Almost a month after the earthquake, heavy rains came in the night to the muddy new settlements of bamboo and canvas planted in the rubble of Popayan.

In the old colonial district, the storm loosened fresh chunks of white plaster and tile from the crippled churches, the treasures of this 447-year-old city before 18 seconds of tremors on Holy Thursday.

In the tent cities and shantytowns suddenly sprawling over pastures and parks, dug into hillsides and planted on cracked roadbeds, thousands of families endured the more quiet horrors that have followed the physical shocks.

"We sat together and prayed, and we wrapped the little ones in blankets of llama wool, but the cold came through and the blankets weren't enough," said Angela Vidal, a stooped woman draining the puddles from around an American-made tent in the camp of El Guayabal. "The children woke up in a bad way, with coughs and sore throats and two had rashes all over their faces, even in their mouths."

In the morning, the children and women of that family of 14 went to a medical post to wait their turn among the day's newly ill. Young Red Cross volunteers shoveled trenches to drain rainwater from the 23 blue-and-white tents--like those American families take on vacations--that now hold about 450 of the estimated 70,000 homeless.

The rainy season has begun here in Colombia's southwestern mountains, 400 miles from Bogota, and for Popayan's long-neglected population it is potentially the most disastrous trial. A familiar rush of emergency aid is giving way in this historic but poor city to a return of the mundane ills of underdevelopment.

"The immediate emergency is passing, but now there is a social earthquake coming to Popayan," Mayor Guillermo Salazar said. "If we don't know how to manage the situation, it could be much worse than the physical earthquake, and the greatest damages will come not in a few seconds, but over time."

For many in this city of 130,000, even the wreckage of the March 31 quake shows a deeper social malady.

The first reports told of the collapse of the historic cathedral--with dozens at mass trapped inside--and the ruin of Popayan's heritage as a rich center of colonial and early republican rule.

But beyond the architectural treasures, about 2,500 homes out of a total of 20,000 were found by an initial government survey to have been destroyed. Another 7,000 were judged to be 50 percent to 80 percent ruined, and 4,500 more suffered lesser damage.

The new engineering school was torn up, and the Army officers' training school and battalion headquarters looked at though they had been bombed. But most of the damage and the 157 recorded deaths fell in the southern districts, where the poor had come in from the countryside and built homes of brick, wood and tin.

Now, many of the sturdiest homes and the intact apartment buildings stand vacant as Popayan's middle class and even its oldest families leave the city. Government officials estimate that as many as 50,000 may have left since the earthquake, most of them professionals with the means and the skills to start again in another city.

Many of those left behind are poor workers and peasants from the surrounding country, whose houses disappeared with the quake and whose livelihoods were tenuous.

"The earthquake has shown us the great social and economic fault beneath this city," said Alvaro Valencia, curator of the local museum and brother of the late Guillermo Valencia, who was president in the mid-1960s. "Almost everyone is poor, and there is no work and no land."

When its colonial wealth and its aristocratic families declined, Popayan began to live by agriculture--1,500 and 2,000-acre farms of coffee and cattle owned by the local families in the surrounding countryside. Colombia was torn by 10 years of rural violence after World War II, and hundreds of thousands of peasants moved to cities seeking jobs.

Popayan's population rose by 70 percent in 10 years, Valencia said, but the new jobs never came. Like many provincial capitals, its only large employer became the state. There were no industries and, before the quake, most people seemed to live on inherited properties, government salaries, tiny businesses or economic sleight of hand.

"I think this city must have lived by miracle before," said Guillermo Echeverri, the secretary of public works here for the provincial government. "It was a city that had a good history, but not much more."

Now, with the earthquake, that delicate economic balance is gone--and there is no foundation to build on. "Every person who stays in Popayan is a problem," said Echeverri, "because this is not yet a city with a capacity to support them."

It will be at least a year before Popayan rebuilds the housing that was destroyed by the quake, and possibly two years before there are adequate homes for all the poor, officials say. In the meantime, the poor must wait, four families to a tent for those in the camps, and beneath tree branches and plastic for the thousands left outside.

"We are just waiting to see what the government does," said Francisco Orrozco, who lives with a family of 10 in the Pandiguando district. "We're living on the little resources that we have, and hoping that there will be some new sources of jobs."

Government officials are already seeking to put the city back to work by slowly choking off free supplies of food. "We are saving the food for the children and the elderly," said Maria Antonia de Velasco, the president of the local Red Cross.

"The city is up to its neck in food, but the people see no reason to work. We are trying to push them back into the economy, get them going again."

But in the tent cities, the people respond that there are no jobs. "We don't have anything to rebuild with, and we don't know where all the money is going that has been given to the government," said Francisco Javier Silva Duque, a community leader in Pandiguando, where 1,300 adults and 770 children share 31 tents allocated by the Army.

Jolted by the earthquake, the Conservative Party administration of President Belisario Betancur has allocated about $250 million for the revitalization of the city, including about $5 million in low-interest credits for the rebuilding or repair of homes. Within months, officials say, construction will be a booming business, and new programs have been planned to attract light industry and multinational companies.

But even the new jobs and homes will not still the social earthquake dawning in Popayan. City officials expect the arrival of further thousands from Colombia's poor countryside in search of jobs and cheap new housing. While the middle class leaves, Popayan's population could double in a year, officials say.

"They are already coming, and now that they are here we cannot throw them out," said Mayor Salazar. "For six months or two years we can build new housing. But what we have to ask ourselves is, what will these people do before they can find homes and what will they do on the day after the rebuilding is over?"