3,713 research outputs found

    General theory of the modified Gutenberg-Richter law for large seismic moments

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    The Gutenberg-Richter power law distribution of earthquake sizes is one of the most famous example illustrating self-similarity. It is well-known that the Gutenberg-Richter distribution has to be modified for large seismic moments, due to energy conservation and geometrical reasons. Several models have been proposed, either in terms of a second power law with a larger b-value beyond a cross-over magnitude, or based on a ``hard'' magnitude cut-off or a ``soft'' magnitude cut-off using an exponential taper. Since the large scale tectonic deformation is dominated by the very largest earthquakes and since their impact on loss of life and properties is huge, it is of great importance to constrain as much as possible the shape of their distribution. We present a simple and powerful probabilistic theoretical approach that shows that the Gamma distribution is the best model, under the two hypothesis that the Gutenberg-Richter power law distribution holds in absence of any condition (condition of criticality) and that one or several constraints are imposed, either based on conservation laws or on the nature of the observations themselves. The selection of the Gamma distribution does not depend on the specific nature of the constraint. We illustrate the approach with two constraints, the existence of a finite moment release rate and the observation of the size of a maximum earthquake in a finite catalog. Our predicted ``soft'' maximum magnitudes compare favorably with those obtained by Kagan [1997] for the Flinn-Engdahl regionalization of subduction zones, collision zones and mid-ocean ridges.Comment: 24 pages, including 3 tables, in press in Bull. Seism. Soc. A

    Estimating the maximum possible earthquake magnitude using extreme value methodology: the Groningen case

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    The area-characteristic, maximum possible earthquake magnitude TMT_M is required by the earthquake engineering community, disaster management agencies and the insurance industry. The Gutenberg-Richter law predicts that earthquake magnitudes MM follow a truncated exponential distribution. In the geophysical literature several estimation procedures were proposed, see for instance Kijko and Singh (Acta Geophys., 2011) and the references therein. Estimation of TMT_M is of course an extreme value problem to which the classical methods for endpoint estimation could be applied. We argue that recent methods on truncated tails at high levels (Beirlant et al., Extremes, 2016; Electron. J. Stat., 2017) constitute a more appropriate setting for this estimation problem. We present upper confidence bounds to quantify uncertainty of the point estimates. We also compare methods from the extreme value and geophysical literature through simulations. Finally, the different methods are applied to the magnitude data for the earthquakes induced by gas extraction in the Groningen province of the Netherlands

    Shaking earth: Non-linear seismic processes and the second law of thermodynamics: A case study from Canterbury (New Zealand) earthquakes

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    We would like to express our gratitude to GeoNet for making available the data used in this work. This work was partially sup-ported by the RNM104 and RNM194 (Research Groups belonging to Junta de Andalucia, Spain) , the Spanish National Projects [grant project PID2019-109608GB-I00] , and the Junta de Andalucia Project [grant project A-RNM-421-UGR18] . English language editing was performed by Tornillo Scientific.Earthquakes are non-linear phenomena that are often treated as a chaotic natural processes. We propose the use of the Second Law of Thermodynamics and entropy, H, as an indicator of the equilibrium state of a seismically active region (a seismic system). In this sense, in this paper we demonstrate the exportability of first principles (e.g., thermodynamics laws) to others scientific fields (e.g., seismology). We suggest that the relationship between increasing H and the occurrence of large earthquakes reflects the irreversible transition of a system. From this point of view, a seismic system evolves from an unstable initial state (due to external stresses) to a state of reduced stress after an earthquake. This is an irreversible transition that entails an increase in entropy. In other words, a seismic system is in a metastable situation that can be characterised by the Second Law of Thermodynamics. We investigated two seismic episodes in the Canterbury area of New Zealand: the 2010 Christchurch earthquake (M = 7.2) and the 2016 Kaikoura earthquake (M = 7.8). The results are remarkably in line with our theoretical forecasts. In other words, an earthquake, understood as an irreversible transition, must results in an increase in entropy.Research Groups belonging to Junta de Andalucia, Spain RNM104- RNM194Spanish National Projects PID2019-109608GB-I00Junta de Andalucia A-RNM-421-UGR1

