Imaging Stress and Faulting Complexity Through Earthquake Waveform Similarity

While the rupture processes of nearby earthquakes are often highly similar, characterizing the differences can provide insight into the complexity of the stress field and fault network in which the earthquakes occur. Here we perform a comprehensive analysis of earthquake waveform similarity to characterize rupture processes in the vicinity of Ridgecrest, California. We quantify how similar each earthquake is to neighboring events through cross correlation of full waveforms. The July 2019 Ridgecrest mainshocks impose a step reduction in earthquake similarity, which suggests variability in the residual stress field and activated fault structures on length scales of hundreds of meters or less. Among these aftershocks, we observe coherent spatial variations of earthquake similarity along the mainshock rupture trace, and document antisimilar aftershock pairs with waveforms that are nearly identical but with reversed polarity. These observations provide new, high‐resolution constraints on stress transfer and faulting complexity throughout the Ridgecrest earthquake sequence. Plain Language Summary Earthquakes that occur nearby to one another typically broadcast similar seismic signals. In this work, we show that the M6.4 and M7.1 earthquakes that occurred as part of July 2019 Ridgecrest, California, earthquake sequence triggered measurable changes in the similarity of earthquake waveforms throughout the nearby region. This implies high levels of complexity in the crustal stress field and active fault structures on the scale of tens to hundreds of meters. The Ridgecrest mainshocks caused earthquakes to become less similar on average, with systematic spatial variations along the rupture planes in correspondence to the level of mainshock fault slip. These observations form the basis for future work relating measurements of earthquake similarity to changes in stress and strength in Earth's crust. Key Points We use earthquake waveform similarity as a tool to study how stress and faulting evolve during the Ridgecrest sequence Ridgecrest aftershocks have lower similarity than pre‐event seismicity, implying stress and fault heterogeneity at 100‐m length scales Ridgecrest aftershocks show coherent spatial variations in similarity that correlate with along‐strike variations in mainshock fault slip