Source characteristics of the 2015 M_w6.5 Lefkada, Greece, strike‐slip earthquake

Abstract

We present a kinematic slip model from the inversion of 1 Hz GPS, strong motion, and interferometric synthetic aperture radar (InSAR) data for the 2015 Mw6.5 Lefkada, Greece, earthquake. We will show that most of the slip during this event is updip of the hypocenter (10.7 km depth) with substantial slip (>0.5 m) between 5 km depth and the surface. The peak slip is ~1.6 m, and the inverted rake angles show predominantly strike‐slip motion. Slip concentrates mostly to the south of the hypocenter, and the source time function indicates a total duration of ~17 s with peak moment rate at ~6 s. We will show that a 65° dipping geometry is the most plausible due to a lack of polarity reversals in the InSAR data and good agreement with Coulomb stress modeling, aftershock locations, and regional moment tensors. We also note that there was an ~20 cm peak‐to‐peak tsunami observed at one tide gauge station 300 km away from the earthquake. We will discuss tsunami modeling results and study the possible source of the amplitude discrepancy between the modeled and the observed data at far‐field tide gauges.

On the Segmentation of the Cephalonia–Lefkada Transform Fault Zone (Greece) from an InSAR Multi-Mode Dataset of the Lefkada 2015 Sequence

“…The projection of the three components of GPS measurements into the LoS of every InSAR dataset confirmed a disagreement between the GPS projected values and the InSAR results. In fact, the GPS and InSAR inconsistency is not surprising and it was already observed [11]. While we cannot exclude potential sources of error, this divergence could be attributed, as also stated by Melgar et al [11], to early afterslip signal contained in InSAR maps, taking into account that the InSAR data include few days of possible slow deformations after the mainshock [7,8,11].…”

“…In fact, the GPS and InSAR inconsistency is not surprising and it was already observed [11]. While we cannot exclude potential sources of error, this divergence could be attributed, as also stated by Melgar et al [11], to early afterslip signal contained in InSAR maps, taking into account that the InSAR data include few days of possible slow deformations after the mainshock [7,8,11]. It is thus possible that our dataset contains postseismic signal; the InSAR input is, of course, still essential since our goal is to define the fault segmentation of the area.…”

“…On 17 November 2015, an earthquake (Mw 6.4) ( Figure 1b) struck the western coast of Lefkada island, which stimulated a wealth of publications [7][8][9][10][11][12][13][14][15][16][17][18]. Sokos et al [19] were the first to identify that the mainshock broke a strong asperity, left unbroken, in-between two large subevents of the previous 2003 doublet earthquake of Mw 6.2.…”

A 20-yr database (1997-2017) of co-seismic displacements from GPS recordings in the Aegean area and their scaling with Mw and hypocentral distance

“…Over the last twenty (20) years, displacements from Global Navigation Satellite System (GNSS) data, specifically from Global Positioning System (GPS) have become a useful measurement in seismology and earthquake geology. Such data have been used to quantify the intensity of ground deformation following strong earthquakes, to infer the geometry and kinematics of the seismic fault in case of "blind" ruptures as well as to contribute to fault inversion models (Ganas et al, 2009;2013;Hreinsdottir et al 2009;Devoti et al 2012;Saltogianni et al, 2015; Briole et al 2015;Chousianitis et al, 2016;Avallone et al, 2017;Melgar et al, 2017;Howell et al, 2017;Chousianitis, and Konca, 2018).…”

“…Accordingly, GNSS technology is widely used in earthquake source studies where it is usually inverted on its own, or jointly with other geophysical data sets (e.g. InSAR, seismology), to image the kinematic source process of M6+ events (Huang et al 2013;Chousianitis et al, 2016;Melgar et al, 2017;Avallone et al, 2017). High-rate GNSS has also been employed in studies of long-period ground motions, and in structural monitoring (Moschas and Stiros, 2011;2014).…”