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鳴門教育大学学校教育研究紀要
第２８号
Bulletin of Center for Collaboration in Community
Naruto University of Education
No.２８, Feb., ２０１４
Active tectonics of Iran deduced from earthquakes,
active faulting and GPS evidences
Jamshid AHMADIAN, Mamoru MURATA, Alireza NADIMI
Hiroaki OZAWA and Takeshi KOZAI
№２８ 11
鳴門教育大学学校教育研究紀要 ２８，１１−２２
原著論文
Active tectonics of Iran deduced from earthquakes, active faulting and
GPS evidences
Jamshid AHMADIAN a, b，Mamoru MURATA c，Alireza NADIMI d，
Hiroaki OZAWA e and Takeshi KOZAI c
a- Center for collaboration in community, Naruto University of Education, Naruto, Tokushima 772-8502, Japan
b- Department of Geology, Payame Noor University, P.O. Box 19395-3697, Tehran, IRAN
c- Natural Science Education (Science), Naruto University of Education, Naruto, Tokushima 772-8502, Japan
d- Department of Geology, Faculty of Science, University of Isfahan, P.O. Box 81746-73441, Isfahan, Iran
e- International Cooperation Center for the Teacher Education and Training, Naruto, Tokushima 772-8502, Japan
Abstract：Iran is an ideal natural laboratory for studying the kinematics and dynamics of plate interactions
because of the various tectonic processes encountered, including continental collision, subduction of oceanic
lithosphere (Makran) and a sharp transition between a young orogen (Zagros) and a subduction zone (Makran).
In this research, tectonic evolution of Iranian Plateau during Cenozoic convergence between Arabian and
Eurasian plates is reviewed and youngest tectonic activities in the plateau such as active faults, earthquakes,
magmatism, and young volcanism and GPS velocities are described. Iran is one of the most seismically active
countries in the world, being crossed by several major fault lines that cover at least 90% of the country. These
earthquakes occurred along the active faults of Iran and show various mechanisms of fault movements.
Keywords：Iran, Earthquake, Active Tcetonics, Active Fault, Zagros Collision.
Ⅰ．Introduction
Iran is one of the world’s best examples of a youthful stage
of continent-continent collision, in which active faults,
earthquake epicentres and young volcanos are mostly located
within the political borders of the country. The continent-
continent collision between the Arabian and Eurasian plates
following the closure of the Neo-Tethys Ocean resulted in the
development of the Zagros (Sto
¨
cklin, 1968; Falcon, 1974;
Berberian and King, 1981). The collision appears to have
commenced during the Late Eocene-Early Oligocene (e.g.
Vin cent et al., 2007; Agard et al., 2005, 2011). However, the
most conspicuous manifestations of the collision, the Zagros
and Alborz Mountains, have undergone their most significant
deformation during the Middle Miocene-Holocene (Allen et
al., 2004), and earlier deformation is largely confined to a
much narrower belt between the Sanandaj-Sirjan zone and
High Zagros (Agard et al., 2005).
The Zagros orogen extends from the Turkish-Iranian
border to the NW, to the Makran area in the SE (where
oceanic subduction is still active; Smit et al., 2010; Fig. 1A).
The Zagros Orogen is sub-divided into several tectonic units
and consists of the Zagros Simply Folded Belt (ZSFB),
Zagros Imbricate Belt (High Zagros Belt or Crush Zone),
Sanandaj-Sirjan Zone (SSZ) and Urumieh- Dokhtar
Magmatic Arc (UDMA) (e.g. Sto
¨
cklin, 1968; Falcon, 1974;
Alavi, 1994; Berberian and King, 1981; Agard et al., 2005).
Other tectonic units of Iran are Central Iran, Eastern Iran,
Alborz and Kopeh Dagh ranges (Fig. 1A).
In this research, we review tectonic evolution of Iran
during Late Cenozoic- Quaternary and describe youngest
tectonic activities in the Iran such as active faults,
earthquakes and GPS velocities.
Ⅱ. Geotectonic setting
Zagros Orogenic Belt: The tectonic evolution of the Zagros
Mountains was entirely due to plate tectonics and the
converging of the Arabian and Eurasian continents (Fig. 1A).
