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Mechanism solutions (DC part) for the Baladeh mainshock compared with results obtained by different methods and from different publications
Source publication
The M
w
6.2 Baladeh earthquake occurred on 28 May 2004 in the Alborz Mountains, northern Iran. This earthquake was the first strong shock in this intracontinental orogen for which digital regional broadband data are available. The Baladeh event provides a rare opportunity to study fault geometry and ongoing deformation processes using modern seismo...
Contexts in source publication
Context 1
... comparison, source mechanisms obtained in this study for the Baladeh mainshock, together with those obtained by other authors, are given in Table 5 and Fig. 10. All mechanisms obtained with different inversion constraints show a WNW- ESE-oriented almost pure thrust mechanism. ...
Context 2
... determined moment tensors of 16 aftershocks assuming point sources (Table 4). Only the de- viatoric part of the moment tensor was consid- ered during inversion, i.e. the isotropic part of Table 5 Fig . 11 Results for earthquake no. ...
Context 3
... of waveforms from the mainshock of the M w 6.2 Baladeh earthquake (which occurred on 2 May 2004) for the moment tensor resulted in a pure thrust mechanism with a fault plane strik- ing WNW-ESE. Other solutions obtained from teleseismic data (the last three solutions in Table 5) have an additional minor left-lateral strike- slip component. The two earlier instrumentally recorded major earthquakes, in 1957 (M s 6.8) and 1962 (M s 7.3), had similar NW-SE-oriented thrust mechanisms with minor strike-slip components (McKenzie 1972;Wu and Ben-Menahem 1965). ...
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Citations
... We compiled available well-constrained EFMs for the study area from: (1) online catalogues including Centroid Moment Tensor catalogue (CMT) (Dziewonski et al. 1981;Ekström et al. 2012), Iranian Seismological Center (IRSC) , International Seismological Centre (ISC) (Lentas 2018;Lentas et al. 2019), Kandilli Observatory and Earthquake Research Institute (KOERI) (Cambaz et al. 2019), and Zurich Moment Tensors (ZUR_RMT) (Bernardi et al. 2004), and (2) published literature (Fara 1964;Jackson and McKenzie 1984;Jackson 1992Jackson , 2001Priestley et al. 1994;Gao and Wallace 1995;Jackson et al. 2002;Tatar and Hatzfeld 2009;Nemati et al. 2011Nemati et al. , 2013Donner et al. 2013Donner et al. , 2014Ansari et al. 2015;Yetirmishli et al. 2019;Azad et al. 2019;Khosravi et al. 2019;Hosseini et al. 2019;Niksejel et al., 2021;Tibaldi et al. 2020;Walker et al. 2021). Then, by declustering (Reasenberg 1985) the EFM dataset, we created a catalogue of declustered (mainshock) focal mechanisms containing 410 focal mechanisms of earthquakes with a magnitude ≥2.5 MS (see the Supplementary file). ...
In this paper, we study the tectonic stress around the South Caspian Basin (SCB), which includes the Kopeh Dagh, Alborz, Talesh, eastern Greater Caucasus mountain belts, the Apsheron sill, and the Balkhan-Ashkabad fault zone. We apply the stress inversion to focal mechanisms of 410 mainshocks that have occurred over the last 69 years. These mechanisms indicate that the surrounding fault zones of the SCB exhibit diverse types of faulting, ranging from thrust to strike-slip, normal, and their ombinations. The results of the stress inversion align with the kinematics of the major
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... Cross-correlation factors are shown for both P-wave and S-wave windows J Seismol left-lateral strike-slip faulting. Previously, some evidence of an NNE-SSW structure was reported; During the 2004 M w 6.2 Baladeh earthquake, westward propagation of aftershocks terminated abruptly near Chalus river valley (Tatar et al. 2007;Donner et al. 2013;Fig. 1) where the N-S strike-slip mechanism was also observed (Tatar et al. 2007). ...
