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Complete Report for Seattle fault zone (Class A) No. 570

Brief Report ||Partial Report

citation for this record: Johnson, S.Y., Blakely, R.J., Brocher, T.M., Bucknam, R.C., Haeussler, P.J., Pratt, T.L., Nelson, A.R., Sherrod, B.L., Wells, R.E., Lidke, D.J., Harding, D.J., and Kelsey, H.M., compilers, 2004, Fault number 570, Seattle fault zone, in Quaternary fault and fold database of the United States: U.S. Geological Survey website, http://earthquakes.usgs.gov/hazards/qfaults, accessed 09/16/2014 01:25 AM.

Synopsis This 4- to 7-km-wide east-trending fault zone extends from the Cascade Range foothills on the east across the Puget Lowland to Hood Canal, crossing Lake Sammamish, Lake Washington, Puget Sound, Bainbridge Island, and the Kitsap Peninsula. Various strands of the fault zone lie largely concealed beneath the major population centers of Seattle, Bellevue, and Bremerton. It forms the northern boundary of a belt of bedrock exposures that cross much of the Puget Lowland. The depth to bedrock north of the fault zone is as much as 1 km (Yount and others, 1985 #4746; Johnson and others, 1999 #4729). The fault zone has been imaged on seismic-reflection profiles collected in Puget Sound and adjacent waterways (Yount and Gower, 1991 #4744; Johnson and others, 1994 #4730; Pratt and others, 1997 #4737; Johnson and others, 1999 #4729), correlates with large gravity and magnetic anomalies (Danes and nine others, 1965 #4723; Blakely and others, 2002 #4716), and is represented by a prominent velocity anomaly on tomographic models (Brocher and others, 2001 #4718; Calvert and others, 2001 #4722). These data indicate the zone consists of three or more south-dipping thrust faults that form the structural boundary between the Seattle uplift on the south and the Seattle basin on the north. Blakely and others (2002 #4716) have named three of these structures the frontal fault, the Blakely Harbor fault, and the Orchard Point fault. Nelson and others (2003 #5868) termed the "frontal fault" the "Seattle fault." The Seattle fault zone also includes north-dipping reverse or thrust faults, such as the Toe Jam Hill fault (Nelson and others, 2000 #4733; 2002 #4736; 2003 #5868), which forms a complex scarp in densely forested terrain on Bainbridge Island. Slip on both south- and north-dipping faults within the zone probably is associated with offset on a south-dipping master fault (e.g., Pratt and others, 1997 #4737) at depth. Surface-deforming earthquakes have occurred on the Seattle fault in the latest Holocene, most recently about 1050-1020 cal. yr B.P. (Bucknam and others, 1992 #602; Atwater, 1999 #4715; Nelson and others, 2000 #4733; 2002 #4736; 2003 #5868; 2003 #6250).

Name comments Danes and others (1965 #4723) first suggested the presence of a major east-trending fault in the Puget Lowland near Seattle on the basis of gravity and magnetic anomalies and drill-hole data. Rogers (1970 #4738) also noted the large geophysical anomalies in the same location and suggested the name "Seattle-Bremerton fault." Gower and others (1985 #4725) briefly outlined geologic and geophysical relationships across this feature, which they designated "inferred structure I." Yount and Holmes (1992 #4745) introduced the name "Seattle fault" for this feature, which they considered a south-dipping thrust or reverse fault. Recognition that the structure includes multiple parallel faults and other structures led to the use of the name "Seattle fault zone" (Johnson and others, 1999 #4729; Brocher and others, 2001 #4718; Nelson and others, 2003 #5868).
County(s) and State(s) , WASHINGTON
KING COUNTY, WASHINGTON
KITSAP COUNTY, WASHINGTON
Physiographic province(s) PACIFIC BORDER
Reliability of location Good
Compiled at 1:100,000 scale.

Comments: Strands of the Seattle fault zone are generally concealed beneath a cover of water, dense vegetation and thick Pleistocene glacial and interglacial deposits. Inferred locations of south-dipping faults in the Seattle fault zone are based on high-resolution seismic-reflection profiles (Johnson and others, 1999 #4729; Brocher and others, 2001 #4718), high-resolution aeromagnetic surveys (Blakely and others, 2002 #4716), and geologic mapping (e.g., Haeussler and Clark, 2000 #4726). Two north-dipping, en echelon reverse faults spanning about 5 km of fault length between Bremerton and Puget Sound were identified on the basis of LIDAR surveys (e.g., Bucknam and others, 1999 #4721; Harding and Berghoff, 2000 #4728; Haugerud and others, 2001 #4735; 2003 #6211). The map compilation for this effort is based on Johnson and others (1999 #4729), Haeussler and Clark (2000 #4726), Blakely and others (2002 #4716), and other available geologic and geophysical data.

