z &; 

L. Earth Resources Iaboratory 

Deparbpent of Earth, Atmospheric, and Planetary Sciences 

Massechusetts Institute of Technology 

, Cambridge, MA 02139 

SEIQ-ANNUAL REPORT To: National Aeronautics and Space Aclmmstr ation (-m-i-) 

-D.. m- 1-L 1me rnm-pretation of Ckustai Dynamics Data in TerCIEl of PLate 

Interactiona and Active Tectonics of the "Anatdim plate" and 

Surrouna Regions in the Middle East 

NASA GRANT: NAG5753 

PIUNCIPAL INYESIIGATOR: Y. Nal3 Toksor 

PWKID. 15 YIarCh 1987-14 September 1987 

DATE. 7 October 1987 

13-77 

(NASA-CR-1813 15) %BE IITEBFAEIAIICI 02 tJE7-2fC53 

C6GSTAL DPIJACIICS EllTA IN !KEBES CE ELATE 

IATEBACTICNS ANZ. BCTfBE TEC'ICBICZ OF THE 

ALATCLXABi PLATE A&D SGKFCUPClkG REGIUNS IN Unclas 

BtE PlIDDlE (Wassactasetts Znst. cf Tech-) ~3146 0099096 
THE INTERPRETATION OF CRUSTAL DYNAMICS DATA IN TERMS OF PLATE 

INTERACTIONS AND ACTIVE TECTONICS OF THE "ANATOLIAN PLATE" 

AND SURROUNDING REGIONS IN THE MIDDLE EAST 

INTRODUCTION 

The long term objective of this project is to interpret NASA's Crustal 

Dynamics measurements (SLR) in the Eastern Mediterranean region in terms of 

relakive plate motions and int.raplat,e. deformateion. Oiir approach is t.0 combine 

realistic modeling studies with analysis of available geophysical and geological 

observations to provide a framework for interpreting NASA's measurements. 

This semi-anniJa! repert concentrates 011 our rezer,t rc-,u!ts regargc,g the 

tectonics of Anatolia and surrounding regions from ground based observations. 

We also briefly report on our progress to use GPS measurements to densify SLR 

observations in the Eastern Mediterranean. Refer to the previous annual report 

for a discussion of our modeling results. 

I. STRIKE-SLIP FAULT GEOMETRY IN TURKEY AND ITS INFLUENCE ON 

EXRTHQUAKE ACTIVITY (see Appendix I) 

Analysis of Turkish strike-slip faults indicates that detailed fault geometry 

plays an important role in controlling earthquake rupture. Empirical 

relationships are used to estimate possible locations and sizes of future strikeslip events. These results have implications for earthquake activity on other 

strike-slip faults such as the Sm Andreas in Ca!ifcrnia. 

TI. THE SEGMENTATION, SEISMICITY AND WTHQUAKE POTENTIAL OF THE 

EASTERN PART OF THE NORTH ANATOLIAN FAULT ZONE (see Appendix II) 

in the vicinity of the Erzincan basin show a close relation to fault geometry. 

Results of this detailed study suggest that each segment may have its own 

characteristic earthquake. Furthermore, we have identifled a 100 km long 

seismic gap along the North Anatolian fault east of Erzincan. This segment last 

ruptured in 1784, and is the only segment of the 900 km long main section of 

the NAJ? that did not experience a large earthquake during the well known 

1939-1967 sequence. Future monitoring of this area with GPS could provide 

important information on possible earthquake precursors (see section IV 

below). 

Historical and instrumental earthquakes of the North Anatolian fault zone 

111. TECTONIC ESCAPE ORIGIN AND COMPUX EVOLUTION OF THE ERZINCAN 

PULL-APART BASIN, EASTERN TURKEY (see Appendix 111) 

Erzincan basin in an effort to explain the relationship between continental 

block kinematics and basin formation. We propose a two stage pull-apart 

mechanism associated with the continental collision of the Arabian and 

Eurasian plates along the Bitlis Suture Zone in eastern Turkey. The first stage 

of westward pull-apart opening occurs between two divergent segments of the 

North Anatolian Fault Zone, accommodating westward tectonic escape of the 

Anatolian block. The second stage involves translational-rotational opening by 

the formation of the obliquely oriented, left-lateral Ovacik fault. This 

interpretation has implications for the detailed nature of plate interactions in 

this region. 

N. GLOBAL POSITIONING SYSTEM (GPS) MEASUREMENTS OF FAULTING AND 

REGIONAL DEFORh€ATION IN THE EASTERN MEDITERRANEAN (see Appendix IV) 

A new tectonic model is presented for the pull-apart opening of the 
We are currently involved in a collaborative effort to use GPS technology to 

investigate relative plate motions and intraplate deformation in the Eastern 

Mediterranean region. At this point, the project involves MIT, Lamont-Doherty 

Geological Observatory, University of Colorado, WEGENER, and local participants 

from Greece and Turkey. Our major effort has been devoted to coordinating 

planned activities with the various participants and establishing a detailed field 

program for measurements in Turkey. Our primary objectives include: 

To monitor strain accumulation and release along the major fault systems 

in Turkey with special emphasis on the North Anatolian fault (NAF) and 

East Anatolian fault (EM). 

To measure directly internal deformations of the Anatolian plate wedged 

include: a) Westward "escape" of the Anatolian plate; b) Eastward "escape" 

of the Northeast Anatolian block; c) North-south compression in Eastern 

Anatolia; and d) North-south extension in Western Anatolia. 

TO determine present-day relative movements of the African, Arabian, 

Anatolian, and Eurasian plates, This objective is an extension of the 

NASA/WEGENER Geodynarnics Project to measure relative plate movements 

in the Eastern Mediterranean with Satellite Laser Ranging (SLR) 

observations. 

he+*--- +Le Aw-l.;-- AC-:--- --A P. - -V-L-- m--- VYY..uwIa uuw -uuLuu, ruLLLaii, aiiu bui asiai piausa. iucsc iiicasuremenis . 

While our participation in this project is being supported primarily by NSF, 

we report on it here because: a) it is directly relevant to interpretation of the 

SLR measurements in the eastern Mediterranean, b) NASA (Ted Flinn) has 

piayed a major role in coordinating the various groups involved, and c) NASA 

will likely provide. logistical and data support for this field effort. 

PUBLICATIONS 

Barka, A., and L. Gulen, Tectonic escape origin and complex evolution of the 

Erzincan pull-apart basin. eastern Turkey, Geological Sciety of 

America Ehdletin, submitted, 1987. 

Barka, A, and K. Kadinsky-Cade, Strike-slip fault geometry in Turkey and its 

Barka. A., M.N. Toksoz, K. Kadinsky-Cade, and L. Gulen. The segmentation, 

influence on earthquake activity, Tectmacs, submitted, 1987. 

seismicity and earthquake potential of the eastern part of the North 

Anatolian fault zone, Tectmophysics, in preparation. 1987. 

Barka, A.. and K. Kadinsky-Cade, Strike-slip fault geometry and earthquake 

Barka, A., K. Kadinsky-Cade, and M.N. Toksoz. North Anatolian fault geometry 

and earthquake activity, Seismol. Res. Lett.,58, 31-32, 1987. 

activity in Turkey, EOS, Pans. Am. Ceophys. Lmia, 68, 362, 1987. 
APPENDIX I 

Camaidge, MA02142 

September. 1987 
ABsmAcr 

The geometry of Turkish strike-slip faults has been reviewed and described. 

From this data set it appears that fault geometry (the distribution of 

discontinuities such as bends and stepovers along the main fault trace) plays an 

important role in the segmentation of the Turkish fault zones into large 

earthquake rupture zones. Large earthquake ruptures generally do not 

propagate past individual stepovers that are wider than 5-10 km, or bends that 

have angles greater than 3O0-3So. Most important, however, is the effect on 

segmentation of the total "geometric pattern", i.e., the distribution of adjacent 

bends and stepovers based not only on distance from one another but also on 

relative discontinuity size. Certain geometric patterns are particularly common, 

and can be viewed as responsible for strain accumulation along portions of the 

fault zone. Fault geometry not only plays a role in segmentation, but also in 

characteristics of earthquake behavior. For example, large earthquake 

epicenters often occur near restraining bends or double bends. However, the 

epicenters are generally not observed within the actual restraining areas (Le., 

along subsegments or within stepovers along the fault zone that are subject to a 

relatively high amount of compressive stress). Furthermore, aftershocks and 

swarm activity can often be associated with releasing areas (areas subject to a 

relatively large component of extension). The direction of block motion relative 

to the geometric pattern also plays an important role in earthquake occurrence 

and rupture behavior. The direction of block motion was constrained in this 

study using focal mechanisms and fault zone morphology. 
There has been a lot of recent interest in relationships between fault 

geometry, Fault segmentation and seismic activity (e.g., Allen, 1988; Bakun et 

d., 1980; Barks and Hancock, 1982; Koide, 1983; King and Nabelek, 1985; .Bilham 

and Hurst. 1986; Slernmons and Depolo, 1988: Schwartz and Coppersmith, 1986; 

Sibson. 1986; King, 1986). The terms fault “geometry” - and “segme?.,,,&,ie~” =rs 

taken here to mean respectively, (1) the distribution of bends and offsets along 

the main fault trace and (2) the rupture zone of a single large or great 

earthquake that has occurred recently or could be expected to occur in the 

future. Strike-slip faults lend themselves particularly well to the study of these 

relationships because variations in strike-slip fault geometry are easy to observe 

at the surface. Furthermore, because depths of shallow earthquakes are usually 

not as well constrained as their epicentral locations (except when the events are 

directly overlain by a seismic network), it is usually difficult to associate 

earthquake locations with geometric features at specitled depths as would be 

required by the study of dip-slip Fault geometry. In this study we examine the 

relationships between fzult geometry, fault segmentation and seismic activity in 

detail, focusing on strike-slip fault geometry and earthquakes in Turkey. There 

is a wealth of data available for Turkish faults that has not been examined in a 

comprehensive way from this perspective. This region will be used as a case 

study. Results will be applicable to strike-slip €aults in other parts of the world. 

Fadt Segmentation 

The concept of fault segmentation is based on the observations that large 

earthquakes in major fault zones tend to have abutting rclpture zones with very 

little overlap and that large earthquakes have been known to occur repeatedly 

along identical sections of a fault zone ( e.g., Kelleher et d., 1973; hdo, 1975; 

Nishenko and McCann, 1981; Sieh, 1981; Sykes and Nishenko, 1984). Based on an 
examination Of seismic and structural geology data in Turkey, we have settled 

on the following scheme for defing fault segments. We have used two 

independent data sources to determine segmentation: (a) the extent of surface 

rupture zones produced by large earthquakes when known, and (b) the location 

of "moderate" or "large" geometric discontinuities (see definitions below), as 

well as characteristics of seismicity along the fault zone. 

Geometric discontinuities include stepovers (offsets in the fault trace) and 

bends (see Figure 1). From mapping active fault traces and surface ruptures 

produced by large earthquakes, it is clear that the main fault trace is 

discontinuous at many scales. For example, extensional features such as sag 

ponds or extension cracks (formed by releasing stepovers), and compressional 

features such as pressure ridges (formed by restraining stepovers) can occur at 

scales ranging from a few centimeters to several tens of meters. We have 

chosen to divide geometric discontinuities into three categories in this study: 

small, moderate and Large. Each category has characteristic ranges of stepover 

width d and bend angle a : for small discontinuities d < 1 Km and a C 5"; for 

moderate dicontinuities d = 1-5 Km and a = 5" - 30"; and for large 

discontinuities d > 5 Km and a > 30". These values are listed in Table 1. From 

observations made during the course of this study, we have determined that the 

small discontinuities are very common, and that they do not play an important 

role in earthquake rupture behavior, unless many of them occur in close 

proximity to one another and can effectively be added together to form a larger 

discontinuity. 

During the procedure of defining fault segmentation we give first priority to 

the extent of surface rupture from large earthquakes. When the surface rupture 

crosses several moderate discontinuities, we divide the fault segments into 

subsegments. When there has not been a recent Large earthquake along the 

fault zone, segmentation is defined by comparing fault geometry characteristics 
with those of other fault segments that have experienced a recent large 

earthquake. 

Distribution of geometric discontinuities with depth 

One difficulty in this analysis is that we cannot constrain how far the 

surface discontinuities extend through the crustal thickness. For example, two 

types of stepover are assumed tc? exist in crcss=se&hi. The &sic type invoives a 

"Aower-Like structure" (Bakun et al., 1980; Segall and Pollard. 1980; Harding, 

1985 Naylor et al., 1986). In this case the stepover does not extend through the 

whole crust. The segments separated by the stepover are connected at depth 

(Figure l-Ca and Cb). Many sag ponds and pressure ridges may overlie these 

ilower structures. The maximum width of this type of stepover can reach 10 km 

This maximum width may be controlled by the thickness and rhoc?bgy d the 

brittle-ductile zone at the top of the upper crust (see King, 1988). A single 

earthquake rupture may propagate through this type of stepover. The second 

type of stepover extends through the whole crust, thus really separating two 

diderent fault segments (Figure l-Cc). This type may be characteristic of a more 

brittle upper crust. It can be as narrow as 1 km. The character of the 

earthquakes may be variable, both from one segment to the next across a 

stepover, and in the stepover region itself (characteristic size. €oca1 mechanism, 

etc.) This second type of stepover is more likely to control fault segmentation 

than the Arst type. From surface observations alone we cannot distinguish 

between the two stepover types. 

Tectonic Overuiew of Turkey 

Major tectonic elements of Turkey and adjacent areas are illustrated in 

Figure 2. Northward motion of the Arabian plate relative to Eurasia causes 

lateral escape of the Anatolian block to the west (e.g., Ketin, 1948; McKenzie, 

1972; Sengor, 1979) and the Northeast Anatolian block to the east. The North 
hatolian fault and the East Anatolian fault consitute the northern and southern 

boundaries, respectively, of the westward-moving Anatolian block. The motion of 

the Northeast Anatolian block is complicated by an extensive internal 

deformation of the block along conjugate faults. 

In this study fault segmentation within four regions Will be reviewed in 

detaiL The location of these regions is shown in Figure 2. The regions include: 

(1) the main part of the North Anatolian fault (NAF) zone, (2) the western part of 

the NA.F in the vicinity of the Sea of Marmara and Istanbul, (3) the East Anatolian 

Fault (W) zone, and (4) the complex conjugate fault system of the Northeast 

Anatolian block After reviewing fault segmentation in these four regions, we 

shall discuss the factors that appear to control segmentation, and the 

distribution of large earthquake epicenters, foreshocks and aftershocks. relative 

to the fault segments. 

SEGMENTATION OF WOR Sl'RJKE43LlIJ FAULT ZONES IN TURKEY 

I) THE NORTH ANATOLIAN FAULT ZONE 

The North Anatolian fault zone is a 1500 km long seismically active rightlateral strike-slip fault that takes up the relative motion between the Anatolian 

Block and Black Sea plate. This fault zone extends from the Karliova triple 

junction (39.3' N, 41.1" E; "K' in Figure 2) as far as mainland Greece. The main 

fault trace contains mainly moderate and large stepovers, bends or 

combinations of these discontinuities (Figure 3). Estimates of the age of the 

North Anatolian fault zone range from late Miocene to Pliocene (13-5 Ma; see, 

e.g., Ketin, 1969; Barka and Hancock, 1984; SengGr et al., 1985). Estimates of 

the total relative displacement along the fault range from 25 to 120 km (e&, 

Bergougnan, 1976 Seymen, 1975; Sengor. 1979; Barka, 1981; Barka and 

Hancock, 1984; Sengor et al., 1985). Based on field observations by the fist 
author, we believe that the age of the NAF is uppermost Miocene to Pliocene, and 

that the total relative displacement varies from 40 km near Erzincan (Figure 38) 

to approximately 15 km near the Marmara sea (decreasing to the west; Barka 

and Wen, in press). 

Between 1939 and 1967, most of the North-Anatolian fault ruptured in a 

westward-migrating series of 6 large earthquakes (magnitude 7-81. producing 

continuous surface breaks from Erzincan to the west end of the Mudurnu Valley 

(39.5"E - 31" E: see Ketin 1948. 1969 Ambraseys, 1970, 1975). There is evidence 

for at least two other similar large earthquake sequences in the last 1000 yean 

along the NAF zone: in 994-1045 and in 1667-1668 (Ambraseys. 1970. 1975; 

Ambraseys and Finkel, 1987). Focal mechanisms for moderate and large 

earthquakes along this portion of the fault zone are mostly pure right-lateral 

strike-slip solutions (Canitez and Ucer, 1967: McKenzie, 1972). Rates of slip 

along the North Anatolian fault zone are estimated at 0.5 - 0.8 cm/year from 

geological data (Tokay, 1973; Seymen. 1975; Barka and Hancock, 1984). and 1-11 

crn/yr from seismological results (Brune, 1968; McKenzie. 1972; Canitez, 1973; 

Toksoz et d., 1979). Segmentation of the North Anatolian fault will be described 

below by reference to segment numbers shown in Figure 3. The same 

procedure will be followed for other parts of Turkey, by reference to the 

appropriate Agure in each case. 

(1) This segment is roughly 50 km long, and extends from the Karliova triple 

junction to the stepover separating segments (1) and (2) (see Figure 3A). It has 

a clear physiographic expression (Allen, 1969), and includes a 16" smooth bend 

near its west end. The 8/17/49 earthquake (M = 6.7-7) is associated with this 

fault segment based on damage reports (Lahn, 1952), on a relocated epicenter 

(Dewey, 1976) that is only 10 krn from the western end of the fault (with 

epicentral error 10-20 km) and on general agreement between earthquake 
magnitude and fault length (based on log k0.78 M-3.62 for the North hatohan 

fault system from ToksZiz et d., 1979). During the 1949 earthquake surface 

rupture over a length of at Least 25 km occurred along this segment 

(Ambraseys, 1987 pers. comm.). The 1946 and 1986 earthquakes shown in 

Figure 3A occurred to the east of the intersection of the North and East 

Anatolian faults, based on surface breaks (Tasman, 1948: Wallace, 1966 Ketin 

1969 see also Barka et al., 1987). Some of the large aftershocks of the 1968 

Varto earthquake also created surface ruptures on the 1949 segment (segment 

1: Ketin, 1969). 

(2) This segment is 100 km long, and extends from the restraining stepover that 

separates it from segment (1) to the Erzincan releasing stepover (segment (3); 

see Figure 38). According to Ambraseys (1975) the last large earthquake on this 

fault segment occurred in 1784. The surface rupture during that earthquake 

was 90 km long. An Ms = 6 earthquake occurred near the middle of segment (2) 

in 1987 (Dewey, 19’76). It was characterized by pure strike-slip faulting 

(McKenzie, 1972), and produced a surface break approximately 4 km long with a 

horizontal slip of 20 cm (Ambraseys, 1975). This is the only segment along the 

North Anatolian fault zone between Varto (east of segment 1, Figure 3A) and the 

western end of the Mudurnu valley (western end of segment 8, Figure 4A) that 

has not experienced a large earthquake during this century. Segment (2) thus 

appears to be a seismic gap (for further discussion see Barka et al., 198’7). 

