Ground‐Motion Simulations for the M 6.9 Irpinia 1980 Earthquake (Southern Italy) and Scenario Events

In this paper, we adopt three ground‐motion simulation techniques (EXSIM, Motazedian and Atkinson, 2005, DSM, Pacor et al., 2005 and HIC, Gallovič and Brokešová, 2007), with the aim of investigating the different performances in near‐fault strong‐motion modeling and prediction from past and future events. The test case is the 1980, M 6.9, Irpinia earthquake, the strongest event recorded in Italy. First, we simulate the recorded strong‐motion data and validate the model parameters by computing spectral acceleration and peak amplitudes residual distributions. The validated model is then used to investigate the influence of site effects and to compute synthetic ground motions around the fault. Afterward, we simulate the expected ground motions from scenario events on the Irpinia fault, varying the hypocenters, the rupture velocities and the slip distributions. We compare the median ground motions and related standard deviations from all scenario events with empirical ground motion prediction equations (GMPEs). The synthetic median values are included in the median ± one standard deviation of the considered GMPEs. Synthetic peak ground accelerations show median values smaller and with a faster decay with distance than the empirical ones. The synthetics total standard deviation is of the same order or smaller than the empirical one and it shows considerable differences from one simulation technique to another. We decomposed the total standard deviation into its between‐scenario and within‐scenario components. The larger contribution to the total sigma comes from the latter while the former is found to be smaller and in good agreement with empirical inter‐event variability

Modelling directivity effects of the October 21, 2002 (Mw = 5.7), Molise, Southern Italy, earthquake

Acceleration time series recorded by the Italian Strong Motion Network (RAN) during the October 31, 2002 (Mw=5.8), Molise earthquake, are employed in order to investigate source effects on the ground motion in the epicentral area. We consider two different seismogenic sources: a fault model inferred from inversion of teleseismic, regional and local seismic signals [Vallée and Di Luccio, 2005], and a fault model based on seismotectonic data [Basili and Vannoli, 2005]. Both source studies suggest a deep location of the earthquake fault plane (ranging from 6.0 to 20.1 km and from 12.0 to 19.9 km, respectively), however, with considerably different fault lengths (5.2 and 10.5 km, respectively), and widths (14.2 and 8 km, respectively). Due to these differences, only the second model allows for effective horizontal unilateral rupture propagation. Finite fault effects are modelled by the Deterministic-Stochastic-Method (DSM) [Pacor et al., 2005], and the Hybrid Integral-Composite source model (HIC) [Gallovic and Brokesova, 2006]. In both methods k-square slip distributions on the faults are considered. We simulate the October 31, 2002 earthquake considering: 1) Vallée and Di Luccio [2005] faultwith a bilateral rupture propagation, and 2) Basili and Vannoli [2005] fault with unilateral directions of the rupture propagation. The spectral attenuation is modelled using a regional estimate of the quality factor [Castro et al., 2004] and k values estimated from acceleration records. Comparison between synthetic and recorded data at nearby stations (hypocentral distances < 60 km) performed in terms of frequency content and peak ground motion, favours the model with unilateral propagation of the rupture. Assuming the source model with unilateral rupture propagation, we utilize both asymptotic and full wave field methods in order to simulate ground shaking scenarios for an area extending up to 150 km epicentral distance. These results are then subjected to comparison with peak ground accelerations recorded in the far field

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

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 previouswork 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

