What controls the remobilization and deformation of surficial sediment by seismic shaking? Linking lacustrine slope stratigraphy to great earthquakes in South–Central Chile

Abstract

Remobilization and deformation of surficial subaqueous slope sediments create turbidites and soft sediment deformation structures, which are common features in many depositional records. Palaeoseismic studies have used seismically-induced turbidites and soft sediment deformation structures preserved in sedimentary sequences to reconstruct recurrence patterns andin some casesallow quantifying rupture location and magnitude of past earthquakes. However, current understanding of earthquake-triggered remobilization and deformation lacks studies targeting where these processes take place, the subaqueous slope and involving direct comparison of sedimentary fingerprint with well-documented historical earthquakes. This study investigates the sedimentary imprint of six megathrust earthquakes with varying rupture characteristics in 17 slope sediment cores from two Chilean lakes, Riñihue and Calafqu en, and evaluates how it links to seismic intensity, peak ground acceleration, bracketed duration and slope angle. Centimetre-scale stratigraphic gaps ranging from ca 1 to 20 cmcaused by remobilization of surficial slope sedimentwere identified using high-resolution multi-proxy core correlation of slope to basin cores, and six types of soft sediment deformation structures ranging from ca 1 to 25 cm thickness using high-resolution three-dimensional X-ray computed tomography data. Stratigraphic gaps occur on slope angles of ≥2.3°, whereas deformation already occurs from slope angle 0.2°. The thickness of both stratigraphic gaps and soft sediment deformation structures increases with slope angle, suggesting that increased gravitational shear stress promotes both surficial remobilization and deformation. Seismic shaking is the dominant trigger for surficial remobilization and deformation at the studied lakes. Total remobilization depth correlates best with bracketed duration and is highest in both lakes for the strongest earthquakes (M w ca 9.5). In lake Riñihue, soft sediment deformation structure thickness and type correlate best with peak ground acceleration 2365

Orbital‐ and Millennial‐Scale Changes in Lake‐Levels Facilitate Earthquake‐Triggered Mass Failures in the Dead Sea Basin

“…During 35–15 ka, 66% of the events are Type II deposits which are comparable in composition to aragonite‐detritus laminae (Figure 2), with thickness mostly <5 cm (Table ), and unrelated to other typical preconditioning factor(s) for subaqueous landslides such as enhanced sedimentation rate (Figure 3). Surficial sediment remobilization triggered by earthquakes that is, reported from Chilean lakes and offshore Japan may explain these new observations of very thin layers of mixed sediments from the Dead Sea (McHugh et al., 2016; Moernaut et al., 2017; Molenaar et al., 2021). These factors connected to lake‐level change can collectively favor the observed pattern of seismogenic mass failures in the Dead Sea.…”

Recognising surface versus sub-surface deformation of soft-sediments: Consequences and considerations for palaeoseismic studies

“…Rossetti and Goes, 2000;Basilone et al, 2016, p.320;Kumar et al, 2021), with erosion above slump folds indicating that folding took place at the surface prior to deposition, and 'blanketing' by overlying beds (Ortner and Kilian, 2016, p.357). Surficial deformation and remobilisation of sediment occurred at depths of up to 20 cm from the sediment surface in Chilean lakes, with this depth increasing with greater slope angles and larger magnitude earthquakes (Molenaar et al, 2021). The stratigraphic record preserved by seismoturbidites in basinal sediments is crucial to recognise earthquake-induced surficial deformation of sediments in slope settings (Molenaar et al, 2021).…”

“…Surficial deformation and remobilisation of sediment occurred at depths of up to 20 cm from the sediment surface in Chilean lakes, with this depth increasing with greater slope angles and larger magnitude earthquakes (Molenaar et al, 2021). The stratigraphic record preserved by seismoturbidites in basinal sediments is crucial to recognise earthquake-induced surficial deformation of sediments in slope settings (Molenaar et al, 2021).…”

“…Kuhlman et al, 2016). Molenaar et al (2021) also recognised that, although much of the deformation observed in sediment cores from lakes in Chile is linked to surficial deformation associated with megathrust earthquakes, other SSDs are created deeper in the sediment pile by seismic-induced dewatering of intercalated volcanic deposits, which would consequently weaken overlying sediment and facilitate sub-surface deformation (Moernaut et al, 2019). Tephra layers dewater during seismic shaking leading to an increase in density of these layers and a weakening of the overlying lake sediment, which then fails and translates downslope (Moernaut et al, 2019, p.100).…”

Magnitude and source area estimations of severe prehistoric earthquakes in the western Eastern Alps

“…Therefore, the inferred earthquake events are relatively scaled above the lake's individual intensity threshold based on their imprint size. For Piburgersee, SSDS are scaled based on three development stages ranging from folded layer, incipient breccia to intraclast breccia with increasing intensity (Molenaar et al, 2021;Oswald et al, 2021b;Wetzler et al, 2010) including the deposit thickness and a normalization to the range 0 to 1. The largest imprint in each record corresponds to a value of 1.…”