Detection of Spatial and Temporal Stress Changes During the 2016 Central Italy Seismic Sequence by Monitoring the Evolution of the Energy Index

We consider approximately 23,000 microearthquakes that occurred between 2005 and 2016 in central Italy to investigate the crustal strength before and after the three largest earthquakes of the 2016 seismic sequence (i.e., the Mw 6.2, 24 August 2016 Amatrice, the Mw 6.1, 26 October 2016 Visso, and the Mw 6.5, 30 October 2016 Norcia earthquakes). We monitor the spatiotemporal deviations of observed radiated energy, ES, with respect to theoretical values, ESt, derived from a scaling model between ES and M0 calibrated for background seismicity in central Italy. These deviations, defined here as Energy Index (EI), allow us to identify in the years following the Mw 6.1, 2009 L’Aquila earthquake a progressive evolution of the dynamic properties of microearthquakes and the existence of high EI patches close to the Amatrice earthquake hypocenter. We show the existence of a crustal volume with high EI even before the Mw 6.5 Norcia earthquake. Our results agree with the previously suggested hypothesis that the Norcia earthquake nucleated at the boundary of a large patch, highly stressed by the two previous mainshocks of the sequence. We highlight the mainshocks interaction both in terms of EI and of the mean loading shear stress associated to microearthquakes occurring within the crustal volumes comprising the mainshock hypocenters. Our study shows that the dynamic characteristics of microearthquakes can be exploited as beacons of stress change in the crust and thus be exploited to monitor the seismic hazard of a region and help to intercept the preparation phase of large earthquakes

Improving the Italian strong ground motion attenuation relationship: preliminary results with an updated accelerometric data set

Strong ground motion attenuation relationships are fundamental tools for seismic hazard evaluation. In Italy the most widely used attenuation relationship is the Sabetta and Pugliese (1987 and 1996, here afters referred to as SP96) for evaluating peak ground acceleration, peak ground velocity, Arias intensity and pseudovelocity response spectra, of the Italian territory. The equation has been derived using 95 records relative to 17 earthquakes with magnitude ranging from 4.6 to 6.8. The SP96 relation is based on the strongest events since the installation of accelerometric instruments in Italy, dated 1972, such as Friuli 1976, Valnerina 1979, Irpinia 1980, and Lazio-Abruzzo 1984, which is the most recent event. In the time span 1984 – 2007 other moderate seismic events occurred in Italy, namely the East Sicily 1991, Umbria-Marche 1997- 1998, Pollino 1998 and Molise 2002, with moment magnitude > 5, and huge data sets have been obtained due to the installation of many temporary stations and digital instruments. The Umbria-Marche and Molise accelerometric data sets allowed the calculation of regional attenuation relationships that show a considerably different trend compared to the SP96. In this time span a project for an updated Italian accelerometric data base construction has been started with the aim of collecting all the acceleration time histories recorded since 1972 and re-evaluating, updating and improving event parameters, data processing and station geological/geotechnical characteristics. The aim of this research is the implementation of a new weighted regression analysis with the expanded and updated database, including coefficients to model the magnitude-dependent decay rate, the faulting mechanism, the local site effects and the magnitude-dependent variance. In addition, the fit of the SP96 equation to the new accelerometric data set spanning from 1972 to 2004 is evaluated with the aid of different statistic techniques, in order to verify the need of deriving a new attenuation equation

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

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

Supplements to Source scaling and ground motion variability along the East Anatolian Fault

<p>This folder includes the Supplements to : <strong>Source scaling and ground motion variability along the East Anatolian Fault, </strong>D. Bindi, R. Zaccarelli, F. Cotton, G. Weatherill, S. R. Kotha. published by The Seismic Record. Description of the files is provided in the README file.</p&gt

Inverse problems in seismology: source time function evaluation and site effects detection

Dottorato di ricerca in geofisica. 12. ciclo. A.a. 1998-99. Relatore Claudio EvaConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Spectral decomposition of the Engineering Strong Motion (ESM) flat file: regional attenuation, source scaling and Arias stress drop

<jats:title>Abstract</jats:title><jats:p>We perform a spectral decomposition of the Fourier amplitude spectra disseminated along with the Engineering Strong Motion (ESM) flat file for Europe and Middle East. We apply a non-parametric inversion schema to isolate source, propagation and site effects, introducing a regionalization for the attenuation model into three domains. The obtained propagation and source components of the model are parametrized in terms of geometrical spreading, quality factor, seismic moment, and corner frequency assuming a ω<jats:sup>2</jats:sup>source model. The non-parametric spectral attenuation values show a faster decay for earthquakes in Italy than in the other regions. Once described in terms of geometrical spreading and frequency-dependent quality factor, slopes and breakpoint locations of the piece-wise linear model for the geometrical spreading show regional variations, confirming that the non-parametric models capture the effects of crustal heterogeneities and differences in the anelastic attenuation. Since they are derived in the framework of a single inversion, the source spectra of the largest events which have occurred in Europe in the last decades can be directly compared and the scaling of the extracted source parameters evaluated. The Brune stress drop varies over about 2 orders of magnitude (the 5th, 50th and 95th percentiles of the ∆σ distribution are 0.76, 2.94, and 13.07 MPa, respectively), with large events having larger stress drops. In particular, the 5th, 50th and 95th percentiles for<jats:bold>M > </jats:bold>5.5 are 2.87, 6.02, and 23.5 MPa, respectively whereas, for<jats:bold>M < </jats:bold>5.5, the same percentiles are 0.73, 2.84, and 12.43 MPa. If compared to the residual distributions associated to a ground motion prediction equation previously derived using the same Fourier amplitude spectra, the source parameter and the empirical site amplification effects correlate well with the inter-event and inter-station residuals, respectively. Finally, we calibrated both non-parametric and parametric attenuation models for estimating the stress drop from the ratio between Arias intensity and significant duration. The results confirm that computing the Arias stress drop is a suitable approach for complementing the seismic moment with information controlling the source radiation at high frequencies for rapid response applications.</jats:p&gt