The Ahar‐Varzeghan Earthquake Doublet (<i>M</i><sub>w</sub> 6.4 and 6.2) of 11 August 2012: Regional Seismic Moment Tensors and a Seismotectonic Interpretation

Donner, Stefanie; Ghods, Abdolreza; Rössler, Dirk; Landgraf, Angela; Ballato, Paolo

doi:10.1785/0120140042

Cited by 28 publications

(19 citation statements)

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“…1 c; Faridi and Sartibi 2012 ). The maximum observed surface deformation is estimated to be 70 cm right-lateral motion and 25 cm vertical with an average net slip of 72 cm (Donner et al 2015 ). It is not completely clear which of the two events generated the surface rupture; however, it is favorably oriented along one of the nodal planes of the first event (as reported by global CMT), and it is difficult to associate it with the focal mechanism of the second event (see Fig.…”

Section: The Double Earthquake Of August 11 2012mentioning

confidence: 99%

“…Field observations after the doublet reported an E-W trending fault trace (Copley et al 2013 ), but these authors could not with certainty state which of the two events produced the surface rupture. However, Donner et al ( 2015 ) argued that the surface rupture was produced by only the first mainshock since its fault plane is favorably oriented along the surface rupture trace.…”

Section: Introductionmentioning

confidence: 99%

“…The strike, dip, and rake value they found is in close agreement with the global-CMT ( http://www.globalcmt.org ) solution, but the centroid depth and scalar seismic moment are far from that. In another study, Donner et al ( 2015 ) estimated seismic moment tensors of the two mainshocks and the following large aftershocks ( Mw ≥ 4.3) by inverting their surface wave data. Combining the regional seismic moment tensor with geomorphological analyses of the region, they suggest a temporally and spatially complex style of deformation.…”

Section: Introductionmentioning

confidence: 99%

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Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet

Amini

Roberts

Raeesi³

et al. 2018

J Seismol

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An intraplate earthquake doublet, with 11-min delay between the events, devastated the city of Varzeghan in northwestern Iran on August 11, 2012. The first Mw 6.5 strike-slip earthquake, which occurred after more than 200 years of low seismicity, was followed by an Mw 6.4 oblique thrust event at an epicentral separation of about 6 km. While the first event can be associated with a distinct surface rupture, the absence of a surface fault trace and no clear aftershock signature makes it challenging to identify the fault plane of the second event. We use teleseismic body wave inversion to deduce the slip distribution in the first event. Using both P and SH waves stabilize the inversion and we further constrain the result with the surface rupture extent and the aftershock distribution. The obtained slip pattern shows two distinct slip patches with dissimilar slip directions where aftershocks avoid high-slip areas. Using the estimated slip for the first event, we calculate the induced Coulomb stress change on the nodal planes of the second event and find a preference for higher Coulomb stress on the N-S nodal plane. Assuming a simple slip model for the second event, we estimate the combined Coulomb stress changes from the two events on the focal planes of the largest aftershocks. We find that 90% of the aftershocks show increased Coulomb stress on one of their nodal planes when the N-S plane of the second event is assumed to be the correct fault plane.Electronic supplementary materialThe online version of this article (10.1007/s10950-018-9734-0) contains supplementary material, which is available to authorized users.

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Section: The Double Earthquake Of August 11 2012mentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet

Amini

Roberts

Raeesi³

et al. 2018

J Seismol

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“…Previous studies argue both nodal planes. Donner et al (2015) argue that the earthquake waveform data together with the the rock mechanism suggest that the slip on eastwest plane is less probable and the north-south plane with eastward dipping is more presumable as the causative fault for the second mainshock. Nevertheless, one possibility is that the second mainshock is an elastic rebound which responds to the abrupt change of Coulomb stress arrangements close to the first mainshock's fault.…”

Section: Second Mainshock;mentioning

confidence: 91%

“…In the previous studies and calculation by national and international agencies distinct depth for the first shock is determined. Donner et al (2015) assume that the start of rupture is located at 14 km and the centroid they estimate using waveform inversion is located at shallower depth (6±1) km. Adopting their estimations, the constructed fault plane in this study have 14 km width and all main five segments start from surface and slop down 14 km (dip =90) as shown in Figures 7.…”

Section: Assessing the Source Model For The Doubletmentioning

confidence: 99%

Stress Transfere and Statistical Analysis of 2012 Ahar-Varzeghan Seismic Sequnce, Northwestern Iran

