Earthquake and I slept through it
Quake's aftershocks rumble in Indiana
By Tim Evans and Erin Dostal
Posted: April 18, 2008Read Comments(147)Recommend (23)E-mail Print Share Del.icio.us Digg Reddit Yahoo Google A A The 5.2-magnitude earthquake that rattled windows and nerves across Indiana today was not an anomaly, experts said, and even larger quakes are likely to rock the state in the future.
That’s because Indiana sits near the New Madrid seismic zone, which generated the largest quake ever recorded in the continental U.S., and on top of a smaller fault that runs along the Wabash River valley.
Today’s was the strongest quake to strike the area in 40 years.
It is impossible to say when or where the next quake will hit Indiana, or what the magnitude might be, said Scott Wilkerson, chairman of the geosciences department at DePauw University in Greencastle.
“Predicting earthquakes in the future is a dicey game, at best,” he said. “But I would expect to see this kind of earthquake probably in the next 10 to 20 years, maybe longer, with smaller quakes from time to time. It is something that is going to continue.”
As far as the prospect of an even larger quake that would do significant property damage or claim lives, Wilkerson said: “It could happen here, but certainly not with near the frequency you would expect to see in places like California.”
The epicenter of today’s 5:37 a.m. quake, emanating from seven miles below the Earth’s surface, was near the community of West Salem, Ill., about 125 miles southwest of Indianapolis, according to the U.S. Geological Survey.
The magnitude of an earthquake is not altered by distance from the epicenter, but its Modified Mercalli Intensity reading - the detectable shaking - does decrease with distance. At its epicenter, the quake had an intensity of VI, or strong, on a scale of one to 10 using Roman numerals, while the intensity level in the Indianapolis area was rated IV or “light,” with little potential for damage.
U.S. Geological Survey said the quake appears to have occurred in the Wabash Valley Seismic zone and was felt as far away as Kansas, the Upper Peninsula of Michigan and Georgia.
At least six significant aftershocks followed the first quake, with the largest hitting at 11:14 a.m. and registering magnitude 4.6. Wilkerson said it was unusual to have such a strong aftershock with a 5.2 quake but said more aftershocks - most not noticeable - could continue for a week or longer.
Resident, business reaction
Barbara Shannon, 74, Princeton, was among those awakened by the initial quake.
“It shook the bed,” she said. “You could hear it coming, and it really hit hard. I jumped up and said, ‘It’s an earthquake.’.”
She said her husband, Cork, thought something had exploded.
“It’s like a semi hit your house,” she said.
Shannon said a couple of pictures fell from their place atop a television.
No injuries were reported.
The brunt of the impact was felt in Illinois, where dozens of homes sustained minor damage, but Indianapolis didn’t escape unscathed.
John Hittel, project manager at St. Mary’s Catholic Church on New Jersey Street in Downtown, said two windows were broken and several pieces of decorative stonework were damaged. A crack also developed in the ceiling of the Marian Center, where the parish offices are located.
City reaction
Indianapolis Mayor Greg Ballard said emergency responders checked buildings, bridges and utilities throughout Marion County but found no damage.
At Indianapolis International Airport, the air traffic control tower was evacuated and departures were briefly delayed while the tower and runways were inspected for damage. Seven outbound flights were delayed for an average of 15 minutes, and three inbound flights were placed in a holding pattern until the inspections were completed.
About 30 miles from the quake’s epicenter, nearly 1,500 Vincennes University students in five dormitories were evacuated when campus police ordered a resident assistant to sound the fire alarm.
“People were crying. People were on their cell phones. No one knew what was going on,” said freshman Elisabeth Pinnegar, 19, Pittsboro. “We live in Indiana. This doesn’t happen here.”
Common event in region
The lack of frequent, noticeable events like those that routinely rock places like California or Japan tends to create a comfort zone that allows Hoosiers to forget about the potential for Midwest quakes, said John Steinmetz, director of the Indiana Geological Survey and the state geologist.
But, according to U.S. Geological Survey reports, 150 to 200 earthquakes happen each year in the Midwest, though most are too weak to be detected by anything other than sophisticated monitoring equipment.
“Fortunately, earthquakes of a serious magnitude are infrequent enough (in Indiana) that we don’t need to be afraid of what might happen in the next day or week,” Steinmetz said. “But we shouldn’t drop the sense of vigilance. We should have a plan.”
