Calculations show 2.5 magnitude
By MARGIE WUEBKER
mwuebker@dailystandard.com
Geologists have pinpointed an area in Dublin Township as the
epicenter for a small earthquake that rocked the Rockford area
early Friday morning.
Michael Hansen, network coordinator for The Ohio Seismic Network,
a division of the Ohio Department of Natural Re-sources, said
calculations indicate the 2.5 magnitude activity came from the
northwest corner of the Ohio 118 and Purdy Road intersection,
approximately one mile south of Rockford.
“I feel quite certain that is the spot based on activity
picked up by network equipment at more than three locations,”
Hansen told The Daily Standard on Monday afternoon. “The
activity noted at 7:10 a.m. is clearly recorded.”
That activity showed up most notably at the nearest recording
location — the Wright State University-Lake Campus along
Ohio 703, east of Celina. The site is one of 23 volunteer seismograph
locations situated at colleges and universities throughout the
state.
Seismic activity also registered on equipment at the Ohio State
University branch campus in Lima, Clark State Community College
in Springfield and the Ohio Geological Survey headquarters at
Alum Creek State Park near Delaware. Activity recorded at Bowling
Green State University and Wright State’s main campus
in Fairborn was not used in factoring the epicenter location,
according to Hansen.
The Mercer County Sheriff’s Office received nearly 30
telephone calls from concerned citizens regarding a sharp boom
or thud followed by a brief period of shaking. The calls, which
began about 7:15 a.m., came primarily from an area north of
U.S. 33 and west of Ohio 118. However, residents as far south
as Celina and in neighboring St. Marys also heard and felt the
strange phenomena.
Linda Pifer, a licensed practical nurse at The Laurels of Shane
Hill, 10731 Ohio 118, Rockford, was taking medication into a
patient’s room when she heard the boom and felt the earth
sway.
“I told the other girls on duty it felt like an earthquake,”
Pifer recalls. “They laughed and told me it was just the
guys outside blowing snow. I didn’t buy that for a minute.”
Nancy Taylor, an accounts payable/payroll coordinator at the
nursing home located near the epicenter, was en route from her
River Trail Road home, north of Rockford, at the time.
“I didn’t feel any shaking,” she said. “I
heard the boom and thought it was thunder, but I quickly realized
there was no lightning.”
Her husband, John, was still home when the windows started to
rattle and Precious Moments figurines danced across display
shelves. Everything returned to normal in a matter of seconds.
“I first thought somebody was blasting at the stone quarry
but later found out that was not the case,” he said. “I
went into town and the cop reported others had heard and felt
the same thing. He said the aeronautical folks reported no low-flying
aircraft or sonic booms. No one seemed to know the reason until
later.”
No damage was reported with Hansen noting that it usualy does
not show up until an earthquake reaches around 4.5 magnitude.
“Given the small magnitude, it’s unusual so many
people noticed,” the geologist added. “That really
makes this one interesting.”
Hansen believes amplification of the earthquake’s P and
S waves may be the cause. Fast-moving P waves cause booming
noises as bedrock moves beneath the earth’s surface. The
secondary S waves cause the telltale shaking.
Mercer County, along with Auglaize and Shelby counties, sets
atop the Teays River valley, an ancient stream once comparable
to the modern Ohio River. It was destroyed by glaciers during
the Pleistocene Ice Age approximately 2 million years ago.
Remnants of the Teays River are preserved as flat-bottomed valleys
in hilly, unglaciated southern Ohio and as deep valleys now
filled with sediment in areas where the glaciers moved.
“There are 400 feet of sediment in the valleys beneath
your part of Ohio,” Hansen said. “That’s 400
feet of sediment before you hit bedrock. Lets face it, a house
or any building that sets atop unconsolidated sediment like
sand and gravel will shake more than a similar structure on
bedrock.”
This is the first earthquake in the Anna Seismogenic Zone since
1994 when a 2.9-magnitude earthquake occurred in western Shelby
County and the first in Mercer County since a 3.3-magnitude
earthquake in 1977 caused a surprising degree of shaking and
minor damage, including cracked sidewalks.
The Anna Seismogenic Zone, which includes Mercer, Auglaize,
Shelby and Champaign counties, has been the site of more than
40 earthquakes since 1875, including the largest and most damaging
event in Ohio history. People in several states felt the 5.4-magnitude
earthquake March 9, 1937. It was centered in southern Mercer
County, but caused the most damage in the Shelby County community
of Anna. Nearly every chimney toppled and a school had to be
razed due to structural damage.
“It’s been quiet in your neck of the woods for quite
sometime,” Hansen said. “There is no way to predict
when the next one will occur.”
Individuals who felt the Friday morning event are encouraged
to fill out a short questionnaire describing the effects they
felt. It can be reached by logging onto the Web site at www.dnr.state.oh.us/ohioseis/earthquakes
and then clicking on the link to USGS Community Internet Intensity
Map.
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