Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: SUNDAY, March 13, 1994 TAG: 9403150158
SECTION: CURRENT PAGE: NRV16 EDITION: NEW RIVER VALLEY
SOURCE: PAUL DELLINGER STAFF WRITER
DATELINE: BLACKSBURG LENGTH: Medium
But Martin C. Chapman and others in Virginia Tech's Department of Geological Sciences are working on it. They still cannot give forecasts but they can provide risk assessments for specific areas.
``We haven't had a large earthquake [in Virginia] since the turn of the century,'' Chapman said. ``If you wait long enough, you'll have another one ... We can just assume that what's gone on in the past will continue going on in the future.''
An 1897 quake in Giles County hit 5.8 on the Richter Scale. In 1875, probably around Goochland County in Central Virginia, one measured from 5.0 to 5.5 on that quake-measurement scale.
By comparison, the recent Los Angeles earthquake measured 6.6.
Worldwide, there have been as many as 1 million earthquakes in a year. But most of those happen beneath the sea, and relatively few of the others cause major damage. The damage comes when quakes occur in built-up, populated areas.
Chapman's task is assessing risk factors to provide an idea of how stable a Virginia area is likely to be over time. The thick book that has resulted, with the weighty title ``Virginia Tech Seismological Observation,'' includes maps and tables for doing that based on past seismic activity.
Records of Virginia quake activity have been kept dating back to 1663. Since then, there have been more than 60 quakes large enough to merit recording.
A more active approach is Tech's seismology network, the brainchild of Gilbert Bollinger, who retired as department head last May after 25 years at Tech. The network receives data from 15 remote Virginia stations that monitor small shocks as well as large. Sometimes they turn out to be man-made blasts in construction or mining, but the people doing the monitoring are now pretty good at recognizing those.
``We can generally tell from the character of the signal,'' Chapman said.
``The seismic hazard in Virginia is not at the same level as you have in California,'' he said. ``But the fact is that we have a history of moderate earthquakes in the state and it's virtually certain we'll continue to have some.''
While a quake might happen about every decade in California, he said, the frequency in Virginia would be more like once a century. But a quake measuring 6.0 on the Richter scale could have a more severe impact in Virginia because this state has none of the earthquake mitigation measures underway in California since the 1930s, he said.
Virginia has a lot of masonry structures that are not reinforced, for example. Those are notoriously dangerous, even in small quakes. ``It's something that planners in the state and building officials ... need to be aware of,'' Chapman said.
Without the network of seismographs, no such study was possible. Now the quake watchers can define the general boundaries of seismic zones.
It was that research program which drew Chapman back to Tech, where the Scott County native had graduated and gotten his master's degree. He was with an Atlanta, Ga., engineering company when he returned in 1983 partly because ``we had a pretty good research program going on here,'' he said.
Tech's station is one of four in the southeastern United States that monitors quake activity.
Revolving drums with pens attached show straight inked lines except where some event has occurred and the lines become squiggly, like those on a lie detector when someone is not truthful.
But that method is soon to be replaced by computer monitoring, Chapman said.
Others involved in the research include engineer Jim Dixon, research associate Matt Sibol and program director Arthur Snow, along with graduate students who do much of the data monitoring.
Fred Krimgold, technology director for Tech's outreach programs in Fairfax, agreed with the importance of installing proper construction safeguards even where few quakes have happened.
He and Chapman look at possibilities ranging from collapsed chimneys to collapsed power stations if a quake should happen.
``Because we've never thought about earthquakes in the past, we're pretty vulnerable,'' Krimgold said. ``It has happened as recently as a century ago, and it is going to happen again.''
by CNB