Strongest since 1968
Professor Michael Hamburger of Indiana University’s Department of Geological Sciences said Friday’s quake was the strongest to hit the area since one of a similar magnitude was recorded near Carbondale, Ill., in 1968.
Earthquakes occur throughout the region at “moderately frequent” but irregular intervals, according to the U.S. Geological Survey, with quakes causing moderate damage every 10 to 20 years.
During the past 20,000 years, the Midwest has had at least eight earthquakes estimated at magnitudes ranging from about 6.5 to 7.5, according to Geological Survey data. In February 1812, the largest quake recorded in the continental U.S. destroyed the community of New Madrid, Mo. The estimated 7.5 quake was so strong that historical accounts say the shaking caused church bells to ring in Washington, D.C.
The Geological Survey says quakes here “can be felt over an area as much as 10 times larger than a similar magnitude earthquake on the West Coast.”
Wilkerson, the DePauw professor, said that is because of the bedrock that lies beneath much of the area. That same geological feature means many structures in the Midwest can withstand stronger quakes than those in areas with less bedrock.
“You will certainly feel the jolt of the earth shaking,” he said, “but you probably won’t see the same damage or undulating of the ground.”
More could be on the way, experts say
Larry Braile, head of the Department of Earth and Atmospheric Sciences at Purdue University, predicted more to come.
Braile said research indicates the Wabash Valley zone will have a magnitude-4 earthquake about every two years, on average, while quakes reaching a magnitude of 5.0 can be expected about every 10 to 20 years.
Each point increase in magnitude represents a 10-fold increase in the shaking level of the quake, meaning the action of a 5.0 quake is 10 times that of a quake that registers 4.0.
The average recurrence of a 6-plus magnitude quake is about 100 years; it’s about 1,000 years for a 7-plus magnitude quake. At 6.0 and above, Braile said, quakes have the potential for serious damage. The last Midwest quake to reach 6.0 occurred in 1895.
“You could say we are overdue for a 6-plus,” he said.
The Associated Press contributed to this story.
http://www.indystar.com/apps/pbcs.dll/article?AID=/20080418/NEWS/80418002
I didn't feel the aftershock at work either but others did. I did see some hanging things swinging and swaying like the wind blew them. hmmm I have worked so much and have been so tired even an earthquake didn't wake me.
By Tim Evans and Erin Dostal
Posted: April 18, 2008Read Comments(147)Recommend (23)E-mail Print Share Del.icio.us Digg Reddit Yahoo Google A A The 5.2-magnitude earthquake that rattled windows and nerves across Indiana today was not an anomaly, experts said, and even larger quakes are likely to rock the state in the future.
That’s because Indiana sits near the New Madrid seismic zone, which generated the largest quake ever recorded in the continental U.S., and on top of a smaller fault that runs along the Wabash River valley.
Today’s was the strongest quake to strike the area in 40 years.
It is impossible to say when or where the next quake will hit Indiana, or what the magnitude might be, said Scott Wilkerson, chairman of the geosciences department at DePauw University in Greencastle.
“Predicting earthquakes in the future is a dicey game, at best,” he said. “But I would expect to see this kind of earthquake probably in the next 10 to 20 years, maybe longer, with smaller quakes from time to time. It is something that is going to continue.”
As far as the prospect of an even larger quake that would do significant property damage or claim lives, Wilkerson said: “It could happen here, but certainly not with near the frequency you would expect to see in places like California.”
The epicenter of today’s 5:37 a.m. quake, emanating from seven miles below the Earth’s surface, was near the community of West Salem, Ill., about 125 miles southwest of Indianapolis, according to the U.S. Geological Survey.
The magnitude of an earthquake is not altered by distance from the epicenter, but its Modified Mercalli Intensity reading - the detectable shaking - does decrease with distance. At its epicenter, the quake had an intensity of VI, or strong, on a scale of one to 10 using Roman numerals, while the intensity level in the Indianapolis area was rated IV or “light,” with little potential for damage.
U.S. Geological Survey said the quake appears to have occurred in the Wabash Valley Seismic zone and was felt as far away as Kansas, the Upper Peninsula of Michigan and Georgia.
At least six significant aftershocks followed the first quake, with the largest hitting at 11:14 a.m. and registering magnitude 4.6. Wilkerson said it was unusual to have such a strong aftershock with a 5.2 quake but said more aftershocks - most not noticeable - could continue for a week or longer.
Resident, business reaction
Barbara Shannon, 74, Princeton, was among those awakened by the initial quake.
