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Abstract Natural faults likely include both Velocity‐Weakening (VW) and Velocity‐Strengthening (VS) areas. We developed a laboratory method to replicate this frictional heterogeneity using a 760 mm long Polymethyl methacrylate (PMMA) block with 11 VW patches (bare PMMA) separated by VS barriers (Teflon tape). We compared the behavior of this Multiple Patches (MP) arrangement to those from One single VW Patch (OP) with the same total VW fault area. Seismic events that occurred in clusters with foreshocks and aftershocks were observed only in the MP tests, and total slip, maximum slip rate, seismic moment, and recurrence time of the largest event (termed the mainshock) in a slip cycle, were an order of magnitude smaller in the MP tests compared to the OP tests. Slower loading rates, corresponding to longer recurrence time, produced larger mainshock magnitudes in the OP tests, as expected due to fault healing. In contrast, the mainshock magnitude in the MP tests decreased with increasing recurrence time due to the increased effectiveness of VS barriers at slower loading rates. In some MP tests, foreshock‐like events migrated at ∼0.7 m/s, followed by faster reverse migration at ∼7 m/s, resembling Rapid Tremor Reversal (RTR) in subduction zones. We used a numerical simulation to quantitatively reproduce the RTR‐like behavior, help explain its mechanics, and constrain the friction properties of the laboratory system. Overall, our findings highlight how identical structural features on heterogeneous faults can behave differently under different loading conditions due to the velocity dependence of VS barriers. 

Abstract Many natural faults are believed to consist of velocity weakening (VW) patches surrounded by velocity strengthening (VS) sections. Numerical studies routinely employ this framework to study earthquake sequences including repeating earthquakes. In this laboratory study, we made a VW asperity, of lengthL, from a bare Poly(methyl methacrylate) PMMA frictional interface and coated the surrounding interface with Teflon to make VS fault sections. Behavior of this isolated asperity was studied as a function ofL(ranging from 100 to 400 mm) and the critical nucleation length, , which is inversely proportional to the applied normal stress (2–16 MPa). Consistent with recent numerical simulations, we observed aseismic slip for  < 2, periodic slip for 2 <  < 6, and non‐periodic slip for 10 < . Furthermore, we compared the experiments whereLwas contained by VS material to standard stick‐slip events whereLwas bounded by free surfaces (i.e.,L = the total sample length). The free surface case produced ∼10 times larger slip during stick‐slip events compared to the contained fault ruptures, even with identical . This disparity highlights how standard, complete‐rupture stick‐slip events differ from contained events expected in nature, due to both the free surface conditions and the heterogeneous normal stress along the fault near the free ends, as confirmed by Digital Image Correlation analysis. This study not only introduces the Teflon coating experimental technique for containing laboratory earthquake ruptures, but also highlights the utility of as a predictive parameter for earthquake behavior.