Fig. 3

Monthly stacked inter-station cross-correlation functions for transverse–transverse (T–T) components (left) and radial–radial (R–R) components (right) in the frequency range 0.1–0.5 Hz for station pair UEMC06–UEMC09. The four-digit number on the left of a trace indicates the month and year corresponding to the trace (e.g., 1303 means March 2013). The number on the right of a trace represents the number of time segments stacked to produce the stacked cross-correlation function