Magnitude of Historical Earthquakes, from Macroseismic Data to Seismic Waveform Modelling: Application to the Pyrenees and a 1905 Earthquake in the Alps - Historical Seismology: Interdisciplinary Studies of Past and Recent Earthquakes - page 367

Ta b l e 2 Instrumental and macroseismic moment magnitudes computed in this paper (bold char-
acters) or reported from publications (normal characters). MM are published macroseismic mag-
nitudes

MM Instrumental M W Macroseismic M W

5.3 (1)

Arudy 29-02-1980 - 5.2

5.2 (1)

Arette 13-08-1967 5.1 5.0

Juncalas 24-05-1750 - - 5.8

Bigorre 21-06-1660 - - 6.1

4.6 (3)

Epagny 15-07-1996 - 4.9

4.3 (3)

Grand-Bornand 14-12-1994 - 4.4

5.7 (2)

Chamonix 29-04-1905 5.5 5.6

References: 1 Levret et al. (1994), 2 Karnik (1969), 3 Braunmiller et al. (2005).

5.6 M w obtained in this paper by applying our differential macroseismic method to
three recent earthquakes. Table 2 gives a summary of the M w inferred from both
macroseismic and instrumental data together with published macroseismic magni-
tudes MM.

5 Conclusion

The two XX century damaging earthquakes studied in this paper, Arette (1967)
in the Pyrenees and Chamonix (1905) in the Alps, show that the magnitudes M w
of moderate-size earthquakes inferred from our differential macroseismic method
are in reasonable agreement with those directly computed from the low-frequency
instrumental observations. They are also in close agreement with the macroseis-
mic magnitudes MM published for these two events by Levret et al. (1994) and
Karnik (1969), respectively. For the Arette (1967) earthquake, we find a macroseis-
mic value M w

0, while our instrumental estimate is 5.1. For the Chamonix
(1905) earthquake, the macroseismic value M w

= 5 .

= 5 . 6 is close to our instrumental

estimate 5.5 M w . The macroseismic magnitude MM 8 issued by Rothe (1972)

for the Arette (1967) event is much larger than the value 5.0 M w reported here. As
a consequence the focal depth of this I 0

= 5 .

= VIII latter earthquake must have been

much shallower than previously thought.
Present-day macroseismic investigations performed on earthquakes of magni-
tude 4.5 M w thus appear to be extremely useful for calibrating moderate size

historical earthquakes when working in the low intensity range [II-V] at some dis-
tances from the epicentre. As an application, we have computed seismic moment
magnitude of two historical earthquakes in the Pyrenees (Bigorre (1660) 6.1 M w ,
and Juncalas (1750) 5.8 M w ). The accuracy of these latter magnitudes is estimated
around

∼

± 0.2.