Some Interesting Facts about Correlation Between Gravity Anomalies and Heights with Implications Towards the Correction Density Estimation
Abstract:It has been well known that free-air anomalies and gravitational effects of the topographic masses are mutually proportional, at least in general. However, it is rather intriguing that this feature is more remarkable in elevated mountainous areas than in lowlands or flat regions, as we demonstrate on practical examples. Further, since the times of Pierre Bouguer we know that gravitational effect of the topographic masses is station-height-dependent. In our presentation we show that the respective contributions to this height dependence, although they are nonzero, are less significant in the cases of both the nearest masses and the more remote ones while the contribution of the masses within hundreds and thousands of meters from the gravity station is dominant. We also illustrate that, surprisingly, gravitational effects of the non-near topographic masses can be apparently independent on their respective volumes, while their gravitational effects are still well proportional to the gravity station heights.
On the other hand, based on interpretational reasons, Bouguer anomaly should not correlate very much with the heights of the measuring points or, more specifically, with the gravitational effect of the topographic masses. Standard practice is to estimate a suitable (uniform) reduction or correction density within the study area in order to minimize such an undesired correlation and, vice versa, the minimum correlation is often utilized as a criteria for estimating such density.
Our main objective is to point out, from the aspect of the correction density estimations, that the contributions of the topographic masses should be viewed alternatively, depending on the particular distances of the respective portions of those masses from the gravity station. We have tested majority of the existing methods of such density estimation and developed a new one which takes the facts mentioned above into consideration.
This work was supported by the Slovak Research and Development Agency under the contracts APVV-0827-12 and APVV-0194-10.