Four large earthquakes measuring 6.3 each and their aftershocks affected Herat Province in western Afghanistan in early October 2023. The first two earthquakes occurred on 7 October at 11:11 AFT and 11:42 AFT near the city of Herat, followed by many aftershocks. On 11 and 15 October, two other magnitude 6.3 earthquakes struck the same area. Thrust faulting was associated with these earthquakes. The World Health Organization estimated 1,482 fatalities, 2,100 injuries, 43,400 people affected and 114,000 people requiring humanitarian aid. The 11, 15 and 28 October earthquakes caused a combined seven deaths and 344 injuries.
The earthquakes struck Afghanistan during an ongoing humanitarian crisis following the Taliban takeover in 2021, and existing aid groups were experiencing a lack of funds prior to the disaster. Some aid agencies including UNICEF and the Red Cross appealed for donations in response to the earthquakes. Many international organizations and countries participated in rescue and relief efforts. Hospitals were overwhelmed by the number of injured and lack of proper equipment. Additional thousands were made homeless as the country enters the winter.
Tectonic setting
Afghanistan is situated within the broad and complex zone of collision between the Arabian Plate, the Indian Plate, and the Eurasian Plate. The western part of the country is subdivided into the North Afghan Platform to the north and a series of accreted terranes to the south. The North Afghan Platform has remained relatively tectonically stable since the Variscan Orogeny during the Late Palaeozoic, when it became part of Eurasia. To the south there is a collage of continental fragments and magmatic arcs that have been progressively accreted, particularly in the Mesozoic era. The boundary between these two crustal areas is the major right-lateral strike-slip Harirud (or Herat) Fault, which is far less seismically active than the Chaman Fault that runs through the east of the country. To the north of the Harirud Fault, the near parallel Band-e Turkestan Fault does show signs of recent activity, also in a right-lateral sense.
The seismicity of Afghanistan is attributed to the complex and active tectonic interactions between the Arabian, Eurasian, and Indian plates. Within of the 7 October earthquakes epicenters, there have been seven magnitude 6.0 or greater earthquakes with epicenters in Iran. These include a 7.3 earthquake in May 1997 and a 7.1 earthquake in 1979. In June 2022, eastern Afghanistan was affected by an earthquake that killed over 1,000 people.
Earthquakes
The first event, measuring a magnitude of 6.3, struck at 11:11 AFT (06:41 UTC). A magnitude 5.5 aftershock occurred eight minutes later. Another magnitude 6.3 event struck at 11:42 AFT (07:12 UTC), followed by a magnitude 5.9 aftershock. On 11 October, a third 6.3 earthquake occurred within the same area and another event of the same magnitude occurring on 15 October. While the United States Geological Survey estimated the fourth event had a magnitude of 6.3. The United States Geological Survey said all four earthquakes were the result of shallow thrust faulting. The fault plane solution indicate a rupture source striking east–west with a north or south dip. On October 28, a 5.0 event hit the area, followed by a 4.8 aftershock the next day.
According to seismologists, these earthquakes had epicenters between the Siakhubulak Fault in the north and Herat Fault in the south. According to satellite data from Sentinel-1A, an area measuring by and extending east–west around the location of these earthquakes was uplifted. Meanwhile the satellite detected subsidence in a small area east of the uplifted zone. The seismologists added that the ground deformation was diffuse and inferred the earthquakes were associated with a blind thrust fault. The fault responsible is likely a structure located between the Herat and Siakhubulak faults.
Italy's National Institute of Geophysics and Volcanology released two possible finite fault models for the second large earthquake. In both models, no slip occurred at the top depth of the model. The first model is a north-dipping, east-southeast–west-northwest striking thrust fault. The rupture mechanism was reverse-faulting with a small right-lateral component, initiating at a depth of . In this model, the maximum slip was at depth and immediately east of the hypocenter. Slip of or greater was observed east and west of the hypocenter although the largest slip (>) was observed to the east.