The timing of the collision of the Arabian and Eurasian plates
is generally known to be in the Miocene. Study by Agard et
al. (2005) in the High Zagros Mountains noted deposited
Late Oligocene-Early Miocene conglomerates unconformably
overlying the Eocene domain of the Iranian Plate and the
81.4-86.3 Ma obducted ophiolite of the Arabian Plate. This
indicates that the timing of ocean closure and the inception of
collision must have taken place between the mafic intrusions
at 38 Ma and the 25-23 Ma Oligocene-Miocene deposits.
鳴門教育大学学校教育研究紀要
12
The Zagros Orogen has a complex history. During the
Miocene, plate convergence underwent a change in direction
from NE to NNE (McQuarrie et al., 2003) and was
accompanied by folding and thrusting in the Zagros Imbricate
Belt (see Molinaro et al., 2005). Lacombe et al. (2006)
documented a Late Miocene to Early Pliocene pre- and syn-
folding NE stress field in the ZSFB. Navabpour et al. (2007)
identified various strike-slip, compressional and tensional
stress regimes in the Zagros Imbricate Belt. Their
investigations indicate that the main fold and thrust structure
that developed during the Miocene in a generally
compressional stress regime with an average 032°direction of
the σ
1 stress axis. During three successive strike slip faulting
stages developed strike-slip structures. The faults resulted
from a different σ
1 direction in the Early Miocene (053°),
Late Miocene-Early Pliocene (026°), and post-Pliocene
(002°) times, evolving from pre-fold to post-fold faulting
(Navabpour et al., 2007).
Sanandaj-Sirjan Zone: The SSZ remains a poorly
documented part of the Zagros Orogen that is separated from
the Zagros imbricate belt on the southwest by the Main
Zagros thrust (MZT) (Fig. 1A). The northeastern boundary of
SSZ is unclear because it is covered by Quaternary deposits,
and contrary to its southern part, the northern part does not
have any major faults. The SSZ may be separated from the
Central Iran by steeply dipping faults (Sto
¨
cklin, 1974), and
Morley et al. (2009) interpreted that the southern UDMA was
uplifted and deformed along an important transpressional
zone of deformation. Alavi (1994) even considered the
boundary between UDMA and SSZ as the main Zagros
Suture Zone.
Urumieh-Dokhtar Magmatic Arc: The UDMA situated
between the SSZ and Central Iran, runs parallel to the Zagros
Mountains and the SSZ (Fig. 1A). It forms a topographic
ridge separating the SSZ from Central Iran, and bears huge
volcano-sedimentary deposits, in places >10 km thick
(Dimitrijevic, 1973). It is generally assumed that the UDMA
was the magmatic arc overlying the slab of the Neo-Tethyan
oceanic lithosphere which was subducted beneath the Iranian
Plate (Berberian and Berberian, 1981; Alavi, 1994;
Ahmadian et al., 2009, 2010). The UDMA is one of the most
important belts of metalogeny in Iran (e.g. Haschke et al.,
2010; Sarjoughian et al., 2012). Alkaline, post-collisional
Pliocene-Quaternary volcanism are found in volumetrically
large amounts in the latter area only, but small outcrops of
(presumably Quaternary) alkaline basalt are found in many
places, mainly along fault zones.
Central Iran: The Central Iran is surrounded by fold-and-
thrust belts, within the Alpine-Himalayan orogenic system of
western Asia. Being situated to the northeast of the Zagros-
Makran Neo-Tethys suture and its sub-parallel Cenozoic
magmatic arc (UDMA), the Central Iran is an area of
Figure 1. A) Structural units and tectonic features of the Arabia-Eurasia collision zone in Iran. MF- Mesopotamian
Foredeep and Persian Gulf, ZSFB- Zagros Simply Folded Belt, ZI- Zagros Imbricate Belt, SSZ- Sanandaj-Sirjan
Zone, UDMA- Urumieh-Dokhtar Magmatic Arc, MRF- Main Recent Fault and MZT- Main Zagros Thrust.
