Northwest Zagros Research Articles

Seismotectonic investigation in northwest Zagros, Iran: analysis of Ezgeleh Mw 7.3 aftershocks

Seismotectonic investigation in northwest Zagros, Iran: analysis of Ezgeleh Mw 7.3 aftershocks

The younger Dryas layer at Boncuklu Tarla and the beginning of village life in the upper Tigris Basin

Recent archaeological excavations in the Boncuklu Tarla, Çemka Höyük, and Körtik Tepe settlements in the Upper Tigris Basin have provided a number of finds from the pre-PPNA Period, the Younger Dryas. The new data also opens up the concept of the Proto-Neolithic Period to discussion again, which has been controversial for a long time in the East Jazeera and Northwest Zagros Region. In this context, architectural remains and other small finds discovered in the Boncuklu Tarla settlement area make it possible to re-examine the transition to sedentary life in the Upper Tigris Basin during the Late Epipalaeolithic/Proto-Neolithic Period and the PPNA Period. These archaeological finds show that there were some semi-sedentary or sedentary communities in the Upper Tigris Basin, which exhibits unique geographical and climatic features, starting with the Younger Dryas Period. This is different from the Natufian culture that is thought to have emerged in the Mediterranean temperate climate zone and is known only in the Southern Levant Region.

Cooking in caves: Palaeolithic carbonised plant food remains from Franchthi and Shanidar

Research on Palaeolithic hunter-gatherer diet has focused on the consumption of animals. Evidence for the use of plant foods is comparatively limited but is rapidly expanding. The authors present an analysis of carbonised macro-remains of processed plants from Franchthi Cave in the Aegean Basin and Shanidar Cave in the north-west Zagros Mountains. Microscopic examination of the charred food remains reveals the use of pounded pulses as a common ingredient in cooked plant foods. The results are discussed in the context of the regional archaeobotanical literature, leading the authors to argue that plants with bitter and astringent tastes were key ingredients of Palaeolithic cuisines in South-west Asia and the Eastern Mediterranean.

Facies analysis and paleoenvieonmental reconstruction of the Oligocene-Early Miocene deposits in the western Lorestan Zone (North West Zagros Basin, Iran)

Facies analysis and paleoenvieonmental reconstruction of the Oligocene-Early Miocene deposits in the western Lorestan Zone (North West Zagros Basin, Iran)

Complex co- and postseismic faulting of the 2017–2018 seismic sequence in western Iran revealed by InSAR and seismic data

The largest earthquake in the Zagros Mountains struck the city of Azgeleh on the Iran–Iraq border on 12 November 2017. This Mw 7.3 earthquake was followed by an intense seismic sequence. Implementing the double-difference earthquake location technique, we relocate 1069 events recorded by our local seismic network, deployed after the mainshock. The spatial distribution of the epicenters indicates linear alignments of the events nucleated along at least four notable clusters. The clusters are characterized by at least one significant earthquake, such as the Tazehabad earthquake of 25 August 2018 (Mw 5.9) along a dense, east–west trending cluster and the Sarpol-e Zahab earthquake of 25 November 2018 (Mw 6.3) along the cluster with a northeast–southwest trend. We use two-pass differential SAR interferometry (DInSAR) and Small BAseline Subset (SBAS) methods to study the coseismic permanent displacements of the Azgeleh, Tazehabad and Sarpol-e Zahab events as well as the one-year postseismic deformation field of the 2017–2018 seismic sequence, respectively. We use non-linear and linear optimization algorithms to derive the source geometry and the slip distribution along the fault planes. The inversion is conducted by introducing also seismological constraints, leading to the definition of a listric geometry for the Azgeleh mainshock rupture that accommodates the slip area at depth of 10–16 km along a sub-horizontal plane (dipping ~3°) and a low-angle (~16°) ramp. The thrust and dextral movements along this NNW-striking (~345°) fault have triggered a tear fault responsible for the Tazehabad event ruptured an east–west trending (~267°), north-dipping (~78°) sinistral shear fault. We present the dextral slip distribution of the Sarpol-e Zahab event along a NE-striking (~34°) fault, as a synthetic Riedel structure for the southern segment of the Khanaqin fault, dipping 63° to the southeast. We find the postseismic deformation field associated with the seismic sequence is not confined only to the mainshock source (the Azgeleh fault), but also develops along the Tazehabad and Sarpol-e Zahab faults. We additionally propose afterslip along a duplex, flat-ramp-flat structure down-dip and up-dip of the Azgeleh coseismic slip area. The up-dip afterslip develops onto the shallow detachment (~3°) at depth of ~8 km and the down-dip afterslip propagate onto the mid-crustal décollement level within the Pan-African basement. The Azgeleh, Tazehabad, Sarpol-e Zahab and Khanaqin faults mark the Lurestan Arc–Kirkuk Embayment sharp margin in the Northwest Zagros and play a key role in the lateral escape of the Lurestan Salient and vertical strain partitioning in the Zagros front.

