The Application Of Receiver Function And T Wave In The Study Of The Topography Of The Earth's Discontinuities

The interior discontinuities of the earth play an import part in the study of the earth's interior velocity structure,mineral composition,the evolution and interaction between different layers. Affected by anisotropy caused by the mineral arrangement,temperature anomaly,subducted slab and the mantle super plume, the discontinuities of the earth can afford some topography instead of horizontal flatting. Abundant studies suggest that the topography at each discontinuity can give some information about the material temperature and the mantle convection.In this study, we use the receiver function and Oceanic T wave to study the topography of the interior discontinuities. Due to the different methods to study the topography, we separate our work into two groups: (1) the deterministic study on the topography of the discontinuities. Depending on the traditional receiver function study, we have made some improvements in the following aspects: (a) we firstly write the 2D common convection point method, and then we test the correctness and robustness for two complicate input 2D velocity models. (b) For further application, we improved the 2D code to 3D, and then use this method to study the topography of the upper mantle discontinuities beneath Venezuela and Tibet region. During the data processing, for improvement, we also introduced the gauss weight function to rate the energy from different distance convection points. Another improvement is also made by weighting the original receiver function, and this weight will be introduced to the CCP stacking procedure. (c)At last, for comparison, we have written a 3D gravity inversion method to get a large scale Moho topography result which is used to compare with the result of the receiver function. (2) The statistic study on the topography of the discontinuities.. In this study, we calculate the effect of the topography of the Oceanic bottom to the synthetic T wave generation. From synthetic test results, the topography of the Oceanic bottom plays an important part in the generation of the synthetic T wave. After that, we also study the empirical relationship between the earthquake focal mechanism and the energy of the T wave; the other work about T wave is that we use the T wave generated by deep earthquake to study the quality factor of the subducted slab.(A) The deterministic study on the topography of the discontinuitiesIt is an ordinary way to use the precursor phases to obtain the topography of the discontinuities, such as the study of the S₄₁₀S,S₆₆₀S,P₄₁₀P,P₆₆₀P can be used to study the topography of the 410 and 660Km discontinuities. In this paper, we mainly use the H-Kappa stacking receiver function method and the 3D common convection point method to study the large scale topography of the crust and upper mantle discontinuities. The main studies in this paper are as follows:(1) Utilizing the grid search H-Kappa stacking receiver function method, we obtain the thickness of the crust and the Vp/Vs ratio (Kappa) beneath the stations. Such results are useful to interpret the regional tectonic and petrology.(2)In this study, we develop the 2D Common Convection Point (CCP) stacking receiver function method to 3D. After testing the correctness and robustness of our code and method, we use the CCP stacking method to study the upper mantle discontinuities of Venezuela and Tibet region to get the topography of the 4101am 660km discontinuities. During the data process, we introduce the gauss weighting function and the Nth-root stacking method to improve the quality of the image. Benefit from the Clapeyron slope of mineral physics experiment at high temperature and high pressure, we translate our topography result of the discontinuity to the mineral temperature variation, thus our method can be used to detect the subducted slab (cold),hotspots and plume (hot).(3) We develop a code based on the method of Prof,Fu and Prof,Liu, and then apply this method to get the crustal thickness of the whole China region. The purpose of this study is used to give a comparison to the receiver function method.(4) By analyzing the PKKPbc and its precursor, we obtain the seismic constrain of the Core Rigidity Zone (CRZ) composed by the outer core light element at the top of the outer core. In addition, after comparing the time difference between the precursor and the main PKKPbc phase at different outer core conversion point positions, we find the seismic evidence for the tangent cylinder structure in the outer core.As a summary, in this article, we systematically present a whole method including the receiver function extraction,the receiver function signal to ratio improvement,receiver function stacking to get inner earth image,mineral physics experiment at high temperature and high pressure to interpret the topography result. Based on the upper method, we can obtain the topography of the discontinuities immediately, which is correlated with the distribution of the subducted slab and hotspots and plume. Because more and more stations and data will be available soon, the method in our article will have a bright future. Utilizing the gravity method to inverse the topography of Moho will provide another independent way to give a comparison with the receiver function method, and will hopefully be a good supplement for the receiver function.(B) The statistic study on the topography of the discontinuities.To small scale topography study, considering the frequency issue, it is hard to use a certain phase to study the small scale topography. We mainly use the statistic method to study the small scale topography of the discontinuities. In this article we mainly take the study of the effect on the small scale topography at the Oceanic bottom to the generation of the synthetic T wave as an example. After comparing the T wave energy generation by different small scale topography at the Oceanic bottom, we find the existence of the small scale topography at the Oceanic bottom plays an important part in the generation of the T wave in the SOFAR channel. Furthermore, we also give two application studies of the T wave including (1) the empirical relationship between the T wave energy and the fault mechanism parameter of the earthquakes (2) the study of the Fiji-Tonga slab quality factor from the T wave generated by deep earthquakes in this region.