Mainshocks/aftershocks study of the August 2012 earthquake doublet on Ahar-Varzaghan complex fault system (NW Iran)

Momeni, Seyyedmaalek; Tatar, M.

doi:10.1016/j.pepi.2018.08.001

Cited by 10 publications

(36 citation statements)

References 40 publications

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“…The mean and trend of data were removed and band-pass filtered by a fourth-order Butterworth filter between 0.03 and 0.08 Hz and cut from origin time for a length of 250 s. The Green's functions for the trial point source were computed using the discrete wavenumber (DWN) method (Bouchon, 2003) and the similarity between the observed and calculated waveforms measured by the variance reduction (VR) parameter of the Isola code. Details of the inversion procedure are explained in a study by Momeni and Tatar (2018). We used a velocity model of the area obtained in a detailed microseismic study by Tatar et al (2012) (Supplementary Table S2).…”

Section: Moment Tensor Of the 7 May 2020 M51 Mainshockmentioning

confidence: 99%

Long-term triggered seismicity on the Mosha fault by Damavand volcano, Iran: Implications on the seismic hazard of Tehran metropolis

Momeni

Madariaga

2022

Front. Earth Sci.

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The seismic history of the Mosha fault, the largest and most active fault of Eastern Tehran metropolis, and its relation to the Damavand active volcano, the highest mountain in the Middle East, is investigated. We deduce that the central Mosha, near the Damavand, has a higher seismicity than either its western or eastern segments. On 7 May 2020, an Mw 5.1 earthquake occurred on the central Mosha, about 40 km east of Tehran and 10 km southwest of the Damavand crest, and it was felt intensely in Tehran. Its rupture is imaged and located in a region that presented a relative seismic quiescence compared to its eastern and western parts, during the last 14 years, suggesting its partial locking and heterogeneous distribution of fault frictional strength on this segment of Mosha. Its significant directivity to the west is confirmed by the mainshock rupture model, its PGA distribution, and distribution of early aftershocks. The rupture model suggests a relatively small stress drop of 2.6 bar, which is consistent with the comparatively high rupture dimension of 9 km for a Mw 5.1 earthquake, and indicates the easy rupture expansion on the central Mosha near the Damavand Volcano. The central Mosha experienced earthquakes in 1930, 1955, and 1983, as well as high microseismic activity and the 2020 seismic sequence, all of which strongly point to a possible influence of the Damavand Volcano on the seismicity of the central Mosha. This is corroborated by the observation of hydrothermal zones on the Mosha fault and the extension of a sill-like Damavand young magma chamber until central Mosha in tomography studies. We propose that the existing heat may increase the pore pressure on the fault, which lowers the effective normal stress, facilitates the nucleation-expansion of the rupture, and unclamps the fault. Damavand could act as a fuse and nucleate earthquakes, and if the rupture extends toward the west, it could have a significant directivity effect on low-frequency seismic waves that reach Tehran without attenuation and affect tall structures. In addition, high site amplification for frequencies up to 16 Hz due to the deep sedimentary basin, mainly in the mid-city of Tehran, will be remarkable for short buildings.

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Section: Moment Tensor Of the 7 May 2020 M51 Mainshockmentioning

confidence: 99%

Long-term triggered seismicity on the Mosha fault by Damavand volcano, Iran: Implications on the seismic hazard of Tehran metropolis

Momeni

Madariaga

2022

Front. Earth Sci.

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“…The result suggests that if the first shock triggered the second one, it is more likely that the second shock occurred along an almost perpendicular geometry (10 • /50 • /36 • ) to the first shock. This result supports the interpretation of some other studies such as Donner et al (2015), and contradicts the findings of Ansari (2016) and Momeni & Tatar (2018) about the rupturing plane for the second shock. Applying the obtained result about the focal mechanism of the doublet, we compute ∆CFS maps for optimum thrust and strike-slip ruptures in the area.…”

Section: Subduction Sequence; Large Thrust Earthquakesupporting

confidence: 71%

Analysis of earthquake sequences and activity rates: implications for seismic hazard

Yazdi¹

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First and foremost, I wish to express my sincere gratitude to Dr. Jorge Gaspar-Escribano. Undeniably, without his invaluable guidance, this work would never have been made possible. I have been fortunate to be his student from the first year of my PhD program, have been introduced to the topic of main research in his class and benefited from his expertise during these years. I am profoundly indebted to his precious advise, his patience and his humane mentorship. My utmost appreciation to Dr. Miguel Ángel Santoyo, from whom not only have I learned how to look into the earthquake phenomenon but he has also intrigued me with his integrity as a righteous and humble researcher always and specifically during my two months stay at

