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  • 1
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    Source functions of a two-asperity fault model (2014)
    Oxford University Press
    Details
    Publication Date: 2014-02-13
    Description: A fault made of two coplanar asperities subject to a constant strain rate is considered. The fault is modelled as a discrete dynamical system made of two blocks coupled by a spring and pulled at constant velocity on a rough plane. Such a system exhibits a variety of slipping modes, including the slip of single asperities and the simultaneous slip of both asperities. The associated source function can be expressed by the seismic moment rate as a function of time. The moment rate depends on the state of the system preceding the earthquake, which can be described by a single variable expressing the difference between the stresses imposed to the two asperities. We present a systematic study of the moment rate as a function of this variable and show how the moment rate changes as a function of the model parameters. The observed source function of the 2010 Maule (Chile) earthquake, that was the result of the failure of two main asperities, is interpreted in the framework of the proposed model.
    Print ISSN: 0956-540X
    Electronic ISSN: 1365-246X
    Topics: Geosciences
    Published by Oxford University Press on behalf of The Deutsche Geophysikalische Gesellschaft (DGG) and the Royal Astronomical Society (RAS).
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  • 2
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    Role of viscous dissipation in the dynamics of lava flows with power-law rheology (2011)
    Elsevier
    Details
    Publication Date: 2011-09-01
    Print ISSN: 0377-0273
    Electronic ISSN: 1872-6097
    Topics: Geosciences
    Published by Elsevier
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  • 3
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    A model for the formation of lava tubes by the growth of the crust from the levees (2010)
    American Geophysical Union
    Details
    Publication Date: 2010-09-15
    Print ISSN: 0148-0227
    Electronic ISSN: 2156-2202
    Topics: Geosciences
    Published by American Geophysical Union
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  • 4
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    Dynamics of a seismogenic fault subject to variable strain rate (2011)
    Copernicus
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    Publication Date: 2011-06-29
    Description: The behaviour of seismogenic faults is generally investigated under the assumption that they are subject to a constant strain rate. We consider the effect of a slowly variable strain rate on the recurrence times of earthquakes generated by a single fault. To this aim a spring-block system is employed as a low-order analog of the fault. Two cases are considered: a sinusoidal oscillation in the driver velocity and a monotonic change from one velocity value to another. In the first case, a study of the orbit of the system in the state space suggests that the seismic activity of the equivalent fault is organized into cycles that include several earthquakes and repeat periodically. Within each cycle the recurrence times oscillate about an average value equal to the recurrence period for constant strain rate. In the second case, the recurrence time changes gradually from the value before the transition to the value following it. Asymptotic solutions are also given, approximating the case when the amplitude of the oscillation or of the monotonic change is much smaller than the average driver velocity and the period of oscillation or the duration of the transition is much longer than the recurrence times of block motions. If the system is not isolated but is subject to perturbations in stress, the perturbation anticipates or delays the subsequent earthquake. The effects of stress perturbations in the two cases of strain rate oscillations and monotonic change are considered.
    Print ISSN: 1023-5809
    Electronic ISSN: 1607-7946
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 5
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    Dynamics of a two-fault system with viscoelastic coupling (2013)
    Copernicus
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    Publication Date: 2013-01-04
    Description: A fault system made of two segments or asperities subject to a constant strain rate is considered. The fault is modelled as a discrete dynamical system made of two blocks coupled by a Maxwell spring dashpot element and pulled at constant velocity on a rough plane. The long-term behaviour of the fault is studied by calculating the orbits of the system in the phase space. The model shows the role of viscoelastic relaxation in the Earth's crust in controlling the occurrence times of earthquakes. If a viscoelastic coupling is present, earthquakes are anticipated or delayed with respect to the elastic case. The limit cycles made of two alternate asperity failures, which are observed in the case of purely elastic coupling, are no longer produced. The model is applied to the 1964 Alaska earthquake, which was the effect of the failure of two asperities and for which a remarkable post-seismic relaxation has been observed in the subsequent decades. In such a fault system, viscoelastic coupling of the asperities appears to have a great influence on the occurrence times of earthquakes.
