Papers by Alexandros Chatzipetros
Bulletin of the Geological Society of Greece
This paper presents research results on the geological structure of Kastas hill in Amphipolis, as... more This paper presents research results on the geological structure of Kastas hill in Amphipolis, as well as the broader area. They consist of geological and geomorphological observations at Kastas and 133 hills and the surrounding areas, on their geological structure, the stratigraphy and the paleoenvironment. Kastas hill is the site of the largest burial mound discovered in Greece to date. The slopes of its embankment were recorded and modelled in detail using near field photogrammetry. The problem of distinguishing between in situ geological formations and ex situ anthropogenic deposits is also addressed. The bulk volume of Kastas hill consists of natural sediments; these sediments are exposed as successive alternating beds of grayish loose and cohesive sands with scattered pebbles and locally with cobbles. Clayey beds up to ~20-30 cm thick intercalate between the sands. At the top of the hill the anthropogenic deposits are typical of Macedonian tumuli, with soil and clay alternatio...
Proceedings of the VIII European Geoparks Conference, 2009
Bulletin of the Geological Society of Greece, 2016
Throughout the Vertiskos and Kerdylion Units in northern Greece a wide range of Oligocene-Miocene... more Throughout the Vertiskos and Kerdylion Units in northern Greece a wide range of Oligocene-Miocene ore mineralization, including porphyry, epithermal, skarn, carbonate replacement and intrusion-related vein types are documented. Μetalogenesis have been strictly related to the active since Tertiary extensional regime set in back-arc environment conditions. The area of interest is monitored by a network of 20 different permanently installed GPS stations. The processing of the primary geodetic data is based on the triangulation of the GPS stations. In particular, the total of 20 different GPS stations were combined each other, forming different sets of three stations. Each set leads to a triangle formation, while each station is located on a triangle vertex. The recorded geodetic data of a GPS station is combined with the other two stations geodetic data, calculating the maximum horizontal extension and rotation of the triangle centroid, representing the triangle. Based on the aforementioned procedure, 399 different triangles were constructed within the study area, providing 399 different maximum horizontal extension and rotation values. Based on the extracted maximum horizontal extension values, the interpolation method was applied, leading to the construction of a map, including 50 nano-strain step contours, while the maximum and minimum values are 543.5029 and 2.1114 nano-strains, respectively. The exact ore mineralization locations were highlighted onto the aforementioned map in order to be examined their relationship to the maximum extension values. The extracted results show that the majority of ore mineralization locations are included into the medium to maximum horizontal extension areas. This proves the fact that several tectonic structures related to the ore mineralization formation are relatively active or not active in the present. Especially, at the southern part of the study area, ore mineralization localities exhibit remarkably higher maximum horizontal extension values, as a result of active since Oligocene fault zones of Stratoni-Varvara, Megali Panaghia-Gomati, Sochos and Mygdonia. Finally, the presented GPS rotational data are in agreement with the published palaeomagnetic data for the study area. In particular, counter-clockwise and clockwise rotations appear at the northern and the southern part respectively. Α transition zone of zero rotation values is observed between the two parts, enclosing probably a tectonic structure, separating the counter-clockwise and clockwise rotation blocks.
