Just after two o'clock this afternoon a magnitude 4.5 earthquake struck the Big Island, located about 9 kilometers north west of Mauna Kea's summit and at a depth of approximately 19 kilometers. The earthquakes haven't stopped since then although none have been as strong as the first one. Although not a big earthquake anything over magnitude 4 on Mauna Kea has the potential to do some harm to the telescopes at the summit.
Fortunately the earthquake struck while we had a crew at the summit so they were quickly able to inspect both the JCMT and UKIRT. The JCMT was unscathed but a broken shear pin on UKIRT's south column was discovered which meant the telescope had been shoved out of alignment by the event and if it wasn't fixed we'd have no idea where the telescope would be pointing tonight. The amount of movement necessary to break a shear pin is tiny, less than a millimetre perhaps, but that small movement is multiplied several times on the sky and we could literally spend hours just trying to find out what we are looking at without a quick fix.
Fortunately our engineers and technicians were able to put the telescope back where it should be although this was a crude readjustment and we'll have to do a proper alignment in the next night or two, but it's currently good enough for government work! Still, this event is very unusual. We do experience earthquakes underneath Mauna Kea from time to time, but a cluster like this is very rare, I don't remember one like this occurring since I arrived here 15 years ago, but that's not to say it hasn't happened before, it's just unusual.
I think the following video was taken about a year and a half ago by a visiting observer from The University of Nottingham in the UK - they experienced a magnitude 4.4 earthquake underneath Mauna Kea during the run and the shear pins broke requiring a night-time fix by the observers. I remember being on the other end of the phone during this event! The stuff about the earthquake starts at about the 5-minute mark (and you'll see how physical effort at the summit is difficult!) but the whole video is interesting if you're curious about life on the summit!