scholarly journals The northern Thessaly strong earthquakes of March 3 and 4, 2021, and their neotectonic setting

2021 ◽  
Vol 58 ◽  
pp. 222
Author(s):  
Alexandros Chatzipetros ◽  
Spyros Pavlides ◽  
Michael Foumelis ◽  
Sotiris Sboras ◽  
Dimitris Galanakis ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Seismic Hazard Assessment ◽  
Shear Zones ◽  
Normal Faults ◽  
Seismogenic Fault ◽  
Rock Falls ◽  
Tectonic Structures ◽  
Northern Greece ◽  
Stress Changes ◽  
Active Tectonic

A sequence of earthquakes occurred on March 3rd and 4th in Northern Thessaly, northern Greece, associated with previously unknown, blind normal faults within the crystalline Palaeozoic basement of the Pelagonian geotectonic zone. Surficial ground deformation, such as liquefaction phenomena in fluvial plains, as well as soil fissures and rock falls, have been mapped. Geological indications of the unmapped seismic fault, i.e., reactivated shear zones, open cracks, etc., have been identified within the bedrock. Based on geological indications, the main fault projection to the surface could be considered a 15 km NW-SE trending structure and average dip of 45o to the NE. The seismic source of the main shock was modelled, and the Coulomb static stress changes calculated for receiver faults similar to the source. The determination of the active tectonic regime of the region by geodetic data and the well-known faults of NE Thessaly plain are also presented, as well as the revised historical and instrumental seismicity. This earthquake raises new concerns and challenges, revising some established views, such as the status of main stress orientations, the orientation of active tectonic structures, the occurrence of a seismogenic fault in a mountainous massif of crystalline rocks without typical geomorphological expression and the role of blind faults in Seismic Hazard Assessment.

Fault Distribution, Segmentation and Earthquake Generation Potential of the Philippine Fault in Eastern Mindanao, Philippines

2015 ◽  
Vol 10 (1) ◽  
pp. 74-82 ◽  
Author(s):  
Jeffrey S. Perez ◽  
◽  
Hiroyuki Tsutsumi ◽  
Mabelline T. Cahulogan ◽  
Desiderio P. Cabanlit ◽  
...  
Keyword(s):  
Seismic Hazard ◽  
Hazard Assessment ◽  
Seismic Hazard Assessment ◽  
Tectonic Structures ◽  
Active Tectonic ◽  
Earthquake Generation ◽  
Geometric Segmentation ◽  
Fault Distribution

The 1,250-km-long, NNW-trending, arc-parallel Philippine fault, one of the world’s most active tectonic structures, traverses the Philippine archipelago and has been the source of surface-rupturing earthquakes during the last four centuries. In this paper, we will discuss Philippine fault distribution and segmentation in Mindanao Island by integrating detailed fault mapping together with new geological and paleoseismic data and the analysis of historical surface-rupturing earthquakes. Using geometric segmentation criteria, we have identified nine geometric segments separated by discontinuities such as en echelon steps, bends, changes in strike, gaps, steps and bifurcation in the surface trace. Fault segments ranges from 20 to 100 km in length and are capable of generating earthquakes ofMw6.6 toMw7.4. The results of our study have important implications for earthquake generation potential and seismic hazard assessment of the Philippine fault in Mindanao Island.

Surface Deformation in Northeast Italy by using time series InSAR techniques with Sentinel-1 data

2020 ◽  
Author(s):  
Giulia Areggi ◽  
Cristiano Tolomei ◽  
Lorenzo Bonini ◽  
Giuseppe Pezzo
Keyword(s):  
Time Series ◽  
Surface Deformation ◽  
Ground Deformation ◽  
Geodetic Data ◽  
Plate Motion ◽  
Tectonic Structures ◽  
Synthetic Aperture Radar Data ◽  
Area Of Interest ◽  
Spatial Coverage ◽  
Active Tectonic