    Print ISSN: 1023-5809
    Electronic ISSN: 1607-7946
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 6
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    Conditions for large earthquakes in a two-asperity fault model (2011)
    Copernicus
    Details
    Publication Date: 2011-10-17
    Description: A fault with two asperities is modelled as a system made of two blocks coupled by a spring and sliding on a plane under the same values of static and dynamic friction. An analytical solution is given for the simultaneous motion of the blocks and the corresponding orbits are plotted in the phase space. It is proven that, whichever the initial state is, the long-term behaviour of the system is one of an infinite number of limit cycles, characterized by a particular pattern of forces. The region where the system is located when the blocks are stationary can be divided into narrow stripes corresponding to different orbits of the points belonging to them. This implies that the system is sensitive to perturbations and has relevant implications for a fault, which is subject to stress transfers from earthquakes generated by neighbouring faults. In this case, the fault may experience a larger earthquake, with the simultaneous failure of the two asperities, which restores a stress distribution compatible with periodic behaviour. The seismic moment associated with simultaneous asperity failure is always greater than the maximum value that can be released in a limit cycle. For strongly coupled asperities, the moment can be several times larger.
    Print ISSN: 1023-5809
    Electronic ISSN: 1607-7946
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 7
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    Simulation of the long-term behaviour of a fault with two asperities (2010)
    Copernicus
    Details
    Publication Date: 2010-12-15
    Description: A system made of two sliding blocks coupled by a spring is employed to simulate the long-term behaviour of a fault with two asperities. An analytical solution is given for the motion of the system in the case of blocks having the same friction. An analysis of the phase space shows that orbits can reach a limit cycle only after entering a particular subset of the space. There is an infinite number of different limit cycles, characterized by the difference between the forces applied to the blocks or, as an alternative, by the recurrence pattern of block motions. These results suggest that the recurrence pattern of seismic events produced by the equivalent fault system is associated with a particular stress distribution which repeats periodically. Admissible stress distributions require a certain degree of inhomogeneity, which depends on the geometry of fault system. Aperiodicity may derive from stress transfers from neighboring faults.
    Print ISSN: 1023-5809
    Electronic ISSN: 1607-7946
    Topics: Geosciences , Physics
    Published by Copernicus on behalf of European Geosciences Union.
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  • 8
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    Cooling of a channeled lava flow with non-Newtonian rheology: crust formation and surface radiance (2012)
    Details
    Publication Date: 2021-05-11
    Description: We present here the results from dynamical and thermal models that describe a channeled lava flow as it cools by radiation. In particular, the effects of power-law rheology and of the presence of bends in the flow are considered, as well as the formation of surface crust and lava tubes. On the basis of the thermal models, we analyze the assumptions implicit in the currently used formulae for evaluation of lava flow rates from satellite thermal imagery. Assuming a steady flow down an inclined rectangular channel, we solve numerically the equation of motion by the finite-volume method and a classical iterative solution. Our results show that the use of power-law rheology results in relevant differences in the average velocity and volume flow rate with respect to Newtonian rheology. Crust formation is strongly influenced by power-law rheology; in particular, the growth rate and the velocity profile inside the channel are strongly modified. In addition, channel curvature affects the flow dynamics and surface morphology. The size and shape of surface solid plates are controlled by competition between the shear stress and the crust yield strength: the degree of crust cover of the channel is studied as a function of the curvature. Simple formulae are currently used to relate the lava flow rate to the energy radiated by the lava flow as inferred from satellite thermal imagery. Such formulae are based on a specific model, and consequently, their validity is subject to the model assumptions. An analysis of these assumptions reveals that the current use of such formulae is not consistent with the model.
    Description: Published
    Description: 510-520
    Description: JCR Journal
    Description: open
    Keywords: Rheology ; 04. Solid Earth::04.08. Volcanology::04.08.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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  • 9
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    Conditions for crust and tube formation in lava flows with power-law rheology (2012)
    Istituto Nazionale di Oceanografia e di Geofisica Sperimentale-OGS
    Details
    Publication Date: 2021-05-11
    Description: We studied the conditions of crust and tube formation of a lava flow moving under the effect of gravity in a rectangular cross-section channel and assumed a power-law rheology for lava. We followed the work of Valerio et al. (2008), who studied the effect of surface cooling on the formation and accretion of the crust in the central region of the channel, assuming for lava a Newtonian rheology. According to these authors, tube formation is influenced by topography and channel morphology. In this work, we extended this study to a non-Newtonian rheology, in particular to the power-law rheology. Results indicate that a power-law rheology strongly influences the condition of crust formation but does not produce significant differences as a function of topographical or morphological variations.
    Description: Published
    Description: 309-319
    Description: JCR Journal
    Description: restricted
    Keywords: Power law rheology ; 04. Solid Earth::04.04. Geology::04.04.99. General or miscellaneous
    Repository Name: Istituto Nazionale di Geofisica e Vulcanologia (INGV)
    Type: article
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