On the short term variations of solar activity during solar cycle 21

Short-term variations of the last solar activity cycle were studied by the flare and coronal indices using Gleissberg method. Systematic short-term variations are found from their course during the 21st solar activity cycle. Comparison of their autocorrelograms constructed by the new set of data obtained from the magnitude of the fluctuations showed us the existence of the phase shift between the temporal variations of the two indices.     

The 73-day periodicity of the flare index during the current solar cycle 22

The flare index of the current solar cycle 22 is analysed to detect periodicities. Power spectral analysis of the time series of solar flare index data reveals a periodicity around 73 and 53 days. We find that a periodicity of 73 days was in operation from November 1988 to the end of December 1991. We also find that when the 73-day periodicity or the 154-day periodicity is in operation the flare index is well correlated with the relative sunspot numbers.     

A new approximation in determination of zonation boundaries of ignimbrite by ground penetrating radar: Kayseri,Central Anatolia,Turkey

Ground penetrating radar (GPR) method is used as a tool to identify the zonation boundaries in ignimbrite series through their columnar section. Ignimbrites can be classified in terms of welding degree, colour, texture and mineralogical compositions. The research area comprises a part of İncesu (Kayseri) ignimbrite at Central Anatolia, Turkey. This ignimbrite is divided into three levels and each level has clear differences in terms of macroscopic and microscopic views. This paper presents the results of an application of GPR for the determination of zonation boundary within the ignimbrite flow unit in the view of their textural and petrological features. RAMAC CU II equipment was used with 250 MHz shielded antenna on parallel ten profiles to observe the physical difference among the ignimbrite levels of the study area. Two levels out of three have been defined at the İncesu ignimbrite and supported by field geology and petrographical studies. The first level, which is extremely fractured structure, is about 1.5 m thick and matches with middle level of the İncesu ignimbrite. The second level has an average 50–75 cm thickness and matches with lower level of the ignimbrite. In this manner, vertical lithological variations should be taken into consideration during petrological investigation of the ignimbrites.     

A probabilistic seismic hazard assessment for the Turkish territory: part II—fault source and background seismicity model

Over the years, several local and regional seismic hazard studies have been conducted for the estimation of the seismic hazard in Turkey using different statistical processing tools for instrumental and historical earthquake data and modeling the geologic and tectonic characteristics of the region. Recently developed techniques, increased knowledge and improved databases brought the necessity to review the national active fault database and the compiled earthquake catalogue for the development of a national earthquake hazard map. A national earthquake strategy and action plan were conceived and accordingly with the collaboration of the several institutions and expert researchers, the Revision of Turkish Seismic Hazard Map Project (UDAP-Ç-13-06) was initiated, and finalized at the end of 2014. The scope of the project was confined to the revision of current national seismic hazard map, using the state of the art technologies and knowledge of the active fault, earthquake database, and ground motion prediction equations. The following two seismic source zonation models are developed for the probabilistic earthquake hazard analysis: (1) Area source model, (2) Fault and spatial smoothing seismic source model (FSBCK). In this study, we focus on the development and the characterization of the Fault Source model, the background spatially smoothed seismicity model and intrinsic uncertainty on the earthquake occurrence-rates-estimation. Finally, PSHA results obtained from the fault and spatial smoothed seismic source model are presented for 43, 72, 475 and 2475 years return periods (corresponding to 69, 50, 10, and 2% probability of exceedance in 50 years) for PGA and 5% damped spectral accelerations at 0.2 and 1.0 s.     

Periodic behavior of solar flare index during solar cycles 20 and 21

Short-term periodicities of solar activity were studied with the flare index by using Discrete Fourier Transform for the time interval 1966–1986. Two noticeable periodicities (18.5 and 5 months) have been found. The existence of these periodicities comparing with the early findings is discussed.     

On the SID durations

This Letter is based on analysis of data on Sudden Ionospheric Disturbances (SID) listed inSolar Geophysical Data. The mean durations of 1272 SIDs taken from the SGD lists were calculated with respect to their associated X-ray flares. In general, all of our calculated mean durations showed a large scatter in the mean values. The comparison of our values by the estimated Solar Geophysical Data Center SID durations indicated an apparent discrepancy in the mean duration relative to that estimated by SGD for the case of low levels of SID importance. In our opinion this apparent discrepancy suggests a need for a correction in SGD's assumptions in the importance range from –1 to +1.     

A geohazard reconnaissance study based on geoscientific information for development needs of the western region of Istanbul (Turkey)

The role of geoenvironmental information is becoming increasingly important as legislative changes have forced developers and planning authorities to consider more implications and impact on the environment of large-scale development initiatives. Therefore, integration of surface and subsurface geoscientific information for development needs has prime importance and provides a means of identifying potential problems and opportunities at an early stage in any planned development. However, from the experience of recent natural disasters, it is evident that this was not case the taken into consideration in many countries. In addition to thousands of casualties, many urbanized areas, industrial districts and large-scale engineering structures suffered severe damages from the natural hazards due to many reasons including the lack of preliminary engineering geological maps and zoning maps of the settlement areas. Turkey is one of the countries which is exposed to natural hazards such as earthquakes, landslides and floods. In particular, the devastating 1999 Kocaeli earthquake, which affected the Marmara Region of Turkey, focused the attention on densely urbanized and industrialized metropolitan areas such as Istanbul. The rapid growth of Istanbul, particularly towards west with minimal geoscientific information resulted in an overwhelming pressure on the natural environment. In addition, a large earthquake, which is expected to occur in the Marmara Sea within the next 30 years, also pose a threat to the city and its surroundings. In this study, on the basis of the geological, geomorphological and geophysical reconnaissance study, an integrated geoscientific data were collected from the western region of Istanbul and evaluated for geohazards. The paper focuses on the geological and geomorphological aspects that control the occurrence of some geohazards such as earthquake-induced liquefaction, landslides and flooding. In this context, the geological map of the region was revised and Quaternary deposits were classified into 11 units, in detail. Liquefaction-prone areas were evaluated by using geomorphological criteria based on field investigation, by the examination of the available records from 88 boreholes drilled on recent deposits and by the data from resistivity profiles. The landslides within the region were classified according to their type, relative depth and activity. In addition, fluvial and marine flood-prone areas were also delimited within the region. Finally, a series of maps such as landslide inventory maps, and maps showing liquefaction- and flood-prone areas were produced with the aid of Geographic Information Systems (GIS) to assist in designing further detailed site investigations and to reduce costs by ensuring a more focused approach to strategic planning and site selection.