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A. 124°W JKLe 123°45'W 123°30'W B.

Leech River Fault Sooke Lake dam Wrangellia 48°30'N Mylonitic fabric

Sombrio Pt. Hydroelectric
plant dams
N Juan de Fuca EMe Parts C&D Victoria
10 km EOCa
Strait DGrDeMenFe; ,B2a0r1ri5e and 75 N

C. JKLe Site B 45 Site C 60 Qa.
90 Colwood Delta
30 75 N 50 EMe 71 45

Site A 25 52
30 20
2 km

D.

Site A Site B Site C
N
2 km

Quat. deposits, undi . (Qa) Mapped fault Ice ow South-facing scarp or bench
Observed lidar-derived Linear swale or sag
Eoc.-Olig. Carmanah Grp. (EOCa) Inferred striae North-facing scarp or bench
Eoc. Metchosin Fm. (EMe)
Jur.-Cret. Leech River Complex and Covered Foliation Probable scarp
Pandora Peak Unit (JKLe)
Wrangellia terrane, undi . Topographic scarp

Figure 2. (A) Simplified geologic map of the Leech River fault and surroundings (after Massey et al., 2005). Red lines denote topo-
graphic scarps, pressure ridges, topographic benches, and linear swales and sags identified in this study. See geological legend at
base of figure. DDMF—Darrington–Devil’s Mountain fault. (B) Mylonitic fabrics within the Leech River Complex near its contact with
the Metchosin Fm. (C) Map showing trace of identified features relative to bedrock (Massey et al., 2005), surficial deposits (Blyth and
Rutter, 1993), and local ice flow indicators (blue arrows, this study). Foliation measurements from this study are shown in bold and
those from Muller (1983) are shown in italics. Foliation data outlined in white are at the lithologic contact (this study). (D) Fault traces
as in part C, colored according to facing direction and feature type, draped on LiDAR hillshade image.

trenching, and geophysical studies have the seismic hazard it may pose to the nearby activity is also recognized 10–20 km
proven successful at highlighting a net- population of Victoria, British Columbia offshore of the Leech River fault along a
work of oblique reverse forearc faults, both (Figs. 1 and 2A) (see Cassidy et al., 2000; structure in the Juan de Fuca Strait (Barrie
on- and offshore of Washington and Mosher et al., 2000; Balfour et al., 2011). and Greene, 2015) (Figs. 1 and 2A), but
Oregon, that can produce earthquakes up Several previous authors suggest that this direct evidence for recent rupture onshore
to 7.5 in magnitude (McCaffrey and fault, which places Jurassic-Cretaceous has remained ambiguous.
Goldfinger, 1995; ten Brink et al., 2006; schists of the Leech River Complex to
Blakely et al., 2014; Sherrod et al., 2016). the north against Eocene basalts of the Here, we use a combination of techniques
In particular, LiDAR, seismic, and aero- Metchosin Formation to the south (Fig. 2A) to delineate Quaternary fault-related fea-
magnetic data have been paramount in the (Fairchild and Cowan, 1982; Rusmore and tures along the Leech River fault, including
recognition of the Seattle fault as a signifi- Cowan, 1985), was last active in the (1) mapping of fault scarps from hillshade
cant seismic hazard source within the Eocene (MacLeod et al., 1977; Johnston and local slope images generated from a
greater Seattle region (SF, Fig. 1) (Johnson and Acton, 2003). Yet, trenching, coring, high resolution (~2 m horizontal by ~10 cm
et al., 1999; Blakely et al., 2002; Kelsey et and geophysical studies indicate multiple vertical) LiDAR digital elevation model
al., 2008; Nelson et al., 2014). Quaternary ruptures of adjacent fault sys- (DEM) collected by Natural Resources
tems in Washington state, USA, including Canada (James et al., 2010); (2) first-order
The potential Quaternary activity of the Southern Whidbey Island fault, the bedrock and surficial field mapping;
the Leech River fault, an ~60-km-long Utsalady Point fault, and the Darrington– (3) collection of detailed structural and
terrane-bounding fault in the southern Devil’s Mountain fault (Fig. 1) (Johnson et geomorphic data at key sites; and (4) com-
Vancouver Island forearc (Muller, 1977; al., 1996, 2001; Sherrod et al., 2008; pilation of our observations with data from
MacLeod et al., 1977), has drawn signifi- Personius et al., 2014). Quaternary seismic previous studies (e.g., Fairchild and
cant attention in recent years because of Cowan, 1982; Blyth and Rutter, 1993;

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