The power of Indonesian tsunamis surprised the researchers

The appearance of the Indonesian tsunami along with the destructive power it carries is completely beyond the expectations of the researchers.

Scientists expressed surprise at the strength of the tsunami that devastated Palu, Indonesia, last weekend, according to the New York Times. They thought that the earthquake that had appeared earlier was hard to bring with such destructive power waves.

Map of the US Geological Survey.

"We anticipate earthquakes that can cause tsunamis, but not so great," said Jason Patton, a geophysicist who works for Temblor consulting firm and lecturer at Humboldt University in California. "When these kinds of events happen, we often discover many things that have never been observed before."

The 7.5-magnitude earthquake appeared on the evening of September 28, shaking up along the coast of Sulawesi island, about 80km north of Palu. According to some witnesses, within 30 minutes, waves of up to 6 meters hit the shore, destroying many buildings, smashing vehicles and killing hundreds of people in the city.

The high death toll may reflect the current shortage of Indonesia's advanced tsunami detection and warning system, according to experts. Other communities on Sulawesi Island, including Donggala City, were also devastated by the tsunami, but there was little information on the extent of damage or the number of deaths outside Palu.

The tsunami disaster is often the result of earthquakes when large parts of the Earth's crust deform , shifting vertically along the fault. This process abruptly displaces a huge amount of water, creating a wave of high-speed movement along the ocean basin and causing damage in the way the earthquake forms thousands of kilometers.

A bridge destroyed by earthquakes and tsunamis in Palu, Indonesia.(Photo: Reuters).

The 2004 Indian Ocean tsunami created waves of more than 30 meters and killed nearly 250,000 people from Indonesia to South Africa, resulting from a 9.1-magnitude earthquake in Sumatra. In contrast, the fault on September 28 belongs to a horizontal fault fracture, in which the Earth's crust mainly moves horizontally. This type of displacement usually does not cause tsunamis.

But in certain situations, tsunamis can still happen. The horizontal slip fracture may be accompanied by a longitudinal movement causing disturbed seawater, or an estimated 113 km of fault zone that can run through an area, where the seabed is raised or lowered, so when The fault is shaken during the earthquake, it pushes the sea water forward.

Residents of Palu who returned to the house were destroyed on September 29, trying to collect what was still usable.(Photo: AFP).

Another possibility is that tsunamis are indirectly produced. Vibrant shaking in an earthquake can cause landslides in the sea, causing seawater to shift and create waves. Such events are not uncommon, such as tsunamis in an earthquake of 9.2 degrees in Alaska in 1964. Dr. Patton said the combination of many factors could lead to tsunamis. " We will not know what caused the disaster until we studied the sea floor," said Dr. Patton.

Tsunamis can be affected by Palu's position at the end of the narrow bay. The coastal line and the bay shape contribute to concentrating the energy and directing it to the bay, increasing the height of the wave as it approaches the shore. For example, Crescent City, California, USA suffered more than 30 tsunamis, including a tsunami after the Alaska earthquake of 1964, due to the area's seabed shape as well as its location and terrain. city. Regardless of the real cause, the 7.5 degree earthquake is not expected to cause a ceiling wave on a large scale but concentrated in one area.

Earthquake victims gathered in one place after leaving Palu.(Photo: AFP).

Because tsunamis arise too close to Palu, people rarely have time to escape. The government's tsunami warning was lifted after a half-hour earthquake. Currently, Indonesia only uses seismologists, global positioning systems and hydrographs to detect tsunamis that are limited in accuracy, according to Louise Comfort, a professor at the University of Pittsburgh. Comfort is participating in a project that brings a new tsunami sensor to Indonesia.

In the United States, the National Oceanic and Atmospheric Administration (NOAA) has a complex network of 39 sensors on the sea floor, which can detect extremely small pressure changes indicating the path of the tsunami. The data is then transmitted via satellite for analysis and warning if needed. Dr. Comfort said Indonesia also has a similar network of 22 sensors but is no longer used due to difficult maintenance or damage. Dr. Comfort's project helps bring the new system to Indonesia, uses sea contact and avoids the use of floats that can be hit by ships.

"It is heartbreaking when you know the technology is available. Indonesia is located in the Fire Ring. Tsunami will also appear , " Dr. Comfort stressed.