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- Kuteynikova, Maria, et al.
(författare)
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Numerical modeling and laboratory measurements of seismic attenuation in partially saturated rock
- 2014
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Ingår i: Geophysics. - : Society of Exploration Geophysicists. - 1942-2156 .- 0016-8033. ; 79:2, s. L13-L20
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Tidskriftsartikel (refereegranskat)abstract
- To better understand the effects of fluid saturation on seismic attenuation, we combined numerical modeling in poroelastic media and laboratory measurements of seismic attenuation in partially saturated Berea sandstone samples. Although in laboratory experiments many physical mechanisms for seismic attenuation take place simultaneously, with numerical modeling we separately studied the effect of a single physical mechanism: wave-induced fluid flow on the mesoscopic scale. Using the finite-element method, we solved Biot’s equations of consolidation by performing a quasistatic creep test on a 3D poroelastic model. This model represents a partially saturated rock sample. We obtained the stress-strain relation, from which we calculated frequency-dependent attenuation. In the laboratory, we measured attenuation in extensional mode for dry and partially water-saturated Berea sandstone samples in the frequency range from 0.1 to 100 Hz. All the measurements were performed at room pressure and temperature conditions. From numerical simulations, we found that attenuation varies significantly with fluid distribution within the model. In addition to binary distributions, we used spatially continuous distributions of fluid saturation for the numerical models. Such continuous saturation distribution was implemented using properties of an effective single-phase fluid. By taking into account the matrix anelasticity, we found that wave-induced fluid flow on the mesoscopic scale due to a continuous distribution of fluid saturation can reproduce seismic attenuation data measured in a partially saturated sample. The matrix anelasticity was the attenuation measured in the room-condition dry sample.
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| 2. |
- Lupi, Matteo, et al.
(författare)
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Regional earthquakes followed by delayed ground uplifts at Campi Flegrei Caldera, Italy : Arguments for a causal link
- 2017
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Ingår i: Earth and Planetary Science Letters. - : Elsevier BV. - 0012-821X .- 1385-013X. ; 474, s. 436-446
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Tidskriftsartikel (refereegranskat)abstract
- Earthquake-triggered volcanic activity promoted by dynamic and static stresses are considered rare and difficult-to-capture geological processes. Calderas are ideal natural laboratories to investigate earthquake volcano interactions due to their sensitivity to incoming seismic energy. The Campi Flegrei caldera, Italy, is one of the most monitored volcanic systems worldwide. We compare ground elevation time series at Campi Flegrei with earthquake catalogues showing that uplift events at Campi Flegrei are associated with large regional earthquakes. Such association is supported by (yet non-definitive) binomial tests. Over a 70-year time window we identify 14 uplift events, 12 of them were preceded by an earthquake, and for 8 of them the earthquake-to-uplift timespan ranges from immediate responses to 1.2 yr. Such variability in the response delay may be due to the preparedness of the system with faster responses probably occurring in periods during which the Campi Flegrei system was already in a critical state. To investigate the process that may be responsible for the proposed association we simulate the propagation of elastic waves and show that passing body waves impose high dynamic strains at the roof of the magmatic reservoir of the Campi Flegrei at about 7 km depth. This may promote a short-lived embrittlement of the magma reservoir's carapace otherwise marked by a ductile behaviour. Such failure allows magma and exsolved volatiles to be released from the magmatic reservoir. The fluids, namely exsolved volatiles and/or melts, ascend through a nominally plastic zone above the magmatic reservoir. This mechanism and the associated inherent uncertainties require further investigations but the new concept already implies that geological processes triggered by passing seismic waves may become apparent several months after passage of the seismic waves. (C) 2017 Elsevier B.V. All rights reserved.
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