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  • 1
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    Local and regional P wave spectral attenuation model for Iran (2020)
    Oxford University Press
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    Publication Date: 2020-09-22
    Description: Summary A robust frequency-dependent local and regional P wave attenuation model is estimated for continental paths in the Iranian Plateau. In order to calculate the average attenuation parameters, 46337 vertical-component waveforms related to 9267 earthquakes, which are recorded at the Iranian Seismological Center (IRSC) stations, have been selected in the distance range 10 to 1000 km. The majority of the event's magnitudes are less than 4.5. This collection of records provides high spatial ray path coverage. Results indicate that the shape of attenuation P wave curve versus distance is not uniform and has three distinct sections with hinges at 90 and 175 km. A tri-linear model for attenuation of P wave amplitude in the frequency range 1–10 Hz is proposed in this study. Fourier spectral amplitudes are found to decay as R−1.2 (where R is hypocentral distance), corresponding to geometric spreading within 90 km from the source. There is a section from 90 to 175 km, where the attenuation is described as R0.8, and the attenuation is described well beyond 175 km by R−1.3. Moreover, the average quality factor for Pg and Pn waves (QPg and QPn), related to anelastic attenuation is obtained as Qpg = (54.2 ± 2.6)f(1.0096±0.07) and Qpn = (306.8 ± 7.4)f (0.51±0.05). There is a good agreement between the results of the model and observations. Also, the attenuation model shows compatibility with the recent regional studies. From the results it turns out that the amplitude of P waves attenuates more rapidly in comparison with the global models in local distances.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Royal Astronomical Society.
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  • 2
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    Developing a customized system for generating near real time ground motion ShakeMap of Iran’s earthquakes (2020)
    Taylor & Francis
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    Publication Date: 2020-10-14
    Print ISSN: 1363-2469
    Electronic ISSN: 1559-808X
    Topics: Architecture, Civil Engineering, Surveying , Geosciences
    Published by Taylor & Francis
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  • 3
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    Analysis of artifacts and systematic errors of the Iranian Seismological Center’s earthquake catalog (2019)
    Springer
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    Publication Date: 2019-05-01
    Description: This study reviews the history of seismometry in Iran and specifically the evolution of Iranian Seismological Center’s (IRSC) seismic network and investigates the artifacts and systematic errors of this center’s earthquake catalog. Our analysis indicates instability of magnitude estimation in the IRSC catalog to the extent that in the western and eastern parts of Iran, events with the same USGS reported mb magnitude could result in MN values 0.3 units apart. This catalog is contaminated with quarry and mine blasts, in which about 19% of the reported events are most likely not tectonic earthquakes. In addition, heterogeneity of magnitude of completeness as a function of space and time is observed. While Mc has gradually improved since 2006, its reduction in different parts of the country varies between 0 to 0.5 units of magnitude. In addition to artifacts, more than 54% of the reported events were located using a simplified velocity model and need to be relocated using more accurate velocity models. Moreover, in the hypocenter determination of about 7% of earthquakes, at least data from one station with wrong coordinates was employed. For these two groups of events, a clear dependence exists between the azimuthal gap and the value of the observed shift in the location parameters; with increasing the azimuthal gap, the shift increases. Investigations on the manually picked phases in the IRSC catalog show a large number of phase misidentification cases which are the other source of systematic errors. Examining the depth reported for events associated with mine blasts in a region in southern Iran implies systematic errors and high overestimation of depth for these events. The reported depth for most of these blasts is more than 10 km. © 2019, Springer Nature B.V.
    Print ISSN: 1383-4649
    Electronic ISSN: 1573-157X
    Topics: Geosciences , Physics
    Published by Springer
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  • 4
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    Investigating the role of source mechanism, surface topography, and attenuation on the observed PGA pattern in May 28, 2004, Mw 6.2 Baladeh earthquake (Iran) (2016)
    Springer
    Details
    Publication Date: 2016-01-08
    Description: In this paper, we use seismic waveform simulation to investigate the influence of source mechanism complexity, surface topography, and quality factor on the observed peak ground motions in May 28, 2004, moment magnitude (Mw) 6.2 Baladeh earthquake. The observed peak ground acceleration (PGA) pattern in this event, which is the biggest earthquake to hit the Central Alborz Mountains of Iran in modern instrumental era, is irregular in some respects. First, the observed PGA contours are elongated toward north-west and, second, the maximum observed PGA value of 1049 cm/s2 on the horizontal component of Hasan Keyf station 50 km away from the epicenter is quite high and irregular for an earthquake of this magnitude, at such long distance. In this study, we employ the spectral element method, implemented in SPECFEM3D software package to simulate the 3D wave propagation from several source models in the area. Our results suggest directivity effect is the main cause of the anomalous observations in this earthquake and could account for the elongation of PGA contours and also the anomalous maximum PGA value observed at Hasan Keyf strong motion station. We show that the surface topography has minor effect on the observed peak ground acceleration and the resulting PGA maps. Also by finding the bounds of seismic quality factor effect on the peak ground acceleration values, we show that this factor could not account for the elongation of iso-acceleration contours in the north-west direction. © 2016, Springer Science+Business Media Dordrecht.
    Print ISSN: 1383-4649
    Electronic ISSN: 1573-157X
    Topics: Geosciences , Physics
    Published by Springer
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  • 5
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    The Iranian Seismological Center’s Performance during the COVID-19 Pandemic and after the Occurrence of Large Earthquakes (2020)
    Seismological Society of America
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    Publication Date: 2020-12-02
    Description: The COVID-19 pandemic is an ongoing global health emergency that has overshadowed almost all aspects of human life in most of the world. The seismic monitoring centers are a crucial component of the earthquake crisis management, and continuity of their operations during different crises is critical. Occurrence of any unusual condition (such as COVID-19 crisis) could result in failures in detecting seismic events. This article aims to share the experiences at the Iranian Seismological Center (IRSC) in 2020 during the first months of the COVID-19 epidemic: how the monitoring changed in comparison with the routine surveillance system. One of the main impacts of the pandemic was loss of active stations due to a halt in routine maintenance visits to the seismic stations. The restrictions imposed by the government to contain the virus resulted in loss of 8% of the stations of IRSC network. We analyze how seismic noise changed during the lockdown. The results show that unlike many other places in the world, Iran did not see a seismic noise reduction during the lockdowns from the pandemic. In addition, we describe the response of IRSC following large earthquakes. The increase in workload after big earthquakes is discussed and some lessons from these crises are shared. The need to update seismic monitoring software to allow for some automatic processing and to carefully revise the processing routines to balance the workload during large earthquakes is discussed. Also, re-evaluation of seismic station locations for better maintenance access could lead to fewer problems at the time of crisis like the current pandemic.
    Print ISSN: 0895-0695
    Electronic ISSN: 1938-2057
    Topics: Geosciences
    Published by Seismological Society of America
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