Long-Term Seismicity in Regions of Present Day Low Seismic Activity: the Example of Western Europe

Soil Dynamics and Earthquake Engineering 20 (2000) 405±414 www.elsevier.com/locate/soildyn

Long-term seismicity in regions of present day low seismic activity: the example of western Europe

Thierry Camelbeecka,*, Pierre Alexandrea, Kris Vannestea, Mustapha Meghraouib

aRoyal Observatory of Belgium, avenue circulaire 3, B-1180, Brussels, Belgium bEcole et Observatoire des Sciences de la Terre, rue ReneÂ Descartes 5, F-67084 Strasbourg, France

Abstract In western Europe, the knowledge of long-term seismicity is based on reliable historical seismicity and covers a time period of less than 700 years. Despite the fact that the seismic activity is considered as low in the region extending from the Lower Rhine Embayment to England, historical information collected recently suggests the occurrence of three earthquakes with magnitude around 6.0 or greater. These events are a source of information for the engineer or the scientist involved in mitigation against large earthquakes. We provide information relevant to this aspect for the Belgian earthquake of September 18, 1692. The severity of the damage described in original sources indicates that its epicentral intensity could be IX (EMS-98 scale) and that the area with intensity VII and greater than VII has at least a mean radius of 45 km. Following relationships between average macroseismic radii and magnitude for earthquakes in stable continental regions, its magnitude Ms is estimated as between 6.0 and 6.5. To extend in time our knowledge of the seismic activity, we conducted paleoseismic investigations in the Roer Graben to address the question of the possible occurrence of large earthquakes with coseismic surface ruptures. Our study along the Feldbiss fault (the western border of the graben) demonstrates its recent activity and provides numerous lines of evidence of Holocene and Late Pleistocene large earthquakes. It suggests that along the 10 km long Bree fault scarp, the return period for earthquakes with magnitude from 6.2 to 6.7 ranges from 10,000 to 20,000 years during the last 50,000 years. Considering as possible the occurrence of similar earthquakes along all the Quaternary faults in the Lower Rhine Embayment, a large earthquake could occur there each 500± 1000 years. These results are important in two ways. (i) The evidence that large earthquakes occur in western Europe in the very recent past which is not only attested by historical sources, but also suggested by paleoseismic investigations in the Roer Graben. (ii) The existence of a scienti®c basis to better evaluate the long-term seismicity in this part of Europe (maximal magnitude and return period) in the framework of seismic hazard assessment. q 2001 Elsevier Science Ltd. All rights reserved.

1. Introduction measurable. The fault length along which the rupture propa- gates has a minimum value of the order of 10 km, which

A large part of tectonic deformation is relaxed during corresponds to a Mw 6.0 magnitude. earthquakes, which result from the unstable slippage of The densely populated areas of northwest Europe, where two crustal blocks along a fault zone. The affected fault seismic activity is apparently low and very destructive area can vary from a few m2 for the weakest detected earth- earthquakes virtually unknown, would be at high risk quakes to some thousands of km2 for the larger ones. In from the occurrence of such a large earthquake. Ordinary continental zones, the seismogenic layer, where earthquakes dwellings and industries can already be at risk from small originate, extends from a shallow depth to depth ranging earthquakes when they occur close to vulnerable cities. Two from 10 to 25 km depending on the considered region. recent examples are the Ms 4.6 1983 LieÁge (Belgium) The base of the seismogenic layer corresponds to the earthquake [14] and the Ms 5.3 1992 Roermond (The mechanical limit under which tectonic deformations occur Netherlands) earthquake [3] which caused in the epicentral as a plastic ¯ow. Earthquakes are quali®ed as large when areas losses estimated in excess of 100 million Euros. These they affect the whole seismogenic layer. In this case, surface two examples focus the importance to evaluate the potential faulting can occur and the surface coseismic deformation is (in term of magnitude and return period) for large earthquakes in this part of Europe. * Corresponding author. Fax: 132-2-373-0339. In the region between the Lower Rhine Embayment and E-mail address: [email protected] (T. Camelbeeck). England, there is no surface rupturing earthquake known in

Fig. 1. Map of the region considered in this study. Historical earthquakes with estimated epicentral intensity of VII or greater are indicated. The data for the instrumental period (1910±1995) are taken from the catalogue of the Royal Observatory of Belgium for epicenters in Belgium and from the International Seismological Center for epicenters outside Belgium.

