Journal: Iranian Journal of Geophysics

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Publisher

Iranian Geophyisical Society

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ISSN

2008-0336
2783-168X

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2021 - 20232
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Publications 1 - 2 of 2
  • Distribution of tropospheric ozone over southwest Asia
    Item type: Journal Article
    Damanafshan, Mahsa; Ali Aliakbari Bidokhti, Abbas; Alizadeh, Omid; et al. (2023)
    Iranian Journal of Geophysics
    In this study, the distribution of tropospheric ozone as an air pollutant and an important greenhouse gas has been investigated in various layers of the troposphere over Southwest Asia. This research has been conducted for a 5-year period (2012-2016) using the Copernicus Atmosphere Monitoring Service Reanalysis (CAMSRA) dataset, the result of the third European Centre for Medium-Range Weather Forecasts (ECMWF) project on atmospheric composition reanalysis. The analysis of the monthly mean concentration of tropospheric ozone over Southwest Asia and its time series (6-hourly data for the 5-year period) over three areas in northwestern and southeastern Iran, and Tehran show that the concentration of ozone has an annual cycle, with the maximum in summer. The maximum ozone in different layers of the troposphere (at the surface, and 700 and 500 hPa) occurs during summer. The maximum concentration in the lower layers (up to 700 hPa) is mostly caused by anthropogenic sources, while in the middle to upper troposphere, it is the result of the injection of stratospheric air into the troposphere. The high concentration of NO2 in highly populated metropolitan areas, such as Tehran and industrial areas in the Persian Gulf and the Gulf of Oman, contributes to the photochemical production of ozone. In these areas, the concentration of ozone is higher during the daytime and summer compared to the nighttime and winter. This is due to the increase in the photochemical production of ozone when the incoming solar radiation is high. Moreover, there are two hot spots of ozone concentration at 500 hPa over two regions: the eastern Mediterranean region and the east of the Caspian Sea toward Afghanistan. Large-scale subsidence and the occurrence of the tropopause fold and/or the stratosphere to troposphere transport (STT) in these two regions, linked to the Indian summer monsoon, are the main causes of the occurrence of high concentrations of ozone in the middle troposphere. The monsoon diabatic heating can induce Gill-type Rossby waves that propagate westward and cause descent via the interaction with the midlatitude westerlies. The topography of the region, e.g., the Zagros Mountains, is also effective in increasing this descent. In general, every horizontal airflow that encounters steep isentropic slopes at the upper and middle troposphere is forced to descend. We were able to detect a wave-like pattern in ozone concentration at the 300 hPa level, which can be linked to a corresponding pattern of vertical velocities in the region. Furthermore, the statistical analysis indicates that high ozone concentration events frequently occur in southeastern Iran. This could be due to transient variations in the monsoon circulation over India, the Tibetan anticyclone, and the mid-level anticyclone, all of which also affect the transport of the stratospheric ozone in the region.
  • Estimation of earthquake occurrence rate based on the crust deformation of Iran
    Item type: Journal Article
    Lotfi, Alireza; Zafarani, Hamid; Khodaverdian, Alireza (2021)
    Iranian Journal of Geophysics
    The Iranian Plateau is one of the most seismically active regions in the world, where the recurrence time of large-magnitude events is often more than a thousand years. The Mw 7.3, 1990 Rudbar earthquake, which caused 40,000 deaths and 500,000 homeless, and the Mw 6.5, 2003 Bam earthquake, which caused around 26,000 losses and 30,000 wounded, are two of the largest and the most destructive earthquakes in the region. Seismic hazard assessment is useful in the classification of areas that are more prone to earthquake losses. The earthquake occurrence rate is an important factor in seismic hazard analysis, which is commonly based on the earthquake catalogs. Hence, providing complete and reliable catalogs is necessary to achieve more accurate estimates. Unfortunately, factors such as the incompleteness of catalogs, the long-term recurrence time of large earthquakes, and the inadequate short-term instrumental record of about 100 years have resulted in unreliable earthquake occurrence rates estimates. To reduce uncertainties, some models have been developed for some places in the world such as California, Canada, Japan, New Zealand, and Italy based on the combination of various data as inputs, such as seismicity information, geological data such as fault slip rates, and geodetic information such as GPS data. The utilization of these models can increase the knowledge about the spatio-temporal distribution of earthquakes and reduce the uncertainty of results. The purpose of this study is to convert the strain rate into the earthquakes occurrence rate for some zones in Iran. Strain rates are derived from the available comprehensive deformation model of the Iranian Plateau, in which the long-term crustal flow of the Iranian Plateau is computed by using various data sets, including the latest fault traces, geologic fault offset rates, GPS velocities, principal stress directions, and velocity boundary conditions. In the comprehensive deformation model of the Iranian Plateau, based on the existing information on relative displacement of geologic features, the long-term geological offset rates for 33 of 171 fault traces were collected as input. Moreover, geodetic velocities of 239 GPS benchmarks were considered. Comparison with the results of the existing catalogs shows that for the whole Iranian Plateau, the occurrence rate based on strain is higher than the occurrence rate based on the catalog. We expect that utilizing the occurrence rate based on strain in the hazard model in further studies can have a significant effect on the ground motion parameters for Iran in comparison with previous catalog-based seismic hazard assessments.
Publications 1 - 2 of 2