7.0 magnitude earthquake and tsunami affecting Turkey and Greece
An earthquake with a moment magnitude of 7.0 occurred on 30 October 2020 about northeast of the Greek island of Samos. Although Samos was closest to the epicentre, it was the large Turkish city İzmir, northeast that was heavily affected—more than 700 residential and commercial structures were seriously damaged or destroyed. One hundred and seventeen people died in İzmir Province while an additional 1,034 were injured. In Greece, there were two fatalities and 19 injured. The earthquake is the deadliest in the year 2020, and the third major earthquake to strike Turkey that year. It generated an unusually large tsunami. The event is called the Samos earthquake by the International Seismological Centre.
Tectonic setting.
The Aegean Sea is a seismically active region with complex plate tectonics interaction both within and surrounding the Aegean Sea plate. The region has several major plate boundary including the North Anatolian Fault which runs through northern Turkey, where the Anatolian sub-plate slides past the Eurasian plate along this right-lateral strike-slip fault. Another major boundary is the East Anatolian Fault where the Arabian plate interacts with the Anatolian plate. This transform fault was responsible for the 2020 Elazığ earthquake.
At its southern edge, the African plate converges north towards the Aegean Sea plate at a rate of /yr. It subducts beneath the Aegean, occasionally producing great megathrust earthquakes and tsunamis including the 365 Crete earthquake. The subduction rate along the Hellenic subduction zone at /yr, however, greatly exceeds the velocity of the African plate. North–south extension within the Aegean Sea plate in the back-arc region compensate the subduction rate. Shallow crustal earthquakes within the Aegean Sea plate is a result of this extension, accommodated by east–west trending normal faults.
The first record of an earthquake in the Samos and İzmir region date back to 200 BC, describing an earthquake of magnitude 6.0–6.5, and intensity VII–VIII. Another earthquake with an estimated magnitude of 7.0 struck the region in 47 AD. On the island of Samos, these earthquakes have minimal effects. However, nearby İzmir have suffered serious catastrophe as a result of these earthquakes. The most destructive event in the region was the 1688 Smyrna earthquake, which had an epicentre near İzmir. With an estimated magnitude 7.0, the earthquake killed 15,000–20,000 people in the city. Other major events took place in 1739 and 1788, causing major damage in the city. On 11 August 1904, Samos was rocked by a magnitude 6.8 earthquake, causing substantial damage in Greece and Turkey, and killing four people. That earthquake according to researchers, was caused by an onshore fault (Pythagorion Fault) on the island.
Earthquake.
The earthquake was the result of normal faulting at a shallow crustal depth within the Aegean Sea plate in the eastern Aegean Sea, about north of the closest plate boundary, the Hellenic Trench, where the African plate moves north at a rate of approximately /yr with respect to the Eurasian plate. Due to its geological setting away from a plate boundary, it is considered an intraplate earthquake. A focal mechanism analysis indicated that the earthquake occurred on a moderately dipping normal fault striking either eastward or westward. This mechanism indicates north–south oriented extension that is common in the Aegean Sea. The United States Geological Survey stated that normal faulting events of this size typically have a fault area of x .
The North Samos Fault, also known as the Kaystrios Fault, is an east–west striking, north–northeast dipping normal fault located offshore, north of the coast of Samos. The fault was previously determined to have the potential to produce an earthquake of magnitude 6.8. It likely ruptured entirely during the earthquake for a length of approximately . The epicentral location suggests it was on the western extension of the geologically active Büyük Menderes Graben. The earthquake released a seismic moment of 3.3 × 1019 N-m, corresponding to a moment magnitude of 7.0. A maximum slip of at a depth of was inferred. The earthquake produced up to of slip on the seafloor, causing a moderate tsunami, and tectonic uplift and subsidence on land.
Strong ground motion.
The earthquake achieved a peak ground acceleration (pga) of 0.27 "g" in Samos. Weaker ground acceleration was recorded at 0.1 "g" in İzmir, however, in the Bayraklı and Karşıyaka metropolitan districts, these ground motions were amplified with longer periods of 1.5 seconds. Ground motions were severely amplified in these districts due to the soil condition consisting of loose sediments. In the Turkish town of Kuşadası, the pga was 0.18 "g". At away from the epicentre, on Turkish soil, the highest pga was recorded 0.98 "g". The maximum intensity was recorded on Samos Island, VIII ("Severe"), a revision from X ("Extreme"). Shaking was also felt on the Greek island of Crete, and in some regions of Athens.
Foreshocks and aftershocks.
The earthquake was preceded by a foreshock sequence consisting of 39 events beginning three months prior to the mainshock. Within the first month, more than 1,800 aftershocks measured 2.0 or larger. More than 40 aftershock were larger than 4.0; the largest measuring 5.2 and 5.1. These aftershocks were distributed across a trend striking east–west. The aftershock distribution illuminated a fault plane dipping north, consistent with a known offshore fault structure. The low aftershock activity within the critical asperity that ruptured possibly indicated a near-total strain release during the mainshock.
Geological effects.
The earthquake produced significant coseismic uplift on the island of Samos. Surface ruptures were also observed on the island. The beaches, ports, and coasts of Samos were partially raised in the aftermath. At Karlovasi, up to of permanent uplift was measured at a breakwater off the coast. Approximately west of Karlovasi is the Akra coast consisting of marble, which was raised 20 cm. Between and of uplift was measured at Ayios Nikolaos, located southwest of the epicentre. An aftershock measuring 4.5 on 20 January 2021 generated of additional uplift in the same area. Similar measurements were taken at a marina in Marathokampos. The Pythagoreio Fault in Pythagoreio, southeast of the earthquake, generated of surface deformation during the quake. An estimated uplift of is thought to have occurred at Potokaki as reported by tourists. According to the Earth Applied Sciences Disasters Program of NASA, synthetic-aperture radar data revealed Samos Island was raised by as much as meanwhile its northern coast subsided by the same amount. The ground uplift and subsidence pattern suggested a coseismic rupture along a fault located north of the island, dipping at an angle towards the north.
