Detected MSTIDs of each subnetwork. Parameter evolution of detected TIDs before the EQ during 22:00–24:00 UTC, representing non-uniformly scaled polar plots for TIDs of the corresponding grid networks (a)–(d), the location representing for the azimuth vs. velocity of 0–360 degree and 0–900 m/s, the circle size for wavelength of 50–600 km, and the color code for different time intervals.