Hi, I’m Ali Sealander with UTD Geonews and today
we are going to talk about what caused a large earthquake
that recently shook Greece and Turkey. On October 30, 2020 a magnitude 7.0 earthquake
struck Samos Island, Greece, just off the shore of Turkey. The devastating quake caused
over 1000 injuries, and unfortunately has so far resulted in at least 115 deaths.
marking it as the deadliest earthquake of 2020. A resulting tsunamic reached many coastal
cities, including the beautiful city of Izmir which unfortunately was
especially hard-hit with over 20 buildings destroyed.
This region is very seismically active. Over the last 70 years it has seen 36 earthquakes
with a magnitude of 6.5 or greater.
The earthquake occurred 21 km beneath the surface and was caused by rupture and movement
on a normal fault. This is the type of fault where the rock above the fault plane moves
downward relative to the rock below it. The fault movement is caused by extension, or
stretching, of the rocks to the point of producing motion along the fault and an earthquake.
The fault associated with the earthquake trends east-west which means that extension is happening
in a north-south orientation
But what is causing this extension and why do we have all this faulting and seismicity
in the area? To get to the bottom of this we need to delve into the plate tectonics
of this region. The Samos earthquake occurred within the Anatolian microplate which is crammed
between three other plates. To the north is the massive Eurasian plate, to the southeast
is the Arabian plate and to the south is the African plate. The Arabian plate is colliding
with Anatolia squeezing it against the Eurasian plate so that Turkey has to escape to the
west. Meanwhile, the African plate moves northward and sinks beneath a convergent plate margin.
Here, the African plate subducts, or sinks, beneath the southwestern Anatolian microplate
in a subduction zone.
As a result of continental collision in the east and subduction in the west, the Anatolian
microplate is very dynamic. This tectonic activity can be visualized using GPS
tracking how different parts of the Anatolian plate moves in response to these different
forces.
What we can see is that the Anatolian plate is essentially making a plate tectonic U-turn.
In eastern Turkey the Anatolian microplate is moving slowly west-northwest away from
colliding Arabian Plate,
in central Turkey it moves more rapidly westward, and in the west the
Anatolian plate beneath the Aegean sea is moving very rapidly south.
These movements are accompanied
by a lot of deformation and faulting which cause a lot of earthquakes all over the Anatolian
plate. It was one of these faults, right in the center of the Anatolian plate, that slipped
and caused this devastating temblor.
That explains the faults, but what about the stretching that cause the faults to rupture?
The answer is found in the convergent plate boundary 350 miles south of where the earthquake
occurred. The northern part of the African plate that is subducting beneath the Aegean
sea is very dense. In fact, it's so dense that as it is subducting it basically falls
back on itself. The subducting crust collapses and rolls backward to the south as it sinks.
And even though the African plate moves slowly northward towards Eurasia, the sinking and
rollback of its dense crust is faster than the plate’s movement, causing the subduction
zone to retreat southward. Basically, for every one step forward, the African plate
in this region is taking two steps back. And like a friend falling into a pool, the African
plate pulls the Anatolian plate with it,
stretching it along the way.
It's this pulling to the south that is causing the stretching or extension
several hundred miles north of the convergent plate boundary.
As you can see the Anatolian Microplate is very active.
And more earthquakes can be expected in and around the area in the future.
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