B) Distribution of earthquakes in Iran resulting from Arabia-Eurasia collision (Lacombe . 2006).
Open circles represent 4501 earthquakes (magnitude between 2.4 and 7.4) recorded from 1964 to 2002 (after the
International Seismological Centre, online bulletin, Guest ., 2006).
№２８ 13
continuous continental deformation in response to the
ongoing convergence between the Arabian and Eurasian
plates (Fig. 1A). The Central Iran consists, from east to west,
of three major crustal domains: the Lut, Tabas and Yazd
blocks (Alavi, 1991) separated by a series of intersecting
regional-scale faults.
Although the stratified cover rocks can be correlated
between the different blocks, locally significant facies and/or
thickness variations occur across the domain boundaries. The
eastern region of the Yazd Block, between the Yazd and
Tabas blocks, provides remarkable exposures of the deeper
sections of the Central Iranian platform strata, among which
Late Neoproterozoic and Lower Paleozoic rocks are abundant
(Nadimi, 2007).
Eastern Iran: The eastern limit of Arabia-Eurasia
deformation occurs at roughly longitude 61°E, close to the
political border between Iran and Afghanistan (Fig. 1A).
Further east there is a sharp cut-off in seismicity,
mountainous topography and active fault activity. The
present-day right lateral strain across eastern Iran is measured
by GPS at ~16 mm/yr (Vernant et al., 2004). Walker and
Jackson (2002) used offset Quaternary basalts to estimate a
slip rate of ~1.5 mm/yr on the Nayband fault, which suggests
that the major part of the present-day strain is accommodated
elsewhere. The southern part of the Eastern Iran consists of
Makran Range that is an accretionary prism of an active
subduction zone. In this area, oceanic crust of Oman Sea is
subducting under continental crust of the Eastern Iran.
Alborz Range: The Alborz Range in northern Iran is
roughly 600 km long and 100 km across, running along the
southern side of the Caspian Sea (Fig. 1A). Alborz represent
a good example of an intra-continental belt, with a stretched
continental domain inverted during Late Triassic time
(Zanchi et al., 2006) and the Tertiary (e.g. Guest et al., 2006;
Ritz et al., 2006), as a result of both Palaeo-Tethyan and Neo-
Tethyan closures. The Alborz is thus an integral part of the
Arabia- Eurasia collision zone, and accommodates present-
day convergence through orogen normal shortening and
lateral escape of the South Caspian basin in the west, and
more complex deformation partitioning, including right-
lateral movements, to the east (Hollingsworth et al., 2006).
Kopeh Dagh Range: The Kopeh Dagh trends at 120°-
300°for 700 km through northeast Iran and Turkmenistan
between the Caspian Sea and the Afghanistan border (Fig.
1A). It separates the Turan region from central Iran, and so
shows how plate convergence happens at the northern side of
the collision zone. The range is up to 3000 m in altitude,
some 2000 m higher than the Turkmen foreland to the north.
North-south shortening across the west of the range may be
~75 km, based on a line balanced section by Lyberis and
Manby (1999). This represents ~30% shortening of the 250
km wide western Kopeh Dagh region.
Ⅲ. Earthquakes in Iran
Iran is situated in a highly seismic part of the world, and
has been frequently struck by catastrophic earthquake during
recorded history. These earthquakes have resulted in great
loss of life, and, in rendering large numbers of people
homeless and disrupting the agricultural and individual basis
of their lives, have been wasteful of national resources.
Iran is surrounded by tectonically active zones.
Earthquakes are regularly felt on all sides of Iran (Fig. 1B).
