Peak Ground Velocity and Shaking Duration Control Coseismic Surficial Sediment Remobilization on Lacustrine Slopes and Emplacement of Seismoturbidites

Abstract Lacustrine paleoseismology has evolved into one of the most prominent techniques to establish long and high-resolution records of past earthquakes, particularly in subduction zones. A thorough understanding of the relation between the various components of strong ground motion and the resulting sedimentary signature is, however, still missing. Therefore, characterization of the source parameters of paleoearthquakes, such as magnitude and location, up to now relies solely on qualitative or semiquantitative considerations, linking the occurrence or absence of coseismic imprints (e.g., turbidites) to seismic shaking strength. These intensity values are usually expressed on the macroseismic scale, as such information is more readily available compared to instrumental data, especially for the numerous historical earthquakes that outdate the first use of seismometers. However, these are relatively subjective ground-motion measures, unable to capture key aspects of strong ground motion (e.g., peak ground acceleration [PGA], peak ground velocity [PGV], and duration). In this study, we determine the relation between these quantitative ground-motion values calculated for the bottom of a lake and the sedimentary shaking imprints identified therein. To achieve this, we focus on the sedimentary signature of instrumentally recorded megathrust earthquakes in south-central Chile. This includes the 1960 Mw 9.5 Valdivia earthquake and the 2010 Mw 8.8 Maule earthquake. A compilation of existing sedimentological data shows that coseismic deposits related to either of these events are identified in over 20 lakes. For these deposits, PGV scales log–logistically to the relative abundance of turbidites in each lake (within a 13 and 40 cm/s minimum and maximum threshold, respectively), whereas the turbidite volume correlates to both strength (PGA and/or PGV) and duration of shaking. By linking lacustrine imprint characteristics for both earthquakes to local ground motions, we bridge the gap between sedimentology and seismology, opening perspectives toward quantitative characterization of paleoearthquakes based on the signature of their imprint in lake sediment sequences.