The bottom simulating reflection (BSR) is widely observed along continental margins and is believed to mark the base of gas hydrate stability zone (BGHSZ). In some regions, double or multiple overlapping BSRs are observed, yet their formation mechanisms and geologic implications are not well understood. Here we present 3D seismic images from the 2018 NZ3D experiment that covers a $14\times 60{\text{km}}^2$ survey area on New Zealand's northern Hikurangi subduction margin. We observe double BSRs in five locations. Beneath the Tuaheni Basin in the mid-slope, a secondary BSR (BSR2) lies ∼100-360 m deeper than the primary BSR (BSR1) and its 3D geometry mimics the unconformity at the base of the basin. At three thrust ridges located 18-38 km from the deformation front, BSR2 lies ∼55-130 m below and is sub-parallel to BSR1. At another thrust ridge ∼14 km from the deformation front, BSR2 forms above the BSR1, and the two BSRs converge towards the peak of the ridge. Through 3D modeling of BGHSZ and analysis of the geometry and reflection characteristics of the double BSRs, we identify three potential mechanisms for their formation (1) rapid sedimentation, (2) tectonic uplift, (3) overpressure/heat advection caused by fluid migration. Our study demonstrates that formation of double BSRs is closely linked to subduction processes along the northern Hikurangi margin, and double BSRs may be used as indicators for areas with recent sedimentation, tectonic and/or fluid activities.

底部模拟反射（BSR）在大陆边缘广泛观察到，并被认为是天然气水合物稳定带（BGHSZ）的基础。在某些地区，观察到双重或多个重叠的BSR，但对其形成机理和地质意义尚不甚了解。在这里，我们展示了来自NZ3D 2018实验的3D地震图像，涵盖了$14\times 60{\text{公里}}^2$位于新西兰北部Hikurangi俯冲带边缘的调查区域。我们在五个位置观察到双重BSR。在中坡的图阿赫尼盆地下方，次生BSR（BSR2）比主要BSR（BSR1）深约100-360 m，其3D几何形状模仿了盆地底部的不整合面。在距变形前沿18-38 km的三个推力山脊处，BSR2位于下方〜55-130 m，并且与BSR1次平行。在距变形前沿约14 km的另一个逆冲脊上，BSR2在BSR1上方形成，两个BSR朝着脊顶收敛。通过对BGHSZ进行3D建模并分析双BSR的几何特征和反射特征，我们确定了其形成的三个潜在机理（1）快速沉积，（2）构造隆升，（3）由流体运移引起的超压/热平流。我们的研究表明，双重BSR的形成与北部Hikurangi边缘的俯冲过程密切相关，并且双重BSR可以用作近期沉积，构造和/或流体活动区域的指示。