The timescale and mechanisms of fault sealing and water-rock interaction after an earthquake

• Hydrogeochemical monitoring of a basalt-hosted aquifer, which contains Ice Age meteoric water and is situatedat 1220 m below sea level in the Tjornes Fracture Zone, northern Iceland, has been ongoing since July 2002.Based on hydrogeochemical changes following an earthquake of magnitude (Mw) 5.8 on 16 September 2002, weconstrained the timescales of post-seismic fault sealing and water–rock interaction. We interpret that the earthquakeruptured a hydrological barrier, permitting a rapid influx of chemically and isotopically distinct Ice Agemeteoric water from a second aquifer. During the two subsequent years, we monitored a chemical and isotopicrecovery towards pre-earthquake aquifer compositions, which we interpret to have been mainly facilitated byfault-sealing processes. This recovery was interrupted in November 2004 by a second rupturing event, which wasprobably induced by two minor earthquakes and which reopened the pathway to the second aquifer. We concludethat the timescale of fault sealing was approximately 2 years and that the approach to isotopic equilibrium(from global meteoric water line) was approximately 18% after >10^4 years. Key words: earthquake, fault sealing, hydrogeochemistry, Iceland, Tjornes Fracture Zone, water–rock interaction

Publikations- och innehållstyp

pop (ämneskategori)

art (ämneskategori)