Megathrust roughness and structural complexity are thought to be controls on earthquake slip at subduction zones because they result in heterogeneity in shear strength and resolved stress. However, because active megathrust faults are difficult to observe, the causes and scales of complexity are largely unknown. Here we measured the in situ properties of the megathrust of the Middle America subduction zone in a three-dimensional seismic reflection volume to determine how fault properties vary. We quantify spatial variability in the megathrust roughness, overburden and rock physical properties. Heterogeneity in the megathrust roughness exists at length scales of a few kilometres because the megathrust is dissected by active lower-plate normal faults, which offset the megathrust and renewed fault roughness. Spatial variations in the rock physical properties at the plate interface are characterized by correlation length scales of hundreds of metres. Frontal prism taper, historical seismicity and the variation in earthquake stress drop values local to the megathrust are all affected by the heterogeneity at these length scales. Both geometric and rheological complexities may therefore control the mechanical behaviour of the subduction plate interface, which includes earthquake rupture characteristics.

大推力的粗糙度和结构复杂度被认为是俯冲带地震滑动的控制因素，因为它们导致剪切强度和分解应力的不均匀性。但是，由于很难观测到活动的巨型逆冲断层，因此复杂性的成因和规模在很大程度上是未知的。在这里，我们在三维地震反射体中测量了中美洲俯冲带大推力的原位特性，以确定断层特性如何变化。我们量化了巨推力粗糙度，覆盖层和岩石物理特性的空间变异性。巨推力粗糙度的非均质性存在于几公里的长度范围内，这是因为巨推力是由活动的下板正断层解剖的，这抵消了巨推力和新的断层粗糙度。板块界面岩石物理特性的空间变化以数百米的相关长度尺度为特征。在这些长度尺度上，前棱锥锥度，历史地震活动性和超大推力局部的地震应力降值的变化都受到异质性的影响。因此，几何和流变复杂性都可以控制俯冲板界面的力学行为，包括地震破裂特征。