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Earthquake-triggered remobilization of surficial slope sediment: A paradigm-shift in turbidite paleoseismology? : Identification, quantification and dating of cm-scale unconformities in lacustrine and oceanic slope sequences / Ariana Molenaar
VerfasserMolenaar, Ariana
Betreuer / BetreuerinnenMoernaut, Jasper
ErschienenInnsbruck, 2018
Umfang7 unterschiedlich gezählte Seiten, 66 Seiten : Illustrationen, Diagramme, Karten
HochschulschriftUniversität Innsbruck, Masterarbeit, 2018
Datum der AbgabeJuli 2018
SpracheEnglisch
DokumenttypMasterarbeit
Schlagwörter (DE)Paleoseismologie / Erdbeben / Sedimentologie / Chile / Japan Trog / Turbidite
Schlagwörter (EN)paleoseismology / earthquake / sedimentology / Chile / Japan Trench / turbidite
URNurn:nbn:at:at-ubi:1-23254 Persistent Identifier (URN)
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Earthquake-triggered remobilization of surficial slope sediment: A paradigm-shift in turbidite paleoseismology? [5.24 mb]
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Zusammenfassung (Englisch)

Reliable knowledge on past earthquake recurrence is of key importance for seismic hazard assessment. However, short time-span of instrumental earthquake records relative to typical recurrence time of the largest earthquakes in a study area inhibits good estimations. Turbidite paleoseismology seeks to further extend the time-span of seismological observations through the study of turbidite records within lakes and oceans caused by earthquake-induced remobilization of slope sediment. For a good interpretation of these records, a thorough understanding of the processes under which sediment is remobilized is essential. However, many past studies simply assumed that remobilization took place by failure of thick subaquatic slope sequences which transformed into turbidity currents downslope. In contrast, recent research on basin cores of both lake and ocean showed that earthquake-triggered generation of turbidity currents occurred by remobilization of the upper few cm of surficial sediment, termed “surficial slope remobilization”. The goal of this study is to further develop our understanding of the mechanism and relevance of this process in both lakes and ocean margins. Slope sequences of both lacustrine (Lago Riñihue, Chile) and ocean (Japan Trench) settings were investigated. Different methods were chosen for pinpointing, quantification and dating of cm-scale unconformities: Stratigraphic correlation for Lago Riñihue and analysis by geochemical and geophysical proxies for the Japan Trench. In both settings surficial remobilization-related unconformities were identified and their erosional thickness quantified. Dating suggested good correlation between cm-scale erosion and historical earthquake records. Also, deformation structures were observed within the sediment of Lago Riñihue. A correlation between deformation occurrence and earthquake intensity was interpreted from our data. Former research hypothesized that earthquake-triggered surficial remobilization occurred over a uniform thickness on large slope segments. However, our results showed great variation in remobilization depth within individual slope segments. No clear correlation was observed between remobilization thickness and earthquake intensity. Deformation and remobilization depth did show linear correlation with slope angle increase for the lower slope angles of Lago Riñihue. The shear strength of Lago Riñihue and Japan Trench sediment was studied to further investigate the potential impact of seismic shaking on sediment consolidation, termed “seismic strengthening”. Sharp increases in shear strength were linked to individual earthquakes strongly suggesting that seismic shaking caused overconsolidation of the slope sediments. Further research is required to fully understand the process of surficial remobilization and its interconnection with soft sediment deformation and consolidation of sediment by seismic shaking.

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