Scenes of the legendary battle between Poseidon and the giant Polybotes, which occurred on the Greek island of Kos, are depicted on dozens of surviving ceramic objects. Poseidon is shown killing his opponent with his trident, while carrying a huge rock that he had ripped off the island of Kos to bury Polybotes. The legend is interpreted to represent a strong earthquake that caused a large coastal rock fall or rock avalanche. The oldest ceramics representing this disaster date from ca. 540 BCE. The disaster is interpreted to date from this time and was a major event that reverberated throughout the Greek world, triggering the imagination of its artists for several generations. Legend and ancient literary sources suggest that the event took place in southeastern Kos, near the then capital city of Astypalaia, located NW of Zini mountain. Geological studies show a large, relatively recent, rock avalanche on the steep coast on the SE side of Zini mountain. Possible tsunami sand deposits with reworked marsh foraminifera are found 7 m above sea level on NE Zini, only 1 km from the archeological site of the old city of Astypalaia and large boulders are stranded on the opposite rocky coastline up to 6 m above sea level. Noise and dust from a rock avalanche would have been terrifying for the inhabitants of Astypalaia and any tsunami would have overwashed the port at Kamari. In the absence of suitable geological dating methods, ceramics provide the best chronology for the event.
{"title":"THE MYTH OF THE BATTLE BETWEEN POSEIDON AND POLYBOTES: WAS THE INSPIRATION FROM A LATE HOLOCENE ROCK AVALANCHE AT ZINI, KOS ISLAND?","authors":"J. D. de Boer, G. Pe‐Piper, D. Piper","doi":"10.12681/bgsg.28851","DOIUrl":"https://doi.org/10.12681/bgsg.28851","url":null,"abstract":"Scenes of the legendary battle between Poseidon and the giant Polybotes, which occurred on the Greek island of Kos, are depicted on dozens of surviving ceramic objects. Poseidon is shown killing his opponent with his trident, while carrying a huge rock that he had ripped off the island of Kos to bury Polybotes. The legend is interpreted to represent a strong earthquake that caused a large coastal rock fall or rock avalanche. The oldest ceramics representing this disaster date from ca. 540 BCE. The disaster is interpreted to date from this time and was a major event that reverberated throughout the Greek world, triggering the imagination of its artists for several generations. Legend and ancient literary sources suggest that the event took place in southeastern Kos, near the then capital city of Astypalaia, located NW of Zini mountain. Geological studies show a large, relatively recent, rock avalanche on the steep coast on the SE side of Zini mountain. Possible tsunami sand deposits with reworked marsh foraminifera are found 7 m above sea level on NE Zini, only 1 km from the archeological site of the old city of Astypalaia and large boulders are stranded on the opposite rocky coastline up to 6 m above sea level. Noise and dust from a rock avalanche would have been terrifying for the inhabitants of Astypalaia and any tsunami would have overwashed the port at Kamari. In the absence of suitable geological dating methods, ceramics provide the best chronology for the event.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"29 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2022-03-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83645634","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The current investigation concerns the impact observed at natural and human environment, due to the implementation of the Aposelemis water supply project, as additional aqueduct of Heraklion and Agios Nikolaos cities, as well as other important tourist areas, in NE Crete, Greece. Aposelemis project is differentiated from standard water supply dam projects, through a special component of an underground tunnel that diverts uphill surface water from Lasithi Plateau into the reservoir. The study concerns the first years of project’s operation, and focuses at four affected areas, namely the Lasithi Plateau upland area, dam’s region, river estuary and water supplied cities. The investigation was based on various site visits, while a significant aspect involves local stakeholders’ observation, opinion and perception on the environmental impact of the project in everyday life, through four detailed questionnaires posed to the affected areas’ population. The recorded consequences were characterized as positive or negative and evaluated according to their size and importance, estimated for the current period and also for the future. Among the main positive effects are urban areas’ drinking water supply and improved upland plateau’s flood water drainage, while among the negative consequences appear multiple water resources’ impacts and feelings of downstream lakeside residents. The investigation indicates the initial environmental impact and sets the basis for further future research towards sustainability.
