TECTONOPHYSICAL STUDY OF THE VERKHOVOI FAULT ACTIVITY ON THE NORTHERN SLOPE OF THE KYRGIZ RIDGE

Abstract

An active fault was identified on the northern slope of the Kyrgyz ridge in the area near Research Scientific RAS in Bishkek. It belongs to a large system of crustal faults of the ridge. In our study, tectonophysical methods were used to analyse the regularities of the tectonic stress field reconstructed from seismological data on earthquake focal mechanisms. The stress distribution pattern near the investigated fault suggests its activity either in the recent past or at the present time. This conclusion is supported by the fact that at the eastern and western terminations of the fault, crustal stretching zones are located in a crosswise pattern. The Coulomb stresses on the fault surface were analysed, and the analysis results give grounds to state that its long section crossing the Alamedin river valley should be viewed as potentially hazardous. In the field, we observed abundant broken rock fragments and rock falls in the zone where the fault crosses the Alamedin and Aksu river valleys. It is known that rock falls have occurred more often in the last 3–5 years. The study results show slow movements along the fault. These strike-slip displacements have been going on for at least 10–15 years. According to the modern concepts of the preparation stage of an earthquake source, slow displacements along a fault gradually accelerate several years before an earthquake. Therefore, the studied fault (we named it Verkhovoi) should be considered a potentially hazardous zone wherein earthquakes can occur in future. A magnitude from 6.5 to 7.5 may be expected, depending on whether only the eastern part or the entire fault (i.e. 20 or 50 km, respectively) will be involved in a future seismic event. Further studies of the Verkhovoi fault are needed to clarify a trend in the development of slow sliding along the fault, which will allow understanding whether this process precedes dynamic rock failure (i.e. an earthquake) or tends to gradually decrease.