Loyalty Is M 7.7 10-Feb-2021

A magnitude 7.7 EQ at 33 km depth occurred in the Loyalty Islands, 2271 km north of us this morning.

My RS1D RC144 on Banks Peninsula, NZ gave the following record:

The upper plot is the raw data; middle plot shows waves with timescales less than 1 s; and lower plot shows wave with timescales greater than 1 s. The travel times for P and S waves were calculated using https://service.iris.edu/irisws/traveltime/1/. The surface waves were assumed to travel at 3.5 km/s.

There are some interesting features about this event:

  1. By the time the P waves reached Banks Peninsula, most of the short period waves had dissipated, leaving mainly waves with periods greater than 1 s.
  2. There were no apparent S waves.
  3. The Rayleigh and Love surface waves arrived about 120 s later than expected, but persisted for 15 minutes or more.

Fascinating analysis. Barely detected it here, possibly due to local noise. Seems to have been ringing for a few days now. Thanks for sharing!

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