Are “third microseisms” in anomalous tremor before the great Wenchuan earthquake?

We studied anomalous tremor before the 2008 great Wenchuan earthquake and the 2001 great Kunlunshan by analyzing seismic data from stations of National Digital Seismograph Network of China.Our results show that some anomalous tremor microseismic activities are related to West Pacific Typhoons,which are the secondary microseisms that are due to the non-linear interaction of ocean waves as proposed by Longuet-Higgins.However,we found that there are time-frequency shift between microseismic signals at different site after further investigation. This anomalous feature should not belong to secondary microseismic activity.We suggest that third microseisms are likely induced during process of the secondary microseisms propagation.