Giant Seismites and Megablock Uplift in the East African Rift: Evidence for Late Pleistocene Large Magnitude Earthquakes
Giant Seismites and Megablock Uplift in the East African Rift: Evidence for Late Pleistocene Large Magnitude Earthquakes
复制标题
东非裂谷的巨型震岩和巨型隆起：更新世晚期大地震的证据
作者：
H. Hilbert;E. Roberts
在许多地震活跃地区，沉积记录代替了全面的仪器地震监测、短暂的历史记录和有限的断裂沟调查，以保存的软沉积变形特征层（称为震积岩）的形式提供了地震活动的重要档案。本文报道了东非裂谷系西支Rukwa裂谷盆地晚第四纪-近代（≤~ 28000年BP）冲积湖相地层中广泛存在的震积岩。我们记录了在坦桑尼亚姆贝亚地区首府附近的浅层、地下地层中最高度变形的沉积物的例子。这包括一个引人注目的碎屑“大块岩复合体”，它保存了垂直位移的完整地层块（大块岩）下面的可移动沉积物，有些超过20米宽。这些震积岩的记录扩展了发震沉积构造的数据库，并证明了东非裂谷系西支发生的晚更新世-近代大震级地震。了解地震活动如何使近地表沉积物变形，对于预测和准备现代地震灾害至关重要，特别是在东非裂谷和其他构造活跃的发展中地区。
In lieu of comprehensive instrumental seismic monitoring, short historical records, and limited fault trench investigations for many seismically active areas, the sedimentary record provides important archives of seismicity in the form of preserved horizons of soft-sediment deformation features, termed seismites. Here we report on extensive seismites in the Late Quaternary-Recent (≤ ~ 28,000 years BP) alluvial and lacustrine strata of the Rukwa Rift Basin, a segment of the Western Branch of the East African Rift System. We document examples of the most highly deformed sediments in shallow, subsurface strata close to the regional capital of Mbeya, Tanzania. This includes a remarkable, clastic ‘megablock complex’ that preserves remobilized sediment below vertically displaced blocks of intact strata (megablocks), some in excess of 20 m-wide. Documentation of these seismites expands the database of seismogenic sedimentary structures, and attests to large magnitude, Late Pleistocene-Recent earthquakes along the Western Branch of the East African Rift System. Understanding how seismicity deforms near-surface sediments is critical for predicting and preparing for modern seismic hazards, especially along the East African Rift and other tectonically active, developing regions.