Jökull - 01.01.2014, Blaðsíða 62

Ingi Þ. Bjarnason
Figure 1. The Vatnajökull region. Volcanic centres are indicated by thin lines, and volcanic rift zones are in olive green
shades (Einarsson and Sæmundsson, 1987). Inner rings of volcanic centres denote caldera rims. The star denotes the epicen-
ter of the 5.6 (MW ) earthquake of Bárðarbunga in 1996. The moment tensor solution (’ball shape’) indicates thrust faulting
with a significant non-double couple component (Harvard University, USA). The bent red line denotes the Gjálp subglacial
eruption fissure of 1996. Triangles show the location of the ICEMELT broadband seismic stations. Index map shows the
volcanic rift zones, the ICEMELT network (Bjarnason et al., 1996a) and focal mechanism of the Vatnafjöll earthquake of
1987. – Vatnajökulssvæðið. Virk eldstöðvakerfi og öskjubarmar eru táknuð með þunnum línum, gliðnunar- og gosbelti eru
ólífugræn (Einarsson og Sæmundsson, 1987). Stjarna sýnir staðsetningu skjálfta í Bárðarbungu árið 1996 af stærðinni
5,6 (MW ). Rauði og hvíti ’boltinn’ táknar vægisþinu skjálftans (Harvard í BNA). Vægisþinan sýnir samgengishreyfingu á
óvenjulegu misgengi eða margbrotna hreyfingu. Bogna rauða línan táknar staðsetningu sprungugossins í Gjálp árið 1996.
Þríhyrningar sýna staðsetningu breiðbandsskjálftamæla í ICEMELT netinu (Bjarnason o.fl., 1996a). Á innsetningarkortinu
kemur fram staðsetning ICEMELT netsins, lega gosbelta og brotlausn skjálftans í Vatnafjöllum árið 1987.
jökulhlaups from sudden volcanic melting of glacier
ice. More frequently, however, did these volcanoes re-
lease energy in small eruptions without causing much
harm to the community (Björnsson and Einarsson,
1990), even though the jökulhlaup which followed the
1996 eruption caused considerable damage to the road
system in South Iceland (Haraldsson, 1997).
The proximity in time and space between the 1996
main event and the Gjálp eruption suggests a con-
nection between the two. The main objective of the
present communication is to investigate the nature of
the events described and the possible connection. The
aim in particular is to analyse the source properties
of the medium size earthquakes in the Bárðarbunga
1973–1996 earthquake sequence and other patterns
in the seismicity that may relate to volcanism in the
Northwest Vatnajökull during the 20th century.
62 JÖKULL No. 64, 2014