scholarly journals IDENTIFYING FAULT ACTIVITY IN THE CENTRAL EVOIKOS GULF (GREECE)

2018 ◽  
Vol 40 (1) ◽  
pp. 439 ◽  
Author(s):  
Th. Rondoyanni ◽  
D. Galanakis ◽  
Ch. Georgiou ◽  
I. Baskoutas
Keyword(s):  
Late Quaternary ◽  
Active Faults ◽  
Point Of View ◽  
Geological Mapping ◽  
Normal Faults ◽  
Geophysical Research ◽  
Alluvial Deposits ◽  
Moderate Seismicity ◽  
Limestone Bedrock ◽  
Topographic Relief

Geological mapping on a 1:5.000 scale and a tectonic analysis in the wider Chalkida region of the Island of Evia and the adjacent Drossia area of Central Greece, have allowed the identification of a number of active and potentially active normal faults. These faults have been formed or reactivated during the Late Quaternary, since they affect Pleistocene brackish and terrestrial deposits. Some of the faults affect the contact of the limestone bedrock with the Quaternary formations, presenting characteristic polished surfaces. The faults, in places covered by the alluvial deposits of the Chalkida plain, are also detected by geophysical research. Among the identified faults, the most important are considered the Aghios Minas- Chalkida, the Avlida and the Lefkadi active faults. The first one extends from Drossia to the Chalkida area, crossing the sea straights, and has an ENE-WSW direction and a south dip. The other two, are parallel antithetic faults oriented WNW-ESE, and bound the South Evoikos Gulf on the Greek mainland and the Evia Island respectively. The mapping and evaluation of active faults in this region of moderate seismicity, with low topographic relief and consequent absence of morphotectonic features, is especially important from a seismic hazard point of view.

scholarly journals LATE QUATERNARY AND HOLOCENE FAULTS OF THE NORTHERN GULF OF CORINTH RIFT, CENTRAL GREECE

2017 ◽  
Vol 50 (1) ◽  
pp. 164 ◽  
Author(s):  
S. Valkaniotis ◽  
S. Pavlides
Keyword(s):  
Late Quaternary ◽  
Active Faults ◽  
Geological Mapping ◽  
Tectonic Activity ◽  
Normal Faults ◽  
Central Greece ◽  
The North ◽  
Gulf Of Corinth ◽  
Area Of Study

New results for the recent tectonic activity in the northern part of the Gulf of Corinth rift are presented. Geological mapping and morphotectonic study re populate the area of study with numerous active and possible active faults. The area is dominated by individual and segmented normal faults along with major structures like Marathias and Delphi-Arachova faults. The results are in accordance with recent studies that reveal a more complex and wider structure of Corinth Rift to the north.

scholarly journals Active Tectonics in the Kvarner Region (External Dinarides, Croatia)—An Alternative Approach Based on Focused Geological Mapping, 3D Seismological, and Shallow Seismic Imaging Data

2020 ◽  
Vol 8 ◽  
Author(s):  
Tvrtko Korbar ◽  
Snježana Markušić ◽  
Ozren Hasan ◽  
Ladislav Fuček ◽  
Dea Brunović ◽  
...  
Keyword(s):  
Active Faults ◽  
Active Tectonics ◽  
Strike Slip ◽  
Focal Mechanisms ◽  
Geological Mapping ◽  
Multidisciplinary Research ◽  
Shallow Seismic ◽  
Moderate Seismicity ◽  
Recent Activity ◽  
External Dinarides

Active tectonics in long-lived orogenic belts usually manifests on the preexisting inherited structures. In the Kvarner region of the External Dinarides, an area with low-to-moderate seismicity related to the Adriatic microplate (Adria) northward movement, we deal with faults in predominantly carbonate rocks within tectonically complex NW-SE striking fold-and-thrust belt, which makes the identification and parametrization of the active structures challenging. Moreover, anthropogenic modifications greatly complicate access to the surface geological and geomorphological data. This paper demonstrates results of focused multidisciplinary research, from surface geological mapping and offshore shallow seismic surveys to earthquake focal mechanisms, as an active fault identification and parametrization kit, with a final goal to produce an across-methodological integrated model of the identified features in the future. Reverse, normal, and strike-slip orogen-parallel (longitudinal) to transverse faults were identified during geological mapping, but there is no clear evidence of their mutual relations and possible recent activity. The focal mechanisms calculated from the instrumental record include weak-to-moderate earthquakes and show solutions for all faulting types in the upper crust, compatible with the NE-SW oriented principal stress direction, with the stronger events favoring reverse and strike-slip faulting. The 3D spatial and temporal distribution of recent earthquake hypocenters indicate their clustering along predominantly subvertical transversal and steeply NE-dipping longitudinal planes. High-resolution shallow seismic geoacoustical survey (subbottom profiler) of the Quaternary sediments in the Rijeka Bay revealed local tectonic deformations of the stratified Late Pleistocene deposits that, along with overlaying mass-transport deposits, could imply prehistorical strong earthquake effects. Neotectonic faults onshore are tentatively recognized as highly fractured zones characterized by enhanced weathering, but there is no evidence for its recent activity. Thus, it seems that the active faults are blind and situated below the thin-skinned and highly deformed early-orogenic tectonic cover of the Adria. A strain accumulating deeper in the crust is probably irregularly redistributed near the surface along the preexisting fault network formed during the earlier phases of the Dinaric orogenesis. The results indicate a need for further multidisciplinary research that will contribute to a better seismic hazard assessment in the densely populated region that is also covered by strategic infrastructure.

