Low velocity zone (LVZ) is a common structural feature in geological faults. To examine the effect of LVZ on faulting, a laboratory fault model considering the LVZ is constructed and loaded to different levels. Subsequently ruptures are triggered on one of its contact boundaries with the host rock. The bilateral rupture propagation along this laboratory fault that separates different materials shows distinct directionality in both rupture speeds and rupture modes. The rupture in the positive direction with respect to the fault is always crack-like growing at the Generalized Rayleigh (GR) wave speed. However, in the negative direction both stable and unstable slip pulses are observed. Higher load and thinner LVZ facilitate the unstable slip pulses. The trailing tip for both types of pulses propagates at the GR wave speed, the leading tip of the stable pulse propagates with the GR wave speed while that of the unstable pulse features a supershear speed.

低速带（LVZ）是地质断层的常见构造特征。为了检查LVZ对断层的影响，构建了一个考虑LVZ的实验室故障模型并将其加载到不同级别。随后在与母岩的接触边界之一上引发破裂。沿该实验室断层分开不同材料的双边破裂传播在破裂速度和破裂模式上都表现出明显的方向性。相对于断层的正向破裂总是以广义瑞利（GR）波速增长。然而，在负方向上观察到稳定和不稳定的滑差脉冲。更高的负载和更薄的LVZ有助于不稳定的滑差脉冲。两种脉冲的尾尖均以GR波的速度传播，