21 research outputs found
Simulation of the 2009, Mw = 4 Tehran earthquake using a hybrid method of modal summation and finite difference
The Greater Tehran Area is the most important city of Iran and hosts about 20% of the country?s population. Despite the presence of major faults and the occurrence of historical earthquakes, the seismicity is relatively low at present. Thus, it is important to estimate the ground motion for preventive, reliable seismic hazard assessment. An earthquake with magnitude Mw = 4, which occurred close to Tehran, 17 October 2009, is the first local earthquake that has been recorded by the local strong ground motion network in Tehran. To simulate the ground motion caused by the earthquake a hybrid technique is used. It combines two methods: the analytical modal summation and the numerical finite difference, taking advantage of the merits of both. The modal summation is applied to simulate wave propagation from the source to the sedimentary basin and finite difference to propagate the incoming wavefield in the laterally heterogeneous part of the structural model that contains the sedimentary basin. Synthetic signals are simulated along two East?West and Southeast?Northwest profiles. Frequency, response spectra, and time domain, waveforms and peak values, parameters are computed synthetically and compared with observed records. Results show agreement between observed and simulated signals. The simulation shows local site amplification as high as 6 in the southern part of Tehran
Molecular characterization of Mycobacterium tuberculosis isolates from Tehran, Iran by restriction fragment length polymorphism analysis and spoligotyping
Towards a reliable seismic microzonation in Tehran, Iran
A hybrid method for the calculation of realistic synthetic seismograms in laterally heterogeneous, anelastic media has been used to model the ground motion in Tehran city. The synthetic records compare reasonably well with the observed ground motion due to the 2004 Firozabad Kojor earthquake located 60 km north of Tehran. The ratio between the response spectrum for the signals calculated along a laterally varying structure, Sa(2D), and that for the signals at the bedrock regional reference structure, Sa(1D), shows a high amplification of seismic waves in Tehran. The procedure can be readily implemented for the entire Tehran city, which experienced large historical earthquakes in the past, simply by extending the analysis, made so far, in space and to different scenario earthquakes, consistent with the local and regional tectonics
Shear-Wave Velocity Tomography of the Lithosphere\u2013Asthenosphere System beneath the Iranian Plateau.
We conducted a tomographic inversion of Rayleigh-wave dispersion to obtain 2D phase and group velocity tomographic images in 10\u2013100 s period range and shear-wave velocity structures for the Iranian plateau. For this purpose, the fundamental mode of Rayleigh waves, recorded along 1586 paths by 29 broadband stations, was identified by applying the frequency time analysis (FTAN) to each epicenter\u2013station path which, at the same time, satisfies the two-station method conditions. The fundamental modes identified by FTAN have been used to determine the path-average interstation phase and group velocities at selected periods. With this procedure, 243 group and phase velocity dispersion curves were processed to obtain tomographic maps by applying the Yanovskaya\u2013Ditmar formulation for periods in the 10\u2013100 s range. Averaged dispersion curves of phase and group velocities, which represent six rather homogeneous regions, are computed. Finally, we used a fully nonlinear inversion procedure to derive tomographic images of the elastic structure of the lithosphere and asthenosphere of the six main structural and seismotectonic features of the Iranian plateau. The dense path coverage in the Iranian plateau permits us to produce images that have substantially higher lateral resolution compared to images currently available from global and regional group velocity studies. Tomographic maps at high frequencies are well correlated with the upper crust structure, especially with sediment layers thickness. Estimated shear-wave velocity structures are well correlated with shield-like lithosphere structure in Zagros. No low-velocity zone (LVZ) is detected in Alborz and the South Caspian, which can imply the thrusting of oceanic crust of the southern Caspian Sea under the Alborz to the south. LVZs are derived for the region east of Iran, central Iran, and Kopeh Dagh
3- Dimensional Modal Summation simulation of 2003 Mw=6.6 Bam Earthquake South Eastern Iran