{"title":"Environmental impact of Aposelemis dam and tunnel water supply project in NE Crete, Greece","authors":"C. Vogiatzi, C. Loupasakis","doi":"10.12681/bgsg.27329","DOIUrl":"https://doi.org/10.12681/bgsg.27329","url":null,"abstract":"The current investigation concerns the impact observed at natural and human environment, due to the implementation of the Aposelemis water supply project, as additional aqueduct of Heraklion and Agios Nikolaos cities, as well as other important tourist areas, in NE Crete, Greece. Aposelemis project is differentiated from standard water supply dam projects, through a special component of an underground tunnel that diverts uphill surface water from Lasithi Plateau into the reservoir. The study concerns the first years of project’s operation, and focuses at four affected areas, namely the Lasithi Plateau upland area, dam’s region, river estuary and water supplied cities. The investigation was based on various site visits, while a significant aspect involves local stakeholders’ observation, opinion and perception on the environmental impact of the project in everyday life, through four detailed questionnaires posed to the affected areas’ population. The recorded consequences were characterized as positive or negative and evaluated according to their size and importance, estimated for the current period and also for the future. Among the main positive effects are urban areas’ drinking water supply and improved upland plateau’s flood water drainage, while among the negative consequences appear multiple water resources’ impacts and feelings of downstream lakeside residents. The investigation indicates the initial environmental impact and sets the basis for further future research towards sustainability.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"70 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-11-22","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76032511","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Chatzipetros, S. Pavlides, M. Foumelis, S. Sboras, D. Galanakis, C. Pikridas, S. Bitharis, E. Kremastas, Athanasios Chatziioannou, I. Papaioannou
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.
{"title":"The northern Thessaly strong earthquakes of March 3 and 4, 2021, and their neotectonic setting","authors":"A. Chatzipetros, S. Pavlides, M. Foumelis, S. Sboras, D. Galanakis, C. Pikridas, S. Bitharis, E. Kremastas, Athanasios Chatziioannou, I. Papaioannou","doi":"10.12681/bgsg.27225","DOIUrl":"https://doi.org/10.12681/bgsg.27225","url":null,"abstract":"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.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"122 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-10-26","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76608263","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
D. Galanakis, S. Sboras, G. Konstantopoulou, M. Xenakis
On March 3, 2021, a strong (Mw6.3) earthquake occurred near the towns of Tyrnavos and Elassona. One day later (March 4), a second strong (Mw6.0) earthquake occurred just a few kilometres toward the WNW. The aftershock spatial distribution and the focal mechanisms revealed NW-SE-striking normal faulting. The focal mechanisms also revealed a NE-SW oriented extensional stress field, different from the orientation we knew so far (ca. N-S). The magnitude and location of the two strongest shocks, and the spatiotemporal evolution of the sequence, strongly suggest that two adjacent fault segments were ruptured respectively. The sequence was followed by several coseismic ground deformational phenomena, such as landslides/rockfalls, liquefaction and ruptures. The landslides and rockfalls were mostly associated with the ground shaking. The ruptures were observed west of the Titarissios River, near to the Quaternary faults found by bore-hole lignite investigation. In the same direction, a fault scarp separating the alpidic basement from the alluvial deposits of the Titarissios valley implies the occurrence of a well-developed fault system. Some of the ground ruptures were accompanied by extensive liquefaction phenomena. Others cross-cut reinforced concrete irrigation channels without changing their direction. We suggest that this fault system was partially reactivated, as a secondary surface rupture, during the sequence as a steeper splay of a deeper low-to-moderate angle normal fault.
