Stuart Crampin
Department of Geology and Geophysics, University of Edinburgh;
The successful real-time stress-forecast of the M=5, 13th November, 1998, earthquake in the South of Iceland Seismic Zone, SISZ (Crampin, Volti & Stefansson, 1999), confirms the interpretation of phenomena seen with hindsight before four earthquakes worldwide and now seen routinely before five (as of 9th March, 1999) larger earthquakes in a part of SISZ. (Further stress-forecasts will almost certainly be made in SISZ over the next year.) The evidence suggests we have a routine procedure for monitoring stress-changes, and consequently, stress-forecasting the time and magnitude, but not directly the location, of future larger earthquakes specified by an earlier-smaller-magnitude to later-larger-magnitude window. (The window is necessary because of errors in estimating both rates of increase of time-delays and levels of fracture criticality.) Such routine stress-forecasting using natural sources is not available elsewhere without the unique nearly-continuous swarm activity of parts of the onshore transform zone of the Mid-Atlantic Ridge of the SISZ.
What is the next step? The suggested stress-monitoring sites using cross-well seismology between deep deviated boreholes appears to be the optimum solution. Such sites are being promoting near vulnerable cities, but they would be very expensive to drill, equip, and monitor.
A hopefully-cheaper solution is to monitor the seismic gap in the Flatey-Husavik Fault in the Tjornes Fracture Zone. There is a group of vertical wells near Husavik that could be used to approximate to the ray path directions necessary to monitor changes of stress. These are a 1360m-deep well, with several shallower wells within a few hundred metres. The overriding attraction is they are close to a seismic gap where a M~=7 may be expected in the next few years. The various options for designing a stress-monitoring site with these parameters will be discussed.
Partners are being sought for an EU research proposal to be submitted before the 15th June deadline.