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Malagnini, Luca
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Malagnini, Luca
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luca.malagnini@ingv.it
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- PublicationOpen AccessMoment magnitude and local magnitude of small earthquakes nucleating along a low angle normal fault in the Upper Tiber Valley (Italy)(2015-12-18)
; ; ; ; ; ; ; The computation of the moment magnitude of small earthquakes (MW < 3) allows the investigation of key aspects of the physics of the seismic source, like the scaling properties of earthquakes. In order to do that, we analyse the crustal propagation of seismic waves in the Upper Tiber Valley (Northern Apennines, Italy) using 38,000 high-resolution broadband seismograms from 1192 well-located micro-earthquakes that occurred between 2010 and 2014, in the local magnitude range -1.0 ≤ ML ≤ 3.8. Because we use weak-motion data, we maximize the signal-to-noise ratios by applying a complex technique based on Random Vibration Theory (RVT). Our analysis of the data produced two main results: i) we are able to calculate the seismic moment (and moment magnitude) for very small events, down to at least MW = -1.5. ii) we determined a relationship between MW and ML , and use RVT to show that ML ~ log10 (M0) for small earthquakes.93 84 - PublicationOpen AccessTime Variability of crustal attenuation during the Amatrice-Visso-Norcia earthquake sequence in the Central Apennines (Italy)(2018-12-10)
; ; ; ; ; ; ; ; ; ; ; Over the last decade our work has been mostly about reducing uncertainties over spectral measurements in seismology (e.g. Malagnini and Munafò, 2018; Malagnini and Dreger, 2016; Munafò et al., 2016; Akinci et al., 2014). Here we measure time-domain peak values from narrow bandpass-filtered time histories and transform them into spectral estimates by using the theoretical results of Random Vibration Theory (Cartwright and Longuet-Higgins, 1956) and the Parseval Theorem. We develop a novel approach to quantify time domain fluctuations of highfrequency seismic attenuation and apply it to a massive data set of seismic waveforms from the Central Apennines in Italy, which includes recordings spanning the recent earthquake sequence of Amatrice-Visso-Norcia (2016-2017). Our observations show that the crustal seismic wave propagation in the region is strongly affected by transients triggered by the main events. The time varying attenuation is probably due to the associated migration of crustal fluids, in addition to seasonal oscillations related to precipitation-induced variations of crustal stresses. We also observe oscillation periods in the attenuation time series corresponding to solid Earth tides. Sensitivity to tides is stronger in the aftermath of the mainshocks, indicating an important role played by rock damage.117 28 - PublicationRestrictedRegional body-wave attenuation using a coda source normalization method: application to MEDNET records of earthquakes in Italy(2007)
; ; ; ; ;Walter, W.; Lawrence-Livermore National Laboratory ;Mayeda, K.; Weston Geophysical Corporation, Lexington, Massachusetts, USA. ;Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Scognamiglio, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ; ; We develop a new methodology to determine apparent attenuation for the regional seismic phases Pn, Pg, Sn, and Lg using coda-derived source spectra. The apparent Q, combining path and site attenuation, is determined from the difference between the geometrical spreading-corrected amplitude and the independently determined source spectra derived from the coda methodology. We apply the technique to 50 earthquakes with magnitudes greater than 4 in central Italy as recorded by MEDNET broadband stations around the Mediterranean at local-to-regional distances. A power law attenuation of the form Q(f) = Qof^gamma fit all the phases quite well over the 0.5 to 8 Hz band. The measured apparent Q values are quite repeatable from event to event. Finding the attenuation function in this manner guarantees a close match between inferred source spectra from direct waves and coda techniques. This is important if coda and direct wave amplitudes are to produce consistent seismic results.153 26 - PublicationOpen AccessValutazione della risposta sismica della citta' di Firenze alle forti scosse dell'Appennino Umbro-Marchigiano, Settembre - Ottobre 1997(1997)
