Turkey Earthquake

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Turkey Earthquake

Introduction

The terrible earthquake that struck western Turkey on August 17, 1999

measured a massive Mw7.4 on the Richter scale (also known as the

Kocaeli, Turkey, earthquake) Turkey has had a long history of large

earthquakes that often occur in progressive adjacent earthquakes.

Starting in 1939, the North Anatolian fault produced a sequence of

major earthquakes, of which the 1999 event is the 11th with a

magnitude greater than or equal to 6.7. Starting with the 1939 event

in western Turkey, the earthquake locations have moved both eastward

and westward. The westward migration was particularly active and

ruptured 600 km of contiguous fault between 1939 and 1944. This

westward propagation of earthquakes then slowed and ruptured an

additional adjacent 100 km of fault in events in 1957 and 1967, with

separated activity further west during 1963 and 1964.

The August 17, 1999 event fills in a 100 to 150 km long gap between

the 1967 event and the 1963 and 1964 events. This gap was first noted

by Toksoz, Shakal, and Michael in 1979 and it's hazard was later

analyzed by Stein, Barka, and Dieterich in 1997. The latter paper

estimated that there was a 12% chance of this earthquake occurring in

the 30 years from 1996 to 2026.

The Cause

[IMAGE]The earthquake originated at a shallow depth of about 10.5

miles (17 km) and generated strong ground motion (and moderate to high

accelerations) in a zone along the Gulf of Izmit of the Sea of Marmara

to east of Adapazari. It occurred along the northernmost strands of

the North Anatolian fault system. Turkey lies upon 3 major plates, two

of which forms the North Anatolian fault one of the world's longest

and best-studied strike-slip (horizontal motion) faults. The Eurasian

and Anatolian/Aegean plates were the cause of the earthquake. They had

overlapped along a distance of 68 miles (110 kilometres). This

particular earthquake occurred on the east-west trending. This

particular quake was due to conservative actions. This is when two

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