Wednesday, April 1, 2020

Earthquake at NearSys Station, 31 March 2020

Shortly before 6:00, NearSys Station experienced a magnitude 6.5 earthquake near Challis. The earthquake was not severe here, some 140 miles from the epicenter. Nonetheless, it was a powerful shake that left the furniture creaking and chandelier rocking.

My slinky-style seismograph measures vertical displacement best. And when this 30 second long quake struck, the seismograph was left shaking for over 14 minutes. Over 20 aftershocks were detected over the next 21 hours. Aftershocks are still being detected 24 hours later.

The time between the arrival of the P and S wave is on the order of 15 seconds. The P wave arrives first because it travels the fastest. The S wave is slower and if we measure the difference in their arrival times, we can determine the distance to the earthquake's epicenter. Grom what I see on earthquake tables, a difference of 15 seconds is about 150 km, or 91 miles.

Seismogram of the earthquake and many of its aftershocks

The extracted earthquake and first aftershock

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