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“…Previous studies based on seismology, InSAR and field observations reach different conclusions on the localization and rupture geometry of these two main events (Alipour 2013;Copley et al 2013;Donner et al 2015;Ghods et al 2015;Zafarani et al 2015;Rezapour 2016;Yadav et al 2016;Amini et al 2018;Momeni & Tatar 2018;Yazdi et al 2018; see Table 1). Most of them agree on the EW strike of M1, while there is no agreement on its dip and the strike and dip of the M2 fault plane.…”

Section: U N C E Rta I N T I E S O N T H E L O C a L I Z At I O N A N...mentioning

confidence: 92%

“…1). Indeed, prior to this doublet, the instrumental seismic activity recorded by the Iranian permanent National Seismic network of the Iranian Seismological Center (IRSC) in the Ahar-Varzaghan region was negligible (Momeni & Tatar 2018). The last major historical earthquakes that have occurred on the NTF are the 1780 magnitude 7.4 and 1721 magnitude 7.6-7.7 events (Ambraseys & Melville 1982;Berberian 1994;Berberian 1997) both showing ∼50 km of surface ruptures (red ellipses on Fig.…”

Section: Introductionmentioning

confidence: 99%

Kinematics of the 2012 Ahar–Varzaghan complex earthquake doublet (Mw6.5 and Mw6.3)

Momeni

Aoudia

Tatar

et al. 2019

Geophysical Journal International

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an earthquake doublet (M w 6.5 and M w 6.3), separated in time by 11 min, occur in the northwest of Iran. The hypocentres of these earthquakes are close (∼6 km) and located near the cities of Ahar and Varzaghan. The rupture process of both main shocks is retrieved by inverting the near-field strong motions data and using the elliptical subfault approximation method. Our calculations show that the two earthquakes are occurring on two distinct fault planes: the first main shock (M1) has nucleated at a depth of ∼8.5 km, and is located ∼4 km east of the eastern termination of the E-W trending surface rupture. The slip reaches the ground surface west of the hypocentre on an E-W striking fault (N88 • E) that dips almost vertically (80 • S). This earthquake exhibits a right-lateral strike-slip mechanism. The entire slip is imaged on a single patch that ruptures with an average speed of 2.4 km s −1 . The rupture duration is ∼5.6 s and the earthquake releases a seismic moment of ∼8.41E + 18 N•m. The slip reaches the surface with a right-lateral dislocation value of ∼1 m, which is consistent with the observed surface rupture. About 11 min later, the second main shock (M2) nucleates ∼5 km to the west and 4 km to the north with respect to the hypocentre of the M1, and at a depth of ∼16.5 km. The M2 rupture evolves toward shallower depths and to the west on an ENE-WSW oriented fault plane (strike ∼256 • ) with a dip of ∼60 • northward. The slip is essentially distributed on two distinct patches with strike-slip and reverse mechanisms, respectively. The first patch has a pure right-lateral strike-slip mechanism, and ruptures at a relatively fast speed of over 2.8 km s −1 , and last for about 2.6 s until it reaches the second patch. The latter has a reverse mechanism (rake∼112 • ) and extends the rupture toward shallow depths, and to the west at a speed of ∼2.5 km s −1 , and its rupture lasts for ∼2.5 s. The top of the slip distribution of M2 stops at a depth of ∼8 km. We observe that aftershocks surround the M1 and most of the M2 slip models. They are not distributed in the region of high slip (∼3.1 m) of M1. We show that the rupture of M2 is controlled by the static Coulomb stress changes caused by M1, with the maximum slip of M2 located in the positive Coulomb stress caused by M1. The M2 rupture stops where it reaches the area of high negative Coulomb stress change (over −10 bars). The cumulative Coulomb stress fields of both main shocks show a transfer of positive static Coulomb stress change of >0.1 bars on the eastern segment of the North Tabriz Fault. This segment did not rupture since the 1721 M∼7.6-7.7 event that has destroyed the city of Tabriz, and that currently hosts 2 million people. The occurrence of this earthquake doublet with different mechanisms reveals the slip partitioning of the oblique convergence regime of NW Iran on the Ahar-Varzaghan complex fault system.

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Mainshocks/aftershocks study of the August 2012 earthquake doublet on Ahar-Varzaghan complex fault system (NW Iran)

Cited by 10 publications

References 40 publications

Long-term triggered seismicity on the Mosha fault by Damavand volcano, Iran: Implications on the seismic hazard of Tehran metropolis

Long-term triggered seismicity on the Mosha fault by Damavand volcano, Iran: Implications on the seismic hazard of Tehran metropolis

Analysis of earthquake sequences and activity rates: implications for seismic hazard

Kinematics of the 2012 Ahar–Varzaghan complex earthquake doublet (Mw6.5 and Mw6.3)

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