Identification of soil-structure interaction effects based on geodetic monitoring of a railway bridge

The monitoring of bridges using geodetic methodologies permits the direct measurement of displacements and potential identification of effects of soil-structure interaction. In this study the response of the historical Gorgopotamos railway (Central Greece) has been measured using a Robotic Total Station (RTS) during the passage of trains on different times of the year and under various soil conditions. The measurements revealed that the initial impact response of the deck to the train loading presents differences which seem to correlate with the differences in the moisture content of the bridge foundation ground

Energetic rupture, coseismic and post-seismic response of the 2008 MW 6.4 Achaia-Elia Earthquake in northwestern Peloponnese, Greece: an indicator of an immature transform fault zone

International audiencemoment magnitude M W 6.4 crustal earthquake in northwestern Peloponnese, Greece, was a strong-shaking dextral strike-slip event with teleseismic broad-band and high-frequency energy magnitudes M e of 6.8 and 7.2, respectively. A high stress drop 5-10 times the global average is associated with excessive high-frequency energy. The NE-SW trending fault plane shown by the aftershock distribution and focal mechanism is not associated with previously mapped faults, and no obvious coseismic surface rupture was discovered. Contrasting the enhanced rupture energy, the event created no substantial coseismic or post-seismic surface deformation, likely due to a fault buried below a detached thick and compositionally weak flysch layer. Comparative spatial analysis including over 30 regional strike-slip events between 1965 and 2009 reveals a NE-SW striking diffuse transform fault zone subparallel to the Cephalonia Transform Fault. The dextral sense of motion along the transform zone is consistent with the ongoing Global Positioning System (GPS)-derived deformation along the West Hellenic Arc and the motion on the Cephalonia Transform Fault. Characterizing this system is important to constraining the seismic hazard near Patras, a major port city immediately NE of the 2008 event

THE 2014 MW 6.9 NORTH AEGEAN TROUGH (NAT) EARTHQUAKE: SEISMOLOGICAL AND GEODETIC EVIDENCE

A strong earthquake (Mw 6.9) on 24 May 2014 ruptured the North Aegean Trough (NAT) in Greece, west of the North Anatolian Fault Zone (NAFZ). In order to provide unbiased constrains of the rupture process and fault geometry of the earthquake, seismological and geodetic data were analyzed independently. First, based on teleseismic long-period P- and SH- waveforms a point-source solution yielded dominantly right-lateral strike-slip faulting mechanism. Furthermore, finite fault inversion of broad-band data revealed the slip history of the earthquake. Second, GPS slip vectors derived from 11 permanent GPS stations uniformly distributed around the meizoseismal area of the earthquake indicated significant horizontal coseismic slip. Inversion of GPS-derived displacements on the basis of Okada model and using the new TOPological INVersion (TOPINV) algorithm permitted to model a vertical strike slip fault, consistent with that derived from seismological data. Obtained results are consistent with the NAT structure and constrain well the fault geometry and the dynamics of the 2014 earthquake. The latter seems to fill a gap in seismicity along the NAT in the last 50 years, but seems not to have a direct relationship with the sequence of recent faulting farther east, along the NAFZ

Εκτίμηση συντελεστή ασφαλείας για την ταπείνωση της στέψης χωμάτινων φραγμάτων

The crest settlements of embankment dams with a central clay core are usually described as an exponential function of time. They play a major role in the safety and operational capacity of the dam, especially when taking into account that extreme crest settlements that have been observed for some of these dams have resulted in a significant reduction of the storage capacity of the reservoir and maintenance works at large scales and cost (e.g. Ataturk dam, Turkey). We studied the crest settlements of > 40 embankment dams, 10-41 years old, located at different parts of the world. Our analysis shows that the safety threshold for the crest settlements should not be a constant but increase with the age of the dam and that most of suggested thresholds in the literature are too conservative. A safety threshold of 1% (crest settlement to dam height ratio) appears to be realistic for the whole operational life of the dam. The Kremasta dam, whose age and size places it to a most critical situation, has a crest settlement to dam height ratio value well below the above threshold

Interpretations of Reservoir Induced Seismicity may not always be valid : the case of seismicity during the impoundment of the Kremasta dam (Greece, 1965-1966)

The ‘Kremasta seismic sequence’ in western Greece is one of the most commonly cited examples of Reservoir Induced Seismicity (RIS). Here, we show that this ‘sequence’ is a result of normal tectonic activity and that only some small, unrelated microseismic events are reservoir induced. Shortly after the beginning of the impoundment of the Kremasta Dam in 1965, the then newly established seismic monitoring network in Greece recorded two Ms ≥ 6.0 events and numerous small shocks spread over a 120 km wide region. These were interpreted as a single seismic sequence (namely the Kremasta seismic sequence), and assumed to be reservoir induced. We revisit the epicenter locations of these events and interpret them in the framework of the regional tectonic context and the local hydrogeology. Placing these events into the local context shows that they represent an amalgamation of separate, ordinary (tectonic) seismic sequences. Further, the regional rocks are highly fragmented by small faults and the spatial distribution of seismic events is not consistent with a model of stress transfer from reservoir loading. In addition, it is not likely that events at such long (> 20-30 km) distances from the reservoir could be induced by an initial reservoir load head of 30 m. Whilst the larger magnitude events are tectonic, after impoundment local residents reported an unusual frequency of small microseismic events felt only within 10 km of the dam. We provide evidence that these are a result of the collapse of numerous shallow karstic cavities adjacent and beneath the reservoir due to increased water load (locally 100-150 m depth). This study has significant implications for interpretation of seismic triggering mechanisms in other regions: earthquake occurrence within the proximity of reservoirs during and after impoundment time cannot be assumed to be RIS unless supported by seismological, geological and hydrogeological evidence