Near‐source seismic demand and pulse‐like records: A discussion for L'Aquila earthquake

Abstract

Rupture directivity effects in ground motion are known since many years to both seismologists and earthquake engineers, i.e. in sites that are in a particular geometrical configuration with respect to the rupture, the velocity fault-normal signals may show a large pulse which occurs at the beginning of the record and contains the most of energy. The results are waveforms different from ordinary ground motions recorded in the far field or in geometrical conditions not favorable with respect to directivity. Current attenuation laws are not able to capture such effect well, if at all, and current probabilistic seismic hazard analysis is not able to predict the resulting peculiar spectral shape. Moreover, it is believed that structures with dynamic behavior in a range of periods related to the pulse period may be subjected to underestimated seismic demand. In the paper this is investigated and increments in both elastic and inelastic seismic actions are quantified using a large dataset of records, from the next generation attenuation project (NGA), in which a fraction is comprised of velocity pulses identified in other studies. These analyses employ recently developed tools and procedures to assess directivity effects and to quantify the associated threat in terms of seismic action on structures. Subsequently, the same tools are used in one of the first attempts to identify near-source effects in the data recorded during a normal faulting earthquake, the mainshock of the recent Abruzzo (central Italy) sequence, leading to conclude that pulse-like effects are likely to have occurred in the event, that is (1) observation of pulse-like records in some near-source stations is in fair agreement with existing predictive models, (2) the increment in seismic demand shown by pulse-like ground motion components complies with the results of the analysis of the NGA data, and (3) seismic demand in non-impulsive recordings is generally similar to what expected for ordinary records. The results may be useful as a benchmark for inclusion of near-source effect in design values of seismic action and structural risk analysis. || Note that this modification of attenuation may be considered as a narrow band one [13], i.e. elastic demand is magnified for selected frequency corresponding to the pulse period. Former models to modify ordinary GMPEs to account for directivity are broad band; e.g. that of Somerville et al. [1]. Statistical tests on integral parameters distributions would be useful to confirm or not these comparisons, but the large sample sizes and asymmetric shape distributions (see Figure 4) suggest that the most parametric tests would not be useful, while non-parametric are not as powerful.Results of seismological studies have shown that the Abruzzo event was a normal faulting earthquake (or dip-slip), with a rectangular rupture plane of about 17×14 km 2 and located at a depth ‡ ‡ ‡ In the application of the attenuation relationship [25], the surface wave magnitude (M s ) value of the L'Aquila earthquake is assumed to be the...

Collapse risk and residual drift performance of steel buildings using post-tensioned MRFs and viscous dampers in near-fault regions

“…PSHA has been recently modified to account for near source conditions, i.e., Near-source Probabilistic Seismic Hazard Analysis (NS-PSHA); more details, including implementation and applications, can be found in (Iervolino and Cornell 2008;Tothong et al 2007;Shahi and Baker 2011;Chioccarelli and Iervolino 2010. According to this methodology, Equation (4) is adjusted to account for potential near-source directivity through an additional term, Z, which defines the site-to-source geometry: (5) In this case, the probability that a specific IM value is exceeded, P [IM > x|m, r, z], depends on the probability of occurrence of a pulse, the distribution of possible pulse periods and the peculiar spectral shape induced by the pulse.…”

“…The pulse period prediction is based on the empirical model in Chioccarelli and Iervolino (2010). More details for the NS-PSHA calculations adopted herein, including the GMPE modification to account for the 'bump' of spectral ordinates around the pulse period, can be found in Chioccarelli and Iervolino (2013).…”

Performance of industrial buildings during the Emilia earthquakes in Northern Italy and recommendations for their strengthening

“…2 show that ground accelerations decayed concentrically very rapidly around the epicentre; accelerations in the order of 0.08 g are reported for the 29 May earthquake at 25 km from the epicentre. Differently from L'Aquila Earthquake, in which the mainshock was classified as a pulse-like event with strong directivity (Chioccarelli and Iervolino 2010), the velocity time histories did not show any full velocity cycles of structural engineering interest (Iervolino et al 2012). Figure 3 shows the response spectra of the N-S and E-W components of the ground motions recorded at the Mirandola station for both of the strong earthquakes of 20 and 29 of May.…”

Collapse Risk Evaluation of Self-Centering Steel MRFS With Viscous Dampers in Near-Fault Regions

“…Different IM are used in these equations (in this work S a (T 1 ) is adopted). PSHA has been recently modified to account for near source conditions, i.e., Near-source Probabilistic Seismic Hazard Analysis (NS-PSHA); more details, including implementation and applications, can be found in [2,[45][46][47][48][49]. According to this methodology, Equation (4) is adjusted to account for potential near-source directivity by an additional term, Z, which defines the site-to-source geometry: …”

“…Finally, the pulse period prediction is based on the empirical model in [47], although others are available (e.g., [46]). More details for the NS-PSHA calculation used here, including the GMPE modification to account for the 'bump' of spectral ordinates around the pulse period, can be found in [48].…”