3) This segment is defined by the extent of surface rupture produced by the 

12/26/1939 Great Erzincan earthquake (M, = 8). Segment (3) is divided into 4 

subsegments. Subsegment 3a is 60 km long, and has a strong physiographic 

expression in its western half. It is separated from segment (2) by a 4-5 km wide 

releasing stepover which forms the Erzincan basin. This basin is characterized 

by short en-echelon strike-slip faults and contemporaneous volcanics. 
Subsegment 3a is separated from 3b by a 20" restraining bend (Tatar, 1978; 

&&a, 1981). Subsegment 3b is about 100 km long, and extends from this bend, 

situated about 10 km NW of the Erzincan basin, to Susehri - the location of 

another pull-apart basin (Hempton snd Dunn, 1984). The Susehri stepover is 

located between boxes b and c in the inset map of Figure 3. Subsegment 3c 

extends from Susehri to the Niksar basin, through the Kelkit valley. It is 110 lcm 

long md re!aUve!y straight. Smithwest of tine iu'iksar bash a 15' restraining 

bend separates subsegment 3c from 3d. Subsegment 3d is 90 km long and ends 

south of Amasya where the 1939 earthquake rupture stopped. 

The epicenter of the 1939 Great Erzincan earthquake was located near the 

20" restraining bend separating subsegments 3a and 3b. Many of the 1939 

earthquake aftershocks caused darnage in the Erzincan and Niksar pull-apart 

ba,sins [rrgu? \- st &., 1387; Tabban. i980; see ais0 Wad and Meyer. 1983). A fault 

plane solution for a moderate size earthquake ( mb = 4.8. 11/16/1983) near the 

city of Erzincan is characterized by ENE-WSW extension (International 

Seismological Centre Bulletin solution) in agreement with our interpreted pullapart character of the Erzincan basin. 

(4) This segment is 50 km long, and defined by the M, = 7 earthquake of 

11/20/1942. Segment (4) extends from Niksar to the Erbaa basin. It contains a 

14" sharp restraining bend north of Erbaa. Pull-apart basins separate segments 

(3c) from (4) and (4) from (5) (south of Niksar and between Erbaa and Tasova; 

see Figure 3c). Dewey's relocated epicenter for the 1942 earthquake is not well 

constrained. Isoseismals for this event (Blumenthal. 1943; 1945a,b; Pamir and 

Akyol, 1943) outline a zone of maximum intensity (I=IX) along the fault segment 

that is about 5 km long and centered on the 14' sharp bend north of Erbaa. The 

rupture zone for this event extended along the full length of segment (4) (Dewey, 

.. 

1976: Giindogdu, 1984). 
(5) This segment is 250 km long, and extends from east of Tasova (Figure 3c) to 

northwest of Kursunh (Figure 3d). It is defined by the rupture zone of the 

11/20/1943 M. = 7.3 earthquake. Segment (5) has two bends: a smooth bend 

(about 25") in the eastern part between Tasova and Kargi, and a sharp bend at 

34' E, north of Tosya (about 15"). Subsegment 5a corresponds to the smooth 

bend area, and contains three releasing stepovers. From west to east these are 

located at Kargi (41.1' N. 34.4" E), with fault separation 1 h; at 41.-1' N, 35.2' E, 

with fault separation 1.5 km. and at 40.9' N, 38.0' E, with separation 1 km. Only 

the second stepover exhibits a clear pull-apart morphology (Ladik Lake). 

Subsegment 5b comprises the fault zone west of the sharp bend, and contains 

several small releasing stepovers in the area just north of Kursunlu-Ilgaz. The 

westernmost stepover is about 1.5 km wide, and defhes the termination of 

segment 5. The relocated epicenter of the 194.3 earthquake (M = 7.3) is not well 

constrained ( * 20-30 km: Dewey, 1976). but was definitely located near the 

western end of segment (5) (near Tosya; see also relocations by Alsan et al., 

1975, and Canitez and Buyiikasikoglu, 1984). The area of maximum damage 

during this event was also Tosya near the 15" restraining sharp bend (Figure 3D). 

The 1943 earthquake caused surface breaks along the full length ol segment (5) 

(Ketin. 1948, 1969; Ambraseys, 1970). Aftershocks of the 1943 earthquake 

(Karnik, 1969; magnitudes 4.5-5.) appear to have occurred near the western end 

of the fault. although these events have not been relocated. 

(6) This segment is about 180 km long, and extends from the area northwest of 

Kursunlu (Rayramoren) to Abant Lake (Figures 3D, 4A). the surface rupture of 

the 1944 earthquake (M = 7.3) covered this whole segment (Ketin. 1948, 1969 

Ambraseys, 1970). The relocated epicenter of the 1944 event (Dewey, 1976) 

occurred at the east end of segment (6), north of Cerkes. Aftershocks of the 

1944 earthquake with magnitude M > 5 were mostly concentrated near the ends 
of segment (6) (Ambraseys and Zatopek, 1969; Dewey, 1978) and caused 

additional damage at Diizce and Gerede, and in the Mudurnu Valley (Ambraseys 

and Zatopek. 1969 Dewey, 1976: Riad and Meyers, 1985). The area of the 1.5 b 

releasing stepover that separates s-gments (5) and (8) just northwest of 

Kursunlu has been the site of continuous earthquake activity (small and 

moderate-sized events), both before and after the 1943 earthquake sequence. A 

s~-y sesduzted by me of the authors of this paper (A. Barka) irrthe towns of 

Cerkes, Kursunlu. Ilgaz and Tosya (Figure 3D) indicates that the 1943 

earthquake only damaged the region east of Kursunlu. whereas damage from the - 

1944 earthquake was restricted to areas west of Kursunlu. The town of Kursunlu 

and surrounding villages were most dected not by the 1943 and 1944 events, 

but by an M=6.8 earthquake that occurred in 1951 along a strike-slip fault 

parallel to the main trace (Pins, 1953). This ez-itiquaice aiso caused 

reactivation of the eastern part of the 1944 rupture zone (Pinar, 1953). 

Segment 6 is relatively straight, except for a 15" restraining double bend that is 

located 10 km east of Ismetpasa (40." N, 32.6" E; Tokay. 1973). Fault creep at 

Ismetpasa, fist recognized by Ambraseys (1970), is about 1 cm/year (Aytun, 

1982). Segment 6 has been subdivided (sa, b, c) to reflect different 

characteristics of recent seismicity along the segment. Subsegment 6a, along 

with 5b. has been subject to continous background activity (e.g., Dewey, 1976). 

Subsegment 6b is the restraining double bend area. Subsegment 6c is much 

straighter than the others, and has been undergoing aseismic creep at least at 

5 

its eastern end. 

11) THE MARMARA SEA REGION 

A) Onshore ureas 

In these areas segmentation is defined both by the location of geometric 

discontinuities and by surface ruptures corresponding to known earthquakes. 
Several segments correspond to portions of the fault that have not ruptured 

recently, but that have the potential to rupture by analogy with nearby ruptured 

segments. To the west of segments (7), (8) and (9) (see Figure 4A) the NAF can 

be divided into three strands (Southern, Middle, and Northern strands). This 

division is based on field observations, offshore bathymetry and some surface 

breaks for large earthquakes. After a review of segments (7) - (9). the three 

strands will be described separately. 

(7), (8) and (9) Segments '7 and 8 are 45 and 79 km long respectively, and are 

separated by a restraining double bend. The 1957 Me = 7.0 earthquake caused 

surface breaks to occur along most of segment 7. During the 1967 M. = 6.8 

earthquake the westernmost 20 km of segment 7 reruptured in addition to 

segment 8. Surface displacement on the reruptured fault segment was smaller. 

however, than that on segment 8 (Ambraseys and Zatopek, 1969). The relocated 

epicenters for the 195'7 and 1967 earthquakes are both very near the zone of 

overlap between segments 7 and 8 (Dewey, 1976). The epicentral locations and 

surface breaks for these events (although the surface breaks are much better 

documented for the 1967 shock than for the 195'7 case: see Ambraseys and 

Zatopek. 1969 Ambraseys, 1970) suggest that both earthquakes ruptured away 

from the zone of overlap: 1967 to the west and 1957 to the east. The eastern end 

of segment 7 corresponds to a directional change in the fault which is 11" 

between segments 6 and 7. Observations of slip produced by the 1967 

earthquake (Ambraseys and Zatopek. 1969: Arnbraseys, 1970) show that in 

general the ratio of strike-slip to dip-slip motion along the main fault trace 

decreases towards the west and northwest as the strike of the fault changes. 

The largest aftershock (1967,./7,/30; M=5.6) of the 1967 earthquake occurred at 

the west end of segment 9, south of Adapazari. It had a normal faulting focal 

mechanism, with extension in a NE-SW direction (McKenzie, 1972). This type of 
_

 

mechanism and the reduced strike-slip to dip-slip ratio at the west end of the 

fault appear to be caused by the change in trend of the fault segment from NESW to WNW-ESE. The appearance of normal faulting west of 30.5" E has been 

noted by McKenzie (1972, 1978). Evms et d. (1984) and Jackson and McKenzie 

(1984) as well. The exact location of the 1943/6/20 earthquake (M = 6.5, Figure 

4A) is not well known. It caused most damage -in the towns of Adapazari and 

Xendek. ad its reiocateted epicenter (Dewey, 1976) lies between those towns as - 

well. It could be related to segment 9, which is active based on fleld observations 

by one of the authors (A Barka), or to the western half of segment 8. 

Southern Strand 

From a review of available literature concerning historical earthquakes that 

have occurred near the Marmara Sea during the past 2000 years It qpezs thtk 

there is no evidence for significant seismic activity dong the southern strand 

before the Nineteenth Century (except for an earthquake in 170 AD, which 

caused intensity IX-X effects in Manyas (Figure 4c; see Sipahioglu. 1983). 

However, since 1855 at least four large earthquakes have occurred along the 

Southern strand. A combination of rupture zones caused by these events and of 

geometric discontinuities along the Southern strand has been used to divide the 

strand into segments. 

- 

(10) - (la) The two NE-SW trending strike-slip faults forming segment 10 (Figure 

4B) bound the Yenisehir Basin. which is considered here to be a pull-apart basin 

from examination of aerial photographs. Segment 11 (Figure 4C) trends E-W and 

is dominated by normal faulting, and 12 is a NE-SW trending segment dominatd 

by right-lateral strike-slip motion. The last large earthquakes to occur on these 

segments were two intensity IX events in 1855 (Sanhson. 1855; Sieberg, 1932; 

Ergin et al., 1967; Karnik. 1971; Soysal et al., 1991). The fist event (Feb. 29, 

1855) caused damage near segment 12. whereas the second event (April 11, 
1855) produced extensive damage mostly to the north of Bursa, neap segment 11 

(Sandison, 1855). In segments IO, 11, and 12 NE-sw trending faults are 

associated with predominantly strike-slip motion whereas E-W trending faults 

exhibit a predominantly normal slip motion that is clearly identifiable in the 

surface morphology of the region. The extensive damage to the north of Bursa 

during the April 11, 1855 event is compatible with the north-dipping geometry of 

the E-W trending segment 11, which is clearly reflected by the fault morphology. 

Segment 13 is composed of poorly-defined NW-SE trending surface breaks 

characerized by NE-SW extension. The 1984 M=6.8 earthquake had a NW-SE 

trending pure dip-slip mechanism with NE-SW extension (McKenzie, 1972, 1978). 

Surface ruptures for this earthquake, as mapped by Erentoz and Kurtm 

(1984) and by Ketin (1988), confirm the extensional nature of this segment. 

Dewey's (1978) relocated epicenter €or the 1984 event is well constrained and 

lies only about 15 km north of the mapped surface breaks. 

(14) - (15) The Yenice-Conen segment (14) experienced a magnitude 7.2 rightlateral strike-slip earthquake in 1953 (McKenzie, 1972; Dewey, 1976). The 

mapped surface break for this event was 50 km long (Ketin and Roesli, 1953). No 

previous historical activity has been recorded for this segment. Segment (14) 

includes a restraining double bend with a bend angle of 17". Segment (15) is 

separated from (14) by a -15 km wide restraining stepover that extends from 

Pazarkby to Edremit (Bingo1 et d., 1973). We have found no information about 

historical activity on segment (15) which continues to the southwest as far as 

the Aegean Sea. 

In summary, the Southern strand between Yenisehir and Edrernit contains 

two segments for which there is no evidence for recent rupture: segments (10) 

and (15). 
According to reliable records, the middle strand is not known to have 

experienced any large earthquakes for at least 200 years. From an examination 

of historical records, the last known large earthquake in this area occurred in 

1064 A.D. Fault segmentation is thus defined by the distribution of geometric 

discontinuities and by analogy with already ruptured segments ah!! the 

northern and southern strands, 

(16) Although this segment has not experienced any large earthquakes during 

this century, it is very distinct rnorphologicaly. The NE end of segment 16 splays 

od clearly from segment 8. About 10 km west of the splay area the fault zone 

widens and turns into many short subparallel segments as it changes direction 

towards the -W by I?". In contrast, the main part of segment 16 to the SW of this 

directional change, is narrower and more distinct. Segment 16 terminates at a 

releasing stepover near Geyve which is characterized by a pull-apart 

rncrpholog y. 

(17) The NW side of the Geyve pull-apart is the NE end of segment 17. This 

segment passes south of Iznik (Figure 4B), and skirts the southern shore of Lake 

Iznik. It changes direction at Sijloz and then terminates abruptly as shown in 

figure 4B. The region near segment 17 has not experienced a known large 

earthquake since 1064 (Sieberg, 1932; Sipahioglu, 1983). 

(18) Segment 18 consists of three subsegments. The two western ones trend 

ENE-WSW (Figure 4B; subsegments leb, 18c). They are parallel to each other, 

separated by 3-7 km, and have lengths 20 and 35 krn respectively. The eastern 

subsegment trends E-W, extends from Soloz to Gerniik. and is approximately 25 

km long (Figure 4B, subsegment 19a). The onshore portion of subsegments tab 

and 18c is clearly visible at the surface. The offshore portions of these 
subsegments are inferred from unpublished seismic reflection data and 

bathymetry (personal communication; M.T.A. 1984) and by Comparison with a 

similar geometric fault pattern near Izmit (segments 24a. b in Fuure 4B; to be 

discussed later). 

(19) This segment is composed of two strands. The Arst strand has an onshore 

portion that is morphologically distinct. The ofhhore portion of both strands is 

inferred from the shape of Bandirma Bay from bathymetric observations and by 

comparison with the interpreted geomet. ,' of segments 18 and 24 (Fiure 4B). . 

Segment 19 has not experienced an earthquake with intensity larger than VI1 in 

the last 1400 years: the area was last seriously damaged by an earthquake in 

543 (Sieberg. 1932; Soysal et d., 1981). 

The offshore fault pattern in the Southern Marmara Sea between segments 

18 and 19 (Figures 4B-4C) is not clear. This area could be similar to the segment 

13 area (a normal fault segment separating two strike-slip faults) or 

alternatively it could be made up of a series of releasing en-echelon strike slip 

faults. Two historical earthquakes which may have some relation to this part of 

the fault zone occurred in 985 and 1064. These events were felt strongly 

be tween Bandirma and Gernlik (Sipahioglu, 1983). 

(20) This segment has not experienced any known earthquakes historically, but 

that may be due to the sparse population in the area. Segment 20 is very clear 

in aerial photographs. It can also be seen on LPuVDSAT images (McKenzie. 1978). 

Its morphological expression is much clearer than that of segment 14. Segment 

20 has a sharp restraining bend in its central part (17-18') and a classic pullapart basin (containing the village Asagiinova, which means "descending into a 

plain") at location x in Figure 4C. 

(21) This segment extends from Can to Bayramic. It has a 15O-2Oo sharp bend 
near its southwest end, north of BaFhc (Bing61 et al., 1973). No earthquakes 

have been reported historically dong this segment. 

(22) The southwest continuation of the fault zone beyond segment 21 has not 

been studied SO far. However, this branch of the fault zone (loosely labelled 

segment 22) appears to continue towards the southwest as far as Ezine (Bingal 

et d., 1973). Subsequently it may continue ints the Aegea_r? SB= 

Most of this strandiies offshore, beneath the northern half of the hf8rma.m 

Sea. In this section we shall review the onshore segments that can be identifled 

and described based on Aeld surveys. In the next section we shall present out 

intepretation of the offshore structures and segmentation. 

(23)-(24) Segment 23 extends from Sapanca Lake through Golciik. where it 

changes direction and continues to the SW (see Figure 4B). This directionalchange is 20'. Segment 24a is separated from segment 23 by a reieasing 

stepover that is about 4-5 km wide (Izmit Bay). Segment 24b is separated from 

segment 24a by another releasing stepover. also about 7 km wide. In these 

three segments (24a, 24b. and the.western part of 23) the NE-SW trending fault 

branches are dominated by right-lateral strike-slip motion, whereas the eastern 

half of segment 23, which trends E-W, has a combination of normal slip and 

strike-slip motion. This difference is clearly reflected in the morphology of the 

area. Although historical earthquakes have damaged Izmit and Karamursel 

frequently (Sipahioglu, 1983), this region has not experienced a Large 

earthquake during the 20th century. Toksoz et al., (1979) consider this area to 

be a seismic gap. The most recent notable earthquakes to have affected the 

segment 23-24 area occurred in 1878 (Itmit-Sapanca Lake region; estimated 

maximum magnitude 6.7 according to Karnik, 1971) and in 1894 (intensity IX, 
damaging the area between Izmit and Istanbul; see Eginitis, 1894, 1895). Until 

now the area extending from Sapanca lake through the Gulf of Izmit has been 

considered to be a single through-going graben characterized by N-S extension 

(Crampin and Evans, 1988). The intwpretation described here, which includes 

segments 23, 24a and 24b, is derived by extending aerial photograph 

observations and detailed Aeld work by one of the authors (AB.) offshore along 

bathymetric trends. 

(25) This segment is located at the west end of the Marmara Sea. It has a 14' 

restraining bend in the central part and a 5 km restraining stepover at its 

eastern end which creates the Ganos mountains ("GM" in Figure 4D). The 1912 

M, = 7.3 earthquake produced surface rupture along most of segment 25 

(Macovei, 1912; Karnik. 1971; Tabban and Ates. 1978: Ambraseys and Rnkel, 

1997). The eastern and western ends of the segment run into the western 

Marmara basin and Saros basin respectively (Lyberis. 1984; Le Pichon et d., 

1984) both of which are interpreted here as pull-apart basins. 

_. 

