A new study led by the Institut de Ciències del Mar (ICM) has found that strike-slip faults have more potential to generate coastal tsunamis than previously thought.
New data from the Averroes marine fault in the Alboran Sea show that the seismic zone is overdue for a large earthquake (M7.0) which, in turn, would trigger a 6-meter-high tsunami that would partially destroy and flood the Andalusian coasts.
“These giant waves can pose a threat to coastal populations, damage marine and land-based infrastructure, and cause an economic and environmental crisis. These results will be essential to improve planning measures to mitigate the impact of a possible tsunami,” explains the ICM geologist Ferran Estrada.
Tsunamis are triggered by sudden displacements of the seafloor and are usually caused by seismic activity on normal and reverse faults. However, strike-slip faults, which separate laterally moving blocks, are usually ruled out as tsunami triggers.
“The Averroes fault has, at its northwest end, a vertical jump of up to 5.4 meters capable of generating a strong magnitude-7 earthquake. We have studied the activity of the fault over the last 124,000 years and, according to historical records, the last earthquake generated by this fracture was in 365 AD,” adds Estrada.
Thanks to a mathematical model of the deformation of the sea floor, the research team was able to calculate the behaviour of the water masses in the Alboran Sea in the case of a new seismic episode on the fault.
According to this simulation of possible scenarios, tsunami waves would propagate in two main branches and reach and inundate densely populated sectors of the southern coast of Spain and northern Morocco.
These waves could be up to six meters high and would take between 21 and 35 minutes to reach the coast.
“These are episodes that are too fast for current early warning systems to operate successfully. These findings indicate that the tsunami-generating potential of strike-slip faults should be taken into account for the re-evaluation of tsunami early warning systems,” concludes the ICM researcher.
Here the abstract of the Nature’s paper:
“Tsunamis are triggered by sudden seafloor displacements, and usually originate from seismic activity at faults. Nevertheless, strike-slip faults are usually disregarded as major triggers, as they are thought to be capable of generating only moderate seafloor deformation; accordingly, the tsunamigenic potential of the vertical throw at the tips of strike-slip faults is not thought to be significant.
“We found the active dextral NW–SE Averroes Fault in the central Alboran Sea (westernmost Mediterranean) has a historical vertical throw of up to 5.4 m at its northwestern tip corresponding to an earthquake of Mw 7.0.
“We modelled the tsunamigenic potential of this seafloor deformation by Tsunami-HySEA software using the Coulomb 3.3 code. Waves propagating on two main branches reach highly populated sectors of the Iberian coast with maximum arrival heights of 6 m within 21 and 35 min, which is too quick for current early-warning systems to operate successfully.
“These findings suggest that the tsunamigenic potential of strike-slip faults is more important than previously thought, and should be taken into account for the re-evaluation of tsunami early-warning systems.” [Nature, ICM, CSIC]
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