GNSS seismology for the 2012 Mw = 6.1 Emilia Earthquake: exploiting the VADASE algorithm

Here we present the application to the Emilia (Italy) earthquake (Mw=6.1, May 20, 2012, 02:03:51 UTC) of VADASE algorithm, able to estimate coseismic displacements and waveforms both in real-time and off-line, in a global reference frame, just using the standard broadcast products and carrier phase observations continuously collected by a stand-alone GNSS receiver. We used VADASE off-line, since no real-time data were available, and we compared its solutions to those coming from four well known scientific software used as reference: TRACK, Bernese, APP-PPP and CSRS-PPP. We collected 1 Hz data at seven GPS permanent stations and, at first, we estimated the coseismic displacements and waveforms through the ionospheric-free combination L3 over an interval of 2 minutes. Then, we repeated the computation just using L1, since VADASE is also able to work with single frequency data only. Overall, in both cases, the agreement between VADASE and the reference software were assessed at 1-2 cm level, slightly worse for the L1 solutions, being the agreement among the four reference software at 0.5 - 1.5 cm level. These results pave the way to the use of single-frequency receivers for GNSS seismology purposes. In addition to the comparison between GNSS results, the availability of triaxial accelerometer collocated with a GPS station, allowed the comparison between VADASE and accelerometer solutions.