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LOOKING FOR TRACES OF THE 18 SEPTEMBER 1692 EARTHQUAKE

EXCURSION GUIDE – 18/09/2009 Prepared by Thierry Camelbeeck and Thomas Lecocq (Royal Observatory of

Belgium)

The 18 September 1692 earthquake

The strongest known seismic event in Western Europe north of the Alps occurred on 18

September 1692 approximately at 14:15 (local time) in the bordering region between Belgium,

The Netherlands and Germany. The earthquake produced significant destructions in the

northern part of the Belgian Ardenne and caused widespread damage from Kent in England to

the Rhineland in Germany and to Champagne in France.

The knowledge of the 18 September 1692 has greatly improved during the last ten years by

the numerous new documents found in different record-offices in Belgium, Germany, The

Netherlands and France. Based on these new data, Alexandre et al. (2008) proposed a new

macroseismic map in terms of the EMS-98 macroseismic scale, from which, it is suggested a

better epicenter location, than in previous investigations, within the area of Verviers-Soiron-

Herve-Montzen. However this conclusion should be revisited in the light of possible new

discoveries in the archives for localities in the Belgian Ardenne and the Eifel mountains.

With a magnitude between 6 and 6 ¼, it is the largest known historic earthquake which

occurred in Northwest Europe.

Figure 1. Epicentre area of the 1692 “Verviers” earthquake

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This earthquake is one of the unique examples of a large earthquake in Western Europe. The

contemporary accounts provide descriptions of very heavy damage and destructions on a large

area, which is exceptional in the historical seismicity of the region. During the recent years,

attention has also been paid to identify traces of the seismic activity in the architectural

heritage (Barszez et al., 2009) with the purpose of better constrain the potential of destruction

of future large earthquakes in our region and to furnish more information of past strong

earthquakes.

At the first stop of this excursion, we will provide an example of the methodologies in

development to assess the impact of earthquakes in the architectural heritage by presenting the

case study of the village of Soiron.

From the seismic hazards and risks point of view, it is important to study the destructive past

earthquakes and their seismotectonic framework. Evaluating the permanency of such

earthquake activity can only be done by identifying the geological structures that have

generated such large seismic events and studying their tectonic activity rate. Since more than

ten years different investigations have been conducted to evidenced possible active faults in

the epicentre area of the 1692 earthquake. The two following stops will be devoted to this

problematic

Traces of the 1692 earthquake in the architectural heritage: the case study of Soiron (Stop 1: presentation by Hervé Degée (ULg)

and Thierry Camelbeeck (ROB) Two historical sources contemporaneous of the earthquake report its effects in Soiron.

[Servais Ronval, Notes du Registre paroissial de Soiron, ed. by Graindor M (1964) La Vie

quotidienne à Soiron au temps jadis, Olne, pp 178] : « tremblement de terre espouvantable qui

a abbatu les maisons, cheminées dont les miennes l’ont esté et le chasteau de Soiron gasté et

irréparable …….et, fait à fait qu’il s’avançoit on voyait hausser la surface de la terre, en

sorte que plusieurs personnes et animaux en furent culbutez… ».

[Nicolas Ignace de Woelmont, Histoire de la maison de Woelmont, excerpts ed. by Graindor

(1968) : L'Avouerie et les anciens seigneurs de Soiron, vol 2, La maison de Woelmont,

Verviers, pp 129] : «….dont la secousse fut si grande quelle renversat la vieille tour du

chasteau de Soiron et délabrat tellement les autres édifices qu’ils sont iréparables et je fus

obligé davoir toute sorte douvriers pendant six sepmaines pour les appuyer et rapiècer, faute

de quoy, ils seroyent assurément tombés….. ».

The account notices substantial to very heavy damage for the houses and perhaps destruction.

The owner of the castle provides detailed information about its heavy damage.

The church was also strongly damaged. A new one was rebuilt from 1723 to 1725, except the

tower. The descriptions correspond at least to intensity VIII and it is not impossible that

intensity could be IX (EMS-98 intensity scale).

Two different studies have been undertaken to evaluate the damage caused in Soiron by the

1692 earthquake. The first concerns the study of the different repairing traces in the tower of

the church to establish if they can be originated by the earthquake (Gerardy, 2009). The

second one is conducting by the “Département of Architecture” of the Polytechnic Faculty of

Mons in cooperation with the Royal Observatory of Belgium and concerns the houses of the

village center.

