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On 20 June 1990 a major earthquake (Ms 7.7) occurred in northern Iran. The damage was substantial and spread over a widely populated area. An overview of the geology and seismology of the area is presented, foreshock and aftershock activities are examined; the attenuation model of the peak ground acceleration is developed for both horizontal and ve...
Citations
... The deadly earthquake of Manjil adjacent to the Caspian Sea, which claimed the lives of 35,000 -, occurred (Utsu 2002) in the vicinity of a large Quaternary region of a low shear wave velocity (V ) . Furthermore, the S30 (Niazi & Bozorgnia 1992) earthquakes occurred in Dasht-e Bayaz and Bam, also resulted a large number of casualties (15,000 and 52,000 civilians). Actually this earthquake hit areas of considerable potential for resonating seismic waves, and this was probably one of the reasons for large number of casualties (Ambraseys & Tchalenko 1969;Tchalenko 1970;Tchalenko & Berberian 1975). ...
Earthquakes are one of the most devastating natural hazards, resulting in untold casualties and destruction worldwide. The extent of destruction depends on various factors, of which the distribution of Quaternary sediments where a construction site lies stands out. These sediments control the amount of shear wave velocity and site amplifications. This study investigates the effect of alluvium on Peak Ground Acceleration (PGA) in Tehran and Karaj regions using the shear wave velocity map (VS30). The global VS30 map is modified using additional geotechnical and geological data. Next-generation attenuation properties are used for calculating PGA. The obtained PGA distribution map for the study area clearly shows the effect of VS30 on PGA changes. The inverse relationship between these two parameters is observed as a longitudinal strip stretched between Rey and Eslamshahr. On the edge of the triple escarpments at the Palaeo-, Mega- Lake of Rey, the PGA values vary with quaternary sediments. These sediments are responsible for the effect on the construction site, which resonates the seismic waves. Even with increasing distance from the fault, the PGA value is enhanced ue to the presence of these sediments.
... This event was recorded in June 20 th , 1990, induced by an earthquake at 19 km focal depth and the moment magnitude of 7.3. The maximum horizontal acceleration of the record was nearly 55% of ground acceleration [19]. [20]. ...
... Ms 7.7 and Mw 7.3) occurred on June 20, 1990, in populated areas of northern Iran (Gilan and Zanjan Provinces) along an unknown complex system of reverse faults, later called Baklor-Kabateh-Zardgoli fault. The segments comprise Baklor segment in west, Kabateh segment in center and Zard-Goli segment in east, arranged in a generally WNW trending en-echelon system (Niazi & Bozorgnia, 1992;Hamzehloo et al., 1997;Sarkar et al., 2003;Tatar & Hatzfeld, 2009;Berberian & Walker, 2010). Earthquake rupture dip was reported close to vertical (Berberian & Walker, 2010). ...
Alborz Mountains is a region of active deformation within Arabia-Eurasia collision zone. The study fault system in western Alborz comprises abundant evidence of active faulting accompanied by occurrence of historical earthquakes. Active tectonics of Manjil- Rudbar fault zone whose movement caused destructive 1990 Manjil-Rudbar earthquake was concentrated in this article through geomorphic and structural analyses. Major fault segments were mapped in order to recognize structural and geomorphic features of the fault zone. Satellite images were used to improve the visualization of fault traces in order to constrain their geometry considering structural linkage between different fault segments. Faults are supported by field geologic data and kinematic measurements. There are left-lateral strike-slip and oblique reverse movements observed all over the fault zone corresponding to recent fault activities of Rudbar, Manjil, Kelishom and Jirandeh (Kashachal) faults. A more complete catalogue of earthquake focal mechanisms is presented to consider general seismic framework of the region. Fault plane solutions indicate a radial pattern of thrusting in western Alborz. We analyzed drainage offsets and Quaternary alluvial fans along major structures in order to understand precise role of major faults in ongoing deformation processes. Most river offsets along active faults are small (about 100m), while left-lateral displacement of up to 500m is also observed in streams cut along major faults.
... The average 30 m shearwave velocity for the Ab-bar station is b 30 ¼ 621 m=s and the surface geology is stiff alluvium [43]. According to Niazi and Bozorgnia [49], the Ab-bar station was around 10 km away from the fault trace and recorded the highest PGA. Therefore, it is also expected that the ground-motion acceleration record at the Abbar station was amplified due to source directivity and should be omitted from calculations because this factor is difficult to build into the employed model (i.e., Eq. (1)). ...