Geologic setting The east-trending thrust faults of the Seattle fault zone accommodate north-south compression due to the northward-migrating forearc of the Cascadia convergent margin (Wells and others, 1998 #4742; McCaffrey and others, 2000 #4731; Miller and others, 2001 #4732). Geodetic studies (e.g., Khazaradze and others, 1999 #4734) indicate about 4-5 mm/yr of north/south crustal shortening in western Washington, some of which is accommodated by slip on the Seattle fault zone (Wells and Johnson, 2000 #4743). The fault zone forms the boundary between uplifted Tertiary rocks of the Seattle uplift on the south and thick Tertiary to Quaternary strata of the Seattle basin on the north. Gravity and seismic studies (e.g., Brocher and others, 2001 #4718) indicate that Eocene volcanic rocks exposed at the surface in the Seattle uplift are buried by as much as 9-10 km of younger sediments in the Seattle basin.

Length (km) 69 km.

Comments:

Map compilation, based on Johnson and others (1999 #4729), Haeussler and Clark (2000 #4726), and Blakely and others (2002 #4716), indicates minimum fault length of 68 km. Seismic refraction work suggests that the Seattle basin is about 70 to 75 km long in an east to west direction (Brocher and others, 2000 #4717). If the formation of the Seattle basin was largely controlled by movement on the Seattle fault zone (Johnson and others, 1994 #4730; Pratt and others, 1997 #4737), then fault length is about 70 to 75 km.


Average strike N85°W
Sense of movement Thrust

Comments: The Seattle fault zone is a complex zone that accommodates north-south shortening (Yount and Holmes, 1992 #4745; Johnson and others, 1994 #4730; Pratt and others, 1997 #4737; Johnson and others, 1999 #4729; Brocher and others, 2001 #4718; Blakely and others, 2002 #4716). Dominant slip is south-side up on south-dipping faults, producing the Seattle uplift. The zone also includes north-dipping reverse faults, such as the Toe Jam Hill fault and Waterman Point fault (Nelson and others, 2000 #4733; Haugerud and others, 2001 #4735; Nelson and others, 2002 #4736; Nelson and others, 2003 #5868; Haugerud and others, 2003 #6211; 2003 #6250).

Dip 25°-80°

Comments: Dip proposed by various investigators spans a broad range. Using industry seismic-reflection data, Johnson and others (1994 #4730) inferred a mean dip of 45?-60?S to a depth of ~ 6 km for the northern fault in the Seattle fault zone (Frontal fault of Blakely and others, 2002 #4716), and suggest the dip of the zone shallows with depth. Using a different industry seismic-reflection database, Pratt and others (1997 #4737) inferred a dip of ~45?S for the Frontal fault in the upper ~6 km and presented a model showing a dip of about 20?-25?S at depths of 6-16 km. Johnson and others (1999 #4729) used high-resolution seismic-reflection data to infer that the dip of the Frontal fault in the upper 1 km varies along strike from 44?-65?S. Haeussler and others (2000 #4727) used outcrop structural data in central Kitsap County to infer that the Frontal fault dips 65?-70?S near the surface but shallows to roughly 30? at depths of 5-6 km beneath Gold Mountain, west of Bremerton. Based on microseismicity, Brocher and others (2001 #4718) favor a model in which the Seattle fault zone dips steeply from the surface to a depth of about 25 km.