the historical account. Despite that fact, from their estimated 2. Seismic activity in the region between the Lower magnitude around 6.0 [11], the earthquakes having occurred Rhine Embayment and the North Sea in 1382 in the southern North Sea and in 1580 in the Chan- nel can be considered as large earthquakes. In this paper, we Studies of long-term seismicity in any region of the world present arguments for the occurrence of a third large histor- require the longest historical perspective possible. In terms ical earthquake since the 14th century, the Verviers of the available documents, the seismic history of the (Belgium) event of September 18, 1692. In contrast to the studied region (Fig. 1) before the instrumental period, can two other events, having occurred at sea, detailed informa- be divided into three periods: tion of damage in the epicentral area has been found, which can be valuable in terms of mitigation for future large earth- 1. Before 700: the silence of Roman sources and the nearly quakes in this part of Europe. total absence of local sources have as a consequence that In the considered studied area, the more active region with even strong earthquakes stay unknown. the occurrence since 1350 of at least six earthquakes with 2. From 700 to 1350: sources allow a catalogue of the felt estimated Ms magnitude greater than 5.0 is the Lower Rhine earthquakes to be established, but the available informa- Embayment, mainly the Roer Graben. The strong subsidence tion gives very few data to estimate local intensities and of the Roer Graben during the last 150,000 years [7], the epicenters. Quaternary faults and associated morphology and the seismic 3. From 1350 to 1900: sources from different origins activity are evidence of recent and present day crustal defor- (chronicles, annotations, parish registers, account regis- mation. ters, etc.) give us more details on local effects and allow Since 1995, we have undertaken detailed paleoseismic reliable estimation of damages and the perceptibility area investigations along the Feldbiss fault [5,6,17] on the of the earthquakes. It is then possible to determine the western border of the Roer Graben to evaluate its more probable epicentral area of the earthquakes and also to recent activity in terms of large paleoearthquakes. We estimate their magnitude by comparison with recent present the main results of the study and we discuss their earthquakes for which the magnitude has been instru- impact in terms of future seismic hazard assessment. mentally determined [2,9]. T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414 407

Fig. 2. Cumulative annual rate of earthquakes as a function of magnitude for the region plotted in Fig. 1.

Even though instrumental recordings of earthquakes began (Belgium) earthquake of June 11, 1938 (Ms 5.0) and at the end of the last century, the reliability of the calculated two events having occurred in the Lower Rhine Embay- earthquake parameters were very unsatisfactory at least up ment, the Euskirchen (Germany) earthquake of March 14, to 1965 for the epicenter location and to 1980 for the focal 1951 (Ms 5.3) and the Roermond (The Netherlands) earth- depth determination [4]. Before 1960, with the exception of quake of April 13, 1992 (Ms 5.3). larger shocks, macroseismic reports often provide a better During the historical period, several strong earthquakes epicenter location than those calculated from arrival data occurred, mainly in the Lower Rhine Embayment, but the read on the seismograms. It is important, therefore, to discri- real importance of some of them was neglected until very minate the reliable from the less reliable data in the catalo- recently. Melville et al. [11] studied the historical earth- gue when we want to use it for seismic hazard assessment. quake activity in the Channel and the southern North Sea The catalogue of earthquakes established at the Royal and concluded that the events on May 21, 1382 and April 6, Observatory of Belgium for the region de®ned in Fig. 1 is 1580 probably both had a magnitude around 6.0. By their supposed to be complete for Ms magnitude greater than 4.7 estimated magnitude, these earthquakes should be consid- since 1350 (all historical events with epicentral intensity VII ered as large earthquakes rupturing the whole seismogenic or more), Ms 3.3 since 1911 and Ms 1.8 since 1985. layer. The annual cumulative frequency of earthquakes as a Recently found original historical sources suggest that the function of magnitude (Ms) for the whole region (Fig. 2) earthquake having occurred on September 18, 1692 in the was calculated taking into account earthquakes with magni- Belgian Ardenne is probably the strongest known earth- tude greater than 4.7 since 1350, with magnitude ranging quake in the studied region [1]. from 3.3 to 4.7 since 1911 and with magnitude ranging from 1.8 to 3.3 since 1985. A simple regression analysis gives the law: log N 2.7 2 0.87Ms which means an earthquake of 3. The Verviers earthquake of September 18, 1692 is a magnitude greater than or equal to 6.0 every 330 years, 5.5 large earthquake every 120 years and 5.0 every 45 years. During the 20th century, three earthquakes had a magni- The classical catalogues of Perrey [13] and Sieberg [15] tude greater than or equal to 5, the Brabant Massif indicate an epicentral area in the Brabant Massif between 408 T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414

Fig. 3. Macroseismic map of the September 18, 1692 earthquake. Only three isoseismals can be sketched with any con®dence. From the analysis, the epicenter seems to have been located near the city of Verviers and the estimated magnitude ranges between 6.0 and 6.5.

