Journal of Geophysical Research Earth Surface
Supporting Information for
High-Resolution Mapping of Two Large-Scale Transpressional Fault Zones in the
California Continental Borderland: Santa Cruz-Catalina Ridge and Ferrelo faults
Mark Legg1, Monica D. Kohler2, Natsumi Shintaku3, and Dayanthie Weeraratne 4
Mark Legg: Legg Geophysical, Huntington Beach, CA, USA
Monica D. Kohler: Department of Mechanical and Civil Engineering; California Institute of Technology, Pasadena,
CA, USA
Natsumi Shintaku: Department of Geological Sciences, Brown University, Providence, RI, USA
Dayanthie Weeraratne: Department of Geological Sciences, California State University, Northridge, Northridge, CA,
USA
Contents of this file
Text S1 Fault Triple Junctions
Figures S1, S2, S4
Tables S1 to S4.
Additional Supporting Information (Files uploaded separately)
Captions for Datasets Figure S3 Multichannel seismic reflection profiles across the
northern Santa Cruz-Catalina Ridge (see Fig. 7 for profile locations).
Introduction
This appendix of supplementary material consists of four figures, five tables, and a brief text that
provide more detailed information relevant to the main paper. A list of references for the
supplementary data is also included.

Figure S1 is a map of multichannel seismic reflection profiles in the northern California
Continental Borderland available for the research project. The exploration industry and
USGS data are available from the National Archive of Marine Seismic Surveys [NAMSS,
2006] and Infobank [2013].

Figure S2 shows seven stratigraphic columns for various locations in the California
Continental Borderland that were published by scientists at the U.S. Geological Survey
and California Geological Survey [Greene and Kennedy, 2007]. Updated stratigraphic
data for some areas (Santa Monica Basin and San Pedro Basin) are being prepared by
government and academic scientists as new data become available.
1

Figure S3 shows four multichannel seismic reflection profiles across the northern end of
the Santa Cruz-Catalina Ridge. One (USGS-126E) is part of the USGS line 126 44channel deep penetration data (2424 cu. in. tuned airgun source array); the other three
are high-resolution, 24-channel, shallow penetration data (4-kjoule sparker source). All
profiles are migrated sections. The USGS data were processed in Menlo Park and are
available from NAMSS. The high-resolution lines were processed by Legg and are brute
stacks using a constant velocity of 5000 ft/sec, and frequency-wave number migration at
4800 ft/sec. More thorough processing of these data is incomplete at present.

Figure S4 is a map showing the major faults interpreted for this study and used to
estimate earthquake potential in the region.

Table S1 presents the map projection and geographic coordinates of the boundaries of
raster multibeam bathymetry images used to interpret seafloor faulting for this study.
These data can be used to georeference the images for use in a geographic information
system (GIS).

Table S1B provides a list of the image file names for the multibeam bathymetry used in
this study. These data are archived in the Southern California Earthquake Center Data
Center.

Table S2 provides hypocentral location parameters for the earthquake focal mechanisms
shown in this study. Location data are from the Southern California Seismic Network
(SCSN) and include more accurate relocations when available from special studies.

Table S3 is a compilation of the major fault segments and sections mapped in this study
used to estimate earthquake potential (maximum magnitude).

Table S4 is a compilation of large historic earthquakes in California, not on the San
Andreas fault, used to provide examples of large complex earthquakes that may occur
offshore southern California.