One of the most tectonically active rifts worldwide is the WNW-ESE trending Corinth Gulf in Greec... more One of the most tectonically active rifts worldwide is the WNW-ESE trending Corinth Gulf in Greece, exhibiting extension range of 7-16 mm/yr. Numerous E-W to NW-SE active fault zones are recorded, while several active fault segments appear onshore. The active fault zones of the southern part of Corinth Gulf are generally dipping to the north, while the corresponding ones of the northern part are dipping to the south, confirming the active rift character of Corinth Gulf. According to the Greek Database of Seismogenic Sources (GreDaSS), 15 different active individual seismogenic sources (fault zones) are determined in the Corinth Gulf region. Most of the seismically active faults within the rift, related to historical seismic events, are located along its southern margin. The Corinth Gulf rift is monitored by 14 GPS permanent stations, recording the margins movement. The processed raw data of every three stations are combined and a series of parameters is calculated based on the triangle formed by each three stations set. Totally 26 such triangles were examined. The estimated parameters are: maximum horizontal extension, total velocity, maximum shear strain, area strain and rotation. The aforementioned parameters are referred to the triangle centroid. The estimated maximum horizontal extension rates show N-S direction, more or less perpendicular to the fault's strike, being in good agreement with the fault zones. The highest values (341.47 nano-strains, 312.15 nano-strains, 247.17 nano-strains) are observed into the Corinth Gulf area, while the values decrease with the distance away from Corinth Gulf. Total velocity is the result of the combination of North and East velocity components, showing a NE-SW direction. The fact that the total velocities have been estimated with respect to the Eurasia fixed reference frame (European Terrestrial Reference Frame 2000), confirm the aforementioned direction. The total velocity values range between 15.16 and 30.11 mm/yr, while the lowest are observed at the northeastern part and the highest at the southwestern part of the study area. Maximum shear strain constitutes an indicator of identifying active faults. The greatest values (402.60 nano-strains, 348.66 nano-strains, 326.46 nano-strains) are concentrated into the Corinth Gulf, as in the case of maximum horizontal extension. Area strain represents the surface deformation (dilatation and contraction), indicating normal faulting or thrusting. A great percentage of the centroids (approximately 85%) show positive values, while the negative values are observed in areas, mainly at the southeastern part of Corinth Gulf. Interpretation of their origin is problematic, however it is probable that they are local phenomena, caused by micro-movements and/or measurement errors. The positive area strain values range between 10.65 and 334.29 nano-strains and the negative between-3.02 and-137.73 nano-strains, respectively. Regarding the rotation of the examined area, an overarching clockwise rotation is presented, while a small percentage (approximately 15%) of the examined centroids shows counterclockwise rotation. Rotation values were modeled in order to be examined the rotation rates in-1,-5 and-10 Myr and to be estimated the rotation rates for the next 1, 5 and 10 Myr.
Περίληψη Η περιοχή που μελετήθηκε στην παρούσα εργασία, ήταν πρωτίστως η ρηξιγενής ζώνη του Αρακα... more Περίληψη Η περιοχή που μελετήθηκε στην παρούσα εργασία, ήταν πρωτίστως η ρηξιγενής ζώνη του Αρακαπά και έπειτα ως δευτερεύουσα η ρηξιγενής ζώνη της Γεράσας, οι οποίες βρίσκονται στην Νοτιοδυτική Κύπρο και αναπτύσσονται στην οφιολιθική σειρά του Τροόδους. Η οφιολιθική σειρά του Τροόδους, ηλικίας, Ανώτερο Κρητιδικό (Καμπάνιο), αναπτύχθηκε σε μία ωκεάνια λεκάνη, που αποτελούσε υπο-τμήμα της Νεοτηθύος. Κατά το τέλος του Ανώτερου Κρητιδικού (Μαιστρίχτιο), τα παλαιότερα πετρώματα, του Συ-μπλέγματος των Μαμωνιών, προσκολλούνται στην οφιολιθική σειρά και στοιχίζονται δίπλα-δίπλα με αυ-τήν, κατά μήκος ρηγμάτων μετασχηματισμού ή οριζόντιας μετατόπισης. Η εξελικτική πορεία του