{"title":"Neogene-Quaternary tectonic regime and macroseismic observations in the Tyrnavos-Elassona broader epicentral area of the March 2021, intense earthquake sequence","authors":"D. Galanakis, S. Sboras, G. Konstantopoulou, M. Xenakis","doi":"10.12681/bgsg.27196","DOIUrl":"https://doi.org/10.12681/bgsg.27196","url":null,"abstract":"On March 3, 2021, a strong (Mw6.3) earthquake occurred near the towns of Tyrnavos and Elassona. One day later (March 4), a second strong (Mw6.0) earthquake occurred just a few kilometres toward the WNW. The aftershock spatial distribution and the focal mechanisms revealed NW-SE-striking normal faulting. The focal mechanisms also revealed a NE-SW oriented extensional stress field, different from the orientation we knew so far (ca. N-S). The magnitude and location of the two strongest shocks, and the spatiotemporal evolution of the sequence, strongly suggest that two adjacent fault segments were ruptured respectively. The sequence was followed by several coseismic ground deformational phenomena, such as landslides/rockfalls, liquefaction and ruptures. The landslides and rockfalls were mostly associated with the ground shaking. The ruptures were observed west of the Titarissios River, near to the Quaternary faults found by bore-hole lignite investigation. In the same direction, a fault scarp separating the alpidic basement from the alluvial deposits of the Titarissios valley implies the occurrence of a well-developed fault system. Some of the ground ruptures were accompanied by extensive liquefaction phenomena. Others cross-cut reinforced concrete irrigation channels without changing their direction. We suggest that this fault system was partially reactivated, as a secondary surface rupture, during the sequence as a steeper splay of a deeper low-to-moderate angle normal fault.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"82184087","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The main goal of an Earthquake Early Warning System (EEWS) is to estimate the expected peak ground motion of the destructive S-waves using the first few seconds of P-waves, thus becoming an operational tool for real-time seismic risk management in a short timescale. EEWSs are based on the use of scaling relations between parameters measured on the initial portion of the seismic signal, after the arrival of the first wave. Herein, using the abundant seismicity that followed the 3 March 2021 Mw=6.3 earthquake in Thessaly we propose scaling relations for PGA, from data recorded by local permanent stations, as a function of the integral of the squared velocity (IV2p). The IV2p parameter was estimated directly from the first few seconds-long signal window (tw) after the P-wave arrival. Scaling laws are extrapolated for both individual and across sites (i.e., between a near-source reference instrument and a station located close to a target). The latter approach is newly investigated, as local site effects could have a significant impact on recorded data. Considering that further study on the behavior of IV2p is necessary, there are indications that this parameter could be used in future on-site single‐station earthquake early warning operations for areas affected by earthquakes located in Thessaly, as itpresents significant stability.
{"title":"The scaling of PGA with IV2p and its potential for Earthquake Early Warning in Thessaly (Central Greece)","authors":"I. Spingos, F. Vallianatos, G. Kaviris","doi":"10.12681/bgsg.27062","DOIUrl":"https://doi.org/10.12681/bgsg.27062","url":null,"abstract":"The main goal of an Earthquake Early Warning System (EEWS) is to estimate the expected peak ground motion of the destructive S-waves using the first few seconds of P-waves, thus becoming an operational tool for real-time seismic risk management in a short timescale. EEWSs are based on the use of scaling relations between parameters measured on the initial portion of the seismic signal, after the arrival of the first wave. Herein, using the abundant seismicity that followed the 3 March 2021 Mw=6.3 earthquake in Thessaly we propose scaling relations for PGA, from data recorded by local permanent stations, as a function of the integral of the squared velocity (IV2p). The IV2p parameter was estimated directly from the first few seconds-long signal window (tw) after the P-wave arrival. Scaling laws are extrapolated for both individual and across sites (i.e., between a near-source reference instrument and a station located close to a target). The latter approach is newly investigated, as local site effects could have a significant impact on recorded data. Considering that further study on the behavior of IV2p is necessary, there are indications that this parameter could be used in future on-site single‐station earthquake early warning operations for areas affected by earthquakes located in Thessaly, as itpresents significant stability.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"20 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-09-13","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72878941","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A widely felt strong shallow earthquake with Mw 6.3 magnitude occurred in Thessaly (Central Greece) on March 3, 2021. This recent strong event attracted our interest to apply and evaluate the capabilities of the Accelerating Deformation method. Based on the recently proposed generalized Benioff strain idea which could be justified by the terms of Non-Extensive Statistical Physics (NESP), the common critical exponent was calculated in order to define the critical stage before a strong event. The present analysis comprised a complex spatiotemporal iterative procedure to examine the possible seismicity patterns at a broad region and identify the best one associated with the preparation process before the strong event. The starting time of the accelerating period, the size and location of the critical area are unknown parameters to be determined. Furthermore, although, the time of failure is already known, in the present research it was not set as a fixed value in the algorithm to define the other unknown parameters but instead different catalogue ending dates have been tried out to be with an objective way. The broad region to be investigated was divided with a square mesh and the search of events around a point has been carried on with different size circular and elliptical shapes. Among the obtained results, the solution which exhibits the most dominant scaling law behavior as well as the one which exhibits the smallest spatial area and yet the more dominant scaling law behavior are presented.
