In what can be termed as unusual, a shallow focus (14 km depth) earthquake of 6.3 magnitude struck about 40 kms northwest of Herat in Afghanistan at around 11:00 am local time on October 7 (Saturday). The earthquake occurred as the result of thrust faulting near the far western terminus of the Hindu Kush Mountain range. Just 30 minutes after the first quake, Herat was struck by another shallow earthquake (about 13.5 km depth) of the same intensity — 6.3 magnitude. According to the U.S. Geological Survey (USGS): “[The first] earthquake was followed by a second earthquake [with 6.3 magnitude] that occurred approximately 30 minutes later. Both earthquakes occurred on east-west striking fault planes that dip to either the north or south. The earthquakes occurred within the Eurasia plate in an intracontinental mountain belt”. There were about a half-a-dozen aftershocks following the earthquakes.
Four days later, on October 11 (Wednesday), Herat witnessed yet another shallow earthquake at around 5.10 am local time with the focus of the quake being just 9 km below the surface. It had the same intensity (6.3 magnitude) as the previous ones on October 7.
All three earthquakes have been thrust faults, otherwise known as reverse faults. Thrust faults form due to horizontal compressive stresses and so cause shortening of the crust. Here one block or wall (the hanging wall) moves up relative to the other (called the footwall).