The 2017 Malard and 2020 Damavand moderate crustal earthquakes (Mw 4.8) occurred about 40 km west and about 55 km northeast of Tehran, the capital and economic heart of Iran, with a metropolitan population of over 15 million. Seismic hazard assessment in the region has been affected by few historically documented destructive earthquakes with magnitudes around 7.0 (e.g., 312–280 B.C, 958, 1177, and 1830 A.D.); however, in the absence of large contemporary earthquakes, a detailed analysis of moderate earthquakes is essential. In this study, seismic sources of the two earthquakes are characterized in terms of focal mechanism, fault geometry, and rupture directivity through waveform inversion, hypocenter relocation, and empirical Green’s function methods. The eastern segment of the well-known Mosha fault is responsible for the 2020 Damavand earthquake, with a left-lateral strike-slip mechanism ruptured unilaterally westward where Tehran is situated. The 2017 Malard earthquake is a peculiar case in a poorly studied region. For this event, we propose a left-lateral strike-slip mechanism corresponding to E-W trending Mahdasht fault. This event was preceded by a swarm of events, 12 km northward, that started a few months earlier and terminated right before the mainshock. The energy released due to this precursory activity was higher than the Malard mainshock and its aftershocks. The events seem to align along an N-S transverse basement fault that, further southward, may intersect with the Mahdasht fault system.
... The largest earthquakes with known mechanisms, which could be related to the North Alborz fault, are the 1998/12/03 M W 5.4 dominantly reverse event (western segment of the fault) and also the 2004/05/28 M W 6.4 reverse earthquake (Royan fault). Tatar et al. (2007) reported that the 2004 Baladeh earthquake, which had a reverse mechanism with a left-lateral strike-slip component, occurred at a depth of 22 km for the centroid depth (Donner et al., 2013). The earthquake is a microplate margin event involving the interaction between the SCB and Alborz regions based on its depth, faulting location, and low-stress drop. ...
Field evidence, seismicity, and geodetic data are combined to define the tectonic evolution along the northern domain of the Western and Central Alborz ranges, which have experienced significant earthquakes. One of our main focuses is to present the geometric-kinematic characteristics of active fault planes in the North Alborz fault zone and its subsidiary faults as a basis for seismic hazard assessment. To evaluate the seismotectonics in the region, three active segments of the seismic zone are identified. These segments primarily exhibit reverse mechanisms and left-lateral strike-slip components and act as the boundaries of neotectonic stress domains around the transition zone between Alborz and the South Caspian Basin. The spatial distribution of the strike-slip and dip-slip faulting over the Western and Central Alborz range supports our understanding of the geodynamic processes of the region. Our map of local active faults reveals five main systems with N–S, NE–SW, ENE–WSW, E–W, and NW–SE directions. Field studies indicate that strike-slip movements predominate and are consistent with a ∼WNW-ESE-oriented left-lateral wrench system. Pure left-lateral strike-slip faults trending E-W, extensional faults trending NE–SW, and compressional faults trending NW-SE are identified. Regional field investigations reveal spatial variations in the fault zone width of the northern domain of the Western and Central Alborz. The findings demonstrate that fault zone structures and their spatial distribution along the width of the area are strongly affected by the strain partitioning process in the transpressional zone. A spectacular well-exposed transpressional zone from the Western and Central Alborz region is described in detail, where outer domains are faults with a dominant reverse mechanism, and the inner domain is a wrench zone that includes faults with a dominant strike-slip mechanism.
The seismic activity in the Northern Alborz region is mainly concentrated along the North Alborz fault zone and its subsidiary fault planes, of which some are identified for the first time in this research. Significant seismic events have occurred at locations where these newly identified fault planes interact. The maximum values of the geodetic strain axes in Western and Central Alborz are consistent with the area of high seismicity.
... Three-dimensional wave propagation can be used to effectively represent the wave propagation due to the fault rupture process. Here, a horizontally layered crustal model (Table 5, Donner et al. 2013) is assumed and a finite difference (FD) method implemented in the FDSim3D code (Kristek and Moczo 2014) is used (with no advantages relative to some other codes like Axitra) to simulate ground motion at low frequencies. Program FDSim3D is designed for the finite-difference (FD) simulation of seismic wave propagation and earthquake ground motion in 3D local surface heterogeneous viscoelastic structures with a planar-free surface. ...
