Lithospheric Structure under the Caucasus Mountains from Joint Inversion of Receiver Functions and Rayleigh Wave Dispersion
Date Issued
2014
Date
2014
Author(s)
Li, Shih-Ting
Abstract
The Caucasus mountain belts may be considered as the northernmost boundary of the collision created by the impinging of Arabia to Eurasia. In this study, we jointly invert receiver functions and surface wave data to estimate the velocity structure under a combined seismic network in Georgia covering the central-western part of the Greater and Lesser Caucasus. This seismic network consists of 10 broadband stations from the Institute of Earth Sciences, Academia Sinica of Taiwan and the other 4 from the Georgia Seismic Center. The method can obtain the detail velocity structure with little trade-off between absolute velocity and depth of the discontinuity.
For the surface wave constraints, we extract surface Rayleigh wave phase dispersion using two-station method and the results indicate that the phase velocity under the Lesser Caucasus is higher than Great Caucasus by 0.25 km/s in average. As for the receiver functions, we select teleseismic earthquakes and deconvolve Z from R components for each station using different Gaussian filters. Because of the azimuthal variations and ray parameter-dependent variations are found at some stations, we first focus on the earthquakes with back azimuth from 90° to 120°.
The Moho depth obtained by joint inversion is about 40-50 km for the stations in the Greater Caucasus, and the depth increases toward the eastern part of the array under the central Great Caucasus. The results are consistent with the depths obtained using the H-κ stacking technique. As for the Lesser Caucasus, the boundary of Moho is less obvious, with a wider zone of gradient between 45 and 65 km. The Moho depth is 2-5 km shallower than the previous estimates using a threshold value Vs = 4.2 km/s as the definition. Interestingly, we discover a very thin but sharp low-velocity layer at the depth of 5 km beneath station TRLT, which is located on the Javakheti volcanic plateau with active earthquake swarms nearby. More evidences are required to confirm whether the low-velocity layer is associated with a magma chamber underneath, similar to the findings from the receiver function studies in the Altiplano-Puna volcanic region, Central Andes.
Subjects
高加索
地殼構造
接收函數
大陸碰撞
表面波
Type
thesis
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