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Earthquakes in Greece

What Causes Quakes in Greece?

Greece is one of the world's most seismically active countries.

Fortunately, most Greek earthquakes are relatively mild but there is always the potential for more severe seismic activity. Greek builders are aware of this and modern Greek buildings are built to be safe during earthquakes. Similar quakes often strike nearby Turkey and result in much more extensive damage and injuries due to less-strict building codes.

Most of Greece, Crete, and the Greek islands are contained in a "box" of fault lines running in different directions. This is in addition to the earthquake potential from the still-lively volanoes, including the Nysiros Volcano, thought by some experts to be overdue for a major eruption.

Check on A Recent Earthquake in Greece

The Institute of Geodynamics in Greece lists recent earthquake data on its website, which offers both a Greek- and English-language version.

They show the epicenter, intensity, and graph other information about every temblor that strikes Greece.
Undersea Earthquakes

Many of the quakes that strike Greece have their epicenters under the sea. While these can shake up surrounding islands, they rarely cause severe damage.

The ancient Greeks attributed earthquakes to the God of the Sea, Poseidon, perhaps because so many of them were centered under the waters.

The Athens Earthquake of 1999

One severe quake was the Athens Earthquake of 1999, which struck just outside of Athens itself. The suburbs where it struck were among Athens' poorest, with many old buildings. Over a hundred buildings collapsed, more than 100 people were killed, and many others were injured or left homeless.

The Earthquake of 1953

On March 18, 1953 a quake called the Yenice-Gonen Quake struck Turkey and Greece, resuling in the devastation of a number of places and islands. Many of the "typical" Greek buildings we see on the islands today actually date from after this quake, which occurred before modern building codes were in place.

Earthquakes in Ancient Greece

Many earthquakes are recorded in ancient Greece, some of which were severe enough to wipe out cities or cause coastal settlements to virtually disappear.

The Eruption of Thira (Santorini)

Some earthquakes in Greece are caused by volcanoes, including the one which forms the island of Santorini. This is the volcano that exploded in the Bronze Age, sending up a huge cloud of debris and dust, and turning a once-round island into a pale crescent of its former self. Some experts see this disaster as ending the ascendency of the Minoan civilization based on Crete just 70 miles away from Thira. This eruption also caused a tsunami, though how devastating it really was is a matter of debate for both scholars and volcanologists.

Tsunamis in Greece

After the devastating tsunami which struck the Pacific Ocean in 2004, Greece decided to install a tsunami-detection system of its own. At present it is still untested but is meant to give warning of any potentially large waves approaching the Greek islands. But fortunately, the type of earthquake which caused 2004's devastating Asian tsunami is not common in the region of Greece.

Historical Seismicity of Greece

Research Article

Seismic response analysis of multidrum classical columns

Dimitrios Konstantinidis 1, Nicos Makris 2 *
1Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, U.S.A.
2Department of Civil Engineering, University of Patras, Patras 26500, Greece

email: Nicos Makris (nmakris@upatras.gr)

*Correspondence to Nicos Makris, Department of Civil Engineering, University of Patras, Patras 26500, Greece

On leave from Department of Civil and Environmental Engineering, University of California, Berkeley, U.S.A.

Funded by:
National Science Foundation; Grant Number: CMS-0116354

Keywords
multidrum classical columns • sliding • rocking • seismic response • earthquake engineering

Abstract

This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times.
The numerical study presented in this paper is conducted with the commercially available software Working Model 2DTM, which can capture with fidelity the sliding, rocking, and slide-rocking response of rigid-body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in-house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment.

The study reveals that relative sliding between drums happens even when the g-value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes Mw=6.0-7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in-between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd.

HISTORICAL EARTHQUAKE EVENTS

National Observatory of Athens, Institue of Geodynamics

National Observatory of Athens

University of Athens, Department of Geophysics-Geothermal

Tectonic Summary of Greece

The earth's lithosphere beneath the eastern Mediterranean constitutes a broad boundary region between three major tectonic plates, the Eurasia, Africa, and Arabia plates. The motions of the major plates drive smaller plates, and it is the shapes and motions of these smaller plates that determine the locations and focal mechanisms of most earthquakes in the region. The seismotectonics of southern Greece are governed primarily by the motion of the Africa plates with respect to the relatively small Aegean Sea plate.