B) Wshore ureas 

The Marmara Sea is composed of a series of basins and ridges that are 

discontinuous in nature. Our interpretation of the distribution of active fault 

segments beneath the Marmara Sea is shown in Figure 5. This interpretaion is 

much less well constrained that that in the onshore areas. Is is put forward here 

in an attempt to provide a comprehensive model of active fault trends in 

northwestern Turkey. The deepest part of the sea is the northern half. Basins A, 

B and C are approximately 1152, 1265 and 12f6 meters deep respectively. The 

depths of intervening ridges are 648 m between A and 8, and 450 m between I3 

and C (Pfannenstiel, 1944; Turkish Navy bathymetry map, 1984). The northern 

half of the Marmara Sea is interpreted as a large pull-apart basin between 
.. .. 

segments 24 and 25 (Figure 4). This basin is subdivided into smaller basins (A, 

E, C) separated by strike-slip fault segments trending NE-SW. The southern half 

of the Marmara Sea is shallower than 100 m. but can also be divided into ridges 

and basins which are visible on reflection profiles (Marathon, 1974). A 

reexamination of these proAles suggests that the size of these structures and 

the amount OC vertical offset along bounding faults are smaller in the southern 

half of the Marmara Sea than in the northern half. The interpretation shown in 

Figure 5 results from an extrapolation of onshore fault geometry. from 

bathymetry and from examination of seismic reflection profiles. The normal 

faults bounding the basins are unrnistakeable features on the reflection profiles. 

In contrast the strike-slip faults are zones of disturbed and discontinuous 

reflectors. more difficult to interpret, that can be traced from one prome to the 

next, often crossing several profiles. The strike-slip faults are less well imaged 

by the seismic reflection technique due to their near-vertical dip. 

The interpretation presented in Figure 5 is different from previous ones in 

the area. It is based on the onshore results described above. In Fgure 6 four 

other interpretations are shown. In Figure 6B. Pinar (1943) correctly identifles 

faults south of the Marmara sea (including segment 14, that would later rupture 

in 1953), but simply draws a line though the Marmara Sa basins, interpreting 

their origin as tectonic. In Figure 6C, Pfannenstiel (1944) describes the northern 

ridges and basins as normal fault-bounded horsts and grabens, and suggests 

that the basins are connected by NE-SW trending faults. In Figure 6D, Sengor 

(1986) includes basins C and X (as Labeled in Figure 5), and connects them with a 

suspected fault. In Figure 6E, Crampin and Evans (1986) consider the Marmara 

Sea to be one long E-W trending graben. Figure 6A is our inherpetation for 

comparison. It is characterized by long NE-SW trending strike-slip faults 

separated by pull-apart areas. This model is by no means finalized, however. 

Future work needs to be done in the offshore areas. 
Historical earthquake activity in the Marmara Sea region indicates that the 

fault system in the northern half of the sea is more ac€ive than in the southern 

half. Istanbul, on the North Shore, has been repeatedly affected by damaging 

(I>VIII) earthquakes throughout historical record (about 2000 years: see, e.g,, 

Ambraseys, 1971; Soysal et al., 1981). whereas Bandirma, Bursa, and Iznik, along 

the south shore, have been damaged much less frequently (Sipahioglu, 1983). 

The area of maximum damage cased by the 1894 Istanbul earthquake (kM; see 

Eginitis, 1894, 1895). may coincide with two major strike-slip fault segments, 24a 

and 24b. The size of the earthquake and the combined length of the fault 

segments are quite comparable. The only focal mechanism available *om the 

northern half of the Marmara Sea is that of the 1963 earthquake located near 

basin C (see Figure 5). which is characterized by NNE-SSW extension (McKenzie. 

1972). 

Microseismicity in the Marmara Sea region (both onshore and offshore), 

recorded during the past 10 years, exhibits a swarm-like character (Ucer st d., 

1985) with swarms concentrated mostly near our inferred pull-apart basins, and 

also near normal faults that have a strike-slip component (e.g., segments 11 and 

23). 

In conclusion, we feel that the offshore structures in the Marmara Sea are 

consistent with a simple offshore extrapolation of onshore structures around the 

Marmara Sea. Thus the area could be described as a series of long strike slipfaults separated by pull-apart basins. The latter would be associated with 

bathymetric lows, concentrations of microseismicity, and extensional focal 

mechanisms such as that of the 1963 earthquake. Further data are needed to 

verify this model. 
-- 

III) THE E'TA" FAULT ZONE 

Relative motion between the hatoban Block and the Arabian plate is taken 

up by the left-lateral East hatolim fault zone. This fault zone extends from the 

Karliova triple junction (39.3O N, 41.10 E) to the Mediterranean (See Figures 1 

and 7). The East Anatolian fault zone is similar in many ways to the North 

hatOlian fault zone. It is characterized by a series of major discontinuities 

(bends and stepovers). The age of the fadt zone is Pliocene (Arpat and Saroglu, 

1972, 1975) and the total displacement dong the fault has been 22-27 km (&at 

and Saroglu, 1972, 1975; Yalcin, 1978). This implies a geological slip rate of 

about 0.5 cm/yr, which is comparable to that along the NAF zone (see also 

Dewey et al., 1986). Only a few M > 8.5 earthquakes have occurred during this 

century along the East Anatolian fault (W) zone: in 1905, 1906 and 1971. The 

1971 M=8.7 Bingol earthquake, which occurred near the northeast end of the 

fault zone. had a pure left-lateral strike-slip mechanism (McKenzie. 1972). 

However, the fault zone is known to have experienced several intensity 2 VI11 

earthquakes historically. Most of these events occurred within the fist 1000 

years A.D. (Ambraseys, 1970). In addition, some earthquakes caused damage in 

towns along the fault zone after 1000 A.D. (Soysal et al., 1981). These were 

mostly concentrated near the NE and SW ends of the fault zone, but cannot be 

tied to specific segments. 

(1) This segment extends from the Karliova triple junction to Bingol (Figure 7). 

It is about 60 km long and is composed of many closely-spaced parallel strikeslip fault strands. A detailed map of these fault traces is provided by Arpat and 

Saroglu (1972). The 1971 Bingol earthquake (M = 6.7) produced surface breaks 

mostly along the southwestern half of segment 1 (Seymen and Aydin, 1972; .firpat 

and Saroglu, 1972). The relocated epicenter for the 1971 earthquake is at the 

southwestern end of the surface breaks (Dewey, 1976). Two historical 
earthquakes of a similar size have been documented for the general area 

surrounding this segment (1789 and 1875; exact locations not known; see Soysal 

et al., 1981). 

(2) This segment can best be described as a restraining double bend. It extends 

from Hazar Lake to Genc (see Figure ?a). It can be divided into 3 subsegments: 

a straight section between HazW Lake and Palu (Za), a restraining area near 

Gokdere (2b). and a continuation section near Genc (Zc). The restraining bend 

angle at Palu is about 30". The restraining area is characerized by thrusting and 

folding structures (Arpat and Saroglu, 1972; Sengiir et al, 1965). The largest 

known and most recent seriously destructive earthquake along the EAF zone 

occurred in 995 A.D. (Ambraseys, 1970) along segment 2. This earthquake 

damaged towns all along segment 2, and had a particularly destructive effect on 

the area between Palu and Cijkdere (double bend area), where streams were 

diverted (Ambraseys. 1970). Within this century a number of moderate-sized 

earthquakes have affected segment 2, particularly since about 1948 (e.g., 

Tabban, 1980). 

51' 

The Palu-Hazar trend of subsegment 2a continues to the southwest as far as 

Hazar lake (Figure 7d), over a distance of about 125 km. The directional change 

between this trend and that of segment 1 (Bingol-Karliova segment) is 19". The 

extended trend of segment 2a may be related to the proximity of the Bitlis 

thrust system. which is located just southeast of and adjacent to the fault zone 

in that area. The strike of the thrust system is approximately parallel to the EM 

zone. This situation suggests that the fault zone is subject to a relatively high 

convergent strain in this area (see also Jackson and YcKenzie, 1984; Sengor et 

al.. 1985). 

(3) This segment is about 50 km long, and is centered north of Poturge (Figure 

7B). The northeast end of the segment, near Keferdiz, is a 17' restraining bend. 
The historical site Of Claudius (coinciding approximately with Keferdiz) 

experienced at least four damaging earthquakes in the period 10-1000 AD. 

(Ambraseys, 1970), but the exact location of these events relative to segment (3) 

is unknown. Ambraseys and Finke: <1987) recently suggested that the 1908 M= 

6.7 earthquake may have been associated with this segment. This event would 

not have been large enough to rupture dl of segment 3. 

(4) This segment runs mostly along the Sir0 valley, between a 2 km wide 

releasing stepover at its northeast end and a 7.5 km wide restraining stepover 

near Celikhan. Segment 4 ruptured during the 1905 M = 6.8 Malatya earthquake 

(Ambraseys and Finkel. 1987). 

’ 

(5) Segment 5 corresponds to the Celikhan restraining area. It has been 

dsbimed by extensive thrusting and folding which is directly connected to the 

main Bitlis frontal thrust system. A moderate size earthquake (6/14/84, M = 5.9, 

Jackson and McKenzie, 1964) was relocated by Dewey (1976) within the 

restraining area. It focal mechanism was characerized by east-west extension. 

(6) This segment is about 70 km long, and extends from the Celikhan 

restraining bend area to the Golbasi releasing area shown in Figure 7d. A pair of 

moderate-size-earthquakes occurred recently in this area (May 5, 1986: Erdik, 

1986). The first event was located northeast of Colbasi (Bayraktutan, pers. 

comrn., 1987). Its focal mechanism indicates NE-SW compression, resulting in a 

combination of thrusting and left-lateral strike-slip faulting on a north-dipping 

fault (based on Harvard moment tensor solution in U.S. Geological Survey 

Earthquake Data Report). The second event had a pure strike-slip mechanism 

(from Harvard moment tensor solution in U.S. Geological Survey Earthquake 

Data Report) that was consistent with !eft lateral slip on the East Anatolian fault 

near the Siirgu splay fault. 
(7) We are deftning segment 7 to extend from the Gclbasi area at'least as far as 

the Tiirkoglu triple junction (a length of 90 km). This segment has been mapped 

by Yalcin (1978). The East Anatolian fault continues towards the southwest 

beyond its intersection with the Decd Sea fault. When it reaches the NE end of 

the Adana basin, the East Anatolian fault changes direction towards the 

southwest, where it becomes the Misis-Yumurtalik fault segement (Figure 1; 

Ketin, 1948; McKenzie, 1978; Sengor et al., 1985; Giilen et d., 1987). Segment . 

(7) contains a small double bend (Figure ?e: (x), (y) ). The portion of segment (7) 

that lies between (x) and (y) makes an angle of 18* with the fault trace on either 

side, is characterized by P-shear. and acts as a 1.5 km wide restraining area. 

Several moderate-sized earthquakes have qccurred in the segment 7 area 

during this century, as defhed by damage at or near the nearby town of K 

Maras (Tabban, 1980; Ercan, 1982). The last seriously damaging earthquakes 

near Maras-Ceyhan occurred in 11 14-11 15 (Sieberg. 1932; Salomon-Calvi, 1941: 

Soysal et al., 198l), but descriptions of damage are not detailed enough to 

assign these events to a speciflc fault segment. The Gijlbasi area which separates 

segments 6 and 7 is a 13 km wide releasing bend and stepover combination. It 

has R-shear characteristics. The bend angle between segments 6 and ?a is about 

18O. In the Colbasi area the fault zone is divided into two main strands. These 

are separated from each other by a series of lakes, which are caused by the 

pull-apart geometry. There are no known damaging earthquakes in this area in 

the historical record. 

A few general speculative comments can be made about the EAF zone as 

compared with the NAF zone. Although the total displacement along these fault 

zones are comparable, the characeristic earthquake sizes and recurrence times 

are likely to be different. This is due to differences in fault geometry between 

the two zones: (a) Major geometric discontinuities along the fault zone are more 
closely spaced in the EM case than in the NAF case, making the EM segments 

shorter than the NAF' segments. (b) me two major restraining features 

(segments 2b and 5) along the EAF zone contribute to a longer recurrence time 

for larger earthquakes than in the NA~' case. There is evidence in the historical 

record, for example, that the NAF ne= Erzincan has experienced a great 

earthquake every 300 years (Bwka et al., 1987), whereas the historical record 

for the EAF zone suggests a longer recurrence interval of, perhaps, 1000 years. 

Segment 2 is the longest segment along the EAF zone, and is capable of 

experiencing very large earthquakes due to its large restraining double bend 

geometry. Almost 1000 years have elapsed since the last earthquake occurred 

in this area. Ignoring possible creep effects, or other inelastic deformation, a 

much as 5 m of left-lateral strain may have accumulated along this segment (0.5 

cm/yr, 1000 years). 

It3 NORTHEASTERiV TURKEY BLOCK 

The Eastern Turkey block, a wedge-shaped region located to the east of 39" 

E, is bounded by the Northeast Anatolian fault to the north and by the North 

Anatolian fault zone and its eastward extension to t,he south( see Figure 1). East 

of 41.5" E this southern boundary disappears: it is no longer defined by surface 

morphology or seismological observations (Tchalenko, 1977). The Eastern 

Turkey block difTers from the Anatolian block to the west in that strain is 

released by internal fault zones (mozaic structure) in the former, whereas in the 

latter most of the strain is released along major boundary faults. Internal 

deformation in the Eastern Turkey block occurs along the following structures; 

(a) NNE-SSW and/or NE-SW trending left-lateral s trike-slip faults, (b) NW-SE 

trending right-lateral strike-slip faults, (c) E-W trending thrusts and folds, and 

(d) N-S trending extension cracks (Arpat et al., 1977: Sengor, 1980 Saroglu and 

Cuner, 1981: Saroglu and Yilmaz. 1985: Saroglu, 1985). 

.. 
This phase of deformation in the Eastern Turkey block began in Late 

Miocene time (Sengiir et d., 1985). Large earthquakes within the last century 

in this region have occurred mostly along the strike-slip faults (e.g., Toksiiz et 

ai,, 1977; Toksijz et d., 1983; Eyidogm et al., 1986). 

. 

We shall restrict our attention in this area to strike-slip faults. although not 

all of these strike-slip fault segments have experienced large earthquakes 

during this century. 

Ho~asm -NmmanJauit zone (-re 8A) 

This strike-slip fault zone is about 50 krn long, and is characterized by leftlateral strike-slip motion. At the surface the fault zone is divided into many 

short parallel segments, forming a shear zone that is about 5 km wide. An 

abrupt change in strike (about 15a-10a) occurs "W of Horasan. On 10/30/83 a 

magnitude 6.9 earthquake occurred along this fault zone, north of the bend. 

Surface breaks and the highest intensities produced by this event were both 

located within 20 km and northeast of the bend (Barka et af., 1983). More than 

3000 aftershocks were recorded during a portable network survey in the 

epicentral area (Toksoz et al., 1983; Eyidogan et d., 1980). The aftershocks were 

clustered near the zone of highest intensity during the fist month, and then 

migrated away frm the bend. Most of the aftershock migration was to the 

northeast along the fault zone, although some aftershocks were recorded 

southwest of the bend and on either side oE the main fault zone. Altough the 1983 

earthquake had a focal mechanism that was predominantly left-lateral strikeslip with a small thrust component (Eyidogan et d., 1986). the continuation of 

the fault zone southwest of the bend could be expected to rupture( in the 

future) with a higher component of thrusting. 

Caldiran fault (Figure 8Bj 
This fault is approximately 50 km long, and contains a 17'-19' bend new 

Caldiran (Arpat et d., 1977; Toksiiz et d., 1977). According to seismic waveform 

modeling, the 1976 Caldiran earthquake (hk7.3) ruptured the fault bilaterally 

starting from the bend (surface and body wave modeling; see King and Nabelek, 

1985). 

BrJikgiilii fault (Figure BC! 

This fault zone is about 80 m long in Turkey, and extends into Iran where it 

is called the Northwest Fault System (Tchalenko, 1977). The Turkish section ha9 

been mapped in detail by Arpat et d. (1977). It consists of many small 

subparallel segments, some of which may combine at depth. The northwestern 

section is divided into 2 branches with M angular separation of about 35'. This 

geometry creates a releasing area, a "fiegatisre flower structure I, tnarciing, I++ 

1985), characterized by an abundance of N-S trending normal faults and the 

presence of a lake. Southeast of that area the two branches converge, and the 

motion on the €auk has a iarger strike-slip component. A short segment near 

Dogubeyazit is separated from the main fault strand. It is bounded by a 

releasing stepover at one end and a restraining stepover at the other end. 

Acocording to Ambraseys and Melville (1982) an earthquake of intensity IX 

(known as the "Ararat earthquake") occurred on the Turkish part of the 

Balikoglu fault in 1840. 

hLtak and Karayazi faults (figure 80) 

The Tutak fault is about 95 km long and has been mapped by Saroglu and 

Guner (1979). It includes a 19" bend near Mizrak. Northwest of that bend the 

fault segment is parallel to the Karayazi fault (mapped by Kocyigit, 1985) and 

the area between the parallel segments is a 16 km wide restraining stepover. 

Southeast of the bend the Tutak fault is not represented by a continuous surface 
trace. In the middle of that southeast segment in particular, the fault is broken 

UP into short discontinuous pieces. Saroglu and Giiner (1979) assume that the 

Tutak fault is active, based on a fault morphology which is very similar to that of 

the Caldiran fault and on the existence of many relics of destroyed sites. 

However, details of these historical events are not well known. Both the Tutak 

and Karayazi faults are clearly visible in aerial photographs. 

h.zurum fault zone (-re BE) 

This is a 5-10 km wide left-lateral shear zone. Its southern end truncates a , 

series of ENE-WSW trending thrust faults. Near its northern end the Erzunun 

fault zone changes direction abruptly (a 30° restraining bend). Immediately 

northeast of that bend the fault zone still has a predominantly strike-slip 

character, distinctly different From the southwest trending thrust faults south of 

Erzurum. The town of Erzurum has experienced several earthquakes 

historically. Records of activity go back as far as 1200 AD. with notable events 

occurring in 1482 (30,000 people killed) and 1859 (heavy damage in the vicinity 

of Erzurum, in particular along the southern thrust system; see Karnik, 1969). 

and many moderate size earthquakes Listed for the 18th and 19th centuries 

(Sipahioglu. 1983). Both the left-lateral strike-slip fault zone and southern thrust 

fault appear to be active, as evidenced by displaced streams and other 

morphological features (Barka et al., 1983; Saroglu. 1995; Barka and 

Bayraktutan, 1985; Kocyigit et d., 1985). 
DISCUSSION 

From the Turkish data it can be Seen that a finite number of geometric 

patterns recur in the segmentation, with some being more common than others. 

This point is illustrated by the classification of geometric patterns shown in 

Rgure 9. All of the earthquakes with known surface rupture discussed earlier in 

this study have been At in the categories - of Figure 9. Unmptured regrr?~fits 

shown on the right. They have been recognized as possible future ruptured 

segments based on (poorly known) rupture in the historical record and/or 

comparison of fault geometry with that of ruptured segments in the central 

column of Figure 9. Geometric patterns such as those in Figure 9 can be 

associated with strike-slip earthquakes in other parts of the world as well. A 

compilation of these data is currently under way (Barka and Kadmsky-Cade. in 

. 

prep.). 

