Then last year, scientists discovered two male skeletons riddled with bone fractures, evidence that during a brief reprieve from the eruption, a strong earthquake tumbled buildings and crushed people in their homes.

The team spent months piecing together the story of these victims, two men over the age of 55 whose injuries bore an eerie resemblance to modern-day victims of building collapses during earthquakes. Drawing on expertise in volcanology, anthropology and archaeoseismology, researchers conclude in the journal Frontiers in Earth Science that the men probably survived the first phase of the eruption and were sheltering in a house when a wall fell on them, toppled by a strong earthquake.

The study is unusual because it drew on the expertise of scientists from so many fields. Raffaello Cioni, a volcanologist at the University of Florence who was not involved in the work, called the analysis “really accurate and convincing.”

For centuries, Pompeii has been a source of grim fascination to scientists and the general public. A historical account of the eruption by Pliny the Younger, a lawyer and author, describes tremors that shook the ground before and during the eruption. But deciphering a clear signature of a quake has been difficult since so many destructive forces chaotically overlapped.

“This is a very complex task, to recognize the effects of the earthquake during an eruption, because both phenomena can happen in succession, or concurrently,” said Domenico Sparice, a volcanologist at the Vesuvius Observatory in Naples, who led the work. “It is like a jigsaw puzzle, in which all the pieces must fit together.”

The eruption of Mount Vesuvius unfolded in phases, beginning in the late morning. Around 1 p.m., the volcano began spewing out gas, ash and rocks in an eruption column that extended 18 miles high, creating a hail of pumice stones that buried the city and collapsed roofs, triggering a first wave of death. Those who survived this first phase may have tried to escape on foot, walking on the layer of pumice stones, using branches as walking sticks. But a scorching “pyroclastic flow” — a fast-moving current of ash, gas and rock fragments — killed survivors, likely suffocating them.

Pliny the Younger lived through the eruption as a teenager in Misenum, about 18 miles west of Vesuvius, and described earthquakes the night after the eruption began as “so intense that everything seemed not only to be shaken but overturning.” He also recorded a quake at daybreak — which shook the ground so much that chariots that had been wedged in place with stones were jarred out of place.

But scientists had not discovered direct evidence of earthquakes until they found walls that failed in ways inconsistent with volcanic explanations. Then, they found the skeletons. The first individual’s body was riddled with fractures to the ribs, skull and pelvis. The second individual’s legs were buried under a wall fragment, but he was also huddled on his left side with a hand protecting his head. Scientists think he could have been trying to shield himself.

The new find adds detail to the horror that unfolded early morning on the second day of the eruption, after most of the magma had erupted. A caldera formed when part of the volcano collapsed, causing a dangerous second phase of the eruption and an earthquake, Cioni said. The new evidence raises the possibility that earthquakes could have added to the hazard, as the ground shaking stressed roofs laden with pumice rocks.

Gianni Gallello, a distinguished researcher at the University of Valencia who specializes in using chemistry to understand the ancient past, said the study introduces an intriguing variable to the hazards that day in Pompeii that will add to the complex puzzle of reconstructing this tragic event. But he said it remains a question whether these men died from the wall collapse or were buried after they had died from another cause.

“In science, there is never an end. We are continuously improving and adding new information,” Gallello said. “This is the never-ending story.”