Most shallow earthquakes in central and northern Greece (depths less than 50 km) result from interaction between the Eurasia plate and the small Aegean Sea plate, which is moving southwest with respect to the Eurasia plate with a velocity of about 30 mm/year. The boundary between the Aegean plate and the Eurasia plate in central and northern Greece is diffuse. Seismicity is concentrated in east-trending and northeast-trending zones of deformation. The east-trending zones are most prominent in mainland Greece, are characterized by predominantly normal faulting, and have produced earthquakes with magnitudes of about 7. The northeast-trending belts are characterized by predominately strike-slip fault earthquakes. A northeast-trending zone of predominantly strike-slip earthquakes occurs off the west coasts of Cephalonia and Lefkada, western Greece, and other northeast-trending zones occur beneath the Aegean Sea east of the Greek mainland. In the twentieth century, an earthquake of magnitude 7.2 occurred on a northeast-trending strike-slip fault beneath the northern Aegean Sea.

The Africa plate subducts beneath the Aegean Sea plate along the Hellenic arc, from the western Peloponnesus through Crete and Rhodes to western Turkey, at a rate of almost 40 mm/year. Shallow-focus earthquakes (focal depths less than 50 km) occur on faults in the boundary-region of the two plates. From Crete to the west and northwest, most shallow earthquakes near the Hellenic-arc plate boundary are produced as the result of reverse or strike-slip motion, although some normal-faulting earthquakes do occur. To the east of Crete, the Hellenic-arc plate boundary is characterized by normal-fault and strike-slip earthquakes. In the twentieth century, the largest shallow-focus earthquakes to have occurred near the Hellenic-arc plate boundary had magnitudes of about 7.2. Historical sources and archeological studies suggest that earthquakes centered near Crete in 365 AD and 1303 AD may have been much larger than any Hellenic arc earthquake of the twentieth century. In other parts of the world, convergent-plate tectonic environments similar to that of the Hellenic arc have produced earthquakes of magnitude 8 and larger.

Shallow-focus earthquakes also occur in the volcanic arc that is associated with the subduction of the Africa plate beneath the Aegean Sea plate, in the Dodecanese and Cyclades Islands, over 100 km north of Crete. The region near the volcanic arc is characterized by normal faulting. The magnitude 7.8 earthquake of July 9, 1956, south of Amorgos, produced a large tsunami that affected the entire Aegean Sea.

Intermediate-depth earthquakes (depths greater than 50 km) occur within the subducting Africa plate beneath central Greece and the Dodecanese and Cyclades Islands. An earthquake having a focal depth of about 100 km and a magnitude of 7.7 occurred beneath the Dodecanese Islands in 1926. Intermediate-depth earthquakes typically cause less damage on the ground surface above their foci than is the case with similar magnitude shallow-focus earthquakes, but they are sometimes felt at greater distances from the epicenter.

A belt of shallow-focus seismicity along the western coast of Greece to the north of Lefkada, and extending north along the Adriatic coast of the Balkan Peninsula, is characterized by reverse fault earthquakes occurring in response to northeast-southwest crustal convergence. This zone produced an earthquake of magnitude 7.0 in 1979, centered beneath the coast of Montenegro.


