Delineation of potential seismic sources for seismic zoning of Iran

A total of 235 potential seismic sources in Iran and neighboring regions are delineated based on available geological, geophysical, tectonic and earthquake data for seismic hazard assessment of the country. In practice, two key assumptions are considered; first, the assumption of earthquake repeatedness, implying that major earthquakes occur preferentially near the sites of previous earthquakes; second, the assumption of tectonic analogy, which implies that structures of analogous tectonic setting are capable of generating same size earthquakes. A two-step procedure is applied for delineation of seismic sources: first, demarcation of seismotectonic provinces; second, determination of potential seismic sources. Preferentially, potential seismic sources are modeled as area sources, in which the configuration of each source zone is controlled, mainly, by the extent of active faults, the mechanism of earthquake faultings and the seismogenic part of the crust.     

Alkaline lamprophyric province of Central Iran

Paleozoic lamprophyres exhibit good exposures in the western part of the Central–East Iranian microcontinent. These rocks crop out as volcanoes, dykes, and plugs. The constituent minerals are amphibole, clinopyroxene, plagioclase, K‐feldspar, olivine, Cr‐spinel, titanite, biotite, and ilmenite. The main textures in volcanic lamprophyres are porphyritic, trachytic, microlithic, and variolitic, whereas in dykes and plugs, intergranular texture is common. These lamprophyres are regionally metamorphosed in some areas. Petrographical and geochemical characteristics of the studied rocks suggest that they are classified as alkaline lamprophyres and camptonites. They are enriched in alkalis (Na₂O + K₂O), large ion lithophile elements, and light rare earth elements, and the features of trace element concentrations are similar to those of within‐plate basalts. This study suggests that the lamprophyres were derived from different degrees of partial melting of metasomatized amphibole‐bearing spinel lherzolite. Subduction of Paleo‐Tethys oceanic crust from the Early to late Paleozoic resulted in enrichment in fluids in the mantle, and lamprophyric magmatism occurred along the minor and major faults. This limited but typical lamprophyric magmatism in a broad area of Central Iran suggests that, in spite of the long length of the Paleozoic (～250 my), it was a relatively calm era from the viewpoint of magmatism in Central Iran.     

A GIS-based time-dependent seismic source modeling of Northern Iran

The first step in any seismic hazard study is the definition of seismogenic sources and the estimation of magnitude-frequency relationships for each source. There is as yet no standard methodology for source modeling and many researchers have worked on this topic. This study is an effort to define linear and area seismic sources for Northern Iran. The linear or fault sources are developed based on tectonic features and characteristic earthquakes while the area sources are developed based on spatial distribution of small to moderate earthquakes. Time-dependent recurrence relationships are developed for fault sources using renewal approach while time-independent frequency-magnitude relationships are proposed for area sources based on Poisson process. GIS functionalities are used in this study to introduce and incorporate spatial-temporal and geostatistical indices in delineating area seismic sources. The proposed methodology is used to model seismic sources for an area of about 500 by 400 square kilometers around Tehran. Previous researches and reports are studied to compile an earthquake/fault catalog that is as complete as possible. All events are transformed to uniform magnitude scale; duplicate events and dependent shocks are removed. Completeness and time distribution of the compiled catalog is taken into account. The proposed area and linear seismic sources in conjunction with defined recurrence relationships can be used to develop time-dependent probabilistic seismic hazard analysis of Northern Iran.     

Geochemistry and petrology of garnet‐bearing S‐type Shir‐Kuh Granite,southwest Yazd,Central Iran

