J. Geod. Sci. 2017; 7:113–129
Research Article Open Access
Kutubuddin Ansari*, Ozsen Corumluoglu, and Sunil Kumar Sharma Numerical Simulation of Crustal Strain in Turkey from Continuous GNSS Measurements in the Interval 2009-2017 https://doi.org/10.1515/jogs-2017-0013 Keywords: Anatolian Fault, Crustal Strain, TPGN Received April 15, 2017; accepted September 18, 2017
Abstract: The present study investigates the crustal strain in Turkey by using data from the Turkish permanent GNSS 1 Introduction network (TPGN) and international GNSS services (IGS) ob- servations for a period of 9 years, 2009 t0 2017. The posi- Turkey is a seismically active area within the complex tional variation of GNSS sites is studied to understand the zone of collision between the Eurasian Plate and both coordinate reliability, interseismic and coseismic eects the African and Arabian Plates. The large part of the coun- and linear velocities as well as three dimensional princi- try lies on the Anatolian Plate which is a small plate pal strains across the country. The study of coordinate re- bounded by two major strike-slip fault zones, the right- liability shows that the horizontal and vertical residuals lateral North Anatolian Fault (NAF) and left-lateral East in 2013 and 2015 are of the order of 100 mm per coordi- Anatolian Fault (EAF) (Fig. 1). The Anatolian block is being nate or higher than those of 2009 and 2011 and 10 times pulled by the Hellenic trench rather than being pushed by higher than those of 2017. The changes in baseline length the Arabian plate, as a result the Arabian plate has been in relative to an arbitrary zero-oset for the selected period rapid collision with the Eurasian plates in Eastern Turkey shows that the most of the sites have displacement in the since 23.03 to 5.332 Ma (Miocene period) (Tatar et al., 2012). interval −10 to 10 mm but some sites have larger varia- The easternmost part of Turkey lies on the western end tions. These displacements are mostly related to motion of the Zagros folds and thrust belt, which is dominated of the Turkish tectonic plate, regional crustal deformation by thrust tectonics. The GNSS derived velocities relative to and small amounts of errors in GNSS positioning. The most Eurasia in Eastern Turkey is ~10 mm/yr with the regional GNSS site velocities located all over Turkey give signi - tectonics (Walters, 2012; McClusky et al., 2000). The west- cant information for the study. The GNSS data shows that ern part of the country is also aected by the zone of ex- the Anatolian plate relative to the Eurasia is moving in a tensional tectonics in the Aegean Sea caused by the south- western direction in the central part of Turkey and starts ward migration of the Hellenic arc. Western Turkey is ex- to move in a south-westerly direction in the west part of tending in N-S direction with an upper bound rate of 20 the country. The westward motion of Anatolia increases mm/yr south of 39.5oN (Ayhan et al., 2003). This region gradually from 20 mm/yr in central Anatolia to 30 mm/yr is also undertaking about 3.6 mm/yr extension in E-W di- in south-west Turkey. The numerical simulation of the rection (Eyidogan, 1988). The western Turkish border is a crustal strain in the Aegean region shows a maximum region of roughly 700×700 km2 showing small deforma- −6 1.0446×10 compressional principal strain rate while the tions (Jackson, 1994). The region has apparently experi- second principal strain rate is zero. The strain in Central enced collisional shortening probably due to the westward Anatolia is evidently dominated by extensional deforma- motion of the plate along continental Greece into a sta- tions and the principal strain rate reaches to 0.9589×10−6 with maximum extension. The Marmara Region network is subject to an extensional principal strain (0.6608×10−6) which is also revealed in the Mediterranean Region with a *Corresponding Author: Kutubuddin Ansari: Department of Geomatics Engineering, Izmir Katip Celebi University, Izmir-Turkey, 0.5682×10−6 extension. The present analysis of GNSS data E-mail: [email protected] over the region may complement towards the understand- Ozsen Corumluoglu: Department of Geomatics Engineering, Izmir ing of the stability of regional tectonics and long term Katip Celebi University, Izmir-Turkey aseismic strain inside the country. Sunil Kumar Sharma: College of computer and information Sci- ences, Majmaah University, Majmaah-Saudi Arabia
Open Access. © 2017 Kutubuddin Ansari et al., published by De Gruyter Open. This work is licensed under the Creative Commons Attribution-NonCommercial-NoDerivs 4.0 License. 114 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma tionary Ionic margin (Cianetti et al., 2001). The eect of this shortening into Western Turkey and across the Aegean Sea is a set of thrust faults, a series of folds, and sutures in mainland Greece (Scott, 1981). The boundary of south- west is marked by the Hellenic Arc and the region dis- tinguished by gravity anomalies, seismicity, volcanic and oceanic arc inside the trench supports the explanation of this region as a subduction zone (Scott, 1981). The bulk of seismicity increases signi cantly in the west of Turkey Figure 2: The historical earthquakes of Turkey (according to our and generates a ring in the southern Aegean Sea around literature search) with red circle and the earthquakes from 2009 to the relative to the seismic region. The bulk of this ring in 2017 with red rectangular the south is the Hellenic subduction trench (Giunchi et al. 1996). This subduction arc is a result of the African and Aegean plates converging at a rate of ~33 mm/yr (Delph of Anatolia. The largest geodetic and modeled strain rate of −15 −1 et al., 2015). The African plate is moving slowly relative to 80 nanostrain/yr (2.6 × 10 s ) is achieved in the western Eurasia in a northward direction along the Hellenic trench part of the NAF (Jimenez-Munt and Sabadini, 2002). The (Jackson 1994). The subduction of the African plate along implications of low strains are studied in the western and the Cyprian arc in the south of Turkey is not well de ned central Marmara Sea block that accounts for recoverable but it occurs there rather than the Hellenic arc (Reilinge et growth of elastic strain (Meade et al. 2002). By integrating al., 1997). the GNSS data from all over Turkey with the IGS network, we tried to estimate the crustal strain in Turkey between the years 2009 and 2017.