There are several huge earthquakes events during previous
one hundred year ago. About 15,000 people died in 1976 as a
result of an earthquake in western Iran. More than 20,000
people died in a 7.7 Richter scale earthquake in 1978 in
Tabas, Central Iran. In 1981, more than 1000 people died in
Kerman as a result of an earthquake. Around 40,000 people
died in a 7.2 Richter scale earthquake in the northern Iranian
province of Gilan. In June of 2002, more than 1100 people
lost their lives in an earthquake in northwestern Iran. The
casualties of the Bam earthquake of December 2003, Mw 6.6
will perhaps never be known exactly, but is thought to be
between 26,000 (the official figure) and 40,000 (Berberian
2005). On February 22, 2005, a major earthquake (Mw 6.4)
killed hundreds of residents in the town of Zarand and several
nearby villages in north Kerman. The February 22 earthquake
is 125 km northwest of the destructive earthquakes of June
11, 1981 (Mw6.6, ~3,000 deaths) and July 28, 1981 (Mw7.3,
~1,500 deaths) and about 250 km northwest of the
devastating Bam earthquake of December 26, 2003. The
2005 Qeshm earthquake, Mw 6.0 was a powerful earthquake
that occurred on November 27, 2005, in Qeshm Island,
southern Iran.
Varzeghan Earthquake (Miyajima et al., 2012;
http://www.iiees.ac.ir; http://irsc.ut.ac.ir): on the late
afternoon of Saturday August 11, 2012 the northwest of Iran
was shaken by two of the strong earthquakes in Iranian
history (Fig. 2). First was hit by Mw 6.4 at 16:54 local time
(12:23 GMT), and about 11 minutes later, a Mw 6.3 struck 10
km to the west. The deaths were more than 330 persons.
Successively Varzeghan-Ahar earthquakes are the cluster
ones or “earthquake sequence”, and involved more than
hundreds moderate and small temblors and are centered on
Varzeghan area. After about three months from the main
鳴門教育大学学校教育研究紀要
14
shock of earthquake, only during one day, on November 07,
2012, Seismological Center of Tehran University has
recorded about 55 aftershocks with Mw 5.1 Richter and
smaller.
In 2013, several huge earthquakes have been occurred in
Iran (Fig. 3) (http://irsc.ut.ac.ir). The April 9, 2013 M6.3
(6.4: USGS: http://www.usgs.gov) earthquake in southern
Iran, Boushehr occurred as result of NE-SW oriented thrust-
type motion in the shallow crust of the Arabian plate (Fig.
3A). The depth and style of faulting in this event are
Figure 2.
A) Varzeghan Earthquake,
Mw6.4 and 6.3, 2012-11-08
(
from http://irsc.ut.ac.ir/index.php
).
B) Focal mechanisms of
Var zeg han Earthquake from
various seismological centers.
The focals show active strike-
slip faulting of the earthquake.
Figure 3.
Recent major earthquakes of
Iran in 2013
(earthquake data from
http://irsc.ut.ac.ir/index.php).
A) Boushehr Earthquake,
Mw6.3, 2013-04-09.
B) Sistan Earthquake,
Mw7.5, 2013-04-16.
C) Minab Earthquake,
Mw6.1, 2013-05-11.
№２８ 15
consistent with shortening of the shallow Arabian crust
within the Zagros Mountains in response to active
convergence between the Arabian and Eurasian plates
(http://www.usgs.gov).
The April 16, 2013 M 7.5 (7.8: USGS) earthquake east of
Sistan (Khash), occurred as a result of normal faulting at an
intermediate depth in the Arabian plate lithosphere,
approximately 80 km beneath the Earth’s surface (Fig. 3B).
Regional tectonics are dominated by the collisions of the
Arabian and India plates with Eurasia; at the longitude of this
event, the Arabian plate is converging towards the north-
northeast at a rate of approximately 37 mm/yr with respect to
the Eurasian plate (http://www.usgs.gov). Oman oceanic
lithosphere is subducted beneath the Eurasian plate at the
Makran coast of Iran and Pakistan, and becomes
progressively deeper to the north.
The May 11, 2013 M 6.1 earthquake east of Minab,
occurred as a result of strike-slip faulting (Fig. 3C). Regional
tectonics are dominated by the collisions of the Arabian and
Eurasian plates to the west and subduction of Oman oceanic
lithosphere to the east.
