第122回ジオダイナミクスセミナー
Geodynamics Seminar
"Global finite-frequency tomographic models reveal
a variety of plumes in the mantle: implications"
講師：R. Montelli (Princeton University, USA)
主催 ： 愛媛大学地球深部ダイナミクス研究センター
日時 ： ２００５年３月１８日（金）17：00〜
場所 ： 愛媛大学理学部講義棟 ２０１教室
要 旨
Diffraction theory predicts that traveltimes of
finite-frequency waves are affected by
heterogeneities within
a narrow region around the ray-theoretical path,
called Fresnel zone. Because of wavefront healing,
heterogeneities whose scale-length is smaller then
the size of the Fresnel zone do not significantly
affect the traveltimes.
Dahlen et al. (2000) show how to correct for
wavefront healing effects with a method we refer to
as finite-frequency modeling.
We perform global tomographic studies of P- and S-
waves by using the finite-frequency modeling and
irregular model parameterizations.
Our tomographic models reveal a collection of plumes
in the mantle. Deep plumes are present beneath
Ascension, Azores, Canary, Cape Verde, Cook Island,
Easter, Kerguelen, Samoa and Tahiti. Plumes rising
from the base of the mantle but not reaching yet the
surface are located in the Coral Sea,
east of Solomon and south of Java. Plumes beneath
Eifel, Etna and Seychelles
remain mostly confined to the upper mantle. Several
plume images extend only
down to the mid-mantle. For these plumes a deep
origin cannot be simply rule out because
resolution shows that they could have a very thin,
not resolvable, tail. Also, none of the imaged
plumes exhibits the typical mushroom-shaped structure.
Both in the P-model and S-model plumes are wide,
with radii as large as 300?400 km. Such headless,
wide plumes and their geometry have important
implications for the dynamics of the mantle
問い合わせ先：山崎 大輔 TEL （089）927-8408
E-mail yamazaki@sci.ehime-u.ac.jp