A new methodology for computing synthetic seismograms, complete of the main direct, refracted, converted phases and surface waves, in three \u2013 dimensional anelastic lateral heterogeneous media is applied to the modeling of the local records of the 2003 Bam Mw 6.6 Earthquake, South-Eastern Iran. The method is based on the combination of the Modal Summation (MS) technique with the Asymptotic Ray Theory (ART). The three \u2013 dimensional models are determined by a set of vertically heterogeneous sections (1D structures) that are juxtaposed on a regular grid. The distribution of these sections in the grid is done in such a way to satisfy the condition of applicability of the WKBJ approximation, i.e. the lateral variation of all the elastic parameters has to be small with respect to the prevailing wavelength. The procedure, described very briefly, has been applied for the area of destructive 26 December 2003 Bam earthquake Mw= 6.6
Assessing performances of pattern informatics method: a retrospective analysis for Iran and Italy
5Pattern Informatics (PI) algorithm, which was introduced at the beginning of past decade, uses instrumental earthquake catalogs to investigate the time dependent rate of seismicity in the study area and, based on the information from past events, calculates the probabilities for the occurrence of future large earthquakes. The main measure in this method is the number of events above a specified magnitude threshold Mc that is counted over a gridded area. PI has been applied in several regions of the world and different variants of the method have been developed over the past decade. Hence the problem of formally evaluating and comparing the performances of the different PI variants needs to be addressed from an operational perspective, in order to identify the preferred application scheme and as well as to improve the performances of the method.
In this study, PI is applied for the first time to the retrospective analysis of the earthquake catalogs of Iran and Italy, so as to check if this method could forecast the past large events in these two regions with different level of data completeness and complex seismotectonic setting. The original PI algorithm and one of its modified variants, as well as the Relative Intensity (RI) model, are used to check the stability and statistical significance of the obtained results. In order to assess and compare the obtained results, the performances of the different PI variants are analyzed considering different evaluation strategies, which turn out to provide significantly different scores even for the same algorithm variant. We show that a critical point in the assessment of the obtained results is related with the definition and quantification of the space uncertainty of the issued forecasts, i.e. with the extent of the territory where large earthquakes are to be expected. Accordingly, we emphasize the need for an appropriate definition of the evaluation strategies, clearly and unambiguously indicating the area where a large earthquake has to be expected.
The study shows that, with respect to application in Iran and Italy, the performances of PI algorithm (both original and modified variants) are highly dependent on the selected evaluation strategy and do not provide better information than the simple RI model, which does not account for temporal properties of seismicity evolution. The overall performances can be improved by introducing specific thresholds that discard the less active cells; however, being based on some posterior optimization, a rigorous prospective testing is required to assess the forecasting capability of the method. In this paper we aim to set up the rules for such testing, including advance definition of the evaluation strategy.nonemixedM. Y. Radan; H. Hamzehloo; A. Peresan; M. Zare; H. ZafaraniM. Y., Radan; H., Hamzehloo; Peresan, Antonella; M., Zare; H., Zafaran
Simulation of selected strong motion records of the 2003 Mw=6.6Bam earthquake (SE Iran), the modal summation-ray tracing methods in the WKBJ approximation.
A new analytical methodology for computing synthetic seismograms in 3-D anelastic media is applied to the modelling of the local records of the 2003 Bam Mw 6.6 earthquake, Southeastern Iran. The method is based on the combination of the modal summation technique with the asymptotic ray theory. The 3-D models are determined by a set of vertically heterogeneous sections (1-D structures) that are juxtaposed on a regular grid. The distribution of these sections in the grid is done in such a way to satisfy the condition of applicability of the WKBJ approximation, that is, the lateral variation of all the elastic parameters has to be small with respect to the prevailing wavelength. The procedure, described very briefly, has been applied for the area of the destructive 2003 December 26 Bam earthquake Mw 6.6, with a maximum cut-off frequency of 6 Hz. Synthetic seismograms show fine agreement with recorded signals when comparing shapes, amplitudes and spectra and evidence the relevance of 3-D effects
Analysis of precursory seismicity patterns in Zargos (Iran) by CN algorithm.