Segmentation appears from these data to be caused by two main factors: 

(1) the distribution of moderate to large geometric ciiscontinuities (as defined in 

Table 1) along the fault zone, and (2) the direction of block motion relative to 

' the main trend of the fault zone (as evidenced, for example, by earthquake slip 

vectors). These effects will be discussed in the cases of restraining and releasing 

discontinuities. 

Restraining discontinuities 

From Figure 9 the restraining bends associated with ruptured segments 

mostly fall into the "moderate" category of Table 1 (5'-30a). Smaller bends 

seem to neither impede nor concentrate earthquake rupture. Larger bends are 

not present in our data set, although one situation where larger bends may have 

actually prevented the propagation of earthquake rupture is at the 40" ManyasGonen restraining bend separating the 1953 and 1964 earthquakes (NAF 

segments 13-14). Moderate size restraining bends tend to occur within the 
rupture zone rather than at either end of it, and are very common. We feel that 

the change in fault direction may cause strain to accumulate dong the fault 

strand located on one side of the bend, the restraining side (that which o&rs 

most resistance to fault slip due to its orientation relative to the direction of 

block motion), so that fault bends may actually contribute to the occurrence of 

large earthquakes. Thus the angle of the restraining bend and length of the 

restraining segment could both be expected to influence the amount of strain 

accumulation and resulting earthquake size. We do not have enough data in 

Turkey alone to verify this hypothesis, but examination of strike slip 

earthquakes in other parts of the world suggests that this is true (Barka and 

Kadinsky-Cade, in prep.). 

Restraining stepovers associated with ruptured segments are not as 

common in the Turkish data set. Rupture propagation is prevented by 

restraining stepovers in the cases of the 1949 NAF segment 1-earthquake (d=5 

km) and the 1971 EAF segment 1 earthquake (d=lO km). Smaller stepovers 

occurring in our data set do not usually impede rupture propagation. 

An important point is that the discontinuities do not act in isolation from 

one another. If two discontinuities occur along a given segment, controlling 

factors are their relative sizes and their separation from each other. This can be 

seen in two examples. First, the 1939 segment of the NAF (segment 3): In this 

situation the 20" bend separating 3a from 3b, north of Erzincan, dominates the 

15" bend on segment 3d south of Niksar, even though the two bends are 

separated by more than 200 km and by the Susehri releasing stepover (2 krn 

wide: located at the subsegment 3b-3c intersection). When we say "dominates", 

we mean that the earthquake rupture is controlled more by the 20" bend. In 

this case the 1939 earthquake initiated near the 20" bend and ruptured away 

from it bilaterally, as will be seen later. Note that the 15" bend was located 

adjacent to the 10 km wide releasing stepover separating NAF segments 3 and 4. 

.l t i 
ne second example Of relationships between discontinuities within a segment is 

NAF segment 6 (1967 earthquake, Mudurnu valley). Here we have two restraining 

double bends along the same segment. The eastern one, which is mentioned in 

Rgure 9, dominates. The epicenter: of the 1957 and 1967 earthquakes were 

located at this double bend. Rupture occurred mostly away from this area in 

both cases. The other smaller double bend plays no role in the rupture. The 

I%? e%zst riiptiir-es right througn it. The conclusion to be drawn from these two 

examples is that the complete geometric pattern needs to be examined in each 

case, not just one discontinuity at a time. 

Epicenters of large earthquakes often seem to occur near restraining bends 

within a segment (see also Barka and Hancock, 1982: King and Nabelek, 1985; 

Barka and Kadinsky-Cade. in prep.). There are two examples of well-constrained 

epicenters that fail into this category. The 1976 Caldiran (Eastern Turkey, 

Figure ab) earthquake epicenter was located very close to the 17'-19' 

restraining bend, and the earthquake ruptured bilaterally based on an inversion 

of teleseismic body waves (King and Nabelek, 1985). Examples of this and other 

epicenters near restraining bends are shown in Figure 10. The 1939 Erzincan 

earthquake had an epicenter near the bend (the accuracy of the location is not 

ideal, but adequate here because the fault was very long; see Figure 3 and lo), 

and ruptured bilaterally. Other Turkish earthquakes (1942, 1943, and 1967 along 

the NU) had epicenters close to restraining bends, but the resolution of these 

locations relative to the length of the surface fault trace is not sufficient for a 

detailed comparison of epicenter with fault geometry. In both of the better 

constrained cases the epicenter was located near the bend, and rupture took 

place away from the bend. In general we saw no evidence for epicenters within 

restraining areas - Le., on the section of the fault segment that is located on one 

side of the restraining bend and is subject to a higher amount of compressive 

strain than the other side or, alternatively, within a restraining stepover area. 
_- .+ 

f 

A critical factor influencing the occurrence of lkge earthquakes, other 

than the fault geometry, is the direction of block motion relative to the 

geometric pattern. An example of this can be seen by looking at the single 

restraining bend examples at the top of Figure 9. The 19'76 Caldiran earthquake 

ruptured bilaterally From the bend area. The 1855 earthquakes occurred 

separately, one on either side of the bend. The 1983 Horasan-Narman 

earthquake only ruptured one side of the segment, between the bend and one 

end of the fault. From an er 

pure strike-slip faulting on 

earthquakes were characterized by pure strike-slip motion on one side of the 

bend and a strong component of normal faulting on the other side. The 1983 

ination of fault morphology, the 1976 case caused 

ier side of the bend. However the 1855 

earthquake had pure strike-slip motion, but the morphology of the Fault on the 

unruptured side of the bend shows a strong component of compression. These 3 

examples illustrate the influence OF the direction of block motion. This direction 

can be defhed using geode tic measurements (generally not available in Turkey), 

fault plane solutions if available, or Fault morphology, the latter including 

primarily observations of physiographic fault expressions at the surface. 

Releasing discontinuities 

Releasing stepovers and bends can be recognized by morphological 

depressions (basins) and/or extensional structures. Releasing discontinuities 

control segmentation, although compared with restraining stepovers we have 

fewer examples in Turkey that can be used to constrain the sizes of 

discontinuities responsible €or segmentation. The 1840 Balikgolu (Figure 8c) 

releasing bend (40") seems to have been too large to allow the propagation of 

rupture though the bend. The 5 krn wide stepover separating NU segments 2 

and 3 (near Erzincan) and the 10 km wide stepover separating NAF segments 3 

and 4 (near Niksar) both acted as barriers to rupture propagation. The 1 km 
wide stepover separating NAF segments 4 and 5 also prevented rupture 

propagation. However the 1 km stepover west of the restraining bend in NU 

segment 8 did not stop the 1944 earthquake rupture. The diaerence between 

these last two cases may have been the added contribution of a restraining bend 

adjacent to the stepover in the first case. In general the size and distance of 

discontinuities relative to restraining discontinuities is important. NAF segment 

5 has several small to moderate releasing stepovers to the west of the 15' 

restraining bend, but the segment only terminates at one of them, a 1.5 km wide 

stepover. Three other moderate releasing stepovers are located east of the 

bend, but none of them cause segmentation. The 1.5 km wide Susehri releasiw 

stepover that separates subsegments 3b and 3c did not cause segmentaion in 

1939. In conclusion, from available observations. it seems that the large 

releasing discontinuities (Table 1) cause segmentation (Le., bound the fault 

segments), but the smaU to moderate ones often do not. Influencing factors in 

the moderate discontinuity cases are their location and size relative to one 

another and to the restraining discontinuities along the segment. 

Aftershocks of large earthquakes and earthquake swarm activity both tend 

to occur in releasing bend and releasing stepover areas. Although epicentral 

Locations of small and moderate earthquakes are often not well determined in 

Turkey, there is stilt some evidence for this phenomenon. The first example of 

this is the 1939 Erzincan earthquake (NAF segment 3), where large felt 

aftershocks occurred in the segment 2-3 releasing bend/releasing stepover area 

and in the segment 3-4 stepover area. Another example is the 1967 Yudurnu 

valley earthquake (NAF' segment a), where aftershocks were concentrated along 

the releasing segment (with a higher normal faulting component) west of the 

smooth relasing bend. The third example is the Marmara Sea region. In this last 

case, earthquake swarms (Ucer et d.. 1995) coincide with pull-apart basins. This 

observation confirms previous results in California (e.g;., Eaton et al, 1970; Hill, 
1977; Weaver and Hill, 1979 Segall and Pollard, 1980). In the case of aftershocks 

it has been explained by Auid pore pressure arguments (Sibson, 1986). 

Most of the earthquakes in this study do not have well-located foreshocks, 

either because they did not occur or because they were difficult to locate due to 

their small magnitude. In the case of the 1939 great Erzincan earthquake, 

however, local residents reported that several small earthquakes were felt in the 

Erzincan basin about one week preceding the 1939 event (Pamir and Ketin, 1941: 

Parejas et al, 1942). This basin is a large releasing stepoverbend combination 

located relatively close to the main 20" restraining stepover of NAF' segment 3. 

A secondary relasing feature within or near a restraining area provides a weak 

point that may rupture fist. This appears to have been the case also for the 

1975 Haicheng, China earthquake (Jones et al., 1982), and for the 1930 Salmas, 

Iran earthquake (Tchalenko and Berberian. 1974). The damaging foreshock that 

occurred in the Iran case has not been accurately located, but the distribution 

of damaged villages during the foreshock is not inconsistent with a location in 

the releasing stepover area adjacent to a restraining stepover. 

Geological factors associated with fault discontinuities 

Although it is beyond the scope of this paper to document all of the 

geological elfec ts that are responsible for the observed Cault discontinuities, 

some of the more important effects will be reviewed here. First it should be 

noted that complex fracture patterns are characteristic of simple shear 

laboratory experiments (e.g., Tchalenko. 1970; Wilcox et al., 1973; Barlett et al., 

1981; Naylor et al., 1986). These patterns can be due, for example, to rotation of 

the material within the fault zone. 

En echelon fault patterns can often be explained by the rheology of the top 

part of the upper crust. First, the occurrence of ductile material such as a thick 

pile of sediments (Harding, 1985) or clay-rich rocks can cause discontinuities. 
For example SarOglU and Barka (1983) documented some cases in Turkey (e.g,, 

1983 Horasan-Narman earthquake; see also Barka et ai., 1983) in which the 

effect of serpentinite-rich ophiolitic melange on fault zones was to widen the 

zones and break them up into many smaller faults with unclear surface 

expression (compared to the single break areas). Second, a decrease in 

conAning pressure near the earth’s surface may in some cases cause a widening 

of the zone of deformation. 

The occurrence of bends can be explained by a number of factors. First,. 

pre-existing zones of we.akness can be an important factor at any scale. For 

example, on a large scale. the eastern half of the North Anatolian fault zone 

follows the Antolid/Taurid/Pontid suture zone, and the western half follow the 

Intra Pontid suture zone (both Eocene-Miocene features). Second. changes in 

stress orientation or magnitude can cause bends. A third factor includes 

heterogeneities in rock type. The discontinuities may also form progressively as 

a rupture either follows a boundary (Rogers, 1973) or encounters (at a higher 

angle) a boundary between dissimilar rock types (Jackson and McKenzie, 1984). 

In the second case, the rupture could initially change direction due to a 

refraction efTect; subsequently the bend angle could increase due to diflerential 

deformation across the boundary. 

Geometric fault discontinuities are often associated with clear 

morphological features. Near restraining segments mountains are often 

observed. An example of this is the Ilgaz Mountains on segment 5 of the North 

Anatolian fault (near Tosya). These mountains are comparable to the San Gabriel 

Mountain range (1875 earthquake), Black Mountain (1906 earthquake) or Middle 

Mountain (1966 Parkfield earthquake) along the San Andreas fault. Releasing 

features are often associated with Low areas as has been seen several times in 

the detailed Turkish fault descriptions. 
Finally, restraining bends are sometimes associated with kink structures or 

folds with an orientation that is oblique to the fault zone, indicating variations in 

rheology within the moving blocks or plates. Examples of this are the Palmyra 

kink (Lebanon-Syria) or the Kirikhan-Gaziantep kink ( southern Turkey), both 

adjacent to the Dead Sea fault. 

Geometric discontinuities along strike-slip faults are stable in the short 

term, but they can be subject to progressive deformation over a longer tie 

period. For example progressive deformation of single or double bends can 

cause an increase in a which eventually blocks movement on the fault. The fault 

is then replaced by newer faults. Examples of this can be observed in New 

Zealand and California. A progressive increase of a to 40" at a restraining double 

bend along the Alpine fault in New Zealand has caused motion along subparallel 

faults (Awatera. Clarence, Hope faults: see Rynn and Scholz, 1978). Similarly, 

near the Black Mountain - San Juan Bautista double bend (California) motion is 

taken up by the Calaveras and Hapard faults (Sykes and Nishenko, 1964). In 

southern California many subparallel faults take up motion near bends in the 

San Andreas fault (e.g., Scholz 1977; Ziong and Yerkes, 1985). One possible 

interpretation for these subparallel faults is that slip has become diflicult along 

the main fault strand. 

By reviewing the geometry of Turkish strike-slip faults we have reached the 

conclusions that fault geometry plays an important role in the segmentation of 

strike-slip faults and in earthquake rupture processes. By increasing our data 

base to include other strike-slip faults in the world (particularly the well-studied 

California cases) we feel confident that a careful examination of fault geometry 

can help define or estimate rupture lengths of large earthquakes, and possibly 

mainshock epicenter, foreshock and aftershock locations in some cases. From ' 
the Turkish data we can say specifically that: 

a) The geometric discontinuities tend to occur in characteristic 

patterns, each associated with a characteristic earthquake 

mechanism. 

b) The size of the discontinuities is important. Small discontinuities 

(see Tabie ij generally do not cause segmentation. Large 

discontinuities usually do cause segmentation. Moderate 

discontinuities have to be examined carefully *in relation to one 

another and to the direction of block motion in order to determine 

their role. 

c) The distribution and size of moderate discontinuities relative to one 

another along a segment are very important in determining the nature 

of the earthquake mechanism along the segment. It is therefore 

advisable to be very cautious about analyzing fault geometry 

statistically. 

d) Seismological background information and additional information 

such as geodetic measurements or fault morphology need to be 

included in the interpretation of segmentation based on fault 

geometry. 

e) Epicenters of large earthquakes seem to be associated with 

restraining bends in fault segments, but not actually occur within 

restraining subsegments (on one side of the bend) or within restraining 

s t epovers. 

f) Aftershocks and swarm activity can sometimes be related to 

releasing discontinuities. Foreshocks may be related to releasing 
features located close to areas of major strain accumulation. 

The fleld work on which a large part of this study was based would not have 

been possible without the M.T.A. Institute's (Ankara, Turkey) support of one of 

the authors. We would like to thank M. NaA Toksoz for many helpful discussions. 

This work was supported by L'. S. Geological contract number 14-08-0001-G1151, 

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Prof. Paper, 1360. 43-91. 1985. 
FIGURE CAPllONS 

1) Geometrical pattern defhitions for strike-slip faults, as used in the text. In 

all map views fault movement is assumed to be right-lateral. The 

direction of block motion is considered to be east-west. A-Stepovers. 

These can be of releasing or restraining type depending on the 

direction of the step. Cases Ab, C. d characterize different amounts of 

horizontal separation between fault segments as shown on the page. B - 

Bends. Smooth bends refer to a gradual change in fault orientation. 

Sharp bends refer to an abrupt change. C - cross-sectional views of 

stepovers. Whether the two fault segments join at depth or remain as 

two separate planes depends on the brittle-ductile characteristics of 

the upper crust. Flower-like structures (fault planes joining at depth) 

can be either negative or positive depending on whether the stepover iS 

of releasing or restraining type. 

2) Major tectonic elements of Turkey. Compiled from Arpat and Saroglu (1972, 

1975), Sengbr et d. (1985). Boxes indicate areas shown in Flgures 3.4, 

7 and 0. The North and East Anatolian faults intersect at the Karliova 

triple junction (K, at approximately 39"N. 41"E). Kahraman Maras, also 

referred to in text, is represented by an M near 37W, 37OE. 

2) Geometrical pattern definitions for strike-slip faults, as used in the text. In 

all map views fault movement is assumed to be right-lateral. The 

direction of block motion. is considered to be east-west. A-Stepovers. 

These can be of releasing or restraining type depending on the 

direction of the step. Cases Ab, c, d characterize different amounts of 

horizontal separation between fault segments as shown on the page. R - 

Rends. Smooth bends refer to a gradual change in fault orientation. 

Sharp bends refer to an abrupt change. C - cross-sectional views of 

stepovers. Whether the two fault segments join at depth or remain as 

two separate planes depends on the brittle-ductile characteristics of 

the upper crust. Flower-like structures (fault planes joining at depth) 

can be either negative or positive depending on whether the stepover is 

of releasing or restraining type. 

3) Active fault segments in the central and eastern sections of the North 

Anatolian fault zone. The inset map shows the general location of the 

main trace. Boxes in the inset map indicate areas which are blown up 

in the lower part of the figure. Years displayed as smaller numbers 

refer to large earthquakes that occurred where numbers are shown. 

Larger numbers (1-6) along fault zone correspond to fault segments. 

The interpreted length and position of each segment are described in 

the text. Thicker dashed lines denote ruptured segments. Thinner 

plain lines are unruptured faults (e.g., segment '2). For references see 

text. 

4) Active Fault segments in the western section OF the North Anatolian fault 

zone, near the Marmara Sea (South of Istanbul). For explanation see 

Figure 3. 

5) Interpreted distribution of active fault segments beneath the Marmara Sea. 

Thin lines are bathymetric contours from Pfannenstiel(1944). Major 
.. 

basins are indicated by A, 8, and C. Maximum basin depths are derived 

from the Turkish Navy bathymetry map (1984). The fault plane solution 

for the 1963 earthquake is taken from McKenzie (1972). Fault 

segments in the southern half of the Marmara Sea are interpreted 

from reflection profiles (Marathon, 1974). Note the pull-apart nature of 

the northern Marmara Sea. 

6) Comparison of previous Agure with published interpretations. A - 

interpretation of this study. B - from Pinar (1943). C - from 

Pfannenstiel(l944). D - from Sengor ( 1986). E - from Crampin and 

Evans (1986). See text for discussion. 

7) Active fault segments, East Anatolian fault. Only one large earthquake (1971. 

segment 1) has occurred here during this century. For explanation see 

Figure 3. 

8) Major block boundaries and internal active faults, Eastern Turkey. Note 

conjugate character of most of these faults. Compiled from Toksbz et 

al. (1977). Arpat (1977). Saroglu and Guner (1979), Barka et d. (1983) 

and Barka and Bayraktutan (1984). 

9) Schematized geometric fault patterns, and ruptured and unruptured 

D-'-!'- I -*. segments that can be assnci&.ed with the ptteins. ~L~LS (srnau 

discontinuities) are not shown for each case in the schematics. For 

comparison purposes only (insufficient information for earthquake 

prediction). Left-lateral faults are inverted to give equivalent rightlateral fault geometry. 

