Esther Keeney of Carroll Township has been worried the earth might swallow her up because of the earthquakes and tremors that have been rattling the area for weeks.
She's been writing down every earthquake and tremor she's felt or heard since Oct. 2. So far, the number totals at least 60, and the list includes several booms as recently as Monday.
"It scares ya, I'll tell ya," the 66-year-old said Tuesday evening. "I was sitting on the chair, and I could feel it shaking. My china cabinet started vibrating, and pictures fell. It broke a window out in the bedroom."
Keeney said she felt better after listening to Charles Scharnberger, a retired Millersville University earth sciences professor, and Jeri Jones of Jones Geological Services talk about the earthquakes at a public meeting Tuesday evening.
The two tried to allay any fears with the standing-room-only crowd in the Carroll Township building that the big one is yet to come.
"I really do not believe that you are in any great danger here," Scharnberger said. "I think it's very, very unlikely that this is building up to something big. I think these are going to continue for a while, and . . . as Jeri said, they're going to go away as mysteriously as they came."
Scharnberger explained that the region was stretched apart at the time the Atlantic Ocean began to open more than 200 million years ago, and earthquakes are commonly found in areas associated with old rifting.
These earthquakes could be caused by old faults in the subsurface, even though they don't show up on geological mapping, or it could be rock breaking at a place where there was never a significant amount of movement in the past, he said.
Scientists expect to find out more with the seismic stations that were placed last week in the Dillsburg area. Scharnberger said it will take a few weeks to get results.
Here are some questions that Scharnberger and Jones answered Tuesday night:
Why the noise?
Earthquakes produce a variety of frequencies. When the rock breaks, it produces high frequencies, which tend to die out as they propagate out through the rock.
Let's say an earthquake occurs at a depth of 10 miles under the surface. Having gone through 10 miles of rock, all those high frequencies have died out.
But let's say these earthquakes are only occurring one mile below the surface, "as I strongly suspect is the case here," Scharnberger said. Now the high frequencies can get through the rock without being dissipated. So they hit the surface, and they make a boom.
Why the sulfur smell?
It's probably being created by the iron-ore bodies in the area, Jones said. The earth shakes a little bit, and it might release some of the sulfur gases up through the ground.
What effect does it have on pets?
Animals will begin to act strangely before an earthquake occurs, Scharnberger said.
He had a cat that suddenly leapt off the floor and onto the back of the couch, and it arched its back and its fur stood up right before a 4.0-magnitude earthquake hit in Lancaster County in 1984.
It might be that the animals are hearing higher frequency sounds than humans are picking up.
What is the likelihood that residents could lose their wells?
Helen Delano, a senior geologic scientist, cited one case study that was done after magnitude-5.0 earthquake in northwestern Pennsylvania. Houses on the top of the hill had water drop significantly in their wells, and houses at the edges of the hill had their well levels rise - and in some cases it came squirting out of the wells.
Over time, most of those wells have recovered, Delano said. It took some time, and some residents did deepen their wells to get through that time.
"I don't think anyone totally lost water," she said.
A total of six earthquakes - two just a minute apart - were recorded Oct. 19.
Jeri Jones of Jones Geological Services showed a slide with all of the earthquakes:
1.9: 4:21:22 a.m.
2.1: 4:22:07 a.m.
1.8: time not available
1.7: time not available
1.5: time not available
1.5: time not available
Residents can check out what seismographs are picking up by going to the Lamont-Doherty Cooperative Seismic Network at www.ldeo.columbia.edu/lcsn. Click on the link "Finger Quake for Recent Seismic Events in the Northeastern U.S."