By FRANK BAJAK and CARLA SALAZARLIMA, Peru (AP) â¿¿ 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. Its acute vulnerability, from densely clustered, unstable housing to a dearth of first-responders, 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.