Kyriazis Pitilakis

Recommendations for the quantitative analysis of landslide risk

This paper presents recommended methodologies for the quantitative analysis of landslide hazard, vulnerability and risk at different spatial scales (site-specific, local, regional and national), as well as for the verification and validation of the results. The methodologies described focus on the evaluation of the probabilities of occurrence of different landslide types with certain characteristics. Methods used to determine the spatial distribution of landslide intensity, the characterisation of the elements at risk, the assessment of the potential degree of damage and the quantification of the vulnerability of the elements at risk, and those used to perform the quantitative risk analysis are also described. The paper is intended for use by scientists and practising engineers, geologists and other landslide experts.

Site effects at Euroseistest—I. Determination of the valley structure and confrontation of observations with 1D analysis

This paper describes the process of construction of the 2D model of Volvis geological structure and results of empirical and theoretical approaches to the evaluation of site response at Euroseistest. The construction of the 2D model is based on a re-interpretation of the available geophysical and geotechnical data in an effort to improve the definition of the subsoil structure at Euroseistest in terms of the most important parameters needed to model site response. The results of this re-interpretation are compared with a previous published 2D model of the same alluvial valley. Different analysis of the measurements and different criteria in the synthesis of data have led to a different model, even if both studies had access to the same field measurements. This underscores the fact that a model results of an interpretation and is not uniquely determined by the data, no matter how detailed they are. The well known subsoil structure opened the possibility to correlate the geometry and the dynamic properties of the 2D model with the results of site response determined from a detailed analysis of two events in frequency and time domains and 1D numerical modeling. The study of site response shows the important effect of the lateral variations on the ground motion and suggests that the contribution of locally generated surface waves to the resonant peak may be important. In the case of Volvis graben, the limitations of the 1D approximation to simulate ground motion under complex soil conditions in both frequency and time domains are also shown. This paper lays the ground for a companion article dealing with 2D site effects in this basin.

GEOTECHNICAL AND GEOPHYSICAL DESCRIPTION OF EURO-SEISTEST, USING FIELD, LABORATORY TESTS AND MODERATE STRONG MOTION RECORDINGS

EURO-SEISTEST is a European test site established in the Mygdonian basin, near Thessaloniki, in Northern Greece. Its aim is to allow detailed and well documented studies in many fields of engineering seismology, earthquake engineering, soil dynamics and seismology. Theoretical and experimental seismic ground response analysis along the valley is one of the most important tasks of the project. The very detailed knowledge of the geological and geotechnical structure of the site as well as numerous data from a continuous seismological and geodetical survey and dense semi-permanent and permanent instrumentation, offer the possibility of conducting detailed empirical and theoretical studies on the effects of surface geology on seismic ground motion. EURO-SEISTEST is a unique test site for checking the reliability of existing theoretical models of site effects, to develop new ones, and to interpret the physics of seismic ground response. The paper presents: (a) the general layout of the test site, (b) the main results of the extensive geophysical and geotechnical surveys, to determining the geometry and the dynamic properties of soil formations, and (c) the validation of valleys structure with instrumental estimates of the site effects along the valley. Emphasis is given to comparisons and correlations between results derived from different methods of seismic prospection (refraction, surface wave inversion, borehole seismics) and geotechnical in situ tests. In order to better constrain the structure of the valley and the dynamic properties of the soil formations, specific criteria and procedures are developed for soil characterisation.

Site effects at euroseistest : II. Results from 2D numerical modeling and comparison with observations

This paper presents results of numerical modeling of site response for Euroseistest. Ground motion across a very detailed model of the subsoil of this valley has been simulated for vertically incident SH waves. The predominance of locally generated surface waves is very clear in the synthetic seismograms. These results are then compared with published studies of observed site effects at this basin and with a detailed analysis of two events in the time domain. It is discussed in which sense it is possible to obtain a good fit between observations and 1D models, even though the real behavior involves locally generated Love waves. For this reason, it can be misleading to rely on an incomplete observation such as empirical transfer functions. Finally, it is stressed that in order to predict ground motion in alluvial valleys the information contained in the phase cannot be neglected.

Development of Seismic Risk Scenarios Based on a Hybrid Method of Vulnerability Assessment

A hybrid methodology of vulnerability analysis is presented, involving elements from both empirical and theoretical methods. A model for correlating analytically calculated structural damage indices to loss (in monetary terms) is also proposed and calibrated against available statistical data. Probability damage matrices derived using this methodology are incorporated into a cost-benefit model tailored to the problem of estimating the feasibility of seismically rehabilitating the existing stock of reinforced concrete buildings in Thessaloniki, Greece. Losses calculated using the suggested procedure are found to be in good agreement with losses incurred during the 1978 Thessaloniki earthquake. The results of the present study also indicate that benefit/cost ratios for reinforced concrete buildings are quite low. Hence, it appears that a pre-earthquake strengthening programme is not economically justifiable.

Erratum to: New code site classification, amplification factors and normalized response spectra based on a worldwide ground-motion database

A global dataset of more than 3,000 ground motion records from 536 sites from Greece, Italy, Turkey, USA and Japan is compiled and used to propose code-oriented elastic acceleration response spectra and soil amplification factors for a new site classification system, which, besides the classical geotechnical parameters

Design spectra and amplification factors for Eurocode 8

N_{SPT}, S_{u}

The Small-Strain Shear Modulus and Damping Ratio of Quartz and Volcanic Sands

and PI, uses also the fundamental period of the site, the thickness of soil deposits and the average shear wave velocity to the seismic bedrock, instead of