{"title":"Accelerating deformation seismicity patterns before the March 3, 2021 Thessaly strong earthquake. First results","authors":"Georgios Chatzopoulos","doi":"10.12681/bgsg.27155","DOIUrl":"https://doi.org/10.12681/bgsg.27155","url":null,"abstract":"A widely felt strong shallow earthquake with Mw 6.3 magnitude occurred in Thessaly (Central Greece) on March 3, 2021. This recent strong event attracted our interest to apply and evaluate the capabilities of the Accelerating Deformation method. Based on the recently proposed generalized Benioff strain idea which could be justified by the terms of Non-Extensive Statistical Physics (NESP), the common critical exponent was calculated in order to define the critical stage before a strong event. The present analysis comprised a complex spatiotemporal iterative procedure to examine the possible seismicity patterns at a broad region and identify the best one associated with the preparation process before the strong event. The starting time of the accelerating period, the size and location of the critical area are unknown parameters to be determined. Furthermore, although, the time of failure is already known, in the present research it was not set as a fixed value in the algorithm to define the other unknown parameters but instead different catalogue ending dates have been tried out to be with an objective way. The broad region to be investigated was divided with a square mesh and the search of events around a point has been carried on with different size circular and elliptical shapes. Among the obtained results, the solution which exhibits the most dominant scaling law behavior as well as the one which exhibits the smallest spatial area and yet the more dominant scaling law behavior are presented.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"14 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-29","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78436535","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
A. Ganas, S. Valkaniotis, P. Briole, A. Serpetsidaki, V. Kapetanidis, Ilektra Karasante, I. Kassaras, G. Papathanassiou, I. Karamitros, V. Tsironi, P. Elias, V. Sarhosis, A. Karakonstantis, Emmanouela Konstantakopoulou, P. Papadimitriou, E. Sokos
Here we present a joint analysis of the geodetic, seismological and geological data of the March 2021 Northern Thessaly seismic sequence, that were gathered and processed as of April 30, 2021. First, we relocated seismicity data from regional and local networks and inferred the dip-direction (NE) and dip-angle (38°) of the March 3, 2021 rupture plane. Furthermore, we used ascending and descending SAR images acquired by the Sentinel-1 satellites to map the co-seismic displacement field. Our results indicate that the March 3, 2021 Mw=6.3 rupture occurred on a NE-dipping, 39° normal fault located between the villages Zarko (Trikala) and Damasi (Larissa). The event of March 4, 2021 occurred northwest of Damasi, along a fault oriented WNW-ESE and produced less deformation than the event of the previous day. The third event occurred on March 12, 2021 along a south-dipping normal fault. We computed 22 focal mechanisms of aftershocks with M≥4.0 using P-wave first motion polarities. Nearly all focal mechanisms exhibit normal kinematics or have a dominant normal dip-slip component. The use of InSAR was crucial to differentiate the ground deformation between the ruptures. The majority of deformation occurs in the vertical component, with a maximum of 0.39 m of subsidence over the Mw=6.3 rupture plane, south and west of Damasi. A total amount of 0.3 m horizontal displacement (E-W) was measured. We also used GNSS data (at 30-s sampling interval) from twelve permanent stations near the epicentres to obtain 3D seismic offsets of station positions. Only the first event produces significant displacement at the GNSS stations (as predicted by the fault models, themselves very well constrained by InSAR). We calculated several post-seismic interferograms, yet we have observed that there is almost no post-seismic deformation, except in the footwall area (Zarkos mountain). This post-seismic deformation is below the 7 mm level (quarter of a fringe) in the near field and below the 1 mm level at the GNSS sites. The cascading activation of the three events in a SE to NW direction points to a pattern of domino-style earthquakes, along neighbouring fault segments. The kinematics of the ruptures point to a counter-clockwise change in the extension direction of the upper crust (from NE-SW near Damasi to N-S towards northwest, near Verdikoussa).
