Dino Bindi

Pan-European ground-motion prediction equations for the average horizontal component of PGA, PGV, and 5 %-damped PSA at spectral periods up to 3.0 s using the RESORCE dataset

This article presents a set of Ground-Motion Prediction Equations (GMPEs) for Europe and the Middle East, derived from the RESORCE strong motion data bank, following a standard regression approach. The parametric GMPEs are derived for the peak ground acceleration, peak ground velocity, and 5 %-damped pseudo-absolute acceleration response spectra computed over 23 periods between 0.02 and 3 s, considering the average horizontal-component ground-motions. The GMPEs are valid for distances less than 300 km, hypocentral depth up to 35 km and over the magnitude range 4–7.6. Two metrics for the source-to-station distance (i.e. Joyner-Boore and hypocentral) are considered. The selected dataset is composed by 2,126 recordings (at a period of 0.1 s) related to 365 earthquakes, that includes strong-motion data from 697 stations.The EC8 soil classification (four classes from A to D) discriminates recording sites and four classes (normal, reverse, strike-slip, and unspecified) describe the style of faulting. A subset which contains only stations with measured Vs30 and earthquakes with specified focal mechanism (1,224 records from 345 stations and 255 earthquakes) is used to test of the accuracy of the median prediction and the variability associated to the broader data set. A random effect regression scheme is applied and bootstrap analyses are performed to estimate the 95 % confidence levels for the parameters. The total standard deviation sigma is decomposed into between-events and within-event components, and the site-to-site component is evaluated as well. The results show that the largest contribution to the total sigma is coming from the within-event component. When analyzing the residual distributions, no significant trends are observed that can be ascribed to the earthquake type (mainshock-aftershock classification) or to the non-linear site effects. The proposed GMPEs have lower median values than global models at short periods and large distances, while are consistent with global models at long periods \((\hbox {T} > 1)\) s. Consistency is found with two regional models developed for Turkey and Italy, as the considered dataset is dominated by waveforms recorded in these regions.

SITE EFFECTS BY H/V RATIO: COMPARISON OF TWO DIFFERENT PROCEDURES

In this article, H/V ratio are evaluated using different spectral techiniques applied to both earthquake and microtremor data (Nakamura technique). In particular, in order to avoid numerical instability, two different numerical techiniques are taken into account: (a) a smoothing procedure applied to the spectra of the seismogram components and (b) a regularization method applied to the H/V ratio (Landweber scheme). The data set consists of more than 70 earthquake events recorded by three component sensors displaced in the town of Fabriano (Central Italy) during the Umbria-Marche sequence started on September 1997. The local magnitudes range between 2.7 and 4.4, while the epicentral distances range between nearly 30 and 60 km. The stations were set to continuous recording so that a huge amount of microtremors was stored. The results are compared in terms of predominant frequencies and amplification levels in order to point out the influence of the adopted methods. The H/V ratio provides similar results if applied to a smoothed version of both earthquake and microtremor spectra, confirming that Nakamura technique is a cheap and a fast method to collect information on the site amplification effects. Moreover, the results relevant to earthquake data seem not to depend on the method used to stabilize the H/V ratio, whereas those relevant to microtremor data does. The explanation of this fact is suggested by the behaviour of the Landweber filter showing that the predominant frequency detected by means of microtremor data lies in a high instability region of the spectra.

Ground-Motion Predictions from Empirical Attenuation Relationships versus Recorded Data: The Case of the 1997–1998 Umbria-Marche, Central Italy, Strong-Motion Data Set

We evaluate the goodness of fit of attenuation relations commonly used for the Italian national territory (Sabetta and Pugliese, 1996) by using the maximum likelihood approaches of Spudich et al. (1999) and Scherbaum et al. (2004). According to the classification scheme proposed by Scherbaum et al. (2004), the Sabetta and Pugliese (1996) relationships show consistent discrepancies between the predicted and the observed peak ground acceleration (pga) at rock sites in the Umbria- Marche region, central Italy; however, at soft sites the agreement between observations and prediction is satisfactory. The bias of the residuals, computed with the Sabetta and Pugliese (1996) models for pga, peak ground velocity, (pgv) and pseudovelocity response spectrum (psv) (for M l = 4–6 and epicentral distances up to 100 km) is negative. This means that on the average, the predictions overestimate the observations, but the overestimation decreases with increasing magnitude. Then, we present regional predictive relations (UMA05) for maximum horizontal pga, pgv, and 5%-damped psv, derived from the strong-motion data recorded in the Umbria-Marche area and classified as to four site categories. The UMA05 attenuation relationships for rock sites are log 10 (PGA) = −2.487 + M 1 − 1.280 log 10 ( R 2 + 3.94 2 ) 0.5 ± 0.268 log 10 (PGV) = −1.803 + 0.687 M 1 − 1.150 log 10 ( R 2 + 2.74 2 ) 0.5 ± 0.300 and log 10 (PGA) = −2.500 + 0.544 M 1 − 1.284 log 10 R h ± 0.292 log 10 (PGV) = −1.752 + 0.685 M 1 − 1.167 log 10 R h ± 0.297, where pga is measured in fraction of g and pgv in centimeters per second, M l is the local magnitude in the range 4–6, R is the epicentral distance in the range 1–100 km, and R h is the hypocentral distance in kilometers. We used the random effect model (Brillinger and Priesler, 1985; Abrahamson and Youngs, 1992; Joyner and Boore, 1993; Joyner and Boore, 1994) to estimate the component of variance related to the earthquake-to-earthquake, station-to-station, and record-to-record variability, and to quantify the benefit of introducing a site classification in the attenuation model to reduce the variance. The introduction of the site classification in the attenuation model allows a reduction of the station-to-station component of variability (from 0.19 to 0.14 for pga, and from 0.21 to 0.18 for pgv). We also found that the record- to-record component represents the largest contribution to the model uncertainty.