Recent earthquake damage distributions have demonstrated that the influence of local geology on ground shaking is a significant factor in engineering seismology. So, calculating the site effect is a priority to get a trustworthy assessment of the seismic risk for a location, in addition to studying the local seismic sources. The signal amplitude can be amplified by this effect throughout a range of periods. The site effect has been calculated using a variety of computational and experimental techniques, such as seismic noise measurements. In this study, to calculate the site effect, the analysis of accelerograms recorded by Iran’s strong motion network of the Road, Housing, and Urban Development Research Center was used. Here, 294 records from 63 stations were used to calculate the H/V (horizontal to vertical spectral ratio) curve as well as the near-surface high-frequency attenuation parameter (κ0). The classification method is based on determining the peak period at each station. To examine site effect consideration, we use the hybrid method composed of the finite difference method for low frequencies (< 1 Hz) and a stochastic finite fault method for high-frequency radiation (> 1 Hz) to simulate an earthquake scenario on the Niavaran fault, which is located north of Tehran, Iran. According to the findings, different site classes cause spectral amplitude variations ranging from 11 to 28% at different periods (T = 0.2, 0.5, 1.0, and 4.0 s).
... The aftershocks sequences distribution did not coincide with the 16 Jun, 2020 main earthquake, neither in map view nor with respect to depth. The studied aftershocks are extended and clustered at the north western side of the main shock which may indicated a secondary fault plane activation, or suggested that the seismicity in the north western side were activated by the 16 Jun, 2020 mainshock due to stress triggering (Donner et al. 2013). The best double-couple mechanism determined using the full waveform moment tensor analysis for the current earthquake was consistent with previous findings (e.g., Abou Elenean 1997; Megahed 2004;Hussein et al. 2013; The main objective of the current work was to comprehensively study recent seismicity and its spectral parameters in addition to understanding the tectonic setting of the northern Red Sea and the interaction of its extensional movement with the Gulf of Aqaba and Gulf of Suez for seismic hazard assessment and risk management modulation. ...
The northern Red Sea in eastern Egypt is one of the world’s newest marine basins. The northern Red Sea is a very active seismic region and poses a significant hazard to the nearest cities on the Red Sea coast. On June 16, 2020, a moderate earthquake ( M L = 5.4), as published by the Egyptian National Seismic Network (ENSN), occurred in the northern Red Sea followed by several aftershocks, ranging in magnitude from 2.0 to 3.4. The best-fitting double-couple movement obtained using the full waveform moment tensor inversion of the main earthquake indicated strike-slip movement, with a minor normal component. The two nodal main shock planes were oriented NNE–SSW and ESE–WNW, respectively. The aftershocks sequences distribution did not coincide with the 16 Jun, 2020 main earthquake, neither in map view nor with respect to depth which may pointed to a secondary fault plane activation and stress triggered by the mainshock. The aftershocks clustered at the north western side of the main earthquakes and extend in the north western direction, which supported that the ESE–WNW plane is the fault plane. The spectral parameters of the S-wave displacement spectra of the main earthquake and its significant aftershock sequences were determined using the spectral inversion method and Brune’s $$\omega^{2}$$ ω 2 modulation. The obtained spectra are flat in the frequency range from 0.8 Hz to each corner frequency, and they decreased rapidly at frequencies of < 10 Hz. The calculated seismic moment, moment magnitude, corner frequency, source radius, and stress drop vary from 8.293E+18 to 7.541E+22 dyn·cm, 2.4 to 5.0, 2.2 to 8.2 Hz, 171 to 633 m, and 0.02 to 13 MPa, respectively. The moment magnitude is equal to or slightly higher than the local magnitude reported by ENSN. The calculated stress drops for the earthquakes increased with increasing earthquake size.
