ОСОБЕННОСТИ ГЛУБИННОГО СЕЙСМИЧЕСКОГО СТРОЕНИЯ ТИХООКЕАНСКОГО ТЕКТОНИЧЕСКОГО ПОЯСА В СТВОРЕ ОПОРНОГО ПРОФИЛЯ 8-ДВ

Abstract

The article presents the results of deep seismic studies over the Sikhote-Alin fragment of the 8-DV reference geophysical profile running across the large fold structures of the Pacific tectonic belt, that is, the Sikhote-Alin orogenic belt with the superimposed Middle Amur sedimentary basin and the East Sikhote-Alin volcanoplutonic belt. A deep seismic section of the Earth's crust and upper mantle with the distribution of longitudinal wave velocities is constructed. In the upper part of the section, P-wave velocities vary from 4.0–5.0 km/s within the Middle Amur sedimentary basin and the eastern part of the Eastern Sikhote-Alin volcanoplutonic belt to 5.5–5.6 km/s in the central part of the Sikhote-Alin orogenic belt. It is found that the thick Paleozoic assemblage of sediments within the Middle Amur sedimentary basin is complexly faulted and folded. Crystalline rocks with compressional wave velocities of 6.0–6.2 km/s occur at depths of 8 to13 km in different parts of the Middle Amur sedimentary basin and at depths of 4 to 6 km within the Sikhote-Alin orogenic complex. Compressional wave velocities of the crust in the Sikhote-Alin fragment of the 8-DV profile are between 6.3 and 6.35 km/s. The crust varies in thickness from 32–34 km in the northern part of the fragment to 36–37 km in its central and eastern parts. Along the Moho, P-wave velocities are 8.1 to 8.3 km/s; a number of areas of reduced Vp from 7.8 to 8.0 km/s were identified in the junction zones of large crustal blocks. P-wave data were used to identify anomalies which were correlated with structural-tectonic zones, deep fault zones, and seismicity. Thus, along the deep Central Sikhote-Alin fault, the Middle Amur basin is identified, which is infilled by low-velocity sediments of considerable thickness, with Paleozoic sediments shifted to between 4 and 5 km at its junction with the Sikhote-Alin orogenic. Zones of increased heterogeneity in the upper crust projected onto the area within the contours of the Middle Amur sedimentary basin are characterized by increased seismicity.