Seismicity of the Atlantis Massif detachment fault, 30°N at the Mid‐Atlantic Ridge
Seismicity of the Atlantis Massif detachment fault, 30°N at the Mid‐Atlantic Ridge
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大西洋中脊北纬 30° 亚特兰蒂斯地块滑脱断层的地震活动
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发表时间：
2012
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影响因子：
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通讯作者：
J. McGuire
中科院分区：
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作者：
J. Collins;Deborah K. Smith;J. McGuire
在大西洋中脊北纬 30° 处形成亚特兰蒂斯地块的海洋核心复合体中，过去 1.5-2 Ma 中沿滑脱断层的滑动将下地壳和地幔岩石带到了海底。 1999年至2003年间收集的水声数据表明，地震活动发生在地块顶部附近，主要发生在东南部，而沿邻近山脊轴检测到的地震活动很少。 2005年，在该地块及其周围部署了五台短周期海底地震仪（OBS）作为试点实验，以帮助限制该地区的地震活动分布。对六个月OBS数据的分析表明，与早期水声研究的结果相比，绝大多数地震活动位于轴谷内。在 OBS 部署期间，在阵列内，地震活动主要由相对恒定的背景率和两个大型余震序列组成，其中包括 5 个震级在 4.0 到 4.5 之间的远震事件。余震序列位于轴谷西侧，毗邻亚特兰蒂斯地块，靠近山脊转换交点。它们遵循大森定律，占已检测到的地震的一半以上。 OBS 数据还表明，与水声检测到的地震活动位于同一区域的亚特兰蒂斯地块内，与活动断层相关的地震活动水平较低但持续。在地块内，数据表明有一条南北走向的正断层，以及一条靠近突出的、变换平行、朝北陡坡的左旋走滑断层。这两个特征都可以通过与亚特兰蒂斯变换的弱耦合相关的内角应力场的变化来解释。或者，地块内的正断层可能表明脱离面从轴下方约 60° 的初始倾角滚动到接近水平时的变形，而走滑事件可能表明邻近脱离面的变换平行运动。
At the oceanic core complex that forms the Atlantis Massif at 30°N on the Mid‐Atlantic Ridge, slip along the detachment fault for the last 1.5–2 Ma has brought lower crust and mantle rocks to the seafloor. Hydroacoustic data collected between 1999 and 2003 suggest that seismicity occurred near the top of the Massif, mostly on the southeastern section, while detected seismicity along the adjacent ridge axis was sparse. In 2005, five short‐period ocean bottom seismographs (OBS) were deployed on and around the Massif as a pilot experiment to help constrain the distribution of seismicity in this region. Analysis of six months of OBS data indicates that, in contrast to the results of the earlier hydroacoustic study, the vast majority of the seismicity is located within the axial valley. During the OBS deployment, and within the array, seismicity was primarily composed of a relatively constant background rate and two large aftershock sequences that included 5 teleseismic events with magnitudes between 4.0 and 4.5. The aftershock sequences were located on the western side of the axial valley adjacent to the Atlantis Massif and close to the ridge‐transform intersection. They follow Omori's law, and constitute more than half of the detected earthquakes. The OBS data also indicate a low but persistent level of seismicity associated with active faulting within the Atlantis Massif in the same region as the hydroacoustically detected seismicity. Within the Massif, the data indicate a north‐south striking normal fault, and a left‐lateral, strike‐slip fault near a prominent, transform‐parallel, north‐facing scarp. Both features could be explained by changes in the stress field at the inside corner associated with weak coupling on the Atlantis transform. Alternatively, the normal faulting within the Massif might indicate deformation of the detachment surface as it rolls over to near horizontal from an initial dip of about 60° beneath the axis, and the strike‐slip events may indicate transform‐parallel movement on adjacent detachment surfaces.