<p>Geodetic data provide useful information on surface deformation over long period of time. Applying time series methods to geodetic data, several phenomena were studied. In particular, the potentials of geodetic data were exploited to detect and measure slow tectonic signals such as interseismic strain accumulation. During the interseismic period, when the faults are locked, an accumulation of deformation can occur in response to active tectonic stresses. Considering that such energy can be released through earthquakes, the estimation of surface deformation and the long-term strain rate reveals itself a useful approach for seismic hazard investigations. In this study, we used remote sensing Synthetic Aperture Radar data to evaluate the ground deformation in the Southeastern Alps (Northeastern Italy), an area characterized by an active convergent regime (Adria plate motion is ~ 2mm/yr) as well as several active tectonic structures. We used SAR images provided by Sentinel-1A/B satellites spanning the 2015-2019 temporal interval by applying the multi temporal Small Baseline Subset Interferometry (SBAS) technique. The method is based on a combination of a large number of interferograms characterized by small temporal and geometric baseline in order to reduce decorrelation effects and increase the spatial coverage over the area of interest. The outcomes consist of displacement time series and a mean ground velocity map for each coherent pixels with respect to the satellite Line-of-Sight (LoS). Some detected patterns can be attributed to subsidence phenomena, affecting the plain in the area under analysis, and due to the compaction of the sediments.</p>

scholarly journals SEISMIC HAZARD ASSESSMENT FOR THE CORINTH GULF AND CENTRAL IONIAN ISLANDS BY MEANS OF THE LINKED STRESS RELEASE MODEL

2017 ◽  
Vol 50 (3) ◽  
pp. 1369
Author(s):  
O. Mangira ◽  
E. Papadimitriou ◽  
G. Tsaklidis ◽  
G. Vasiliadis
Keyword(s):  
Historical Data ◽  
Seismic Hazard Assessment ◽  
Stress Release ◽  
Tectonic Structures ◽  
Ionian Islands ◽  
Corinth Gulf ◽  
Stress Release Model ◽  
Stress Changes ◽  
Spatio Temporal ◽  
Release Model

Εarthquake generation causes spatio-temporal stress changes on adjacent fault segments that can alter the occurrence probability of subsequent earthquakes onto them. The interaction is investigated with the Linked Stress Release Model, applied to fit historical data from two areas that accommodate high seismicity, the Corinth Gulf and the Central Ionian Islands. These two areas are divided in two subareas, based on seismotectonic features; Corinth Gulf is divided in the western and eastern part, whereas the area of Central Ionian Islands is divided in Kefalonia and Lefkada subareas. The results establish interactions between the subareas, especially in the Central Ionian Islands, and underline the differences in tectonic structures and earthquake mechanisms between these areas. Particularly, the seismicity in the Central Ionian Islands is proved to be more complex and active and yet more difficult to be examined, whereas the LSRM fits the Corinth Gulf data more easily.

scholarly journals Ground deformation and fault modeling of the 2016 sequence (24 Aug. – 30 Oct.) in central Apennines (Central Italy)

2017 ◽  
Vol 51 ◽  
pp. 76 ◽  
Author(s):  
Spyros Pavlides ◽  
Alexandros Chatzipetros ◽  
George Papathanasiou ◽  
George Georgiadis ◽  
Sotiris Sboras ◽  
...  
Keyword(s):  
Ground Deformation ◽  
Hanging Wall ◽  
Central Italy ◽  
3D Models ◽  
Fault Reactivation ◽  
Aerial Images ◽  
Rock Falls ◽  
Central Apennines ◽  
Seismogenic Sources ◽  
Stress Changes

A chain fault reactivation took place in central Apennines, from August 24 to October 30, 2016, producing five moderate-to-strong earthquakes ranging from Mw5.5 to Mw6.6. This paper presents the results from the study of the ground co-seismic ruptures around the Monte Vettore and Vettoretto, and Norcia. Surface co-seismic ruptures, were observed in the Vettore and Vettoretto segment of the fault for some kilometers (~7 km) in the August earthquakes, which were partly re-activated  and  expanded  northward  during  the  October  earthquakes.  Ruptures  with  5-15  cm displacements are observed both in scree and weathered mantle (elluvium) and the bedrock, mainly fragmented carbonate rocks with small tectonic surfaces. After the October seismic sequence the co-seismic displacement doubled and reached more than 50cm. Oblique low-altitude aerial images were acquired at several sites using a UAV and 3D models were constructed using photogrammetric extrapolation. Numerous observed and mapped rock falls, slides of earth-materials etc, occur mainly along the mountain roads, on artificial slopes. They were studied with preliminary mapping from satellite imagery, and examples are presented of large landslides in the epicentral region with pre and after- the earthquake images. The first four events are associated with four individual fault segments respectively, all aligned along the mountain-fronts of Mt Gorzano and Mt Vettore. The last fifth and strongest event was the result of linkage and breaching of the previous fault segments. We modelled the fault segments intofive seismogenic sources in order to calculate the post-sequence static stress changes produced by the five seismogenic sources (or source faults) to the surrounding faults (receiver faults). Our results suggest possible triggering effects for neighbouring faults located along the strike of the source faults and delay effects for faults which are directly located either on the footwall or hanging-wall.

