Response of an artesian well in southern Armenia to the 1400 km distant Izmit earthquake of August 17,1999

摘要

Co- and postseismic variations of the specific electrical conductivity were observed at an artesian well in southern Armenia after the M=7.4 Izmit earthquake of August 17, 1999. The epicentral distance was 1400 km. The static strain at the observation site was calculated to 1.3 X 10~(-11), which is quite low when compared to periodic strain variations in the order of 10~(-8) induced by the earth tides. Nevertheless, the conductivity dropped by 3 % within one hour after the earthquake, further decreasing by another 3 % during the consecutive 3 weeks before it slowly recovered within a few months to reach the pre-event value. Additionally, the water discharge increased by 25 % immediately after the earthquake. We developed a model that explains the observations in terms of a changed mixing ratio between two fluid systems as a result of a pressure disturbance triggered by the seismic waves passing the observation site.