“This is really screwed up,” said José M. Nazario, 76, said as he again looked in on his small, two-story house near the center of Guánica. The structure still stands, but the series of quakes damaged windows and tiles, broke a dish cabinet, knocked out drawers and broke a toilet. For four nights, he has slept in his Toyota Corolla.
“They say a 7 or 8 could be coming,” he said. “I don’t know. But they keep getting stronger.”
The United States Geological Survey has warned of a strong chance of continuing aftershocks of 5.0-magnitude or greater, but said Saturday morning that the chance of a temblor stronger than Tuesday’s big quake was only 4 percent.
Elizabeth Vanacore, a seismologist with the Puerto Rico Seismic Network, said tremors would continue for at least a few more weeks. A strong aftershock, like the one on Saturday morning, will also cause its own aftershocks, Ms. Vanacore said.
The fact that there are multiple faults within and around the island means that one earthquake can activate nearby faults, which Ms. Vanacore said may have caused Saturday morning’s earthquake.
“We suspect that we have at least a few faults involved right now,” she said. She likened the high density of faults to a crowded subway car, in which people bump into each other, causing a chain reaction of collisions.
She said there were three possibilities for what happens next. The most likely is that the aftershock sequence will continue, but get weaker and eventually stop. There also is a low probability that there could be another 6.4 earthquake, an event known as a doublet. The most ominous — but least likely — possibility is that Tuesday’s 6.4 earthquake was a foreshock for a stronger earthquake that has not yet come.
“I know everyone is quite afraid because they’ve been feeling earthquakes for weeks,” she said.
At an improvised aid center in Guánica set up for things like water, toilet paper, diapers and vienna sausages, residents described Saturday’s aftershock and the sense of nervousness that has again taken hold.