IO) Relationships between single bends. ruptured fault segments and location of 

epicenters. Solid stars are interpreted epicentral locations. Dashed 

arrows show distance from interpreted epicenters to the ends of the 

earthquake surface breaks. A - 1939/12/26 Erzincan earthquake. 

Dewey's (1976) relocated epicenter is shown as an open star. It is 

constrained to within about 20 km. Given the rupture length of the 

event, an epicentral location at the bend is a reasonable assumption. B 

- 1942/12/20 Erbaa-Niksar earthquake. A well-constrained 

instrumental epicenter is not available for this event. Maximum 

intensities were concentrated in the bend area, between Tepekisla and 

Zilhor (Pamir and -01, 1943) C - 1943,./11,./26 Tosya. earthquake. A 

well-constrained instrumental epicenter is not available for this event 

either. Maximum intensities were concentrated between Tosya and 

Ilgaz (see Figure 3; Barka, 1981). D - 1976/11/24 Caldiran earthquake. 

The International Seismological Centre bulletin epicenter is indicated 

by the open star. The inversion of seismic waves generated by this 

event (King and Nabelek, 1986) confirms that rupture took place 

bilaterally, away from the bend area. 
Table 1: Classification of geometric discontianities 

moderate 

l<d<6km 

5" < Q < 30" 

~ ~~ 

large 

d>5km 

Q > 30" 

Type of Geometric 

Discontinuity 

S t epover 

Width (d) 

Bend Angle 

(a1 

' 

small 

d < lkm 

CY < 5" 
RESTR"W RELEASM 

CROS S-S FCTIONAL VIEWS 

a) NEGATIVE 

SINGLE PLANE AT DEPTH 

F LOWER-LIK E STRUCTURES 

TWO SEPARATE PLANES 

AT DEPTH 

c) 
G 
ORIGINAL PASE IS 

OF POOR QUALITY I 

P 

3 

Y e 

w 

v) 
ORlGeNAe PAGE IS 

OF POOR QUAIJTY 

’. . 

r - .. . 

1% 

.. 

I 
OR!S;INAL PAGE IS 

OF POOR QUALITY 
A 

J 

26 28 
I 
ORlGlNAL PAGE IS 

OF POOR QUALITY 
. 
. 

h 

$ f 

\\ 
APPENDIX I1 

THE SEGMENTATION, SEISMICIlY AND EARTHQUAKE POTENTIAL OF 

THE EASTERN PART OF THE NORTH ANATOLIAN FAULT ZONE 

A. Barka 

M.N. Toksijz 

K. Kadinsky-Cade 

L. Giilen 

Earth Resources Laboratory 

Massachusetts Institute of Technology 

42 Carleton Street 

Cambridge, MA 02142 , 

April, 1987 

-1 
ABSTRACT 

Historical and instrumental earthquakes of the North Anatolian fault zone in 

the vicinity of the Enincan basin have been examined in relation to fault 

segmentation. Results of this study suggest that each segment may have its own 

characteristic earthquakes. The epicenter of the 1939 great Erzincan 

earthquake (M=8) occurred near a 20' restraining bend located about 50 km 

from the eastern end of the 360 km long segment that ruptured during that 

earthquake. This segment was terminated at each end by releasing stepovers. 

Aftershocks mostly occurred in the releasing stepover/releasing bend '*ea 

located at the eastern end of this segment. Historical records suggest that the 

1939 event is characteristic of great earthquakes that occur approximately 

every 300 years on this segment. Recurrence times of large earthquake3 (I = 

- IX) is about 100 to 150 years in the Erzincan region. The segment to the east of 

the Erzincan segment is identifled as a potential seismic gap. It is approximately 

100 km long, and extends from the Erzincan releasing stepover to a restraining 

stepover-bend combination near Yedisu. This segment last ruptured in 1784. It 

is the only segment of the 900 km long main section of the North Anatolian fault 

that did not experience a large earthquake during the well-known 1939-1967 

sequence of .Ma = 7-8 earthquakes that ruptured the fault zone between Varto 

and the western end of the Mudurnu valley. 

-2 
INTRODUCTION 

It has recently been acknowledged that fault geometry plays a critical role 

in the earthquake rupture process (e.g.* Segall and Pollard, 1980; Bakun et d., 

1980; Lindh and Boore, 1981; King and Nabelek. 1985: Sibson, 1988; Schwartz 

and Coppersmith 1988; Barka and Kadinsky-Cade, 1987). The term "fault 

geometry" includes stepovers, bends, and their r??%?,v cr?_rrrbinakis.?s. Each 

geometric pattern appears to have a characteristic dynamic rupture 

mechanism. Through fault geometry one can defhe €auk segments, each having 

its own characteristic earthquakes. 

In this paper we identify an approximately 100 krn long fault segment in the 

eastern part of the North Anatolian fault zone which has not ruptured in the last 

200 years. This segment is deflned by geometric discontinuities. Through the 

analysis of geometric discontinuities along this and neighboring segments we 

examine the effect of fault geometry on the location of large earthquake 

epicenters, foreshocks, aftershocks and interpreted sites of strain 

accumulation. 

The largest known earthquake to have occurred on the North Anatolian fault 

(NAF') is the 1939 Erzincan earthquake ( -44, =8.0). This earthquake caused great 

damage and killed 32,700 people. It ruptured a section of the NAF that extends 

from the Erzincan basin to the Amasya province, with surface breaks covering a 

distance of 360 km. The right-lateral displacement reached 3.7 m in places 

(Pamir and Ketin, 1941; Ketin, 1948, 1969; Ambraseys, 1970). Both historically 

and during modern times, the Ertincan area has been one of t.he most active 

seismic regions in Turkey ( Sieberg, 1932: Ergin et al., 1967; Soysal et al., 1981; 

Tables 1 and 2). 

-3 
Figure 1 shows major tectonic elements of Turkey in an area where the 

northward motion of the Arabian plate causes active convergence. As a result, 

the Anatolian block escapes westward and the northeast Anatolian block 

eastward (Ketin, 1948. McKenzie 1972 Kasapoglu and Toksijz, 1983 Giilen, 1984; 

Dewey et al., 1986). The Anatolian block is bounded by the right-lateral North 

Anatolian fault to the north, and by its conjugate, the East Anatolian fault, to the 

south, These two fault zones intersect at the Karliova Triple junction (Ketin. 

1966; Allen, 1969; McKenzie, 1972; Dewey, 1976: Tchalenko, 1977; Sengar. 1979; 

Toksoz et d., 1979, Jackson & MacKenzie, 1984: Sengar et d., 1986; Dewey et d., 

1986). The eastern part of the Anatolian block is divided into two smaller blocks 

( A, and A2 Figure2 ) by the left-lateral strike-slip Ovacik fault. This fault 

intersects the NAF zone at the southeast end of the Erzincan basin. The 

eastward escape of the NE Anatolian block is complicated by the extensive 

internal deformation and by the existence of a number of sub-blocks. A 

dominant tectonic feature in this region is the NAF, which forms a boundary 

between the two blocks escaping in opposite directions. The NAF intersects the 

Northeastern Anatolian fault (NEAF, forming the northern boundary of the NE 

Anatolian block) northwest of Erzincan (Figures 1 and 2). Figure 2 shows major 

blocks and boundary faults between the Erzincan and Karliova triple junctions. 

- 

Between 1939 and 1967 most of the North Anatolian Fault west of Erzincan 

ruptured through a westward migrating series of major earthquakes, as shown in 

Figure 1. Earthquakes along the NAF east of Erzincan followed a more 

complicated pattern, as can be seen in Figure 2. 

Fault Segments 

Eased on the geometric discontinuities of the main fault traces and extent 

of ruptures of large earthquakes we have identified the fault segments. The 
.. 

.. 

North Anatolian fault zone consists of several segments as shown in Figure 2 

(Barka and Kadinsky-Cade, 1987; Barka and Giilen, 1987). 

Segment 1: This segment extends from Karliova to the Yedisu restraining 

stepover, where it bends around to the southwest, changing direction by 16" in a 

convergent sense. Segment 1 has a clear physiographic expression particularly 

along the Elmali Valley (Allen, 1969). During the last 50 years this segment has 

ruptured in two separate earthquake sequences. The Arst sequence includes the 

1948 Varto and 1949 Elmali earthquakes (Mz6.0 and M=7.0 respectively), and the 

second includes the 1966 M=7.0 Varto earthquake and its aftershocks. (Mz5.3- 

6.2; see also Table 2). 

Segment 2: This segment strikes N 70a W and is approximately 100 km long. 

Segment 2 extends from the Yedisii p!gz in the east to tha EiZinCm &~uviai 

plain (western end). The physiographic fault expression is very clear where the 

fault runs along the Euphrates valley and through the village of Caykornu. The 

physiographic expression disappears, however, as soon as the segment enters 

the Erzincan alluvial plain, although the segment may continue further west 

under the plain. The 1784 earthquake, which last ruptured this entire segment, 

created surface breaks along, a 90 km distance, and caused lm of vertical 

displacement (Arnbraseys, 1975). The 1967 M=6 Piilumiir earthquake was also 

located along this segment. Surface breaks for the 1967 event were, however, 

only 4 km tong; this earthquake was accompanied by 20 cm of right-lateral 

surface displacement (Ambraseys, 1975). 

Segment 3: This segment is defined by the extent of surface rupture produced 

by the 1939 Great Erzincan earthquake. Segment (3) is divided into 4 

subsegrnents. Subsegment 3a is 60 krn long, and has a strong physiographic 

expression in its western half. It is separated from segment (2) by a 4-5 km wide 

-6 
releasing stepover which forms the Erzincan basin. This basin is characterized 

by short en-echelon strike-slip faults and contemporaneous volcanics. 

Subsegment 3a is separated from 3b by a 20' restraining bend. Subsegment 3b 

is about 100 km long, and extends from this bend, situated about 10 km NW of 

the Erzincan basin. to Susehri - the location of ahother pull-apart basin 

(Hempton and DUM, 1983). Subsegment 3c extends from Susehri to the Niksar 

basin through the Kelikit valley. It is 110 km long and relatively straight. 

Southwest of the Niksar basin a 15" restraining bend separates subsegment 3c 

from 3d. Subsegment 3d is 90 km long, and ends south of Arnasya where. the 

1939 earthquake rupture stopped. 

The epicenter of the 1939 Great Erzincan earthquake was located near the 

20' restraining bend separating subsegments 3a and 3b. Many of the 1939 

earthquake aftershocks caused damage in the Erzincan and Niksar pull-apart 

basins (Ergin et d., 1967; Tabban. 1980; see also Riad and Meyer, 1983). A fault 

plane solution for a moderate size earthquake ( M,, = 4.8, 11/18/1983) near the 

city of Erzincan is characterized by ENE-WSW extension (International 

Seismological Centre Bulletin solution ), in agreement with our interpreted 

pull-apart character of the Erzincan basin. 

Northeast Anatolian Fault - This fault zone consists of several segments with a 

combined length of approximately 350 kin. The southwesternmost segment 

(Segment A) is located to the north of the Erzincan region (Figure 2). 

Approximately 70 km long, it strikes NE-SW. Although very little is known about 

this fault segment, it is assumed to have an oblique movement, consisting 

mostly of left-lateral slip with a subordinate thrust component. (Tats, 1978). 

The study of earthquake records (Soysal et ai., 1981; Sipahioglu. 1983; Rad and 

Meyers, 1985) indicates that it might be less active than the segments of the 

North Anatolian Fault zone. Apart from the 1939 Tercan earthquake (Mz5.9) and 

6 
several aftershocks of the 1939 great Erzincan earthquake, the only kown 

historical event associated with this segment is the 1254 I=IX earthqu&e. This 

event caused surface breaks to occur over a 50 km length on segment A 

(Ambraseys. 1975). 

Ovacik fault - This is another left-lateral fault. It is located near Ovacik, and 

extends up to the southeast end of the Erzincan basin. This fault is about 120 lun 

!cng ~54 trsz&s NE-SB. Near Ovacik, where the fault cuts Quaternary alluvial 

fans, physiographic expressions are very clear (Arpat and Saroglu, 1975). The 

Ovacik fault has also been participating in the opening of the Erzincan basin; be 

only earthquake might have occurred on the Ovacik segment is the 01/26/1960 

M=5.9 event (macroseismic location; Ergin et al., 1987). There are no historical 

events that can be speciflcatly associated with this segment. ' 

It should be noted that the area between segments 2 and 4, including the 

Ovacik fault and segment A of the NEAF zone, is located within the serpentiniterich ophiolites and ophiolitic melange associated with the Anatolid/TauridPontid suture zone. 

Seismicity 

Historical Earthquake Records 

The history of damaging earthquakes in the Erzincan region was recognized 

and well documented even before the great earthquake of 1939 (Mi Kernal, 

1932). Sieberg (1932) listed some of the Erzincan earthquakes and stated that 

between 1045 and 1784, at least 17 catastrophic earthquakes had occurred in 

the Erzincan region. In Table 1 we have tabulated the significant earthquakes 

affecting the Erzincan region since 1000 AD., based on sources referenced in the 

table. 

-7 
Figure 3a iS an intenSlty-time plot of hown earthquakes which ha= 

af!ected the Erzincan region. From this @re, earthquakes can be Categorized 

according to three sizes: (a) small and moderate, with Modifled Mercalli intensity 

I S VIII, (b) large earthquakes with VI11 15 Ix and (c) great earthquakes for 

which I5 X. According to Figure 3a, at least 3 great earthquakes have occurred 

during the last 1000 years, including the one in 1939. Ambraseys (1970) 

reported that the 1045 earthquake produced a surface break of a length 

comparable to the one which occurred in 1939 and that the 1458 earthquake 

caused the death of about 32,000 people, comparable to the casualties of the 

1939 earthquake. The 1668 earthquake is controversial. With the exception of 

Arnbraseys (1975), most of the existing references describe it as an earthquake 

of intensity about VIII-IX. Ambraseys (1975) reports that the 1688 earthquake 

produced a 360 km surface break and that the lateral displacement was as 

much as 4 m, which is again comparable to that of 1939. At least 10 large 

earthquakes (VI11 5 I S IX) have occurred in the Erzincan region since 1000 A.D., 

causing considerable damage and Large numbers of casualties. 

Figure 3b shows the number of earthquakes that occurred between 1000 

and 1900 in the Erzincan region, versus intensity. The dashed tine is drawn only 

through the 12 VI11 points, because the historical record may be incomplete for 

smaller events. According to this plot. the recurrence interval for the great 

earthquakes in category (c) (intensity X or greater) is about 400-450 years if the 

1668 event is excluded. With the 1668 earthquake, the recurrence interval 

becomes about 300 years. These recurrence intervals, combined with the 

amount of displacement created during the great earthquakes (3-4m), give a 

slip-rate of approximately 1 cm//yr. This is comparable to the creep rate 

observed at Ismetpasa, on the central part of the NU. from geodetic 

measurements (Eren et al., 1984) and creepmeter data (Toksoz, 1984, USGS 

-8 
report). Note that the 1 cm/year slip rate estimated here for the NU zone near 

Erzincan does not include a possible additional creep component. This slip-rate 

is at least two times higher than that obtained from geOlogical(PIio-Quaternary) 

results along the NAJ? (0.4-0.5 cm/yr, Seymen, 1975. Barks and Hancock, 1984). 

This reveals that the motion may be progressively accelerating or episodic. 

Note also that segments 1-3 form a boundary between opposite-moving blocks 

(the Anatolian and Northeast Anatolian blocks). ThQP = highs? slip i&.ie is 

expected in this area than along the main section of the NAF to the west. From 

Figure 3b the recurrence interval for large earthquakes (VI11 SfS 1x1 is 

approximately 100-150 years. 

Imtmmdtzi Earthquake Records 

Figure 4 shows the distribution of epicenters for earthquakes with -M, > 

4.9, that have occurred between Erzincan and Varto since 1900. These events are 

listed in Table 2. The following points should be made concerning the listed 

earthquakes: 

a) There is a quiescent period between 1900 and 1930 in the Erzincan region. 

b) Although Pamir and Ketin (1941) did not have any field observation (Ketin 

1987, pers. cornrnuncation), they showed ESE-WNW trending isoseismals covering 

the mea between Tercan and Baskoy for the epicenter of the 1939/11/21 Tercan 

earthquake that may have been on the NEAF zone. This is not only suggested by 

some catalogs, but also by the amount of damage that occurred in and near 

Karakulak (e.g., 130 buildings collapsed), and in some other destroyed villages 

which are all situated next to the fault zone (Parnir and Ketin, 1941; Ergin et d., 

1967; Tabban. 1980). 

c) The December 27, 1939 Erzincan earthquake (M=8) is one of the largest 
earthquakes to have occurred in this area. We will SurmmiZe known iniormation 

concerning foreshocks, main shock, aftershocks, and surface breaks in the 

Erzincan region. Pamir and Ketin (1941) reported that two foreshocks were felt 

within the week preceding the main shock in the Erzincan region. The epicenter 

of the main shock was within the Erzincan region in the range 39.7 a - 39.8"N. 

39.4" - 39.5'E (e.g. Tillotson, 1940; Pamir and Ketin, 1941; Ergin et d., 1967; 

Karnik. 1969 Dewey, 1976). The main surface breaks were associated with 

segment 3. Within the basin some discontinuous extension cracks striking WNWESE were also observed, and in the salt playa east of Erzincan the fissures were 

80-100 cm wide (Pamir and Ketin. 1941). The villages along the northern margin 

of the Erzincan basin were completely destroyed by either the main shock Or 

the aftershocks. The eastern end of the surface breaks coincided with the 

eastern end of the Erzincan basin (Pamir and Ketin, 1941; Ketin 1969). 

Numerous aftershocks occurred in the Erzincan region as.wel1 as in many other 

places (e.g. Nature. 1940 a, b, c): According to Nature (1940~). on February 3, 

1940. two villages were destroyed in the Erzincan region (close to the NEAF zone, 

segment A) by a shock which also killed 45 people and injured many more. 

Parnir and Ketin (1941) also state that between February 3 and 20, 1940, many 

earthquakes were felt in the region. However, available earthquake catalogs do 

not contain many of these earthquake records. Aftershocks 11, 14, 15, 17, and 

18 (listed in Table 2) were felt strongly in the Erzincan region and caused some 

damage in the villages. In particular, aftershock 15 caused 40 buildings to 

collapse, and aftershock 18 was responsible for 15 deaths and 100 injuries 

(Tabban, 1980). Most of the aftershocks were located in or near the Erzincan 

basin. 

d) Although some catalogs indicate that the August 17, 1949 earthquake 

(M=6.?-?) was close to the eastern end of segment 2. this earthquake was on the 
easternmost segment of the NAF zone. called the Karliovcr-nmoLi segment 

(Lahn, 1952) (Segment 1 in Figure 2). 

e) According to some catalogues, the epicenter of the 1960/01/26 ( Mz5.9) 

earthquake might have occurred near the northeastern part of the Ovacik fault 

(see Figure 5 and Table 2) (Ergin et al., 1967; Tabban, 1980). 

f) The relocated epicenter of the 1967/07/26 k5.6-8.2 earthquake (Dewey. 