Ⅳ. Active faults
1. Tectonic structure
The collision of two continental plates produces a zone of
very complex tectonic structures. Many kinds of such
tectonic structures formed also during Cenozoic times in the
Zagros Orogen and other parts of Iranian Plateau, as a
consequence of the collision between the Arabian and the
Eurasian plates (Sto
¨
cklin, 1968; Falcon, 1974). Most of these
structures are still active. Tectonic deformation in Iran during
the last 3-5 Ma resulted mainly in the N-S-trending
convergence and dextral strike-slip faulting (e.g. Berberian
and King, 1981; Berberian, 1981) and partly in thrusting and
accompanying folding.
There are many active faults in Iran that stretched with
different trends in the structural zones of Iran (Fig. 4). In
each zone, active faults have their special properties and
formed in different tectonic scenario. Some of the active
faults reactivated during the Zagros Orogen and later strike-
slip movements in Iran. The major active faults in Iran are
considered as tectonic boundary of the structural zones of
Iran and smaller tectonic blocks (Fig. 4). In many places
these faults dissect Pliocene to Quaternary rocks and
sediments and have formed young sedimentary basins.
2. Active fault sets
Relative to the main NW-SE trend of tectonic structures in
the Zagros Orogen, the fault pattern consists of major NW-
trending longitudinal faults, NE-SW-trending transverse, N-S-
trending oblique and E-W-trending oblique faults (Fig. 4).
Longitudinal NW-SE-trending faults in Iran are parallel to
the MZT. The fault set, developed in the Cenozoic times, is
Figure 4. Map of active faults of Iran (Hessami ., 2003).
鳴門教育大学学校教育研究紀要
16
part of a system NW-SE-trending dextral strike-slip faults
that cut the upper continental crust of the Iranian Plateau (e.g.
Berberian and King, 1981).
The MZT is the most important longitudinal fault in Iran.
The fault is a tectonic boundary between the Iranian Plate to
the north and the Zagros Fold-Thrust Belt to the south (Fig.
1A). The whole MZT is a c. 1350 km-long suture zone
between the Arabian and Eurasian plates (e.g. Sto
¨
cklin,
1968; Agard et al., 2005). The northwestern part of the MZT
that known as the Main Recent Fault is currently active and a
dextral strike-slip sense is noted along its plane (e.g. Talebian
and Jackson, 2002). Evidence of large earthquakes noted on
the MRF plane e.g. Ms 7.4 in 1909 and Ms 6.7 in 1957
(Ambraseys and Moinfar, 1973) led several authors (e.g.
Braud and Ricou, 1971; Talebian and Jackson, 2002) to
consider the MRF and the North Anatolian Fault as an almost
continuous active strike-slip zone along the northern Arabian
Plate and Anatolian Microplate margins.
Transverse NE-SW-trending faults in Iran are
perpendicular to the trend of MZT (Fig. 4). Some of these
faults that are located near the Zagros orogenic belt have
normal and sinistral components of movements and were
formed during NE-SW shortening and NW-SE-trending
lateral extensional movements. These faults are very small
and are shorter than 100 km in length. Other NE-SW-
trending faults that are located far from the orogenic belt, e.g.
in the northeast Iran, were formed around the Central-East-
Iran Microcontinent (Figs. 4 and 5). The faults have sinistral
strike-slip component of movement. The Doruneh Fault with
a length of ca 700 km is one of the longest and most
prominent faults in Iran that is bordered northern boundary of
Central Iranian Microcontinent. The fault trend changes from
east to west and from NW-SE, E-W and NE-SW (Fig. 4). The
western termination of the fault is considered a transverse
fault. The Doruneh Fault performs an important role in the
regional tectonics, by accommodating up to 15 mm/yr of
north-south right-lateral shear between central Iran and
Afghanistan (Vernant et al., 2004). The geomorphology of
the western part of Doruneh fault contains numerous
indications of cumulative left-lateral slip over various scales.
N-S-trending faults form one set of oblique sets in relation
to the main NW-SE-trend of tectonic structures in the Zagros
Orogen (Figs. 4 and 5). The major fault systems in the
Central and Eastern Iran are oriented N-S, and are known to
Figure 5.
Strike-slip faulting in the Central and Eastern
Iran.
Modified from Walker and Jackson (2004).