Seismogenic potential of the High Durance Fault constrained by 20 yr of GNSS measurements in the Western European Alps

2020 ◽  
Vol 222 (3) ◽  
pp. 2136-2146
Author(s):  
M Mathey ◽  
A Walpersdorf ◽  
C Sue ◽  
S Baize ◽  
A Deprez
Keyword(s):  
Velocity Field ◽  
Surface Deformation ◽  
Active Faults ◽  
Slip Rate ◽  
Fault Model ◽  
Fault Slip ◽  
Normal Faults ◽  
European Alps ◽  
Moderate Seismicity ◽  
Fault Slip Rate

SUMMARY Due to the steady moderate seismicity observed along the Briançon seismic arc, in the south-western French Alps, three temporary GNSS (Global Navigation Satellite System) surveys took place in 1996, 2006 and 2011, across a ∼50 × 60 km² wide area, to investigate the surface deformation field. The horizontal velocity field computed from these three surveys showed an east–west extension in the network. A fourth campaign was led in 2016, creating a 20 yr observation span, resulting in measurements which reach a sufficient accuracy to assess whether extension found within the Briançon network is localized onto any particular tectonic feature. Several faults in this area are known to be active normal faults. Assessing the localization of the deformation may lead to a better understanding of the active tectonics of the Alpine belt. To address this issue, a robust velocity field was computed from the combination of the different campaign and permanent GNSS data. Strain rate tensors were derived for the first time in this area on a 0.1 × 0.1 deg grid to assess the distribution of the deformation. The regional deformation appears localized in the Briançon area and reaches up to 20 ± 5 nanostrain yr−1 in the centre of the network. The observed velocities were projected on a profile across the network and compared with modelled interseismic deformation to characterize the behaviour of the major active faults known in the study zone. While a two-fault model provides the best fit to the data, a single fault model has only marginally higher residuals, with parameters which are more consistent with the seismotectonics of the region. The localization of the single modelled fault is consistent with the location of the High Durance Fault (HDF). Therefore, we used the known geological location of this structure as a priori information in a block model to compute a fault slip rate at the interface between the two blocks. The velocities on the interface indicate 0.4–0.5 mm yr−1 of extension, and therefore strain accumulates along the HDF throughout the seismic cycle. The geodetically derived fault slip rate is converted into an equivalent seismic moment release rate, which is consistent within its uncertainty bounds with the known historical and instrumental seismicity of the Briançon area.

Volcanoes geological mapping and structural geology with UAS High Resolution Digital Terrain Model : the Kuei-Shan Tao case example (Eastern Taiwan).

2021 ◽  
Author(s):  
Benoit Deffontaines ◽  
Kuo-Jen Chang ◽  
Samuel Magalhaes ◽  
Gérardo Fortunato
Keyword(s):  
High Resolution ◽  
Okinawa Trough ◽  
Volcanic Rocks ◽  
Digital Terrain Model ◽  
Structural Features ◽  
Point Of View ◽  
Geological Mapping ◽  
Lava Flows ◽  
Aerial Photographs ◽  
Structural Scheme

