We develop and test a method to estimate local Vp/Vs ratios for compact similar earthquake clusters using the precise P and S differential times obtained using waveform cross-correlation. We demonstrate how our technique works using synthetic data and evaluate likely errors arising from near-source takeoff angle differences between P and S waves. We use a robust misfit function method to compute Vp/Vs ratios for both synthetic data sets and several similar event clusters in southern California, and use a bootstrap resampling approach to estimate standard errors for real data. Our technique has higher resolution for near-source Vp/Vs ratios than typical tomographic inversion methods and provides constraints on near-fault rock properties.

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