Seismotectonic-Geologic Hazards Zoning of Iran

Seismotectonic-geologic hazards zoning map of Iran is drawn based on deterministic seismic hazards evaluation using the seismicity records, structural trends, tectonic settings, fault ruptures and neotectonics activities in Iran. This map has been prepared to indicate the seismotectonic-geologic hazards of Iran. It contains the earthquake hazards parameters such as b value and Mmax for the nineteen seismotectonic provinces. Furthermore, Moho discontinuity depth, seismogenic layer depths and seismic rates for all provinces are investigated. The majority of deformation in Iran has been concentrated in the continental crust of the country. Zagros and Alborz experience deep earthquakes that are an indication of existence of the thick-skinned tectonics. Finally, some provinces such as Piranshahr- Borojen, East Iran, Naien- Rafsanjan and East Alborz, which include main suture zones of Iran, have faced high seismic hazards.


INTRODUCTION
The deterministic assessment of the seismotectonic-geologic hazards of Iran involves specifying the magnitude ranges and dominant mechanism of earthquakes that might bring about destructive effects on the regions and main cities.A seismotectonic province is a homogenous statistical unit that has distinguishable time, location and magnitude ranges for expected seismic events (Arian, 2010).Each seismotectonic province has a range of seismogenic layer depths and dominant mechanism of earthquakes, as these are related to tectonic settings, neotectonics activities, Mechanical Stratigraphy and deformational models of crust.Therefore, earthquake hazard parameters can be estimated for them.
In this study, regional tectonics (Qorashi and Arian, 2011) was integrated with seismologic data to prepare the seismotectonic-geologic hazards of Iran.The main steps in this study have been summarised as follows: -Seismic records such as archaeological, historical (Berberian andYeats, 1999, 2001) and instrumental seismic data up to the year 2014 which have provided information on the seismic sources have been gathered from different sources.
The Seismotectonic-geologic hazards map is identified based on the physiographic-tectonic zoning map of Iran's sedimentary basins (Arian, 2013).These basins described the locations of different structural units of Iran (Fig. 1).
-Seismicity parameters were estimated for each seismotectonic province.

Materials and Methods
At the first time, Ambraseys and Melville (1982) provided Iran's historical earthquakes and, subsequently, Earthquake Catalogue of Iran was compiled by Berberian (1994).Investigation of seismicity of Iran reveals that significant destructive earthquakes are related to the primary active faults of different tectonics settings (Engdahl, et al., 2006).Iran is one of the seismically active areas of the Alpine-Himalayan orogenic belt.

Earthquake Hazard Parameters
Seismic hazard analysis requires an assessment of earthquake hazard parameters and the future earthquake potential in a region.Earthquake hazard parameters such as, maximum expected magnitude, Mmax, seismic rate and b value have been evaluated for each seismotectonic province of Iran by Kijko and Selevoll (1992) method.The results, which are shown in Table 1, were estimated for each seismotectonic provinces of Iran.

Zagros province
The dominant structural trends in Zagros province (Fig. 2) are NW-SE in north-western part and E-W in the south-eastern section.From tectonics  point of view, this province contains the overthrust and simple folded belts of Zagros which has been formed in the north-eastern part of Arabian plate's passive margin.Zagros Mountains extend to East Taurus Mountains in Turkey and are called Zagros-East Taurus hinterland (Fig. 1).Focal mechanisms of numerous earthquakes are reversed and thrust (Beberian, 1995) such as Naghan and Ardal (Ms=6.1, 1977) and/ or right slip in related to N-S strike slip faults such as Kazeron (SE Boshehr Ms=6.2, 2013) or Kareh Bas (Firozabad-Fars Ms=6.1, 1994, Arian et al, 2006).Zagros province experiences low to moderate earthquakes with high frequency, short repeat time and 10-20Km focal depth.The intensity of earthquakes is in middle levels in which there are several ductile rocks (thick evaporates) in sedimentary covers such as Hormuz, Dashtak, and Gachsaran formations.Sometimes in the northern margin of this province, focal depths exceed to 70Km (Hatzfeld et al.2003) that is an indication of initial stages of thick-skinned tectonics.The most severe seismic hazards in Zagros province, including large cities such as Ilam, Ahvaz, Yasoj, Boshehr and Shiraz, are landslides in high regions of northern margins, settlements in some lowlands and coastal areas and Tsunami in southern margins.

