A magnitude 3.3 earthquake struck southeastern Tehran on Tuesday near Ghiamdasht county raising fears that the Iranian capital might be prone to stronger quakes.

Mehdi Zare, a faculty member of the International Research Institute of Seismology and Earthquake Engineering, told Roydad 24 that Tuesday’s earthquake near Eyvanki fault indicates that it is still active, causing minor quakes.

“This fault zone, whose northwestern end reaches the 15th district of Tehran, has an earthquake-generating capacity of up to magnitude 7.5,” he warned. At least one and a half million people would die in case of an earthquake with a magnitude of 7 in Tehran, say experts.

The Tuesday morning quake was about 20 km southwest of Tehran and at a depth of 10 km (6.21 miles), the Volcano Discovery said.

Iran is crisscrossed by major geological fault lines and is one of the most earthquake-prone countries in the world because it is located where the Arabian, Indian, and Eurasian tectonic plates meet.

Iran has a history of massive earthquakes in recent decades, with some killing up to tens of thousands of people and causing billions of dollars in damages, such as the magnitude 6.6 quake in Kerman province in 2003 that killed 31,000 and flattened the ancient city of Bam.

Iranian officials have warned that there are 166,000 hectares of worn-out structures across the country which means a major earthquake like in Turkey and Syria could result in “hundreds of thousands of deaths.”