; ; ; ; ; ; ;Braun, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Donati, S. ;Holtz, C.; Osservatorio Ximeniano ;Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Palombo, B.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Rovelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia; ;; ; ; 164 123 - PublicationOpen AccessSmart working e Ricerca: il punto di vista dei Ricercatori e Tecnologi dell’INGV(2021-05-19)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Obiettivi: Le finalità di questo articolo sono quelle di sottolineare le specificità della Ricerca rispetto alla amministrazione. Metodologia: è stata svolta un’analisi qualitativa giuridico-normativa e una indagine online quantitativa a 585 ricercatori e tecnologi dell’INGV sullo smart working. Risultati: nell’articolo vengono richiamate le norme che affermano come le attività di ricerca e le attività gestionali debbono avere una valutazione diversa. Inoltre, il CCNL della sezione Ricercatori e Tecnologi già rende “smart” e “agile” il lavoro di ricerca senza ricadere nella legge sullo smart working. Le risposte all’indagine mostrano una forte coesione nel rivendicare i principi di autonomia e libertà della ricerca. Limiti e implicazioni: negli EPR si fa Ricerca e la Ricerca ha bisogno di flessibilità e specificità organizzativa rispetto ad una P.A. prevalentemente amministrativa e lo smart working mal si adatta al mondo della Ricerca. Originalità: il percorso bottom-up di rivendicazione dei diritti della ricerca, attraverso interviste online, è originale e innovativo per evidenziare l’analisi delle criticità del lavoro agile che non deve essere applicato senza considerare il modello rispondente alle proprie esigenze e caratteristiche.768 88 - PublicationRestrictedMws of Seismic Sources udder Thick sedimentsMoment magnitudes differing by up to 0.5 units have been published for the same events of the 2012 Ferrara seismic sequence. With respect to the mainshock that occurred on 20 May 2012, results by Malagnini et al. (2012) and Pondrelli et al. (2012) represent opposite extremes: although the former used model Padania, a region-specific velocity structure based on all the available geological and geophysical information from local studies, the latter used a global crustal model with a set of phase corrections calibrated over the central Apennines by Ekström et al. (1998). Model Padania well reproduces the observed dispersion of surface-wave group velocities in a band of shorter periods, between 33 and 100 s, whereas Pondrelli et al. (2012) performed their inversions in the 50–150 s period band. Here, we show that because surface waves generated within the thick sediments of the Po river floodplain dominated the seismograms, the source excitation terms that came out of a regression scheme performed on the ground motions recorded during the sequence were systematically affected by a broadband increase of the spectral amplitudes at frequencies below 0.4 Hz (frequency range of the regressions: from 0.1 to 22.5 Hz). As a consequence, the two largest events of the sequence share a common true moment magnitude Mw ∼ 5.6, even though their enhanced spectral level from 0.1 to 0.4 Hz is consistent with Mw ∼ 6.0.
169 4 - PublicationRestrictedEstimating Absolute Site Effects(2004)
; ; ; ; ;Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Mayeda, K.; Lawrence Livermore National Laboratory Ground-based Nuclear Explosion Monitoring Program ;Akinci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Bragato, P. L.; Istituto Nazionale di Oceanografia e di Geofisica Sperimentale Centro di Ricerche Sismologiche; ; ; We use previously determined direct-wave attenuation functions as well as stable, coda-derived source excitation spectra to isolate the absolute S-wave site effect for the horizontal and vertical components of weak ground motion. We use selected stations in the seismic network of the eastern Alps. A detailed regional attenuation function derived by Malagnini et al. (2002) for the region is used to correct the vertical and horizontal S-wave spectra. These corrections account for the gross path effects (i.e., all distance-dependent effects), although the source and site effects are still present in the distance-corrected spectra. The main goal of this study is to isolate the absolute site effect (as a function of frequency) by removing the source spectrum (moment-rate spectrum) from the distance-corrected S-wave spectra. Typically, removing the S-wave source spectrum is difficult because of inadequate corrections for the source radiation pattern, directivity, and random interference. In addition to complexities near the source, 2D and 3D structure beneath the recording site will result in an azimuth-dependent site effect. Since the direct wave only samples a narrow range in takeoff and backazimuth angles, multistation averaging is needed to minimize the inherent scatter. Because of these complicating effects, we apply the coda methodology outlined by Mayeda et al. (2003) to obtain stable moment-rate spectra. This methodology provides source amplitude and derived source spectra that are a factor of 3–4 times more stable than those derived from direct waves. Since the coda is commonly thought of as scattered energy