本文对截至2021年4月30日收集和处理的2021年3月北色萨利地震序列的大地测量、地震和地质数据进行了联合分析。首先，我们重新定位了区域和本地网络的地震活动数据，并推断了2021年3月3日破裂面的倾角(NE)和倾角(38°)。此外，我们利用Sentinel-1卫星获取的上升和下降SAR图像来绘制同震位移场。我们的研究结果表明，2021年3月3日发生的Mw=6.3破裂发生在位于Zarko (Trikala)和Damasi (Larissa)村之间的ne向39°正断层上。2021年3月4日的地震发生在大马西北方，沿西北纬向断层，造成的变形小于前一天的地震。第三次地震发生在2021年3月12日，沿着一条向南倾斜的正断层。利用p波第一运动极性计算了22个M≥4.0级余震震源机制。几乎所有的震源机构都表现出正常的运动学或具有主要的正常倾滑分量。InSAR的使用对于区分破裂之间的地面变形至关重要。大部分变形发生在垂直分量上，在达马西以南和以西的Mw=6.3破裂面上最大沉降量为0.39 m。测量总水平位移0.3 m (E-W)。我们还使用了位于震中附近的12个永久站点的GNSS数据(采样间隔为30秒)来获得站点位置的三维地震偏移。只有第一个事件在GNSS站产生显著的位移(正如断层模型所预测的那样，断层模型本身受到InSAR的很好约束)。我们计算了几个震后干涉图，但我们观察到，除了下盘区域(Zarkos山)之外，几乎没有震后变形。这种震后形变在近场低于7毫米水平(四分之一条纹)，在GNSS站点低于1毫米水平。从东南到西北方向的三个事件的级联激活指向了一个多米诺骨牌式地震的模式，沿着邻近的断层段。断裂的运动学指向上地壳伸展方向的逆时针变化(从达马西附近的NE-SW到Verdikoussa附近的N-S向西北方向)。
{"title":"Domino-style earthquakes along blind normal faults in Northern Thessaly (Greece): kinematic evidence from field observations, seismology, SAR interferometry and GNSS","authors":"A. Ganas, S. Valkaniotis, P. Briole, A. Serpetsidaki, V. Kapetanidis, Ilektra Karasante, I. Kassaras, G. Papathanassiou, I. Karamitros, V. Tsironi, P. Elias, V. Sarhosis, A. Karakonstantis, Emmanouela Konstantakopoulou, P. Papadimitriou, E. Sokos","doi":"10.12681/BGSG.27102","DOIUrl":"https://doi.org/10.12681/BGSG.27102","url":null,"abstract":"Here we present a joint analysis of the geodetic, seismological and geological data of the March 2021 Northern Thessaly seismic sequence, that were gathered and processed as of April 30, 2021. First, we relocated seismicity data from regional and local networks and inferred the dip-direction (NE) and dip-angle (38°) of the March 3, 2021 rupture plane. Furthermore, we used ascending and descending SAR images acquired by the Sentinel-1 satellites to map the co-seismic displacement field. Our results indicate that the March 3, 2021 Mw=6.3 rupture occurred on a NE-dipping, 39° normal fault located between the villages Zarko (Trikala) and Damasi (Larissa). The event of March 4, 2021 occurred northwest of Damasi, along a fault oriented WNW-ESE and produced less deformation than the event of the previous day. The third event occurred on March 12, 2021 along a south-dipping normal fault. We computed 22 focal mechanisms of aftershocks with M≥4.0 using P-wave first motion polarities. Nearly all focal mechanisms exhibit normal kinematics or have a dominant normal dip-slip component. The use of InSAR was crucial to differentiate the ground deformation between the ruptures. The majority of deformation occurs in the vertical component, with a maximum of 0.39 m of subsidence over the Mw=6.3 rupture plane, south and west of Damasi. A total amount of 0.3 m horizontal displacement (E-W) was measured. We also used GNSS data (at 30-s sampling interval) from twelve permanent stations near the epicentres to obtain 3D seismic offsets of station positions. Only the first event produces significant displacement at the GNSS stations (as predicted by the fault models, themselves very well constrained by InSAR). We calculated several post-seismic interferograms, yet we have observed that there is almost no post-seismic deformation, except in the footwall area (Zarkos mountain). This post-seismic deformation is below the 7 mm level (quarter of a fringe) in the near field and below the 1 mm level at the GNSS sites. The cascading activation of the three events in a SE to NW direction points to a pattern of domino-style earthquakes, along neighbouring fault segments. The kinematics of the ruptures point to a counter-clockwise change in the extension direction of the upper crust (from NE-SW near Damasi to N-S towards northwest, near Verdikoussa).","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"51 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"88852751","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
The development of hypergene Stefanina Cave, the hydrological conditions, and the maximum discharge of the paleo-flow are studied, based on its pattern in ground-plan, the geometry of the passage, and the peak flow velocity from the dimensions of the scallops. The village of Stefanina is located East of Thessaloniki and the cave NE of the village. A study was conducted measuring the orientation of the discontinuities of the rocks inside and outside the cave, the scallops in various sites to estimate the flow velocities, and in addition, were taken photographs for the full analysis of its cross-section. The cave-in ground-plan has a pattern of branches, which is often associated with recharging through karstic depressions. The shape of the passages is both curvilinear and angular, depending on the foliage and the fractures. The symmetrical phreatic passage shape has been evolved to a vadose canyon, forming a keyhole passage in cross-section. This is indicative of a water table drop. The scallops are visible in a meandering channel, where the discharge of the paleo-flow is estimated. The estimated peak flow velocity ranges from 0.4 to 2.7 m / s, while the area-specific peak flow discharge is estimated to be 2.2 m3/s. On the one hand, the scallops represent the peak flow velocity, on the other hand, the karst springs have a limited maximum discharge, regardless of the size of the catchment, making it impossible to use the calculated paleo-discharge to estimate the respective catchment area.
