface discharge.

The Southern Atlas Front in Tunisia and its foreland basin: Structural style and regional-scale deformation

Surface and subsurface data together with balanced cross-sections are used to emphasize the structural style and regional-scale deformation of the Southern Atlas Front in Tunisia and its foreland basin. This E–trending shaped belt reflects successive tectonic events. Mixed thick- and thin-skinned structural style characterizing this belt is defined by shallow thrusts rooted down into deep E–trending basement thrusts with major decollement level located within Triassic salt. A NW–trending system is also recognized in the front and particularly responsible for the belt's curved shape, which probably acts as transfer areas between the wide-ranging E–trending major structures. The intermediate areas are characterized by salt tectonics probably active during Jurassic and Lower Cretaceous, in response to active synsedimentary normal faults and differential sedimentation loading. The shortening amount varies and decreases from West to East and from North to South: ~7.45% in the West, ~3.3% in west-central part, ~2% in the central area to insignificant (~1.4%) in the east. From north to south, the Northern Chotts Range narrow zone accommodates overall the Cenozoic shortening with ~6.95% and less than 1% in the Chotts region. This variation coincides with the pre-Cenozoic basin's architecture acquired during Mesozoic Tethyan evolution, which generates the main Jurassic E–trending Chotts basin. Inside this basin, distributary sub-basins are formed in relation with NW–trending faults active during the Cretaceous period. The Chotts basin appears, therefore, as Mesozoic rift rollover structure well-preserved in the front of the belt. The compilation of data suggests that the Front of the southeasternmost end of the Atlassic domain is distinguished by the reactivation of inherited fault systems acting during alpine orogeny as major southward thrusts. The foreland shows a structural singularity to be formed by a preserved almost unmodified and well exposed large Mesozoic rollover structure.

Luminescence dating of sediments from central Atacama Desert, northern Chile

Abstract This study examines the feasibility of applying luminescence dating methods to quartz and potassium feldspar (K-feldspar) grains from Quaternary continental deposits of the Mejillones Peninsula and Coastal Cordillera in Central Atacama, northern Chile. Sediment burial ages were calculated using single-aliquot regenerative-dose (SAR) protocols applied to the optically stimulated luminescence (OSL) signal of quartz as well as infrared stimulated luminescence (IRSL) and post-infrared infrared stimulated luminescence (post-IR IRSL) signals of K-feldspar. Considering that the target sedimentary deposits comprise the Late Pleistocene age range, K-feldspar grains were dated using fading-corrected IRSL signals measured at 50 °C (IR50) and post-IR IRSL measured at 225 °C (pIRIR225) to minimize the potential effect of residual doses on calculated ages. The results of the analytical procedures indicate that quartz grains extracted from the studied sediments present a very weak or even no fast OSL component. The combination of a low OSL sensitivity, signal instability and equivalent dose distributions with high overdispersion (>40% for most samples) hinder reliable age estimation using quartz aliquots. Bleaching test results show that the IR50 signal from K-feldspar aliquots is well reset after 20–24 h of light exposure, while the pIRIR225 signal may present residual doses corresponding to between 10 and 15% of the natural signal. IR50 fading rates are ∼6–7%/decade for most studied samples, with exception of one sample which yielded a g-value of 18.77 ± 2.06%/decade. Fading rates for the pIRIR225 signal yielded variable results among sampling sites, with g-values ranging between 0.70 ± 0.24 and 6.77 ± 1.05%/decade. The dating results point out that quartz OSL ages are largely underestimated in relation to K-feldspar fading-corrected IR50 and pIRIR225 ages. Fading-corrected pIRIR225 K-feldspar ages indicate that the alluvial sedimentation in the downthrown block of an active normal fault in Mejillones Peninsula occurred between 163.4 ± 18.4 ka and 87.4 ± 6.6 ka. K-feldspar ages also allow to constrain the age of fault scarp degradation and fault reactivation in two main branches of the Atacama Fault System. In the Naguayan Fault, pIRIR225 ages indicate that faulting occurred after 21.4 ± 3.2 ka while in the Salar del Carmen Fault, faulting is recorded after 14.7 ± 1.0 ka.

