A magnitude 4.1 earthquake hit this morning, 7:50 local time, the Northern Apennines between Prato and Bologna provinces, in proximity to Brasimone lake and Castiglione dei Pepoli village. Up to now, the quake is the main shock of an ongoing seismic sequence started at 2:15 that already counts 74 events, 5 of witch with magnitude in the range 3 to 4 (data taken from Iside INGV database).
Here is what La Gilberta with the S13 seismic sensor has recorded from 2:00 to 8:00 UTC.
Just yesterday we installed the SEP educational seismometer! Below we show the same event (high pass 1Hz filter) recorded by the new sensor that works at 10 s period. The waveform has been filtered because the S waves train saturated the dynamic range of the recording. We probably need to lower the gain of the digitizer. However, it seems that the SEP seismometer is working very well even in its temporary setting. Many other earthquakes of the Brasimone sequence are clearly visible in the recordings, but we also discovered another surprise.
The SEP also recorded the Mw 6.5, Vanuatu Islands [Sea] UTC=2015-01-23,03:47:28 (-17.04, 168.55, 216). These are the PKP waves, which traveled through the Earth’s outer core, for about 20 minutes (the earthquake origin time is 3:47 while the arrival time is about 4:07). Pisa is located at about 150° distance from the Vanuatu so, from the theoretical travel-time, the first arrival should be a PKP followed by a PP phase, as explained here.So it has been a very busy day for our instruments!