PALU, Indonesia — The sun was starting to dip, turning the sky a brilliant orange hue. Then the ground shook.
It felt more powerful than those in recent memory.
In Palu, they thought they knew all the risks. Indonesians live along one of the world’s most active fault lines — and Palu, in particular, sits atop a gradually slipping plate.
But a tsunami surge through the narrow bay and mud flows burying villages and residents were never among their fears until last month.
Indonesia has spent millions on disaster preparedness since a massive earthquake and tsunami in December 2004.
But this time, everything that was meant to work did not.
A warning system based on computer simulations failed to gauge the chances of a huge tsunami, estimating waves far smaller. Tsunami detection buoys were not functioning or in the wrong location.
Even the sensors that did work fooled scientists to think the worst was over — even while a third deadly tsunami surge was bearing down on Palu.
Now, the devastation in the central region of Sulawesi island will add a new chapter to the understandings of how shifts on the ocean floor can spawn deadly walls of water and can turn firm soil into muddy rivers that entombed hundreds of people.
Scientists say the back-to-back disasters — which have killed nearly 1,800 people, with more than 5,000 feared missing — were among the most complicated they had seen. It began Sept. 28 just after 6 p.m. with a magnitude 7.5 slip-strike quake, where the earth moves side by side.
Normally, quakes that thrust up the seabed prompt a tsunami watch — such as the giant dome of seawater that crashed across Asia’s Indian Ocean region in 2004, killing almost 230,000 people, including tens of thousands in Indonesia.
The Sept. 28 slip-strike, located about 48 miles from Palu, was not something that experts usually predict would prompt a powerful tsunami.
“It was not a straightforward event,” said Adam Switzer, principal investigator at the Singapore-based Earth Observatory. “This earthquake was beyond the bounds of the warning systems” available.
The immediate analysis also was compromised by problems with Indonesia’s network of tsunami-detection buoys, which detect changes in the sea even deep below the surface. These work far more accurately than tidal sensors, confirming the height of a wave before it appears.
Dozens of buoys in the Java Sea were broken, damaged or stolen. Others that functioned were not at the right spot, and estimated the tsunami risk inaccurately — predicting the waves would probably be two feet, or nine feet in an absolute worst-case scenario.
Instead, the tsunami sent water as high as 20 feet in some places.
With the buoys, “a satellite will immediately receive information that the tsunami has been detected, and we will know which areas would be hit and the height of the waves,” said Sutopo Purwo Nugroho, spokesman for Indonesia’s disaster management agency.
“But,” he added, “the buoys have not operated” fully since 2012.
Soon after 6 p.m., water in Palu’s clear bay started receding, forming rings in the ocean. Miranti Malewa, 35, was driving by the coast to evening prayers. But when she stepped on the pedal to accelerate, her car didn’t seem to move forward.
“I felt like we were a marble in a bowl,” she recalled, “going backward and forwards.”
Across the road, she saw floors of the Mercure Hotel collapse.
“There was a little voice in my head that said, ‘Maybe it is a tsunami,’ ” she said.
Though earthquakes were common in Palu, she could not remember a tsunami following any of them. Then she saw a horse that had broken free of a carriage “running like crazy.” She hit the gas, steering away from the bay.
At 6:10 p.m., the first tsunami surge hit.
The next one came in 2½ minutes, even bigger this time. The final wave rose high above the beachfront, crashing down onto houses and kiosks and dragging hundreds of lives along with it.
Cascading secondary effects were devastating areas farther inland, turning solid ground into unstable liquid mud. Houses and electricity poles appeared to be chasing people as they were carried by the slurry of soil, witnesses said. Entire neighborhoods were obliterated.
It was over. But, for Indonesian officials, the problems were just beginning.
A series of missteps — including logistical difficulties that slowed the initial emergency response and overwhelmed local officials who all but disappeared — have raised questions about how Indonesia is prepared for the next inevitable quake-triggered disaster.
Indonesia’s budget for disaster monitoring has fallen in recent years to $46 million from $131 million. The disaster director at Indonesia’s geophysics agency, Rahmat Triyono, said the cuts have left his a “very limited” tsunami detection system, relying on simulations rather than the more accurate buoys.
Retno Budiharto of the National Search and Rescue Agency found himself staggered by the challenges when teams arrived in Palu the day after the disaster. Buildings and hotels had flattened “like a pancake,” he said.
There was no fuel, electricity or running water. Crews attempted to free a woman from the rubble of a restaurant that had pinned her leg.
“We tried to open up a space for her, but if we forced it, the entire floor could come down on us,” he said. “Our equipment couldn’t do the trick.”
Her leg was amputated to free her.
Days passed. Aid convoys were finding it hard to make their way through the badly damaged roads. A crack in the runway at Palu’s airfield left it barely operational, struggling to handle aircraft to evacuate people and bring supplies.
The desperate people of Palu also found that they could not turn to their local leaders.
Palu’s mayor, Hidayat, survived but has been conspicuously absent from public view since the disaster struck. Like many Indonesians, Hidayat goes by one name.
Also missing is the vice mayor, Sigit Purnomo Syamsuddin, a rock-star-turned-politician who is better known by his stage name Pasha and remains active in his popular band despite his position.
Graffiti scrawled on one wall in Palu asked how the mayor could sleep at night while the city starved. The Washington Post could not reach the mayor or vice mayor for comment.
The mayor’s office, meanwhile, has been a reflection of a government in deep disarray.
On Saturday, more than a week after the disaster, a pile of trash smoldered in the large front lawn, sending a plume of acrid smoke toward dozens of people camped on sun-scorched grass. Donated clothes spilled from torn plastic bags piled next to the office entrance near a partially wrecked police truck.
“He should be doing more,” said Indriani, 43, who was camped with hundreds of others in a park in front of the mayor’s office, among the hundreds of thousands now homeless in the region. “Even if he isn’t helping, at least he could come meet his people.”
Meanwhile, foreign aid agencies were scrambling to book flights and find their way overland to Palu.
But they said only local partners or Indonesian aid groups would be allowed to access the disaster zone. The same rules were put in place after an August quake in Lombok, neighboring the resort island of Bali, that killed more than 460 people.
“It’s very clear that they want Indonesians leading the response and others following and assisting,” Winnie Byanyima, the executive director of Oxfam International, said in an interview with The Post.
She has appealed for the United Nations and other international agencies to be granted greater access to operate in and around Palu.
“The disaster is huge,” she said.
On Friday, Byanyima said, Oxfam received permission for the ministry to send three international staff to Palu, an increase from the one that was originally given access.
The government, Byanyima said, stipulated that food aid needed to be distributed through the Indonesian Red Cross. The ministry could not be reached for comment on Saturday.
A portion of international aid efforts have shifted to Balikpapan, a port city more than 200 miles west of Palu. Supplies will take a roughly 18-hour journey by ship across the Makassar Strait.
Officials say it will take months, if not years, to rebuild the area.
All there is to do, meanwhile, is wait.
“I’ll be here for a while,” said Merita Rore, 48, camped out with other displaced people at a public park. “We’re just trying to be safe.”
Mahtani reported from Hong Kong. Ainur Rohmah in Jakarta contributed to this report.