... The first thing needed for the depth correction is to determine the radial displacement eigenfunctions associated with Rayleigh waves, r 1 (ω), the vertical displacement eigenfunctions associated with Rayleigh waves, r 2 (ω), and the transverse displacement eigenfunctions associated with Love waves, l 1 (ω), for the region surrounding ZNJN station both at the centroid depth of the benchmark earthquake, h, and at the surface of Earth (see Denolle et al. 2013Denolle et al. , 2014. Figure 6 shows the ratios of these displacement eigenfunctions that were obtained by the Chebyshev Spectral Collocation algorithm (Denolle et al. 2012, VEA Package). The velocity model and density profiles in calculating these parameters were adapted from the model obtained by Donner et al. (2013) (Table 3). Although this model was achieved by analyzing the group-velocity dispersion curves of surface waves obtained at the Alborz mountains region, however, Donner et al. (2014Donner et al. ( , 2015 demonstrated that it is also applicable to a broad regional scale including the NW of Iran. ...
... These ratios were obtained based on the velocity and density profiles under seismic ZNJN station (Table 2) Table 3 The velocity model used in this study. This model was adapted from the model obtained by Donner et al. (2013) Top of layer* (km) PGD max values, it can be said that although the matching accuracy of the amplitudes is less than the phase information, the use of the PCC method has resulted in better retrieval of amplitude information in some components of the station pairs. ...
Although research on seismic interferometry is now entering a phase of maturity, earthquakes are still the most troublesome issues that plague the process in real applications. To address the problems that arise from spatially scattered and temporally transient enormous earthquakes, preference is usually given to the use of time-dependent weights. However, small earthquakes can also have a disturbing effect on the accuracy of interpretations if they are persistently clustered right next to the perpendicular bisector of the line joining station pairs or in close proximity to one of the stations. With regard to the suppression of these cluster earthquakes, commonly used solutions for dealing with monochromatic microseismic cluster events (e.g., implementing a band-reject filter around a comparatively narrow frequency band or whitening the amplitude spectra before calculating the cross-spectrum between two signals) may not have the necessary efficiency since earthquake clusters are generally a collection of events with different magnitudes, each having its own frequency and energy contents. Therefore, the only solution left in such a situation is to use stronger non-linear time-dependent weights (e.g., square of the running average or one-bit normalization), which may cause Green’s function amplitude information to be lost. In this paper, by simulating the records of a benchmark earthquake MN 5.2 with the help of empirical Green’s functions (EGF) obtained after the Ahar-Varzeghan Earthquake Doublet (MN 6.4 and MN 6.3), it is shown that the amplitude-unbiased phase cross-correlation is a relatively efficient approach in the face of the issues concerning long-standing cluster events.
... However, such analyses are not yet routine and can only be applied to events larger than M w ∼ 5-5.5. Recent studies show that regional moment tensors can constrain centroid depths for events larger than M w ∼ 3-3.5, with errors of 2-4 km (e.g., Ghods et al., 2012;Donner et al., 2013Donner et al., , 2014, but these analyses require a good station distribution at regional distances. Berberian (1995) first suggested that seismic activity in the Zagros is concentrated on a small number of large, steeply dipping, basement-cored faults-termed "master blind thrusts"-that pass upward into the lower sedimentary cover where they control observed steps in exposed stratigraphic level. ...
We use calibrated earthquake relocations to reassess the distribution and kinematics of faulting in the Zagros range, southwestern Iran. This is among the most seismically active fold‐and‐thrust belts globally, but knowledge of its active faulting is hampered by large errors in reported epicenters and controversy over earthquake depths. Mapped coseismic surface faulting is extremely rare, with most seismicity occurring on blind reverse faults buried beneath or within a thick, folded sedimentary cover. Therefore, the distribution of earthquakes provides vital information about the location of active faulting at depth. Using an advanced multievent relocation technique, we relocate ∼2,500 earthquakes across the Zagros mountains spanning the ∼70‐year instrumental record. Relocated events have epicentral uncertainties of 2–5 km; for ∼1,100 of them we also constrain origin time and focal depth, often to better than 5 km. Much of the apparently diffuse catalog seismicity now collapses into discrete trends highlighting major active faults. This reveals several zones of unmapped faulting, including possible conjugate left‐lateral faults in the central Zagros. It also confirms the activity of faults mapped previously on the basis of geomorphology, including oblique (dextral‐normal) faulting in the NW Zagros. We observe a primary difference between the Lurestan arc, where seismicity is focused close to the topographic range front, and the Fars arc, where out‐of‐sequence thrusting is evident over a width of ∼100–200 km. We establish a focal depth range of 4–25 km, confirming earlier suggestions that earthquakes are restricted to the upper crust but nucleate both within and beneath the sedimentary cover.