that samples all ray parameters and backazimuths, it is not very sensitive to the source radiation pattern and 3D structure. This property makes it an excellent choice for use in obtaining average parameters to describe the source, site, and path effects in a region. Due to the characteristics of the techniques used in this study, all the inverted quantities are azimuthally averaged, since the azimuthal information is lost in the processing. Our results show that (1) all rock sites exhibited deamplification phenomena due to absorption at frequencies ranging between 0.5 and 12 Hz (the available bandwidth), on both the horizontal and vertical components; (2) rock-site transfer functions showed large variability at high-frequency; (3) vertical-motion site transfer functions show strong frequency dependence; (4) horizontal-to-vertical (H/V) spectral ratios do not reproduce the charactersitics of the true horizontal site transfer functions; and (5) traditional, relative site terms obtained by using reference rock sites can be misleading in inferring the behaviors of true site transfer functions, since most rock sites have nonflat responses due to shallow heterogeneities resulting from varying degrees of weathering. Our stable source spectra are used to estimate the total radiated seismic energy and to compare against similar results obtained for different regions of the world. We find that the earthquakes in this region exhibit nonconstant dynamic stress drop scaling, which gives further support for a fundamental difference in rupture dynamics between small and large earthquakes.193 21 - PublicationOpen AccessPrediction of High-Frequency Ground Motion Parameters Based on Weak Motion Data(InTechOpen, 2012)
; ; ; ; ;D'Amico, S.; MALTA ;Akinci, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Galea, P.; ; ; Large earthquakes that have occurred in recent years in densely populated areas of the world (e.g. Izmit, Turkey, 17 August 1999; Duzce, Turkey, 12 November 1999; Chi-Chi, Taiwan 20 September 1999, Bhuj, India, 26 January 2001; Sumatra 26 December 2004; Wenchuan, China, May 12, 2008; L’Aquila, Italy, April 6, 2009; Haiti, January 2010 Turkey 2011) have dramatically highlighted the inadequacy of a massive portion of the buildings erected in and around the epicentral areas. For example, the Izmit event was particularly destructive because a large number of buildings were unable to withstand even moderate levels of ground shaking, demonstrating poor construction criteria and, more generally, the inadequacy of the application of building codes for the region. During the L’Aquila earthquake (April, 06, 2009; Mw=6.3) about 300 persons were killed and over 65,000 were left homeless (Akinci and Malagnini, 2009). It was the deadliest Italian earthquake since the 1980, Irpinia earthquake, and initial estimates place the total economic loss at over several billion Euros. Many studies have already been carried out describing the rupture process and the characteristics of local site effects for this earthquake (e.g. D’Amico et al., 2010a; Akinci et al., 2010). It has been observed that many houses were unable to withstand the ground shaking. Building earthquake-resistant structures and retrofitting old buildings on a national scale may be extremely costly and may represent an economic challenge even for developed western countries, but it is still a very important issue (Rapolla et al., 2008). Planning and design should be based on available national hazard maps, which, in turn, must be produced after a careful calibration of ground motion predictive relationships (Kramer, 1996) for the region. Consequently, the assessment of seismic hazard is probably the most important contribution of seismology to society. The prediction of the earthquake ground motion has always been of primary interest for seismologists and structural engineers. For engineering purposes it is necessary to describe the ground motion according to certain number of ground motion parameters such as: amplitude, frequency content and duration of the motion. However it is necessary to use more than one of these parameters to adequately characterize a particular ground motion. Updating existing hazard maps represents one of the highest priorities for seismologists, who contribute by recomputing the ground motion and reducing the related uncertainties. The quantitative estimate of the ground motion is usually obtained through the use of the so-called predictive relationships (Kramer, 1996), which allow the computation of specific ground-motion parameter as a function of magnitude, distance from the source, and frequency and they should be calibrated in the region of interest. However this is only possible if seismic records of large earthquakes are available for the specific region in order to derive a valid attenuation relationship regressing