Relocation of microearthquakes in Beijing and its northwest neighbouring area

This study relocated 348 microearthquakes which occurred in Beijing and its northwest neighbouring area (39° – 41°N, 114° – 117°E) during 1979–March of 1992. In the relocation the Powell searching technique was used and the associated error of earthquake hypocenters was estimated by numerical tests. Precision of hypocenter locations is improved by rechecking and supplementing readings of arriving times of the seismic phases used, testing and selecting appropriate crustal model, and modifying the computer program. The overall averageRMS residual of arriving times has been reduced to 0.45 s from the previous value of 0.80 s. For nearly 10 per cent of the relocated hypocenters, which are mostly in border region of the area covered by the Beijing Telemetered Seismic Network, have been shifted more than 10 km. After the relocation the number of earthquakes with focal depth determination has been increased to 313 from the previous 132.