Occurrence of partial and total coseismic ruptures of segmented normal fault systems: Insights from the Central Apennines, Italy

Normal faulting earthquakes rarely rupture the entire extent of active normal faults, and can also jump between neighbouring faults. This confounds attempts to use segmentation models to define the likelihood of future rupture scenarios. We attempt to study this problem comparing the offsets produced in single earthquakes with those produced by multiple earthquakes over longer timescales, together with detailed studies of the structural geology. We study the active normal fault system that caused the Mw 6.3 2009 L'Aquila earthquake in central Italy, comparing the spatial distribution of coseismic offsets, cumulative offsets that have developed since 15 ± 3 ka, and the total offsets that have accumulated since the faults initiated at 2–3 Ma. Our findings suggest that: 1) faults within a segmented fault system behave as a single interacting fault segment over time periods including multiple earthquake cycles (e.g. 2–3 Ma or 15±3ka), with single earthquakes causing either partial or total ruptures of the entire system; 2) an along-strike bend causes throw and throw-rates enhancements within the bend throughout the seismic history of the fault system. We discuss the synchronised and geometrically controlled activity rates on these faults in terms of the propensity for floating earthquakes, multi-fault earthquakes, and seismic hazard.

From subsurface to surface: a multidisciplinary approach to decoding uplift histories in tectonically‐active karst landscapes

AbstractWe present an integrated study of subsurface and surficial karst landforms to unravel the uplift history of karst landscape in a tectonically‐active area. To this end, we apply a multidisciplinary approach by combining cave geomorphology and Th/U dating of speleothems with remote sensing plus geophysical imaging of surface landforms. We use as an example Mt. Menikio in northern Greece where four caves share well‐defined epiphreatic/shallow phreatic characteristics that are related to the distribution of surface and buried doline fields and provide evidence for three distinct water table stillstands (e.g. expressed as cave levels) now lying at ~130 m, ~800 m and ~1600 m a.m.s.l. Our dating constraints delimit the age of the lower water table stillstand prior to 77 ka ago and imply a maximum rate of relative base level drop of 0.45 mma‐1, which is consistent with relative tectonic uplift rate estimates along currently active normal faults. We interpret the elevation of the higher water table stillstands to reflect earlier phases of uplift related to the regional tectonic events associated with the development of the North Anatolian Fault and the Northern Aegean area. Our analysis shows that the combined study of epiphreatic/shallow phreatic caves and surficial karst landforms together, is a robust way to investigate the uplift history of a karst landscape in a tectonically‐active setting. © 2019 John Wiley & Sons, Ltd.

The July 20, 2017 M6.6 Kos Earthquake: Seismic and Geodetic Evidence for an Active North-Dipping Normal Fault at the Western End of the Gulf of Gökova (SE Aegean Sea)

On July 20, 2017 22:31 UTC, a strong Mw = 6.6 earthquake occurred at shallow depth between Kos Island (Greece) and Bodrum (Turkey). We derive a co-seismic fault model from joint inversion of geodetic data (GNSS and InSAR) assuming that the earthquake can be modelled by the slip of a rectangular fault buried in an elastic and homogeneous half-space. The GNSS observations constrain well most of the model parameters but do not permit to discriminate between south- and north-dipping planes. However, the interferograms, produced from C-band ESA Sentinel 1 data, give a clear preference to the north-dipping plane. We also map surface motion away from the satellite along the Turkish coast (from Bodrum towards the east) which reached about 17 cm onshore islet Karaada. The best-fit model is obtained with a 37° north-dipping, N283°E striking normal fault, in agreement with the published moment tensor solutions. The resolved slip vector is dominantly normal with a slight component of left-lateral motion (15°). The surface projection of the seismic fault outcrops in the Gokova ridge area, a well-developed bathymetric feature inside the western Gulf of Gokova. Our geodetic model fits the pattern of the shallow, north-dipping aftershocks obtained from rigorous relocation of all available recordings in the region (about 1120 events; relocated mainshock is at 36.955°N, 27.448°E; depth at 9.2 km ± 0.5 km). The relocated aftershocks also indicate clustering at both ends of the rupture and seismicity triggering mainly towards the east and the north, within 2 weeks following the mainshock. We also analysed regional GPS data (interseismic velocities) and obtained an extension rate of 3.2 mm/yr across the Gokova rift, along a direction N165°E.

