| 1. |
- Amini, Samar, et al.
(författare)
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Directivity analysis of the 2017 December Kerman earthquakes in Eastern Iran
- 2020
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Ingår i: Journal of Seismology. - : Springer. - 1383-4649 .- 1573-157X. ; 24, s. 531-547
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Tidskriftsartikel (refereegranskat)abstract
- Using an empirical Green’s function (EGF) approach and data from local to regional distances we analyzed rupture propagation directivity in the three mainshocks (ML 6.0–6.1) and in six of the largest aftershocks (ML 5.0 – 5.5) of the 2017 Kerman, Iran, seismic sequence. The EGF procedure was based on data from smaller events (ML 4.0 – 4.8). Deconvolution was applied separately to P and S phases. Using the P-wave data, we calculated relative source-time functions and examined azimuthal variations in rupture duration. In the S-wave analysis, we investigated along strike rupture directivity of the mainshocks and the largest aftershocks by evaluating azimuthal variation of the amplitude spectra. Two of the mainshocks and four of the aftershocks clearly showed rupture propagation from the south-east toward the north-west. The third mainshock and one of the aftershocks suggested almost bilateral rupture propagation, and one aftershock showed rupture directivity to the southeast. It seems that the rupture propagation direction in the area is generally to the north-west and the events which have different propagation directions are located within the NW and SE ends of the faulting area. We suggest that the general rupture propagation direction in the area is steered by regional tectonic stress field regarding the faulting orientations which have been affected by stress redistribution around a restraining bend.
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| 2. |
- Amini, Samar, et al.
(författare)
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Fault slip and identification of the second fault plane in the Varzeghan earthquake doublet
- 2018
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Ingår i: Journal of Seismology. - : SPRINGER. - 1383-4649 .- 1573-157X. ; 22:4, s. 815-831
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Tidskriftsartikel (refereegranskat)abstract
- 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.
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| 3. |
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| 4. |
- Amini, Samar
(författare)
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Source analysis of multiplet earthquakes (two case studies in Iran)
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Multiplet earthquakes are large earthquakes of similar magnitude which occur close in time in the same limited geographical area. They are not common but they considerably increase the potential hazard in the area in which they occur. This thesis studies source properties and triggering mechanisms of two sets of multiplet events in Iran, which both occurred in unexpected areas, but close to some major active fault systems. The first multiplet is an earthquake doublet (Mw 6.5 and Mw 6.4) which occurred in northwestern Iran and caused more than 300 fatalities and significant injuries. In paper I, a teleseismic body-waveform inversion was used to deduce the slip distribution pattern on the fault plane of the first mainshock. The estimated slip pattern was utilized to calculate the Coulomb stress changes on the second fault plane and on the following aftershocks. Based on this analysis, the ambiguity between the primary and auxiliary fault plane of the second mainshock could be resolved. The second set of events is a triplet (Mw 6.1 - 6.0) that occurred in eastern Iran, close to the Kerman province. In paper II, the rupture propagation patterns of the three mainshocks were analyzed using Empirical Green’s Function (EGF) deconvolution. Two different approaches were used: One, the analysis of the azimuthal variation of the apparent rupture duration based on the width of the observed relative source time functions, and the second, the analysis of along-strike rupture directivity by assessing azimuthal variations of the relative amplitude spectra. The second approach was also used to investigate the rupture directivity of the largest aftershocks in the sequence (Mw 5 - 5.5). A clear tendency for rupture propagation towards the northwest was observed for the sequence, which suggests that the regional stress field has a central role in controlling the rupture propagation direction. In paper III, the slip distribution patterns of the triplet earthquakes were analyzed using teleseismic body-waveform inversion, and the similarities and differences in the rupture processes of the three mainshocks were investigated. Using the Coulomb stress analyses, the stress interactions between the mainshocks were examined, leading to identification of the primary and auxiliary planes. Finally, we suggest that the hazard estimates in complex continental regions such as Iran need to consider the probability of multiplets, which might allow a reduction of the seismic risk associated to the occurrence of further large earthquakes subsequent to a devastating earthquake.
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| 5. |
- Amini, Samar, et al.
(författare)
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Tomographic upper-mantle velocity structure beneath the Iranian Plateau
- 2012
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Ingår i: Tectonophysics. - : Elsevier BV. - 0040-1951 .- 1879-3266. ; 554-557, s. 42-49
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Tidskriftsartikel (refereegranskat)abstract
- The Iranian plateau is one of the most structurally complex and tectonically inhomogeneous regions in the world. In this study, we analyze Pn arrival-times from regional seismicity in order to resolve lateral velocity variations within the uppermost-mantle under the Iranian Plateau. More than 48,000 Pn first arrival times selected from the EHB catalog were used with epicentral distances of 200 to 1600 km. We used regularized isotropic and anisotropic damped least-squares inversion to image lateral velocity variations in the upper mantle. Our velocity model, with high lateral resolution, shows positive anomalies in the Zagros mountain belt with a distinct transition approximately along the Main Zagros Thrust to the lower mantle velocity zone of Central Iran. Anomalously low velocities are observed predominantly beneath NW Iran and eastern Turkey, suggesting a zone of relatively weak mantle. Low velocity region under the Damavand volcano reveals the hot upper mantle beneath the central Alborz mountains.
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| 6. |
- Raeesi, Mohammad, et al.
(författare)
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Quantitative Analysis of Seismicity in Iran
- 2017
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Ingår i: Pure and Applied Geophysics. - Univ Western Ontario, Dept Earth Sci, London, ON, Canada. Univ Gavle, Dept Ind Dev IT & Land Management, Gavle, Sweden. Lantmateriet, Gavle, Sweden. Uppsala Univ, Dept Earth Sci, Uppsala, Sweden. Univ Colorado, CIRES, Boulder, CO USA. Univ Colorado, Dept Geol Sci, Boulder, CO USA. : Springer Science and Business Media LLC. - 0033-4553 .- 1420-9136. ; 174:3, s. 793-833
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Tidskriftsartikel (refereegranskat)abstract
- We use historical and recent major earthquakes and GPS geodetic data to compute seismic strain rate, geodetic slip deficit, static stress drop, the parameters of the magnitude–frequency distribution and geodetic strain rate in the Iranian Plateau to identify seismically mature fault segments and regions. Our analysis suggests that 11 fault segments are in the mature stage of the earthquake cycle, with the possibility of generating major earthquakes. These faults primarily are located in the north and the east of Iran. Four seismically mature regions in southern Iran with the potential for damaging strong earthquakes are also identified. We also delineate four additional fault segments in Iran that can generate major earthquakes without robust clues to their maturity.The most important fault segment in this study is the strike-slip system near the capital city of Tehran, with the potential to cause more than one million fatalities.
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