The definition of the brittle-ductile transition (BDT) depth could be used to improve seismic hazard assessment studies in seismically active regions (Maggini and Caputo, 2021). The BDT represents a proxy of the seismic/aseismic transition and fundamentally corresponds to a mechanical boundary for coseismic rupture propagation processes. Close to this transition, deformation within the viscous crustal body generally induces elastic deformation also within the contiguous elasto-brittle body and when sufficient energy has been accumulated it is commonly released seismically. A rheological modelling was previously performed by Maggini and Caputo (2020, 2021) in the broader Aegean Region including the southern Balkans. Moreover, the seismicity cutoff depth of several seismogenic volumes was compared with the modelled BDT depth thus confirming that the rheological and seismological transitions are tightly correlated. Accordingly, the brittle-ductile transition depth is a very reliable marker for constraining the width of seismogenic sources. Based on these premises, we investigated the epicentral area of the November 2019 seismic sequence which mainly affected the city of Durres. It corresponds to the north-western sector of Albania characterized by an on-going compressional regime due to the persistent continental-continental collision between the Adria microplate and European block that has is maximum expression in the Dinarides-Hellenides fold-and-thrust belt. In this sector of the accretionary wedge, the thrust front is segmented and the kinematics partitioned by the ENE-WSW Shkodra and Lushnje transfer faults (Caputo and Pavlides, 2013). The mainshock occurred on the 26th November 2019 in the Durres area with a Mw = 6.4. Following the inversion of InSAR and GNSS data (i.e. Caporali et al., 2020; Ganas et al., 2020; Govorcin et al., 2020; Papadopoulos et al., 2020; Pezzo et al., 2021; Vittori et al., 2021), it is well constrained that the event was associated with a blind thrust fault. However, authors interpretations differ in terms of dip-angle and dip-direction of the causative source. In particular, some authors suggest a low-angle NE-dipping blind thrust (i.e. Caporali et al., 2020; Ganas et al., 2020; Papadopoulos et al., 2020; Vittori et al., 2021), while some others prefer a high-angle SW-dipping back-thrust plane (Govorcin et al., 2020; Pezzo et al., 2021). Solving this ambiguity is not among the principal aims of this research, instead it is to provide an additional constraint, independent from seismological data, on the seismotectonics of this sector of the Albanides fold-and-thrust belt and particularly on the maximum depth of the seismogenic sources and hence on their maximum width. Following a similar methodology from Maggini and Caputo (2020b) we obtained, with dedicated MatLab scripts, a pseudo 3D rheological model of the 26th November 2019 epicentral area from which an ENE-WSW oriented profile is then extracted. The transect, which runs from Adria to western Balkans (A-B; Fig. 1) across the epicentral volume and perpendicular to the major tectonic structures, clearly shows the presence of different brittle and ductile layers characterizing the broader seismogenic volume. By plotting the hypocentral locations proposed by the different authors on the same profile, it is possible to observe the presence of a lense-shaped ductile body at ca. 18-25 km-depth within the upper plate delimited to the west by the major shear zone of the basal detachment. As above mentioned, such conditions are ideal for accumulating stresses within the contiguous elasto-brittle rock volume and this indeed is where the hypocentre of the mainshock has been located (Papadopoulos et al., 2020; http://terremoti.ingv.it; www.emsc-csem.org). Furthermore, and considering that the plate boundary represents a major weakness zone, it is likely that rupture propagation has then followed the basal detachment up-dip towards the west. Based on this reconstruction, the focal depth of ca. 22 km and the estimated seismic moment, the rupture surface remained entirely blind.
Rheological Modelling of the 26 November 2019 Durres Epicentral Area
Russo Davide
Primo
;Maggini MassimilianoSecondo
;Caputo RiccardoUltimo
2022
Abstract
The definition of the brittle-ductile transition (BDT) depth could be used to improve seismic hazard assessment studies in seismically active regions (Maggini and Caputo, 2021). The BDT represents a proxy of the seismic/aseismic transition and fundamentally corresponds to a mechanical boundary for coseismic rupture propagation processes. Close to this transition, deformation within the viscous crustal body generally induces elastic deformation also within the contiguous elasto-brittle body and when sufficient energy has been accumulated it is commonly released seismically. A rheological modelling was previously performed by Maggini and Caputo (2020, 2021) in the broader Aegean Region including the southern Balkans. Moreover, the seismicity cutoff depth of several seismogenic volumes was compared with the modelled BDT depth thus confirming that the rheological and seismological transitions are tightly correlated. Accordingly, the brittle-ductile transition depth is a very reliable marker for constraining the width of seismogenic sources. Based on these premises, we investigated the epicentral area of the November 2019 seismic sequence which mainly affected the city of Durres. It corresponds to the north-western sector of Albania characterized by an on-going compressional regime due to the persistent continental-continental collision between the Adria microplate and European block that has is maximum expression in the Dinarides-Hellenides fold-and-thrust belt. In this sector of the accretionary wedge, the thrust front is segmented and the kinematics partitioned by the ENE-WSW Shkodra and Lushnje transfer faults (Caputo and Pavlides, 2013). The mainshock occurred on the 26th November 2019 in the Durres area with a Mw = 6.4. Following the inversion of InSAR and GNSS data (i.e. Caporali et al., 2020; Ganas et al., 2020; Govorcin et al., 2020; Papadopoulos et al., 2020; Pezzo et al., 2021; Vittori et al., 2021), it is well constrained that the event was associated with a blind thrust fault. However, authors interpretations differ in terms of dip-angle and dip-direction of the causative source. In particular, some authors suggest a low-angle NE-dipping blind thrust (i.e. Caporali et al., 2020; Ganas et al., 2020; Papadopoulos et al., 2020; Vittori et al., 2021), while some others prefer a high-angle SW-dipping back-thrust plane (Govorcin et al., 2020; Pezzo et al., 2021). Solving this ambiguity is not among the principal aims of this research, instead it is to provide an additional constraint, independent from seismological data, on the seismotectonics of this sector of the Albanides fold-and-thrust belt and particularly on the maximum depth of the seismogenic sources and hence on their maximum width. Following a similar methodology from Maggini and Caputo (2020b) we obtained, with dedicated MatLab scripts, a pseudo 3D rheological model of the 26th November 2019 epicentral area from which an ENE-WSW oriented profile is then extracted. The transect, which runs from Adria to western Balkans (A-B; Fig. 1) across the epicentral volume and perpendicular to the major tectonic structures, clearly shows the presence of different brittle and ductile layers characterizing the broader seismogenic volume. By plotting the hypocentral locations proposed by the different authors on the same profile, it is possible to observe the presence of a lense-shaped ductile body at ca. 18-25 km-depth within the upper plate delimited to the west by the major shear zone of the basal detachment. As above mentioned, such conditions are ideal for accumulating stresses within the contiguous elasto-brittle rock volume and this indeed is where the hypocentre of the mainshock has been located (Papadopoulos et al., 2020; http://terremoti.ingv.it; www.emsc-csem.org). Furthermore, and considering that the plate boundary represents a major weakness zone, it is likely that rupture propagation has then followed the basal detachment up-dip towards the west. Based on this reconstruction, the focal depth of ca. 22 km and the estimated seismic moment, the rupture surface remained entirely blind.I documenti in SFERA sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
