Abstract:Knowledge and visualization of the present-day relationship between earthquakes, active tectonics and crustal deformation is a key to understanding geodynamic processes, and is also essential for risk mitigation and the management of geo-reservoirs for energy and waste. The study of the complexity of the Greek tectonics has been the subject of intense efforts of our working group, employing multidisciplinary methodologies that include detailed geological mapping, geophysical and seismological data processing u… Show more
“…In Equations (10), Tc is given in s and δmax is in mm and Cs is a coefficient which for a firm soil becomes unity. Two extreme scenarios can be examined from the seismicity of the region [112,113] to establish the spectral demand: (a) a magnitude 6.2 from an epicentral distance 15 km; and (b) a magnitude 7.2 from an epicentral distance 100 km. The displacement demands for the estimated period are the green shadowed area ranging between approximately 3 and 7 cm in Figure 12.…”
The seismic response of five cultural heritage towers erected between the 9th and 10th century AD are investigated herein. Firstly, their architectural and modal characteristics were studied in the light of seismic events that hit the monuments. There exist several historical reports of strong earthquakes, as well as damaged structures and collapses. The limit analysis is adopted to examine the post-elastic behavior of the towers up to collapse due to out-of-plane failure. Recurrent damage modes were collected from recent earthquakes and a classification of four possible collapse mechanisms in towers and slender masonry structures is here proposed: overturning, separation of perpendicular walls, diagonal cracking, and dislocation of the belfry. A thorough examination of the towers under investigation verified the proposed damage classification. The capacity curves were derived combining the capacity curves of each of the collapse mechanisms. Damage thresholds were defined on these curves in correspondence with damage states. The studied group of structures is representative of a wider typology. A statistical approach was adopted to describe damage with seismic intensity, and vulnerability curves were generated. The results of this study will improve the understanding of the performance and the collapse mechanisms of slender masonry structures under seismic loading and provide a characterization of seismic vulnerability for the studied cultural heritage types of towers.
“…In Equations (10), Tc is given in s and δmax is in mm and Cs is a coefficient which for a firm soil becomes unity. Two extreme scenarios can be examined from the seismicity of the region [112,113] to establish the spectral demand: (a) a magnitude 6.2 from an epicentral distance 15 km; and (b) a magnitude 7.2 from an epicentral distance 100 km. The displacement demands for the estimated period are the green shadowed area ranging between approximately 3 and 7 cm in Figure 12.…”
The seismic response of five cultural heritage towers erected between the 9th and 10th century AD are investigated herein. Firstly, their architectural and modal characteristics were studied in the light of seismic events that hit the monuments. There exist several historical reports of strong earthquakes, as well as damaged structures and collapses. The limit analysis is adopted to examine the post-elastic behavior of the towers up to collapse due to out-of-plane failure. Recurrent damage modes were collected from recent earthquakes and a classification of four possible collapse mechanisms in towers and slender masonry structures is here proposed: overturning, separation of perpendicular walls, diagonal cracking, and dislocation of the belfry. A thorough examination of the towers under investigation verified the proposed damage classification. The capacity curves were derived combining the capacity curves of each of the collapse mechanisms. Damage thresholds were defined on these curves in correspondence with damage states. The studied group of structures is representative of a wider typology. A statistical approach was adopted to describe damage with seismic intensity, and vulnerability curves were generated. The results of this study will improve the understanding of the performance and the collapse mechanisms of slender masonry structures under seismic loading and provide a characterization of seismic vulnerability for the studied cultural heritage types of towers.
