<title>Ground penetrating radar study of the Cheko Lake area, Siberia</title>

SUMMARY We performed an integrated acoustic and GPR study of the Cheko Lake area (101 o E, 62 o N) during summer 1999. The GPR study aimed at imaging lake bottom and shallow sedimentary layers to plan coring of sediments coeval with the catastrophic 1908 explosion. The water of the Cheko Lake strongly attenuates radar waves. Therefore, the central and northern sectors of the lake (30 m average depth) were surveyed by means of acoustic techniques only. Integrated acoustic and GPR techniques were used in the shallow southern sector. More than 5 km of radar profiles were obtained in the lake, using 50 MHz and 100 MHz antennas. 150 metres of 200 MHz multi-fold profiles were obtained across the only accessible sectors on land. The GPR profiles processed to date successfully image discontinuities at depths greater than 700 cm. Comparison with acoustic results shows that GPR provides high resolution images of the depth range of interest (0-500 cm) which complement the information obtained from sub- bottom profilers and can be calibrated by the gravity cores. A deep (700 cm) flat sub-horizontal reflector, shallow (0- 200 cm) dipping layers, sigmoidal structures and local chaotic lenses are the primary features imaged by GPR in the lake.