Joint Autocorrelation and Receiver Function Analysis of Sedimentary Structures Using Strong Ground Motion Records

Abstract

Joint analysis of the receiver and autocorrelation functions was performed to estimate the structure of the P- and S-wave velocities V_P and V_Sas well as the depth to the seismic bedrock using strong motion records obtained in Narita, Kanto basin, Japan. From data of over 1000 P-waves and their coda induced by local seismic events, the autocorrelation revealed a clear reflection in the sedimentary layer, and the receiver function revealed clear Ps and PpPs converted phases at the seismic bedrock. The sediment thickness and V_S were measured from the H–κ stack of the vertical and transverse components of the autocorrelation and the Ps and PpPs phases in the receiver function. The previous V_S structure model obtained with only the transverse autocorrelation in Narita was found to be appropriately evaluated, whereas the corresponding V_P structure model must be improved. Because the H–κ stack requires an assumed V_P value, an appropriate value of V_P is crucial for accurate estimation of V_S and the thickness of the sediment. Thus, the frequency analysis of the H–κ–V_P stack was performed to estimate V_P, V_S, and the thickness of the sedimentary structure. From the results of this analysis, V_S was determined to have been estimated appropriately for the present case in Narita. However, V_P had been estimated to be lower than the value estimated by this study. It is clear that an appropriate assumption of V_P is important to capture the Ps and PpPs phases in the receiver function.

Appendix

Numerical studies contribute to our understanding of the appearance of Ps and PpPs phases in the receiver function in the sedimentary layered structure. The velocity structure model including the crust and mantle was used for the numerical simulation of the receiver function. The model was extracted at the location of the KiK-net Narita station from the JIVSM (Koketsu et al., 2012). The Ps phase at the Moho is known to be sensitive to the angle of incidence from the teleseismic record. Figure 11a shows the receiver function (passband with 1–8 Hz) computed at different angles of incidence of the P-wave. It was also observed that the Ps and PpPs phases at the seismic bedrock were not sensitive to the angle of incidence. However, the amplitude of both the Ps and PpPs phases decrease when the angle of incidence is low. As has already been shown, the Ps phase at the Moho arrives late when the angle of incidence is high.

The receiver function was also used to detect the dipping structure from the ambiguity of the Ps phase arrival time, which depends on the back azimuth of seismic events (e.g. Li et al., 2019). Figure 11b shows the receiver function in the dipping structure, assuming the bottom layer is dipping 10° to the north. The angle of incidence was assumed to be 60°. It was observed that the arrival of the Ps phase at the Moho is delayed depending on the back azimuth. However, the arrival of the Ps and PpPs phases at the seismic bedrock did not depend on the back azimuth, whereas the amplitude did.

Fig. 11

Theoretical receiver function computed using the velocity structure model JIVSM by Koketsu et al. (2012) at the KiK-net Narita station. PHS and PAC means the Philippines Sea Plate and Pacific Plate, respectively. a Calculation results for several angles of incidence. b Receiver function in the dipping structure, computed with the assumptions that the bottom half-space layer is dipping 10° to the north and the angle of incidence of the P-wave incident is 60°

From this investigation, the receiver function is able to capture the phases of Ps and PpPs at the seismic bedrock, and the arrival time of these phases is not sensitive to the angle of incidence and back azimuth. This means it is efficient to detect the velocity structure of the sediment by the receiver function technique using any property of the seismic event. However, it also suggests it would be difficult to detect the angle of incidence of the P-wave and the dipping structure using the Ps and PpPs phases at the seismic bedrock.