Hydrologic Effects of Pymatuning Earthquake
Within hours after the Pymatuning earthquake of September 25, 1998, in northwestern Pennsylvania, local residents reported wells becoming dry, wells beginning to flow, and the formation of new springs. About 120 household-supply wells reportedly went dry within 3 months after the earthquake. About 80 of these wells were on a ridge between Jamestown and Greenville, where water-level declines of as much as 100 feet were documented. Accompanying the decline in water levels beneath the ridge was an increase in water levels in valley wells of as much as 62 feet. One possible explanation of the observed hydrologic effects is that the earthquake increased the vertical hydraulic conductivity of shales beneath the ridge, which allowed ground water to drain from the hilltops. Computer simulations of ground-water flow beneath the ridge between Jamestown and Greenville indicate that increasing the vertical hydraulic conductivity of shale confining beds about 10 to 60 times from their pre-quake values could cause the general pattern of decreased water levels on hilltops and increased levels in valleys.
Well Hydrograph
| SITE IDENTIFIER | 412350080223701 |
| LOCAL NUMBER | MR-1364 |
| LOCATION | Latitude 41`23'50", Longitude 80`22'37", Hydrologic Unit 05030102, at Greenville, Pa. |
| OWNER | Borough of Greenville |
| AQUIFER | Sandstone of Cussewago Formation of Early Mississippian age |
| WELL CHARACTERISTICS | Drilled artesian well, diameter 6 in, depth 235 ft, cased to 41 ft, open hole |
| INSTRUMENTATION | Continuous strip-chart recorder |
| DATUM | Elevation of land-surface datum is 965 ft above sea level, from topographic map. Measuring point: Top of plywood cover, 2.26 ft above land-surface datum |
| REMARKS | Water levels affected by intermittent pumping |
| PERIOD OF RECORD | March 1964 to September 2005 |
| EXTREMES FOR PERIOD OF RECORD (through September, 1997) | Highest water level, 1.43 ft below land-surface datum, Dec. 25, 1968; lowest, 8.31 ft below land-surface datum, Feb. 12, 1967 |
| FUNDING FOR WELL | The observation well was operated by USGS in cooperation with the Pennsylvania Department of Environmental Protection |
Twenty-Year Update
Lead author of the project report Gary Fleeger (PaGS ret.) updated the status of water levels in affected groundwater wells in a 2018 article in Pennsylvania Geology.
Within hours after the Pymatuning earthquake of September 25, 1998, in northwestern Pennsylvania, local residents reported wells becoming dry, wells beginning to flow, and the formation of new springs. About 120 household-supply wells reportedly went dry within 3 months after the earthquake. About 80 of these wells were on a ridge between Jamestown and Greenville, where water-level declines of as much as 100 feet were documented. Accompanying the decline in water levels beneath the ridge was an increase in water levels in valley wells of as much as 62 feet. One possible explanation of the observed hydrologic effects is that the earthquake increased the vertical hydraulic conductivity of shales beneath the ridge, which allowed ground water to drain from the hilltops. Computer simulations of ground-water flow beneath the ridge between Jamestown and Greenville indicate that increasing the vertical hydraulic conductivity of shale confining beds about 10 to 60 times from their pre-quake values could cause the general pattern of decreased water levels on hilltops and increased levels in valleys.
Well Hydrograph
| SITE IDENTIFIER | 412350080223701 |
| LOCAL NUMBER | MR-1364 |
| LOCATION | Latitude 41`23'50", Longitude 80`22'37", Hydrologic Unit 05030102, at Greenville, Pa. |
| OWNER | Borough of Greenville |
| AQUIFER | Sandstone of Cussewago Formation of Early Mississippian age |
| WELL CHARACTERISTICS | Drilled artesian well, diameter 6 in, depth 235 ft, cased to 41 ft, open hole |
| INSTRUMENTATION | Continuous strip-chart recorder |
| DATUM | Elevation of land-surface datum is 965 ft above sea level, from topographic map. Measuring point: Top of plywood cover, 2.26 ft above land-surface datum |
| REMARKS | Water levels affected by intermittent pumping |
| PERIOD OF RECORD | March 1964 to September 2005 |
| EXTREMES FOR PERIOD OF RECORD (through September, 1997) | Highest water level, 1.43 ft below land-surface datum, Dec. 25, 1968; lowest, 8.31 ft below land-surface datum, Feb. 12, 1967 |
| FUNDING FOR WELL | The observation well was operated by USGS in cooperation with the Pennsylvania Department of Environmental Protection |
Twenty-Year Update
Lead author of the project report Gary Fleeger (PaGS ret.) updated the status of water levels in affected groundwater wells in a 2018 article in Pennsylvania Geology.