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Abstract

The paper represents results from a wellhead station, installed in a 400 m deep artesian well, drilled in the city of Bursa, NW part of Turkey. Water pressure variations are measured by a borehole sensor at a mean pressure level of 1.6 bars. The air-pressure variations are measured in parallel at the surface next to the borehole. The data processed is a series of 421 day (29.04.2004-23.06.20059 5-minutes ordinates. The station is situated in a strongly dangerous seismic region, surrounded by a set of seismic stations. The main objective of the observations is the study of non-tidal signals in pore-pressure related to earthquakes, possibly event precursors. The paper shows how to process the data, in order to reveal anomalies in the residuals, which can be studied as such signals. Namely, the original data are reduced by: (i) a well determinde tidal signal, (ii) the effect of the external air-pressure, by using an appropriate model, (iii) a simple polynomial model of the drift and (iV) some annual meteorological waves with basic fequency 1 cycle/year. The estimation and the reduction are made by the tidal program VAV, solving a system of equations by the least squares method, dealing at once in parallel with all components.