2 The GNSS Observations
The global navigation satellite system (GNSS) is a tool that has been used to measure surface displacements within the accuracy of a few millimeters in seismically active re- gions. Causative faults or dislocations that slip and simu- late the measured surface displacement and velocity eld Figure 1: Large-scale tectonic features of the Turkey, the yellow can then be modelled to better understand where strain is arrows show approximate plate motions relative to stable Eurasia. accumulating in a seismic area. The high-precision GNSS The three sites namely (BALK, BOYT and SURF) are TPGN sites and is used geodetically to constrain the motion of sites in the ANKR is an IGS site seismological areas and examine the deformation of the crust (Ansari 2014). The permanent GNSS reference site The strong and shocking earthquakes experienced in networks are being implemented throughout the world. Turkey and the surrounding area in the last centuries The establishment of the GNSS plays a precious role for shows a most seismotectonic regional feature (Fig. 2, Ta- the study of Earth sciences. These types of networks are ble 1). The new catalogue given by Duman (Duman et al, used to augment the regional geodetic framework. The 2016) also represents fault plane solution parameters for analyses of continuous time series, in cases where no the 1517 earthquakes with Mw ≥ 4.0 in Turkey and its near abrupt changes have occurred in time series due to earth- vicinity from 1906 to 2012 (Duman et al, 2016). The para- quakes and the principal strain accumulation from the in- metric information includes epicenter, seismic moment, terseismic velocities, are the most common elds of in- nodal planes and principal axes. Based on magnitude, the terest (Sagiya et al. 2000, Lenk et al., 2003). The infor- distributions of the selected solutions included in the cat- mation about the mechanism of earthquakes during co- alogue are: 13 of Mw >7.0, 118 of 6.0
Table 1: The list of historical earthquakes of Turkey available in literature according to my search till 2017
Date Time (LT) Place Location Magnitude Reference 17 CE - Alaşehir 38.21◦N; 28.31◦E -- Internet Classics Archive 13-12-115 - Antioch 36.10◦N; 36.10◦E 7.5 Ms NGDC 141 or 142 - Lycia 36.70◦N; 28.00◦E VIII - NGDC 262 - Southwest Anatolia 36.50◦N; 27.80◦E IX - NGDC 19-05-526 - Antioch - VIII - Procopius 14-12-557 - Constantinople 40.90◦N; 28.70◦E X - Agathias et al. 1975 1268 - Cilicia 37.50◦N; 35.50◦E ~7 - Wikipedia.org ◦ ◦ 10-09-1509 - Constantinople 40.90 N; 28.70 E 7.2 Mw Wikipedia.org ◦ ◦ 23-02-1653 - Smyrna 38.20 N; 28.20 E 7.5 Mw NGDC 17-08-1668 - Anatolia 40.00◦N; 36.00◦E 8.0 USGS 10-07-1688 - Smyrna 38.40◦N; 26.90◦E 7.0 Ms NGDC 28-02-1855 01:00 Bursa 40.20◦N; 29.10◦E 6.7 - NGDC 02-06-1859 02:00 Erzurum 39.90◦N; 41.30◦E 6.1 Ms NGDC ◦ ◦ 03-04-1881 11:30 Chios 38.25 N; 26.25 E 7.3 Mw NGDC 10-07-1894 12:24 Gulf of Izmit 40.73◦N; 29.25◦E 7.0 Ambraseys 2001 29-04-1903 01:46 Malazgirt 39.14◦N; 42.65◦E 6.0 Ms Bogazici University 09-08-1912 03:29 Mürefte 40.75◦N; 27.20◦E 7.3 Ms Bogazici University 04-10-1914 00:07 Burdur 37.82◦N; 30.27◦E 6.9 Ms Bogazici University 13-09-1924 16:34 Horasan 40.00◦N; 42.10◦E 6.8 Ms Bogazici University 22-10-1926 21:59 Kars 40.70◦N; 43.70◦E 6.0 Ms NGDC 31-03-1928 02:29 Smyrna 38.50◦N; 28.00◦E 6.5 Ms Bogazici University 18-05-1929 08:37 Suşehri 40.20◦N; 37.90◦E 6.1 Ms Bogazici University 07-05-1930 00:34 Hakkâri 38.10◦N; 44.70◦E 7.2-7.5 Ms NGDC 04-01-1935 16:41 Erdek 40.40◦N; 27.50◦E 6.4 Ms Bogazici University 19-04-1938 12:59 Kırşehir 39.10◦N; 34.00◦E 6.6 Ms Bogazici University 26-12-1939 23:57 Erzincan 39.77◦N; 39.53◦E 7.8 Ms USGS 15-11-1942 19:01 Bigadiç 39.20◦N; 28.20◦E 6.1 Ms Bogazici University 20-12-1942 14:03 Erbaa 40.87◦N; 36.47◦E 7.0 - Toksoz et al 1979 20-06-1943 17:32 Hendek 40.60◦N; 30.50◦E 6.6 Ms Bogazici University 26-11-1943 22:24 Ladik 41.05◦N; 33.72◦E 7.4 - Toksoz et al 1979 01-02-1944 03:25 Gerede 40.80◦N; 32.20◦E 7.5 - Toksoz et al 1979 06-10-1944 04.34 Ayvalık 39.37◦N; 26.53◦E 6.8 Ms Bogazici University 17-08-1949 - Karlıova 39.54◦N; 40.57◦E 6.8 - Toksoz et al 1979 13-08-1951 18:36 Kurşunlu 40.88◦N; 32.87◦E 6.9 - Toksoz et al 1979 18-03-1953 21.06 Yenice 40.02◦N; 27.53◦E 7.2 Ms Bogazici University 16-07-1955 09:07 Söke 37.55◦N; 27.05◦E 6.8 Ms Bogazici University 25-04-1957 04:25 Fethiye 36.50◦N; 28.60◦E 7.1 Ms Bogazici University 26-05-1957 06:36 Abant 40.67◦N; 31.00◦E 7.1 - Toksoz et al 1979 06-10-1964 16:31 Manyas 40.10◦N; 27.93◦E 7.0 Ms Bogazici University 19-08-1966 12.23 Varto 39.17◦N; 41.56◦E 6.7 - Toksoz et al 1979 22-07-1967 16:56 Mudurnu 40.67◦N; 30.69◦E 7.2 - Toksoz et al 1979 03-09-1968 10.19 Bartın 41.79◦N; 32.31◦E 6.5 - Bogazici University 28-03-1969 03.48 Alaşehir 38.50◦N; 28.40◦E 6.5 Ms Bogazici University 28-03-1970 23.02 Gediz 39.20◦N; 29.50◦E 7.2 Ms Bogazici University 22-05-1971 16.44 Bingöl 38.83◦N; 40.52◦E 6.9 - USGS 06-09-1975 12.20 Lice 38.50◦N; 40.70◦E 6.6 Ms Bogazici University 24-11-1976 14:22 Muradiye 39.12◦N; 44.03◦E 7.5 Ms Bogazici University 116 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma
30-10-1983 07.12 Erzurum 40.33◦N; 42.19◦E 6.9 Ms Bogazici University 13-03-1992 17:18 Erzincan 39.70◦N; 39.69◦E 6.8 - Bernard et al, 1997 01-10-1995 17:57 Dinar 38.06◦N; 30.13◦E 6.1 Ms Bogazici University 27-06-1998 16:55 Ceyhan 36.88◦N; 35.31◦E 6.2 Ms Bogazici University ◦ ◦ 17-08-1999 03:02 Izmit 40.77 N; 30.00 E 7.6 Mw Karakaisis 2003 ◦ ◦ 12-11-1999 18:57 Düzce 40.75 N; 31.16 E 7.2 Mw USGS ◦ ◦ 03-02-2002 07:11 Afyon 38.57 N; 31.27 E 6.5 Mw USGS ◦ ◦ 27-01-2003 05:26 Pülümür 39.46 N; 39.79 E 6.1 Mw USGS ◦ ◦ 01-05-2003 00:27 Bingöl 39.01 N; 40.46 E 6.4 Mw USGS ◦ ◦ 08-03-2010 02:32 Elâzığ 38.87 N; 39.99 E 6.1 Mw USGS ◦ ◦ 19-05-2011 23:15 Kütahya Province 39.14 N; 29.07 E 5.8 Mw USGS ◦ ◦ 23-10-2011 13:41 Van Province 38.63 N; 43.49 E 7.2 Mw USGS ◦ ◦ 09-11-2011 21:23:35 Van Province 38.35 N; 43.40 E 5.7 Mw Earthquake Report ◦ ◦ 10-06-2012 15:44:17 25 km from Oludeniz 36.44 N; 28.92 E 5.8 Mw Earthquake Report ◦ ◦ 14-06-2012 08:52:53 Silopi 37.34 N; 42.49 E 5.3 Mb Earthquake Report ◦ ◦ 08-01-2013 16:16:09 Aegean Sea 39.66 N; 25.57 E 5.7 Mw Earthquake Report ◦ ◦ 07-09-2013 19:59:08 Western Turkey 39.90 N; 27.50 E 5.3 Mw EMSC ◦ ◦ 24-11-2013 20:49:40 Yenicaga 40.80 N; 31.89 E 5.0 Mw USGS ◦ ◦ 28-12-2013 15:21:03* Cyprus Region 35.91 N;31.22 E 6.0 Mw GEOFON ◦ ◦ 24-05-2014 12:25:01 Kamariotissa 40.31 N;25.45 E 6.9 Mw USGS ◦ ◦ 04-09-2014 21.00.04* Tekirova, Turkey 36.17 N;30.87 E 5.3 Mw GEOFON ◦ ◦ 07-10-2015 00:27:33 Western Turkey 36.15 N;29.89 E 5.1 Mw EMSC ◦ ◦ 29-11-2015 02:28:14 Central Turkey 38.82 N;37.84 E 5.0 Mw EMSC ◦ ◦ 02-12-2015 23:27:10* Kigi 39.26 N; 40.34 E 5.3 Mw GEOFON ◦ ◦ 15-10-2016 08:18.33* Eregli 42.23 N;30.73 E 5.3 Mw USGS ◦ ◦ 06-02-2017 13:58:01 Ayvacik, Canakkale 39.56 N;26.13 E 5.4 Mw USGS *Universal Time (UT); Local Time (LT); National Geophysical Data Center (NGDC); United States Geological Survey (USGS); Euro-Med Seismological Centre (EMSC); GFZ Seismological Centre Germany (GEOFON)
Ergintav et al. 2002). Turkey is one of the most active accessed from the TUSAGA-Aktif (https://www.tkgm.gov. countries in terms of plate tectonics and is frequently hit tr/tr/icerik/tusaga-aktif-0) website and IGS site data are by severe earthquakes. Especially the movements of sev- available at CDDIS data server (ftp://cddis.gsfc.nasa.gov/) eral plates including the Anatolian Plate, Eurasian Plate, in the receiver independent exchange (RINEX) format. The Arabian Plate, African Plate, and Aegean Sea Plate are three IGS sites namely ISTA, ANKR and TUBI data are used crucial for geodetic studies and applications (Aktug et in the present study but not TRAB site’s because the IGS al., 2009). The Turkish Permanent GNSS Network (TPGN) site TRAB data is not available at the website nowadays. was established in 1999 and has been operated by the The TPGN data is collected by various types of receivers General Command of Mapping (GCM, national mapping like Turbo Rogue SNR 8000, Trimble 4700, Leica Cors 1500 agency of Turkey) and the General Directorate of Land Reg- and Trimble 4000 SSI and the antennas of the choke-ring istry and Cadaster since 2006 (Ansari et al., 2017). The ba- design (Lenk et al., 2003). We studied the Turkish region sic requirement of continuously tracking TPGN sites was using GNSS observations from 40 GNSS sites distributed for monitoring tectonic activities in Turkey and both of- all over Turkey from 2009 up to 2017 as continuous ob- ine and real-time data availability, imposed by global, re- servations as well as observations from above mentioned gional geodetic and local survey activities. Currently 146 three IGS sites in Turkey. Our selection provides the max- permanent sites are kept running and they cover the whole imum spatial density of TPGN sites over the Turkish terri- area of Turkey including Northern Cyprus. In addition, a tory. All of the selected sites are equipped with dual fre- set of four international GNSS service (IGS) sites, namely quency GNSS receivers with geodetic class antennas. The Istanbul (ISTA), Gebze (TUBI), Ankara (ANKR) and Tra- complete observation list of all selected continuous GNSS bzon (TRAB) is also available in Turkey to link the re- sites is shown in Table 2. gional and the global solutions. The TPGN sites data can be Numerical Simulation of Crustal Strain in Turkey Ë 117
