Geotechnical reconnaissance of an extensive cover-collapse sinkhole phenomena of 2020–2021 Petrinja earthquake sequence (Central Croatia)

Abstract

This article presents geotechnical reconnaissance data that characterize the formation of 122 new and 49 historical cover-collapse sinkholes within 1.13 km2 area in 12 months following the MW 6.4 earthquake that occurred on 29 December 2020, in Petrinja, Croatia. Data include a geological background, seismic sequence information, sinkhole geometric characteristics, rainfall data, and results of detailed geotechnical subsurface investigation. The sinkhole geometrical features were collected using aerial and satellite imagery, terrestrial lidar, and manual measurements. Soil properties and groundwater levels were obtained from four geotechnical boreholes, accompanied by in situ geotechnical characterization and standard penetration tests (SPTs). Soil parameters were obtained from consolidated undrained conventional triaxial compression, oedometer, soil water retention, and index tests performed on 31 soil samples. Clayey cover, 4–10 m thick, with sporadic gravel lenses overlying cavernous, intensely karstified carbonate rocks, characterizes the sinkhole area. Clays are mostly overconsolidated, with varying degrees of saturation ranging from very small to fully saturated. Seasonal and climate-induced variations in the groundwater table interact with artesian/subartesian karst aquifer, thus affecting the suction and the shear strength. Soil water retention curves (SWRCs) indicate that desaturation is possible for deeper groundwater tables, thus further affecting the effective stress, shear strength, and interparticle tensile forces. Finally, the observed vertical walls that accompanied sinkholes opening can occur in the overconsolidated cohesive cover clay layer with varying degree of saturation. The presented data provide essential geomechanical information necessary to understand the associated sinkhole failure mechanism. This article will help future investigators to perform detailed analyses and provide a background for complementing future sinkhole precursor research. Geotechnical, geological, seismic, and precipitation data generally indicate that the formation of cover-collapse sinkholes in the study area is a consequence of a specific local geological setting but is significantly expedited by earthquake-induced dynamic loading and complemented by multiple hydro-mechanical factors.

Large Anthrax Outbreak in a New Locality in Croatia, 2022

“…The distance between the earthquake epicenter and Lonjsko Polje is about 30 km. After the earthquake, the phenomena of soil collapsing and the formation of 122 new cover-collapse sinkholes ranging from 1–25 m in diameter and 0.2–11 m in depth, filled with water and vegetation, occurred in the villages of Mečenčani and Borojevići in Sunja River Valley, which is one of the Lonjsko Polje Nature Park tributary rivers situated on its south border [ 18 ]. These villages are part of the “anthrax district” and are about 50 km away, separated by the Sava River from the pasture of Osekovo on the north border of Nature Park, where the first cases of animal disease were reported.…”

The Largest Geodetic Coseismic Assessment of the 2020 Mw = 6.4 Petrinja Earthquake

“…There were at least seven casualties and dozens of injuries; most of the heavily damaged buildings (around 2902 based on OpenStreetMap and Copernicus reports) were in the cities of Petrinja, Sisak, and Glina [21]. As of the end of 2021, a result of the earthquake was the emergence of 122 new sinkholes and 49 historical cover-collapse sinkholes in the vicinity of the villages of Mečečani and Borojevići, approximately 20 km SE of the epicenter [13].…”

“…The earthquake in Petrinja has been the subject of multiple research studies. Some have focused on fault ruptures and sinkholes [9,10,13,14,16,[22][23][24], while others have examined its effects on buildings and the economy [11,12,17,25]. A lot of the previous research has focused on techniques such as Interferometric Synthetic Aperture Radar (InSAR) [7,21,[26][27][28][29] and the Global Navigation Satellite System (GNSS) [8,15,30].…”

“…That earthquake was the mainshock of a seismic sequence with the epicenter ~3 km west-southwest of the city of Petrinja at a depth of 10 km and ruptured the Pokupsko-Petrinja fault [7][8][9][10][11]. The highest intensity of the mainshock is estimated as VIII-IX° MCS [11][12][13][14][15][16]. The mainshock was preceded by two foreshocks on 28 December 2020, with magnitudes of Mb 5.2 and Mw 4.8 [7] (Figure 2).…”