Velocity Contrast across the Zhaotong-Ludian Fault in Southwest China from the Analysis of Fault Zone Head Waves and TeleseismicP-Wave Arrivals

Abstract

We image the Zhaotong-Ludian fault (ZLF) in the southeastern margin of the Tibetan plateau (SE Tibetan plateau) using waveforms from local and teleseismic earthquakes recorded by 14 seismic stations. We identify two types of fault zone head wave (FZHW) from two clusters of earthquakes by applying an automatic picking algorithm and a horizontal particle motion analysis. The first type of FZHWs shows a linear time–distance moveout and is only observed at stations on the southeast side of the fault in the northeastern section of the ZLF. The moveout slope suggests an average cross-fault velocity contrast of ∼2.5%. The second type of FZHWs exhibits a constant moveout and is recorded by stations on both sides of the ZLF in the southwestern section from a cluster of earthquakes located in a low-velocity zone. The difference in cross-fault velocity contrast between the northeast and southwest segments of the ZLF is also confirmed by teleseismic P-wave travel-time data. We attribute the prominent velocity contrast in the northeast section to a lithological difference between the South China block in the southeast and the Daliangshan subblock on the northwest side of the fault. The striking difference between the northeast and southwest sections also implies that earthquakes nucleating in one segment would hardly rupture through the entire fault, which can significantly affect our estimates of the maximum magnitude of future earthquakes occurring on the fault.

Azimuthal Variation in the Spectra of the 2019 Ridgecrest Earthquake Clusters and its Application to Understanding Fault Zone Structure

“…To characterize FDZ structure, current techniques usually utilize near-fault arrays to obtain a cross-sectional view at an array location. For example, the waveform modeling of fault zone trapped waves has been widely utilized to image the width and the shear wave velocity reduction of the FDZ (e.g., Lewis & Ben-Zion 2010;Li et al, 2014;Qiu et al, 2021), whereas fault zone head waves offer precise information on the velocity contrast across the fault interface at depth (e.g., McGuire & Ben-Zion, 2005;Zhao & Peng, 2008;Allam et al, 2014;Zheng et al, 2022). Waveform modeling of the reflection of body waves in FDZs has also been used to derive fault zone structure in high resolution (Li et al, 2007;Yang and Zhu 2010).…”