... However, major proportion of analog strong motion records is felt to be too poor to be included in practical engineering applications. As an example, using the conventional filtering method, only 3 out of 27 records of Tabas 1978, Mw 7.4 [2] and 15 out of 68 records of Manjil 1990, Mw 7.1 [3] earthquakes have been corrected and other important records of these events are remained useless. In the case of digital instruments, in spite of improvement of dynamic range, sampling period and analog-to-digital (A/D) process, a large number of time histories recorded by these instruments cannot be corrected using the conventional method. ...
During the past earthquakes, many valuable acceleration time histories were recorded by analog and digital accelerometers. These records are important sources of information in the field of earthquake engineering and engineering seismology. However, a large number of these records are contaminated by noise and it is necessary to correct them for practical applications. On the other hand, only a few records can be corrected using conventional filtering because of mathematical limitations of the method. However, advances in the field of time–frequency analysis and wavelet transform theory provide useful non-linear and adaptive de-noising methods for removing of non-stationary and high-energy noise from the recorded signals. In this paper, the characteristics and capabilities of the modified non-linear adaptive wavelet de-noising method are examined for correction of highly noisy strong motion records. In the frequency domain, it is shown that this method can attenuate the noise in the whole frequency range of engineering interest while in the time domain it can detect and remove non-stationary noise. In addition, the displacement response spectra of these wavelet de-noised records are more stable than conventional filtered records with respect to different correction functions. It is found that a large number of noisy acceleration records that are usually discarded from sets of records used for estimating the ground motions can be corrected using this new method.
... The observations also do not appear to agree with the interpretation of Gao & Wallace (1995) that the 1990 May 21 (21:27 GMT) aftershock took place on the eastern bend of the Manjil thrust with right-lateral strike-slip mechanism. Both Gao & Wallace (1995) and Niāzi & Bozorgniā (1992), influenced by Moinfar & Nāderzādeh (1990) who misidentified landslides as coseismic surface faults, erroneously considered the Manjil thrust as a right-lateral strike-slip fault. ...
... Pursuant to Moinfar & Nāderzādeh (1990), Zāre' (1991a,b) and Zāre' & Moinfar (1993, 1994 followed by Māheri (1991), Niāzi & Bozorgniā (1992), Haghshénās (1998) and many others, introduced two coseismic surface faults for the 1990 earthquake. (i) The 'Harzevil fault' along the Sefidrud dam axis (the Manjil thrust of Berberian & Qorashi 1984;Berberian et al. 1992; see Figs 4 and 5 for the locations) with no data of the length or amount of displacements; and (ii) the 'earthquake fault of the Sefid Rud Dam' with 3 km length and 10-70 cm displacement ( Zāre' 1991a) or 5 km with 0.3 m left lateral and 0.5 m upward movement of the northern part at the left abutment hill top of the Sefidrud Dam ( Zāre' 1991b). The latter was considered as 'the most important earthquake fault that is associated with the main event'. ...
The Rudbar earthquake of 1990 June 20, the first large-magnitude earthquake with 80 km left-lateral strike-slip motion in the western `High-Alborz' fold-thrust mountain belt, was one of the largest, and most destructive, earthquakes to have occurred in Iran during the instrumental period. We bring together new and existing data on macroseismic effects, the rupture characteristics of the mainshock, field data, and the distribution of aftershocks, to provide a better description of the earthquake source, its surface ruptures, and active tectonic characteristics of the western `High-Alborz'. The Rudbar earthquake is one of three large magnitude events to have occurred in this part of the Alborz during recorded history. The damage distribution of the 1485 August 15 Upper Polrud earthquake suggests the east-west Kelishom left-lateral fault, which is situated east of the Rudbar earthquake fault, as a possible source. The 1608 April 20 Alamutrud earthquake may have occurred on the Alamutrud fault farther east. Analysis of satellite imagery suggests that total left-lateral displacements on the Rudbar fault are a maximum of ~1 km. Apparent left-lateral river displacements of ~200 m on the Kashachal fault and up to ~1.5 km of the Kelishom fault, which are situated at the eastern end of the Rudbar earthquake fault, also appear to indicate rather small cumulative displacements. Given the relatively small displacements, the presently active left-lateral strike-slip faults of the western High-Alborz fold-thrust belt, may be younger than onset of deformation within the Alborz Mountains as a whole.
