| 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. |
- Enferadi, S., et al.
(författare)
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Feasibility study of earthquake early warning in Tehran, Iran
- 2021
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Ingår i: Journal of Seismology. - : Springer Nature. - 1383-4649 .- 1573-157X. ; 25:4, s. 1127-1140
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Tidskriftsartikel (refereegranskat)abstract
- In this study, we examine the scientific feasibility of an Earthquake Early Warning System in Tehran, Iran, by the integration of the Tehran Disaster Mitigation and Management Organization (TDMMO) accelerometric network and the PRobabilistic and Evolutionary early warning SysTem (PRESTo). To evaluate the performance of the TDMMO-PRESTo system in providing the reliable estimations of earthquake parameters and the available lead-times for The Metropolis of Tehran, two different approaches were analyzed in this work. The first approach was assessed by applying the PRESTo algorithms on waveforms from 11 moderate instrumental earthquakes that occurred in the vicinity of Tehran during the period 2009-2020. Moreover, we conducted a simulation analysis using synthetic waveforms of 10 large historical earthquakes that occurred in the vicinity of Tehran. We demonstrated that the six worst-case earthquake scenarios can be considered for The Metropolis of Tehran, which are mostly related to the historical and instrumental events that occurred in the southern, eastern, and western parts of Tehran. Our results indicate that the TDMMO-PRESTo system could provide reliable and sufficient lead-times of about 1 to 15s and maximum lead-times of about 20s for civil protection purposes in The Metropolis of Tehran.
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| 3. |
- Gospodinov, Dragomir, et al.
(författare)
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On the applicability of the RETAS model for forecasting aftershock probability in underground mines (Kiirunavaara Mine, Sweden)
- 2022
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Ingår i: Journal of Seismology. - : Springer. - 1383-4649 .- 1573-157X. ; 26:5, s. 1023-1037
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Tidskriftsartikel (refereegranskat)abstract
- Aftershock series of even comparatively small seismic events can pose a risk to the mining operation or the personnel in deep underground mines as the main shocks and some of the aftershocks can cause damage in the rock mass. Stochastic modeling was applied in this study for the analysis of the temporal evolution of aftershock occurrence probability during a M1.85 aftershock sequence in Kiirunavaara Mine, Sweden. The Restricted Epidemic-Type Aftershock Sequence (RETAS) model was chosen for estimation of the aftershock occurrence probability. This model considers all events with magnitude above the magnitude of completeness M0 and has the advantage of including the Modified Omori Formula (MOF) model and Epidemic-Type Aftershock Sequence (ETAS) model as its end versions, considering also all intermediate models. The model was applied sequentially to data samples covering cumulative periods of time, starting from the first 2 h after the main event and increasing them by 2 h until the period covered the entire 72-h sequence. For each sample, the best-fit RETAS version was identified and the probability of a M ≥ 0.5 aftershock for every next 2 h was determined through Monte Carlo simulation. The feasibility of the resulting probability evolution for suspension and re-starting of the mining operations was discussed together with possible prospects for future development of the methodology.
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| 4. |
- Hamed, A. A., et al.
(författare)
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On the strength of the phase cross-correlation in retrieving the Green's function information in a region affected by persistent aftershock sequences
- 2021
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Ingår i: Journal of Seismology. - : Springer Nature. - 1383-4649 .- 1573-157X. ; 25:3, s. 987-1003
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Tidskriftsartikel (refereegranskat)abstract
- 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 M-N 5.2 with the help of empirical Green's functions (EGF) obtained after the Ahar-Varzeghan Earthquake Doublet (M-N 6.4 and M-N 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.
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| 5. |
- Niazpour, Bita, et al.
(författare)
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Source study of 2017 Hojedk triplet earthquake sequence, southeast Iran
- 2021
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Ingår i: Journal of Seismology. - : Springer Nature. - 1383-4649 .- 1573-157X. ; 25, s. 85-101
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Tidskriftsartikel (refereegranskat)abstract
- In December 2017, a triplet earthquake sequence of M(w)5.8-6.1 occurred near Hojedk, southeast Iran. The sequence was not destructive, but occurred in a highly seismically active region that previously experienced the 1981-1998 Sirch-Golbaf earthquake sequence and destructive 2003 M(w)6.6 Bam earthquake. We apply a waveform inversion method based on the modeling of regional seismic broadband data to derive the point source and kinematic rupture parameters of the triplet and its five significant aftershocks. The choice of an earthquake source model with a reduced number of parameters and a sequential inversion process with several iterations result in unique and stable earthquake source solutions. Within the inversion process, we combine the modeling of low- and high-frequency seismological data to retrieve the moment tensor and the kinematic source parameters. Synthetic seismogram and spectra are generated for an accurate regional velocity model. Our results suggest that the triplet ruptured a segmented fault system, with centroid locations aligned along a single lineament. Estimation of rupture directivity suggests the activation of SE-NW structure. In conclusion, we suggest that the triplet was associated with the failure of one or more aligned blind thrust faults, oriented SE-NW and dipping to the NE, in a restraining bend between strike-slip faults in a region that is a part of the greater system of the present continental shortening in Iran.
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