LIMA, Peru (AP) -- The earthquake all but flattened colonial Lima, the shaking so violent that people tossed to the ground couldn't get back up. Minutes later, a 50-foot (15-meter) wall of Pacific Ocean crashed into the adjacent port of Callao, killing all but 200 of its 5,000 inhabitants. Bodies washed ashore for weeks.
Plenty of earthquakes have shaken Peru's capital in the 266 years since that fateful night of Oct. 28, 1746, though none with anything near the violence.
The relatively long "seismic silence" means that Lima, set astride one of the most volatile ruptures in the Earth's crust, is increasingly at risk of being hammered by a one-two, quake-tsunami punch as calamitous as what devastated Japan last year and traumatized Santiago, Chile, and its nearby coast a year earlier, seismologists say.
Yet this city of 9 million people is sorely unprepared. From densely clustered, unstable housing to a dearth of first-responders, its acute vulnerability is unmatched regionally. Peru's National Civil Defense Institute forecasts up to 50,000 dead, 686,000 injured and 200,000 homes destroyed if Lima is hit by a magnitude-8.0 quake.
"In South America, it is the most at risk," said architect Jose Sato, director of the Center for Disaster Study and Prevention, or PREDES, a non-governmental group financed by the charity Oxfam that is working on reducing Lima's quake vulnerability.
Lima is home to a third of Peru's population, 70 percent of its industry, 85 percent of its financial sector, its entire central government and the bulk of international commerce.
"A quake similar to what happened in Santiago would break the country economically," said Gabriel Prado, Lima's top official for quake preparedness. That quake had a magnitude of 8.8.
Quakes are frequent in Peru, with about 170 felt by people annually, said Hernando Tavera, director of seismology at the country's Geophysical Institute. A big one is due, and the chances of it striking increase daily, he said. The same collision of tectonic plates responsible for the most powerful quake ever recorded, a magnitude-9.5 quake that hit Chile in 1960, occurs just off Lima's coast, where about 3 inches of oceanic crust slides annually beneath the continent.
A 7.5-magnitude quake in 1974 a day's drive from Lima in the Cordillera Blanca range killed about 70,000 people as landslides buried villages. Seventy-eight people died in the capital. In 2007, a 7.9-magnitude quake struck even closer, killing 596 people in the south-central coastal city of Pisco.
A shallow, direct hit is the big danger.
More than two in five Lima residents live either in rickety structures built on unstable, sandy soil and wetlands, which amplify a quake's destructive power, or in hillside settlements that sprang up over a generation as people fled conflict and poverty in Peru's interior. Thousands are built of colonial-era adobe.
Most quake-prone countries have rigorous building codes to resist seismic events. In Chile, if engineers and builders don't adhere to them they can face prison. Not so in Peru.
"People are building with adobe just as they did in the 17th century," said Carlos Zavala, director of Lima's Japanese-Peruvian Center for Seismic Investigation and Disaster Mitigation.
Environmental and human-made perils compound the danger.
Situated in a coastal desert, Lima gets its water from a single river, the Rimac, which a landslide could easily block. That risk is compounded by a containment pond full of toxic heavy metals from an old mine that could rupture and contaminate the Rimac, said Agustin Gonzalez, a PREDES official advising Lima's government.
Most of Lima's food supply arrives via a two-lane highway that parallels the river, another potential chokepoint.
Lima's airport and seaport, the key entry points for international aid, are also vulnerable. Both are in Callao, which seismologists expect to be scoured by a 20-foot (6-meter) tsunami if a big quake is centered offshore, the most likely scenario.
Mayor Susana Villaran's administration is Lima's first to organize a quake-response and disaster-mitigation plan. A February 2011 law obliged Peru's municipalities to do so. Yet Lima's remains incipient.
"How are the injured going to be attended to? What is the ability of hospitals to respond? Of basic services? Water, energy, food reserves? I don't think this is being addressed with enough responsibility," said Tavera of the Geophysical Institute.
By necessity, most injured will be treated where they fall, but Peru's police have no comprehensive first-aid training. Only Lima's 4,000 firefighters, all volunteers, have such training, as does a 1,000-officer police emergency squadron.
But because the firefighters are volunteers, a quake's timing could influence rescue efforts.