San Gorgonio Pass Special Fault Study Area
Whitney Behr, Kim Blisniuk, Jim Brune, Sarah Carena, Judi Chester, Gary Fuis, Thomas Goebel, Peter Gold, Egill Hauksson, Dick Heermance, Katherine Kendrick, Vicki Langenheim, Nat Lifton, Jon Matti, Sally McGill, Craig Nicholson, Mike Oskin, Kate Scharer, Warren Sharp, Zheqiang Shi, Kerry Sieh, Josh Spinler and Mike Rymer.
Michele Cooke, David Oglesby and Doug Yule
2 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Small region within a large system
The San Gorgonio Pass comprises the southern Big Bend of the San Andreas fault
Field et al., 2014, UCERF3
3 San Gorgonio Pass SFSA, SCEC annual meeting 2015
The San Gorgonio Pass
(modified from McGill et al., GSA Bull. 2013)
4 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Guiding questions
§ What is the subsurface geometry of active faulting through the San Gorgonio Pass?
§ What is the earthquake potential in the San Gorgonio Pass?
§ What is the probability of a through-going San Andreas rupture?
5 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Time line of activity
Start of SCEC4
end of SCEC4
2012 2013 2014 2015 2016
2015 annual meeting
1 day workshop54 participants
2 dayWorkshop
33 participantsEstablished as one of two SFSA
Gold et al.JGR
McGill et al., JGR
Goebel et al., JGI
Kendrick et al.,
JGR
CFM v.5Plesch
et alMcGillet al.,
GSA BullCFM v.4Nicholson
et al.Herbert, Cooke & Marshall,
JGR
Many future papers
6 San Gorgonio Pass SFSA, SCEC annual meeting 2015
geology
geophysics
seismicity Geodesy
Crustal deformation
models
Dynamic rupture models
Data and tools
NicholsonHaukssonGoebelCarena
Behr, Blisniuk, Brune, Chester, Gold, Heermance, Kendrick, Lifton, Matti, McGill, Oskin, Scharer, Sharp, Sieh, Rymer, Yule
SpinlerMcGill
Cooke
Shi, Day,Oglesby,Tarnowski
FuisLangenheimOglesby
7 San Gorgonio Pass SFSA, SCEC annual meeting 2015
What is the active geometry of faults?
§ SSIP seismic line 6 crosses within the SGP SFSA
§ Reveals multiple NE dipping strands of the San Andreas
Fuis, Bauer, Goldman, Ryberg, Langenheim, Scheirer, Rymer, Stock, Hole and Catchings, submitted
8 San Gorgonio Pass SFSA, SCEC annual meeting 2015
What is the active geometry of faults?
Crafton Hills complex
blind, oblique en echelon faults
San Andreas-Banning strand
Mill Creek strand
Mission Creek strand
Garnet Hill strand
San Gorgonio Pass thrust
North Palm Springs fault
blind Palm Springs fault
Pinto Mountain fault SGP detachments
North Frontal Thrust fault North Frontal Deep detachment
San Jacinto fault zone
Increasing fault complexity in SGP & adjacent areas defined by seismicity
CFM 5.0 Updated 3D Fault Set
Nicholson, Plesch and Hauksson
9 San Gorgonio Pass SFSA, SCEC annual meeting 2015
What is the active geometry of faults?
10 San Gorgonio Pass SFSA, SCEC annual meeting 2015
2015
]
Mc Gill et al., 2015
McGill, Spinler et al., unpublished
How is slip partitioned?
11 San Gorgonio Pass SFSA, SCEC annual meeting 2015
How is slip partitioned? § Variable slip rates along the San
Andreas through the San Gorgonio Pass.
§ Mechanical models match this variability
(modified from Herbert & Cooke, BSSA 2012)
data gap
(McGill et al., GSA Bull. 2013)
(McGill et al., in prep)
12 San Gorgonio Pass SFSA, SCEC annual meeting 2015
How is slip partitioned?
§ Active strands • Mill Creek-Mission Creek • Banning-Garnet Hill
(Gold, Behr et al., JGR 2015)
13 San Gorgonio Pass SFSA, SCEC annual meeting 2015
How is slip partitioned? Mill Creek strand
§ No offset of Holocene/Latest Pleistocene alluvial deposits at Upper Raywood Flats
§ The Pinto Mountain fault offsets the Mill Creek strand
(Kendrick et al., JGR. 2015)
(Kendrick et al., JGR. 2015)
14 San Gorgonio Pass SFSA, SCEC annual meeting 2015
How is slip partitioned? The Mill Creek strand § Lidar scarp analysis suggests that slip may
by-pass upper Raywood flats via the Galena Peak fault.