... The theoretically observed waveforms as well as the Greens functions are calculated using a spectralelement solver based on a 1-D structural model for the Alborz mountains (Fichtner et al., 2009;Donner et al., 2013). Gaussian noise was added to the synthetic seismograms to render them more realistic. ...
Seismic moment tensors help us to increase our understanding about e.g. earthquake processes, tectonics, Earth or planetary structure. Based on ground motion measurements of seismic networks their determination is in general standard for all distance ranges, provided the velocity model of the target region is known well enough. For sparse networks in inaccessible terrain and planetary seismology, the waveform inversion for the moment tensor often fails. Rotational ground motions are on the verge of becoming routinely observable with the potential of providing additional constraints for seismic inverse problems. In this study, we test their benefit for the waveform inversion for seismic moment tensors under the condition of sparse networks. We compare the results of (1) inverting only traditional translational data with (2) inverting translational plus rotational data for the cases of only one, two, and three stations. Even for the single station case the inversion results can be improved when including rotational ground motions. However, from data of a single station only, the probability of determining the correct full seismic moment tensor is still low. When using data of two or three stations, the information gain due to rotational ground motions almost doubles. The probability of deriving the correct full moment tensor here is very high.
... Parameters of the recent Alborz earthquakes determined by body-wave modeling indicate shallow thrust and left-lateral strikeslip faulting with centroid depths ranging from 8 to 13 km (Jackson et al., 2002), except for a slightly greater centroid depth of 22 km for the 28 May 2004 M w 6.2 Firuzābād Kojur (Baladeh) earthquake possibly along the Khazar reverse fault (Berberian, 1981(Berberian, , 1983a(Berberian, , 1983b in basement (Tatar et al., 2007a(Tatar et al., , 2007bDjamour et al., 2010;Donner et al., 2013). Recent seismic evidence in the Alborz such as: ...
... Most Iranian continental-crust earthquakes are shallow, with centroid depths around 10 km (Jackson et al., 2002). P and SH waveform analysis of the 28 May 2004 M w 6.2 Firuzābād-e Kojur (Baladeh) earthquake in the western Alborz (Fig. 9) showed a centroid depth of 22 km with a thrust mechanism and a damage zone located ~25 km south of the Khazar fault line (Tatar et al., 2007a(Tatar et al., , 2007bDonner et al., 2013). The centroid depth, together with the aftershock distribution (Tatar et al., 2007a(Tatar et al., , 2007b, revealed a south-dipping thrust plane projected to the surface on the hanging wall of the Khazar reverse fault (Fig. 9) and casts doubt on the active reverse faults in the Alborz Mountains being thin-skinned features. ...
