Seismic hazard assessment of Tehran,Iran with emphasis on near-fault rupture directivity effects

Many destructive earthquakes happened in Tehran, Iran in the last centuries. The existence of active faults like the North Tehran is the main cause of seismicity in this city. According to past investigations, it is estimated that in the scenario of activation of the North Tehran fault, many structures in Tehran will collapse. Therefore, it is necessary to incorporate the near field rupture directivity effects of this fault into the seismic hazard assessment of important sites in Tehran. In this study, using calculations coded in MATLAB,Probabilistic Seismic Hazard Analysis(PSHA) is conducted for an important site in Tehran. Following that, deaggregation technique is performed on PSHA and the contribution of seismic scenarios to hazard is obtained in the range of distance and magnitude. After identifying the North Tehran fault as the most hazardous source affecting the site in 10000-year return period, rupture directivity effects of this fault is incorporated into the seismic hazard assessment using Somerville et al.(1997) model with broadband approach and Shahi and Baker(2011) model with narrowband approach. The results show that the narrowband approach caused a 27% increase in the peak of response spectrum in 10000-year return period compared with the conventional PSHA. Therefore, it is necessary to incorporate the near fault rupture directivity effects into the higher levels of seismic hazard assessment attributed to important sites.     

Matrix–fracture transfer shape factor for modeling flow of a compressible fluid in dual-porosity media

The matrix–fracture transfer shape factor is one of the important parameters in the modeling of fluid flow in fractured porous media using a dual-porosity concept. Warren and Root [36] introduced the dual-porosity concept and suggested a relation for the shape factor. There is no general relationship for determining the shape factor for a single-phase flow of slightly compressible fluids. Therefore, different studies reported different values for this parameter, as an input into the flow models. Several investigations have been reported on the shape factor for slightly compressible fluids. However, the case of compressible fluids has not been investigated in the past. The focus of this study is, therefore, to find the shape factor for the single-phase flow of compressible fluids (gases) in fractured porous media. In this study, a model for the determination of the shape factor for compressible fluids is presented; and, the solution of nonlinear gas diffusivity equation is used to derive the shape factor. The integral method and the method of moments are used to solve the nonlinear governing equation by considering the pressure dependency of the viscosity and isothermal compressibility of the fluid. The approximate semi-analytical model for the shape factor presented in this study is verified using single-porosity, fine-grid, numerical simulations. The dependency of the shape factor on the gas specific gravity, pressure and temperature are also investigated. The theoretical analysis presented improves our understanding of fluid flow in fractured porous media. In addition, the developed matrix–fracture transfer shape factor can be used as an input for modeling flow of compressible fluids in dual-porosity systems, such as naturally fractured gas reservoirs, coalbed methane reservoirs and fractured tight gas reservoirs.     

印度河扇水道堤岸外侧更新世沉积物波发育特征与形成过程分析*

印度河扇更新世发育的沉积物波结构复杂、形态多样,其形成过程的认识程度低。本次研究通过高分辨率地震数据和地震解释技术,研究了印度河扇沉积物波的波长、形态、波峰变化等形态特征;阐述了沉积物波与沉积物变形特征的差异、识别了两者的区分标志;总结了水道堤岸斜坡和区域斜坡上沉积物波的分布规律;在此基础上,讨论了沉积物波的形成机理和控制因素,分析了沉积物波的形成过程,并建立了印度河扇沉积物波的形成模式。研究表明: (1)研究区沉积物波波长平均为486.84 m,最大1473 m;波高在10~60 m之间,平均30 m。(2)沉积物波的形态有对称型和非对称型,其迁移方式有上坡迁移型、加积型和下坡迁移型;沉积物波主要发育在水道堤岸的斜坡上,在区域斜坡上也发育少量的沉积物波,这2种沉积物波波脊的走向差异很大,水道堤岸斜坡上的沉积物波主要分布于水道凹岸堤岸的外侧,距离水道越远其规模(波长、波高)越小,波脊走向近于NE-SW方向,与水道的走向平行或斜交;区域斜坡上的沉积物波波脊的走向多为NW-SE向,平行于区域斜坡的走向,离源区越远规模越大。(3)水道堤岸斜坡上的沉积物波是由水道型浊流在离心力的作用下,溢出水道的凹岸,在堤岸外侧的斜坡上沉积形成的,堤岸斜坡的角度对沉积物波的发育规模影响不大,浊流的强度和输沙量对其规模影响大;区域斜坡上发育的沉积物波是由顺坡而下的非水道化的浊流沉积形成;滑塌变形造成的起伏地貌以及早期沉积物波的存在,也都影响了后期沉积物波的发育。     

Power spectrum analysis of limb and disk spicule using Hinode Ca H-line broadband filter