Task 5 - Potenza - Deliverable D17: Bedrock shaking scenarios

The main goal of this report is the computation of the bedrock seismic scenarios in the Potenza city (Southern Italy) to be used for evaluating damage scenarios (described in PS3-Deliverables D18-D19-D24). This area represents one of the prediction case studies, planned in the framework of Project S3 which aim is the production of ground shaking scenarios for high and moderate magnitude earthquakes. The area around Potenza was affected by several destructive earthquakes in historical time (Table 2.1.1) and a number of individual sources representing the causative faults of single seismic events with magnitude up to 7 were identified. Deeper and smaller faults are present very close to the Potenza city, generating events with M up to 5.7 (1990 Potenza earthquake). Due to the involved source-to-site distances (about 25 km) and to the computation resolution of the simulation techniques, the site is represented by a single point. In total 9 faults were identified and the deterministic shaking scenarios are computed for each of them. The following strategy is adopted to provide ground motions. We compute shaking scenarios at level 1, using a simplified simulation technique (DSM, Pacor et al.; 2005) for all the faults. By these simulations we identify the three faults (F3, F7. and F8) producing the maximum expected shaking at the Potenza city, in terms of peak ground acceleration, peak ground velocity and Housner intensity. Based on these results, simulations at level 2, using the broad band technique HIC (Gallovic and Brokeshova, 2007) have been performed at Potenza for F3, F7 and F8 sources. For the Potenza city, we decided to predict the shaking scenarios at level 2, in order to provide suitable estimates of the low frequency ground motion (e.g. velocity time series) and engineering parameters (e.g. Arias intensity) strictly related to the duration of the signals. For each source, we generated hundreds of rupture models varying slip distribution, nucleation points and rupture velocity, and for each model we simulated the acceleration time series by HIC. Then we computed the probability density functions (PDF) of the ground motion parameters (PGA, PGV, PGD, Arias and Housner intensities) and estimated several statistical quantities in order to select families of accelerograms to be used for damage analysis: mean and associated standard deviation, median, 75% percentile, 84% percentile, mode, minimum and maximum. Finally we provided to the engineering Research Unit 6 of this project three sets of 7 accelerograms, having ground motion parameters equal to the statistical requirements computed by the synthetic distributions. The first set includes 7 accelerograms (three components), each of them having PGA equal to the mean, median, mode, 75-percentile, 84-percentile, minimum and maximum values of the PGA distribution. The second set and third sets include 7 accelerograms (horizontal components only), having PGA and Housener Intensity in the neighborhood of the median values of the corresponding distributions. A further comparison of adopted procedure for the predicted ground motion at Potenza was performed with respect to stochastic ground motions generated with EXSIM method (Motazedian and Atkinson; 2005). Even if the scenarios modelling was carried out varying different kinematic parameters, the statistical parameter were quite similar. Finally to provide shaking scenarios in term of macroseismic intensity, we applied a probabilistic empirical approach, developed in Progetto DPC-INGV S1.Progetto INGV-DPC S3 “Scenari di scuotimento in aree di interesse prioritario e/o strategico”Published4.2. TTC - Scenari e mappe di pericolosità sismicaope

Task 3 - Molise - Deliverable D7: Validation shaking scenarios.

The main goal of this report is the computation of the bedrock seismic motion at 5 municipalities located in the Molise area (Bonefro, S.Giuliano, Colletorto, S.Croce di Magliano, Ripabottoni, hereafter referred to as sites BNF, SGI, CLT, SCM and RPB, respectively). This area represents one of the validation case studies, planned in the framework of Project S3 which aim is the production of ground shaking scenarios for moderate magnitude earthquakes. Indeed, the recently occurred Molise earthquake represents a proper opportunity to compare synthetic simulations with real data. Acceleration time series were recorded during the October 31, 2002 and November 1, 2002 main shocks by analog and digital instruments managed by the Italian Civil Protection Department [DPC-SSN, 2004] while acceleration and velocity records were collected during the first month of seismic activity by DPC, INGV, INOGS, Dip.Te.Ris.(Genoa) (see §2.1 and Deliverable D6). Both strong and weak motion data were employed to infer regional ground motion prediction equations and spectral attenuation models (§2.3 and §2.4) while acceleration time series recorded during the first main shock by nearby stations were used to constrain the seismogenic sources of the October 31 and November 1, 2002 twin earthquakes (§4.1). Bedrock shaking scenarios at different level of complexity were produced by ground motion prediction equations (scenarios of level 0, §4.2), high frequency (f>1Hz) simulations (scenarios of level I, §4.3) and broad band (0-12 Hz) simulations (scenarios of level II, §4.4). Comparison of results obtained with different simulations methods confirms the complexity of the Molise area as regard to both seismogenic and attenuation properties of the crust. Especially for this area the ground motion prediction is constrained by the demand of simulations reproducing different features of the seismic wavefield. In particular, the input motion for site effect modelling, performed at sites located in the epicentral area, was computed with a broad band technique able to reproduce the complete wave field in the frequency band 0-10 Hz in terms of acceleration time series (scenarios of level II scenarios)

Task 1 - Scenari di scuotimento - Deliverable D0: Tecniche di simulazione

Progetto INGV-DPC S3 “Scenari di scuotimento in aree di interesse prioritario e/o strategico”Published4.1. Metodologie sismologiche per l'ingegneria sismicaope