On 5 June at 20:51 local time, the Cascade Volcano Observatory’s (CVO) seismic network detected a volcano-tectonic earthquake with magnitude M 3.9 that occurred about 4 km south of the summit at 4.3 km depth.
It was preceded by several earthquakes in the hour prior to the M 3.9, and tens of aftershocks have occurred so far with event rates declining in a manner typical of mainshock-aftershock sequences. The earthquake was felt in the vicinity around the volcano.
The mainshock characteristics and location are consistent with past swarms in the Mount Hood area, including a M 4.5 on June 29, 2002, that was located ~1 mile east of the M 3.9. Aftershocks will likely continue for hours or days, some of which may be felt.
Seismologists from the CVO and Pacific Northwest Seismic Network don’t indicate that the seicmic event could be related to volcanic hazard at the volcano.
Source: Cascade Volcano Observatory volcano activity update 8 June 2021