Detection thresholds for large to great subduction earthquakes in Alaska

Project overview

This project will undertake field and laboratory investigations and subsequent data analysis to investigate whether the upper part of coastal marshes in the Prince William Sound area of Alaska possess records of vertical deformation of less than 1 m caused by earthquakes <Mw 8.0 during the last few millennia. Studies of coastal marshes in this area have already produced evidence for 1m+ land-level changes caused by multiple >Mw8.0 earthquakes over the past 4000 years.  The sampling design of these studies which focuses on marsh-front locations does not detect smaller land-level changes caused by smaller earthquakes during this time-period.  This new study will use a new, complementary method looking at sediments from the upper part of coastal marshes to investigate whether we can reconstruct smaller amounts of deformation (<1m) and therefore create a more complete catalogue of earthquake events in this region during the last few millennia.

The project will involve analysis of sediment cores from Girdwood marsh in the Prince William Sound segment of the Alaskan megathrust, collected during summer 2023.  Sediment core and surface sediment samples will be analysed for microfossils (diatoms) that record changes in water level over time, and statistical analysis will allow reconstruction of abrupt land-level changes in the cores.  Together with radiocarbon dating of the sediments this will allow estimates of the timing and magnitude of land-level changes in-between the 1m+ events already identified in the Girdwood record.

This is a fully funded opportunity (including 1 year tuition fees for a UK student and a stipend of £17,999.50 for 12 months) as part of a USGS Earthquake Hazard Program grant.

If you are interested in this project, please contact the lead supervisors: Dr. Sarah Woodroffe (s.a.woodroffe@durham.ac.uk) and Dr. Simon Engelhart (simon.e.engelhart@durham.ac.uk).

Sediment samples from Kenai in Alaska showing the stratigraphic position of the 1964 event (white arrows), perimarine peat/peat contact (L) through to tidal flat (R).

Key references

Hamilton, S and Shennan, I, 2005. Late Holocene relative sea-level changes and the earthquake deformation cycle around upper Cook Inlet, Alaska. Quaternary Science Reviews., 24 (12-13), 1479-1498.

Shennan, I, Garrett, E, Barlow, N, 2016. Detection limits of tidal-wetland sequences to identify variable rupture modes of megathrust earthquakes. Quaternary Science Reviews 150, 1-30.

Shennan, I, Bruhn, R, Barlow, NLM, Good, K & Hocking, EP, 2014. Late Holocene great earthquakes in the eastern part of the Aleutian megathrust.  Quaternary Science Reviews. 84: 86-97