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REGION DE DOUR

Earthquake22 March 1987

Magnitude
2.6ML
Depth
7.0km
Max. int.
4
Belgian time
22:05:351987-03-22
UTC
21:05:351987-03-22

Main parameters

Magnitude and intensity

Two numbers often confused, with the values of this earthquake and of the Observatory’s catalogue.

Preparing the animation…

1Magnitude: the size of the earthquake

The magnitude (ML 2.6) measures the size of the earthquake at its source, from the amplitude of the waves recorded by seismographs: a single value for the whole earthquake. Since 1985, 94 % of the 3,122 earthquakes with a magnitude in the Observatory’s catalogue have a smaller one.

Animation drawn from the page and the Observatory’s catalogue (tectonic earthquakes since 1985, ML or MW magnitudes); short descriptions of the European Macroseismic Scale EMS-98.

Date and time1987-03-22 21:05:35 UTC
1987-03-22 22:05:35 Belgian time
MagnitudeML 2.6
Epicentral coordinates50.406° N, 3.816° E
Maximum intensity4
Depth of hypocenter7.0 km
Event IDROB 740

Data source : ROB (Royal Observatory of Belgium)
Last update : 2011-06-27 18:19:24 Belgian time

Location map

Where and when the earthquake began

The focus, the epicentre and their uncertainties, with this earthquake’s values.

Preparing the animation…

1Focus and epicentre

An earthquake starts at depth, at the focus (or hypocentre): here 7 km below the surface. The point on the surface right above it is the epicentre (50.406° N, 3.816° E), the one the map shows.

Values from the page and the Observatory’s catalogue (tectonic earthquakes since 1985).

  • Epicentre
  • Station that recorded the event

Macroseismic intensities

Intensities assessed for each municipality by the seismologists of the Royal Observatory, from the official questionnaires sent to the municipalities, letters received, the press and published studies. They make up the Belgian Traditional Macroseismic database (BTM).

Intensity data points
106
Maximum intensity
IV
Farthest municipality
27km · RESSAIX
Source quality
A
Show
Maximum intensity (Imax), EMS-98
  • I
  • II
  • III
  • IV
  • V
  • VI
  • VII+
  • Epicentre

Points by intensity

IntensityPoints
I85
III10
IV11
Total106
List of the points (106)

Sources of the intensities

SourcePoints
Official ROB questionnaire, version 499
Francois et al. (1989)7
  • Francois M, Camelbeeck T, Chiapparo A (1989). L’étude macroseismique des séismes de Dour du 22 mars 1987 et de Gulpen du 17 octobre 1988. Annales de la société géologique de Belgique 112, 393-400.

Belgian Traditional Macroseismic database: Neefs B, Van Noten K, Vanneste K, Camelbeeck T (2025). The Belgian traditional macroseismic (BTM) database of the twentieth century. Journal of Seismology 29, 1005–1036. doi:10.1007/s10950-024-10266-9
Data set: Neefs B, Van Noten K, Vanneste K, Camelbeeck T (2024). The Belgian Traditional Macroseismic (BTM) Database of the 20th Century [data set]. Royal Observatory of Belgium. doi:10.24414/2b5w-j029

Notes and method

For each municipality, an assessment on the European Macroseismic Scale EMS-98: minimum and maximum intensity (Imin, Imax), equal or forming a range (III–IV) that reflects the spread of the testimonies in the municipality, “F” when the earthquake was felt but no degree could be given.

Seismic activity in the area

Known earthquakes around the epicentre, from the catalogue of the Royal Observatory of Belgium.

Within 10 km of the epicentre

90 other earthquakes in the catalogue since 1911. 37 of them occurred after this one.

Latest earthquakes before this one

DatePlaceMagnitudeIntensityDistance km
1987-03-22REGION DE DOURML 1.7–0.4
1987-03-22REGION DE DOURML 1.3–0.4
1987-03-22REGION DE DOURML 0.7–0.2
1987-03-21REGION DE DOURML 2.540.2
1987-03-21REGION DE DOURML 1.0–0.8

Largest known earthquakes

DatePlaceMagnitudeIntensityDistance km
1920-01-17HORNUML 3.763.8
1952-10-27QUAREGNONMWH 3.554.7
1954-07-10FLENUMWH 3.567.1
1911-04-12MONS-WASMUELMWH 3.148.3
1934-11-12CUESMESMW 3.158.3

Municipality of Colfontaine

8 other earthquakes in the catalogue since 1987. One of them occurred after this one. This is the largest known earthquake in the municipality.

