Seismic Vulnerability of the Ancient Pompeii through the Evaluation of the 62 AD Earthquake Effects

ABSTRACT

The ancient Pompeii was hit by a sequence of earthquakes during the 1^st century with disastrous consequences on the buildings. Many constructions were repaired after the ground shaking, others, in particular public buildings present, still today, signs of active works at the time of the Vesuvius eruption. Moreover, cracks and deformations originated from the 1^st century tremors are visible on the walls and represent a precious source of information on the ultimate performance of the constructions. Despite a high in-plan geometric heterogeneity, the Pompeians’ housing stock was limited to two storeys with, often, an in-plan and along the height uniform distribution of masses, strength and stiffness, hence a reduced torsional motions tendency under earthquake actions. Furthermore, the seismic performance of the building could be influenced by the masonry arrangement and components properties, ranging, in the analysed cases, from the opus quadratum to the structura fabric, i.e. a concrete nucleus covered by stones or bricks leaf. The paper provides the key features, although of qualitative type, of the constructions vulnerability level during the last phase of the Pompeii’s history, basing on the “seismic” improvement interventions, on ancient deformations and repaired cracks, compared to the buildings configuration and the used constructive techniques.

KEYWORDS:

• 62 AD earthquake
• building configuration
• masonry stability
• Pompeii
• seismic improvement
• seismic vulnerability

Notes

¹ At least regarding the 62 AD earthquake. At the end of the 19th century, Prof. De Rossi (De Rossi 1879) hypothesized that the seismic impulses characterizing the catastrophic 62 AD event had a predominant WSW—ENE direction, as well as a perpendicular direction

² Even though it is worth emphasizing that Pompeii housing stock was characterized by an high heterogeneity. Houses range from small properties including few rooms, to Casa del Fauno 3000 mq surface extent building.

³ The stones are, in general, limestones and tuffs. Such rocks present a good adhesion to the mortar.

⁴ Excluding the oldest Pompeii building phases.

⁵ “ … nam nisi celeriter ex altera parte properabit motus qui inclinata restituat, ruina necessario sequitur …” (Seneca 63–65 AD) Liber VI, 21, 2

⁶ “… tum supera terram quae sunt extructa domo rum ad caelumque magis quanto sunt edita quaeque, inclinata minent in eandem prodita partem protractaeque trabes inpendent ire paratae …” (Lucretius 1st century BC).

⁷ Heterogeneous masonries with scarce quality in the fabric organization present diffuse cracks, also micro-cracks, with a rather disordered development, if subject to an in-plane horizontal action.

⁸ In addition to a generation of a three-dimensional response of the building with the “shear walls” participation, a proper quoins execution entails the modification of the overturning mechanism. In fact, in the case the loss of equilibrium affects only a wall part, more or less limited in dependence of the constraint effectiveness with the orthogonal panel.

⁹ Although in Pompeii there are still some cases of portico with a sort of parapet among the columns not linked to anti-seismic reasons, even if that wall is characterized by a lowest height as compared to the one in Villa dei Misteri.

¹⁰ Nonetheless, it is worth observing that the bricks use might probably implied an unskilled labor employment and consequences on the arrangement and components selection of the opus latericium, albeit the brick work speeded the wall execution.