Near-source high-rate GPS, strong motion and InSAR observations to image the 2015 Lefkada (Greece) Earthquake rupture history

Antonio Avallone,Antonella Cirella,Cristiano Tolomei,Daniele Cheloni,Nikos Theodoulidis,Alessio Piatanesi,Athanassios Ganas,Pierre Briole

doi:10.1038/s41598-017-10431-w

Abstract

The 2015/11/17 Lefkada (Greece) earthquake ruptured a segment of the Cephalonia Transform Fault (CTF) where probably the penultimate major event was in 1948. Using near-source strong motion and high sampling rate GPS data and Sentinel-1A SAR images on two tracks, we performed the inversion for the geometry, slip distribution and rupture history of the causative fault with a three-step self-consistent procedure, in which every step provided input parameters for the next one. Our preferred model results in a ~70° ESE-dipping and ~13° N-striking fault plane, with a strike-slip mechanism (rake ~169°) in agreement with the CTF tectonic regime. This model shows a bilateral propagation spanning ~9 s with the activation of three main slip patches, characterized by rise time and peak slip velocity in the ranges 2.5–3.5 s and 1.4–2.4 m/s, respectively, corresponding to 1.2–1.8 m of slip which is mainly concentrated in the shallower (<10 km) southern half of the causative fault. The inferred slip distribution and the resulting seismic moment (M0 = 1.05 × 1019 N m) suggest a magnitude of Mw 6.6. Our best solution suggests that the occurrence of large (Mw > 6) earthquakes to the northern and to the southern boundaries of the 2015 causative fault cannot be excluded.

Highlights

On 2015 November 17th (07:10:07 UTC), the Lefkada Island (Greece) was struck by an earthquake of magnitude, Mw, estimated between 6.4 and 6.61–7, which occurred at a depth[2] of 9.6 km (Fig. 1)
These stations consist of six Strong Motion (SM) belonging to the Institute of Engineering Seismology and Earthquake Engineering (ITSAK) accelerometric network[8] and of six continuous GPS stations belonging to different networks developed for both scientific (NOANET30) or commercial (METRICANET, SMART-NET Greece and TREE Company SA Greece) purposes
Among the available HRGPS stations, the two closest sites to the epicentre (PONT and SPAN) recorded the main shock with a 5-Hz sampling frequency, whereas all the others were acquiring at 1-Hz (Fig. 2b), except LFKD station that acquired with a 30-s sampling rate

Summary

Introduction

On 2015 November 17th (07:10:07 UTC), the Lefkada Island (Greece) was struck by an earthquake of magnitude, Mw, estimated between 6.4 and 6.61–7, which occurred at a depth[2] of 9.6 km (Fig. 1). The main shock relocation as well as the relocated aftershocks in the time period 2015/11/17-2015/12/302, are in agreement with the tectonic regime of the area, that is dominated by one of the major active structural discontinuities of the eastern Mediterranean, the Cephalonia Transform Fault (CTF)[9,10,11]. This fault zone accommodates the relative deformation between the Apulia-Eurasia collision zone on the north and the Hellenic arc subduction zone on the south, with a relative motion of ~20 mm/yr[12, 13]. The comparison between the distribution of the largest (M > 6) events along the CTF zone in the last century and our fault modelling of the 2015 main shock suggests that the occurrence of moderate (M66.6) earthquakes to the northern and to the southern boundaries of the 2015 causative fault cannot be ruled out

Methods

Results

Conclusion