HR: 09:45h
AN: S51B-08    [PDF]
TI: Monitoring of fluid-rock interaction in active fault zones: a new method of earthquake prediction/forecasting?
AU: * Claesson, L
EM: lillemor@hi.is
AF: Nordic Volcanologic Institute, Grensasvegur 50, Reykjavik, IS-108 Iceland
AU: Skelton, A
EM: alasdair.skelton@geo.su.se
AF: Stockholm University, Department of Geology and Geochemistry, Stockholm, 106 91 Sweden
AU: Graham, C
EM: colin.graham@ed.ac.uk
AF: University of Edinburgh, School of Geosciences, West Mains Road, Edinburgh, EH9 3JW United Kingdom
AU: Dietl, C
EM: Carlo.Dietl@mail.uni-wuerzburg.de
AF: Julius-Maximilians-Universitat, Geologisches Institut, Pleicherwall 1, Wurzburg, 97070 Germany
AU: Morth, M
EM: magnus.morth@geo.su.se
AF: Stockholm University, Department of Geology and Geochemistry, Stockholm, 106 91 Sweden
AU: Torssander, P
EM: peter.torssander@geo.su.se
AF: Stockholm University, Department of Geology and Geochemistry, Stockholm, 106 91 Sweden
AB: We propose a new method for earthquake forecasting based on the "prediction in hindsight" of a Mw 5.8 earthquake on Iceland, on September 16, 2002. The "prediction in hindsight" is based on geochemical monitoring of geothermal water at site HU-01 located within the Tj”rnes Fracture Zone, northern Iceland, before and after the earthquake. During the 4 weeks before the earthquake exponential ($<$800%) increases in the concentration of Cu, Zn and Fe in the fluid, was measured, together with a linear increase of Na/Ca and a slight increase of $\delta^{18}$O. We relate the hydrogeochemical changes before the earthquake to influx of fluid which interacted with the host rock at higher temperatures and suggest that fluid flow was facilitated by stress-induced modification of rock permeability, which enabled more rapid fluid-rock interaction. Stepwise increases (13-35 %) in the concentration of, Ba, Ca, K, Li, Na, Rb, S, Si, Sr, Cl, Br and SO$_{4}$ and negative shifts in $\delta^{18}$O and $\delta$D was detected in the fluid immediately after the earthquake, which we relate to seismically-induced source switching and consequent influx of older (or purer) ice age meteoric waters. The newly tapped source reservoir has a chemically and isotopically distinct ice-age meteoric water signature, which is the result of a longer residence in the crust. The immediancy of these changes is consistent with experimentally-derived timescales of fault-sealing in response to coupled deformation and fluid flow, interpreted as source-switching. These precursory changes may be used to "predict" the earthquake up to 2 weeks before it occurs.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 7209 Earthquake dynamics and mechanics
DE: 7223 Seismic hazard assessment and prediction
SC: Seismology [S]
MN: 2003 Fall Meeting