The Jurassic Shir‐Kuh granitoid batholith in Central Iran intrudes Lower Jurassic sandstones and shales. The batholith consists of three main facies: (i) a granodioritic facies to the north; (ii) a monzogranitic facies spread throughout the batholith; and (iii) a leucogranitic facies along the northwestern margin. The granodiorites are composed mainly of plagioclase, quartz, K‐feldspar, biotite, and some muscovite, garnet, cordierite, ilmenite, zircon, apatite, and monazite. This facies contains variable amounts of restite minerals which are mainly defined by calcic plagioclase cores and small aggregates of biotite. The monzogranites, with mineral assemblages similar to those in the granodiorites, range from relatively mafic (cordierite‐bearing) to felsic (muscovite‐rich) rocks. The leucogranites, exposed as small stock and dykes, consist mainly of quartz, K‐feldspar, and sodic plagioclase. The batholith is peraluminous, calc‐alkaline, and typical of S‐type, as indicated by Na₂O content (2.74%), molecular Al₂O₃/(CaO + Na₂O + K₂O) (A/CNK) ratio (1.17), K₂O/Na₂O ratio (1.39), and isotopic data ([⁸⁷Sr/⁸⁶Sr]_i = 0.715). The rocks are characterized by enrichment in large ion lithophile elements such as Rb, Th and K and depletion in high field strength elements such as Nb and Ti. Chondrite‐normalized rare earth element (REE) patterns are characterized by light rare earth element (LREE) enrichment, with values of (La/Yb)_N between 4.5 and 19.53, unfractionated heavy rare earth element (HREE) with values of (Gd/Yb)_N between 0.98 and 2.88, and a distinct negative Eu. The parental magma of the Shir‐Kuh Granite was derived from a plagioclase‐rich metasedimentary source (local anatexis of metagreywacke) in the crust, with heat input from mantle melt components. The separation of restite crystals from the primary melt followed by the fractional crystallization appears to have been an effective differentiation process in the batholith.     

Estimation of earthquake parameters in the Alborz seismic zone,Iran using generalized inversion method

Generalized inversion of the S-wave amplitude spectra from the strong-motion network data in the Alborz, Iran has been used to estimate simultaneously source parameters, site response and S-wave attenuation (Qs). To obtain an optimum inverse solution, and also for decreasing the uncertainty level, a frequency-dependent site amplification as a constraint, was imposed to five reference site responses. This constraint removes the undetermined degree of freedom in the inversion. Furthermore, for removing the trade-off between geometrical spreading and anelastic attenuation, a geometrical spreading factor was adopted from the Motazedian [20] study. A point source model has been calibrated against the resulting source terms and consequently source parameters, like corner frequency, moment magnitude and high frequency fall off coefficient, for each event has been determined separately. Also, based on the available data and their connectivity two sub-regions including western and eastern parts of Alborz located east and west of 52.5°E have been considered to see that if there is any possible systematic difference in their seismic source characteristics. The average stress drops obtained are about 182 and 116 bars, respectively for eastern and western Alborz. Another result of the study is the site responses, which have been determined for all of 81 stations individually. Though soil nonlinearity was detected at the Ab-bar station (experienced strong ground shaking, i.e., PGA>0.5 g) near to the epicenter of Manjil M7.4 earthquake of June 20, 1990, but an analysis of residuals showed generally a weak influence of soil nonlinearity (i.e., dependence of amplification on shaking level); probably because of the relatively weak levels of acceleration in our database. Finally, the shear wave quality factor (i.e., Qs) has been determined as a function of frequency represented by a linear equation in logarithmic scale. To evaluate the outcomes of the current study, the results have been compared with similar studies wherever it was available. The results of the current study are of utmost importance for seismic hazard assessment of the metropolitan area of Tehran, where 15 million people live, one-fifth of the population of Iran.     

基于小波与分形理论的地震异常检测

为了提高地震异常检测精度,探讨了小波与分形结合的地震异常检测方法.首先采取功率谱密度对地震波的分形性质进行分析,得出其具有且仅在几个高频段具有自仿射分形性质,这为分形的合理应用提供了依据并揭示了现有单一综合分形维方法的不足;继而提出了频率、时间有序的无次采样小波包变换(FOTO-NWPT),该算法为地震波分形分析创造了优良平台.基于前两者,提出了小波与分形优势结合的地震异常检测方法：由FOTO-NWPT将地震波分解在若干尺度上,依据尺度关联维分析构建地震剖面分形参数空间,参数奇异标志了地震异常.工程实验证明,该方法比现有方法的科学性和实用性更强,为实现度量参数化精细地震勘探提供了一条新的思路.     