根据高近系Stefanina洞的平面格局、通道几何形状和扇贝尺寸的峰值流速，研究了高近系Stefanina洞的发育、水文条件和古水流的最大流量。Stefanina村位于塞萨洛尼基东部和村庄东北的洞穴。研究人员测量了洞穴内外岩石不连续的方向，在不同的地点测量了扇贝的流速，此外，还拍摄了照片，以便对其横截面进行全面分析。塌陷区平面图有分支的图案，这通常与通过岩溶洼地进行补给有关。通道的形状既有曲线又有棱角，这取决于树叶和裂缝。对称的潜水通道形态演化为水气峡谷，断面上形成锁眼通道。这是地下水位下降的迹象。扇贝在一条蜿蜒的河道中可见，在那里估计了古水流的流量。估算峰值流速为0.4 ~ 2.7 m /s，区域比峰值流量为2.2 m3/s。一方面，扇贝代表峰值流速，另一方面，无论集水区大小，岩溶泉的最大流量都是有限的，因此无法用计算的古流量来估计各自的集水区面积。
{"title":"Paleohydrology of the Stefanina Cave (Greece)","authors":"G. Lazaridis, Kyriaki Fellachidou, Maria Georgaki","doi":"10.12681/BGSG.26168","DOIUrl":"https://doi.org/10.12681/BGSG.26168","url":null,"abstract":"The development of hypergene Stefanina Cave, the hydrological conditions, and the maximum discharge of the paleo-flow are studied, based on its pattern in ground-plan, the geometry of the passage, and the peak flow velocity from the dimensions of the scallops. The village of Stefanina is located East of Thessaloniki and the cave NE of the village. A study was conducted measuring the orientation of the discontinuities of the rocks inside and outside the cave, the scallops in various sites to estimate the flow velocities, and in addition, were taken photographs for the full analysis of its cross-section. The cave-in ground-plan has a pattern of branches, which is often associated with recharging through karstic depressions. The shape of the passages is both curvilinear and angular, depending on the foliage and the fractures. The symmetrical phreatic passage shape has been evolved to a vadose canyon, forming a keyhole passage in cross-section. This is indicative of a water table drop. The scallops are visible in a meandering channel, where the discharge of the paleo-flow is estimated. The estimated peak flow velocity ranges from 0.4 to 2.7 m / s, while the area-specific peak flow discharge is estimated to be 2.2 m3/s. On the one hand, the scallops represent the peak flow velocity, on the other hand, the karst springs have a limited maximum discharge, regardless of the size of the catchment, making it impossible to use the calculated paleo-discharge to estimate the respective catchment area.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"1 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"83060206","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
S. Mavroulis, M. Mavrouli, P. Carydis, K. Agorastos, E. Lekkas
In early March 2021, when Greece was struggling with the evolving third wave of the COVID-19 pandemic with the highest numbers of daily cases and fatalities from its initiation, Thessaly was struck by a seismic sequence, which included the 3 March, Mw = 6.3 mainshock, its strongest Mw = 6.1 aftershock the following day and numerous large aftershocks. The mainshock caused extensive damage to houses and infrastructure, while the aftershock aggravated damage and caused widespread concern among residents. Based on post-event field surveys in the affected area, it is concluded that the old unreinforced houses with load-bearing masonry walls in the northeastern part of the Thessaly basin suffered the most, while the recent constructions remained intact. As a result, hundreds of homeless were in need of immediate temporary sheltering, which immediately mobilized the Civil Protection authorities to manage the emergency situation. This emergency had something unique, which made its management a challenge: the implementation of the earthquake emergency response actions was incompatible with the measures to limit the further spread of the SARS-CoV-2 virus in the community during the evolving third pandemic wave. Many of the actions have been adapted to the unprecedented conditions through a prism of a multi-hazard approach to disaster management and their impact. Among others, more and different types of emergency shelters were used to prevent overcrowding, emergency supplies distribution processes were modified to prevent transmission through hands and surfaces, places for the identification and isolation of suspected COVID-19 cases were designated in emergency shelters and extensive and regular screening testing of the local population was conducted for the detection of SARS-CoV-2 virus. From the analysis of the daily reported COVID-19 cases in the earthquake-affected area during the pre- and post- disaster periods as well as from results of rapid testing during the post-disaster period, it was found that the viral load of the earthquake-affected villages was not increased, despite the difficult and unprecedented conditions. It can be suggested that the adaptation of the measures to the new conditions has worked beneficially to reduce the spread of the new virus among those affected and the involved staff. For this reason, this approach could be considered as good practice and important lesson learned, which can be applied to similar future compound emergencies in areas with similar geoenvironmental and epidemiological characteristics.
