PUSHING THE FRONTIER OF RELATIVE SEA LEVEL STUDIES AND PALEOSEISMOLOGY

As we approach the 50^th anniversary of the May 1960 great earthquake in Chile we aim to review key research themes emerging that have arisen since then and suggest some critical issues that remain in linking relative sea-level change to improved understanding of deformation during subduction zone earthquake cycles.

Differentiating between seismic and non-seismic causes of coastal zone submergence and emergence lies at the core of this research. We revisit the approaches outlined by the pioneering researchers, seek to clarify key criteria that distinguish prehistoric seismic deformation from non-seismic relative sea-level change and make a call for more explicit hypothesis testing. Debates during the last 10 years demonstrate the need for robust correlation and modelling methods.

We present results from south central Alaska to illustrate the challenges of upscaling from studies of individual sites to studies of subduction zone segmentation. The key theme that arises from studies of Late Holocene great earthquakes is that of temporal and spatial variability. Quantitative estimates suggest both temporal and spatial similarities and differences for different earthquake cycles. There is not a fixed recurrence interval. The shortest interval is between 180 and 720 years. The longest interval is 790 – 920 years, which is between the penultimate and the 1964 earthquakes. Evidence for different great earthquakes suggests co-seismic rupture area of one, two or three plate boundary segments. Earthquakes ~900 and ~1500 years ago simultaneously ruptured adjacent segments of the Aleutian megathrust (Kodiak and Prince William Sound segments) and the western part of the Yakutat microplate, with a combined area ~15% greater than 1964, giving an earthquake of greater magnitude and increased tsunamigenic potential.