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 LindvallFugro Consultants, Inc.

April 6, 2011

Geologic Map of the Northern San Fernando Valley

Fault Model 2.1 from UCERF2 Source Model

Fault Model 2.2 from UCERF2 Source Model

Santa Susana and Holser not included in FM 2.2

UCERF2 – missing sources along 3 range fronts

Reverse Faults Interpreted from 9 Reprocessed Oil Industry Seismic Reflection Profiles

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

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

Revised Mission Hills and Verdugo Seismic Sources

Revised Geometry of Northridge West and Northridge 1994 Seismic Sources

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

Weighting of Multi-fault Ruptures on Santa Susana-Sierra Madre System

  SS SSE SF1 SM C Mag

Single fault ruptures 0.65 6.8

0.4 6.3

0.55 6.6

0.6 7.2

0.75 6.6

2-fault ruptures 0.3 0.3 7.0

0.2 0.2 6.7

0.1 0.1 7.3

0.2 0.2 7.3

3-fault ruptures 0.05 0.05 0.05 7.1

0.05 0.05 0.05 7.3

0.05 0.05 0.05 7.4

4-fault ruptures (none)

Total weights = 1 1 1 1 1

C

SMSS SSE

SF

Summary of Single-Fault Parameter Revisions

Source WeightSlip Rate (mm/yr)

Length (km) Dip (°)

Dip Azimuth1

(°)

Upper Seis. Depth (km)

Lower Seis. Depth (km)

Width (km)

Area (km2)

Mag 12

(M)

Mag 23

(M)

Holser4 H 1.00 0.4 ± 0.4 19.7 58 S 188 0 7.0 8.3 162 6.3 6.2

Mission Hills MH 0.70 1.25 ± 0.25 13.5 40 N 10 0 14.0 21.8 295 6.6 6.5

Verdugo V 0.70 0.5 ± 0.4 28.2 55 N 31 0 14.5 17.7 498 6.8 6.7

Northridge West NW 0.70 1.5 ± 1.0 11.0 40 S 200 7 20.0 20.2 222 6.4 6.3

Northridge 1994 N94 0.70 1.5 ± 1.0 22.4 40 S 202 7 20.0 20.2 454 6.7 6.6

Santa Susana4 SS 0.65 5.0 ± 2.0 27.2 55 N 10 0 16.3 19.9 542 6.8 6.7

Santa Susana East SSE 0.40 2.0 ± 1.0 8.1 50 N 20 0 15.0 19.6 159 6.3 6.2

San Fernando SF 0.55 2.0 ± 1.0 15.6 45 N 6 0 15.0 21.2 331 6.6 6.5

Sierra Madre SM 0.60 2.0 ± 1.0 59.6 54 N 17 0 14.2 17.6 1046 7.2 7.1

Cucamonga C 0.75 5.0 ± 2.0 28.1 45 N 347 0 7.8 11.0 309 6.6 6.5

Notes:Changes from UCERF2 Source Model In Red1Measured orthogonal to strike of source end-points2Mag 1 = Average of Hanks and Bakun (2008) and Ellsworth B (2003) rutpure area relations used in UCERF2 and USGS20083Mag 2 = Average of Hanks and Bakun (2008) and Somerville (2006) rutpure area relations4In USGS08 model, Holser and Santa Susana were effectively given a weight of 0.5 since they were excluded from F2.2

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 = Cucamonga1Mag 1 = Average of Hanks and Bakun (2008) and Ellsworth B (2003) rupture area relations used in UCERF2 and USGS20082Mag 2 = Average of Hanks and Bakun (2008) and Somerville (2006) rupture area relations3The 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 Sources Weight

Approx. Rupture Area

(km2) Mag 11 (M) Mag 22 (M)

MH + V 0.30 793 7.0 6.9

N94 + NW 0.30 676 6.9 6.8

SS + SSE 0.30 700 7.0 6.9

SSE + SF3 0.20 448 6.7 6.6

SF + SM 0.10 1377 7.3 7.2

SM + C 0.20 1356 7.3 7.2

SS + SSE + SF3 0.05 990 7.1 7.0

SSE + SF + SM3 0.05 1494 7.3 7.3

SF + SM + C 0.05 1687 7.4 7.3

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?

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

Shortening Rates from Cross Sections

Cross Section 1 (Figure 9)

Model FaultSlip Rate (mm/yr)

Dip (°)Shortening Rate (mm/yr)

Min Max Mean Min Max Mean

UCERF2

Holser 0.0 0.8 0.4 58 0.0 0.4 0.2Northridge 0.5 2.5 1.5 35 0.4 2.0 1.2San Gabriel2 0.5 1.5 1.0 61 0.0 0.0 0.0Santa Susana 3.0 7.0 5.0 55 1.7 4.0 2.9SUM 4.0 11.8 7.9 - 2.1 6.5 4.3

Revised Source Model

Holser 0.0 0.8 0.4 58 0.0 0.4 0.2Mission Hills 1.0 1.5 1.25 40 0.8 1.1 1.0Northridge 0.5 2.5 1.5 40 0.4 1.9 1.1San Gabriel2 0.5 1.5 1.0 61 0.0 0.0 0.0Santa Susana 3.0 7.0 5.0 55 1.7 4.0 2.9SUM 5.0 13.3 9.2 - 2.9 7.5 5.2

Cross Section 2 (Figure 10)

Model FaultSlip Rate (mm/yr)

Dip (°)Shortening Rate (mm/yr)

Min Max Mean Min Max Mean

UCERF2

Northridge 0.5 2.5 1.5 35 0.4 2.0 1.2San Fernando 1.0 3.0 2.0 45 0.7 2.1 1.4San Gabriel2 0.5 1.5 1.0 61 0.0 0.0 0.0SUM 2.0 7.0 4.5 - 1.1 4.2 2.6

Revised Source Model

Mission Hills 1.0 1.5 1.25 40 0.8 1.1 1.0Northridge 0.5 2.5 1.5 40 0.4 1.9 1.1San Fernando 1.0 3.0 2.0 45 0.7 2.1 1.4San Gabriel2 0.5 1.5 1.0 61 0.0 0.0 0.0Santa Susana East 1.0 3.0 2.0 50 0.6 1.9 1.3

SUM 4.0 11.5 7.8 - 2.5 7.1 4.8

Cross Section 2

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.

Topography and geomorphology define multiple range fronts

LiDARLiDAR

Santa Susana fault on LiDAR-based hillshade

Aliso C

ynA

liso Cyn

Lim

ekiln

Cyn

Lim

ekiln

Cyn

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

Cucamonga Fault Zone

Results from Horner et al. (2007)

Day Canyon Fan Study Site

Modified from Morton and Matti (1987)

Oblique Aerial Photograph of Day Canyon Fan Surface

Topographic Profile Analysis

Three profiles across strand C One profile across strand A

and B All profiles were constructed

from total station surveys

Topographic Profile Analysis

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

Sample Ages of Qyf1a Surface (West)

Weighted mean model surface age = 33,395 ± 332 years Excluding samples that plot outside the yellow box

Results - Day Canyon Fan

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)

Comparison with Morton and Matti (1987) Slip Rate

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