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Maercklin, Nils
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Maercklin, Nils
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- PublicationOpen AccessConverted phase identification and retrieval of Vp/Vs ratios from move-out reflection analysis: application to the Campi Flegrei caldera(2007)
; ; ; ; ; ;Vassallo, M.; Dipartimento di Scienze Fisiche, Università di Napoli Federico II (RISSC-Lab), Italy ;Zollo, A.; Dipartimento di Scienze Fisiche, Università di Napoli Federico II (RISSC-Lab), Italy ;Dello Iacono, D.; Dipartimento di Scienze Fisiche, Università di Napoli Federico II (RISSC-Lab), Italy ;Maercklin, N.; Dipartimento di Scienze Fisiche, Università di Napoli Federico II (RISSC-Lab), Italy ;Virieux, J.; Institute Geosciences Azur, CNRS, Nice, France; ; ; ; Here, we propose a method for the determination of Vp/Vs ratios in a horizontally layered propagation media using maximization of a coherency function along theoretical travel-times of PS reflected phases. The theoretical travel-times are computed using the information about the propagation media that is extracted by velocity analysis or by topographic analysis performed on the first arrivals. The method is also a valid tool for the identification of the PS phases associated with a fixed seismic reflector, and it is particularly suitable for data that is stored in common mid-point and common conversion point bin- ning; for this kind of data the hypothesis of horizontally and layered media can usually be verified. We applied the method to both simulated and real datasets. The use of the real data that was acquired in the Campi Flegrei caldera (southern Italy) allowed us to estimate a relatively high Vp/Vs ratio (3.5 ± 0.6) for a very shallow layer (maximum depth, 600 m). This hypothesis has been tested by theoretical rock physical modeling of the Vp/Vs ratios as a function of porosity, suggesting that the shallow layer appears to be formed of unconsolidated, water-saturated, volcanic and marine sediments that filled Pozzuoli Bay during the post-caldera activity.228 209 - PublicationRestrictedFrom Induced Seismicity to Direct Time-Dependent Seismic Hazard(2012-12)
; ; ; ; ;Convertito, V.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Maercklin, N.; AMRA S.c.a.r.l. Analysis and Monitoring of Environmental Risk ;Sharma, N.; Dipartimento di Scienze Fisiche Università degli Studi di Napoli “Federico II” ;Zollo, A.; Dipartimento di Scienze Fisiche Università degli Studi di Napoli “Federico II”; ; ; The growing installation of industrial facilities for subsurface exploration worldwide requires continuous refinements in understanding both the mechanisms by which seismicity is induced by field operations and the related seismic hazard. Particularly in proximity of densely populated areas, induced low-to-moderate magnitude seismicity characterized by high-frequency content can be clearly felt by the surrounding inhabitants and, in some cases, may produce damage. In this respect we propose a technique for time-dependent probabilistic seismic-hazard analysis to be used in geothermal fields as a monitoring tool for the effects of on-going field operations. The technique integrates the observed features of the seismicity induced by fluid injection and extraction with a local ground-motion prediction equation. The result of the analysis is the time-evolving probability of exceedance of peak ground acceleration (PGA), which can be compared with selected critical values to manage field operations. To evaluate the reliability of the proposed technique, we applied it to data collected in The Geysers geothermal field in northern California between 1 September 2007 and 15 November 2010. We show that the period considered the seismic hazard at The Geysers was variable in time and space, which is a consequence of the field operations and the variation of both seismicity rate and b-value.We conclude that, for the exposure period taken into account (i.e., two months), as a conservative limit, PGA values corresponding to the lowest probability of exceedance (e.g., 30%) must not be exceeded to ensure safe field operations. We suggest testing the proposed technique at other geothermal areas or in regions where seismicity is induced, for example, by hydrocarbon exploitation or carbon dioxide storage.193 30 - PublicationRestrictedThe Effectiveness of a Distant Accelerometer Array to Compute Seismic Source Parameters: The April 2009 L'Aquila Earthquake Case History(2011)
