Late Holocene Palaeo-Seismicity of Southern Tierra del Fuego from Sediment Records. Lago Fagnano, Patagonia
Supervised by Professor Mike Bentley & Professor Antony Long
Southernmost Patagonia is seismically active and has seen powerful 20th Century earthquakes that have affected cities such as Punta Arenas and Ushuaia. Much of this seismicity derives from fault motion along the Magallanes-Fagnano fault, a continental transform fault that cuts across the southern Magellan Strait and forms the Lago Fagnano basin. Managing seismic risk in the region ideally requires an understanding of earthquake recurrence intervals but the relatively short historical record means that the recurrence interval is difficult to measure robustly.
This project aims to address this issue by developing a proxy record of earthquake occurrence through the Late Holocene. Such records can be retrieved from sediment sequences (disturbance or slumping) in marine or lacustrine sequences, evidence of coastal movements (e.g. from sea-level proxy data), or evidence of fault movements (derived by dating geomorphic and sediment evidence of fault slip events). In the Lago Fagnano area the opportunity exists to retrieve both sediment and fault slip evidence of earthquake recurrence. Reconnaissance work on a large bog at the eastern end of the lake (see picture) shows that it contains an alternating sequence of peat and clastic sediment layers. These layers are interpreted to represent overwash from the lake during large seiches (‘lake tsunami’) created by earthquakes. Thus there is a continuous and dateable proxy record of seiche (earthquake) activity along the Magallnes-Fagnano fault. Moreover there is a network of mapped faults in the area, some of which have been previously trenched and a preliminary earthquake chronology developed.
The successful student will undertake a comprehensive coring program at the end of Lago Fagnano to identify and date sedimentary evidence of earthquakes. S/he will also investigate surface faults including efforts to date evidence of fault slip events across the area. The ultimate aim is to provide an integrated Late Holocene chronology of earthquakes in the region, and thus better inform management of the regional seismic hazard. The work will be integrated with ongoing international work on the sediments within Lago Fagnano.
The successful student will receive training in coring, sediment analysis, microfossil analysis, radiocarbon dating, neotectonics, and seismic hazard.