<p>Volcanic areas in the World are often difficult to map especially in a structural point of view as (1) fault planes are generally covered and filled by more recent lava flows and (2) volcanic rocks have very few tectonic striations. Kuei-Shan Tao (11km from Ilan Plain – NE Taiwan) is a volcanic island, located at the soutwestern tip of the South Okinawa trough (SWOT). Two incompatible geological maps had been already published both lacking faults and structural features (Hsu, 1963 and Chiu et al., 2010). We propose herein not only to up-date the Kuei-Shan Tao geological map with our high resolution dataset, but also to create the Kuei-Shan Tao structural scheme in order to better understand its geological and tectonic history.</p><p>Consequently, we first acquired aerial photographs from our UAS survey and get our new UAS high resolution DTM (HR UAS-DTM hereafter) with a ground resolution <10cm processed through classical photogrammetric methods. Taking into account common sense geomorphic and structural interpretation and reasoning deduced form our HR UAS-DTM, and the outcropping lithologies situated all along the shoreline, we have up-dated the Kuei-Shan Tao geological mapping and its major structures. To conclude, the lithologies (andesitic lava flows and pyroclastic falls) and the new structural scheme lead us to propose a scenario for both the construction as well as the dismantling of Kuei-Shan Tao which are keys for both geology and geodynamics of the SWOT.</p>

scholarly journals Tectonic stress regime in the 2003–2004 and 2012–2015 earthquake swarms in the Ubaye Valley, French Alps

2018 ◽  
Vol 175 (6) ◽  
pp. 1997-2008 ◽  
Author(s):  
Lucia Fojtíková ◽  
Václav Vavryčuk
Keyword(s):  
Seismic Activity ◽  
Joint Inversion ◽  
Earthquake Swarm ◽  
Active Faults ◽  
Tectonic Stress ◽  
Geological Mapping ◽  
Earthquake Swarms ◽  
Stress Regime ◽  
French Alps ◽  
Principal Axes

Abstract We study two earthquake swarms that occurred in the Ubaye Valley, French Alps within the past decade: the 2003–2004 earthquake swarm with the strongest shock of magnitude ML = 2.7, and the 2012–2015 earthquake swarm with the strongest shock of magnitude ML = 4.8. The 2003–2004 seismic activity clustered along a 9-km-long rupture zone at depth between 3 and 8 km. The 2012–2015 activity occurred a few kilometres to the northwest from the previous one. We applied the iterative joint inversion for stress and fault orientations developed by Vavryčuk (2014) to focal mechanisms of 74 events of the 2003–2004 swarm and of 13 strongest events of the 2012–2015 swarm. The retrieved stress regime is consistent for both seismic activities. The σ 3 principal axis is nearly horizontal with azimuth of ~ 103°. The σ 1 and σ 2 principal axes are inclined and their stress magnitudes are similar. The active faults are optimally oriented for shear faulting with respect to tectonic stress and differ from major fault systems known from geological mapping in the region. The estimated low value of friction coefficient at the faults 0.2–0.3 supports an idea of seismic activity triggered or strongly affected by presence of fluids.

scholarly journals Methodology for Earthquake Rupture Rate estimates of fault networks: example for the Western Corinth Rift, Greece

2017 ◽  
Author(s):  
Thomas Chartier ◽  
Oona Scotti ◽  
Hélène Lyon-Caen ◽  
Aurélien Boiselet
Keyword(s):  
Active Faults ◽  
Slip Rate ◽  
Seismic Hazard Assessment ◽  
System Level ◽  
Fault System ◽  
Normal Faults ◽  
Accurate Estimation ◽  
Probabilistic Seismic Hazard Assessment ◽  
Earthquake Rupture ◽  
Multiple Faults

Abstract. Modelling the seismic potential of active faults is a fundamental step of probabilistic seismic hazard assessment (PSHA). An accurate estimation of the rate of earthquakes on the faults is necessary in order to obtain the probability of exceedance of a given ground motion. Most PSHA studies consider faults as independent structures and neglect the possibility of multiple faults or fault segments rupturing simultaneously (Fault to Fault -FtF- ruptures). The latest Californian model (UCERF-3) takes into account this possibility by considering a system level approach rather than an individual fault level approach using the geological , seismological and geodetical information to invert the earthquake rates. In many places of the world seismological and geodetical information long fault networks are often not well constrained. There is therefore a need to propose a methodology relying only on geological information to compute earthquake rate of the faults in the network. In this methodology, similarly to UCERF-3, a simple distance criteria is used to define FtF ruptures and consider single faults or FtF ruptures as an aleatory uncertainty. Rates of earthquakes on faults are then computed following two constraints: the magnitude frequency distribution (MFD) of earthquakes in the fault system as a whole must follow an imposed shape and the rate of earthquakes on each fault is determined by the specific slip-rate of each segment depending on the possible FtF ruptures. The modelled earthquake rates are then confronted to the available independent data (geodetical, seismological and paleoseismological data) in order to weigh different hypothesis explored in a logic tree. The methodology is tested on the Western Corinth Rift, Greece (WCR) where recent advancements have been made in the understanding of the geological slip rates of the complex network of normal faults which are accommodating the ~15 mm/yr North-South extension. Modelling results show that geological, seismological extension rates and paleoseismological rates of earthquakes cannot be reconciled with only single fault rupture scenarios and require hypothesising a large spectrum of possible FtF rupture sets. Furthermore, in order to fit the imposed regional Gutenberg-Richter MFD target, some of the slip along certain faults needs to be accommodated either with interseismic creep or as post-seismic processes. Furthermore, individual fault’s MFDs differ depending on the position of each fault in the system and the possible FtF ruptures associated with the fault. Finally, a comparison of modelled earthquake rupture rates with those deduced from the regional and local earthquake catalogue statistics and local paleosismological data indicates a better fit with the FtF rupture set constructed with a distance criteria based on a 5 km rather than 3 km, suggesting, a high connectivity of faults in the WCR fault system.

