3:30 PM - 4:30 PM
[S14-P-09] Seismic discontinuities in the upper mantle around Vietnam inferred from receiver functions
Vietnam is tectonically located on Indochina and South China blocks that are separated by right-lateral Red River fault. Tapponnier et al. (1982) suggested that Indochina block was extruded southeastward by northward push of India to Asia. To investigate the structure of such blocks and its surroundings in the upper mantle, various seismological studies including tomography and splitting analysis have been performed around Indochina Peninsula. However, it seems that surveys on the seismic discontinuities in the upper mantle are insufficient in terms of their detection and determination of their undulation. In this study, we try to image seismic discontinuities in the upper mantle beneath Vietnam by using receiver functions.
We collected teleseismic P waveforms excited from earthquakes with magnitudes greater than 5.5 that occurred during March 2008 and Dec. 2015. The number of the used broadband stations deployed in Vietnam is 11. RFs are calculated through a spectral division of radial component over vertical component with a Gaussian low-pass filter of 0.16 Hz. The total number of the gathered RFs is 1,884 for all stations. The depth conversion of the time-domain RF is performed with IASP91 velocity model (Kennett and Engdahl, 1991). RF images are created by common conversion point (CCP) stacking technique.
Beneath Vietnam, the obtained RF images shows the 410 and 660 km discontinuities in the upper mantle (the 410 and 660). In a RF transect for northwest-southeast direction, we could image a depression of the 660 by 30 km in the northern part in Vietnam, compared with the depths in the southern part. Because the depth of the 410 is not changed, it seems that this represents a thickened mantle transition zone. Based on a study of global P-wave tomography, the Indian Plate subducts eastward and lies on the 660 under the northern Vietnam. Therefore, the depression of the 660 is presumably caused by cold material of the subducted slab.
We collected teleseismic P waveforms excited from earthquakes with magnitudes greater than 5.5 that occurred during March 2008 and Dec. 2015. The number of the used broadband stations deployed in Vietnam is 11. RFs are calculated through a spectral division of radial component over vertical component with a Gaussian low-pass filter of 0.16 Hz. The total number of the gathered RFs is 1,884 for all stations. The depth conversion of the time-domain RF is performed with IASP91 velocity model (Kennett and Engdahl, 1991). RF images are created by common conversion point (CCP) stacking technique.
Beneath Vietnam, the obtained RF images shows the 410 and 660 km discontinuities in the upper mantle (the 410 and 660). In a RF transect for northwest-southeast direction, we could image a depression of the 660 by 30 km in the northern part in Vietnam, compared with the depths in the southern part. Because the depth of the 410 is not changed, it seems that this represents a thickened mantle transition zone. Based on a study of global P-wave tomography, the Indian Plate subducts eastward and lies on the 660 under the northern Vietnam. Therefore, the depression of the 660 is presumably caused by cold material of the subducted slab.