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Recent Modifications to UCERF2 Fault Sources for Seismic Hazard Evaluation of LADWP Van Norman Complex San Fernando Valley and Transverse Ranges UCERF3.

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Presentation on theme: "Recent Modifications to UCERF2 Fault Sources for Seismic Hazard Evaluation of LADWP Van Norman Complex San Fernando Valley and Transverse Ranges UCERF3."— Presentation transcript:

1 Recent Modifications to UCERF2 Fault Sources for Seismic Hazard Evaluation of LADWP Van Norman Complex San Fernando Valley and Transverse Ranges UCERF3 Statewide Fault-Model & Paleoseismic Data Workshop (SoCal) Scott Lindvall Fugro Consultants, Inc. April 6, 2011

2 Geologic Map of the Northern San Fernando Valley

3 Fault Model 2.1 from UCERF2 Source Model

4 Fault Model 2.2 from UCERF2 Source Model Santa Susana and Holser not included in FM 2.2

5 UCERF2 – missing sources along 3 range fronts

6 Reverse Faults Interpreted from 9 Reprocessed Oil Industry Seismic Reflection Profiles

7 Tectonic Geomorphic Features from DEM Created from 1920’s 5-foot Topographic Maps Surface deformation corresponds to underlying faults and suggests continuity of Mission Hills and Northridge Hills faults with Verdugo fault

8 Modifications to UCERF2  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

9 Revised Mission Hills and Verdugo Seismic Sources

10 Revised Geometry of Northridge West and Northridge 1994 Seismic Sources

11 Revised Sierra Madre, San Fernando, and Santa Susana Seismic Sources

12 Weighting of Multi-fault Ruptures on Santa Susana- Sierra Madre System SSSSESF 1 SMCMag Single fault ruptures fault ruptures fault ruptures fault ruptures(none) Total weights =11111 C SM SS SSE SF

13 Summary of Single-Fault Parameter Revisions SourceWeight Slip Rate (mm/yr) Length (km) Dip (°) Dip Azimuth 1 (°) Upper Seis. Depth (km) Lower Seis. Depth (km) Width (km) Area (km 2 ) Mag 1 2 (M) Mag 2 3 (M) Holser 4 H ± S Mission HillsMH ± N VerdugoV ± N Northridge WestNW ± S Northridge 1994N ± S Santa Susana 4 SS ± N Santa Susana EastSSE ± N San FernandoSF ± N Sierra MadreSM ± N CucamongaC ± N Notes: Changes from UCERF2 Source Model In Red 1 Measured orthogonal to strike of source end-points 2 Mag 1 = Average of Hanks and Bakun (2008) and Ellsworth B (2003) rutpure area relations used in UCERF2 and USGS Mag 2 = Average of Hanks and Bakun (2008) and Somerville (2006) rutpure area relations 4 In USGS08 model, Holser and Santa Susana were effectively given a weight of 0.5 since they were excluded from F2.2

14 Summary of Combined Fault Parameters Notes: MH = Mission Hills, V = Verdugo, N94 = Northridge 1994, NW = Northridge West, SS = Santa Susana, SSE = Santa Susana East, SF = San Fernando, SM = Sierra Madre, C = Cucamonga 1 Mag 1 = Average of Hanks and Bakun (2008) and Ellsworth B (2003) rupture area relations used in UCERF2 and USGS Mag 2 = Average of Hanks and Bakun (2008) and Somerville (2006) rupture area relations 3 The east-west striking portion of the San Fernando fault source west of Pacoima Wash is eliminated in combined-fault ruptures involving the Santa Susana East fault source Combined SourcesWeight Approx. Rupture Area (km 2 )Mag 1 1 (M)Mag 2 2 (M) MH + V N94 + NW SS + SSE SSE + SF SF + SM SM + C SS + SSE + SF SSE + SF + SM SF + SM + C

15 Slip Rate Issues – Transverse Ranges  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?

16 Quaternary Faults and Belt of North-South Contraction (~5mm/yr)

17 Shortening Rates from Cross Sections Cross Section 1 (Figure 9) ModelFault Slip Rate (mm/yr) Dip (°) Shortening Rate (mm/yr) MinMaxMeanMinMaxMean UCERF2 Holser Northridge San Gabriel Santa Susana SUM Revised Source Model Holser Mission Hills Northridge San Gabriel Santa Susana SUM Cross Section 2 (Figure 10) ModelFault Slip Rate (mm/yr) Dip (°) Shortening Rate (mm/yr) MinMaxMeanMinMaxMean UCERF2 Northridge San Fernando San Gabriel SUM Revised Source Model Mission Hills Northridge San Fernando San Gabriel Santa Susana East SUM

18 Cross Section 2

19 Santa Susana Fault  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.

20 Topography and geomorphology define multiple range fronts LiDAR

21 Santa Susana fault on LiDAR-based hillshade Aliso Cyn Limekiln Cyn

22 Is there a 5 or 10 mm/yr reverse fault in this image?

23 Cucamonga Fault Zone Results from Horner et al. (2007)

24 Day Canyon Fan Study Site Modified from Morton and Matti (1987)

25 Oblique Aerial Photograph of Day Canyon Fan Surface

26 Topographic Profile Analysis  Three profiles across strand C  One profile across strand A and B  All profiles were constructed from total station surveys

27 Topographic Profile Analysis  Uplift across scarps A and B (Qyf 1a )= 20 ± 0.5 m  Total uplift of Qyf 1a surface across A, B, and C = 34 ± 0.7 m

28 Sample Ages of Qyf 1a Surface (West) Weighted mean model surface age = 33,395 ± 332 years  Excluding samples that plot outside the yellow box

29 Results - Day Canyon Fan Total uplift = 34 ± 0.7 m (across 3 scarps) 10 Be 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)

30 Comparison with Morton and Matti (1987) Slip Rate Geomorphic and soil chronologic study 36 m of uplift of surface Qyf 1a 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 ~ mm/yr is significantly greater than our estimate of ~1.9 mm/yr using cosmogenic ages of fan surface


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