Iceland - seismic swarm and magmatic intrusion .

Northeast of Iceland, the Tjörnes fracture zone is home since September 25, 2013 of an ongoing seismic swarm. There are over 1000 shocks in a limited area, at a depth between 9 and 13 km., and all almost of the same magnitude. The three largest earthquakes have a magnitude of about 3 (green stars on the map) .

 

                      Time and magnitude of earthquake   03 Oct 08:50 GMT       

      Iceland - Tjörnes fracture area - earthquakes of the past 48 hours / to 03.10.2013 - Doc IMO

According Kristín Jónsdóttir, a geophysicist at the Icelandic Met Office , such activity, common in Iceland, is linked to a magmatic intrusion . She adds that such density of activity is unusual, although this region is known for its seismic activity.
 The Husavik - Flatey Fault, an active dextral strike- slip fault partly exposed on land on the Flateyjarskagi Peninsula, runs parallel with the spreading vector in this portion of Iceland and is the main structure of the Tjörnes Fracture Zone transform fault (modified from Gudmundsson , 2000)

Séismes on Tjörnes Fracture Zone - gray dots : 1994 to 2012 - Red dots, 24.09 to 01.10.2013
HFF : the Húsavík - Flatey fault / doc.IMO

The Tjörnes fracture zone ( TFZ ) connects the rift zones of northern Iceland to the Kolbeinsey ridge further north ; it was initiated during the Miocene, there are 7 million to 9 million years, following a jump of the axis of expansion to the east.

A deformation zone , 150 km long from east to west and 50 km wide north-south , was developed that included the transform faults and three extensional grabens oriented north-south , filled with sediment of 0,5-4 km thick .

Two bands oriented west -northwest , characterized by high seismicity, mark the TFZ : to the north, the Grimsey alignment and to the south, the Húsavík-Flatey fault (HFF ) .

Observations made by the IMO in recent years confirm the model of a tectonic evolution of the TFZ : the spread to the north of the Iceland northern rift zone has gradually shifted to the series of rifts NNE-SSW , along the seismic Grimsey alignment .

Sources :

- Icelandic Met Office

- The Tectonic Evolution of the Tjörnes Fracture Zone, offshore Northern Iceland - Ridge Jumps and Rift Propagation – By R.S. Detrick & al.

- Present kinematics of the Tjörnes Fracture Zone, North Iceland, from campaign and continuous GPS measurements – by S. Metzger  & al.

- Fracture networks and fluid transport in active fault zones – By A. Gudmundsson & al.