Late Eocene – Early Miocene facies and stratigraphic development, Taranaki Basin, New Zealand: the transition to plate boundary tectonics during regional transgression

AbstractEight latest Eocene to earliest Miocene stratigraphic surfaces have been identified in petroleum well data from the Taranaki Basin, New Zealand. These surfaces define seven regional sedimentary packages, of variable thickness and lithofacies, forming a mixed siliciclastic–carbonate system. The evolving tectonic setting, particularly the initial development of the Australian–Pacific convergent margin, controlled geographic, stratigraphic and facies variability. This tectonic signal overprinted a regional transgressive trend that culminated in latest Oligocene times. The earliest influence of active compressional tectonics is reflected in the preservation of latest Eocene – Early Oligocene deepwater sediments in the northern Taranaki Basin. Thickness patterns for all mid Oligocene units onwards show a shift in sedimentation to the eastern Taranaki Basin, controlled by reverse movement on the Taranaki Fault System. This resulted in the deposition of a thick sedimentary wedge, initially of coarse clastic sediments, later carbonate dominated, in the foredeep close to the fault. In contrast, Oligocene active normal faulting in a small sub-basin in the south may represent the most northerly evidence for rifting in southern Zealandia, related to Emerald Basin formation. The Early Miocene period saw a return to clastic-dominated deposition, the onset of regional regression and the southward propagation of compressional tectonics.

Subdividing the tectonic elements of Aegean and Eastern Mediterranean with gravity and GPS data

Western Anatolia has been formed by the motions of the African plate, Arabian plate and Hellenic Subduction zone. The Hellenic Subduction zone, which has high seismicity, is the main tectonic feature of the eastern Mediterranean Sea related to the subduction of the African Plate beneath the Aegean Sea Plate. The Hellenic Subduction zone has a complex lithospheric structure and shows complex differences in the Aegean Sea in terms of continental crust thickness and mantle velocity. In the study area, the directions of Global Positioning System (GPS) velocity vectors which are towards SE change towards S from North of Western Anatolia to Hellenic Subduction zone. It is thought that the factor which controls this mechanism is the shear force or subduction zone located in Aegean Sea. Western Anatolia region, which is located in Western Anatolia Extensional province, includes several morphologically significant N–S trending active normal faults. Besides, the NE–SW and NW–SE trending faults, which their kinematic features change from north to south, are very effective on the tectonic regime of the region. Additionally, for determining the boundaries of these tectonic elements, the Complete Spherical Bouguer (CSB) gravity anomaly of study area was calculated by using World Gravity Map (WGM2012) model. Moreover, in historical and instrumental studies, the high seismicity of the study area is remarkable. It is thought that this case is also related with the mechanism which oriented the GPS velocity vectors to southward. Consequently, the dominant kinematic structure of the region was classified by combining the GPS velocity vectors computed for Izmir and its surroundings bounded by Western Anatolia, Aegean Sea and Eastern Mediterranean and the CSB gravity anomaly. Finally, the results were interpreted together with focal depth distributions of earthquakes and Bouguer gravity data.