Probing Fault Frictional Properties During Afterslip Updip and Downdip of the 2017 Mw 7.3 Sarpol‐e Zahab Earthquake With Space Geodesy

AbstractWe use interferometric synthetic aperture radar (InSAR) data collected by the Sentinel‐1 mission to study the coseismic and postseismic deformation due to the 2017 Mw 7.3 Sarpol‐e Zahab earthquake that occurred near the Iran‐Iraq border in Northwest Zagros. We find that most of the coseismic moment release is between 15‐ and 21‐km depths, well beneath the boundary between the sedimentary cover and underlying basement. Data from four satellite tracks reveal robust postseismic deformation during ~12 months after the mainshock (from November 2017 to December 2018). Kinematic inversions show that the observed postseismic InSAR line‐of‐sight (LOS) displacements are well explained by oblique (thrust + dextral) afterslip both updip and downdip of the coseismic peak slip area. The dip angle of the shallow afterslip fault plane is found to be significantly smaller than that of the coseismic rupture, corresponding to a shallowly dipping detachment located near the base of the sediments or within the basement, depending on the thickness of the sedimentary cover, which is not well constrained over the epicentral area. Aftershocks during the same time period exhibit a similar temporal evolution as the InSAR time series, with most of aftershocks being located within and around the area of maximum surface deformation. The postseismic deformation data are consistent with stress‐driven afterslip models, assuming that the afterslip evolution is governed by rate‐strengthening friction. The inferred frictional properties updip and downdip of the coseismic rupture are significantly different, which likely reflect differences in fault zone material at different depths along the Zagros.

Timing of the Arabia-Eurasia continental collision—Evidence from detrital zircon U-Pb geochronology of the Red Bed Series strata of the northwest Zagros hinterland, Kurdistan region of Iraq: COMMENT

Timing of the Arabia-Eurasia continental collision—Evidence from detrital zircon U-Pb geochronology of the Red Bed Series strata of the northwest Zagros hinterland, Kurdistan region of Iraq: COMMENT

Timing of the Arabia-Eurasia continental collision—Evidence from detrital zircon U-Pb geochronology of the Red Bed Series strata of the northwest Zagros hinterland, Kurdistan region of Iraq: REPLY

Timing of the Arabia-Eurasia continental collision—Evidence from detrital zircon U-Pb geochronology of the Red Bed Series strata of the northwest Zagros hinterland, Kurdistan region of Iraq: REPLY

Paleontology and paleoecology of coralline algal assemblages from the Early–Middle Miocene deposits in NW of the Zagros basin, Iran

