Preliminary Observations on Historical Castle Trakošćan (Croatia) Performance under Recent ML ≥ 5.5 Earthquakes

Abstract

Trakošćan Castle, built on a rocky peak in the late 13th century, is a cultural heritage site protected as a historical entity by the Republic of Croatia. The Castle is constructed as a highly irregular masonry structure with timber or shallow masonry arches, vaults or dome floors. It was substantially renewed, upgraded and partially retrofitted from the 16th century until the year 2000. The M5.5 (VIII EMS) and M6.2 (VIII-IX EMS) earthquakes, which struck the city of Zagreb on 22 March 2020 and the Pokupsko-Petrinja area on 29 December 2020, strongly shook the Castle’s structure. Earthquake damage was observed and assessed by visual inspection accompanied by ambient vibration measurements. The slight cracks that appeared on masonry arches were found to be critically positioned, and can likely lead to the arches’ collapse if their spreading is not prevented. Ambient vibration measurements, which were compared to pre-earthquake ones, revealed the decrease in the fundamental frequencies of the Castle’s central tower unit and the second floor, thus possibly indicating the loss of structural stiffness as a consequence of the earthquake damage.

The Effects of Strong Earthquakes on Built Heritage: A Preliminary Case Study of Rector’s Palace in Dubrovnik’s Old City

“…The destructive M w = 5.3 and M w = 6.4 earthquakes that struck Croatia in 2020 [1][2][3][4] not only caused significant physical damage to buildings and loss of life [5,6] but also posed a grave threat to the country's rich cultural heritage assets [7][8][9][10]. By drawing insights from these events that shed light on the consequences of earthquakes on heritage preservation efforts and the measures taken to mitigate such risk, the vulnerability at both urban and single asset scales in the Old City of Dubrovnik (see Figure 1) was explored to subsequent exposure, i.e., the effect of destructive earthquakes.…”