Post by Inge B.
Tjörnes Fracture Zone is the northern one of the two big fracture zones in Iceland. They connect the northern resp. the southern parts of the rift and there is also a theory about microplates underlying these zones (s. Foulger, etal.).
The main geological features in the north of Iceland are this TFZ and the Northern Volcanic Zone which is connected by the TFZ to the Kolbeinsey Ridge, the part of the MAR north of Iceland out in the Arctic Ocean. The Northern Volcanic Zone comprises 5 volcanic systems (from S to N): Kverkfjöll, Askja, Fremrinámur, Krafla and Þeistareykir.
Two, probably even three constituent parts make out this zone from N to S: The Grímsey Oblique Rift (GOR), sometimes also called Grímsey lineament, the Húsavík-Flatey-Fault (HFF) and sometimes there is named a third fault reaching from south of Húsavík over to the Eyjafjarðar Trough, where the last earthquake swarm event took place during the winter. (for a map, see Metzger, p. 422)
The now ongoing quake swarm didn’t come as a surprise to the scientists involved, because there has been continuously ongoing research on the region and the newest GPS measurements indicated very strongly a locking at rather shallow depth. This means that plate movements are arrested in a way, and therefore stress builds up – explaining the non-continous rifting events as described eg. by Irpsit. Plates seemingly often move in jumps and bolts and seldom smoothly (silent slip as an exception from the rule).
The locking was found out by analysing eg. seismology, also seismologic history of the region, which has often had heavy quakes in the past (2 magn. 6,5 in 1872), but also last not least GPS. And this is where the newest research comes in. The scientists discovered strong uplift in parts of the TFZ, i.e. in the southeast esp. And that even, after they had taken out by calculation the 2007-8 uplift at the volcanic system of Þeistareykir . While at the same time there was some subsidence in the west, which describes a plate movement to the southeast, meeting some hindrance around the valley of Jökulsá á Fjöllum, the biggest river valley in the region. Such blocking normally is released in considerable quake activity. And that is what is going on at the moment.
Up to now, there have been 4 big earthquakes and over 700 earthquakes within 3 days at a whole, the map showing the location of the hypocenters of the big ones and the rupture direction. Interesting that three of them have the same rupture direction and that the development is such that there is another center of activity now to the southwest of the first action.
Copyright: IMO by Inge B. (disclaimer: I am just an interested layman, no geologist). Literature:
- Th. Thordarson, A. Hoskuldsson: Iceland. Classic Geology in Europe 3. Harpenden 2002, esp. pp.136 …
- S. Metzger, et all.: Present Kinematics of the Tjörnes Fracture Zone, North Iceland, from compaign and continues GPS measurements. (2012) http://www.n.ethz.ch/~smetzger/download/GJI_2012.pdf
Images by IngeB and me. Please also check Irpsits comment from yesterday explaining how rifting works in Iceland. And keep in mind, we are all no volcanologists or geologists, just layman.
Etna’s southeast crater is erupting right now:
The action is taking place at the new southeast crater again. Best cams are http://www.guide-etna.com/webcam/ and this one http://www.radiostudio7.it/webcam.asp?web=2&id=2 And White Island showed some incandescence last night:
Check http://www.geonet.org.nz/volcano/info/whiteisland El Hierro experienced some earthquakes again. For info on this check http://www.01.ign.es/ign/head/volcaSenalesDiasAnterioresCuasiReal.do?nombreFichero=CJUL_2013-04-03&estacion=CJUL&tipo=1&Anio=2013&Mes=04&Dia=03 http://earthquake-report.com/2011/09/25/el-hierro-canary-islands-spain-volcanic-risk-alert-increased-to-yellow/ and http://elhierro1.blogspot.com.es/