N. Mirzaei | University of Tehran (original) (raw)
Papers by N. Mirzaei
Temporal variations of radon concentration in soil and groundwater might be one of the few promis... more Temporal variations of radon concentration in soil and groundwater might be one of the few promising precursors for earthquake prediction. In this study, the relation between radon concentration and aftershocks of Bam Earthquake (26/12/2003, Ms=6.8) has been investigated. The radon monitoring station was located at 29N and 58.4E, precisely on Bam Fault where there have been high occurrences of seismic activities. The study was carried out using an active method involving an Alpha Gurad PQR2000, Alpha Pump and relative accessories which is a device capable of accurately measuring radon concentrations every 10 minutes. Air was being pumped from ground to the measuring
Two models, which contribute to the knowledge on intermediate term earthquake prediction are furt... more Two models, which contribute to the knowledge on intermediate term earthquake prediction are further examined, improved and applied. The first of these models, called Time and Magnitude Predictable (TIMAP) regional model is based on repeat times of mainshocks generated by tectonic loading on a network of faults which are located in a certain seismic region (faults' region). The second model, called Decelerating-Accelerating Strain (D-AS) model, is based on triggering of a mainshock by its preshocks. Parameters of the TIMAP model have been specified for the Aegean area and applied by a backward test in 86 circular faults' regions of this area. The test shows the validity of this time dependent model with 29% false alarms. Data concerning decelerating and accelerating seismic (Benioff) strain, which preceded 46 strong (M≥6.3) recent mainshocks in a variety of global seismotectonic regimes, show that the generation of a mainshock is triggered by quasi-static stress changes due to accelerating preshocks which occur in a broad (critical) region and by static stress changes due to the large number (frequency of occurrence) of small preshocks generated in a narrow (seismogenic) region. Retrospective predictions (postdictions) of these 46 mainshocks by the D-AS model confirms previous results concerning the prediction uncertainties (2σ) of the model in the origin time (± 2.5 years), epicenter location (≤ 150 km) and magnitude (± 0.4) of an ensuing mainshock with a probability ~ 80%. Information is also given on the successful prediction by the D-AS model of: 1) the Cythera strong (M = 6.9) earthquake which occurred on 8 January 2006 in the southwestern part of the Hellenic Arc and 2) of the Rhodes strong (M = 6.4) earthquake which occurred on 15 July 2008 in the Eastern part of this Arc. A backward combined application of both models in the Aegean area shows an uncertainty ≤120km in the epicenter location of an ensuing mainshock. Papazachos et al. (2006), taking into consideration the above mentioned published information on the observed accelerating and decelerating precursory seismicity and based on such seismicity which preceded globally occurred strong mainshocks (M>6.0) developed the Decelerating-Accelerating Strain (D-AS) model for intermediate term earthquake prediction. This model is based on empirical relations and parameters most of which have been also derived theoretically and can be physically interpreted.
Tehran, capital of Iran, is under the threat of large magnitude earthquakes (above 7) located on ... more Tehran, capital of Iran, is under the threat of large magnitude earthquakes (above 7) located on very near faults. Previous studies on the effect of local surface geology on earthquake ground motion by using 1D calculation of SH transfer function (Jafari et al, 2001; JICA & CEST, 2000) and by using experimental methods (Haghshenas, 2005) based on earthquake and ambient noise vibration recordings resulted in very different and unexpected results. By assuming a layer with Vs = 700 m/s as seismic bedrock, 1D SH transfer functions show indeed a weak amplification for frequencies above 2 Hz, while the site-to-reference spectral ratios exhibit a significant amplification (up to 8) within a large frequency band from 0.3 to 8 Hz. Such discrepancy might be explained by very thick and stiff sedimentary layers overlaying very rigid bedrock. In order to better constrain shear-wave velocities at depth, we thus derived dispersion curves of Rayleigh waves by using SPAC and FK array methods and ext...
Seismological Research Letters
Annals of Geophysics
This article presents the results of disaggregation of ground motion hazard obtained for two of I... more This article presents the results of disaggregation of ground motion hazard obtained for two of Iran’s urban centers, Kermanshah and Sanandaj. Disaggregation of peak ground acceleration (PGA) and spectral acceleration hazard corresponding to mean return periods of 475 and 50 years is performed. 12 area seismic sources in the study region as well as 15 area seismic sources in a 150-km distance from the region are delineated. The scenario earthquakes are characterized by bins of magnitude, M, source-to-site distance, R, and number of standard deviations, ε, that the ground-motion parameter is away from its median value for that M-R pair as estimated by a prediction equation. In most cases, the sources closer to the site dominate. Larger, more distant earthquakes contribute more significantly to hazard for longer periods than for shorter periods. Disaggregation plots can provide useful information on the distance and magnitude of predominant sources, which can be used to generate scena...
