Tsunami risk higher than expected in Los Angeles, Istanbul

A new study has revealed that the risk of occurrence of destructive tsunami is higher in places such as Kingston, Istanbul, and Los Angeles.

Geologists studying the Haiti earthquake have said that like Haiti's capital, these cities too lie near the coast and are near an active geologic feature called a strike-slip fault where two tectonic plates slide past each other like two hands rubbing against each other.

This latest research has suggested that even a moderate earthquake on a strike-slip fault could generate tsunamis through submarine landslides, raising the overall tsunami risk in these places.

"The scary part about this is that you do not need a large earthquake to trigger a large tsunami," said Matt Hornbach, research associate at the University of Texas.

"Organisations that issue tsunami warnings usually look for large earthquakes on thrust faults. But, according to our study, a moderate earthquake on a strike-slip fault could cause an alarm too," said Hornbach.

Within minutes after the magnitude 7 earthquake struck Haiti, a series of tsunami waves, some as high as 9 feet (3 metres), crashed into parts of the shoreline.

A few weeks later, a team of scientists from the US and Haiti conducted geological field surveys of sites on and offshore near the earthquake's epicentre.

The scientists determined that the tsunami was generated primarily by weak sediment at the shore that collapsed and slid along the seafloor, displacing the overlying water.

Combined with newly discovered evidence of historic tsunamis, the survey revealed that a third of all tsunamis in the area are generated in this way.

"We found that tsunamis around Haiti are about 10 times more likely to be generated in this way than we would have expected," said Hornbach.

The findings were published in the journal Nature Geoscience.