Application of the Generalized Inversion Technique (GIT) to a Microzonation Study: Numerical Simulations and Comparison with Different Site-Estimation Techniques

The reliability of the results obtained by applying the Generalized Inversion Technique (GIT) to site response estimates is assessed by means of numerical simulations. This study was developed in the framework of the UMBRIA-MARCHE microzonation project. The analysis with synthetic data demonstrates that the generalized inversion technique is capable of revealing the site effects. Furthermore, this approach shows that a priori information relevant to the Q quality factor is needed if a source estimate is required. We also analyze data recorded by five seismological stations installed in Fabriano (central Italy) with a minimum interstation distance of 100 m. The results computed with the generalized inversion technique are compared with those obtained by the reference site method and the receiver function technique. Whereas the first two methods provide highly consistent site-response estimates, the receiver function technique provides lower levels amplification. Furthermore, the time duration used in the analysis seems to be a critical parameter for the receiver function technique alone. Manuscript received 15 April 1999.

Comparisons among the five ground-motion models developed using RESORCE for the prediction of response spectral accelerations due to earthquakes in Europe and the Middle East

This article presents comparisons among the five ground-motion models described in other articles within this special issue, in terms of data selection criteria, characteristics of the models and predicted peak ground and response spectral accelerations. Comparisons are also made with predictions from the Next Generation Attenuation (NGA) models to which the models presented here have similarities (e.g. a common master database has been used) but also differences (e.g. some models in this issue are nonparametric). As a result of the differing data selection criteria and derivation techniques the predicted median ground motions show considerable differences (up to a factor of two for certain scenarios), particularly for magnitudes and distances close to or beyond the range of the available observations. The predicted influence of style-of-faulting shows much variation among models whereas site amplification factors are more similar, with peak amplification at around 1s. These differences are greater than those among predictions from the NGA models. The models for aleatory variability (sigma), however, are similar and suggest that ground-motion variability from this region is slightly higher than that predicted by the NGA models, based primarily on data from California and Taiwan.

Site Response of Strong Motion Stations in the Umbria, Central Italy, Region

We used near-field and regional records from 16 earthquakes ( M L 4.6-5.9) located in the epicentral area of the 1997 Umbria-Marche sequence to estimate the site response of 40 strong motion stations. The distribution of hypocenters covers a distance range from 5 to 100 km. We estimated site amplification factors using two techniques, namely a generalized spectral inversion method and horizontal-to-vertical-component spectral ratios (HVSRs) of ground acceleration. For the first approach, we inverted observed spectral amplitudes for site, Q , and source using a reference site. Since the site response estimated using HVSRs assumes that the vertical component of motion is amplification free, we also separated source and site effects by inverting the vertical component of the acceleration spectra. We found that although most of the stations do not show important amplifications on the vertical component, a few of them have a significant vertical amplification at low frequencies ( f Q , representative of the S -wave train, shows a frequency dependence that can be approximated by the relation Q S = 31.2 f 1.2 , between 0.3 and 9.5 Hz. However, at high frequencies ( f > 10 Hz), this dependence weakens, and Q S takes an approximately constant value of 438.

