Comment on “Nature of the recent vertical ground movements inferred from high-precision leveling data in an intraplate setting: NE Ardenne, Belgium” by A. Demoulin and A. Collignon

Abstract

[01] Using yearly leveling surveys performed from 1993 to 1998 in the Ardenne, as well as historic leveling results from 1948 and 1974, Demoulin and Collignon [2000] (hereinafter referred to as D&C) observed that the total vertical ground movement (less than 1 cm) over a 20-to 30year period is barely higher than the yearly displacements measured to a few millimeters per year. They eliminated various sources of errors from their measurements and subsequently interpreted the resulting short-term oscillating crustal displacements as true tectonic motions within the upper crust accompanying the long-term deformation of uplifting areas in intraplate settings. Their justification is that the leveling discontinuities coincide with faults they assume to be active. In their conclusions, D&C suggested that such motions and their variations could be used to monitor potential seismogenic faults and even to foretell earthquakes. [2] Unfortunately, it is our opinion that the data analysis of D&C is inadequate and does not support the subsequent interpretation. Specifically, we interpret the apparent oscillations in the leveling data as the expected expression of the noisy character of leveling differences with amplitudes ranges of 0.5 to 1 cm. If this premise is accepted then there is also no evidence to suggest that the boundary faults in the study area are active. We thus feel that the conclusions of D&C are premature until their observations can be corroborated by improved observations or by other independent measurements. In this note, we present a careful statistical analysis to support our position.