Seattle Fault Restoration Point Former sea cliff Present ...earthweb.ess.washington.edu/brown/downloads/ESS403... · Event 1000 >2000 3000 Main T 8 T 14 Lake Washington Event Timeline

Restoration Point!

Restoration Point!

Former sea cliff!

Raised wave-cut

terrace!

Present terrace!

Seattle Fault!

Seattle fault uplift

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N-S contraction drives

uplift and basin formation

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-! =8!*2,9!'(>!*2359?&2#*!$0@*)!59*!82&/5!.!$A!59*3*!$&%5!92@*!'**+!-66!*@*+5%!(+!59*!/2%5!$(//(0+!1*23%<!

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Restoration

Point

1998 trenches

1999 trenches

Mossy Lane

Toe Jam Hill fault scarp

12-ft lidar DEM

WEST POINT West Point Sewage Treatment Plant construction excavation

“Snags” in Lake Sammamish: 1100 years old

Conclusions

•! An event that would have had catastrophic

consequences occurred about 900 AD.

•! Individual faults have long recurrence times

(1000’s of years).

•! Many active faults are known and more are

being identified.

•! Jury still out on how often we can expect a

devastating crustal quake.