1976) was located on the eastern half of segment 2, although the macroseismic 

epicenter was in Piiliiir. 

Discvssion and Conclzrsions 

It is possible to make a correlation between the pattern of seismic activity 

the geometry ana distribution of active fault segments in the Erzincan 

region. Both hislorical data and the 1939 earthquake have shown that great 

earthquakes in this region can be associated with segments 3 a, b, c, d. The 

epicenter of the 1939 earthquake occurred near the 20" restraining bend 

between subsegments 3s and 3b of the NAF. ( Barka and Hancock, 1982; Barka 

and Kadins ky-Cade, 1987). Furthermore, observations of compressional 

deformation and uplifting within the young deposits along subsegments 3a and 

3b can be interpreted as surface expressions of high strain accumulation in the 

area, which eventually results in the occurrence o€ very large earthquakes. 

Since the recurrence interval for great earthquakes is about 300-400 years, the 

last earthquake having occurred in 1939, at present the probability of an 

earthquake of comparable magnitude is small. 

In the Erzin.can region, many of the small to moderate aftershocks ( 

category a in Figure 3a) can be related to the releasing stepover area in the 

-1 1 
eastern half Of the Erzincan basin, between segments 2 - 3a and the Omcik fault 

(Barka and Gulen, 1987). Moreover the fault plane solution of the 1983/11/18 

earthquake (M4.8), located near the city of Erzincan shows normal fault- 

(Figure 5): this clearly supports the idea of a tensile stress regime produced by 

the pull-apart extension in the Erzincan basin. Some of the small to moderate 

earthquakes in the area may also be associated with the Ovacik fault, with 

segment A of the NEAF zone, or with internal block deformation, as in the case of 

the Kigi-Karliova area in block AI (Figure 4). There have been no large 

earthquakes (category b) for at least 200 years in the vicinity of Erzincan. 

excluding the segment 1 and Varto earthquakes (194.6, 1949, 1966). The last 

large earthquake occurred in 1784 and was located on segment 2, according to 

Ambraseys (1975) (Figure ea). who also reported 90 km surface faulting along a 

115' trend. Although the damage and casualties were less severe than in 1939 

(Sieberg 1932), the 1784 earthquake was extremely destructive for the Erzincan 

region, killing 5,000-15,000 people (see Table 1). The recurrence interval for 

category b events is about 100-150 years, and earthquakes most likely 

correspond to segment 2, the Ovacik fault or segment A of the NEAF zone. Of 

these, segment 2 has the highest potential for generating large earthquakes in 

the near future, because (a) segments 1-3a of the NA?? zone form a boundary 

between the eastward-moving NE Anatolian block and the main westward-moving 

Anatolian block, so that the rate of movement is naturally expected to be higher 

than along other parts of the NAF zone: and (b) during the 20th century segment 

2 is the only segment along the NAF zone which has not experienced a large 

earthquake between Varto and the western end of the Yudurnu valley (900 km) 

(see also Ambraseys and Zatopek 1969). Note that segment 1 has already broken 

twice in the last 40 years (Figure 6c.d). The largest event which has occurred on 

segment 2 during the instrumental period (since 1900) is the 1967 Pulumur 

earthquake ( Ms = 5.6 - 6.2 ), (Figure 6d). Ambraseys (1975) has reported that 

-12 
this earthquake produced a short rupture, 4 km long, with 20 cm maximum 

dextral slip, at the eastern half of segment 2. However, if we consider the 

approximately 100 krn length of segment 2, the 1967 event is not large enough 

to fU the gap (Figure 7). Therefore segment 2 appears to have the highest 

potential for a Large earthquake in the Erzincan region in the near future. The 

segment 2 gap, which is separate from the gap mentioned by Toksaz sf d., 

(1979: see Figure 7). was first mentioned by Ambraseys and Zatopek ! 1969). 

Only a few poorly located earthquakes (e.&, 1960, M=5.9) can be associated 

with the Ovacik fault since 1900. Although the rate of movement is somewhat 

smaller along this fault than on the NAF zone (Barka and Giilen, 1987). the 

Ovacik fault segment is another candidate for future large earthquakes. 

Segment A of the NW zone is similar to the Ovacik fault. The 1939/11/21 

T~rcar! ezrthquake arid iS4O/OZ/OS (#E in Table 2) aftershock of the great 

1939/12/26 earthquake might have occurred on segment A. From the historical 

earthquake records, we are only aware of the 1254 large earthquake, which 

created 50 km of surface faulting along segment A, trending 60" with 5 rn (?) 

maximum vertical displacement (Ambraseys, 1975). 

The unruptured fault segments, including segment 2, the Ovacik fault, and 

Segment A, occur within the serpentinite-rich ophiolitic complexes in the 

vicinity of Erzincan. Thus creep is an expected phenomenon which probably 

takes up some of the motion along the fault segments. Nevertheless this does 

not exclude the potential for future large earthquakes. 

In conclusion, defining segmentation of the fault zones through geometric 

discontinuities and combining resulting segments with existing earthquake data 

can provide information about seismic gaps and earthquake rupture processes. 

A possible explanation for the high concentration of seismic activity in the 

-13 
Erzincan region is the fact that many different fault segments begin, terminate 

or intersect within that region. The geometric arrangement of fault 

discontinuities (restraining bends, triple junctions and releasing stepovers) and 

the rock type (e.g., serpentinite) contribute to the relative ease or diflticulty of 

movement along fault segments in the region. These factors are responsible for 

the division of earthquakes into categories a, b or C. Our interpretation of fault 

geometry and earthquake data in the Erzincan region suggests that a large 

earthquake similar to the 1784 event is expected to occur soon. This earthquake 

could cause considerable damage in Erzincan and surrounding areas. Further 

detailed studies are required in order to better characterize this seismic 

hazard. 

, -14 
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Barka, AA and Emcock. P.L. Relationship between lault geometry and some 

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Karnik, V. SeMicity of thr Euzopem amu. D. Rcids! Pgh. Gem, DDi&c& 

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Ketin. I. Uber die nordanatolische horitontalverschiebung, Bull !An Res 

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King, G. and Nabglek. J. Role of fault bends in the initiation and termination of 

-17 
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Lindh, AC., and Eoore, D.M. Control of rupture by fault geometry during the 

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McKenzie, D. Active tectonics of the Mediterranean Region. -clophw. J. R. At&. 

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__ 

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_- 

Segall, P. and Pollard, D.D. Mechanics ol discontinuous laulta, J. Ceophy+. Res., 

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-19 
Sipahioglu, S. An evaluation of earthquake activity of the Horasan-Narmm 

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ORlGlNAL PAGE 15 

OF POOR QUALiN 

n~~i CAPTIONS 

Rgure 1. Tectonic map of Turkey shodng the surface rupture dong the North 

hatolian and other faults due to major eadhqmkes since 1900. The 

Anatolian and NE Anatdim blocks are wedged Out to the west and east 

respectively by the convergence of Arabia and Eurasia d~ shown in the 

inset map (lower left). ne rectangle in the burs delineates the area 

of study and is enlarged in FQure 2. (Compiled from hat dc Saroglu 

1972: Arpat 1976; Barka 1984; Sengar et id.. 1988). 

Eg??_rt 2. Sinpiitled geometry of major blocks and their boundary-fault zones 

between Erzincan and Karliova. Thick and dashed zonas and dates 

indicate ruptured fault segments and dates of related earthquakes, 

reapcctively. Dotted area is the Erzincan basin, Ai and A, are subblocks mthin the Anatolian block. 

hue 3(a) brthquake activity histogram of the Erzincan region. 1. Intensity, 

T. time. Numbers above the dots are the number of casualties 

resulting from each particular event. a. b, c are the categories ol 

earthquakes, S-2, S-3. S-4 and S-A are the fault segments. For - explanation and references see the text and Tables 1 and 2 

respectively. (b) log (number of earthquakes) ==US itikeriiity. XW - 

i900, in the Erzincan region. The dashed line is drawn through the I L 

VI11 data points (log N = -0.271 I + 2.98). 

of the NAF zone between Ertincan and Karliove for the interval 1900- 

1983. X = instrumental data dy, 9 = macroseismc information only, 

C = best of instrumental or rnacroscmmc information, D = 

instrumental and macroseismic data agree. Details are given in Table 

2. 

Figure 4. Distribution of earthquake epicenters (M>4.9) in the easternmost part 

figure 5. Fault plane solutions between Erzincan and Karliova (McKenzie, 

1972). Vote that a) the 1983/11;'19 earthquake, M, = 1.9, has a normal 

fault solution which agrees with the openinq of the Erzlncan basin and 

b) solutions east of the Karliova junction have a clear thrust 

component. 

figure 6. Sequence of events which produced surface faulting in the ErtincanKarliova region in the Last 200 years. For explanation see text. 

figure 7. Space-time distribution of surface ruptures of 20th century 

earthquakes. indicating a clear seismic gap between 39.9 and 40.9" E. 

where segment 2 lies. The area to the east of 41.9: has been identified 

already as another seismic gap (Toksoz el rd . 1979). 
Table 1. List of historical earthquakes’ 

in the Erzincan Region. 

1784 

1987 

VIII-IX 

VJ 

was destroyed 

5.000- 15.000 
ORIGINAL. PAGE IS 

OF POOR QUALITY 

Tabla 2 List of instrumental earthquakes *th Ms > 4.9, for the 

19O(E1= intetval in the eastern part of the NAF zone. 

Epicenter 

Number Dates Lat. N Long. E H Reference 

(1) 1907/04/06 Y39.30 40.40 4.9 3.2 

1 %E/-;- 

1909/05/03 

1930/04/09 

l930/ 12/ 10 

1934/11/12 

1935,'05,'11 

1935/10/13 

1939:'ll '21 

1939/ 12/26 

1939/12/29- 

1340:02 03 

1940/ 02,'O.I 

Damage at Kigi 

. eOJs.3 40.3 3- 

'39. 40 5.3 

'39.8 39.3 5. 

39.8 : 39.1 5.8 

39.5 39.4 5.4 

'39.7 39.2 5.8 

Slight damage at Kernak and Erzincan 

39.2 40.5 5.9 

'39. 41. 5.9 

Kigi 

(Tcrcan?) 

*39.3 40.6 61 

a39.4 40.2 5.1 

3s 3 40.5 4.9 

39.4 40.5 5. 

940. 39.7 5.9 

39.7 40.4 4.7 

39.9 39.7 5.9 

43 deaths at Erzincan, heab-y damage 

at Karakulak 

'39.8 39.4 8 

39.7 39.5 8 

39.9 39.5 7.9 

'39.7 39.7 5 

40.1 39.9 9 

45 deaths, Besin and Pulur destroyed 

'39.7 39.5 5 

2 

4 

2 

4 

2 

3 

1 

4 

3 

2 

1 

4 

4 

1 

4 

3 

1 

3 

2 

1 

4 

3 

4 

5 

(94 

3 
Epicentot 

Number Dates s Lat. N Lo%. E M Reference 

5.2 1 

39.7 5. 4 

30.9 4.9 3 

at Enincan 2 

( 14) 1940/04/22 39.5 40. 

'39.7 

39.8 

039.7 39.7 5. 4 

vicinity of Enincan 2 

(15) 1940/05/29 

40 buidings collapsed in the wllages, 

19461 121'13 

194919.i 17 

1949, '9 i 17 

1949/8/' 17 

1949/11. C! 

1332 c2, 34 

1950 c,9 27 

1953,. 12 15 

'39.9 38. e 5. 

039.7 39.7 5.3 

39.7 39.7 5. 

at Erzincan 

39.9 39.4 5.9 

'39.7 39.7 5.7 

39.7 39.4 5.9 

15 deaths, 100 injured at Enincan 

'39.3 41.1 5.9 

40. ' 41.6 

39.3 41.2 5.7 

8 

839 deaths at Varto and Usturkiran 

*slight damage at Pulumur 5.2 

39. 40.5 6.7 

39.4 40.9 6.5 

39.6 40.6 7. 

839.4 40.9 

300 deaths at Karliova 

39.6 40.4 5.2 

40.1 40.6 5.3 

039.5 40.6 5. 

O39.6 40.6 5.2 

039.3 40.3 4.9 

slight damage at K~gi 

m39.3 41. 4.9 

m39.4 4 1. 4.9 

two deaths at Varto 

39.7 41.2 5.5 

39. 1 41.4 5.3 

4 

4 

3 

2 

1 

4 

3 

2 

1 

4 

3 

2 

2 

1 

4 

3 

6 

2 

1 

4 

3 

3 

3 

2 

3 

3 

2 

I 

4 
Epicenter 

28 q9.1 . 41. 5.2 

1954/10/24 .40. 40. 

1957/07/07 39.2 40.2 

.39.2 40.3 

39.4 40.5 

7 injured at Kigi 

1959/01/14 O39.5 40.4 

1959/09/10 39.7 41.4 

39.0 41.7 

(39.3 41.4) 

1959/10/25 O39.2 41.5 

39.3 41.0 

. Odarnap at Varto 

A( Qf.)\ 1959/12/25 O39. I(”! =&.ut .I 

1960/0 1/26 40.1 38.6 

039.5 39.5 

1960//08,’09 39.9 39.5 

felt at Kemah and Erzincan 

Y39.5 39.5 

1964/09,4 39. 40.2 

99.8 40.3.40.2 

fe 1 t at Caylrli 

1964./11,’16 39.4 40 3 

39.5 40 3 

‘39 9 39 9 

felt at Erzmcan 

1905/08/31 99.4 40.7 

39.3 40.9 

39 4 40.9 

- M Reference 

4 

5.8 

5.3 

5.3 

5.1 

5.1 

5.6 

5.1 

5. 

4.0 

e.Z(?j 

5. . 

5.9 

5. 

4.9 

5 

4.6 

5.1 

4.9 

4.9 

5 

4.9 

5.6 

25 deaths, 40 injured at Karliova 

4 1.5 5.3 

39. 1 41.6 6 

39 2 4 1.6 5.6 

1966,’03,’07 ‘79.2 

4 r?eaths at Varto 

4 

1 

4 

3 

z. 

3 

1 

4 

2 

1 

4 

4 

1 

4 

2 

1 

4 

1 

4 

2 

1 

4 

3 

2 

4 

3 

2 

1 

4 

3 

2 
Epicenter 

Long. E M Reference 

Number 

8 

Dates Lat. N 

(41) 1966/08/19 '39.2 6.8 1 

4 

3 

2 

39.2 41.6 7.1 

39.2 41.6 0.9 

2394 deaths at Varto and its vicinity 

(42) 1966/08/19 O39.3 41.2 

39.4 41.3 

(43) 1966/08/14 O39.3 41.1 

39. 41.8 

(44) 1966/08/20 O39.4 40.9 

39.4 40.9 

39.4 40.9 

39.4 

Damage at Karliova 

41 

(45) 1968/08/20 39.1 39. 8 

039.1 40.7 

39.2 40.7 

5 

5.3 

5. 

5.1 

5.3 

5.3 

5.1 

.a2 

5.5 

5.4 

6.1 

1 

3 

1 

3 

1 

4 

3 

5' 3 (46) 1967/0 1/30 '39.4 41.5 

(47) 1967/07/26 '39.5 40.3 5.6 

39.5 40.4 6.2 

39.5 40.3 6.2 

39.5 40.4 5.6 

97 deaths at Pulumur 

4km surface faulting 

118 azimuth. 20 crn rtght-lateral displacement 

1968/'09,/24 '39 2 40.3 5.1 

39 2 40. 1 5.1 

39 2 40 3 5.1 2 deaths. 97 injured at Kqi 

6 krn length of surface faulting 

150 azimuth. 25 cm vertical dsplacement 

1968/09/25 '39.3 40 2 5.1 

39.2 40 2 4.8 

1969/09/10 '39 3 41.4 

39 2 41.4 

33 3 11 1 

1970,/09,'03 3 ic,urn[1 at Kymahy 

5.2 

5 

5.2 

7 

1 

4 

3 

2,7 

1 

4 

1 

4 

3 

2 
EDicenttr 

Number Dates fat. N Long. E M Reference 

(52) 1971/05/22 a39.1 40.6 5.4 3 

* Indicates preferred epicenter location which is shown in FqUre 4. 

~Dewey, 1978 

I Tabban. 1980 

soysd et al., 1961; Sipahioglu. 1983 

Wad and Meyera 1985 

Nature, 1940~ 

lahh 1952 

Ambraseys, 1975 
I. 

I 

ORIGINAL PAGE !% 

OF POOR QUALm 

I 

'\ 

I 
.. I 

0 
.. 

32.000 

U 

32.000 

bN 

l.! 

1. 

03 

0 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

\ 

0 \. \ 

\ 

\ 

\ 

a 

a '0 

\ 

\ 

\ 

\* 

I 

VI viu vi X XI V IX 
. 

.- 

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-0 0 

/w 

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3 

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\ 
APPENDIX I11 

TECTONIC ESCAPE ORIGIN AND COMPLEX EVOLUTION 

OF THE ERZINCAN PULL-APART BASIN, EASTERN TURKEYAYKUT BARKA 

AND . 

LEVENT GULEN 

Earth Resources Laboratory 

Department of Earth, Atmospheric and Planetary Sciences, 

Massachusetts Institute of Technology, 

Cambridge, Massachusetts 02 139, USA 

September. 1986 

Submitted to 

Geological Society of America Bulletin 
ABSTRACT: 

A new tectonic model is presented for the pull-apart opening of the brincm basin 

in an effort to expiah the relationship betwem continental block kinematics and basin 

formation Our field studies indicated that the Ertincan PUll-Crpart basin Is not a typical 

rhombic pull-apart basin, but it has a rather complex, two-stage pull-apwt opening mechanism Thir complexity is created by the nature of the tectonic escape Of Crustal blocks, 

following the continental collision of the Arabian and Eurasian plates dong the Bitlis 

Suture Zone in eastern Turkey. 

The first stage of westward pull-apart opening occurs between two diVerQ0nt Segments of the North Anatolian Fault Zone, along which westward tectonic orcaw Of the 

Anatolian block is taking place, creating the northern part of the Errincan Basin. 

The second stage of translational-rotational basin opening is initiated as a result of 

fragmentation of the Anatolian Block and one of the segments of the North Anatolian 

Fault Zone by the formation of the obliquely oriented, left-lateral strike-slip Ovacik Fault. 

The present day basin geometry indicates 921 km left-lateral offset and approximately 

10" clockwise block rotation along the Ovacik Fault. 

This complex, two-stage, divergent and translational-rotational, pull-apart basin open - 

ing mechanism quite satisfactorily accounts for the geometry of the Ertincan Basin and 's 

well supported by the available geological evidence. 

