Scientists were surprised by the magnitude of the tsunami that devastated the Indonesian city of Palu on Friday, saying an earthquake like the one before would not necessarily create destructive waves.
"We expected it to trigger a tsunami" It just is not that big, "said Jason Patton, a geophysicist who works for a consulting firm, Temblor, and teaches at Humboldt State University in California.  But he added, "When such events happen, we will sooner discover things that we have not observed before.
The magnitude 7.5 earthquake that occurred in the early evening was on the coast of Sulawesi about 50 miles north of Palu, and shortly thereafter ̵
High casualty may also reflect Indonesia's lack of advanced tsunami systems (19659006) Other communities in Sulawesi, including Donggala City, were also displaced by the Tsunami hit, although there are few details yet about the destruction or fatalities outside of Palu.
Catastrophic tsunamis are often the result of so-called Megathrush earthquakes, in which large parts of the earth's crust are deformed and move vertically along a fault This suddenly displaces enormous amounts of water and creates waves that travel at high speed through ocean basins Thousands of miles from the origin of the quake cause destruction.
The Indonesian Ocean tsunami in 2004, which had waves as high as 100 feet, killing nearly a quarter of a million people from Indonesia to South Africa resulting from a magnitude 9.1 megathrust earthquake in Sumatra.
In contrast, the mistake that broke on Friday was a so-called strike misstep, in which the earth's movement is largely horizontal. This type of movement would not normally cause a tsunami.
But under certain circumstances it may. Patton said.
A strike-slip fault could have some vertical movement that could displace seawater. Or the fault's rupture zone, which in this case was estimated to be about 70 miles, can pass through an area where the seabed rises or falls, so that if the error shifts during the quake, it pushes seawater ahead.
Another possibility is that the tsunami was created indirectly. The violent tremors during the quake could have caused underwater erosion that displaced water and caused waves. Such events are not unusual; some of these occurred, for example, during the  1964 9.2-magnitude Alaska earthquake.
Dr. Patton said a combination of factors could have contributed to the tsunami. Seabed research will be crucial to understanding the event. "We will not know what caused that to happen," he said.
The tsunami could also have been influenced by Palu's location at the end of a narrow bay. The coastline and contours of the seafloor could have focused the wave energy and led up the bay, which would increase the wave height when approaching the coast.
Such effects have been observed earlier. Crescent City, California, has been hit by more than 30 tsunamis, including one after the 1964 Alaska quake that killed 11 people due to the contours of the seabed in the area and the topography and location of the city
Emergence of the waves would not be expected to cause a quake of magnitude 7.5 an ocean-wide event, but rather a more localized, as it was the case on Friday.
With the tsunami that came so close to Palu, there was little time for people to escape. A tsunami warning was issued by the government and lifted about half an hour after the quake, apparently after the tsunami hit Palu.
Indonesia currently uses only seismographs, GPS systems, and tidal gauges to detect tsunamis that are limited in effectiveness, said Louise Comfort, a professor at the University of Pittsburgh Graduate School. She was involved in a project to introduce new tsunami sensors in Indonesia.
In the United States, the National Oceanic and Atmospheric Administration has a sophisticated network of 39 seabed sensors that can detect extremely small pressure changes during a tsunami. The data is then forwarded via satellite and analyzed, and a warning is issued if necessary.
Dr. Comfort said that Indonesia has a similar network of 22 sensors, which are no longer used because they have not been serviced or damaged.
The project she is working on would bring Indonesia a new underwater powered communication system to avoid the use of surface buoys that could be damaged or damaged by ships.
Dr. Comfort said she had discussed the project with three Indonesian government agencies. Plans to install a prototype system in West Sumatra have been postponed this month. "They could not find a way to work together," she said.
"It's heartbreaking to know that the technology is there," she added. "Indonesia is at the ring of fire – tsunamis will happen again."