High Resolution Studies of Deep Earth Structure ...

• Main Author: Xiaoming, Ding
• Format: Text
• Language: English
• Published: California Institute of Technology 1998
• Subjects: Computer Science; Geophysics; FOS Earth and related environmental sciences; Iceland
• Online Access: https://dx.doi.org/10.7907/z21r-bk54; https://resolver.caltech.edu/CaltechTHESIS:08032023-144000226

Recent advances in seismic tomography has imaged major deep structure in the lower mantle. The ring of fast velocities originally derived from global long-period inver­sions has been resolved into interspersed sheet-like structure which appears to be old slabs. Beneath some of the structure, there are high velocity zones (HVZ) with variable thickness approaching the core mantle boundary (CMB). Detailed broadband modeling of waveforms produced by seismic paths sampling one of these zones yields a picture of D" zone, with one thermal negative above the layer and one positive approaching the CMB, which would seem to be quite compatible with pancaked slab debris. In contrast, modeling waveforms produced by sampling the slowest velocity regions along the CMB reveals a thin ultra low velocity zone (ULVZ). The dimensions of these zones range from a few hundred km beneath Iceland to a few thousand km beneath Africa. Seismic data recorded on TERRAscope and Berkeley Digital Seismic Network are used to study the HVZ ...