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Joint inversion of GPS and high-resolution GRACE gravity data for the 2012 Wharton basin earthquakes / Michel Diament in Journal of geodynamics, vol 136 (May 2020)  

Public [article]  inJournal of geodynamics > vol 136 (May 2020) . - n° 101722 Titre : Joint inversion of GPS and high-resolution GRACE gravity data for the 2012 Wharton basin earthquakes Type de document : Article/Communication Auteurs : Michel Diament , Auteur ; Valentin O. Mikhailov, Auteur ; Elena P. Timoshkina, Auteur Année de publication : 2020 Projets : TOSCA / Article en page(s) : n° 101722 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] coordonnées GPS [Termes IGN] déformation de la croute terrestre [Termes IGN] données GRACE [Termes IGN] élasticité [Termes IGN] Indien (océan) [Termes IGN] séisme [Termes IGN] viscosité Résumé : (auteur) The Wharton basin is situated in the north-eastern part of the Indian Ocean. In 2012 it hosted the largest intraplate strike-slip earthquakes ever recorded by geophysical networks. The Mw 8.6 earthquake of April 11, 2012, was preceded by a major foreshock (Mw 7.2) on January 10 and was followed two hours afterward by a Mw 8.2 event. These three large events occurred at the diffuse boundary between the Indian and Australian plates and were almost pure strike-slips on sub-vertical rupture surfaces. Using GRACE data, we first extracted the coseismic and postseismic gravity signals caused by these earthquakes. Then we fitted both GPS and the highest available spatial resolution of GRACE data using the geometry of the fault system suggested by Hill et al. (2015). We propose a regularization, which allows to solve for a linear problem in order to invert GPS and GRACE data under constraints on the rake angle. Our inversion yields a uniform displacement field on all elements of a given fault plane. Our solution shows that even the main displacement occurred on WNW trending faults, comparable displacement also occurred on a rupture striking NNE. Hence, we show that the deformation in this diffuse plate boundary region in 2012 was accommodated by displacements along both fault-systems. A viscoelastic relaxation of the asthenosphere with a Maxwell viscosity 1019 Pa∙s successfully explains the postseismic displacements at GPS sites and postseismic gravity signals. The limited postseismic aftershock activity suggests small postseismic slip in the area of the 2012 Wharton earthquakes contrary to what is often observed after large subduction event. Because a part of the observed signal could be related to afterslip, our obtained Maxwell viscosity value should be considered as a lower limit of the asthenospheric viscosity below the Wharton basin. Numéro de notice : A2020-876 Affiliation des auteurs : UMR IPGP-Géod+Ext (2020- ) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1016/j.jog.2020.101722 Date de publication en ligne : 20/03/2020 En ligne : https://doi.org/10.1016/j.jog.2020.101722 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=99670 [article]

Comparative study of temporal variations in the earth’s gravity field using GRACE gravity models in the regions of three recent giant earthquakes / Valentin O. Mikhailov in Izvestiya, Physics of the Solid Earth, vol 50 n° 2 (March 2014)  

Public [article]  inIzvestiya, Physics of the Solid Earth > vol 50 n° 2 (March 2014) . - pp 177 - 191 Titre : Comparative study of temporal variations in the earth’s gravity field using GRACE gravity models in the regions of three recent giant earthquakes Type de document : Article/Communication Auteurs : Valentin O. Mikhailov, Auteur ; Isabelle Panet , Auteur ; M. Hayn, Auteur ; Elena P. Timoshkina, Auteur ; Sylvain Bonvalot, Auteur ; V. Lyakhovsky, Auteur ; Michel Diament , Auteur ; Olivier de Viron, Auteur Année de publication : 2014 Article en page(s) : pp 177 - 191 Note générale : bibliographie Original Russian Text © V.O. Mikhailov, I. Panet, M. Hayn, E.P. Timoshkina, S. Bonvalot, V. Lyakhovsky, M. Diament, O. de Viron, 2014, published in Fizika Zemli, 2014, No. 2, pp. 187–198. Langues : Anglais (eng) Résumé : (auteur) Comparative analysis of coseismic and postseismic variations of the Earth’s gravity field is carried for the regions of three giant earthquakes (Andaman-Sumatra, December 26, 2004, magnitude M w = 9.1; Maule-Chile, February 27, 2010, M w = 8.8, and Tohoku-Oki, March 11, 2011, M w = 9.0) with the use of GRACE satellite data. Within the resolution of GRACE models, the coseismic changes of gravity caused by these seismic events manifest themselves by large negative anomalies located in the rear of the subduction zone. The real data are compared with the synthetic anomalies calculated from the rupture surface models based on different kinds of ground measurements. It is shown that the difference between the gravity anomalies corresponding to different rupture surface models exceeds the uncertainties of the GRACE data. There-fore, the coseismic gravity anomalies are at least suitable for rejecting part of the models that are equivalent in the ground data. Within the first few months after the Andaman-Sumatra earthquake, a positive gravity anomaly started to grow above the deep trench. This anomaly rapidly captured the area of the back-arc basin and largely compensated the negative coseismic anomaly. The processes of viscoelastic stress relaxation do not fully allow for these rapid changes of gravity. According to the calculations, even with a sufficiently low viscosity of the upper mantle, relaxation only covers about a half of the observed change of the field. In order to explain the remaining temporal variations, we suggested the process of downdip propagation of the coseismic rupture surface. The feasibility of such a process was supported by numerical simulations. The sum of the gravity anomalies caused by this process and the anomaly generated by the processes of viscoelastic relaxation accounts well for the observed changes of the gravity field in the region of the earthquake. The similar postseismic changes of gravity were also detected for the region of the Tohoku-Oki earthquake. Just as in the case discussed above, this earthquake was also followed by a rapid growth of a positive postseismic anomaly, which partially counterbalanced the negative coseismic anomaly. The time variations of the gravity field in the region of the Maule-Chile earthquake differ from the pattern of changes observed in the island arcs described above. The postseismic gravity variations are in this case concentrated in a narrower band above the deep trench and shelf, and they do not spread over the continental territory, where the negative coseismic anomaly is located. These discrepancies reflect the difference in the geodynamical settings of the studied earthquakes. Numéro de notice : A2014-657 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1134/S1069351314020062 Date de publication en ligne : 07/03/2014 En ligne : http://dx.doi.org/10.1134/S1069351314020062 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=78488 [article]