Yazdi¹,

Escribano²,

Santoyo³

2017

Proceedings - 1st Congress in Geomatics Engineering - CIGeo

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Abstract:In 11 of August 2012, two destructive earthquakes with Mw= 6.4 and 6.2 occurred between cities Ahar and Varzeghan (Northwest Iran). They had a close epicentral distance of 6 Km and also had a short time lag of 11 minutes. Following that, a high-rate of aftershock activity began where during the first month more than 2000 events (M≥0.7) affected several villages in the area. The seismic released energy induced significant damage and losses in an extensive zone. Right after the seismic doublet occurrence, a surface rupture with a primarily east-west orientation was observed. The idea of having an almost vertically dipped fault plane for the first shock is more consistent with the trace of the upper edge on the surface and the focal mechanism solutions which propose a steady dipping EW. Previous studies propose different geometries for the generating faults of the second earthquake. In this study, we associate the surface rupture with the first mainshock and both nodal plane explaining the relationship between the two main seismic events are discussed after Coulomb failure stress calculation due to the first shock. Then the stress transfer because of the doublet is analyzed in order to determine its consistency with the statistical modeling prediction for the aftershock population and spatial distribution. For statistical modeling a temporal version of Epidemic Type Aftershock Sequence (ETAS) is applied on one-year seismicity including events with minimum magnitude of 2.5. Key words: Statistical Seismology, ETAS, Coulomb Failure stress, IRAN Resumen:Dos terremotos destructivos, de magnitudes Mw=6.4 y 6.2, ocurrieron el 11 de agosto de 2012 entre las ciudades iraníes de Ahar y Varzeghan. Los epicentros se situaron cerca entre sí, a una distancia de 6 km, y con un intervalo temporal de 11 muinutos. La serie de réplicas subsiguiente se desarrollo con una tasa alta, de más de 2000 eventos en el primer mes (M≥0.7). El movimiento sísmico produjo considerable daño y pérdidas en una zona extensa. El primer evento causó una ruptura semi-vertical, consistente con uno de los planos nodales del mecanismo focal y con una ruptura en superficie con orientación este-oeste. En cuanta a la falla causante del segundo evento principal, existen varias hipótesis. En este trabajo se realiza un modelo de transferencia de esfuerzos estáticos de Coulomb debidos al primer evento para delimitar las zonas cargadas de esfuerzos en las que es más plausible que se haya desencadenado el segundo evento principal. Seguidamente, se considera el cambio de esfuerzos producido por los dos eventos a fin de determinar cuales son las zonas cargadas positiva y negativamente de esfuerzos. De forma complementaria, se desarrolla un modelado estadístico de la población de réplicas y su distribución espacial. Se usa la versión temporal del modelo ETAS (Epidemic Type Aftreshock Sequence) para identificar los eventos que son réplicas y se analiza su distribución espacial en relación a la distribución de los incrementos / decrementos de esfuerzos de Coulom...

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Landscape evolution in orogenic plateaus: Insights from quantitative morphotectonic analysis of the Turkish–Iranian Plateau and Caucasus regions

Kaveh‐Firouz,

Burg,

Giachetta

2023

Earth Surf Processes Landf

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To investigate the recent landscape evolution of the orogenic Turkish–Iranian Plateau (TIP) and the Lesser/Greater Caucasus ranges, we perform a quantitative analysis of topography and drainage networks at a regional scale. This analysis focuses on climatic–topographic swath profiles, local relief distribution, longitudinal river profiles, normalized channel steepness index (ksn), paleo‐river profile, and chi analysis (χ). In general, we find that the evolution of topographic relief and river networks are locally controlled by Late Cenozoic volcanism, contrasts in rock strength, and neotectonic activity along regional tectonic structures. However, our results show that the influence of these factors on the landscape evolution of the Greater Caucasus is significantly different from the Lesser Caucasus and TIP. This study shows that a combination of enhanced aridity, rapid uplift of orographic barriers along the TIP margins, and exposure of resistant rock types associated with the regional volcanic activity resulted in low‐relief plateau and the Lesser Caucasus surfaces that are preserved in the upper/middle Kura–Arax and Qezel‐Owzan river catchments. High local relief in the flanks of the Greater Caucasus and west Alborz, downstream increase in channel steepness, and perturbations in the χ plots of the three main rivers indicate that the topography is in a transient state.We reconstruct the paleo‐river profiles from the relict section of the upper Kura–Arax and Qezel‐Owzan rivers and show that the last drastic fall of the Caspian base‐level, which occurred during the Late Miocene–Early Pliocene, can explain the incision of ~500–1000 m gorges (i.e., Amardos) below major knickpoints. Furthermore, local cross‐divide differences of the χ parameter reveal that disequilibrium in the plan‐form geometry of the drainage networks, attributed to the upstream migration of the regional knickpoints towards the plateau interior and integration of plateau areas into the external fluvial system.

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The Ahar‐Varzeghan Earthquake Doublet (M_w 6.4 and 6.2) of 11 August 2012: Regional Seismic Moment Tensors and a Seismotectonic Interpretation

Cited by 28 publications

References 46 publications

Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet

Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet

Stress Transfere and Statistical Analysis of 2012 Ahar-Varzeghan Seismic Sequnce, Northwestern Iran

Landscape evolution in orogenic plateaus: Insights from quantitative morphotectonic analysis of the Turkish–Iranian Plateau and Caucasus regions

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The Ahar‐Varzeghan Earthquake Doublet (Mw 6.4 and 6.2) of 11 August 2012: Regional Seismic Moment Tensors and a Seismotectonic Interpretation

Cited by 28 publications

References 46 publications

Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet

Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet

Stress Transfere and Statistical Analysis of 2012 Ahar-Varzeghan Seismic Sequnce, Northwestern Iran

Landscape evolution in orogenic plateaus: Insights from quantitative morphotectonic analysis of the Turkish–Iranian Plateau and Caucasus regions

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The Ahar‐Varzeghan Earthquake Doublet (M_w 6.4 and 6.2) of 11 August 2012: Regional Seismic Moment Tensors and a Seismotectonic Interpretation