Mineral potential mapping in Central Iran using fuzzy ordered weighted averaging method

The aim of this work is to introduce the application of the fuzzy ordered weighted averaging method as a straightforward knowledge‐driven approach to explore porphyry copper deposits in an airborne prospect. In this paper, the proposed method is applied to airborne geophysical (potassium radiometry, magnetometry, and frequency‐domain electromagnetic) data, geological layers (fault and host rock zones), and various extracted alteration layers from remote sensing images. The central Iranian volcanic–sedimentary belt in Kerman province of Iran that is located within the Urumieh–Dokhtar (Sahand–Bazman) magmatic arc is chosen for this study. This region has high potential of mineral occurrences, especially porphyry copper, containing some active world‐class copper mines such as Sarcheshmeh. Two evidential layers, including the downward continued map and the analytic signal of such filtered magnetic data, are generated to be used as geophysical plausible traces of porphyry copper occurrences. The low values of the resistivity layer acquired from airborne frequency‐domain electromagnetic data are also used as an electrical criterion in this study. Four remote sensing evidential layers, including argillic, phyllic, propylitic, and hydroxyl alterations, are extracted from Advanced Spaceborne Thermal Emission and Reflection Radiometer images in order to map the altered areas associated with porphyry copper deposits. The Enhanced Thematic Mapper plus images are used to map iron oxide layer. Since potassium alteration is the mainstay of copper alteration, the airborne potassium radiometry data are used. Here, the fuzzy ordered weighted averaging method uses a wide range of decision strategies in order to generate numerous mineral potential/prospectivity maps. The final mineral potential map based upon desired geo‐data set indicates adequately matching of high‐potential zones with previous working mines and copper deposits.     

On the development of a seismic source zonation model for seismic hazard assessment in western Saudi Arabia

A new seismic source model has been developed for the western part of the Arabian Peninsula, which has experienced considerable earthquake activity in the historical past and in recent times. The data used for the model include an up-to-date seismic catalog, results of recent studies of Cenozoic faulting in the area, aeromagnetic anomaly and gravity maps, geological maps, and miscellaneous information on volcanic activity. The model includes 18 zones ranging along the Red Sea and the Arabian Peninsula from the Gulf of Aqaba and the Dead Sea in the north to the Gulf of Aden in the south. The seismic source model developed in this study may be considered as one of the basic branches in a logic tree approach for seismic hazard assessment in Saudi Arabia and adjacent territories.     

Geostatistical assessment for the regional zonation of seismic site effects in a coastal urban area using a GIS framework

Earthquake-induced hazards are profoundly affected by site effects related to the amplification of ground motions, which are strongly influenced by local geologic conditions such as soil thickness, bedrock depth, and soil stiffness. Seismic disasters are often more severe over soft soils than over stiff soils or rocks due to differences in local site effects. In this study, on the basis of a geotechnical information system (GTIS) framework, we developed an advanced geostatistical assessment for the regional zonation of seismic site effects. In particular, to reliably predict spatial geotechnical information, we developed a procedural methodology for building an advanced GTIS within a geographic information system framework and applied it to the Busan area in Korea. The systemized GTIS comprised four functional components: database, geostatistical analysis, geotechnical analysis, and visualization. First, to build the GTIS, we collected pre-existing geotechnical data in and around the study area, and then conducted a walk-over site survey to acquire surface geo-knowledge data. Second, we determined the optimum geostatistical estimation method using a cross-validation-based verification test, considering site conditions. The advanced GTIS was used in a practical application to estimate the site effects in the study area. We created seismic zoning maps of geotechnical earthquake parameters, such as the depth to bedrock and the site period, and present them as part of a regional synthetic strategy for earthquake risk assessment.     

Temporal variations of seismicity parameters in the Central Alborz,Iran

Temporal changes of b-value, fractal (correlation) dimensions of epicenters (D _e ) and occurrence time of earthquakes (D _t ) and relations between these parameters were calculated to investigate precursory changes before 28 May 2004, Baladeh-Kojour earthquake (M _w = 6.3) of Central Alborz, Iran. 2086 events with M _N ≥ 1.7 were selected for our analyses. A wide range of variation was seen in these parameters: b-value ～ 0.6–1.11, D _e ～ 0.97–1.64, and D _t ～ 0.13–0.93. The results showed decreases in all fractal parameters several months before the main shock. This decrease, which might have arisen due to clusters of events occurred between 2002–2003, was followed by a systematic increase, corresponding to the increased level of low-magnitude seismicity. It seems that changes in fractal parameters may be precursors of Baladeh-Kojour earthquake which was caused by seismic activation and quiescence. Furthermore, a positive correlation between b-value and D _e was detected before the main shock (D _e = 0.87 + 0.7b) and during aftershock sequences (D _e = 2b ± 0.09), which was further on changed to a negative one (D _e = 2.56–1.32b).     

