INVESTIGATION CONCERNING INFLUENCE OF SEISMIC ACTIVITY ON THE REGIME OF HYDROTHERMAL DEPOSIT PCHELINSKI BANI, BULGARIA

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INVESTIGATION CONCERNING INFLUENCE OF SEISMIC
ACTIVITY ON THE REGIME OF HYDROTHERMAL DEPOSIT
PCHELINSKI BANI, BULGARIA

• BORYANA YORDANOVA DENEVA
• PhD student
• University of Mining and Geology "St. Ivan
  Rilski" Bulgaria

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STRUCTURE OF THE PAPER

• Introduction
• Geological setting and Hydrogeological background
• Information base
• Results and Discussion
• Conclusions
• References

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GENERAL DESCRIPTION OF THE INVESTIGATED OBJECT

• Pchelinski Bani thermal water deposit is a
  hydrogeological structure of a fissure-vein type.
• Basic collectors of thermal water are Upper
  Cretaceous granodiorites (gu?dK2).
• The water from the hydrothermal deposit is
  hyperthermal (72.8 ºC), sulfate sodium by
  composition with mineralization 0.98 g/l and high
  content of metasilic acid, fluoride and radon.
• The main water source is the captured thermal
  spring "Pchelin", which drains the whole thermal
  zone.
• The spring has an expressed postseismic reaction
  a sharp decrease in its discharge immediately
  after strong earthquakes, occurring both on the
  territory of Bulgaria and its neighboring
  countries.

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INFORMATION BASE

• The investigations on the thermal water regime
  have been carried out empirically - on the basis
  of an analysis of data obtained from
• The regime observations on the spring discharge
  for a period of 28 years (1975 - 2003).
• The water level observations in a monitoring well
  for a 20-year period (1983 - 2003).

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RESULTS AND DISCUSSION
Figure 1 Visualization of thermal spring
discharge data during 1975-2003
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Discharge variations and corresponding seismic
activity data
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Figure 2 Locations of the earthquake
epicenters that affected the thermal spring
discharge
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Figure 4 Parallel observations of thermal
spring discharge and water level in monitoring
borehole during 1983.
Figure 3 Visualization of water level data
obtained during the period 01.01.1983 -
30.09.1990.
As a consequence of earthquake with a magnitude
of 6.9 according to the Richter scale, occurred
on 06.08.1983 in the territory of Northern
Greece, thermal spring discharge had decreased
with 7.6 l/s (from 12.3 to 4.6 l/s) and water
level had dropped with 7 cm.
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CONCLUSIONS

• The thermal spring discharge is affected by
  seismic activity occurring in the regions of
  Aegean Sea, Marmara Sea, FYR Macedonia, Romania
  and Bulgaria.
• Two points of sharp level lowering were
  registered in the monitoring borehole. Changes
  have appeared as a result of strong seismic
  activity in the region of Strazica (Bulgaria,
  1986) and Aegean Sea (Greece, 1988).

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FUTURE INVESTIGATIONS

• Implementation of continuous water level
  monitoring - installation of a continuing device
  in the monitoring borehole (Borehole N2)
• Implementation of parallel measurements of
  thermal spring discharge and water level in the
  monitoring borehole (Borehole N2)
• Investigations for possible variations in water
  chemical content and temperature as a result from
  seismic activity
• Including the hydrothermal deposit in an
  extensive monitoring set for investigation of
  seismic impacts on similar hydrogelogical
  structures on the territory of Bulgaria and its
  neighboring countries.

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• Control measurement of water level in Borehole N2
  May 2004.

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Dear colleagues, thank you for your kind
attention! Boryana Deneva