Piranshahr-Borojen province
The dominant structural trend in Piranshahr-Borojen province (Fig. 2) is NW-SE.From tectonics point of view, this province contains the north margin of overthrust belts of Zagros formed on the north-eastern part of Arabian plate's passive margin.Focal mechanisms of several earthquakes are a right slip about main recent faults of Zagros such as Doroud (Ms=6.1, 2006).
Piranshahr-Borojen province is struck by moderate to high earthquakes with low frequency, long repeat time and 10-15Km focal depth.The intensity of earthquakes is at high levels.Sometimes, focal depths exceed to 70Km which is an indication of initial stages of thick-skinned tectonics.The most severe seismic hazards in Piranshahr-Borojen province, including cities such as Kermanshah, Khoramabad, Borojerd and Shahrekod, are landslides in high regions of northern margins, settlements in some lowlands and surface faulting.

Bandar-E Abbas province
The dominant structural trend in Bandar-e Abbas province (Fig. 2) is NE-SW.From tectonics point of view, this province contains the south-eastern part of overthrust and simple folded belts of Zagros.Focal mechanisms of several earthquakes are reversed and thrust such as Khorgo (Ms=7, 1977).
Bandar-e Abbas province is hit by moderate to high earthquakes with low frequency, short repeat time and 10-20Km focal depth.The intensity of earthquakes is in middle levels in which there are ductile rocks in sedimentary covers.The most severe seismic hazards in Bandar-e Abbas province, containing large cities such as Bandar-e Abbas, Gheshm, Bandar-e Lengeh and Hajiabad, are rapid uplifting in northern margins, settlements in some lowlands and coastal areas and Tsunami in southern margins.

Makran province
The dominant structural trend in Makran province (Fig. 2) is E-W.From tectonics point of view, this province contains the accretionary prism on trench of Oman sea subduction that extends to Pakistan (Fig. 1).Focal mechanisms of a vast number of earthquakes are reversed and thrust such as Pasni in Pakistan (Ms=8.3, 1945).Makran province experiences low to moderate earthquakes with low frequency, very long repeat time and down to 20Km focal depth.The intensity of earthquakes is in the middle to high levels.The most severe seismic hazards in Makran province, which contains large cities such as Bandar-e Chabahar and Nikshahr, are rapid uplifting in northern margins, settlements in some lowlands and coastal area and Tsunami in southern margins.

Jazmorian province
The dominant structural trend in Jazmorian province (Fig. 2) is E-W.From tectonics point of view, this province contains a fore arc basin (Jazmorian plain) which extends to Mashkel plain in Pakistan (Fig. 1).Focal mechanisms of many earthquakes are reversed and thrustand sometimes normal (in relation to bending of subducting oceanic lithosphere) such as NW Saravan with 69 Km focal depth (Ms=5.2,2009) and SE Khash with 82 Km focal depth (Ms=7.7,2013).Jazmorian province experiences moderate earthquakes with middle frequency, medium repeat time and down to 150Km focal depth.The intensity of earthquakes is in middle levels by very deep hypocenters.
The most important seismic hazards in the Jazmorian province, containing large cities such as Saravan and Iranshahr, are rapid uplifting and settlements in some lowlands.It should be noted that low seismicity in Makran and Jazmorian provinces is related to slow subduction rate and steeper dip of Benioff zone.Current subduction rate of oceanic crust (related to late Cretaceous) is 19 millimetres per year (Vernant et al. 2004).

Urmieh-Sirjan province
The dominant structural trend in Urmieh-Sirjan province (Fig. 2) is NW-SE.From tectonics point of view, this province contains two different units: A) Urmieh-Dokhtar magmatic arc (Fig. 1) which is the result of subduction beneath the southern active continental margin of Cimmerian plate.B) Sanandaj-Sirjan overthrust belts (Fig. 1) is formed by metamorphic rocks of the north-eastern part of Arabian plate (Alavi, 1994).Focal mechanisms of several earthquakes are reversed and thrust such as Changureh (Ms=6.4, 2002) The Urmieh-Sirjan province is struck by low to moderate earthquakes with low frequency, medium repeat time and down to 10Km focal depth.The intensity of earthquakes is in high levels in which there are cold igneous rocks.Sometimes, focal depths exceed to 70Km that it is an indicator for initial stages of thick-skinned tectonics.The most serious seismic hazards in Urmieh-Sirjan province, which contains large cities such as Urmieh, Sirjan, Sanandaj, Hamadan, Arak, Ghom and Isfahan, are landslides in high regions of northern margins, settlements in some lowlands and surface faulting.

