Maarten Van Daele

Lacustrine turbidites as a tool for quantitative earthquake reconstruction: new evidence for a variable rupture mode in south central Chile

Understanding the long-term earthquake recurrence pattern at subduction zones requires continuous paleoseismic records with excellent temporal and spatial resolution and stable threshold conditions. South central Chilean lakes are typically characterized by laminated sediments providing a quasi-annual resolution. Our sedimentary data show that lacustrine turbidite sequences accurately reflect the historical record of large interplate earthquakes (among others the 2010 and 1960 events). Furthermore, we found that a turbidites spatial extent and thickness are a function of the local seismic intensity and can be used for reconstructing paleo-intensities. Consequently, our multilake turbidite record aids in pinpointing magnitudes, rupture locations, and extent of past subduction earthquakes in south central Chile. Comparison of the lacustrine turbidite records with historical reports, a paleotsunami/subsidence record, and a marine megaturbidite record demonstrates that the Valdivia Segment is characterized by a variable rupture mode over the last 900 years including (i) full ruptures (Mw ~9.5: 1960, 1575, 1319 ± 9, 1127 ± 44), (ii) ruptures covering half of the Valdivia Segment (Mw ~9: 1837), and (iii) partial ruptures of much smaller coseismic slip and extent (Mw ~7.5–8: 1737, 1466 ± 4). Also, distant or smaller local earthquakes can leave a specific sedimentary imprint which may resolve subtle differences in seismic intensity values. For instance, the 2010 event at the Maule Segment produced higher seismic intensities toward southeastern localities compared to previous megathrust ruptures of similar size and extent near Concepciόn.

Can turbidites be used to reconstruct a paleoearthquake record for the central Sumatran margin?: COMMENT

Chris Goldfinger, Jason R. Patton, Maarten Van Daele, Jasper Moernaut, C. Hans Nelson, Marc de Batist, and Ann E. Morey Oregon State University, College of Earth, Ocean and Atmospheric Sciences, 104 Ocean Administration Building, Corvallis, Oregon 97331, USA Renard Centre of Marine Geology (RCMG), Department of Geology and Soil Science, Ghent University, Krijgslaan 281/S8, Gent B-9000, Belgium Geological Institute NO G47, Sonneggstrasse 5, 8092 Zürich, Switzerland Instituto Andaluz de Ciencias de la Tierra (IACT) CSIC-Universidad de Granada, Campus de Fuentenueva s/n, 18002 Granada, Spain

Landslides cause tsunami waves : insights from Aysen Fjord, Chile

On 21 April 2007, an Mw 6.2 earthquake produced an unforeseen chain of events in the Aysen fjord (Chilean Patagonia, 45.5°S). The earthquake triggered hundreds of subaerial landslides along the fjord flanks. Some of the landslides eventually involved a subaqueous component that, in turn, generated a series of displacement waves—tsunami-like waves produced by the fast entry of a subaerial landmass into a water body—within the fjord [Naranjo et al., 2009; Sepulveda and Serey, 2009; Hermanns et al., 2013]. These waves, with run-ups several meters high along the shoreline, caused 10 fatalities. In addition, they severely damaged salmon farms, which constitute the main economic activity in the region, setting free millions of cultivated salmon with still unknown ecological consequences.

Varve formation during the past three centuries in three large proglacial lakes in south-central Alaska

The sediments stored in the large, deep proglacial lakes of south-central Alaska are largely unstudied. We analyzed sediments in 20 cores, up to 160 cm long, from Eklutna, Kenai, and Skilak Lakes, using a combination of repeated lamination counting, radionuclide dating, event stratigraphy, and tephrochronology. We show that the characteristically rhythmic layers were deposited annually. Most of these glacial varves consist of one coarse-grained base and a fine-grained top, but varves composed of multiple coarse-grained turbidite pulses are common too. They are likely related to successive episodes of high sediment discharge during flooding, and they become more frequent in all three lakes, along with increased sedimentation rates, during the nineteenth century late phase of the Little Ice Age. These flood turbidites were generated by rain events and intense melting of snow and ice. Other (mega) turbidites are a result of earthquake-triggered slope collapses (e.g., A.D. 1964). Some event layers are present in all three lakes. In addition, the annual time series of varve thickness (normalized annual sedimentation rate) are significantly correlated among the three lakes (p > 0.27; p < 0.001). Differences between the varve thickness records can be attributed partly to the dam construction at Eklutna Lake and outbursts from an ice-dammed lake at Skilak Lake. Geomorphologic differences among the catchments result in further differences in sedimentation patterns in the three lakes.

Holocene event record of Aysén Fjord (Chilean Patagonia) : an interplay of volcanic eruptions and crustal and megathrust earthquakes

In the first months of 2007, the Aysen region in southern Chile was affected by a crustal seismic swarm. Its largest earthquake (M-w 6.2) occurred in April and had its epicenter in Aysen Fjord. Seismic intensities became so high that hundreds of onshore mass movements were triggered, several of which entered into the fjord, resulting in mass transport deposits (MTDs) preserved at the fjord bottom. Here we present a Holocene record of paleo-earthquakes in the previously unstudied Patagonian fjordland based on MTD stratigraphy. High-resolution seismic data retrieved using two different seismic systems (sparker and TOPAS) reveal multiple older MTDs on different stratigraphic levels. Correlation of the seismic stratigraphy with sedimentological data obtained from a long Calypso core (MD07-3117) allows conclusion on the seismic origin of these deposits. Additionally, radiocarbon dating permits constructing an age model, validated by tephrochronology, providing an age for the different MTD levels. We thus present a highly detailed paleoseismological history of the Aysen region, including at least six major Holocene earthquakes, one of which is likely related to a known megathrust earthquake. Other earthquakes are related to activity of the Liquine-Ofqui Fault Zone (LOFZ), forming the main source of seismic hazard in the area. We can infer a general average recurrence time for LOFZ earthquakes of -2,100years in the vicinity of Aysen Fjord with clustered events during the early and late Holocene. Finally, we argue that cascading events (causal link between volcanic and seismic events) may be a frequent phenomenon along the LOFZ.