Earthquakes in Greece Earthquake Precursors What Causes Quakes in Greece? Greece is one of the world's most seismically active countries. Fortunately, most Greek earthquakes are relatively mild but there is always the potential for more severe seismic activity. Greek builders are aware of this and modern Greek buildings are built to be safe during earthquakes. Similar quakes often strike nearby Turkey and result in much more extensive damage and injuries due to less-strict building codes. Most of Greece, Crete, and the Greek islands are contained in a "box" of fault lines running in different directions. This is in addition to the earthquake potential from the still-lively volanoes, including the Nysiros Volcano, thought by some experts to be overdue for a major eruption. Check on A Recent Earthquake in Greece The Institute of Geodynamics in Greece lists recent earthquake data on its website, which offers both a Greek- and English-language version. They show the epicenter, intensity, and graph other information about every temblor that strikes Greece. Undersea Earthquakes Many of the quakes that strike Greece have their epicenters under the sea. While these can shake up surrounding islands, they rarely cause severe damage. The ancient Greeks attributed earthquakes to the God of the Sea, Poseidon, perhaps because so many of them were centered under the waters. The Athens Earthquake of 1999 One severe quake was the Athens Earthquake of 1999, which struck just outside of Athens itself. The suburbs where it struck were among Athens' poorest, with many old buildings. Over a hundred buildings collapsed, more than 100 people were killed, and many others were injured or left homeless. The Earthquake of 1953 On March 18, 1953 a quake called the Yenice-Gonen Quake struck Turkey and Greece, resuling in the devastation of a number of places and islands. Many of the "typical" Greek buildings we see on the islands today actually date from after this quake, which occurred before modern building codes were in place. Earthquakes in Ancient Greece Many earthquakes are recorded in ancient Greece, some of which were severe enough to wipe out cities or cause coastal settlements to virtually disappear. The Eruption of Thira (Santorini) Some earthquakes in Greece are caused by volcanoes, including the one which forms the island of Santorini. This is the volcano that exploded in the Bronze Age, sending up a huge cloud of debris and dust, and turning a once-round island into a pale crescent of its former self. Some experts see this disaster as ending the ascendency of the Minoan civilization based on Crete just 70 miles away from Thira. This eruption also caused a tsunami, though how devastating it really was is a matter of debate for both scholars and volcanologists. Tsunamis in Greece After the devastating tsunami which struck the Pacific Ocean in 2004, Greece decided to install a tsunami-detection system of its own. At present it is still untested but is meant to give warning of any potentially large waves approaching the Greek islands. But fortunately, the type of earthquake which caused 2004's devastating Asian tsunami is not common in the region of Greece. Historical Seismicity of Greece Research Article Seismic response analysis of multidrum classical columns Dimitrios Konstantinidis 1, Nicos Makris 2 * 1Department of Civil and Environmental Engineering, University of California, Berkeley, CA 94720, U.S.A. 2Department of Civil Engineering, University of Patras, Patras 26500, Greece email: Nicos Makris (nmakris@upatras.gr) Correspondence to Nicos Makris, Department of Civil Engineering, University of Patras, Patras 26500, Greece On leave from Department of Civil and Environmental Engineering, University of California, Berkeley, U.S.A. Funded by: National Science Foundation; Grant Number: CMS-0116354 Keywords multidrum classical columns • sliding • rocking • seismic response • earthquake engineering Abstract This paper presents a numerical investigation on the seismic response of multidrum classical columns. The motivation for this study originates from the need to understand: (a) the level of ground shaking that classical multidrum columns can survive, and (b) the possible advantages or disadvantages of retrofitting multidrum columns with metallic shear links that replace the wooden poles that were installed in ancient times. The numerical study presented in this paper is conducted with the commercially available software Working Model 2DTM, which can capture with fidelity the sliding, rocking, and slide-rocking response of rigid-body assemblies. This paper validates the software Working Model by comparing selected computed responses with scarce analytical solutions and the results from in-house numerical codes initially developed at the University of California, Berkeley, to study the seismic response of electrical transformers and heavy laboratory equipment. The study reveals that relative sliding between drums happens even when the g-value of the ground acceleration is less