Transform Fault Research Articles

Up-to-date PSHA along the Gulf of Aqaba-Dead Sea transform fault

The Gulf of Aqaba Dead Sea Transform fault (DSTF) is a plate boundary. Its southern section separates Sinai Peninsula, Egypt and Saudi Arabia. Also, it passes through several countries. A development plan with a huge budget is drawn to develop the Gulf of Aqaba region. This plan includes the construction of King Salman Bridge. Therefore, the assessment of the seismic hazard (SH) at this seismically active region is inevitable for the sustainability of these mega projects. This paper presents a probabilistic seismic hazard assessment (PSHA) study along the DSTF. An earthquake catalogue including the paleo-seismological studies, historical records and instrumental seismicity is compiled. It is processed by converting various magnitude types to the moment magnitude (Mw) using recently derived mathematical equations. Three de-clustering techniques have been used to de-cluster the catalogue. Then, a completeness test is performed. The obtained earthquake catalogue is implemented to plot two different smoothed seismicity maps (SSMs). These maps and two areal source models are utilized to represent the seismicity along the DSTF. Five ground-motion prediction equations (GMPEs) are used to predict the ground-motion, three out of them are for the seismic sources located at shallow active crust tectonic regime and two for the intermediate depth earthquakes generating at the subduction zone south of Cyprus. The previously mentioned SH inputs are implemented through the logic-tree framework. The produced maps illustrate that the PGA values in the DSTF region range from 0.02g to 0.4g and 0.06 to 0.48 for 475 and 2475 years return period (RP), respectively. Also, seismic hazard maps using the non-de-clustered catalogue are produced.

Looking beyond kinematics: 3D thermo-mechanical modelling reveals the dynamics of transform margins

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

PSInSAR and GNSS derived deformation study in the west part of Narmada Son Lineament (NSL), western India

The Narmada Son Lineament located in the middle part of the Indian plate is to be considered seismically active part and already experienced six moderate earthquakes in the last century. The geological studies summarize that the reactivation of existing faults of the paleo-rift are the main source of the tectonic deformation in this part. In the present study the PSInSAR technique with Sentinel 1A dataset, 2016–2019, is being applied for the measurement of deformation pattern of NSL. The derived results were collectively analyzed with the time-series dataset (2009–2019) of a GNSS site located in the study area. The results reveal association of very low amount of deformation along the Son Narmada Fault (SNF). The area towards south of the SNF portrays approximately 2.0 mm of annual Line of Sight (LoS) displacement, which we believe is significant for this region. The estimated deformation lies mainly along the Tapti North Fault (TNF) and Barwani Sukta Fault (BSF) and represented by the existence of a number of transverse faults in the area. The presence of seismic activity in this part justifies the area of maximum deformation accumulation.

Delineation of tectonically active zones in the Island Belt Uplift region, Kachchh Basin, western India: A geomorphic and geodetic approach

In the present study, we have identified the tectonically active zones along the Island Belt Uplift (IBU), an upthrown block of E-W trending Island Belt Fault (IBF). Major and minor transverse faults have segmented the IBU into four sub-uplifts, viz. Pachham Uplift (PU), Khadir Uplift (KU), Bela Uplift (BU), and Chorar Uplift (CU) from west to east, respectively. The work includes geodetic and morphotectonic analysis of the IBU region. The Normalized Steepness Index (Ksn) analysis was performed supported by swath profiling to mark the tectonic activity variations along and across the strike of the IBF in the IBU region. Further, the Ksn contour map was prepared by using a power-law function of slope (S) of the longitudinal profiles of the river, concavity index (ө), and upstream area (A), which is an integral part of the Stream Power Incision Model (SPIM). The Ksn analysis suggests that the maximum amount of tectonic activity is restricted along the northern escarpment of the IBU, which falls in the vicinity of IBF and it's associated longitudinal and transverse faults. Based on the results of Ksn analysis, we have marked the tectonically active zones in the IBU region, which shows that amongst four sub-uplifts, the PU and BU were found most active (Zone-I), the KU expresses moderate activity (Zone-II), while CU demonstrated to be least active (Zone-III). The results were also confirmed by documentation of active tectono-geomorphic features like strath terraces, river offsets, straight fault scarps, triangular facets, linear valleys, fault ridges, Quaternary upwarps, laterally displaced crests and alluvial fans within the IBU. The active deformation pattern calculated using the Global Positioning System (GPS) data-set from 2009–2019 along IBU reveal maximum deformation rate of ∼2.5 ± 0.5 mm/yr in the PU, ∼2.0 ± 0.5 mm/yr in the BU while, the KU shows the deformation rate of ∼1.2 ± 0.5 mm/yr, which coincides well with the results of Ksn. The Ksn analysis results were also validated by comparing them with existing Gradient Length Anomaly (GLA) and Differential Interferometric Synthetic Aperture Radar (DInSAR) data. The ongoing tectonic activity in the study area is also manifested by the occurrence of moderate seismic activities in the identified active zones. The active tectono-geomorphic features and fault scarp geometry were analyzed and compared with the existing experimental models of basement fault and overlying sedimentary covers, which allow us to understand the nature of fault components of IBF. The analysis reveals that the IBF has been influenced by both dip-slip and strike-slip fault components of motion, which can be further confirmed by geophysical analysis. The results of Ksn analysis and field evidence were merged to prepare Active Fault Map of the IBU region that can be implemented for future seismic hazard assessment.

