POTENTIAL APPLICATION OF THE SCINTREX CG-3M GRAVIMETER FOR MONITORINGVOLCANIC ACTIVITY - RESULTS OF FIELD TRIALS ON MT ETNA, SICILY

A series of field trials have been conducted for II months on and arou nd Mt. Etna (Sicily) to test the performance of the new automated Scin trex CG-3M gravimeter on active volcanoes. The results show that the d ata from the CG-3M compare favourably with those from the traditionall y employed LaCoste and Romberg (L&R) model D gravimeter. Under severe field conditions the Scintrex meter, because of its greater ruggedness and fully automated capabilities, yields results superior to those fr om the L&R D models. Repeated measurements (568) in a wide range of fi eld conditions yielded errors in Delta g between stations of +/-3.5 to +/-4.4 mu Gal. Our tests also showed that both the strong drift in st ationary conditions (similar to 1 mGal d(-1)) and changes of the instr umental calibration factor with time (whose rate decreased from 6 to I ppm d(-1) during the Ii-month study) can be reduced by regular checks to acceptable standards. Thus, (a) using experimental data, the instr umental drift was forecasted and corrected (by the real-time automatic al compensator of the instrument) to within about 20 mu Gal d(-1), and (b) using the measurements along an 18-station profile on hit. Etna ( total gravity range approximate to 300 mGal), and an 80-km-long calibr ation line away from the volcano (six stations, total gravity range = 365 mGal) the changes of the calibration factor were determined and co rrected to within about 30 ppm.