§ Fault kinematics consistent with slip transfer
(Morelan, Oskin, Chester and Elizondo, in prep)
Galena Peak fault
Subsidiary Fault Kinematics
Mission Creek FaultN N
NPoles to Faults Slip Vectors
B-Axes
n=15 n=5
n=5
Mission Creek fault
N N
NPoles to Faults Slip Vectors
B-Axes
n=90 n=43
n=43
Raywood Flat Area
N N
NPoles to Faults Slip Vectors
B-Axes
n=290 n=199
n=199
Transfer Fault
N
Poles to Faultsn=458
N
Slip Vectorsn=265
N
B-Axesn=265
East of Mill Creek Fault BendN
Poles to Faultsn=107
n=79
N
B-Axes
N
Slip Vectorsn=79
West of Mill Creek Fault Bend
Mill Creek fault
Transfer fault RaywoodFlat
Mission Creek fault
MFJOMCJO
FaultBend
15 San Gorgonio Pass SFSA, SCEC annual meeting 2015
How is slip partitioned? The Banning Strand
§ Offset alluvial fan reveals relatively slow slip rates ~(4-5 mm/yr) along the Banning fault
§ Slip rate at SE end of Indio Hills (Scharer) is also 2-6 mm/yr
Holocene rate: 3.9+2.3/-1.6 to 4.9+1.0/-0.9 mm/yr
Gold, Behr et al., JGR 2015
16 San Gorgonio Pass SFSA, SCEC annual meeting 2015
How is slip partitioned?: Banning strand & San Gorgonio Pass thrust
Heermance and Yule, in prep
17 San Gorgonio Pass SFSA, SCEC annual meeting 2015
0.6 to 0.9 km offset since 25 +5/-4 ka: 27 +8/-6 mm/yr
1.3 to 1.7 km offset since 69 +2/-2 ka: 22 +3/-3 mm/yr
2.1 to 2.4 km offset since 88 +11/-7 ka: 25 +4/-3 mm/yr
Mission Creek strand: 22-25 mm/yr (~90 ka, ~70 ka, & ~25 ka)Banning strand: 4-6 mm/yr since ~6ka
Blisniuk, Scharer, Sharp, Burgmann in prep
How is slip partitioned?: The Mission Creek strand
18 San Gorgonio Pass SFSA, SCEC annual meeting 2015
How is slip partitioned? effect of active Mill creek
§ Strike slip is transferred to the Mill Creek strand. • San Jacinto and Banning have slower slip rates
Mill Creek not in model Mill Creek slipsNo slip
τ
slip
τ
Cooke, in prep.
19 San Gorgonio Pass SFSA, SCEC annual meeting 2015
0 20 40 60 80 100 120 140 160 1800
5
10
15
20
25
30
distance from Cajon pass (km)
dext
ral s
lip (m
m/y
r)
0 20 40 60 80 100 120 140 160 1800
5
10
15
20
25
30
distance from Cajon pass (km)
dext
ral s
lip (m
m/y
r)
How is slip partitioned? effect of active Mill Creek
Slip partitioning is sensitive to active fault geometry through the pass
San BernardinoBanningMill Creek – Mission Creek
Coachella
Cooke, in prep.
? ?
?
???
20 San Gorgonio Pass SFSA, SCEC annual meeting 2015
What is the stress state?
§ Insights from microseismicity • Large stress drops within
the San Gorgonio Pass
Goebel et al., JGR 2015
21 San Gorgonio Pass SFSA, SCEC annual meeting 2015
−117.5˚ −117˚ −116.5˚
34˚
34.5˚
35˚
−117.5˚ −117˚ −116.5˚ −117.5˚ −117˚ −116.5˚
What is the stress state? § Insights from crustal deformation models
• Off-fault deformation matches better the stress inversions from focal mechanisms than interseismic stressing rates
Interseismicstressing rate
Off-faultstressing rate
Focal Mechanisms
Yang et al 2012
Mean Normal StressCompressive <->Tensile
Cooke, in prep.
22 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Correlation to stress drops in SGP
Goebel et al., JGR 2015Mean Normal Stress
Compressive <->Tensile
Off-fault stressingRegions of large stress drops correlate with compressive mean stress of off-fault deformation Stress drop may relate to fault geometry rather than material contrast at step in base of seismicity
Depth =5km
Depth =11km
Depth =17kmGoebel et al., JGR 2015
23 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Can earthquakes rupture through the Pass? Paleoseismology
• Only 4 earthquakes in 5500 years• Complex slip patterns: 0.5 – 2.5 m uplift in single event
• Most recent event was ~1400 A.D.