Postglacial faulting near Crater Lake, Oregon, and its possible association with the Mazama caldera-forming eruption

2019 ◽  
Vol 131 (9-10) ◽  
pp. 1440-1458
Author(s):  
Charles R. Bacon ◽  
Joel E. Robinson
Keyword(s):  
Crater Lake ◽  
Active Faults ◽  
Large Earthquake ◽  
Normal Displacement ◽  
Normal Faults ◽  
Caldera Collapse ◽  
Normal Extension ◽  
Slip Rates ◽  
Crater Lake National Park ◽  
Lateral Offset

Abstract Volcanoes of subduction-related magmatic arcs occur in a variety of crustal tectonic regimes, including where active faults indicate arc-normal extension. The Cascades arc volcano Mount Mazama overlaps on its west an ∼10-km-wide zone of ∼north-south–trending normal faults. A lidar (light detection and ranging) survey of Crater Lake National Park, reveals several previously unrecognized faults west of the caldera. Postglacial vertical separations measured from profiles across scarps range from ∼2 m to as much as 12 m. Scarp profiles commonly suggest two or more postglacial surface-rupturing events. Ignimbrite of the ca. 7.6 ka climactic eruption of Mount Mazama, during which Crater Lake caldera formed, appears to bury fault strands where they project into thick, valley-filling ignimbrite. Lack of lateral offset of linear features suggests principally normal displacement, although predominant left stepping of scarp strands implies a component of dextral slip. West-northwest–east-southeast and north-northwest–south-southeast linear topographic elements, such as low scarps or ridges, shallow troughs, and straight reaches of streams, suggest that erosion was influenced by distributed shear, consistent with GPS vectors and clockwise rotation of the Oregon forearc block. Surface rupture lengths (SRL) of faults suggest earthquakes of (moment magnitude) Mw6.5 from empirical scaling relationships. If several faults slipped in one event, a combined SRL of 44 km suggests an earthquake of Mw7.0. Postglacial scarps as high as 12 m imply maximum vertical slip rates of 1.5 mm/yr for the zone west of Crater Lake, considerably higher than the ∼0.3 mm/yr long-term rate for the nearby West Klamath Lake fault zone. An unanswered question is the timing of surface-rupturing earthquakes relative to the Mazama climactic eruption. The eruption may have been preceded by a large earthquake. Alternatively, large surface-rupturing earthquakes may have occurred during the eruption, a result of decrease in east-west compressive stress during ejection of ∼50 km3 of magma and concurrent caldera collapse.

scholarly journals Topographic Anaglyphs from Detailed Digital Elevation Models Covering Inland and Seafloor for the Tectonic Geomorphology Studies in and around Yoron Island, Ryukyu Arc, Japan

Geosciences ◽  
2018 ◽  
Vol 8 (10) ◽  
pp. 363 ◽  
Author(s):  
Hideaki Goto ◽  
Kohsaku Arai ◽  
Taichi Sato
Keyword(s):  
Late Quaternary ◽  
Active Faults ◽  
Aerial Photographs ◽  
Stress Axis ◽  
Tectonic Geomorphology ◽  
Surface Model ◽  
The North ◽  
Digital Elevation ◽  
Ryukyu Arc ◽  
Island Shelf

Anaglyphs produced using a digital elevation model (DEM) are effective to identify the characteristic tectono–geomorphic features. The objective of this study is to reinvestigate the tectonic geomorphology and to present novel tectonic maps of the late Quaternary in and around the Yoron island based on the interpretation of extensive topographical anaglyphs along the map areas that cover the inland and seafloor. Vintage aerial photographs are used to produce the 3-m mesh inland digital surface model (DSM); further, the 0.6-s to 2-s-mesh seafloor DEM is processed using the cloud point data generated through previous surveys. Thus, we identify anticlinal deformation on both the Pleistocene marine terrace and the seafloor to the north of the island. The deformation axis extends in a line and is parallel to the general trend of the island shelf. The Tsujimiya fault cuts the marine terraces, which extend to the Yoron basin’s seafloor. If we assume that the horizontal compressive stress axis is perpendicular to the island shelf, these properties can easily explain the distribution and style of the active faults and deformation. This study presents an effective methodology to understand the island arc tectonics, especially in case of small isolated islands.