Shear Zone Development in Serpentinized Mantle: Implications for the Strength of Oceanic Transform Faults

AbstractOceanic transform faults display fewer and smaller‐magnitude earthquakes than expected for their length. Several mechanisms have been inferred to explain this seismic slip deficit, including increased fault zone damage resulting in elevated fluid flow, and the alteration of olivine to serpentine. However, to date, these possible mechanisms are not supported by direct observation. We use micro to kilometer scale observations from an exhumed oceanic transform fault in the Troodos Ophiolite, Cyprus, to determine mineral‐scale deformation mechanisms and infer likely controls on seismic behavior of serpentinized lithospheric mantle in active oceanic transform faults. We document a range of deformation fabrics including massive, scaly and phyllonitic serpentinite, attesting to mixed brittle‐ductile deformation within serpentinite shear zones. The progressive development of a foliation, with cumulative strain, is an efficient weakening mechanism in scaly and phyllonitic serpentinite. Further weakening is promoted by a transition in the serpentine polytype from lizardite‐dominated massive and scaly serpentinites to chrysotile‐dominated phyllonitic serpentinite. The development of a foliation and polytype transition requires dissolution‐precipitation processes. Discrete faults and fractures locally crosscut, but are also deformed by, foliated serpentinites. These brittle structures can be explained by local and transient elevated strain rates, and play a crucial role in strain localization by providing positive feedback for dissolution‐precipitation by increasing permeability. We propose that the evolution in structure and deformation style documented within the serpentinized lithospheric mantle of the Southern Troodos Transform Fault Zone is a viable explanation for the dominantly creeping behavior and long‐term weakness of oceanic transform faults.

Study of structural, deformation temperature, and strain analysis of the quartzarenites of south-central Kaladgi basin, exposed at and around Mullur ghat and Kallur village of Belgaum district, Karnataka, India

Kaladgi rocks are magnificently exposed in Belgaum district of Karnataka state, with adjacent to Maharashtra, the Kaladgi Basin, evolved as a consequence of crustal extension which are resting on the basement of the Archaean Gneisses and are also overlaid by Deccan Traps. The outcrops in the present study area have very well-exposed quartzarenites of south-central part of Kaladgi Basin. New meso- and microscale structural analyses indicate that Kaladgi rocks suffered at least two episodes of deformation preserved in ductile and ductile-brittle structures. Finite strain analyses of the XZ and YZ sections on the collected samples from the Kaladgi basin show pure flattening strain pattern on Hsu and Flinn diagram. This simple flattening strain is attributed due to the sedimentation or lithological loading in the basin. This study area traversed by 3 transverse faults, namely F1, F2, and F3 through K-1, K-5, and M-4 locations, respectively. Finite strain analyses show high strain value in XZ section along the faults as F1 show 1.32 to 1.44, F2 has 2.3 to 1.45, and F3 reflect 1.57 Rs values. Deformation temperature based on the microstructures has high value along the faults as 400 to 500°C; however, rest of the area show low temperature deformation <300°C. This study brings new insights on deformation structures in field and under a microscope.