-1- 
Although th 'PUll-Vart bmin' concept was first in*oducOd In 1968 (BUchfiel md 

Stewart), it has received tho artmtiocr of structural gOologLt8 since 1974 with the 

papers of Crowd1~1974a, b) on basim In southern CalifOrda Within the last dewdo a 

iarge body of knowledge have beon acquired through detailed geological and geophysical 

studies and a significant progress had been made In undOrStanding tho mechmiSm Of diff5r,rm? types ef p!!!!-zpsrt basin formation and evolution In rtrike-slip settings A 

coliection of papers and their references, that are contained in two book8 (BallmCO and 

Reading, 1980; Biddk and Christie-Blldr, 1988), which aro devotod to strika-slip basin 

formation and sedim~trtion, provldo an excellent rewiev on pull-apW bash 

Ths purpose of this paper is to discuss the origin and evolution of tho kilncan 

pull-apart basin (hereafter referred to as the EPAB) emohaslting thm Important m!r of 

continental block kinematics in the basin formation, . and present a now, complex 

pull-apart mechanism for basins in continental collision areas where tectonic escape prevails. 

The EPAB is situated on tho North Anatolian fault Zone (NAFZI and its long axls 

strikes in NW-SE direction being parallel to the general trend of the fault zone 

(Figure-1). The EPAB is approximately 50 km. long and widens towards SE reaching I5 

km. width Two other left-laterai faults, the Northeast Anatolian fault and the Ovacqk 

fault obliquely intersect the NAF zone at the NW and SE of the basin, respectively (Figure- 1 ).

The EPAB has recently attracted considerable attention in the literature. However, JE 

shown in Figure-Pa and b, it has been described as a typical rhombic pull-apart bas ,- 

-2 - 
bounded by two parallel master faults belonging to the segment8 of the NAFZ in 

previous studies (Sangor, 1979; Aydin and Nur, 1982; Hempton and Dunne, 1984; 

et aL,198S). Our detailed fieid studles have indicated that the EPAB is not a 

all the 

Songor 

typical 

rhombic pull-apart basin, but it has a rather complex pull-apart mechanirm and basin evolution due to the critical role of the obliquely oriented (nOn-maSterr), Ovacik fault 

(F@1re-3). 

In the proceeding sections we will present the detail. of stratigraphv and structure of 

the EPAB based on our field observations and discuss tho pull-apart mechanism and 

basin evolution within a regional tectontc framework. 

GEOLOGICAL SETTING AND STRATIGRAPHY 

In this region, there were two branches of Neo-Tetm beforo 

$engot and Yilmat. 1981). The northern branch used ta separate 

Eocene (Stbcklin, 1974; 

the Pontides from the 

Anatolide/Tauride platform and closed in Eocene forming the Pontlde-Anatolide/Tauride 

suture zone (PATSZ). Further south, the continental collision of the AnatoliddTauride plat - 

form with the Arabian plate took place in mid-late Miocene (Hall, 1978; Petincek, 1980; 

$engor and Yilrnazl981). This closure eliminated the southern branch of the Neo-Tethvs 

forming the Bitlis Suture zone (BSZ). The continental collision along the BSZ caused further deformation and modified the northern PATSZ along which, E-W trending narrca 

compressional basins occurred These basins are bounded by mostly E-W trending thrus.: 

and their internal deformation deliniatcs E-W trending folds. As a result of the continuea 

convergence following the continental collision along the BSZ, the formation of the Nor... 

Anatolian, East Anatolian, and Northeast Anatolian fault zones, which make up the bounc. 

arias of major continental blocks such as Anatolian and Northeast Anatolian bloc. *. 

(Figure-11, tectonically overprinted some of the existing basins and created new ones 3 .- 

-3- 

ORIGINAL PAGE IS 

,of! POOR QUALfrV 
The stratigraphic chwactoristicr Of the Neoqene-Quaternary sedimenty swaes in 

eastern Turkey indlcat8 that there We three main Stages of deposition being related to 

the above tectonic evolution of this region 

1972; Luttig and Steffens, 1976; $en* and Kld& 1978) whlch deposited 

sandstondlimestom lithologies parsing upwards into shallow whn md8 and reefal 

carbonates (Ketln,1950; Altinil.1966; $en* and Kldd, 1979). Thla fad- Unconformably 

overlies older sedimentary units or ophiolitlc melango lltholdgkr of the 

Pontlde-Anatolide/Tawide suture tone, reaching up to 7SOm thickness (Ketin, 1950; 

Nebart.1961; Altinli, 1966). A marine regression towards Iato MIoc~ tlm@ ca~val with 

the continental collision along the BSZ. is indicated by the incrmaring evaporitic 

intercalations and appearance of lacustrine and f luvisl sediments in the stratigraphic 

record (Ketin.1960 Altinli, 1966; Kurtman et at., 1978; Bekta$,lOliL 

The second stage of deposition filled approximately E-W trending narrow 

compressional basins located close proximity to the suture zones. The Mu$ basin 

(Kurtman et al., 1978; $aro@u and Gher.1981; Sengor et a1.,1985) and Cayirli-tercan basln 

(Ketin, 1950; Irrlitt, 1972) are typical examples of this kind (Figure- 1). The Mihar-Ahrnedlye 

basin which is situated to the NW of the EPAB, also falls in this category (Figure-31 

This stage is characterized by lacustrine and fluvial facies represented DV 

evaporite/ranstone/mari/conglomerate lithologies. The thickness of this unit varies f tom 

place to place reaching up to 1750m. (Kurtman.1972; Tatar,19781. Nebert (196 1 

-4 - 

OiiiGiNAL PAGE IS 

OF PDOR QUALITY 
reported Hipparion fossils from these sediments, indicating iate Mima a@, 

also confinned by Irrlitr(l972), in the western extension Of the Mlhm-mlye basin 

is 

The third and final stag. of doposition occv either within Compressianrl basins as a 

continuation of the second stag. (ag. Mus basin. Cayirli-Tarcan Basin), or within newly 

formed basins along strike-slip fault zones (e.@ EPAB, Niksar Basin; seo Figure-1). Mostly lacustrine and fluvial deposits of Plio-Quaternary ago represent this staga 

In the EPAB, all the exposed basin sediments belong to thi8 third strg. of deposition. 

which is characterizod by Plio-Quaternary fluvial facies, -&t- contaim play8 dwosits. 

Coarse ciastics and basin margin conglomerates (Flgure-3). Conglomerates arm c0rnpoS.d 

of clasts of ophiolitic melango and Cretaceous-early Miocma carbomto8. OCcadOnd thin 

tephra and crossbedded * thick conglomorrte layom aro two charrctrlrticr of this 

sequence. Thickness of this fossii-barren conglomerates reach up to 2OOm Moreover. 

sand to boulder site fragments and their ungraded. immature appouance suggest a rapid 

deposition in a tectonically active environment. Unfortunately, the total thickness of the 

sediments in the EPAB basin is not known, because of the non-existence of deep wells 

and seismic data However, if it is assumed that the basin length versus sediment thickness relationship of Hempton and Dunne(1984) is correct then, one can infer about 2.5 

to 3km sediment thickness for the EPAB as a rough approximation. in the EPAB, alluvtar 

. fans are more developed along the northern margin They are steep and composed of 

recent debris flows and coarse grained braided stream deposits. Along the southern margin, fan sediments are deposited more gently and contain no recent debris flows. Braided 

stream flows are. also finer grained on the southern fans (Hempton and Dunne, 1984) 

The central part of the basin is filled mostly by silts, sands, and gravels. The Euphrates 

river becomes a meandering type as soon as it enters into the basin. A large salt playa 

abuts the meander plain at one of the lowest basin elevations containing thermal ana 

-5- 
ORlGlNAL PAGE IS 

OF POOR QUALITY 

&out 18 small volcanic cones am aligned along th. northom mar- WIO only one 

corn occurs closo to the southern margin of tho basin They consist of daciter and 

rhyolltor Th. age of the volcanism is 3.1-0.28mv.(B~,1979 Wmptarr mt! L!=mm,?SW. 

STRUChJRM GEOLOGY ._ 

A genmai N-S compressional tectonic regimo dominatm tho nootoctonlcr of the 

whole region in eastern Turkey duo to tho continuing active convorgmco following the 

mid-Miocono continental collision along the Bitlir suturo tom For example ewly-middle 

Miocene sediments are folded and thrusted throughout this region (Pamir and Ketin, 1941; 

Altinll, 1966; Tatar, 1978L as well as along the northern margin of tho Arabian plate 

(Rigo de Righi and Cortesini, 1964; Ketin, 1966; Peringek, 1980; Otkqr, 1982). As shown in 

Figure-3, early-middle Miocene limestone units and the E-W trending Mihar-Ahmediye 

basin sediments are foldod with fold axial tracer striking E-W and the basin is bounded 

by E-W trending thrusts in the north and south. Many other Miocene basins exhibit simllar deformational styles in eastern Turkey (Kurtman et al.. 1978; $aroQlu and GGner, 198 t 

Sangor et al., 1985). 

The EPAB differs from the above mentioned basins becuse of its NW-SE trendipq 

long axis and its apparent younger age. The basin's NW-SE trend parallels the trend c' 

the NAFZ and this suggests an intimate genetic relationship between the NAFZ and €PA6 

In fact, the NAFZ forms the entire northern boundary of the EPAB and serves as a FJ: 

-6- 
SEGMENT-1: This easternmost segment is about 78 km long ad trends 110' N 

azimuth The best physiographic fault exP~essIoM, such as linea vally and ridges, are 

developed to the east of the Tanyeri villags The southern block is uplifted about 30 m 

relative to the northern one along thls segment 

SEGMENT-2: This segment forms the northern boundy of tho EPAB. It has WPloximately SS krn length and trends 12s" azimuth Tho southeastern end of thk segrlMm 

consists of a number of small en echelon faults fault tracas and re1.t.d shew lono 

deformation are best developed near'Bahlk village. As shown In Figure4 tho fault Plan0 

steeply dips to the south and the southern block is uplifted The ana)yri+ Of structures -. 

indicate a dominant rigth-lateral strike slip and a subordinate thrust components along the 

Segment-2. Furthermore, along the northwestern haif flower type of thrusting (Hwding et 

al., 1985) are also common The 15'difference between the Segment-1 and 2 trends. 

along with an approximately 4 krn releasing stopover between them indlcato that these 

two segments functioned as divergent master faults at the initial opening stages of the 

EPAB. 

SEGMENT-3 This segment starts around Ahmediye village and extends westward abou: 

320 krn striking 105' N azimuth (Figure.3). Within the area of interest, it shows clear 

geomorphologic fault expressions in the vicinity of the Mihar village. The 1939 Grear 

Ertincan earthquake (M18.0) activated not only this segment, but also Segment-2, produc - 

ing 4 m right-lateral and 1 m. vertical displacements with the uplifted southern blocs 

(Pamir and Ketin,1941; Ketin.1969). The 20. difference between the trends of !-- 

-7- 

ORIGINAL PAGE IS 

OF POOR QUW 
OVACIK FAULT: The Ovacik fwit is also another important ttnrchrral 

contributd to the evolution of the EPAB (Figw0.3). It IS a Ieft-latral strike-slip fault 

and is mapped in detail by Arpw and $aroaiu (19751. The Ovaclk fault is obiiw podtioned relative to the NAFZ and starts from the southemtOrn end Of th. *AB, extends 

about 12Wm towards SW *it!! e# N z;t!;;;;;tk 1; ciiii ihe QUtmiw @acid moraines of 

the Ovacik basin (located to the south of the study area, seo Flguro-1) wh.ra the fault 

plan8 steeply dips SE indicating dominant ieft-latwrt strika-sllp and rubordhut0 thSt 

components with the uplifted southern block 

The mechanical interpretation of the above mentionad segments of the NAFz 1s Shown 

in Figwe.Sa According to this interpretation, Segment-1 and 3 are main displacement 

shears (D-shear), Segment-2 is a Riedel shear (R-shear), and the southeastam end of the 

Segment-2 has also a R 1 -shear (Riedel within Rledet, tchalenko,19701 

Relative stress directions obtained from analysis of mesoscopic scale fractures measured in the Neogene-Quaternary sediments are shown in Figure-5b. In this analysis, single , conjugate faults and slickenslide lineations were used Mancock and Barka, 1981. 

Angelier, 1984; Hancock, 198s). Stress orientations that are obtained from the analysls 

indicate NNW-SSE compression and related ENE-WSW extension which agree with a sec - 

ondary stress field related to the right-lateral NAFZ 

The fault piano solutions of 1939.12.26 (M.8.01, 1967.7.26 (M=5.8), and 1983.1 1 18 

(M.4.81 earthquakes are given in Figure.5~. These solutions are consistent with the above 

interpretation of mesoscopic fracture analysis. Note that, the solution obtained frr - 

-8- 
ORIGIN AND EVOLUTION OF THE ERZINCAN PULL-APART BASIN (EPAB): 

Contrary to the northern margin of the EPAB, Our detailed field studles and aerial 

photo interpretations show no evidence that the southern mwgin of tho basin is controlled by an active strike-slip fault which extends southeastward, well outside of the 

basin limits (see Figure-21, as suggested by $engOd1979), Aydln and Nur(1382), and 

Hempton and Dunne(l984L Although the southern boundary of the basin is quit. llnear, in 

fact bounded by a fault, this fault is abruptly terminated by the Ovacik Fault (Figure-3). 

As a result, the southern basin boundary fault does not form en echelon master fault 

pair with the northern one (Segment-2 of the NAFZ) to open the *AB as a 'typical 

rhombic pull-apart basin'. furthermore, the basin margin. and alluvial fan slopes in the 

north are at least twice as steep than the ones along the southern boundary, suggesting 

that, these basin bounding faults have different characters. 

It seems that, the pull-apart opening of the EPAB first occurred between the 

Segment-1 and 2 of the NAF zone (Figure-5). In fact, this area has the lowest elevation 

within the EPAB and is occupied by the alluvial plain of the Euphrates river and a salt 

playa Since, there is a 15. angle and 4km. releasing stepover between these segments 

they can function as divergent master faults (see Mann et al., 1983 for detailed dtscussion on divergent master faults). This configuration can open only a westward 

widening pull-apart basin (the basin area labeled with M in Figure-5a). However, even 

this arrangement is not satisfactory to explain the present-day basin geometry, whrci 

exhibits southeastward widening, where the pull-apart stepping is narrow. We sugges ! 

-9- 

ORlGIiYAL PAGE IS 

OF POOR QUAUTY 
the Ovacik fault does not only explain the compkx pull-apwt opening of ~pm by 

solving the above geometric promlm satlsfactorlly, but also negates tho need to search 

for or infer a major strikr-sllp master fault which would extend well to the east of the 

Ovacik fault. Based on the above discussion and prmmtrd eVld.nc8, we suggest the 

following model for the ar!g!r! =A :vc!ut!=:: of :hi - 

The continental colllslon along the Bitlis Suture tone In mM-late Mlocum tlma caused 

the break up of tho AnatolldeITwrido platform Into a numbor of contirwmrl blocks 1e.g. 

Anatolian block, Northeast Anatolian block) by the formation of major strike-dip faults 

such as the North Anatolian, East' Anatollan. and Northeast Anatollcn fault zones 

(Figure- 1). Under the N-S compression, the Anatolian and Northeast Anatolian blocks 

tectonically escape from the zone of maximum compression westward and eastward. 

respectively. The eastern part of the NAFZ functlons as a common strike-slip boundary 

between those blocks. According to our interpretation, the two segments of the NAFZ 

(Segment-1 and 3) initially had roughly 20 km wide releasing stepovw with a separation 

of 60 krn in the Ertincan area (Figwe-6a). The aspect ratio of the original stepover 

(20/60.0.33) corresponds to approximately 20' angle, which allows formation of a R-shear 

in between, rather than 20 km wide pull-apart opening (Figure-ba). Being consistent wltn 

en echelon structures of a strike-slip fault zone which evolves under simple shear 

(Tchalenko and Ambraseyr, 1970; Wilcox et a1.,1973; Harding, 1974 Barlett et al., 1982 

Hancock,lSSb), newly formed Segment-2 (R-shear) makes 15. angle with Segment- 1, leav - 

ing 4 km stepover (Figure-6b). This small, secondary stepover and the 15. divergence 

angle causes the initial westward pull-apart opening of the EPAB due to the right-lateral 

displacement along the NAFZ, caused by the westward escaping Anatolian blc 1 I 

-10- 
(Figure-6c). The beginning of the volcanic activity within the EPAB is probably related to 

this stag., becaw. about 16 small volcanic cones am aligned along the southeastern 

part of tho SWMlt-2 (fiWre-3 and 6c). If this asrumption 1s true, then the timing of 

this stage can be estimated as roughly 3.1 my. before PreSmt, bared on the oldest ages 

obtained from the volcanic% 

After some amount of initial opening (M1 are8 after Ca 28 km right-lateral displacement), eastern part of the Anatolim block, as wail as the Segment-1 of the NAFZ, 

were further divided into two; Al, A2 blocks and S-la, S-lb Segments, respectively 

(Figure-Bd), by the formation of the Ieft-lateral strike-slip Ovacik fWk Thlr break up of 

the Anatollan block is probably confined only to the uppar lO-lbkm, brlttl. zone of the 

continental crust, but at present we do not have ay direct evidence to SubStantllte it. 

The fragmentation of the Anatolian block into A1 and A2 blocks WII probably required 

because of the locking effect of the restraining bend, where the Segment-2 and 3 of 

the NAFZ intersect, against the westward motion of the. Anatollan Block The presence 

of unexpected positive flower structures along the northwestern half of the Segmcnt-2 

and Segment-3, indeed suggest such a locking effect, indicating interne compression 

around the restraining bend region (Figure-3 and 6d). Also the occurence of great earthquakes (M =8) in this region provide another supporting evidence. Having this new block 

configuration, the segments of the NAFZ and the Ovacik Fault can accomplish the westward tectonic escape of th? A2 block under continuing N-S compression. 

Now, the tectonic escape is also accompanied by a clockwise rotation of the A2 

block relative to A1 along the Ovacik Fault. This clockwise rotation is caused by r~c. 

restraining intersection along the NAFZ, in comparison to the straight, freely movmq 

Ovacik Fault. While great earthquakes produce intermittent right-lateral displacements alorq 

the NAFZ by unlocking the restraining bend, the built up of shear strain during lock?: 

-1 1- 
.. 

ORlGtNAL PAGE IS 

OF POOR QUALITY 

p-ioh causa clockwise rotation of tho A2 block rehtlve to Al. Tho block rotation 

towed position If only the northam stdo row is inserted into tho watw, then the 

row-boat rotates clockwise, pivoting around the row-watm interface point, whiio stili 

sliding westward In thit example, the row-boat rWwaS tho A2 block, tho northern 

row, that is inrmtd intn th+ *it=, wt: !!k: the ?::*Shki biiG haasing drag forces 

along the northern side. Having this block kinematics in mind, w8 suggest ht, tho southern basin boundary of the EPAB (S-la, Figure-6d) WII tho formar westward continuation 

of tho Segmont-1. As a result of tha formation of the Ieft-1-MrJ Ovaclk Fault, 

Segment-1 was broken into two pieces (S-la and S-lb) and tho S-1. hn boon ercglng 

westward and rotating clockwise sin& then This mechanism implies tht th. S-Ia functions as a clockwise rotating break- away zone for the second stag0 opmlng of the 

basin area labeled with N m Figure-Bd The fault plane solution of the 1983.11.18 earthquake (M84.8, see Figure-Sc), which gives WSW-EM extension, provides a compelling 

evidence for the above interpretation thus, the complex two-stago, divergent and 

translational-rotational, pull-apart opening model for the EPAB quite satisfactorily explains 

the basin geometry and is well supported by the available geological evidencs. 