Total o f fsets across Dehshir (D), Anar (A),
West Lut (WL, Nayband), and East Lut (EL,
Nehbandan) faults are indicated in km. GPS
velocities relative to stable Eurasia (red
arrows, Vernant ., 2004) indicate ~16
mm/yr of right-lateral shear across WL and
EL fault systems. Slip-rate on individual
faults (green numbers in mm/yr) is averaged
over the Quaternary for West Lut (Walker
and Jackson, 2002) and the Holocene for
Dehshir (Meyer ., 2006), Anar and East
Lut (Meyer and Le Dortz, 2007).
№２８ 17
be right-lateral strike-slip faults from seismological and field
investigations of earthquakes (e.g. Berberian and Yeats,
1999; Berberian et al., 1999, 2001), from the right-lateral
displacement of geomorphological features and rivers (e.g.
Tirrul et al., 1983), and from the role of the faults in
accommodating right-lateral shear between Iran and
Afghanistan (e.g. Jackson and McKenzie, 1984). There are
numerous active faults in this set that from east to west are
consist Nehbandan (east Lut Block), Nayband (west Lut
Block), Anar and Dehshir faults. There are several huge
earthquakes events along the faults such as Ms 7.7, 16
September 1978 Tabas (Berberian, 1979), Mw 7.1, 28 July
1981 Sirch (Berberian et al., 1984), Mw 6.1, 23 February
1994 Sefidabeh (Berberian et al., 2000), Mw 7.2, 10 May
1997 Zirkuh (Berberian et al., 1999), Ms 6.6, 14 March 1998
Fandoqa (Berberian et al., 2001), and Mw 6.6, 26 December
2003 Bam (Fu et al., 2004) earthquakes.
E-W-trending faults form second set of oblique sets in
relation to the main NW-SE-trend of tectonic structures in the
Zagros Orogen (Figs. 4 and 5). These faults have formed
along the northern boundary of Central Iranian
Microcontinent and southern boundary of the South Caspian
Block and during N-S-trending convergence of the Iranian
tectonic blocks. This fault set has the lowest frequency in
Iran. The Alborz faults in south Caspian, central part of the
Doruneh and Dasht-e Bayaz faults are some examples of the
set. The Dasht-e Bayaz earthquake (31 August 1968, M 7.2)
was associated with E-W-trending sinistral fault zone more
than 80 km long (Tchalenko and Ambraseys, 1970).
V. Discussion
This section focuses on the tectonic evolution of Iran,
during Arabian-Eurasian convergence and later strike-slip
movements in the Pliocene to Holocene.
1. GPS data and present day kinematics in Iran
Nilforoushan et al. (2003) and Vernant et al. (2004)
provided GPS measurements and the first-order present-day
kinematics of Iran (Fig. 6). GPS measurements suggest right-
lateral displacements in northwestern Iran (Vernant et al.,
2004). GPS velocities along the northeastern boundary of the
Arabian Plate relative to Eurasia are systematically smaller
than the NUVEL-1A estimations. In the western part of Iran,
distributed deformation occurs among several fold and thrust
belts. In northwestern Iran large right-lateral motions are
expected along the NW-SE Tabriz fault system and along a
north-south fault bordering the western Caspian coast. The
right-lateral deformation occurring between the western
Caspian Sea and the Central Iranian Block could be
distributed along NW-SE Iranian and Armenian fault
systems.
Between the Central Iranian Block and the Arabian Plate,
the central Zagros accommodates about 7±2 mm/yr of north-
south shortening. The shortening rate decreases in northern
Zagros, implying a right-lateral strike-slip rate along the
MRF of 3±2 mm/yr, much smaller than geological
estimates. North of the Central Iranian Block, the Alborz
mountain range accommodates 8±2 mm/yr of north-south
Figure 6.
Schematic illustration of the main
results of GPS study of Vernant
.,
(2004).
Hatching shows areas of coherent
motion, grey zones are actual
deformation areas (see legend). Heavy
arrows in black indicate the actual
motion of the Arabian plate relative to
the Eurasia. Grey arrows are
deformation rates directly measured
with GPS. Rates in eastern Turkey are
deduced from McClusky ., (2000).
