The 2020 Samos (Aegean Sea) M7 earthquake: a normal fault with rupture directivity and near surface slip explaining the tsunami generation and coastal uplift

On 30 October 2020, a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea, whose earthquake mechanism corresponds to an E-W normal fault dipping to the north. During the aftershock period in December 2020, a hydrographic survey off the northern coastal margin of Samos Island was conducted onboard R/V NAFTILOS. The result was a detailed bathymetric map with 15 m grid interval and 50 m isobaths and a morphological slope map. The morphotectonic analysis showed the E-W fault zone running along the coastal zone with 30–50° of slope, forming a half-graben structure. Numerous landslides and canyons trending N-S, transversal to the main direction of the Samos coastline, are observed between 600 and 100 m water depth. The ENE-WSW oriented western Samos coastline forms the SE margin of the neighboring deeper Ikaria Basin. A hummocky relief was detected at the eastern margin of Samos Basin probably representing volcanic rocks. The active tectonics characterized by N-S extension is very different from the Neogene tectonics of Samos Island characterized by NE-SW compression. The mainshock and most of the aftershocks of the October 2020 seismic activity occur on the prolongation of the north dipping E-W fault zone at about 12 km depth.

Download Full-text

GPR signature of Quaternary faulting: a study from the Mt. Pollino region, southern Apennines, Italy

10.5194/se-2021-75 ◽

2021 ◽

Author(s):

Maurizio Ercoli ◽

Daniele Cirillo ◽

Cristina Pauselli ◽

Harry M. Jol ◽

Francesco Brozzetti

Keyword(s):

Late Quaternary ◽

Active Faults ◽

Normal Fault ◽

Data Interpretation ◽

Seismic Gap ◽

Southern Apennines ◽

Near Surface ◽

Radar Images ◽

Sedimentary Fill ◽

Continental Basin

Abstract. With the aim of unveiling evidence of Late Quaternary faulting, a series of Ground Penetrating Radar (GPR) profiles were acquired across the Campotenese continental basin (Mt. Pollino region) in the southern Apennines active extensional belt (Italy). A set of forty-nine 300 MHz and 500 MHz GPR profiles, traced nearly perpendicular to a buried normal fault, were acquired and carefully processed through a customized workflow. The data interpretation allowed us to reconstruct a pseudo-3D model depicting the boundary between the Mesozoic bedrock and the sedimentary fill of the basin, which were in close proximity to the fault. Once reviewing and defining the GPR signature of faulting, we highlight in our data how near surface alluvial and colluvial sediments appear to be dislocated by a set of conjugate (west and east-dipping) discontinuities that penetrate inside the underlying Triassic dolostones. Close to the contact between the continental deposits and the bedrock, some buried scarps which offset wedge-shaped deposits are interpreted as coseismic ruptures, subsequently sealed by later deposits. Although the use of pseudo-3D GPR data implies more complexity linking the geophysical features among the radar images, we have reconstructed a reliable subsurface fault pattern, discriminating master faults and a series of secondary splays. We believe our contribution provides an improvement in the characterization of active faults in the study area which falls within the Pollino seismic gap and is considered potentially prone to severe surface faulting. Our aim is for our approach and workflow to be of inspiration for further studies in the region as well as for similar high seismic hazard areas characterized by scarcity of near-surface data.

Download Full-text

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)

Pure and Applied Geophysics ◽

10.1007/s00024-019-02154-y ◽

2019 ◽

Vol 176 (10) ◽

pp. 4177-4211 ◽

Cited By ~ 11

Author(s):

Athanassios Ganas ◽

Panagiotis Elias ◽

Vasilis Kapetanidis ◽

Sotirios Valkaniotis ◽

Pierre Briole ◽

...

Keyword(s):

Normal Fault ◽

Aegean Sea

Download Full-text

Surface Slip Retardation by ion Implantation

MRS Proceedings ◽

10.1557/proc-93-385 ◽

1987 ◽

Vol 93 ◽

Author(s):

W. S. Samipath ◽

F. M. Kustas ◽

R. Wei ◽

P. J. Wilbur

Keyword(s):

Stainless Steel ◽

Ion Implantation ◽

Slip Line ◽

Line Formation ◽

Simple Test ◽

Near Surface ◽

Ion Energy ◽

Surface Slip ◽

Current Densities ◽

Nitrogen Ion

ABSTRACTIon implantation is shown to retard surface slip and thereby induce improvements in wear and fatigue resistance of metals. A simple test is described which can be used to study the effects of ion implantation in retarding motion of dislocations in the near-surface regions of metals. In this test, regions of annealed and etched surfaces of metals are masked and implanted with ions. The specimens are then deformed until significant plastic deformation is introduced and the slip-lines are observed under the microscope. Evidence of improved resistance to slip-line formation in nitrogen ion implanted surface regions is presented for copper, α-iron and 303 stainless steel. The test is shown to be a useful tool for comparing the effects of ion implantation conditions on surface slip retardation, since adjacent regions of the surface can be implanted to different conditions and the resistance to slip line formation in the different regions can be compared. For example, the resistance to slip line formation in 303 stainless steel was found to be greater in regions that were implanted at ultrahigh current densities (1500 μA/cm2) than in regions implanted at lower current densities (100 μA/cm2) to the same dose and at the same ion energy.

