Predicting the movements of permanently installed electrodes on an active landslide using time-lapse geoelectrical resistivity data only

Abstract

S U M M A R YIf electrodes move during geoelectrical resistivity monitoring and their new positions are not incorporated in the inversion, then the resulting tomographic images exhibit artefacts that can obscure genuine time-lapse resistivity changes in the subsurface. The effects of electrode movements on time-lapse resistivity tomography are investigated using a simple analytical model and real data. The correspondence between the model and the data is sufficiently good to be able to predict the effects of electrode movements with reasonable accuracy. For the linear electrode arrays and 2-D inversions under consideration, the data are much more sensitive to longitudinal than transverse or vertical movements. Consequently the model can be used to invert the longitudinal offsets of the electrodes from their known baseline positions using only the time-lapse ratios of the apparent resistivity data. The example data sets are taken from a permanently installed electrode array on an active lobe of a landslide. Using two sets with different levels of noise and subsurface resistivity changes, it is found that the electrode positions can be recovered to an accuracy of 4 per cent of the baseline electrode spacing. This is sufficient to correct the artefacts in the resistivity images, and provides for the possibility of monitoring the movement of the landslide and its internal hydraulic processes simultaneously using electrical resistivity tomography only.

Resolution capacity of geophysical monitoring regarding permafrost degradation induced by hydrological processes

“…Firstly, their rough surface characteristics consisting of very coarsegrained material and boulders, their small-scale topography and their high ice contents make good-quality measurements and data inversions difficult to achieve (Hilbich et al, 2009;Hauck and Vonder Mühll, 2003). Secondly, the movement of the landforms disturbs permanent installations and significantly alters the measurement geometry with time (Wilkinson et al, 2010;Loke et al, 2013). Hilbich et al (2009) demonstrated the general applicability of repeated ERT surveys for monitoring permafrost evolution on rock glaciers and highlighted the use of synthetic modelling to aid the sometimes ambiguous interpretation of the results.…”

Interpolation of landslide movements to improve the accuracy of 4D geoelectrical monitoring

“…467 with 92.07% and 91.99% of the data, respectively, having reciprocal errors smaller than 5% 500 (Wilkinson et al, 2010). Data with reciprocal errors above 5% were removed from the data set 501 before inversion.…”

Time-lapse monitoring of fluid-induced geophysical property variations within an unstable earthwork using P-wave refraction

“…Noninvasive geophysical methods, which are capable of estimating physical properties of significant volumes of the subsurface, are well-suited for this application (Donohue et al, 2011). Electrical resistivity tomography (ERT) (Loke and Barker, 1996), for example, has, over recent years, been used for near-surface time-lapse imaging of natural slopes and landslides (e.g., Miller et al, 2008;Uhlenbrook et al, 2008;Cassiani et al, 2009) or, more relevant to the topic of the present work, monitoring the internal condition and temporal dynamics of geotechnical assets (e.g., Sjodahl et al, 2008, Wilkinson et al, 2011Chambers et al, 2014;Gunn et al, 2015a). Favored by the sensitivity of resistivity data to changing hydrogeological conditions, ERT, however, requires an additional stage of calibration, often site dependent, to invert for parameters more relevant to the mechanical description of the investigated target (e.g., moisture content, as in Cassiani et al, 2009;Chambers et al, 2014).…”