**1. Introduction**

Sakhalin Island belongs to the tectonically active region of Northeast Asia. Within its boundaries, the border between the largest tectonic plates of the Earth the Eurasian Plate, North American and Pacific ones—passes through the island territory. А wide boundary zone represented by a set of independently moving microplates expands along the convergent boundaries of these plates.

The border between the Amur and Okhotsk (Okhotsk Sea) Plates, the largest microplates, is often associated with the Central Sakhalin Fault of meridional strike. Inside the Sakhalin, the interplate border is drawn along the Western Sakhalin Fault in the south, and as the arc line, partially coinciding with the Eastern Sakhalin Fault (**Figure 1**) [1, 2], in the Central and Northern Sakhalin. Alternatively, this border goes along the Central Sakhalin Fault (Tym-Poronai Fault in the Northern Sakhalin) [3].

#### **Figure 1.**

*Kinematics of the modern plate movements in the Okhotsk Sea region. (A) Relative to Eurasian Plate (not moving); (B) relative to Kuril Islands microplate. The arrows show the directions and values.*

According to the paper [4], the interplate border is drawn along both the Western Sakhalin Fault and the Central Sakhalin Fault. The analysis of neotectonic stress to the West and East of the Central Sakhalin Fault allowed us to obtain new information about location of the border aforementioned [5–7].

In addition to our previous publications [5, 7], this chapter presents the results of extended tectonophysical studies based on a set of methods [6, 8–10], and the field measurements of 2019–2020 campaigns are involved. The paper presents the manifold manifestations of the geodynamic and seismic processes in the crust between the Amur and Okhotsk microplates, lying within the convergence zones of the Pacific, Eurasian, and North American tectonic plates.

The research aim is to study the recent tectonics, to reconstruct neotectonic stress by a set of methods, and to review the published seismological and geophysical data to approve or disprove the interplate border location. This involves the demonstration of effective but underused structural and tectonophysical methods to study the tectonics of some regions and to develop a model of the stressed state of Sakhalin Island. The above methods are able to give the characteristics of the post-Miocene stress field, but we will show (taking into account the seismological and GPS motion data) that the modern stress field in the Sakhalin crust is inherited mostly from the post-Miocene model. The modern stress nonuniformity as well as the climate change is proved to control both engineering geological processes and geotechnical conditions on the territory under consideration.