Download Full-text

Morphotectonic analysis along the northern margin of Samos Island, related to the seismic activity of October 2020, Aegean Sea, Greece

10.5194/egusphere-egu21-3849 ◽

2021 ◽

Author(s):

Paraskevi Nomikou ◽

Dimitris Evangelidis ◽

Dimitris Papanikolaou ◽

Danai Lampridou ◽

Dimitris Litsas ◽

...

Keyword(s):

Seismic Activity ◽

Normal Fault ◽

Aegean Sea ◽

The South ◽

The West ◽

Northern Margin ◽

Hydrographic Survey ◽

Southern Margin ◽

Eastern Aegean ◽

Division Line

On October 30th 2020 a strong earthquake of magnitude 7.0 occurred north of Samos Island at the Eastern Aegean Sea. This seismic event was another destructive active deformation in the long seismic history of Samos since the ancient times. Preliminary reports focused the seismic epicenter at about 10 km north of Karlovassi, situated at the western part of the Samos E-W trending coastline. The earthquake mechanism corresponds to an E-W normal fault dipping to the north. The activated fault was assumed to be running along the northern margin of Samos Island, which bounds from the south the Samos basin.Immediately after the seismic activity and during the aftershock period in December 2020 an hydrographic survey off the northern coastal margin of Samos Island was conducted with R/V NAUTILOS of the Hellenic Navy Hydrographic Service, using the multibeam SeaBat 7160 RESON. The result of the hydrographic survey was a detailed bathymetric map with 15m grid interval and 50m isobaths.&#160; The main morphological aspects of Samos Basin are a 14 km long, 6 km wide and 690 m deep elongated E-W basin developed north of Samos Island.The southern margin of the basin is abrupt with morphological slopes of more than 10o, following the major E-W normal fault surface, running along the coastal zone, with an overall throw of more than 500m. In contrast, the northern margin of the basin shows a gradual slope increase towards the south from 1o to 5o. Numerous small canyons trending N-S transversal to the main direction of the Samos coastline are observed along the southern margin, between 600 and 100 m water depth. &#160;These canyons have a length around 2,7 km and width between 100-300 m. Two large submarine landslides with a canyon width of 1,3 km and 0,8 Km, are located north of Karlovasi. The creation of the canyons is probably due to the uplift of Northern Samos Island and their 500 m vertical height difference corresponds to the average fault throw that has controlled the steep slopes of the margin. The orientation of the fault scarp changes at the western Samos coastline from E-W to ENE-WSW facing the neighboring Ikaria Basin, which is developed to the west of Samos Basin. The division line between the Ikaria and Samos basins runs N-S from the northern slopes and coast of the Kerketeas mountain (1443m). The aftershocks of the 30th October main shock are limited east of the N-S division line with only a minor activity 15 km to the west within the eastern margin of the Ikaria Basin.

Download Full-text

The Røde Ø Conglomerate of inner Scoresby Sund and the Carboniferous(?) and Permian rocks west of the Schuchert Flod. A general sedimentological account

Bulletin Grønlands Geologiske Undersøgelse ◽

10.34194/bullggu.v102.6643 ◽

1972 ◽

Vol 102 ◽

pp. 1-48

Author(s):

J.D Collinson

Keyword(s):