Figure 3: The coordinate reliability of GNSS sites from the year 2009 to 2017 118 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma
Figure 3: The coordinate reliability of GNSS sites from the year 2009 to 2017 Numerical Simulation of Crustal Strain in Turkey Ë 119
Figure 3: The coordinate reliability of GNSS sites from the year 2009 to 2017 120 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma
Figure 3: The coordinate reliability of GNSS sites from the year 2009 to 2017
The GNSS surveys have been processed on a daily early warning, earthquake likelihood monitoring, and re- basis by using GAMIT-GLOBK GNSS processing software search into underlying physical processes. The estimation (King and Bock 2010). We used international Earth rota- of the crustal movements is based on the comparison of tion service (IERS), Earth orientation parameter (EOP) and the site coordinates measured for some time period. a set of IGS sites like ARUC (Armenia) and NICO (Cyprus) to Let us consider the three dimensional coordinates of link regional and global solutions. The satellite state vec- geodetic network points are (x, y, z) and changes of geode- tors, tropospheric zenith delay parameters and regional tic network coordinates calculated according to the data of site coordinates per site on a daily basis are estimated repeated measurements (∆x, ∆y, ∆z). Suppose (u, v, w) are along with the solutions of phase ambiguities for dou- the shifts of coordinates in rectilinear functions of coordi- bly dierenced phase observations. We applied loose con- nates in the geodetic coordinate system, the crustal defor- straints for the regional and relatively tight constrains for mations of Earth can be given by third order tensor: IGS orbit processing. The regional daily solutions have ∂u ∂u ∂u been combined with the global solutions and performed ∂x ∂y ∂z T x y z ∂v ∂v ∂v by the Scripps Orbit and Permanent Array Centre (SOPAC). ( , , ) = ∂x ∂y ∂z ∂w ∂w ∂w Computations of the reference frame were constrained on ∂x ∂y ∂z the daily basis and the daily solutions for positions and ve- ε ε ε 11 12 13 locities of a reliable set of IGS sites were used with respect = ε21 ε22 ε23 (1) to Eurasia xed reference frame 2008 (EUREF 2008). ε31 ε32 ε33
where
3 Estimation of strain from GNSS u = u(x, y, z) = ∆x, v = v(x, y, z) = ∆y data and w = w(x, y, z) = ∆z
The terms ϵij (i=1, 2, 3 and j=1, 2, 3) are known as strain The geodetic methods are used to measure the movement tensor elements, which we can use to estimate the value of the Earth surface and strain in the upper few hundred of the tensor element by using following formula: meters of the Earth’s crust. This data records the slight fault related strain and deformation of the crust that does Eij ϵij = (2) not generate seismic waves as well as the rapid motion that E occurs during earthquakes. Geodetic measurements have Where applications for seismic hazard assessment, earthquake Numerical Simulation of Crustal Strain in Turkey Ë 121
x1 y1 z1 ∆xn, ∆yn, ∆zn, n=1, 2, 3 ...n are the coordinate dierences x2 y2 z2 of GNSS sites in the GNSS network during the rst and last E = : : : campaign. xn yn zn For certain levels of surface through the crust, there is a normal vector (n) which will act on the surface (Kelly and 2012). Hence from Cauchy’s law, for the surface, ∆x1 y1 z1 ϵijn =ϵn (3) ∆x2 y2 z2 E11 = , : : : ∆xn yn zn ε ε ε n n 11 12 13 1 1 x ∆x z ε 1 1 1 ε21 ε22 ε23 n2 = n2 (4) x ∆x z 2 2 2 ε31 ε32 ε33 n3 n3 E12 = , : : : xn ∆xn zn The Eq. (4) is a standard eigenvalue problem from Lin- ear Algebra, to nd the eigenvalues of ϵ and associated x y ∆x 1 1 1 eigenvectors n, the Eq. (4) can be written in following form: x y ∆x E = 2 2 2 13 ε ε ε n : : : 11 12 13 1 0 0 1 x y ∆x ε n n n ε21 ε22 ε23 − 0 1 0 n2 ε31 ε32 ε33 0 0 1 n3 ∆y1 y1 z1 0 = 0 ∆y2 y2 z2 E21 = , : : : 0 ∆y y z n n n Or x ∆y z 1 1 1 ε ε ε ε n 11 − 12 13 1 0 x2 ∆y2 z2 E22 = , ε21 ε22 − ε ε23 n2 = 0 (5) : : : ε31 ε32 ε33 − ε n3 0 xn ∆yn zn To evaluate the eigenvalues of ϵ, we will have to put x1 y1 ∆y1 x y ∆y the determinant of Eq. (5) equal to zero, hence the charac- E 2 2 2 23 = teristic equation for ϵ forms Eq. (5) which can be written : : : xn yn ∆yn like this:
ε3 − c ε2 + c ε − c = 0 (6) 1 2 3 ∆z1 y1 z1 Where ∆z2 y2 z2 E31 = , : : : c1 = ε11 + ε22 + ε33 2 2 2 ∆zn yn zn c2 = ε11ε22 + ε22ε33 + ε33ε11 − ε12 − ε23 − ε31 2 2 2 c3 = ε11ε22ε33 − ε11ε23 − ε22ε31 − ε33ε12 + 2ε12ε23ε31 x1 ∆z1 z1 x ∆z z (7) E 2 2 2 32 = , The eigenvalues of ϵ(ϵ1,ϵ2,ϵ3) are called principal : : : strain and the three corresponding eigenvectors are called xn ∆zn zn principal directions, the direction in which the principal x y ∆z 1 1 1 strain acts. Once the principal strains are found from Eqs. x y ∆z 2 2 2 (6) and (7), we can calculate the principal direction by the E33 = : : : following equations: xn yn ∆zn (ε11 − ε) n1 + ε12n2 + ε13n3 = 0 ε21n1 + (ε22 − ε) n2 + ε23n3 = 0 (8) ε31n1 + ε32n2 + (ε33 − ε) n3 = 0 122 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma
Table 2: The list of IGS (*) and TPGN sites and corresponding velocities plus errors used in the study
No. Site Lon 0E Lat 0N VE σE VN σN 01 ANKR* 32.76 39.89 −23.12 0.69 −0.61 0.86 02 ISTA* 29.02 41.10 −2.95 0.68 −0.90 0.87 03 TUBI* 29.45 40.79 −5.39 0.69 −2.08 0.83 04 NICO* 33.40 35.14 −2.98 2.31 4.98 1.03 05 ARUC* 44.09 40.29 2.09 0.97 13.32 4.18 06 ADAN 35.35 37.00 −10.42 1.61 0.50 1.54 07 ANMU 32.87 36.07 −7.13 1.95 2.88 0.92 08 ANTL 30.67 36.89 −10.76 1.63 −5.44 0.68 09 ANTE 37.37 37.07 −6.25 1.83 15.10 2.30 10 ARDH 42.69 41.11 0.86 0.70 9.56 3.72 11 BING 40.50 38.89 −8.33 1.06 17.17 3.06 12 BALK 27.89 39.64 −20.74 0.75 −7.48 1.16 13 BOYT 34.80 41.46 −3.13 0.75 2.81 1.38 14 CANA 26.41 40.11 −22.26 0.69 −8.87 1.57 15 CESM 26.37 38.30 −18.16 1.17 −24.01 1.59 16 DENI 29.09 37.76 −19.44 1.32 −13.16 0.89 17 ELAZ 39.26 38.64 −14.31 1.11 15.10 2.69 18 ERZR 41.26 39.91 0.27 0.80 9.77 3.29 19 FETH 29.12 36.63 −11.68 1.73 −16.73 0.89 20 GEME 36.08 39.19 −18.56 0.88 9.37 1.74 21 GIRS 38.39 40.92 −1.17 0.69 6.61 2.43 22 HAKK 43.74 37.57 1.26 1.63 9.99 4.04 23 HATA 36.16 36.20 −5.60 2.32 13.46 2.24 24 ISTN 28.83 40.99 −1.38 0.69 −1.34 0.94 25 IZMI 27.08 38.39 −20.02 1.55 −19.48 1.78 26 KAPN 33.53 37.71 −18.78 1.34 6.85 1.06 27 KNYA 32.48 37.86 −24.73 1.53 15.24 1.24 28 KUTA 29.90 39.48 −21.74 0.79 −4.29 0.75 29 KIRL 27.28 41.74 −0.53 0.82 −2.71 1.35 30 MARD 40.73 37.31 −3.84 1.61 20.05 3.13 31 OZAL 43.99 38.66 −0.88 1.25 25.95 4.11 32 SINP 35.15 42.03 −12.22 2.45 −1.91 2.51 33 SIRN 42.46 37.53 −5.80 1.61 16.86 3.66 34 SIVE 39.33 37.75 −5.72 1.87 18.51 3.00 35 SURF 38.82 37.19 −5.86 1.60 18.55 2.55 36 TEKR 27.50 40.96 −1.16 0.69 −4.79 1.27 37 TRBN 39.71 41.01 −0.46 0.69 7.19 2.82 38 ZONG 31.78 41.45 −0.92 0.77 0.73 0.72 39 YOZT 34.82 39.82 −19.73 0.76 6.72 1.41 40 TVAN 42.29 38.53 −3.06 1.61 22.18 3.76 Numerical Simulation of Crustal Strain in Turkey Ë 123
The principal strain value in this equation gives rise to higher than that for 2009 and 2011 and 10 times higher the three components of the associated principal direction than that value for 2017.Even if the eects of poor ducial vector n1, n2and n3. data quality, receiver error, long baselines combine solu- tion and atmospheric errors increase the residuals of the measurements, this type of survey adds little information 4 Result and Discussion to short term crustal deformation studies. If we do not care about error in measurements, the three dimensional resid- uals and standard deviation which are arti cially low in- Here, we investigated the variations of positions of GNSS dicate the coordinate stability of GNSS sites. sites due the regional deformation and local earthquakes. A better measure of repeatability for typical day-to-day The results are discussed in terms of coordinate reliabil- data arises from the GNSS occupations of the site SURF in ity, interseismic and coseismic eects and linear velocities. 2009 which have standard deviations of 0.456, 0.484 and The three dimensional principal strain is estimated at the 1.772 mm for the north, east and up components respec- regional basis and the contribution of small earthquakes tively. The GNSS site BOYT in 2015 has almost maximum in the study of crustal strain is also raised here. standard deviation of 56.044, 81.732 and 192.482 mm for the north, east and up components respectively. We found 4.1 Coordinate reliability that the formal a posteriori coordinate variance and co- variance matrix estimated during the campaign network adjustment accurately re ects site coordinate repeatabil- The coordinate reliability is the overall consistency of a ity as de ned above, unlike daily coordinate variance- GNSS position measurement. The measurement is said to covariance matrix estimates from the GNSS parameter in- be highly reliable if it generates similar results under con- version. sistent conditions. The reliability is the characteristic of a set of test scores that relates to the amount of random er- ror from the measurement process that might