3. Dura, T; Horton, BP; Cisternas, M; Ely, LL; Hong, I; Nelson, AR; Wesson, RL; Pilarczyk, JE; Parnell, AC; Nikitina, D.Subduction zone slip variability during the last millennium, south-central Chile.Quat. Sci. Rev., 2017, 175: 112-137 Subduction zone slip variability during the last millennium, south-central Chile
Prehistoric earthquakes; Subduction zone segmentation; Tsunami deposits; Diatom paleoecology; Coastal paleoseismology; Coastal hazards
The Arauco Peninsula (37 degrees-38 degrees S) in south-central Chile has been proposed as a possible barrier to the along-strike propagation of megathrust ruptures, separating historical earthquakes to the south (1960 AD 1837, 1737, and 1575) and north (2010 AD, 1835, 1751, 1657, and 1570) of the peninsula. However, the 2010 (Mw 8.8) earthquake propagated into the Arauco Peninsula, re-rupturing part of the megathrust that had ruptured only 50 years earlier during the largest subduction zone earthquake in the instrumental record (M-w 9.5). To better understand long-term slip variability in the Arauco Peninsula region, we analyzed four coastal sedimentary sections from two sites (Tirua, 38.3 degrees S and Quidico, 38.1 degrees S) located within the overlap of the 2010 and 1960 ruptures to reconstruct a similar to 600-year record of coseismic land-level change and tsunami inundation. Stratigraphic, lithologic, and diatom results show variable coseismic land-level change coincident with tsunami inundation of the Tirua and Quidico marshes that is consistent with regional historical accounts of coseismic subsidence during earthquakes along the Valdivia portion of the subduction zone (1960 AD and 1575) and coseismic uplift during earthquakes along the Maule portion of the subduction zone (2010 AD, 1835, 1751). In addition, we document variable coseismic land-level change associated with three new prehistoric earthquakes and accompanying tsunamis in 1470-1570 AD, 1425-1455, and 270-410. The mixed record of coseismic subsidence and uplift that we document illustrates the variability of down-dip and lateral slip distribution at the overlap of the 2010 and 1960 ruptures, showing that ruptures have repeatedly propagated into, but not through the Arauco Peninsula and suggesting the area has persisted as a long-term impediment to slip through at least seven of the last megathrust earthquakes (similar to 600 years). (C) 2017 Elsevier Ltd. All rights reserved. DOI
2. Rubin, CM; Horton, BP; Sieh, K; Pilarczyk, JE; Daly, P; Ismail, N; Parnell, AC.Highly variable recurrence of tsunamis in the 7,400 years before the 2004 Indian Ocean tsunami.Nat. Commun., 2017, 8 Highly variable recurrence of tsunamis in the 7,400 years before the 2004 Indian Ocean tsunami
The devastating 2004 Indian Ocean tsunami caught millions of coastal residents and the scientific community off-guard. Subsequent research in the Indian Ocean basin has identified prehistoric tsunamis, but the timing and recurrence intervals of such events are uncertain. Here we present an extraordinary 7,400 year stratigraphic sequence of prehistoric tsunami deposits from a coastal cave in Aceh, Indonesia. This record demonstrates that at least 11 prehistoric tsunamis struck the Aceh coast between 7,400 and 2,900 years ago. The average time period between tsunamis is about 450 years with intervals ranging from a long, dormant period of over 2,000 years, to multiple tsunamis within the span of a century. Although there is evidence that the likelihood of another tsunamigenic earthquake in Aceh province is high, these variable recurrence intervals suggest that long dormant periods may follow Sunda megathrust ruptures as large as that of the 2004 Indian Ocean tsunami. DOI PubMed
1. Dura, T; Cisternas, M; Horton, BP; Ely, LL; Nelson, AR; Wesson, RL; Pilarczyk, JE.Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile.Quat. Sci. Rev., 2015, 113: 93-111 Coastal evidence for Holocene subduction-zone earthquakes and tsunamis in central Chile
Prehistoric earthquakes; Tsunami deposits; Diatom paleoecology; Coastal paleoseismology; Coastal hazards
The similar to 500-year historical record of seismicity along the central Chile coast (30-34 degrees S) is characterized by a series of similar to M 8.0-8.5 earthquakes followed by low tsunamis (<4 m) occurring on the megathrust about every 80 years. One exception is the AD 1730 great earthquake (M 9.0-9.5) and high tsunami (>10 m), but the frequency of such large events is unknown. We extend the seismic history of central Chile through a study of a lowland stratigraphic sequence along the metropolitan coast north of Valparaiso (33 degrees S). At this site, higher relative sea level during the mid Holocene created a tidal marsh and the accommodation space necessary for sediment that preserves earthquake and tsunami evidence. Within this 2600-yr-long sequence, we traced six laterally continuous sand beds probably deposited by high tsunamis. Plant remains that underlie the sand beds were radiocarbon dated to 6200, 5600, 5000, 4400, 3800, and 3700 cal yr BP. Sediment properties and diatom assemblages of the sand beds for example, anomalous marine planktonic diatoms and upward fining of silt-sized diatom valves point to a marine sediment source and high-energy deposition. Grain-size analysis shows a strong similarity between inferred tsunami deposits and modern coastal sediment. Upward fining sequences characteristic of suspension deposition are present in five of the six sand beds. Despite the lack of significant lithologic changes between the sedimentary units under- and overlying tsunami deposits, we infer that the increase in freshwater siliceous microfossils in overlying units records coseismic uplift concurrent with the deposition of five of the sand beds. During our mid-Holocene window of evidence preservation, the mean recurrence interval of earthquakes and tsunamis is similar to 500 years. Our findings imply that the frequency of historical earthquakes in central Chile is not representative of the greatest earthquakes and tsunamis that the central Chilean subduction zone has produced. (C) 2014 Elsevier Ltd. All rights reserved. DOI
