Nearby accelerometer seismograms show that Norcia moved about 40cm to the west and 10cm upwards in about 4s during the M6.5 Central Italy earthquake. This information on permanent ground displacements is available in near real-time and can be used for rapid, early emergency response after a significant earthquake.
The Italian National Accelerometer Network (RAN) has a station NRC at the town of Norcia, a few kilometers SSW of the epicenter of the 30 Oct 2016 M6.5 Italy earthquake:
The ground motion seismogram for about 40sec at NRC are plotted below. The upper 3 traces show ground acceleration: up-down (blue), horizontal away-and-towards the earthquake rupture (magenta), and perpendicular horizontal motion (yellow). The middle three traces show the corresponding ground velocity, and the lower traces show the ground displacement*.
The displacement seismograms (lower traces) show an artifact “drift” after about 40m30sec due to instrument limitations. But before this time there is a clear offset of the traces of about 4ocm starting after the first P arrival from the earthquake hypocenter (P). This offset is the true, absolute movement of the ground at Norcia during the earthquake rupture. This movement is “carried” with the S waves and other “near-field” motions emanating from the earthquake rupture as it propagates away from the hypocenter.
Zooming in on this motion in a 3D particle motion plot (below, left) and on the displacement seismograms (below, right), shows that this movement is to the west (about 40cm) and upwards (about 10cm) and occurred over about 4sec:
Viewing the first 5s of particle motion from above, we see that the horizontal movement at NRC is mainly in a WSW direction (azimuth 250-260° E of N):
This direction of motion corresponds to that expected for an extensional rupture aligned along the Apennines range with main release of rupture energy to the east of Norcia. Indeed, GPS displacements show the same direction and amplitude of motion for stations near Norcia:
And displacements from satellite inferometry (InSAR) show a similar amplitude of motion westwards at Norcia:
The good match of the accelerometer displacements to those from GPS and InSAR is important, because the accelerometer data (and some GPS data) is available in real-time and can be used for rapid, early emergency response after a significant earthquake.
* Traces are processed by: 1) removing the mean of the signal before the P wave (background signal before event recorded) and 2) integrating. This converts the original ground acceleration to ground velocity. A second application of this processing produces ground displacement.
Italian National Accelerometer Network (RAN)
INGV 2016, SUMMARY REPORT ON THE 30 OCTOBER, 2016 EARTHQUAKE IN CENTRAL ITALY Mw 6.5 Gruppo di Lavoro INGV sul Terremoto in centro Italia, 10 November 2016 [PDF]