{"title":"The March 2021 Thessaly earthquakes and their impact through the prism of a multi-hazard approach in disaster management","authors":"S. Mavroulis, M. Mavrouli, P. Carydis, K. Agorastos, E. Lekkas","doi":"10.12681/BGSG.26852","DOIUrl":"https://doi.org/10.12681/BGSG.26852","url":null,"abstract":"In early March 2021, when Greece was struggling with the evolving third wave of the COVID-19 pandemic with the highest numbers of daily cases and fatalities from its initiation, Thessaly was struck by a seismic sequence, which included the 3 March, Mw = 6.3 mainshock, its strongest Mw = 6.1 aftershock the following day and numerous large aftershocks. The mainshock caused extensive damage to houses and infrastructure, while the aftershock aggravated damage and caused widespread concern among residents. Based on post-event field surveys in the affected area, it is concluded that the old unreinforced houses with load-bearing masonry walls in the northeastern part of the Thessaly basin suffered the most, while the recent constructions remained intact. As a result, hundreds of homeless were in need of immediate temporary sheltering, which immediately mobilized the Civil Protection authorities to manage the emergency situation. This emergency had something unique, which made its management a challenge: the implementation of the earthquake emergency response actions was incompatible with the measures to limit the further spread of the SARS-CoV-2 virus in the community during the evolving third pandemic wave. Many of the actions have been adapted to the unprecedented conditions through a prism of a multi-hazard approach to disaster management and their impact. Among others, more and different types of emergency shelters were used to prevent overcrowding, emergency supplies distribution processes were modified to prevent transmission through hands and surfaces, places for the identification and isolation of suspected COVID-19 cases were designated in emergency shelters and extensive and regular screening testing of the local population was conducted for the detection of SARS-CoV-2 virus. From the analysis of the daily reported COVID-19 cases in the earthquake-affected area during the pre- and post- disaster periods as well as from results of rapid testing during the post-disaster period, it was found that the viral load of the earthquake-affected villages was not increased, despite the difficult and unprecedented conditions. It can be suggested that the adaptation of the measures to the new conditions has worked beneficially to reduce the spread of the new virus among those affected and the involved staff. For this reason, this approach could be considered as good practice and important lesson learned, which can be applied to similar future compound emergencies in areas with similar geoenvironmental and epidemiological characteristics.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"2 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-07-08","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76190397","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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.
{"title":"The tectonostratigraphic architecture of the Serbo-Macedonian massif in the Vertiskos and Kerdilion mountains (Northern Greece)","authors":"A. Plougarlis, M. Tranos, L. Papadopoulou","doi":"10.12681/bgsg.25054","DOIUrl":"https://doi.org/10.12681/bgsg.25054","url":null,"abstract":"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.","PeriodicalId":9519,"journal":{"name":"Bulletin of the Geological Society of Greece","volume":"68 1","pages":""},"PeriodicalIF":0.0,"publicationDate":"2021-03-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80180295","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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