Moho Depth and Sedimentary Thickness in the Capital Region

Receiver functions are calculated with teleseismic P waveforms recorded by broadband and short period stations of the Capital Digital Seismic Network, then the thickness and Poisson ratio of crust are investigated with the H‐Kappa method. The inversion results demonstrate that the crust thickens gradually from SE to NW with an average thickness of 34 km. The crustal Poisson ratios which are indicative of different tectonic regions, have a good correlation with the active faults. The regions with high Poisson ratios fall into the cross zone of active faults with cracked rocks. Because the velocity of the basement is much higher than that of sedimentary layer, the radial direct P wave propagating through the sedimentary layer becomes very weak as compared to the converted multiple phase in the sedimentary layer. At typical periods the first arriving energy consists of the direct P and the secondary conversion phases, and produces apparent delay of peaks. The quantitative relationship between the delay times of first arriving energy relative to direct P wave and the thickness of sediments was established by forward calculation, which enables to quickly estimate sediment thickness by the delay times of the first arrival pulse.