Article

Anatomy of strong ground motion: near-source records and three-dimensional physics-based numerical simulations of the Mw 6.0 2012 May 29 Po Plain earthquake, Italy

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Abstract

Stimulated by the recent advances in computational tools for the simulation of seismic wave propagation problems in realistic geological configurations, this paper presents a 3D physicsbased numerical analysis of near-source ground motion during the MW 6.0 2012 May 29 earthquake in the Po Plain, Northern Italy. To reproduce with sufficient accuracy some of the most peculiar features of the near-source strong-motion records and of the spatial variability of damage distribution, this study required a sequence of investigations, starting from the analysis of a wide set of near-source records, to the calibration of an improved kinematic seismic source model, up to the development of a 3D numerical model of the portion of the Po Plain interested by the earthquake. The latter includes the basin geometry, characterized by sediment thickness sharply varying from few tens of metres to some kilometres. The spatial resolution of the numerical model is suitable to propagate frequencies up to about 1.5 Hz. Numerical simulations were performed using the open-source high-performance code SPEED, based on the Discontinuous Galerkin Spectral Elements method. The 3D numerical model, coupled with the updated slip distribution along the rupturing fault, proved successful to reproduce with good agreement, measured through quantitative goodness-of-fit criteria, the most relevant features of the observed ground motion. These include: (i) the large fault normal velocity peaks at the near-source stations driven by updip directivity effects; (ii) the small-scale variability at short distance from the source, resulting in the out-of-phase motion at stations separated by only 3 km distance; (iii) the propagation of prominent trains of surface waves, especially in the Northern direction; (iv) the map of earthquake-induced ground uplift with maximum values of about 10 cm, in substantial agreement with geodetic measurements and (v) the two-lobed pattern of the peak ground velocity map, well correlated with the distribution of macroseismic intensity.

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... Compared to other validation tests of physics-based simulations against near-source records of large magnitude earthquakes in tectonic areas (Guidotti et al., 2011;Paolucci et al., 2015;Smerzini and Villani, 2012), where the largest source of discrepancy came from the limited high-frequency constraints of the kinematic slip model along the extended fault, in this case, while the source is well constrained and widespread site investigations are available throughout the Mexico City area, the vastity of the lake-bed zone makes it very difficult to follow by a 3D model the detail of stratigraphy and of its lateral variability. For this reason, the most challenging aspect of this validation is the ability of physics-based simulations to produce a reasonably good approximation of recorded ground motions in a wide area and in a frequency range as extended as possible, considering the extremely low VS in the lake-bed zone. ...
... Moreover, a nonlinear elastic constitutive rheology was also implemented (Stupazzini et al., 2009). Besides being verified over different benchmarks (Mazzieri et al., 2013) and validated against recordings of past earthquakes, such as the April 6, 2009, ' quila, n ral I aly (di Michele et al., 2022;Evangelista et al., 2017), and the May 29, 2012, Po Plain, Northern Italy (Paolucci et al., 2015), SPEED has proved to be an effective tool, complementary to empirical ground motion models, for seismic hazard and risk assessments in large urban areas (Infantino et al., 2020;Smerzini and Pitilakis, 2018;Stupazzini et al., 2021). ...
... For the crustal structure surrounding the basin, a 1D model determined from the inversion of receiver functions at the CU site (Cruz-Atienza et al., 2010) was adopted (Crust materials in Table 1). Quality factors QS for the crustal materials are taken equal to VS/10, which is in accordance to typical values adopted in literature(e.g., Paolucci et al., 2015), while QP is considered as 2·QS. Considering that, on top of the Oligocene volcanic rocks, layers of few hundred meters thickness are found, consisting of a mixture of tuffs, sands, gravels and recent lava flows (Singh et al., 1995), a surficial layer with VS=750 m/s was adopted for the first 200 m of the hill zone, consistent with the calibration presented later on. ...
Article
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In this study, a 3D physics-based numerical approach, based on the spectral element numerical code SPEED, is used to simulate seismic wave propagation due to a local earthquake in the Mexico City area. The availability of detailed geological, geophysical, geotechnical, and seismological data allowed for the creation of a large-scale (60 km × 60 km in plan, 10 km in depth) heterogeneous 3D numerical model of the Mexico City area, dimensioned to accurately propagate frequencies up to about 1.3 Hz. The results of numerical simulations are validated against the ground motion recordings of the July 17, 2019, Mw3.2 earthquake, with peak ground acceleration exceeding 0.3 g about 1 km away from the epicenter. A good agreement with records is found, quantitatively evaluated through goodness-of-fit checks. Furthermore, for the lake zone, the simulated decay trend of the peak ground velocity with epicentral distance is reasonably close to the observations, for both horizontal and vertical components. In spite of some limitations, the simulations are successful to provide a realistic picture of seismic wave propagation both in the hill and in the lake zones of Mexico City, including the onset of long-duration quasi-monochromatic ground motion in the basin, with strong amplification at low frequencies (between 0.4 and 0.7 Hz). The numerical results also suggest that surface waves, with predominant prograde particle motion at the ground surface and large ellipticities, dominate the wavefield in the lake zone. Based on these positive outcomes, we conclude that this numerical model may be useful for both a better insight into the seismic response of the Valley of Mexico and the simulation of ground motions during larger-magnitude earthquakes, to generate improved seismic damage scenarios in Mexico City.
... The signal-based validation can be conducted when recordings of historical events are available, whereas GMM-based validation is feasible for both historical and future earthquake scenarios. In this paper, a scenariospecific simulation from the Mw 6.0 2012 May 29 earthquake in the Po Plain, Italy [5], is chosen to demonstrate the application of the framework (without adding complexities in terms of the simulation uncertainties and their spatial extents). In the subsequent sections, the proposed framework is presented and the pertinent implications are discussed. ...
... The results from physics-based ground motion simulation of the Mw 6.0 2012 May 29 Po Plain, Italy [5] are chosen as the case study to demonstrate the proposed framework. Fig. 1 shows the basin depth and the location of recording stations within the simulation domain. ...
... The broadband ground motions utilized in this study are obtained by merging the high-and low-frequency contents at 1.5Hz. It is noted that the low-frequency simulated ground motions (up to about 1.5Hz) have been previously validated in terms of elastic engineering demands against recordings and empirical GMMs [5], and a generally good agreement has been found between simulations and recordings in both time and frequency domains, especially for the horizontal NS and the vertical component. The ANN-based methodology to estimate the high-frequency content has also been validated previously [10]. ...
Conference Paper
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This study proposes a two-level framework for region-specific validation of simulated ground-motions, including signal-based and ground-motion model (GMM)-based comparisons. The validation framework is demonstrated on a simulation of the Mw 6.0 2012 May 29 Po Plain earthquake, Italy, investigating the peak inelastic displacement Sdi and the equivalent number of cycles Ne demands from the simulations with respect to the counterpart recordings and empirical models. Results of the study indicate that Sdi responses of the considered single-degree-of-freedom nonlinear systems subjected to the simulated ground motions generally underestimate those from the recordings and empirical GMMs, particularly for short vibration periods. The Ne from simulations slightly underestimate the Ne from recordings and empirical GMMs, however, peculiar overestimations have been observed around the transition frequency between the low-and high-frequency simulation results. Discrepancies observed, particularly in short periods ranges and around transition frequency may be due to the limitations in the approach utilized for generating the high-frequency ground motion content, and the insufficient small-scale heterogeneity in the rupture model and velocity structure. Moreover, the GMM-based comparisons indicate that region-specific GMMs can be a better benchmark for the purpose of inelastic demand validation than GMMs established based on continental and/or global data. The proposed validation framework can assist in further securitizing the validity of simulated ground motions and provide insights regarding the possible improvements of simulation underlying components for the purpose of engineering utilization in design and seismic risk assessment.
... With the continuous growth of computational power in the last decades, physics based simulation (PBS) emerged as an aspiring, alternative approach to empirical ground motion prediction equations (GMPEs), which has already been applied to seismic scenarios at various sites including the United States [81,82], Japan [37,46], New-Zealand [53,26], Turkey [45], China [4], the Netherlands [65], Italy [32,66]. PBS aims at describing, as reliably as possible, the seismic wave propagation problem and therefore it is crucial, on the one hand, to properly characterize the mechanical properties of the different portion of the computational domain and, on the other, to have a reliable seismic excitation source, see, e.g. ...
... e.g. [12,66,19]. Nowadays, thanks to the availability of openly accessible data, as for example [30,84], this challenge can be tackled in specific regions of the world. ...
... We found that for the majority of the stations the agreement between simulations and observations is from fair to good. These results are aligned with those obtain for other, different earthquake scenarios as, e.g., [66,42]. ...
Article
As a mean to assess the risk dam structures are exposed to during earthquakes, we employ an abstract mathematical, three dimensional, elasto-acoustic coupled wave-propagation model taking into account (i) the dam structure itself, embedded into (ii) its surrounding topography, (iii) different material soil layers, (iv) the seismic source as well as (v) the reservoir lake filled with water treated as an acoustic medium. As a case study for extensive numerical simulations we consider the magnitude 7 seismic event of the 30th of October 2020 taking place in the Icarian Sea (Greece) and the Tahtalı dam around 30 km from there (Turkey). A challenging task is to resolve the multiple length scales that are present due to the huge differences in size between the dam building structure and the area of interest, considered for the propagation of the earthquake. Interfaces between structures and highly non-conforming meshes on different scales are resolved by means of a discontinuous Galerkin approach. The seismic source is modeled using inversion data about the real fault plane. Ultimately, we perform a real data driven, multi-scale, full source-to-site, physics based simulation based on the discontinuous Galerkin spectral element method, which allows to precisely validate the ground motion experienced along the Tahtalı dam, comparing the synthetic seismograms against actually observed ones. A comparison with a more classical computational method, using a plane wave with data from a deconvolved seismogram reading as an input, is discussed.
