The North Anatolian fault zone of Turkey has become widely

publicized in recent years because of the remarkable series of earthquakes

that began along it in 1939 -- most of which have been associated with

dextral surface displacements that have successively delineated the fault

trace from east to west (Ketin and Roesli, 1953; Ambraseys and Zátopek,

1968). It is not so generally recognized that even prior to 1939 the fault

zone could easily have been recognized on the basis of abundant and through-going

features of Quaternary displacements, and that the North Anatolian

fault is almost completely analogous to the better-known active transcurrent

faults of the circum-Pacific region, such as the San Andreas fault of

California and the Alpine fault of New Zealand

Allen, Clarence R.

Caltech Authors - Main

ACTIV~ FAULTING IN NORTHERN TURKEY1 
Clarence R. Allen 
Seismological Laboratory, California Institute of Technology 
The North Anatolian fault zone of Turkey has become widely 
publicized in recent years because of the remarkable series of earthquakes 
that began along it in 1939 -- most of which have been associated with 
dextral surface displacements that have successively delineated the fault 
.-trace from east to west {Ketin and Roesli, 1953; Ambraseys and Zatopek, 
1968). ·It is not so generally recognized that even prior to 1939 the fault 
zone could easily have been recognized on the basis of abundant and through-
going features of Quaternary displacements, and that the North Anatolian 
fault is almost completely analogous to the better-known active transcurrent 
faults of the circum-Pacific region, such as the San Andreas fault of 
California and the Alpine fault of New Zealand. 
Convincing evidence of throughgoing Quaternary trans cur rent faulting 
can be traced continuously for more than 900 km along the North Anatolian 
fault in a broad arc from west of Abant (Bolu Prov. ) to east of Karhova 
(Bingo! Prov.), except for two areas of en-echelon offset near Niksar {Tokat 
Prov. ) and Erzincan. Distinctive "rift topography" and abundant features of 
Quaternary faulting such as scarps in alluvium, offset streams, side-hill 
ridges, springs, and sag ponds mark the fault throughout its extent; and 
the very linearity of the fault over literally hundreds of kilometers is com-
pletely analogous to that of other regional transcurrent faults {Allen, 1965). 
1 
Contribution No. 1577, Division of Geological Sciences, California Institute 
of Technology. 
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It should be particularly emphasized that, except for the two areas of 
en-echelon off set, Quaternary displacements delineate a continuous 
fault over the entire 900-km interval - - not the fragmented and dis-
continuous zone that is suggested by most existing geologic maps of the 
region. 
As is typical of other active fault systems in mountainous areas, 
physiographic features of Quaternary displacement along the North 
Anatolian fault are much better preserved.in the passes between river 
drainage systems than in the fault-controlled valleys that delineate most 
of the fault trace. This is due not only to the more active erosional and 
depositional processes that tend to obliterate scarps in the river valleys, 
but also because the lowland areas have been subject to cultural modifica-
ti on by farming for m4ny hundreds of years. De spite the absence of obvious 
evidence of faulting in some of the most heavily cultivated lowland areas, 
such as in the valley south of Bolu, nearly every fault-controlled drainage 
divide between major rivers is marked by a conspicuous sag pond at the 
very crest of the pass. Among the more notable of these are: Abant Gol 
(Lake), 32 km southwest of Bolu; Umman Gol, on the high divide 19 km 
northwest of Ilgaz (~ank1r1 Prov.); Golbel, at the major pass 18 km 
northeast of Osmanc1k (<;:orum Prov.); and at the main divide east of the 
Erzincan Valley, about 65 km southeast of Erzincan. 
Inasmuch as most of the trace of the North Anatolian fault is 
delineated by major river valleys that ha.ve been eroded within the crushed 
zone, drainages that cross the .fault at right-angles are relati"'.'ely rare, 
and lateral stream offsets are thus not as common as along some. other 
major transcurrent faults. Nevertheless, in those mountainous areas 
' I I 
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where the fault cuts across numerous closely spaced tributary streams, 
consistent dextral stream off sets are conspicuous and convincing. From 
