Deterministic ground-motion scenarios for engineering applications: the case of thessaloniki, Greece.

In this paper we present a deterministic study to estimate seismic ground motions expected in urban areas located near active faults. The purpose was to generate bedrock synthetic time series to be used as seismic input into site effects evaluation analysis and loss estimates for the urban area and infrastructures of Thessaloniki (Northern Greece). Two simulation techniques (a full wave method to generate low frequency,~< 1Hz, and a hybrid deterministic-stochastic technique to simulate high-frequency seismograms, ~> 1 Hz) were used to compute time series associated with four different reference earthquakes having magnitude from 5.9 to 6.5 and located within 30 km of Thessaloniki. The propagation medium and different source parameters were tested through the modeling of the 1978 Thessaloniki earthquake (M 6.5). Moreover two different nucleation points were considered for each fault in order to introduce additional variability in the ground motion estimates. Between the two cases, the quasi-unilateral rupture propagation toward the city produces both higher median PGA and PGV values and higher variability than bilateral ones. Conversely, the low-frequency ground motion (PGD) is slightly influenced by the position of the nucleation point and its variability is related to the final slip distribution on the faults of the reference earthquakes and to the location of the sites with respect to the nodal planes of the radiation pattern. To validate our deterministic shaking scenarios we verified that the synthetic peak ground motions (PGA, PGV) and spectral ordinates are within one standard deviation of several ground-motion prediction equations valid for the region. At specific sites we combined the low- and high-frequency synthetics to obtain broadband time series that cover all the frequency band of engineering interest (0-25 Hz). The use of synthetic seismograms instead of empirical equations in the hazard estimates provides a complete evaluation of the expected ground motions both in frequency and time domains, including predictions at short distances from the fault (0 – 10 km) and at periods larger than 2 – 3 seconds

High Reynolds number and turbulence effects on aerodynamics and heat transfer in a turbine cascade

Experimental data on pressure distribution and heat transfer on a turbine airfoil were obtained over a range of Reynolds numbers from 0.75 to 7.5 x 10 exp 6 and a range of turbulence intensities from 1.8 to about 15 percent. The purpose of this study was to obtain fundamental heat transfer and pressure distribution data over a wide range of high Reynolds numbers and to extend the heat transfer data base to include the range of Reynolds numbers encountered in the Space Shuttle main engine (SSME) turbopump turbines. Specifically, the study aimed to determine (1) the effect of Reynolds number on heat transfer, (2) the effect of upstream turbulence on heat transfer and pressure distribution, and (3) the relationship between heat transfer at high Reynolds numbers and the current data base. The results of this study indicated that Reynolds number and turbulence intensity have a large effect on both the transition from laminar to turbulent flow and the resulting heat transfer. For a given turbulence intensity, heat transfer for all Reynolds numbers at the leading edge can be correlated with the Frossling number developed for lower Reynolds numbers. For a given turbulence intensity, heat transfer for the airfoil surfaces downstream of the leading edge can be approximately correlated with a dimensionless parameter. Comparison of the experimental results were also made with a numerical solution from a two-dimensional Navier-Stokes code

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 stations’ distribution

Evaluation of FRP concrete compression member under repeated load and harsh environment

Strengthening and rehabilitation have been increasingly applied in many structures to improve their capacity and serviceability. Fiber Reinforced Polymer (FRP) materials are universally known for their ability to improve the load capacity of damaged structural elements because of their high linear-elastic behavior. However, enhancing the capacity of structural elements that are exposed to repeated load coupled with harsh environment is an area that requires further investigation. This research focused on experimental analysis of the behavior and response of confined and unconfined concrete compression members (300mm x 150mm) under repeated load while exposed to 1440 cycles of seawater splash zone in United Arab Emirates (UAE). Confining concrete compression members with Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) sheets have increased the load capacity compared to the control sample at room temperature by 110% and 84%, respectively. Results showed that the average value of compressive strength for the confined concrete exposed to sea water splash zone conditions for CFRP and GFRP specimens has decreased by 33% and 23%, respectively, compared to the confined concrete in the room temperature. However, GFRP specimens showed higher performance in compressive strength under sea water splash zone than those of the CFRP specimens. Different mode of failures such as delamination, de-bonding and combination of such modes were observed and related to various exposure factors and mechanical properties

The Mw 6.3, 2009 L’Aquila earthquake: source, path and site effects from spectral analysis of strong motion data

