On 20 June 1978, the city was hit by a powerful earthquake, registering a moment magnitude of 6.5.
The earthquake was followed two hours later by an aftershock of 5.1 moment magnitude.
On the Richter scale, the moment magnitude of the earthquake is estimated at 6.8.
In particular, for very large earthquakes moment magnitude gives the most reliable estimate of earthquake size.
It was the third most powerful earthquake in the recorded history of the world, with a moment magnitude of 9.2.
Over 600 earthquakes have been recorded since September 18, including events of moment magnitude 4.8, 5,4, and 5.5.
The earthquakes had a preliminary moment magnitude of 5.8 and 5.4 respectively.
The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe.
Most of the earthquakes had moment magnitudes of less than 3.0.
The main shock with moment magnitude 6.7 M is highlighted in dark blue.