Distribution of Seismic Velocities and Attenuation in the Crust beneath the North Anatolian Fault (Turkey) from Local Earthquake Tomography

We investigate the crustal structure beneath the western part of the North Anatolian fault zone (NAFZ), an area where at least five damaging earthquakes occurred during the twentieth century. This study is based on local earthquake tomography using the data from aftershocks of the Izmit event (17 August 1999, M 7.4) recorded by stations of permanent and temporary networks. We derive the distribution of V P , V S , and the V P / V S ratio based on the iterative inversion for both V P - V S and V P - V P / V S using the LOTOS code. Innovatively, in this study we perform an inversion for frequency-dependent S -wave attenuation (1/ Q S ). The reliability of the results is assessed through synthetic tests. The distributions of the resulting seismic parameters ( V P , V S , V P / V S , and Q S ) highlight important geodynamical features in the study area. The low-velocity and high-attenuation patterns mostly correlate with the fracturing zones of the NAFZ. Low velocities are also observed beneath the main sedimentary basins (e.g., Adapazari, Duzce, and Kuzuluk). High-velocity and low-attenuation patterns correlate with blocks presumed to be rigid (Kocaeli, Armutlu, and Almacik blocks). The rupture traces of the largest earthquakes in this area pass generally in the transition areas between high and low velocities, while moderate and weak seismicity is mostly concentrated in low-velocity areas. Based on these results we propose and discuss the role that the Almacik block could have played in producing the largest earthquakes in the study area in the twentieth century.

Crustal attenuation characteristics in northwestern Turkey in the range from 1 to 10 Hz

We have analyzed the aftershocks ( M L <4.5) following the 1999 Izmit earthquake ( M w 7.4) to infer the frequency-dependent attenuation characteristics of both P and S waves, in the frequency range from 1 to 10 Hz and in the distance range from 10 to 140 km. A linear-predictive model is assumed to describe the spectral amplitudes in terms of attenuation and source contributions. The results show that both P and S waves undergo a strong attenuation along ray paths shorter than 40 km, while the secondary arrivals significantly contribute to the spectral amplitudes over the distance range from 40 to 60 km, as also confirmed by the computation of synthetic seismograms. For longer ray paths, the decrease in attenuation suggests an increase in the propagation efficiency with depth. Finally, the spectral attenuation curves are flattened, or sloped upward at low frequencies in the range from 100 to 140 km, due to the contemporary arrivals of direct waves and postcritical reflections from the Moho. In terms of geometrical spreading and anelastic attenuation, the attenuation in the range from 10 to 40 km is well described by a spreading coefficient n = 1 for both P and S waves, and the quality factors can be approximated by QS ( f ) = 17 f 0.80 for 1 ≤ f ≤ 10 Hz and QP ( f ) = 56 f 0.25 for 2.5 ≤ f ≤ 10 Hz. For ray paths in the range from 60 to 80 km, the attenuation weakens but the interaction between seismic waves and propagation medium is more complex. The multilapse time window analysis (mltwa) is applied to quantify the amount of scattering loss and intrinsic absorption for S waves. The seismic albedo B decreases from 0.5 at 1 Hz to 0.3 at 10 Hz, while the total quality factor QT increases from about 56 to 408. The multiple lapse time-window analysis (mltwa) results provide only an average estimate of the attenuation properties in the range from 10 to 80 km. In fact, by neglecting the variation of attenuation with depth, the mltwa results underestimate attenuation for distances less than 40 km, and do not capture the significant features caused by the integrated energy of the secondary arrivals observed in the range from 40 to 60 km.

Source Parameters Estimated from the Aftershocks of the 1997 Umbria–Marche (Italy) Seismic Sequence

We derived the source parameters of 563 aftershocks (1.4 ≤ M L ≤ 4.5) of the 1997 Umbria–Marche seismic sequence by analyzing three-component digital recordings of a temporary network and developed a local magnitude scale using the whole available data set (more than 25,000 waveforms) from synthetic Wood–Anderson seismograms. Then, considering a subnetwork composed of nine portable stations, more than 12,000 earthquake spectra were corrected for the near-surface attenuation parameter k and the path attenuation. The corrected spectra were used to compute the seismic moment, the source radius, and stress drop assuming an ω–2 Brune source model. We calculate the relationship log M = 17.46 + 1.12 M L between seismic moment and local magnitude for the studied area. The source dimension versus seismic moment relationship did not show any breakdown in the similarity of the rupture process, even when events of magnitude less than 2.2 (the threshold value for the completeness of the considered catalog.) were considered. The average stress drop obtained analyzing the S -wave spectra was 38 ± 10 bar, and the source dimension ranged between about 40 and 500 m.

Interferometric Analysis of Strong Ground Motion for Structural Health Monitoring: The Example of the L’Aquila, Italy, Seismic Sequence of 2009

Abstract Structural health monitoring (SHM) aims to improve knowledge of the safety and maintainability of civil structures. The usage of recording systems exploiting wireless communication technology is particularly suitable for SHM, especially for rapid response following earthquakes. In this study, both of these issues are combined, and we report on the application of seismic interferometry to SHM using a dataset of seven earthquakes collected using a novel wireless system of accelerometers during the L’Aquila, Italy, seismic sequence in 2009. We show that interferometric analysis allows the estimation of the shear-wave velocity of seismic phases propagating throughout a structure, and, most important for SHM purposes, allows the monitoring of the velocity variations during the aftershock sequence. Moreover, innovatively we apply the S transform to the building response functions retrieved by interferometry to estimate the fundamental resonance frequency and the quality factor Q .