In the present article new predictive relations are proposed for the peak values of the horizontal components of ground acceleration, velocity, and displacement, using 619 strong motion recordings from shallow earthquakes in the broader Aegean area, which are processed using the same procedure in order to obtain a homogeneous strong motion database. The data set is derived from 225 earthquakes, mainly of normal and strike-slip focal mechanisms with magnitudes 4.5 Յ M Յ 7.0 and epicentral distances in the range 1 km Յ R Յ 160 km that have been relocated using an appropriate technique. About 1000 values of peak ground acceleration (PGA), velocity (PGV), and displacement (PGD) from horizontal components were used to derive the empirical predictive relations proposed in this study. A term accounting for the effect of faulting mechanisms in the predictive relations is introduced, and the UBC (1997) site classification is adopted for the quantification of the site effects. The new relations are compared to previous ones proposed for Greece or other regions with comparable seismotectonic environments. The regression analysis showed a noticeable (up to ϳ30%) variance reduction of the proposed relations for predicting PGA, PGV, and PGD values compared to previous ones for the Aegean area, suggesting a significant improvement of predictive relations due to the use of a homogeneous strong motion database and improved earthquake parameter information.

A response-spectra database is compiled of hundreds of seismic records from intermediate-depth earthquakes (earthquakes whose foci are located between 45 to 300 km from the earth's surface) with moment magnitudes of M 4.5-6.7 that occurred in the South Aegean subduction zone. The database consists of high-quality data from both acceleration-sensor and broadband velocity-sensor instruments. The database is much larger than previous databases used in the development of past empirical regressions enabling the determination of various parameters of ground-motion attenuation not previously examined. New variables accounting for the highly complex propagation of seismic waves in the Greek subduction zone are introduced based on the hypocentral depth and the location of the event, as these factors control the effects of the back-arc low-velocity/low-Q mantle wedge on the seismic-wave propagation. The derived results show a strong dependence of the recorded ground motions on both hypocentral depth and distance, which leads to the classification of the dataset into three depth-hypocentral distance categories. Ground motions from in-slab earthquakes, especially with hypocentral depths h > 100 km, are amplified for along-arc stations, an expected effect of channeled waves through the high-velocity slab. The ground motions are also strongly attenuated in the back-arc region, due to the low-Q mantle wedge, which are almost independent of the recording hypocentral distance. In contrast, for shallower in-slab events (60 km < h < 100 km), the corresponding differentiation of seismic motion for along-arc and back-arc stations is observed beyond a specific critical distance range. Moreover, for longer periods, both along-arc amplification and back-arc anelastic-attenuation factors strongly diminish, suggesting that the longer wavelengths of seismic waves are not affected by the complex geophysical structure, resulting in more similar ground motions for both back-arc and along-arc stations. Finally, results for interface events (h < 45 km) occurring along the outer Hellenic arc suggest their wave propagation is not affected by the presence of the low-velocity/low-Q S mantle wedge, but is mainly controlled by the differences of the anelastic attenuation between the Mediterranean and Aegean lithospheres.

The recording on high-resolution broadband seismic networks of several great interface subduction earthquakes during the last decade provide an excellent opportunity to extend source-scaling relations to very large magnitudes and to place constraints on the potential range of source parameters for these events. At present, there is a wide range of uncertainty in the median rupture areas predicted for any given seismic moment by current relationships between magnitude and rupture area for subduction interface earthquakes. Our goal is to develop an updated set of earthquake source-scaling relations that will reduce this current large degree of epistemic uncertainty and improve the accuracy of seismic-hazard analysis and the prediction of the strong-motion characteristics and tsunamis of future subduction earthquakes. To achieve this goal, we compiled a database including slip models of interface earthquakes that occurred worldwide with moment magnitudes ranging from M 6.75-9.1. We characterized the seismic sources based on well-established criteria to estimate the asperity areas as well as the average slip on the faults, and we used these parameters to compute an updated set of magnitude scaling relations of the various characteristics of the fault. Additionally, we followed an alternative approach to quantifying slip models for use in developing characteristic slip models of future earthquakes. This involved analyzing the 2D Fourier transforms of the slip functions in the compiled database and deriving a wavenumber spectral model of the slip distribution.

