Pn-Wave Receiver Function

The receiver function (RF) method is the most widely adopted method for imaging crustal structures using earthquake data. Through attenuation during long-distance propagation, high-frequency components are scarce in teleseismic waveforms, resulting in low-frequency RFs and low-resolution crustal images. The Pn-wave contains more high-frequency components because of the short epicentral distance. To improve the resolution of crustal structure studies, we propose the Pn-wave receiver function (PnRF) method. Unlike other near-earthquake phases, the Pn-wave can be considered a plane wave in the crust beneath seismic stations, and interference from other phases can be avoided at epicentral distances of 5-15 degrees. PnRFs calculated from both numerical synthetic data and observational data at broadband seismic stations show that all converted waves are present in PnRFs at the predicted time according to the theory of plane waves. PnRFs calculated by observational data of a dense nodal array clearly show not only the converted wave from the Moho but also the converted wave from the crustal interface, which is too weak to be observed in tele-RFs because the Pn-wave has a larger incident angle and higher frequency than the teleseismic P-wave. When used in conjunction with dense nodal array observations, the PnRF method has the potential to image crustal structures with a high resolution close to that of the deep seismic reflection method. As an economical seismic method, the receiver function method is widely adopted to image crustal structures using earthquake data. However, its resolution is very low because teleseismic waveforms retain only low-frequency components and lose high-frequency components due to attenuation during propagation over epicentral distances greater than 3,000 km. In this study, we propose the Pn-wave receiver function (PnRF) method. Unlike other regional seismic phases, the Pn-wave can be taken as a plane wave after returning to the crust, and interference from other phases can be avoided in the epicentral distance range of 500-1,600 km. Our numerical simulation tests and observational data show that the amplitudes of converted waves in PnRFs are 2-3 times larger than those in teleseismic receiver functions (tele-RFs), which implies that PnRFs have a greater sensitivity to detect weak interfaces than tele-RFs. The most important advantage of the PnRF method is that it can image crustal structure with far higher resolution than the tele-RF method, even close to that of the expensive deep seismic reflection method, because Pn-waves contain more high-frequency components. The Pn-wave as a regional seismic phase is proposed to calculate the receiver function for imaging crustal structure Converted wave amplitudes in the Pn-wave receiver function are 2-3 times larger than those in the teleseismic P-wave receiver function It is a high-resolution method to study crustal structure because Pn-wave is richer in high-frequency components than teleseismic P-wave