G. M. Steblov

Geodetic constraints on the rigidity and relative motion of Eurasia and North America

GPS observations in northeastern Asia, when combined with observations from the global network for the period 1992–1999, yield an angular rotation vector between Eurasia and North America consistent with and a factor of two more precise than estimates derived using GPS or VLBI data previously available from only western Eurasia. The new vector implies a pole of relative rotation 1200 km more to the northwest than predicted by the NUVEL-1A global plate model, suggesting a significant change in the relative motion of Eurasia and North America over the past 3 Myr. The standard deviations of horizontal velocities from rigid plate motion for nineteen stations in Eurasia and ten in North America are less than 1 mm/yr; the observations place an upper bound of 2 mm/yr at 95% confidence for relative motion between western and eastern Eurasia.

Rapid aseismic moment release following the 5 December, 1997 Kronotsky, Kamchatka, Earthquake

Model inversions of displacements of continuously operating GPS stations in Kamchatka show that aseismic afterslip during 2 months following the Mw=7.8, 5 December, 1997 Kronotsky subduction earthquake released as much moment as the earthquake itself. The rapidly decaying transient slip on the subduction underthrust occurred near the downdip edge of the coseismic rupture and extended laterally away from it, including a region of vigorous foreshock activity. A logarithmic decay function fit to the cumulative afterslip curve has a relaxation time of about 3 days. Rapid afterslip can contribute significantly to the moment release of partially coupled subduction zones.

The mechanism of postseismic deformation triggered by the 2006–2007 great Kuril earthquakes

Received 21 January 2011; accepted 15 February 2011; published 24 March 2011. [1] In 2006–2007, a doublet of great earthquakes (Mw >8 ) struck in the center of the Kuril subduction zone, a thrust event followed by an extensional event. Our observations of the Kuril GPS Array in 2006–2009 outline a broad zone of postseismic deformation with initial horizontal velocities to 90 mm/a, and postseismic uplift. We show that most of the postseismic signal after the great Kuril doublet is caused by the viscoelastic relaxation of shear stresses in the weak asthenosphere with the best‐fitting Maxwell viscosity in the range of (5–10) × 10 17 Pa s, an order of magnitude smaller than was estimated for several subduction zones. We predict that the postseismic deformation will die out in about a decade after the earthquake doublet. Our results suggest large variations among subduction zones in the asthenospheric viscosity, one of the most important rheological parameters. Citation: Kogan, M. G., N. F. Vasilenko, D. I. Frolov, J. T. Freymueller, G. M. Steblov, B. W. Levin, and A. S. Prytkov (2011), The mechanism of postseismic deformation triggered by the 2006–2007 great Kuril earthquakes, Geophys. Res. Lett., 38, L06304, doi:10.1029/2011GL046855.

Dynamics of the Kuril-Kamchatka subduction zone from GPS data

The Kuril-Kamchatka subduction zone is the most mobile and seismically active region in Northeast Eurasia. The Kuril island arc is one of the few tectonically active regions, where until recently there had been no space geodetic network. The first GPS stations were installed on the Kamchatka Peninsula in 1997, and on the islands of the Kuril arc from Kamchatka to Hokkaido, in 2006. The collected geodetic data allowed us to reveal the geometry of the interplate coupling along the whole Kuril-Kamchatka arc, and also to estimate the source parameters and their features for a number of major earthquakes in this area.

Monitoring of the eruption of the Sarychev Peak Volcano in Matua Island in 2009 (central Kurile islands)

In June 2009, one of the greatest eruptions of the Sarychev Peak volcano in Matua Island (48°06′ N, 153°12′ E) for the recent historical period occurred. With the help of satellite sounding methods, the first signs of volcanic activity were recorded and all the stages of the explosive eruption were traced. During the expeditionary investigations in the active volcano, unique data on the character of the eruption were obtained. The volume of erupted material was 0.4 cubic km, which lead to an increased area of Matua Island by 1.4 square km. The GPS observation station set at the distance of 7 km from the volcano recorded the rapid displacement of the Earths’s surface during the first two days of the active phase of eruption. This eruption of the Sarychev Peak volcano occurred 2.5 years after the catastrophic Simushir earthquakes in the period of intensive relaxation of stresses in the middle of the central part of the Kurile island arc.

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.

Viscoelastic deformations after the 2006–2007 Simushir earthquakes

Continuous measurements at the Kuril GPS network since 2006 have revealed anomalous coseismic and postseismic displacements of the Earth’s crust, which accompanied the great 2006–2007 earthquake doublet in the central Kuriles and were observed during 2.5 years after the events. Prior to the earthquakes, all observation sites of the Kuril network were moving towards the continent due to the subduction deformation of the continental margin. After the events, the direction of displacement had changed to the opposite direction at the stations located on the Matua, Ketoy, and Kharimkotan Islands, which were the nearest to the seismic events, and experienced a significant turn on the Urup Island nearby. Modeling of postseismic viscoelastic relaxation of strains in the asthenosphere suggested an acceptable explanation for the long-term anomalous offsets revealed. By solving the corresponding inverse problems, we estimated the viscosity of the upper mantle and constrained the slip distribution of the 2006 Simushir earthquake.

Post-seismic motions after the 2006–2007 Simushir earthquakes at different stages of the seismic cycle

We analyzed long-term satellite geodesic observations after the Simushir earthquakes of 2006–2007. Application of a key model of the structure of the island arc regions combined with a model of nonstationary convective system in the upper mantle allowed us to find a consistent explanation of the motion of the Earth’s surface and distinguish the segments of the island arc at different stages of the seismic cycle.

The new GPS evidence for the region of Bering microplate

The question concerning the integrity of major tectonic plates is still unclear for several regions covering the plate junction zones. The Northeast Asia is one such region, where there is no common concept of the configuration of plate boundaries. From the classical viewpoint, the dynamics of Northeast Asia is determined by the superposition of the relative rotations of the three major plates (Eurasian, North American and Pacific). According to the alternative viewpoint, the fragments that were split from these plates rotate independently in the form of microplates (Bering, Okhotsk, and Amur). The analysis of kinematics for the GPS stations located in eastern Chukotka, western Alaska, and on the Bering Sea islands suggests the existence of the Bering microplate rotating clockwise relative to the North American plate.

Cyclic variations in the Earth’s flattening and questions of seismotectonics

For more than a decade, the global network of GPS stations whose measurements are part of the International GPS Service (IGS) have been recording cyclic variations in the radius vector of the geodetic ellipsoid with a period of one year and amplitude of ~10 mm. The analysis of the figure of the Earth carried out by us shows that the observed variations in the vertical component of the Earth’s surface displacements can induce small changes in the flattening of the Earth’s figure which are, in turn, caused by the instability of the Earth’s rotation. The variations in the angular velocity and flattening of the Earth change the kinetic energy of the Earth’s rotation. The additional energy is ~1021 J. The emerging variations in the flattening of the Earth’s ellipsoid lead to changes in the surface area of the Earth’s figure, cause the development of deformations in rocks, accumulation of damage, activation of seismotectonic processes, and preparation of earthquakes. It is shown that earthquakes can be caused by the instability of the Earth’s rotation which induces pulsations in the shape of the Earth and leads to the development of alternating-sign deformations in the Earth’s solid shell.