ALBERT

Description: On 23 October 2011 an M w  7.1 earthquake occurred in eastern Turkey, close to the towns of Van and Ercis, causing more than 600 casualties and widespread structural damage. The earthquake ruptured a 60–70 km long northeast–southwest fault with a thrust mechanism, in agreement with regional tectonic stress regime. We studied the fault process of the event and the recorded ground motions using different sets of data. Regional records (0.005–0.010 Hz) are used to constrain the centroid moment tensor solution. Near-regional data, 100–200 km from the fault, are used for relocation of the hypocenter and, in the frequency range 0.05–0.15 Hz, for inversion of the rupture propagation by two methods: multiple point-source model (ISOLA) and multiple finite-extent (MuFEx) source model. MuFEx also provides an estimate of the model uncertainty, which is quite large due to unfavorable station distribution. We arrive at several plausible scenarios (equally well fitting the observed data including Global Positioning System coseismic displacements) with different styles of the rupture propagation. A few alternative source models are used for broadband (0.1–10 Hz) ground-motion simulations by means of the hybrid integral-composite source model. Only models comprising source complexities, such as a delayed rupture of shallow asperities, enable explanation of the acceleration record at the only available near-fault station, which exhibits a long duration and two prominent wave groups. These complex rupture models are used to simulate the ground motion in the near-fault area, specifically, at Van and Ercis, where records of the mainshock were missing, providing reasonable agreement with the observed spatial distribution of damage.

Description: In this paper, we adopt three ground-motion simulation techniques (the stochastic finite-fault simulation code from Motazedian and Atkinson, 2005; the hybrid deterministic-stochastic approach with approximated Green's functions from Pacor et al., 2005; and the broadband hybrid integral-composite technique with full-wavefield Green's functions from Gallovic and Brokesova, 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 in the last 30 years. First, we simulate the recorded strong-motion data and validate the model parameters by computing spectral acceleration and peak amplitude 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 + or -1 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 interevent variability.

Description: This study investigates the engineering applicability of two conceptually different finite-fault simulation techniques. We focus our attention on two important aspects: first to quantify the capability of the methods to reproduce the observed ground-motion parameters (peaks and integral quantities); second to quantify the dependence of the strong-motion parameters on the variability in the large-scale kinematic definition of the source (i.e., position of the nucleation point, value of the rupture velocity, and distribution of the final slip on the fault). We applied an approximated simulation technique, the deterministic-stochastic method and a broadband technique, the hybrid-integral-composite method, to model the 1984 Mw 5.7 Gubbio, central Italy, earthquake, at five accelerometric stations. We first optimize the position of the nucleation point and the value of the rupture velocity for three different final slip distributions on the fault by minimizing an error function in terms of acceleration response spectra in the frequency band from 1 to 9 Hz. We found that the best model is given by a rupture propagating at about 2:65 km=sec from a hypocenter located approximately at the center of the fault. In the second part of the article we calculate more than 2400 scenarios varying the kinematic source parameters. At the five sites we compute the residuals distributions for the various strongmotion parameters and show that their standard deviations depend on the source parameterization adopted by the two techniques. Furthermore, we show that Arias Intensity (AI) and significant duration are characterized by the largest and smallest standard deviation, respectively. Housner Intensity is better modeled and less affected by uncertainties in the source kinematic parameters than AI. The fact that the uncertainties in the kinematic model affects the variability of different ground-motion parameters in different ways has to be taken into account when performing hazard assessment and earthquake engineering studies for future events.

Description: Published

Description: 647-663

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: reserved

Description: In questo lavoro viene calcolato il moto sismico di riferimento da utilizzarsi per l’analisi degli effetti di sito in 5 comuni localizzati nell’area epicentrale del terremoto del Molise del 2002: Bonefro (BNF), S. Giuliano di Puglia (SGI), Colletorto (CLT), S. Croce di Magliano SCM) e Ripabottoni (RPB). Le simulazioni del moto vengono effettuate sulla base di tre diversi livelli di complessità, che comportano sia l’utilizzo di equazioni empiriche predittive del moto del suolo (Ground Motion Predictive Equations, GMPE) sia l’impiego di tecniche di simulazione a sorgente estesa. In particolare, sono state adottate una tecnica di simulazione di alta (1-20 Hz) frequenza (DSM – Deterministic Stochastic Method, PACOR et al. [2005]) e un tecnica di simulazione broad-band (HIC - Hybrid Integral Composite method, GALLOVIC e BROKESOVA [2004; 2007]). Inizialmente, la tecnica DSM è stata impiegata per selezionare il modello di sorgente da adottare fra due diverse possibilità proposte in letteratura [VALLÉE e DI LUCCIO, 2005; BASILI e VANNOLI, 2005]. Il confronto fra accelerazioni simulate e osservate a distanze ipocentrali minori di 60 km, suggerisce l’adozione del secondo modello, poiché esso risulta essere l’unico in grado di produrre la propagazione unilaterale della rottura in direzione ovest-est che sembra caratterizzare l’evento del 31 ottobre. Successivamente, vengono realizzati gli scenari di scuotimento al bedrock mediante le equazioni empiriche predittive (livello 0), le simulazioni di alta frequenza (livello 1) e le simulazioni broad-band (livello 2). L’analisi degli scenari di livello 0 mostra che, a causa della profondità delle scosse principali degli eventi molisani del 2002, in media i valori di accelerazione di picco osservati risultano meglio riproducibili mediante relazioni empiriche predittive che contemplano anche la dipendenza dalla profondità della sorgente (come, ad esempio, la relazione di AMBRASEYS [1995]). Le simulazioni di livello 1 relative all’evento del 31 ottobre, mostrano un’area di massimo scuotimento localizzata a est della zona epicentrale, caratterizzata da un valore massimo di PGA di circa 160 gal mentre, per l’evento del 1 novembre, si ottiene un’area di massimo scuotimento situata in corrispondenza della proiezione in superficie della faglia. L’effetto cumulato dei due eventi principali risulta in buon accordo con le osservazioni macrosismiche [GALLI e MOLIN, 2004]. Le simulazioni di livello 2, mostrano infine che, in condizioni di near-source, il moto del suolo risulta influenzato dal livello di dettaglio con il quale viene rappresentata la cinematica della sorgente sismica. Il moto sismico di riferimento per l’analisi degli effetti di sito viene definito nell’ultima parte del lavoro, mediante il confronto fra gli scenari al bedrock simulati ai diversi livelli di complessità. I risultati ottenuti mostrano che, fino a distanze ipocentrali di circa 30 km, le tecniche DSM e HIC producono serie temporali consistenti fra loro e in near-source i valori di picco simulati con entrambe le tecniche risultano anche consistenti con la relazione empirica proposta da AMBRASEYS [1995]. In area epicentrale, i valori del picco di accelerazione al bedrock risultano compresi tra 60 e 120 gal, con valori massimi simulati nella località di S. Giuliano di Puglia (SGI) per l’evento del 31 ottobre 2002, mentre per l’evento del 1 novembre 2002 sono compresi fra 30 e 200 gal, con valori massimi nella località di Ripabottoni (RPB). Le simulazioni prodotte mediante HIC risultano inoltre essere maggiormente adatte alla riproduzione di un moto del suolo realistico in termini di durata e contenuto spettrale a bassa frequenza.

Description: Published

Description: 15-31

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: N/A or not JCR

Description: open

Description: 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.

Description: In press

Description: 4.1. Metodologie sismologiche per l'ingegneria sismica

Description: JCR Journal

Description: restricted