Earthquake relocation in the Central Alborz region of Iran using a non-linear probabilistic method

In this study, we calculate accurate absolute locations for nearly 3,000 shallow earthquakes (≤20 km depth) that occurred from 1996 to 2010 in the Central Alborz region of northern Iran using a non-linear probabilistic relocation algorithm on a local scale. We aim to produce a consistent dataset with a realistic assessment of location errors using probabilistic hypocenter probability density functions. Our results indicate significant improvement in hypocenter locations and far less scattering than in the routine earthquake catalog. According to our results, 816 earthquakes have horizontal uncertainties in the 0.5–3.0 km range, and 981 earthquakes are relocated with focal-depth errors less than 3.0 km, even with a suboptimal network geometry. Earthquake relocated are tightly clustered in the eastern Tehran region and are mainly associated with active faults in the study area (the Mosha and Garmsar faults). Strong historical earthquakes have occurred along the Mosha and Garmsar faults, and the relocated earthquakes along these faults show clear north-dipping structures and align along east–west lineations, consistent with the predominant trend of faults within the study region. After event relocation, all seismicity lies in the upper 20 km of the crust, and no deep seismicity (>20 km depth) has been observed. In many circumstances, the seismicity at depth does not correlate with surface faulting, suggesting that the faulting at depth does not directly offset overlying sediments.     

吉林省前郭地区地震各向异性的初步探讨

2013年11月吉林省前郭地区连续发生地震,本文利用11月1日到24日前郭地区6个流动地震台站记录的地震波形数据资料,使用剪切波分裂分析方法初步获得了每一个台站的剪切波快波偏振方向和慢波延迟时间,并初步探讨了研究区域地壳应力的分布.快波偏振方向主要为北西向和北东向,但是在整体上北西向的一致性较好,北东向的结果较为零散,反映了研究区域内复杂的应力特征.北西向的各向异性方向与发震断裂的走向垂直,与地震在空间上的展布方向一致.北西向的快剪切波偏振方向与地表运动速度场的方向也是一致的.快波偏振方向的分布与逆冲兼走滑的震源机制解结果基本吻合.慢波延迟时间的结果在0.85~6.93 ms·km-1范围内.MS5.3、5.8级地震前后慢波延迟时间的特征性变化反映了地壳应力的积累,以及随着地震发生应力的释放.     

Theoretical concepts of the fractal principle in the seismic process

A chain of theoretical concepts of the seismic process is constructed based on experimental results of the destruction of the solid sample under uniaxial compression obtained by G.A. Sobolev. These concepts satisfy the fractal principle and make it possible to specify calculation operations with parameters of the natural seismicity. Seismological data on aftershocks of the Racha earthquake of 1991 is processed using new procedures. As a result, the spatial structure of the focus has been specified, which makes it possible to construct detailed models of its potential.     

Assessment of seismic damage of thin and lightly reinforced concrete walls using fractal dimension of cracking

Length, maximum width, and residual width of cracks are key indicators of structural damage. However, pattern and propagation of cracks on the affected structural component should be also considered. In addition, damage evaluation based on visual inspection is a subjective and capricious procedure because the damage assessment relies on the expertise and judgment of the inspector engineer. In order to assess a rapid and reliable evaluation approach of seismic damage, pattern and propagation of cracks observed in thin and lightly reinforced concrete walls for low‐rise housing subjected to seismic demands are evaluated in this study by means of fractal dimension of cracking pattern. The proposed parameters are based on the results of an experimental program that comprised 39 low‐rise RC wall specimens having typical variables of this type of housing, such as low compressive strengths of concrete, thin walls, low axial loads, low reinforcement ratios, and web shear reinforcement made of deformed bars and welded‐wire meshes. A statistical analysis is carried out for computing values of fractal dimension associated to cracking patterns at key damage conditions. Recommendations of this study can help the inspector in estimating the current limit state or performance level of the wall and the story‐drift ratio experienced by the wall during shaking. Copyright © 2016 John Wiley & Sons, Ltd.     