Text Section S1 Fault Triple Junctions provides more detailed discussion of fault triple
junctions that were mapped in the Borderland and how these resemble major fault
intersections mapped onshore in southern California. In addition, tectonic significance is
discussed.
S1 Fault Triple Junctions.
Intersections between prominent faults within Borderland fault systems were recognized by
Crowell [1974] and described as convergent and divergent fault wedge tips. Based upon our
detailed mapping of these intersections with the high-resolution bathymetry and seismic profiles,
and the regional tectonic evolution, we prefer to describe these features as fault “triple
junctions”. Legg et al. [2007] suggest that Borderland restraining bend triple junctions result
from the bypass of Miocene transform faults with trends parallel to the Middle Miocene relative
plate motion vector (~N55ºW) by younger right-slip faults that are more favorably oriented to the
post-Miocene plate motion vector (~N40°W; Fig. 14). Triple junctions at opposite ends of the
Santa Catalina Island block (Figs. 4, 6 and 8) resemble fault intersections along the San
Bernardino Mountains segment of the San Andreas fault (Fig. 14; restraining bend northwest of
Palm Springs, PS). The northern triple junction where the San Clemente fault merges with the
Catalina Ridge fault (Fig. 6A) mirrors the intersection of the San Jacinto fault with the San
Andreas fault at Cajon Pass. The San Clemente fault transfers significant right slip to the Santa
Cruz-Catalina Ridge fault zone whereas the Catalina Ridge (and Catalina escarpment) fault
2
appears to be cut-off and accommodates diminishing slip. A higher slip rate for the San
Clemente fault is manifest in the abundant seismicity to the south and by sharply defined
tectonic geomorphology along the San Clemente Island escarpment [Legg and Goldfinger,
2002].
The triple junction at the southern end of the Catalina Ridge (Fig. 8A) resembles the
Banning Pass to Palm Springs section of the San Andreas fault system (Fig. 14). The San
Pedro Basin fault bypasses the Catalina fault restraining bend by linking to the San Diego
Trough fault; this is similar to how the Eastern California Shear Zone through the Mojave (Fig.
14) attempts to bypass the Big Bend of the San Andreas fault [Savage et al., 1990]. The
process of fault bypass is more advanced in the Inner Borderland because it began during the
middle to late Miocene epoch when the plate boundary deformation was focused offshore,
before the opening of the Gulf of California and plate boundary jump to the southern San
Andreas fault system. The Catalina fault may still be active, but at a reduced rate because
Catalina Island uplift has ceased and is now subsiding [Castillo et al., 2012]. Northeast-facing
(upslope direction) seafloor scarps along the base of Catalina Ridge Escarpment (Fig. 6A) may
represent Holocene faulting. The scarp morphology may indicate subsidence or tilting of the
island block down toward the northwest, but the character of faulting is undetermined at this
time.
Major triple junctions along the Ferrelo fault zone recognized in this study include
intersections with the transverse San Nicolas Island escarpment and with the southeasttrending faults along Tanner and Cortes Banks (Fig. 12). The San Nicolas Island fault
resembles the transpeninsular Agua Blanca fault except that the former exhibits reverse slip on
a moderately north-dipping fault and the latter exhibits right slip on a vertical fault. Both faults
likely have a long history of complex deformation within the evolving transform plate boundary.
The Outer Borderland crustal block rifted away from the northern Baja California continental
margin [Howell and Vedder, 1981; Legg, 1991]. The branches from these triple junctions may
provide important piercing points to define the initial breakaway geometry of the Outer
Borderland block. Detailed investigation of the deformation in the sedimentary basins at these
triple junctions could provide precise timing of important events during the evolution of the
Pacific-North America transform plate boundary.
Relocation studies of two moderate Inner Borderland earthquakes with significant