Recent Seismic Activity in the Bejaia–Babors Region (Northeastern Algeria): The Case of the 2012–2013 Bejaia Earthquake Sequences

From November 2012 to May 2013, the coastal region of Bejaia (northeastern Algeria), experienced three distinct seismic sequences in about 6 months. The first one was on 28 November 2012 started with a mainshock of magnitude Mw = 5.1, and the second one occurred on 22 February 2013, a few kilometers southeast from the first one and culminated with a magnitude Mw = 4.3 earthquake. The last sequence comprised two shocks of moderate magnitude: a Mw 5.2 event on 19 May 2013, followed by a Mw 5.0 event on 26 May. Earthquakes were relocated using the double-difference method with differential times derived from phase-picked data and waveform cross-correlation delays. We compiled a dataset of 252 accurately relocated events that are associated with focal mechanism solutions consistent with a near-vertical, right-lateral strike-slip fault striking NW–SE. The data analysis is coherent with a new fault extending over 35 km from the Gulf of Bejaia to the northeast of Kherrata. This newly discovered active fault, we name it the Babors Transverse Fault, appears to be segmented in four segments (S1–S4) evidenced by separate earthquake clusters. Static Coulomb stress changes and the spatiotemporal evolution of seismicity suggest static stress triggering, with the rupture first activated in the S1 segment in the northwest, migrating to S2, and terminating in S3 and S4 in the southeast. Stress tensor inversion from focal mechanisms implies that the dominant local stress field is a pure strike-slip regime, with N–S maximum horizontal compression in good agreement with the velocity field displaying reorientation compared to the oblique convergence of Africa–Eurasia. In this study, the newly identified Babors Transverse and Tizi N’Berber–Darguinah faults, in association with the NNW–SSE offshore active fault of the Greater Kabylian block (in the north) and the NNW–SSE right-lateral strike-slip Lâalam fault (in the south), form an en echelon fault system that acts as a transfer zone between offshore thrust faulting and the Ghardimaou–North Constantine strike-slip fault.

Geo- and seismo- tectonics of Eastern Himalaya: Exploring earthquake source zones from foredeep to Tibetan hinterland

In this review we present our knowledge base on the seismicity and related tectonics of around 1200+ km stretch of the Eastern Himalaya from eastern Nepal to Arunachal Himalaya (AH) including southern Tibet hinterland in the north and frontal foredeep in the south. Succinct discussion on the India-southern Tibet convergence rate, geology and tectonic setup of eastern Himalaya, and variation in strain rate vis-a-vis location of large (Mw ≥ 7.0) earthquakes from the region is followed by analysis of five segments with unique seismotectonic characteristics from eastern Nepal to Mishmi region. Critical review leads us to reiterate the role of transverse structures across the Himalaya in shaping the seismotectonic response; the August 1988 eastern Nepal foothills and September 2011 Sikkim earthquakes are related to activity along transverse structures inherited from the Indian continental crust lithosphere, and thus arguably segmenting the Main Himalayan Thrust to restrict catastrophic rupture length for thrust earthquakes. The West-Central Bhutan lacks even normal level of seismicity compared to its immediate west (Sikkim-Darjeeling) and east (Eastern Bhutan-Western AH); this could be due to the fact that transverse seismogenic conjugate faults are also absent in this earthquake starved West-Central Bhutan. Alternatively, from the point of low strain rate scenario, this segment may be due for a bigger thrust event. The south Tibetan rifts are closely related to the Himalayan transverse faults and we suggest that the easternmost Cona-Oiga rift is possibly linked to the Western AH- Assam foredeep transverse Kopili- Bomdila trans-tensional faults.

