2.1 Seismic records
In this study, we use P waves recorded at regional distances. To ensure sufficient signal-to-noise ratio (SNR) for reliable P-wave onset time picking while avoiding the influence of source complexity, we choose events of magnitudes 4.0-6.2. This results in a total of 822 events selected in the Sichuan-Yunnan region from 1994 to 2020. Figure 1 shows the distributions of the events as well as the 284 stations used in this study. The events are mainly distributed in and around the major fault zones in the western part of the study region as expected, especially along the Longmenshan Fault Zone where the MW7.9 Wenchuan earthquake occurred in 2008. On the other hand, most of the stations are located in the eastern part of the study region. In the end, we use a collection of more than 300,000 vertical-component broadband records downloaded from the data management centers of the China National Seismic Network (SEISDMC, doi:10.11998/SeisDmc/SN) and the Incorporated Research Institutions for Seismology (IRIS, http://www.iris.edu).