The analysis of the non-typhoon-induced microseisms before the 2008 Wenchuan earthquake

To distinguish typhoon and non-typhoon effects on the tremor before the 2008-05-12 great Wenchuan earthquake, we investigate microseisms recorded by broadband seismographs in mainland of China before the earthquake. Our results indicate that the microseisms consist of two main parts that show different dynamical characters. The one in the frequency band of 0.2 similar to 0.25 Hz is related to typhoon Rammasun, which is strong near the coast of East China but weak in the inland of China, and its seismic source is located on the seabed near the track of Rammasun. The other one in the frequency band of 0.1 similar to 0.18 Hz bore no relation to Rammasun. This non-typhoon-induced microseism is strong near the epicenter of the earthquake but weak in the coast and western areas of China. Locating seismic sources of non-typhoon-induced microseism by the source scanning algorithm, we show that the sources are distributed around the epicenter of Wenchuan.