west to east, probably the most diagrammatic such areas are: ( 1) 12. km 
. ~ 
north of Ilgaz (yankirJ. Prov.), between the villages of ~ik and yomar, 
where many streams of different sizes are offset by varying amounts 
the large streams more than the small; (Z.) 40 km east of Karg1 
(Kastamonu Prov.), where more than 15 tributary canyons of the Soruk 
Deresi near the village of Tahtakoprii are .consistently offset; (3) near 
Destek ( Tokat Prov.), where more than 2.0 streams tributary to the 
Destek ~ay1 are clearly off set; (4) along the mountain front 10 km north-
west of Erzincan, where several large canyons are off set as much as l /Z. 
km; and ( 5) along the easternmost segment of the fault 10 km northwest 
of Karhova (Bingol Prov.), where numerous north-flowing tributaries of 
the Elmah Deresi are uniformly offset near the village of Cerme. In 
nearly all of these examples, the offsets are in the direction of the "uphill" 
regional topographic gradient, thus precluding apparent off set by differential 
erosion (Allen, 1962.). Some of the largest rivers are seemingly offset as 
much as 50 km in a dextral sense, such as the F1rat Nehri near Erzincan, 
the K1z1hrmak near Karg1, and the Saganh ~ay1 east of Gerede; whether 
or not these suggestive offsets are in fact tectonic in origin, however, must 
remain doubtful for the moment. 
Many of the areas noted above are not easily visited, but three 
easily accessible and widely separated areas where the fault is diagram-
matically exposed are as follows: 
(I) Rift topography is particularly well developed east and west of 
the city of Gerede (Bolu Prov. ), in full view of the main istanbul-Ankara 
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highway. The distinct trough along the fault zone lies athwart the topo-
graphic gradient, so that nwnerous stream courses within the trough 
demonstrate tectonic off set, capture, and damming (Erin~, Bilgin, 
and Bener, 1961; Wallace, 1968). A conspicuous large sag pond lies 
2 km west of the city, and several fault-dammed ponds occur 20 km 
farther east nea~ the village of Ka~kb. The scarp of the 1944 earth-
quake (M = 7. 6) is clear throughout much of this segment and is almost 
invariably located along the line of earliei: scarps; the trace passed 
directly through Gerede, and several walls can still be seen to be 
laterally off set. 
(2) North of Ladik (Samsun Prov.),. the North Anatolian fault for 
many kilometers is particularly reminiscent of the San Andreas fault in 
its general physiographic expression. Numerous elongate closed 
depressions mark the fault trace, and the road follows a distinct side-
hill ridge for 2 kms through the village of Arslantas, where the fault is 
crossing from one drainage system to another. About one meter of dextral 
displacement was reported here at the time of the 1943 earthquake 
(M = 7. 6). The fault crosses the main highway and railroad to Samsun 
13 km northwest of Arslantas, and although several good sag ponds ·occur 
on each side of the railroad, the fault trace is not obvious from the nearby 
highway. 
( 3) The valley east ~f su,ehri (Sivas Prov. ) is a major fault-
controlled feature. Especially near the villag~ ,of ,Kiic;iikgiiz~l, 12 km 
east of Suvehri, elongate sag !pond 1~ and fresh ~c~rps cut the pat, valley 
floor, in part resulting from the disastrous 1939 earthquake (M = 8. 0), 
. I I l I I l . ' •' / • I ' 
which took many lives in this area. Numerous scarps, springs, and sag 
I ' : ' I ' ' I ! I! I • I t I ! ' 'I 
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ponds continue farther southeast along the fault. Particularly near 
<;:obanh, 45 km southeast, the main river through the village is distinctly , 
off set at the fault, the adjacent lakes are clearly fault-dammed, and the 
nearby village of Tii.me4ker lies at the end of a diagrammatic fault 
trough. 
One of the most surprising features of the North Anatolian fault 
is the very abrupt eastward termination of Quaternary displacements 
10 km east of Karhova (Binge>! Prov. ), near the village of Kargapazar. 
Northwest from this point features of active faulting are as fresh and 
impressive as anywhere along the fault throughout northern Turkey, yet 
within an interval of less than 5 km, virtually all throughgoing features 
of Quaternary displacement die out. Still farther east, the dominant 
tectonic style seems to be that of block faulting along more northwesterly 
trends. It is in this area that the 1966 earthquake (M = 7) occurred near 
Varto (Mu~ Prov. ), which is nearly in line with the North Anatolian fault. 
