For many generations, Bedouin people living in the Abu Dabbab area on the Egyptian Red Sea coast have heard distinct noises–like the rumbling of a quarry blast or cannon shot–accompanying small earthquakes in the region. Now, a new study published in the Bulletin of the Seismological Society of America offers an explanation for this uniquely noisy seismic event.
Seismic activity in the area of the Egyptian seaside resort Abu Dabbab may be caused by an active fault that lays below a 10-kilometer thick block of old, now rigid igneous rock. The surface of the block slides along the active parts of the fault, lubricated by fluids from the Red Sea that have penetrated the crust, according to Sami El Khrepy of King Saud University in Riyadh, Saudi Arabia and colleagues.
The researchers think this large and rigid block of igneous crust acts as a sort of broadcaster, allowing the full sounds of seismic movement to rise through the rock with little weakening of the acoustic signal. The high-frequency sounds of earthquakes can then be heard by humans at the surface.
Earlier studies had suggested that the Abu Dabbab earthquakes were caused by magma rising through the crust, but the new report “found that a volcanic origin of the seismicity is unlikely, and the area is not expected to be subjected to volcanic hazard,” said El Khrepy.
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