Mauna Kea earthquake ‘felt’ by SCUBA-2

Last Wednesday on the 19th of October, just after 2pm, a 4.5 magnitude earthquake shook the Big Island. These earthquakes are not an uncommon occurrence here, with frequent tremors occurring of around a magnitude of 4 and below. However, this particular earthquake happened just to the west and about 19 km below Mauna Kea and was felt by other observatories on the summit, including UKIRT where the shear pins, which protect the telescope structure from violent shakes, had to be replaced.

JCMT escaped unscathed, but the tremor was detected in the SCUBA-2 temperature logs, as can be seen in the graph above. The units on the left-hand axis are in degrees Kelvin. The mechanical energy that entered the instrument due to the earthquake was registered as a small temperature rise in the mixing chamber of SCUBA-2’s dilution refrigerator. This change in temperature was just 20 mK, or 0.02 degrees.  There were a number of aftershocks that followed, and these were also detected by the temperature sensors in the fridge, but these are harder to spot on this graph.