ucerf3 statewide fault-model & paleoseismic data workshop (socal)
DESCRIPTION
UCERF3 Statewide Fault-Model & Paleoseismic Data Workshop (SoCal). Scott Lindvall Fugro Consultants, Inc. April 6, 2011. Recent Modifications to UCERF2 Fault Sources for Seismic Hazard Evaluation of LADWP Van Norman Complex San Fernando Valley and Transverse Ranges. - PowerPoint PPT PresentationTRANSCRIPT
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