Normal Fault ◽

Sediment Supply ◽

Upper Permian ◽

Lower Permian ◽

Western Boundary ◽

The West ◽

Near Surface ◽

Surface Precipitation ◽

North West ◽

The North

The Røde Ø Conglomerate is a formation of red sandstones and conglomerates in the inner part of Scoresby Sund. It has an elongated north-south outcrop within an area of high-grade metamorphic rocks. It is bounded on the west by a normal fault, downthrowing to the east and dying out northwards. The sediments rest unconformably on migmatites along their eastern boundary. Within the Røde Ø Conglomerate, four lithofacies associations are recognised. A conglomerate association is the most abundant and occurs along the western side of the outcrop against the fault. It is coarse and poorly sorted, and easterly palaeocurrents are suggested. The association is interpreted as the product of alluvial fans building eastwards. This association passes laterally eastwards through an interbedded complex into a silty sandstone association which, in turn, passes into a gypsiferous sandstone association. These are both thought to be largely suspension deposits at the distal limit of the fans. The gypsum is the result of near surface precipitation due to high evaporation. On Storø, on the eastern side of Rødefjord and east of the other associations, a cross-bedded sandstone association referable to a normal fluviatile model occurs. Palaeocurrents here were to the north and north-west. It is suggested that movements along the western boundary fault were probably the cause of the rapid uplift needed to supply the coarse sediment. The rocks west of the Schuchert Flod were described by Kempter (1961) who recognised three major subdivisions, the Bjørnbos Corner Formation of alleged Carboniferous age, the Gurreholmsdal Formation (Lower Permian) and the Karstryggen Group (Upper Permian). The Bjørnbos Corner Formation is an arkosic conglomerate whose sedimentation is not obviously related to any presently observed tectonic feature. The Gurreholmsdal Formation shows a pattern of sedimentation broadly similar to the Røde ø Conglomerate with conglomerates in the west, near the Stauning Alper Fault passing eastwards and downcurrent into finer arkoses and eventually into micaceous sandstones which have northerly palaeocurrents. Sediment supply is again thought to have been due to movement on the western fault margin. It is not possible to date the Røde Ø Conglomerate by comparison with the Schuchert sequence in any conclusive way, though it can be tentatively suggested that the same regional tensional event might have been responsible for both sedimentary events.

Download Full-text

Prediction Equations for Significant Duration of Earthquake Ground Motions considering Site and Near-Source Effects

Earthquake Spectra ◽

10.1193/1.2358175 ◽

2006 ◽

Vol 22 (4) ◽

pp. 985-1013 ◽

Cited By ~ 137

Author(s):

Justin J. Kempton ◽

Jonathan P. Stewart

Keyword(s):

Source Parameters ◽

Body Waves ◽

Time Interval ◽

Rupture Directivity ◽

Prediction Equations ◽

Deep Basin ◽

Ground Acceleration ◽

Near Surface ◽

Significant Duration ◽

Source Distance

For engineering systems having a potential for degradation under cyclic loading (e.g., landslides, soil profiles subject to liquefaction, some structural systems), the characterization of seismic demand should include the amplitude and duration of strong shaking within the system. This article is concerned with significant-duration parameters, which are defined as the time interval across which a specified amount of energy is dissipated (as measured by the integral of the square of the ground acceleration or velocity). We develop ground-motion prediction equations for significant-duration parameters as a function of magnitude, closest site-source distance, site parameters that reflect shallow geologic conditions as well as deep basin structure, and near-source parameters. The relations are developed using a modern database and a random-effects regression procedure. We find significant duration to increase with magnitude and site-source distance (effects that had been identified previously), but also to decrease with increasing shear-wave velocity of near-surface sediments and to increase with increasing basin depth. Parameters that principally measure the duration of body waves were also found to decrease in near-fault areas subject to forward rupture directivity, although such effects were not apparent for other duration parameters that tend to reflect the combined duration of body and surface waves.

Download Full-text

A new Miocene detachment from Antiparos Island (Cyclades, Greece)

10.5194/egusphere-egu2020-19863 ◽

2020 ◽

Author(s):

Dimitrios Baroutsos ◽

Konstantinos Soukis ◽

Erich Draganits ◽

David A Schneider ◽

Bernhard Grasemann ◽

...

Keyword(s):

