Earthquakes can occur in swarms[1] (distinct from aftershocks), with many of a similar size (i.e. Not a big quake followed by smaller ones) occurring in a small area over "relatively short" periods of time (i.e. days, weeks, or years).

The USGS map shows the 7.7 quake being followed by about 19 other smaller quakes near or in Indonesia within just a few hours. These are probably aftershocks.

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[1]https://en.wikipedia.org/wiki/Earthquake_swarm