Recent Dillsburg, York County, Pennsylvania earthquake sequence has been relatively poorly recorded by regional and national seismographic network stations when compared with other earthquakes that occurred in the northeastern United States. There are only four stations within 100 km from the epicenter and the nearest station, MVL (Millersville University), was about 53 km away from the epicenter (see the map above).

Hence, the location of the largest shock (mainshock) on 10/10/2008 at 04:22:07 EDT as well as much smaller foreshocks and aftershocks were poorly determined, which can be seen from the widely scattered epicenters of those earthquakes. Usually, foreshocks, mainshock and aftershocks of such small sized earthquake sequence will occur very close to each other as a "cluster".

17 small earthquakes that occurred around Dillsburg since Oct. 5th, 2008 until Oct. 23, 2008 are plotted with red circles. The circle size is proportional to magnitude of each event. On Oct. 23, 2008, field crew from the Lamont Cooperative Seismographic Network (LCSN) deployed three portable digital seismographs in the epiecentral area in order to determine more accurate epicenters of future earthquakes in the region.

Three portable seismographic stations deployed around the mainshock epicenter are plotted as blue triangles in the map, whereas permanent seismographic stations of the LCSN are plotted with solid triangles: MVL (Millerville University), FMPA (Franklin and Marshall College). Other earthquakes that occurred in the region are plotted with open circles. The largest event was magnitude 4.1 that occurred on 04/23/1984 in Lacaster seismic zone.

Waveform (seed volume for the mainshock, 10/19/2008 08:22:07 UTC)

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