Addition of Mission Hills (MH) which is allowed to combine with Verdugo

Addition of Mission Hills (MH) which is allowed to combine with Verdugo

• Addition of Mission Hills (MH) which is allowed to combine with Verdugo

• Addition of Santa Susana East (SSE) which is allowed to combine with San Fernando East (SFE) and Santa Susana (SS)

• Modified trace of San Fernando (SF) to follow more closely to 1971 rupture and is separated into SF East and SF West to allow the connection with Santa Susana East (SSE)

• Santa Susana (SS) assigned full weight (1.0) with slip rate of 5 mm/yr

• Holser (H) assigned full weight (1.0) and decreased lower seismogenic depth

• Split Northridge into Northridge 1994 (N94) and Northridge West (NW) sources; lower seismogenic depth increased to include 1994 EQ focus

• Multi-fault (combined) ruptures allowed on:

• Santa Susana (SS), Santa Susana East (SSE), San Fernando (SF), Sierra Madre (SM), and Cucamonga (C) – with various weights for each 1, 2, or 3 fault scenario
• Mission Hills (MH) and Verdugo (V) – weighting: single = 0.7; combined = 0.3
• Northridge 1994 (N94) and Northridge West (NW) – weighting: single = 0.7; combined = 0.3

Many reverse and oblique faults in Transverse Ranges have slip rates based on offset Plio-Pliestocene strata or no data at all, such as the Verdugo

• Many reverse and oblique faults in Transverse Ranges have slip rates based on offset Plio-Pliestocene strata or no data at all, such as the Verdugo

• These long-term geologic rate estimates may not represent Holocene rates

• Late Pliestocene and Holocene rates are not available for many faults

• Reverse faults produce broad, diffuse zones of deformation and are therefore difficult capture slip across entire zone (e.g., Mission Hills + Northridge Hills) – Are we capturing all tectonic slip or summing correctly? Tectonic slip vs secondary hanging wall or flexural slip?

• GPS rates – can they reliably be used to help constrain rates for individual faults or groups of faults?

• Santa Susana and Cucamonga faults assigned slip rates of 5 ± 2 mm/yr in UCERF2 – are these too high?

UCERF2 rate of 5 ± 2 mm/yr

• UCERF2 rate of 5 ± 2 mm/yr

• Dip slip rate of 2.1 to 9.8 mm/yr based on 4.9 to 5.9 offset of Pliocene Fernando Fm and age of initiation 0.5 to 2.3 Ma during Saugus Fm deposition (Huftile and Yeats, 1996)

• The 2.1 to 9.8 mm/yr is a broad range (lots of uncertainty). Could it be near the low end?

• Yeats (2001) prefers rate of 7 to 9.8 mm/yr by assuming slip occurred in last 0.6 to 0.7 Ma

• Where is the geomorphic signature?

• Lack of strong geomorph would argue for a lower slip rate, but no data to refute long term geologic rates.

Three profiles across strand C

• Three profiles across strand C

• One profile across strand A and B

• All profiles were constructed from total station surveys

Uplift across scarps A and B (Qyf1a)= 20 ± 0.5 m

• Uplift across scarps A and B (Qyf1a)= 20 ± 0.5 m

• Total uplift of Qyf1a surface across A, B, and C = 34 ± 0.7 m

Weighted mean model surface age = 33,395 ± 332 years

• Weighted mean model surface age = 33,395 ± 332 years

• Excluding samples that plot outside the yellow box

Total uplift = 34 ± 0.7 m (across 3 scarps)

• Total uplift = 34 ± 0.7 m (across 3 scarps)

• 10Be Model surface age = 33,395 ± 332 yr

• Weighted mean age corrected for depth/latitude/altitude
• Assumes zero erosion and zero inheritance

• Uplift rate = 1.1 ± 0.1 mm/yr

• Horizontal Shortening rate = 1.6 ± 0.3 mm/yr

• Dip Slip rate = 1.9 ± 0.35 mm/yr

• Using measured fault dip of 32.5 ± 5° from Matti et al. (1982)

Geomorphic and soil chronologic study

• Geomorphic and soil chronologic study

• 36 m of uplift of surface Qyf1a across 3 strands
• Surface age of ~13 ka estimated using soil comparisons with radiometrically dated soil at Cajon Pass

• Morton and Matti (1987) dip-slip rate of ~4.5 - 5.5 mm/yr is significantly greater than our estimate of ~1.9 mm/yr using cosmogenic ages of fan surface