... Nevertheless, these techniques allow for a very efficient calculation of synthetic seismograms in laterally homogeneous layered models, taking into account anelastic attenuation. Thus, the proposed site-specific geological model has been defined starting from the soil structure provided by the Italian Accelerometric Archive, ITACA, [39] considering a soil class C, then adopting the mechanical layers parameters (thickness, density, P and S waves velocity, and attenuation) discussed in [40], which represent the geological setting of the investigated area. ...
... The 29 May 2012 earthquake in the Emilia-Romagna region of Italy, which was the second main shock of the Emilian sequence, activated this seismogenic source, producing a detectable uplift of the buried Mirandola anticline. The final geometry of the fault adopted is the one validated in the study proposed by [40]. The Finale Emilia seismic source was formed after the occurrence of the 20th May 2012 earthquake, which was the first mainshock of the Emilian sequence giving rise to a detectable uplift of the associated buried anticline. ...
... Finally, concerning the existence of the Ferrara's source, it dates back to the earthquake that occurred on 17th November 1570 based on data relating to both the recent tectonic activity of the Ferrara Arch [45], and from the subsoil geological structure [47]. Thus, based on the above considerations, some of the characteristics of the four considered seismic sources are reported in Table 2. Table 2. Some characteristics of the four selected seismogenic sources [40,44]. The acronyms are related to: edi = epicentral distance; depth = focal depth of the earthquake occurred; strike = defines the orientation of the fault counter-clockwise till the North; dip = represents the inclination of the fault plane; rake = the direction the hanging wall moves during rupture measured relative to the fault strike; sre = represents the angle formed between the focal point and the site. ...
Article
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The current paper aims at investigating the seismic capacity of a masonry building aggregate in the historical centre of Mirandola based on a reliable ground motion simulation procedure. The examined clustered building is composed of eleven structural units (SUs) mutually interconnected to each other, which are made of brick walls and are characterized by wooden floors poorly connected to the vertical structures. Non-linear static analyses are performed by adopting the 3Muri software to characterize the seismic capacity of both the entire aggregate and the individual SUs. In this framework, a multi-scenario physics-based approach is considered for the definition of the seismic input in terms of broadband seismic signals inclusive of source and site effects. Finally, the incidence of the seismic input variability is discussed for the prediction of the global capacity response of the case study building.
... Notably, a similar approach has been tested by Paolucci et al. (2015) and Shen et al. (2022), although they only used the average ground displacement information pertaining to the last 5 s of the simulation. Conversely, we opted for checking the cumulative displacement over the full time-series without taking the arbitrary choice of a fixed time window. ...
... Conversely, we opted for checking the cumulative displacement over the full time-series without taking the arbitrary choice of a fixed time window. As a result, our validation method goes beyond the visual comparison proposed by Paolucci et al. (2015), ensuring a quantitative assessment. However, this method should always be used together with the validation using strong motion dataset and not alone due to the fact that InSAR displacement can only accurately represent the displacement caused by low frequency seismic waves and they are also likely to be affected by post-seismic displacement caused by afterslip. ...
... Numerical simulations provide a comprehensive and intuitive view of ground motion, including its spatial variability on a wide scale, which cannot be achieved by any other approaches (Paolucci et al. 2015). To provide insights into the variability of surface ground motion, representative snapshots of velocity wavefield with 5 s time intervals are shown in Figs. 5, 6, 7. The total source duration of the M w 7.8 Gorkha earthquake Galetzka et al. 2015;Yagi and Okuwaki 2015;Liu et al. 2016;Wei et al. 2018), and about 1/6 of the fault plane ruptured after ten seconds of the onset. ...
... The observed data are compared with the synthetic deformation (Fig. 9b), which is computed by projecting the three components of displacement to the LOS direction. Following Paolucci et al. (2015), each component is averaged over the last 5 s of the simulation. The agreement between the observed and synthetic data is quite good. ...
Article
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The 2015 Mw7.8 Gorkha earthquake is the latest strong event with magnitude greater than Mw7.5 in the Himalayas. The occurrence of this event provides a good opportunity to better understand the characteristics of ground motion produced by a low dip thrust fault. In this study, we constructed a kinematic source model and established a numerical model that incorporates realistic surface topography, velocity structure and the Kathmandu basin for the Gorkha event. Based on the source and structure models, ground motions in the periods of 2–20 s were simulated by a spectral-element method. Our results are as follow. (1) Ground motions show prominent directivity along strike. (2) The basin effect can amplify the amplitude of ground motion in Kathmandu especially on the horizontal component. (3) Horizontal ground motions in Kathmandu valley exhibit obvious amplification in the frequency range of 0.2–0.4 Hz, which is absent in vertical component. The results of this work are of importance for future studies on assessing seismic hazard in the Himalayas.
... San Felice sul Panaro) have been observed following both the May 20 th and 29 th shocks (Pizzi and Scisciani 2012;Emergeo Working Group 2013). Moreover, the May 20 th aftershocks, occurred within a close time interval (less than 4 minutes with M L between 4.8 and Paolucci et al. (2015) for the M W = 5.9 on May 29 th 5.0), may have had some effects on pore water pressure build-up within the saturated cohesionless layers, especially in the municipality of Terre del Reno (villages of Sant'Agostino, San Carlo, Mirabello) where the most and largest liquefaction effects were observed (Sinatra and Foti 2015;Facciorusso et al. 2016). ...
... Regarding the distance metrics, we used the Joyner-Boore distance (Rjb) to account for the effect of the extended source in ITA18, as the sites analyzed in this study are very close to the seismic sources of the mainshocks. The fault geometries, reported in Fig. 1, are taken from the available literature and limited to the area with source slip greater than 0 m: Pezzo et al. (2018) for the M w 6.1 on May 20 th and Paolucci et al. (2015) for the M w 5.9 on May 29 th . ...
Article
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This paper presents a comprehensive geological and geotechnical study of the whole area affected by liquefaction following the 2012 Emilia earthquakes, including all the available information from the field reconnaissance surveys, in situ tests, and laboratory analyses. The compilation was performed at 120 liquefied sites to verify and validate the reliability of liquefaction charts in alluvial sediments, and to assess liquefaction induced by the 2012 seismic sequence in the Emilia plain. The results reveal a wide range of grain sizes (from clean sands to sandy silts) and compositional characteristics (quartz-rich to litharenitic) in the 2012 ejecta, and show a strong relationship between the liquefaction and stratigraphic architecture of the subsurface. The availability of in situ tests at the liquefied sites makes it possible to verify and validate the reliability of the liquefaction charts in alluvial sediments with respect to the real observations. For the analyzed Emilia case studies, the use of non-liquefiable crust provides better estimations of the liquefaction manifestations when coupled with the thickness of the liquefiable layer rather than with the liquefaction potential index. Altogether, this work makes available to the international scientific community a consistent liquefaction database for in-depth earthquake studies.
... Three-dimensional (3D) physics-based numerical simulations of seismic wave propagation can provide a detailed and accurate characterization of the seismic ground motion and allow us to explore its spatial heterogeneity. This kind of numerical simulations have proven to be essential for the explanation of anomalies in the observed ground motion during past earthquakes (e. g. Paolucci et al. 2015;Cruz-Atienza et al. 2016;Klin et al. 2019), also in cases in which topographic effects are involved (e.g. Puglia et al. 2013;Luo et al. 2020). ...
... The physical properties assigned to each geological formation were estimated from geophysical investigations conducted in the area in the aftermath of the 2016 earthquake (Puzzilli et al. 2019). We described the intrinsic attenuation of seismic waves with the shear quality factor Q μ , which was evaluated from V S with the widely used rule of thumb Q μ = 0.1 V S [m/s] (e. g. Paolucci et al. 2015) and with the bulk quality factor Q κ , which was in turn estimated as Q κ = 3.5 Q μ in accordance with the theory exposed by Morozov (2015). ...
Article
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The combined effect of topography and near-surface heterogeneities on the seismic response is hardly predictable and may lead to an aggravation of the ground motion. We apply physics-based numerical simulations of 3D seismic wave propagation to highlight these effects in the case study of Arquata del Tronto, a municipality in the Apennines that includes a historical village on a hill and a hamlet on the flat terrain of an alluvial basin. The two hamlets suffered different damage during the 2016 seismic sequence in Central Italy. We analyze the linear visco-elastic seismic response for vertically incident plane waves in terms of spectral amplification, polarization and induced torsional motion within the frequency band 1–8 Hz over a 1 km ² square area, with spatial resolution 25 m. To discern the effects of topography from those of the sub-surface structure we iterate the numerical simulations for three different versions of the sub-surface model: one homogeneous, one with a surficial weathering layer and a soil basin and one with a complex internal setting. The numerical results confirm the correlation between topographic curvature and amplification and support a correlation between the induced torsional motion and the topographic slope. On the other hand we find that polarization does not necessarily imply ground motion amplification. In the frequency band above 4 Hz the topography-related effects are mainly aggravated by the presence of the weathering layer, even though they do not exceed the soil-related effects in the flat-topography basin. The geological setting below the weathering layer plays a recognizable role in the topography-related site response only for frequencies below 4 Hz.
