Fig. 3

Depth sections of the reflection responses at Station E.STHM. a Velocity profile (blue) and the relationship between lag time \(\tau\) and depth (green) that were used to generate the depth sections. b Estimated reflection responses for different numbers of stacks based on magnitude thresholds. Blue lines indicate the ratios of averages to standard deviations of individual earthquakes (\({a}_{i}^{ave}\left(\tau \right)/{\sigma }_{i}^{a}(\tau )\)). Red lines show the ratios of averages to standard deviations of weighted stacks (\({a}^{ave}\left(\tau \right)/{\sigma }^{a}(\tau )\)). Black lines indicate \(\pm 3\). The frequency band is 1–10 Hz. c Reflection responses for various frequency bands estimated from all 33 earthquakes. d Reflection responses for various frequency bands estimated from all earthquakes deeper than 60 km (purple; 113 events), 80 km (red; 33 events), and 100 km (green; 20 events)