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SEVENIG (DE)

Earthquake22 April 1997

Magnitude
1.7ML
Depth
11.5km ± 2.3
Belgian time
23:27:341997-04-22
UTC
21:27:341997-04-22

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 1.7) 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, 74 % 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 time1997-04-22 21:27:34 UTC
1997-04-22 23:27:34 Belgian time
MagnitudeML 1.7
Epicentral coordinates50.168° N, 6.204° E
Uncertainty ± 1.2 km
Depth of hypocenter11.5 ± 2.3 km
Event IDROB 1216

Data source : ROB (Royal Observatory of Belgium)
Last update : 2009-05-30 18:17:43 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 11.5 km below the surface. The point on the surface right above it is the epicentre (50.168° N, 6.204° 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

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

5 other earthquakes in the catalogue since 1986. 3 of them occurred after this one. By magnitude, it is the 4th largest of the 6 earthquakes of known magnitude in the area.

Latest earthquakes before this one

DatePlaceMagnitudeIntensityDistance km
1987-12-17GRAND DUCH.LUXEMB.ML 1.9–7.7
1986-09-03SW of PRUM (DE)ML 1.9–6.8

Largest known earthquakes

DatePlaceMagnitudeIntensityDistance km
2026-10-13HECKHUSCHEID (DE)ML 2.4–1.7
1986-09-03SW of PRUM (DE)ML 1.9–6.8
1987-12-17GRAND DUCH.LUXEMB.ML 1.9–7.7
1997-04-22This earthquakeML 1.7––
2012-03-18REULAND (BE)ML 1.3–6.0
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, 12 km deep. The P wave, the fastest, travels at about 5.9 km/s; the S wave at about 3.6 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
11
Epicentral distance
25.9 – 240.7km
Mean velocity, P wave
5.9km/s
Mean velocity, S wave
3.6km/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 11.5 km. P wave: 8 measurements, root-mean-square deviation 0.22 s. S wave: 8 measurements, root-mean-square deviation 0.35 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)4 stations
VIAVianden25.918021:27:39.07+5.01 s21:27:41.99+7.93 s2.92
ROBRobertville32.434821:27:39.88+5.82 s21:27:43.56+9.50 s3.68
MEMSMembach50.934421:27:43.12+9.06 s21:27:48.85+14.79 s5.73
WLFWalferdange56.218421:27:44.40+10.34 s21:27:50.40+16.34 s6.00
Network LDG3 stations
GIVFGivet99.026621:27:50.90+16.84 s21:28:02.10+28.04 s11.20
BAIFBaives143.326621:27:58.00+23.94 s21:28:13.60+39.54 s15.60
HAUHAUDOMPRE240.717721:28:13.70+39.64 s21:28:40.60+66.54 s26.90
Network FR2 stations
RUPRuppelstein80.513021:27:48.00+13.94 s21:27:56.26+22.20 s8.26
ABHAlteburg101.410821:27:51.33+17.27 s21:28:03.41+29.35 s12.08
Dutch seismic network (KNMI)1 station
HGNHeimansgroeve69.034421:27:46.26+12.20 s21:27:53.92+19.86 s7.66
Network STR1 station
DOMFDOMPIERRE-SUR-HELPE167.526921:28:01.87+27.81 s21:28:21.22+47.16 s19.35
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