SOURCE PARAMETERS OF MODERATE AND STRONG EARTHQUAKES IN THE BROADER AREA OF ZAKYNTHOS ISLAND (W. GREECE) FROM REGIONAL AND TELESEISMIC DIGITAL RECORDINGS

The source parameters of all the moderate and strong events that occurred in the broader area of Zakynthos Island for the period 1997–2009 are determined using two different techniques depending on epicentral distance. For the strong events we employed teleseismic body-wave modeling between 30° and 90°, while for moderate events a regional moment tensor inversion approach was used. In both cases we used broadband waveform data with a good signal-to-noise ratio. The calculated focal mechanisms are representative of the displacement and strain fields of the broader area. Those associated with the Cephalonia transform fault are consistent with dextral strike-slip motion. The area between the island of Zakynthos and the Western coast of Peloponnese is also characterized by strike–slip faulting, while reverse faulting is mainly observed south of Zakynthos Island. Using both techniques, we also retrieved the source parameters of the biggest events of the seismic sequence of April 2006 near the southern coast of Zakynthos Island. The depths of the located events of the sequence vary mainly between 10 and 25 km. The fault plane solutions revealed thrust type faulting in all cases, something which can be related with upward motions in the southern part of the Island observed by DGPS measurements

MONITORING OF SURFACE DISPLACEMENTS IN THE KALOCHORI AREA (THESSALONIKI, GREECE) USING A LOCAL GNSS NETWORK

Οι εδαφικές κινήσεις στην περιοχή του Καλοχωρίου μετρήθηκαν από το Γεωδυναμικό Ινστιτούτο του ΕΑΑ με χρήση τοπικού δικτύου GNSS. Το δίκτυο ιδρύθηκε τον Οκτώβριο του 2013 στο πλαίσιο του έργου INDES-MUSA και μετρήθηκε τέσσερις (4) φορές μεταξύ Οκτωβρίου 2013 - Απρίλιου του 2015.Τα σημεία του δικτύου είναι 18 και αποτελούν μπουλόνια σε δρόμους, πλατείες καθώς και καρφιά σε βάθρα της ΓΥΣ. Τα αποτελέσματα (στο σύστημα αναφοράς ITRF 2008) που προέκυψαν από επεξεργασία με το λογισμικό GAMIT δείχνουν κατακόρυφες μετατοπίσεις της τάξεως των σύν-πλήν 2 εκατοστών, εκτός από την περίμετρο του φράγματος του Καλοχωρίου το οποίο ανυψώθηκε από 2-5 εκατοστά. Οι οριζόντιες μετακινήσεις δεν δείχνουν κάποια συσχέτιση με τεκτονικές κινήσεις της ευρύτερης περιοχής.The ground motions in the Kalochori region (well known for its subsidence history during the 2nd half of 20th century) were investigated by NOA using a mobile GNSS (GPS) network, comprising 18 stations. The network was measured four (4) times during the period October 2013 - April 2015 under the framework of the research project INDES-MUSA. Our GPS measurements were processed with GAMIT software and show vertical (ITRF 2008) motions ranging from -2 cm to +2 cm (i.e. just above the margins of measurement error) with the exception of the Kalochori dam where an uplift of 2-5 cm was observed. We also found no evidence for local (non-tectonic) motions and/or interseismic strain

Semi-empirical relationships to assess the seismic performance of slopes from an updated version of the Italian seismic database

Funder: Dipartimento della Protezione Civile, Presidenza del Consiglio dei Ministri; doi: http://dx.doi.org/10.13039/100012783; Grant(s): ReLUIS research project - Working Pachage 16: Geotechnical Engineering - Task Group 2: Slope stabilityAbstractSeismic performance of slopes can be assessed through displacement-based procedures where earthquake-induced displacements are usually computed following Newmark-type calculations. These can be adopted to perform a parametric integration of earthquake records to evaluate permanent displacements for different slope characteristics and seismic input properties. Several semi-empirical relationships can be obtained for different purposes: obtaining site-specific displacement hazard curves following a fully-probabilistic approach, to assess the seismic risk associated with the slope; providing semi-empirical models within a deterministic framework, where the seismic-induced permanent displacement is compared with threshold values related to different levels of seismic performance; calibrating the seismic coefficient to be used in pseudo-static calculations, where a safety factor against limit conditions is computed. In this paper, semi-empirical relationships are obtained as a result of a parametric integration of an updated version of the Italian strong-motion database, that, in turn, is described and compared to older versions of the database and to well-known ground motion prediction equations. Permanent displacement is expressed as a function of either ground motion parameters, for a given yield seismic coefficient of the slope, or of both ground motion parameters and the seismic coefficient. The first are meant to be used as a tool to develop site-specific displacement hazard curves, while the last can be used to evaluate earthquake-induced slope displacements, as well as to calibrate the seismic coefficient to be used in a pseudo-static analysis. Influence of the vertical component of seismic motion on these semi-empirical relationships is also assessed.</jats:p

Influence of site response and focal mechanism on the performance of peak ground motion prediction equations for the Greek region