Paleoseismology studies Paleoseismologic investigations of shoreline deposits and trenching studies have been conducted along and near fault strands of the Seattle fault zone. Detailed investigations of shoreline deposits of Puget Sound and sediments and submerged forests of Lake Washington are described in some of the sites listed below. These off-fault investigations document evidence for late Holocene land-level changes, tsunamis, and (or) landslides that are interpreted to be effects of large earthquakes and faulting in this region. The evidence from many of these off-fault sites can be confidently correlated with the A.D 900-930 (1050-1020 cal. yr B.P.) earthquake along the Seattle fault zone (e.g., Atwater, 1999 #4715). Evidence from some other off-fault sites, however, cannot be confidently related to a specific fault or zone of faults. The off-fault sites discussed below are included herein with the Seattle fault zone based on existing reports and interpretations as well as in part based on their proximity to the Seattle fault zone. Some other coastal study sites nearby in the Puget Lowland, such as the Shine, Winslow, and Hansville sites (e.g., Bucknam and others, 1992 #602; Sherrod, 2001 #4740), have been reported to show evidence that indicates an absence of late Holocene land-level changes, tsunami deposits, and other possible earthquake-related features. These other sites may provide information that limits the extent of late Holocene earthquake-related uplift, subsidence, and tsunamis. However, these other sites apparently do not record direct evidence of earthquake and faulting events and they are not included herein. In addition to the paleoseismology sites listed below, Schuster and others {, 1992 #600} reported rock avalanches and limiting radiocarbon ages from the southeastern Olympic Mountains. They concluded that these avalanches probably were triggered by seismic shaking related to earthquakes in the last few thousand years, and suggested that the Seattle fault zone was one of a few obvious candidates for the earthquakes that might have triggered these avalanches. These rock avalanche study sites are discussed in more detail in the paleoseismology studies of the Saddle Mountain faults [575], which are located along the southeastern flank of the Olympic Mountains directly southeast of the rock avalanches studied by Schuster and others {, 1992 #600}.

Vasa Park site (570-1). This site is located along an eastern strand of the Seattle fault zone near the west shore of Lake Sammamish, about 16 km east of Seattle. Based on detailed study of an excavation across the main strand of the fault zone at this locality, Sherrod and others (2001 #4739) reported a fault, within a complex zone of faults, that places weathered Miocene volcaniclastic sediments on the southwest over Pleistocene glacial deposits to the northeast. They noted that these relations show clear evidence of Pleistocene or younger faulting, but also noted that any Holocene history is unknown, because post-glacial soils and colluvial deposits were previously removed from this site. Sherrod and others (2001 #4739) also reported that a ravine, about 4 km east of this site, exposes proglacial lake sediments thrust over younger outwash and till.

Toe Jam Hill site, trenches 570-2 to 570-6. Nelson and others (2000 #4733; 2002 #4736; 2003 #5868) presented the results of a trenching investigation that included 5 trench sites along the scarp of the Toe Jam Hill fault, a north-dipping backthrust in the Seattle fault zone. From east to west, the names assigned to these 5 trench sites (Nelson and others, 2000 #4733; 2002 #4736; 2003 #5868) and the corresponding site numbers assigned herein are, Crane Lake (570-2), Blacktail (570-3), Mossy Lane (570-4), Saddle (570-5), and Bear's Lair (570-6). Four of these sites are located within about 200 m of an adjacent trench. Consequently, the Blacktail and Mossy lane trench sites and the Saddle and Bear's Lair trench sites are grouped and shown as only two trench symbols on maps related to this compilation. Results from these trenching investigations indicate 3, or possibly 4, ground-rupturing earthquakes between about 2500 and 1000 yr B.P.

Waterman Point site, trenches 570-7 to 570-9. Nelson and others (2003 #6250) presented data from a trenching investigation that included 3 trench sites along the scarp of the Waterman Point fault, a north-dipping backthrust in the Seattle fault zone. From east to west, the names assigned to these 3 trench sites (Nelson and others, 2003 #6250) and the corresponding trench-site numbers assigned herein are, Nettle Grove (570-7), Madrone Ridge (570-8), and Snowberry (570-9). The Madrone Ridge and Snowberry trench sites are only about 200 m apart and are shown as a single trenchsite symbol on maps related to this compilation. All three trenches showed evidence of a large earthquake about 1100-900 yr B.P., but stratigraphy in the Madrone Ridge trench suggests a second, younger undated surface-rupturing earthquake (Nelson and others, 2003 #6354).