Facies distribution as a response to early rift tectonic activity in the Sergipe-Alagoas Basin, northeastern Brazil

Accommodation rates in rift basins are mainly controlled by tectonics. However, during early rift stages, normal fault activity is dispersed and incipient, which makes it difficult to recognize the effects of early crustal extension. The sedimentary stacking pattern of rift-related depositional environments can be decisive to address this question. This paper aimed to evaluate the stratigraphic record of the Tithonian-Berriasian (?) Serraria Formation (Sergipe-Alagoas Basin, Brazil), which was deposited in the Afro-Brazilian Depression, as a result of the early extension of West Gondwana. In total, 14 lithofacies were described, interpreted and arranged into 7 facies associations. At the base of the formation, bars and sand sheets were deposited by low discharge braided channels, which were deposited on top of lacustrine mudstones of the Bananeiras Formation. There is a change in stratigraphic architecture in the middle of the section, where fluvial channels become deeper due to increasing discharge, promoting an increase in grain size of the transported bedload and greater rates of coarse sand and gravel bar stacking. Rare crevasse channels and restricted aeolian dune fields occur adjacent to braided channel belts. Upwards, the Serraria Formation becomes dominated by delta front and delta plain deposits. The fluvial and aeolian facies associations represent a progressive decrease in accommodation, while the upper fluvio-deltaic interval means an increase in accommodation, pointing to the early rift stage climax. The fluvial “Caioba” sandstone on top of the Serraria Formation indicates reestablishment of fluvial drainage either due to decreasing tectonism or due to low accommodation at the time of deposition. Thus, the sedimentary stacking pattern of Serraria Formation represents higher frequency cycles within an early rift tectonic system tract.

Evolution of a rapidly slipping, active low-angle normal fault, Suckling-Dayman metamorphic core complex, SE Papua New Guinea

Evolution of a rapidly slipping, active low-angle normal fault, Suckling-Dayman metamorphic core complex, SE Papua New Guinea

Hydrogeochemical and Isotopic Constraints on the Pattern of a Deep Circulation Groundwater Flow System

Characterization of a deep circulation groundwater flow system is a big challenge, because the flow field and aqueous chemistry of deep circulation groundwater is significantly influenced by the geothermal reservoir. In this field study, we employed a geochemical approach to recognize a deep circulation groundwater pattern by combined the geochemistry analysis with isotopic measurements. The water samples were collected from the outlet of the Reshui River Basin which has a hot spring with a temperature of 88 °C. Experimental results reveal a fault-controlled deep circulation geothermal groundwater flow system. The weathering crust of the granitic mountains on the south of the basin collects precipitation infiltration, which is the recharge area of the deep circulation groundwater system. Water infiltrates from the land surface to a depth of about 3.8–4.3 km where the groundwater is heated up to around 170 °C in the geothermal reservoir. A regional active normal fault acts as a pathway of groundwater. The geothermal groundwater is then obstructed by a thrust fault and recharged by the hot spring, which is forced by the water pressure of convection derived from the 800 m altitude difference between the recharge and the discharge areas. Some part of groundwater flow within a geothermal reservoir is mixed with cold shallow groundwater. The isotopic fraction is positively correlated with the seasonal water table depth of shallow groundwater. Basic mineral dissolutions at thermoneutral conditions, hydrolysis with the aid of carbonic acid produced by the reaction of carbon dioxide with the water, and hydrothermal alteration in the geothermal reservoir add some extra chemical components into the geothermal water. The alkaline deep circulation groundwater is chemically featured by high contents of sodium, sulfate, chloride, fluorine, silicate, and some trace elements, such as lithium, strontium, cesium, and rubidium. Our results suggest that groundwater deep circulation convection exists in mountain regions where water-conducting fault and water-blocking fault combined properly. A significant elevation difference of topography is the other key.

