The well‐established variation in the depth of earthquakes along both branches of the East African Rift System offers an opportunity to probe the controls on the depth‐extent of seismogenesis, and the length‐scales over which this may vary. We present an updated compilation of well‐determined earthquake depths from teleseismic and regional seismic data for the East African Rift System, combined with a summary of the depth distribution of smaller‐magnitude microseismicity from 13 local network deployments. Moderate‐to‐large magnitude (M_w > 5) earthquakes, unrelated to the movement of magmatic fluids, beneath Afar, the Main Ethiopian Rift, and the northernmost sections of the Eastern Branch, are confined to the upper crust. Seismicity along the Western Branch, and the southern‐most sections of the Eastern Branch extends deeper, into the lower crust, in places to depths close to the local Moho. Along the Eastern Branch, in northern Tanzania, the transition between these two regimes occurs over a distance of ≤40 km, requiring a change to a higher temperature cutoff for the deeper earthquakes; an effect that must be compositional in origin. This compositional variation in the lower crust is most likely related to the degree of hydration. Earthquakes deep within the lower crust are therefore likely to be a proxy for an anhydrous crustal composition.

中文翻译：

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东非地震成因厚度的变化

沿东非裂谷系统两个分支建立的公认的地震深度变化提供了一个机会，以探索对地震发生深度范围以及其变化范围的长度尺度的控制。我们提供了从东非裂谷系统的远震和区域地震数据中确定的地震深度的最新汇编，并结合了来自13个本地网络部署的小震级微地震的深度分布的摘要。中到大幅度（M _w > 5）在阿法尔下方，埃塞俄比亚主裂谷和东部分支的最北段之下，与岩浆流体运动无关的地震被限制在上地壳内。西部分支和东部分支的最南端的地震活动更深，延伸到下地壳，直至靠近当地莫霍面的深度。沿着坦桑尼亚北部的东部分支，这两个区域之间的过渡发生在≤40km的距离上，因此对于更深的地震，需要更改为更高的温度极限；必须是起源组成的效果。下地壳的这种成分变化很可能与水合程度有关。因此，下地壳深处的地震很可能是无水地壳成分的代表。