Depositional system and palaeoclimatic interpretations of Middle to Late Pleistocene travertines: Kocabaş, Denizli,south‐west Turkey

Travertine deposits in western Turkey are very well‐exposed in the area of Kocaba?, in the eastern part of the Denizli Basin. The palaeoclimatic significance of these travertines is discussed using U/Th dates, stable isotope data and palynological evidence. The Kocaba? travertine occurrences are characterized by successions of depositional terraces associated with palaeosols and karstic features. The travertines have been classified into eight lithotypes and one erosional horizon, namely: laminated, coated bubble, reed, paper‐thin raft, intraclasts, micritic travertine with gastropods, extra‐formational pebbles and a palaeosol layer. The analysed travertines mostly formed between 181 ka and 80 ka (Middle to Late Pleistocene) during a series of climatic changes including glacial and interglacial intervals; their δ¹³C and δ¹⁸O values indicate that the depositional waters were mainly of basinal thermal origin, occasionally mixed with surficial meteoric water. Palynological results obtained from the palaeosols showed an abundance of non‐arboreal percentage and xerophytic plants (Oleaceae and Quercus evergreen type) indicating that a drought occurred. Marine Isotope Stage 6 is represented by grassland species but Marine Isotope Stage 5 is represented by Pinaceae–Pinus and Abies, Quercus and Oleaceae. Uranium/thorium analyses of the Kocaba? travertines show that deposition began in Marine Isotope Stage 6 (glacial) and continued to Marine Isotope Stage 4 (glacial), but mostly occurred in Marine Isotope Stage 5 (interglacial). The travertine deposition continued to ca 80 ka in the south‐west of the study area, in one particular depression depositional system. Palaeoenvironmental indicators suggest that the travertine depositional evolution was probably controlled by fault‐related movements that influenced groundwater flow. Good correlation of the stable isotope values and dates of deposition of the travertines and palynological data of palaeosols in the Kocaba? travertines serve as a starting point for further palaeoclimate studies in south‐west Turkey. Additionally, the study can be compared with other regional palaeoclimate archives.     

Back-analysis of a seismically induced highway embankment failure during the 1999 Düzce earthquake

An earthquake of magnitude 7.2 on the Richter scale occurred on 12 November 1999 in the Düzce-Bolu region of Turkey. The region was also hit approximately 3 months before during the devastating Kocaeli earthquake of 17 August 1999. Besides high casualties and damage to various engineering structures and buildings, slope and embankment failures on the highway and the country roads occurred. In this study, the authors are concerned with the back-analysis of an embankment failure that occurred on the four lanes E-5 highway connecting Ankara to Gstanbul at Bakacak in the Bolu Province during the 1999 Düzce earthquake. Both pseudo-dynamic and dynamic limiting equilibrium methods are used to back analyse the conditions for the initiation of failure and also displacement responses of the embankment during the earthquake shaking. After having given a brief summary of the investigations on the post-failure state, the geology and geotechnical characteristics of the site, and the dynamic limiting equilibrium method developed and used for analyses are described. The results of the back-analysis based on a pseudo-dynamic approach, revealed that the maximum ground acceleration to initiate the failure of the embankment was probably about 0.125 g. On the other hand, the application of a method for computing the displacement and velocity responses of the failed embankment showed that the failure was possible when the embankment was subjected to ground accelerations similar to that recorded at the Düzce station. In addition, the computations also revealed that the time history of accelerations could be very important for the failure of slopes and embankments.     

