Jökull - 01.01.2019, Síða 78

Variation in b-value of caldera earthquakes of Bárðarbunga Volcano
Figure 5. A) The b-value as a function of time during 2014–2019 for windows of 600 events. Red and blue
curves give the 95% confidence interval. The dataline to the far left shows the b-value of the pre-eruption period
beginning on Jan. 1, 2010, with 95% confidence interval. B) Magnitude of the caldera earthquakes as a func-
tion of time. Only events of magnitude 2 and larger are shown. – A) Línurit sem sýnir b-gildi sem fall af tíma
2014–2019. Hvert gildi er reiknað fyrir 600 skjálfta úrtak. Rauða og bláa línan sýna 95% öryggismörk. Gildið
lengst til vinstri sýnir b-gildið á tímabilinu frá 2010 og fram að gosi. B) Stærðir skjálfta í Bárðarbunguöskjunni
á sama tímakvarða. Aðeins skjálftar af stærðinni 2 og stærri eru sýndir.
There is a pronounced difference between the
earthquake population occurring during a collapse pe-
riod of the volcano and the period when we infer
inflation and uplift of the volcano is taking place.
The maximum magnitude of inflation-related earth-
quakes appears to be below 5, whereas during the
collapse period earthquakes exceeding magnitude 5
were common. In fact, they seem to form a special
class of earthquakes with unusual magnitude distri-
bution. Similar difference was observed during the
Krafla rifting episode of 1975–1984 in the Northern
Volcanic Zone. Earthquakes during repeated inflation
periods of Krafla volcano rarely exceeded magnitude
4, and the only caldera earthquakes larger than mag-
nitude 5 occurred during the first and largest deflation
event that had maximum deflation of 2 m (Einars-
son, 1986; 1991b). Since the calderas of Krafla and
Bárðarbunga are of similar dimensions it is tempting
JÖKULL No. 69, 2019 77