ALBERT

Description: We present an approach to infer the slip and rupture velocity distributions on the fault plane from the non-linear inversion of the apparent source time functions, obtained from the empirical Green's function deconvolution method. The main advantage of this technique is that it allows overcoming, in the forward modelling, the limitations related to the computation of the Green's function, as the choice of a correct and reliable earth propagation model. We perform a parameter resolution and uncertainty study, which is based on the analysis of the misfit function in the neighbourhood of the best-fitting model. In this paper, we present the results obtained by applying the technique to synthetic and real records from an M w 4 event which occurred during the 2009 L’Aquila (central Italy) aftershock sequence. Results show a heterogeneous slip distribution, characterized by two main high slip patches located NW of the hypocentre and an average slip of 3.7 cm, corresponding to a seismic model of about 0.82  x 10 15 Nm.

Description: The space–time distribution of coseismic slip of the 2011 February 21, M w 6.2, Christchurch earthquake, New Zealand, is explored, differently from all previous studies, through a joint inversion of geodetic and strong-motion data. The geodetic data consist of both global position system (GPS), from campaign and continuous stations, and synthetic aperture radar (SAR) interferograms from two ascending satellite tracks. The strong motion data consist of 10 stations located in the Canterbury plains, these stations offering a good azimuthal coverage of the event. The kinematic rupture model for the analysed event was obtained using the parametrization and non-linear inversion scheme proposed by Delouis et al. In particular, for any subfault we explore for the local source time function (local slip history), slip direction and rupture onset time. The geometry of the fault plane used for the kinematic inversion is inferred from the analysis of the geodetic data. To validate our results we perform a resolution study for both the single and complete data sets, and an errors analysis of our final kinematic rupture model. Considering the complexity highlighted by superficial deformation data, we adopted a fault model consisting of two partially overlapping segments, with dimensions 15  x 11 and 7  x 7 km 2 , corresponding to different faulting types. This two-fault model, instead of single-fault model, is needed to reconstruct the complex shape of the superficial deformation data. The total seismic moment resulting from the joint inversion is 3.0  x 1025 dyne · cm ( M w  = 6.2) with an average rupture velocity of 2.0 km s –1 .

Description: Automated location of seismic events is a very important task in microseismic monitoring operations as well for local and regional seismic monitoring. Since microseismic records are generally characterized by low signal-to-noise ratio, automated location methods are requested to be noise robust and sufficiently accurate. Most of the standard automated location routines are based on the automated picking, identification and association of the first arrivals of P and S waves and on the minimization of the residuals between theoretical and observed arrival times of the considered seismic phases. Although current methods can accurately pick P onsets, the automatic picking of the S onset is still problematic, especially when the P coda overlaps the S wave onset. In this paper, we propose a picking free earthquake location method based on the use of the short-term-average/long-term-average (STA/LTA) traces at different stations as observed data. For the P phases, we use the STA/LTA traces of the vertical energy function, whereas for the S phases, we use the STA/LTA traces of a second characteristic function, which is obtained using the principal component analysis technique. In order to locate the seismic event, we scan the space of possible hypocentral locations and origin times, and stack the STA/LTA traces along the theoretical arrival time surface for both P and S phases. Iterating this procedure on a 3-D grid, we retrieve a multidimensional matrix whose absolute maximum corresponds to the spatial coordinates of the seismic event. A pilot application was performed in the Campania-Lucania region (southern Italy) using a seismic network (Irpinia Seismic Network) with an aperture of about 150 km. We located 196 crustal earthquakes (depth 〈 20 km) with magnitude range 1.1 〈 M L  〈 2.7. A subset of these locations were compared with accurate manual locations refined by using a double-difference technique. Our results indicate a good agreement with manual locations. Moreover, our method is noise robust and performs better than classical location methods based on the automatic picking of the P and S waves first arrivals.

Description: Anatomy of a microearthquake sequence on an active normal fault Scientific Reports 2, 16052012 doi: 10.1038/srep00410 T. A. Stabile C. Satriano A. Orefice G. Festa A. Zollo The analysis of similar earthquakes, such as events in a seismic sequence, is an effective tool with which to monitor and study source processes and to understand the mechanical and dynamic states of active fault systems. We are observing seismicity that is primarily concentrated in very limited regions along the 1980 Irpinia earthquake fault zone in Southern Italy, which is a complex system characterised by extensional stress regime. These zones of weakness produce repeated earthquakes and swarm-like microearthquake sequences, which are concentrated in a few specific zones of the fault system. In this study, we focused on a sequence that occurred along the main fault segment of the 1980 Irpinia earthquake to understand its characteristics and its relation to the loading-unloading mechanisms of the fault system.