Geophysical Journal International
Annals of Geophysics
A unified catalog of earthquakes in Iran and adjacent regions (the area bounded in 22º-42ºN and 4... more A unified catalog of earthquakes in Iran and adjacent regions (the area bounded in 22º-42ºN and 42º-66ºE) covering the period of 4th century B.C. through 2012 with Mw≥4 is provided. The catalog includes all events for which magnitude have been determined by international agencies and most reliable individual sources. Since the recurrence time of maximum credible earthquake cannot be directly estimated from the mb, empirical formulae are established to convert mb to Ms, mb to Mw and Ms to Mw for each major seismotectonic province separately. The unified catalog is declustered using conjugated distance-time windows. In order to estimate completeness thresholds, magnitude-time (M-T) diagram and Stepp’s method are applied on the declustered catalog for each seismotectonic province. The magnitude of completeness (Mc) decreases with development of local and regional seismic stations. The results of present study are particularly important in seismic hazard analysis in Iran.
Bulletin of Engineering Geology and the Environment
Bulletin of the Seismological Society of America
Journal of Theoretical and Applied Physics
This study introduce a new frequency parameter called s fcwt , which can be used to estimate eart... more This study introduce a new frequency parameter called s fcwt , which can be used to estimate earthquake magnitude on the basis of the first few seconds of P-waves, using the waveforms of earthquakes occurring in Japan. This new parameter is introduced using continuous wavelet transform as a tool for extracting the frequency contents carried by the first few seconds of P-wave. The empirical relationship between the logarithm of s fcwt within the initial 4 s of a waveform and magnitude was obtained. To evaluate the precision of s fcwt , we also calculated parameters s max p and s c. The average absolute values of observed and estimated magnitude differences (jM est À M obs j) were 0.43, 0.49, and 0.66 units of magnitude, as determined using s max p , s c , and s fcwt , respectively. For earthquakes with magnitudes greater than 6, these values were 0.34, 0.56, and 0.44 units of magnitude, as derived using s max p , s c , and s fcwt , respectively. The s fcwt parameter exhibited more precision in determining the magnitude of moderate-and small-scale earthquakes than did the s c-based approach. For a general range of magnitudes, however, the s max p-based method showed more acceptable precision than did the other two parameters. Keywords Early warning systems Á Continuous wavelet transform Á Magnitude estimation relation Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Journal of Seismology, 1999
A total of 235 potential seismic sources in Iran and neighboring regions are delineated based on ... more A total of 235 potential seismic sources in Iran and neighboring regions are delineated based on available geological, geophysical, tectonic and earthquake data for seismic hazard assessment of the country. In practice, two key assumptions are considered; first, the assumption of earthquake repeatedness, implying that major earthquakes occur preferentially near the sites of previous earthquakes; second, the assumption of tectonic analogy, which implies that structures of analogous tectonic setting are capable of generating same size earthquakes. A two-step procedure is applied for delineation of seismic sources: first, demarcation of seismotectonic provinces; second, determination of potential seismic sources. Preferentially, potential seismic sources are modeled as area sources, in which the configuration of each source zone is controlled, mainly, by the extent of active faults, the mechanism of earthquake faultings and the seismogenic part of the crust.
We have investigated local seismicity around Shahroud fault system at the eastern Alborz. This fa... more We have investigated local seismicity around Shahroud fault system at the eastern Alborz. This fault system plays significant role in the tectonic of the east Alborz. In this paper we analyzed micro-earthquakes recorded by three networks; two local temporary dense seismological networks installed around a part of Shahroud fault system for several months during 2007 and 2008 and the permanent seismological network of the Geophysics Institute of University of Tehran. The seismicity of both permanent and temporary networks have been distributed around Shahroud fault system, especially the Astaneh fault. Processing the data concludes a P wave velocity structure range within the east Alborz from 5.4 km/s to 6.3 km/s between the surface and upper than the Moho depth. We suggested 4 km for sedimentary cover thickness and the seismogenic zone thickness was obtained 20 km. Also two near vertical seismicity dips corresponding with two segments of the Astaneh fault were specified. We detected a north-dipping blind fault at the south of the area which helps us suggesting the flower structure as subsurface geometry of the faults at the eastern Alborz.
