Seismic Source Spectral Properties of Dynamic Rupture With a Self‐Similar, Self‐Healing Slip Pulse: Origins of Double‐Corner Displacement Spectra and Implications for Small Earthquake Rupture Modes

Abstract We investigate the spectral characteristics and source properties of earthquake rupture models with self‐similar, self‐healing slip pulses. We compare pulse‐like and crack‐like rupture models across various idealized and heterogeneous source scenarios to identify conditions under which far‐field displacement spectra characterized by two corner frequencies (double‐corner frequency spectra) emerge. Five primary mechanisms are identified as causes of second high‐frequency corners: (a) slip‐pulse width, (b) rupture directivity, (c) gradual rupture arrest, (d) characteristic length of slip heterogeneity, and (e) Mach waves from supershear rupture. Spectra associated with slip‐pulse width are most evident at small take‐off angles from the fault normal, while those linked to rupture directivity and characteristic slip heterogeneity appear at large take‐off angles. Estimated stress drops depend strongly on rupture mode and speed. Pulse‐like models exhibit greater variability in estimated stress drops due to unknown rupture speeds than crack models, with pulse‐like ruptures systematically underestimating moment‐based stress drops by up to 40%. Comparisons to a recent study of Mw 3.0 to 5.5 earthquakes in Japan indicate a relationship between normalized corner frequency and scaled energy that fits better with pulse‐like rupture models than with crack models, indicating small‐ to moderate‐size earthquakes predominantly exhibit pulse‐like rupture behavior. The gradual rupture arrest mechanism can produce double‐corner spectra; however, it is unlikely to represent realistic earthquake sources due to its spectral decay. Our results highlight the importance of incorporating pulse‐like rupture dynamics into source models and point out challenges in interpreting source spectra and stress drop estimates when rupture characteristics are uncertain.