Very high rate (10 Hz) GPS seismology for moderate-magnitude earthquakes: The case of theMw6.3 L'Aquila (central Italy) event

The 2009 April 6th Mw 6.3 L'Aquila destructive earthquake was successfully recorded by closely
23 spaced 10-Hz and 1-Hz recording GPS receivers and strong motion accelerometers located above or
24 close to the 50° dipping activated fault. We retrieved both static and dynamic displacements from
25 Very High-Rate GPS (VHRGPS) recordings by using Precise Point Positioning kinematic analysis.
26 We compared the GPS positions time series with the closest displacement time series obtained by
27 doubly-integrating strong motion data, first, to assess the GPS capability to detect the first seismic
28 arrivals (P waves) and, secondly, to evaluate the accelerometers capability to detect co-seismic
29 offsets up to ~45 s after the earthquake occurrence. By comparing seismic and VHRGPS frequency
30 contents, we inferred that GPS sampling rates greater than 2.5 Hz (i.e. 5 or 10 Hz) are required in
31 the near-field of moderate magnitude events to provide “alias-free” solutions of coseismic dynamic
32 displacements. Finally, we assessed the consistency of the dynamic VHRGPS results as a constraint
33 on the kinematic rupture history of the mainshock. These results suggested that the high-rate
34 sampling GPS sites in the near field can be as useful as strong motion station for earthquake source
35 studies.