Brussels and Antwerpen. By analogy with the February 23, earthquakes have been written. Some reports concern 1828 earthquake located in eastern Brabant, Van Gils and damage to ordinary buildings, which are the only ones Zaczek located the 1692 event near the city of Tirlemont which can be used within the framework of the EMS-98 [16]. Vogt called into question an epicenter in the Brabant macroseismic scale [8]. In an attempt to evaluate intensity, area [19]. He noted that the maximal damage is not located we will assume that houses are included in the vulnerability in the regions of Brussels±Antwerpen and Tirlemont, but class A and then B and we will use as suggested in Ref. [8] rather in the zone LieÁge±Verviers±Aachen. the range of values given by the two assignments. During the last 10 years, a large number of new original In Ensival, a ®rst source indicated `plusieurs maisons sources have been collected and analysed. Alexandre and furent eÂcraseÂes'; a second one ìl y a eut plusieurs maisons Kupper provide a detailed description of the available infor- endomageÂe et des chemineÂe renverseÂe'. This could corre- mation [1]. Fig. 3 shows the damage and the way by which spond to substantial to heavy damage (grade 3) or very the earthquake was felt. Isoseismal curves, corresponding to heavy damage (grade 4) and perhaps in some cases to intensity V, VI and VII±VIII have been tentatively repre- destruction (grade 5). The quantity of damage cannot be sented. The map takes into account information from the estimated, it is then impossible to exactly determine the 185 historical sources known up to now. The sources are all intensity, but it should be at least VII. original and contemporary with the event. In Polleur, no chimneys were safe Ìn dem Dorfe Bleuer We have few data from Germany. This is probably due to ¼ war nicht ein Schornstein ganz geblieben ¼'. In this the fact that little critical research has been undertaken case, there is a description of a quantity (many or most) there. The map shows that the damage is widespread, for typical damage, corresponding to grade 2 or 3 (more from Kent in England to the Rhenan region and to Cham- likely). The range of intensity values is VII±VIII. pagne. This earthquake is one of the most strongly felt In Soiron `tremblement de terre espouvantable qui a during the historical period in England [12] even though abbatu les maisons, chemineÂes dont les miennes l'ont esteÂ this country is located at the periphery of its perceptibility et le chasteau de Soiron gasteÂ et irreÂparable ¼ et, fait aÁ fait zone. qu'il s'avancËoit on voyait hausser la surface de la terre, en Fig. 4 indicates the localities in the epicentral area, the sorte que plusieurs personnes et animaux en furent culbu- northern part of the Ardenne, where original accounts of the tez'. The account notices substantial to very heavy damage T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414 409 plusieurs morts, et beaucoup des deÂgats surtout par les chemineÂes renverseÂes, l'eÂglise de Saint Lambert eut divers domages, de meÃme aÁ Saint Laurent et au cloistre des ReÂveÂr- ends PeÁre JeÂsuittes'. As usual for historical sources, damage to monumental buildings is well represented in the accounts of the 1692 earthquake. An example is given by the church of Theux for which detailed reports of the costs of reconstruction give us a good idea of the damage. In Walhorn, the priest wrote Ìn diversis locis domus fuerunt eversae et homines occisi. Castrum de Crapoel plane deperditum'. He gives a general account of the destruction due to the earthquake and gives an example with the castle of Crapoel in Walhorn. At greater distance, detailed description of damages allow us to assess a minimal value for intensity. An example is an account in the chronicle of the Forest Abbey near Brussels from which an intensity VI±VII is suggested: `Le 18 septembre 1692 ¼ Je me trouvais sur notre chausseÂeet tout tremblait sous moi. Tous nos pigeons quitteÁrent le colombier et s'envoleÁrent confuseÂment. Notre eÂglise trembla et tout le plaÃtrage se deÂtacha de la vouÃte, les tuiles tombeÁr- ent de beaucoup de toitures et dans la cave de la laiterie le lait fut projeteÂ hors des basins. Beaucoup de pierres se deÂtacheÁrent des pignons, des carreaux tombeÁrent du fron- tispice de l'eÂglise, dans Bruxelles beaucoup de maisons et Fig. 4. Epicentral area of the September 18, 1692 earthquake. The cities for toitures endommageÂes et beaucoup de personnes tueÂes par which an original account of the earthquake is available are indicated. les pierres tombeÂes des murs et des toits.' The information collected [1] allowed us to attempt to for the houses and perhaps destruction. The owner of the estimate the magnitude of the earthquake. The magnitude castle provides more information about its heavy damage. of strong historical earthquakes can be evaluated by means `¼ dont la secousse fut si grande quelle renversat la vieille of the spatial distribution of damage and/or the felt areas tour du chasteau de Soiron and deÂlabrat tellement les autres compared to that of recent earthquakes for which a magni- eÂdi®ces qu'ils sont irreÂparables et je fus obligeÂ davoir toute tude has been instrumentally determined. Ambraseys [2] sorte douvriers pendant six sepmaines pour les appuyer et calculated laws valid for northwestern Europe whereas rapieÁcer, faute de quoy, ils seroyent assureÂment tombeÂs'. Johnston [9] published relationships valid for stable conti- The church was also badly damaged. A new one was rebuilt nental regions. These two sets of relationships are relatively from 1723 to 1725, except the tower. The descriptions similar and we provide in Table 1 the estimated magnitude correspond at least to intensity VIII and it is not impossible for the 1692 earthquake using the latter. that intensity could be IX. From this estimation of Ms between 6.0 and 6.5, it can be In LieÁge, Huy and Aachen the description of damage to deduced that the earthquake ruptured the whole seismogenic houses suggests that intensity was at least VII in these cities layer. We suspect that the seismogenic fault having gener- `¼toute la ville de LieÁge fut fortement eÂbranleÂe, il y eut ated the earthquake could be the Hockay fault zone [4]. Two

