Static and Dynamic Scaling Relationships for Moderate and Small Earthquakes in the Yunnan Region

Source spectra for moderate and small earthquakes are obtained after removing the path effect,site effect,and instrument response,etc. in the observed S-wave spectra. Based on the Brune source model and by means of genetic algorithm, the source parameters including seismic moment, stress drop, source dimension, etc. are determined, the radiated seismic energy for small-to-moderate earthquakes is measured with consideration of underestimation and compensation brought forth by limited bandwidth of the instrument,and the scaling relationships of static and dynamic parameters for earthquakes with M;2. 0 ～ 5. 3 in the Yunnan region are analyzed. The results show that the seismic moment is between 2. 1 × 10;N·m and 1. 2 × 10;N·m,and there is a linear relation of lgM;= 1. 01M;+ 10. 59 between the seismic moment and local magnitude. The source dimension varies from 86. 9m to 1220. 4m. The seismic moment and rupture radius remain a linear correlation of lgM;= 0. 003a + 12. 90. The stress drop is in the range of 0. 03 ～ 57. 55MPa,and increases with seismic moment for M;< 4 × 10;N·m,but it doesn’t vary with seismic moment for M;> 4 × 10;N·m. The seismic moment shows dependency of corner frequency. Assuming a constant stress drop,we can obtain the relationship of lgf;= - 1/3 lgM;+ 5. 32 between the seismic moment and corner frequency using least squares fitting. The theoretical radiated seismic energy is between 3. 01 × 10;J and 2. 06 × 10;J. The linear relationship between the radiated seismic energy and local magnitude is lgE;= 1. 18M;+ 5. 69. The scaled energy increases with seismic moment for M;< 4 × 10;N·m,however it doesn’t seem to vary with seismic moment for M;> 4 × 10;N·m. The apparent stress is in the range of 0. 02 ～ 31. 4 MPa,and also seems independent of seismic depth.