νησιού συνεχίζεται και στο Ανώτερο Ολιγόκαινο – Κατώτερο Μειόκαινο, κατά τη διάρκεια του οποίου ξεκινάει και η ανύψωση του νησιού. Στο τέλος του Μειόκαινου, τοποθετείται και η Ακολουθία της Κερύνειας πάνω στην οφιολιθική σειρά του Τροόδους. Κατά την περίοδο Μειόκαινου – Πλειόκαινου, η ιζηματογέ-νεση ήταν ακόμη σε εξέλιξη και τέλος, στο Πλειστόκαινο το νησί της Κύπρου, δέχεται την κύρια ανύψωση του (Σχήμα 1). Η ρηξιγενής ζώνη του Αρακαπά, όπως καλείται σήμερα, χαρακτηρίζεται ως ένα «απολιθωμένο» ρήγμα μετασχηματισμού και δημιουργήθηκε αρχικά, ταυτόχρονα με την οφιολιθική σειρά του Τροόδους. Το «απολιθωμένο» ρήγμα μετασχηματισμού του Αρακαπά, αναπτύχθηκε με παράταξη ανατολής-δύσης, διαχωρίζοντας το σχηματισμό του Δάσους της Λεμεσού, από την υπόλοιπη οφιολιθική σειρά του Τροό-δους. Κάπως έτσι, το Δάσος της Λεμεσού, οριοθετείται στο βορειότερο τμήμα του από τη ρηξιγενής ζώνη του Αρακαπά και στο νοτιοδυτικό τμήμα του από τη ρηξιγενή ζώνη της Γεράσας (τυπικό δεξιόστροφο ρήγμα οριζόντιας μετατόπισης, με ανάπτυξη παράταξης ΒΔ – ΝΑ). Η ρηξιγενής ζώνη του Αρακαπά, κατά την περίοδο του Τριτογενούς, δέχθηκε μία «τεκτονική ανανέωση» και άρχισε να επιδράει στην ευρύτερη περιοχή του Δάσους της Λεμεσού, ως ένα πραγματικό αριστερόστροφο ρήγμα οριζόντιας μετατόπισης. Στη νεότερη τεκτονική της περιοχής, αναγνωρίστηκαν δύο τεκτονικά γεγονότα. Κατά το τεκτονικό γεγο-νός D1, Μειοκαινικής – Πλειοκαινικής ηλικίας (Νεογενές), οι δύο αυτές ρηξιγενείς ζώνες του Αρακαπά και της Γεράσας λειτούργησαν ταυτόχρονα, ως δύο ρήγματα οριζόντιας μετατόπισης, δίνοντας ώθηση στην ευρύτερη περιοχή του Δάσους της Λεμεσού, να διαφύγει πλευρικά προς τα ΝΑ (Σχήμα 2 / Σχήμα 4). Στη συνέχεια, κατά το Πλειστόκαινο (Τεταρτογενές), η περιοχή επηρεάστηκε από έκταση, αναπτυσσό-μενη κατά μήκος του άξονα Β-Ν και αναγνωρίστηκε, ως το πρόσφατο τεκτονικό γεγονός D2, το οποίο λειτουργεί στην περιοχή μέχρι και σήμερα (Ολόκαινο). Το συγκεκριμένο τεκτονικό γεγονός, καθίσταται, ως η σημερινή ενεργός τεκτονική (Σχήμα 3 / Σχήμα 4). Άρα, στα τεκτονικά γεγονότα D1 και D2, τα καθε-στώτα τάσης που υφίστανται, όπως παρουσιάζεται και στο Σχήμα 2 και 3, είναι καθεστώς οριζόντιας μετατόπισης και έκτασης, αντίστοιχα. * Βαρνάβας Α. και συν: Τεκτονική ανάλυση της ευρύτερης περιοχής των ρηγμάτων της Γεράσας και του Αρακαπά στη νοτιοδυτική Κύπρο
On June 12th, 2017, a strong seismic event occurred offshore the southeastern shores of Lesvos Is... more On June 12th, 2017, a strong seismic event occurred offshore the southeastern shores of Lesvos Island in eastern Aegean region, Greece, causing extensive damage to infrastructure, injuries and one fatality. The mainshock had a magnitude of Mw = 6.3, while the aftershock sequence includes events of significant magnitude (Mw = 5.2, Mw = 4.7 and Mw = 4.9). Based on the aftershock sequence spatial distribution, bathymetric data and the tectonic regime of the area, the seismogenic fault was modeled and it is a NW-SE normal fault with a very small left-lateral component. The tips of the modeled fault are 26˚18'40.7843"E/38˚56'40.7626"N and 26˚30'41.4278"E/38˚52'51.4243"N, while the calculated length and width of the fault are 18.74 km and 14.36 km respectively. Furthermore, the modeled fault strikes at N112E, while it dips towards the SW by 50 • and its rake plunge is-91 •. Based on the aforementioned modeled fault characteristics, the stress transfer during the main shock was estimated for three different fault depths. Specifically, shear, normal and Coulomb stress changes were determined for the top (0.0 km depth), the middle (5.5 km depth) and the bottom (11.0 km depth) of the seismogenic fault. The analysis of shear stress change shows that stress transfer from the northwestern to the southeastern part of the study area occurs mainly between 0.0 and 5.5 km depth, while in deeper parts of the fault the shear stress is gradually eliminated from 5 to-5 bar. Regarding the normal stress, the three depth models show concentration of the highest values, approximately 5 bar, near the surface, abrupt decrease and almost zero values in 5.5 km depth and gradual increase, approximately 4 bar, up to the 11.0 km depth. The Coulomb stress change analysis shows