Summary:
The temporal and spatial slip distribution assessment is a vital tool for seismologists and other geoscientists towards understanding the spatiotemporal evolution of the earthquake rupture. Such an evaluation requires data which are typically extracted after a large event, meaning the earthquake’s source parameters, including focal mechanism, fault geometry and hypocentral relocation. The slip inversion method has application potential for shakemaps, emergency response and aftershock hazard assessment. The LinSlipInv software (Gallovic and Zahradnik, 2011; Gallovic et al., 2014) is implemented using local and near-regional data recorded by seismographs belonging to the Hellenic Unified Seismological Network (HUSN), as well as by the accelerometric network of the Geodynamic Institute of the National Observatory of Athens (GI-NOA), the Institute of Engineering Seismology & Earthquake Engineering (ITSAK) and for the eastern regions, the Kandilli Observatory and Earthquake Research Institute (KOERI) and the Turkey Earthquake Data Center System (AFAD). Selected strong earthquakes (with Mw ≥ 6.0) that occurred during the last decade in various regions of the Hellenic territory are examined. Towards the slip distribution determination via LinSlipInv, focal mechanisms, velocity models and fault geometries, were examined.
The slip distribution results were used as input to extrapolate ground deformation using the DIS3D Program (Erickson, 1987), even in cases where no surficial trace of the fault is observed. The obtained slip distribution and crustal deformation are compared with the ones determined by other studies, including InSAR and GPS.
The slip distribution results were promising. The results for the 26 January 2014 Cephalonia event, derived by the LinSlipInv software utilizing local and near-regional data, indicate a single rupture episode, with the maximum slip calculated at 40 cm. Concerning the ground deformation derived by the obtained slip distribution, the values in the horizontal and vertical component are low, mainly due to the magnitude and the focal depth of the event. The results revealed a maximum of 2 cm of horizontal displacement, to the east of the fault, on Cephalonia Island.
The calculated slip of the 24 May 2014 Lemnos earthquake revealed a complex source, comprised of three discrete patches. The slip snapshots revealed that the slip migrated updip, whereas the total maximum slip value reached 1.4 m. In addition, the slip velocity snapshots identified a bilateral rupture. More specifically, an initial westward rupture propagation was observed, followed by a major slip patch heading to the east. The obtained ground deformation results in Lemnos indicate a right lateral horizontal movement.
The local to near-regional slip inversion results for the 17 November 2015 Lefkada event revealed directivity towards the SSW. In addition, two slip episodes can clearly be identified, whereas the maximum obtained slip value was 1.2 m. Regarding the ground deformation, the dextral movement was verified by the herein obtained results, using the DIS3D software. Small uplift values were obtained for the southern part of the Lefkada Island (7 cm maximum uplift).
According to the LinSlipInv inversion results for the 12 June 2017 Lesvos earthquake, the maximum slip was ~1.0 m and a single patch was identified. The space-time rupture evolution, as revealed by slip velocity snapshots obtained per 1 s, indicated a unique slip patch and rupture directivity towards the NW, which could partly explain the damage observed in the Vrissa village. However, extended destruction is also due to other factors, such as soil conditions and vulnerability of the buildings. An extensional regime and a NNE horizontal movement on the Lesvos Island were identified by the application of the DIS3D software along with subsidence reaching 20 cm offshore, in the vicinity of the causative fault.
The slip distribution results derived by the LinSlipInv software for the 20 July 2017 Kos earthquake presented a unique patch with a maximum slip value of 1.8 m. The suggested causative fault is the one dipping to the north. Regarding the ground deformation, a N-S extension is observed. Values of horizontal movement of the order of 5 cm were obtained in Marmaris. Subsidence up to 30 cm was identified in the Gökova gulf.
