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

Abstract

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 turbidite's 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 (M w~9 .5: 1960, 1575, 1319 ± 9, 1127 ± 44), (ii) ruptures covering half of the Valdivia Segment (M w~9 : 1837), and (iii) partial ruptures of much smaller coseismic slip and extent (M w~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.

A systematic review of geological evidence for Holocene earthquakes and tsunamis along the Nankai-Suruga Trough, Japan

“…This is in contrast to other subduction zone settings, where the integration of records from multiple sites has yielded a more comprehensive understanding of prehistoric great earthquakes, including in Alaska (Shennan et al, 2014a, b), Cascadia Nelson et al, 2006) and Chile (Moernaut et al, 2014). We identify four key issues that currently limit the contribution of palaeoseismic records to understanding seismic hazards along the Nankai-Suruga Trough: 1) alternative hypotheses for proposed palaeoseismic evidence; 2) insufficient chronological control to correlate between evidence at different sites; 3) research designs insufficient to address maximum earthquake and tsunami magnitudes and 4) incomplete appreciation of the variation in palaeoseismic thresholds over time and between sites.…”

“…The issue of equifinality affects turbidite palaeoseismology globally and key ways forward include establishing site sensitivity through calibration of deposits with the historical record, correlation of multiple cores using independent marker horizons (e.g. tephras), sedimentary provenance analysis, and confluence tests Moernaut et al, 2014;Pouderoux et al, 2014;Van Daele et al, 2015).…”

“…Such issues are less often encountered where intervals exceeding several centuries separate recorded palaeoearthquakes, as appears to be the case in Alaska (Shennan et al, 2014b), and where earthquake timing is constrained by very high resolution chronologies, such as those based on annual varves (e.g. Moernaut et al, 2014). More precise constraints on the timing of palaeoseismic evidence are clearly desirable, particularly to assist with characterising the sedimentary fingerprint of historical earthquakes.…”

A multi-centennial record of past floods and earthquakes in Valle d'Aosta, Mediterranean Italian Alps

“…intensities that may be strong enough to trigger seismically induced deposits (e.g. Moernaut et al, 2014;Howarth et al, 2014;Van Daele et al, 2015;Wilhelm et al, 2016b). GBIIIa and HB are dated to 1962 ± 12 and 1941 ± 16 years, respectively (Fig.…”

“…Reconstruction of past earthquake magnitudes and location is approached by comparing regional records of seismic-induced deposits (e.g. Strasser et al, 2006;Wilhelm et al, 2016b) or through the deposit's spatial extent and thickness (Howarth et al, 2014;Moernaut et al, 2014).…”