Effect of time-dependence on probabilistic seismic hazard maps and deaggregation for the central apennines, Italy

We produce probabilistic seismic hazard assessments for the Central Apennines, Italy, using time-dependent models that are characterized using a Brownian Passage Time (BPT) recurrence model. Using aperiodicity parameters,  of 0.3, 0.5, and 0.7, we examine the sensitivity of the probabilistic ground motion and its deaggregation to these parameters. For the seismic source model we incorporate both smoothed historical seismicity over the area and geological information on faults. We use the maximum magnitude model for the fault sources together with a uniform probability of rupture along the fault (floating fault model) to model fictitious faults to account for earthquakes that cannot be correlated with known geologic structural segmentation. We show maps for peak ground acceleration (PGA) and 1.0-Hz spectral acceleration (SA1) on rock having 10% probability of exceedence (PE) in 50 years. We produce maps to compare the separate contributions of smoothed seismicity and fault components. In addition we construct maps that show sensitivity of the hazard for different  parameters and the Poisson model. For the Poisson model, the addition of fault sources to the smoothed seismicity raises the hazard by 50 % at locations where the smoothed seismicity contributes the highest hazard, and up to 100 % at locations where the hazard from smoothed seismicity is low. For the strongest aperiodicity parameter (smallest ), the hazard may further increase 60-80 % or more or may decrease by as much as 20 %, depending on the recency of the last event on the fault that dominates the hazard at a given site. In order to present the most likely earthquake magnitude and/or the most likely source-site distance for scenario studies, we deaggregate the seismic hazard for SA1 and PGA for two important cities (Roma and l’Aquila) . For PGA, both locations show the predominance of local sources, having magnitudes of about 5.3 and 6.5 respectively. For SA1 at a site in Rome, there is significant contribution from local smoothed seismicity, and an additional contribution from the more distant Apennine faults having magnitude around 6.8. For l’Aquila, the predominant sources remain local. In order to show the variety of impact of different  values we also obtained deaggregations for another three sites. In general, as  decreases (periodicity increases), the deaggregation indicates that the hazard is highest near faults with the highest earthquakes rates. This effect is strongest for the long-period (1 s) ground motions

Simulating earthquake scenarios in the European Project LESSLOSS: the case of the metropolitan area of Lisbon (MAL)

In the framework of the ongoing European project “LESSLOSS – Risk Mitigation for Earthquakes and Landslides” two sub-projects are devoted to earthquake disaster scenario predictions and loss modeling for urban areas and infrastructures. This paper is dealing with the sub-project 10, SP10, Task Programme “Scenario earthquake definitions for three cities”. Finite-fault seismological models are proposed to compute the earthquake scenarios for three urban areas – Istanbul (Turkey), Lisbon (Portugal) and Thessaloniki (Greece). For each case study, ground motion scenarios are developed for the most probable two events with different return periods, locations and magnitudes derived from historical and geological data. In this study, we simulate the accelerometric time series and response spectra for high frequency ground motion in the city of Lisbon and surrounding counties (Metropolitan Area of Lisbon), using two possible earthquake models: the inland source area of Lower Tagus Valley, M 5.7 (4.7) and a hypothesis of the offshore source area of the 1755 Lisbon, M 7.6. The non-stationary stochastic method RSSIM (Carvalho et al. 2004) and a new hybrid stochastic-deterministic approach, DSM (Pacor et al., 2005) are used in order to evaluate the ground shaking and to characterize its spatial variability. Then the site effects are evaluated by means of an equivalent stochastic non-linear one-dimensional ground response analysis of stratified soil profile units properly designed. Results are here presented in terms of PGA maps, for offshore and inland scenarios. The mean and worst shaking scenarios for the Metropolitan Area of Lisbon have been delineated at the bedrock. Local effects amplify the synthetic PGA values by approximately a factor of 2. This means that PGA values computed for bedrock in Lisbon city can increase from 0.12g up to 0.25g and up to 0.5g in surroundings, for the inland scenario, and from 0.045g up to 0.090g for a M7.6 offshore scenario

DETERMINISTIC SCENARIOS AS INPUT MOTION FOR LOSS ASSESSMENT

A predominantly deterministic viewpoint has been adopted for computing seismic ground motion both for urban areas (SP10) and infrastructures loss modeling (SP11) at three selected areas: the cities of Lisbon (Portugal) and Thessaloniki (Greece), and the metropolis of Istanbul (Turkey). The generation of earthquake ground motion scenarios involves both the particular choice of earthquake sources with associated fault rupture parameters, and the ensuing ground motion field calculated by an appropriate numerical tool, or empirically estimated, at a set of selected points within the urban area of interest. Ground shaking values are predicted for rock conditions and for two distinct frequency bands, i.e. the high frequency range (from 1.0 Hz to 4-5 Hz) in the case of damage evaluation for the vast majority of ordinary building, and the low frequency (≤ 2 Hz) more appropriate for lifeline system damage assessment. The advanced simulation techniques allowed to properly consider the finite fault effects and directivity, which imply extreme expected values, and they are capable of quantifying the spatial variability of the ground motion near the extended fault