Imaging of Mantle Diapir by Seismic Waves

我们在枥木县日光地区和宫城县鬼户地区进行了临时地震观测，发现了异常地震结构。通过对这些密集地震观测或其他固定观测网的数据分析，我们得到了以下结果：对地壳和上地幔三维地震衰减结构的估计表明，地壳和上地幔中存在倾斜的低q体。低q体的空间分布与走时层析成像的地震低速体的空间分布大致一致。日光和鬼户地区地壳中发现的低速低q体在空间上与该地区分布的活火山或破火山口结构密切相关。在这些地区发现了地壳中s波反射体，它们在空间上也与活火山和火山口结构密切相关。地幔楔中与地幔地幔相对应的地震低速、低q体、深部低频微地震和地壳中s波反射体反映了弧火山的根源，与其上浅层内陆地震的发生密切相关。基于这些观测，我们建立了一个定性模型来解释观测到的浅层地震活动模式。

We carried out temporary seismic observations in two areas, Nikko area in Tochigi Prefecture and Onikobe area in Miyagi Prefecture, where anomalous seismic structure has been revealed. Based on the analyzes of data by these dense seismic observations or other stationary observation networks, we obtained the following results.Estimation of 3D seismic attenuation structure of the crust and upper mantle shows the existence of the inclined low-Q bodies in the crust and upper mantle. Spatial distribution of the low-Q bodies roughly coincides with that of seismic low-velocity bodies imaged by the travel time tomography.Low-velocity, low-Q bodies detected in the crust of Nikko and Onikobe areas are closely correlated in space with active volcanoes or caldera structure distributing in these areas. Mid-crustal S-wave reflectors have been detected in these areas, and they are also closely related in space with active volcanoes and caldera structure.Seismic low-velocity, low-Q bodies in the mantle wedge corresponding to the mantle diaptr, deep low-frequency microearthquakes and midcrustal S-wave refllectors reflect the root of arc volcanoes, and it is closely related with the occurrence of shallow inland earthquakes above it. Based on these obsservations we have constructed a qualitative model to explain the observed pattern of shallow seismic activity.