“…Snapshot from the New Seismotectonic Atlas of Greece v1.0 (Kassaras et al, 2020), presenting focal mechanisms (period 1995 -June 2020, by SL-NKUA) and active faults (NOAFAULTs, Ganas et al, 2018), coloured by faulting type, along with volcanism and hydrothermal activity. The epicenter of the October 30 th 2020 mainshock is presented by a yellow star.…”
Section: Figmentioning
confidence: 99%
“…The epicenter of the October 30 th 2020 mainshock is presented by a yellow star. Inset map: past instrumental seismicity (1901( -June 2020 from the compilation of Kassaras et al, 2020) and focal mechanisms of significant earthquakes at crustal depths (from the compilation of in the broader region of the 2020 Samos earthquake. The interactive GIS web application of the New Seismotectonic Atlas of Greece v1.0 is available at the following link: http://www.geophysics.geol.uoa.gr/atlas.html Ring et al, 2007) On 30 October 2020 11:51 UTC, a Mw=6.9 earthquake occurred in the offshore area north of Samos Island, in the Gulf of Ephesos/Kuşadasi (Fig.…”
On 30 October 2020 11:51 UTC, a Mw=6.9 earthquake struck the offshore region north of Samos Island, Greece, in the Gulf of Ephesos/Kuşadasi, causing two fatalities and 19 minor injuries at Samos Island, as well as 115 casualties and over 1,030 injuries in Western Turkey. Preliminary results indicate that the mainshock occurred on a north-dipping normal fault, with a focal mechanism of 270º/50º/-81º. The selection of the fault plane is supported by evidence of uplift at western Samos and over 10 cm of subsidence at the northernmost edge of the central part of the island. The distribution of relocated hypocenters shows clustering of events, east of the mainshock’s epicenter, where most major aftershocks have occurred. To the west, a smaller group of aftershocks is observed, separated by a spatial gap in seismicity. The latter is likely related to the region of the fault plane where most of the co-seismic slip occurred, with Coulomb stress-transfer towards the western and eastern margins of the rupture triggering aftershock activity. The apparent complexity of the mainshock’s source time function, supported by preliminary results, could indicate the rupture of more than one structures. This could explain the relatively weak magnitude of the largest aftershock (Mw=5.0). The mainshock caused damage mainly to non-engineered constructions, i.e. old residential buildings, churches and monuments in Samos Island, and minor damage to the majority of the building stock of the island built according to the National Seismic Code. On the other hand, it caused severe damage at Izmir, especially to high-rise buildings. The mainshock also triggered a small tsunami that reached heights of over 1 m, mainly affecting the Turkish coast.
“…Thus, we link the relatively small lesson of the Mw 7.0 Samos earthquake with some similar, yet more devastating events, some of which have changed history. Figure 4 Snapshot from the online GIS platform New Seismotectonic Atlas of Greece v1.0 56 , 57 , presenting focal mechanisms (period 1995–June 2020, by SL-NKUA) and active faults 58 , colored by fault type, along with volcanism and hydrothermal activity. The epicenter of the October 30th 2020 main shock is presented by a yellow star.…”
Section: Historical Earthquakes and Volcanic Eruptionsmentioning
confidence: 99%
“… Snapshot from the online GIS platform New Seismotectonic Atlas of Greece v1.0 56 , 57 , presenting focal mechanisms (period 1995–June 2020, by SL-NKUA) and active faults 58 , colored by fault type, along with volcanism and hydrothermal activity. The epicenter of the October 30th 2020 main shock is presented by a yellow star.…”
Section: Historical Earthquakes and Volcanic Eruptionsmentioning
Earthquakes are a consequence of the motions of the planet’s tectonic plates, yet predicting when and where they may occur, and how to prepare remain some of the shortcomings of using scientific knowledge to protect human life. A devastating Mw 7.0 earthquake on October 30, 2020, offshore Samos Island, Greece was a consequence of the Aegean and Anatolian upper crust being pulled apart by north–south extensional stresses resulting from slab rollback, where the African plate is subducting northwards beneath Eurasia, while the slab is sinking by gravitational forces, causing it to retreat southwards. Since the retreating African slab is coupled with the overriding plate, it tears the upper plate apart as it retreats, breaking it into numerous small plates with frequent earthquakes along their boundaries. Historical earthquake swarms and deformation of the upper plate in the Aegean have been associated with massive volcanism and cataclysmic devastation, such as the Mw 7.7 Amorgos earthquake in July 1956 between the islands of Naxos and Santorini (Thera). Even more notable was the eruption of Santorini 3650 years ago, which contributed to the fall of the Minoan civilization. The Samos earthquake highlights the long historical lack of appreciation of links between deep tectonic processes and upper crustal deformation and geological hazards, and is a harbinger of future earthquakes and volcanic eruptions, establishing a basis for studies to institute better protection of infrastructure and upper plate cultures in the region.
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