Hydrogeophysical modelling of Hisarcik (Kütahya) geothermal field,western Turkey

Western Anatolia hosts many low-to-moderate and high-temperature geothermal sources in which active faults play a dominant role to control the recharge and the discharge of geothermal fluid. In this study, we used the two-dimensional geoelectric structure of Kütahya Hisarcık geothermal field, and created a conceptual hydrogeophysical model that includes faults, real topographical variations and geological units. The temperature distribution and fluid flow pattern are also investigated. The depth extension of Hisarcık Fault, electrical basement and low resistivity anomalies related to the presence of geothermal fluid are determined by using resistivity studies in the area. Numerical simulations suggest that Hisarcık fault functioning as a fluid conduit primarily enables hot fluid to be transported from depth to the surface. It is shown that the locations of predicted outflow vents coincide with those of hot springs in the area.     

张家口蔚县农村房屋抗震性能调查及统计分析

为进一步了解蔚县地区农村房屋的抗震性能,在该地区选取43个村庄、7732栋房屋进行实地调查和统计分析。主要调查房屋结构、建筑材料、房屋抗震构造措施等内容,分析各结构类型房屋抗震薄弱环节及房屋抗震性能,并统计分析经济、交通、地形等因素与房屋结构类型及抗震性能的关系,提出提高该地区农村房屋抗震性能的建议。     

Splash detachment of sand particles under varying contact stress field of wind-driven raindrop impact

The effects of wind-driven rain (WDR) on sand detachment were studied under various raindrop obliquities. Results suggested a significant reduction in compressive stress on sand surfaces for a two-dimensional experimental set-up in a wind tunnel. During experiments, sand particles in splash cups were exposed to both wind-free rain (WFR) and WDR driven by horizontal winds of 6.4, 8.9 and 12.8 m s⁻¹ and rainfall intensities of 50, 60, 75 and 90-mm h⁻¹ to assess the sand detachment rate (D, in g m⁻² s⁻¹). The effects of sand moisture state (dry and wet) on the detachment of different-sized particles (0.20–0.50 and 0.50–2.00 mm, respectively) were also tested. Factorial analysis of variance showed that shear and compressive stress components evaluated by horizontal and vertical kinetic energy flux terms (KE_x and KE_y, respectively, in J m⁻² s⁻¹) along with their vector sum (KE_r, in J m⁻² s⁻¹) explained the variation in D. Neither sand size nor sand moisture was statistically significant alone although binary interactions of KE_r, KE_x and KE_y with the sand size and three-way interaction of KE_x, sand size and moisture were statistically significant. These results can be explained by size-dependent variation in sand compressibility and surface friction related to the total stress field developed by a given partition of shear and compressive stresses of wind-driven oblique raindrops (KE_x/KE_y). Further analysis of the variation of the unit sand detachment rate (D_u = D/KE_r = g J⁻¹) with rain inclination (α, in degrees) better revealed the effect of WDR obliquity on D_u that further changed with sand size class and moisture state. Finally, the difference in the resulting stress field differentiable by the oblique raindrop trajectories of the experiment over sand surface significantly affected the non-cohesive particle detachment rates, to some extent interacted with size-dependent compressibility and interface shear strength of sand grains.     

Source parameters for the M<Subscript>w</Subscript> = 6.6, 03 February 2002, Çay Earthquake (Turkey) and aftershocks from GPS,Southwestern Turkey

The 03 February 2002 Çay Earthquake (M_w ～6.7) occurred on the fault segment between Eber and Ak?ehir Lakes followed by a large aftershock (M_w ～5.6) near the western end of the fault and two sequential aftershocks. We computed the coseismic surface displacements from static GPS measurements to determine the fault geometry parameters and uniform slip components. The coseismic displacements were obtained through combining the regional pre-earthquake and post-earthquake GPS data. Fault geometry and slips were acquired through the inversion of GPS data modeling the events as elastic dislocations in a half-space and assuming all four events took place on the same fault plane. Results suggest that one-segment fault of ～33 km length and dipping ～43° northward suffices to model the dislocation, assuming uniform slip distribution with 0.51 m dip slip, 0.26 m left-lateral slip extending to a depth down to ～11.5 km which is consistent with seismological evidence. The results also verify the normal faulting in the eastern flank of Isparta Angle which has long been assumed as a thrusting structure. While the available data cannot identify the four individual events on the same day, an attempted distributed slip model differentiates dip slip and left-lateral slips near the hypocenter with maximum values of ～1 and 0.6 m, respectively.     

Site classification of Turkish national strong-motion stations

Since 1973, the General Directorate of Disaster Affairs of Turkey has deployed several strong-motion accelerographs at selected sites. Within the framework of the project entitled Compilation of National Strong Ground Motion Database in Accordance with International Standards, site conditions were investigated within the upper 30-m depth by surface seismic and standard penetration tests. Preliminary characterization of the sites is made by making use of both geophysical and geotechnical criteria of NEHRP Provisions and Eurocode-8 site classification systems. The liquefaction susceptibility of those sites which comprise saturated cohesionless deposits is also determined. Mean shear-wave velocity, mean penetration resistance, site class, and liquefaction susceptibility of each site are tabulated. The Turkish strong-motion database supplemented by detailed information on site conditions is a valuable source of information particularly for those studies that put emphasis on the relationship between site conditions and strong-motion parameters.     

Active fault database of Turkey

We have updated the active fault map of Turkey and built its database within GIS environment. In the study, four distinct active fault types, classified according to geochronological criteria and character, were delineated on the 1:25,000 base map of Turkey. 176 fault segments not included in the former active fault map of Turkey, have been identified and documented. We infer that there are 485 single fault segments which are substantially potential seismic sources. In total 1964 active-fault base-maps were transferred into the GIS environment. Each fault was attributed with key parameters such as class, activity, type, length, trend, and attitude of fault plane. The fault parameters are also supported by slip-rate and seismogenic depth inferred from available GPS, seismological and paleoseismological data. Additionally, expected maximum magnitude for each fault segment was estimated by empirical equations. We present the database in a parametric catalogue of fault segments to be of interest in earthquake engineering and seismotectonics. The study provides essential geological and seismological inputs for regional seismic hazard analysis of all over Turkey and its vicinity.     

Evolution of seismic hazard maps in Turkey

A review on the historical evolution of seismic hazard maps in Turkey is followed by summarizing the important aspects of the updated national probabilistic seismic hazard maps. Comparisons with the predecessor probabilistic seismic hazard maps as well as the implications on the national design codes conclude the paper.