The paleontology and paleoecology of coralline red algal assemblages of Asmari carbonate platform in north-west Zagros basin (Lurestan province) are described. The Asmari Formation was deposited during the Burdigalian to Langhian interval. This Formation unconformably overlies Eocene dolomites of Shahbazan Formation and is conformably underlain by Gachsaran Formation. The thin section analysis of carbonate facies from Asmari Formation yielded a rich assemblage of coralline red algae that deposited on a carbonate ramp environment. These associations were predominant on inner and middle ramp settings. The coralline red algal assemblage comprises both geniculate and non-geniculate forms. Encrusting, encrusting to layered, arborescent and lumpy were the growth forms. The distribution of them across the ramp profile is related to the paleobathymetric position. Thin section analysis shows that Lithothamnion and Mesophyllum are the most abundant, whereas Lithoporella, Neogoniolithon, Sporolithon and Spongites are less abundant and Phymatholithon together with Corallina are rare. Neogoniolithon, Lithothamnion and Lithoporella were predominant in calm waters of euphotic-mesophotic inner ramp. Spongites and Corallina together with fragments of reworked melobesioids constituted the high energy parts of euphotic zone. Neogoniolithon is present in the shallower parts of a middle ramp. Deep and calm waters of the oligophotic zone in middle ramp characterized by the dominance of Mesophyllum and Lithothamnion. The presence of Lithoporella, Spongites and Sporolithon among the red algal assemblage indicates that carbonate production took place in warm waters of the tropical to subtropical zone.

Detection of landslide induced by large earthquake using InSAR coherence techniques – Northwest Zagros, Iran

The Iran earthquake of November 12, 2017 is one of the most significant earthquakes throughout the history of Iran, which shook the regions of NW Zagros Mountains, Sarpol-e Zahab Region, and Northwest of Iran with a sheer magnitude of 7.3 Mw. The earthquake triggered many succeeding landslides, causing the largest seismic landslide in Iran (Maleh-Kabood) over the past few centuries. The seismic landslide was detected using coherence change detection techniques. Nine Single Look Complex (SLC) of Sentinel-1A, B imageries were processed to build interferometric coherence products. The coherence results enabled the detection of the surface area for the Maleh-Kabood landslide caused by the Azgleh earthquake. Its instability was recognized over time. The results also indicated that the surface deformation of Maleh-Kabood landslide continued on owing to aftershocks of a size greater than 4.5 Mw following the Azgleh earthquake. The results are indicative of the robustness of the InSAR coherence technique in detecting surface deformation as well as seismic landslide studies and environmental monitoring. The results also stipulated the potential of Sentinel-1A, B C-band coherence maps as suitable tool for the detection of active landslides.

Timing of the Arabia-Eurasia continental collision—Evidence from detrital zircon U-Pb geochronology of the Red Bed Series strata of the northwest Zagros hinterland, Kurdistan region of Iraq

One of the major debated aspects of the Zagros orogenic system in the Middle East is the timing of onset of continental collision between Arabia and Eurasia. The Zagros hinterland in the Kurdistan region of Iraq contains an ~2-km-thick clastic depositional sequence of the Red Bed Series (RBS) that rests unconformably on the Arabian foreland and structurally below the Main Zagros fault, which carries the allochthonous volcaniclastic rocks of the Walash and Naopurdan groups in its hanging wall. Detrital zircon (DZ) U-Pb geochronol- ogy constrains both the depositional age and the provenance of the RBS and pinpoints the timing of initial arrival of Eurasian sediment on the Arabian plate. The youngest DZ U-Pb ages for the laterally extensive (~150 km) basal RBS (Suwais unit) imply a middle Oligocene (ca. 26 Ma) maximum depositional age. The provenance data reveal dominant DZ U-Pb age modes of late Paleocene (ca. 55–60 Ma) and middle Eocene (ca. 37–44 Ma) and, importantly, the presence of ~10%–15% DZ grains that are unequivocally derived from Eurasia, includ- ing of Jurassic (150–200 Ma) and late Paleozoic (270–380 Ma) DZ age modes. These data suggest that the RBS deposits were mainly sourced from forearc- and/or arc-related terranes along the southwest margin and hinterland of Eurasia. We advocate that by ca. 26 Ma, Neo- Tethys oceanic crust had been consumed and that Arabia-Eurasia continental collision well was underway as indicated by deposition of strata with Eurasian provenance on the Arabian margin. These DZ U-Pb data from the RBS highlight the significance of provenance data from synorogenic deposits in revealing the timing of initial continent collision by document- ing the earliest arrival of upper-plate sediment on the lower plate.

