1. Mark Petersen, Arthur Frankel, Steve Harmsen, and Gavin Hayes
Key scientific issues for Pacific NW region in the next version of the U.S. National Seismic Hazard Maps
Mark Petersen, Arthur Frankel, Steve Harmsen, and Gavin Hayes
U.S. Geological Survey
Golden, CO and Seattle, WA

2. Scientific research and information Products
Earthquake sources
Wave propagation (linear and nonlinear)
Fault interaction, triggering,
Episodic Tremor and Slip
Earthquake monitoring,
Ground-motion studies
Crustal deformation studies
Paleoseismology, LIDAR, geologic mapping
Potential field mapping
Seismic reflection, refraction, surface wave, tomography, geotechnical, borehole studies
Products
National seismic hazard maps
Urban seismic hazard maps
Site-specific PSHA
Scenario ground motion maps
Shakemaps
Loss estimation (e.g. PAGER)
Earthquake forecasts
Synthetic seismograms
Liquefaction, landslide,
and surface rupture hazard maps
Applications
Seismic provisions in building codes
Seismic design
Seismic retrofit
Emergency preparedness and management
Early warning
Land-use planning
Earthquake insurance

3. Probabilistic Seismic Hazard Methodology Example
Earthquake Sources b a
Ground motion
Hazard curve r1
M 7.6 d1 d4
annual probability of exceeding pga r2 d2
peak ground acceleration
M7.6 d3
high seismicity
zone
San Andreas fault
distance
0.25g
0.5g
peak ground acceleration (pga) r3
Specify recurrence
rates of earthquakes
for each source that
can affect site of
Interest
Time independent
or time dependent
Attenuation relations
tell you median ground
motions that each potential earthquake will produce at site, and variability
Hazard curve:
describes probability
of having ground motions
≥ a certain intensity

4. From National Seismic Hazard Maps to Building Codes
USGS develops national seismic hazard maps with input from external community
Building Seismic Safety Council develops design procedure to apply to hazard maps, published in 2009 NEHRP Provisions (FEMA)
International Code Council adopts design procedures for 2012 IBC and IRC
(also adopted in
ASCE )
Early Pacific NW Workshop
Advisory Committee
Special workshops (e.g., turbidite data – 2010 and depth of seisogenic zone )
Merging of
UBC, SBC and
BOCA codes
into IBC
Engineers choose design criteria (1997 and 2009)

5. Source models for the National Seismic Hazard Maps
Earthquake Sources Where do earthquakes occur and how often?
Earthquake catalogs
(instrumental and
historical)
Geologic mapping, fault slip rates
EQ chronologies from paleoseismology
potential fields, seismic reflection/refraction
Source models for the National Seismic Hazard Maps
Photo from Nelson et al. (2003)
From McCrory (2004))
Cedar trees killed by subsidence from the
1700 Cascadia subduction zone earthquake.
Crustal velocity
measurements (GPS)
Core samples from turbidites in abyssal plain
Photo from Brian Atwater
From Zeng and Shen
From C. Goldfinger

6. Earthquake Ground motions
Subduction interface ground motions
Western Pacific GSN
Strong Ground motion
BC Hydro developing new equations (forearc and backarc relations)

7. National Seismic Hazard Mapping Project involved in
hazard analysis in many coastal areas of the U.S. and world
American Samoa
Alaska
Hawaii
Conterminous U.S.
Alaska

8. Cascadia Subduction Zone: What are the gaps in knowledge
Cascadia Subduction Zone: What are the gaps in knowledge? What are the critical research issues?
Fault geometry and Seismogenic depths
Earthquake sizes and recurrence rates
Ground motions

9. Crustal Sources Olympia fault (no recurrence info)
Tacoma fault
Olympia fault
Olympia fault (no recurrence info)
Tacoma fault (event 1100 years ago)
Other?
South Whidbey Is. fault
Seattle fault

10. Subduction Zone Source Geometry and Seismogenic Depth
Location of the subducting slab (seismic reflection data, low level seismicity e.g., McCrory et al.)
Shallow dip – few large earthquakes
Determine location of coseismic rupture extent (e.g., episodic tremor and slip (ETS) events dissipate % stress accumulation below 25 km (Chapman and Melborne, 2009), thermal models of 350° isotherm (Fleuck et al., 1997); geodetic models (McCaffrey et al, 2007), Chile earthquake extends down 55 km (Hayes, 2009).

