Abstract
This article reports fractal dimension analysis applied to soil CO2 fluxes measured in an Italian seismic area. The work was carried out with the use of a calibrated flux chamber unit. The fractal dimension (FD) from isotropic variograms was used as a method to understand related scale-dependent phenomena. The aim was to investigate the spatial variability of CO2 flux measurements in four directions (horizontal, vertical, 45° and 135° directions) related to different distances between the measuring points and from a fault. High fractal dimension values were found (2.5 ≤ FD ≤ 3.0). These imply strong anti-persistent behavior near to and far from the fault. Lower fractal dimensions were addressed at longer distances from the fault.
Highlights
Surveys of soil gas have been commonly used to trace buried faults and to study the behavior of endogenous gases of specific origins in the shallow environment [1,2,3,4,5,6,7,8] and have received significant attention over the last few years as earthquake precursors [6,9,10,11,12,13,14,15]
Fractal geometry is the analysis of geometric
Accounting for the above findings, this paper focused on the study of the spatial analysis and variability of CO2 flux from soil using fractal dimensions calculated with the semi-variogram method
Summary
Surveys of soil gas have been commonly used to trace buried faults and to study the behavior of endogenous gases of specific origins in the shallow environment (i.e., trace gases such as radon and helium, and carrier gases such as carbon dioxide, nitrogen, methane, etc.) [1,2,3,4,5,6,7,8] and have received significant attention over the last few years as earthquake precursors [6,9,10,11,12,13,14,15]. Changes in stress/strain associated with seismic activity may force the migration of crustal fluid, in particular along active faults, thereby altering the geochemical characteristics of the surface fault zone [16,17,18]. The movement of these gasses by diffusion and/or advection along active faults will create flow anomalies, with concentrations substantially higher than the background levels; such anomalies may provide accurate information about the position and morphology of the shallow fracturing zone, as well as the permeability within the fault zone [3,4,7,19,20,21].
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