The predictive performance of ground motion prediction equations relative to peak horizontal acceleration (PHA) defined for the Greek region were found not to benefit from the inclusion of terms accounting for site response. This can be in part due to an inadequacy of standard methods for site classification to evaluate the expected amount of PHA amplification. Indeed, the adoption of a new method to derive classification from the analysis of regression residuals seems able to improve the predictive performance in comparison to the use of conventional classification. However, this improvement is limited by an intrinsic drawback of classification criteria, i.e. the implicit assumption that amplification be a site-specific property not depending on event characteristics. Instead, for the study area and at least within the range of earthquake magnitude and distance investigated, the inclusion of focal mechanism among the explanatory variables of equations both for PHA and for peak horizontal velocity (PHV) does not improve the predictive performances independently on how fault styles are categorized

Seismic hazard assessment in Polyphyto Dam area (NW Greece) and its relation with the "unexpected" earthquake of 13 May 1995 (<i>M</i>_s = 6.5, NW Greece)

Seismic hazard assessment and seismicity changes are investigated in the Kozani–Grevena area, at the western margin of internal Hellenides in NW Greece. The region is of great interest, since it was characterized by very low seismic activity until 1995, when the "unexpected" Kozani–Grevena earthquake (<i>M</i>_s = 6.5) occurred. This event is of significant importance for Greece, since it, along with the 1999 Athens earthquake, initiated the modification of the Greek Building Code. In order to detect any seismicity changes, the seismicity of the region was divided into three time windows: the first up to 1973, the second from 1900 to 1994 and the third covering the entire instrumental period. <br><br> For the above mentioned time windows, seismic hazard assessment was performed using the extreme values method. The results indicate an increase of the peak ground acceleration (PGA) values after the impoundment, with the exception of the area in the vicinity of the NE edge of the Dam. Before the occurrence of the 1995 event, the epicentral region also exhibited higher PGA values than before the impoundment. The most significant increase in PGA values is observed SE of the Polyphyto artificial lake, where the largest values are observed for the second and the third period. The coincident increase in the number of earthquakes and in the PGA values may be attributed to the impoundment of the Polyphyto Dam. <br><br> The maximum expected magnitude is calculated by the extreme values method and Gumbel's third asymptotic distribution. The results reveal similar values of maximum expected magnitudes (<i>M</i>_max = 6.5), independent of the seismicity rate, indicating that the 13 May 1995 earthquake was not an "unexpected" event, since the magnitude of an oncoming earthquake depends mainly on the tectonics of the region and the characteristics of the active faults

Displacements recorded on continuous GPS stations following the 2014 M6 Cephalonia (Greece) earthquakes: Dynamic characteristics and kinematic implications

We report cm-size dynamic displacements of continuous GPS stations onshore the island of Cephalonia, Ionian Sea, Greece, following the passage of seismic waves from two (2) shallow earthquakes on Jan 26, 2014 and Feb 3, 2014, respectively. First, we estimated the displacements from the high-rate GPS data collected at NOA station VLSM, near to the epicenters, by using state-of-art data processing strategies. The time series of displacements were analyzed both in time and frequency domains. From the dynamic analysis of 1Hz data it is shown that the second event was recorded at station VLSM with higher amplitudes on both horizontal components, despite its smaller (22 %) moment magnitude, possibly due to its shallower depth. The static field of deformation is characterized by cm-size permanent motion in opposing directions between stations KIPO (western Cephalonia) and VLSM (eastern Cephalonia), in agreement with the right-lateral kinematics of both ruptures. The 7.4 cm northward motion of station KIPO implies that the western peninsula of Cephalonia island (Paliki) belongs to a separate crustal block with respect to the rest of the island. The northward motion of KIPO also implies that the Cephalonia Transform Fault (CTF) did not rupture during the 2014 events, because KIPO is located at the hanging wall of CTF. It is possible that the amount of accumulated strain along CTF since 1983 (M=6.8) can be released by a seismic event of M6.5-6.7, at any time. © 2015, Academy of Sciences of the Czech Republic. All rights reserved

Suitability estimation for urban development using multi-hazard assessment map

© 2016 Preparation of natural hazards maps are vital and essential for urban development. The main scope of this study is to synthesize natural hazard maps in a single multi-hazard map and thus to identify suitable areas for the urban development. The study area is the drainage basin of Xerias stream (Northeastern Peloponnesus, Greece) that has frequently suffered damages from landslides, floods and earthquakes. Landslide, flood and seismic hazard assessment maps were separately generated and further combined by applying the Analytical Hierarchy Process (AHP) and utilizing a Geographical Information System (GIS) to produce a multi-hazard map. This map represents the potential suitability map for urban development in the study area and was evaluated by means of uncertainty analysis. The outcome revealed that the most suitable areas are distributed in the southern part of the study area, where the landslide, flood and seismic hazards are at low and very low level. The uncertainty analysis shows small differences on the spatial distribution of the suitability zones. The produced suitability map for urban development proves a satisfactory agreement between the suitability zones and the landslide and flood phenomena that have affected the study area. Finally, 40% of the existing urban pattern boundaries and 60% of the current road network are located within the limits of low and very low suitability zones