Dillsburg, PA, magnitude 2.9

Dillsburg area shaken by another earthquake

CARL LINDQUIST -- The York Dispatch

Updated: 06/03/2010 10:12:24 AM EDT

An earthquake measuring 2.9 on the Richter Scale struck Northern York County on Thursday morning.

The U.S. Geological Survey reported the earthquake hit the area at 8:25 a.m. Thursday. The Geological Survey said the earthquake was about 3 miles from Wellsville and 4 miles from Dillsburg.

The earthquake that struck Thursday matched the strength of the strongest previous earthquake to hit the area. It occurred in April 2009.

Franklin and Marshall College seismogram

Local geologist Jeri Jones said several people called him Thursday morning to report an earthquake.

One caller told him pictures were knocked off the wall of her home, he said. Another caller said a relative in Mechanicsburg also felt shaking.

York County 911 also reported people calling to report an earthquake. No injuries or damage was reported.

The quake that hit Thursday continues the seismic activity reported in the Dillsburg area, which has been rattled by hundreds of distinct tremors since October 2008. Jones said the last major seismic activity occurred on Oct. 25, when the U.S. Geological Survey reported a series of earthquakes with magnitudes of 1.8, 2.6 and 2.8.

Jones Geological Services and Dillsburg

Jeri Jones of Jones Geological Services is often mentioned in media accounts of the Dillsburg earthquakes. His company's website has a piece on the Dillsburg series of small events on its web page, mostly focused on the activity last Fall. The isoseismal map contours values of Modified Mercalli intensity from the magnitude 2.1 earthquake of October 19, 2008.

Jones poses the following question:

What makes this swarm of shallow earthquakes interesting to investigate?

1. The number of tremors felt over the last ten weeks
2. The regular “boom” that accompanies many of these tremors
3. A sulfur smell associated with the larger tremors and sometimes within the groundwater

Latest Dillsburg quakes - LCSN at the ready

A seismology team from Columbia University set up portable seismographs in the area. Retired Millersville University professor emeritus of geology Charles Scharnberger holds a map showing earthquake intensity zones. Zone III in center is the most intense with decreasing intensity outside the zone (photo credit: Dan Gleiter, The Patriot-News/2008).

From PennLive.com:

Friday April 24, 2009, 10:28 AM
2 earthquakes reported in Dillsburg area
by LARA BRENCKLE, Of The Patriot-News

A 2.9-magnitude earthquake rattled residents around the Franklintown, Pa., area early this morning, setting off concerns that the series of temblors that rocked northern York County in the fall and early winter have returned. The U.S. Geological Survey reported today's quake occurred at 1:36 a.m.

On Thursday, residents of Dillsburg also experienced tremors, with a 2.4 magnitude quake startling residents there. Dillsburg Borough manager Karen Deibler was in her office when Thursday's quake struck.

"I don't think a lot of people knew what was going on last night because it's been such a long time (since we've had one)," Deibler said.

The last spate of earthquakes occurred from October to January.

It's been quiet, however, and Deibler said people figured they were over. "Nobody really knows what to think at this point," she said.