Late Miocene ◽

Hanging Wall ◽

Normal Fault ◽

Aegean Sea ◽

Axial Plane ◽

Amphibolite Facies ◽

Eastern Coast ◽

Lower Grade ◽

Mylonitic Foliation ◽

Metamorphic Core Complexes

Numerous studies throughout the world have focused on the structure and evolution of metamorphic core complexes and the exhumation of subducted rocks in back-arc areas of orogenic belts. The Cycladic Islands (central Aegean Sea, Greece) are key areas for studying mechanisms of high-pressure rock exhumation. In that domain, the highly attenuated upper plate is preserved only as sparse extensional allochthons in the hanging wall of crustal-scale detachments. Several detachment systems have been identified on a number of islands indicating overall bivergent extension during the late Oligocene&#8211;Miocene. The island of Antiparos is situated at the center of the Cyclades, SW of the larger Paros Island where the top-to-N Paros-Naxos Detachment has exhumed pre-Alpine basement and metamorphosed Permian-Mesozoic rocks of the Cycladic Blueschist Unit (CBU). The tectonostratigraphic relationship of an enigmatic element, the Dryos Unit, remains unclear.Detailed mapping in Antiparos revealed the existence of a sub-horizontal normal fault along the eastern coast of the island. This fault juxtaposes CBU in the footwall against the Dryos Unit and scarce (?)late Miocene clastic sediments in the hanging wall.The CBU occupies most of the island and consists of marble alternating with schists and gneiss layers. The earlier HP assemblages are totally overprinted by mainly amphibolite facies metamorphism. An axial plane foliation to NE-SW isoclinal folds is accompanied by NE-SW stretching lineation. As indicated by recrystallization of feldspars and high-grade deformation mechanisms these structures formed under amphibolite facies conditions. Towards the detachment the foliation is reworked by a brittle-ductile mylonitic foliation and a brittle-ductile S -C&#8217; fabric can be observed.Numerous kinematic indicators such as &#963;- and &#948;-clasts, Riedel shears, flanking structures S-C&#8217; fabric, observed within the ultramylonitic rocks of the footwall and the mylonites/cataclasites of the hanging wall indicate top-to-NE sense of shear, comparable to the sense of shear in the Paros-Naxos detachment.The Dryos Unit is observed only along the central eastern coast of Antiparos, above the low-angle detachment and comprises lower grade (greenschist facies) metabasite, calc-phyllite and pink marble. Deformation in the structurally upper part is characterized by intense refolding and a steep axial plane foliation. At the structurally lower part a strong mylonitic foliation prevails, overprinted by intense cataclastic deformation. The stretching lineation is mostly NW-SE but in the lower part and towards the detachment it rotates to NE-SW. The late Miocene sediments are found adjacent to the Dryos rocks in two localities, comprising mainly sandstone, mudstone and conglomerate in which, large blueschist clasts are abundant.The new data presented in this study combined with existing data from Paros Island substantially add to the continuation and structure of the complex Paros-Naxos detachment system, domed at an island scale. Furthermore, it suggests that most probably the Dryos Unit is not an upper part of the Cycladic Blueschist Unit but belongs to a different unit, possibly of Pelagonian origin.

Download Full-text

Seismic coastal uplift in a region of subsidence: Holocene raised shorelines of Samos Island, Aegean Sea, Greece

Marine Geology ◽

10.1016/s0025-3227(00)00064-5 ◽

2000 ◽

Vol 170 (1-2) ◽

pp. 41-58 ◽

Cited By ~ 38

Author(s):

S.C. Stiros ◽

J. Laborel ◽

F. Laborel-Deguen ◽

S. Papageorgiou ◽

J. Evin ◽

...

Keyword(s):

Aegean Sea ◽

Coastal Uplift

Download Full-text

Is there a link between faulting and magmatism in the south-central Aegean Sea?

Geological Magazine ◽

10.1017/s0016756812000453 ◽

2012 ◽

Vol 150 (2) ◽

pp. 193-224 ◽

Cited By ~ 22

Author(s):

S. KOKKALAS ◽

A. AYDIN

Keyword(s):

Spatial Relationship ◽

Normal Fault ◽

Aegean Sea ◽

Hydrothermal Activity ◽

Strike Slip ◽

Normal Faults ◽

Upper Crust ◽

South Central ◽

Tectonic Features

AbstractA distinct spatial relationship between surface faulting, magmatic intrusions and volcanic activity exists in the Aegean continental crust. In this paper, we provide detailed structural observations from key onshore areas, as well as compilations of lineament maps and earthquake locations with focal plane solutions from offshore areas to support such a relationship. Although pluton emplacement was associated with low-angle extensional detachments, the NNE- to NE-trending strike-slip faults also played an important role in localizing the Middle Miocene plutonism, providing ready pathways to deeper magma batches, and controlling the late-stage emplacement and deformation of granites in the upper crust. Additionally, the linear arrangements of volcanic centres, from the Quaternary volcanoes along the active South Aegean Volcanic Arc, are controlled primarily by NE-trending faults and secondarily by NW-trending faults. These volcanic features are located at several extensional settings, which are associated with the main NE-trending faults, such as (i) in the extensional steps or relay zones between strike-slip and oblique-normal fault segments, (ii) at the overlap zones between oblique-normal faults associated with an extensional strike-slip duplex and (iii) at the tip zone of a NE-trending divergent dextral strike-slip zone. The NE trend of volcano-tectonic features, such as volcanic cone alignments, concentration of eruptive centres, hydrothermal activity and fractures, indicates the significant role of tectonics in controlling fluid and magma pathways in the Aegean upper crust. Furthermore, microseismicity and focal mechanisms of earthquakes in the area confirm the activity and present kinematics of these NE- trending faults.

Download Full-text