aftershock sequences provide evidence that multiple fault segments were involved in the
rupture process (Figs. 6 and 8). Furthermore, these earthquake sequences were located at
junctures between major faults (“triple junctions”) where some aftershock activity appears to
occur on adjacent fault splays (Fig. 6A). Future large Borderland earthquakes are likely to
involve complex ruptures with multiple fault segments active during rupture including branching
to other major fault zones. For example, rupture on the San Clemente Island fault may
propagate to the north and continue on the Santa Cruz-Catalina Ridge fault zone producing a
major (M>7) earthquake (Table S3). Abundant youthful fault segments identified in the seafloor
morphology and high-resolution seismic profiles provide numerous potential links for such long
and complex earthquake rupture events (Figs. 6, 8, 10 and 11). The existence of major lowangle Miocene detachment faults throughout the region (Figs. 8 and 9) may provide additional
subsurface (“blind faulting”) links to facilitate long and complex rupture events.
Large earthquakes (M>7) typically involve long and complex rupture patterns that may involve
multiple faults (Table S4). The 1992 Landers, the 1872 Owens Valley, and the 2010 El MajorCucapah, and the 1999 Hector Mine earthquakes were large strike-slip events with complex
rupture patterns through extended continental crust. The 1952 Kern County earthquake involved
reverse slip with a component of left-lateral strike slip. The complexity of faulting mapped along
the major Borderland fault zones is similar and equally likely to sustain future large earthquake
ruptures.
3
Figure S1. Map showing tracklines of digital multichannel seismic reflection surveys (MCS)
available in the study area. Data include exploration industry lines available from the NAMSS
(black), USGS high-resolution profiles (green), and various university high-resolution profiles
(magenta). Red lines are faults mapped in this study. Not all of the data shown were used in this
study, although published geologic maps and cross-sections based on special studies of various
survey data were used to prepare the fault maps and interpretations presented here. CAT =
Santa Catalina Island, SCZ = Santa Cruz Island, SMB = Santa Monica Basin; SPB = San Pedro
Basin; SRCR = Santa Rosa-Cortes Ridge; SRI = Santa Rosa Island, SCL = San Clemente
Island, SBI = Santa Barbara Island, LA = Los Angeles. EK = Emery Knoll, EK rim = offset rim of
Emery Knoll crater [Legg et al., 2004].
4
Figure S2. Stratigraphy of the northern California Continental Borderland around the Ferrelo
and Santa Cruz-Catalina Ridge fault zones based on seafloor samples (dart cores and dredge)
and high-resolution seismic reflection profiles. Location of stratigraphic columns shown in Figure
S1. [Modified from Greene and Kennedy, 1987]
5
Figure S4. Map showing major late Quaternary faults mapped for this study. San Clemente fault
zone mapping based on Legg and Goldfinger [2002]. Fault parameters for earthquake potential
are listed in Table S3.
6
Table S1A. Geographic location of multibeam bathymetry map images.
Reference
X (pixels)
Y (pixels)
Longitude
Latitude
North Borderland (1200 dpi)
[Legg1_100m_315_grad.tif]*
NW Corner
SE Corner
523
8459
96
7165
-121° 00.0’
-117° 00.0’
34° 30.0’
31°30.0’
North Borderland (800 dpi)
[Legg1_100m_090_grad.tif – 5044x5252]*
NW Corner
SE Corner
1
5044
1
5252
-121° 00.0’
-117° 00.0’
35° 00.0’
31°30.0’
[Legg1_100m_180_grad.tif – 5124x4561]*
NW Corner
SE Corner
0
5124
0
4561
-121° 00.0’
-117° 00.0’
34° 30.0’
31°30.0’
Catalina (800 dpi)
[Legg2_100m_90.tif – 5297x4259]*
NW Corner
SE Corner
2
5294
3
4257
-119° 36.0’
-117° 30.0’
34° 05.0’
32° 40.0’
[Legg2_100m_180.tif – 5046x4059]*
NW Corner
SE Corner
2
5042
3
4056
-119° 36.0’
-117° 30.0’
34° 05.0’
32° 40.0’
North Ferrelo (800 dpi)
[Legg3_100m_90.tif – 5048x3273]*
NW Corner
SE Corner
2
5044
7
3267
-120° 40.0’
-118° 40.0’
34° 05.0’
33° 00.0’
[Legg3_100m_180.tif – 4809x3118]*
NW Corner
SE Corner
3
4802
7
3113
-120° 40.0’
-118° 40.0’
34° 05.0’
33° 00.0’
South Ferrelo (800 dpi)
[Legg4_100m_90.tif – 5150x4347]*
NW Corner
SE Corner
2
5146
5
4342
-120° 00.0’
-118° 00.0’
33° 20.0’
31° 40.0’
