UCERF2 Deformation ModelCan 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 rates.

- Geodesy used to “inform” assigned slip rates in a number of areas, but not done systematically for entire State.

Geologic slip rate characterizationObjective:

- 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 characterizationGeologic 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 characterizationTime Interval Example: Little Salmon fault. 1 My and Late Holocene geologic slip rates in good agreement, ~5 mm/yr

Slip rate characterizationBlackwater 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 characterizationBattle 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?

<1,600,000 <130,000 <15,000 <1500%

10%

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<0.2 0.2-1.0

1-5 >5

Age Category (years)

Slip rate category(mm/yr)

• 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 low.

• 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 consistency.

• We can use the USGS Quaternary Faults Database to assign slip rate categories to UCERF faults that we don’t have slip rates for.