Distinguishing intraplate from megathrust earthquakes using lacustrine turbidites

Abstract : Subduction zone seismicity arises from megathrust, crustal, and intraslab earthquakes, and understanding the recurrence patterns of each type is crucial for hazard assessments. Lake sediments can record earthquakes from all three seismogenic sources. Here, we studied the turbidite record of Lo Encañado, an Andean lake located in central Chile. We show that Lo Encañado turbidites can be attributed to (1) subaquatic slope failure by earthquake shaking (coseismic phase), (2) floods or human impact, and (3) postseismic catchment response. All historical events with shaking intensities >VI (modified Mercalli intensity) have triggered coseismic turbidites, but only the intraplate earthquakes triggered subaerial slope failures followed by postseismic turbidites. We argue that this contrasting result is due to different spectra of seismic waves from these earthquake sources: higher-frequency accelerations from intraplate earthquakes are hardly attenuated in rocks around the lake, whereas lower-frequency accelerations from megathrust earthquakes are amplified in soft lake sediments. We tested our findings by comparing acceleration response spectra of recent and historical intraslab and megathrust earthquakes along a longitudinal profile. Results suggest that the location of Andean lakes is ideal to distinguish earthquake sources.
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Submitted on : Saturday, November 9, 2019 - 6:57:02 PM
Last modification on : Sunday, November 10, 2019 - 1:28:53 AM

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Maarten van Daele, Cristian Araya-Cornejo, Thomas Pille, Kris Vanneste, Jasper Moernaut, et al.. Distinguishing intraplate from megathrust earthquakes using lacustrine turbidites. Geology, Geological Society of America, 2019, 47 (2), pp.127-130. ⟨10.1130/G45662.1⟩. ⟨hal-02357289⟩

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