Arabian Sea Earthquake Risk Predictions Were Underestimated
May 13, 2013

Arabian Sea Earthquake Risk Predictions Were Underestimated

Lee Rannals for — Your Universe Online

Researchers writing in the journal Geophysical Research Letters say the western Indian Ocean earthquake and tsunami hazard potential is greater than scientists had originally predicted.

Scientists from the University of Southampton say the risk from undersea earthquakes and tsunami beneath the Arabian Sea at the Makran subduction zone was underestimated. They said their findings highlight the need for further investigation of pre-historic earthquakes and should be fed into hazard assessment and planning for the area.

"Thermal modeling suggests that the potential earthquake rupture zone extends a long way northward, to a width of up to 350 kilometers which is unusually wide relative to most other subduction zones," says Gemma Smith, lead author and PhD student at University of Southampton School of Ocean and Earth Science, which is based at NOCS.

The team found that the thickness of the sediment on the subducting plate could be a contributing factor to the magnitude of an earthquake and tsunami there. They said the area has the potential to experience an earthquake similar in magnitude to the 2004 Sumatra quake.

"If the sediments between the plates are too weak then they might not be strong enough to allow the strain between the two plates to build up," says Smith. "But here we see much thicker sediments than usual, which means the deeper sediments will be more compressed and warmer. The heat and pressure make the sediments stronger. This results in the shallowest part of the subduction zone fault being potentially capable of slipping during an earthquake."

She said these factors mean the Makran subduction zone is potentially capable of producing major earthquakes, up to magnitude 8.7 to 9.2.

"Past assumptions may have significantly underestimated the earthquake and tsunami hazard in this region," Smith added.

This area has shown little earthquake activity since a magnitude 8.1 earthquake in 1945 and magnitude 7.3 in 1947. Scientists thought that due to the low seismicity and limited recorded historic earthquakes, the area was incapable of generating major earthquakes. However, the maps Smith and colleagues created showed larger fault rupture zones than thought.

Despite previous thoughts, the area isn't completely unprotected. Science Applications International Corporation said in 2010 that it delivered three Tsunami Buoy systems and long-term maintenance services to an area near the Makran subduction zone. These systems are part of a larger network of tsunami buoy systems that provide the entire region with critical data to assess the magnitude of tsunamis generated in the Indian Ocean.