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 362

the reference magnitude and “b”, the total error on the macroseismic M w may be
estimated to 0.2.

The same differential technique can be applied to the pair of earthquakes Arudy
(1980) - Bigorre (1660). An average difference of intensity

±

I = 1 . 9 ± 0 . 2

is observed in the distance range 30-200 km (Fig. 4). It corresponds to M =

0 09. As no M W is available for the Arudy (1980) event, we start from the

teleseismic body wave magnitude m b

. 86 ± 0 .

= 5 . 1 (Gagnepain-Beyneix et al. 1982) and

we get m b 09 for the Bigorre (1660) earthquake, a value close to the

6.1 M W estimated from the Argeles-Gazost (1980) reference event.
When comparing the Juncalas (1750) to the Arudy (1980) earthquakes in the
distance range 30-200 km, we find

= 5 . 96 ± 0 .

I = 1 . 3 ± 0 . 3 and M = 0 . 60 ± 0 . 12. Start-

ing again from m b = 5 . 1 we get a magnitude m b = 5 . 7 ± 0 . 1 for this second

largest historical earthquake of the region (M W =

.

8 based on the 4.5 M W Argeles-
Gazost (2006) earthquake). Table 1 gives the different magnitudes reported here and
our final preferred solution for M w .
Similarly, we can compute a magnitude for the Arette (1967) earthquake from
the Arudy (1980) event. We get m b

5

= 4 . 9 ± 0 . 1from I =− 0 . 4 ± 0 . 2 and

M =− 0 . 17 ± 0 . 10. Starting from the magnitude m b = 4 . 6(M w = 4 . 5) of the

Argeles-Gazost (2006) event, we get the slightly larger value m b = 0).

The Arette (1967) earthquake thus has m b and M w magnitudes close to 5. Such a
magnitude is much smaller than the macroseismic magnitude MM

5 . 1(M w = 5 .

= 5 . 8 found by

Rothe (1972) from macroseismic data (I 0 = VIII, h = 15 km). It is closer to the

value MM 2 proposed by Levret et al. (1994). Following the procedure used

by Rothe (1972), it is easy to fit both I 0

= 5 .

5 by changing the
focal depth to 2.5 km, a depth also shallower than that found by Levret et al. (1994)
(h

= VIII and MM =

= 5 km). It is thus likely that the hypocentre of the second largest damaging

Pyrenees earthquakes

300

1750

1660

250

1980

2006

200

1967

150

100

Fig. 4 The same as Fig. 3,
but for the Bigorre (1660),
Juncalas (1750),
Arudy (1980), Arette (1967)
and Argeles-Gazost (2006)
earthquakes

50

0

2 3 4 5 6 7 8

Macroseismic intensity