Deformations in the Middle America Trench According to Earthquake Focal Mechanisms and Their Features in the Area of the 2017 Мw 8.2 Chiapas Earthquake, Mexico

2022

Geodin. tektonofiz.

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Deformation features of the subducting Pacific lithospheric plate are considered according to the data on earthquake focal mechanisms. The territory includes the convergent boundaries between the Pacific Plate and the North American (in the Aleutian arc region), the Okhotsk, the Eurasian and the Philippine plates.It has been shown that the angle of subducting Pacific Plate in the Aleutian subduction zone affects the focal mechanisms of earthquakes that occurred in the upper, 35 km part of the oceanic plate in the zone of its bending. There occur normal-fault earthquakes at a steep-angle subduction and rare thrust earthquakes at a shallow-angle subduction. The azimuthal orientation of P-axes of the focal mechanism solutions in the upper (1–70 km) contact zone corresponds to the Pacific Plate displacement vector when the plate fragments are subducting west-northwestwards. There occurs a change in azimuthal orientation of the compression axes in the subducting plate at a depth of more than 70 km: the axes occupy different azimuthal sectors showing difference in the orientation of their slope, with the orientations of the T-axes become multidirectional.The calculation of seismotectonic deformations was carried out based on the data on focal mechanisms of 7768 earthquakes. It was revealed that the Exx and Ezz deformation fields are the most homogeneous at depths of 1–70 km. The pattern of seismotectonic deformations changes abruptly for deep parts of the subducting plate (105–200, 200–400, and 400–700 km), there are observed heterogeneous deformation fields Exx, Eyy and Еzz with alternating episodes of extension and shortening.There has been proposed the author’s scheme of the influence of the upper mantle convection structure on the geometry of the subducting plate (slab) as a potential catalyst for the processes responsible for the separation of seismic activity zones and the change of earthquake types with depth and in different parts of the extended subduction zone.

Section: использованные материалы методыunclassified

Focal Mechanisms of Earthquakes in the Subduction Zone of the Western Pacific Plate

Bushenkova

2022

Geodin. tektonofiz.

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Reconstruction of seismotectonic deformations of Asia in different layers of the Earth’s crust

Russian Journal of geophysical technologies

2022

Self Cite

The calculation of seismotectonic deformations for different depth levels 1–15, 16–35, 36–70 km was performed according to the data of 1819 mechanisms of earthquake foci that occurred in Central Asia (φ = 25° – 60° N, λ=60° – 115° E) for the period from 1976 to the end of July 2020 with M>4.7. The orientation of the main axes of the strain tensor reconstructed from the mechanisms of earthquake foci with M>4.7 coincide at different depth levels with mainly submeridional and north-eastern shortening and varying elongation from sublatitude to north-western and near-vertical. The consistency of the orientation of the main axes of shortening and elongation reconstructed from seismological materials and from the published results of calculating GPS observations, is traced.

Seismotectonic Deformations in the Pacific and Okhotsk Lithospheric Plates Contact Zone

Bushenkova

2021

Interexpo GEO-Siberia

The seismotectonic deformations were determined in the Pacific and Okhotsk (Eurasian) lithospheric plates subduction zone based on 2458 mechanisms of earthquake foci data for 1977-2019. The deformation features of medium in different deep layers are shown. The deformation field uniformity in the depth range of 1-70 km and the deformation field inhomogeneity for the submerged plate deep parts (105-200, 200-400 and 400-700 km) are revealed. One of the deformations field change reasons is the influence of ascending and, especially, descending currents of thermogravitational convection in the upper mantle sublithospheric part, in particular, the convection structure influence on the subducting plate geometry