Geoinformatika 2016; 1(57) : 48-56 (in Russian)

INTERRELATION BETWEEN THE VELOCITY STRUCTURE OF THE MANTLE BENEATH THAILAND AND ITS SURROUNDINGS AND SEISMITY OF THE REGION

L.N. Zaets, I.V. Bugaenko, T.A. Tsvetkova

Institute of Geophysics, NAS of Ukraine, 32 Palladin Ave., Kyiv 03680, Ukraine, e-mail: larysa_zaiets@ukr.net, igor_bugaenko@ukr.net, tsvet@igph.kiev.ua

Purpose. As part of the constructed three-dimensional P-velocity model of the mantle of Southeast Asia, we considered velocity structure of the mantle beneath Thailand and its environment in order to identify possible prerequisites in the deep structure of the mantle for the manifestation of earthquakes in the region.
Design/methodology/approach. 3-D P-velocity  model of the mantle of Southeast Asia was obtained with the method of Taylor s approximation of  solving the problem of seismic tomography of  P-waves  arrival time introduced by V.S. Geyko.
Findings. For areas beneath Thailand and its environment that are characterized by high seismicity, we identified commonalities of velocity structure of the mantle, such as:
–   allocation of mantle-velocity columns. In velocity characteristics of the mantle, these zones appear as subvertical region sequences of high and low-velocity anomalies, which are the consequences of the fluid process in an inhomogeneous velocity environment (blocks Indobirmaniya, Shan Thai, Sinobirmaniya block, Kho Rat);
–   propagation of low velocity of the lower mantle (2600 km);
–   propagation of high-velocity inclined layers. From the Indobirmaniya block under the Shan Thai block the inclined layer is immersed in the transition zone of the upper mantle; from the Sinobirmaniya, under the Kho Rat block, the transition zone of the upper mantle is immersed in the middle mantle;
–   bulge up of top of the upper mantle transition zone – Sinobirmaniya, Shan Thai, Kho Rat.
In addition to the traditional view of the gradient environment latitude and longitude sections, we considered the behavior of velocity gradients in depth.
Practical value/implications. The introduced velocity gradients permitted to receive seismic boundaries of the second kind, which allowed us to clarify characteristics of the environment represented as a contour residual velocity relative to the reference model. It was shown that the seismic boundary of the second kind stressed mantle column highlighted on the vertical cross sections. On the surface, the mantle-velocity column corresponds to fault zones (block Kho Rat (Thailand)).

Keywords: mantle, velocity structure, earthquake, Thailand.

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