http://hdl.handle.net/2122/195 Search the Channel search http://www.earth-prints.org/simple-search http://hdl.handle.net/2122/4182 Title: Crustal seismic velocity in the Marche region (Central Italy): computation of a minimum 1-D model with seismic station corrections. <br/> <br/>Authors: Scarfì, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia; Imposa, S.; Dipartimento di Scienze Geologiche, Università di Catania; Raffaele, R.; Dipartimento di Scienze Geologiche, Università di Catania; Scaltrito, A.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia <br/> <br/>Abstract: A 1-D velocity model for the Marche region (central Italy) was computed by inverting P- and S-wave arrival times of local earthquakes. A total of 160 seismic events with a minimum of ten observations, a travel time residual ≤ 0.8 s and an azimuthal gap lower than 180° have been selected. This “minimum 1-D velocity model” is complemented by station corrections, which can be used to take into account possible near-surface velocity heterogeneities beneath each station. Using this new P-wave velocity model and the program HYPOELLIPSE (Lahr, 1999), the selected local events were relocated. Earthquake locations in this study are of higher quality with respect to the original ones. The obtained minimum 1-D velocity model can be used to improve the routine earthquakes locations and represents a further step towards more detailed seismotectonic studies of the area. http://hdl.handle.net/2122/4172 Title: Matlab software for the analysis of seismic waves recorded by three-element arrays <br/> <br/>Authors: Pignatelli, A.; Italian National Data Center, viale Pinturicchio 23/E, 00196 Roma, Italy; Giuntini, A.; Italian National Data Center, viale Pinturicchio 23/E, 00196 Roma, Italy; Console, R.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Roma2, Roma, Italia <br/> <br/>Abstract: We develop and implement an algorithm for inverting three-element array data on a Matlab platform. The algorithm allows reliable estimation of back azimuth and apparent velocity from seismic records under low signal-to-noise conditions. We start with a cubic spline interpolation of the waveforms and determine the differences between arrival times at pairs of array elements. The time differences are directly computed from cross-correlation functions. The advantages of this technique are (a) manual picking of the onset of each arrival is not necessary at each array element; (b) interpolation makes it possible to estimate time differences at a higher resolution than the sampling rate of the digital waveforms; (c) consistency among three independent determinations provides a reliability check; and (d) the value of apparent velocity indicates the nature of the recorded wavelet and physically checks the results. The algorithm was tested on data collected by a tri-partite array (with an aperture of 250 m) deployed in 1998 by the National Data Center of Israel, during a field experiment in southern Israel, 20km southwest of the Dead Sea. The data include shallow explosions and natural earthquakes under both high and low signal-to-noise conditions. The procedure developed in this study is considered suitable for searching of small aftershocks subsequent to an underground explosion, in the context of on-site inspections according to the Comprehensive Nuclear-Test-Ban Treaty (CTBT). http://hdl.handle.net/2122/4155 Title: Volumetric observations during paroxysmal eruptions at Mount Etna: pressurized drainage of a shallow chamber or pulsed supply? <br/> <br/>Authors: Harris, A. J. L.; HIGP/SOEST, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia <br/> <br/>Abstract: The October 17 to November 5, 1999, eruption of Mount Etna’s Bocca Nuova crater emplaced a V15U106 m3 flow field. The eruption was characterized by 11 paroxysmal events during which intense Strombolian and lava fountain activity fed vigorous channelized PaPa flows at eruption rates of up to 120 m3 s31. Each paroxysm lasted between 75 and 450 min, and was separated by periods of less intense Strombolian activity and less vigorous (610 m3 s31) effusion. Ground-based, satellite- and model-derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay. This is consistent with a scenario whereby the system was depressurized during the first eruptive period (October 17^23), repressurized during an October 24 pause, and then depressurized again during the second period (October 25^28). The imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1.5^5.7U106 m3 and 1.2^ 3.6U106 m3, respectively, or an increase in the time-averaged supply to 11.6^13.6 m3 s31 and 12.5^14.9 m3 s31. Two models are consistent with the observed episodic fountaining, derived volumetric trends and calculated volume imbalance: a magma collection model and a pulsed supply model. In the former case, depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining. In the pulsing case, variations in magma flux account for pressurization^depressurization and supply the excess volume. Increases in rise rate and volatile flux, coupled with rapid exsolution during ascent, trigger fountaining. Limiting equations that define critical foam layer volumes and magma rise rates necessary for Hawaiian-style fountaining favor the latter model. http://hdl.handle.net/2122/4155 Title: Volumetric observations during paroxysmal eruptions at Mount Etna: pressurized drainage of a shallow chamber or pulsed supply? <br/> <br/>Authors: Harris, A. J. L.; HIGP/SOEST, University of Hawaii, 2525 Correa Road, Honolulu, HI 96822, USA; Neri, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia <br/> <br/>Abstract: The October 17 to November 5, 1999, eruption of Mount Etna’s Bocca Nuova crater emplaced a V15U106 m3 flow field. The eruption was characterized by 11 paroxysmal events during which intense Strombolian and lava fountain activity fed vigorous channelized PaPa flows at eruption rates of up to 120 m3 s31. Each paroxysm lasted between 75 and 450 min, and was separated by periods of less intense Strombolian activity and less vigorous (610 m3 s31) effusion. Ground-based, satellite- and model-derived volumetric data show that the eruption was characterized by two periods during which eruption rates and cumulative volume showed exponential decay. This is consistent with a scenario whereby the system was depressurized during the first eruptive period (October 17^23), repressurized during an October 24 pause, and then depressurized again during the second period (October 25^28). The imbalance between the erupted and supplied volumes mean that the two periods involved the collection of 1.5^5.7U106 m3 and 1.2^ 3.6U106 m3, respectively, or an increase in the time-averaged supply to 11.6^13.6 m3 s31 and 12.5^14.9 m3 s31. Two models are consistent with the observed episodic fountaining, derived volumetric trends and calculated volume imbalance: a magma collection model and a pulsed supply model. In the former case, depressurization of a shallow reservoir cause the observed volumetric trends and foam collapse at the reservoir roof powers fountaining. In the pulsing case, variations in magma flux account for pressurization^depressurization and supply the excess volume. Increases in rise rate and volatile flux, coupled with rapid exsolution during ascent, trigger fountaining. Limiting equations that define critical foam layer volumes and magma rise rates necessary for Hawaiian-style fountaining favor the latter model.