Temporal variations of radon concentration in soil and groundwater might be one of the few promis... more Temporal variations of radon concentration in soil and groundwater might be one of the few promising precursors for earthquake prediction. In this study, the relation between radon concentration and aftershocks of Bam Earthquake (26/12/2003, Ms=6.8) has been investigated. The radon monitoring station was located at 29N and 58.4E, precisely on Bam Fault where there have been high occurrences of seismic activities. The study was carried out using an active method involving an Alpha Gurad PQR2000, Alpha Pump and relative accessories which is a device capable of accurately measuring radon concentrations every 10 minutes. Air was being pumped from ground to the measuring
Two models, which contribute to the knowledge on intermediate term earthquake prediction are furt... more Two models, which contribute to the knowledge on intermediate term earthquake prediction are further examined, improved and applied. The first of these models, called Time and Magnitude Predictable (TIMAP) regional model is based on repeat times of mainshocks generated by tectonic loading on a network of faults which are located in a certain seismic region (faults' region). The second model, called Decelerating-Accelerating Strain (D-AS) model, is based on triggering of a mainshock by its preshocks. Parameters of the TIMAP model have been specified for the Aegean area and applied by a backward test in 86 circular faults' regions of this area. The test shows the validity of this time dependent model with 29% false alarms. Data concerning decelerating and accelerating seismic (Benioff) strain, which preceded 46 strong (M≥6.3) recent mainshocks in a variety of global seismotectonic regimes, show that the generation of a mainshock is triggered by quasi-static stress changes due to accelerating preshocks which occur in a broad (critical) region and by static stress changes due to the large number (frequency of occurrence) of small preshocks generated in a narrow (seismogenic) region. Retrospective predictions (postdictions) of these 46 mainshocks by the D-AS model confirms previous results concerning the prediction uncertainties (2σ) of the model in the origin time (± 2.5 years), epicenter location (≤ 150 km) and magnitude (± 0.4) of an ensuing mainshock with a probability ~ 80%. Information is also given on the successful prediction by the D-AS model of: 1) the Cythera strong (M = 6.9) earthquake which occurred on 8 January 2006 in the southwestern part of the Hellenic Arc and 2) of the Rhodes strong (M = 6.4) earthquake which occurred on 15 July 2008 in the Eastern part of this Arc. A backward combined application of both models in the Aegean area shows an uncertainty ≤120km in the epicenter location of an ensuing mainshock. Papazachos et al. (2006), taking into consideration the above mentioned published information on the observed accelerating and decelerating precursory seismicity and based on such seismicity which preceded globally occurred strong mainshocks (M>6.0) developed the Decelerating-Accelerating Strain (D-AS) model for intermediate term earthquake prediction. This model is based on empirical relations and parameters most of which have been also derived theoretically and can be physically interpreted.
Tehran, capital of Iran, is under the threat of large magnitude earthquakes (above 7) located on ... more Tehran, capital of Iran, is under the threat of large magnitude earthquakes (above 7) located on very near faults. Previous studies on the effect of local surface geology on earthquake ground motion by using 1D calculation of SH transfer function (Jafari et al, 2001; JICA & CEST, 2000) and by using experimental methods (Haghshenas, 2005) based on earthquake and ambient noise vibration recordings resulted in very different and unexpected results. By assuming a layer with Vs = 700 m/s as seismic bedrock, 1D SH transfer functions show indeed a weak amplification for frequencies above 2 Hz, while the site-to-reference spectral ratios exhibit a significant amplification (up to 8) within a large frequency band from 0.3 to 8 Hz. Such discrepancy might be explained by very thick and stiff sedimentary layers overlaying very rigid bedrock. In order to better constrain shear-wave velocities at depth, we thus derived dispersion curves of Rayleigh waves by using SPAC and FK array methods and ext...
Seismological Research Letters
Annals of Geophysics
This article presents the results of disaggregation of ground motion hazard obtained for two of I... more This article presents the results of disaggregation of ground motion hazard obtained for two of Iran’s urban centers, Kermanshah and Sanandaj. Disaggregation of peak ground acceleration (PGA) and spectral acceleration hazard corresponding to mean return periods of 475 and 50 years is performed. 12 area seismic sources in the study region as well as 15 area seismic sources in a 150-km distance from the region are delineated. The scenario earthquakes are characterized by bins of magnitude, M, source-to-site distance, R, and number of standard deviations, ε, that the ground-motion parameter is away from its median value for that M-R pair as estimated by a prediction equation. In most cases, the sources closer to the site dominate. Larger, more distant earthquakes contribute more significantly to hazard for longer periods than for shorter periods. Disaggregation plots can provide useful information on the distance and magnitude of predominant sources, which can be used to generate scena...
