At 5:54 p.m. Greenwich Mean Time in Potsdam, Germany, a horizontal pendulum suddenly started shaking. The pendulum scratched out spikes in ground movement for a few hours before settling down.

All of this sounds perfectly typical for a seismograph, but in fact, the event was quite extraordinary: The date was 17 April 1889, and this was the first recorded teleseismic event, a magnitude 5.8 earthquake that had shaken Tokyo, Japan, a little more than an hour prior.

Now, 130 years after that Tokyo quake kicked off the modern science of terrestrial seismology, a more sophisticated seismometer is retracing those first shaky steps 225 million kilometers and a planet away.

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