The strong motion data of 2009 April 6 L’Aquila (Central Italy) earthquake (Mw = 6.3) and of 12 aftershocks (4.1 ≤ Mw ≤ 5.6) recorded by 56 stations of the Italian strong motion network are spectrally analysed to estimate the source parameters, the seismic attenuation, and the site amplification effects. The obtained source spectra for S wave have stress drop values ranging from 2.4 to 16.8 MPa, being the stress drop of the main shock equal to 9.2 MPa. The spectral curves describing the attenuation with distance show the presence of shoulders and bumps, mainly around 50 and 150 km, as consequence of significant reflected and refracted arrivals from crustal interfaces. The attenuation in the first 50 km is well described by a quality factor equal to Q( f ) = 59 f 0.56 obtained by fixing the geometrical spreading exponent to 1. Finally, the horizontal-to-vertical spectral ratio provides unreliable estimates of local site effects for those stations showing large amplifications over the vertical component of motion

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

Toward validation of simulated accelerograms via prediction equations for nonlinear SDOF response

Seismic structural risk analysis of critical facilities may require nonlinear dynamic analysis for which record selection is one of the key issues. Notwithstanding the increasing availability of database of strong-motion records, it may be hard to find accelerograms that fit a specific scenario (e.g., in terms of magnitude and distance) resulting from hazard assessment at the site of interest. A possible, alternative, approach can be the use of artificial and/or simulated ground motion in lieu of real records. Their employment requires systematic engineering validation in terms of structural response and/or seismic risk. Prediction equations for peak and cyclic inelastic single degree of freedom systems’ response, based on Italian accelerometric data, are discussed in this study as a possible benchmark, alongside real record counterparts, for the validation of synthetic records. Even if multiple events would be in principle required, an extremely preliminary validation is carried out considering only four simulated records of the 1980 Irpinia (southern Italy) M w 6.9 earthquake. Simulated records are obtained through a broadband hybrid integral-composite technique. Results show how this simulation method may lead to generally acceptable results. It is also emphasized how this kind of validation may provide additional results with respect to classical signal-to-signal comparison of real and simulated records

Comparison between empirical predictive equations calibrated at global and national scale and the Italian strong-motion data

In Italy in the last years many ground motion prediction equations (hereinafter GMPEs) were calibrated both at national and regional scale using weak and strong motion data recorded in the last 30 years by several networks. Moreover many of the Italian strongest earthquakes were included in global datasets in order to calibrate GMPEs suitable to predict ground-motion at very large scale. In the last decade the Sabetta and Pugliese (1996) relationships represented a reference for the ground motion predictions in Italy. At present all Italian strong-motion data, recorded from 1972 by RAN (Italian Accelerometric Network), and more recently by other regional networks (e.g. RAIS, Strong motion network of Northern Italy), are collected in ITACA (ITalian ACcelerometric Archive). Considering Italian strong-motion data with Mw  4.0 and distance (Joyner-Boore or epicentral) up to 100 km, new GMPEs were developed by Bindi et al. (2009), aimed at replacing the older Italian relationships. The occurrence of the recent 23rd December 2008, Mw 5.4, Parma (Northern Italy) earthquake and the 6th April 2009, Mw 6.3, L’Aquila earthquake, allowed to upgrade the ITACA data set and gave us the possibility to validate the predictive capability of many GMPEs, developed using Italian, European and global data sets. The results are presented in terms of quality of performance (fit between recorded and predicted values) using the maximum likelihood approach as explained in Spudich et al. (1999). Considering the strong-motion data recorded during the L’Aquila sequence the considered GMPEs, in average, overestimate the observed data, showing a dependence of the residuals with distance in particular at higher frequencies. An improvement of fit is obtained comparing all Italian strong-motion data included in ITACA with the European GMPEs calibrated by Akkar and Bommer (2007 a,b) and the global models calibrated by Cauzzi and Faccioli (2008). In contrast, Italian data seem to attenuate faster than the NGA models calibrated by Boore and Atkinson (2008), in particular at higher frequencies

Record Processing in ITACA, the New Italian Strong-Motion Database

The development of the new Italian strong-motion database ITACA (ITalian AC-celerometric Archive, http://itaca.mi.ingv.it) is in progress under the sponsorship of the National Department of Civil Protection (DPC) within Project S4, in the framework of DPC-INGV 2007–2009 research agreement. This work started from the alpha version of ITACA [8], where 2,182 3-component records from 1,004 earthquakes, mainly recorded by the National Accelerometric Network, RAN, operated by DPC, were processed and included in the database. Earthquake metadata, recording station information and reports on the available geologicalgeophysical information of 452 recording sites, corresponding to about 70% of the total, were also included. Subsequently, ITACA has been updated and will reach its final stage by the end of Project S4, around mid-2010, with additional features, improved information about recording stations, and updated records, including the Mw6.3 L’Aquila earthquake. All records were re-processed with respect to the alpha version [9], with a special care to preserve information about late-triggered events and to ensure compatibility of corrected records, i.e., velocity and displacement traces obtained by the first and second integral of the corrected acceleration should not be affected by unrealistic trends. After a short introduction of ITACA and its most relevant features and statistics, this paper mainly deals with the newly adopted processing scheme, with reference to the problems encountered and the solutions that have been devised