This study illustrates the application of the CN algorithm for the analysis of precursory seismicity patterns in the Zagros region (Iran), an area characterized by a complex seismotectonic setting and by remarkable seismic activity. CN is a formally defined and widely tested algorithm for intermediate-term middle-range earthquake prediction, based on the analysis of routinely compiled earthquake catalogs. To allow its application, the global and regional catalogs available for the territory of Iran have been analyzed so as to compile a data set sufficiently complete and homogeneous over a time span of about 3 decades, as required for CN application. A number of tests have been performed with respect to changes in the input catalogs, assuming different magnitude completeness levels as well as considering different magnitude thresholds for the selection of target earthquakes. Different variants of the regionalization have been outlined according to the seismotectonic model, and it was concluded that precursory seismicity patterns for the largest events need to be researched in the whole Zagros tectonic domain. Accordingly, an experiment was set up aimed at validation of intermediate- term middle-range prediction of earthquakes with magnitude M 65 6.0 in the Zagros region. Starting in March 2012, CN prediction results have been routinely updated based on the events with M 65 Mc = 4.0 as they are reported in the International Seismological Centre catalog
High rates of nontuberculous mycobacteria isolation from patients with presumptive tuberculosis in Iran
Nontuberculous mycobacteria (NTM) can cause disease which can be indistinguishable from tuberculosis (TB), posing a diagnostic and therapeutic challenge, particularly in low- and middle-income settings. We aimed to investigate the mycobacterial agents associated with presumptive clinical pulmonary TB in Iran. A total of 410 mycobacterial isolates, obtained between March 2014 and January 2016, from 7600 clinical samples taken from consecutive cases of presumptive diagnosis of TB were identified. Phenotypic and molecular tests were used to identify the isolated organisms to the species level. Single-locus and multilocus sequence analysis based on 16S rRNA, rpoB, hsp65 and ITS locus were used to confirm the results. Of 410 consecutive strains isolated from suspected TB subjects, 62 isolates (15.1%) were identified as NTM. Patients with positive NTM cultures met American Thoracic Society diagnostic criteria for NTM disease. Mycobacterium simiae was the most frequently encountered (38.7%), followed by Mycobacterium fortuitum (19.3%), M. kansasii (17.7%) and M. avium complex (8.0%). Isolation of NTM, including M. simiae, from suspected TB cases is a serious public health problem and merits further attention by health authorities, physicians and microbiologists Keywords: Iran, mycobacterium, Mycobacterium simiae, nontuberculous, tuberculosi
The 7H11 Agar Medium Supplemented with Calf Bovine Serum for Susceptibility Testing of Mycobacterium tuberculosis Isolates Against Pyrazinamide
Despite its importance, pyrazinamide (PZA) is a blind spot in drug susceptibility testing in tuberculosis laboratories. The aim of this study was to set up a reliable agar-based proportion method for detection of PZA-resistant phenotypes using Middlebrook 7H11 agar supplemented with calf bovine serum (CBS) compared with albumin/dextrose/catalase (ADC) enrichment and pncA/rpsA sequencing results. The 7H11 agar medium supplemented with 10 ADC or 10 CBS (pH 6.2) and 100 mu g/mL PZA was used to detect PZA resistance among 64 Mycobacterium tuberculosis isolates. Sanger sequencing and whole-genome sequencing were performed to track mutations in the pncA, rpsA, and their upstream regions. A total of 43 rifampicin/multidrug-resistant, 20 drug-susceptible, and 1 isoniazid mono-resistant M. tuberculosis isolates were investigated. The 7H11+ADC and 7H11+CBS could detect 22 and 23 PZA-resistant strains, respectively. With the same specificity, the sensitivity and accuracy of 7H11+CBS was found to be a little greater than 7H11+ADC in PZA resistance detection compared with sequencing results. Twenty-four mutant strains were found to have different mutations in pncA-upstream, pncA and rpsA genes, in which Gly97Asp was the most dominant mutation. The results obtained from 7H11+CBS were comparable to the results of 7H11+ADC. Therefore, the 7H11 agar proportion method would be a less-expensive test using CBS and produces reliable results