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Ymittos Athens, Greece

Papoulia J.,Hellenic Center for Marine Research | Fahjan Y.M.,Gebze Institute of Technology | Hutchings L.,Lawrence Berkeley National Laboratory | Novikova T.,Geodynamics Institute
Journal of Earthquake Engineering | Year: 2015

We perform a probabilistic seismic hazard analysis (PSHA) for broad-band strong ground motion within the Saronikos Gulf region, Greece, from potential earthquakes along the 30 km long Aigina fault in the northern part of the Gulf. We perform the PSHA utilizing empirical Greens functions (EGFs) merged with synthetic Greens functions (SGFs) along with models of finite rupture in place of standard "attenuation relations." Our approach considers all significant magnitudes for PSHA and full broadband ground motion simulations. Calculations are source and site specific, and could reduce uncertainties in estimating standard engineering parameters. We use a range of rupture scenarios for all significant magnitude earthquakes along the fault. The hazard calculation is for frequencies 0.0-15.0 Hz. Recordings of small earthquakes from an onshore/offshore local seismic array were used as EGFs for frequencies of 1.5-15.0 Hz, the finite difference code E3D was utilized to synthesize SGFs for frequencies 0.0-1.5 Hz, and an algorithm for merging the EGFs with SGFs was developed. The full-waveform calculations are important for non-linear dynamic analysis of structures in the coastal zone and potential hazard to long period structures. Results of proposed PSHA identify 2%, 10%, and 50% hazard at the selected sites of Saronikos Gulf.Finally, we compare our PSHA results to those obtained by standard practice which involves prediction equations (GMPEs) recently developed in the Next Generation Attenuation (NGA) project and empirical predictive attenuation relations proposed for Greece. We believe that differences with the NGA results are due to site-and source-specific information utilized in this study, and incorporation of this information may significantly reduce the uncertainty in seismic hazard calculations. Copyright © A. S. Elnashai. Source

Ganas A.,Geodynamics Institute | Lagios E.,National and Kapodistrian University of Athens | Petropoulos G.,Kings College London | Petropoulos G.,University of Bristol | Psiloglou B.,Institute of Environmental Research and Sustainable Development
International Journal of Remote Sensing | Year: 2010

A time series of Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) images (AST08) have been processed to allow radiative heat flux estimations of the Nisyros volcano. ASTER night-time images were acquired on four different dates: 7 April 2001, 13 June 2002, 26 October 2002 and 23 July 2005. The results show a steady state energy release with heat fluxes ranging from 15 to 30 W m-2 over the craters of Kaminakia, Polyvotis and Stefanos, respectively. It is suggested that this range of values indicates a background heat flux of this volcano following the unrest of 1995-1997, and that the volcano has entered again into the quiet phase. Also, on the basis of the average spatial extent of the thermal anomaly a total radiative heat flux of 36 MW was estimated at the moment of ASTER overpass. Heat flux values for Nisyros are in good agreement with other published estimates derived from low-temperature fumarolic volcanoes (Stromboli and Vulcano, Italy) using Landsat TMdata. It is also evidenced that the ASTER radiometer can be used as an important imaging tool for the monitoring of geophysical properties associated to volcanic activity, as is the volcanic heat flux. © 2010 Taylor & Francis. Source

Karastathis V.K.,Geodynamics Institute | Papadopoulos G.A.,Geodynamics Institute | Novikova T.,Geodynamics Institute | Roumelioti Z.,Aristotle University of Thessaloniki | And 2 more authors.
Natural Hazards and Earth System Science | Year: 2010

We examine the possible non-linear behaviour of potentially liquefiable layers at selected sites located within the expansion area of the town of Nafplion, East Peloponnese, Greece. Input motion is computed for three scenario earthquakes, selected on the basis of historical seismicity data, using a stochastic strong ground motion simulation technique, which takes into account the finite dimensions of the earthquake sources. Site-specific ground acceleration synthetics and soil profiles are then used to evaluate the liquefaction potential at the sites of interest. The activation scenario of the Iria fault, which is the closest one to Nafplion (Combining double low line6.4), is found to be the most hazardous in terms of liquefaction initiation. In this scenario almost all the examined sites exhibit liquefaction features at depths of 6-12 m. For scenario earthquakes at two more distant seismic sources (Epidaurus fault - M6.3; Xylokastro fault g-6.7) strong ground motion amplification phenomena by the shallow soft soil layer are expected to be observed. © 2010 Author(s). Source

Ganas A.,Geodynamics Institute | Grecu B.,National Institute for Earth Physics | Batsi E.,Geodynamics Institute | Radulian M.,National Institute for Earth Physics
Natural Hazards and Earth System Science | Year: 2010

The purpose of this paper is to study the interaction of the Vrancea seismic activity (Romania) in space as result of Coulomb, static stress transfer during M = 7 + events. In this area, three large events occurred in 1977, 1986 and 1990 at mid-lower, lithospheric depths and with similar focal mechanisms. Assuming elastic rheology for the deforming rocks it is suggested that frictional sliding on pre-existing fault produced the 1986 M = 7.1 event (depth 131 km), that was possibly triggered by the 1977 M = 7.4 event (depth 94 km). We calculated a static stress transfer of 0.52-0.78 bar to the hypocentre of the 1986 event. On the contrary, the occurrence of the 1990 event is uncertain: it is located inside the relaxed (shadow) zone of the combined 1977 and 1986 static stress field considering an azimuth for maximum compression of N307° E. It follows that, the 1990 earthquake most likely represents an unbroken patch (asperity) of the 1977 rupture plane that failed due to loading. However, if a different compression azimuth is assumed (N323° E) then the 1990 event was also possibly triggered by static stress transfer of the 1977 and 1986 events (combined). Our modeling is a first-order approximation of the kind of earthquake interaction we might expect at intermediate lithospheric depths (80-90 to 130-140 km). It is also suggested that static stress transfer may explain the clustering of Vrancea earthquakes in space by the rupturing of two (possibly three) NW-dipping major zones of weakness (faults) which accommodate the extension (vertical elongation) of the slab. © 2010 Author(s). Source

Khairunniza-Bejo S.,University Putra Malaysia | Petrou M.,Imperial College London | Ganas A.,Geodynamics Institute
International Journal of Remote Sensing | Year: 2010

In this article, a new simple method of landslide detection and identification is proposed. It is based on the use of local mutual information and image thresholding. A binary change image is then produced. Connected component analysis is used to identify the connected regions. Landslides are identified as the largest connected regions in this image. Mathematical morphology is used to approximate the landslide region. This method is simple and suitable for the detection of large changed regions where the ratio of the unchanged to changed pixels in the image is approximately one to a few tens. Compared to the image differencing method, this method gives more reliable results. © 2010 Taylor & Francis. Source

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