... e.g. [12,19,65]. Nowadays, thanks to the availability of openly accessible data, as for example [30,83], this challenge can be tackled in specific regions of the world. ...
... We found that for the majority of the stations the agreement between simulations and observations is from fair to good. These results are aligned with those obtain for other, different earthquake scenarios as, e.g., [41,65]. ...
Preprint
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As a mean to assess the risk dam structures are exposed to during earthquakes, we employ an abstract mathematical, three dimensional, elasto-acoustic coupled wave-propagation model taking into account (i) the dam structure itself, embedded into (ii) its surrounding topography, (iii) different material soil layers, (iv) the seismic source as well as (v) the reservoir lake filled with water treated as an acoustic medium. As a case study for extensive numerical simulations we consider the magnitude 7 seismic event of the 30th^{\rm th} of October 2020 taking place in the Icarian Sea (Greece) and the Tahtali dam around 30 km from there (Turkey). A challenging task is to resolve the multiple length scales that are present due to the huge differences in size between the dam building structure and the area of interest, considered for the propagation of the earthquake. Interfaces between structures and highly non-conforming meshes on different scales are resolved by means of a discontinuous Galerkin approach. The seismic source is modeled using inversion data about the real fault plane. Ultimately, we perform a real data driven, multi-scale, full source-to-site, physics based simulation based on the discontinuous Galerkin spectral element method, which allows to precisely validate the ground motion experienced along the Tahtali dam, comparing the synthetic seismograms against actually observed ones. A comparison with a more classical computational method, using a plane wave with data from a deconvolved seismogram reading as an input, is discussed.
... In fact, both fault normal and fault parallel channels of MIR01 and MIR02 are identified as impulsive by all the algorithms. Furthermore, in 29 May 2012 (07:00) earthquake, impulsive signals can be connect to the updip directivity effect [81]. Pulse periods that are calculated by the 3 different algorithms that we use vary between 0.6 s to 3.1 s. ...
... Slip distribution of 20 May 2012 is modified fromFigure S7of Electronic Supplement of Pezzo et al.[80]. Slip distribution of the 29 May 2012 (07:00) Emilia-Romagna earthquake modeled by Paolucci et al.[81] and can be seen inFigure 8of the mentioned study. Red star indicates the epicenter of each event. ...
Article
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Near fault seismic records may contain impulsive motions in velocity-time history. The seismic records can be identified as impulsive and non-impulsive depending on the features that their waveforms have. These motions can be an indicator of directivity or fling step effect, and they may cause dangerous effects on structures; for this reason, there is increasing attention on this subject in the last years. In this study, we collect the major earthquakes in Italy, with a magnitude large or equal to Mw 5.0, and identify the impulsive motions recorded by seismic stations. We correlate impulsive motions with directivity and fling step effects. We find that most earthquakes produced impulsive signals due to the directivity effect, though those at close stations to the 30 October 2016 Amatrice earthquake might be generated by the fling step effect. Starting from the analyzed impulses, we discuss on the potential influence of site effects on impulsive signals and suggest a characterization based on the main displacement directions of the impulsive horizontal displacements. Finally, we discuss on the damage of three churches in Emilia, which were subject to impulsive ground motion, underlying in a qualitative way, how the characteristics of the pulses may have had influences the structural response of the façades.
... Firstly, empirical GMMs are affected by a scarcity of recordings from large-magnitude ruptures in the near-fault region due to the low occurrence frequency of these ruptures and the lack of nearby strong-motion recording instruments. Secondly, GMMs consider simplified representations of the rupture process on the fault (i.e., source), the propagation of seismic waves through the crust and sedimentary layers (i.e., path), and the non-linear sub-surface soil response (i.e., site) effects [6]. Hence, these models provide limited means to scrutinize the region-and site-specific interplay of physical parameters (and their uncertainty) that affect the resulting ground motion and geohazards (e.g., liquefaction, landslide). ...
... Despite the long history of numerical simulations, such as purely stochastic methods based on random vibration theory or Green's function methods [18], the physics-based approach to ground-motion modelling demonstrates higher predictive capabilities. This uses site-and/or region-specific data to explicitly model the physical process of slip and its heterogeneity, the rupture evolution in time and space, the wave propagation in the Earth's crust and basin generated waves, and non-linear sub-surface soil response, among other features [6,[19][20][21][22][23][24]. It therefore provides an analyst with a robust means of explicitly addressing aleatory variability in the underlying parameters and epistemic uncertainty due to the range of scientifically plausible models. ...
Article
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The Sendai Framework for Disaster Risk Reduction 2015-2030 (SFDRR) highlights the importance of scientific research, supporting the ‘availability and application of science and technology to decision making’ in disaster risk reduction (DRR). Science and technology can play a crucial role in the world’s ability to reduce casualties, physical damage, and interruption to critical infrastructure due to natural hazards and their complex interactions. The SFDRR encourages better access to technological innovations combined with increased DRR investments in developing cost-effective approaches and tackling global challenges. To this aim, it is essential to link multi- and interdisciplinary research and technological innovations with policy and engineering/DRR practice. To share knowledge and promote discussion on recent advances, challenges, and future directions on ‘Innovations in Earthquake Risk Reduction for Resilience’, a group of experts from academia and industry met in London, UK, in July 2019. The workshop focused on both cutting-edge ‘soft’ (e.g., novel modelling methods/frameworks, early warning systems, disaster financing and parametric insurance) and ‘hard’ (e.g., novel structural systems/devices for new structures and retrofitting of existing structures, sensors) risk-reduction strategies for the enhancement of structural and infrastructural earthquake safety and resilience. The workshop highlighted emerging trends and lessons from recent earthquake events and pinpointed critical issues for future research and policy interventions. This paper summarises some of the key aspects identified and discussed during the workshop to inform other researchers worldwide and extend the conversation to a broader audience, with the ultimate aim of driving change in how seismic risk is quantified and mitigated.
... Platforms like Cybershake and Cybershake NZ conducted numerous PBS demonstrating its effectiveness (Graves et al., 2011;Tarbali et al., 2019). Further, numerous researchers have successfully integrated PBS into their studies, validating its efficacy (Paolucci et al., 2015;Cui et al., 2013;Shaw et al., 2018;Infantino et al., 2020;Sreejaya et al., 2023;Alikhanzadeh & Zafarani, 2023). Additionally, PBS has existing spatial correlation features which are required in the hazard and risk applications of spatially distributed structures (Schiappapietra andSmerzini 2021, Sharma et al., 2024). ...
Article
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This study proposes a new simplified Ground Motion Model (GMM) for vertical spectra by combining comprehensive datasets from the NESS and NGA-West2 databases. The proposed Artificial Neural Network (ANN) architecture-based model requires only 288 unknowns to predict spectral accelerations (Sa) at 33 distinct periods ranging from 0 to 4 s. Notably, this model inherently captures known physical phenomena with reduced variability using a minimum number of unknowns compared to the GMMs existing literature, thus offering a valuable addition to current hazard estimation frameworks. Furthermore, recognizing the necessity for physics-based simulations in vertical ground motion analysis, we introduce a physics-based broadband model for vertical spectra using ANN methodology. The proposed broadband model exhibits better robustness due to the comprehensiveness of the dataset utilized and the inclusion of source path and site characteristics at the input layer. Additionally, the model effectively captures the physical trends with minimal deviation. Further, we verified the predictive ability of the developed models through a comprehensive case study of the 2008 Iwate–Miyagi earthquake. The proposed models serve as essential tools for physics-based broadband simulations and hazard assessments in active shallow crustal regions.
... 22 SEM has been successfully implemented for many recent earthquakes. [23][24][25][26][27][28][29][30] The numerical simulation method begins with the physical mechanism of earthquakes and simulates the entire process to generate seismic motion. In addition, some researchers have used physical parameters to generate seismic ground motion. ...
Article
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The development of the economy and technology has attracted greater attention to regional seismic resistance, a key technology for which is the simulation of regional seismic ground motions. This study proposes a simple and highly operable method for the generation of regional seismic ground motions, which includes five steps. First, a seismic ground motion recorded at a seismic station is selected as the original ground motion. The original ground motion is then decomposed into eight sub-signals by wavelet packet transform (WPT). Next, the eight sub-signals are adjusted by the frequency attenuation model. The generated ground motion is then amplitude modulated by the peak ground acceleration (PGA) attenuation model. The frequency attenuation model and the PGA attenuation model are obtained by fitting seismic data from the 1999 Chi-Chi earthquake. Finally, the propagation of the ground motion is considered. The proposed method can provide a time history of seismic ground motions for any point in a region. To investigate the rationality and applicability of the proposed method, the characteristics of the generated seismic ground motions are compared with those of true seismic ground motions. The average error of the PGA of the generated ground motions and the true ground motions is 0.072g; thus, the proposed method is suitable for use in small-scale regions. Furthermore, 4-story and 15-story structures are used for structural response analysis. The story drift ratio error between the generated ground and true ground motions is found to be within an acceptable error range. The proposed method provides a new way to generate ground motions for regional seismic investigation.
... One alternative is to simulate earthquake ground motions using for example 3D physicsbased approaches that are capable of generating synthetic time-histories at bedrock considering a local or regional 3D crustal model and an extended-source model (e.g., Frankel et al. 2018;Paolucci et al. 2015;Pitarka et al. 2021). However, such approaches still suffer from the limited knowledge of the propagation medium which prevents, in most cases, obtaining time histories covering a sufficiently large frequency band (0.1-20 Hz). ...
