Campi Flegrei Earthquake: Cracks in Walls: When to Worry

After the magnitude 4.7 earthquake that struck the Campi Flegrei on July 31st , the strongest recorded in the area in the last forty years, cracks appeared on the walls of many homes between Pozzuoli and Quarto . Some are simply crumbling plaster, others may indicate something more serious. This article explains how to read the cracks based on their shape, location, width, and progression, using the same criteria technicians use to study crack patterns. It is not a diagnostic guide: only a professional inspection can determine whether a building is safe. The following information is for informational purposes only and does not constitute any guarantee of safety.

The earthquake of July 31st and the first inspections

The magnitude 4.7 earthquake (Md 4.7 ± 0.3, Mw 4.4 ± 0.3 according to the INGV ) was recorded at 19:46 PM on July 31 at a depth of approximately 3 kilometers, with its epicenter between Pozzuoli and Quarto, in the Solfatara area . The seismic swarm continued for over 24 hours with nearly 170 earthquakes recorded, the strongest aftershocks measuring magnitudes 3.8 and 3.1. According to the INGV, the trend is consistent with data observed so far, but it is not possible to predict the duration, number, and magnitude of future events.

In Pozzuoli, 21 people were injured and more than twenty families were evacuated. Quick inspections, as explained by Roberto Castelluccio, professor of Technical Architecture at the Federico II University in Naples, revealed widespread damage, especially to partition walls , plaster , cornices, and fascias, while the structural parts of the concrete buildings were undamaged. This is typical of seismic zones: the most fragile elements fail first, while the load-bearing structures can hold up. But every building is different, and each case must be assessed individually.

The crack pattern: what a technician looks at

When an engineer analyzes the cracks in a building, he doesn't look at a single lesion, but at the crack pattern : the set of lesions, interpreted in its geometry. As technical texts on building pathology explain, in many cases it is not the size of the lesion that determines its severity, but rather its shape , orientation , position , and progression.

Cracks are divided into two large families: physiological cracks , which generally do not represent an imminent danger and result from thermohygrometric shrinkage of materials, settlement, or local installation defects; and pathological cracks , which express structural distress to which the masonry reacts by seeking a new equilibrium, often with a lower degree of safety. A crack develops in three phases: capillary cracking , with minimal cracking; advanced capillary cracking , in which the cracking increases; and complete detachment , with loss of surface continuity. The reference standard for classifying and describing cracks is UNI 11182 , which technicians use in surveys.

How to read the shape of cracks

Shape is the first clue. Here are the main types described in the technical literature and what they can indicate.

Vertical cracks
The vertical lesions at the wall intersections or corners often indicate defects in the connection between walls, that is, a deficient bite between masonry piers. The verticals under or above the windows concern the so-called piano bandsA continuous vertical crack, running the entire height of a wall, warrants attention. Vertical crush fractures, where the masonry yields due to excessive compression, are considered among the most dangerous types of damage.

Diagonal cracks
Inclined lesions, often at about 45 degrees, appear near doors, windows and corners, where the continuity of the masonry is interrupted and the stresses are concentrated. They are typical of differential settlements of the foundation soil, which subsides differently at various points.

Stepped or zigzag cracks
The lesions that follow the mortar joints, with a step-like progression, are characteristic of masonry in brick or tuffMortar is the most fragile element, and failure occurs through it. These are a frequent sign after an earthquake and must be carefully evaluated.

Horizontal cracks
Horizontal cracks are caused almost exclusively by vertical movements of the ground or by an increase in loads, for example a superelevationThey are particularly worrying when they appear at the base of the wall or on load-bearing walls, where they may indicate out-of-plane bending mechanisms.

Cross or X-shaped cracks
The cracks that intersect to form a St. Andrew's cross, inclined at 30-45 degrees, typically appear after a seismic event: they are a sign of cyclical shear stress and may indicate a possible structural compromise. In these cases, caution is required.

Arched cracks
The cracks with an arched shape on the ground floor may be due to localised subsidence of the ground. On the upper floors, however, they indicate possible subsidence of beams o attics.

Spiderweb cracks
Fine, widespread cracks, which branch out across the surface like a spiderweb, generally affect the plaster only: they are often linked to shrinkage of the material or changes in temperature and humidity. However, they should not be ignored if they spread or deepen.