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Figure 2. Tower of the Soiron church: observations of disturbances and repairs

Figure 3. Stress concentration generated by shear action on the tower of the Soiron church

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Morphological expression of faulting along the “Hockay fault zone” STOP 2: Wesny (presentation by Alain Demoulin (ULg) and Thierry Camelbeeck (ROB) The analysis of the DEM and the aerial photographs of the northern part of the Belgian

Ardenne evidenced some lineaments or structures that could be related with faults. The

clearest break in slope in a NNW-SSE direction that can be traced over several kilometers is

located 1.5 km east of the centre of Verviers and is called the Verviers scarp (Fig. 4). This

lineament is 7.5 km long, has an azimuth of 150° with a slight curve to a NW-SE orientation

towards the south, and is sloping to the west. The Verviers scarp was first recognized by

Demoulin as a possible active fault (2006). At both sides of the Vesdre, the general view of

the scarp is defined by the highest terrace at the supposed footwall (terrace Hombiet and Haut

Tombeux S), which seems to connect with a high terrace of the supposed hanging wall

(Ottomont W and Linaigrettes), which is approximately 32 meters lower. We doubt that these

terraces in the footwall and hanging wall belong to the same terrace level and thus the height

difference cannot be interpreted as cumulative vertical fault movement.

Figure 4: Digital Elevation Model of the studied area with indication of some structural

elements, discussed during the excursion. The red stars indicate the epicentre of the 1989-

1990 seismic sequence. The three stops of the excursion are indicated in red.

In a broader geostructural view, and based on the 1/25000 scale geological map of Fléron-

Verviers, the scarp coincides with the Verviers fault. This fault is well traceable on the

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geological map with lithological contacts defining some hundreds of meters of vertical (west

dipping) and horizontal (sinistral) offset. The geomorphologic expression gets less clear

towards the north, but around Battice, 7 km north of Verviers, the supposed prolongation of

the Verviers fault is better known as the Ostend fault. This fault is the eastern border fault of

the Graben de la Minerie, a geologic structure evidenced by mining activities in the last

century. These mining studies revealed that the Ostend fault is a sinistral oblique fault

displacing Westphalian sediments 300 m horizontally and 48 m vertically (dipping to the

west).

STOP 3: crête de la Vecquée (presentation by Thomas Lecocq and Thierry Camelbeeck

(ROB) Southwards, the Hockai faulted zone (HFZ), which is located 5 km southwest of the Botrange,

i.e. the highest point of Belgium, lies on first sight roughly in the prolongation of the traced

Verviers scarp. The HFZ was first recognized by Ahorner (1983) as a seismically active

structure by epicentre alignment of registered earthquakes. From 30 September 1989 until 16

April 1990, a seismic swarm with more than 400 micro-earthquakes struck the region. This

seismic swarm was measured by a mobile network of 4 stations and the permanent Belgian

seismic network (Camelbeeck 1993). The spatial repartition of the hypocentres of 92 well

locatedevents of the sequence represents a fault plane with an azimuth of 330° and a dip of

70° to the east, which is opposite to the Verviers fault scarp. Most of the fault plane solutions

are also in good agreement with this fault orientation and are indicative for a sinistral strike

slip fault with a minor normal component dipping to the east.

On the DEM and aerial photographs, we could observe a NNW-SSE lineament approximately

2.5 km west of the earthquake swarm around Baronhé at the Crête de la Vecquée, an

Oligocene denudation surface, which is now a high ridge of 565 meters in altitude. The

lineament is characterized by a gentle slope to the east and a more important sinistral

component that displaces the Crête de la Vecquée 100 m laterally. This scarp could

correspond with the upward prolongation of the fault that was inferred from the seismic

swarm. Further evidence of the existence of the HFZ can be found in the NNW-SSE

orientation of the upper stream of the Hoegne, which seems to be influenced by the HFZ by

its orientation and by the fact that and the place where it cuts through the Crête de la Vecquée.

The geomorphologic evidence to connect the Verviers scarp with the HFZ in the south is not

that convincing, considering also the opposite dip of the both faults, but they can be regarded

as belonging to the same geostructural zone with a more important sinistral component.

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REFERENCES

AHORNER Lüdwig. (1983). Historical seismicity and present-day micro-earthquake activity

of the Rhenish Massif, Central Europe. In Plateau Uplift, K Fuchs et al. (editors),

Springerverslag, Berlin, 198-221.

ALEXANDRE Pierre, KUSMAN David, PETERMANS and CAMELBEECK Thierry (2008).The 18

September 1692 earthquake in the Belgian Ardenne and its aftershocks. Modern Approaches in Solid

Earth Sciences - Historical Seismology: interdisciplinary studies of past and recent earthquakes 209-

230.

BARSZEZ Anne-Marie, PHILIPRONT Amélie, CAMELBEECK Thierry et SABBE Alain

(2009). Comment déceler l’origine sismique de certains désordres affectant le patrimoine

architectural et comment y remédier ? Les cahiers de l’Urbanisme, 71, 86-92.

CAMELBEECK Thierry (1993). Mécanisme au foyer des tremblements de terre et

contraintes tectoniques : le cas de la zone intraplaque belge [Ph.D. thesis]: Université

Catholique de Louvain, 295 p.

DEMOULIN Alain (2006). La néotectonique de l’Ardenne-Eifel et des régions avoisinantes.

Académie royale de Belgique, classe des Sciences, collection in-8°, 3è série, tome XXV.

GERARDY Lucie (2009). Etude du comportement sismique de l’église de Soiron. Travail de

fin d’études master en Ingénieur Civil des constructions à l’Université de Liège (promoteur :

Hervé Degée).