scholarly journals Polyphase evolution of Pelagonia (northern Greece) revealed by geological and fission-track data

Solid Earth ◽  
2015 ◽  
Vol 6 (1) ◽  
pp. 285-302 ◽  
Author(s):  
F. L. Schenker ◽  
M. G. Fellin ◽  
J.-P. Burg
Keyword(s):  
Early Cretaceous ◽  
Late Cretaceous ◽  
Fission Track ◽  
Regional Scale ◽  
Normal Faults ◽  
Recent Sediment ◽  
Northern Greece ◽  
Rapid Cooling ◽  
Fission Track Ages ◽  
Pelagonian Zone

Abstract. The Pelagonian zone, situated between the External Hellenides/Cyclades to the west and the Axios/Vardar/Almopias zone (AVAZ) and the Rhodope to the east, was involved in late Early Cretaceous and in Late Cretaceous–Eocene orogenic events whose duration and extent are still controversial. This paper constrains their late thermal imprints. New and previously published zircon (ZFT) and apatite (AFT) fission-track ages show cooling below 240 °C of the metamorphic western AVAZ imbricates between 102 and 93–90 Ma, of northern Pelagonia between 86 and 68 Ma, of the eastern AVAZ at 80 Ma and of the western Rhodope at 72 Ma. At the regional scale, this heterogeneous cooling is coeval with subsidence of Late Cretaceous marine basin(s) that unconformably covered the Early Cretaceous (130–110 Ma) thrust system from 100 Ma. Thrusting resumed at 70 Ma in the AVAZ and migrated across Pelagonia to reach the External Hellenides at 40–38 Ma. Renewed thrusting in Pelagonia is attested at 68 Ma by abrupt and rapid cooling below 240 °C and erosion of the gneissic rocks. ZFT and AFT in western and eastern Pelagonia, respectively, testify at ~40 Ma to the latest thermal imprint related to thrusting. Central-eastern Pelagonia cooled rapidly and uniformly from 240 to 80 °C between 24 and 16 Ma in the footwall of a major extensional fault. Extension started even earlier, at ~33 Ma in the western AVAZ. Post-7 Ma rapid cooling is inferred from inverse modeling of AFT lengths. It occurred while E–W normal faults were cutting Pliocene-to-recent sediment.

scholarly journals EVALUATING THE TRIGGERING FACTORS OF THE ROCK FALLS OF 16TH AND 21ST DECEMBER 2009 IN NEA FOKEA, CHALKIDIKI, NORTHERN GREECE

2017 ◽  
Vol 43 (3) ◽  
pp. 1131
Author(s):  
B. Christaras ◽  
G. Syrides ◽  
G. Papathanassiou ◽  
A. Chatzipetros ◽  
T. Mavromatis ◽  
...  
Keyword(s):  
Tectonic Setting ◽  
Slope Instability ◽  
Rock Falls ◽  
Northern Greece ◽  
Local Authorities ◽  
Protective Measures ◽  
The Road ◽  
Triggering Factors ◽  
Country Road ◽  
Asphalt Road

This paper aims to present the characteristics of the rock falls generated on the 16th and 21st of December 2009 at the Nea Moudania – Kassandria country road in Kassandra Peninsula, Chalkidiki, Greece. Both of those events induced damages to the asphalt road and forced the local authorities to close the road to traffic until the construction of protective measures. In order to evaluate the rock fall hazard and analyze the slope instability in the area, the present study focuses on three main triggering factors: rainfall, stratigraphy and tectonic setting.

scholarly journals The tectonostratigraphic architecture of the Serbo-Macedonian massif in the Vertiskos and Kerdilion mountains (Northern Greece)

2021 ◽  
Vol 57 (1) ◽  
pp. 1
Author(s):  
Anastasios Plougarlis ◽  
Markos Tranos ◽  
Lambrini Papadopoulou
Keyword(s):  
Cross Sections ◽  
Large Volume ◽  
General Trend ◽  
Shear Zones ◽  
Structural Features ◽  
Ultramafic Rocks ◽  
Northern Greece ◽  
Tectonic Contact ◽  
Western Side ◽  
Map Scale

