1,721,061 research outputs found
Scale dependence in the dynamics of earthquake propagation: Evidence from seismological and geological observations
No full textWe attempt to reconcile current understanding of the earthquake energy balance with recent estimates of fracture energy from seismological investigations and surface energy from geological observations. The complex structure of real fault zones suggests that earthquakes in such fault structures are dominated by scale-dependent processes.We present a model for an inelastic fault zone of finite thickness embedded in an elastic crust represented at a macroscopic scale by a mathematical plane of zero thickness. The constitutive properties of the fault zone are governed by physical processes controlling gouge and damage evolution at meso- and micro-scale. However, in order to model and interpret seismological observations, we represent dynamic fault weakening at the macroscopic scale in terms of traction evolution as a function of slip and other internal variables defining a phenomenological friction or contact law on the virtual mathematical plane. This contact law is designed to capture the main features of dynamic fault weakening during earthquake rupture. In this study we assume that total shear traction is friction and corresponds to shear resistance of the whole fault zone.We show that seismological observations, depending on finite and limited
wavelength and frequency bandwidth, can only provide an estimate of breakdown stress drop and breakdown work (a more general definition of seismological fracture energy) representing a lower bound of the total intrinsic power of dissipation on the fault zone. We emphasize that geological estimates of surface energy can be compared with seismological estimates of breakdown work only if they are representative of the same macroscopic scale. In this case, it emerges that, contrary to surface energy, seismological breakdown work represents a non-negligible contribution to the earthquake energy budget
On the mechanical work absorbed on faults during earthquake ruptures
No full textIn this paper we attempt to reconcile a theoretical understanding of the earthquake energy balance with current geologic understanding of fault zones, with seismological estimates of fracture energy on faults, and with geological measurements of surface energy in fault gouges. In particular, we discuss the mechanical work absorbed on the fault plane during the propagation of a dynamic earthquake rupture. We show that, for realistic fault zone models, all the mechanical work is converted in frictional work defined as the irreversible work against frictional stresses. We note that the γeffof Kostrov and Das (1988) is zero for cracks lacking stress singularities, and thus does not contribute to the work done on real faults. Fault shear tractions and slip velocities inferred seismologically are phenomenological variables at the macroscopic scale. We define the macroscopic frictional work and we discuss how it is partitioned into surface energy and heat (the latter includes real heat as well as plastic deformation and the radiation damping of Kostrov and Das). Tinti et al. (2005) defined and measured breakdown work for recent earthquakes, which is the excess of work over some minimum stress level associated with the dynamic fault weakening. The comparison between geologic measurements of surface energy and breakdown work revealed that 1–10% of breakdown work went into the creation of fresh fracture surfaces (surface energy) in large earthquakes, and the remainder went into heat. We also point out that in a realistic fault zone model the transition between heat and surface energy can lie anywhere below the slip weakening curve
The first month of the 2016 central Italy seismic sequence. Fast determination of time domain moment tensors and finite fault model analysis of the ML 5.4 aftershock
Full text linkWe present the revised Time Domain Moment Tensor (TDMT) catalogue for earthquakes with ML larger than 3.6 of the first month of the ongoing Amatrice seismic sequence (August 24th- September 25th).
Most of the retrieved focal mechanisms show NNW–SSE striking normal faults in agreement with the main NE-SW extensional deformation of Central Apennines. We also report a preliminary finite fault model analysis performed on the larger aftershock of this period of the sequence (Mw 5.4) and discuss the obtained results in the framework of aftershocks distribution
Correction to: "Earthquake fracture energy inferred from kinematic rupture models on extended faults" (vol 110, art no B12303, 2005)
No full textModeling the dynamic rupture propagation on heterogeneous faults with rate- and state-dependent friction RID B-5039-2010
No full textWe investigate the effects of non-uniform distribution of constitutive parameters on the dynamic propagation of an earthquake rupture. We use a 2D finite difference numerical method and we assume that the dynamic rupture propagation is governed by a rate- and state-dependent constitutive law. We first discuss the results of several numerical experiments performed with different values of the constitutive parameters a (to account for the direct effect of friction), b (controlling the friction evolution) and L (the characteristic length-scale parameter) to simulate the dynamic rupture propagation on homogeneous faults. Spontaneous dynamic ruptures can be simulated on velocity weakening (a < b) fault patches: our results point out the dependence of the traction and slip velocity evolution on the adopted constitutive parameters. We therefore model the dynamic rupture propagation on heterogeneous faults. We use in this study the characterization of different frictional regimes proposed by Boatwright and Cocco (1996) based on different values of the constitutive parameters a, b and L. Our numerical simulations show that the heterogeneities of the L parameter affect the dynamic rupture propagation, control the peak slip velocity and weakly modify the dynamic stress drop and the rupture velocity. Moreover, a barrier can be simulated through a large contrast of L parameter. The heterogeneity of a and b parameters affects the
dynamic rupture propagation in a more complex way. A velocity strengthening area (a > b) can arrest a dynamic rupture, but can be driven to an instability if suddenly loaded by the dynamic rupture front. Our simulations provide a picture of the complex interactions between fault patches having different frictional properties and illustrate how the traction and slip velocity evolutions are modified during the propagation on heterogeneous faults. These results involve interesting implications for slip duration and fracture energy
Real-Time Determination of Seismic Moment Tensor for the Italian Region
No full textWe describe the automatic (AUTO) and the reviewed (REV) seismic time-domain moment tensor (TDMT) procedures implemented recently at the Istituto Nazionale di Geofisica e Vulcanologia (INGV), Italy. The solutions are obtained from the high-quality data of the recently installed Italian broadband network and of the Mediterranean seismographic network (MedNet). AUTO- and REV-TDMT adopt the long-period full waveform inversion code developed by Dreger and Helmberger (1993). AUTO-TDMT is triggered by local and regional events with magnitude ML ≥ 3.5 detected by the INGV seismic center.Moment tensor solutions are available within about 10 min after earthquake location, and they are automatically published on the World Wide Web for solution qualities exceeding a predefined threshold. REV-TDMT solutions are posted on the World Wide Web and included in the INGV-TDMT catalog after manual revision. The catalog we describe has great potential to improve our understanding of the regional seismicity and of the ongoing tectonics because the TDMT solutions are the only moment tensors and moment magnitudes released for Italy for many of the events with ML ≤4.2
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
- …
