Earthquake‐induced soft‐sediment deformations and seismically amplified erosion rates recorded in varved sediments of Köyceğiz Lake (SW Turkey)

Abstract

Earthquake‐triggered landslides amplify erosion rates in catchments, i.e., catchment response (CR) to seismic shocks. In addition to historical eyewitness accounts of muddy rivers implying CRs after large earthquakes, several studies have quantitatively reported increased sediment concentrations in rivers after earthquakes. However, only a few paleolimnological studies could detect CRs within lacustrine sedimentary sequences as siliciclastic‐enriched intercalations within background sedimentation. Since siliciclastic‐enriched intercalations can easily be of nonseismic origin, their temporal correlation with nearby earthquakes is crucial to assign a seismic triggering mechanism. In most cases, either uncertainties in dating methods or the lack of recent seismic activity has prevented reliable temporal correlations, making the seismic origin of observed sedimentary events questionable. Here we attempt to remove this question mark by presenting sedimentary traces of CRs in the 370‐year‐long varved sequence of Köyceğiz Lake (SW Turkey) that we compare with estimated peak ground acceleration (PGA) values of several nearby earthquakes. We find that earthquakes exceeding estimated PGA values of ~20 cm/s2 can induce soft‐sediment deformations, while CRs seem only to be triggered by PGA levels higher than 70 cm/s2. In Köyceğiz Lake, CRs produce Cr‐ and Ni‐enriched sedimentation due to the seismically mobilized soils derived from ultramafic rocks in the catchment. Given the varve chronology, the residence time of the seismically mobilized material in the catchment is determined to be 5 to 10 years.

Earthquake‐Induced Chains of Geologic Hazards: Patterns, Mechanisms, and Impacts

“…Lake sediment can be a useful archive of post-seismic sediment input (Howarth et al, 2016), although lacustrine turbidites and deformed layers (Karlin & Abella, 1992;Moernaut et al, 2014;Sims, 1973) might not always represent landslide inputs from surrounding catchments. Along the Anatolian Fault in Turkey, Avşar et al (2014Avşar et al ( , 2016 used the geochemical fingerprint of ultramafic rocks associated with EQTLs to pin down the timing and duration of sediment pulses, which they found lasted 5-10 years. Alluvial deposits also can record sediment perturbations after earthquakes, with a notable example being the alluvial fill around Pokhara, now recognized as the legacy of catastrophic sedimentation following medieval earthquakes (Schwanghart et al, 2016).…”

Integrated Paleoseismic Chronology of the Last Glacial Lake Lisan: From Lake Margin Seismites to Deep‐Lake Mass Transport Deposits

“…Sediment sequences containing MTDs have widely been used successfully for paleoseismic studies. Recently, for example, this approach has been applied effectively in the Cascadia region (Adams, 1996;Goldfinger et al, 2007;Goldfinger et al, 2003;Morey et al, 2013), France (Chapron et al, 1999;Wilhelm et al, 2016), British Columbia, Canada (Blais-Stevens & Clague, 2001), Switzerland (Schnellmann et al, 2006;Strasser et al, 2013), Chile (Blumberg et al, 2008;Moernaut et al, 2014), and Turkey (Avşar et al, 2016;Schwab et al, 2009). Earthquake triggering for mass transport at Lake Lisan (paleo-Dead Sea) is supported by its location on the seismically active Dead Sea Transform (DST) and by the on-shore association of deformations associated with faulting (Marco & Agnon, 2005).…”

Interpreting Soft Sediment Deformation and Mass Transport Deposits as Seismites in the Dead Sea Depocenter

“…Soft‐sediment deformation is a disruption of unlithified sediments (Alsop et al, ; Owen et al, ; Van Loon, ) and is widely documented in both subaerial (McKEE et al, ; Moretti, ; Pedersen et al, ) and subaqueous environments (Avşar et al, ; Gladkov et al, ; Jiang et al, ; Sims, ). Commonly, the disturbances are triggered either by seismic shaking (Liu‐Zeng et al, ; Monecke et al, ; Sakaguchi et al, ; Sims, ; Strasser, Kölling, et al, ) or by nonseismic triggers, for example, tides (Greb & Archer, ), storm waves (Molina et al, ), floods (Li et al, ), and sediment overloads (Moretti et al, ; Moretti & Sabato, ).…”