Larger earthquakes recur more periodically: New insights in the megathrust earthquake cycle from lacustrine turbidite records in south-central Chile

Abstract

Historical and paleoseismic records in south-central Chile indicate that giant earthquakes on the subduction megathrust −such as in AD1960 (M w 9.5)− reoccur on average every ~300 years. Based on geodetic calculations of the interseismic moment accumulation since AD1960, it was postulated that the area already has the potential for a M w 8 earthquake. However, to estimate the probability of such a great earthquake to take place in the short term, one needs to frame this hypothesis within the longterm recurrence pattern of megathrust earthquakes in south-central Chile. Here we present two long lacustrine records, comprising up to 35 earthquake-triggered turbidites over the last 4800 years. Calibration of turbidite extent with historical earthquake intensity reveals a different macroseismic intensity threshold (≥VII½ vs. ≥VI½) for the generation of turbidites at the coring sites. The strongest Highlights  Multi-threshold turbidite paleoseismic records in south-central Chilean lakes  Probability estimates for M w ≥ 7.7 and M w ≥ 8.6 megathrust earthquakes  Quasi-periodicity suggests a dominant role for a large megathrust asperity

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

“…(Kempf et al, 2017) and to a turbidite in Lake Riñihue (1,929-2,103 cal years B.P.) (Moernaut et al, 2018). This earthquake caused intensities of VI½ < VII½ at the latter study site, which is less than intensities of ≥VII½ for the largest earthquakes on the northern part of the Valdivia segment.…”

“…Lazo Hinrichs (2008) report seismic intensities of IV in Puerto Aysén for this megathrust earthquake, which did not trigger any landslides in the fjord. (Moernaut et al, 2018). Nevertheless, an intensity of VII½-VIII is still considerably lower than local intensities up to IX for a LOFZ earthquake and probably unable to trigger onshore landslides (Howarth et al, 2014).…”

“…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.…”

“…Wang et al, 2007), LOFZ, and volcanoes of south central Chile; (b) region around Aysén Fjord with indication of the Liquiñe-Ofqui Fault Zone (LOFZ) (after Cembrano et al, 2000;Melnick et al, 2009;Thomson, 2002;Vargas et al, 2013), volcanoes in the vicinity of the fjord, tephra, and pumice fallout isopachs of major Holocene eruptions in the area (H = Hudson, MEN = Mentolat and MAC = Macá) (after Naranjo & Stern, 1998, and the region of the 2007 seismic swarm and main shock (after Legrand et al, 2011;Mora et al, 2010); and (c) shaded relief map of the inner part of the fjord with indication of onshore and offshore mass movements that were triggered by the 2007 main shock of M w 6.2 on 21 April (after Sepúlveda et al, 2010;Van Daele et al, 2013). (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. The latter is known to have caused tsunamis in the region but remains obscure in all other aspects .…”

Suspended Sediments in Chilean Rivers Reveal Low Postseismic Erosion After the Maule Earthquake (Mw 8.8) During a Severe Drought

“…Large earthquakes, including megathrusts, are well recorded in the stratigraphy of lacustrine sediments (Howarth et al, 2012;Moernaut et al, 2015Moernaut et al, , 2018. In southern Chile, lacustrine turbidites sourced from hemipelagic sediments are generated over a macroseismic intensity threshold of VI ½ to VII ½ (Moernaut et al, 2018). Earthquakes may also trigger lake tsunamis, subaquatic landslides, and delta collapses.…”