An earthquake of 7.8-magnitude hit the south-eastern city of Khash, in Iran. This was one of the strongest earthquake to hit Iran in more than 50 years. Since the city of Khash was the epicentre of the earthquake, is very close to Pakistan, the earthquake was strongly felt there.
Outer crust of Earth is broken up into big or small pieces called plates that float on the soft mantle. Earthquakes happen when something causes these plates to move majorly from their position. Therefore, earthquakes always happen along plate boundaries. In this particular case, the Arabian Plate slid under the huge Eurasian Plate.
Thankfully, the area where earthquake struck is remote, there have not been many casualities but the tremors were felt as far as Indian capital of Delhi, and in several Gulf cities.