Near-field fault slip of the 2016 Vettore Mw 6.6 earthquake (Central Italy) measured using low-cost GNSS

Abstract

The temporal evolution of slip on surface ruptures during an earthquake is important for assessing fault displacement, defining seismic hazard and for predicting ground motion. However, measurements of near-field surface displacement at high temporal resolution are elusive. We present a novel record of near-field co-seismic displacement, measured with 1-second temporal resolution during the 30^th October 2016 M_w 6.6 Vettore earthquake (Central Italy), using low-cost Global Navigation Satellite System (GNSS) receivers located in the footwall and hangingwall of the Mt. Vettore - Mt. Bove fault system, close to new surface ruptures. We observe a clear temporal and spatial link between our near-field record and InSAR, far-field GPS data, regional measurements from the Italian Strong Motion and National Seismic networks, and field measurements of surface ruptures. Comparison of these datasets illustrates that the observed surface ruptures are the propagation of slip from depth on a surface rupturing (i.e. capable) fault array, as a direct and immediate response to the 30^th October earthquake. Large near-field displacement ceased within 6-8 seconds of the origin time, implying that shaking induced gravitational processes were not the primary driving mechanism. We demonstrate that low-cost GNSS is an accurate monitoring tool when installed as custom-made, short-baseline networks.

Figure 1

(a) Location map of 6.6 Mw October 30th Vettore earthquake. Red lines are surface ruptures from this event mapped by the EMERGEO working group using ground observations. MV01, MV02, MV03 and MV04 are GNSS units used in this study. Additional GNSS stations operated by other researchers are: VETT (INGV – IGM network benchmark), ARQT (INGV, RING network), RIFP and MSAN (INGV – CaGeoNet network). IT.CLO is a strong motion station situated near the village of Castelluccio. The location of the earthquake epicentre was retrieved from http://cnt.rm.ingv.it/en/event/8863681 . Map coordinates are latitude and longitude decimal degrees of the geographic co-ordinate system WGS84. Topographic elevation is based on 90 m SRTM data. Map generated using GMT software v. 4.5.15 (http://www.soest.hawaii.edu/gmt/). (b) Mt. Vettore fault close to MV01. (c) Mt. Vettore fault close to MV03. (d) Antithetic fault SW of MV01-MV02 baseline.

Figure 2

(a,b) Time-series of three component relative displacement recorded by GNSS receivers (06:40:00–06:41:00 UTC; see Fig. 1a for locations). Data points represent calculated positions of the GNSS receiver in the hangingwall relative to its corresponding unit in the footwall, at 1 Hz. The inset plot shows the ground track with time on a horizontal plane. Horizontal dashed lines represent the finite co-seismic displacement of each component estimated from the temporal record. Vertical dashed lines represent key times in the sequence. For each GNSS pair, the start and end of co-seismic displacement is estimated as the time when all three components of displacement first reach their finite co-seismic displacement values. Horizontal and vertical error bars are included but are too small to see. (c) Three-component acceleration with time for station IT.CLO of the Italian Strong Motion Network. See Fig. 1a for location of IT.CLO.