THE VIRGINIAN-PILOT
Copyright (c) 1996, Landmark Communications, Inc.
DATE: Wednesday, July 17, 1996 TAG: 9607170409
SECTION: LOCAL PAGE: B3 EDITION: FINAL
SOURCE: BY NAOMI AOKI, STAFF WRITER
LENGTH: 55 lines
The earth definitely shook, rattled and rolled under Hampton Roads last Thursday, but there was no earthquake.
In fact, local experts are stumped about exactly what the shaking was.
About 3:30 p.m. Thursday, many area residents heard a loud boom and felt vibrations strong enough to rattle windows and cabinet doors. Fifteen minutes later, they got a second wave of vibrations.
Both events lasted about 30 seconds and registered about a 2 on the Richter scale on the seismograph at Tidewater Community College in Virginia Beach. The seismograph is the only one in Virginia east of Petersburg.
``That is part of the problem,'' said Micheal Lyle, geophysicist at TCC.
Seismographs measure intensity of vibrations and the distance from their origin but do not indicate where the vibrations come from. Without other seismic readings, it is impossible to pinpoint the source of the disturbance.
Thursday's shakes were not picked up by any other seismographs, making it nearly impossible to locate their source. That fact also indicates the booming and the rattling were not earthquakes, Lyle said. If it had been an earthquake, it should have registered on the seismograph at the Virginia Tech Seismological Observatory in Blacksburg, he said.
Lyle and his colleagues are calling the shaking ``sound events,'' which could have been caused by a number of things, including aircraft activity, explosions or heavy construction.
The mystery is that with Hurricane Bertha on the way, construction was at a standstill, Langley Air Force Base had evacuated its planes by 1:30 p.m. Thursday and Oceana Naval Air Station had hangared its aircraft and sent its ships out to sea. Spokesmen from Langley and Oceana said they were as baffled as Lyle about the cause of the tremors.
The tremors caused quite a stir, particularly in Virginia Beach. The switchboard lit up at the police communications center in Virginia Beach, a spokesman said. The Office of Emergency Services and TCC's geophysical sciences department fielded numerous calls. Other Hampton Roads cities reported less activity.
Lyle says seismic readings in this area are not unusual. During his 12 years at TCC, he has seen many readings of minor vibrations, but area residents don't usually feel any shaking.
``The vibrations usually happen between 8 a.m. and 5 p.m., which is unusual,'' Lyle said. ``I find it hard to believe the earth is on an eight-to-five workday.''
Although there are fault lines in Eastern Virginia, there has been very little activity in thousands of years, said Martin Chapman, a research associate at the Virginia Tech observatory.
An earthquake has not originated in Hampton Roads in more than 100 years, although Hampton Roads probably shook during a 1984 earthquake in Cunningham, near Charlottesville. It rated a 4 on the Richter scale.
The biggest known earthquake in Virginia's history was in Goochland County in 1875, an estimated 5 on the Richter scale, Chapman said. by CNB