【摘要】 通过分析发生在日本周边深源地震的宽频带波形资料,估计了日本列岛下的660km不连续面(d660)的深度变化。许多宽频带波形记录到了在d660顶部发生反射的sScS的后续波。sScS后续波与sScS间的到时差包含了震中与台站下方的d660深度变化的信息。我们成功地检测到这两种震相并将其分离,到目前为止还没有这方面研究的报道。我们由sScS与其后续波的到时差来求每个震中与记录台站下的d660的深度变化。研究结果显示,西部日本下的d660较深(大于660km),这可能是滞留在地幔转换带中的冷的太平洋板块造成的。在日本中部,d660变深,显然这不是太平洋板块本身造成的,因为日本中部已经位于该滞留板片的东部。日本东北部下的d660变得较浅,这可能是太平洋板片形状变化或下地幔热物质上涌形成局部热异常造成的。更多还原

【Abstract】 The broadband waveform records from deep earthquakes occurred around Japan are analyzed to estimate the depth variations of the 660 km discontinuity (d660) beneath the Japan Islands. A postcursor to sScS, which is identified as a top-side reflection from the d660, is detected in many records. The differential travel time between the postcursor and sScS contains information on the d660 depths beneath the hypocenter and the receiver. We have successfully detected the postcursor and separated residuals of the differential travel times to those from the d660 reflections beneath the hypocenter and receiver, which was not done in the previous studies. The residuals are interpreted as the depth change in d660 beneath each hypocenter and receiver. A deeper d660 is found beneath western Japan, which may be caused by cold materials of the stagnant Pacific slab. Beneath central Japan, d660 also exhibits depressions, which is not attributable to the Pacific slab itself because this region is located east of the stagnant slab. The d660 becomes shallower beneath northern and central Japan, which may be caused by a local hot anomaly related to either the cusps of the Pacific slab or a hot upwelling from the lower mantle.更多还原