Scientists ask, 'Howzit shakin'?'
Geophysicists want residents to tell them how earthquakes felt
Island residents are helping the U.S. Geological Survey understand how an earthquake feels so they can estimate potential damage from a bigger temblor, geophysicists say.
The USGS has a "Did you feel it?" system where people can go a Web site and provide information on shaking from an earthquake for a map outlining the seismic intensity.
"The neat thing is these maps now are made from citizen science," USGS geophysicist David Wald said by telephone from Golden, Colo. "The population of the island is pretty savvy and Internet-connected, and when they feel an earthquake, they know where to go not only to get information, but to give information."
'DID YOU FEEL IT?'
Islanders can report whether they felt a particular earthquake by going to the Web page earthquake.usgs.gov/dyfi.
Recent significant Hawaii earthquakes will be listed. Click on the appropriate earthquake or on "new earthquake" if it is not already on the list.
After clicking on an earthquake, a map will come up of what has been reported. Readers then should click on the "Did you feel it? Tell us!" section above the map, and a questionnaire for that earthquake will come up to fill out.
Calculating the intensity or possible threshold of damage for a certain-size area helps to understand how much potential damage would occur with a stronger earthquake, especially in those areas with growing populations, Wald said.
The USGS used data from instruments and "Did you feel it?" accounts from residents to develop an intensity map for the Kiholo Bay earthquake Oct. 15 in West Hawaii, said Cecily Wolfe, a University of Hawaii geophysicist and seismologist.
She said the "human reports" were important for analysis of the 2006 earthquake, which USGS scientist Margaret Hopper compared with 1929 and 1951 West Hawaii earthquakes.
The system was not in place in those years, and Hopper had to go back to old historic data in engineering and news accounts and photos for those intensity maps, Wolfe said.
Wald said much more data was available for the Oct. 15 earthquake because of residents' response on the Internet about how they felt it.
In the past, USGS did a mass-mail campaign with questionnaires for people to describe how they felt an earthquake and assign intensities, he said. "It would take months and quite a bit of resources."
USGS scientists presented Hopper's intensity maps on the three West Hawaii earthquakes at a recent Seismological Society of America meeting in Kona.
She used the Modified Mercalli Intensity Scale, which has 12 levels of increasing intensity ranging from the first level of imperceptible shaking to catastrophic destruction at the highest level.
The 2006, 1951 and 1929 earthquakes were similar in magnitude, with the highest intensity of 8 felt on the Big Island in all three cases.
An 8 level means, "Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage was great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned."
Wolfe said she was particularly surprised that the intensity levels for the 1951 earthquake were similar to the Kiholo Bay earthquake, because the earthquakes were at different depths.
Scientists want to see earthquake predictions and early warnings, Wald said.
"We want better-built structures," Wald said, noting buildings will collapse even if earthquakes could be predicted.
The Geological Survey also has been working on a new global system that will estimate the number of fatalities from an earthquake based on the number of people at different shaking levels and the vulnerability of the structures they live in, Wald said.
He said USGS is increasing instruments in Hawaii to get motion information for shake maps.
"It's part of the whole plan for an advanced seismic system. The progress is slower than we hoped; funding is less than we hoped."