**4.1 Contorted structures**

24 Earthquake Research and Analysis – Seismology, Seismotectonic and Earthquake Geology

851 40.00 44.60 - **5.2** 1941 39.45 43.32 20 **5.9**  856 40.00 44.60 - **5.3** 1945 38.41 43.76 60 **5.2**  858 40.00 44.60 - **5.2** 1945 38.00 43.00 30 **5.2**  1840 39.70 44.40 - **6.8** 1945 38.63 43.33 10 **5.4**  1857 38.40 42.10 - **6.7** 1966 38.14 42.52 28 **5.2**  1869 38.40 42.10 - **5.0** 1966 38.10 42.50 50 **5**  1871 38.50 43.40 - **5.5** 1968 38.15 42.85 53 **5**  1881 38.50 43.30 - **5.0** 1972 38.23 43.86 46 **5**  1884 38.40 42.10 - **6.1** 1976 38.61 43.20 56 **5.2**  1891 39.15 42.50 - **5.5** 1976 39.17 43.95 33 **7.2**  1894 38.50 43.30 - **5.0** 1976 39.09 43.71 49 **5.2**  1900 38.50 43.30 - **5.0** 1976 39.18 43.71 46 **5.2**  1902 39.00 43.30 - **5.0** 1976 39.31 43.66 53 **5.2**  1903 39.10 42.50 30 **6.2** 1977 39.35 43.48 24 **5**  1907 39.10 42.50 30 **5.2** 1977 39.29 43.62 46 **5.2**  1907 39.10 42.50 30 **5.4** 1977 39.27 43.70 39 **5.3**  1908 38.00 44.00 30 **6** 1977 39.13 43.90 34 **5**  1913 38.38 42.23 10 **5.5** 1977 39.31 43.53 38 **5.2**  1915 38.80 42.50 30 **5.7** 1979 39.12 43.91 44 **5.2**  1924 38.00 43.00 30 **5.2** 1988 38.50 43.07 49 **5.6**  1929 38.00 42.00 30 **5.2** 2000 38.41 42.95 48 **5.5** 

Table 1. Earthquake records with magnitude 5 and higher occured in the study area (from Utkucu, 2006; KOERI, 2009), (Lat. = Latitude, Long. = Longitude, Mag. = Magnitude)

Soft sediment deformation structures are observed in horizontally bedded, sandy, silty and clayey lacustrine deposits of Lake Van. Deformation structures exist in different levels of these shallow water deposits with the other sedimentary structures as cross-beds and wave ripples. Soft sediment deformation structures are classified differently according to morphologic properties or occurrence processes of the structure (Rossetti, 1999; Dramis &

In this study, soft sediment deformation structures, observed in lacustrine deposits of Lake Van, were classified as contorted structures (simple-complex convolute bedding and ball-

**4. Deformation structures (Seismites)** 

Blumetti, 2005; Neuwerth et al., 2006; Taşgn & Türkmen, 2009).

**(Ms) Date Lat. Long. Depth** 

**(km)** 

**Mag. (Ms)** 

**Mag.**

**Date Lat. Long. Depth** 

**(km)**

Two types of contorted deformation structures exist in lacustrine deposits. These are simplecomplex convolute bedding and ball-pillow structures.

### **4.1.1 Simple and complex convolute bedding**

Simple and complex convolute structures are observed frequently in sandy and silty lacustrine sediments of Lake Van. These structures consist of little anticline or syncline like convolutions. The dimensions of these structures access up to 130 cm wide and 70 cm high. Simple convolute beds occur from one folded layer (Fig. 3a), while complex structures are composed of an outer trough and irregular inner laminates (Fig. 3b).

Simple and complex convolute structures may occur by overpressure, seismic shaking or storm waves. The convolute structures are bounded by undeformed horizontal beds in lacustrine sediments of Lake Van. This undeformed beds support the seismic origin suggestion (Cojan & Thiry, 1992). Additionally, the existence of folds at the centre of the complex convolute structures display the repeated tectonic activities (Bhattacharya & Bandyopadhyay, 1998).

Fig. 3. (a) Simple convolute bedding and (b) complex convolute bedding in lacustrine deposits of Lake Van.

#### **4.1.2 Ball and pillow structures**

These structures are observed in sandy and silty deposits of Lake Van. They are composed of spherical or semi-spherical sand bodies in silty deposits (Fig. 4). This sand balls are covered by a silty crust. They have laminations at the inner part of the structures. Some structures are remaining connected to the overlying bed or the others are completely isolated from the bed. These structures in Lake Van sediments are very similar to presented in previous works (Hempton et al., 1983; Allen, 1986; Rossetti, 1999).

Ball and pillow structures occur with liquefaction of unconsolidated sediments. Because of the seismic tremors, liquefied sand size sediments are merged each other and create a balllike structure (Montenat et al., 1987; Ringrose, 1989; Cojan & Thiry, 1992; Rodriguez-Pascua et al., 2000).
