Dynamics of non-self-similar earthquakes illuminated by a controlled fault asperity

Most ordinary earthquakes follow self-similar scaling, where source duration scales with the one-third power of seismic moment. However, some earthquake clusters show non-self-similar scaling, where source duration remains nearly constant regardless of seismic moment. Their source mechanisms, previously proposed to involve fixed source dimensions with variable stress drop or accelerating rupture velocity, are not fully validated due to uncertainties in estimating source properties, often caused by observational biases such as path effects. Here, we present a robust dynamic source model for non-self-similar earthquakes based on laboratory experiments with size- and shape-controlled sources. A thin circular gouge patch, placed on the meter-scale laboratory fault, generated microearthquakes exhibiting non-self-similar scaling, with magnitudes ranging from M _w -7.3 to -6.0. A dynamic rupture model, constrained by the observed source parameters and the controlled source configuration, suggests that such scaling arises from a combination of variable stress drop and self-healing friction, even without a substantial rupture barrier confining the final source size. Therefore, non-self-similar earthquakes are not limited to specific environments, such as velocity-weakening patches on creeping faults, but can occur in a broader range of tectonic settings, wherever slip is governed by self-healing friction on isolated asperity patches with variable stress drop.