Geophysical Journal International
Annals of Geophysics
A unified catalog of earthquakes in Iran and adjacent regions (the area bounded in 22º-42ºN and 4... more A unified catalog of earthquakes in Iran and adjacent regions (the area bounded in 22º-42ºN and 42º-66ºE) covering the period of 4th century B.C. through 2012 with Mw≥4 is provided. The catalog includes all events for which magnitude have been determined by international agencies and most reliable individual sources. Since the recurrence time of maximum credible earthquake cannot be directly estimated from the mb, empirical formulae are established to convert mb to Ms, mb to Mw and Ms to Mw for each major seismotectonic province separately. The unified catalog is declustered using conjugated distance-time windows. In order to estimate completeness thresholds, magnitude-time (M-T) diagram and Stepp’s method are applied on the declustered catalog for each seismotectonic province. The magnitude of completeness (Mc) decreases with development of local and regional seismic stations. The results of present study are particularly important in seismic hazard analysis in Iran.
Bulletin of Engineering Geology and the Environment
Bulletin of the Seismological Society of America
Journal of Theoretical and Applied Physics
This study introduce a new frequency parameter called s fcwt , which can be used to estimate eart... more This study introduce a new frequency parameter called s fcwt , which can be used to estimate earthquake magnitude on the basis of the first few seconds of P-waves, using the waveforms of earthquakes occurring in Japan. This new parameter is introduced using continuous wavelet transform as a tool for extracting the frequency contents carried by the first few seconds of P-wave. The empirical relationship between the logarithm of s fcwt within the initial 4 s of a waveform and magnitude was obtained. To evaluate the precision of s fcwt , we also calculated parameters s max p and s c. The average absolute values of observed and estimated magnitude differences (jM est À M obs j) were 0.43, 0.49, and 0.66 units of magnitude, as determined using s max p , s c , and s fcwt , respectively. For earthquakes with magnitudes greater than 6, these values were 0.34, 0.56, and 0.44 units of magnitude, as derived using s max p , s c , and s fcwt , respectively. The s fcwt parameter exhibited more precision in determining the magnitude of moderate-and small-scale earthquakes than did the s c-based approach. For a general range of magnitudes, however, the s max p-based method showed more acceptable precision than did the other two parameters. Keywords Early warning systems Á Continuous wavelet transform Á Magnitude estimation relation Publisher's Note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Journal of Seismology, 1999
A total of 235 potential seismic sources in Iran and neighboring regions are delineated based on ... more A total of 235 potential seismic sources in Iran and neighboring regions are delineated based on available geological, geophysical, tectonic and earthquake data for seismic hazard assessment of the country. In practice, two key assumptions are considered; first, the assumption of earthquake repeatedness, implying that major earthquakes occur preferentially near the sites of previous earthquakes; second, the assumption of tectonic analogy, which implies that structures of analogous tectonic setting are capable of generating same size earthquakes. A two-step procedure is applied for delineation of seismic sources: first, demarcation of seismotectonic provinces; second, determination of potential seismic sources. Preferentially, potential seismic sources are modeled as area sources, in which the configuration of each source zone is controlled, mainly, by the extent of active faults, the mechanism of earthquake faultings and the seismogenic part of the crust.
We have investigated local seismicity around Shahroud fault system at the eastern Alborz. This fa... more We have investigated local seismicity around Shahroud fault system at the eastern Alborz. This fault system plays significant role in the tectonic of the east Alborz. In this paper we analyzed micro-earthquakes recorded by three networks; two local temporary dense seismological networks installed around a part of Shahroud fault system for several months during 2007 and 2008 and the permanent seismological network of the Geophysics Institute of University of Tehran. The seismicity of both permanent and temporary networks have been distributed around Shahroud fault system, especially the Astaneh fault. Processing the data concludes a P wave velocity structure range within the east Alborz from 5.4 km/s to 6.3 km/s between the surface and upper than the Moho depth. We suggested 4 km for sedimentary cover thickness and the seismogenic zone thickness was obtained 20 km. Also two near vertical seismicity dips corresponding with two segments of the Astaneh fault were specified. We detected a north-dipping blind fault at the south of the area which helps us suggesting the flower structure as subsurface geometry of the faults at the eastern Alborz.