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

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Title: Larger earthquakes recur more periodically: New insights in the megathrust earthquake cycle from lacustrine turbidite records in south-central Chile.
Authors: Strasser, M.1, Moernaut, J.1,2, Pino, M.2, Van Daele, M.3, Heirman, K.3, Kempf, P.3, De Batist, M.3, Fontijn, K.4, Valdebenito, G.5, Urrutia, R.6
Source: Earth & Planetary Science Letters. Jan2018, Vol. 481, p9-19. 11p.
Subjects: Turbidites, Paleoseismology, Earthquake intensity, Poisson processes, Earthquakes
Geographic Terms: 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 yr. 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 long-term 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 yr. Calibration of turbidite extent with historical earthquake intensity reveals a different macroseismic intensity threshold (≥VII1/2 vs. ≥VI1/2) for the generation of turbidites at the coring sites. The strongest earthquakes (≥VII1/2) have longer recurrence intervals (292 ±93 yrs) than earthquakes with intensity of ≥VI1/2 ( 139 ± 69 yr ). Moreover, distribution fitting and the coefficient of variation (CoV) of inter-event times indicate that the stronger earthquakes recur in a more periodic way (CoV: 0.32 vs. 0.5). Regional correlation of our multi-threshold shaking records with coastal paleoseismic data of complementary nature (tsunami, coseismic subsidence) suggests that the intensity ≥VII1/2 events repeatedly ruptured the same part of the megathrust over a distance of at least ∼300 km and can be assigned to M w ≥ 8.6 . We hypothesize that a zone of high plate locking – identified by geodetic studies and large slip in AD 1960 – acts as a dominant regional asperity, on which elastic strain builds up over several centuries and mostly gets released in quasi-periodic great and giant earthquakes. Our paleo-records indicate that Poissonian recurrence models are inadequate to describe large megathrust earthquake recurrence in south-central Chile. Moreover, they show an enhanced probability for a M w 7.7–8.5 earthquake during the next 110 years whereas the probability for a M w ≥ 8.6 (AD1960-like) earthquake remains low in this period. [ABSTRACT FROM AUTHOR]
Copyright of Earth & Planetary Science Letters is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)
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  Data: 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 yr. 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 long-term 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 yr. Calibration of turbidite extent with historical earthquake intensity reveals a different macroseismic intensity threshold (≥VII1/2 vs. ≥VI1/2) for the generation of turbidites at the coring sites. The strongest earthquakes (≥VII1/2) have longer recurrence intervals (292 ±93 yrs) than earthquakes with intensity of ≥VI1/2 ( 139 ± 69 yr ). Moreover, distribution fitting and the coefficient of variation (CoV) of inter-event times indicate that the stronger earthquakes recur in a more periodic way (CoV: 0.32 vs. 0.5). Regional correlation of our multi-threshold shaking records with coastal paleoseismic data of complementary nature (tsunami, coseismic subsidence) suggests that the intensity ≥VII1/2 events repeatedly ruptured the same part of the megathrust over a distance of at least ∼300 km and can be assigned to M w ≥ 8.6 . We hypothesize that a zone of high plate locking – identified by geodetic studies and large slip in AD 1960 – acts as a dominant regional asperity, on which elastic strain builds up over several centuries and mostly gets released in quasi-periodic great and giant earthquakes. Our paleo-records indicate that Poissonian recurrence models are inadequate to describe large megathrust earthquake recurrence in south-central Chile. Moreover, they show an enhanced probability for a M w 7.7–8.5 earthquake during the next 110 years whereas the probability for a M w ≥ 8.6 (AD1960-like) earthquake remains low in this period. [ABSTRACT FROM AUTHOR]
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  Data: <i>Copyright of Earth & Planetary Science Letters is the property of Elsevier B.V. and its content may not be copied or emailed to multiple sites without the copyright holder's express written permission. Additionally, content may not be used with any artificial intelligence tools or machine learning technologies. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract.</i> (Copyright applies to all Abstracts.)
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        Value: 10.1016/j.epsl.2017.10.016
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        Text: English
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        PageCount: 11
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      – SubjectFull: Turbidites
        Type: general
      – SubjectFull: Paleoseismology
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      – SubjectFull: Earthquake intensity
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      – SubjectFull: Chile
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