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  • 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics  (3)
  • 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring  (2)
  • Birkhauser Verlag  (3)
  • American Association for the Advancement of Science
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  • 1
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    Three Decades of Seismic Activity at Mt. Vesuvius: 1972–2000 (2006)
    Birkhauser Verlag
    Details
    Publication Date: 2022-06-14
    Description: We analyse the seismic catalogue of the local earthquakes which occurred at Somma-Vesuvius volcano in the past three decades (1972–2000). The seismicity in this period can be described ascomposed of a background level, characterised by a low and rather uniform rate of energy release and by sporadic periods of increased seismic activity. Such relatively intense seismicity periods are characterised by energy rates and magnitudes progressively increasing in the critical periods. The analysis of the b value in the whole period evidences a well-defined pattern, with values of b progressively decreasing, from about 1.8 at the beginning of the considered period, to about 1.0 at present. This steady variation indicates an increasing dynamics in the volcanic system. Within this general trend it is possible to identify a substructure in the time sequence of the seismic events, formed by the alternating episodes of quiescence and activity. The analysis of the source moment tensor of the largest earthquakes shows that the processes at the seismic source are generally not consistent with simple double-couples, but that they are compatible with isotropic components, mostly indicating volumetric expansion. These components are shown to be statistically significant for most of the analysed events. Such focal mechanisms can be interpreted as the effect of explosion phenomena, possibly related to volatile exsolution from the crystallising magma. The availability of a reduced amount of high quality data necessary for the inversion of the source moment tensor, the still limited period of systematic observation of Vesuvius micro-earthquakes and, above all, the absence of eruptive events during such interval of time, cannot obviously permit the outlining of any formal premonitory signal. Nevertheless, the analysis reported in this paper indicates a progressively evolving dynamics, characterised by a generally increasing trend in the seismic activity in the volcanic system and by a significant volumetric component of recent major events, thus posing serious concern for a future evolution towards eruptive activity.
    Description: Published
    Description: 123-144
    Description: partially_open
    Keywords: seismicity ; microearthquakes ; earthquake-source mechanism ; earthquake catalogue ; b values ; Vesuvius ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics ; 04. Solid Earth::04.06. Seismology::04.06.08. Volcano seismology
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 436 bytes
    Format: 668871 bytes
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  • 2
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    3-D Modelling of Campi Flegrei Ground Deformations: Role of Caldera Boundary Discontinuities (2006)
    Birkhauser Verlag
    Details
    Publication Date: 2017-04-04
    Description: Campi Flegrei is a caldera complex located west of Naples, Italy. The last eruption occurred in 1538, although the volcano has produced unrest episodes since then, involving rapid and large ground movements (up to 2 m vertical in two years), accompanied by intense seismic activity. Surface ground displacements detected by various techniques (mainly InSAR and levelling) for the 1970 to 1996 period can be modelled by a shallow point source in an elastic half-space, however the source depth is not compatible with seismic and drill hole observations, which suggest a magma chamber just below 4 km depth. This apparent paradox has been explained by the presence of boundary fractures marking the caldera collapse. We present here the first full 3-D modelling for the unrest of 1982–1985 including the effect of caldera bordering fractures and the topography. To model the presence of topography and of the complex caldera rim discontinuities, we used a mixed boundary elements method. The a priori caldera geometry is determined initially from gravimetric modelling results and refined by inversion. The presence of the caldera discontinuities allows a fit to the 1982–1985 levelling data as good as, or better than, in the continuous half-space case, with quite a different source depth which fits the actual magma chamber position as seen from seismic waves. These results show the importance of volcanic structures, and mainly of caldera collapses, in ground deformation episodes.