scholarly journals Assessing the impact of sedimentation on fault spacing at the Andaman Sea spreading center

Geology ◽  
2020 ◽  
Author(s):  
Clément de Sagazan ◽  
Jean-Arthur Olive
Keyword(s):  
Active Faults ◽  
Spreading Rate ◽  
Andaman Sea ◽  
Spreading Center ◽  
Normal Faults ◽  
Mid Ocean Ridge ◽  
Plate Separation ◽  
Slow Spreading ◽  
Ocean Ridge ◽  
The Impact

The stabilizing effect of surface processes on strain localization, albeit predicted by several decades of geodynamic modeling, remains difficult to document in real tectonic settings. Here we assess whether intense sedimentation can explain the longevity of the normal faults bounding the Andaman Sea spreading center (ASSC). The structure of the ASSC is analogous to a slow-spreading mid-ocean ridge (MOR), with symmetric, evenly spaced axis-facing faults. The average spacing of faults with throws ≥100 m (8.8 km) is however large compared to unsedimented MORs of commensurate spreading rate, suggesting that sedimentation helps focus tectonic strain onto a smaller number of longer-lived faults. We test this idea by simulating a MOR with a specified fraction of magmatic plate separation (M), subjected to a sedimentation rate (s) ranging from 0 to 1 mm/yr. We find that for a given M ≥ 0.7, increasing s increases fault lifespan by ~50%, and the effect plateaus for s > 0.5 mm/yr. Sedimentation prolongs slip on active faults by leveling seafloor relief and raising the threshold for breaking new faults. The effect is more pronounced for faults with a slower throw rate, which is favored by a greater M. These results suggest that sedimentation-enhanced fault lifespan is a viable explanation for the large spacing of ASSC faults if magmatic input is sufficiently robust. By contrast, longer-lived faults that form under low M are not strongly influenced by sedimentation.

scholarly journals Recent active faults in Belgian Ardenne revealed in Rochefort Karstic network (Namur Province, Belgium)

2001 ◽  
Vol 80 (3-4) ◽  
pp. 297-304 ◽  
Author(s):  
S. Vandycke ◽  
Y. Quinif
Keyword(s):  
Stress Field ◽  
Active Faults ◽  
Ground Surface ◽  
Local Stress ◽  
Tectonic Activity ◽  
Normal Faults ◽  
Regional Stress ◽  
Bedding Planes ◽  
Local Modification ◽  
A Minor

AbstractThis paper presents observations of recent faulting activity in the karstic network of the Rochefort Cave (Namur Province, Belgium, Europe). The principal recent tectonic features are bedding planes reactivated as normal faults, neo-formatted normal faults in calcite flowstone, fresh scaling, extensional features, fallen blocks and displacement of karstic tube. The seismo-tectonic aspect is expanded by the presence of fallen blocks where normally the cavity must be very stable and in equilibrium. Three main N 070° fault planes and a minor one affect, at a decimetre scale, the karst features and morphology. The faults are still active because recent fresh scaling and fallen blocks are observable. The breaking of Holocene soda straw stalactites and displacements of artificial features observed since the beginning of the tourist activity, in the last century, also suggest very recent reactivation of these faults. This recent faulting can be correlated to present-day tectonic activity, already evidenced by earthquakes in the neighbouring area. Therefore, karstic caves are favourable sites for the observation and the quantification of recent tectonic activity because they constitute a 3-D framework, protected from erosion. Fault planes with this recent faulting present slickensides. Thus a quantitative analysis in term of stress inversion, with the help of striated faults, has permitted to reconstruct the stress tensor responsible for the brittle deformation. The principal NW-SE extension (σ3 horizontal) is nearly perpendicular to that of the present regional stress as illustrated by the analysis of the last strong regional earthquake (Roermond, The Netherlands) in 1992. During the Meso-Cenozoic, the main stress tectonics recorded in this part of the European platform is similar to the present one with a NE-SW direction of extension.The discrepancy between the regional stress field and the local stress in the Rochefort cave can be the result of the inversion of the σ2 and σ3 axes of the stress ellipsoid due to its symmetry or of a local modification at the ground surface of the crustal stress field as it has been already observed in active zones.

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