An M 6.7 intermediate-depth (66 km), in-slab earthquake occurring near the island of Kythera in Greece on 8 January 2006 was well recorded on networks of stations equipped with acceleration sensors and with broadband velocity sensors. All data were recorded digitally using recording instruments with resolutions ranging from almost 11 to 24 bits. We use data from these networks to study the distance dependence of the horizontal-component Fourier acceleration spectra (FAS) and horizontal-component pseudoabsolute response spectral acceleration (PSA). For purposes of simulating motions in the future, we parameterize the distance decay using several forms of the geometrical-spreading function, for each of which we derive Q as a function of frequency. By extrapolating the distance decay back to 1 km, we obtain a reference spectrum that can be used in future simulations. This spectrum requires a more complicated spectral shape than the classic single-corner-frequency model; in particular, there appears to be an enhancement of motion around 0.2-0.3 Hz that may be due to the radiation of a 3-5 sec pulse from the source. We infer a κ 0 value of about 0.055 sec for rock stations and a stress parameter in the range of 400-600 bars. We also find distinctive differences in the site response of stations on soft soil and soil; both the FAS and the 5% damped PSA amplifications have similar peak amplitudes (about 2 and 4 for soil and soft-soil sites, respectively, relative to the rock sites) at similar frequencies (between about 0.4 and 2.0 Hz, with the soft-soil amplifications peaking at somewhat lower frequencies than the soil amplifications). One of the most distinctive features of the data is the clear difference in the motions for along-arc and back-arc stations, with the former being significantly higher than the latter over a broad range of frequencies at distances beyond about 250 km. The motions from the Kythera earthquake are roughly comparable to those from intermediate-depth earthquakes elsewhere, but they appear to be significantly higher than those from recordings of shallow earthquakes in Greece of comparable magnitude and hypocentral distance. Name Date Origin Time Epicenter: Latitude Epicenter: Longitude Depth M

Using a recently completed database of uniformly processed strong-motion data recorded in Greece, we derive a ground-motion prediction model (GMPM) for horizontal-component peak ground velocity, peak ground acceleration, and 5% damped pseudoacceleration response spectra, at 105 periods ranging from 0.01 to 10 s. The equations were developed by modifying a global GMPM, to account for more rapid attenuation and weaker magnitude scaling in the Greek ground motions than in the global GMPM. Our GMPM is calibrated using the Greek data for distances up to 300 km, magnitudes from 4.0 to 7.0, and time-averaged 30 m shear-wave velocities from 150 to 1200  m/s. The GMPM has important attributes for hazard applications including magnitude scaling that extends the range of applicability to M 8.0 and nonlinear site response. These features are possible because they are well constrained by data in the global GMPM from which our model is derived. An interesting feature of the Greek data, also observed previously in studies of mid-magnitude events (6.1–6.5) in Italy, is that they are substantially overpredicted by the global GMPM, which may be a repeatable regional feature, but may also be influenced by soil–structure interaction. This bias is an important source of epistemic uncertainty that should be considered in hazard analysis.

We present a Hellenic database of intensity measures from uniformly processed strong ground motion recordings, together with metadata on earthquake source attributes and recording site conditions. The database consists of information from 471 earthquakes between 1973 and 2015 that produced 2993 usable recordings from 333 sites. A key element of this work is a unified presentation of data from two major data providers that operate in Greece (Institute of Engineering Seismology and Earthquake Engineering and the Institute of Geodynamics, National Observatory of Athens) along with a university-operated local urban array (University of Patras). Consistent procedures were applied to develop source parameters that include hypocenter locations, moment magnitudes (directly estimated or derived using a conversion procedure), fault-plane solutions, and finite-fault parameters (generally, for events with M&gt;6.0). The time-averaged shear-wave velocity in the upper 30 m parameter is provided for all 333 recording sites based on geophysical measurements where available (102) and proxy-based estimates otherwise. Most events are in the magnitude range of 3.8–7, occurred at shallow hypocentral depths (&lt;30  km), and provide data for rupture distances generally between 10 and 300 km. The combined ground motion, seismic source, and site database is anticipated to be useful for engineering applications, including ground-motion model development and time series selection for response-history analyses.

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