Change in the coda envelope decay before and after the ScS arrival

Examining seismogram envelopes of regional earthquakes in the world in periods from 1s to 20s for a wide lapse time range up to 2000s, we classified them focusing on the envelope characteristics before and after the ScS arrivals. We found that the coda decay gradient became smaller after the ScS arrival for all the period bands irrespective of focal depths; however, the change of coda decay gradient becomes smaller as the period becomes shorter and the hypocenter becomes shallower. We also found that envelopes have offsets before and after the ScS arrivals at 10s and 15s periods for deep focus earthquakes (>150 km) at some stations. It is prominent in seismogram envelopes recorded in Central Asia. Such a change in envelope around the ScS arrival is not clear in seismograms of shallow events (<50 km). These observations suggest that scattered waves of the ScS waves sometimes dominate scattered S waves and scattered surface waves. Such a regional variation of coda decay after the ScS arrival may reflect the difference in the medium heterogeneity of mantle.