Today my DIY seismic sensor captured a pair of strong earthquakes off the coast of New Zealand, over 9400 km away. One of the things I like about long-distance earthquakes is the clean surface waves that the sensor records.

Here are the surface waves from a mag 7.4 foreshock:

A few hours later, there was a massive magnitude 8.1 earthquake in the same area. The surface waves from this one look even prettier:

Note the two wave trains – a shorter Love wave train (about 20:07 to 20:11) followed by the Rayleigh wave with longer duration (starting around 20:12).

Note also the different wave frequencies – the Love wave’s main harmonic is at roughly 0.04 Hz (a period of roughly 24 sec) while the Rayleigh wave is at about 0.06 Hz (~ 16s period).

Check the project site for more details.