The Main Ethiopian Rift (MER) has developed during the 18 Ma-Recent separation of the Nubian and Somalian plates. Extension in its central and northern sectors is associated with seismic activity and active magma intrusion, primarily within the rift, where shallow (5 km) seismicity along magmatic centers is commonly caused by fluid flow through open fractures in hydrothermal systems. However, the extent to which similar magmatic rifting persists into the southern MER is unknown. Using data from a temporary network of five seismograph stations, we analyze patterns of seismicity and crustal structure in the Abaya region of the southern MER. Magnitudes range from 0.9 to 4.0; earthquake depths are 0–30 km. ratios of 1.69, estimated from Wadati diagram analysis, corroborate bulk-crustal ratios determined via teleseismic P-to-S receiver function H- stacking and reveal a relative lack of mafic intrusion compared to the MER rift sectors to the north. There is a clear association of seismicity with the western border fault system of the MER everywhere in our study area, but earthquake depths are shallow near Duguna volcano, implying a shallowed geothermal gradient associated with rift valley silicic magmatism. This part of the MER is thus interpreted best as a young magmatic system that locally impacts the geothermal gradient but that has not yet significantly modified continental crustal composition via rift-axial magmatic rifting.

中文翻译：

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埃塞俄比亚南部主要裂谷​​的地震活动性和地壳结构：来自阿巴亚湖的新证据

埃塞俄比亚主裂谷（MER）是在 18 Ma-最近的努比亚和索马里板块分离期间发展起来的。其中部和北部地区的延伸与地震活动和活跃的岩浆侵入有关，主要在裂谷内，沿岩浆中心的浅层（5 公里）地震活动通常是由流体流过热液系统中的开放裂缝引起的。然而，类似的岩浆裂谷持续到 MER 南部的程度是未知的。使用来自五个地震台站临时网络的数据，我们分析了 MER 南部阿巴亚地区的地震活动模式和地壳结构。幅度范围从 0.9 到 4.0；地震深度为0-30公里。根据瓦达蒂图分析估计的1.69 的比率证实了块状地壳通过远震 P-to-S 接收器函数H -叠加确定的比率，表明与北部的 MER 裂谷区相比，相对缺乏镁铁质侵入。在我们的研究区，地震活动与 MER 西部边界断层系统有明显的关联，但杜古纳火山附近的地震深度较浅，这意味着与裂谷硅质岩浆作用相关的地温梯度较浅。因此，这部分 MER 最好被解释为年轻的岩浆系统，它局部影响地温梯度，但尚未通过裂谷-轴向岩浆裂谷显着改变大陆地壳成分。