As far back as the 5th century BC the ancient Greek historian Thucydides theorised that tsunamis were caused by earthquakes. A millennium and a half later, we take a look at the science behind tsunami prediction.
Tsunamis are a real threat to millions of people worldwide. In Southeast Asia especially we know the devastation they can wreak after the Boxing Day tsunami in 2004 which claimed nearly a quarter of a million lives.
In September 2018, a tsunami struck Sulawesi, Indonesia. The Indonesian government estimates it left 2,000 dead, 680 lost, 70,000 homeless and 11,000 injured with an economic cost of US$530 million.
With the potential human and material cost of these natural disasters being so high, being able to predict tsunamis becomes a major imperative.
How Tsunamis Are Predicted
Scientists predict tsunamis by assessing data, so how and what data is acquired is crucial. Seismic readings are usually the first sign of an impending tsunami. Seismic waves travel much faster than water, meaning they can be recorded by seismograph stations some minutes before the tsunami hits.
Then there are Deep-ocean Assessment and Reporting of Tsunamis (DART) systems. They measure minute changes in water pressure on the ocean floor through a bottom pressure recorder attached by cable to a buoy. The buoy transmits the data to satellites which relays it to the tsunami warning centre.
The United States has spread DART systems around the Pacific Ocean, Atlantic Ocean and Caribbean Sea to act as an early warning system. In Southeast Asia both Thailand and Indonesia use DART buoys as part of their tsunami warning systems.
Similarly, tide gauge stations measure the change in sea level around coastal regions and transmit their data to a nearby science agency.
Using a combination of these, along with historical data and computer simulations, scientists try their best to predict mother nature’s violent outbursts.
Not Without Error
Tsunami prediction is not without its pitfalls, however. It can prove tricky as there are many variables to consider. Not all earthquakes cause tsunamis and the need to minimise false alarms is paramount. Basically, mistakes can happen.
For instance, the Japanese government was able to get a localised tsunami warning out three minutes after the earthquake in 2011. Unfortunately, their forecast for the size of the tsunami was off by a huge margin, a three-metre-plus tsunami had been predicted. The Japan Meteorological Agency had to apologise and rethink how they categorise tsunamis.
Besides human error, technology is also an issue. It turns out there is some controversy over the reliability of DART buoys. The Americans found that within a year of being in the field only 60% were estimated to be operational.
Last year up to 80% of Thailand’s tsunami warning system needed maintenance work, according to a Thai official. Meanwhile in Indonesia 22 new DART buoys were deployed in the years after the 2004 tsunami, all of which have since fallen into disrepair and are non-operational.
Although it is true that there are problems with methodology and technology, it is also true that a lot of progress has been made in the last 14 years in terms of awareness and preparedness for tsunamis. We should make sure that progress continues.
As Kirsi Madi, director of the United Nations International Strategy for Disaster Reduction said, ‘Education remains the number one preventive measure that can save more lives in order to leave no one behind in the future.’