Asymptotic Distributions of M-Estimates for Parameters of Multivariate Time Series with Strong Mixing Property

The article «Asymptotic Distributions of M-Estimates for Parameters of Multivariate Time Series with Strong Mixing Property» was published in «Engineering. Proceedings» and presented at the 7th International conference on Time Series and Forecasting, Gran Canaria, Spain, 19-21 July 2021. Authors – A. Kushnir and A. Varypaev.

The paper investigates the asymptotic properties of statistical estimates for the vector parameter \mathbf{u} \in R^q of a multidimensional random time series z_{t} \in R^m , t \in \mathbb{Z} , satisfying the strong mixing conditions. The authors have considered estimates \widetilde{\mathbf{u}}_{n}(\overline{z}_{n}) that are solutions of the equations \bigtriangledown_{\mathbf{u}}Q_{n}(\overline{z}_{n};\mathbf{u}) = 0, \overline{z}_{n} = (z^T_{1},...,z^T_{n})^T, where Q_{n}(\overline{z}_n;\mathbf{u}) are some objective functions for which \bigtriangledown_{\mathbf{u}}Q_{n}(\overline{z}_{n};\mathbf{u}) satisfies some constraints. It was proved, that under these constraints, the estimates \widetilde{\mathbf{u}}(\overline{z}_{n}) are \sqrt{n} – consistent and asymptotically normal with a limit covariance matrix \mathbf{D(u) = \Phi^{-1}(u)\Psi(u)\Phi^{-1}(u)} uniquely determined by the objective functions Q_{n}(\overline{z}_{n};\mathbf{u}).

The results of this paper are a generalization of the methods for constructing and analyzing the asymptotic properties of M-estimates, which were previously studied for the case of independent identically distributed observations.

Source: Kushnir, A.; Varypaev, A. Asymptotic Distributions of M-Estimates for Parameters of Multivariate Time Series with Strong Mixing Property // Eng. Proc. 2021, 5, 19. 10.3390/engproc2021005019

Earthquake Prediction: Old Expectations and New Results

It is known that there is no satisfactory physical model of earthquakes. The paradox of seismicity is known, according to which the implementation of seismic slip according to the generally accepted Reid`s elastic rebound model, due to the corresponding values of temperature and pressure, cannot occur at depths of more than several tens of kilometers. To get around these difficulties, models were proposed for the role of the fluid phase and various types of metamorphic transformations in the occurrence of deeper earthquakes.

More“Earthquake Prediction: Old Expectations and New Results”

Computer vision helps estimating the viscosity of lava domes

Lava domes form when a highly viscous magma erupts on the surface. Several types of lava dome morphology can be distinguished depending on the flow rate and the rheology of magma: obelisks, lava lobes, and endogenic structures. The viscosity of magma nonlinearly depends on the volume fraction of crystals and temperature. The paper “A method for magma viscosity assessment by lava dome morphology” published in the Journal of Volcanology and Seismology (Q2; JIF: 0.543) presents a new approach to magma viscosity estimation based on a comparison of observed and simulated dome morphological forms of lava domes. This joint research was performed by scientists from the Institute as well as from the Institute of Mathematics and Mechanics of the Ural Branch of the Russian Academy of Sciences, and the Lomonosov Moscow State University and supported by the Russian Science Foundation (Project No. 19-17-00027).

More“Computer vision helps estimating the viscosity of lava domes”

Deficit of Large Aftershocks as an Indicator of Afterslip at the Sources of Earthquakes in Subduction Zones

Earthquakes are accompanied by postseismic processes that begin right after the main shock and are manifested in aftershocks and aseismic deformations. The main driving mechanisms of postseismic deformation are viscoelastic relaxation in the crust and in the Earth’s upper mantle and postseismic slips (afterslip), reflecting the frictional properties of the plate interface in the source zone of a large earthquake. Afterslip may occur as aftershocks and/or slow aseismic slips (creep).

More“Deficit of Large Aftershocks as an Indicator of Afterslip at the Sources of Earthquakes in Subduction Zones”

А modified k-nearest neighbors method and its application to estimation of seismic intensity

In the article published in «Pure and Applied Geophysics», a modified k-nearest neighbors method is introduced, which is designed for statistically meaningful estimation of the field intensity based on locations of events. This method is used to perform a detailed analysis of the seismic intensity field in the region of Japan, shown on the figure, and found spots of increased seismic activity.

More“А modified k-nearest neighbors method and its application to estimation of seismic intensity”

Active cloaking and illusion of electric potentials in electrostatics

Cloaking (or “camouflage”) and illusion have long appeared in literature for children and science fiction. The “Star Trek” movies used cloaked (invisible to the enemy) spaceships (as presented in the cartoon in Fig. 1). In Charles Perrault’s Cat in Boots, a clever cat asks an ogre to turn into a little mouse and the ogre turns creating an illusion.

More“Active cloaking and illusion of electric potentials in electrostatics”

Displacements Before and After Great Earthquakes: Geodetic and Seismic Viewpoints

In the April issue of Pure and Applied Geophysics, an article on a pilot comparison of pre- and postseismic displacements associated with the most powerful earthquakes based on observations of the global positioning system GPS and networks of seismic stations appeared *.

The data of GPS stations of the Global Navigation Satellite System (GNSS) and the integral characteristics of the local seismic regime, including the accumulated displacements obtained from the catalogs of the earthquake hypocenters’ parameters before and after all mega-earthquakes – 2004 Sumatra-Andaman Mw9.2 in the Indian Ocean, 2011 off the coast of the Tohoku region Mw9.1 in Japan, 2010 on the shelf of the Maule region Mw8.8 in Chile – and the great earthquakes in Chile 2015 west of Illapel Mw8.3, in the Gulf of Alaska 2018 off Kodiak Island Mw7.9, and in New Zealand 2016 nearby the city of Kaikoura Mw7.8.

More“Displacements Before and After Great Earthquakes: Geodetic and Seismic Viewpoints”