Late Quaternary deformation in parts of the Belt of Schuppen of Dimapur and Peren districts, Nagaland, NE India

Geomorphic evidences and geochronology suggest recent tectonic activity in the Belt of Schuppen of Dimapur and Peren districts of Nagaland. Multiple levels of strath terraces forming remarkable geomorphic expressions are observed along the Chathe and Jharnapani river valleys. They indicate episodic uplift of the hanging‐wall blocks of the thrust systems. The major lineaments prominently trend parallel to the NE–SW regional thrusts, some being perpendicular or oblique. Active normal faults displacing bedrock and overlying fill sediments point to recent tectonic activity. The parallel and trellis drainage patterns are lineament‐controlled. Uplift of the terrain is evident from successive palaeochannels of the Chathe River younging towards the southwest. Three major aggradational phases of the terrace sediments are inferred from optically stimulated luminescence (OSL) chronology, the oldest beginning around 21 ka, the second around 11–7 ka, and the youngest between 3.5 and 1 ka. A sand lens of a tilted strath terrace exposed between Kukidolong and Chumukedima is dated at 7 ka, indicating tectonic events after 7 ka. Five major phases of bedrock uplift/incision have been estimated during 20 ka (0.13 mm/year), 11 ka (0.92 mm/year), 9 ka (2.29 mm/year), 6 ka (0.67 mm/year), and 1.8 ka (2.6 mm/year). Transverse topographic symmetry and asymmetry factor data suggest tilting towards the NE and SW. Other morphometric indices, such as channel sinuosity, stream length gradient index, valley floor to valley height ratio, and mountain front sinuosity, suggest that the area is tectonically active, which corroborates field observations.

High-Angle Normal Faulting at the Tangra Yumco Graben (Southern Tibet) since ∼15 Ma

Several active graben systems in Tibet and the Himalaya are the expression of ongoing east-west extension, but the significance and history of normal faulting in this large region are still debated. Here, we present geo- and thermochronological data for a granite intrusion in the footwall of an active high-angle normal fault at the Tangra Yumco graben to constrain the onset and history of normal faulting. Crystallization of the granitic rocks occurred at 87±1 Ma, as revealed by U/Pb zircon dating. After an initial phase of rapid cooling from magmatic temperatures, a later phase of slow cooling is recorded by Rb/Sr biotite ages between ∼72 and ∼60 Ma. The elevation dependence of the Rb/Sr ages suggests that cooling was controlled by erosion, which proceeded at a rate of ∼0.05 km/My during the latest Cretaceous and early Paleocene. The subsequent history of normal faulting is recorded by zircon (U-Th)/He ages of 12.5±1.1 and 9.7±0.7 Ma, apatite fission-track ages between 10.8±1.7 and 7.8±1.2 Ma, and apatite (U-Th)/He ages from 4.9±0.4 to 3.0±0.2 Ma. Thermokinematic modeling of these age data indicates that normal faulting started at 14.5±1.8 Ma at a rate of ∼0.3 km/My and accelerated to ∼0.7 km/My in the Pliocene. Our age constraint for the initiation of faulting supports a widespread onset of rifting in Tibet at ∼15–10 Ma, as reported for other graben systems. Finally, we suggest that the distribution of high-angle and low-angle normal faults is controlled by their position relative to the India-Asia convergence vector and by lateral variations in the thermal state of the lithosphere.

Active sediment creep deformation on a deep-sea terrace in the Japan Trench

AbstractEighty-six new acoustic survey lines along and across the Japan Trench revealed active sediment creep deformation on a deep-sea terrace at water depths of 400–1200 m in an area of arcuate-shaped depressions that are probably associated with tectonic erosion. The most active region of creep is located on the top at the surface of the depression south of 38° N. The area of creep deformation is characterized by arcuate-shaped topographic lineaments with active folds and active normal faults stepping down trenchward. In contrast to the southern region, normal faults at the top of the depression north of 38° N cut a sedimentary sequence (Unit 1) that is acoustically transparent with continuous weak reflectors, and this is covered by the undeformed layered sediment sequence of Unit 2. Unit 2 corresponds to the period of rising sea level that extended from the latest Pleistocene to the early Holocene (14–6 ka). Thus, creep is ongoing at the top of the depression south of 38° N in the surface layer, whereas it stopped north of the depression between 14 and 6 ka. These observations might indicate that the active region jumped from north to south due to probably retrogressive sliding.