a large number of strong-motion data (e.g. Campbell and Bozorgnia, 1994; Boore et al., 1993; Ambraseys et al., 1996, Ambraseys and Simpson, 1996; Sabetta and Pugliese, 1987, 1996; Akkar and Bommer 2010). For the Italian region the most used attenuation relationships are those obtained by Sabetta and Pugliese (1987, 1996) regressing a few data recorded for earthquakes in different tectonic and geological environments. It has been shown in several cases that it is often not adequate to reproduce the ground motion in each region of the country using a single model. Furthermore the different crustal properties from region to region play a key role in this kind of studies. However, the attenuation properties of the crust can be evaluated using the background seismicity as suggested by Chouet et al. (1978) and later demonstrated by Raoff et al. (1999) and Malagnini et al (2000a, 2007). In other words, it becomes possible to develop regionallycalibrated attenuation relationships even where strong-motion data are not available. One of the purposes of this work is to describe quantitatively the regional attenuation and source characteristics for constraining the amplitude of strong motion expected from future earthquakes in the area. In this work we describe how to use the background seismicity to perform the analysis (details in Malagnini et. 2000a, 2007). In particular, this chapter describes the procedures and techniques to study the ground motion and will focus on describing both strong motion attenuation relationships and the techniques used to derive the ground motion parameters even when strong ground motion data are not available. We will present the results obtained for different regions of the Italian peninsula, showing that the attenuation property of the crust and of the source can significantly influence the ground motion. In addition, we will show that stochastic finite-fault modeling based on a dynamic frequency approach, coupled with field investigations, confirms to be a reliable and practical method to simulate ground motion records of moderate and large earthquakes especially in regions prone to widespread structural damage.181 168 - PublicationRestrictedA break in self-similarity in the Lunigiana-Garfagnana region (northern Apennines)(2005)
; ; ; ; ; ; ; ; ; In this study, stable source parameters are determined for small earthquakes in the Lunigiana-Garfagnana region using an empirical methodology based on coda envelope measurements that are significantly less affected by the source radiation pattern, directivity, and heterogeneous path variation, than traditional direct wave measurements. We find evidence that the scaled energy ~e(=ER/M0) increases with moment and source spectra are not self-similar for 3.0 Mw 4.6. The calibration procedure allows for an independent check of three important features: (1) that the empirical path corrections provide consistent amplitude measurements for the same event at different stations, distances, and azimuths; (2) that the long-period levels of the source spectra are consistent with independent M0 derived from long-period waveform modeling; (3) that small event spectra are flat below a conservative estimate of the corner frequency and thereby effectively accounting for near-site attenuation. Citation: Morasca, P., K. Mayeda, R. Go¨k, L. Malagnini, and C. Eva (2005), A break in self-similarity in the Lunigiana-Garfagnana region (northern Apennines)152 1 - PublicationOpen AccessRegional Moment Tensors of the 2009 L'Aquila Earthquake Sequence(2011)
; ; ; ;Herrmann, R.; Saint Louis University ;Malagnini, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;Munafo, I.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma1, Roma, Italia ;; Broadband waveform inversion of ground velocities in the 0.02 0.10 Hz frequency band is successfully applied to 181 earthquakes with ML ≥ 3 of the April, 2009, L'Aquila, Italy, earthquake sequence. This was made possible by the development of a new regional crustal velocity model constrained by deep crustal profiles, surfacewave dispersion and teleseismic Pwave receiver functions and tested through waveform fit. Although all earthquakes exhibit normal faulting, with the fault plane dipping southwest at about 55º for the majority of events, a subset of events had much shallower dips. The issue of confidence in the derived parameters was investigated by applying the same inversion procedure by two groups who subjectively selected different traces for inversion. The unexpected difficulty in modeling the regional broadband waveforms of the mainshock as a point source was investigated through an extensive finitefault modeling of broadband velocity and accelerometer data, which placed the location of major moment release updip and about 47 seconds after the initial firstarrival hypocentral parameters.285 2221