A powerful 7.3 magnitude earthquake that struck the Iraq-Iran border region killed over 530 people and left 8,000 injured in both countries, sent people fleeing their homes into the night and was felt as far west as the Mediterranean coast, authorities reported on Monday.

Iran straddles the seam between the Eurasian and Arabian tectonic plates and is therefore prone to frequent and deadly tremors. A magnitude 6.6 quake on Dec. 26, 2003, devastated the historic city of Bam, 1,000 km southeast of Tehran, killing about 31,000 people.

The last major casualty earthquake to hit Iran before Sunday’s deadly quake struck in East Azerbaijan province in August 2012, killing over 300 people. That earthquake was a strike-slip earthquake, which is common along the active fault underlying Iran.

The Smithsonian describes strike-slip earthquakes: “When two pieces of Earth, with stress built up from grinding against each other for many years, suddenly slip in a side-by-side motion and travel in the “along strike” direction. The lurch sends waves traveling through the surrounding rocks which can cause the earth to jolt and roll at the surface.”

The Dead Sea Transform, which runs under Israel and Jordan is also a strike-slip fault between the Africa and Arabia plates. According to the U.S. Geological Survey the strike-slip movement along this plate boundary “has been a significant hazard in the densely populated Levant region (eastern Mediterranean). For example, the November 1759 Near East earthquake is thought to have killed somewhere between 2,000-20,000 people.”

Sunday’s earthquake

The Iranian seismological centre registered around 118 aftershocks since the primary event and said more were expected. The head of Iranian Red Crescent said more than 70,000 people were in need of emergency shelter.

The magnitude 7.3 quake was centered 19 miles (31 kilometers) outside the eastern Iraqi city of Halabja, according to the most recent measurements from the U.S. Geological Survey. It struck at a depth of 23.2 kilometers (14.4 miles), a shallow depth that can have broader damage. Magnitude 7 earthquakes on their own are capable of widespread, heavy damage, which was made worse in Iran as many houses in rural areas are made of mud bricks that can crumble easily in a quake

The Iraqi city of Halabja, closest to the epicenter, is notorious for the 1988 chemical attack in which Saddam Hussein’s regime killed some 5,000 people with mustard gas — the deadliest chemical weapons attack ever against civilians.

Iraqi seismologist Abdul-Karim Abdullah Taqi, who runs the earthquake monitoring group at the state-run Meteorological Department, said the main reason for the lower casualty figure in Iraq was the angle and the direction of the fault line in this particular quake, as well as the nature of the Iraqi geological formations that could better absorb the shocks.