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02-03-04: Scientists find center of Rockford quake

Calculations show 2.5 magnitude


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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