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Soft-sediment deformation structures are often used as evidence for paleo-earthquakes. When several deformed horizons are present, one has to ask whether repeated slope failure at the sediment surface has built-up the stratigraphic record. Another option would be that a single failure event could have concurrently created surficial and sub-surface deformed horizons at different stratigraphic levels. The implications of these differing models are important for the timing of palaeo-earthquakes. In a new paper, Alsop et al. used the late Pleistocene Lisan Formation from the Dead Sea Basin to catalogue and establish key criteria that help distinguish surface versus sub-surface intrastratal deformation of soft-sediments. The paper is available for free for 50 days!

The recognition of sedimentological traces of earthquakes in the form of seismites within Pleistocene sediments is the main objective of the GREBAL project (Recognition of traces left by earthquakes in Pleistocene sediments affected by glacio- isostatic rebound in the Baltic Sea Basin). The investigations focus primarily on Poland, Germany, Latvia, Estonia and Lithuania. Project leader Małgorzata (Gosia) Pisarska-Jamroży has summed up new results from this international research effort.

1. Key points

This is the first attempt to apply a computational fluid dynamic modeling-based quantitative “fossil seismograph” to develop a large earthquake record.

The record is calibrated to historic earthquakes, for which the Dead Sea area has a famously long span, and it confirms a clustered earthquake recurrence pattern and a group-fault temporal clustering model.

The record yields much shorter mean recurrence for large (≤ 1.4 kyr vs. 7-11 kyr) and moderate (≤ 500 yr vs. 1600 yr) earthquakes than previously obtained, thus reveals a much higher seismic hazard than previously appreciated on this slow-slipping plate boundary.

The 2nd announcement for the International Palaeoseismological Field Workshop ‘Soft-sediment deformation structures and palaeoseismic phenomena in the South-eastern Baltic Region’ is out now. Download the PDF here and check this website for more informatin on the project. The workshop will be held from 17 – 21 September, 2018, and is organised by the Lithuanian Geological Survey, Lithuanian Geological Society,  Adam Mickiewicz University in Poznań, and Klaipėda University.

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Is it just me or is the frequency of papers being published increasing…? Anyway, here’s the literature update with studies on paleoseismology and active tectonics. Today we have: Faulting in the Canyonlands, seismites from the Jurassic, a fake earthquake in Cologne, dynamic triggering, news from the San Jacinto Fault, ground motion variation between repeating earthquakes, metrics to evaluate seismic hazard maps, submarine tectonic geomorphology, the 1897 Great Assam Earthquake, and a collection of papers on geophysical imaging and interpretation of outcrops. Enjoy!

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The Megablock Complex: An example from the East African Rift

Recognizing and interpreting seismite horizons (soft-sediment deformation generated by earthquakes) preserved in the sedimentary record is an underappreciated approach for paleoseismic analysis. The addition of sedimentological studies to a toolkit that includes other well-established methods, such as instrumental seismic monitoring and fault trenching, can provide a less expensive and more practical option for earthquake hazard prediction and preparation in certain areas. For example, this may be a good option in less developed regions and in areas where fault trenching may not be possible. Moreover, there is a lot that we can learn rheologically from the study of seismites that could be invaluable for modeling the behavior of the surface/near-surface during seismic activity. Similarly, investigating Quaternary strata in areas that may be prone to seismicity, which may or may not have a recorded history of major earthquakes, can illuminate important information about earthquake recurrence patterns and intervals, in much the same way as fault trenching. more