Restoration Point (570-10) and Alki Point (570-11) sites. Bucknam and others (1992 #602) documented several meters of abrupt late Holocene uplift at these two coastal sites in the Seattle fault zone. Based on isotopic age dating and other information, they concluded that this uplift probably reflected land-level changes related to a major earthquake along the Seattle fault zone about 1000-1100 years ago. Other studies and more precise age dating (e.g., Atwater and Moore, 1992 #597; Atwater, 1999 #4715), suggest that uplift at these sites probably is related to subsidence at the West Point site (see below) and imply that the earthquake responsible for these land-level changes can be more tightly constrained to about 1050-1020 cal. yr B.P. (A.D. 900-930). Sherrod and others (2000 #4741) later produced detailed paleoecological data from the uplifted terrace at Restoration Point and reported that their evidence indicates that other comparable uplift events have not occurred at this site in the last ~7500 years.

West Point (570-12) and Cultus Bay (570-13) sites. The West Point site is located in tidal flat sediments at West Point along west edge of Seattle and east coast of Puget Sound. Based on tidal marsh stratigraphy and radiocarbon ages from this site, Atwater and Moore (1992 #597) documented evidence for subsidence and a tsunami generated in the Puget Sound about 1100-1000 years ago. The evidence suggests that a large earthquake on the Seattle fault zone generated the tsunami by causing abrupt uplift south of the fault (e.g., at Restoration Point and Alki Point described above) and complimentary subsidence to the north at West Point. Atwater and Moore (1992 #597) also correlated tsunami deposits of similar age at Cultus Bay on southern Whidbey Island with this event, but reported that there is no evidence of related land-level changes at Cultus Bay. Atwater (1999 #4715) later reported high-precision radiocarbon ages from a Douglas Fir log at the West Point site, which constrain the age of this earthquake to between 1050-1020 cal. yr B.P. (A.D. 900-930) (Atwater, 1999 #4715).

Snohomish River delta sites (570-14). The Snohmomish River delta is located directly north of Everett, Washington along Puget Sound. Based on detailed study of channel-bank stratigraphy at numerous sites along the delta and radiocarbon ages, Bourgeois and Johnson (2001 #4720) reported evidence for at least three episodes of liquefaction, at least one event of abrupt subsidence, and at least one tsunami since ca. A.D. 800. They report radiocarbon ages, which combined with stratigraphic relations, indicate that a prominent event of strong shaking produced liquefaction, abrupt subsidence, and a tsunami between A.D. 800-980. Bourgeois and Johnson (2001 #4720) concluded that these features probably resulted from the earthquake on the Seattle fault zone 1050-1020 cal. yr B.P. (A.D. 900-930).

Lake Washington sites (570-15). The eastern part of the Seattle fault zone crosses Lake Washington. At several sites in and along the lake, submarine landslides, turbidites, and submerged forests on submarine landslides provide evidence of prehistoric earthquakes along the Seattle fault and (or) along faults elsewhere in Cascadia (e.g., Karlin and Abella, 1992 #598; Jacoby and others, 1992 #599; Prunier and others, 1997 #6712; Karlin and others, 2004 #6713). Jacoby and others (1992 #599) dated submerged trees on landslide deposits in the lake and reported that the most recent landslides in three separate localities may have occurred simultaneously, about 1000 years ago. Based on tree-ring pattern matching with a dated log from the West Point site (570-12), they concluded that bark-year trees from the Lake Washington sites all died in the same year and same season as did the tree from the West Point site that later yielded a high-precision radiocarbon age of A.D. 900-930 (discussed above, and see Atwater and Moore, 1992 #597; Atwater, 1999 #4715). They noted that these results suggest that these landslides probably were triggered by the same seismic events that produced subsidence and tsunami deposits at West Point. More recently Karlin and others (2004 #6713) reported results of high-resolution seismic reflection, sidescan sonar swath, and sediment coring investigations in Lake Washington; these investigations also obtained magnetic susceptibility profiles and radiocarbon ages from terrigenous sediments in cores. Results of these studies provide detailed information on the distribution, geometry, age, and causes of submarine landslides in Lake Washington, and identify numerous large blockslides, sediment slumps, and debris flows. They also identified probable seismically induced turbidite (seismite) layers in their core samples. They noted that massive submarine block slides and retrogressive submarine slope failures probably were triggered by large earthquakes on the Seattle fault and (or) large to great temblors elsewhere in Cascadia. They further noted that magnetic profiling and radiocarbon ages from cores of probable seismites imply seven sedimentary disturbances in the lake in the last 3500 years. They correlated one of the turbidites with the A.D. 1700 Cascadia subduction zone earthquake, and correlated another with the A.D. 900-930 earthquake along the Seattle fault zone. They suggested that the other turbidite layers probably are also seismites caused by landslides during earthquakes; and they concluded that, collectively these deposits appear to provide a record of strong ground motion in this region that has occurred about every 300-500 yr during the past 3500 yr.