Participatory developing strategies for water management in South Khorasan province,Iran

Groundwater over-exploitation has been increasing in Iran. Competing demands have grown in the face of perennial water shortages, a situation which has been exacerbated by drought conditions in the past decade. This paper describes the strategy development process recently undertaken in South Khorasan, Iran, in which the inclusion of stakeholder views was central to the approach. It involved government officials and various public and private sector interest groups. Particular efforts were made to involve well irrigators, who are likely to be heavily impacted by changes required to reduce groundwater pumping to a sustainable level. The paper concludes with a discussion of lessons learned.     

页岩气地震勘探中页岩各向异性的地震模拟研究

页岩的强各向异性特征挑战地震波传播数值模拟方法的精度极限, 特别是易引起频散的高频波(>100 Hz)传播的数值模拟.鉴于目前我国页岩气地震勘探主要以常规地震声波资料为主,本文首先介绍了一种VTI介质声波方程的任意偶数阶有限差分数值模拟方法,并讨论其稳定性条件和吸收边界条件.任意偶数阶的差分解可有效提高计算精度,压制数值频散噪声.针对页岩较强的各向异性特征,本文比较了不同模型的声波方程和VTI介质声波方程计算得到的地震响应.数值结果表明,各向异性对地震波的运动学(相位)和动力学(振幅)特性影响作用明显.因此,在页岩气地震勘探资料处理的各个环节必须充分考虑各向异性的影响,采取有别于常规油气勘探的处理流程和技术.     

层次分析方法在划分中长期地震危险区中的应用

文中介绍了层次分析方法的原理及方法,建立了中长期地震危险性预测的层次结构模型.通过构造判断矩阵并求解其特征向量,给出了各影响因素相对预测目标的重要性排序权值.在此基础上,对未来吉林省中长期地震危险区进行了划分.     

吉林省中部地区中等地震前广义分维Ds、Dt值及地震活动指数YH值的变化

分析了吉林省中部地区中等地震前分维曲线Ds,Dt及地震活动演化指数YH值异常变化过程，所得结果对吉林省未来中强地震预报是有一定意义的。     

Probabilistic aftershock hazard analysis,two case studies in West and Northwest Iran

Aftershock hazard maps contain the essential information for search and rescue process, and re-occupation after a main-shock. Accordingly, the main purposes of this article are to study the aftershock decay parameters and to estimate the expected high-frequency ground motions (i.e., Peak Ground Acceleration (PGA)) for recent large earthquakes in the Iranian plateau. For this aim, the Ahar-Varzaghan doublet earthquake (August 11, 2012; M _N =6.5, M _N =6.3), and the Ilam (Murmuri) earthquake (August 18, 2014 ; M _N =6.2) have been selected. The earthquake catalogue has been collected based on the Gardner and Knopoff (Bull Seismol Soc Am 64(5), 1363-1367, 1974) temporal and spatial windowing technique. The magnitude of completeness and the seismicity parameters (a,??b) and the modified Omori law parameters (P,??K,??C) have been determined for these two earthquakes in the 14, 30, and 60 days after the mainshocks. Also, the temporal changes of parameters (a,??b,??P,??K,??C) have been studied. The aftershock hazard maps for the probability of exceedance (33%) have been computed in the time periods of 14, 30, and 60 days after the Ahar-Varzaghan and Ilam (Murmuri) earthquakes. For calculating the expected PGA of aftershocks, the regional and global ground motion prediction equations have been utilized. Amplification factor based on the site classes has also been implied in the calculation of PGA. These aftershock hazard maps show an agreement between the PGAs of large aftershocks and the forecasted PGAs. Also, the significant role of b parameter in the Ilam (Murmuri) probabilistic aftershock hazard maps has been investigated.