Pore-fluid pressure greatly affects the probability of failure and
reactivation of the faults, both in the SISZ and in
the TFZ. A detailed study has been made of the mineral
veins (old channels of geothermal water) on the fault planes in the
Pleistocene rocks of the SISZ and in the
Pleistocene-Tertiary rocks in the TFZ. One of the
principal questions addressed in this study is: how rapidly do seismogenic
faults in these zone heal and how do changes in fluid pressure in one region
(e.g. in association with major earthquakes or volcanic eruptions) affect
slip on faults in other regions. It is likely that changes in fluid pressure
can be transmitted over considerable distances and thus trigger earthquakes
in areas relatively far away from the source of the initial pressure change.
Fluid pressure also affects friction on fault planes, hence the probability
of fault slip.
This work has now been extended to the Fennoscandian area, where the detailed data on seismicity and postglacial uplift make a comparative study with the seismic zone in Iceland important. The stress field controlling the seismic zones in Iceland is primarily related to the horizontal divergent plate movements, and the crustal structure of Iceland is essentially oceanic. By contrast, the stress field controlling faulting, fluid flow and current seismicity in Fennoscandia appears to be largely generated by the postglacial uplift in this region, and the crustal structure of Fennoscandia is entirely continental. A manuscript entitled: Postglacial crustal doming, stresses and fracture formation with application to Norway, has been submitted to Tectonophysics [30].
This research is particularly important in view of the major geothermal activity associated with earthquake fractures in South Iceland and elsewhere. The work on earthquake fracture healing is partly in collaboration with Philip Meredith, University College, London.