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David Schmidt Ray Weldon Reed Burgette Randy Krogstad Haiying Gao

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Presentation on theme: "David Schmidt Ray Weldon Reed Burgette Randy Krogstad Haiying Gao"— Presentation transcript:

1 The accumulation and release of interseismic strain on the Cascadia Subduction Zone
David Schmidt Ray Weldon Reed Burgette Randy Krogstad Haiying Gao Department of Geological Sciences University of Oregon Funding provided by USGS NEHRP

2 Talk Overview Sources of deformation on the plate interface
Making observations of deformation Strain accumulation Transient release of strain (Safer and Tobin, 2011) Graphic: Hyndman & Wang (1995)

3 Deformation in Cascadia
Coast moves east and up between earthquakes. Coast moves west and down during earthquakes. Graphic: Leonard et al. (2009)

4 Observations of Interseismic Deformation
Uplift rates from spirit leveling Observations span 1930-present. Uplift referenced to eustatic sea level. 1- uncertainties ~0.5 mm/yr. Differenced Tidal Records, CC-AS 1940 1960 2000 1980 year Sea level (m) -0.25 0.25 (Burgette et al., JGR, 2009) Uplift (mm/yr)

5 Observations of Interseismic Deformation
Uplift rates from spirit leveling Observations span 1930-present. Uplift referenced to eustatic sea level. 1- uncertainties ~0.5 mm/yr. Uplift rate (mm/yr) West East East from 20-km-depth slab contour (km) (Burgette et al., JGR, 2009) Uplift (mm/yr)

6 Horizontal Observations of Interseismic Deformation
Horizontal GPS Velocities from PBO data products and McCaffrey et al. (2007). Limited to stations with data for > 2 years

7 Horizontal Observations of Interseismic Deformation
Rotation of Oregon Removed (pole of McCaffrey et al., 2007) Original Velocity Field

8 Horizontal Observations of Interseismic Deformation
50 150 100 Compressional Strain Rate (nanostrain/yr) Rotation of Oregon Removed (pole of McCaffrey et al., 2007) Original Velocity Field

9 Modeling Methodology Fixed parameters Defined Convergence rate
JDF-OCR Euler pole for the southern end (Wells & Simpson, 2001). JDF-NA Euler pole for the northern end (Mazzotti et al., 2003) Plate geometry of McCrory et al. (2006). Upper edge of locked zone begins at trench.

10 Modeling Methodology Fixed parameters Defined Convergence rate
JDF-OCR Euler pole for the southern end (Wells & Simpson, 2001). JDF-NA Euler pole for the northern end (Mazzotti et al., 2003) Plate geometry of McCrory et al. (2006). Upper edge of locked zone begins at trench. 5 15 25 1 2 3 4 Depth of Slab (km) Slip Rate Deficit (cm/yr) Down-Dip Locking Backslip calculation (Savage, 1983). Free parameters Depth of locking; Depth of transition zone. Optimization by grid search of parameter space Step 1: Depths constrained along west-east leveling profiles (fit both uplift and strain). Step 2: Optimize along-strike locking with entire dataset. Graphic: Geological Survey of Canada

11 Depth of transition zone (km)
Slip Rate Deficit (cm/yr) 35 25 4 Depth of transition zone (km) Narrow Transition Zone 15 3 Narrow Locked Zone 5 5 15 25 35 2 Depth of locked zone (km) Misfit (χ2) 1 1 3 5 7 9 11 Combined inversion (uplift and strain) Data misfit weighted by data uncertainties

12 Misfit for combined Leveling & Horizontal Strain
Slip Rate Deficit (cm/yr) 4 3 2 5 15 35 25 1 Misfit (χ2) 1 3 5 7 9 Depth of transition zone (km) 11 Depth of locked zone (km)

13 Observed Predicted Residual Uplift (mm/yr) | Misfit | (mm/yr)

14 Compressional Strain Rate (nanostrain/yr)
Observed Strain Rate Predicted Strain Rate 50 150 100 Compressional Strain Rate (nanostrain/yr)

15 Episodic Tremor and Slip (ETS)
Transient slip on the plate interface Accompanied by emergent tremor Located km depth Recurrence months Magnitude ~6 Lohman (2010)

16 2007 Slow Slip Event estimated slip (cm) east (mm) east (mm) east (mm)
KTBW east (mm) P423 east (mm) KTBW P423 P420 P420 east (mm) time (days) estimated slip (cm)

17 2007 Slow Slip Event KTBW predicted east (mm) P423 east (mm) Nucleation point centered beneath Puget Sound. Northward propagation resolved by GPS data. 4 cm peak amplitude, Mw≈6.8. P420 east (mm) time (days) estimated slip (cm)

18 Consecutive Slow Slip Events
Slip rate (mm/day) 3 2 1

19 Slow Slip and Tremor in Oregon
5 4 3 2 1 Slow Slip (cm) Slow Slip and Tremor in Oregon Slip inferred from GPS time series Mosaic of events (June 2007, May 2008, August 2009) Tremor from Boyarko and Brudzinski (2010)

20 Slip Rate Deficit (cm/yr)
5 4 3 2 1 Slow Slip (cm) 3 2 1 Slip Rate Deficit (cm/yr)

21 Newport Leveling Profile
5 4 3 2 1 Slow Slip (cm) Newport Leveling Profile coastline West East Locked ETS Zone Transition Zone 3 2 1 Slip Rate Deficit (cm/yr) Figures by Randy Krogstad (UO)

22 5 4 3 2 1 Slow Slip (cm) Summary A Cascadia locking model constrained by leveling and horizontal strain rates from GPS. Wide locked zone in WA and CA; Narrow in OR. Mo Accumulation Rate: x1022 Nm/century Mw Accumulation Rate: per century Spatial separation of locked and ETS zones in OR. <10% long term locking in ETS zone 3 2 1 Slip Rate Deficit (cm/yr)

23

24 BC WA OR CA Holtkamp and Brudzinski (2010)

25 Seismic Moment Rate (1018 Nm/yr)
10 20 30 40 1 2 3 4 Slip Rate Deficit (cm/yr) Position of 1 cm/yr slip rate deficit contour (% of models) 1000 800 600 North (km) 400 200 2 4 6 Seismic Moment Rate (1018 Nm/yr)

26 Slip Rate Deficit (cm/yr) 4 3 2 1
Horizontal GPS Observations and Predictions Slip Rate Deficit (cm/yr) 4 3 2 Leveling Observations and Predictions 1

27

28 Compressional Strain Rate
Strain Rate from Original GPS Strain Rate from GPS w/ rotation removed 50 150 100 Compressional Strain Rate (nanostrain/yr)

29 Observations of Interseismic Deformation
Elevation (m) Uplift rate (mm/yr) West East East from 20-km-depth slab contour (km) (Burgette et al., JGR, 2009) Uplift (mm/yr)

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