Latest earthquakes before this one

DatePlaceMagnitudeIntensityDistance km
1987-03-22REGION DE DOURML 1.7–0.4
1987-03-22REGION DE DOURML 1.3–0.4
1987-03-22REGION DE DOURML 0.7–0.2
1987-03-21REGION DE DOURML 2.540.2
1987-03-15REGION DE DOURML 0.6–0.1

Largest known earthquakes

DatePlaceMagnitudeIntensityDistance km
1987-03-22This earthquakeML 2.64–
1987-03-21REGION DE DOURML 2.540.2
1987-03-22REGION DE DOURML 1.7–0.4
1987-02-04REGION DE DOURML 1.3–0.4
1987-03-22REGION DE DOURML 1.3–0.4
Notes and method

Tectonic and induced earthquakes from the Observatory’s catalogue, suspected ones included; quarry blasts, explosions and other events are not counted. Epicentral distances on the WGS84 ellipsoid.

Municipality: 2025 municipal boundaries (Statbel), applied to every earthquake, including those before the merger of municipalities. For an epicentre outside Belgium, only the circular area is given. Each earthquake’s name is the catalogue’s: it may refer to a place near the epicentre.

Magnitude: the one given on each earthquake’s page (ML preferably, otherwise MW or MS); magnitudes of different types are compared as they are.

The epicentres of historical earthquakes are only known to within a few kilometres, sometimes more: whether they fall in the area is indicative. Small earthquakes have only been recorded as the station network grew: the area’s older earthquakes are mostly the largest ones, and recent activity looks more frequent.

Arrival times at the stations

How is an earthquake located?

Using the P and S waves measured for this earthquake.

Preparing the animation…

1Two waves leave the focus

When the earthquake occurs, two waves leave the focus, 7 km deep. The P wave, the fastest, travels at about 5.7 km/s; the S wave at about 3.3 km/s. These are the average speeds that best match this earthquake’s measurements.

Animation drawn from the arrivals measured for this earthquake and the speeds of the chart; only stations within 120 km are shown, and the circles are drawn at the surface.

Each station first records the P wave, the fastest, then the S wave. The farther a station is from the epicentre, the later the waves reach it and the wider the gap between the two.

Stations
13
Epicentral distance
3.7 – 215.6km
Mean velocity, P wave
5.7km/s
Mean velocity, S wave
3.3km/s
  • P wave
  • S wave
  • Curve fitted to the measurements
Notes and method

Curves: travel time of a direct wave in a homogeneous medium. The velocity of each wave and an origin-time shift, common to both, are fitted to the measurements by least squares. Hypocenter at a depth of 7.0 km. P wave: 7 measurements, root-mean-square deviation 0.11 s. S wave: 5 measurements, root-mean-square deviation 0.23 s.

Stations farther than 120 km are left out of the fit: the first waves to reach them have travelled beneath the crust, through the mantle, where they propagate faster.

Table of measurements

Station measurements

P- and S-wave arrivals and ground displacement measured at each station. Click a column heading to change the order.

km°UTCUTCs
Belgian seismic network (Royal Observatory of Belgium)10 stations
BLABlaugies3.718221:05:37.36+1.46 s21:05:38.33+2.43 s0.97
MSRMontignies-sur-roc7.123821:05:37.87+1.97 s––
BOUBougnies9.410221:05:38.16+2.26 s21:05:39.82+3.92 s1.66
STAStambruges13.832921:05:38.55+2.65 s21:05:40.90+5.00 s2.35
LESLessines34.0321:05:42.22+6.32 s––
SNFSeneffe35.27021:05:42.38+6.48 s21:05:47.28+11.38 s4.90
UCCSUccle58.141–21:05:53.50+17.60 s–
DOUDourbes65.412221:05:47.75+11.85 s––
MEMSMembach157.38121:06:02.26+26.36 s––
WLFWalferdange186.511521:06:07.00+31.10 s21:06:29.30+53.40 s22.30
Bensberg seismic network (University of Cologne, Germany)2 stations
KLLKalltalsperre178.98021:06:05.25+29.35 s––
STBSteinbachtalsperre215.68321:06:19.23+43.33 s21:06:37.49+61.59 s18.26
Dutch seismic network (KNMI)1 station
ENNEPEN (Intl)154.57421:06:02.40+26.50 s21:06:22.00+46.10 s19.60
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