Geomorphic expression Late Holocene uplift in the Seattle fault zone produced a terrace commonly 5 to 7 m high along shores of Puget Sound (Bucknam and others, 1992 #602). This belt of uplift extends 5-10 km southward from the Frontal fault and 30 km eastward from Dyes Inlet to the Duwamish River. Faulted glacial deposits near Bellevue (Sherrod and others, 2001 #4739) show that late Quaternary faulting continues eastward across Lake Washington. Late Holocene backthrusting within the Seattle fault zone produced short (1- to 2-km-long), 3- to 7-m-high scarps along the Toe Jam Hill fault (Bucknam and others, 1999 #4721; Nelson and others, 2000 #4733; 2002 #4736; 2003 #5868), and Waterman Point fault (Haugerud and others, 2001 #4735; Haugerud and others, 2003 #6211; Nelson and others, 2003 #6250). Additional tectonic landforms have undoubtedly been buried or eroded during Pleistocene glaciation. The Puget Lowland was occupied at least five times during the Pleistocene by a lobe of the continental ice sheet, with the most recent ice retreat occurring about 16 ka (Porter and Swanson, 1998 #6237). Much of the present landscape reflects this glacial history (Booth, 1994 #4719). The tops of bedrock hills on the Seattle uplift stand as much as 300-400 m higher than the tops of drumlins comprised of glacial drift to the north in the Seattle basin.

Age of faulted surficial deposits The Seattle fault (frontal fault of Blakely and others, 2002 #4716) is largely concealed beneath young glacial deposits and vegetation. Interpretations of seismic-reflection data suggest it juxtaposes Tertiary bedrock and Quaternary glacial and interglacial deposits at shallow depth (Johnson and others, 1994 #4730; Pratt and others, 1997 #4737; Johnson and others, 1999 #4729). Sherrod and others (2001 #4739) describe a possible exposure of the Seattle fault near the west shore of Lake Sammamish, juxtaposing Miocene bedrock and undated Quaternary glacial deposits. Recent LIDAR topographic imagery suggests the Seattle fault may be a blind structure since deglaciation (about 15,000 yr B.P.) along much of its trace. In this scenario, upper Quaternary deposits are folded above the buried fault tip, but not ruptured at the surface. The Blakely Harbor fault is also concealed, but geologic and geophysical data suggest it juxtaposes Miocene nonmarine deposits and Eocene-Oligocene marine deposits at shallow depth across much of the central Puget Lowland. The Port Orchard fault is similarly concealed, however, geologic and geophysical data indicate that at shallow depth it forms a contact between Eocene-Oligocene marine deposits and Eocene volcanic rocks (Johnson and others, 1994 #4730; 1999 #4729; Blakely and others, 2002 #4716). Trenches across the scarps of north-dipping faults show displacement of Pleistocene to late Holocene deposits. The Toe Jam Hill fault cuts Miocene bedrock, Pleistocene glacial deposits, and postglacial (latest Pleistocene to Holocene) deposits. The faulted strata are as young as 1100-900 yr B.P. (Nelson and others, 2000 #4733; 2002 #4736; 2003 #5868). The fault along the Waterman Point scarp cuts Eocene-Oligocene bedrock and glacial and postglacial Pleistocene and late Holocene deposits (Nelson and others, 2003 #6250).
Historic earthquake
Most recent prehistoric deformation Latest Quaternary (<15 ka)