PRAVABATI DEVI: A FACE IN THE CROWD

In addition to being the better half of man woman is an integral part of society but for whom man cannot bring any change in the society. History stands a great testimonial to this. The freedom movement of the nation would not have been possible without the participation of the women. Many women of Odisha forwent their domestic work, crossed their conservative boundary of family and joined the freedom movement of India. In this context, the women of Sambalpur had not lagged behind. One such luminary of the soil is Prabhavati Devi who had shown her valour and valiant role in the freedom struggle of the land. She went to Bari Ashram with the noble mission of imbibing all the virtues from the inspiring company of Malati Devi and Rama Devi. Thereafter, she took active part in various national movements such as Satyagraha, Non cooperation, Salt Movement, Individual Satyagraha, Quit India movement and Bhoodan Movement and went to jail. She carried out many social activities by establishing Matruniketan and Balniketan to serve depressed and deprived people. Because of her unique contribution both in political and social field, she has been accorded many awards both from government and non- government organizations.

Evaluation of DEM based Neotectonics of Sulaiman range and lobe region (SRLR), Balochistan-Pakistan

The Indian plate’s western boundary is extremely tilted towards the direction of convergence between Asia and India signifying an exceptional example of massive scale oblique continent-continent collision. This transform boundary motion is sinistral in nature and Digital Elevation Model (DEM) based geomorphometry permits the investigation of 3-D characteristics of the regional topography. This technique is specifically useful along inter-plate transform margins where the visual interpretation and topographic assessment is unable to observe the trends of the landforms evolution. In this context, the geomorphometry of the regional surface might be influenced largely by climate change and lower rate of active deformation. The geomorphic indices; Isobase Levels (IBLs), Topographic Asymmetry factor (T-factor) and Hack Gradient Index (HGI) have been executed to analyze fluvial drainage networks in connection to neotectonic movements. The sinistral movement along the Chaman Fault system and relatively less deformed Katawaz Block are the major surface dynamics to compute the style of deformation in the Sulaiman Range and Lobe Region (SRLR). Within the SRLR, the Sulaiman Fold and Thrust Belt (SFTB) is thrusting with a rate of 4–15 mm/yr in a North-South (NS) trend between IndoPak-Eurasian and a shortening of 4–6 mm/yr in East-West (EW) context. Seismicity is typically towards NorthWest-SouthEast (NW-SE) accommodating the moment release in the current century between the IndoPak-Eurasian transform plate boundary in the western most of the western Himalayan Syntaxis. The results obtained from the applied geomorphic indices indicate significant uplift in terms of higher IBL and HGI values all along the SRLR (Harnai, Katwaz, Qilla Saifullah, Zhob, Loralai, Jissa Shareef, Sakhi Sarwar and Fort Munro). The T-factor results also display tilt block neotectonics that are in agreement with the results of IBL and HGI.

Occurrence and characterization of tremolite asbestos from the Mid Atlantic Ridge

Tremolite is one of the most common amphibole species and, in the fibrous form (i.e., characterized by crystals/particles consisting of fibres with length > 5 µm, width < 3 µm and aspect ratio > 3), one of the six asbestos minerals. Until now the attention of crystallographers has focused only on samples from continental environment. Here we report the first chemical and structural data of a tremolite asbestos found along the Mid Atlantic Ridge (MAR) at the eastern intersection of the Romanche Transform Fault (Equatorial MAR). Tremolite is associated with chlorite and lizardite and was formed through the green shale facies lower than zeolite in a predominantly fluid system. MAR tremolite asbestos shows very slight deviations from the ideal crystal structure of tremolite. Differences in cation site partitioning were found with respect to tremolite asbestos from ophiolitic complexes, attributed to the different chemical–physical conditions during the mineral formation. In particular, oceanic tremolite asbestos is enriched in Al and Na, forming a trend clearly distinct from the continental tremolites.

Anisotropy of magnetic susceptibility study to locate the feeder zone and lava flow directions of the Rajmahal Traps (India): Implications to Kerguelen mantle plume interaction with Indian Plate

Rajmahal Traps (RT) represents the earliest eruption from the Kerguelen hotspot activity over Indian Plate. The results of anisotropy of magnetic susceptibility (AMS) fabrics depict distribution anisotropy with the maximum susceptibility axes (Kmax) predominantly clustered NE-SW with plunge in NE. It infers that the feeder zone for RT was located in the NE quadrant of the volcanic province and along the Narmada-Son-Brahmaputra Transform (NSBT) fault. Our results further suggest that the NSBT system provide the major topographic control for the lava flow channel distribution in the Rajmahal province. It implies that the fracture zone was available during the lava emplacement, which records the earliest Kerguelen plume activity. Comparison between AMS fabrics and field topography suggests the distal horizontal magma flow and fissural mode in the absence of volcanic vent in the region, when the plume centre was located in the Comei-Cona region of Tibet.