    Unfolding the procedure of characterizing recorded ultra low frequency, kHZ and MHz electromagetic anomalies prior to the L'Aquila earthquake as pre-seismic ones. Part I

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    Ultra low frequency, kHz and MHz electromagnetic anomalies were recorded prior to the L'Aquila catastrophic earthquake that occurred on April 6, 2009. The main aims of this contribution are: (i) To suggest a procedure for the designation of detected EM anomalies as seismogenic ones. We do not expect to be possible to provide a succinct and solid definition of a pre-seismic EM emission. Instead, we attempt, through a multidisciplinary analysis, to provide elements of a definition. (ii) To link the detected MHz and kHz EM anomalies with equivalent last stages of the L'Aquila earthquake preparation process. (iii) To put forward physically meaningful arguments to support a way of quantifying the time to global failure and the identification of distinguishing features beyond which the evolution towards global failure becomes irreversible. The whole effort is unfolded in two consecutive parts. We clarify we try to specify not only whether or not a single EM anomaly is pre-seismic in itself, but mainly whether a combination of kHz, MHz, and ULF EM anomalies can be characterized as pre-seismic one

    Current challenges for preseismic electromagnetic emissions: shedding light from micro-scale plastic flow, granular packings, phase transitions and self-affinity notion of fracture process

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    Are there credible electromagnetic (EM) EQ precursors? This a question debated in the scientific community and there may be legitimate reasons for the critical views. The negative view concerning the existence of EM precursors is enhanced by features that accompany their observation which are considered as paradox ones, namely, these signals: (i) are not observed at the time of EQs occurrence and during the aftershock period, (ii) are not accompanied by large precursory strain changes, (iii) are not accompanied by simultaneous geodetic or seismological precursors and (v) their traceability is considered problematic. In this work, the detected candidate EM precursors are studied through a shift in thinking towards the basic science findings relative to granular packings, micron-scale plastic flow, interface depinning, fracture size effects, concepts drawn from phase transitions, self-affine notion of fracture and faulting process, universal features of fracture surfaces, recent high quality laboratory studies, theoretical models and numerical simulations. Strict criteria are established for the definition of an emerged EM anomaly as a preseismic one, while, precursory EM features, which have been considered as paradoxes, are explained. A three-stage model for EQ generation by means of preseismic fracture-induced EM emissions is proposed. The claim that the observed EM precursors may permit a real-time and step-by-step monitoring of the EQ generation is tested

    Satellite interferometric data for seismic damage assessment

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    Radar satellites allow the collection of data on large areas without direct access to structures. Thereby, they appear very attractive for Structural Health Monitoring (SHM) purposes. Data collected by satellites can be processed to obtain temporal histories of displacements through which the health state of a monitored system can be potentially identified. However, anomalies in the time histories of displacements are not necessarily due to damage. Environmental phenomena, such as variations in atmospheric temperature, and rain, can modify the behavior of structures without compromising their safety. The impact of these phenomena on the structural response can hinder the identification of anomalies or lead to false alarms if such alterations are misinterpreted as damage. Furthermore, if the monitored system is a historical structure, uncertainties on the structural behavior are inevitably increased during aging. The purpose of this article is to discuss the possibility of identifying damage due to seismic actions considering the impact of variations of environmental factors on the time histories of the displacements retrieved by satellite data. The structural health condition of a historical structure located in the city of Rome (Italy) hit by the October 2016 Central Italy earthquakes is investigated based on interferometric satellite data. The satellite data are acquired by COSMO-SkyMed (CSM) of the Italian Space Agency between 2010 and 2019 and are processed by CNR IREA
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