Lut province
The dominant structural trend in Lut province (Fig. 2) is NW-SE.From tectonics point of view, this province contains a retro arc (back arc) basin (Lut plain) which extends to Helmand plain in Pakistan (Fig. 1).Focal mechanisms of several earthquakes are reversed and thrust and/ or right slip about N-S strike slip faults such as Nayband and Nehbandan.
Lut province experiences low earthquakes with low frequency, medium repeat time and down to 10Km focal depth.The intensity of earthquakes is in high levels in which there are hot igneous rocks.The most serious seismic hazards in Lut province, which contains Lut plain, are settlements, surface faulting and volcanic hazards in southern and western parts of the plain.

East Iran province
The dominant structural trend in East Iran province (Fig. 2) is N-S.From tectonics point of view, this province contains a collision belt brought about by eastward subduction of East-Central Iran miniplate (Fig. 1) beneath Central blocks of Afghanistan.This collision belt has been formed by a dextral transpression zone.Focal mechanisms of many earthquakes are right slip in relation to N-S strike slip faulting such as Zirkuh (Berberian et al.,1999) in Qa'enat (Ms=7.2,1997) and thrust such as west Zabol (Ms=6.2, 1993).
East Iran province is hit by moderate to high earthquakes with middle to high (on fault terminations) frequency, medium repeat time and down to 15Km focal depth.The intensity of earthquakes is at high levels.The most serious seismic hazards in East Iran province, which contains large cities such as Nehbandan, Zahedan and Khash, are landslides in high regions, settlements in some lowlands, surface faulting and dispersed volcanic hazards.

Gonabad-Birjand province
The dominant structural trend in Gonabad-Birjand province (Fig. 2) is NW-SE.From tectonics point of view, this province contains the northern part of East-Central Iran miniplate (Fig. 1).It has been impressed by splays at the north termination of Nehbandan fault system.Focal mechanisms of numerous earthquakes are left slip in relation to W-E strike slip faulting such as Dasht-e Bayaz (Ms=7.4,1968) and right slip in relation to NW-SE strike slip with thrust component along longitudinal faults such as South Ghaen (Ms=5.6, 2012).
Gonabad-Birjand province experiences moderate to high earthquakes with low frequency, long repeat time and down to 10Km focal depth.The intensity of earthquakes is at high levels.The most serious seismic hazards in Gonabad-Birjand province, which contains large cities such as Gonabad and Birjand, are landslides in high regions, settlements in some lowlands, and surface faulting.

Tabas-Minab province
The dominant structural trend in Tabas-Minab province (Fig. 2) is N-S.From tectonics point of view, this province contains the Tabas, Nayband, Kuh Banan, Gowk, Bam, Sazvaran and Minab fault systems.Focal mechanisms of several earthquakes are dextral strike-slip faulting with reverse component in southern part such as Bam (Ms=6.6, 2003) and reverse faulting with dextral strike slip component in northern part such as Tabas (Ms=7.4, 1978) and western part such as Zarand (Ms=6.5, 2004).
Tabas-Minab province experiences moderate to high earthquakes with low frequency, long repeat time and down to 15Km focal depth.The intensity of earthquakes is at high levels.Southward earthquake migration is index characteristic in this province.The most severe seismic hazards in Tabas-Minab province, containing large cities such as Tabas, Minab, Kerman, Bam, Jiroft and Jask, are landslides in high regions, settlements in some lowlands, surface faulting.

Kashmar-Anarak-Bafgh province
The dominant structural trend in Kashmar-Anarak-Bafgh province (Fig. 2) is NE-SW.From tectonics point of view, this province contains the northern and western part of East-Central Iran miniplate (Fig. 1).Focal mechanisms of several earthquakes are sinistral strike-slip faulting and thrusting.
Kashmar-Anarak-Bafgh province experiences low to moderate earthquakes with low frequency, medium repeat time and down to 20Km focal depth.The intensity of earthquakes is at low levels.The most serious seismic hazards in Kashmar-Anarak-Bafgh province, which contains large cities such as Kashmar, Anarak and Bafgh, are settlements in some lowlands and surface faulting.