be xed in 4.2 Estimation of Interseismic and the scores. If the score value is less, it means that the mea- Coseismic Eects surements contain large errors; while if the score is high, it means that the measurements contain small errors. We We used a set of coordinate time-series to determine used data from 2009 to 2017 from one IGS site (ANKR) and the interseismic or coseismic eects at each site. These three GNSS sites namely BALK, BOYT and SURF at dier- are the measured displacements in the absence of any ent locations of Turkey to evaluate the reliability of our es- earthquakes or during the earthquakes. There are several timated coordinates from the coordinate computations in- crustal earthquakes at magnitude of greater than 5 Mw cluding the residuals of daily coordinate sets. The GNSS have occurred in the survey area during 2009 to 2017 site BALK is located 30 km away from Karacahisar in West- (Fig. 2, red square symbol). The post-seismic and precur- ern Turkey, one of the north-west exposure of the early sory displacements can be expected to be small when Archean (3140 ±2 Ma) to late Proterozoic (657 ±5 Ma) crust they are compared with coseismic displacements and it of Turkey (Kröner, 1990). The second and third GNSS site is easy to obtain uniform interseismic eects over the re- BOYT and SURF are respectively located at the north and gion by removing the coseismic displacements due to the south boundaries of Turkey (Fig. 1). The locations of these large earthquakes (Clarke et al, 1998). The strain over times sites (BOYT and SURF) are out of the boundary of the Ana- which is accommodated in the most part of the crust due tolian fault and they may be considered more stable than to the discontinuity of slip on faults are large if they are the others which are located inside the fault. The IGS site compared with those at the repeat times of large earth- ANKR is situated almost in the centre of Turkey and the quakes.The geodetical measurements at the surface re- other three selected sites (BALK, BOYT and SURF) which ects the long term deformation of the underlying (litho- are triangular sites will assist to conclude the coordinate spheric) material, irrespective of whether that deforma- reliability of the Turkish territory. We obtained a measure tion is continuous (Bourne et al, 1998) or discontinuous for the reliability of our coordinate estimates to each cam- (Savage and Burford, 1970) in the absence of earthquake paign solution from data including the residuals of daily or during the earthquake. The measurements are capable coordinate sets (Fig. 3). of measuring directly this long term upper crustal strain The horizontal and vertical residuals in 2013 and 2015 (Clarke et al, 1998). The changes in baseline length relative are generally of the order of 100 mm per coordinate or to an arbitrary zero-oset for the period 2009 to 2017 have 124 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma been shown in Fig. 4. The best-weighted linear t to each 4.4 The Uni ed strain eld set of baseline length measurements is also shown in same gure. The smooth changes in baseline lengths especially We proceed to evaluate the strain eld in Turkey rather at the IGS sites (ANKR and ISTA) demonstrate that our ref- than a t of a polynomial function to the entire velocity erence frame is maintained from epoch to epoch without eld from the uni ed velocity eld, which can result in scale errors. Most of sites have displacement in the inter- either excessive damping or instability of the interpola- val −10 mm to 10 mm but some sites have large variations. tion. We made discrete estimation of the crustal strains ac- These displacements are mostly related to the motion of cording to the geographical region of Turkey by using the the Turkish tectonic plate. The coordinate variation also GNSS data of repeated geodetic network measurements includes regional crustal deformation and may be caused (Fig. 6). The assessment of the horizontal crust movements by small amounts of errors in GNSS positioning. However, is based on the comparison of the site coordinates mea- this alone is insu cient to reveal the interseismic and co- sured during the period 2009 to 2017. The three dimen- seismic eects. sional crustal strains of the geodetic network were cal- culated by using the Eq. (1) to (8). The principal strains and principal directions have been estimated by the MAT- 4.3 Linear site velocities LAB program and the results are presented in the Table 3. The seven o cial geographical regions which are the Mar- We observed two-dimensional velocity eld of the