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.     

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.     

Solar rotation rate from stable sunspot tracings

Positions of sunspots between 1966 and 1976 as observed at Kandilli Observatory were used to determine the differential rotation of the Sun. A total of 202 sunspot groups which were E, F, G, H, and J-types were chosen, and a least-squares solution was calculated with their daily rotations. A gradient difference was found between the two hemispheres of the Sun.     

Stream flow forecasting using neuro‐wavelet technique

This paper proposes the application of a neuro‐wavelet technique for modelling monthly stream flows. The neuro‐wavelet model is improved by combining two methods, discrete wavelet transform and multi‐layer perceptron, for one‐month‐ahead stream flow forecasting and results are compared with those of the single multi‐layer perceptron (MLP), multi‐linear regression (MLR) and auto‐regressive (AR) models. Monthly flow data from two stations, Gerdelli Station on Canakdere River and Isakoy Station on Goksudere River, in the Eastern Black Sea region of Turkey are used in the study. The comparison results revealed that the suggested model could increase the forecast accuracy and perform better than the MLP, MLR and AR models. Copyright © 2008 John Wiley & Sons, Ltd.     

The Characteristics of Polygonal Impact Craters on Venus

Polygonal impact craters (PICs) are craters whose shape in plan view is more or less angular instead of being circular or ellipsoidal. This type of craters are present and often common on the Moon, Mercury, Mars and several asteroids and icy moons and after the careful analysis we found on Venus 131 impact craters, which show at least two straight rim segments. This survey proves that there are polygonal impact craters on Venus and they may provide a good tool to analyse the properties of the planet’s surface/crust/lithosphere as well as the impact process itself. This study also collaborates our previous results, that PICs are not an anomaly among craters, but an integral part of all impact craters regardless of their size or environment. We compared the polygonal impact craters to “normal”-shaped craters by using different characteristics (diameter, altitude, geologic setting, morphologic class, floor reflectance, degradation stage, and wall terracing). It turned out that the smaller crater sizes favor the formation of straight rim segments, but otherwise these craters show similar characteristics to other craters. Our study also shows that there are regions where the straight segments of the crater rims most clearly follow the orientations of the dominant tectonic features of the area. Thus, the orientations of crater walls reflect–at least in some places–the local tectonics and zones of weakness also on Venus and could thus tell us about the directions and distributions of fractures or other zones of weakness in the crust.