What controls the remobilization and deformation of surficial sediment by seismic shaking? Linking lacustrine slope stratigraphy to great earthquakes in south-central Chile
Molenaar, A.; Van Daele, M.; Vandorpe, T.; Degenhart, G.; De Batist, M.; Urrutia, R.; Pino, M.; Strasser, M.; Moernaut, J. (2020). What controls the remobilization and deformation of surficial sediment by seismic shaking? Linking lacustrine slope stratigraphy to great earthquakes in south-central Chile. ESSOAr: Earth and Space Science Open Archive (preprint): 1-66. https://dx.doi.org/10.1002/essoar.10504161.1
In: ESSOAr: Earth and Space Science Open Archive. American Geophysical Union: Washington, DC.
Download PDFCite Tools ShareAbstractRemobilization and deformation of surficial subaqueous slope sediments create turbidites and soft sediment deformation structures (SSDS), which are common features in many depositional records. Paleoseismic studies have used seismically-induced turbidites and SSDS preserved in sedimentary sequences to reconstruct recurrence patterns and—in some cases—allow quantifying rupture location and magnitude of past earthquakes. However, our 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. Here we investigate the sedimentary imprint of six megathrust earthquakes in 17 slope sediment cores from two Chilean lakes, Riñihue and Calafquén, and link it to magnitude, seismic intensity, peak ground acceleration (PGA) and Arias Intensity (Ia). Centimeter-scale stratigraphic gaps—caused by remobilization of surficial slope sediment—were identified using high-resolution multi-proxy core correlation of slope to basin cores and six types of SSDS using high-resolution 3D X-ray computed tomography data. Centimeter-scale gaps occur at the studied sites when Ia and moment magnitude (Mw) exceed 3.85 m/s and 8.8, respectively. Total remobilization depth correlates best with Ia and is highest in both lakes for the strongest earthquakes (Mw ~9.5). In lake Riñihue, SSDS thickness and type correlates best with PGA providing first field-based evidence of progressive SSDS development with increasing PGA for SSDS caused by Kelvin-Helmholtz instability (KHI). 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 SSDS increases with slope angle suggesting that increased slope angle—and thereby gravitational shear stress—promotes both remobilization and deformation. Seismic shaking is the dominant trigger for remobilization and deformation at our studied lakes. We propose that long duration and low frequency content of seismic shaking facilitates surficial remobilization, whereas ground motion amplitude controls KHI-related SSDS development.
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