TPGN mara Region (dark green), the Black Sea Region (light sites constrained to EUREF 2008. Figure 5 shows the ob- green), the Aegean Region (blue), the Mediterranean Re- served velocity eld and their uncertainties between the gion (purple), the Central Anatolia Region (brown), the years 2009 to 2017 for the TPGN sites and numerical values Eastern Anatolia Region (orange), and the Southeastern can be found in Table 2. The horizontal velocities clearly Anatolia Region (yellow) are identi ed as regions show- show the overall crustal shear wave velocities of the Ana- ing dierent deformation regimes (Fig. 6). These regions tolian crust. The kinematics of Anatolia is normally con- closely correlate with the major litho-tectonic domains of sidered with westward motion (Taymaz et al., 1991) or its the crystalline basement, thus possibly pointing to the im- reduction in the southern part of the Hellenic subduction portance of lithosphere compositional heterogeneities for (Wortel and Spakman, 2000). The velocities of most GNSS the strain eld. In the Aegean region the network shows sites located all over Turkey give signi cant information maximum 1.0446×10−6compressional principal strain rate for the study. The GNSS data shows that the Anatolian while the second principal strain rate is zero. The Central plate relative to the Eurasia is moving in west direction in Anatolia Region strain is evidently dominated by exten- central part of Turkey and starts to move in a southwest sional deformations and the principal strain rate reaches direction in the west part. The westward motion of Ana- to 0.9589×10−6with maximum extension. The Marmara Re- tolia increases gradually from 20 mm/yr in central Anato- gion network is subject to an extensional principal strain lia to 30 mm/yr in southwest Turkey. The westwards rate (0.6608×10−6) which is also revealed in the Mediterranean of slip enhances consistently from 16.3±2.3 mm/year to Region with 0.5682×10−6 extension. The identi ed strain 24.0±2.9 mm/year within about 400 km in the NAF zone parameters of deformation from geodetic networks are im- (Reilinger et al., 2006). South-western Anatolia also con- portant for understanding seismic processes in the Turkish tains the crustal deformation about 13.5 mm/yr with an region. The observed strain rate from all regions of Turkey extension in N-S direction. The central Anatolian GNSS may causally be related to the strong earthquakes during velocities relative to Eurasia at 30ºE show a motion to- the years 2009 to 2017 as listed in Table 1. wards the west at a velocity of 18 and 23 mm/yr. This direc- The big earthquake (Ms >5) mainly occurred in the tion of motion changes towards southwest approximately eastern and western parts of Turkey (Fig. 2) but the con- at 29ºE and terminates at the subduction of the African tribution of smaller earthquakes also increases the geode- Plate (Jackson, 1994). The GNSS velocities with respect to tic and seismic extension rates in the country. The smaller Eurasia provides counterclockwise rotation from EAF to earthquakes in the new catalogue are almost evenly dis- the Aegean Sea (McClusky et al. 2000) while the paleomag- tributed throughout the regions (Duman et al, 2016). ◦ netic observations indicate an up to 270 clockwise rota- The empirical relationship between the number of earth- tion within the past 5 Ma in the central parts of the NAF quakes N(M) having a magnitude Ms greater than M are zone (Piper et al., 2009; Tatar et al., 1995). given by Gutenberg and Richter in 1954 (Gutenberg and Richter, 1954) log N(M) = a − bM (9) Numerical Simulation of Crustal Strain in Turkey Ë 125
Figure 4: The changes in baseline length relative to an arbitrary zero-oset for the period 2009 to 2017 126 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma
Figure 4: The changes in baseline length relative to an arbitrary zero-oset for the period 2009 to 2017
Table 3: The three dimensional principal strain inside the country based on numerical simulation GNSS sites during the year 2009 to 2017
−6 −6 −6 Region ϵ1.10 ϵ2.10 ϵ3.10 Aegean Region −1.0446 0 −0.0227 Marmara Region 0.6608 −0.0885 0.0013 Black Sea Region −0.3171 −0.0860 0.0044 Mediterranean Region 0.5682 0.0015 −0.3089 Central Anatolia Region 0.9589 −0.1982 0.0050 Eastern Anatolia Region −0.0326 0.0207 0.0112 Southeastern Anatolia Region −0.0198 0.0361 0.0111
Where a and b are arbitrary constants. The magnitude of earthquake can be replaced properly by a relationship us- ing scalar moments M0 because M0 has a uniform interpre- tation for both small and large earthquakes.