http://specialpapers.gsapubs.org/cgi/content/abstract/2016.2525_04v1
Abstract
The megacity of Tehran, the political, economic, and military center of Iran, is exposed to a risk of large-magnitude earthquakes originating on several adjacent and inner-city active faults. The city lies at the southern foot of the central Alborz Mountains, which frame the South Caspian Basin and have been the source of damaging historical left-lateral strike-slip and reverse-fault earthquakes. The most recent destructive earthquake in Alborz was the Rudbār left-slip earthquake of Mw 7.3 on 20 June 1990 northwest of Tehran, taking more than 40,000 lives and destroying three cities. This earthquake was in a seismic gap, and its source fault did not show clear geomorphic signs of being active prior to the earthquake. East of Tehran, the 22 December 856 Komesh (Dāmghān) earthquake had a magnitude previously estimated at Ms 7.9, with estimated losses of 40,000–200,000 lives. Our reevaluation of historical, archaeological, and structural evidence reduces estimates of both magnitude and losses, similar to the 1990 Rudbār earthquake. The latest earthquake to affect the present Tehran metropolitan area was the Lavāsānāt earthquake on the central section of the Moshā fault, on 27 March 1830, with its epicenter located ~30 km northeast of the city, which had a magnitude of Mw ~7.0–7.4. Prior to this event, the Ruyān earthquake north of Tehran struck the same section of the fault on 23 February 958, with a magnitude previously estimated as Ms 7.7, although our reevaluation reduces the magnitude to around Mw ≥7.0 (7.0–7.4). Both the 958 and 1830 earthquakes along the central segment of the Moshā fault, with an interval of 872 yr, might have loaded the North Tehran fault system near the cities of Tehran and Karaj, as well as the faults underneath the metropolitan area. The North Tehran fault system west of Tehran might have sustained an earthquake of Mw ~7.0 in May 1177. The earthquake histories of the Niāvarān, Darakeh, Farahzād, and Kan left-lateral strike-slip faults (part of the North Tehran fault system at the mountain front north of the city), the inner-city Mahmudieh and Dāvudieh south-dipping reverse faults, the central-eastern section of the North Tehran fault system (now within the metropolitan area) as well as blind thrusts under the city are unknown. Except for the 1830 distant earthquake, no medium- to large-magnitude earthquake (Mw 6.5–7.5) has occurred within the Tehran metropolitan area during the past >839 yr along the faults beneath the metropolitan area or in the immediate vicinity. This may indicate a 839-yr-long period of strain accumulation within a long interseismic period between large-magnitude earthquakes in Tehran.
With the active-fault hazard to the rapidly growing population along several faults, it is necessary for the government to: (1) conduct extensive paleoseismic trenching to identify the most hazardous of Tehran's faults, previous rupture areas, average coseismic slip rates, earthquake magnitudes, and average recurrence periods of earthquakes from at least eight fault systems within the metropolitan area; (2) deal with extensive corruption of the construction and building-inspection industries; and (3) enforce the 1969, 1988, and 1999 Iranian Code for Seismic Resistant Design of Buildings. As with the 12 January 2010, Mw 7.0 Haiti earthquake, losses from the next Tehran earthquake of Mw ≥7.0 could exceed 100,000 people. It is necessary to prepare and implement an earthquake management master plan as a disaster prevention tool, enforce the building code with transparency, and retrofit public structures and infrastructure in order to mitigate earthquake risk in Tehran and protect the lives of ~15 million people (roughly 20% of the country's population) living in the Tehran and Alborz (Karaj city) Provinces.
... In addition, performing full waveform inversion for moment tensors in a frequency range suitable for surface waves in northern Iran, we also observed instabilities in the resolution of the components M xx and M yy , causing a bias of strike-slip mechanisms tending to thrust mechanisms (e.g. Donner et al. 2013). ...
... Further details of the source can be found in Table 1. The theoretically observed waveforms are computed based on the 1-D structural model for the Alborz mountains (Table 2; Donner et al. 2013). To be flexible for potentially more complex studies in the future, we applied a spectral-element solver (Fichtner et al. 2009). ...
... Interestingly, the ambiguity in depth with one possible solution in very shallow depth (h ≤ 6 km) and another one at the lower end of the seismogenic zone of Iran (h > 17 km) is also visible in the real world. Moment tensor studies in the Alborz mountains and in the NW part of Iran have shown exactly the same effect (Donner et al. 2013(Donner et al. , 2015. ...
We assess the potential of additional rotational ground motions to increase the resolution of the full seismic moment tensor and its centroid depth during waveform inversion. For this purpose, we set up a test case of a shallow, medium-sized strike-slip source. In two scenarios, one based on theoretical station distribution and one based on real station distribution, we compare the results based on inversion of translational ground motion data only and based on both, translational and rotational ground motion data. The inversion is done with a Bayesian approach to overcome the drawbacks of deterministic approaches and provide a comprehensive quantification of uncertainties. Our results indicate that the resolution of the moment tensor can be increased drastically by incorporating rotational ground motion data. Especially, the usually problematic components Mxz and Myz as well as all components containing spatial derivatives with depth benefit most. Also, the resolution of the centroid depth is much better.