Table 1

Relationship between magnitude (Ms), average macroseismic radii and maximal observed intensity (Imax) determined by Johnston [9] for intraplate earthquakes. Data corresponding to the April 13, 1992 Roermond earthquake (Ms 5.3) and the 1692 Verviers earthquake are indicated. It can be deduced that the magnitude of the latter event ranges between 6.0 and 6.5

Magnitude I VIII (km) I VII (km) I VI (km) I V (km) I IV (km) Imax (km)

6.0 6 20 89 230 410 8.5 6.5 26 56 160 330 550 9.0

Event I VIII I VII I VI I V I IV Magnitude

13/4/1992 6 40 100 170 5.3 18/9/1692 ? 45 120 250 ? 6.0±6.5 410 T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414

Fig. 5. Major Quaternary faults along the Lower Rhine Embayment. The Roer Graben is bounded on the northeast by the Peel fault, which produced the

Ms 5.3 1992 Roermond earthquake, and on the southwest by the Feldbiss fault, along which our paleoseismological investigations were conducted near the city of Bree. Strong historical earthquake epicenters are represented in parallel with those of the events having occurred during the 20th century. years ago, we began to look for possible indices of active scarp corresponds to the more recent seismic events along faulting, but without signi®cant results to date. the Bree fault scarp [5,6,10,18]. This earthquake is a unique example of a large earth- It has been possible to identify the most recent large quake in western Europe. The contemporary accounts earthquake along the scarp in all the trenches (Table 2, known up to now provide descriptions of very heavy Fig. 10). In trenches 1 and 4, it displaced a well known damage and destruction over a large area, which is desert pavement (Beuningen level, Bg) formed during the exceptional in the historical seismicity of the region. A Late Glacial Maximum (14±19 ka bp), respectively by 0.5 preliminary investigation indicates that traces of damage and 0.12 m. In trench 1, the Holocene soil, formed in the remain in the architectural heritage. It should, then be more recent coversands of the Late Glacial, is also affected possible to better constrain the potential destruction of whereas a possible historical illuviation horizon is displaced future large earthquakes in our region by improving our in trench 4, suggesting that the most recent event occurred knowledge of the 1692 earthquake. during the late Holocene and possibly during historical time. 14C datings in trenches 1 and 2 suggest a date between 600 and 900 AD. In trenches 2 and 3, the fault separates the 4. Paleoseismic investigations along the western border Middle Pleistocene Main Maas River Terrace from Early of the Roer Graben Holocene and Late Pleistocene deposits. The most recent displacement is evidenced in trench 2 by a well de®ned The Royal Observatory of Belgium undertook in 1995 a colluvial wedge, allowing an estimation of the slip of the program to identify active faults and conduct associated order of 0.7 m. In trench 3, the surface slope is higher and paleoseismic studies along the Belgian side of the Roer farming activities have strongly eroded the scarp. The Graben (Fig. 5). Near the town of Bree (Belgian Limburg), consequence is that it is not possible to have a measurement and along the Feldbiss fault zone (the western border fault of of the more recent displacement. the Roer Graben) a prominent NW±SE trending fault scarp The study of soft-sediment deformation and liquefaction offsets the main terrace of the Maas River (deposited observed in trench 2 [18] suggests the occurrence of at least between 350,00 and 700,000 years Before Present (bp)). three distinct events during the last 30 ka. These deforma- The geomorphic expression of the scarp consists of a tions were probably generated during moderate to relatively 10 km long escarpment that