Mid-to-Late Holocene history of mass movement deposits at maar Lake Issarlès (Ardèche, France): a paleosismological record ?
Bibliographic record
Abstract
Located in Massif Central (Ardèche, Auvergne-Rhône-Alpes, France), Lake Issarlès experienced since 1954 decametric lake level changes due to EDF water management. It has been hypothesized in several endoreic and maar lakes that lake level fluctuations can increase the recurrence of mass movement deposits (MMDs) because of their steep slopes (Kliem et al., 2013). The deep basin of the maar Lake Issarlès is filled by several meters of MMDs clearly visible in seismic reflection surveys and sediment cores. Here, we present results from a multiproxy study (geophysics, radiography, XRF, radionuclides & radiocarbon dating) that investigates the potential of Lake Issarlès as a paleo-seismological recorder (Defive et al., 2023).Derived from a geophysical survey using a 4 kHz from Knudsen in June 2019 (five months before Le Teil earthquake; see details below) a coring campaign was conducted in 2020 from an anchored platform in the central deep basin, together with a new seismic reflection survey using high-resolution sub-bottom profiler Echoes 10 000. Acoustic sub-bottom data highlight several MMDs in the central basin and at the bottom of slopes, and a recent thin reflector close to the water-sediment interface. At about 7 meters in sediments, a metric sized MMD prevents deeper acoustic penetration. The 7 m-long composite sequence, documented by radiography, geochemistry, radiocarbon, radionuclides and “varves” counting, consists of laminated sediment interrupted by rapidly deposited layers such as clayey layers, MMDs, slumps and turbidites. The first event could be linked to the recent damaging Mw 4.9 (MLv 5.4) earthquake that occurred on November 11th, 2019 in Le Teil village, 60 km east from Lake Issarlès. Another event is contemporaneous with the installation of underground pipes between 1947 and 1953 by EDF, and two events are synchronous with regional historical earthquakes occurred at Tricastin in 1934 & 1873 (MLv ~7) (20 km south of Le Teil).The whole sequence reaches back to 6000 years (radiocarbon dating) and delivers at least ten main events. Four main sedimentary units are derived from (1) the recurrence of MMDs visible in the sediment cores & the seismic profiles, (2) the dynamic of the main driver PC1 of the Principal Component Analyses of XRF data as well as the inc/coh ratio fluctuations, which is a proxy of organic matter content (Jouve et al., 2013; Guyard et al, 2007). Changes in sedimentation rates and sedimentary dynamics extracted from this multiproxy study suggests the lake sensitivity to record paleoearthquakes may have fluctuate through time and that the magnitude of past events cannot be extrapolated from the size or volume of the MMDs. Kliem et al. (2013b) Quaternary Science Reviews 71, 131–146.Defive et al. (2023) Quaternaire 34(2), 93-122Jouve et al. (2013) Quaternary Science Reviews 71, 191-204Guyard et al. (2007) Quaternary Science Reviews 26, 2644-2660Chapron et al. (2022) Quaternary International 636, 134-153
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.001 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".