Mikhail B. Gokhberg

Theory of electrokinetic effects occurring at the final stage in the preparation of a tectonic earthquake

Crustal deformation processes occur with relative rapidity when short-term precursors appear at the final preparatory stage of a tectonic earthquake. This paper contains calculations of crustal bulk strain before an earthquake, based on the model of a rigid inclusion. The data give initial conditions for the problem of fluid percolation in a two-phase medium accompanied by electrokinetic effects. The solution provides a description of systems of currents arising in the vicinity of the source region. An analysis of this theoretical evidence yields information on the behaviour of short-term precursors in telluric currents and the geomagnetic field.

Modelling the Connection Between Earthquake Preparation Processes and Crustal Electromagnetic Emission

Abstract The steadily increasing amount of information available today on the natural electromagnetic emission (EME) of the radio frequency band associated with seismic events raises the problem of the origin of this phenomenon. A natural hypothesis is that EME is due to earthquake preparation processes. The present paper is concerned with substantiating a model that postulates EME to be caused by cracking of surficial crustal layers in the zone of earthquake preparation. The crust is assumed to have ordered hierarchical structure. Individual elements of that structure are formed of blocks of different scales and obey principles of similarity. Between the blocks are soft interlayers with a finite strength limit. A regular periodic structure with a cubic lattice is studied. As a result, EME intensity as a function of magnitude is evaluated. Methodological recommendations are given for organization of field observations of EME in relation to earthquake prediction.

On the electromagnetic field of an earthquake focus

Abstract Several mechanoelectromagnetic effects are analysed as probable generating mechanisms of electromagnetic impulses produced by an earthquake in its focus. Based on a simple mechanical concept of earthquakes and well-known theories of electrokinetic, piezomagnetic and induction effects, a dipole model of an earthquake-driven electromagnetic source is developed. Corresponding electric and/or magnetic dipole moment values are calculated as functions of earthquake focus parameters and generating mechanisms and are used to estimate the field intensities observable on the surface at different distances from an epicenter of an earthquake of a given magnitude ( M ). Calculated field values are compared with observational data.

On the origin of electrotelluric disturbances prior to an earthquake in Kalamata, Greece

Abstract A long distance (200 km) electromagnetic signal occured at Keratea (near Athens), few days prior to the September 13th 1986, Kalamata earthquake. We suggest an explanation based on the fact that long range stress occuring before an earthquake should create local electrical potential gradients in heterogeneous ground at great distances. This could be a general explanation for the origin of electrical telluric signals appearing before an earthquake.

Deep electromagnetic sounding of the lithosphere in the eastern Baltic (fennoscandian) shield with high-power controlled sources and industrial power transmission lines (FENICS experiment)

The paper addresses the technique and the first results of a unique experiment on the deep tensor frequency electromagnetic sounding, the Fennoscandian Electrical conductivity from results of sounding with Natural and Controlled Sources (FENICS). In the experiment, Energy-1 and Energy-2 generators with power of up to 200 kW and two mutually orthogonal industrial 109- and 120-km-long power transmission lines were used. The sounding frequency range was 0.1–200 Hz. The signals were measured in the Kola-Karelian region, in Finland, on Svalbard, and in Ukraine at distances up to 2150 km from the source. The parameters of electric conductivity in the lithosphere are studied down to depths on the order of 50–70 km. A strong lateral homogeneity (the one-dimensionality) of a geoelectric section of the Earth’s crust is revealed below depths of 10–15 km. At the same time, a region with reduced transverse crustal resistivity spread over about 80 000 square kilometers is identified within the depth interval from 20 to 40 km. On the southeast the contour of the anomaly borders the zone of deepening of the Moho boundary down to 60 km in Central Finland. The results are compared with the AMT-MT sounding data and a geodynamic interpretation of the obtained information is carried out.

Ionospheric response to submarine earthquake of March 11, 2011, in Japan according to GPS observations

Using available Russian and international Global Positioning System (GPS) network data, we studied the ionospheric response to the M = 8.9 submarine earthquake of March 11, 2011, on the northeastern coast of Honshu Island, Japan, both near and far (about 2000 km away) from the epicenter. In the region over the epicenter, 8.7 min after the event, we detected a characteristic signal of the total electron content (TEC) variations consisting of compression and rarefaction phases and a linear transition zone in between, i.e., in the form of an N-type wave with a steep leading front indicating a rapid uplift of the water surface and, correspondingly, the bottom of the ocean. The shape of the signal can be used for early tsunami warning; i.e., it may indicate the tsunamigenic character of a submarine earthquake. We monitored the subsequent evolution of the ionospheric response as far as 2000 km from the epicenter. It was shown that, besides the wellknown ionospheric N-type wave response to the earthquake, there is also a response in the form of an inverted N-wave, both nearby and far from the epicenter. We detected two more types of ionospheric responses far from the epicenter: a solitary-like wave and an internal gravity wave (IGW). The detected signals have been interpreted.

Tidal Deformations and the Electrokinetic Effect in a Two-Layer Fluid-Saturated Porous Medium

The electrokinetically induced vertical component of the electric field in a multilayer fluid-saturated porous medium caused by tidal deformations of the Earth’s crust is calculated. Petrophysical properties change in a jumplike manner at the boundary between two media. The pore pressure gradient at the boundary abruptly reaches a maximum and then exponentially decays, forming a hydrodynamic skin layer. Due to the electrokinetic effect, the electric field behaves in the same way. Observations of the vertical electric field can be used, in principle, to determine the mechanical properties of the medium experiencing deformation. The magnitudes of the effects lie within a range accessible to measurement.

The ionospheric response to the acoustic signal from submarine earthquakes according to the GPS data

The ionospheric response to the transit of acoustic waves from a number of the strongest submarine earthquakes with magnitudes Mw ≥ 7.7, which occurred during the past few years, is analyzed. The amplitude of the response in the detrended TEC is studied as a function of the magnitude and vertical component of the surface deformation. It is shown that the geomagnetic field can significantly modulate the shape of the ionospheric response, depending on whether the perturbation propagates equatorward or polarward.

International FENICS Experiment on the Tensor Frequency Electromagnetic Sounding of the Lithosphere in the Eastern Baltic (Fennoscandian) Shield

ISSN 1028-334X, Doklady Earth Sciences, 2009, Vol. 427A, No. 6, pp. 979–984.

The evolution of the stress state in Southern California based on the geomechanical model and current seismicity

A three-dimensional geomechanical model of Southern California, which includes the mountain topography, fault tectonics, and main structural boundaries (the top of the lower crust and the Moho), is developed. The main stress state of the model is determined by the own weight of the rocks and by the horizontal tectonic motions identified from the GPS observations. The model enables tracking the changes which occur in the stress-strain state of the crust due to the evolution of the seismic process. As the input data, the model uses the current seismicity and treats each earthquake as a new defect in the Earth’s crust which brings about the redistribution of strains, elastic energy density, and yield stress of the crust. Monitoring the variations in the stress state of the crust and lithosphere arising in response to the seismic process shows that the model is suitable for forecasting the enhancement in seismic activity of the region and delineating the earthquake-prone areas with a reasonable probability on a given time interval.