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The Albanides represent a complex orogen made up of a heterogeneous tectonic nappe pile of Paleozoic, Mesozoic, and Cenozoic domains. Albania is tectonically active, and moderate to strong earthquakes have occurred in the past. However, abundant microseismicity has not been monitored and studied by a dense seismic network. During this study, a seismic network of 40 stations was deployed in southern Albania for one year. A total of 2113 microearthquakes were well located. The most accurately located events and 810 focal mechanisms were used in order to define the seismotectonics and the stress pattern in the area. Results indicate that thrust and strike-slip faulting both exist in southwestern Albania, suggesting a con-tinuation of the complex tectonic setting of the neighboring northwestern Greece to the north. [ABSTRACT FROM AUTHOR]

We have studied using traveltimes of P- and S-waves and initial seismic-pulse rise-time measurements from natural microearthquakes to derive 3D P-wave velocity VP information (mostly structural) as well as P- and S-wave velocity VP/ VS and P-wave quality factor Q VP information (mostly lithologic) in a known hydrocarbon field in southern Albania. During a 12-month monitoring period, 1860 microearthquakes were located at a 50-station seismic network and were used to obtain the above parameters. The data set included earthquakes with magnitudes ranging from -0.1 to 3.0 R (Richter scale) and focal depths typically occurring between 2 and 10 km. Kohonen neural networks were implemented to facilitate the lithological classification of the passive seismic tomography (PST) results. The obtained results, which agreed with data from nearby wells, helped delineate the structure of the reservoir. Two subregions of the investigated area, one corresponding to an oil field and one to a gas field, were correlated with the PST results. This experiment showed that PST is a powerful new geophysical technique for exploring regions that present seismic penetration problems, difficult topographies, and complicated geologies, such as thrust-belt regions. The method is economical and environmentally friendly, mad it can be used to investigate very large regions for the optimal design of planned 2D or 3D conventional geophysical surveys. [ABSTRACT FROM AUTHOR]

The investigated area, located around the Rio-Antirrio Strait, Central Greece, has been the target of a seismic microzonation campaign. Seventy seismic stations have been deployed for a period of 4 months, recording in continuous mode. Despite the high level of urban noise, we compiled a data set of 95 earthquakes recorded at most of the 70 sites. By employing the attributes of self-organizing maps (SOMs), a quality-control and signal-improving method is proposed. A SOM (Kohonen, 1997) is a type of unsupervised neural network. The main property of SOMs utilized is that while the competitive learning algorithm on whom this method is based maps the input data on an n-dimensional grid of neurons, the topological relations (proximity of patterns in input data) are preserved in the output space. SOM is applied to the horizontal-to-vertical spectral ratios (HVSR) of every weak event analyzed for each station separately and allows a better evaluation of the stability of the HVSR. [ABSTRACT FROM AUTHOR]

We determine the attenuation structure of a three-dimensional medium based on first pulse-width measurements from microearthquake data. Ninety-five microearthquakes from a seventy stations local network were considered in this study. Measurements of the first half cycle of the wave, the so-called rise time τ were carried out on high quality velocity seismograms and inverted to estimate the P-waves intrinsic quality factor Qp. The results of this investigation indicate that first pulse width data from a local microearthquake network permit retrieval with sufficient accuracy of the heterogeneous Qp structure. The inferred attenuation variability corresponds to the known geological formations in the region. [ABSTRACT FROM AUTHOR]

New relationships between modified Mercalli intensity (MMI) and engineering ground-motion parameters are developed for Greece. The ground-motion parameters investigated were peak ground acceleration (PGA), velocity, displacement, Arias intensity, and cumulative absolute velocity. The observed earthquake intensity is quantified in terms of the observed MMI at the recording station and the data set consists of 310 time histories recorded from 89 Greek earthquakes. The selected records were found to be characterized by high-frequency, low-energy content and short duration. Two sets of empirical relationships between MMI and the selected ground-motion parameters were derived. The first set of MMI predictive equations are independent of magnitude and epicentral distance, and they were derived by fitting the mean values of the ground-motion parameters using a weighted least-squares regression technique. The influence of magnitude, epicentral distance, and the local site conditions were incorporated into the second MMI predictive model, resulting in a decrease of the model variance. The lowest standard deviation observed for the first MMI predictive model was for PGA, while for the second MMI predictive model, Arias intensity exhibited the smallest variability. Another finding of the present study was that the local site effect has a little influence on the MMI predictive model for peak ground velocity (PGV). The proposed predictive equations are valid for MMI values IV-VIII, and some of them might be used for rapid assessment of the ground shaking and mapping damage potential. [ABSTRACT FROM AUTHOR]