Kinematics of the eastern part of the North Anatolian Fault Zone

The North Anatolian Fault Zone (NAFZ), which marks the boundary between Anatolia and the Eurasian plate, is one of the world's most seismically active structures. Although the eastern part of NAFZ has high seismic hazard, there is a lack of geodetic information about the present tectonics of this region. Even though many scientists would like to study this area, geographical and logistical problems make performing scientific research difficult. In order to investigate contemporary neotectonic deformation on the eastern NAFZ and in its neighborhood, a relatively dense Global Positioning System (GPS) monitoring network was established in 2003. Geodetic observations were performed in three GPS campaigns in an area of 350 km × 200 km with 12-month intervals. In addition, 14 new GPS stations were measured far from the deforming area. Since this region includes the intersection of the NAFZ and the East Anatolian Fault Zone (EAFZ), deformation is complex and estimating seismic hazard is difficult. One important segment is the Yedisu segment and it has not broken since the 1784 earthquake. After the 1992 Erzincan and 2003 Pulumur earthquakes, the Coulomb stress loading on the Yedisu segment of the NAFZ has increased significantly, emphasizing the need to monitor this region. We computed the horizontal velocity field with respect to Eurasia and strain rates field as well. GPS-derived velocities relative to Eurasia are in the range of 16–24 mm/year, which are consistent with the regional tectonics. The principal strain rates were derived from the velocity field. Results show that strain is accumulating between the NAFZ and EAFZ along small secondary fault branches such as the Ovacik Fault (OF).     

Palaeoseismology of the Havran-Balıkesir Fault Zone: evidence for past earthquakes in the strike-slip-dominated contractional deformation along the southern branches of the North Anatolian fault in northwest Turkey

The Havran-Bal?kesir Fault Zone (HBFZ) is one of the major active structures of the Southern Marmara Region, which has been shaped by the southern branch of North Anatolian fault since the Pliocene. HBFZ is a 10–12 km wide, 120 km long, right-lateral strike-slip fault zone that consists of two ENE-striking main faults, namely, the Havran-Balya and Bal?kesir faults. The 90-km-long Havran-Balya fault exhibits right-stepping en echelon geometry and is made up of (1) Havran, (2) Osmanlar, (3) Turplu and (4) Ovac?k fault segments. On the eastern part, the 70-km-long Bal?kesir fault is divided into two fault segments; (1) Gökçeyaz? and (2) Kepsut. We estimated the long-term slip rate between 3.59 and 3.78 mm/yr using river offset. The Kepsut, Gökçeyaz? and Ovac?k fault segments are capable of generating an earthquake with a moment magnitude of up to 7.2. Detailed palaeoseismological studies show that the HBFZ is responsible for some surface faulting earthquakes with an average recurrence interval of 1000–2000 years during the late Holocene. Considering the fact that there was no evidence of a surface-ruptured earthquake for 2000 years, it can be stated that there is a seismic gap on the Gökçeyaz? fault segment.     

Exosat observations of X-rays from classical novae during outburst stage

The initial discovery of soft X-rays from Nova Muscae 1983 was followed by eight additional observations of the three brightest novae whose outburst stage coincided with the lifetime ofEXOSAT satellite; namely three more observations of Nova Muscae 1983, three observations of Nova Vulpeculae 1984#1 (PW Vul), and two observations of Nova Vulpeculae 1984#2. Through these observations we sampled the soft X-ray light curve of classical novae from optical maximum to 900 days after. The observations seem best explained by the constant bolometric luminosity model of a hot white dwarf remnant. Although the measurements suffer from limited statistics, very broad energy bandpass, and incomplete sampling of any single nova, their constraints on the theories of nova outburst are significant. One constraint is that the lifetime of the white dwarf remnant in Nova Muscae 1983 is 2 to 3 years, which leads to the conclusion that the burned envelope massM _burn should be of the order of . The second constraint is that the maximum temperature, of the white dwarf remnant should approximately be within 200 000 K to 400 000 K. We estimate that a white dwarf remnant evolving like the central star of a planetary nebula, with core mass of 0.8 to 0.9M , core luminosity of 2×10⁴ L , and envelope mass of 10^–6 M , can explain the general characteristics of the X-ray measurements for Nova Muscae 1983. In order to have 1.1M core mass, estimated from the early observations of bolometric luminosity in the UV to infrared range, a wind withM5×10^–7 M yr^–1 appears to be necessary. The few observations of Nova Vulpeculae 1984 #1 and Nova Vulpeculae 1984#2, during the first year after outburst, give a risetime and intensity that is consistent with a constant bolometric luminosity model.Paper presented at the IAU Colloquium No. 93 on Cataclysmic Variables. Recent Multi-Frequency Observations and Theoretical Developments, held at Dr. Remeis-Sternwarte Bamberg, F. R. G., 16–19 June, 1986.