Based on a newly developed AI-based method for extracting teleseismic Rayleigh wave dispersion curves by Y. R. Jiang, a large volume of high-quality teleseismic Rayleigh wave dispersion curves was obtained from very broadband dense seismic observation data collected by J. Y. Ning team from October 2022 to July 2023 with station spacing of approximately 16 km. Phase velocity imaging considering finite-frequency effects and S-wave velocity inversion based on the nonlinear Markov Chain Monte Carlo technique were conducted, yielding a S-wave velocity structure of the crust and mantle in the Xiong’an New District. The S-wave velocity structure indicates that the lower crust beneath the Taihang Mountains is in direct contact with asthenosphere, while a relatively thin lithospheric mantle exists beneath the North China Plain to the southeast of Taihang Mountains. The crust in the Taihang Mountains and its southeast adjacent area shows differences in the presence or absence of a thick mafic lower crust. The fault zone at the front of the Taihang Mountains has been the core area for the ascent of mantle thermal material, leading to the foundering of the ancient lithosphere since the Late Mesozoic. Since the Cenozoic, the region has undergone a tectonic process of lithospheric extension and cooling. This study also proposes a dynamic model for the high heat flow in the Xiong’an New District.

Based on the data from the array deployed by Peking University around high-speed rail in Baoding City, Hebei Province, China, in order to obtain spectra with higher signal to noise ratio at farther stations, the paper considers the variation of train type and stacks the spectra of three components of high-speed rail seismic signal produced by the same type trains on the same station. Using the clustering algorithm, the regular pattern of how the three component spectra vary with the train type and station position is obtained. Based on the characteristics of high-speed rail seismic spectra and their variation, we propose the concept of 4D ground-frequency map, and discuss its practicability in monitoring the status of high-speed rail and its surrounding media.

Employing a total of 10461 seismic records induced by 951 high-speed trains recorded by 11 shortperiod stations of a temporary array deployed by Peking University under the high-speed railway viaduct, we observe how the spectral characteristics vary with the speed and model of the train as well as the rail and groundsill by using a clustering algorithm K-Means. For a high-speed train in uniform motion, the spectrum of the produced seismic wave is mainly composed of nearly equally spaced peaks and its fundamental frequency is equal to the ratio of the train speed to the carriage length. By aligning the fundamental frequency, the influence of the train speed is reduced to make the spectrum pattern time-independent and easy for comparison. Clustering results show that the spectra of the high-speed rail seismic events have stable patterns when the train model, rail and groundsill conditions keep the same; the stable spectrum patterns change significantly with the change of the train model, rail and groundsill conditions. The monitoring of the stable spectral characteristics might possibly be used in safety control of high-speed rail.