Prof. Dr. Haluk Eyidoğan
27.12.2020 – 27 December 2020 Sivrice earthquake
When I examined the magnitude 5.5 earthquake that occurred on 27 December 2020 just to the northwest of Lake Hazar (Sivrice), I decided to write this article. I can sense you asking what the connection is. In our profession, we define this lake as a ‘fault lake (sag pond)’. That is why there is a connection. Below, I will try to explain this connection to you without going into too much technical detail.
Young faults and earthquakes
The displacement movement along young (active, living) fault zones creates various tectonic* phenomena that differ from one another. A young fault produces stresses and movements of various types and levels, depending on the physical differences in the structure of the earth’s crust in the region where it is located and on the type of fault (strike-slip, normal and reverse fault). For example, around the main young faults, many geological phenomena emerge, such as scattered fractures, deviated stream beds, ridges, fault valleys, alluvial cones, landslides, fault lakes, water sources and interrupted sedimentary masses. When you place earthquake recorders around young fault zones and make recordings, we can observe a large number of small earthquakes. In earthquake archives, we may come across records of damaging earthquakes from past years related to this fault. Along young fault zones, we can see traces of damage from old earthquakes in existing settlements and archaeological finds. As a result of research that has been ongoing for many years and is still continuing in Anatolia, nearly 500 young, living faults have been found and mapped in detail.
Faults and fault lakes
Numerous fault lakes have formed along the major fault zones in Anatolia. Lakes Manyas, İznik, Sapanca and Abant on the North Anatolian Fault Zone, Lake Burdur and some of the other lakes in the lakes region of western Anatolia, and Lakes Gölbaşı, Azaplı and Hazar on the East Anatolian Fault are examples that emerged as a result of the subsidence basins formed during the movement of the faults turning into lakes. Depending on the placement of the faults, the width of the fault zone and the type of movement, the shapes of the resulting subsidence basins and lakes can also differ. The tectonic structure, and therefore the geographical structure, that emerges according to the right-and-left stepover, branching or bending (flexure) patterns of fault zones in the field also varies. While pits, basins and lakes form in places where tensional, extensional stress is dominant, ridges, folds and elevations form in places where compressional stress occurs (Figure 1). There are three models proposed and discussed for the formation mechanism of basins and lakes caused by strike-slip faults. These are a) the releasing bend model, b) the pull-apart basin model and c) the negative flower structure model. If more detailed geophysical, geological and seismic studies are carried out within such lakes, it will become clear which of the discussed models is more valid.
