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/sec 2 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.

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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.

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 Ͻ140 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 ‫ן‬ 10 18 N m) and the other at the Cephalonia Island (comprising one subevent of 0.5 ‫ן‬ 10 18 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 right-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.

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.

[1] We propose a new strategy to reveal the spatialtemporal evolution of the earthquake rupture process from near-regional data, without assuming a constant rupture velocity. The approach is based on a conjugate gradient method, for which we express analytically the required waveform-misfit derivative with respect to slip on the fault. The derivative is given by back-propagation of residual seismograms towards the source. A good initial source approximation is necessary, being obtained from hypocenter location and centroid-moment tensor solution. The iterative approach then gradually reveals major characteristics of the source process. As an application, we investigate a line source model of a damaging Mw6.3 earthquake in Greece, revealing predominantly unilateral rupture propagation and two or three main slip patches, one of which being significantly delayed, indicating a temporary rupture arrest. The region of largest slip coincides with the region of least abundant aftershocks between hypocenter and centroid. The method has application potential for shakemaps, emergency response, and/or aftershock hazard assessment.

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