; ; ; ; ; ; ; ; ;Maercklin, N.; Dipartimento di Scienze Fisiche Unità di Ricerca in Sismologia Sperimentale e Computazionale Università degli Studi di Napoli Federico II ;Zollo, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia ;Orefice, A.; Dipartimento di Scienze Fisiche Unità di Ricerca in Sismologia Sperimentale e Computazionale Università degli Studi di Napoli Federico II ;Festa, G.; Dipartimento di Scienze Fisiche Unità di Ricerca in Sismologia Sperimentale e Computazionale Università degli Studi di Napoli Federico II ;Emolo, A.; Dipartimento di Scienze Fisiche Unità di Ricerca in Sismologia Sperimentale e Computazionale Università degli Studi di Napoli Federico II ;De Matteis, R.; Dipartimento di Studi Geologici e Ambientali Università degli Studi del Sannio 82100 Benevento, Italy ;Delouis, B.; GeoAzur—Observatoire de la Côte d’Azur Centre National de la Recherche Scientifique—Université de Nice Sophia Antipolis 250, Rue Albert Einstein 06560 Valbonne, France ;Bobbio, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione OV, Napoli, Italia; ; ; ; ; ; ; The seismic sequence that occurred in the Abruzzo Apennines near L’Aquila (Italy) in April 2009 caused extensive damage and a large number of casual- ties (more than 300). The earthquake struck an area in the Italian Apennines chain where several faults, belonging to adjacent seismotectonic domains, create a complex tectonic regime resulting from the interaction among regional stress buildup, local stress changes caused by individual earthquakes, and viscous-elastic stress relaxation. Understanding such complex interaction in the Apennines can lead to a large step for- ward in the seismic risk mitigation in Italy. The Abruzzo earthquake has been very well recorded by interferometric synthetic aperture radar (InSAR) data, much better than the first Italian earthquake ever recorded by satellites, namely, the 1997 Umbria–Marche earthquake. ENVISAT (ENVIronmental SATellite) data for the Abruzzo earthquake are, in fact, very clear and allow an accurate reconstruction of the faulting mechanism. We present here an accurate inversion of vertical deformation data obtained by ENVISAT images, aimed to give a detailed reconstruction of the fault geometry and slip distribu- tion. The resulting fault models are then used to compute, by a suitable theoretical model based on the elastic dislocation theory, the stress changes induced on the neigh- boring faults. The correlation of the subsequent mainshocks and aftershocks of the Abruzzo sequence with the volumes undergoing increasing Coulomb stress clearly evidence the triggering effect of coseismic stress changes on further seismicity. More- over, this analysis put in evidence which seismotectonic domains have been more heav- ily charged by stress released by the Abruzzo mainshocks. The most important faults significantly charged by the Abruzzo sequence belong to the Sulmona and Avezzano tectonic domains. Taking into account the average regional stress buildup in the area, the positive Coulomb stress changes caused by this earthquake can be seen as antici- pating the next earthquakes in the neighboring domains of 15–20 yr.315 22 - PublicationRestrictedPredicting Ground Motion from Induced Earthquakes in Geothermal Areas(2013)
; ; ; ; ; ; ; ; ; ; ;; ;; ; ; ;Induced seismicity from anthropogenic sources can be a significant nuisance to a local population and in extreme cases lead to damage to vulnerable structures. One type of induced seismicity of particular recent concern, which, in some cases, can limit development of a potentially important clean energy source, is that associated with geothermal power production. A key requirement for the accurate assessment of seismic hazard (and potential eventual risk) is a ground-motion prediction equation (GMPE) that predicts the level of earthquake shaking (in terms of, for example, peak ground acceleration) of an earthquake of a certain magnitude at a particular distance. Few such models currently exist in regards to geothermal-related seismicity and consequently the evaluation of seismic hazard in the vicinity of geothermal power plants is associated with high uncertainty. Various ground-motion datasets of induced and natural seismicity (from Basel, Geysers, Hengill, Roswinkel, Soultz, and Voerendaal) were compiled and processed, and moment magnitudes for all events were recomputed homogeneously. These data are used to show that ground motions from induced and natural earthquakes cannot be statistically distinguished. Empirical GMPEs are derived from these data and it is shown that although they have similar characteristics to other recent GMPEs for natural and mining-related seismicity, the standard deviations are higher. Subsequently stochastic models to account for epistemic uncertainties are developed based on a single corner frequency and with parameters constrained by the available data. Predicted ground motions from these models are fitted with functional forms to obtain easy-to-use GMPEs. These are associated with standard deviations derived from the empirical data to characterize aleatory variability. As an example, we demonstrate the potential use of these models using data from Campi Flegrei.89 2 - PublicationOpen AccessAnalysis of PS-to-PP amplitude ratios for seismic reflector characterisation: method and application(2007)
; ; ;Maercklin, N.; RISSC, Italy ;Zollo, A.; RISSC, Italy; Elastic parameters derived from seismic reflection data provide information on the lithological contrast at an interface and support the geological interpretation.We present a method to estimate elastic parameter contrasts at a given interface in a 1-D layered medium from PS-to-PP amplitude ratios. The method is applied to synthetic data to demonstrate its possibilities and limitations. First results for real data acquired in the Campi Flegrei caldera (southern Italy) reveal a gas-bearing layer at around 3 km depth and indicate a strong negative velocity contrast at 7.5 km depth, possibly related to the presence of partial melt.212 216