The lithologies and structural features of the exposed rocks of the Serbo-Macedonian massif in the Vertiskos and Kerdilion Mts. have been studied in detail by carrying out km-long cross-sections. Moreover, a new tectonostratigraphic architecture for the massif is proposed, based on the migmatization and anatexis that the rocks pertain, under which the specific exposed rocks have been placed into the Vertiskos and Kerdilion Units. The latter approach differs from the traditional view, which is based solely on the lithological difference between the units. In particular, in the Vertiskos Mt., mica schists, garnet-bearing two-mica gneisses, and predominantly two-mica gneisses, without a sign of anatexis and migmatization, overlie tectonically, biotite gneisses and layered amphibolite gneisses into which migmatization and anatexis takes place. The former constitute the Vertiskos Unit, whereas the latter have been grouped into the Kerdilion Unit, since they are of similar lithologies and affinities with rocks of the Kerdilion Unit. The Kerdilion Mt. is a large antiform made up of biotite gneisses alternating with marbles, which are similarly characterized by intense migmatization and anatexis. These rocks are intruded by the Oreskia granite, which is foliated and follows the general trend of the country rocks. All the rocks are folded with isoclinal to tight folds, and the contact between the two units is a mylonitic shear zone with a top-to-the-SW sense-of-shear. Also, a large volume of ultramafic rocks occurs between the Vertiskos and Kerdilion Mts., including metamorphosed rocks like metagabbros to massive amphibolites, which is assigned to the Therma-Volvi-Gomati Complex (TVGC). These rocks have been found in tectonic contact, i.e., shear zones with top-to-the-SW sense-of-shear, only with the rocks of the Kerdilion Unit. Taking into account our new tectonostratigraphic architecture, the contact between the Vertiskos and Kerdilion Units is not located along the western side of the marbles, as the latter are exposed in the Kerdilion Mt. It is traced westerly in the Vertiskos Mt. dipping with intermediate angles towards the SW, due to NW-trending, map-scale, isoclinal folding. The ultramafic rocks of the TVGC are in tectonic contact with the rocks of the Kerdilion Unit, but not the two-mica gneisses of the Vertiskos Unit, and the Arnea granite intrudes not only the Vertiskos Unit as previously considered, but the rocks of the Kerdilion Unit, as well.

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.

scholarly journals Coulomb stress transfer and fault interaction over millennia on non-planar active normal faults: the Mw 6.5–5.0 seismic sequence of 2016–2017, central Italy

2017 ◽  
Vol 210 (2) ◽  
pp. 1206-1218 ◽  
Author(s):  
Zoe K. Mildon ◽  
Gerald P. Roberts ◽  
Joanna P. Faure Walker ◽  
Francesco Iezzi
Keyword(s):  
Main Shock ◽  
Central Italy ◽  
Stress Transfer ◽  
Historical Record ◽  
Normal Faults ◽  
Coulomb Stress ◽  
Seismic Sequence ◽  
Fault Interaction ◽  
Slip Rates ◽  
Stress Changes

Abstract In order to investigate the importance of including strike-variable geometry and the knowledge of historical and palaeoseismic earthquakes when modelling static Coulomb stress transfer and rupture propagation, we have examined the August–October 2016 A.D. and January 2017 A.D. central Apennines seismic sequence (Mw 6.0, 5.9, 6.5 in 2016 A.D. (INGV) and Mw 5.1, 5.5, 5.4, 5.0 in 2017 A.D. (INGV)). We model both the coseismic loading (from historical and palaeoseismic earthquakes) and interseismic loading (derived from Holocene fault slip-rates) using strike-variable fault geometries constrained by fieldwork. The inclusion of the elapsed times from available historical and palaeoseismological earthquakes and on faults enables us to calculate the stress on the faults prior to the beginning of the seismic sequence. We take account the 1316–4155 yr elapsed time on the Mt. Vettore fault (that ruptured during the 2016 A.D. seismic sequence) implied by palaeoseismology, and the 377 and 313 yr elapsed times on the neighbouring Laga and Norcia faults respectively, indicated by the historical record. The stress changes through time are summed to show the state of stress on the Mt. Vettore, Laga and surrounding faults prior to and during the 2016–2017 A.D. sequence. We show that the build up of stress prior to 2016 A.D. on strike-variable fault geometries generated stress heterogeneities that correlate with the limits of the main-shock ruptures. Hence, we suggest that stress barriers appear to have control on the propagation and therefore the magnitudes of the main-shock ruptures.

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