ANALYSIS OF THE LONG WAVELENGTH GRAVITY ANOMALIES IN PENNSYLVANIA

The gravity field in Pennsylvania contains several long wavelength anomalies, both positive and negative. Simple wavelength analysis suggests that the causative density anomalies must either be very thin and shallow or more massive and perhaps as deep as 5 to 10 kilometers.

The objective of this project is to remap the gravity field and to: perform wavelength analysis of the resulting map; model the resulting gravity anomalies and test correlations with long-wavelength topographic variations. Particular attention is paid to the Scranton gravity high and the Beaver Falls / Pittsburgh gravity low. Modeling may lead to a better understanding of what, if any, correlations can be made between the anomalies and currently mapped surface geology.

Contour maps of the gravity data were created utilizing both contouring and GIS software. For analysis, a 100 kilometer long gravity profile for the Scranton gravity high and a 200 kilometer long gravity profile for the Beaver Falls gravity low have been created, and the two profiles are being used in gravity-modeling software to develop plausible sub-surface density models to help constrain the geology at depth. Currently the models suggest the bodies are deeply buried, between 5 and 20 kilometers for the two anomalies.

Using the comprehensive LIDAR data set for the state of Pennsylvania, we are working to filter out short- and medium-wavelengths from the topographic data. We will then develop mathematical methods to compare the long wavelength elevation data with the gravity data to determine if there might be a causative relationship. Preliminary work (primarily visual comparison of the Scranton gravity high) suggest a possible correlation with topography.

Subsequent density models will be constrained relevant surficial and subsurface geologic control, such as but not limited to coal deposits in the area of the two gravity anomalies, to determine if a shallower body could potentially have a similar gravitational signature as that displayed by the profiles.

In holistically analyzing the long wavelength anomalies in Pennsylvania’s gravity field, and relationships to subsurface geology and topography, we hope to develop more comprehensive understanding of the role near-surface versus deep-seated density variations have in controlling the observed gravity in Pennsylvania.