NORCIA, Italy -- Italian authorities said that more than 15,000 people had sought assistance from Italy’s Civil Protection agency and were being housed in hotels and shelters following Sunday’s quake. Authorities had still been providing housing to 2,000 people displaced by an August earthquake that killed nearly 300 people.

Civil protection officials said Monday that they expected that number to rise, as it didn’t count the many people who slept in vehicles or made other arrangements and were still likely to seek help.

Drones were being used to survey the devastation of Sunday’s magnitude 6.6 quake, CBS News correspondent Seth Doane reports. It was the strongest quake to hit Italy in 36 years.

Get Breaking News Delivered to Your Inbox

In places, landslides closed roads. Buildings at risk of collapse were bulldozed.

The quake caused no deaths or serious injuries, largely because most fragile city centers had already been closed because of previous damage, and many homes had been vacated.

Italian Premier Matteo Renzi said the nation’s “soul is disturbed” by the series of quakes, starting with the deadly Aug. 24 event that killed nearly 300 people, two back-to-back temblors on Oct. 26, and the biggest of them all, the 6.6-magnitude quake that shook people out of bed Sunday morning.

Renzi vowed to rebuild houses, churches and business, saying, “a piece of Italian identity is at stake at this moment.”

Renzi said at a news conference: “We will rebuild everything -- the houses, the churches, the shops. We are dealing (with) marvelous territories, territories of beauty.”

“Feeling the earth collapse beneath your feet is not a metaphorical expression but is what happened this morning, and half of Italy felt this,” he said.

The quake struck another painful blow to the rich artistic heritage of villages that dot the Apennine Mountains.

Seismologists said the shaking came from a series of faults in the Apennines, and they could not rule out more, possibly stronger quakes in the near future.

“It is normal for the Apennines,” said the president of Italy’s National Institute for Geophysics and Vulcanology, Carlo Doglioni. He cited a similar sequence of three events within a period of months in 1703 in the region.

“Probably its every hundred years you get a repeat of a series of earthquakes,” said Michael Steckler, a geophysicist at the Lamont-Doherty Earth Observatory.

“It’s a big earthquake swarm that’s setting off a number of larger, and many, many smaller, earthquakes throughout the area, as the motion of the faults increases and decreases the amount of stress on some of the adjacent parts of the fault,” Steckler continued.

A set of twin quakes on Wednesday forced residents in the town of Muccia to evacuate, Doane reports.

“It’s strange,” Muccia mayor Mario Baroni told CBS News. “But people can’t stay here. It’s all damaged. It’s very dangerous.”