has 15±20 m of vertical topo- large earthquakes, similar in size to or exceeding the Ms 5.3 graphic relief (Fig. 6). In detail, the scarp is multiple, and Roermond earthquake (April 13, 1992). there is a 1±3 m high frontal scarp (Fig. 7) which offsets The latest one possibly correlated with the most recent young deposits and alluvial terraces in the ¯at valley (Fig. 8). large earthquake observed in the different trenches and a Four trenches (Fig. 9) excavated across the scarp in 1996, second one could correspond to the penultimate large earth- 1997 and 1998 provide numerous evidence that this frontal quake visible in trenches 3 and 4. The vertical displacement T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414 411

Fig. 6. Bree fault scarp (2 km southeast of the city of Bree). It separates the Campine Plateau (at the top) from the Bocholt plain (in the foreground). The scarp results from a succession of large earthquakes having occurred during the last 700,000 years producing a relative uplift of more than 20 m of the Campine Plateau relative to the Bocholt plain. caused by this event is clearly measurable in trench 4 and is 2 to soft-sediment deformations having occurred before 0.33 m. It is not visible in trench 1 because the sediments there 30 ka bp. All the information obtained for these three are too young, and it is not possible to measure any displace- most recent earthquakes along the Bree fault scarp is ment in trenches 2 and 3 due to the complexity of the fault zone summarized in Table 2. at those sites. 14C datings in trench 2 and OSL datings in Our investigation suggests that the return period for large trench 4 suggest its occurrence between 28 and 17 ka bp. earthquakes along a section of fault in the Roer Graben is of A third earthquake can also be characterized by the analy- the order of 10±20 ka during the last 50 ka. We can assume sis of trenches 3 and 4. In trench 3, it is characterized by a that it is at least 10 km from ®eld observations of the frontal vertical displacement of 1.2 m of a coversand unit dated 41± Bree faults scarp. It is, of course, dif®cult to know the length 46 ka bp. In trench 4, it is de®ned by the presence of a of the ruptured fault section during a single earthquake. This colluvial wedge allowing an estimation of 1 m for the verti- value is a minimum which seems compatible with the cal displacement. OSL datings suggest that it occurred observed vertical offsets for the more recent and the penul- between 27 and 63 ka bp. It could also correspond in trench timate large earthquakes [20]. The fault scarp disappears to the southeast where it crosses the Maas Valley, but becomes visible again in The Netherlands, reaching a total length of

Fig. 7. Frontal fault scarp. It is the expression of earthquakes having occurred during the last 50,000 years. The trace of the last rupture is visible at the ground surface. Its direction is indicated by the right hand of one of the three people at the right of the photo and is located more or less 1 m Fig. 8. Frontal fault scarp. It is easily visible at this site which is the place higher on the scarp. Its ¯exuration is easily visible on the fences which are where trench 1 was excavated. Here, the deposits are reworked by a small perpendicular to the fault. The city of Bree is in the background. river crossing the scarp and are very young. 412 T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414

Fig. 9. Morphotectonic map showing the main section of the Bree fault scarp and the sites where the four trenches were excavated (T1 and T2 in 1996, T3 in 1997 and T4 in 1998). The geomorphic expression is delineated by a maximum topographic offset of 15±20 m (Fig. 5), but the fault also shows a frontal scarp (Figs. 6 and 7) with a height of 0.5±3.0 m along strike.

