The thickness of the mechanical layer that hosts a group of faults can be estimated from the spacing of saturated faults (i.e. the constant spacing between faults when the fault system is fully developed and has attained its final fault density). We measured fault spacing for a group of saturated active normal faults on Miyako‐jima Island (southern Ryukyu Arc, Japan) and estimated the thickness of the faulted mechanical layer. The measured fault spacing is 1.30 ±0.14 km, and the thickness of the mechanical layer is < 3 km, which is the upper limit of the seismogenic zone. This faulted mechanical layer corresponds to a sedimentary layer in which earthquakes cannot occur. Results indicate that the shallow (< 3 km depth) normal faults on Miyako‐jima Island do not have the potential to cause medium‐size earthquakes as individual faults. The origin of the shallow normal faults might be related to the presence of a larger‐scale, deeper fault. The results indicate that fault spacing provides important information on the potential magnitude of earthquakes associated with active faults.

中文翻译：

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根据断层间距估算断层机械层的厚度：以日本琉球弧南部的宫古岛为例

可以根据饱和断层的间距（即，当断层系统完全发育并达到其最终断层密度时，断层之间的恒定间距）来估算承载一组断层的机械层的厚度。我们测量了宫古岛（日本琉球弧南段）上一组饱和活动正断层的断层间距，并估算了断层机械层的厚度。测得的断层间距为1.30±0.14 km，机械层的厚度<3 km，这是成地震带的上限。该断裂的机械层对应于不会发生地震的沉积层。结果表明，宫古岛上的浅层（<3 km深度）正断层没有作为单个断层引起中型地震的潜力。浅层正断层的起源可能与更大，更深层断层的存在有关。结果表明，断层间距为与活动断层有关的潜在地震震级提供了重要信息。