Article
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Estimating earthquake ground motions at reference bedrock is a major issue in site-specific seismic hazard assessment. Deriving or adjusting empirical ground motion models (GMMs) for reference bedrock is challenging and affected by large epistemic uncertainties. We propose a methodology to simulate region-specific reference bedrock time histories by combining spectral decompositions of ground motions with Empirical Green’s Functions (EGFs) simulation technique. First, we adopt the nonparametric spectral decomposition approach to separate the contribution of source, path, and site. We remove the average source and site effects from observed small-magnitude recordings in the target region through deconvolution in the Fourier domain. This way, the obtained deconvolved EGFs represent path term only. Then, we couple the EGFs with k− 2 kinematic rupture models for target scenario events. For each target magnitude, a set of rupture models following a ω-squared source spectrum are generated sampling the uncertainties in kinematic source parameters (e.g., slip distribution, rupture velocity, hypocentral location, stress drop, and rupture dimensions). The proposed approach is validated using recorded ground motions at reference sites from multiple earthquakes in Central Italy. The power of this approach lies in its ability to map the path-specific effects into the ground-motion field, providing 3-component time histories covering a wide frequency range, without the need for computationally expensive approaches to simulate 3D wave propagation. The region-specific, site-effects-free dataset produced by this approach can be used alone or in combination with existing empirical datasets to adjust existing GMMs, derive new GMMs, or select hazard-consistent time histories to be used in soil and structural response analyses.
... Alors que la première approche consiste en une modélisation directe conservatrice du scénario de secousses du sol les plus intenses, le second porte sur les statistiques tirées des observations précédentes de forts mouvements du sol) [3]. Dans ce contexte, de nombreux événements historiques de forts mouvements du sol ont été reproduits avec succès en utilisant des simulations numériques textuelles (PBS) [4][5][6][7][8][9][10][11]. Les PBS fournissent d'excellentes informations sur les subtilités de l'anatomie des tremblements de terre, caractérisant le mouvement des ondes sismiques 3D dans des conditions proches de la faille (y compris les effets de directivité possibles) et incluant les intéractions complexes avec la topographie de la surface et les paramètres géologiques (ondes de surface, piégeage d'onde au sein de structures en forme de bassin). ...
Conference Paper
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Cette contribution vise à montrer les résultats et performances du simulateur de propagation d'onde 3D à haute fidélité SEM3D (déposé [1, 2] et open source) sur GPU et sur cloud. SEM3D est principalement employé pour simuler des tremblements de terre dans le domaine solide-fluide, des failles actives à la surface libre, à travers des régions urbaines de ≈100 km × 100 km × 100 km de large. Les benchmarks effectués sur machine AMD sur Google Cloud Platform (GCP) et sur GPU Nvidia A100 sur le supercalculateur Jean Zay de l'IDRIS.
... Most of the remaining validation studies are focused on the comparison of simulated VGMs with recorded motions for historical records. Examples are in Paolucci et al. (2015), Razafindrakoto et al. (2018), and Infantino et al. (2020). ...
Article
Despite the evidence from past earthquakes and several numerical investigations demonstrating the detrimental impact of vertical ground motions (VGMs) on the integrity of bridge structures, incorporating their effects into seismic assessment and design procedures has traditionally been given limited consideration. Current codes utilize rather simplistic approaches to account for the concurrent effects of vertical and horizontal motions in structural performance evaluations, potentially leading to unconservative estimates of structural demands. This paper reviews the main features of VGMs and their effect on the seismic response of bridges. The methods and empirical models available to estimate vertical motions for design purposes are discussed, and research gaps and related research needs are identified. Finally, the emerging role of physics-based ground-motion simulations, as well as their limitations, in supporting future research and informing the development of simplified design procedures is examined. The main areas of interest for future research are identified in the need to carry out systematic sensitivity studies to gain insight into the main earthquake parameters that influence key VGMs features, understand the influence of soil nonlinearities on VGMs amplitude and frequency content, inform the development of empirical models that cover a range of site conditions and source-to-site distances where current models are poorly constrained, generate arrays of motions to update coherency models to properly inform the analysis of distributed infrastructure, investigate the impulsive character of VGMs, and assess the approximations made in estimating VGMs with 1D site response analyses. Specific focus is laid on large-magnitude earthquakes in the near-field.
... In the hazard counterpart, different alternatives can be adopted at an increasing level of complexity. Conventional ground-motion prediction equations (GMPEs) consider simplified representations of SAmp (Paolucci et al., 2015) using code-based amplification factors. These factors are defined by soil categories that can be identified based on the shear wave velocity in the upper 30 m of the soil column (V S, 30 ) from microzonation studies or on V S, 30 maps derived from proxies, such as local topography (Wald and Allen, 2007) or geolithology (Forte et al., 2017). ...
Article
Our study introduces a methodology to improve large-scale seismic damage assessment by incorporating site-specific fragility curves, considering soil–structure interaction (SSI) and site amplification (SAmp) effects. The proposed method proposes an enhanced building exposure model, using publicly available data and the open-source OpenQuake Engine software. The objective is to determine whether a more refined approach incorporating SSI and SAmp can impact the final damage calculation. We evaluate our approach by estimating the damage distribution for the Thessaloniki 1978 earthquake scenario using the actual building stock of Thessaloniki. We present several maps with aggregated damages at different levels to investigate the spatial variability of SSI and SAmp, and their influence on the resulting damages. Our estimated physical damages have been compared with those obtained using approaches from the existing literature. Apparently, using an updated building exposure model to assess damages makes any comparison with past observed damages challenging. Nevertheless, incorporating SSI and SAmp in large-scale damage assessment can provide valuable support for strategic decision-making in cities and improve the accuracy of the expected loss assessment due to a seismic event.
... Numerical simulations are frequently used to produce ground motion synthetics in the low to moderate frequency range (1-2 Hz). Actually, the effective recreation of previous earthquakes using three-dimensional physics-based simulations (PBS) has demonstrated the value of these simulations (Paolucci et al., 2015;Razafindrakoto et al., 2016;Taborda & Bielak, 2013). These 3D PBSs must be carefully calibrated and subjected to multi-criteria verification since they are both potent and sensitive to uncertainty (Bradley, 2019). ...
Article
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We report new findings for producing broad-band ground motion time histories (1–19 Hz) of a future earthquake in a sedimentary basin based on the application of extended rupture modelling together with the use of empirical Green’s functions (EGFs). This technique is used to model a MW6.0 earthquake in Kopili fault zone (KFZ), north-eastern India (NER). We ran simulations for a sediment site (VS30 = 360–760 m/s) and a rock site (VS30 = 760–1500 m/s) to obtain the ground motions, which were then compared with a number of ground motion prediction equations (GMPEs). These GMPEs agree with the simulated ground motion amplitude, confirming that once we have precise source terms along with representative EGFs, the artificial ground motions generated from earthquake scenarios of a specific site may be employed for seismic design safety in that given site. This work may open the door to additional in-depth, site-specific research in this area.
... [12,13,14]. In the recent years three-dimensional (3D) physics-based simulations, based on the DGSE method, have been employed for the study of real earthquake ground motion [15,16,17] and, more recently, for seismic risk scenarios in large urban areas [18,19,20]. However, accounting for the multi-scale nature of wave propagation within a single model poses challenging demands on computational methods and resources due to the coexistence of very different spatial scales, from few tens of kilometers, with reference to the seismic fault, up to few meters, or even less when considering the structural elements. ...
... Finally for the stability and convergence of the used numerical method we refer to [4,5,21]. We refer also to [30,[38][39][40]47] for other interesting applications in computational seismology. Using the mentioned above mathematical model and computational domain we performed for each seismic event three numerical simulations named as scenario 1,2 and 3 (SC1, SC2 and SC3 in the following). ...
Chapter
The aim of this paper is to propose a physics-based simulation of the two earthquakes that hit the surrounding area of the city of L’Aquila (Abruzzo central Italy) in 1461 and 1762, with magnitudes 6.4 Mw and 6.0 Mw, respectively. Both events are placed, by the available literature, on the fault structure named San Pio delle Camere [11]. The physical parameters characterizing the earthquake such as fault plane, epicenter, and magnitude are considered to be fixed. Starting from them three stochastic rupture scenarios are generated from each earthquake using three different slip distributions. The scenarios were evaluated in relation to the possibility to reproduce the macroseismic intensity field available from the historical catalogs. The simulated values of peak velocity are used to derive the value of the macrosiesmic intensity obtained by a suitable empirical relationship specifically derived for Italy.For the numerical simulations we used a three-dimensional soil model used and validated in a previous study related to the 2009 L’Aquila earthquake. The considered slip distributions are able to reproduce quite well the macroseismic effect of the 1461 earthquake. While none of the three scenarios developed satisfactorily reproduce the 1762 earthquake.
... Validating velocity structure models by waveform simulation is straightforward and well suited to the problem of ground motion prediction. In many works this method is applied for validation of basin models, for example: San Bernardino basin, USA (Graves and Wald 2004); Santa Clara valley, USA (Hartzell et al. 2006); Los Angeles basin, USA (Lee and Chen 2016); Taipei basin, Taiwan (Lee et al. 2008); Mygdonian Basin, Greece (Maufroy et al. 2015); Southern California basins (Nweke et al. 2022); Po plain, Italy (Paolucci et al. 2015); Puget Sound basins, USA (Pitarka et al. 2004); Kanto basin, Japan (Takemura et al. 2015). ...