Yule, Scharer in prep
The Cabazon MEGA trench
~0.5 m uplift; ~1 m slip
24 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Can earthquakes rupture through the Pass? Dynamic rupture
San Bernadino Section
San Jacinto Fault
Elsinore Fault
Coachella Section
Banning Strand
San And
reas F
ault
x1
x2x3 planar free surface ( x2 = 0 )
0
−10
−20(km)
rupture nucleation centers north and south of SGP
10 20 30 40 50 60 70 80 90 100 110 120 130 140 150 160 170 180 190 200 (km)
San Bernadio Segment Coachella Valley Segment
0.0 0.5 1.0 1.5 2.0 2.5 3.0Aφ [AU]
normal | strike-slip | reverse full stress tensor, mean of van Mises stress: ⟨σvM⟩ = 8.5e-01 AUsticks: horizontal projection of most compressive eigenvector, e3, length scaledadditionally with σvMbackground shading: stress, Aφ of Simpson (JGR, 102, 17909, 1997)
SCEC CSM, v. 0.1 - made with GMT - twb-at-usc-dot-edu -090613
Hardebeck_FM @ 3 km-122˚ -121˚ -120˚ -119˚ -118˚ -117˚ -116˚ -115˚ -114˚
32˚
33˚
34˚
35˚
36˚
0
10
20
30
40
N/N
0 [%
]
-90 -45 0 45 90
e3 azimuth, ⟨α⟩ = 7.2 [o]
SCEC CFM-v5
0.0 0.5 1.0 1.5 2.0 2.5 3.0Aφ [AU]
normal | strike-slip | reverse full stress tensor, mean of van Mises stress: ⟨σvM⟩ = 1.5e+00 AUsticks: horizontal projection of most compressive eigenvector, e3, length scaledadditionally with σvMbackground shading: stress, Aφ of Simpson (JGR, 102, 17909, 1997)
SCEC CSM, v. 0.1 - made with GMT - twb-at-usc-dot-edu -090613
Yang @ 3 km-122˚ -121˚ -120˚ -119˚ -118˚ -117˚ -116˚ -115˚ -114˚
32˚
33˚
34˚
35˚
36˚
0
10
20
30
40
N/N
0 [%
]
-90 -45 0 45 90
e3 azimuth, ⟨α⟩ = 9.4 [o]
Candidate SCEC CSMs as Reference of Stress Input
• The initial stress field dominates rupture behavior, compared other factors including small-scale fault geometric complexities.
• Different stress models in their present forms will lead to vastly different rupture scenarios regarding the likelihood of through-going rupture along SGP.
Artificial band-limited roughness superposed on fault
0.0 0.5 1.0 1.5 2.0 2.5 3.0Aφ [AU]
normal | strike-slip | reverse full stress tensor, mean of van Mises stress: ⟨σvM⟩ = 1.3e+02 AUsticks: horizontal projection of most compressive eigenvector, e3, length scaledadditionally with σvMbackground shading: stress, Aφ of Simpson (JGR, 102, 17909, 1997)
SCEC CSM, v. 0.1 - made with GMT - twb-at-usc-dot-edu -090613
SHELLS @ 3 km-122˚ -121˚ -120˚ -119˚ -118˚ -117˚ -116˚ -115˚ -114˚
32˚
33˚
34˚
35˚
36˚
0
10
20
30
40
N/N
0 [%
]
-90 -45 0 45 90
e3 azimuth, ⟨α⟩ = 7.2 [o]
0.0 0.5 1.0 1.5 2.0 2.5 3.0
Aφ [AU]
normal | strike-slip | reverse full stress tensor, mean of van Mises stress: ⟨σvM⟩ = 1.1e+02 AU
sticks: horizontal projection of most compressive eigenvector, e3, length scaled
additionally with σvM
background shading: stress, Aφ of Simpson (JGR, 102, 17909, 1997)
SCEC CSM, v. 0.1.2 - made with GMT - twb-at-usc-dot-edu -042115
FlatMaxwell @ 3 km-122˚ -121˚ -120˚ -119˚ -118˚ -117˚ -116˚ -115˚ -114˚
32˚
33˚
34˚
35˚
36˚
0
10
20
30
40
N/N
0 [%
]
-90 -45 0 45 90
e3 azimuth, ⟨α⟩ = 9.7 [o]
Shi and Day
25 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Can earthquakes rupture through the Pass?
§ Ruptures starting on the Banning strand can pass to the San Bernardino strand
§ Ruptures from the San Bernardino strand are less likely to pass to the Banning.
Tarnowski and Ogelsby
Tarnowski, Kyriakopoulos, and Oglesby
26 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Can earthquakes rupture through the Pass?
§ Ruptures starting on the Banning strand can pass to the San Bernardino strand
§ Ruptures from the San Bernardino strand are less likely to pass to the Banning.
Tarnowski, Kyriakopoulos, and Oglesby
27 San Gorgonio Pass SFSA, SCEC annual meeting 2015
San Gorgonio Pass SFSA outcomes § Some but not all ruptures can
pass through the SGP as large events.
§ The region hosts slow slip rates, low strain rates and unusually high stress drops, which owe to fault geometry.
§ Activity distributed among multiple strands rather than along one dominate structure.
§ Cross-disciplinary discussions and collaborations
§ Leveraging for projects funded by USGS and NSF.
28 San Gorgonio Pass SFSA, SCEC annual meeting 2015
Thank you!
Photo along the Mill Creek strand of the San Andreas fault
