Unexpected geological impacts associated with large earthquakes and tsunamis in northern Honshu, Japan (Invited)
Abstract
Palaeoseismic research in areas adjacent to subduction zones has traditionally been concerned with identifying geological or geomorphological features associated with the immediate effects of past earthquakes, such as tsunamis, uplift or subsidence, with the aim of estimating earthquake magnitude and/or frequency. However, there are also other features in the landscape that can offer some insights into the past earthquake and tsunami history of a region. The study of coastal dune systems as palaeoseismic indicators is still in its infancy, but can provide useful evidence of past large earthquakes and by association, the tsunamis they generated. On a catchment-wide basis, past research has linked a sequence of environmental changes such as forest disturbance, landslides, river aggradation and rapid coastal dune building as geomorphological after-effects (in addition to tsunamis) of a large earthquake. In this model large pulses of sediment created by co-seismic landsliding in the upper catchment are moved rapidly to the coast where they leave a clear signature in the landscape. Coarser sediments form an aggradation surfaces and finer sediments form a new coastal dune or beach ridge. Coastal dune ridge systems are not exclusively associated with seismically active areas, but where they do occur in such places their potential use as palaeoseismic indicators is often ignored. Data are presented first of all about the beach ridges of the Sendai Plain where investigations have been carried out following the 2011 Tohoku-oki earthquake and tsunami. A wider regional picture of both palaeoseismicity, palaeotsunamis and beach ridge formation is then discussed. Existing data indicate a strong correlation between past earthquakes and the timing of beach ridge formation over the past 5000 years, however it seems likely that there is a far more detailed record still preserved in Japan's beach ridges and suggestions are offered on the directions for future research in this area.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2013
- Bibcode:
- 2013AGUFMNH44A..01G
- Keywords:
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- 4302 NATURAL HAZARDS Geological;
- 4306 NATURAL HAZARDS Multihazards