Construction of a Velocity Model of Earth’s Upper Crust of the Eurasian–Sea of Okhotsk Plate Conjunction Zone along the Northeastern Segment of the 3-DV Profile Based on the Digital Processing Results of Compressional- and Shear-Wave Refractions

An automated algorithm for monitoring the areas of refraction event tracing along the profile based on the dynamic conversion was developed. Time sections of compressional- and shear-wave refractions recorded by the CDP shooting geometry in the Northeastern segment of the 3-DV survey base line were constructed. A high-velocity model of the upper part of the Earth’s crust was constructed to a depth of 2 km in the Sea of Okhotsk–Eurasian plate conjunction zone. Based on the increased velocity ratio of P- and S-waves, the refracting boundaries in the Ayan–Yuryakh block were rock sections with various lithological compositions in the sedimentary cover. The zone of reduced P-wave velocity and Vp/Vs ratio related to high rock fragmentation was identified in the high-velocity profile of the Chai–Yurya Fault zone, both above and below the refracting boundary. The velocity values of P- and S-waves (6.0–6.1 and 3.6–3.7 km/s, respectively,) and reduced Vp/Vs ratio (~1.65) due to felsic rock intrusions were recorded in the southern part of the Inyali–Debin block within the depth range of 1–1.5 km.