Издатель: Elsevier Science , Место издания: Amsterdam , Год издания: 2010

Short-term active vibroseismic monitoring was conducted to evaluate the crustal stress sensitivity of seismic velocity in the Baikal rift zone. Knowledge of stress sensitivity is required for interpreting long-term active vibroseismic monitoring results and predicting the stress state of the crust in potential earthquake zones. The elastic Earth tide is a natural calibrator of variations in internal stresses in the Earth's crust. Our ultimate goal is to find a relationship between variations in seismic velocity and wave amplitudes and the inner-crust stress changes. Seismically active zones under Lake Baikal that extend over 125.5 km have been illuminated by low-frequency vibrations repeated every 2 h over a period of 2 weeks. The source was a stationary powerful vibrator that generated a force amplitude of about 100 tons within a 5-10 Hz frequency range. The received signals were transformed to cross-correlation functions in an online mode. Our analysis showed variations in the travel times and wave amplitudes of seven different waves, which were compared to the elastic Earth tide. Our main focus was on the inner-crust waves, including the reflection from the Moho boundary and from the top of the upper mantle. Despite the unique high precision of the variation measurements (about 10?5 for travel times), any statistically significant correlations with Earth tides were not found. However, arrival data enabled us to calculate an upper limit for possible velocity stress sensitivity, which falls far short of that predicted by previous researchers. Principal sources of error included not only external noise, but also small, random phase fluctuations in the probing signal generated by the vibrator.