Comments: The most recent known faulting event in the Seattle fault zone occurred about 1050-1020 yr B.P (Atwater, 1999 #4715). This large earthquake (inferred M >7, Bucknam and others, 1992 #602) caused uplift south of the Seattle fault (Bucknam and others, 1992 #602) (see above) and complementary subsidence to the north in the Seattle basin (Atwater and Moore, 1992 #597; Bucknam and others, 1992 #602). Associated effects in the Puget Lowland include tsunami generation (Atwater and Moore, 1992 #597; Bourgeois and Johnson, 2001 #4720), uplift of the southern part of the Seattle uplift (Bucknam and others, 1992 #602), subsidence at the Snohomish River delta (Bourgeois and Johnson, 2001 #4720), and possible subsidence in southern Puget Sound (Sherrod, 2001 #4740). Atwater (1999 #4715) recently precisely dated this event as 1050-1020 cal. yr B.P. using a log buried in a tsunami deposit. The most recent faulting event on the Toe Jam Hill backthrust overlaps in age with and is inferred to correlate with the 1050-1020 yr B.P. event as is the well-dated faulting event on the Waterman Point fault. An earlier late Holocene earthquake on the Toe Jam Hill fault may have occurred about 1200 to 1700 yr B.P., and as many as two more events may have occurred between about 2500 and 1900 yr B.P. (Nelson and others, 2000 #4733; 2002 #4736; 2003 #5868).

Recurrence interval 0.2 to 12 k.y. (<16 ka)--Toe Jam Hill fault

Comments: Detailed paleoseismologic investigations within the Seattle fault zone have been conducted only on Bainbridge Island (Bucknam and others, 1992 #602; Sherrod and others, 2001 #4739; Nelson and others, 2002 #4736; 2003 #5868). One large (M = 7+) late Holocene earthquake, at 1050-1020 yr B.P., was originally inferred on the basis of an uplifted terrace (Sherrod, 1985 #4171; Bucknam and others, 1992 #602; Atwater, 1999 #4715). Numerous studies have documented the regional effects of the 1050-1020 yr B.P. Seattle fault zone earthquake (Atwater and Moore, 1992 #597; Karlin and Abella, 1992 #598; Jacoby and others, 1992 #599; Schuster and others, 1992 #600; Bucknam and others, 1992 #602; Bourgeois and Johnson, 2001 #4720; Sherrod, 2001 #4740). Five trenches crossing the Toe Jam Hill fault (north-dipping backthrust) on southern Bainbridge Island reveal evidence of 3 or 4 ground-rupturing earthquakes between 2500 yr B.P. and ~1000 yr B.P. The youngest of these prehistoric earthquakes overlaps in age with and is inferred to correlate with the 1050-1020 yr B.P. event. Based on the results of trenching studies, Nelson and others (2003 #5868) report radiocarbon-measured recurrence intervals of ~0.2 to 12 k.y. for post-glacial (since 16 ka) earthquakes along the Toe Jam Hill fault. These post-glacial recurrence intervals range from 12,000 yr between late Pleistocene and late Holocene earthquakes to as little as a century or less for late Holocene earthquakes (Nelson and others, 2003 #5868). Nelson and others (2003 #5868) note that the earthquake history of the Toe Jam Hill fault is at least a partial proxy for the earthquake history of the Seattle fault and other faults in the Seattle fault zone (see also, discussion in "Slip-rate category" below).
Slip-rate category Between 0.2 and 1.0 mm/yr

Comments: Preferred rate is about 0.9 mm/yr. Based on analysis of Quaternary structural relief on faults and folds imaged on high-resolution seismic-reflection data in Puget Sound, Johnson and others (1999 #4729) suggested that the Seattle fault (frontal fault of Blakely and others, 2002 #4716) of the Seattle fault zone has a minimum Quaternary slip rate of about 0.5 mm/yr. This estimate assumes that the Frontal fault dips 44?-65?S in the upper 1 km (see above). Assuming more steep or shallower dips would result in slightly slower and faster slip rates, respectively. Calvert and others (2001 #4722) and ten Brink and others (2002 #6353) suggested a similar slip rate on the Seattle fault in eastern Puget Sound. Based on the results of trenching studies, Nelson and others (2003 #5868) reported radiocarbon-measured evidence for post-glacial (since 16 ka) recurrence intervals and slip rates along the Toe Jam Hill fault, a backthrust to the Seattle fault. For post-glacial activity along the Toe Jam Hill fault, their results indicate shorter recurrence intervals and higher slip rates (~2 mm/yr) during the late Holocene compared to longer recurrence intervals and lower slip rates (~0.2 mm/yr) between the late Pleistocene and late Holocene. Nelson and others (2003 #5868) concluded that the higher, late Holocene slip rates along the Toe Jam Hill fault probably reflect an unusual cluster of earthquakes along this strand of the fault zone rather than a recent increase in the rate of north-south shortening across the entire zone. Cumulative slip rates across the Seattle fault zone probably are a minimum of about 0.7  1.0 mm/yr. However, it is likely that the style, geometry, and perhaps rates of fault-related shortening vary laterally and vary along different strands of the zone as suggested above for the Toe Jam Hill fault. It has also been suggested that slip may diminish at the western end of the fault zone where structural relief also decreases (Brocher and others, 2001 #4718).
Date and Compiler(s) 2004
Samuel Y. Johnson, U.S. Geological Survey
Richard J. Blakely, U.S. Geological Survey
Thomas M. Brocher, U.S. Geological Survey
Robert C. Bucknam, U.S. Geological Survey
Peter J. Haeussler, U.S. Geological Survey
Thomas L. Pratt, U.S. Geological Survey
Alan R. Nelson, U.S. Geological Survey
Brian L. Sherrod, U.S. Geological Survey
Ray E. Wells, U.S. Geological Survey
David J. Lidke, U.S. Geological Survey
David J. Harding, NASA, National Aeronautic and Space Administration, Geodynamics Branch
Harvey M. Kelsey, Humboldt State University
References #4715 Atwater, B.F., 1999, Radiocarbon dating of a Seattle earthquake to A.D. 900-930 [abs.]: Seismological Research Letters, v. 70, p. 232.

