D. I. Frolov

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.

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.

First geodetic observations of a deep earthquake: The 2013 Sea of Okhotsk Mw 8.3, 611 km-deep, event

We analyze the first ever GPS observations of static surface deformation from a deep earthquake: the 24 May 2013 Mw 8.3 Sea of Okhotsk, 611 km-deep, event. Previous studies of deep earthquake sources relied on seismology and might have missed evidence for slow slip in the rupture. We observed coseismic static offsets on a GPS network of 20 stations over the Sea of Okhotsk region. The offsets were inverted for the best fitting double-couple source model assuming a layered spherical Earth. The seismic moment calculated from static offsets is only 7% larger than the seismological estimate from Global Centroid Moment Tensor (GCMT). Thus, GPS observations confirm shear faulting as the source model, with no significant slow-slip component. The relative locations of the U.S. Geological Survey hypocenter, GCMT centroid, and the fault from GPS indicate slip extending for tens of kilometers across most of the slab thickness.

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.

Criterion for fracture transition to critical stage

AbstractWe have developed an analysis of data obtained in laboratory investigations of deformation of rocks by acoustic emission and X-ray microtomography. We found that defect accumulation occurs in fundamentally differing manners during loading. At first, defects are generated randomly and have a specific size determined by a typical structural element of a material (e.g., a grain in granite). Then the defects with sizes not dictated by the material structure are generated. The interaction between these defects gives rise to critical defects that are capable of self-development. In all probability, a sample breakdown results from the evolution of the ensemble of critical defects. We found that the fracture stages can be distinguished by the type of energy distribution function of the acoustic emission signals. At the first stage, the distribution is approximated by an exponential function, whereas the second stage is characterized by a power-law function that points to a self-organized criticality state...

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.

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.

Structure of a Deformed Inhomogeneous Material on the Data of Acoustic Emission and X-Ray Computer Microtomography

Accumulation of defects at various stages of the deformation of a structurally inhomogeneous material (granite) has been studied using two nondestructive methods: acoustic emission (AE) and X-ray computer microtomorgaphy (CT). The quasi-static testing of cylindrical samples of a Westerly granite was carried out under uniaxial compression. The control of the defect formation was realized using the real-time monitoring of acoustic emission. For each sample under study, several steps of the loading and tomographic imaging have been performed. We have found that an exponential or power-law function of the energy distribution of the AE signals makes it possible to select a sample region, in which the system of defects has transited into a self-organized criticality state and large cracks have been formed. This result coincides with the data of the X-ray tomography Computer Microtomography.

Recent geodynamics of the Kuril subduction zone

The collected GPS/GLONASS data allow us to reveal new information on the recent geodynamics of the Kuril Island arc. The maximum deformation stress accumulates in the southern and northern parts of the study area, while a long fading transition process of postseismic motions is observed in the central segment of the Kuril arc as a result of the 2006–2007 great Simushir earthquakes of Mw = 8.3 and Mw = 8.1. We have succeeded in revealing the recent interplate coupling geometry of the Pacific and the North American lithospheric plates and also in estimating the seismic potential of different segments of the Kuril subduction zone.