“It shook the bed,” she said. “You could hear it coming, and it really hit hard. I jumped up and said, ‘It’s an earthquake.’.”
She said her husband, Cork, thought something had exploded.
“It’s like a semi hit your house,” she said.
Shannon said a couple of pictures fell from their place atop a television.
No injuries were reported.
The brunt of the impact was felt in Illinois, where dozens of homes sustained minor damage, but Indianapolis didn’t escape unscathed.
John Hittel, project manager at St. Mary’s Catholic Church on New Jersey Street in Downtown, said two windows were broken and several pieces of decorative stonework were damaged. A crack also developed in the ceiling of the Marian Center, where the parish offices are located.
City reaction
Indianapolis Mayor Greg Ballard said emergency responders checked buildings, bridges and utilities throughout Marion County but found no damage.
At Indianapolis International Airport, the air traffic control tower was evacuated and departures were briefly delayed while the tower and runways were inspected for damage. Seven outbound flights were delayed for an average of 15 minutes, and three inbound flights were placed in a holding pattern until the inspections were completed.
About 30 miles from the quake’s epicenter, nearly 1,500 Vincennes University students in five dormitories were evacuated when campus police ordered a resident assistant to sound the fire alarm.
“People were crying. People were on their cell phones. No one knew what was going on,” said freshman Elisabeth Pinnegar, 19, Pittsboro. “We live in Indiana. This doesn’t happen here.”
Common event in region
The lack of frequent, noticeable events like those that routinely rock places like California or Japan tends to create a comfort zone that allows Hoosiers to forget about the potential for Midwest quakes, said John Steinmetz, director of the Indiana Geological Survey and the state geologist.
But, according to U.S. Geological Survey reports, 150 to 200 earthquakes happen each year in the Midwest, though most are too weak to be detected by anything other than sophisticated monitoring equipment.
“Fortunately, earthquakes of a serious magnitude are infrequent enough (in Indiana) that we don’t need to be afraid of what might happen in the next day or week,” Steinmetz said. “But we shouldn’t drop the sense of vigilance. We should have a plan.”
Strongest since 1968
Professor Michael Hamburger of Indiana University’s Department of Geological Sciences said Friday’s quake was the strongest to hit the area since one of a similar magnitude was recorded near Carbondale, Ill., in 1968.
Earthquakes occur throughout the region at “moderately frequent” but irregular intervals, according to the U.S. Geological Survey, with quakes causing moderate damage every 10 to 20 years.
During the past 20,000 years, the Midwest has had at least eight earthquakes estimated at magnitudes ranging from about 6.5 to 7.5, according to Geological Survey data. In February 1812, the largest quake recorded in the continental U.S. destroyed the community of New Madrid, Mo. The estimated 7.5 quake was so strong that historical accounts say the shaking caused church bells to ring in Washington, D.C.
The Geological Survey says quakes here “can be felt over an area as much as 10 times larger than a similar magnitude earthquake on the West Coast.”
Wilkerson, the DePauw professor, said that is because of the bedrock that lies beneath much of the area. That same geological feature means many structures in the Midwest can withstand stronger quakes than those in areas with less bedrock.
“You will certainly feel the jolt of the earth shaking,” he said, “but you probably won’t see the same damage or undulating of the ground.”
More could be on the way, experts say
Larry Braile, head of the Department of Earth and Atmospheric Sciences at Purdue University, predicted more to come.
Braile said research indicates the Wabash Valley zone will have a magnitude-4 earthquake about every two years, on average, while quakes reaching a magnitude of 5.0 can be expected about every 10 to 20 years.
Each point increase in magnitude represents a 10-fold increase in the shaking level of the quake, meaning the action of a 5.0 quake is 10 times that of a quake that registers 4.0.
The average recurrence of a 6-plus magnitude quake is about 100 years; it’s about 1,000 years for a 7-plus magnitude quake. At 6.0 and above, Braile said, quakes have the potential for serious damage. The last Midwest quake to reach 6.0 occurred in 1895.
“You could say we are overdue for a 6-plus,” he said.
The Associated Press contributed to this story.
http://www.indystar.com/apps/pbcs.dll/article?AID=/20080418/NEWS/80418002
I didn't feel the aftershock at work either but others did. I did see some hanging things swinging and swaying like the wind blew them. hmmm I have worked so much and have been so tired even an earthquake didn't wake me.