... The seismicity recorded 8 yr after the Rudbar-Tarom earthquake is significant, with ∼400 events (of magnitude up to 4) over 7 weeks. Furthermore, the aftershock activity in 1998 trends WNW-ESE and is concentrated near the two easternmost segments that broke during the main shock, as in 1990 (Niazi & Bozorgnia 1992;Hamzehloo et al. 1997a). Most of the seismicity is located north of the fault ruptures, indicating a probable north dipping fault contrary to the inferred (from surface observations) steep southward dip of the various segments during 1990 described by Berberian et al. (1992), but more consistent with the vertical plane inferred from the main shock mechanism. ...
The focal mechanism of the destructive earthquake at Rudbar in northern Iran on 1990 June 20 was an unexpected left-lateral strike-slip motion on a previously unknown fault, the Baklor-Kabateh-Zard-Goli fault, within a complex system of reverse faults. We analysed microseismicity recorded by a dense local network deployed for 7 weeks, 8 yr after the main shock, to help evaluate the subsurface geometry and kinematics of the active fault system. In the west, the 1998 microseismicity seems to be related to the reverse Manjil. In the centre, we observe both reverse faulting associated to the Manjil fault and strike-slip faulting associated with de Zard-Goli rupture whose dip progressively changes from 45°N to vertical. In the east, the reverse faulting is located south of the Manjil fault and strike-slip faulting to the vertical Zard-Goli fault. We suggest that because the only stable geometry that accommodates large partitioning motion prevents the strike-slip fault to intersect the reverse fault, the active reverse fault jumps southwards beneath the Shahrud fault.
... The PGA values at Sedeh and Kashmar are smallest because these stations lie at greatest distance from the rupture zone, to the east and north east of the northwesterly propagating rupture, respectively. Niazi and Bozorgnia (1992) have proposed attenuation relations for the horizontal and vertical PGA within the Alborz mountain regions. Sarkar et al. (2003) found support for one of those relations from the horizontal PGA recorded in that region during the 1990 Rudbar earthquake. ...
... It is observed that the predicted values from Abrahamson and Litehiser (1989)'s relation are always far lower, by an order of 0.3 g or so. In fact the observed PGA values are slightly higher than those predicted by Niazi and Bozorgnia (1992) also, at least for the nearer stations. Fig. 8. ...
... The black dots denote the observed values at the nine stations. Graphs 1 and 2 are from attenuation relations of Abrahamson and Litehiser (1989) and Niazi and Bozorgnia (1992), respectively. ...
We analyze the strong motion accelerograms of the large magnitude (mb=6.4, MS=7.7, Mw=7.4, M0=1.32×1020) Tabas earthquake of September 16, 1978. The earthquake occurred due to a unilaterally propagating complex rupture process on a thrust fault system. The imprints of rupture of four (and possibly five) asperities (sub-faults) have been identified on the accelerograms. Using derived ‘SH-wave’ records, the locations of these asperities, which lie on the main causative fault, and the relative times of their occurrence have been determined. A foreshock that occurred about 6s prior to the main shock has also been identified and located. Further, using ‘SH-wave’ spectral data, we provide near field estimates of the strike, dip and slip of these asperities as well as their seismic moment, moment magnitude, fault area, released shear wave energy and average stress drop. The spectra of the sub-events conform to the ω−2 Brune spectra. The total seismic energy of the sub-events is consistent with the radiated energy estimated from teleseismic observations. The fault plane solutions show generally WNW–ESE strike, which is sub-parallel to the regional strike of the geological fault system existing in the area. The stress drops are in the range of 7–30bar, with the exception of the main sub-event that showed a stress drop of 100bar. Overall the sub-events show self-similarity. The average shear wave quality factor QS, which in the near field is quite sensitive to the local site geology, has been found to lie between 600 and 1200. The decay of PGA with distance is found to be compatible with Niazi and Bozorgnia's [Niazi, M., Bozorgnia, Y., 1992. The 1990 Manjil, Iran earthquake: geology and seismological overview, PGA attenuation and observed damage. Bull. Seism. Soc. Am. 82, 774–799] attenuation relation for the region.
