Catchment‐Scale Architecture of the Deep Critical Zone Revealed by Seismic Imaging

Abstract

Weathering and erosion processes are crucial to Critical Zone (CZ) evolution, landscape formation and availability of natural resources. Although many of these processes take place in the deep CZ (∼10–100 m), direct information about its architecture remain scarce. Near‐surface geophysics offers a cost‐effective and minimally intrusive alternative to drilling that provides information about the physical properties of the CZ. We propose a novel workflow combining seismic measurements, petrophysical modelling and geostatistical analysis to characterize the architecture of the deep CZ at the catchment scale, on the volcanic tropical island of Basse‐Terre (Guadeloupe, France). With this original workflow, we are for the first time able to jointly produce maps of the water table and the weathering front across an entire catchment, by means of a single geophysical method. This integrated view of the CZ highlights complex weathering patterns that call for going beyond “simple” hillslope CZ models.

Exploring the Critical Zone Heterogeneity and the Hydrological Diversity Using an Integrated Ecohydrological Model in Three Contrasted Long‐Term Observatories

“…Subplots (a–c) show pressure‐wave velocity ( V p) models obtained from seismic refraction tomography data collected in Naizin (a), Auradé (b), and Strengbach (c) watersheds. Soil and regolith boundaries are defined with V p velocity thresholds of 700 and 1,400 m/s, respectively (Pasquet et al., 2022). Regolith thicknesses estimated along these transects are approximately 10–13 m in Naizin, 3–9 m in Auradé, and 2–5 m in the Strengbach.…”

“…Observations of the weathered material thickness gathered from previous studies (in depth profiles, boreholes, piezometers; Ackerer et al., 2021; Lesparre et al., 2020; Molénat et al., 2013; Pasquet, 2019; Trochon et al., 2023) and estimates derived from geophysical measurements were used to map the regolith thickness within the three watersheds. Geophysical measurements consist of seismic refraction tomography (SRT) data collected at each site to characterize the subsurface structure along hillslopes (more details on the SRT method are given in Supporting Information ).…”

Impacts of aquifer's geometry estimated from seismic refraction tomography on hydrogeophysical variables

“…Therefore, basic but crucial information, such as the interface geometry between the different CZ underground compartments, is often missing (Brooks et al, 2015). Recent studies show that the characterization of the underground CZ structure remains challenging (Flinchum et al, 2018;Gourdol et al, 2020;Kaufmann et al, 2020, Pasquet et al, 2022.…”

“…Moreover, p v is lower in secondary minerals (i.e., clays, oxides) than in parent minerals (i.e., quartz, plagioclase) (Olona et al, 2010;Parsekian et al, 2015). SRT is thus well suited to distinguish the spatial variability of the interfaces between the CZ underground compartments (Befus et al, 2011;Flinchum et al, 6/62 2018;Holbrook et al, 2013;Olona et al, 2010;Olyphant et al, 2016;Huang et al, 2021, Pasquet et al, 2022St. Clair et al, 2015).…”

Mapping Variations in Bedrock Weathering With Slope Aspect Under a Sedimentary Ridge‐Valley System Using Near‐Surface Geophysics and Drilling

“…Seismic refraction can effectively capture the heterogeneity in the subsurface weathered bedrock structure, which can vary drastically from ridge to channel (Leone et al, 2020;Pasquet et al, 2022;Wang et al, 2021). By combining borehole and geophysical methods, recent studies have calibrated geophysical data to direct observations to infer weathering thickness across a landscape (Flinchum, Holbrook, Rempe, et al, 2018;Gu et al, 2020;Hayes et al, 2019;Holbrook et al, 2014Holbrook et al, , 2019Olona et al, 2010).…”