log N(Mo) = A − B log(Mo) (10)
This relationship can be used to assess the contribution of Figure 5: The observed velocity eld and their uncertainties be- smaller earthquakes to the total strain release. Clarke et tween the years 2009 to 2017 for the GNSS sites al. (1997) used the 100 yr catalogue for their quantitative analysis by using the B=0.667 standard distribution and they found that the small earthquakes in the western Gulf of Korinthos were insu cient to account for the discrep- ancy. To understand the more detailed monitoring of the geodetic strain and seismicity in the country, it is neces- sary to test this hypothesis. The empirical predictive equations for the moment magnitude conversion are given in Eq. (11) (Yenier et al 2008). They derived empirical relationships for magnitude conversion using the recently compiled Turkish strong- Figure 6: The seven o cial geographical region of Turkey motion database. The results can play an important role Numerical Simulation of Crustal Strain in Turkey Ë 127
Figure 8: The cumulative (red arrows) and epoch to epoch (blue arrows) displacements over the interval 2009 t0 2017 for TPGN sites relative to the EUREF for coseismic strain due to the earthquakes Figure 7: The quantile-quantile (QQ) plot of magnitude of earth- and epoch network translations quake (Mw) for more advanced earthquake related studies. They put 5 Conclusion the condition that the empirical relationship between Mw vs. Md is not applicable for Md >6 due to the saturation of The variations in the positions of GNSS sites are studied duration magnitude. The events with Md >6 are not taken across the Turkish region to understand the crustal strain into consideration for the regression analysis to avoid the in the country. The coordinate reliability, interseismic and underestimation of Mw for large magnitude events. coseismic eects and linear velocities as well as three di- mensional principal strains have been investigated at the Mw= 1.104m − 0.194, 3.5 ≤ m ≤ 6.3 b b local level. The summary of the study is as follows: Mw= 0.571Ms+2.484, 3.0 ≤ Ms < 5.5 – The study of coordinate reliability shows that the hori- Mw= 0.817 Ms+ 1.176, 5.5 ≤ Ms ≤ 7.7 (11) zontal and vertical residuals in 2013 and 2015 are gen- Mw= 0.817 ML+ 0.422, 3.9 ≤ ML ≤ 6.8 erally of the order of 100 mm per coordinate or higher Mw= 0.746 M + 1.379, 3.7 ≤ M ≤ 6.0 d d than those for the 2009 and 2011 and 10 times higher
The magnitudes Ms and Mb given in Table 1 are con- than that of 2017. A better measure of typical day-to- verted into Mw by using the Eq. (11). The values of con- day repeatability from the GNSS occupations at the stants A and B are estimated from Eq. (5). The estimated sites SURF in 2009 have standard deviation of 0.456, values for A and B are 1.3124 and 0.0174. The quantile- 0.484 and 1.772 mm in the north, east and up compo- quantile (QQ) plot of the magnitude of earthquake (Mw) nents respectively. The GNSS site BOYT in 2015 has al- has been plotted in Fig. 7. It is clear from the gure that most maximum standard deviations of 56.044, 81.732 the QQ plots diverge from the straight line indicating that and 192.482 mm in the north, east and up components the Mw does not approximate the normal distribution. This respectively. means that the Mw presents a trend; it is probably due to the unusual seismic strain which cannot be exactly insta- – The changes in baseline lengths relative to an arbi- ble only from large earthquakes. The cumulative displace- trary zero-oset for the period 2009 to 2017 shows that ments (red arrows) over the interval 2009 t0 2017 for TPGN most of the sites have a displacement in the interval sites which are relative to the EUREF for coseismic strain of −10 mm to 10 mm but some sites have large vari- due to the earthquakes and epoch network translations ations. These displacements are mostly related to the has been plotted in Fig. 8. Actual epoch-to-epoch displace- motion of the Turkish tectonic plate. The coordinate ments after translation (blue arrows) show insigni cant variations also include regional crustal deformations motions of GNSS sites, but sites north of East Turkey show and may be caused by small amounts of errors from steady motion towards the northwest. The insigni cant be- GNSS positioning. havior of displacements in the western region is due the in- cremental seismicity which generates a ring in the south- – The velocities of most GNSS sites located all over ern Aegean Sea around the relatively seismic region. The Turkey give signi cant information for the study. The bulk of this ring in the south is the Hellenic subduction GNSS data shows that the Anatolian plate relative to trench (Giunchi et al. 1996). Eurasia is moving in a western direction in the central part of Turkey and starts to move in a south-western direction in the western part. The westward motion of 128 Ë Kutubuddin Ansari, Ozsen Corumluoglu, and Sunil Kumar Sharma
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