134 research outputs found
Inferences on the source mechanisms of the 1930 Irpinia (Southern Italy) earthquake from simulations of the kinematic rupture process
We examine here a number of parameters that define the source of the earthquake that occurred on 23rd July 1930
in Southern Italy (in the Irpinia region). Starting from the source models proposed in different studies, we have simulated
the acceleration field for each hypothesized model, and compared it with the macroseismic data. We then
used the hybrid stochastic-deterministic technique proposed by Zollo et al. (1997) for the simulation of the ground
motion associated with the rupture of an extended fault. The accelerations simulated for several sites were associated
with the intensities using the empirical relationship proposed by Trifunac and Brady (1975), before being compared
with the available data from the macroseismic catalogue. A good reproduction of the macroseismic field is
provided by a normal fault striking in Apenninic direction (approximately NW-SE) and dipping 55° toward the SW
Uncertainties in strong ground-motion prediction with finite-fault synthetic seismograms: an application to the 1984 M 5.7 Gubbio, central Italy, earthquake.
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 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 DSM, and a broadband technique, the Hybrid-Integral-Composite method HIC, to model the 1984 Mw 5.7 Gubbio, central Italy, earthquake, at 5 accelerometric stations. We first optimize the position of nucleation point and the value of 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/s from a hypocenter located approximately at the center of the fault. In the second part of the paper we calculate more than 2400 scenarios varying the kinematic source parameters. At the five sites we compute the residuals distributions for the various strong-motion parameters and show that their standard deviations depend on the source-parameterization adopted by the two techniques. Furthermore, we show that, Arias Intensity and significant duration are characterized by the largest and smallest standard deviation, respectively. Housner Intensity results better modeled and less affected by uncertainties in the source kinematic parameters than Arias Intensity. 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
On the use of ground-motion simulations within ShakeMap methodology: application to the 2008 Iwate-Miyagi Nairiku (Japan) and 1980 Irpinia (Italy) earthquakes
ShakeMap package uses empirical Ground Motion Prediction Equations (GMPEs) to estimate the ground motion where recorded data are not available. Recorded and estimated values are then interpolated in order to produce a shaking map associated with the seismic event of interest. The ShakeMap approach better works in regions with dense stations coverage, where the observed ground motions adequately constrain the interpolation. In poorly instrumented regions, the ground motion estimate mainly relies on the GMPE, that account only for average characteristics of source and wave propagation processes.
In this study we investigated the improvement of ShakeMap in the near fault area when including synthetic estimates. We focus on the 2008, Mw 7.0, Iwate-Miyagi Nairiku (Japan) earthquake as a case study because recorded by a huge number of stations. As first we calculated the shakemaps to be used as reference maps and then removed several subsets of stations from the original data-set, replacing them with: (i) the estimations of the ground motion obtained by using a specific GMPE valid for that area, using simple source information such as the earthquake magnitude and fault geometry; (ii) the peak values from synthetic time-histories computed with a hybrid deterministic-stochastic method for extended fault, using the rupture fault model obtained from the kinematic source inversion of strong-motion records.
We evaluate the deviations from the reference map and the sensitivity to the number of sites where recordings are not available. Our results show that shakemaps are more and more reliable as the coverage of stations is dense and uniformly distributed in the near-source area. Moreover, the synthetics account for propagation and source properties in a more correct way than GMPE, and largely improve the results. The hybrid maps reach good fitting levels especially when synthetics are used to integrate real data and for particular strong-motion parameters and stationsâ distribution
GroundâMotion Simulations for the M 6.9 Irpinia 1980 Earthquake (Southern Italy) and Scenario Events
In this paper, we adopt three groundâmotion simulation techniques (EXSIM, Motazedian and Atkinson, 2005, DSM, Pacor et al., 2005 and HIC, GalloviÄ and BrokeĆĄovĂĄ, 2007), with the aim of investigating the different performances in nearâfault strongâmotion 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 strongâmotion 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 betweenâscenario and withinâscenario 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 interâevent variability
Approcci deterministici per la stima del moto del suolo: vantaggi e limiti
Nel Progetto DPC-INGV S3 âScenari di scuotimento in aree di interesse prioritario e/o strategicoâ, le
stime del moto del suolo sono state ottenute attraverso lâapplicazione di diverse tecniche di
simulazione di sismogrammi sintetici. Le esperienze maturate nel corso del progetto hanno condotto
alla stesura di linee guida per il calcolo degli scenari di scuotimento al bedrock attraverso approcci
deterministici. In questo ambito Ăš stata introdotta una classificazione degli scenari deterministici
secondo tre diversi livelli di complessitĂ
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
Ground motion shaking scenarios for the 1997 Colfiorito earthquake
In the recent years, two Italian research projects have been devoted to the simulation of ground
shaking scenarios in different areas. A large part of the activities has been performed in the Umbria region
and was in particular related to the 1997 Colfiorito earthquake.
