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Ekström, G.
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Ekström, G.
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- PublicationRestrictedSeismic moment tensors of the April 2009, L'Aquila (Central Italy), earthquake sequence(2010-01)
; ; ; ; ; ; ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Ekstrom, G.; Lamont-Doherty Earth Observatory Columbia University NY USA ;Olivieri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione CNT, Roma, Italia ;Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia; ; ; ; ; On 2009 April 6, the Central Apennines were hit by an Mw= 6.3 earthquake. The region had been shaken since 2008 October by seismic activity that culminated in two foreshocks with Mw > 4, 1 week and a few hours before the main shock. We computed seismic moment tensors for 26 events with Mw between 3.9 and 6.3, using the Regional Centroid Moment Tensor (RCMT) scheme. Most of these source parameters have been computed within 1 hr after the earthquake and rapidly revised successively. The focal mechanisms are all extensional, with a variable and sometimes significant strike-slip component. This geometry agrees with the NE–SW extensional deformation of the Apennines, known from previous seismic and geodetic observations. Events group into three clusters. Those located in the southern area have larger centroid depths and a wider distribution of T-axis directions. These differences suggest that towards south a different fault system was activated with respect to the SW-dipping normal faults beneath L’Aquila and more to the north.240 24 - PublicationRestrictedEuropean–Mediterranean Regional Centroid Moment Tensor catalog: Solutions for years 2003 and 2004(2007-05-11)
; ; ; ; ; ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Ekström, G.; Lamont-Doherty Earth Observatory, Columbia University, Palisades, NY, USA ;Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia; ; ; ; We present an update, for years 2003 and 2004, of the European– Mediterranean Regional Centroid Moment Tensor (RCMT) catalog that we maintain since 1997. This update adds 177 new solutions to the database, relating to moderate-magnitude (4.5 ≤M<5.5) earthquakes. About 30% of our new solutions also appear in the global CMT catalog: comparison of the two independent determinations generally shows very good agreement.Within the time span covered, the most noticeable seismic sequences occurred in Northern Africa (Boumerdes, Algerian coast in 2003 and Al Hoceima, Morocco in 2004) and in Southern Greece and Dodecanese region (August 2003 and 2004). The complete RCMT catalog for the European and Mediterranean region now covers 8 years, and contains about 600 solutions.183 21 - PublicationRestrictedEuropean-Mediterranean regional centroid-moment tensor catalog: solutions for years 2001 and 2002(2004)
; ; ; ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Ekström, G.; Department of Earth and Planetary Sciences, Harvard University, Harvard, USA; ; We present regional centroid-moment tensor (RCMT) solutions for 168 moderate-magnitude earthquakes that occurred in the European-Mediterranean region during 2001 and 2002. Events with moment magnitudes as low as 4.0 were successfully analyzed, although this low threshold is only achievable in regions with the best azimuthal coverage and with stations at a few hundred kilometers distance. Earthquakes with focal depths from 10 to more than 200 km were analyzed. Comparison with standard Harvard CMTs, when available, shows good agreement. The solutions shown in this paper represent an addition to the European-Mediterranean RCMT catalog that we are maintaining. The RCMT catalog now spans 6 years, from 1997 to 2002, and contains 420 solutions. We also outline the main seismic sequences that occurred in the European-Mediterranean region during 2001–2002.203 32 - PublicationOpen AccessTeleseismic analysis of the 1990 and 1991 earthquakes near Potenza(1994-12)
; ;Ekstrom, G.; Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, U.S.A.Analysis of the available teleseismic data for two moderate earthquakes near the town of Potenza in the Southern Apennines shows that both involve strike-slip faulting on a plane oriented approximately east-west. Only the larger, 5 May 1990, earthquake is sufficiently large for analysis by conventional teleseismic waveform inversion methods, and is seen to consist of a foreshock followed 11 seconds later by the main release of moment. The focal mechanism and seismic moment of the 26 May 1991 earthquake is determined by quantitative comparison of its 15-60 s period surface waves with those generated by the 5 May 1990 event. The focal mechanisms for the two events are found to be very similar. The 1991 earthquake has a scalar moment that is approximately 18% that of the 1990 mainshock. Comparison of higher frequency P waves for the two events, recorded at regional distance, shows that the ratio of trace amplitudes is smaller than the ratio of scalar moments, suggesting that the stress drop for the 1991 event is distinctly smaller than for the 1990 mainshock.146 148 - PublicationRestrictedEuropean–Mediterranean Regional Centroid Moment Tensor catalog: Solutions for 2005–2008(2011-03-10)
; ; ; ; ; ; ; ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Ekstrom, G.; Lamont-Doherty Earth Observatory,Columbia University, Palisades, NY, USA ;Postpischl, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Vannucci, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Boschi, E.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione AC, Roma, Italia; ; ; ; ; ; Since 1997 we maintain and systematically update the European–Mediterranean Regional Centroid Moment Tensor (RCMT) catalog, which contains seismic-moment tensors for earthquakes with moderate magnitude (4.5283 43 - PublicationRestrictedThe Italian CMT dataset from 1977 to present(2006)
; ; ; ; ; ; ;Pondrelli, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Salimbeni, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Ekstrom, G.; Department of Earth and Planetary Sciences, Harvard University, Cambridge, MA, USA ;Morelli, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia ;Gasperini, P.; Dip. di Fisica, Universit´a di Bologna, 40128 Bologna, Italy ;Vannucci, G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Bologna, Bologna, Italia; ; ; ; ; The INGV-Harvard European-Mediterranean Regional Centroid Moment Tensor (RCMT) Catalog collects solutions routinely computed since 1997 for earthquakes with moderate magnitude (4.5 ≤ M ≤ 5.5) in the Mediterranean region. The database represents an extension to smaller magnitudes of the Harvard global CMT catalog, based on analysis of seismograms recorded at regional distance, and modeling of intermediate period surface waves. The catalog includes about 600 events, 200 of which in the Italian region. This study extends the catalog back in time, for the Italian region, as long as made possible by available digital data – i.e. since 1977 – with the same analysis and inversion method used for current seismicity. As a result, we present here 65 new moment tensors, for years between 1977 and 1997. These solutions represent 45% of the total number of events analyzed, the existing seismograms being often too scarce to allow a stable solution. The new dataset includes events in many seismic zones where moderate seismicity had previously been scarcely documented, e.g., the Po Plain, the Central to Southern Apennines and the Adriatic Sea. The complete dataset, including previously determined RCMTs and CMTs, represents the seismic deformation in the Italian area during the last 25 years.251 54