11. Using Slab1.0 to Infer Seismogenic Width
Seismogenic width is measured between
inferred shallow and deep limits, along the 3D SZ geometry (rather than assuming linear
geometries from gCMT dips, which show ~10o
bias toward steeper dips, thus causing an underestimation of Sw).
Slide from Gavin Hayes

12. Improvements Offered From Regional Data
Adding double-difference relocated EQ data set from Fuis et al., 2008.
Slide from Gavin Hayes

13. New Research on Cascadia Subduction Source Recurrence
Chris Goldfinger (SSA 2010): 19 events define full ruptures indicating a northern Cascadia margin Holocene recurrence rate of ~500 years; 41 events define a Holocene recurrence for the southern Cascadia margin of ~240 years, currently we apply a 500 year recurrence for full ruptures and additional smaller ruptures. We may want to separate the northern and southern and also to compare off-shore and onshore recurrence.

15. Research Priorities determined at Workshop
Looking at more onshore sites for evidence of M8’s
More core locations for turbidites (Hydrate Ridge to Rogue)
Tracking turbidites with chirp data
Alternative correlation possibilities
How much ground motion does it take to trigger turbidites? Can M7’s do it?
More research into segmentation using uplift and GPS data

16. Issues for the 2013 National Seismic Hazard Maps in Pacific NW
Cascadia subduction zone source model
Recurrence for southern segments? Northern segments?
Clustered behavior?
Geometry (seismicity)? Location of seismogenic layer?
Cascadia subduction zone ground motion models
New data (Chile, Japan, Indonesia)
Other published relations (Kanno et al., Gregor et al.)
Adjustments for longer distances to current equations
Crustal faults
Yakima fold and thrust belt (published slip rates?)
Olympia (evidence of recurrence?)
Tacoma (relationship to Seattle fault?)
Little Salmon (does this rupture simultaneously with Cascadia)
Geodetic models
Update earthquake catalog

17. Conclusions: Questions we need to answer for updating the hazard maps
What do historic large earthquakes teach us about future earthquakes (sizes, locations)? Do these earthquake rupture in one event or clustered? Can we segment faults? Are segment boundaries persistent? What sizes of earthquakes can we expect on a structure?
What is the ground shaking from interface, inslab, deep, and outer rise earthquakes?
Why do these types of earthquakes occur in some areas and not others? (e.g., absence of deep earthquakes beneath Oregon, outer rise events?)
Can we determine seismogenic sections of subduction zones using ETS events, heat flow, seismicity?
Can Accretionary Wedge Sources rupture in large earthquakes? (M New Hebrides in wedge)
Can we quantify strike-slip faults offshore for use in PSHA (e.g., S. CA – San Clemente)

18. Wish List; Improving Slab1.0
i) More active seismic lines which image
shallow SZ geometry.
ii) Point measurements of SZ depth - e.g. Receiver Functions.
iii) Regional earthquake catalogs; preferably relocated.
iv) Independent measurements of SZ coupling - e.g. models derived from GPS data.
Slide from Gavin Hayes

19. Using Slab1.0 to Infer Moment-Release Rate
Analyzing patterns in moment release can tell is vital information about earthquake cycles.
Do background rates vary leading up to, or following mega-thrust earthquakes?
What do areas of low moment release mean? High hazard, or low?
Do moment release rates correlate with oceanic plate structure, upper plate structure, etc? What causes such along- strike variability?
Freymueller, et al. 2008
Amlia Fracture Zone
Slide from Gavin Hayes

20. Conclusions
New recurrence rates on Cascadia – how many additional M 8 earthquakes should we include in the model?
Potential time-dependent (renewal and cluster models) branches in logic tree
Geodetic block models and strain-rate models in addition to geologic models.
New ground motion prediction equations on subduction zone and crustal faults

21. Logic tree applied to National Seismic Hazard Maps 2008