Subsurface temperature changes due to the crustal magmatic activity - Numerical simulation

Geothermal aspects of the hypothesis, relating the earthquake swarms in the West Bohemia/Vogtland seismoactive region to magmatic activity, are addres sed A simple I-D geothermal model of the crust was used to assess the upper limit of the subsurface heating caused by magma intrusion at the assumed f ocal depth of 9 km. We simulated the process by solving the transient heat conduction equation numerically, considering the heat of magma crystallizat ion to be gradually released in the temperature interval 1100 degrees C to 900 degrees C. The temperature field prior to the intrusion was in steady-s tate with a surface temperature of 10 degrees C and heat flow of 80 mWm(-2) , the temperature at the 9 km depth was 270 degrees C. The results suggest that the temperature and heat flow in the uppermost 1 km of the crust begin to grow 100 ka after the intrusion emplacement only, and that the amplitud es of the changes for the realistic lateral extent (a few kilometres) of th e intrusion are very small. It was also found that the rate of magma solidi fication depends strongly on the thickness of the intrusion. Ir rakes about 100 years for a 50 m thick sill to cool down from 1100 degrees C to 600 de grees C, which value represents the lower limit of the solidus temperature. The same cooling takes only 60 days if the sill is 2 m thick. If the natur e of the strongly reflected boundaries, interpreted from the January 1997 N ovy Kostel seismograms, is connected with the fresh emplacement of magma, t he calculated cooling rates have a predictive potential for the temporal ch anges of the wave forms.