Diverse Continental Subduction Scenarios Along the Arabia‐Eurasia Collision Zone

AbstractIt is generally accepted that convergence of the Arabian and African plates is a subduction‐dominated process. However, the subduction scenarios are still debatable. Here we present a 3‐D model of the mantle to a depth of 700 km, based on a joint interpretation of the seismic tomography, residual topography, residual mantle gravity field, and seismicity. At the northwestern edge of the collision zone, we only observe partial underthrust of the Eurasian plate under the West Greater Caucasus. We suggest that this is the initial stage of subduction polarity reversal after the break off of the plate formerly subducted northward. To the southeast, counteracting subduction zones are found beneath northwest Zagros in the south and beneath the East Greater Caucasus and Alborz in the north. This scenario is likely the result of highly buoyant and weak blocks of the Lesser Caucasus, Alborz, and northwest Zagros, which are underlain in the south by the Arabian plate and the Scythian plate and South Caspian from the opposite side. Further to the southeast, a delaminated lithospheric slab is observed under southeast Zagros, while the Arabian and Eurasian plates only partially underthrust East Zagros and Kopet Dagh, respectively. In the southern part of the collision zone under Makran, only remnants of the formerly subducted slabs are found below 200 km.

Geodetic Constraints of the 2017 Mw7.3 Sarpol Zahab, Iran Earthquake, and Its Implications on the Structure and Mechanics of the Northwest Zagros Thrust‐Fold Belt

AbstractWe reveal transient surface deformation following the 2017 Mw7.3 Sarpol Zahab (Iran) earthquake using Interferometric Synthetic Aperture Radar (InSAR) measurements. Based on the coseismic interferograms derived from the Advanced Land Observing Satellite‐2 (ALOS‐2) data, the preferred slip model of the earthquake has a centroid depth of 14.5 ± 4 km and suggests that a basement fault is most likely responsible for the 2017 earthquake in the northwest Zagros fold‐thrust belt zone. Two slip asperities with a maximum slip of 6 m separated by 16 km are observed in the best fitting slip model. The accumulated afterslip in the first month after the mainshock determined from the Sentinel‐1 postseismic interferograms reveals a slip distribution that lies immediately updip of the coseismic slip, implying that frictional properties of the fault vary along the rupture patch. The Bamo Mount in the earthquake area was uplifted by approximately 1 m during the earthquake. We suggest that local topographic growth from both seismic and aseismic faulting behaviors is common within the Zagros fold‐thrust belt zone based on our findings regarding the 2017 earthquake and other significant events in the region.

P–T evolution of meta-peridotite in the Penjwin ophiolite, northeastern Iraq

The Penjwin meta-peridotite rock represents one of the five main metamorphosed ultramafic bodies in Kurdistan region, Northwest Zagros Thrust Zone. It underwent at least two successively low-retrograde metamorphic events with one progressive one which all modified the original mineralogy and texture of primary dunite and harzburgite. The primary upper mantle mineral assemblage olivine + orthopyroxene + chromian spinel is replaced by olivine + tremolite–actiolite + anthopylite + talc + ferichromite + Cr-chlorite assemblage of amphibolite facies. The further retrograde metamorphic amphibolite facies assemblage is replaced by lizardite–chrysotile + Cr-chlorite + syn-serpentinization Cr-magnetite of lower greenschist facies. Later at the main Zagros thrust fault, low greenschist facies underwent progressive metamorphism due to the local effect of shear stress as a result of the exhumation and obduction of Penjwin ophiolite suite over Merga Red bed series during Tertiary. Lizardite–chrysotile transformed to antigorite and producing antigorite + carbonate + syn-serpentinization Cr-magnetite + Cr-chlorite assemblage of upper greenschist facies. Chromian spinel is concentrically zoned as a result of multi-stages retrogressive metamorphic events, in which the Cr # (Cr/(Cr + Al)) increases from core to rim (0.5 to 1). Three zones can be identified from core to rim: The core is primary Al-rich and mantled by ferrichromite of amphibolite facies. The most outer zone of chromian spinel grains is represented by syn-serpentinization Cr-magnetite of greenschist facies.

