The November 2019 Seismic Sequence in Albania: Geodetic Constraints and Fault Interaction

Abstract

The seismic sequence of November 2019 in Albania culminating with the Mw = 6.4 event of 26 November 2019 was examined from the geodetic (InSAR and GNSS), structural, and historical viewpoints, with some ideas on possible areas of greater hazard. We present accurate estimates of the coseismic displacements using permanent GNSS stations active before and after the sequence, as well as SAR interferograms with Sentinel-1 in ascending and descending mode. When compared with the displacements predicted by a dislocation model on an elastic half space using the moment tensor information of a reverse fault mechanism, the InSAR and GNSS data fit at the mm level provided the hypocentral depth is set to 8 ± 2 km. Next, we examined the elastic stress generated by the Mw = 7.2 Montenegro earthquake of 1979, with the Albania 2019 event as receiver fault, to conclude that the Coulomb stress transfer, at least for the elastic component, was too small to have influenced the 2019 Albania event. A somewhat different picture emerges from the combined elastic deformation resulting after the two (1979 and 2019) events: we investigated the fault geometries where the Coulomb stress is maximized and concluded that the geometry with highest induced Coulomb stress, of the order of ca. 2–3 bar (0.2–0.3 MPa), is that of a vertical, dextral strike slip fault, striking SW to NE. This optimal receiver fault is located between the faults activated in 1979 and 2019, and very closely resembles the Lezhe fault, which marks the transition between the Dinarides and the Albanides.

Geodetic Source Modeling of the 2019 Mw 6.3 Durrës, Albania, Earthquake: Partial Rupture of a Blind Reverse Fault

“…The geodetic observations were inverted to estimate the geometry of the source fault, and the distribution of slip upon it, using half space elastic dislocation models (Okada, 1985), which we then use to discuss the effect that the Durrës event may have on local to regional fault systems. Similar geodetic‐based studies of the M w 6.3 Durrës earthquake were conducted by Ganas et al (2020) and Caporali et al (2020). However, these studies made a priori assumptions regarding the fault geometry and hence reached different results and conclusions than our study.…”

“…We could not unambiguously find a preferred optimal rupture plane just based on the geodetic data-to-model misfit, as 10.1029/2020GL088990 models for both fault planes fit the data equally well (misfit < 1 cm). Caporali et al (2020), Ganas et al (2020), and Papadopoulos et al (2020) propose and model only the NE-dipping fault as a causative fault primarily based on the interpretation of the regional structural settings. A similar mechanism for the NE-dipping fault is presented but with different centroid depths and coseismic slip values, mostly due to an applied inversion method with certain assumptions (Table S7).…”

Ground Deformation and Seismic Fault Model of the M6.4 Durres (Albania) Nov. 26, 2019 Earthquake, Based on GNSS/INSAR Observations

“…Our fault model also indicates that the 8 ± 2 km depth proposed by [17] for the hypocentre is not supported by the geodetic data.…”

“…On November 16, 1982, a M w = 5.6 thrust faulting earthquake on a low angle fault (27 • ) event occurred to the SW of Tirana [1]. The M w = 6.4 November 26, 2019 02:54 UTC earthquake ruptured another reverse fault near the city of Durrës [9,[15][16][17][18]; see supplementary Figure S1 for a map with published moment tensors). Its centroid was determined in the range 6-26 km (Table 1; locations and magnitudes from the sources 1-7).…”

Thermal Structure of the Northern Outer Albanides and Adjacent Adriatic Crustal Sector, and Implications for Geothermal Energy Systems

“…Geodetic calculations based on permanent GNSS Stations in the ETRF2000 "European fixed" reference frame [27] indicate that vector motion velocities in the western side of Albania are north-directed, while those in the central and eastern portions are south-directed, implying dextral strike-slip [28]. The projected motion vector velocities along the section trace A-A' in Figures The epicenters are plotted using the location from the ISIDe [26], while magnitude (MW) and focal mechanism data are from the RCMT catalogue [25,29].…”