The 1909 Silakhor earthquake occurred in Silakhor plain (in the south of today's Borujerd County

Borujerd County

Borujerd County is a county in Lorestan Province in Iran. The capital of the county is Borujerd. At the 2006 census, the county's population was 320,547, in 82,676 families. The county is subdivided into two districts: the Central District and Oshtorinan District...

), Persia (modern day Iran

Iran

Iran , officially the Islamic Republic of Iran , is a country in Southern and Western Asia. The name "Iran" has been in use natively since the Sassanian era and came into use internationally in 1935, before which the country was known to the Western world as Persia...

) on January 23, 1909. Around 8,000 fatalities were caused directly from the magnitude 7.3 earthquake

Earthquake

An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time...

. An indefinite number of aftershock

Aftershock

An aftershock is a smaller earthquake that occurs after a previous large earthquake, in the same area of the main shock. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock...

s continued for six months after the main shock. The section on this fault ruptured was the same as the main rupture zone of the 2006 Borujerd earthquake.

Background

Occurring on the local Dorood Fault, the tremor caused 40 kilometres (24.9 mi) of visible surface faulting

Geologic fault

In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement along the fractures as a result of earth movement. Large faults within the Earth's crust result from the action of tectonic forces...

 was recorded on the fault.

Damage and casualties

60 villages within the region were either completely destroyed or damaged beyond repair. Casualties were extensive, occurring in 130 individual villages. However, damage was contained within a 40000 square kilometres (15,444.1 sq mi) area. 8,000 were killed in this sector along with several thousand animals.

Damage was worst within the epicentral area (Silakhor Valley) and surrounding valleys populated by domestic tribes. Signs of ground failure and landslide

Landslide

A landslide or landslip is a geological phenomenon which includes a wide range of ground movement, such as rockfalls, deep failure of slopes and shallow debris flows, which can occur in offshore, coastal and onshore environments...

s was evident for another 20-30 km southeast of the epicenter.