Swellings and detachments
Bumps, swellings in the wall facing and detachments of plaster in blocks can be the antechamber of expulsion or out-of-plane overturning mechanisms: these are among the most serious signs and require immediate removal.

Width, depth, extension and position

In addition to form, the technician evaluates four other parameters.

Width and evolution . A lesion that has been stable for years and is not widening tells a different story than a fissure that appeared after the earthquake and continues to widen. Width alone is not enough: what matters is whether the lesion is active or inactive.

Depth . A crack that extends through the entire thickness of the wall, visible on both sides, is more significant than one that only involves the plaster. To determine this, targeted checks are needed, not just a quick glance.

Extension . A crack that runs along the entire wall has a different significance than a limited section of a few centimeters. Length must be read in conjunction with location and shape.

Location . The crucial factor: does the damage affect a load-bearing element such as beams , pillars , stairs , load-bearing walls, and lintels , or a simple partition wall ? In the first case, the level of attention is maximum.

How to Monitor a Crack at Home

While waiting for the inspection, you can monitor the development with simple methods: mark the two edges of the crack with a pencil or a piece of tape and take periodic photographs with a reference measurement nearby (a ruler or a coin); note the date, location, and estimated width. If the crack widens, deepens, or new cracks appear after subsequent tremors, the situation changes and should be reported immediately. Technicians use more precise instruments, called crack meters , which measure changes in opening over time.

When to worry: the signs that matter

• lesions on load-bearing elements: beams, pillars, stairs, load-bearing walls, lintels
• cross- or X-shaped cracks, widespread step-like cracks, horizontal lesions at the base of the wall
• through lesions, visible on both sides of the wall
• cracks that widen or new fissures appear in the days following the earthquake
• swellings, detachments, out of plumb, falling debris
• doors and windows that no longer close like they used to
• widespread lesions throughout the house

What to do immediately

1. move away from the house and get to safety, away from buildings
2. Do not return if you suspect structural damage
3. notify the Common and Civil protection: after an earthquake, prompt checks are carried out
4. call the Fire fighters (115) only for immediate dangers
5. do not attempt DIY repairs, which may mask the problem
6. photograph the lesions and note where they appeared: this will be useful for the technicians

For all the information on requesting an earthquake damage inspection, consult our dedicated guide.

What will the technician do?

The professional will conduct an on-site inspection , identify the crack pattern, and classify it according to UNI 11182 , distinguishing between physiological and pathological lesions. They can then position crackmeters for monitoring over time, conduct in-depth investigations, and, if necessary, prepare a structural assessment and consolidation plan. Interpreting a crack isn't done from a photo: understanding its shape and location on-site, along with the building's history, is what allows us to distinguish aesthetic damage from structural damage.

FAQ

Is a hairline crack after an earthquake dangerous?
Not necessarily. A hairline crack in plaster or partition wall, stable over time, is often not a structural problem. But width alone isn't enough: shape, location, and development matter, and only a technician can provide a definitive answer.

Vertical, diagonal, or horizontal crack: which is more worrying?
It depends on the location rather than the direction. A horizontal crack at the base of a load-bearing wall and a cross-shaped crack after an earthquake are among the most serious signs. Vertical cracks at corners often indicate anchoring problems, while diagonal cracks indicate differential settlement. In any case, a professional evaluation is necessary.

What does a step crack mean?
A crack following the mortar joints, with a stepped pattern, is typical of brick or tuff masonry: the mortar is the most fragile element, and the crack runs through it. It is a frequent sign after an earthquake and must be carefully assessed.

How do I know if a crack is getting bigger?
You can mark the edges of the crack with a pencil or tape and take periodic photos with a reference measurement next to them. If the crack widens, deepens, or new cracks appear, you should immediately report it to the municipality or a technician.

Is a through crack serious?
A crack visible on both sides of the wall extends through its entire thickness and warrants a thorough technical inspection. The severity depends on the affected element and its progression over time.

Who should I call for an inspection?
The Municipality of residence for quick checks, the Fire Brigade (115) only for immediate dangers, and a qualified technician for an in-depth evaluation of the building.

This article is for informational purposes only and does not replace a technical assessment: it does not constitute any guarantee of safety. If you have any questions about the stability of a building after an earthquake, always consult qualified technicians and the appropriate authorities.