Article
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To advance the methodology for validating velocity models by waveform comparison, we estimated source parameters for small magnitude earthquakes that can be approximated by point sources. Instead of using published source models, we used the reciprocity method to calculate 3D Green’s functions using the target velocity structure itself, and then inverted the earthquake sources. This method greatly reduces the calculations required compared to a full inversion of the source mechanism, depth, and source duration (risetime), making it possible to reproduce input ground motions in the target basin. Here, we validated the Japan Integrated Velocity Structure model of the Osaka basin using five earthquakes around the Osaka basin; these earthquakes allowed us to investigate the impact of the incident waves’ propagation directions. We first estimated source parameters using records at control bedrock sites surrounding the Osaka basin to reproduce the input ground motions. Then, we conducted a 3D finite-difference simulation for sites within the basin. By mapping the distributions of misfit values for individual waveforms, peak ground velocities, and response spectra, we were able to identify areas in the basin that require additional tuning of the velocity model. Graphical Abstract
... A 3D physics-based numerical simulation approach (3D PBS) whose computation code is SPEED (Spectral Element in Elastodynamics with Discontinuous, http://speed.mox.polimi.it/) that could handle different seismology aspects such as seismic faults rupture, seismic wave propagation, localized site irregularities, soil-structure interactions, attracts attention of seismologist and earthquake engineers. SPEED is an open-source software package, developing by cooperation between Department of Mathematics and Department of Civil and Environmental Engineering at Politecnico di Milano, that successfully applied and verified in worldwide regions such as Grenoble in France from Chaljub et al. (2010), L'Aquila, Po Plain in Italy check from Smerzini et al. (2012), Paolucci et al. (2015), Christchurch in New Zealand from Guidotti et al. (2011) and so on. ...
... A 3D physics-based numerical simulation approach (3D PBS) whose computation code is SPEED (Spectral Element in Elastodynamics with Discontinuous, http://speed.mox.polimi.it/) that could handle different seismology aspects such as seismic faults rupture, seismic wave propagation, localized site irregularities, soil-structure interactions, attracts attention of seismologist and earthquake engineers. SPEED is an open-source software package, developing by cooperation between Department of Mathematics and Department of Civil and Environmental Engineering at Politecnico di Milano, that successfully applied and verified in worldwide regions such as Grenoble in France from Chaljub et al. (2010), L'Aquila, Po Plain in Italy check from Smerzini et al. (2012), Paolucci et al. (2015), Christchurch in New Zealand from Guidotti et al. (2011) and so on. ...
Conference Paper
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A realistic prediction of earthquake ground motion and of its spatial variability is one of the key components in the chain of seismic risk assessment of spatially distributed portfolios or infrastructural systems in large urban areas. In this work, a large-scale 3D numerical model is developed to generate physics-based ground shaking scenarios in the city of Thessaloniki in Northern Greece using the computer code SPEED (http://speed.mox.polimi.it) as input for seismic risk studies. The numerical model accounts for kinematic finite-fault sources, a 3D model of the propagation path and local site response conditions. The case study of Thessaloniki is addressed due to the detailed knowledge on its geologic, seismotectonic context as well as on up-to-date exposure and vulnerability models which are key ingredients for future seismic risk analyses. To validate the numerical model, simulated motions are compared against the recordings of a real small-magnitude (Mw4.4) earthquake, and with predictions from conventional approach based on Ground Motion Prediction Equations for a historical 1978 Mw6.5 earthquake whose spatial correlation is analysed.
... Numerical simulations are frequently used to produce ground motion synthetics in the low to moderate frequency range (1-2 Hz). Actually, the effective recreation of previous earthquakes using three-dimensional physics-based simulations (PBS) has demonstrated the value of these simulations (Razafindrakoto et al. 2016;Taborda and Bielak 2013;Paolucci et al. 2015). These 3-D PBSs must be carefully calibrated and subjected to multi-criteria verification since they are both potent and sensitive to uncertainty (Bradley 2019). ...
Preprint
Full-text available
We report new findings for producing broad-band ground motion time histories (1–19 Hz) of a future earthquake in a sedimentary basin based on the application of extended rupture modelling together with the use of empirical Green's functions (EGFs). This technique is used to model a M W 6.0 earthquake in Kopili fault zone (KFZ) north-eastern India (NER). We ran simulations for a sediment site (VS30 = 360 to 760 m/s) and a rock site (VS30 = 760 to 1500 m/s) to obtain the ground motion, which are then compared with a number of ground motion prediction equations (GMPEs). These GMPEs agree with the simulated ground motion amplitude, confirming that once we have precise source terms, the artificial ground-motions generated from earthquake scenarios of a specific site may be employed for seismic design safety in that given site. This work may open the door to additional in-depth, site-specific research in this area.
... polimi. it/, Mazzieri et al. 2013), which has been extensively used in the recent past to perform PBS validated on different real earthquakes (Paolucci et al. 2015;Evangelista et al. 2017;Infantino et al. 2020;Sangaraju et al. 2021) and to construct a prototype dataset of simulated broadband accelerograms with the aim of complementing recordings datasets, still relatively sparse in such near-source conditions . ...
Article
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In this paper we introduce the 3D physics-based numerical simulations (PBS) of ground motion during the Nov 11, 2019, MW 4.9 Le Teil earthquake, which occurred in a low-to-moderate seismicity area in the South-East of France, within the Rhône river valley, which hosts several operating nuclear installations. The numerical code SPEED, developed at Politecnico di Milano, Italy, was used to produce the PBS. After introducing the criteria to construct the numerical model, based on the relatively limited data available, a numerical convergence test was made to identify the frequency range for accurate simulations. Furthermore, the performance of the numerical results against the available strong motion records was assessed quantitatively using Goodness-of-fit (GoF) measures. According to the GoF scores, a good-to-excellent agreement was found on the horizontal components up to 8 Hz, showing that, even without a very detailed 3D numerical model of the medium, that would imply detailed knowledge of the basin shape, of the bedrock-to-basin impedance ratio, as well as of the damping ratio in the basin and its dependence on frequency, the PBS may provide realistic broadband predictions of earthquake ground motion. Nevertheless, as shown by the poorer performance on the vertical component, the high-frequency limitations of PBS, also in relation to the energy radiated by the kinematic source model, is still an issue to be carefully addressed. In spite of these limitations, the results obtained in this work demonstrate that PBS, if suitably calibrated and validated, can be either an alternative or a useful complement to empirical ground motion models, especially in those cases where the region- and site-specific features of ground shaking, including near-source conditions, are typically not accounted for by ergodic empirical models, such as for the seismic risk evaluation of large urban areas and/or of strategic structures, infrastructures and industrial plants.
... In particular, physics-based ground-motion simulation has emerged as a complementary and possibly alternative approach to empirical ground-motion modelling, addressing the abovementioned challenges [37]. This method utilises a representation of the earthquake source using dynamic or kinematic rupture models and solves the wave propagation equations to simulate the shaking time series at the surface of the Earth (e.g., [38][39][40][41][42][43][44][45]). These physics-based simulated ground motions can capture complex source features (such as spatially variable slip distributions, rise-time, and rupture velocities); path effects (geometric spreading and crustal damping); and site effects (wave propagation through basins and shallow site response), providing a valuable supplement to recorded ground motions. ...
Article
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Rapid urban expansion in many parts of the world is leading to increased exposure to natural hazards, exacerbated by climate change. The use of physics-based models of natural hazards in risk-informed planning and decision-making frameworks may provide an improved understanding of site-specific hazard scenarios, allowing various decision makers to more accurately consider the consequences of their decisions on risk in future development. We present results of physics-based simulations of flood, earthquake, and debris flow scenarios in a virtual urban testbed. The effect of climate change, in terms of increasing rainfall intensity, is also incorporated into some of the considered hazard scenarios. We use our results to highlight the importance of using physics-based models applied to high-resolution urban plans to provide dynamic hazard information at the building level for different development options. Furthermore, our results demonstrate that including building elevations into digital elevation models is crucial for predicting the routing of hazardous flows through future urban landscapes. We show that simulations of multiple, independent hazards can assist with the identification of developing urban regions that are vulnerable to potential multi-hazard events. This information can direct further modelling to provide decision-makers with insights into potential multi-hazard events. Finally, we reflect on how information derived from physics-based hazard models can be effectively used in risk-sensitive planning and decision-making.
... As an example, we show the recording of the IV.T0819 station, about 7 km from the epicenters, where the two events can be easily trimmed on the raw traces (Figure 6d), and the recording of the IV.T0820 station, at about 50 km from the epicenters, where the two events tend to overlap (Figure 6e). Moreover, the late-arriving long-period surface waves can significantly increase the duration of ground shaking, causing overlaps along their propagation path, in particular in the Po Plain, where many factors strongly favor the generation of surface waves in the radiation path from the source (e.g., [37,39,40]). The illustrative cases for the δS2S peculiarities are reported in Figure 7. ...
Article
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We present the results of a consistency check performed over a flatfile of accelerometric data extracted from the ITalian ACcelerometric Archive (ITACA), enriched with velocimetric records of events with magnitude M < 4.0. The flatfile, called ITACAext, includes 31,967 waveforms from 1709 shallow crustal earthquakes, in the magnitude range from 3.0 to 6.9, and occurred in the period of 1972-2019 in Italy. The consistency check is carried out by decomposing the residuals obtained from a reference ground motion model, for the ordinates of the 5% damped acceleration response spectra. The residual components are subsequently analyzed to identify a list of events, stations, and records that significantly deviate from the median trends predicted by the model. The results indicate that about 10% of events and stations are outliers, while only 1% of the waveforms present anomalous amplitudes. The asymmetrical azimuthal coverage of seismic stations around the epicenter is the most common issue that can affect the estimates of the repeatable event residual term. On the other hand, peculiarities in the site-response or wrong estimates of the soil parameters (i.e., the average shear-wave velocity in the first 30 m of the subsoil) are the main issues related to the repeatable station residuals. Finally, single records can show large residuals because of issues related to signal acquisition (e.g., multiple events, noisy records) or possible near-source effects (e.g., rupture directivity).