Numerical modelling of post-seismic rupture propagation after the Sumatra 26.12.2004 earthquake constrained by GRACE gravity data / Valentin O. Mikhailov in Geophysical journal international, vol 194 n° 2 (August 2013)  

Public [article]  inGeophysical journal international > vol 194 n° 2 (August 2013) . - pp 640 - 650 Titre : Numerical modelling of post-seismic rupture propagation after the Sumatra 26.12.2004 earthquake constrained by GRACE gravity data Type de document : Article/Communication Auteurs : Valentin O. Mikhailov, Auteur ; V. Lyakhovsky, Auteur ; Isabelle Panet , Auteur ; Y. van Dinther, Auteur ; Michel Diament , Auteur ; T. Gerya, Auteur ; Olivier de Viron, Auteur ; Elena P. Timoshkina, Auteur Année de publication : 2013 Article en page(s) : pp 640 - 650 Note générale : bibliographie Langues : Anglais (eng) Descripteur : [Vedettes matières IGN] Applications de géodésie spatiale [Termes IGN] champ de pesanteur terrestre [Termes IGN] coordonnées GPS [Termes IGN] déformation de la croute terrestre [Termes IGN] données GRACE [Termes IGN] faille géologique [Termes IGN] levé gravimétrique [Termes IGN] modèle de simulation [Termes IGN] rhéologie [Termes IGN] séisme [Termes IGN] subduction Résumé : (auteur) In the last decades, the development of the surface and satellite geodetic and geophysical observations brought a new insights into the seismic cycle, documenting new features of inter-, co-, and post-seismic processes. In particular since 2002 satellite mission GRACE provides monthly models of the global gravity field with unprecedented accuracy showing temporal variations of the Earth's gravity field, including those caused by mass redistribution associated with earthquake processes. When combined with GPS measurements, these new data have allowed to assess the relative importance of afterslip and viscoelastic relaxation after the Sumatra 26.12.2004 earthquake. Indeed the observed post-seismic crustal displacements were fitted well by a viscoelastic relaxation model assuming Burgers body rheology for the asthenosphere (60–220 km deep) with a transient viscosity as low as 4 × 1017 Pas and constant ∼1019 Pas steady state viscosity in the 60–660-km depth range. However, even the low-viscosity asthenosphere provides the amplitude of strain which gravity effect does not exceed 50 per cent of the GRACE gravity variations, thus additional localized slip of about 1 m was suggested at downdip extension of the coseismic rupture. Post-seismic slip at coseismic rupture or its downdip extension has been suggested by several authors but the mechanism of the post-seismic fault propagation has never been investigated numerically. Depth and size of localized slip area as well as rate and time decay during the post-seismic stage were either assigned a priory or estimated by fitting real geodesy or gravity data. In this paper, we investigate post-seismic rupture propagation by modelling two consequent stages. First, we run a long-term, geodynamic simulation to self-consistently produce the initial stress and temperature distribution. At the second stage, we simulate a seismic cycle using results of the first step as initial conditions. The second short-term simulation involves three substeps, including additional stress accumulation after part of the subduction channel was locked; spontaneous coseismic slip; formation and development of damage zones producing afterslip. During the last substep post-seismic stress leads to gradual ∼1 m slip localized at three faults around ∼100-km downdip extension of the coseismic rupture. We used the displacement field caused by the slip to calculate pressure and density variations and to simulate gravity field variations. Wavelength of calculated gravity anomaly fits well to that of the real data and its amplitude provides about 60 per cent of the observed GRACE anomaly. Importantly, the surface displacements caused by the estimated afterslip are much smaller than those registered by GPS networks. As a result cumulative effect of Burgers rheology viscoelastic relaxation (which explains measured GPS displacements and about a half of gravity variations) plus post-seismic slip predicted by damage rheology model (which causes much smaller surface displacements but provides another half of the GRACE gravity variations) fits well to both sets of the real data. Hence, the presented numerical modelling based on damage rheology supports the process of post-seismic downdip rupture propagation previously hypothesized from the GRACE gravity data. Numéro de notice : A2013-820 Affiliation des auteurs : LASTIG LAREG+Ext (2012-mi2018) Thématique : POSITIONNEMENT Nature : Article nature-HAL : ArtAvecCL-RevueIntern DOI : 10.1093/gji/ggt145 Date de publication en ligne : 02/05/2013 En ligne : http://dx.doi.org/10.1093/gji/ggt145 Format de la ressource électronique : URL article Permalink : https://documentation.ensg.eu/index.php?lvl=notice_display&id=80192 [article]