a NW to SE stress transfer (as in shear stress change), receiving the greatest values, approximately 5 bar, at 5.5 km depth. A gradual decrease of values is recorded, associated with the depth increase, while remarkable values, between 2 and 4 bar, are detected in 11.0 km depth (as in normal stress change). In order for the surface deformation to be assessed, the Okada deformation model was implemented. The results show the highest horizontal displacements, ranging between 24 and 42 mm, near the projected fault surface and gradual decrease further away. The horizontal displacement is larger towards the fault's northern part. On a limited scale, a south to southeastern horizontal displacement is observed, associated to a probable fault segment, secondary to the main fault.GPS recordings of nearby permanent stations were also analyzed, and the results show significant similarities with the modeled ones. A typical example is the MYTI station, being the closest to the epicenter one, where the instrumentally recorded displacements show values of 0.018 m Easting, 0.031 m Northing and 0.01 m Upwarding, while the modeled values are 0.016545 m, 0.046635 m and 0.004653 m, respectively. This generally good agreement between modeled and observed surface deformation confirms the modeled geometric characteristics of the seismogenic fault.
The 2014 seismic sequence in Cephalonia and the following 2015 earthquake in Lefkada Islands, Gre... more The 2014 seismic sequence in Cephalonia and the following 2015 earthquake in Lefkada Islands, Greece, showed that the Cephalonia Transfer Fault Zone (CTFZ), which runs along the western coasts of both islands, comprises a wide fault zone of parallel to sub-parallel fault segments. The January-February 2014 sequence of Cephalonia consisted of three moderate to strong events. According to published focal mechanisms, the first strongest shock (January 26, Mw 6.1) was produced by a W-dipping, oblique (right-lateral reverse) fault, the second (January 26, Mw 5.3) by a ENE-dipping, pure reverse fault and the third by a ESE-dipping, almost pure right-lateral strike slip fault. The November 17 2015 (Mw 6.4) Lefkada earthquake was produced by a WNW-dipping, roughly vertical, almost pure right-lateral strike-slip fault. None of the shocks above produced any direct coseismic ground rupture, while published relocated hypocentral locations for the Cephalonia sequence revealed various depths indi...
Acta Geophysica, 2021
Following the M7.0 earthquake that struck the Greek island of Samos and Turkey's western coast, c... more Following the M7.0 earthquake that struck the Greek island of Samos and Turkey's western coast, causing extensive damage and casualties, we combined existing knowledge geodatabases concerning historical seismicity and rupture zones with seismological and geodetic measurements as well as with modelling and in situ observations, to provide an assessment of rapid response to the seismic event. In this paper, we demonstrate that in the frame of the gradual provision of information from the individual scientific disciplines, taking into account their respective potential and limitations, a multidisciplinary approach is able to address more efficiently rapid response issues in order to allow effective preliminary interpretation of the earthquake activity, even within the first 24 h of the event. It focuses on the assessment of the timely provision of information by each discipline, evaluating the access to primary data sources as well as the maturity of the techniques in terms of accuracy and rapid data processing. Within a period of less than a week, several constraints were partially compensated for, allowing the delivery of more robust results and interpretation. The study highlights the readiness level of the various domains that has been significantly improved over the past years, including rapid seismological solutions, systematic availability of free and open Earth Observation data and on-demand online processing through dedicated platforms. Their combination with routinely applied inversion modelling and timely in situ observation is leading to improved operational response levels.