Naien-Rafsanjan province
The dominant structural trend in Naien-Rafsanjan province (Fig. 2) is NW-SE.From tectonics point of view, this province contains the extensive part of Naien-Kerman retro arc foreland basin (Fig. 1).Focal mechanisms of several earthquakes are thrusting.
Naien-Rafsanjan province experiences low to moderate earthquakes with low frequency, medium repeat time and down to 20Km focal depth.The intensity of earthquakes is at low levels.The most serious seismic hazards in Naien-Rafsanjan province, which contains large cities such as Naien, Rafsanjan and Yazd, are settlements in some lowlands and surface faulting.

Great Kavir-Taibad province
The dominant structural trend in Great Kavir-Taibad province (Fig. 2) is NW-SE in the eastern part and NE-SW in the western part.From tectonics point of view, this province contains the Maiamay-Taibad marginal back arc basin, south-eastern part of Great Kavir-Urmieh lake foreland basin and South Great Kavir folded and thrust belt (Fig. 1).The latter case is the result of the collision between the northern part of East-Central Iran miniplate and southeastern part of North-Central Iran miniplate.There are many salt diapirs that have been formed by tectonic forces (Arian, 2012, Asadian and Arian 2009, Pourkermani and Arian, 1997) Focal mechanisms of several earthquakes are thrusting and dextral strike-slip faulting in the eastern part and sinistral strike slip faulting and thrusting in western part such as Garmsar (Ms=5.1, 2007).
Great Kavir-Taibad province is hit by low to moderate earthquakes with low frequency, medium repeat time and down to 10Km focal depth.The intensity of earthquakes is at low levels.The most serious seismic hazards in Great Kavir-Taibad province, which contains large cities such as Semnan, Sabzehvar and Torbat-e Heydarieh, are settlements in some lowlands and surface faulting.

East Alborz province
The dominant structural trend in East Alborz province (Fig. 2) is NW-SE in the eastern part and NE-SW in the western part.From tectonics point of view, this province contains the Torbat-e Jam-Neyshabour retro arc foreland basin and East Alborz (Fig. 1) hinterland formed in a fore arc basin on the north-eastern part of Cimmerian plate.An overthrust belt with SW vergence has been formed.Focal mechanisms of several earthquakes are thrusting such as Neyshabour (Ms=7.4, 1405).
East Alborz province experiences low to moderate earthquakes with high frequency, short repeat time and down to 20Km focal depth.The intensity of earthquakes is at high levels.The most serious seismic hazards in East Alborz province, which contains large cities such as Neyshabour, Esfaraien and Shahrod, are landslides in high regions, settlements in some lowlands, surface faulting.

Kopet Dagh-Middle Caspian province
The dominant structural trend in Kopet Dagh-Middle Caspian province (Fig. 2) is NW-SE.From tectonics point of view, this province contains the Kopet Dagh hinterland (Fig. 1) or Kopet Dagh folded and thrust belt that has been formed in the passive margin of Eurasia plate.Focal mechanisms of several earthquakes are dextral strike slip faulting such as Garmkhan-e Bojnourd (Ms=6.4, 1996) and thrusting.
Dagh-Middle Caspian province experiences low to moderate earthquakes with high frequency, short repeat time and down to 20Km focal depth.Sometimes in the northern margin of South Caspian basin, focal depths exceed to 70Km which is a depiction of its subduction.The intensity of earthquakes is at low levels.The most serious seismic hazards in Dagh-Middle Caspian province, which contains large cities such as Mashhad, Ghochan and Bojnourd, are landslides in high regions, settlements in some lowlands, and surface faulting.

