Ground Motion Prediction For Southeast Coastal Area Of China By Small Earthquake Records From China Earthquake Networks

As the core of engineering seismology, ground motion attenuation relationship could simplify the influence of 3 factors—source, path and site--on ground motion characteristics. It could help to provide reasonable seismic fortification acceleration as well. So far, in the countries and regions which have numerous strong ground motion records, such as the western US and Japan, attenuation relations are established by statistical regression method, which depend on strong ground motion data. In the field of earthquake engineering, it is a hot point to establish ground motion attenuation relationships for the mainland of China which lacks of strong motion data. After the Eleventh Five-Year Plan Period, with the technical development of broadband digital earthquake and earthquake observation, the digital earthquake observation ability has been developed a lot, and both the national and the regional broadband digital earthquake networks achieve abundant digital seismic waveform data. A method is developed to establish attenuation relationships with small earthquake data from regional broadband digital earthquake networks for China Southeast Coastal Area.The main works of this paper:1. In China Southeast Coastal Area(N22°-29°, E109°-120°), 1274 records from 72 small earthquake(Mw=3.5-4.5、source depth≤30km) from 1999 to 2013 is collected from Guangdong, Fujian regional broadband digital earthquake network and national broadband digital earthquake network Data-Backup Center.2. All data is separated into three classes: data from earthquake in the sea, data from earthquake on the land and all data. Fourier spectral envelopes are the objective curves. Five regional source and crust medium parameters(stress drop Δσ, quality factor parameters Q0 and η, geometric attenuation parameters R1 and R2) are inversed by the micro-Genetic Algorithm(μGA) method.3. Kappa filter is used as the near-surface high cut-off frequency. Kappa value is calculated respectively by two methods: Original Kappa and Fixed-Kappa. The relationships between 2 Kappa values and moment magnitude, focal depth and epicenter distance are analyzed. The result shows the Kappa values are irrelevant with moment magnitude and focal depth and relevant with epicenter distance.4. Five inversed parameters and two Kappa values are used to establish ground motion attenuation relationships, respectively. By comparing with strong ground motion data, the reliability of attenuation relationships is verified.5. The inversed regional parameters and Kappa values from small earthquake records are used to synthesize near-field strong ground motion from a M=6.0 earthquake on the Jiulongjiang fault. The response spectra on five test points are compared with those estimated by given regional parameters. The former are higher than the later, caused by the larger inversed regional parameters. The spectra are compared with those estimated by the attenuation relationship. They are close on short periods, the hanging wall effect and rupture directivity effect is shown by the results of the finite fault hybrid source model.