Slip Rates

UCERF2 Deformation Model
Can we do better in UCERF3?
- Large number (> 50%?) of faults in UCERF2 model
characterized as having “poorly-constrained”, “unconstrained”,
“assumed” slip rates.
- UCERF2 used expert-opinion slip rates. Uncertainties are
generalized (1/4 of slip rate for well-constrained slip rates, ½ for
poorly-constrained rates).
- A significant number of Quaternary active faults with no slip
- Geodesy used to “inform” assigned slip rates in a number of
areas, but not done systematically for entire State.
Geologic slip rate characterization
- Examine database for slip rate biases. Are generalized 1 ±
1 mm/yr slip rates closer to 0.1 mm/yr?
- Better coordination between NSHM and UCERF slip rate
reporting. NSHM only reports vertical and horizontal
components in database, fault parallel slip rates calculated
downstream. UCERF assigns preferred rake parallel slip
rates, however legacy issues have lead to inconsistencies in
the assigned slip rates.
- Geologic slip rate and geodesy-based deformation model
coordination. Well-constrained geologic rates can be used
as a-priori rates for block models, or as a check on block
model rates.
Geologic slip rate characterization
Geologic slip rate components:
- Offset feature: How good is the offset feature? What are
the uncertainties in the measurement? Does it span the
entire fault zone?
- Dating constraints: Radiometric dating, relative dating
techniques (soil development, assumptions regarding timing
of deformation)
- Time interval: Is the geologic rate representative of the
shorter term geodetically-observed rate? Number of events?
- Location on fault: Location of offset features either as
points, or paired points. How representative is the slip rate
along the length of the fault?
Slip rate characterization
Time Interval Example: Little Salmon fault. 1 My and Late Holocene
geologic slip rates in good agreement, ~5 mm/yr
Slip rate characterization
Blackwater fault: Well-constrained geologic rate (0.49 ± 0.04 mm/yr), both in
terms of feature offset (1.8 ± 0.1 km) and dating constraints (3.77 ± 0.11 Ma)
(Oskin and Iriondo, 2004).
Geodetic rates seem to suggest otherwise…
Slip rate characterization
Battle Creek fault: Poorly-constrained assigned slip rate (0.5 ± 0.4 mm/yr),
Page and Renne (1994) report ~500ka rate of 0.08 mm/yr and no offset during
past 60 ka
This will need to be reconciled with geodetic block model rates if there is a
significant discrepancy
Slip rate characterization
Location matters! How do slip rates along strike vary?
Slip rate category
Age Category (years)
• Of the 111 UCERF-2 slip rates we can associate with
USGS Quaternary Faults Database slip rate categories,
96 UCERF rates fall in the consistent USGS category, 6
UCERF rates are too high, and 9 UCERF rates are too
• We need to check the 15 that are not consistent and do
some work to associate the rest of the UCERF rates
with their USGS categories so we can check their
• We can use the USGS Quaternary Faults Database
to assign slip rate categories to UCERF faults that
we don’t have slip rates for.

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