STUDIES OF LONG PERIOD CODA DECAY OF LARGE EARTHQUAKES

The earthquake coda is the residual slowly decaying vibration energy arriving long after the main arrivals of an earthquake. It is generally thought to be originated from scattered waves from the heterogeneities inside the Earth. Previous studies of coda focused on short periods and small earthquakes. Here we examine coda of large earthquakes at long periods (50 to 300 s). We used 12 major earthquakes (from 2000 to 2017) and magnitude greater than 8.0, recorded at 120 global seismic network (GSN, II and IU networks) stations. Our preliminary results suggest that the coda energy level is closed related to the magnitude of the earthquake, and the decay of coda energy is similar for different stations and different earthquakes. By compared synthetic seismogram computed by the direct solution method (DSM) and specfem3D-global, we found that the coda energy decay does not depend on the Earth’s 3D velocity or attenuation structure. The decay only depends on the global average Q value, which may provide a way to constrain the 1D global average Q model. The coda energy level may provide a new way to determine big earthquake magnitude. The behavior of the coda energy level with distance and the decay rate may provide information about the earth’s scattering field and the process of earthquake coda generation.