We present observations of a solar quiet region obtained using the Hinode Solar Optical telescope (SOT) in the Ca II H-line with broadband filter taken on November 2006. We study off-limb and on-disk spicules to find a counterpart of the limb spicule on the disk. This investigation shows a strong correspondence between the limb and near limb spicules (on-disk spicules that historically were called dark or bright mottles, especially when observed in Hα, being a rather cool line) from the dynamical behavior (e.g., periodicity). An excellent time sequence of images obtained near the equatorial region with a cadence of 8 s was selected for analysis. 1D Fourier power spectra made at different positions on the disk and above the limb are shown. We take advantage of the so-called mad-max operator to reduce the effects of overlapping and improve the visibility of these hair-like features. A definite signature with strong power in the 3-min (5.5 mHz) and 5-min (3.5 mHz) oscillations for both places exists. A full range of oscillations was found and the high frequency intensity fluctuation (greater than 10 mHz or less than 100 s) corresponding to the occurrence of the so-called type II spicules and, even more impressively, dominant peaks of Fourier power spectra are seen in a wide range of frequencies and for all places of “on” and “off” disk spicules, in rough agreement with what historical works report regarding disk mottles and limb spicules. Also, some statistically significant behavior, based on the power spectrum computed for different positions, is discussed. The power for all kinds of power spectra is decreasing with increasing distance from the limb, except for photospheric oscillations (5 min or p-mode), which show a dominant peak for on-disk power spectra.     

Matching authority and VGI road networks using an extended node-based matching algorithm

The amount of volunteered geographic information (VGI) has increased over the past decade, and several studies have been conducted to evaluate the quality of VGI data. In this study, we evaluate the completeness of the road network in the VGI data set OpenStreetMap (OSM). The evaluation is based on an accurate and efficient network-matching algorithm. The study begins with a comparison of the two main strategies for network matching: segment-based and node-based matching. The comparison shows that the result quality is comparable for the two strategies, but the node-based result is considerably more computationally efficient. Therefore, we improve the accuracy of node-based algorithm by handling topological relationships and detecting patterns of complicated network components. Finally, we conduct a case study on the extended node-based algorithm in which we match OSM to the Swedish National Road Database (NVDB) in Scania, Sweden. The case study reveals that OSM has a completeness of 87% in the urban areas and 69% in the rural areas of Scania. The accuracy of the matching process is approximately 95%. The conclusion is that the extended node-based algorithm is sufficiently accurate and efficient for conducting surveys of the quality of OSM and other VGI road data sets in large geographic regions.     

Comparing Natural Source Zone Depletion Pathways at a Fuel Release Site

Natural source zone depletion (NSZD) refers to processes within chemically impacted vadose and saturated zones that reduce the mass of contaminants remaining in a defined source control volume. Studies of large petroleum hydrocarbon release sites have shown that the depletion rate by vapor phase migration of degradation products from the source control volume through the vadose zone (V‐NSZD) is often considerably higher than the rate of depletion from the source control volume by groundwater flow carrying dissolved petroleum hydrocarbons arising from dissolution, desorption, or back diffusion, and degradation products arising from biodegradation (GW‐NSZD). In this study, we quantified vadose zone and GW‐NSZD at a small unpaved fuel release site in California typical of those in settings with predominantly low permeability media. We estimated vadose zone using a dense network of efflux monitoring locations at four sampling events over 2 years, and GW‐NSZD using groundwater monitoring data downgradient of the source control volume in three depth intervals spanning up to 9 years. On average, vadose zone was 17 times greater than GW‐NSZD during the time interval of comparison, and vadose zone was in the range of rates quantified at other sites with petroleum hydrocarbon releases. Estimating vadose zone and GW‐NSZD rates is challenging but the vadose zone rate is the best indicator of overall source mass depletion, whereas GW‐NSZD rates may be useful as baselines to quantify progress of natural or engineered remediation in portions of the saturated zone in which there are impediments to loss of methane and other gases to the vadose zone.     

Source parameters estimation of 2003 Bam earthquake Mw 6.5 using empirical Green’s function method,based on an evolutionary approach

We determine the source parameters for 2003 (Mw 6.5) Bam, Iran, earthquake using an empirical Green’s function summation approach to model ground motions recorded by two strong motion stations at approximately 45 km epicentral distance. We introduce a genetic algorithm technique to optimize the fit to observed elastic response spectra. The proposed genetic algorithm technique allows us to explore the sensitivity of the results to multiple source parameters, including hypocenter location, focal mechanism (Strike and Dip), P-wave velocity in depth, fault dimension and rupture and healing velocities.     

Oscillations in solar jets observed with the SOT of Hinode: viscous effects during reconnection

Transverse oscillatory motions and recurrence behavior in the chromospheric jets observed by Hinode/SOT are studied. A comparison is considered with the behavior that was noticed in coronal X-ray jets observed by Hinode/XRT. A jet like bundle observed at the limb in Ca II H line appears to show a magnetic topology that is similar to X-ray jets (i.e., the Eiffel tower shape). The appearance of such magnetic topology is usually assumed to be caused by magnetic reconnection near a null point. Transverse motions of the jet axis are recorded but no clear evidence of twist is appearing from the highly processed movie. The aim is to investigate the dynamical behavior of an incompressible magnetic X-point occurring during the magnetic reconnection in the jet formation region. The viscous effect is specially considered in the closed line-tied magnetic X-shape nulls. We perform the MHD numerical simulation in 2-D by solving the visco-resistive MHD equations with the tracing of velocity and magnetic field. A qualitative agreement with Hinode observations is found for the oscillatory and non-oscillatory behaviors of the observed solar jets in both the chromosphere and the corona. Our results suggest that the viscous effect contributes to the excitation of the magnetic reconnection by generating oscillations that we observed at least inside this Ca II H line cool solar jet bundle.