CRUST AND UPPER MANTLE IN THE ZONE OF JUNCTION BETWEEN THE CENTRAL ASIAN AND PACIFIC FOLD BELTS

Spatial distributions of gravity sources and density contrast of geological media, which is reflected by the values of parameter μz , into the crust and upper mantle of Northeast China are analyzed. Features of rheological layering of the tectonosphere and deep spatial relationships of tectonic structures (cratonic blocks, marginal terranes, and sedimentary basins) are defined. In the density contrast distributions the formal signs of Paleozoic subduction of the North-China Craton and Mesozoic subduction of the Pacific Plate under the Amurian Plate were revealed. Crustal deformations are in sharp contrast with upper mantle deformations in structural planes resulting from different directions of tectonic stresses in the Paleozoic and Mesozoic. Thrusting of marginal terranes (Jamusi, Khanka) over the Amurian Plate lithosphere is revealed. Rheology and deep structure of North East China bear many similarities to other regions of the Pacific western margin in Asia and Australia.

THE WAVE GEODYNAMIC IMPACT OF TECTONIC PROCESSES ON THE AMURIAN PLATE

The analysis of data on the migration of earthquakes and slow deformations from the Indo-Eurasian collision and the Western Pacific subduction zones is given, and the wave “geodynamic impact” of these tectonic processes on the Amurian plate and surrounding structures is shown. The interaction and a relative contribution of collision and subduction to the recent geodynamics of the Amurian plate are discussed. A scheme is constructed showing localizations of the slow strain wave manifestation in the areas of central and eastern Asia. The calculations are performed aimed at revealing a transverse migration of earthquakes (M ≥ 6.5) directed from the Japan and the Kuril-Kamchatka trenches toward the Asian continent during the time period from 1960 to 2015. The migration of earthquakes along the profile crossing Hokkaido Island occurs at velocities of 15 and 23 km/yr, whereas the migration velocity from the Kuril-Kamchatka Trench via Sakhalin Island is evaluated from 20 to 40 km/yr at different depths. We focus on an insufficient study of the influence of the Western Pacific subduction on the formation of the deformation field in continental Asia.

Slow strain waves in blocky geological media from GPS and seismological observations on the Amurian plate

Based on the statistical analysis of spatiotemporal distribution of earthquake epicenters and perennial geodetic observation series, new evidence is obtained for the existence of slow strain waves in the Earth. The results of our investigation allow us to identify the dynamics of seismicity along the northern boundary of the Amurian plate as a wave process. Migration of epicenters of weak earthquakes (2 ≤ M ≤ 4) is initiated by the east–west propagation of a strain wave front at an average velocity of 1000 km yr−1. We have found a synchronous quasi-periodic variation of seismicity in equally spaced clusters with spatial periods of 3.5 and 7.26° comparable with the length of slow strain waves. The geodetic observations at GPS sites in proximity to local active faults show that in a number of cases, the GPS site coordinate seasonal variations exhibit a significant phase shift, whereas the time series of these GPS sites differ significantly from a sinusoid. Based on experimental observation data and the developed model of crustal block movement, we have shown that there is one possible interpretation for this fact that the trajectory of GPS station position disturbance is induced by migration of crustal deformation in the form of slow waves.