Aerial view of the basilica submerged under Iznik Lake in Bursa, Turkey -
© Murattellioglu / Shutterstock
An earthquake in 1065 could be the cause of the engulfing of a Turkish basilica according to a study published by our partner The Conversation.
Examination of the soils and sediments near the remains would make it possible to identify possible effects of liquefaction of the soil (quicksand) during seismic tremors.
The analysis of this mystery was carried out by Renaldo Gastineau, doctoral student at ISTerre (Institute of Earth Sciences) Grenoble, Université Grenoble Alpes (UGA).
For thousands of years, humans have shaped the nature and landscapes of the planet according to their needs, even modifying their climate and biodiversity.
The reverse is also true: natural disasters and climate influence the occupation of land by humans.
The historic city of Nicaea (now Iznik, Turkey) lies southeast of the Sea of Marmara and 5 km north of the middle branch of the North Anatolian Fault (MNAF), which is one of the most active in Europe.
This city, established on the shores of Lake Iznik during the Neolithic, was a major political and religious center and was in turn Hellenistic, Byzantine and Ottoman.
In 325 AD
AD, the city hosted the first ecumenical council of Christianity, which is a major foundation of the Christian religion.
The place where this first council met is to this day nowhere to be found.
In 2014, thanks to the lowering of the water level, a basilica buried in the lake was discovered.
Many questions emanated from this discovery: Was this basilica able to accommodate this first council?
When was it built?
How was it destroyed?
What is / are the cause (s) of its submersion?
Remains of Roman Basilica under the waters of Lake Iznik, Turkey.
The Basilica has been dated to V Century AD.
pic.twitter.com/4rZYe4zmdA
- Roman History (@ romanhistory1) February 28, 2015
In view of the historical seismicity documented in this region, earthquakes may have played a role in this plot.
A battered historic town
The city of Iznik presents archaeological remains that bear the scars of several phases of destruction / reconstruction.
The archaeological study of ancient buildings allows us to identify at least four destructive earthquakes since Roman times, without any of these earthquakes being officially associated with the destruction of the basilica in historical accounts.
OUR "EARTHQUAKE" FILE
The fault which borders the city and the lake of Iznik (MNAF) is a slow fault which slips at approximately 5 mm / year.
It has not presented any seismicity since the instrumental period (around 150 years).
However, this observation interval is too short to conclude that this flaw is inactive.
It is therefore necessary to look further into the past for potential traces of earthquakes and to establish a precise calendar of earthquakes over several millennia, in order to be able to assess their recurrence on this fault and the current seismic hazard of this area. .
The lakes, guardians of the past
Albert Einstein once said: “Look deep into nature, and then you will understand everything much better.
What if we take him at his word?
Whether via geochemical or granulometric indices, the sediments that settle at the bottom of lakes over time continuously record climate change or recent anthropogenic pollution.
Some deposits highlight extreme natural events that can be associated with earthquakes, floods or even tsunamis.
As part of the "Basiliznik's secrets" research project, funded by the National Research Agency (ANR), a team of international researchers specializing in different fields (geology, geophysics, archeology, genetics) will use the sedimentary archives of the lake. in order to better understand the Iznik region from a tectonic and archaeological point of view and to better understand the future.
One of the fundamental challenges of this project is to map potential segments of active faults in the lake and to determine the recurrence of earthquakes on these segments in order to better understand the seismic cycle of the MNAF on a large time scale.
To do this, we plan to sample long sediment cores (~ 20 m), which should allow us to go back more than 20,000 years.
Discovery of new fault segments
The acquisition of bathymetric data (topography of the lake bottom) unpublished in 2019 allowed us to highlight two segments of faults in Lake Iznik that were previously unknown.
Sediment cores were sampled in the lake on either side of one of these segments.
These cores were dated and analyzed from a sedimentological and geochemical point of view in order to determine whether this fault segment has generated earthquakes in the past.
Three meters long, these sedimentary archives have recorded 14 historical regional earthquakes over the past 2,000 years.
Our study showed that one of these ruptures (earthquakes) occurred on the fault segment studied between 1010 and 1182 AD.
BC. Historical records confirm that a major earthquake completely devastated the town of Iznik in 1065 AD.
J.-C .. A writing even mentions the disappearance of holy places during this earthquake, suggesting the destruction of the submerged basilica during this tragic event.
OUR “ARCHEOLOGY” DOSSIER
Associated with these sedimentological studies, soil analyzes near the buried basilica will soon be carried out to identify possible liquefaction effects of the soil (quicksand) during seismic tremors, as was the case for a hotel that s sank in Lake Sapanca, 40 km to the north, during the 1999 earthquake in Izmit.
We may thus be able to shed light on the exact causes of the destruction and the burial of the basilica.
The lake: link between biodiversity, climate, archeology and geology
The ground level in the city and the water level in the lake have undergone very significant rapid variations (several meters in a few decades), with important consequences for the local populations.
Climatic, anthropogenic or tectonic causes can be invoked to explain them.
Further investigations will be carried out (dating of paleo-shores for example) to precisely characterize these variations in the level of the lake / soil over time and their causes.
The long-term evolution of climatic factors can be identified through the geochemical study of lake cores.
Human activities such as agriculture, pastoralism and deforestation have strongly impacted the evolution of biodiversity (types of vegetation, animals) in the watershed (around the lake).
The study of the fossil DNA contained in the sediments of the lake will make it possible to document the evolution of biodiversity in the watershed and therefore to understand the evolution of human activities in connection with the evolution of the climate.
With the same sedimentary cores we believe we can identify the impact of climate and earthquakes on human activity around Lake Iznik in the past.
Thus, it is by combining different scientific approaches calling on interdependent disciplines that the study of the Iznik region will allow us to discuss the interactions between climate, tectonics and human societies, since prehistoric times.
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This analysis was written by Renaldo Gastineau, doctoral student at ISTerre (Institute of Earth Sciences) Grenoble, Université Grenoble Alpes (UGA). The original article was published on The Conversation website.
Earthquake
Basilica
History
Geology
Turkey
Archeology
Science