The amplitude-frequency function of pressure variations: Steam-water mixture in the Verkhne-Mutnovskii hydrothermal system

Abstract

The mathematical methods of direct spectral analysis were employed for the database that was drawn from the monitoring of well # 30 during 2004 in order to obtain the amplitude-frequency function of steam-water mixture pressure in the Verkhne-Mutnovskii hydrothermal system (the depth at which pressure was measured was 950 m, the time interval between measurements was 2 min, resulting in a total of about 250000 determinations). We identified large-scale and small-scale types of pressure variability. The large-scale variability reflects the low-frequency component of the variation and is seen as macro-fluctuations involving considerable (as large as 2 bars), sudden or gradual pressure changes. The small-scale variability consists of both irregular and regular oscillations. Medium-frequency and high-frequency components can be identified in the latter variability. The medium-frequency component consists of gradual fluctuations with periods of about 20 min (a frequency of 0.00083 Hz), with the maximum pressure changes between measurements being 0.7 bars. The high-frequency component consists of sudden pressure changes (drops, rises, or spikes), as well as of fluctuations with periods below 5 min.