Engineering ground-motion parameters can be used to describe the damage potential of an earthquake. Some of them correlate well with several commonly used demand measures of structural performance, liquefaction, and seismic-slope stability. The importance of these parameters comes from the necessity of an alternative measure to the earthquake intensity. In the proposed new attenuation relationship we consider peak values of strong motion, spectral acceleration, elastic input energy at selected frequencies, root-mean-square acceleration, Arias intensity, characteristic intensity, Fajfar index, cumulative absolute velocity, cumulative absolute velocity integrated with a 5 cm/sec² lower threshold, and spectrum-intensity energy. This article describes the steps involved in the development of new attenuation relationships for all the preceding parameters, using all existing, up-to-date Greek strong-motion data. The functional form of the empirical equation is selected based on a theoretical model, and the coefficients of the independent variables are determined by employing mixed effects regression analysis methodologies. [ABSTRACT FROM AUTHOR]

During a twelve-month passive tomography experiment in Epirus, in northwestern Greece, a total of 1368 microearthquakes were located. The most accurately located events and focal mechanisms are used here to understand the seismotectonics of the area. The seismicity shows a clear association with the main, previously defined deformation zones. A total of 434 well-defined focal mechanisms were also used for the determination of the stress pattern in the area. The computed stress-field pattern is quite complex close to the surface and almost homogeneous at depths below 15 km. For these depths, the stress field is purely compressional in a west-southwest direction, whereas for shallow depths it is transpressional or even extensional for some smaller areas. The abrupt change in the stress pattern, which occurs as depth increases, suggests the existence of a detachment surface, which is provided by the evaporites that have intruded into the upper layers through the thrust zones. The presence of the evaporites and their lateral extent is mapped by the seismicity distribution and confirmed by seismic tomography. Based on the findings, we estimate a possible total evaporite thickness of almost 10 km at least for the central part of the study area. Such a result is important for the oil exploration efforts that have just started in Epirus. [ABSTRACT FROM AUTHOR]

We investigate the tsunami hazard associated with the Perachora fault at eastern Corinth Gulf, Greece. Realistic faulting parameters are used to model expected coseismic displacements of the seafloor. This study also investigates the effect that rupture complexity has on the local tsunami wave field. Several earthquake scenarios are used as initial conditions for tsunami stimulation either considering the numerous published constant slip models or taking into account the fault rupture complexity with the help of a realistic finite-extent k-2 stochastic kinematic source model with k-dependent rise time. The obtained results indicate that there is substantially more variation in the local tsunami wave field derived from the inherent complexity of the shallow fault zone than predicted by a simple elastic dislocation model. Rupture complexity, as represented by heterogeneous slip-distribution patterns, has an important effect on near-field tsunami records. Tsunami hazards assessments based on only a few scenario earthquakes may not accurately account for natural variation in tsunami amplitude caused by earthquake rupture complexity. [ABSTRACT FROM AUTHOR]

The moment tensor inversion for multiple point sources, based on Kikuchi and Kanamori (1991), was extended to full waveform data at regional (or local) distances. The new code proved to be efficient for retrieving major source contributions of the 2003 Lefkada, Greece, earthquake. The source model was derived from five three-component regional stations (epicentral distances < 140 km), at periods 10-20 s. Two main events dominated the rupture process, one at the Lefkada Island (comprising three subevents of total moment 0.9 x 1018 N m) and the other at the Cephalonia Island (comprising one subevent of 0.5 x 1018 N m). Their spatial and temporal separation is 40 km and 14 s, respectively. They can be understood as two earthquakes. The uncertainty estimate based on reduced data sets (repeatedly excluding a station) shows that the Cephalonia subevent and the major Lefkada subevent are very well resolved regarding their position, time, and focal mechanism. The source model explains well the aftershock distribution, characterized by two clusters at the Lefkada and Cephalonia Islands, respectively. The focal mechanisms of the two main subevents are predominantly fight-lateral strike slip of south-southwest-north-northeast orientation. The Cephalonia subevent occurred on a less steeply dipping fault with a small thrust component. Large deviations from pure double couple were found but interpreted as artifacts. The new software developed in this article (Fortran code and Matlab graphic user interface) is freely available. [ABSTRACT FROM AUTHOR]