than the coefficient of friction, µ, of the sliding interfaces and concludes that: (a) typical multidrum classical columns can survive the ground shaking from strong ground motions recorded near the causative faults of earthquakes with magnitudes Mw=6.0-7.4; (b) in most cases multidrum classical columns free to dislocate at the drum interfaces exhibit more controlled seismic response than the monolithic columns with same size and slenderness; (c) the shear strength of the wooden poles has a marginal effect on the sliding response of the drums; and (d) stiff metallic shear links in-between column drums may have an undesirable role on the seismic stability of classical columns and should be avoided. Copyright © 2005 John Wiley & Sons, Ltd. HISTORICAL EARTHQUAKE EVENTS National Observatory of Athens, Institue of Geodynamics National Observatory of Athens University of Athens, Department of Geophysics-Geothermal Tectonic Summary of Greece* The earth's lithosphere beneath the eastern Mediterranean constitutes a broad boundary region between three major tectonic plates, the Eurasia, Africa, and Arabia plates. The motions of the major plates drive smaller plates, and it is the shapes and motions of these smaller plates that determine the locations and focal mechanisms of most earthquakes in the region. The seismotectonics of southern Greece are governed primarily by the motion of the Africa plates with respect to the relatively small Aegean Sea plate. Most shallow earthquakes in central and northern Greece (depths less than 50 km) result from interaction between the Eurasia plate and the small Aegean Sea plate, which is moving southwest with respect to the Eurasia plate with a velocity of about 30 mm/year. The boundary between the Aegean plate and the Eurasia plate in central and northern Greece is diffuse. Seismicity is concentrated in east-trending and northeast-trending zones of deformation. The east-trending zones are most prominent in mainland Greece, are characterized by predominantly normal faulting, and have produced earthquakes with magnitudes of about 7. The northeast-trending belts are characterized by predominately strike-slip fault earthquakes. A northeast-trending zone of predominantly strike-slip earthquakes occurs off the west coasts of Cephalonia and Lefkada, western Greece, and other northeast-trending zones occur beneath the Aegean Sea east of the Greek mainland. In the twentieth century, an earthquake of magnitude 7.2 occurred on a northeast-trending strike-slip fault beneath the northern Aegean Sea. The Africa plate subducts beneath the Aegean Sea plate along the Hellenic arc, from the western Peloponnesus through Crete and Rhodes to western Turkey, at a rate of almost 40 mm/year. Shallow-focus earthquakes (focal depths less than 50 km) occur on faults in the boundary-region of the two plates. From Crete to the west and northwest, most shallow earthquakes near the Hellenic-arc plate boundary are produced as the result of reverse or strike-slip motion, although some normal-faulting earthquakes do occur. To the east of Crete, the Hellenic-arc plate boundary is characterized by normal-fault and strike-slip earthquakes. In the twentieth century, the largest shallow-focus earthquakes to have occurred near the Hellenic-arc plate boundary had magnitudes of about 7.2. Historical sources and archeological studies suggest that earthquakes centered near Crete in 365 AD and 1303 AD may have been much larger than any Hellenic arc earthquake of the twentieth century. In other parts of the world, convergent-plate tectonic environments similar to that of the Hellenic arc have produced earthquakes of magnitude 8 and larger. Shallow-focus earthquakes also occur in the volcanic arc that is associated with the subduction of the Africa plate beneath the Aegean Sea plate, in the Dodecanese and Cyclades Islands, over 100 km north of Crete. The region near the volcanic arc is characterized by normal faulting. The magnitude 7.8 earthquake of July 9, 1956, south of Amorgos, produced a large tsunami that affected the entire Aegean Sea. Intermediate-depth earthquakes (depths greater than 50 km) occur within the subducting Africa plate beneath central Greece and the Dodecanese and Cyclades Islands. An earthquake having a focal depth of about 100 km and a magnitude of 7.7 occurred beneath the Dodecanese Islands in 1926. Intermediate-depth earthquakes typically cause less damage on the ground surface above their foci than is the case with similar magnitude shallow-focus earthquakes, but they are sometimes felt at greater distances from the epicenter. A belt of shallow-focus seismicity along the western coast of Greece to the north of Lefkada, and extending north along the Adriatic coast of the Balkan Peninsula, is characterized by reverse fault earthquakes occurring in response to northeast-southwest crustal convergence. This zone produced an earthquake of magnitude 7.0 in 1979, centered beneath the coast of Montenegro.
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