Coastal lake sediments reveal 5500 years of tsunami history in south central Chile

Abstract

We present an exceptionally long and continuous coastal lacustrine record of ~5500 years from Lake Huelde on the west coast of Chiloé Island in south central Chile. The study area is located within the rupture zone of the giant AD 1960 Great Chilean Earthquake (M W 9.5). The subsequent earthquake-induced tsunami inundated Lake Huelde and deposited mud rip-up clasts, massive sand and a mud cap in the lake. Long sediment cores from 8 core sites within Lake Huelde reveal 16 additional sandy layers in the 5500 year long record. The sandy layers share sedimentological similarities with the deposit of the AD 1960 tsunami and other coastal lake tsunami deposits elsewhere. On the basis of general and site-specific criteria we interpret the sandy layers as tsunami deposits. Age-control is provided by four different methods, 1) 210 Pb-dating, 2) the identification of the 137 Cs-peak, 3) an infrared stimulated luminescence (IRSL) date and 4) 22 radiocarbon dates. The ages of each tsunami deposit are modelled using the Bayesian statistic tools of OxCal and Bacon. The record from Lake Huelde matches the 8 regionally known tsunami deposits from documented history and geological evidence from the last ~2000 years without overor underrepresentation. We extend the existing tsunami history by 9 tsunami deposits. We discuss the advantages and disadvantages of various sedimentary environments for tsunami deposition and preservation, e.g. we find that Lake Huelde is 2 to 3 times less sensitive to relative sea-level change in comparison to coastal marshes in the same region.

Holocene Event Record of Aysén Fjord (Chilean Patagonia): An Interplay of Volcanic Eruptions and Crustal and Megathrust Earthquakes

“…Since the northern part of the Valdivia segment is currently locked (Moreno et al, 2011), maximal slip is expected in the north, as was the case during the 1960 Great Chilean earthquake. (Kempf et al, 2017) and to a turbidite in Lake Riñihue (1,929-2,103 cal years B.P.) However, should a large amount of slip occur at the latitude of Aysén Fjord, an intensity of VII½-VIII could be regarded as a maximum seismic intensity in the fjord for subduction earthquakes in accordance with observations by Van Daele et al (2015), where this value is reported for the largest earthquake on record.…”

“…However, should a large amount of slip occur at the latitude of Aysén Fjord, an intensity of VII½-VIII could be regarded as a maximum seismic intensity in the fjord for subduction earthquakes in accordance with observations by Van Daele et al (2015), where this value is reported for the largest earthquake on record. Combined with the presence of tsunami deposits in the southern part of the segment (Kempf et al, 2017) and our SL-EF, we infer this to be an (exceptional) earthquake with a large amount of slip in the southern part of the Valdivia segment and less slip in the northern part. We can thus readily expect widespread offshore-originating small-scale MTDs for a megathrust earthquake with high slip (> 30 m) in the southern part of the Valdivia segment.…”

“…In some cases, observed MTDs in lakes and other basins could even be attributed to major prehistorical earthquakes linked to activated faults (Carrillo et al, 2008;McHugh et al, 2006). (Cisternas et al, 2005(Cisternas et al, , 2017Kempf et al, 2017;Moernaut et al, 2014Moernaut et al, , 2018, while knowledge of activity on the LOFZ is restricted to recent seismic swarms such as the one in 2007 as well as an event documented in 1927. In many cases, these studies combine sediment cores with high-resolution seismic data, allowing identification, mapping, and dating of MTDs, as well as determination of their geographical and temporal distribution.…”

Tsunami deposits: Present knowledge and future challenges

“…Another similar approach was used by Kempf et al . () in lakes in Chile, where the application of geophysical data to establish long‐term recurrence intervals of tsunamigenic events was successful.…”

Tracing tsunami signatures of the ad 551 and ad 1303 tsunamis at the Gulf of Kyparissia (Peloponnese, Greece) using direct push in situ sensing techniques combined with geophysical studies

“…These tests allow the evaluation of the local static ground water level, the atmospheric pressure and the hydrostatic pressure for various depths of the dissipation test. Based on these three parameters, the actual P inj is calculated as; P inj = P total À (P hydro + P atm ) (K€ orber et al, 2009;McCall et al, 2014;Geoprobe, 2015). The estimated hydraulic conductivity (K est. )…”