... In the recent past, SPEED has been extensively used for the validation of PBS addressed to real earthquakes in Italy and worldwide (e.g. Paolucci et al., 2015;Evangelista et al., 2017;Infantino et al., 2020), for region-specific seismic hazard and risk evaluations (Smerzini and Pitilakis 2018;Stupazzini et al., 2021), and the construction of a dataset of broadband near-source simulated ground motions for earthquake engineering applications . ...
Article
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An accurate characterization of earthquake ground motion and its variability is crucial for seismic hazard and risk analysis of spatially distributed portfolios in urban areas. In this work, a 3D physics-based numerical approach, based on the high-performance spectral element code SPEED (http://speed.mox.polimi.it/), is adopted to generate ground shaking scenarios for strong earthquakes (moment magnitude MW=6.5–7) in the Thessaloniki area (Northern Greece). These simulations account for kinematic finite-fault rupture scenarios and a 3D seismic velocity including the two main geological structures present in the area (Thessaloniki and Mygdonia basins). The numerical model is successfully validated by comparing simulated motions, on the one hand, with the recordings of a real small-magnitude (MW4.4) earthquake and, on the other, with empirical Ground Motion Models for the historical MW6.5 1978 earthquake. The sensitivity of results to the velocity model, anelastic attenuation, and non-linear soil effects is evaluated. The variability of the ground motion intensity measures in Thessaloniki as a function of the finite-fault rupture realizations (causative fault, magnitude, hypocenter location) is explored to gain insight into its potential impact on seismic risk assessment in urban areas.
... Currently, the SEM is well verified by comparison with the SCEC benchmark and Grenoble benchmark. 22 Additionally, SEM-based validations and applications have been successfully implemented for many recent earthquakes, such as the 2009 M w 6.3 L'Aquila, 23 2010 M w 5.2 Chile, 24 2012 M w 6.0 Po Plain, 25 and historical earthquakes, such as the 1915 M w 6.7 Marsica 26 and 1978 M w 6.5 Volvi, 27 as well as potential scenarios, such as applications to the Shunyi and Tongxian faults in China, 28 the Istanbul North Anatolian fault in Turkey, 29 the Wellington fault in New Zealand and the San Ramon fault in Chile. 18 For large-scale scattering problems in elastodynamics involving the two key issues of multiscale seismic wave propagation (wavelengths from a few meters to hundreds of meters) and the overall evaluation of ground motion (from the source to site), supercomputing is generally necessary if fully numerical methods, especially domain-type methods, are used. ...
... In this paper, the simulations are carried out using the spectral element code SPEED (Mazzieri et al., 2013), which has been extensively used in the recent past to perform PBS validated on different real earthquakes (Paolucci et al., 2015;Evangelista et al., 2017;Infantino et al., 2020;Sangaraju et al., 2021) and to construct a prototype of a near-source simulated accelerograms dataset with the aim of complementing recordings datasets, still relatively sparse in such near-source conditions . ...
Preprint
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In this paper, a comprehensive validation exercise of 3D physics-based numerical simulations (PBS) of seismic wave propagation is presented for a low-to-moderate seismicity area in the south east of France, within the Rhône River Valley, that hosts several operating nuclear installations. This area was hit on Nov 11, 2019, by an unusually damaging Mw 4.9 earthquake (Le Teil event). The numerical code SPEED (http://speed.mox.polimi.it/), developed at Politecnico di Milano, Italy, was used to validate the simulations against the available recordings. When comparing simulations with records, a good to excellent agreement was found up to 8–10 Hz, showing that, even without a very detailed 3D numerical model of the medium, the PBS may provide realistic broadband predictions of earthquake ground motion. This also demonstrates that PBS, if suitably calibrated and validated, may be either an alternative or a useful complement to empirical ground motion models. Referring to the seismic risk evaluation of strategic and critical structures, infrastructures and industrial plants, such as nuclear power plants, the failure of which during an earthquake may endanger safety of population and cause environmental disasters, the 3D PBS may throw light on region- and site-specific features of ground shaking, especially in near-source conditions, that are typically poorly constrained in empirical models.
... For implementation details we refer to [23] and for the stability and convergence of the numerical method we refer to [24], [25], [26]. Other interesting applications in computational seismology can be found in [7], [8], [27], [28], [29]. ...
... In this study, we use the numerical code SPEED (Mazzieri et al. 2013;Paolucci et al. 2015;Infantino et al. 2020). This code implements a discontinuous Galerkin formulation of the spectral element method (DGSEM). ...
Article
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Understanding site–city interaction (SCI) is important for sustainable urban development in seismic regions. Due to vertical expansion of cities, super-tall buildings with deep foundations and large underground chambers are often simultaneously present. However, the role of these structures and their layouts in SCI have not been considered before. This study quantifies the effects of SCI at a congested transport hub in Hong Kong, utilizing 3D numerical modeling. At the site, 16 high-rise buildings surround a center plaza with a large metro station underground. This research demonstrates that the building layout, building inertia, and interaction between underground structures through the soil govern SCI at the site, causing ground motion perturbations and wave trapping between buildings. The presence of buildings causes up to 150–200% amplification in the short-period acceleration spectra and 150% PGA amplifications in the center plaza. Notable SCI effects on structures only appear as excess maximum story accelerations, in the order of 1–2 m/s², and increased destructive kinetic energy. Amid and around the high-rise buildings, SCI effects may significantly increase seismic demand on short structures. Finally, increasing the seismic demand for the design of super-tall and low-rise buildings is recommended to account for the SCI effects.
... The numerical code and its ability to reproduce ground motion spatial correlations have already been validated in different studies (e.g. Stupazzini et al. 2009;Paolucci et al. 2015Paolucci et al. , 2016Paolucci et al. , 2018Infantino et al. 2021). In addition to the 3D PBS of the Mw 6.5 Norcia event, we generate several scenarios by varying either the slip distribution or the hypocentral location to explore different spatial correlation properties, such as the dependency on the rupture process and magnitude. ...
Article
Full-text available
This paper investigates the spatial correlation of response spectral accelerations from a set of broadband physics-based ground motion simulations generated for the Norcia (Central Italy) area by means of the SPEED software. We produce several ground-motion scenarios by varying either the slip distribution or the hypocentral location as well as the magnitude to systematically explore the impact of such physical parameters on spatial correlations. We extend our analysis to other ground-motion components (vertical, fault-parallel, fault-normal) in addition to the more classic geometric mean to highlight possible ground-motion directionality and therefore identify specific spatial correlation features. Our analyses provide useful insights on the role of slip heterogeneities as well as the relative position between hypocentre and slip asperities on the spatial correlation. Indeed, we found a significant variability in terms of both range and sill among the considered case studies, suggesting that the spatial correlation is not only period-dependent, but also scenario-dependent. Finally, our results reveal that the isotropy assumption may represent an oversimplification especially in the near-field and thus it may be unsuitable for assessing the seismic risk of spatially-distributed infrastructures and portfolios of buildings.
... al heterogeneities are supposed to be smooth at regional scale. Therefore, our numerical analyses do not account for the generation of surface waves, and the response of soil deposits is assumed to be predominantly related to SH waves propagating vertically from the underlying bedrock. However, different numerical modeling (e.g., Vuan et al., 2011;R. Paolucci et al., 2015;Klin et al., 2019) and analyses of the recordings of the Emilia sequence (e.g., Bordoni et al., 2012;Luzi et al., 2013) have highlighted that 2D and 3D effects can be significant because of the complex buried morphology of the basin. In these cases, our results might underestimate the amplitude and duration of the seismic motion and, con ...
Article
This study investigates and quantifies the influence of the shallower deposits (down to few hundreds of meters) of the Po Plain sedimentary basin (northern Italy) on the long-period component (i.e., 1 s<T<3 s) of seismic ground motion, in which amplification effects due to the soft sediments above seismic bedrock were observed. A new seismostratigraphic model of the shallow deposits of the entire basin is provided with an unprecedented detail by taking advantage of recently acquired geophysical data. The seismostratigraphic model is used to simulate the ground motion amplification in the Po Plain by means of extensive 1D ground response analysis. Results are compared with seismic observations available at a number of sites equipped with borehole seismic stations, where earthquakes have been recorded both at the surface and at the seismic bedrock depth. Despite the general agreement with observations concerning the seismic resonance frequencies, our model may fail in capturing the amplitude of the actual seismic amplification of the basin in the long-period range. We observe that 3D basin effects related to surface waves generated at the edge of the basin may play a significant role in those zones where seismic hazard is controlled by distant sources. In these cases, 1D modeling leads to average underestimations of 30%, up to a maximum of 60%. The amplification functions need to be corrected for a basin-effects correction term, which in this case is provided by the ground-motion prediction equation of the study area. The corrected amplification functions agree with the empirical observations, overcoming the uneven distribution of the recording stations in strong-motion datasets. These results should be taken into account in future seismic microzonation studies in the Po Plain area, where the 1D approach is commonly adopted in ground response analyses, and in site-specific seismic hazard assessments aimed at the design of structures that are sensitive to the long-period component of seismic ground motion (e.g., long-span bridges and tall buildings).
