An earthquake with a moment magnitude of 7.0 occurred on 30 October 2020 about 14 km (8.7 mi) northeast of the Greek island of Samos. Although Samos was closest to the epicentre, it was the large Turkish city İzmir, 70 km (43 mi) 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 5–10 mm (0.20–0.39 in)/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 35 mm (1.4 in)/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 250 km (160 mi) north of the closest plate boundary, the Hellenic Trench, where the African plate moves north at a rate of approximately 10 mm (0.39 in)/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 50 km (31 mi) x 20 km (12 mi).
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 60 km (37 mi). 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 4.6 m (15 ft) at a depth of 7 km (4.3 mi) was inferred. The earthquake produced up to 1 m (3 ft 3 in) 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 22.27 km (13.84 mi) 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 Mw 4.0; the largest measuring Mw 5.2 and 5.1. These aftershocks were distributed across a 70 km (43 mi) 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 24 cm (9.4 in) of permanent uplift was measured at a breakwater off the coast. Approximately 1.5 km (0.93 mi) west of Karlovasi is the Akra coast consisting of marble, which was raised 20 cm. Between 15 cm (5.9 in) and 20 cm (7.9 in) of uplift was measured at Ayios Nikolaos, located 12 km (7.5 mi) southwest of the epicentre. An aftershock measuring Mw 4.5 on 20 January 2021 generated 8–10 cm (3.1–3.9 in) of additional uplift in the same area. Similar measurements were taken at a marina in Marathokampos. The Pythagoreio Fault in Pythagoreio, 29 km (18 mi) southeast of the earthquake, generated 29 cm (11 in) of surface deformation during the quake. An estimated uplift of 25 cm (9.8 in) 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 10 cm (3.9 in) 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 8 cm (3.1 in) 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 1 km (0.62 mi).
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 1.9 m (6 ft 3 in), however at Akarca, the tsunami reached heights of 6 m (20 ft). In Azmak, the tsunami penetrated 1.3 km (0.81 mi) inland, 0.82 km (0.51 mi) in Akarca, and 0.32 km (0.20 mi) 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 3.8 m (12 ft), inundated up to 290 m (950 ft) inland. The maximum wave height in this area was 6 m (20 ft). A 2.2 m (7 ft 3 in) 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 2.49 km (1.55 mi). It carried a fishing vessel 1.16 km (0.72 mi) along the stream during the inundation. Analysis of video footage on the coast showed that the tsunami had a maximum height of 1.7 m (5 ft 7 in) 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 25 m (82 ft). A maximum inundation of 760 m (2,490 ft) was measured, as well as a flow height of 1.9 m (6 ft 3 in) at a palm tree, 50 m (160 ft) from the shore. At Sığacık, a wave struck the coast with a run-up height of 5.0–5.6 m (16.4–18.4 ft). The tsunami waves were 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 1.5–2.0 m (4 ft 11 in – 6 ft 7 in) traveled as far as 101 m (331 ft) 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 3.35 m (11.0 ft) was measured on the northern coast of Samos about 5.8 km (3.6 mi) 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 70 km (43 mi) 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.