Active fault control in the distribution of Elevated Low Relief Topography in the Central-Western Pyrenees

The activity of normal faults in the Central-Western Pyrenees is mainly detected by the disruption of paleic landforms surviving to Plio-Quaternary incision: the remnants of a Low-Relief Topography (LRT) that probably originated asynchronically during the Oligocene and Miocene. We propose a new method for mapping the LRT remnants that combines automatic analysis of digital topography and cross-checking with regional databases of Quaternary landforms. We focus on an area where the location of the main-drainage divide seems to be influenced by the activity of the Bedous-Pic de Midi du Bigorre set of faults and by the North Maladeta Fault. Neotectonic markers defined by the remnants of LRT envelops are tectonically displaced up to ~700m by the previously identified faults, but also along new faults observed in between them. A western prolongation of the North Maladeta Fault has been identified for the first time, implying a 75km total trace length, almost twice thepreviously published value. A restoration of the fault block motion was performed assuming a regional uplift across the range, enhanced in the northern part of the Axial Zone. This uplift leads to an outer arch extension along the Maladeta-Bedous Fault System. The resulting paleo-topography shows a broad southern paleo-flank (up to ~120km long) with a gentle regional gradient (~1o) and a much shorter and steeper northern paleo-flank (~4o gradient, up to 30km-long). This configuration suggests that the LRT remnants now located North of the main divide were connected to the Ebro Basin. The results are supported by previous studies on age and source provenance of major alluvial systems mantling the northern and southern flanks of the chain.

Submarine morpho-structure and active processes along the North American-Caribbean plate boundary (Dominican Republic sector)

The northern margin of Hispaniola records the oblique collision/underthrusting of the Bahamas Carbonate Province with the island-arc. Due to the collision, northern Hispaniola has suffered several natural disasters caused by major earthquakes and tsunamis, such as the historic earthquake of 1842, the tsunami caused by earthquake-driven slumping in 1918 in the Mona Passage, the seismic crisis of 1943–1953 with five events of M > 7.0 or the seismic crisis of 2003 with a main shock of M6.3 and a large aftershock of M5.3. Using new swath multibeam bathymetry data and vintage single- and multi-channel seismic profiles, we have performed a regional scale analysis and interpretation of the shallow morpho-structure and active processes along the northern margin of the Dominican Republic. We have identified three morphostructural provinces: a) the Bahamas Carbonate Province, b) the Hispaniola Trench and c) the Insular Margin, which are divided into two tectonic domains, the Collision Domain and Underthrusting Domain. The southern slope of the Bahamas Carbonate Province shows a very irregular morphology produced by active erosive processes and normal dip-slip faulting, evidence of an extensional tectonic regime and margin collapse. This collapse is of major extent in the Oblique Collision Domain where there are erosive and fault escarpments with higher dip-slip fault throws. The Hispaniola Trench is formed by the Caicos and Hispaniola basins in the underthrusting domain, and by the Santisima Trinidad and Navidad basins in the Oblique Collision Domain. They have a flat seafloor with a sedimentary filling of variable thickness consisting of horizontal or sub-horizontal turbiditic levels. The turbiditic fill mostly proceeds from the island arc through wide channels and canyons, which transports sediment from the shelf and upper slope. The Insular Margin comprises the Insular Shelf and the Insular Slope. The active processes are generated on the Insular Slope where the Northern Hispaniola Deformed Belt is developed. This Deformed Belt shows a very irregular morphology, with a WNW-ESE trending N verging imbricate thrust-and fold system. This system is the result of the adjustment of the oblique collision/underthrusting between the North American plate and the Caribbean plate. In the Oblique Underthrusting Domain the along-strike development of the imbricate system is highly variable, forming salients and recesses. This variability is due to along-strike changes in the sediment thickness of the Hispaniola Trench, as well as to the variable topography of the underthrusting Bahamas Carbonate Province. In the Oblique Collision Domain, the morphology of the Insular Slope and the development of the Deformed Belt deeply change. The imbricate system is barely inferred and lies upslope. These changes are due to the active collision of Bahamas Carbonate Province with the Insular Margin where the spurs are indented against the Insular Margin. Throughout the entire area studied, gravitational instabilities have been observed, especially on the Insular Margin and to a lesser extent on the southern slope of the Bahamas Carbonate Province. These instabilities are a direct consequence of the active underthrusting/collision process. We have mapped large individual slumps north of Puerto Plata in the Oblique Underthrusting Domain and zones of major slumps in the Oblique Collision Domain. These evidences of active processes must be considered as near-field sources in future studies on the assessment of tsunami hazards in the region.