Crustal structure of Northwest Zagros (Kermanshah) and Central Iran (Yazd and Isfahan) using teleseismic Ps converted phases

Receiver functions are widely employed to detect P-to-S converted waves and are especially useful to image seismic discontinuities in the crust. In this study we used the P receiver function technique to investigate the velocity structure of the crust beneath the Northwest Zagros and Central Iran and map out the lateral variation of the Moho boundary within this area. Our dataset includes teleseismic data (M b ≥ 5.5, epicentral distance from 30° to 95°) recorded at 12 three-component short-period stations of Kermanshah, Isfahan and Yazd telemetry seismic networks. Our results obtained from P receiver functions indicate clear Ps conversions at the Moho boundary. The Moho depths were firstly estimated from the delay time of the Moho converted phase relative to the direct P wave beneath each network. Then, we used the P receiver function inversion to find the properties of the Moho discontinuity such as depth and velocity contrast. Our results obtained from PRF are in good agreement with those obtained from the P receiver function modeling. We found an average Moho depth of about 42 km beneath the Northwest Zagros increasing toward the Sanandaj-Sirjan Metamorphic Zone and reaches 51 km, where two crusts (Zagros and Central Iran) are assumed to be superposed. The Moho depth decreases toward the Urmieh-Dokhtar Cenozoic volcanic belt and reaches 43 km beneath this area. We found a relatively flat Moho beneath the Central Iran where, the average crustal thickness is about 42 km. Our P receiver function modeling revealed a shear wave velocity of 3.6 km/s in the crust of Northwest Zagros and Central Iran increasing to 4.5 km/s beneath the Moho boundary. The average shear wave velocity in the crust of UDMA as SSZ is 3.6 km/s, which reaches to 4.0 km/s while in SSZ increases to 4.3 km/s beneath the Moho.

Serpentinites and their tectonic signature along the Northwest Zagros Thrust Zone, Kurdistan Region, Iraq

Two types of serpentinized peridotites are distinguished within the Northwest Zagros Thrust Zone (NW-ZTZ) in Kurdistan region of Iraq. One is found as lower members of ophiolite sequences, such as the Mawat and Penjwin ophiolites of the upper Cretaceous age. The other is represented by intraformational isolated serpentinite bodies in Betwat, Qaladeza, and Qalander areas within the Walash–Naopurdan volcano-sedimentary unit of the Paleocene to Eocene paleo-arc tectonic setting. Serpentinites within the NW-ZTZ consist mainly of lizardite and chrysotile, with subordinate amounts of syn-serpentinization magnetite, carbonates, chromium chlorite, tremolite, and talc as secondary minerals, and olivine, clinopyroxene, and chromian spinel as primary minerals. Minor antigorite is also found in the sheared serpentinites often found in ophiolite sequences. Petrological and geochemical studies of serpentinites from the NW-ZTZ show that, of the original protoliths of serpentinites, those associated with ophiolites are residual depleted harzburgite and dunite. The \( {\text{Cr}}\# \left( {{{ = {\text{ Cr}}} \mathord{\left/ {\vphantom {{ = {\text{ Cr}}} {\left( {{\text{Cr}} + {\text{Al}}} \right){\text{ atomic ratio}}}}} \right. \kern-\nulldelimiterspace} {\left( {{\text{Cr}} + {\text{Al}}} \right){\text{ atomic ratio}}}}} \right) \) of chromian spinel is more than 0.6, and the forsterite content of olivine is 91–92. On the other hand, the original protolith of isolated serpentinite bodies is less depleted harzburgite or depleted lherzolite, which has spinel with Cr# less than 0.6 and olivine with 90–91 forsterite contents. Whole rock chemistry of major, trace, and rare earth elements shows that the serpentinites of ophiolite sequences are depleted in CaO, Al2O3, and SiO2, Sr, and Zr, and are enriched in MgO, Ni, and Cr, in comparison with the isolated serpentinites. Cr# of the disseminated unaltered chromian spinels indicates that the serpentinites of both types had been originated from the supra-subduction zone tectonic setting; the serpentinites of ophiolite sequences obducted and thrusted over the continental margin during the obduction of the Tethyth oceanic crust onto the Arabian continental margin during the upper Cretaceous period. Isolated serpentinite bodies represent serpentinized forearc mantle wedge peridotites emplaced by diapiric upwelling into non-accretionary forearc tectonic settings during the Paleocene to Eocene age.