South Caspian province
The dominant structural trend in South Caspian province (Fig. 2) is NW-SE in the eastern part and N-S in the western part.From tectonics point of view, this province contains the South Caspian remnant oceanic basin (Berberian, 1983) and northern foreland basin of Central Alborz hinterland (Fig. 1).Focal mechanisms of several earthquakes are reversed to thrust (Jackson et al., 2002) such as Astara (Ms=6.2, 1980).
South Caspian province is struck by low to moderate earthquakes with middle frequency, short repeat time and down to 20Km focal depth.The intensity of earthquakes is at low levels.The most serious seismic hazards in South Caspian province, which contains large cities such as Gorgan, Sary and Rasht, are settlements in some lowlands and Tsunami.

Central Alborz province
The dominant structural trend in Central Alborz province (Fig. 2) is NE-SW in the eastern part and NW-SE in the western part.From tectonics point of view, this province contains the middle part of Great Kavir-Urmieh lake foreland basin and Central Alborz hinterland (Fig. 1) that has been formed in the northern active margin of the Cimmerian plate.Focal mechanisms of several earthquakes are sinistral strike-slip faulting such as Manjil (Ms=7.3, 1990) and reversed with a sinistral strike-slip component such as Boien Zahra (Ms=7.2, 1962).
Central Alborz province experiences moderate to high earthquakes with low frequency, long repeat time and down to 20Km focal depth.The intensity of earthquakes is at high levels.The most serious seismic hazards in Central Alborz province, which contains large cities such as Tehran, Ghazvin and Zanjan, are landslides in high regions, settlements in some lowlands, surface faulting and volcanic hazards around Damavand cone.

Azerbaijan province
The dominant structural trend in Azerbaijan province (Fig. 2) is NW-SE.From tectonics point of view, this province contains the north-western part of Great Kavir-Urmieh lake foreland basin and West Alborz -lesser Caucasus hinterland (Fig. 1).Focal mechanisms of several earthquakes are dextral strike slip faulting such as Salmas (Ms=7.3, 1930) and reversed such as Varzaghan (Ms=6.2,2012), that the latter case was an index case of sympathetic fault segments in Iran.This segment has become active only 9 minutes after an earthquake (Ms=6.4)with the strike-slip dominant mechanism in another segment of the same fault.
Azerbaijan province experiences moderate to high earthquakes with high frequency, medium repeat time and down to 10Km focal depth.The intensity of earthquakes is at high levels.The most serious seismic hazards in Azerbaijan province, which contains large cities such as Tabriz, and Ardebil, are landslides in high regions, settlements in some lowlands, surface faulting and volcanic hazards around Sahand and Sebalan cones.

Persian Gulf province
The dominant structural trend in Persian Gulf province (Fig. 2) is NW-SE.From tectonics point of view, this province contains the foreland basin of Zagros hinterland (Fig. 1) which has been formed on the north-eastern passive margin of the Arabian plate.It extends to Mesopotamian terrain in Iraq.Focal mechanisms of several earthquakes are reversed or thrust.
Persian Gulf province experiences low earthquakes with low frequency, medium repeat time and 10 to 20Km focal depth.The intensity of earthquakes is at middle levels in which there are several ductile rocks in sedimentary covers such as Hormuz and Dashtak formations.The most serious seismic hazards in Persian Gulf province, which contains large cities such as Khorramshahr, Abadan, Mahshahr and Iranian islands, are settlements in some lowlands and coastal areas and Tsunami.
Table 1.Estimated seismic hazard parameters for seismotectonic provinces.

CONCLUSIONS
Seismotectonic-geologic hazards zoning map has been prepared to indicate the Seismic hazard in Iran.Characteristics of this map are as follows: The map is intended as a pattern for the assessment of the geologic hazards in Iran.Some provinces such as Zagros, Persian Gulf, Kopet Dagh-Middle Caspian and South Caspian have rarely been surface faulted.Zagros, Persian Gulf, Kopet Dagh-Middle Caspian, South Caspian Makran and Bandar-e Abbas provinces face Tsunami hazards.
The principal part of deformation in Iran has been concentrated in the continental crust of the country.Zagros and Alborz experience deep earthquakes which is an indication of the existence of thick-skinned tectonics.
Jazmorian and southern margin of Kopet Dagh-Middle Caspian provinces are struck by deep earthquakes which is an indication of slow subduction of oceanic lithosphere.
Some provinces such as Piranshahr-Borojen, East Iran, Naien-Rafsanjan and East Alborz, which include main suture zones of Iran, have faced high seismic hazards.