Some of the minor faulting during this earthquake was indeed parallel to 
the North Anatolian system and dextral in sense (Wallace, 1968; 
Ambraseys and Zatopek, 1968), but the surface breaks obviously lacked 
the continuity of the earlier breaks farther west. Despite the occurrence 
of the 1966 Varto shock, the author feels that the principal active segment 
of the North Anatolian fault terminates on the east near Karhova, and that 
the tectonic style distinctly changes east of that point. 
A possible mechanical· explanation for the abrupt ending of the 
northwest-trending North Anatolian fault near Karhova is that a southwest-
trending conjugate fault terminates at nearly the same point - - forming an 
eastward-pointed wcdgt•. This fault, part of which is described by Altmh, 
Pamir, and Erontoz ( 1963), continues southwestward from Karhova for 
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more than 70 km, marked by fresh scarps, closed depressions, and 
numerous springs for almost the entire distance to Bingol. Still farther 
southwest, only scattered segments show Quaternary activity, and the 
. ·.overall continuity of the fault zone has not been documented. Several 
sag ponds, linear rift valleys, and scarps in alluvium mark the 50-km 
segment between. Palu and Hazar G.olii (Elazig Prov. ), and Hazar Golii 
itself must be regarded as a giant sag pond; distinct Quaternary scarps 
extend both northeast and southwest from ~ts shores, the latter break 
extending at least as far southwest as the F1rat River. The trend of 
this major fault system is such that, if projected still farther southwest 
into areas not studied by the author, it would line up nicely with the Dead 
Sea fault system extending north from Israel. The Dead Sea system is 
clearly sinistral in its sense of displacement (Freund, 1965), and 
whereas only suggestive evidence of sinistral displacement has as yet 
been identified in Turkey, .it seems likely that this sense of displacement 
characterizes the entire northeast-trending system. This might explain 
the abrupt termination of Quaternary faulting at the point where the two 
systems meet near Karhova -- essentially cancelling each other out --
and it is significant that the angle at which they abut is almost identical 
to that between the dextral San Andreas fault and the sinistral Garlock 
fault in California. 
At the western end of the fault, its mode of termination is not as 
clear as on the east. West o!f Abant Gol (Bol~ Prov.), Quaternary dis-
placements are difficult to discern because of heavy forest vegetation and 
. massive landsliding ~n the mountain.ous terrain, but it appears that the 
system frays-out westward into a series of diverging break.a.· No single 
I ' I I " I I : I j • 
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principal fracture can be followed continuously to the Aegean Sea, 
although many of the topographic features in the coastal region are 
clearly fault-controlled and lie parallel to the North Anatolian fault 
trend; several elongate lakes and closed depressions in the Isnik-
Gemlick area (Bursa Prov.) are good examples, as are many of the 
topographic features east and west of izmit (Kocaeli Prov.). 
Pavoni ( 1961) has suggested that the total lateral displacement 
on the North Anatolian fault may be several hundred kilometers. The 
pres.ent author has little to add to this argument except to emphasize 
that the length of the fault, its linearity through regions of diverse 
rock types, and the great width of the crushed zone are comparable to 
those of other regional faults along which large displacements have been 
well documented. As is typical of other such faults, good exposures of 
rocks within the North Anatolian fault are rare; probably the best 
exposure observed by the author was in the canyon of the Kelkit River, 
20 km west of Re1adiye ( Tokat Prov.), where completely crushed and 
pulverized slices of rock have been exposed over a width of several 
hundred meters. The most recent displacements within the zone, as 
indicated by nearby fault scarps, have generally been limited to a single 
strand, despite the great width of the zone that presumably represents a 
long and complex history of fracturing. 
Certainly the most remarkable historic phenomenon associated 
with the North Anatolian fault has been the generally westward progression· . 
of dextral surface displacements along the fault trace starting with the 
great Erzincan earthquake of 1939-- a successcion of events in time and 
space that has been reported nowhere else in the world. This unique 
