Did you feel it?
Then how do you feel about talking about it?
Seismologists studying earthquake intensity now know that Southern Californians feel good about discussing the shaking they endured in Sunday’s temblor near Palm Springs.
By midafternoon Monday, nearly 27,000 people had filled out computerized questionnaires for the United States Geological Survey detailing their personal reactions to the magnitude 5.2 quake.
The 8:41 a.m. shaker was initially pegged at magnitude 5.6 but later downgraded by scientists. The epicenter was about six miles east of the desert hamlet of Anza.
Seismometers were quick to measure the quake’s 8.8-mile depth and to place it on the San Jacinto fault, considered the most active in California.
But the scattered distribution of quake-measuring instruments in desert and mountain areas east of Los Angeles slowed an assessment of its intensity in areas away from the epicenter -- until the questionnaires started pouring in, that is.
By the hundreds at first and then by the thousands, those jarred out of bed or away from their Sunday breakfast tables hurried to their home computers to log on to the geological survey’s earthquake website.
Along with the quake’s magnitude and location, the pasadena.wr.usgs.gov/shake/ca/ website added: “Did you feel it? Tell us!”
Soon, residents’ personal reports were pouring in to the geological survey’s main computer in Pasadena. And it automatically began mapping where the quake was felt.
It became clear that the shaking was experienced from Ridgecrest on the north to Yuma, Ariz., on the south and from Santa Barbara on the west to Kingman, Ariz., on the east.
The interactive map showed the number of responses (three from Santa Barbara) and the intensity (III, or “weak” in Kingman) from each ZIP Code from which respondents were filing.
The intensity levels were calculated from answers to multiple-choice questions on the “Did you feel it?” survey.
The questionnaire asks if you felt it in a building and, if so, what kind of structure it was. It asks if others nearby also felt it and whether the quake was strong enough to awaken you if you were asleep.
Respondents are asked to describe how the ground shook, how many seconds it lasted and their personal reactions to it. “Was it difficult to walk?” asks one question.
“Did you notice the swinging/swaying of doors or hanging objects? Did you notice creaking or other noises? Did objects rattle, topple over or fall off shelves? Did pictures on walls move or get knocked askew? Did any furniture or appliances slide, tip over or become displaced? Was a heavy appliance (refrigerator or range) affected? Were free-standing walls or fences damaged? If you were inside, was there any damage to the building?”
That question was followed by a checklist ranging from “no damage” and “hairline cracks in walls” to “many windows cracked or some broken out,” “outside walls tilted over or collapsed complete” and “building permanently shifted over foundation.”
Respondents are invited to add additional first-person observations at the survey’s end, but the essays are not used to calculate a quake’s intensity.
The intensity of response delighted scientists.
“It’s exceeded anything we’ve seen in the past,” seismologist David Wald of the geological survey in Golden, Colo., said Monday. A former Pasadena-based scientist, he is credited with devising the computerized study.
“The machines can tell us what the ground did. But only people can tell us what it did to them. I call it citizen science. You couldn’t do it without the people.”
Wald devised what is called the Community Internet Intensity program by modifying the system used by seismic researchers Laurie Dengler and Jim Dewey for telephone surveys of those living through earthquakes. Earlier, earthquake intensity assessments were done through postcards mailed to postmasters in quake areas -- an even slower undertaking.
“A phone survey takes an enormous amount of time,” Wald said. “I realized the Internet could do it faster.”
In a major earthquake, those closest to areas shaking with the greatest intensity might not be able to fill out the online survey, he conceded. “They might have other priorities, even if they do have electricity and can get on the Web.”
The online survey and its ZIP Code analysis allow the USGS computer to average out responses from distinct geographical areas and weed out exaggerated and crank replies, he said. And scientists are the only ones who benefit.
“Those who respond are getting something off their chest,” Wald said.
“It’s a way of sharing that experience. It’s cathartic.”
Susan Hough, a seismologist with the USGS in Pasadena, said the personal observations portion of the survey may not be initially read by experts. But they will be retained for future research purposes.
“There is a tendency to say the lights, sounds and smells that some people experience after earthquakes are due to over-imagination. But people are good observers, and people may be picking up things the scientific community hasn’t recognized,” she said.
According to Hough, earthquake survey responses remain confidential and are accessible only to government researchers.
“We cannot violate people’s privacy,” she said. Even if it’s an earthshaking matter.