White arrows are deduced rates from
GPS, geological evidence and
seismology, for motion along the
Chaman Fault and the associated
deformation zone the velocity is
deduced from the REVEL model (Sella
., 2002). All the rates are given in
mm/yr.
鳴門教育大学学校教育研究紀要
18
compression. Sites along the southern Caspian shore indicate
roughly northward motion at 6.5±2 mm/yr relative to
Eurasia.
In the eastern Iran, the western and eastern borders of the
Lut Block are described as large right-lateral strike-slip faults
(e.g. Tirrul et al., 1983; Berberian and Yeats, 1999; Walker
and Jackson, 2002; Vernant et al., 2004). A dextral shear of 16
±2 mm/yr occurs between Zabol in the east of Iran and the
Central Iranian Block (Fig. 6) (Vernant et al., 2004). Conrad
et al. (1982) suggested, using palaeomagnetic data, that no
significant rotation occurs during the Pliocene-Quaternary for
the Lut Block. Therefore the velocity orientation of the Lut
should be consistent with the surrounding orientations
(Vernant et al., 2004).
The tectonics of eastern Iran is mostly concentrated within
the Makran subduction since the oceanic crust is subducting
at 19.5±2 mm/yr roughly north-south under the Makran
Wedge. Based on the GPS and geological information, the
schematic kinematic pattern of the present-day Arabia-
Eurasia convergence zone in Iran was prepared in Figure 6.
2. Arabia and Eurasia convergence and strike-slip
movements
While distributed thickening in the Arabia/Eurasia
collision zone is revealed to have played a dominant role in
building the regional topography, the ways in which the
Cenozoic convergence has been accommodated through
strike-slip faulting in the Zagros (e.g. Authemayou et al.,
2009; Lacombe et al., 2006; Talebian and Jackson, 2004) and
central Iran is debated (e.g. Allen et al., 2011; Meyer and Le
Dortz, 2007; Walker and Jackson, 2004).
This have pointed out earlier that the kinematics of the
Zagros collision is currently partitioning the N-S
convergence, into a NW-SE orogen-parallel right-lateral
strike-slip faulting along the MRF, and NE-SW orogen-
normal shortening in the Zagros folds/thrusts (Authemayou et
al., 2009; Talebian and Jackson, 2004). The kinematic role of
right-lateral strike-slip faulting in the Zagros is diversely
interpreted (Mouthereau et al., 2012). There are viewed as
faults bounding, counterclockwise rotated blocks, which
accommodate an arc parallel elongation between the
partitioned domain of NW Zagros and no partitioned domain
of the SE Zagros (Talebian and Jackson, 2004). This
stretching, observed in the GPS data, is also emphasized by a
component of belt-parallel extension, as recorded by fault
slip data analysis, calcite twining and active/quaternary
faulting (Mouthereau et al., 2012).
Addition to the Zagros Mountains, the strike-slip faulting
in occurred in other parts of the Arabia-Eurasia collision
zone. There are several manners for deformation associated
with strike-slip faulting to accommodate the plate
convergence in continental interior (see Allen et al., 2011).
They can rotate about vertical axes to accommodate N-S
shortening and arc-parallel lengthening, as proposed for the
Zagros (Talebian and Jackson, 2004). Alternatively, they can
accommodate relative motion between non rotating blocks
such as between central and eastern Iran (Dehshir and Anar
faults; Meyer and Le Dortz, 2007). These N-S right-lateral
strike-slip faults absorb the differential displacement between
the collision domain (central Iran) and the Makran
subduction domain (eastern Iran) (Mouthereau et al., 2012).
