1. Low-velocity zone atop the 410-km seismic discontinuity in the northwestern United States T.-R.A. Song, D.V. Helmberger, S.P. Grand Nature 427, 2004 Pei-Ying Patty Lin Earthscope Seminar, Feb.12, 2007

2. DATA Song et al., Nature 427, 530 (2004). XL XK XM TriNet

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

4. Profile A(d:14~17 o ) Song et al., Nature 427, 530 (2004). Thickness of LVZ(km) 0 40 20 Topography depression(km) 60 0 20 TriNet

5. Triplication curves Song et al., Nature 427, 530 (2004). record section B record section A

6. Profile C,F,D,E(d:21~24 o ) Song et al., Nature 427, 530 (2004). H of LVZ(km) 20 70 90 90 Topo (km) 20 20 60 60

7. Results Song et al., Nature 427, 530 (2004). Patches: White: no detected LVZ Red with dashed outline: a possible LVZ Red with solid outline: clear LVZ dots: (receiver functions) White: no negative pulse above 410 and relative strong simple 410 peaks Red: strong negative pulse above 410 119 o ~115 o W 41.5 o 40.2 o 116 o ~114 o W 38.9 o 37.5 o Preferred model 20~90 km thick with 5% S-wave velocity reduction

8. Interpretation Bercovici and Karato, Nature 425, 39 (2003). high Water solubility low Water solubility low Water solubility

9. Additional Thoughts  Which one is the best-fit velocity model?  A  LVZ 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?