Combining electrical resistivity tomography and passive seismic to characterise the subsurface architecture of a deeply weathered lateritic hill within the Avon River critical zone observatory
Jessie Weller, Sara Jakica, Sally Thompson, Matthias Leopold
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引用次数: 0
Abstract
Observing the subsurface architecture of the deep Critical Zone (CZ), which lies beyond the uppermost layer of accessible soil, is a complex but crucial task. Near-surface geophysics offers an alternative to accessing the deep CZ at scales relevant to fluid, nutrient and gas transport. As geophysical instruments are sensitive to different subsurface physical properties, their combination can enhance insight into CZ architecture. However, the agreement between and complementarity of multiple geophysical techniques has not been widely assessed for CZ-related questions. This study employed geophysics to image a highly weathered lateritic hill rich in iron oxides developed from Archean granite within the Avon River Critical Zone Observatory, Western Australia. Data gathered from an electrical resistivity tomography (ERT) and horizontal-to-vertical-spectral-ratio (HVSR) passive seismic transect were used to visualise CZ architecture through specific resistivity values and ambient noise contrasts. Both techniques revealed a notable degree of lateral variability consistent with the formation of the ~3–4 m thick duricrust-capped hilltop, the creation of gullies in the sodic material of the pallid zone exposed along the slope and the deposition of ~11 m thick colluvial sediment at the foot slope. Calculated bedrock depth was consistent between the HVSR and ERT instruments along the hilltop plateau but varied from ~23 m to 31 m on the slope and 32 m to 39 m at the foot slope, respectively. Overall, the vertical variation depicted by the ERT, including the differentiation of two layers within the lateritic weathering profile - the pallid zone and saprolite – made up for the inaccuracy of the HVSR technique in depicting layers of similar composition. Moreover, the HVSR method clearly depicted bedrock depth, overcoming the partial masking of the bedrock by saline groundwater in the ERT model. The complementarity of these two methods allowed the development of a detailed conceptual model of subsurface CZ architecture within a saline lateritic weathering profile.
期刊介绍:
Earth Surface Processes and Landforms is an interdisciplinary international journal concerned with:
the interactions between surface processes and landforms and landscapes;
that lead to physical, chemical and biological changes; and which in turn create;
current landscapes and the geological record of past landscapes.
Its focus is core to both physical geographical and geological communities, and also the wider geosciences