The 2011 Mw 7.1 Van (Eastern Turkey) Earthquake
John Elliott, Alex Copley, Barry Parsons
On the 23rd of October 2011 (13:41 local time), a magnitude 7.1 earthquake struck eastern Turkey (Figure 1), just north of the city of Van (population 370,000), on the eastern edge of Lake Van.
Reference: J.R. Elliott, A. Copley, R. Holley, K. Scharer and B. Parsons (in review) The 2011 Mw 7.1 Van (Eastern Turkey) Earthquake, Journal Geophysical Research.
Introduction & Background
This earthquake resulted in over 600 deaths, largely in the city of Ercis¸ (pop. 97,000) on the northern shore of Lake Van, on the hanging wall of the fault. The largest aftershock (magnitude 5.9) occurred just over ten hours later; although a magnitude 5.7 aftershock on the 9th November killed a further 40 people, largely due to additional damage in the city of Van.
The initial seismological solutions indicate reverse faulting where one side of the fault moves above the other, at about 16 km depth. Hundreds of smaller aftershocks occurred in the days following the main event (EMSC http://www.emsc-csem.org) and were spread out in a ENE-WSW line, indicating the approximate strike of the fault. This earthquake is a result of the on-going collision of the Arabian Plate with Eurasia (Figure 1) which progresses at about two and a half centimetres per year. This collision builds the mountains in Eastern Turkey and also results in the westward expulsion on central Turkey (Anatolia) at a rate of a couple of centimetres per year.
InSAR Observations & Fault Modelling
COMET investigators in collaboration with colleagues at FugroNPA (Rachel Holley http://www.fugro-npa.com/) and the USGS (Kate Scharer http://earthquake.usgs.gov/) have been investigating this earthquake using satellite radar (Figure 2), seismology and high-resolution imagery.
This data shows that the Van earthquake occurred on a pair of northward dipping reverse fault planes, just north of the city of Van (Figure 3). These faults caused the land north of Van to be lifted by over 1 metre. Slip on the fault remained buried, with a maximum motion of about 9 m at 14 km depth and constrained largely to the depth range 9–20 km. From this analysis, an 11 km wide up-dip region has been found to not have ruptured and may pose a continuing seismic hazard to Van and the surrounding populace.
Figure 1: Map of interaction between the Arabian, Eurasian, and Anatolian plates centered on eastern Turkey. Relative plate convergences are marked by white arrows, calculated from DeMets et al. [2010], and plate boundaries dark red) are from Bird [2003]. Earthquake focal mechanisms are from a compilation by Copley and Jackson [2006] (dark grey) and from the GCMT catalogue (light grey) Mw5.5+ for the period 1976–2010 [Ekstrom et al., 2005]. The body wave focal mechanism for the 2010 Van earthquake is shown in red. GPS vectors (black arrows) are from a compilation by [Reilinger et al., 2006], relative to a stable Eurasia. Major faults (red lines) for the region of Turkey are from Saroglu et al. [1992], and for Iran from Walker et al. [2009]. TJ denotes the location of the Karliova triple-junction 150 km WNW of Van.
Figure 2: (a) COSMO-SkyMed interferogram formed from an acquisition 13 days prior to the earthquake and one just four hours after the event. The displacement points in the interferogram have been interpolated to form a continuous surface for clarity. Colours show range changes as fringes re-wrapped to 6 cm, with the colour cycle blue to red indicating increasing motion away from the satellite for the three satellite tracks. The single fault segment is marked by a solid black line, the pair of segments by white lines. Satellite track azimuth (Az) and line-of-sight (LOS) with angle of incidence (i) are shown by black arrows. (b) Unwrapped COSMO-SkyMed interferogram. The peak line-of-sight displacement is 94 cm towards the satellite, and 12 cm away from the satellite.
Figure 3: Perspective view of Van with the InSAR deformation map draped over topography. Each cycle through the coloured rainbow fringes from blue through green to red is equivalent to 10 cm of motion of the ground towards the InSAR satellite. The area north of Van moved +90 cm towards the satellite during the earthquake, whereas the land immediately beneath the city of Van subsided by -15 cm. The fault segments responsible for the earthquake are shown by black and white triangles at the foot of the mountain scarps. The earthquake ruptured these faults at 20 to 10 kilometres depth underground north of Van (yellow star), on the western shore of Lake Van. However, the rupture did not come all the way to the surface, and a large section of the fault (white dotted line) at shallow depths has not yet ruptured.
Further Links
References
Copley, A., and J. Jackson, Active tectonics of the Turkish-Iranian Plateau, Tectonics, 25, TC6006, doi:10.1029/2005TC001906, 2006.
DeMets, C., R. G. Gordon, and D. F. Argus, Geologically current plate motions, Geophysics Journal International, 181, 1–80, doi:10.1111/j.1365-246X.2009.04491.x, 2010.
Ekstrom, G., A. M. Dziewonski, N. N. Maternovskaya, and M. Nettles, Global seismicity of 2003: centroid moment-tensor solutions for 1087 earthquakes, Physics of the Earth and Planetary Interiors, 148, 327–351, doi:10.1016/j.pepi.2004.09.006, 2005.
Reilinger, R., S. McClusky, P. Vernant, S. Lawrence, S. Ergintav, R. Cakmak, H. Ozener, F. Kadirov, I. Guliev, R. Stepanyan, M. Nadariya, G. Hahubia, S. Mahmoud, K. Sakr, A. ArRajehi, D. Paradissis, A. Al-Aydrus, M. Prilepin, T. Guseva, E. Evren, A. Dmitrotsa, S. V. Filikov, F. Gomez, R. Al-Ghazzi, and G. Karam, GPS constraints on continental deformation in the Africa-Arabia-Eurasia continental collision zone and implications for the dynamics of plate interactions, Journal of Geophysical Research, 111, 05411, doi: 10.1029/2005JB004051, 2006.
Saroglu, F., O. Emre, and I. Kuscu, Active Fault Map of Turkey, General Directorate of Mineral Research and Exploration (MTA), Eskisehir Yolu, 06520, Ankara, Turkey, 1992.