P-wave velocities of the upper mantle of the Tethysalpine geosynclines

• Datum: 2020
• Hauptverfasser: Gordienko, V.V., Gordienko, I.V., Gordienko, L.Ya.
• Format: Artikel
• Sprache: Russisch
• Veröffentlicht: S. Subbotin Institute of Geophysics of the NAS of Ukraine 2020
• Schlagworte: Tethys; upper mantle; P-wave velocity
• Online Zugang: https://journals.uran.ua/geofizicheskiy/article/view/222295
• Назва журналу: Geofizicheskiy Zhurnal

The aim of the work is to calculate the velocity distribution of the longitudinal seismic waves (VP) in the upper mantle at depths from the discontinuity M to 400 km. The object is the territory of Tethys — the belt of alpine geosynclines crossing all of Eurasia from Gibraltar to the Indonesian archipelago.The model of the first approximation is constructed according to previous studies and our results on island arcs. It was possible to choose the velocity distribution in the upper mantle of Tethys, according to which the travel time close to the observed one was calculated. The degree of coordination is quite sufficient for the recognition of the used distribution of velocity as real. The data on approximately 18,000 earthquakes, the waves from which reached 27 seismic stations, are used. The location of the epicenters of earthquakes and stations ensured the passage of seismic rays precisely along the upper mantle of different Tethys regions. On the island of Sumatra a comparison was made of the constructed travel times with those obtained earlier in the study of the upper mantle of island arcs and coastal ridges of the Pacific Ring. Harmonization of the travel times is considered satisfactory. The VP distribution obtained in this way is compared with the calculated from the ideas of the advective-polymorphic hypothesis. The velocity model of the upper mantle of the Precambrian platform outside the zones of modern activation is complemented by the influence of the anomalous temperatures of both signs in the subsoil of the geosyncline. The result is somewhat different from the calculated earlier for the upper mantle island arc. There are two main reasons for this difference: probability of a somewhat higher radiogenic heat generation in the rocks of the upper mantle of the arc and somewhat smaller typical crustal thickness under the arc. The discrepancies between the models are small, averaging about 0.03 km/s. They do not exceed associated only with the errors of calculations. A noticeable excess of the magnitude of the discrepancies is detected only at a depth of 400 km, where the uncertainty of the calculation results is maximum.The discrepancy between the experimental and calculated velocity distributions in the upper mantle of Tethys is 0.05 km/s. They can be considered coincident.