In general the statistical-deterministic approach was adopted for evaluating the scenarios for strong
motion parameters (peak values, spectral ordinates, signal integral quantities, and so on) associated with
the occurrence of a characteristic earthquake on a given fault.
This approach is based on the realistic occurrence of a single earthquake related to the fracture of an
a priori well identified active fault. According to the characteristic earthquake model, an earthquake
rupture can repeatedly occurs along the same fault (or fault system) with an almost constant geometry,
mechanism and seismic moment, these parameters being mainly related to the direction and intensity of the
large scale tectonic stress regime. These ideas are supported by numerous paleoseismic studies of active
faults in different tectonic environments [e.g., Pantosti and Valensise, 1990]. On the other hand, each
faulting process may not repeat the same style of nucleation, propagation and arrest during successive
rupture episodes occurring along a given fault zone, depending these characteristics on the pre-fracturing
conditions of rock strength and/or yielding stress along the fault zone. It is therefore assumed that the large
scale source characteristics (i.e., fault size and position, focal mechanism and seismic moment) are a priori
known as the result of previous geological, geophysical and historical seismicity investigations.
The variability of the rupture process is expected to produce variable strong ground motions at the
earth surface, depending on the distribution of the kinematic parameters (final slip distribution, rupture
velocity, slip duration âŠ) along the faulting surface. In order to account for the possible variation of the
source process from one rupture event to another, a large number of synthetic seismograms should be
computed for different (and possible) rupture histories occurring along the characteristic fault selected, so
to provide a representative set of strong motion records to be used for hazard estimation. By this strategy,
the massive computation of synthetics for different possible rupture models does not provide a single
earthquake scenario (as for the standard deterministic approach) but a set of possible scenarios whose
variability substantially reflects the heterogeneity of the source process. The advantage of this approach is
that the variability of the selected strong ground motion parameter at a given site can be described by the
statistical quantities inferred from the large number of simulations available. The earthquake scenario can
then be represented, for example, by a couple of maps, one describing the spatial distribution of the mean
value of the considered ground motion parameter and the other representing the associated variability for
example in terms of standard deviation
Ground motion scenarios for the 1997 Colfiorito, central Italy, earthquake
In this paper we report the results of several investigations aimed at evaluating ground motion scenarios for the September 26th, 1997 Colfiorito earthquake (Mw 6.0, 09:40 UTC). We model the observed variability of ground motions through synthetic scenarios which simulate an earthquake rupture propagating at constant rupture velocity (2.7 km/s) and the inferred directivity. We discuss the variability of kinematic source parameters, such as the nucleation position and the rupture velocity, and how it influences the predicted ground motions and it does not account for the total standard deviation of the empirical predictive model valid for the region. Finally, we used the results from the scenario studies for the Colfiorito earthquake to integrate the probabilistic and deterministic approaches for seismic hazard assessment
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 estimate adopting a probabilistic approach that involves complex source models, site effects, building vulnerability assessment and damage estimation through Damage Probability Matrices (DPMs). The studied area experienced several destructive earthquakes in historical and recent times. 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 used for building damage scenarios. Additionally, site effects, evaluated in the framework of the DPC-INGV S3 project through amplification factors of Housner intensity (IH), have been combined with the bedrock values provided by hazard assessment. Furthermore, a new relationship between IH and macroseismic intensity in
terms of EMS98 has been developed. This relationship has been used to convert the
Probability Density Functions (PDFs) for IH obtained from synthetic seismograms and
convolved by the site effects coefficients into PDFs for EMS98 intensity. Finally, the DPMs approach has been applied to estimate the damage levels of the residential buildings in the urban area of Potenza
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
- âŠ