A. S. Prytkov

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.

GPS-based modeling of the interaction between the lithospheric plates in Sakhalin

The recent geodynamics of Sakhalin are determined by the convergence between the Eurasian and North American lithospheric plates, which is reflected in the high seismicity of the island. The method of inversion of the horizontal velocities of the island surface with account for the geological features of the region is used to analyze the different models of the convergence between the plates. This made it possible to estimate the depth of the mechanical contact between the plates and the velocities of their convergence for the southern, central, and northern segments of the island.

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.

Modeling of coseismic crustal movements initiated by the May 24, 2013, Mw = 8.3 Okhotsk deep focus earthquake

The Okhotsk deep focus earthquake (Mw = 8.3), the largest in the history of instrumental seismology, occurred on May 24, 2013, at 05:45 UTC in the Sea of Okhotsk near the western coast of the Kamchatka Peninsula. For the first time we have succeeded in catching the field of horizontal and vertical coseismic offsets generated by a strong deep seismic event, and investigating its characteristics using continuous GPS measurements. Based on these data and taking into account the seismological information, we have developed a dislocation model of the Okhotsk deep focus earthquake.

Coseismic deformations of the Earth’s surface in Sakhalin related to the August 2, 2007, Mw = 6.2 Nevelsk earthquake

The satellite radiointerferometry data revealed deformations of the coastal part of Sakhalin Island caused by the earthquake with Mw = 6.2 that occurred in the Tatar Strait near Nevelsk. Based on the joint analysis of the satellite and seismological data, dislocation models were contrived for the main shock and its strong aftershocks with the western dip of the fault planes. This made it possible to determine the source mechanisms and the geometrical parameters of the seismic ruptures and to calculate the coseismic vertical and horizontal displacements. In contrast to the one-dimensional model of the insular land displacements determined from the satellite radiointerferometry measurements, this provided a three-dimensional model of the surface deformations for the epicentral zone.

Simulation of the 2011 South Sakhalin mud volcano eruption based on the GPS data

Sakhalin Island is the only region in the Russian Far East where mud volcanism is manifested on land. The South Sakhalin mud volcano is located in the south of the island in the zone of the Central Sakhalin Fault (upthrow-thrust). The horizontal and vertical displacements of the earth’s surface after this mud volcano erupted in 2011 are revealed for the first time based on the GPS observation data. On the basis of the inversion of the measured displacements for the homogeneous elastic half-space, a model of the finite spherical eruption source is constructed. The coordinates, depth, and possible size of the source are defined and the volumes of the erupted clay rock, water, and gas are estimated.

Horizontal motions and the generation of strong earthquakes in the North Sakhalin interiors

The recent geodynamics of Sakhalin Island is best described by the convergence of the Eurasian and North American (Sea of Okhotsk) lithospheric plates, which is manifested in the high seismic activity of the island. In North Sakhalin, the plate boundary is thought to correspond to a system of roughly N-S-trending faults, which belong to the North Sakhalin deep fault, and the Upper-Piltun fault; the latter was ruptured by the 1995 M 7.2 Neftegorsk earthquake. This study first confirmed that the stationary motion of the Sea of Okhotsk plate is retarded on this fault to form with time a series of drag folds and stress field anomalies. The latter are released during the subsequent (in a 400⦒o 1000-year period) strong earthquakes by seismic sliding on the flanks of the Upper Piltun fault. The 2003–2006 GPS observations revealed the free state of this fault zone with relative slip rates of 5–6 mm/yr.

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.

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.

Simulation of the eruption source for the South Sakhalin mud volcano in 2011 based on GPS observations

866 Mud volcanism is a unique natural phenomenon of a great interest to geology and geophysics. It is sup posed that mud volcanoes are indicators of geodynam ics in the Earth’s interior. However, there are only some general ideas about mud volcanoes [1–4], and the problems related to this natural phenomenon have no unambiguous and completely valid solution. Strong eruptions of mud volcanoes cause displace ment and deformation of the Earth’s surface. The present communication discusses how the horizontal and vertical displacements of the Earth’s surface occurred resulting from the 2011 eruption of the South Sakhalin mud volcano and revealed on the basis of GPS observations for the first time allowed us to sim ulate the eruption source. In the Russian Far East, Sakhalin Island is the only region where mud volcanism takes place. The South Sakhalin mud volcano is one of the well known and major volcanos; it is located in the southern part of the island, in the zone of the Central Sakhalin Fault’s (thrusted reverse fault, fault plane steeply dips to the west at 60°–70°) main fault plane exposure to the day surface [4]. In 2005, a local network consisting of five observa tion points was organized to monitor the main rup tures in the zone of the Central Sakhalin Fault. GPS measurements of the network were made in 2005, 2006, 2008, and in autumn 2011, after a quite strong eruption of the mud volcano (the precise eruption date in early 2011 is unknown). In the period prior to the eruption, a small sublati tudinal compression at the rate of 2–4 mm per year and sinking of the surface at the rate of up to 3 mm per year was observed in the study area. Resulting from the eruption, significant horizontal and vertical displace ment occurred in the vicinity of the volcano (Fig. 1). They were calculated from differences in the observa tion point coordinates as of 2011 and resulting from the linear extrapolation of change in the coordinates from 2005–2008 to the beginning of 2011. The maxi mal displacements were observed in the western wing of the Central Sakhalin Fault: observation points nos. MV03 and MV04 moved to the east by 15–33 mm and sunk by 23 mm (Fig. 1). Displacements of the eastern Simulation of the Eruption Source for the South Sakhalin Mud Volcano in 2011 Based on GPS Observations