Spatial patterns, controlling factors, and characteristics of landslides triggered by strike-slip faulting earthquakes: case study of Lefkada island, Greece

The correlation of coseismic landslides with the seismic and morphological parameters has been investigated in detail by many researchers, mainly after the devastating 2008 M8.0 Wenchuan, China earthquake. One of the goals of such studies is to examine the spatial distribution of the earthquake-induced landslides in order to establish a pattern depending on the type of the seismic fault. This research focusses on the island of Lefkada, Ionian Sea, Greece, that is considered one of the most prone to earthquakes regions in Europe due to its proximity to the Cephalonia Transform fault. Landslide data from the two shallow strike-slip faulting earthquakes that occurred on 2003 and 2015 are statistically analyzed in order to evaluate the landslide magnitude and area of slope failures and their frequency-area size distributions. Furthermore, the spatial distribution of failures was investigated in detail regarding its correlation to topography (slope angle, aspect, local relief, elevation), geology, and the characteristics of fault rupture. We conclude that the landslide pattern is not controlled by a single parameter and that it results from a combination and interaction of seismic, morphological, and geological factors. In particular, the parameters of slope angle, geology, and fault rupture/asperities are the ones that are clearly related to the highest landslide densities.

A Twin of the Great Lisbon Earthquake (Based on Materials from the Newspaper Sankt-Peterburgskie vedomosti for the 18th Century)

The article generalizes materials on the earthquake of March 31, 1761, which is almost unknown in our scientific discourse, although very significant in its seismological impacts; it can therefore be considered as a twin of the Great Lisbon disaster of November 1, 1755. The 1761 earthquake struck a large part of Europe and, although it did not involve such disastrous consequences as the 1755 Lisbon quake, it significantly changed the seismic regime observed after after the latter. Both earthquakes were followed by tsunamis on the western margins of Europe and the eastern coasts of North America; they also triggered seismic activations of vast, spatially different regions in Western Europe and North Africa. It is possible to associate a number of strongest seismic events in the West Atlantic region with the 1761 earthquake. In the recent research literature on the topic, predominantly by Portuguese authors, the sources of both earthquakes are located in the eastern part of the Azores–Gibraltar Transform Fault. It is of particular interest that the initial data for this article were taken from the newspaper Sankt-Petersburgskie vedomosti for the 18th century and were supplemented with information from historical catalogs and recent foreign papers.

Ιdentification of spatiotemporal seismicity clusters in central Ionian Islands (Greece)

The spatiotemporal evolution of seismicity of an accurately relocated earthquake catalog in the central Ionian Islands, Greece, is explored, by the systematic identification of the earthquake clusters over the period September 2016–December 2019. Manual waveform phase picking was the input for the relocation leading to 13,632 earthquakes that compose a data set with a completeness magnitude as low as Mc = 1.5. The clustering procedure engages a temporal stochastic point process, the Markovian Arrival Process (MAP), for an initial separation of the background seismicity from potential seismic excitations, using the changes in the seismicity rate and a density-based clustering algorithm, DBSCAN, for the detection of elevated spatial density areas. A high concentration of temporally persistent clusters is identified along the western coastline of Lefkada Island, in the parallel step-over faults between the two major fault branches of the Kefalonia Transform Fault Zone and in the Myrtos Gulf area in Kefalonia, which are spatially correlated to the positive static stress changes induced by the coseismic slip of the Mw6.5 November 17, 2015 Lefkada main shock. The method presented remarkable potential in the identification of clusters in 3-D space along with the seismicity migration during the temporal evolution of seismic sequences. Multiple secondary faults of the Kefalonia segment can be revealed and the dominant triggering mechanisms can be illuminated contributing towards the understanding of the regional faulting properties and mechanics, an outcome that cannot be achieved solely by studying the large earthquakes, due to their rarity. The temporal and spatial clustering properties of microseismicity shed light on the preparation phase of the large earthquakes as being part of this process, thus contributing to the seismic hazard assessment.