    Description: Published
    Description: 1329-1344
    Description: partially_open
    Keywords: Campi Flegrei ; deformations ; caldera ; 3-D ; 04. Solid Earth::04.03. Geodesy::04.03.01. Crustal deformations ; 04. Solid Earth::04.03. Geodesy::04.03.08. Theory and Models ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
    Format: 478 bytes
    Format: 1671146 bytes
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  • 3
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    Time-resolved seismic tomography detects magma intrusions at Mt. Etna (2007)
    American Association for the Advancement of Science
    Details
    Publication Date: 2017-04-04
    Description: The continuous volcanic and seismic activity at Mount Etna makes this volcano an important laboratory for seismological and geophysical studies. We used repeated three-dimensional tomography to detect variations in elastic parameters during different volcanic cycles, before and during the October 2002–January 2003 flank eruption. Well-defined anomalous low P- to S-wave velocity ratio volumes were revealed. Absent during the pre-eruptive period, the anomalies trace the intrusion of volatile-rich (Q4 weight percent) basaltic magma, most of which rose up only a few months before the onset of eruption. The observed time changes of velocity anomalies suggest that four-dimensional tomography provides a basis for more efficient volcano monitoring and shortand midterm eruption forecasting of explosive activity.
    Description: Published
    Description: 821-823
    Description: reserved
    Keywords: NONE ; 04. Solid Earth::04.01. Earth Interior::04.01.02. Geological and geophysical evidences of deep processes ; 04. Solid Earth::04.06. Seismology::04.06.07. Tomography and anisotropy ; 04. Solid Earth::04.08. Volcanology::04.08.06. Volcano monitoring
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 4
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    Tidal Modulation of Nonvolcanic Tremor (2008)
    American Association for the Advancement of Science
    Details
    Publication Date: 2017-04-04
    Description: Episodes of nonvolcanic tremor and accompanying slow slip recently have been observed in the subduction zones of Japan and Cascadia. In Cascadia, such episodes typically last a few weeks, and differ from “normal” earthquakes in their source location and momentduration scaling. The three most recent episodes in the Puget Sound/Southern Vancouver Island portion of the Cascadia subduction zone have been exceptionally well recorded. In each episode, we see clear pulsing of tremor activity with periods of 12.4 and 24-25 hours, the same as the principal lunar and lunisolar tides. This indicates that the small stresses associated with the solid-earth and ocean tides influence the genesis of tremor much more effectively than they do “normal” earthquakes. Because the lithostatic stresses are 105 times larger than those associated with the tides, we argue that tremor occurs on very weak faults.
    Description: Published
    Description: 186 -189
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Nonvolcanic ; tremor ; 04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution ; 04. Solid Earth::04.06. Seismology::04.06.02. Earthquake interactions and probability ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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  • 5
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    What does control earthquake ruptures and dynamic faulting? A review of different competing mechanisms (2009)
    Birkhauser Verlag
    Details
    Publication Date: 2017-04-04
    Description: The fault weakening occurring during an earthquake and the temporal evolution of the traction on a seismogenic fault depend on several physical mechanisms, potentially concurrent and interacting. Recent laboratory experiments and geological field observations of natural faults revealed the presence, and sometime the coexistence, of thermally activated processes (such as thermal pressurization of pore fluids, melting of gouge and rocks, material property changes, thermally-induced chemical environment evolution), elasto-dynamic lubrication, porosity and permeability evolution, gouge fragmentation and wear, etc. In this paper, by reviewing in a unifying sketch all possible chemico–physical mechanisms that can affect the traction evolution, we suggest how they can be incorporated in a realistic fault governing equation. We will also show that simplified theoretical models that idealistically neglect these phenomena appear to be inadequate to describe as realistically as possible the details of breakdown process (i.e., the stress release) and the consequent high frequency seismic wave radiation. Quantitative estimates show that in most cases the incorporation of such nonlinear phenomena has significant, often dramatic, effects on the fault weakening and on the dynamic rupture propagation. The range of variability of the value of some parameters, the uncertainties in the relative weight of the various competing mechanisms, and the difference in their characteristic length and time scales sometime indicate that the formulation of a realistic governing law still requires joint efforts from theoretical models, laboratory experiments and field observations.
    Description: Published
    Description: 741-776
    Description: 3.1. Fisica dei terremoti
    Description: JCR Journal
    Description: reserved
    Keywords: Rheology and friction of the fault zones ; Constitutive laws ; Mechanics of faulting ; Earthquake dynamics ; 04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
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