‘Conjugate’ coseismic surface faulting related with the 29 December 2020, Mw 6.4, Petrinja earthquake (Sisak-Moslavina, Croatia)

Abstract

We provide here a first-hand description of the coseismic surface effects caused by the Mw 6.4 Petrinja earthquake that hit central Croatia on 29 December 2020. This was one of the strongest seismic events that occurred in Croatia in the last two centuries. Field surveys in the epicentral area allowed us to observe and map primary coseismic effects, including geometry and kinematics of surface faulting, as well as secondary effects, such as liquefaction, sinkholes and landslides. The resulting dataset consists of homogeneous georeferenced records identifying 222 observation points, each of which contains a minimum of 5 to a maximum of 14 numeric and string fields of relevant information. The earthquake caused surface faulting defining a typical ‘conjugate’ fault pattern characterized by Y and X shears, tension cracks (T fractures), and compression structures (P shears) within a ca. 10 km wide (across strike), NW–SE striking right-lateral strike-slip shear zone (i.e., the Petrinja Fault Zone, PFZ). We believe that the results of the field survey provide fundamental information to improve the interpretation of seismological, GPS and InSAR data of this earthquake. Moreover, the data related to the surface faulting may impact future studies focused on earthquake processes in active strike-slip settings, integrating the estimates of slip amount and distribution in assessing the hazard associated with capable transcurrent faults.

Rapid Remeasure of Dense Civilian Networks as a Game‐Changer Tool for Surface Deformation Monitoring: The Case Study of the Mw 6.4 2020 Petrinja Earthquake, Croatia

“…A more detailed analysis, combining InSAR and optical correlation data and a varying secondary fault geometry, will help to better assess its potential reverse component. Nevertheless, this analysis do not support the hypothesis of a NE-SW oriented left-lateral conjugate fault as proposed by Markušić et al (2021) and Tondi et al (2021).…”

Implementing the European Space Agency’s SentiNel Application Platform’s Open-Source Python Module for Differential Synthetic Aperture Radar Interferometry Coseismic Ground Deformation from Sentinel-1 Data

“…Reference [14] reports a detailed description of the deformation pattern associated with the Petrinjia earthquake, using both remote sensing (InSAR, Sentinel-1) and field data. Several important coseismic ruptures are observed and mapped in the field [15], testifying to a typical conjugate fault pattern associated with the main NW-SE right lateral seismogenic fault. In [18], a maximum displacement of ~43 cm along the E-W component, a maximum subsidence of −15 cm and an uplift of +19 cm are also reported.…”

“…The fault is easily recognized where there is an abrupt transition from westward to eastward deformation (see transcurrent symbol in Figure 5c,d). The short wavelength irregularities of the deformation profiles suggest a mid-rumor for the signal, which, however, does not impede the discernment of a detailed distribution of the displacement, as well as the location of other secondary and conjugate faults in agreement with [15]. Moreover, according to the deduction reported by [15] from field observation, we also detect the presence of an NNW-SSE trending subsided sector (Figure 5d), in agreement with normal faults in a conjugate Riedel shear of strike-slip tectonics.…”

“…The Croatia earthquake was triggered by a NW-SE right-lateral strike-slip fault [15,16], whereas the Greece earthquake was triggered by a NW-SE normal fault [17] (Figure 1). By choosing both cases, it is possible to validate the results in two different tectonic contests characterized by prevalently horizontal (Croatia) and vertical (Greece) coseismic movements.…”

“…The 2021 Greece earthquake sequence occurred in the Thessaly region and was characterized by three mainshocks [19], with a predominantly extensional kinematics, representing the westward propagation of Tyrnavós graben [20] (see focal mechanisms of Figure 1b). [15] for the Croatia earthquake and from [20] for the Greece earthquake. The base map is a composite of DEM and Hillshade derived from the NASA SRMT DEM.…”