The application of predictive modeling techniques to landslides induced by earthquakes: the case study of the 26 September 1997 Umbria-Marche earthquake (Italy)

Recent accelerometric recordings of earthquakes with moderate and in- termediate magnitude (4.0 ML 5.9), at both local and regional distances, show a significant ground-motion amplification effect at low frequencies (0.6 Hz) in the city of L'Aquila (central Italy). The effect involves very long durations characterized by low frequencies in the coda. Starting from these observations, a series of supplementary investigations was performed in the urban area of L'Aquila by collecting and analyzing both weak- motion data from earthquakes with magnitudes ranging from 2.2 to 4.9 at distances from 20 to 105 km and ambient noise data. All the collected weak-motion data share the same characteristics as the strong- motion records and give a better image of the amplification effect in the city. In order to interpret observations in terms of the local geology, we performed 2D nu- merical modeling of the sedimentary basin underlying the city of L'Aquila using both finite elements and boundary elements based on a geological section derived from gravity measurements. This analysis indicates that the ground-motion amplification in the city of L'Aquila is related to the presence of a sedimentary basin, filled by lacustrine sediments, with a maximum depth of about 250 m. The combined approach to data collection and analysis used here gives useful information for risk assessment in the city of L'Aquila and can be recommended for many other urban areas that share similar characteristics.

Evidence of Low-Frequency Amplification in the City of L’Aquila, Central Italy, through a Multidisciplinary Approach Including Strong- and Weak-Motion Data, Ambient Noise, and Numerical Modeling

In this paper earthquake damage scenarios for residential buildings (about 4200 units) in Potenza (Southern Italy) have been estimated adopting a novel probabilistic approach that involves complex source models, site effects, building vulnerability assessment and damage estimation through Damage Probability Matrices. Several causative faults of single seismic events, with magnitude up to 7, are known to be close to the town. A seismic hazard approach based on finite faults ground motion simulation techniques has been used to identify the sources producing the maximum expected ground motion at Potenza and to generate a set of ground motion time histories to be adopted for building damage scenarios. Additionally, site effects, evaluated in a previous work through amplification factors of Housner intensity, have been combined with the bedrock values provided by hazard assessment. Furthermore, a new relationship between Housner and EMS-98 macroseismic intensity has been developed. This relationship has been used to convert the probability mass functions of Housner intensity obtained from synthetic seismograms amplified by the site effects coefficients into probability mass function of EMS-98 intensity. Finally, the Damage Probability Matrices have been applied to estimate the damage levels of the residential buildings located in the urban area of Potenza. The proposed methodology returns the full probabilistic distribution of expected damage, thus avoiding average damage index or uncertainties expressed in term of dispersion indexes.

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Building damage scenarios based on exploitation of Housner intensity derived from finite faults ground motion simulations

Spatial variability of the time-correlated behaviour in Italian seismicity

Results of geological, geomechanical and seismometric investigations aiming at the analysis of the seismic response in a carbonate ridge of the Nera River valley (Central Apennines – Italy) are discussed. Geological and geomechanical surveys were aimed at defining the stratigraphic and structural setting of the outcropping formations and the jointing conditions of the rock mass. Velocimetric records of both ambient noise and small-magnitude earthquakes were analysed in order to identify amplification conditions. The analysis was carried out in the time domain, through directional energy evaluation, and in the frequency domain, through H/V spectral ratios and spectral ratios with respect to a reference station. A local amplification factor was estimated from Housner intensity. The study revealed a significant seismic amplification in a fault zone. This effect was observed in intensely jointed and mylonitic rock masses, located inside moderately jointed rock masses, and is the result of specific geometries and significant impedance contrasts. A map of fault zones prone to amplification of ground motion was constructed, taking into account the jointing conditions of the rock masses and the structural setting of the investigated ridge. The study relied on an integrated methodological approach, which combined the available data under union and intersection criteria.

Evidence of amplification effects in fault zone related to rock mass jointing

Seismic microzoning of the area struck by Umbria–Marche (Central Italy) Ms 5.9 earthquake of 26 September 1997

Seismic microzoning using numerical modelling: the Umbria-Marche earthquake of the 26 september 1997

1 Istituto de Ricerca sul Rischio Sismico, Milano, Italy. 2 Servizio Sismico Nazionale, Roma, Italy. 3 Istituto de Ricerca sul Rischio Sismico, Milano, Italy. 4 Istituto de Ricerca sul Rischio Sismico, Milano, Italy. 5 Agenzia Nazionale per la Protezione dell' Ambiente, Roma, Italy. 6 Agenzia Nazionale per la Protezione dell' Ambiente, Roma, Italy. CRITERIA FOR A SEISMIC MICROZONING OF A LARGE AREA IN CENTRAL ITALY

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T. Sanò

Papers

Seismic microzoning of the area struck by Umbria–Marche (Central Italy) Ms 5.9 earthquake of 26 September 1997

Seismic microzoning using numerical modelling: the Umbria-Marche earthquake of the 26 september 1997

Criteria for a seismic microzoning of a large area in central Italy