Mathematical modelling of a potential tsunami associated with a late glacial submarine landslide in the Sea of Marmara

Potential tsunami waves were modelled on the basis of the morphology and geological setting of a late glacial submarine landslide localized in the north-eastern sector of the Sea of Marmara, using a three-dimensional algorithm with the purpose of assessing the future risk of tsunamogenic landslides in the region. The landslide occurred off the Tuzla Peninsula on the north-eastern slope of the Ç?narc?k Basin, the easternmost of the three deep Marmara basins. The mass movement appears to be related to the Main Marmara Fault that passes below the toe of the failed mass. Observations from earlier manned submersible dives suggest that the initiation of the slide was facilitated by secondary faults associated with the Hercynian orogeny and involved Palaeozoic shales dipping southwards towards the deep basin. Radiocarbon dating of core material, together with the well-dated Marmara sapropel above the chaotically mixed landslide surface, reveal that the latest landslide event occurred about 17 ¹⁴C ka b.p. The uppermost scar of the landslide is found at 250 m and its toe at about 1,200 m below the present sea level. At the time of the slide, the Marmara Sea Basin was lacustrine, with its water level at ?85 m. In plan view the landslide has a distinctively triangular shape and the lateral extent of its toe is about 10 km. Multibeam bathymetric data indicate that the sliding motion probably occurred in two phases: a slower phase affecting the eastern part, characterized by an undulating surface, and a more rapid phase affecting the western part that possibly created tsunami waves. In the seismic sections, older failed slide masses can be clearly identified; these were probably displaced during marine isotopic stage 6 (～127–160 ka b.p.). The front of this buried material is located more than 1.5 km further south of the fault. We used a three-dimensional, Green’s function-based potential theory approach, rather than shallow-water equations commonly used in conventional tsunami simulations. The solution algorithm is based on a source-sink formulation and an integral equation. The results indicate that the maximum height of the tsunami in the Ç?narc?k Basin could have reached about half the average thickness of the sliding mass over a lateral extent of 7 km. Assuming an average thickness of 30 m for the landslide, and considering that the water level at 17 ka b.p. was at about ?85 m, the modelling shows that the maximum wave height generated by the slide would have been about 15–17 m.     

Strength capacity of unreinforced masonry cylindrical columns under seismic transverse forces

In this paper, the seismic resistance of unreinforced masonry (URM) cylindrical columns is investigated with an equivalent static analysis procedure. To this end, an existing numerical model developed for the stability analysis of masonry elements with rectangular cross-section is utilized and modified for the cylindrical columns. In the numerical model which takes into account the cracking of the sections and the second-order effects, the columns are divided ideally into sufficiently high number of elements, each having uniform curvature. The columns are modeled as prismatic cantilevers undergoing their own weights, eccentric vertical loads and distributed and concentrated static horizontal loads equivalent to the inertia actions. By considering two examples of columns, firstly a reference column and secondly a column from a real building, lateral seismic coefficient versus top drift level curves are obtained. On the basis of these curves, lateral load behavior of the columns is interpreted and maximum seismic load values which can be resisted by each column are determined. Implementing parametric analyses on the reference column, sensitivity of the seismic resistance to parameters such as column slenderness, magnitude and eccentricity of vertical top load, and the flexibility parameter is determined. The influence of some structural imperfections such as the deviation from vertical on the seismic resistance is also discussed in the paper.     

Discovery and exploration of the Gosowong epithermal gold deposit, Halmahera, Indonesia