Description: We present an evolutionary approach for magnitude estimation for earthquake early warning based on real-time inversion of displacement spectra. The Spectrum Inversion (SI) method estimates magnitude and its uncertainty by inferring the shape of the entire displacement spectral curve based on the part of the spectra constrained by available data. The method consists of two components: 1) estimating seismic moment by finding the low frequency plateau Ω0, the corner frequency fc and attenuation factor (Q) that best fit the observed displacement spectra assuming a Brune ω2 model, and 2) estimating magnitude and its uncertainty based on the estimate of seismic moment. A novel characteristic of this method is that is does not rely on empirically derived relationships, but rather involves direct estimation of quantities related to the moment magnitude. SI magnitude and uncertainty estimates are updated each second following the initial P detection. We tested the SI approach on broadband and strong motion waveforms data from 158 Southern California events, and 25 Japanese events for a combined magnitude range of 3 ≤ M ≤ 7. Based on the performance evaluated on this dataset, the SI approach can potentially provide stable estimates of magnitude within 10 seconds from the initial earthquake detection.

Description: Article Being able to predict the final size of an earthquake while rupture is ongoing is a largely debated scientific problem. Here, the authors suggest that the evolution of P-wave peak displacement holds information regarding the early stage of the rupture process and may be a proxy for the final size of the event. Nature Communications doi: 10.1038/ncomms4958 Authors: S. Colombelli, A. Zollo, G. Festa, M. Picozzi

Description: During the 1982–1984 bradyseismic crises in the Campi Flegrei area (Italy), the University of Wisconsin deployed a network of seismological stations to record local earthquakes. In order to analyse the potential of the recorded data in terms of tomographic imaging, a blind test was recently set up and carried out in the framework of a research project. A model representing a hypothetical 3D structure of the area containing the Campi Flegrei caldera was also set up, and a synthetic dataset of time arrivals was in turn computed. The synthetic dataset consists of several thousand P- and S-time arrivals, computed at about fourteen stations. The tomographic inversion was performed by four independent teams using different methods. The teams had no knowledge of either the input velocity model or the earthquake hypocenters used to create the synthetic dataset. The results obtained by the different groups were compared and analysed in light of the true model. This work provides a thorough analysis of the earthquake tomography potential of the dataset recording the seismic activity at Campi Flegrei in the 1982–1984 period. It shows that all the tested earthquake tomography methods provide reliable low-resolution images of the background velocity field of the Campi Flegrei area, but with some differences. However, none of them succeeds in detecting the hypothetical structure details (i.e. with a size smaller than about 1.5–2 km), such as a magmatic chamber 4 km deep and especially the smaller, isolated bodies, which represent possible magmatic chimneys and intrusions.

Description: During the 1982–1984 bradyseismic crises in the Campi Flegrei area (Italy), the University of Wisconsin deployed a network of seismological stations to record local earthquakes. In order to analyse the potential of the recorded data in terms of tomographic imaging, a blind test was recently set up and carried out in the framework of a research project. A model representing a hypothetical 3D structure of the area containing the Campi Flegrei caldera was also set up, and a synthetic dataset of time arrivals was in turn computed. The synthetic dataset consists of several thousand P- and S-time arrivals, computed at about fourteen stations. The tomographic inversion was performed by four independent teams using different methods. The teams had no knowledge of either the input velocity model or the earthquake hypocenters used to create the synthetic dataset. The results obtained by the different groups were compared and analysed in light of the true model. This work provides a thorough analysis of the earthquake tomography potential of the dataset recording the seismic activity at Campi Flegrei in the 1982–1984 period. It shows that all the tested earthquake tomography methods provide reliable low-resolution images of the background velocity field of the Campi Flegrei area, but with some differences. However, none of them succeeds in detecting the hypothetical structure details (i.e. with a size smaller than about 1.5–2 km), such as a magmatic chamber 4 km deep and especially the smaller, isolated bodies, which represent possible magmatic chimneys and intrusions.

Description: [1]  The south of the Iberian Peninsula is a region in which large, damaging earthquakes occur separated by long time intervals. An example was the great 1755 Lisbon earthquake (intensity I max  = X) which occurred SW of S. Vicente Cape (SW Iberian Peninsula). Due to this risk of damaging earthquakes, the implementation of Earthquake Early Warning System (EEWS) technologies is of considerable interest. With the aim of investigating the feasibility of an EEWS in this region of the Iberian Peninsula, empirical scaling relationships have been derived between the early warning parameters and the earthquake size and/or its potential damaging effects for this region. An appropriate and suitable strategy is proposed for an EEWS in the SW Iberian Peninsula, which takes into account the limitations of the existing seismological networks.