A busy week in Italy with lots of earthquakes... the biggest was this morning at M6.5-6.6... early indications are that although many buildings were damaged most people had already evacuated last week because of smaller earthquakes
The WMOK recording is very interesting because it shows big and very low frequency surface waves arriving about 30 minutes after the first shock. If you look carefully from 07:20 to 07:35 you can see the frequency content of the signal changing(the wiggles get closer together). This is because lower frequency seismic waves travel faster (they have longer wavelengths so travel deeper in the earth where pressures are greater)
Soundified
https://drive.google.com/file/d/0B0ITK4QvKwjuZUN3c1BXVlBrOTRmZFJfbDRHV3J6LUYzTC04/view?usp=sharing
if we speed up the seismogram recorded at WMOK and play it as an audio file you can hear these changes in frequency content as changes in pitch.
Italian M6.5 earthquake recorded in Rutland (top) on MAOK school sensor in Oklahoma (middle) and USGS professional site WMOK (bottom) also a M3.8OK earthquake this morning |
Soundified
https://drive.google.com/file/d/0B0ITK4QvKwjuZUN3c1BXVlBrOTRmZFJfbDRHV3J6LUYzTC04/view?usp=sharing
if we speed up the seismogram recorded at WMOK and play it as an audio file you can hear these changes in frequency content as changes in pitch.