Position of Rocks of Riftogenic and Collisional Sedimentary Sequences on Different Paleogeodynamic Diagrams

The distribution of composition fields of syn-rift and syncollisional sandstones and fine-grained clastic/clayey rocks of various structures and different ages are compared on the SiO2–K2O/Na2O, F1–F2, and DF1–DF2 diagrams. Syn-rift sedimentary sequences fill intraplate rifts, rifts at divergent, conservative and convergent plate boundaries, as well as their triple junctions. Syncollisional sediments are referred to rocks of foredeep and intermontane troughs, which are made up of molasses proper, flysch and schliers, and volcanogenic and nonfolded (distal) molasses. Fields of syn-rift and syncollisional sandstones in the SiO2–K2O/Na2O diagram show significant overlap. In the F1–F2 and DF1–DF2 diagrams, the distribution of the fields of syn-rift and syncollisional fine-grained clastic/clayey rocks is also substantially similar. Hence, the above mentioned diagrams cannot be used for reliable discrimination between syn-rift and syncollisional terrigenous associations. Correspondingly, it is hardly possible to use these diagrams alone for determination of geodynamic nature of sediments.

SEAFLOOR SPREADING AND TECTONICS AT THE CHARLIE GIBBS TRANSFORM SYSTEM (52-53ºN, MID ATLANTIC RIDGE): PRELIMINARY RESULTS FROM R/V A. N. STRAKHOV EXPEDITION S50

The Charlie Gibbs offsetting by ~ 340 km the Mid Atlantic Ridge (MAR) axis at 52°-53° N is one of the main transform systems of the North Atlantic. Located between long mid-ocean ridge segments influenced from the south by the Azores and from the north by the Iceland mantle plumes, this transform system has been active since the early phases of North Atlantic rifting. Object of several surveys in the ’70 and ’80, Charlie Gibbs received great attention for its unique structure characterized by two long-lived right-lateral transform faults linked by a short ~ 40 km-long intra-transform spreading centre (ITR) with parallel fracture zone valleys extending continuously towards the continental margins. In October 2020 expedition S50 of the R/V A.N. Strakhov surveyed an area of 54,552 km2 covering the entire Charlie Gibbs transform system and the adjacent MAR spreading segments. We collected new bathymetric, magnetic and high-resolution single channel seismic data, along with basaltic, gabbroic and mantle rocks from 21 dredges. This work contains preliminary data from cruise S50 and discusses the large-scale architecture of this unique, long-lived transform system.

The March 2017 earthquake sequence along the E-W-trending Mcid Aïcha-Debbagh Fault, northeast Algeria

In Northeast Algeria, a sequence of 143 small earthquakes (Md ≤ 4.7) occurred near the Mcid Aicha-Debbagh (MAD) Fault between 4 and 16 March, 2017. During this sequence, 74% of the seismic activity occurred in the first two days. Although the earthquakes were not large, they yielded important new information and have improved our understanding of seismic activity in three distinct regions along the fault. In the Sidi Dris region (western MAD Fault), 106 events (1 ≤ Md ≤ 3.2) were located in an aftershock cluster trending NNE-SSW, highlighting a transverse fault with ∼6 km of strike-slip displacement that locally cuts the MAD Fault. In the El Kantour region (central MAD Fault), 31 events were recorded along a 3 km long fault segment, including the Mw 4.7 mainshock. The mainshock had a focal mechanism consistent with predominantly strike-slip motion on a N110°E-striking fault plane, in agreement with the WNW-ESE orientation of the central MAD Fault segment. Finally, six diffuse events occurred in the Hammam Debbagh region (eastern MAD Fault). A significant event (Md 3.0) in this region had a focal mechanism consistent with strike-slip movement and a normal component trending NW-SE. This is consistent with the fault plane orientations of key events in the time period 2003–2014, likely related to the NW-SE-striking Hammam Debbagh Fault. The present-day stress tensor is characterized by a strike-slip tectonic regime and a σ1 orientation (N342°E) that closely matches the maximum regional compressive stress orientation (NNW-SSE).