Small normal-mechanism surface ruptures were documented near the villages of Kontakaiika, Ayios Nikolaos, and Ayios Elias. Vertical displacements of up to were observed on the ground, and across roads. The coseismic surface ruptures resulted in some damage to roads and brick walls. Although these uplifts were on the order of several centimeters, it added up to a length of .
Small landslides, rockfalls and slope failures were reported along fault scarps on Samos. Some instances of rockfalls caused minor traffic disruption when they partially blocked roads. A small rockfall caused slight damage to an adjacent building in Kokkari. Ground cracks appeared on a road at Malagari. The cracked caused part of the road, and small trees to slide several centimeters closer to the shore as a result of lateral spreading. Minor liquefaction occurred at the beach near the town as well.
Tsunami.
Tsunami information was issued by the Kandilli Observatory Earthquake Monitoring and Tsunami Warning Center to the Earthquake Research Department of Turkey approximately 11 minutes after the earthquake, but was not broadcast to the coastal regions. The tsunami arrived between 10 and 15 minutes after the mainshock.
Multiple social media posts showed water rushing through streets and ports in the region following the earthquake, along with tsunami warnings being issued for the islands of Ikaria, Kos, Chios and Samos. Flooding from the coasts reached heights of , however at Akarca, the tsunami reached heights of . In Azmak, the tsunami penetrated inland, in Akarca, and in Sigacik. Recorded heights of the tsunami from this event were larger than those of other similar magnitude earthquakes in the same region with the exception of the 1956 Amorgos earthquake.
Damage to buildings caused by the tsunami in Greece and Turkey was moderate and non-structural. The tsunami produced unusually long basin oscillations, persisting for over a day after the earthquake. The earthquake itself generated an unusually large tsunami for its magnitude and normal focal mechanism.
In Akarca, north of Samos, the tsunami had a run-up height of , inundated up to inland. The maximum wave height in this area was . A surge flooded and damaged a diving center near the coast. Garden walls and fences along the shore were also damaged. Cars and boats were among the large objects picked up by the surge and moved inland. The only known tsunami fatality was reported in this town.
In Alaçatı on the Çeşme Peninsula, the tsunami flowed up a stream and inundated inland by as much as . It carried a fishing vessel along the stream during the inundation. Analysis of video footage on the coast showed that the tsunami had a maximum height of when it struck.
East of Alaçatı, in Zeytineli, the tsunami severely damaged unoccupied resort houses along a stretch of beach. Debris from damaged structures were strewn along the beach. Concrete blocks were also displaced by as much as . A maximum inundation of was measured, as well as a flow height of at a palm tree, from the shore. At Sığacık, a wave struck the coast with a run-up height of . The tsunami waves where higher in this region due to the presence of a shallow bay which altered the coastal geometry.
Major flooding occurred along the northern coast of Samos although there were no deaths. Many offices and businesses were immediately flooded when the surge broke through windows and doors. Waves of traveled as far as inland. Damage to boats and cars were widely reported in the aftermath. A number of small boats and cars were carried inland or lost at sea by the tsunami. Some boats were smashed along breakwater structures as well. Shops, hotel lobbies, restaurants, offices and homes suffered slight damage when the tsunami inundated the ground level and indoors. A maximum run-up height of was measured on the northern coast of Samos about east of Karlovasi Port. The tsunami caused some material damage to a home that was located at the coast.
Impact.
Overall, minor damage occurred on Samos despite its close proximity to the epicentre. Most of the damage and casualties were from the Bornova and Bayraklı districts of İzmir; located at least north of the epicentre. On 4 November, the mayor of İzmir, Tunç Soyer, stated that 15,000 people in the city were made homeless. Total damage is estimated to be in the millions for Greece, and over $400 million for Turkey. Serious structural damage and pancake-style building collapses caused many deaths in İzmir.
Turkey.
Initially, Turkish Minister of the Interior Süleyman Soylu stated that at least six buildings were destroyed in İzmir, but the city's mayor Tunç Soyer later put the number of collapsed buildings closer to 20. On-site investigations by the Turkish Ministry of Environment and Urbanization revised the number of collapsed and intentionally demolished buildings to 103. At least 700 other buildings suffered serious damage, and in 814, damage was moderate. Slight structural damage was reported in across 7,889 buildings, while the other 159,000 were unaffected. Thirty-five buildings were set for demolition, and by 2023, all but two buildings were in the process of removal. Fifty-eight damaged buildings did not receive the approval for demolition due to their cultural status.
Most of the buildings that collapsed were built in the 1990s, based on outdated earthquake regulations from 1975. Poor construction practices and the absence of code compliance were reasons for the collapse. The buildings that totally failed were typically between 5–10 storeys tall, and at least 30 years old. Additionally, the first floors of these buildings were altered for commercial use such as shops. Taller buildings with heights of , however, did not sustain structural damages. The city is also built on soft sediments in a basin which amplified the intensity of shaking despite its distance from the epicentre. The effects of basin amplification may have worsened the intensity of ground motions, causing structural failures. The observation of damage effects and instrumental data found that ground motions were amplified 2.5–3 times