Low-velocity zone atop the 410-km seismic

discontinuity

in the northwestern United States

T.-R.A. Song, D.V. Helmberger, S.P. GrandNature 427, 2004

Pei-Ying Patty Lin Earthscope Seminar, Feb.12, 2007

DATA

Song et al., Nature 427, 530 (2004).

XL

XK

XMTriNet

Method

Song et al., Nature 427, 530 (2004).

Profile A(d:14~17o)

Song et al., Nature 427, 530 (2004).

Song et al., Nature 427, 530 (2004).

Thickness of LVZ(km) 0 40 20Topography depression(km) 60 0 20

TriNet

Triplication curves

Song et al., Nature 427, 530 (2004).

Song et al., Nature 427, 530 (2004).

record section B

record section A

Profile C,F,D,E(d:21~24o)

Song et al., Nature 427, 530 (2004).

H of LVZ(km) 20 70 90 90 Topo (km) 20 20 60 60

Results

Song et al., Nature 427, 530 (2004).

Patches:White: no detected LVZRed with dashed outline: a possible LVZRed with solid outline: clear LVZdots: (receiver functions)White: no negative pulse above 410 and

relative strong simple 410 peaksRed: strong negative pulse above 410

119o~115oW 41.5o 40.2o

116o~114oW 38.9o 37.5o

Preferred model 20~90 km thick with 5% S-wave velocity reduction

Interpretation

Bercovici and Karato, Nature 425, 39 (2003).

high Water solubility

lowWater solubility

lowWater solubility

Additional Thoughts

Which one is the best-fit velocity model?

ALVZ atop the 410 exists in some regions but may be too thin to be detected.

Is there a possibility of detecting the LVZ with short-period data?