Moreover, we estimate about 921 krn. Ieft-lateral displacement along the Ovacik Fault 

based on the present-day geometry of the EPAB. This offset, in turn, gives approximately lo'clockwise rotation for the A2 block relative to At, if the restraining bend, where 

Segment-2 and 3 of the NAFZ intersect, is assumed to be the pole of rotation 

(Figure- 6d). 

-12- 
-. . 

While this complex opening is in progress in the southeastm haif of the basin, the 

northwestern tip is uplifting as evidenced bY the occurenco of hanging river terraces 

along Esesl and @rdakdero rivers and by the vertical block movements observed along 

the faults (Figure-3 and 6d). Theso features may be explaid by compressional and drag 

forces exerted to the NW part of the Segment-2 and Segmcmt-3, by the westward 

escaping, clockwise rotating A2 block, which pivots arm th. restraining band while 

being slightly tilted southeastwards. However, an important distinction needs to be made 

here. The southeastward tilting of the A2 block could produco tho above uplift features, 

if indeed the vertical block movements observed along tho faults (indicated by plusses 

and minuses in Figwe-Bd) are associated with the tilting Howevor, appwmt vertical 

block movements could also be produced, partly by asalrmic, viscool.rtic deformation of 

crustal blocks along fault zones (Nur and Mavko,1974; Thatchor et rL. 1980; 

Reilinger, 1986). Alternatively, the clockwise rotating break my ton. could be responsible for the uplifting of only the northwestern part of the €PAR If the restraining bend 

region is assumed to be the pole of rotation, then the extension rate, the subsidence 

rate, and presumably the width of the crustal slivers, that are sliced off from the break 

away tone, will gradually increase from NW towards SE of the basin The vertical rotation of these gravitationally unstable crustal slivers (thinner, lighter NW tip, as opposed 

to thicker, heavier SE end) would produce relative uplifting for the northwestern part of 

the EPAB. Although, this second mechanism is quite likely to operate, at present, we can 

not prefer decisively one of the above two models with the available data Of course. 3 

combination of the two would be a third possibility. 

We can go one more step further and speculate that the extreme southeastern tip c* 

the basin will eventually be closed with development of folding and thrusting (Figure- 66% 

because of the intensifying compressional strain as a result of the A1 block's northwar: 

penetration, which is facilitated by the left-lateral strike-slip displacement along '- - 

-13- 
ORIGINAL PAGE 18 

OF POOR QUALITY 

Our above model is based on only field @OgY data Futuro paloomagnotic and 

geodetic studies to test and quantify continentd block rOtath8 and tilting, radiometric 

ago dOteriniMtiOnS on fault segments to better constrain the timing of tho evolutionary 

stages, and daap driliinpseirmir? p&!!!q 10 rewe! t)?: de:rk 6; r'wciire wiii be of 

great value towards testing our proposed model and an improvod und.rstandlng of complex pull-apart basin formation and evolution 

-- 

.- 

Finally, we believe that this work emphasis~ tld 1. utmost importam8 of mOticulOu8 

field studios, along with a regional tectonic approach, for tho study of pull-apwt basins 

in pawticuiar, and of a detailed knowledge of tho fine scale continmt8l/cnrstal block 

structure and its continuously changing nature for the study of continental tectonics in 

general. 

ACKNOWLEDGEMENTS 

The field work studies were supported by the ITIT joint project (b8212) between 

Mineral Research and Exploration Institute of Turkey and Geological Survey of Japan. One 

of us (AAB.) thanks to Dr. Hirokatu Kat0 of GSJ for his continuous encouragement. We 

gratefully acknowledge M.N Toksot for his support and B.C. Burchfiel for his constructive critisitm 

-14- 
REFERENCES 

Angelief, J., 1984, Tectonic anaiyrir of fault dat8 sat*, J. GWW Rea0 v.89, 

p.5835-5848. 

Arpst. E. and $rroplu, F., 1976, Some recent tectonic event8 in Turk~y., Bull Geol SOC. 

Aydin. A and Nw, A. 1982, Evolution of pull-apart barint md thek rcJo independence., 

Ballanco, P. F. and Reading, H. G, 1980, Sedimes in obllqw-slip mobilo tones: 

Barka, A A, 1984, Some neotectonic features of tho Erthrcr, bask Ert)lg SYmg. Spec 

Turkey., v.18, p.91-101 (in Turkish). 

Tectonics, v.1, p.91- 106. 

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-18- 
Hdl, R., 1976, Ophloiit~ emplacomnt md *a evolution Of t)w T- S-0 zone, 

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.. 

Hwdlm T.P.. 1974, P+?rde-% t:+: s::Gc!~~* wM~ 'w& fdk, &uh h hsoc 

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Nur, A and Mavko, G, 1974, Postselsmic vlrcoeiastlc rebound., Science, v.183, 

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activity in Tawlde belt., Proc Fifth Petrd Congr. Turkey, Ankara, p77-93. 

Reilinger, R, 1986, Evldme for portseismic vlrcoel#tlc rekX8tiOtl followkrg th. 1969 

M=7.S Hebgen Lake, Montana, Earthquakr, J. Geophyr. Rn, v.Bt, p9488-94S 

Rlgo do Rlghi, M. and Cortesini, A, 1984, Gravity tectonics in faothllh rtructue belt of . southeast Turkey., Bull Am Ass= Petroi. GeoL, v.48, p.1911-1937. 

$aroQlu, F. and Gfinew, Y., 1981, Factors effecting geomarphologlcal evolution of eastern 

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-20- 

Errincan and Rcfshiye., Yerbilimleri, v.4, p.20 1-236 (in Turkish). 

Geol. SOC. Am., v.81, p.1625-1640. 
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Wilcox, RE, Hwdlne T.P., and Seely, D.R, 1973, wrench tectonics, Bull Am. 

h8oc. Petrol GeoL, v.S7, p.74-96 

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FIGURE CAPTIONS: 

Figwo-1: MaJor tectonic elements of eastern TwkW, Where the post-coliisional N-S 

convergence between the Arabian Plate and P0ntid.S C~IJ~ the escwe of continental 

blocks westward and eastward as indicated bY IWe mows. The study area is enclosed 

by dashed liner Majw faults are highlighted With thick lines. Other active faults, that 

have been mapped, are also shown Abbreviations WC bt. City of btlncan; EF, Ecmiq 

Fault; MF, Malatya Fa.ult; cTB, Gayirli-Tercan Basin; MB, Mu)'Barin; NB, Niksar Basin; OB, 

Ovacik Basin 

Figure-2: Two previous puil-apart mechanism interpretations for tho brlncan Basin aFrom Aydin and Nur (1982) depicting the EPAP as a typical rhombic pull-apart basin 

bounded by the en echelon NAFZ segments. Q Quaternary; T, Tertlw; pMM. Paleozoic 

and Mesozoic basement; HS, hot spring; VC, volcanic cone; F, fault b- Hempton and '_ 

Dunne's (1984) interpretation of the EPAB, which is quite similar to Aydin and Nur's 

(1982) above interpretation. 

Figure-3: Geological map of the Errincan pull-apart basin and 'its vicinity. A generalized stratigraphic column is given as an inset. 11 and t2 denote two levels of terraces. 

that are mapped along the Cardakdere and Esesi rivers. Note the lack of terraces along 

the Euphrates river and its meandering nature. 

Figure4 A sketch of a natural trench on the Segment-2 of the NAFZ, where surface 

breaks of 1939 Ertincan earthquake passed through (looking in the SE direction), showmg 

shear zone related deformation features such as fault planes, folds, and extension 

fissures. The streonet (lower hemisphere pro jcction) illustrates the geometrical orientattc 

-1 5- 
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1.68~~ tall) Is shown for scale. 

Figure.% Interpretation of tectonic structures in the EPAB. a- A mechmical int-0- 

tation of the fault segments (S-1,2,3) of the NAFZ 0, main displacement she=; R, Riedel; 

R1, Rledel within the Riedel. b- Map showing analysis of meroscopic scalo faults measwed within the Neogene-Quaternary sediments, showing NNW-SSQ compression and 

G--W~W errension dong the NAFZ (large arrows). Streoneta-aro equal-area, lower hemisphere projection of reverse (planes with teeth), normal, and strike-slip (indicated by 

small arrows) faults. c- Fault plane solutions clearly indicating tho actlvo opening of the 

EPAB. Solutions of 1939.1226 and 1967.7.26 are from McKaulo (1972) md 1983.11.18 

is from International Seismological Centre Bulletin (1983). Magnitudoa ot tho erthqwker 

are also given on the figure. 

cam ...a. I. 

Figure-6 Tectonic evolution stages of the EPAB. a-. Inferred initial geometry of the 

S1 and S3 segments of the NAFZ, with 60km separation (YY) and 20km wide releasing 

stepover. b- Formation of a R-Shear (S-21, which fills the gap (stopover) between S-1 

and S-3, creates a secondary, roughly 4km wide releasing stepover, that makes 15 

divergence angle with the Segment-1. c- Initial puli-apart opening (ca 25km right lateral 

displacement) of the EPAB (basin area labelled with M1) between non-parallel master (dlvergent) faults 6-1 and S-2) due to the tectonic escape of the Anatolian and Northeas: 

Anatolian blocks westward and eastward, respectively. Volcanic activity also starts at tre 

eastern part of the basin during this stage. d-The formation of the left-lateral 

strike-slip Ovacik Fault divides eastern part of the Anatolian Block and the Segment-1 C' 

the NAFZ into two; A1.A2 and S-la, S-lb segments, respectively. At present, S- 13 

forms the southern basin boundary and the geometry of the basin indicates 921 kleft-lateral strike-slip offset for the Ovacik Fault. suggesting clockwise rotation of .- 

-16- 
~2 block relative to Al. The southern basin area labeled with N represents tb area that 

has opened due to the translational-rotatiO~~l motin Of the A2 block Plusses (+) and 

mh~S08 (-1 denotr the observed relative vertical movementS along the faults (see text 

for further explanations. 

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APPENDIX IV 

GLOBAL POSITIONING SYSTEM MEASUREMENTS OF 

FAULTING AND REGIONAL DEFORMATION IN TURKEY 

M. Nafi Toksoz and Robert E. Reilinger 

Earth Resources Laboratory 

Department of Earth, Atmospheric, and Planetary Sciences 

Massachusetts Institute of Technology 

Cambridge, MA 02139 
. 

GLOBAL, POSITIONING SYSTEM MEASUREMENTS OF FAULTING AND REGIONAL 

DEFORMATION IN TURKEY 

INTRODUCTION 

This is a proposal to use the Global Positioning System (GPS) to investigate 

relative plate motions, intraplate deformation and fault activity in Turkey. The 

proposed experiment will consist of repeated determination of selected 

baselines at approximately two year intervals. We anticipate a joint effort 

involving our collaborating institutions in Turkey (Middle East Technical 

University, Earthquake Research Institute, Defense Mapping Agency), WEGENER 

(Working Group of European Geo-scientists for the Establishment of Networks 

for Earthquake Research), and the United States (NASA Geodynamics Project, 

Massachusetts Institute of Technology (MIT), University of Colorado at Boulder). 

Funding for the United States university participation in this project is being 

provided by the U.S. National Science Foundation (NSF). 

The three primary objectives of this experiment are: 

To monitor strain accumulation and release along the major fault system 

in Turkey with special emphasis on the North Anatolian fault (NAF) and 

East Anatolian fault (EM). 

To measure directly internal deformations of the Anatolian plate wedged 

between the Arabian, African, and Eurasian plates. These measurements 

include: a) Westward "escape" of the Anatolian plate; b) Eastward "escape" 

of the Northeast Anatolian block; c) North-south compression in Eastern 

Anatolia; and d) North-south extension in Western Anatolia. 

To determine present-day relative movements of the African, Arabian, 

Anatolian, and Eurasian plates. This objective is an extension of the 

NASA/WEGENER Geodynamics Project to measure relative plate movements 
in the Eastern Mediterranean with Satellite Laser Ranging (SLR) 

observations. 

We anticipate that this research will enhance our understanding of the 

deformations induced by collision of continental plates, and the physical 

processes responsible €or the generation of seismic activity in this region, 

thereby providing an improved basis for earthquake hazard assessment. 

PROPOSAL 

The details of this proposed measurement campaign were formulated on 

the basis of discussions with members of the Turkish scientiflc community who 

have been working directly with our group at MIT. We have also maintained 

close coordination with WEGENER with which we will pool our instruments in 

order to provide sufficient cnverage to m.e& our rrztua! ~bjectives. We 

emphasize that all aspects of the proposal are open to discussion and can be 

revised by mutual agreement. 

Instrumentation 

All GPS observations will be made with TI 4100 dual frequency receivers. 

We anticipate that a total of 12 instruments can be assembled for this project. 

The source of these instruments is truly international and includes agencies in 

the U.S. and Europe who have agreed to cnm.bir?e their res~urces 1:: B c~ir~~~~ii 

project. Our group will be directly responsible for 3 instruments to be obtained 

from the University NAVSTAR Consortium (LTNAVCO) of which MIT is a founding 

me mb e r. 

Logistics 

MIT will be responsible for transporting the 3 UNAVCO instrurnents together 

with 3 trained operators to Ankara. Expenses for instrument transport to and 

from Turkey as well as all field expenses for these operators will be provided by 
M!T through a grant from NSF. We propose that our cooperating Turkish 

institutions provide 3 additional operators (i.e., one per instrument) as well as a 

vehicle and driver for each instrument for transport within Turkey. The 

Turkish operators will be trained in the field if they do not have previous 

experience with the TI 4100. 

Whenever possible existing monumentation will be used. New monuments 

will be set by the appropriate geodetic agency within Turkey. 

Field Operations 

Three of the 12 GPS instruments will maintain continuous observations at 

fiducial sites separated by distances of a few thousand kilometers (e.g., 

Greenwich, England; Matera, Italy: Dyarbakir, Turkey) in order to provide 

control on the satellite orbits (a fiducial site is a site with a previously 

de ternliried well established position, lor example from SLR measurements). 

Three additional SLR sites near the local GPS observations will be observed 

during each measurement round. This leaves 6 instruments to occupy the 

mobile GPS sites. Most of the mobile GPS stations -will be observed for 3 days 

with substantial overlap between consecutive observing sessions. We propose a 

two phase observation scenario consisting of measurements in Western Turkey 

during the first phase and measurements the following year in Eastern Turkey. 

These two networks will be tied through overlapping observations at !oca! 

fiducial points. The proposed sequence of observations for the provisionally 

selected stations shown on the accompanying map is given below. 

A joint reconnaissance will be performed by our Tilrkish collaborators and 

one member of our group familiar with GPS field operaliucs. 

It can be assumed that repeat measurements will initially be made at two 

year intervals. 
.Point Selection 

The accompanying map shows provisionally selected GPS sites and existing 

SLR sites in Turkey. Not shown are the sites near the fault-crossing geodetic 

networks (i.e., Taskesti, Gerede, and Ismetpasa) along the North Anatolian fault 

which are being proposed separately by WEGENER Points were selected for 

accessibility, to maintain geometric network strength and to most effectively 

address the important tectonic problems in the region. This includes 

monitoring the nature of deformation along the NAF and EN. crustal extension 

in Western Turkey and ongoing continental collision and associated "escape" of 

the Anatolian blocks in Eastern Turkey. The network in Eastern Turkey includes 

two triple junctions: Karliova at the intersection of the NAF and EAF, and Maras 

at the intersection of the EM and the Levant transform (i.e., Dead Sea fault 

zone). 

Schedule 

The fo!!Gwing general schedule is proposed: 

- reconnaissance in Western Turkey in the autumn of 1987 

- monumentation completed in Western Turkey in the spring of 1988 

- first phase of observations in Western Turkey 

in September 1388 

- reconnaissance in Eastern Turkey immediately following 

the first observation period 

- monumentation completed in Eaqtern Turkey in the spring 

of 1989 

- oSservations in Eastern Turkey in the aulumn of 1989 
A possible schedule of observations at the mobile GPS stations shorn in the 

accompanying map is as follows: 

Phase I Western Turkey (September 1988) - 

day 1: observe sites 1, 2, 3, 4, 5, 6 

day 2: move sites 1, 2; observe sites 3, 4, 5, 6 

day 3: observe sites 3, 4, 5, 6, 7, 8 

day 4: move sites 3, 4, 5, 6; observe sites 7, 8 

day 5: observe sites 7, 8, 9, 10, 11, 12 

day 6: move sites 7, 8; observe sites 9, 10, 11, 12 

day 7: observe sites 9, 10, 11, 12, 13, 14 

day 8: move sites 9, 10, 11, 12; observe sites 13, 14 

day 9: observe sites 13, 14, 15, 16, 17, 18 

day 10: move sites 13, 14; observe sites 15, 16, 17, 18 

day 11: observe sites 15, 16, 17, 18, 19, 20 

day 12: move sites 15, 16, 17, 18; observe sites 19, 20 

day 13 observe sites 19, 20. 21, 22, 23, 24 

day 14 move sites 19, 20; observe sites 21, 22, 23, 24 

day 15: observe sites 21, 22, 23, 24, 1, 2 

Phase I: Eastern Turkey (September 1989) - 

day 1: observe sites 1, 2, 3, 4, 5, 6 

day 2: observe sites 1, 2, 3, 4, 5, 6 

day 3: move sites 1. 2; observe sites 3, 4, 5, 6 

day 4: observe sites 3, 4, 5, 6, 7, 8 

day 5: move sites 3, 4, 5, 6; observe sites 7, 8 

day 6: otxerve sites 7, 8, 9, 10, 11, 12 

day 7: move sites 7, 8; observe sites 9, 10, 11, 12 

day 8: observe sites 9, 10, 11, 12, 13, 14 
day 9: move sites 9, 10, 11, 12; observe sites 13, 14 

day 10: observe sites 13, 14, 15, 16, 17, 18 

day 11: move sites 13, 14; observe sites 15, 16,17, 18 

day 12: observe sites 15, 16, 17, 18, 19, 20 

day 13: move sites 15, 16, 17, 18: observe sites 19, 20 

day 14: observe sites 19,20, 21,22, 23, 24 

day 15: C?hserve sites I=, 20, 21, 22, 23, 24 

Data Reduction and Analysis 

All participants in the project will have full access to the data collected. 

Office space, computer time and technical assistance can be provided at MIT for 

a number of Turkish scientists to participate in data reduction. Agreement 

heheen the paiticipiits in the project is to be'reached on the form and time 

of publication of the initial results insofar as the conclusions refer to the 

Turkish geodetic network. 
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