... Berberian et al. (1992) found two historical events that were comparable to that of 1990 June 20; those of 958 February 23 in the Rey-Taleqan region (M, -7.7) and 1608 April 20 in the Rudbarat-Taleqan region (M, -7.6). The 1990 earthquake produced heavy damage spread over a large area and killed over 40000 people, injuring more than 60000 (Niazi & Bozorgnia 1992). Its source region lies in the Alborz Mountains, at the south-west corner of the Caspian Sea, in a convergent environment with a shortening axis approximately N4OoE, as deduced from the source mechanisms determined for previous earthquakes in the area (Jackson & McKenzie 1988). ...
... They identified at least three subevents, all with strike-slip mechanisms corresponding to right-lateral movement along a fault strike pf 215" (left-lateral sense of movement along a WNW-ESE strike direction). In the latest refinement of the source model (Thio et al. 1990, and private communication cited in Niazi & Bozorgnia 1992), four subevents were identified within a 25s time-window with a total moment of 8.5 x 10" N m. The fault planes strike between 283" and 303" and have northward dips ranging from 54" to 82". ...
... 1992). Moinfar & Naderzadeh (1990), cited by Niazi & Bozorgnia (1992), discovered a fresh fault trace of approximately 80 km length, which they identified as the main rupture associated with the 1990 June 20 event. This fault trace strikes N75"W and follows in part the north-eastern boundary of the Manjil Basin (Niazi & Bozorgnia 1992). ...
We study the rupture process of the Iranian earthquake of 1990 June 20 from broad-band data. We redetermined its moment tensor and source mechanism from long-period surface waves. Then we studied the P and SH broad-band recordings from the GEOSCOPE and IRIS seismic networks. We inverted the body waves using a full waveform modelling. For the inversion we used the gradient method of Nábělek, mixed with a limited exploration of the parameter space. In order to control the resolution of inversion, we proceeded by a stepwise procedure increasing the model complexity with every new inversion. We used the reduction of cost functional as a criterion for the validity of the inverted model. We first inverted the body waves considering a single-point source model. We found that body waves are dominated by a large energy release about 20 s from the onset of the signals. In the next step, fixing fault-plane solution, we inverted for the directivity of the source. We found clear evidence of propagation towards the east of the epicentre. We determined a rupture velocity of ∼2.5km s−1. The preceding source inversion reduced the variance of the residuals by about 30 per cent. Further improvement of the fit of the body-wave signals was obtained using an extended line source with constant fault-plane solution. We obtained a very good fit with an asymmetrical model. Initially rupture is bilateral but north-western propagation stops after 10 s. Later rupture continues unilaterally in the south-eastern direction with a rupture velocity of the order of 2.5 km s−1. Finally an inversion was attempted with a line source with varying fault mechanism. The final solution obtained by this procedure reduces the variance of the body-wave residuals by 60 per cent with respect to the variance of the observed body-wave signals. Variations in fault-plane solution along the fault are considered to be well resolved.
... Figure II-I a) [Berberian, et aI., 1991]. The mainshock is also called Rudbar-Tarom earthquake or Manjil Earthquake [Niazi and Bozorgnia, 1992]. [Berberian 1981]. ...
... Assuming the source time functions for both the broad band fit, and the short-period fit, we see that the rupture process of the mainshock is characterized by low moment release then followed by a period high moment release. The results from the broad band and short-period waveform modeling for the source process is consistent with the fact of three fault scarps we saw on the ground during the surface survey and local felt [Niazi and Bozorgnia, 1992]. However, there has been some controversy on the fault scarps associated with the mainshock [Niazi and Bozorgnia, 1992]. ...
... The results from the broad band and short-period waveform modeling for the source process is consistent with the fact of three fault scarps we saw on the ground during the surface survey and local felt [Niazi and Bozorgnia, 1992]. However, there has been some controversy on the fault scarps associated with the mainshock [Niazi and Bozorgnia, 1992]. According to Niazi and Bozorgnia, [1992] the field investigation by Monifar and Naderzadeh [1990] indicated the 80 km long fault scarps are at north end of Manjil basin and have a consistent right-lateral motion. ...
