The RISKRES fieldwork in the Spanish Pyrenees. The 1373 Ribagorça earthquake

In November we participated to the 7th International Colloquium on Historical Earthquakes & Paleoseismology Studies (ICHEPS) in Barcelona (link) and in the next few days, as part of the RISKRES project, we went on a field trip in the Spanish Pyrenees.

The ICHEPS filed trip. Admiring the dropped keystone of the portal at St Martí del Clot. An inscription carved on the keystone commemorates the 1428 Catalonia earthquake.

This region was struck by a number of destructive earthquakes in the later Middle Ages. The first significant event occurred on 2 February 1373, with an epicentre located in the Ribagorça district in the southern central Pyrenees.  The damage inflicted by this earthquake was substantial right across this area, stretching from the city of Lleida to the south to the French side of the Pyrenees to the north (the pagus Tolosanus).

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Macroseismic map for the 1373 Ribagorça earthquake (source: AHEAD).

There are only a limited number of written sources which recorded the event, so the earthquake is poorly known from a seismological perspective. To date, we do not fully understand the real impact of the earthquake even in the epicentral area, where only two contemporary documents and a much later source (written in AD 1548) provide more precise information.  No study so far has attempted to understand the physical impact of this earthquake, but the medieval buildings of this region have great potential to provide fresh evidence about both the impact of the 1373 event and the responses which were adopted by the local population in its immediate aftermath.

With this in mind, our field trip targeted a selection of medieval churches in La Ribagorça and in the area of Lleida. The preliminary results are very promising. We were able to identify several examples of possible earthquake damage in the architecture we surveyed as well as reinforcing structures and restoration works.

You can find some examples below.

Montañana is a wonderful deserted medieval and post-medieval village located in La Ribagorça in Aragon. Well worth a visit. Two Romanesque churches survive here, along with the ruins of two medieval fortifications which control the strategic river valley where the settlement is located.

A view of Montañana.

The church of San Andrés, located on the hilltop of Montañana, has some potential earthquake damage. A dropped key-stone – a typical feature of seismically affected sites – is visible on the Romanesque door of the bell-tower, whose base was doubled in thickness with a reinforcement of  the Gothic period sometime after the damage occurred. Penetrative fractures, and in particular shear cracks (usually caused when a structure suffers from horizontal loads), are visible both in the exterior and the interior of the church.

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The church of St Andrés in Montañana.
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St Andrès in Montañana. Dropped keystone in the Romanesque door of the bell tower. The later Gothic reinforcement has frozen this damage.

The presence of damage possibly caused by earthquake is even more evident in the church of St Juan, a second church located immediately east of the settlement. Here, both the side walls of the church are deformed and tilted outwards. Originally two lateral chapels were built into these walls, but at some point they were destroyed and never rebuilt. The corresponding openings, clearly distinguishable below the original arches, were therefore infilled and walled with rubble. Shear cracks are identifiable on the structures of the church, in particular in the less restored interior. In addition, dropped key-stones and broken stone corners are also visible on both the arches surmounting the portals of the church. Given the spread and the nature of the observable damage, it seems very likely that this building suffered from one or more seismic events in the past.

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The church of St Juan in Montañana.
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St Juan of Montañana. Note the deformed profile of the church’s southern wall.

Further south, in the surrounding of Benabarre (Aragon), is the church of San Pedro ad vincula, a tiny and squat Romanesque church.

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The church of St Pedro ad vincula, Benabarre.

This building displays several vertical and sub-vertical cracks on its apse and northern wall which also appears to be deformed and clearly tilted toward the exterior. Five buttresses were built against the apse, the southern and northern walls with the intention of reinforcing the damaged building. Here, the nature of the damage seems consistent with seismic loading and the scale of the reinforcement appears to be a response not only in order to restore the building, but also to protect it from future earthquakes.

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St Pedro ad vincula, Benabarre. 3D model of the exterior walls and buttresses.
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St Pedro ad vincula, Benabarre. Cracks associated with the reinforced wall.

Llleida was also affected by the same earthquake. Some documents attest that the royal chapel built within the city castle suffered extensive damage and required restoration. Near the castle is the Romanesque and Gothic complex of the cathedral. Here also several possible earthquake effects are still visible. For example, a number of arched doorways leading from the chapter of the cathedral display dropped key-stones in conjunction with broken stone corners, possible indicators of horizontal movements compatible with seismic shaking. Shear fractures and out-of-plane damage appear in some of the walls of the same building, and in the outer cloister of the cathedral.  

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Cathedral of Lleida. the bell tower.
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Lleida. Deformed arch in the chapter of the cathedral.
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Lleida. Penetrative fractures and a damaged window from the façade of the cathedral.

In conclusion, our preliminary field trip was successful in identifying sites possibly affected by the 1373 Ribagorça earthquake, and shed light on some of the architectural elements which were introduced in order to improve structural seismic resilience of these medieval churches.

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