The Gosowong epithermal gold deposit, on the island of Halmahera in eastern Indonesia, is located in an area of primary tropical rain forest with no previous history of gold mining or record of gold mineralisation. The deposit occurs in a newly recognised mineral district which contains a number of epithermal vein systems and at least two centres of low-grade porphyry style Cu–Au mineralisation. Several zones of argillic and advanced argillic alteration have been noted which may be related to additional centres of mineralisation. Gosowong is classified as a low-sulphidation epithermal quartz vein. Bonanza-grade gold–silver mineralisation is developed in shoots over a 400-m strike section of the vein system. Three types of veining are recognized; quartz–adularia veins and breccias; quartz–chlorite–illite veins and breccias; and crystalline or chalcedonic quartz vein stockworks. The area was targetted using a simple geological concept and the deposit was discovered and tested using basic exploration techniques commonly applied in the rugged tropical terrains of Indonesia. Sequential exploration methods comprised reconnaissance drainage sampling of stream sediment, BLEG and float media, ridge and spur soil sampling, prospect scale grid soil sampling, hand trenching and diamond drilling. Lapse time from identification of the initial reconnaissance anomaly to an inferred resource estimate of almost 1 million ounces of gold was less than 3.5 years. This case history illustrates that very detailed exploration is necessary to locate high-grade vein-type gold deposits in a tropical environment, but demonstrates that such resources still remain to be discovered in the relatively under-explored Neogene magmatic arcs of Indonesia.     

Modeling Local Tidal Constituents Using TOPEX/POSEIDON SSH for the Malaysian Marine Region

A new Local Ocean Tide Model, has been produced for the Exclusive Economic Zone (EEZ) of Malaysia, which incorporates some of the latest TOPEX/POSEIDON data for the years 1992 to 1998. Local tide gauge data are used as a comparison, along with another leading Global Ocean Tide Model, Ori96. The leading diurnal and semidiurnal constituents M₂, S₂, N₂, K₁, O₁, P₁ and Q₁ are reproduced using TOPEX/POSEIDON Sea Surface Heights (SSH) in a response analysis type least squares derivation following Munk and Cartwright (1966).     

Hydrogeochemical properties of CO2-rich thermal–mineral waters in Kayseri (Central Anatolia), Turkey

The present study highlights the hydrogeological and hydrogeochemical characteristics of the CO₂-rich thermal–mineral waters in Kayseri, Turkey. These waters of Dokuzpınar cold spring (DPS) (12–13°C), Yeşilhisar mineral spring (YMS) (13–16°C), Acısu mineral spring (ACMS) (20–22.5°C), Tekgöz thermal spring (TGS) (40–41°C), and Bayramhacı thermal-mineral spring (BTMS) (45–46.5°C) have different physical and chemical compositions. The waters are located within the Erciyes basin in the Central Anatolian Crystalline complex consisting of three main rock units. Metamorphic/crystalline rocks occur as the basement, sedimentary rocks of Upper Cretaceous-Quaternary age form the cover, and volcanosedimentary rocks Miocene-Quaternary in age represent the extrusive products of magmatism acting in that period. All these units are covered unconformably by terrace and alluvial deposits, and travertine occurrences have variable permeability. Dokuzpinar cold spring, YMS and ACMS localized mainly along the faults within the region have higher Na⁺ and Cl⁻ contents whereas TGS and BTMS have higher amounts of Ca²⁺ and HCO ₃ ⁻ . The high concentrations of Ca²⁺ and HCO ₃ ⁻ are mainly related to the high CO₂ contents resulting from interactions with carbonate rocks. Whereas the high Na⁺ content is derived from the alkaline rocks, such as syenite, tuff and basalts, the Cl⁻ is generally connected to the dissolution of the evaporitic sequences. These waters are of meteoric-type. BTMS deviates from meteoric water line. The content is related to the increases in the δ¹⁸O compositions due to mineral–water interaction (re-equilibrium) process. CO₂-dominated YMS and ACMS with low temperatures have higher mineralizations. Yeşilhisar mineral spring, ACMS, TGS and BTMS are oversaturated in terms of calcite, aragonite, dolomite, goethite and hematite, and undersaturated with respect to gypsum, halite and anhydrite. Yeşilhisar mineral spring, ACMS and BTMS are also characterized by recent travertine precipitation. Dokuzpınar cold spring is undersaturated in terms of the above minerals. The higher ratios of Ca/Mg and Cl/HCO₃, and lower ratios of SO₄/Cl in BTMS than TGS suggest that TGS has shallow circulation compared to BTMS, and/or has much more heat-loss enroute the surface. The sequence of hydrogeochemical and isotopic compositions of the waters is in an order of DPS>YMS>ACMS>TGS>BTMS and this suggests a transition period from a shallow circulation to a deep circulation path.