Late Cretaceous–Paleocene formation of the proto–Zagros foreland basin, Lurestan Province, SW Iran

Late Cretaceous emplacement of ophiolitic-radiolaritic thrust sheets over the Arabian passive margin was the first manifestation of the protracted closure of the Neotethys Ocean, which ended with the continental collision between Arabia and central Iran and the formation of the present Zagros fold belt. This tectonic stacking produced a flexural basin (the Amiran Basin: 400 × 200 km in size) in the northwest Zagros that was filled with a 1225-m-thick shallowing-upward detrital succession made up of the Amiran, Taleh Zang, and Kashkan Formations. This succession sits unconformably above the Late Cretaceous Gurpi Formation and is overlain by the Oligocene-Miocene Shahbazan-Asmari carbonate succession. Dating of the Amiran-Kashkan succession is based on detailed biostratigraphy using large foraminifera and calcareous nannoplankton. The Cretaceous-Tertiary (K-T) boundary is located within the uppermost 25-45 m of the Gurpi Formation. The overlying Amiran and Taleh Zang Formations have been dated as Paleocene in age. However, the base of the Paleocene within the Gurpi Formation lacks NP1 and NP2 zones, implying a hiatus of ∼2 m.y. at ca. 65.5 Ma, which is inferred to correspond to an early folding phase near the Cretaceous-Paleocene boundary. The upper part of the Kashkan Formation is dated to the earliest Eocene by palynostratigraphy. A large hiatus (or very slow deposition) lasting about 15 m.y. occurs between the Kashkan and Shahbazan Formations in the studied region. The base of the prograding Shahbazan platform deposits is dated by 87Sr/86Sr stratigraphy at ca. 33.9 Ma. The upper part of the Asmari Formation is dated as early-middle Miocene using foraminifera associations. Reconstruction of the Amiran-Taleh Zang-Kashkan succession of the Amiran Basin indicates a thickening of the basin fill from the southern pinch-out along the SE flank of the Kabir Kuh anticline to SW of the Khorramabad anticline, where the flexure is at least 900 m. In contrast, the NE part of the basin underwent coeval contraction and uplift of ∼1300 m. Superimposed smaller undulations onto the large-scale flexure are interpreted as Late Cretaceous-Paleocene folds. Regional comparisons (SE Zagros, Oman, and Turkey) indicate that Late Cretaceous-Early Tertiary deformation affected the entire NE margin of Arabia but that compression was not synchronous, being younger in Lurestan than in the NW Persian Gulf where inversion tectonics occurred from Turonian to mid-Campanian times. The long sedimentary hiatus spanning most of the middle and late Eocene must have been related to deep lithospheric processes linked to the initial events of the protracted closure of the Neotethys Ocean between Arabia and central Iran. The tectono-sedimentary history recorded in the Zagros Basin may help to understand early foreland basin growth in other orogens in which subsequent continental collision has obliterated these early events.

