A sequence of at least 36 earthquakes within a few hours hit the southern Iranian province of Hormozgan on Wednesday, sending tremors across the Persian Gulf that were felt in Dubai, Bahrain and Qatar. According to the Iranian Seismological Center, the strongest of these quakes occurred at 6.06 UTC near the coastal town of Bandar Chark, reaching a local magnitude of 5.2. Manually revisions of the United States Geological Survey (USGS) and the German Geoforschungszentrum Potsdam determined a moment magnitude of 5.5. At least nine other quakes were stronger than magnitude 4.

While the effect of the shaking was limited to slight building trembling in Dubai and other Arabian cities, panic and fleeing people resulted in nearby Iranian places, including the popular tourist island Kish. Due to panic, at least four people were injured while rushing out of buildings. However, no significant building damage has been observed by local authorities yet. Only some cracks in older buildings developed, as the News Agency ISNA reported.

Iran ShakeMap
Intensity calculation for the strongest earthquake (Mw5.5) of the sequence

The northern coast of the Persian Gulf is part of a continental convergence zone. The Arabian Plate in the south moves north towards the Iranian block of the Eurasian Plate. Due to this collision, the Zagros mountain belt formed and marks one of the most seismically active areas in western Asia. Several large earthquakes happened in previous years, including the devastating Mw7.3 Kermanshah earthquake in November 2017, where 629 people were killed and 800,000 others left homeless.

Following the tectonic setting, thrust faulting (reverse) earthquakes are the most common type in this area. Moment tensor analysis performed by GFZ Potsdam also shows a reverse mechanism for the M5.5 mainshock but also indicating some more complex rupture behaviour. At least three M4+ earthquakes happened just minutes before the mainshock. Such a high temporal density of events is not typical for this region and might indicate the presence of fluids in the crust that lead to a cascade-like sequence of smaller ruptures. Overlapping of these events and possible step over on neighboring faults might have attributed to the complex signal.

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Since the earthquake sequence is still ongoing with fresh earthquakes up to magnitude 3.9 in the evening, more seismicity is likely to follow over the past few days. The possibility of an even larger cannot be ruled out but such an event is not likely. Nevertheless, for already cracked buildings and other old structures, persistant shaking might be dangerous, especially from those quakes that occur right beneath settlements on Kish and the mainland of Hormozgan. Therefore, affected residents should not enter these buildings as long as the sequence is ongoing to avoid dangerous situations.