[Legg3_100m_270.tif – 5606x4734]*
NW Corner
SE Corner
0
5601
9
4731
-120° 00.0’
-118° 00.0’
33° 20.0’
31° 40.0’
*Raster image file name includes region (Legg1), grid size (100m), sun angle (045), and gradient color scheme (grad)
where appropriate. Parameters in table above were used to georeference the map in a Geographic Information
System and include the map corner locations in XY (pixels) and geographic coordinate systems. Map Projection is
World Mercator, NAD83. The raster image files are available through the Southern California Earthquake Data Center
(www.scecde.org).
7
Table S1B. List of image files of multibeam bathymetry used for this study.
ALBACORE - Multibeam Bathymetry Raster Image Files
Legg1_100m_180.epsi
Legg1_100m_225.epsi
Legg1_100m_270.epsi
Legg1_nborderland_100m.epsi
Legg2_100m_180.epsi
Legg2_100m_225.epsi
Legg2_100m_270.epsi
Legg2_catalina_50m.epsi
Legg2_catalina_100m.epsi
Legg3_100m_180.epsi
Legg3_100m_225.epsi
Legg3_100m_270.epsi
Legg3_nferrelo_100m.epsi
Legg4_100m_180.epsi
Legg4_100m_225.epsi
Legg4_100m_270.epsi
Legg4_sferrelo_100m.epsi
\GradColor\
Legg1_100m_045.epsi
Legg1_100m_090.epsi
Legg1_100m_135_grad.epsi
Legg1_100m_180_grad.epsi
Legg1_100m_225_grad.epsi
Legg1_100m_270_grad.epsi
Legg1_100m_315_grad.epsi
Legg1_100m_360.epsi
Legg1_200m_135_grad.epsi
Legg1_200m_180_grad.epsi
Legg1_200m_225_grad.epsi
Legg1_200m_270_grad.epsi
Legg1_200m_315_grad.epsi
Gradient color scheme raster images with all eight (8) sun angles were prepared only for the
larger area (North Borderland – Legg_100m) maps. Raster images (tiff) were produced at 1200
dpi pixel resolution for gradient version of North Borderland, 800 dpi for other regions. Original
images created at CSU Northridge were in epsi format.
8
Table S2. Earthquakes in the California Continental Borderland with focal mechanisms.
#
F
Year
Mo
Day
Time
37
36
35
34
33
32
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
t
Io
t
l
t
i
iot
o
o
o
i
i
it
it
2015
2014
2014
2013
2012
2012
2012
2011
2011
2010
2009
2009
2009
2008
2008
2007
2005
2005
2005
2005
2005
2005
2005
2005
2001
2001
1988
1986
02
11
03
05
12
05
01
11
06
08
11
10
6
12
12
09
10
10
10
10
08
07
04
04
08
08
11
07
09
10
05
31
14
30
03
29
11
24
15
08
20
31
07
09
19
18
16
04
12
24
21
21
16
16
20
13
9
8
7
6
5
4
it
i
t
it
it
t
1981
1975
1973
1973
1969
1964
09
01
02
08
10
12
3
2
1
i
t
t
1951
1933
1927
12
03
11
iot
iot
i
i
i
01:45:03
08:42:42
02:24:23
13:24:52
10:36:02
05:14:01
14:18:56
06:56:09
08:17:48
05:42:17
22:45:27
03:31:18
01:00:31
11:05:05
15:39:02
13:11:49
08:51:26
00:29:15
21:11:35
06:18:07
06:35:55
12:59:43
13:26:37
06:36:19
22:06:29
18:04
05:39:28.4
13:47:08
Long
(deg)
-115.665
-118.653
-119.355
-119.1305
-119.582
-119.058
-119.4492
-119.0510
-119.0433
-119.0330
-119.3018
-118.2507
-119.0067
-118.80
-119.3237
-117.3381
-118.145
-118.1472
-118.1633
-118.0975
-118.1105
-119.761
-120.0265
-120.0333
-118.2757
-118.3030
-118.0822
-117.8583
Latitude
(deg)
31.526
32.867
31.383
33.6863
31.1643
33.6918
33.1947
33.6063
33.623
33.5152
33.1655
33.1655
32.8997
33.95
33.8673
32.7820
32.4967
32.4343
32.4545
32.6207
32.5882
33.674
33.6597
33.657
32.8055
32.7667
33.5068
32.9783
D
(km)
1.9
5.4
2.1
10.71
17
16.42
18.37
16.0
8
16.9
6
3.73
14.21
3.0
11.54
5.74
10
10
10
6
10
6
6
6
12.9
9.87
11.70
8.8
04
12
21
06
24
22
15:50:50
21:22:14.8
14:45
23:29:17
08:29:12
20:54:33.2
-119.060
-117.988
-119.04
-119.475
-119.193
-117.117
33.682
32.758
34.07
33.987
33.291
31.811
11.48
15.3
26
11
04
00:46:54.0
01:54
05:51
-118.350
-117.972
-120.9
32.817
33.659
34.35
0
13
10
16.0
10.0
2.3
Mw/ML
Location
4.9
4.1
5.0
3.09
6.3/
3.67/3.98
3.72/4.14
3.3
3.61/3.53
3.9/3.97
4.21/4.35
4.16/3.73
3.82/4.11
5.04/3.17
3.53/3.47
4.0
4.09/4.26
3.71/3.64
4.9/4.99
3.15/3.34
3.43/3.58
4.01/4.11
3.88/3.8
3.89/3.95
4.2
4.4
4.83
5.8Ms/5.
3
6.0/5.3
4.8
5.3/5.9
5.0
5.1
6.2Ms/5.
4
5.9Ms
6.3
7.0
SE San Miguel Flt, N Baja
W of San Clemente Island
W of Patton Escarpment
Santa Cruz-Catalina Ridge
W of Patton Escarpment
Santa Cruz-Catalina Ridge
San Nicolas Island
Santa Cruz-Catalina Ridge
Santa Cruz-Catalina Ridge
Santa Barbara Island
San Nicolas Island
San Clemente Canyon
Catalina Crater
Point Dume
Santa Cruz-Catalina Ridge
Crespi Knoll
North San Clemente Basin
North San Clemente Basin