35 km. Near Bree, the scarp divides into three branches Embayment (their deformation rates are similar or larger which disappear to the north close to the Dutch border. than that of the Bree fault scarp), a large earthquake could In view of the size of the vertical displacement suggested for occur on average every 500±1000 years in the graben area. the antepenultimate earthquake, it could be supposed that this The purpose of future investigations will be to study the event was larger and that it ruptured a greater fault length. If we faulting behavior of these faults to answer this question suppose that the most recent earthquake ruptured the whole and to quantify the average return period of such earth- seismogenic layer (17 km thickness) over a minimum length quakes. corresponding to the length of the Bree scarp with an average slip of 0.4 m, its moment magnitude was at least Mw 6.2. Using the relationships established by Wells and Copper- 5. Conclusions smith [20] for normal faulting earthquakes, the following We presented evidence that large earthquakes occurred in magnitude values have been obtained: the very recent past in the region extending from the Lower Rhine Embayment to England. At least three strong earth- For the two more recent earthquakes: quakes with an estimated magnitude around 6.0 or even considering an average slip of 0.4 m, M 6.5 ^ 0.3 considering a maximal slip of 0.7 m, M 6.5 ^ 0.3 Table 2 considering a minimal fault length of 10 km, Minimal vertical displacements (in metres) and dating of paleoearthquakes M 6.2 ^ 0.3 suggested by the analysis of the four trenches excavated across the Bree For the antepenultimate earthquake: fault scarp [5,10,18] considering an average slip of 1 m, M 6.8 ^ 0.3 Earthquake Trench 1 Trench 2 Trench 3 Trench 4 considering a maximal slip of 1.2 m, M 6.7 ^ 0.3 Most recent (600±900 ad) 0.5 0.7 0.12 Considering as possible the occurrence of similar earth- Penultimate (28±17 ka) 0.33 Antepenultimate (45±30 ka) 1.2 1.0 quakes along all the Quaternary faults of the Lower Rhine T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414 413

Fig. 10. Observations of the coseismic surface displacement due to the most recent large earthquake along the Bree fault scarp (aÐtrench 1; bÐtrench 2; cÐtrench 4). A short description of the stratigraphy is given in Appendix A, in parallel with the trenches observation. greater have occurred since the 14th century. Paleoseismic better constrain the potential of destruction of future large investigation along the Bree fault scarp in the Roer Graben earthquakes in our region. suggests Holocene and Late Pleistocene surface faulting of seismic origin. The importance of the measured vertical offsets in four trenches indicates that the magnitude of Acknowledgements these events ranges from 6.2 to 6.8 and that their return periods along the 10 km long Bree fault scarp range from This study is a part of the PALEOSIS project, an envir- 10,000 to 20,000 years during the last 50,000 years. If all the onment and climate project of the European Commission Quaternary faults in the Lower Rhine Embayment behave (contract ENV4-CT97-0578; DGIL-ESCY). We would like similarly, which should be studied by future paleoseismic to thank Kuvvet Atakan, the local organizer of SDEE'99 for investigations, a large earthquake could occur there on aver- his invitation to present our results. age every 500±1000 years. Our study demonstrates that it is possible to obtain a better evaluation of the long-term seis- Appendix A. mic activity of this part of Europe by using paleoseismological methodology adapted to the tectonic (low deformation rates) and climatic contexts of the region. Short description of the stratigraphy These results are also of importance from the engineering seismology point of view. They suggest that now, it is possible to better constrain the long-term seismic hazard and the Younger Coversand aeolian deposition during the values of maximum magnitude for the assessment of seis- Old and Younger Dryas (12± mic hazard. 10.3 ka bp) In contrast, the September 18, 1692 Verviers earthquake Older Coversand II aeolian deposition at the end of provides numerous descriptions of damage and destruction the Late Weichseilian (,14 ka over a large area and also traces in the architectural heritage. bp) It is a unique example of a large earthquake in western Bg gravel bed of the Beuningen Europe and all the information collected could be used to Complex (14±19.5 ka bp) 414 T. Camelbeeck et al. / Soil Dynamics and Earthquake Engineering 20 (2000) 405±414

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