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.behavior was first pointed out by Ketin ( 1948), and most of the data 
including that of the more recent events has been summarized by 
Ambraseys and Zatopek ( 1968). It should be emphasized, however, 
that the remarkable s.eries of earthquakes during the past 30 years 
does not appear to be typical of events during the last one or two 
hundred years; in talking to many farmers living along the fault trace, 
the author found none who could recall having observed or having heard 
stories of pre-1939 ground displacements. -- despite the fact that 
details of the 1939 and subsequent events are indelibly fixed in their 
memories. This suggests that major earthquake sequences associated 
with surface faulting, such as characterizes the present epoch, are 
relatively infrequent events, and that following the present spasm of 
activity the fault may again be relatively quiescent for a period of per-
haps several hundred years. 
The author has argued that those segments of the San Andreas 
fault in California where Quaternary displacements have been the most 
continuous and throughgoing are the segments most likely to experience 
great earthquakes at very infrequent intervals, whereas those segments 
characterized by branching and complex surfa~e fault patterns have very 
frequent earthquakes but of much smaller average magnitude (Allen, 1968). 
The same seismotectonic generalization may apply to Turkey: easternmost 
and westernmost Turkey, which are characterized by complex and dis-
continuous fault patterns,. see:tn to have very frequent earthquakes of 
moderate magnitudes (Ergin, Giicslii and Uz, 1967), whereas truly great 
earthquakes - - albeit infrequent - - may be limited to those parts of Turkey 
dominated by a long, throughgoing fault system such as the North Anatolian 
fault zone betwetm Abant and Karhova. 
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ACKNOWLEDGMENTS 
The author's work .in Turkey was made possible by the generous 
cooperation of the Minerals Research and Exploration Institute (Maden 
Tetkik ve Arama Enstitusii - - M. T. A. ), Dr. S. Al pan, General Director. 
The field work would have been impossible without the kind help of i. Ketin 
of Istanbul Technical University and Oz can Aksoy of the M. T. A. In 
addition to the logistical help obtained thr.ough Istanbul Technical University 
and the M. T. A., the work was supported by the G. K. Gilbert Award in 
Seismic Geology adminstered through the Carnegie Institution of Washington. 
REFERENCES 
Allen, C.R., 1962, Circum-Pacific faulting in the Philippines-Taiwan 
region: Jour. Geophys. Research, v. 67, p. 4795-4812. 
Allen, C.R., 1965, Transcurrent faults in continental areas: Royal. Soc. 
(London) Philos. Trans. A., v. 258, p. 82-89. 
Allen, C. R. , 1967, The tectonic environments of seismically active and 
inactive areas along the San Andreas fault system: Stanford· Univ. 
Pub. Geol. Sci., v. 11, p. 70-82. 
Altinli, I., Pamir, H., and Erentoz, C., 1963, 1:500,000 Olcekli, Tiirkiye 
Jeoloji Haritas1, Erzurwn: Maden Tetkik ve Arama Enstitusii, 
· Ankara, 131 p. 
Ambraseys, N. N. , and Zatopek, A. , 1968, The Varto Ustiikran (Anatolia) 
earthquake of 19 August 1966 -- summary of a field report: Seismal. 
Soc. America Bull. , v. 58, p. 47-102. 
. ' 
- '10 -
Ergin, K. Guc;lii, U., and Uz, Z., 1967, Tiirkiye ve civarinm deprem 
Katalogu: istanbul Teknik Univer sitesi, Maden Fakiiltesi, 169 p. 
Erin~, S., Bilgin, T., and Bener, M. , 1961, Gerede Civarinda Akarsu 
~ebekesi: istanbul Universitesi, Cografya Ensti{sii Dergisi, v. 7, 
p. 90-99. 
Freund, R., 1965, A model of the structural development of Israel and 
adjacent areas since Upper Cretaceous times: Geol. Mag.' 
v. lOZ, p. 189-205. 
Ketin, L , 1948, Uber die tektonisch-mechanischen Folgerungen aus den 
grossen anatolischen Erdbeben des letzten Dezenniwns: Geol. 
Rundschau, v. 36, p. 77-83. 
Ketin, i., and Roesli, F., 1953, Makroseismische Untersuchungen uber 
das nordwestanatolische Beben vom 18 Marz 1953~ Eclogae Geol. 
Helvetiae, v. 46, p. 187-208. 
Pavoni, N., 1961, Die nordanatolische Horizontalverschiebung: Geol. 
Rundschau, v. 51, p. 12.Z-139. 
Wallace, R. E., 1968,. Earthquake of August 19 1966, Varto area, eastern 
Turkey: Seismal. Soc. America Bull. , v. 58, p. 11-45. 


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Active Faulting in Northern Turkey

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Active Faulting in Northern Turkey

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