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Long Lacustrine Sedimentary Records in South-Central Chile Evaluate the Spatiotemporal Variability of Megathrust Earthquakes

Description: 

Along the Valdivia Segment of the Chilean subduction zone, giant full-segment ruptures such as the 1960 CE (M_w 9.5) earthquake occur on average every ~300 years. Between these events, great partial ruptures such as the 2016 CE, 1837 CE, 1737 CE or the prehistorical 1455 CE earthquakes are known to occur. However, their contribution to overall stress relieve remains unclear, mostly because the along-strike extent and down-dip location of such pre-instrumental ruptures are poorly constrained. Therefore, comprehensive studies on the spatiotemporal variability of these ruptures is crucial to validate earthquake cycle models and improve seismic hazard assessment in South-Central Chile.

Paleoseismic records obtained from short sediment cores in eleven lakes along the Valdivia Segment allowed us to study the along-strike extent of known (pre)historic partial ruptures during the last two millennia. New long-core records from Lago Rupanco and Lago Huillinco additionally allow evaluating the temporal and down-dip rupture variability by expanding the paleoshaking record to the last ca. 5000-8000 years (Lago Rupanco) and linking it to tsunami records (Lago Huillinco). The lacustrine sedimentary imprint of earthquakes causing strong shaking can consist of turbidites, mass transport deposits or in-situ soft sediment deformation structures. High-resolution core scanning (X-CT, XRF, MSCL, etc.) allows us to detect and characterize these event layers in numerous cores and identify those related to megathrust earthquakes to then assess the related earthquake shaking quantitatively. Correlation of regional tephra layers, for which precise ages can be obtained independently, improve the radiocarbon-based age-depth models, resulting in more accurate paleoseismic age control and estimations of recurrence intervals. These lacustrine records will significantly enhance our understanding of the spatiotemporal variability of full and partial ruptures of the Valdivia segment. The analysis of sedimentary records from different lakes will increase our process understanding on the formation of seismogenic and tsunamigenic event layers.

Session: From Faults to Fjords: Earthquake Evidence in Terrestrial and Subaqueous Environments - I

Type: Oral

Date: 5/1/2024

Presentation Time: 08:45 AM (local time)

Presenting Author: Markus

Student Presenter: Yes

Invited Presentation: 

Authors