Here in New Zealand, Google is trying out an earthquake warning system as described here. It’s a bit of an odd system because: (i) it’s on by default and to turn it off you have to go into the innards of your mobile; (ii) the alarm comes up as a message, but only lasts for a few seconds before disappearing completely; (iiii) there’s no documentation or facility for feedback.
Last night while watching TV, my mobile issued an EQ warning at about 21:47 saying there had been an EQ of M 5.2, 12 miles away (we use km, but never mind). I felt nothing, but my wife who was upstairs felt a bit of a shake. We don’t know if the shake occurred before or after the alarm, but they were pretty close.
Here’s what my RS recorded (the ordinate says m/s, but it’s actually counts - SWARM can’t find the calibration for some reason):
In fact the EQ was M 4.2, 14 miles away, so the warning magnitude was substantially (10 times) out, but the distance was near enough. That’s not too bad, but the warning was ineffective because the EQ was so close and the time between P and S waves was only 3 s.
Less impressive is that the warning system failed to alert for a M 5.5 EQ on the Alpine Fault 500 km away that occurred a few hours earlier. The time between P and S waves for this event was 54 s, which would be more effective for a warning. But only if the system worked. We await with trepidation a Great EQ that will occur eventually on the Alpine Fault. Let’s hope Google has sorted out this system by then.