Tuesday, June 24, 2014

We can't feel your ghost quakes

Recent quakes close to Raoul Island
Today there was a large quake in the Kermadecs. This is thousands of kilometers North-East of New Zealand, not far off the volcano Raoul Island.

Unfortunately this quake, and a few other deeper distant events, cause our system some strife!  Our instruments are very sensitive and have no trouble recording distant quakes.

Now if we start with a wee earthquake 101: Earthquake waves are made up of P-waves and S-waves (amongst others). The P wave arrives first and and then the slower S-wave arrives, you can see this on the photo below.

M7.2 Japan Quake arriving on our stations

 The delay in the arrival of the S wave (as well as a few other depth related factors) causes our automated quake system SeisComP3 to think that there were actually multiple large quakes in New Zealand, as shown on our app below.

 We have nicknamed these events 'Ghost Quakes'.

Todays event even gave us "Ghost Aftershocks" with numerous mag 3 and 4 events being posted due to the aftershocks from the large Kermadec event.

We are always working on our automated system and are trying to teach the system to stop doing this, it is a tricky task however!  99% of the time our system works amazingly and you get good quake info really quickly.  If you do get alerted to a large quake the best thing to do it check our website and see if it has been reviewed by one of our team.  Another trick is to check the 'felt reports'  if a large quake has none, its a bit suspect!