BEST: Baikal Explosion Seismic Transect

The Baikal Explosion Seismic Transect is composed of two deep seismic profiles: one across the Baikal Rift Zone at the southern end of Lake Baikal and a second profile along the axis of the rift into the Tunga depression. The main field project was carried out in October 2003 after a pilot project (BASE) in September 2002. Our primary goal is the study of the detailed crustal and upper mantle seismic velocity structure beneath the rift zone. The two profiles are: (1) a 350 km long, NS-trending profile across the rift zone from Kyahta at the Mongolian border to Cheremhovo north of Lake Baikal, and (2) a 300 km long EW-trending profile along-strike of the rift zone at the northern shore of the lake into the Tunga depression to Mondy at the Mongolian border. The primary seismic sources are 10 explosions in boreholes, ranging from 500 kg to 3 tonnes of dynamite supplemented by airgun shots in the lake (100 l airguns volume), and a supervibrator, located at Babushkin at the cross point between the two profiles on the shore of the lake. The data was recorded by 150 portable REFTEK Texan vertical component recorders which were rolled along to give station spacings of 650m. The primary targets of the BEST project are: (1) the crustal velocity structure, with primary attention to the graben geometry; (2) the propagation properties of seismic waves in the area; (3) the amount crustal thinning across the rift zone; 4) seismic Pn wave velocity to identify possible weak zones in the uppermost mantle and (5) relative seismic reflectivity outside and underneath the rift zone. This last aim is to identify locations of major magmatic intrusions into the lower crust and test if there is a correlation to volcanic activity at the surface. The poster will present examples of the new data with modelling results of seismic velocity, together with discussion of the implications regarding magmatism in the lower crust.