... Nowadays, both approaches benefit of the easy access to huge computational resources since (i) highfidelity earthquake scenarios can be constructed at different observational scales (continental, regional, site-specific) and with a progressive level of detail and (ii) several realizations of the scenario space can be investigated. As a matter of fact, three dimensional physics based simulations (PBS) have proven their usefulness by successful reproduction of historical earthquakes (Razafindrakoto et al. 2016;Taborda and Bielak 2013;Paolucci et al. 2015). Those 3-D PBSs are as powerful as sensitive to uncertainty, therefore requiring thoughtful calibration and multi-criteria verification (Bradley 2019). ...
Article
Full-text available
The prediction of the seismic response of critical structures is highly sensitive to many aspects, among which the earthquake source and the geological setting are prominent. The related uncertainty issues must be taken into account in seismic risk mitigation studies, for example through the evaluation of several realizations of a future earthquake scenario. This aspect is crucial when addressing vulnerability studies at a regional scale. When opting for physical-based numerical simulations (PBS), however, the computational burden increases along with the expected degree of fidelity, making it difficult to evaluate more than a few dozens of alternatives. To cope with this disadvantage, in this work an alternative method is proposed, which exploits a rather low number of synthetic earthquake simulations and combines them with the empirical Green function (EGF) method, to finally generate thousands of alternative yet realistic seismic response of the site of interest. This hybrid strong motion predictions benefit of both (i) PBS high fidelity and (ii) data assimilation of strong ground motion records in the seismic area of interest, via EGF method, producing broad-band synthetics at a relative cheap computational price. The power of the hybrid method is tested on a real case scenario, embodied by the ground-shaking prediction at the nuclear site of Cadarache, in the surroundings of the fault of Middle Durance, in South-Eastern France. Thousands of broadband (0–15 Hz) hybrid synthetic seismic response are generated, associated with different fault parameters (EGF method) and based upon a few key physics-based simulations, accurate up to 5 Hz.
Article
Typically, it is challenging to incorporate near-surface soils into 3D physics-based numerical simulations (PBSs) for ground-motion prediction. The low shear wave speed of near-surface soils, coupled with the complexity of the soil seismic response, poses significant difficulties. To overcome these limitations, a hybrid approach was proposed in this study, combining PBSs with artificial neural networks (ANNs). The essence of the hybrid method can be summarized as follows: (1) development of ANN models, establishing a strong-motion database, training the ANNs on it to predict the ground-motion parameters for East–West (EW), North–South (NS), and Vertical (UD) directions afterward; (2) establishment of 3D PBS model, obtaining the ground-motion parameters of the bedrock face corresponding to a certain shear wave speed; (3) application of the trained ANNs to predict the ground-motion parameters on the ground surface, taking the simulated results and related site parameters as inputs, and the outputs are peak ground acceleration (PGA) and 5% damped spectral accelerations (Sa) at different periods on the ground surface. In this study, ANN models were trained on a strong-motion database based on Kiban–Kyoshin Network (KiK-net). After several verifications of the ANN predictions, a case study of the 21 October 2016 M w 6.2 Central Tottori earthquake was conducted. In addition to the comparison with observations, the broadband (0.1–10 Hz) results of the hybrid method were also compared with the results that obtained by transfer function based on recorded data and Next Generation Attenuation (NGA)-West2 ground-motion prediction equations (GMPEs) to demonstrate the effectiveness and applicability of the proposed method. In addition, the distribution of Sa for four periods in simulated area was presented. The performance of the hybrid method for predicting broadband ground-motion characteristics was generally satisfactory.
Article
The devastating 24 August 2016 M w 6.2 earthquake that struck Amatrice, Italy, marked the beginning of a prolonged seismic sequence dominated by three subsequent M w ≥ 6.0 events in the central Apennines region. The earthquake destroyed Amatrice's historic center, claiming the lives of 299 individuals and causing widespread damage in the neighboring villages. The severity of the ground shaking, with a recorded maximum acceleration of 850 cm= s 2 on the east-west component at the Amatrice station, was far greater than the predicted acceleration based on the Italian ground-motion model (GMM). As pointed out by several investigations, the observed ground-motion amplitude and its spatial variability during the earthquake can be linked to specific rupture characteristics, including slip distribution and rupture directivity effects revealed by the observed data (Tinti et al., 2016; Pischiutta et al., 2021). In this study, we conducted physics-based 3D numerical simulations of ground motion for the Amatrice earthquake for frequencies up to 3 Hz. We employed a series of kinematic rupture models and a well-constrained local 3D velocity model incorporating surface topography. The kin-ematic rupture realizations were generated using multiscale hybrid and fully stochastic models , following the technique proposed by Graves and Pitarka (2016). We focused on assessing the sensitivity of near-fault ground-motion amplitudes to earthquake rupture characteristics, in particular, the spatial slip pattern. To evaluate the quality of our simulations, we employed goodness-of-fit measurements performed in comparisons of simulated and recorded ground motions. The simulated ground motions compare well with the recorded data and predictions from GMMs for Italy, ITA18 (Lanzano et al., 2019). However, we found that the simulated interevent ground-motion variability (randomness in the source process) of peak ground velocity, σ (PGV) is higher than the constant σ (PGV) predicted by conventional GMMs. Our simulations using several rupture scenarios demonstrate that the near-fault ground-motion amplification pattern is directly related to the slip distribution pattern. KEY POINTS • The near-fault ground-motion amplification pattern is related to the size and distribution of the slip. • The rupture directivity is controlled by location of the rupture initiation relative to the large slip patches. • Peak ground velocity interevent variability is distance dependent and higher at shorter distances than that of constant ground-motion models.
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Estimation of the seismic risk associated with infrastructures requires site-specific seismic hazard studies. Further, for nonlinear time history analysis, one requires broadband ground motion. In modern times, physics-based simulations (PBS) for deriving the ground motion for future earthquakes have been considered. The PBS helps decrease the uncertainties related to hazard estimation compared to ground motion prediction equations. The PBS methods have a specific frequency threshold limit resulting from high computational demand. Hence, hybrid methods are required to attain broadband spectra for the simulated ground motion. This study uses a new artificial neural network (ANN)-based model to generate broadband ground motion spectra using the low-frequency spectral acceleration from PBS, source, path, and site parameters as input variables. A detailed parametric study and performance evaluation was made to identify the optimal input parameters in conjunction with the best-suited ANN architecture. The performance of the ANN model is demonstrated for Iwate (MwMwM_w 6.9, 2008) earthquake. We found that the predicted values from the developed ANN model agree with the recorded data. Furthermore, time histories are generated using the spectral ordinate matching technique from the estimated broadband spectra.
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Estrategias de reducción de riesgos para una adecuada resiliencia. Se presenta una análisis de la evolución de los sistemas estructurales para una adecuada respuesta ante eventos sísmicos como resiliencia sísmica e un portafolio o comodidad, entendiendo que los sistemas estructurales son muy complicados, contienen numerosos tipos de elementos físicos (p. ej., construcción, transporte y sistemas de redes de tuberías), elementos no físicos (p. ej., sociales, económicos y ecosistemas) y varias relaciones complejas entre diferentes subsistemas para ver una ciudad como un sistema de sistemas en un espacio tridimensional (físico, social y cibernético), la connotación y las propiedades de la resiliencia urbana usando varios subsistemas de una ciudad y sus interacciones. Además, las ciudades enfrentan varios tipos de desastres naturales (p. ej., terremotos, inundaciones y huracanes) y desastres no naturales (p. ej., explosiones e impactos). Por lo tanto, la cuantificación de la resiliencia de los sistemas urbanos después de los desastres es compleja. Hasta la fecha, los estudios de cuantificación de la resiliencia generalmente se realizan desde una perspectiva macroscópica o se enfocan en un número limitado de subsistemas bajo un solo desastre.
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In this paper, we present SEM3D: a 3D high-fidelity numerical earthquake simulator that is tailored to predict the seismic wave field of complex earthquake scenarios from the fault to the epicenter site. SEM3D solves the wave-propagation problem by means of the spectral element method (SEM). The presented demonstrative test case was a blind MW6.0 earthquake scenario at the European experimental site located in the sedimentary basin of Argostoli on the island of Kefalonia (Western Greece). A well-constrained geological model, obtained via geophysical inversion studies, and seismological model, given the large database of seismic traces recorded by the newly installed ARGONET network, of the site were considered. The domain of interest covered a region of 44 km × 44 km × 63 km, with the smallest grid size of 130 m × 130 m × 35 m. This allowed us to simulate the ground shaking in its entirety, from the seismic source to the epicenter site within a 0–10 Hz frequency band. Owing to the pseudo-spectral nature of the numerical method and given the high polynomial order (i.e., degree nine), the model featured 1.35·1010 DOFs (degrees of freedom). The variability of the synthetic wave field generated within the basin is assessed herein, exploring different random realizations of the mean velocity structure and heterogeneous rupture path.
