10 Hz GPS seismology for moderate magnitude earthquakes: the case of the Mw 6.3 L’Aquila (Central Italy) event

Abstract

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