The death toll from this single event was greater than the average annual loss of life from all earthquakes worldwide. An earthquake occurs when the earth shakes due to the release of seismic energy following the rapid movement of large blocks of the crust along a fault. Faults are breaks in the crust that may be hundreds of kilometers long and extend downward 10-20 km into the crust. The Izmit earthquake occurred on the North Anatolian fault , a fault that is of similar length and sense of movement as the San Andreas fault. Unraveling the movement history of large faults that produce devastating but infrequent earthquakes can help predict the potential threat from similar faults elsewhere.
Seismic waves radiate outward from the focus.
Damage is greatest from shallow earthquakes as the seismic waves travel a shorter distance before reaching the surface. Building codes are in place in most earthquake-prone areas but they are of little use if enforcement is lax, as was the case in Turkey. Following the earthquake it was discovered that some contractors had cut corners in the construction of multi-story apartment complexes. The poorly built structures were left as piles of rubble amongst other apartments that remained standing. The focus is the source of the earthquake and the epicenter is the point on the surface directly above the focus.