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The Mw 6.5 Norcia, Italy, earthquake occurred on 30 October 2016 and caused extensive damage to buildings in the epicentral area. The earthquake was recorded by a network of strong-motion stations, including 14 stations located within a 5 km distance from the two causative faults. We used a numerical approach for generating seismic waves from two hybrid deterministic and stochastic kinematic fault rupture models propagating through a 3D Earth model derived from seismic tomography and local geology. The broadband simulations were performed in the 0–5 Hz frequency range using a physics-based deterministic approach modeling the earthquake rupture and elastic wave propagation. We used SW4, a finite-difference code that uses a conforming curvilinear mesh, designed to model surface topography with high numerical accuracy. The simulations reproduce the amplitude and duration of observed near-fault ground motions. Our results also suggest that due to the local fault-slip pattern and upward rupture directivity, the spatial pattern of the horizontal near-fault ground motion generated during the earthquake was complex and characterized by several local minima and maxima. Some of these local ground-motion maxima in the near-fault region were not observed because of the sparse station coverage. The simulated peak ground velocity (PGV) is higher than both the recorded PGV and predicted PGV based on empirical models for several areas located above the fault planes. Ground motions calculated with and without surface topography indicate that, on average, the local topography amplifies the ground-motion velocity by 30%. There is correlation between the PGV and local topography, with the PGV being higher at hilltops. In contrast, spatial variations of simulated PGA do not correlate with the surface topography. Simulated ground motions are important for seismic hazard and engineering assessments for areas that lack seismic station coverage and historical recordings from large damaging earthquakes.
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The combined effect of topography and near-surface heterogeneities on the seismic response is hardly predictable and may lead to an aggravation of the ground motion. We apply physics-based numerical simulations of 3D seismic wave propagation to highlight these effects in the case study of Arquata del Tronto, a hamlet in the Apennines that suffered irregularly distributed damage during the 2016 seismic sequence in Central Italy. We analyze the linear visco-elastic seismic response for vertically incident plane waves in terms of spectral amplification, polarization and induced torsional motion within the frequency band 1–8 Hz over a 1 km ² square area, with spatial resolution 25 m. To discern the effects of topography from those of the sub-surface structure we iterate the numerical simulations for three different versions of the structural model: one homogeneous, one with a surficial weathering layer and a soil basin and one with a complex internal structure. The numerical results confirm the correlation between topographic curvature and amplification and support a correlation between the induced torsional motion and the topographic slope. On the other hand we find that polarization does not necessarily imply ground motion amplification. In the frequency band above 4 Hz the topography-related effects are mainly aggravated by the presence of the weathering layer, even though they do not exceed the soil-related effects in the flat-topography basin. The structure below the weathering layer plays a recognizable role in the topography-related site response only for frequencies below 4 Hz.
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This study assesses the spatial correlation of broadband earthquake ground motions from 3D physics-based numerical simulations in near-source conditions. State-of-the-art models for predicting the spatial correlation are derived from wide datasets including densely recorded earthquakes in different areas worldwide and, therefore, they may be poorly representative of specific regions and near-source effects. A large set of broadband ground motions simulated by the SPEED code, and enriched in the high-frequency range with an Artificial Neural Network technique, is used to investigate the sensitivity of crucial parameters in geostatistical analysis (number of receivers), as well as of source, path, and site effects on spatial correlation, with a level of detail which could not be possible otherwise due to the paucity of recordings. First of all, the comparison of our results with those derived from earthquake recordings validates successfully the numerical approach in predicting the spatial correlation in a broad frequency range. Furthermore, the study points out that spatial correlation of response spectral accelerations is significantly affected by the magnitude, forward direc-tivity effects, ground-motion directionality (fault normal versus fault parallel), and relative position from the causative fault. These features may make critical the use of isotropic and stationary models especially in near-fault conditions. K E Y W O R D S spatial correlation, broadband ground motions, near-source effect, 3D physics-based numerical simulations, seismic risk
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We present a set of ground-motion simulations of the 2008 M-w 5.4 Chino Hills earthquake using different seismic-velocity models available for southern California. The simulations are tailored for a maximum frequency of 4 Hz and a minimum shear-wave velocity of 200 m/s. We use the community models developed by the Southern California Earthquake Center, CVM-S and CVM-H. In the case of CVM-H, we use two available alternatives, with and without considering the geotechnical layers (GTL). We compare the simulation results obtained with the models against each other and validate the synthetics with recordings obtained at more than 300 stations. The comparisons are used to gain insight into the sensitivity of the results to differences in the models and to make conclusions about the strengths of each model's description of the crustal structure and the GTL in the region. The validation is done using a goodness-of-fit (GOF) criterion. We find the GOF values show a better match at frequencies below 1 Hz, within the basins, and below 0.5 Hz in general. The models, however, do not converge at frequencies lower than 0.5 Hz, and the areas where each model leads to better results do not always coincide. The synthetics start to deviate significantly from observations at frequencies above 1 and 2 Hz, although very good agreement with data can still be found at individual locations, even at the higher frequencies. CVM-S yields the best results at frequencies up to 0.25 Hz. Our results reveal significant sensitivity of the ground motion to the differences in the structural representation of basins and shallow layers in the models. This indicates the models need to be cross referenced. We close by offering suggestions on the type of improvements that could be adopted in the future.
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We studied two earthquakes occurred in the Emilia region, Northern Italy, respectively on May 20th 2012, Ml 5.9, and May 29th, Ml 5.8, inverting COSMO-SkyMed and Radarsat-1 surface displacements and GPS observations. Both sources were found to be well modelled by ~E-W, S-dipping thrust faults with a flat-ramp geometry. We identified a displacement pattern of ~10 cm towards the satellite sensors, not associated to any of the largest aftershocks. The pattern is temporally co-located or following the first event and preceding the second one. Spatially it is located halfway between the displacement fields of the two main events. We investigate some possible interpretations of our observations, favouring the hypothesis of a slip along the fault plane of the May 29th event, supported by the results of a Coloumb Failure Function analysis, which suggests an increasing load on the May 29th fault plane, following the first mainshock. The post-seismic deformation was measured for a timespan of about 6 months, using overlapping ascending and descending COSMO-SkyMed acquisitions with a temporal sampling of ~16 days. The dominant deformation patterns are near-vertical and in the order of 1 to 4 cm/y.
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Strong ground motions recorded on the sedimentary deposits of the Po River alluvial plain during the Emilia (Northern Italy) Mw 5.7 earthquake of May 29, 2012 are used to assess the vertical profile of shear-wave velocity above the limestone basement. Data were collected by a linear array installed for site effect studies after the Mw 5.9 mainshock of May 20, 2012. The array stations, equipped with both strong and weak motion sensors, are aligned in the South–North direction, at distances ranging from 1 to 26 km from the epicenter. The vertical components of ground motion show very distinctive, large-amplitude, low-frequency dispersive wave trains. Wavelet analysis yields group-velocity dispersion curve in the 0.2–0.7 Hz frequency band. The availability of a long ambient noise record allows estimates of the site resonance frequency along with its stability among stations. The joint inversion of dispersion of surface waves and ellipticity curves derived from ambient noise H/V allows extending investigations down to the sediment-limestone interface, at a depth of about 5,000 m. Our results add new information about the velocity structure at a scale that is intermediate between the local scale already investigated by other authors with small-aperture arrays using ambient noise and the regional scale inferred from modeling of seismogram waveforms recorded at hundreds of kilometers from the source.
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An efficient mathematical method is presented for computing the near- fault strong ground motions in a layered half-space, giving explicit consideration to the static offset due to surface faulting. In addition, the combined effects of "fling step" and "rupture directivity" on the near-fault ground motions are investigated. First, after checking the fault integration in the representation theorem, it is found that when an observation point is close to the fault plane, Green's functions exhibit near singularities, which consist of extremely sharp peaks in a narrow band close to the observation point. Therefore, direct numerical integration becomes quite onerous for computing near-fault ground motions, because the dynamic Green's functions must then be distributed very densely in order to evaluate accurately the effects of the near singularities. Instead, a new form of the representation theorem is introduced, which exploits the property that the dynamic Green's functions can be approximated by the corresponding static Green's functions in the vicinity of the singularities. The modified theorem, which involves the device of adding and subtracting the static Green's functions from the dynamic ones, is the sum of two fault integrations. The first integration involves the difference of the dynamic and the corresponding static Green's functions, while the second contains only the static Green's functions. This formulation requires much less CPU time than the original one when near-fault ground motions are considered, because the near singularities of the dynamic Green's functions in the first integration are completely eliminated by subtracting the static Green's functions. While the second integration does require a densely distributed set of points to capture the near-singular behavior of the static Green's function, it needs to be performed only once, as it is valid for all frequencies. Subtraction of the static Green's functions from the dynamic functions has the added benefit of making the integration over the wavenumber in the determination of the Green's functions much more efficient, especially for surface faulting. This is because the difference of the dynamic and static integrands converges rapidly to zero with increasing wave- numbers, whereas the original integrands diverge in the case of a source point on the free surface. The proposed methodology is used to investigate the two most important effects in near-fault ground motions, fling step (e.g., Abrahamson, 2001) and rupture direc- tivity (e.g., Somerville et al., 1997), by paying special attention to the contribution of static and dynamic Green's functions. It is found that the fling effects stem mainly from the second integral in the modified representation theorem, which involves the static Green's function. The fling effects are dominant in the slip direction only in the vicinity of the surface fault and are negligible for buried faults, because the static Green's function attenuates rapidly with distance from the fault, r, as the order of (1/r2). Also, more importantly, when an observation point is located above a buried fault, the medium has to remain continuous, and thus cannot "fling." By contrast, the directivity effects stem mainly from the first integral, which involves the dynamic Green's function, and attenuate much more slowly than the fling, on the order from 1/r to . The directivity effects are dominant in the fault-normal direction, especially
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