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Terre Univers Environnement

Developing archaeoseismicity associated to paleolimnology as a new tool to improve seismic hazard assessment

Encadrants : Julia de Sigoyer, Pierre Sabatier, Fabien Arnaud

par Encadrants de stages - 11 octobre 2016 ( maj : 19 juin 2017 )

Lieu du stage : ISTerre Grenoble and EDYTEM Chambéry
Contact email : julia.de-sigoyer@univ-grenoble-alpes.fr
04 76 63 52 14

{{}}The assessment of the seismic hazard in active area requires a catalogue of previous earthquakes, the identification of potential epicenter, and slip distribution on each fault segment. The slip estimation is classically provided by the offset and the age of different geomorphological and geological markers across the fault. In this project we plan to document the catalogue of earthquake using archaeological damage on buildings and lacustrine sediment records. Fault activity, in particular pull-apart basins, often leads to lake formation providing attractive settling areas so that old cities often developed close to the lakes.
The study is focus in the city of antic Nicaea (present Iznik, Turkey), where one of the oldest basilica of the world has just been discovered below 1.5 m of water in Lake Iznik, 20 m from the shore. This basilica has probably hosted the first council of Christian bishops in AD 325 that represents the founding of Christian religion. The basilica has been destroyed and submerged after an unknown catastrophic event most likely caused by an earthquake and probably a resulting tsunami on the nearby North Anatolian Fault. The middle segment of the North Anatolian Fault (MNAF) runs south of the lake, 5 km away from Nicaea. Written sources report 17 earthquakes in Nicaea since the 1st century AD, 5 attributed to ruptures of the MNAF segment. Lake Iznik has recorded in its sedimentary deposits precious paleoseismic, paleoenvironnental and archaeological information. The aim of this study is to develop a multidisciplinary approach to unravel the past earthquake and environmental history of the region of Nicaea performing the study of various archaeological and geomorphological markers deformed or damaged by an earthquake, including offshore investigations of Lake Iznik.
The internship is focused on the study of 5 cores of lacustrine sediments that have been drilled within the flooded basilica (2 in the nef, one in an adjacent building, one away from the building, one in the oldest part of the basilica). The aim is to retrieve the calendar of seismicity since the destruction of the basilica. The cores will be characterized and dated using C14 dating. The deepest sediments will provide a minimum age for the burial of the basilica. Seismites or tsunami evidence could be present in these cores attesting for following earthquakes after the burial of the basilica. The archaeological survey of the flooded basilica is under progress and will provide independent data to date the burial of the basilica (coins were found in tombs within the flooded basilica).

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