I am requesting assistance from fellow shakers regarding a recent seismic swarm in my area. During the last week or two, several tremors - sometimes several in a day are felt and have been reported by the local agency as being small, shallow tremors nearby in the M2-M3 range. Below is a map of my location (near Volivoli) to the reported tremors, so fairly close only about 8km away.
A couple hours ago I have just installed a raspberry shake (Station ID R2551) and am already recording multiple tremors. My question is, why do they only seem to be occuring late at night i.e. could this be something other than earthquakes? Most felt reports are in the early hours of the morning with only a few during the daytime. The signatures definitely look like earthquakes which I have attached below. Please let me know what you think and if
- they seem to be earthquake signatures
- any reason for why they seem to be occurring mostly at night
Thank you very much
We have seen the new installation on our servers; thank you for expanding the local network in Fiji!
Has the situation changed somewhat in this last week, or has it remained the same as you described?
From what you write, this appears to be a low-magnitude seismic swarm, localized W of Nanau Island, with the traces you have posted resembling the ones usually seen in earthquakes, as you have surmised.
Regarding your second question, there is this interesting USGS page: https://www.usgs.gov/faqs/can-position-moon-or-planets-affect-seismicity-are-there-more-earthquakes-morningin-eveningat that expands on this observation.
Furthermore, the increasing felt reports during nighttime or the early hours of the morning could be related to the fact that people may perceive earthquakes to be more common at night because they are more likely to be indoors and in quieter environments, where they can feel the shaking more strongly compared to daytime activity.