1. Brief summary of Seattle URM Policy Committee actions

2. Recent inventory of Seattle URM’s by Nancy Devine; about 1160 URM’s
Debate about cost-benefit studies
Bolts-plus, life safety retrofit
Final meeting of URM Policy Committee was April 4 (Policy Committee started in 2012; Technical Committee 2008)
Staff is writing final report of Committee to be reviewed by Committee and then go to Mayor and City Council (initial report was in 2013)
Recommends city ordinance for retrofit; provides different timelines for retrofit depending on factors such as purpose of building, number of stories, soil condition, number of occupants (7-13 year timeline for completion)
Various funding options and incentives considered; list provided in report

3. Derived from 3D Ground-Motion Simulations
Broadband Synthetic Seismograms for Magnitude 9 Earthquakes on the Cascadia Megathrust
Derived from 3D Ground-Motion Simulations
A. Frankel1, E. Wirth2, J. Vidale2, W. Stephenson1, N. Marafi2 1U.S. Geological Survey 2University of Washington PNSN RAC meeting May 23, 2017

4. The M9 Project: University of Washington funded for 4 years by NSF USGS is collaborating with UW in producing broadband (0-10 Hz) synthetic seismograms for M9 Cascadia earthquakes; considering a range of rupture scenarios
Assessment
of Hazard, including
uncertainties
Assessment of Impact
Evaluation of tall building response and
damage from long-duration, long-period ground shaking (Berman, Eberhard, Marafi)
Evaluation of landslides and liquefaction
from ground shaking (Duvall, Wartman, Kramer, Greenfield, Grant)
Evaluation of tsunami effects on structures
near coast (Motley, LeVeque, Gonzalez)
Development of Shakemaps and tsunami-
Inundation maps for emergency management, improving community resilience (Bostrum, Abramson)
Testing of Earthquake Early Warning (Vidale, Bodin)
Synthetic seismograms
produced from 3D simulations
of M9 Cascadia earthquakes
(Frankel, Wirth, Marafi)
Tsunami simulations for M9
Cascadia earthquakes
(Gonzalez, LeVeque)
Supercomputer time provided
by Pacific Northwest National
Laboratory and Texas Advanced
Computing Center, University of Texas

5. see SSA poster by Thompson et al.
Bill Stephenson developed the 3D velocity model for Cascadia. Used seismic refraction/refraction data and tomography for Seattle basin, Moschetti et al. (2010) crustal tomography, McCrory et al., plate interface ;
Seattle basin model was validated by modeling waveforms and basin amplification of
M6.8 Nisqually earthquake and other local earthquakes (Frankel et al., 2009); also
see SSA poster by Thompson et al.
100 m grid spacing in top 5 km
300 m horizontal spacing 5-60 km depth N S
1100 km
550 km
Minimum Vs= 600 m/s,
Similar to surficial glacial sediments
Figure from Delorey et al. (2014)

6. Background slip
Ave slip velocity= 0.65 m/s
Max rise time 25 s
Deeper, high stress drop M8.0 sub-events (asperities)
Ave slip velocity = 5.4 m/s
Max rise time 1.5 s
Mw 9.0 compound
rupture model
based on modeling
strong-motion records
of Mw 9.0 Tohoku, Japan
and Mw 8.8 Maule, Chile
earthquakes (Frankel,
2013, 2016) and
Mw 8.3 Tokachi-Oki
earthquake (Wirth et al.)
For most
Cascadia cases,
sub-events
dominate
ground
motions for
periods less
than 8 s
Sources are additive; rupture proceeds from same hypocenter
for the background and sub-events

7. M9 CSZ Simulation Results
Movie by Nasser Marafi, UW
Seattle
Snoqual
mie
Portland
Medford
300 second simulation

8. Northern hypo; easternmost downdip edge 200 bar sub-events
Broadband (0-10 Hz) synthetic seismograms from one of the M9 simulations
Combines 3D simulations (≤ 1 Hz) with stochastic synthetics ( ≥1 Hz) using matched filters
0.2 g
Black: NS
Red: EW
Green UD
0.6g
0.4g
091316r10 run
Northern hypo; easternmost downdip edge
200 bar sub-events

9. m
Map of 3 second
spectral acceleration (g)
From run
Hypo at 43.0N 125W
Middle choice for downdip
Edge
Synthetics from simulations
are saved on
a grid with spacing of 1 km m

10. “Logic Tree” for M9 simulations we will do 50 simulations to sample logic tree and assess sensitivity to rupture parameters
Down-dip
edge of rupture

11. Hypo near northern sub-event
Easternmost choice of
downdip edge
Sites in Seattle and Tacoma basins
3 second response
Spectral accelerations
From 2 M9 simulations
(blue and red crosses)
With BC Hydro prediction
And observations from
Maule earthquake for
Close-in stations
11,000 points, 4 km grid spacing
Sites in Seattle and Tacoma basins
Hypo at trench; lat. of Seattle
Mid choice for downdip edge

12. Amplification of response spectra at Seattle Basin sites relative to site outside of basin
Observations from 2001 Satsop earthquake and results from M9 simulations
Uses geometrical average of SA from 2 horizontal components; similar vs30’s inside and
outside basin. Basin amplifications are higher than found from crustal earthquakes.
Approx. basin amp term from Campbell and Bozorgnia (2013)
Crustal earthquakes, Z2.5= 6.5 km

13. ground motions < 8 s dominated by sub-events
Relatively bad and good scenarios for Seattle. Both scenarios use same background slip
ground motions < 8 s dominated by sub-events
Forward rupture directivity affecting
Seattle region
Rupture not directed toward
Seattle region
Same background
slip used for both cases
M8.0 sub-events
M8.0 sub-events “

14. in simulations done to date
Response spectra for Seattle basin site from better and worst-case scenarios
in simulations done to date
compared to design spectrum (MCEr) used in new 40 story building in Seattle
“worst case”
Better case

15. Take Home Points
Basin amplification: Finding Seattle basin amplification larger than that found in empirical study of crustal earthquakes in other regions (NGA West 2). Factor 2-4 compared to factor of 1.5 (relative to rock site just outside basin); Basin-edge generated Rayleigh wave causes much of basin amplification at 1-3 s. Basin amplification depends on azimuth of incoming energy and rupture directivity.
Inter-event variability and uncertainty: Synthetic response spectra (1-10 s) are sensitive to hypocenter, slip distribution, location of sub-events (asperities) and down-dip edge of rupture. Factor of 4 variation in response spectra (1-10 s) observed for different sub-event slip and hypocenters.
Stay Tuned for the results from all 50 simulations; synthetics will be available via Design Safe at University of Texas (TACC)

17. Guess the M9 synthetics (SP2) and actual records from Maule and Tohoku at comparable distances
Velocity waveforms ( Hz)
m/s
Time (s)

18. Guess the M9 synthetics (SP2) and actual records from Maule and Tohoku at comparable distances
Velocity waveforms ( Hz) M9 M9 M9 M9
m/s
Maule EQ, CRMA near Santiago
Tohoku EQ, MYGH12 EW
Time (s)