Current Postgraduate Students
Dr Ed Garrett
My research focusses on reconstructing past environmental change. My current research seeks to uncover evidence for past sea-level changes and extend chronologies of great earthquakes in both south central Chile and Alaska.
In May 1960 south central Chile was struck by the largest earthquake since the inception of modern seismic recording. The Mw 9.5 event unlocked almost 1000 km of the fault that conveys the Nazca plate beneath South America. The 27th February 2010 Mw 8.8 Maule earthquake ruptured a further 500 km long section immediately to the north. More than four centuries of records kept by Spanish settlers and visiting Europeans describe the occurrence and effects of numerous other analogous subduction megathrust events. The inferred distributions of these ruptures suggest that the subduction zone is characterised by persistent seismic segments, bordered by unchanging boundaries. The permanence of these boundaries over longer timescales and the possibility of past earthquakes rupturing multiple segments are currently unknown.
Strain release in the form of slip on the fault interface is responsible for characteristic vertical land-level changes during subduction megathrust earthquakes. In coastal locations these crustal readjustments are experienced in the form of rapid decimetre to metre scale sea-level changes. The 1960 Valdivia event, for example, resulted in coastal submergence of up to 2m, with uplift of offshore islands reaching 5m. Estuaries and tidal wetlands have the potential to preserve evidence of these rapid changes in relative sea level, as well as the occurrence of accompanying tsunamis. The magnitude of vertical coseismic deformation may be approximated though the analysis of changes in microfossil assemblages including diatoms, unicellular algae which respond to changes in salinity.
Stratigraphic and microfossil analyses allow the identification and characterisation of recent earthquakes and tsunamis. The development of earthquake chronologies from longer stratigraphic records affords greater understanding of the location, timing and magnitude of past ruptures.
Publications in press
Garrett, E., Shennan, I., Watcham, E., Woodroffe, S. Accepted. Reconstructing paleoseismic deformation, 1: modern analogues from the 1960 and 2010 Chilean great earthquakes. Quaternary Science Reviews.
Selected conference presentations
Garrett et al., 2013. Late Holocene megathrust earthquakes in south central Chile, Abstract EGU2013-8573, presented at the European Geosciences Union General Assembly, Vienna, Austria, 7-12 April.
Garrett et al., 2012. Evidence for multiple great earthquakes in south central Chile. Abstract 119-4, presented at the Geological Society of America Annual Meeting, Charlotte, North Carolina, 4-7 November.
Garrett et al., 2010. Chilean segment boundary persistence over the late Holocene, Abstract T11D-2137, presented at the American Geophysical Union Fall Meeting, San Francisco, California, 13-17 December.