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).