Palynology and petroleum potential of the Kazhdumi Formation (Cretaceous: Albian–Cenomanian) in the South Pars field, northern Persian Gulf

The Kazhdumi Formation of the Bangestan Group is a well-known source rock that has produced abundant oil in most petroleum fields in the Zagros Basin, which stretches from northwest to southwest Iran over hundreds of kilometres. The formation reaches a thickness of 230 m at the type section in northwest Zagros but thins out to 40–50 m in wells studied from the South Pars giant petroleum field, where it comprises mainly grey shales with occasional intercalations of marls and sandstones. South Pars, best known as the Iranian part of the world's largest non-associated gas field, contains small quantities of oil above and below the Kazhdumi Formation. Palynology has been used to assess the age and palaeoenvironment of the Kazhdumi Formation and to evaluate its petroleum potential. A total of 68 ditch cutting samples recovered from five wells, of which four are oil-prone, have been analyzed. An age between late Albian and Cenomanian is established for the formation based on dinoflagellate cyst biostratigraphy, and four palynofacies types have been recognized using the relative proportions of terrestrial elements, marine palynomorphs and amorphous organic matter (AOM). The ratio of terrestrial to marine elements is high in most samples, indicating a nearshore sedimentary environment. Twenty-two samples from the four oil-prone wells were also selected for geochemical analysis using Rock-Eval pyrolysis. Results show that the Kazhdumi Formation at South Pars, in contrast to the Zagros Basin, is gas-prone (predominantly type III kerogen), thermally immature, and poor in terms of hydrocarbon generation. It could not have produced the oil in those oil-prone wells studied.

Difference in the GPS deformation pattern of North and Central Zagros (Iran)

SUMMARY Measurements on either side of the Kazerun fault system in the Zagros Mountain Belt, Iran, show that the accommodation of the convergence of the Arabian and Eurasian Plates differs across the region. In northwest Zagros, the deformation is partitioned as 3‐6 mm yr −1 of shortening perpendicular to the axis of the mountain belt, and 4‐6 mm yr −1 of dextral strikeslip motion on northwest‐southeast trending faults. No individual strike-slip fault seems to slip at a rate higher than ∼ 2m m yr −1 . In southeast Zagros, the deformation is pure shortening of 8 ± 2m m yr −1 occurring perpendicular to the simple folded belt and restricted to the Persian Gulf shore. The fact that most of the deformation is located in front of the simple folded belt, close to the Persian Gulf, while seismicity is more widely spread across the mountain belt, confirms the decoupling of the surface sedimentary layers from the seismogenic basement. A comparison with the folding and topography corroborates a southwestward propagation of the surface deformation. The difference in deformation between the two regions suggests that right-lateral shear cumulates on the north‐south trending Kazerun strike-slip fault system to 6 ± 2m m yr −1 .

Geological applications of Landsat Enhanced Thematic Mapper (ETM) data and Geographic Information System (GIS): Mapping and structural interpretation in south-west Iran, Zagros Structural Belt

Arabia-Eurasia convergence is achieved in north-west Zagros by a combination of shortening on NW-SE-trending folds and thrusts, mainly in the Zagros Structural Belt, and by right-lateral strike-slip on the NW-SE-trending Main Recent Fault. Structural patterns are often used as indicators of major features on the surface. In the present study, Landsat Enhanced Thematic Mapper (ETM) data from 9 November 2002 was digitally processed to enhance the structural patterns. The contrast stretching of ETM band 4 was found to be the best in displaying lineaments and folds for the area, hence was further processed by using directional filters and generating different combinations of false colour composites (FCCs). Finally, a structural map of the study area (Dezful-Brojerd) was prepared using the processed ETM images. This study indicates that the Landsat ETM data are useful for locating and interpretation of the structural features in the Zagros Structural Belt. Examination of the Landsat ETM 2002 images combined with field visits revealed that the area is highly active and structurally is in a dynamic state due to compressional forces. However the density of the structural features on the imagery calibrated to several field visit data shows that the south and south-east of the study area are not as tectonically active. This may be due to presence of thick evaporite sequence of Gachsaran Formation on the Landsat image.