An Effective Method to Extract Overtones of Surface Wave From Array Seismic Records of Earthquake Events
Surface wave dispersion curves are extensively used to map the lithospheric shear‐wave velocity structures. However, traditional methods have difficulty extracting overtone dispersion curves from both ambient noise and seismic event data. Recently, Wang et al. (2019, https://doi.org/10.1029/2018JB016595) proposed a new array‐based method, the frequency‐Bessel transform (F‐J) method, to extract high frequency overtones from ambient noise data. However, because the Green's functions of earthquakes are complex, the F‐J method cannot be directly applied to extract overtones from earthquake event data. In this paper, we analyze the differences between ambient noise and earthquake event data and verify that the F‐J method can be efficiently applied to event data by controlling the azimuthal range and adopting time windows. For the F‐J method using earthquake records, the time windows calculated by group velocity intervals can improve the overtone extraction efficiency. We named this application of the F‐J method with time windows using event data the multiwindow F‐J (MWFJ) method to distinguish the two techniques. Further verifications were performed using real data from three earthquakes recorded by the U.S. Transportable Array. Compared to traditional methods for extracting overtones from earthquakes, the MWFJ method can effectively extract higher‐frequency (0.02–0.4 Hz, for the data used in this work) and higher‐resolution overtones from event data. Moreover, the overtones extracted from earthquakes are more sensitive to deeper structures than those extracted from ambient noise. The complementarity of the F‐J and MWFJ methods for the extraction of overtones indicates that better imaging results may be obtained by combining these two methods.