Slow Strain Waves in Rocks as Potential Precursors to Seismic Hazard

Abstract

The article reports on instrumental monitoring of rock deformation in the South Baikal geodynamic test site. Based on the analysis of the time series of data sets, two groups of strain components are distinguished by differences in their origin and wave properties. Strain components in the first group are caused by external factors, such as lunar-solar tides and atmospheric pressure variations. The second group includes non-periodic, random and periodic (constant) components generated by internal tectonics. Non-periodic components are manifested as single deformation impulses that differ in intensity and form, and are related to slow displacements along large active faults, which occur outside the monitoring sites. Besides, non-periodic components are related to fast displacements at block interfaces within the monitoring sites. The periodic (constant) component is related to the India-Eurasian collision. It is represented by slow strain waves, which lengths amount to 400–500 m, with amplitudes of few microns, and periods of (1-3)·10−4 Hz. The strain wave directions and rates of their migration in space vary with time. The identified trends of changes of the wave parameters in the South Baikal geodynamic polygon can be related to the preparation of a strong earthquake.