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 365

Fig. 6 The same as Fig. 3 but
for the Chamonix (1905),
Epagny (1996),
Grand-Bornand (1994), and
Vallorcine (2005) earthquakes

140

Max
Min

120

Chamonix 1905

100

80 1996

60

40

20

Vallorcine, 2005

1994

0

3 3.5 4 4.5 5 5.5 6 6.5 7

Macroseismic Intensity

Nice). For the Epagny (1996) event near Annecy and the Grand-Bornand (1994)
event, at mid path between Annecy and Chamonix, we use the values M w computed
from several broad-band stations by Braunmiller et al. (2005): 4.6 and 4.3 M w ,
respectively. Note that the local magnitude M L issued by ReNaSS for these three
reference events are higher by 0.4-0.6 units (4.9, 5.2 and 4.7, respectively). Using
as previously I for the reference earthquakes at a set of five epicentral distances, we

obtain an average magnitude M w = 1 for the Chamonix (1905) earthquake

while it would be 6.1 M L if we start from the short period ReNaSS magnitudes. It
is also interesting to note that the macroseismic magnitude MM

5 . 6 ± 0 .

7 given by
Karnik (1969) for the main shock of the April 29th 1905 Chamonix earthquake is
in better agreement with our 5.6 M w macroseismic estimate than what is excepted
from the ReNaSS M L .

= 5 .

4 Instrumental Magnitude and Discussion

The above magnitude estimates can be compared with the instrumental seismic
moment magnitudes M w for both the Arette (1967) and Chamonix (1905) events,
although very few reliable records are available for the latter.
In 1967, the WWSSN stations provide many long-period records so that a reli-
able measurement of the seismic moment can be performed from the surface-wave
records. Fitting by trials and errors the observed Rayleigh waves in the distance
range 463-2656 km, we find that the best fit is obtained with the following source
parameters: strike of the fault 100 ◦ ,dip 75 ◦ ,rake 160 ◦ and M W

= = =− = 5 . 1

(Alasset 2005). The instrumental magnitude M W 1 we find from the long

period WWSSN records is very close to that computed from the reference events

= 5 .