Acta Geophysica, 2020
It was one of the strongest in the broader area during the last many decades causing two deaths, ... more It was one of the strongest in the broader area during the last many decades causing two deaths, many injuries and extensive damages. We investigated the evolution of the seismic sequence using seismological and geological tools. The aftershock sequence was relocated mainly in order to define the geometry of the main seismic source, depicting a NNW-dipping fault plane. It also revealed significant clustering, associated with other nearby faults, and asymmetric spatio-temporal evolution. Along with morphotectonic analysis on Kos Island, and other published seismological information (e.g. focal mechanisms), we modelled the seismic source of the mainshock, as well as the one of the strongest aftershocks (August 8, M W 5.3). We applied the Coulomb failure criterion in order to investigate the effect of the mainshock on the strongest aftershock, and the rest of the sequence as well. Using the same method, we also investigated the stress changes of both strongest shocks for the prevailing E-W-trending normal faults in this area. Among other conclusions and implications, we deduce that the prevailing tectonic setting of the Gökova Gulf consists of roughly E-W-striking normal faults forming inner horsts and grabens.
Applied Geomatics, 2020
Numerous active fault zones are observed throughout the central and northern part of Greece, whil... more Numerous active fault zones are observed throughout the central and northern part of Greece, while in some cases they are related to destructive earthquakes. The geometric characteristics of these fault zones vary, revealing both extensional and compressional tectonics of these structures. The use of geodetic data, received by permanently installed GPS stations, is a precise way of analyzing the tectonic regime. In particular, 58 permanent GPS stations are included in the study area, having collected primary data for a 7-year period. The calculated East and North velocity components and their errors, respectively, derived from each GPS station, were processed applying a triangulation methodology, based on the triangle construction, combining three different GPS stations each time. The use of dense GPS stations distribution resulted in the extraction of 1,092 different triangles and then, the centroid of each triangle was determined. For each centroid the following parameters were estimated: 1) maximum horizontal extension, 2) total velocity, 3) maximum shear strain, 4) area strain and 5) rotation. The extracted values were interpolated into a grid pattern, showing low to medium values, especially north of the inferred extension of the North Aegean Fault System, the same parameter values are high for the southern part of Greece, confirming the geological and seismological data suggesting that Central-Northern Greece is generally less active than Southern Greece. However, it is noted that the length of the neotectonic faults in the area are capable of producing significant earthquakes, albeit in longer recurrence intervals.
Bulletin of the Geological Society of Greece, 2017
Ground and spring waters, soils and sediments of Anthemountas basin in Northern G reece were anal... more Ground and spring waters, soils and sediments of Anthemountas basin in Northern G reece were analyzed for Potential Toxic Elements (PTEs). In total, twenty three soil and sediment samples, three groundwater (boreholes) and two spring water samples, were analyzed. Contents of Ni in soils and sediments can be as high as 2169 mg/kg. The high correlation coefficient of Ni and Cr, indicates the geogenic origin of Ni, which originates from ophiolitic rocks. Arsenic concentration ranges from 3 to 110 mg/kg in soils and sediments, with the highest contents observed in travertine. The spring waters are characterized by elevated concentrations of As (up to 235 μg/L), N a, K, Fe and Zn, indicating that hydrothermal fluids are responsible for feldspar alte ration of the Monopigado granodiorite. On the contrary, in groundwaters, As conten ts are low (up to 18 μg/L). Electrical resistivity tomographies performed around the groundwater boreholes, revealed the presence of normal faults, locally all...