Geochemistry and U-Pb ages from the Kösdağ Metavolcanics in the southern Central Pontides (Turkey): Complementary data for early Late Cretaceous island arc development in the Northern Neotethys

The Kosdag Metavolcanics (KMs) in the southern Central Pontides are exposed between the Izmir-Ankara-Erzincan Suture Belt in the south and the Sakarya Composite Terrane in the north. They comprise an approximately 40-km-long tectonic unit, bounded by the splays of the North Anatolian Transform Fault in the north and the Kizilca Thrust in the south. The basement of the unit mainly consists of metabasalts, metaandesites, and metarhyolites, with well-developed blastomylonitic textures, which are interlayered by recrystallized pelagic limestone and chert. Late Cretaceous pelagic limestones of the Dikmen Formation disconformably overlie the basement. Geochemically, the KMs exhibit enrichment in Th and La relative to Nb (and Ti), indicating subduction-related magmatic signatures. The KMs are subdivided into two main types, as Type 1 and Type 2, based on their relative Zr-Hf enrichment/depletion features. All of the members of the KMs have a subalkaline nature (Nb/Y - 0.08-0.19 for Type 1; Nb/Y = 0.05-0.13 for Type 2) and display a calc-alkaline affinity. The high Zr/Nb (38.1-52.9 for Type 1, 21.8-41.2 for Type 2), low Zr/Y (4.07-5.25 for Type 1, 1.58-2.44 for Type 2), and Nb/Y (0.08-0.14 for Type 1,0.05-0.10 for Type 2) signatures of the KMs indicate that they have derived from a depleted source, which has been modified by a subduction component. The laser ablation inductively-coupled plasma mass spectrometry (LA-ICP-MS) U-Pb zircon ages of the metarhyolite samples ranged between 94.64 +/- 0.77 Ma and 113.2 +/- 2.3 Ma, suggesting the presence of an intraoceanic subduction zone during the early Late Cretaceous within the Izmir-Ankara-Erzincan branch of the Neotethys Ocean in the Central Pontides.

The uppermost Pleistocene–Holocene mud drape across the Marmara Sea: Quantification of detrital supply from southern Marmara rivers

The Marmara Sea (area 11,350 km2; volume 3378 km3; central basins >1100 m deep) straddles the North Anatolian Transform Fault separating the Eurasian and Aegean-Anatolian tectonic plates. Along with the shallow straits of Dardanelles and Bosphorus (depths ~63 m and ~40 m, respectively), the Marmara Sea forms the only marine connection between the Black Sea and the eastern Mediterranean. During Pleistocene glacial stages, the modern straits were subaerial valleys and the modern Marmara basin was occupied by the landlocked Propontis Lake. Previous researchers attributed major portions of a widely distributed uppermost Pleistocene–Holocene mud blanket (locally >10–25 m thick; volume 43–47 km3) to transport of suspended load through one or both of the straits, as either the Aegean Sea (at ~13.8 cal ka) or the Neoeuxine Lake (today's Black Sea, at ~11.1 cal ka) began to spill into the Marmara basin. To test these suggestions, the thicknesses and volume of the mud blanket were determined from >5000 line-km of airgun, sparker and boomer profiles and > 100 cores, and compared with the contemporary supply from local rivers to decide, by difference, if the straits might have had a significant role. Volume calculations for the detrital supply from rivers rely on (1) decades of daily water- and sediment-discharge data from gauging stations, acquired before 20th century dam construction and, independently, (2) the BQART model which uses a variety of hydrological, geomorphic, geological and climate data. These calculations demonstrate that >85–90% of the detritus in the offshore mud blanket was supplied by steep rivers (Kocasu River and its tributaries) and mountainous streams draining the highlands of the southern Marmara region. Geochemistry of the <38 μm fraction supports this source. Any input through the Dardanelles has been sporadic and limited to perhaps ~5 Gt of suspended load (equivalent to ~5.2 km3 of porous mud when deposited) because of changing directions and rates of flow since the Last Glacial Maximum. Resedimentation through mass wasting and transgressive shoreface erosion appear to be minor compared with river supply. The isolated nature of the Marmara basin and its supply from mostly a single watershed afford an opportunity to verify the reliability of this type of hindcast analysis, based upon sediment-discharge data and catchment models – analysis which cannot be completed with a comparable level of certainty along open marine coastlines elsewhere.