North San Clemente Basin
North San Clemente Basin
Fortymile Bank
West Santa Cruz Basin
Santa Rosa-Cortes Ridge
Santa Rosa-Cortes Ridge
North San Clemente Basin
San Clemente Canyon
San Gabriel Canyon
Crespi Knoll
Santa Cruz-Catalina Ridge
Fortymile Bank
Point Mugu
Anacapa Island
NW San Clemente Ridge
Offshore Ensenada
San Clemente Island
Long Beach
Offshore Point Arguello
F – Figure (map) i = Inner Borderland (Fig. 4); o = Outer Borderland (Fig. 10); t = Tectonic (Fig. 13); Time – Origin
Time (UTC); D = Depth
Magnitude – Mw = Moment Magnitude, ML = Local Magnitude, Ms = Surface Wave Magnitude
White Rows – Moment Tensor, High Variance Reduction (A-quality solutions); Light Gray – Low Variance Reduction
(<40% B-quality solutions); Dark Gray – First-Motion Solutions
Data from SCSN Moment Tensor Database www.data.scec.org/mtarchive/; USGS pasadena.wr.usgs.gov/recenteqs/;
Legg [1980]; Corbett [1984]; Hauksson and Jones [1988]; Hauksson and Gross [1991]; Helmberger et al [1992];
Cruces and Rebollar [1992]; Yang et al. [2012]
9
Table S3. Major fault sections and segments – Borderland transpresional fault system.
[Fault sections in italics; ID corresponds to Fig. S4]
ID
Fault Name
Length (km)
Width (km)
Mmax*
I
San Clemente Fault System
>600
15
8.25
IA
Santa Cruz – Catalina Ridge
170
15
7.61
North End
19
15
6.43
IA1
Pilgrim Banks – N&S
66
15
7.13
IA2
Pilgrim Banks North
30
15
6.74
IA3
Pilgrim Banks South
36
15
6.83
160
15
7.49
IIB
Santa Catalina Island
IIB2
Catalina Ridge
63
15
7.11
IIB3
Catalina Escarpment
87
15
7.27
90
15
7.29
30
17
6.80
138
15
7.45
32
15
6.77
IIC
IIC2
Gulf of Santa Catalina – North San Diego Trough
Crespi Knoll
Catalina Basin
East San Clemente
III
Ferrelo Fault System
>380
10
7.56
IIIA
North Ferrelo
150
10
7.16
30-35
10
6.52
10-22 ea
10
6.32
42
10
6.60
170
10
7.21
Nidever Bank W
75-85
10
6.91
Mid Ferrelo – 2 segments
18, 43
10
6.61
South Ferrelo N
25-30
10
6.46
>63
10
6.78
15-20
10
6.28
6-22 ea
10
6.32
North Ferrelo NE
North Ferrelo – 6 segments
Nidever Bank E
IIIB
Mid Ferrelo
IIIC
South Ferrelo
South Ferrelo N
South Ferrelo – 3 segments
Velero Basin
IIID
Mapping Incomplete
*Maximum magnitudes were derived using methods and magnitude-area relationships as described by
Stein [2007]. Empirical data for the magnitude-area curves are from large continental strike-slip
earthquakes. Reverse or thrust earthquakes may have somewhat larger magnitudes for a given fault
area. However, for the 1989 Loma Prieta earthquake (Mw=6.9) which had an estimated fault area of 640
km2 and oblique-reverse focal mechanism, the estimated maximum magnitude by the method used in the
table above is 6.91 – virtually identical to the moment magnitude computed from the seismological data.
Uncertainties in fault parameters, length and down-dip width exceed the uncertainty in maximum
magnitude estimated from the empirical equations.
10
Table S4. Large historic non-San Andreas California earthquakes with surface rupture
Year
Date
Month Day
Location
M*
Length
(km)
Reference
1872
March 26
Owens Valley
7.8-7.9
>90 to
140
Beanland and Clark [1994]
Hough and Hutton [2008]
1892
February 23
Laguna Salada
N. Baja California
7.2
>22
Mueller and Rockwell [1995]
Hough and Elliot, [2004]
1952
July 21
Kern County
7.7(MS)
>34
Richter [1958]
1992
June 28
Landers - Mojave
7.3
80-85
Sieh et al. [1993]
1999
October 16
Hector Mine Mojave
7.1
48
Treiman et al. [2002]
~120
Hauksson et al. [2011]
El Major – Cucapah
7.2
N. Baja California
*Moment magnitude; MS = surface wave magnitude
2010
April 4
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Castillo, C. M., R. D. Francis, and M. R. Legg (2012), Constraints on late Quaternary subsidence
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Corbett, E. J. (1984), Seismicity and crustal structure studies of southern California: Tectonic
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Crowell, J. C. (1974), Origin of late Cenozoic basins in southern California, in: Tectonics and
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11
Hough, S. E., and A. Elliot (2004), Revisiting the 23 February 1892 Laguna Salada earthquake, Bull. Seis.
Soc. Am., 94, 1571-1578.
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