A comparison between the long-term geological offsets and
short-term geodetic displacement led Walker and Jackson
(2004) to propose a cumulative N-S right-lateral shear in
eastern Iran of 75-105 km. Assuming that the current
kinematic configuration dates back to the inferred
reorganization in the collision at 5-7 Ma (Allen et al., 2004),
these authors postulated that the strike slip faults of central
Iran (e.g. Dehshir and Anar faults) accommodate a small
amount of shortening (Mouthereau et al., 2012). However,
Meyer and Le Dortz (2007) pointed out that a long-term
kinematic model based on extrapolation of GPS rates may
not be valid. They inferred that strike-slip faults of central
Iran have accommodated a cumulative right-lateral shear of
90 km (Dehshir and Anar faults) over the past 20 Myr. A
paleoseismic study showed that the Dehshir fault has been
capable of producing earthquake as big as M~7 (Nazari et al.,
2009). Therefore, there is evidence that right-lateral strike-
slip faulting is not confined to the edges of the Lut block.
Taking into account the lack of current internal deformation
across central Iran (Vernant et al., 2004) it has been
suggested that deformation associated with strike-slip
faulting slowed in the last few Myr and shifted progressively
to the east of the collision (Meyer et al., 2006; Allen et al.,
2011). The view that long-term N-S Arabia/Eurasia plate
convergence in central Iran was partitioned by a combination
of right-lateral strike slip faulting and thrusting has been
emphasized by Allen et al. (2011), analogous to the situation
in the Zagros (Talebian and Jackson, 2004).
As noted earlier and consistently with Allen et al. (2004,
2011), deformation (strike-slip faulting and thrusting) seems
to have slowed in central Iran. This was possibly related to a
change in boundary conditions in the east, associated with the
onset of the Afghan-India collision at ~5-2 Ma that stopped
the possibility for lateral extrusion/ escape (Mouthereau et
al., 2012). Here, in accord with the partitioning model of
№２８ 19
Allen et al. (2011), in which orogen-parallel lengthening is
limited, Mouthereau et al. (2012) propose that the transition
was progressive since 15-10 Ma and related to arc-normal
thickening, which led to the uplift of the Iranian plateau and
to the cessation of active deformation in central Iran. The
progressive thickening in the Iranian plateau (e.g. SSZ)
possibly promoted the decline of activity along NNW-SSE
strike-slip faults like the Dehshir or Anar faults (Mouthereau
et al., 2012). The progressive arc-normal shortening was
contemporaneous with a late stage of westward lateral
extrusion that started after 10-11 Ma along the NAF in
eastern Anatolia (e.g. Armijo et al., 1999) and in the Caspian
Sea (Hollingsworth et al., 2006).
Mouthereau et al. (2012) concluded that the overall long-
term distribution of deformation, a combination of partitioned
strike-slip faulting and thrusting, in the Zagros collision
region (they omit the yet subducting domain of eastern Iran)
may be understood in the context of the N-S indentation of
Arabia continent into Eurasia.
Ⅵ. Conclusions
The following conclusions can be drawn from the studies:
- Iran is subject to most types of tectonic activity,
including active folding and faulting. Since 1900, more than
150,000 fatalities have resulted from earthquakes in Iran.
These earthquakes occurred along the active faults of Iran
and show various mechanisms of fault movements. The study
of earthquake related faulting in Iran has shown the
importance of the early Quaternary tectonic history as well as
that of the pre-Quaternary geological record for the
understanding of the present-day continental deformation
during earthquakes.
- Distributed thickening in the Arabia/Eurasia collision
zone is revealed to have played a dominant role in building
the regional topography, the ways in which the Cenozoic
convergence has been accommodated through strike-slip
faulting in the structural units of Iran. The GPS velocities
data confirmed north-south shortening between Arabian and
Eurasian plates and showed that each tectonic block of Iran
has moved and their boundaries made active faults of Iran.
Acknowledgements
Our special words of thanks go to the people whose
guidance and assistance were indispensable in the successful
completion of this study. The first author, Jamshid Ahmadian
would like to express his deepest gratitude to Dr.Yuzo
Tan aka, the President of Naruto University of Education, for
awarding the research scholarship to him. He also thanks Dr.
Ziari, the President of Payme Noor University, for his
valuable support and contribution on this research. This
work was supported by the foreign visiting researcher
program 2012 of Naruto University of Education and the
joint research project (O) of the joint graduate school(Ph.D.
Program) in science of school education, Hyogo University
of Teacher Education.
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