Geological Society, London, Special Publications, 2016
The total throw across a fault zone may not occur entirely on a single fault strand but may be di... more The total throw across a fault zone may not occur entirely on a single fault strand but may be distributed onto several strands or may be accommodated by distributed deformation within or adjacent to the fault zone. Here we conduct a quantitative analysis of the partitioning of throw into three components, the throw accommodated by: (a) the largest fault strand; (b) subsidiary faults; and (c) continuous deformation in the form of bed rotation in sympathy with the fault downthrow direction. This analysis is applied to seven seismic-scale fault zones at outcrop resolution (maximum throw 50 m) that were mapped over a four-year period during open-cast lignite mining within the late Miocene–Pliocene Ptolemais Basin, West Macedonia, Greece. The analysis shows that the fault zones offsetting the lignite–marl sequence are more localized at higher throws with progressively more of the total throw accommodated by the largest fault strand. Normal drag, which can account for up to 12 m of the t...
Bulletin of Earthquake Engineering, 2016
We combine probabilistic and deterministic approaches in an attempt to tackle a challenging topic... more We combine probabilistic and deterministic approaches in an attempt to tackle a challenging topic in engineering seismology, that of the prediction of strong ground motion in urban areas located close to active faults, with sparse modern seismicity. The case we study is the city of Xanthi in northern Greece and we generate bedrock synthetic time series to be used as input motions into site-specific site effect analysis. We reassess the seismic hazard using the probabilistic method and then perform hazard deaggregation in order to define realistic earthquake scenarios, which we examine in a deterministic way. The scenarios examined are: (a) a reference earthquake of M6.7, return period 100 years and at *30 km distance from the city and (b) a reference earthquake of M5.8, return period 475 years and at *3 km distance from the city of Xanthi. To compute synthetic time series for the distant source, we apply the stochastic method for finite faults. For the near-fault earthquake scenario we adopt a hybrid deterministic-stochastic approach that includes the semi-analytical method implemented in the COMPSYN code for the low frequency (*\3 Hz) part of the spectrum and the stochastic method for the high-frequency (*[3 Hz). The results of the probabilistic and the deterministic approaches converge to a satisfactory degree.
Uploads
Papers by Alexandros Chatzipetros
The area of interest is monitored by a network of 20 different permanently installed GPS stations. The processing of the primary geodetic data is based on the triangulation of the GPS stations. In particular, the total of 20 different GPS stations were combined each other, forming different sets of three stations. Each set leads to a triangle formation, while each station is located on a triangle vertex. The recorded geodetic data of a GPS station is combined with the other two stations geodetic data, calculating the maximum horizontal extension and rotation of the triangle centroid, representing the triangle. Based on the aforementioned procedure, 399 different triangles were constructed within the study area, providing 399 different maximum horizontal extension and rotation values.
Based on the extracted maximum horizontal extension values, the interpolation method was applied, leading to the construction of a map, including 50 nano-strain step contours, while the maximum and minimum values are 543.5029 and 2.1114 nano-strains, respectively. The exact ore mineralization locations were highlighted onto the aforementioned map in order to be examined their relationship to the maximum extension values. The extracted results show that the majority of ore mineralization locations are included into the medium to maximum horizontal extension areas. This proves the fact that several tectonic structures related to the ore mineralization formation are relatively active or not active in the present. Especially, at the southern part of the study area, ore mineralization localities exhibit remarkably higher maximum horizontal extension values, as a result of active since Oligocene fault zones of Stratoni-Varvara, Megali Panaghia-Gomati, Sochos and Mygdonia. Finally, the presented GPS rotational data are in agreement with the published palaeomagnetic data for the study area. In particular, counter-clockwise and clockwise rotations appear at the northern and the southern part respectively. Α transition zone of zero rotation values is observed between the two parts, enclosing probably a tectonic structure, separating the counter-clockwise and clockwise rotation blocks.