Comparison of Palaeostress Analysis, Geodetic Strain Rates and Seismic Data in the the Western Part of the Sultandağı Fault in Turkey

The Sultandağı Fault is an active dip-slip normal fault bounding the southeastern border of the NW-SE striking Afyon-Akşehir Graben, an actively growing rift area in western Anatolia. The historical and instrumental earthquake record periods suggest the existence of a large number of earthquakes that created surface ruptures in this system. The recent activities of the Sultandağı Fault are two earthquakes that occurred on February 3, 2002 (Mw=6.3 and Mw=6.0) and caused a surface rupture up to 26 km along with an approximately 30 cm vertical displacement. Based on the possible continuation of this earthquake migration towards the west, seismic gaps existing in the region, the presence of historical destructive earthquakes and active faults reveal the seismic hazard around the province of Afyonkarahisar. In this study, we determined the fault activities and stress directions in the western part of the Sultandağı Fault by comparing the results from the Palaeostress analysis of fault segments, focal mechanism solutions of recent earthquakes and geodetic analysis. The geologic, geodetic and earthquake data all indicate that both northern and southern master faults of the middle part of the Afyon-Akşehir Graben are dip-slip normal faults and were shaped under a NW-SE and NE-SW-directed bimodal extensional tectonic regime during the Quaternary period.

Sealevel change and tectonic uplift from dated marine terraces along the eastern Mediterranean coast, southeastern Turkey

Tectonic movements among the African, Arabian, Aegean, and Anatolian Plates have deformed the eastern Mediterranean Basin. Since the late Pliocene, these movements caused transtensional opening of the NE-trending Antakya Graben. Tectonic uplift coupled with Quaternary sealevel fluctuations has produced several stacked marine terraces along the Mediterranean coasts on the Antakya Graben. Here, molluscs from terrace deposits that sit on both Graben flanks at elevations between ~ 3 and ~ 175 m were dated using standard electron spin resonance (ESR) dating. For molluscs in situ in the terraces, the ESR ages ranged from ~ 8.3 to ~ 214 ka, but most of the dated terraces contained molluscs reworked from several earlier deposits due to later tectonic movements, sealevel fluctuations, and associated sedimentary processes. By dating in situ fossils, such as Lithophaga, within or just above the basal contacts for the marine terraces, uplift rates were calculated on both sides of the Antakya Graben. North of the Asi River, the regional uplift rate ranges from ~ 0.43 ± 0.11 mm/yr at Samandağ to as high as 2.08 ± 0.70 mm/yr at Mağaracık Dump. South of the Asi River, uplift rates range from 0.81 ± 0.14 mm/yr at the Cliffside terrace to 2.33 ± 0.60 mm/yr at Meydan Dump I. Rather than regional movements, however, local active normal or transtensional faults, such as the Gözene, Altın, and Sinanlı Faults mainly uplifted these deposits.