#597 Atwater, B.F., and Moore, A.L., 1992, A tsunami about 1000 years ago in Puget Sound, Washington: Science, v. 258, p. 1614-1617.

#4716 Blakely, R.J., Wells, R.E., Weaver, C.S., and Johnson, S.Y., 2002, Location, structure, and seismicity of the Seattle fault, Washington—Evidence from aeromagnetic anomalies, geologic mapping, and seismic-reflection data: Geological Society of America Bulletin, v. 114, no. 2, p. 169-177.

#4719 Booth, D.B., 1994, Glaciofluvial infilling and scour of the Puget Lowland, Washington, during ice-sheet glaciation: Geology, v. 22, p. 695-698.

#4720 Bourgeois, J., and Johnson, S.Y., 2001, Geologic evidence of earthquakes at the Snohomish delta, Washington, in the past 1200 years: Geological Society of America Bulletin, v. 113, p. 482-494.

#4718 Brocher, T.M., Parsons, T., Blakely, R.J., Christensen, N.I., Fisher, M.A., Wells, R.E., and SHIPS Working Group, 2001, Upper crustal structure in Puget Lowland, Washington—Results from the 1998 seismic hazards investigation in Puget Sound: Journal of Geophysical Research, v. 106, p. 13,541-13,564.

#4717 Brocher, T.M., Pratt, T.L., Creager, K.C., Crosson, R.S., Steele, W.P., Weaver, C.S., Frankel, A.D., Trehu, A.M., Snelson, C.M., Miller, K.C., Harder, S.H., and ten Brink, U.S., 2000, Urban seismic experiments investigate Seattle fault and basin: Eos, Transactions of the American Geophysical Union, v. 81, p. 551-552.

#602 Bucknam, R.C., Hemphill-Haley, E., and Leopold, E.B., 1992, Abrupt uplift within the past 1700 years at southern Puget Sound, Washington: Science, v. 258, p. 1611-1614.

#4721 Bucknam, R.C., Sherrod, B.L., and Elfendahl, G., 1999, A fault scarp of probable Holocene age in the Seattle fault zone, Bainbridge Island, Washington: Seismological Research Letters, v. 258, p. 1611-1614.

#4722 Calvert, A.J., Fisher, M.A., and SHIPS Working Group, 2001, Imaging the Seattle fault zone with high-resolution seismic tomography: Geophysical Research Letters, v. 28, no. 2337-2340.

#4723 Danes, Z.F., Bonno, M., Brau, E., Gilham, W.D., Hoffman, T.F., Johansen, D., Jones, M,H., Malfait, B., Masten, J., Teague, G.O., 1965, Geophysical investigation of the southern Puget Sound area, Washington: Journal of Geophysical Research, v. 70, p. 5573-5579.

#4725 Gower, H.D., Yount, J.C., and Crosson, R.S., 1985, Seismotectonic map of the Puget Sound region, Washington: U.S. Geological Survey Miscellaneous Investigations Map I-1613, scale 1:250,000.

#4726 Haeussler, P.J., and Clark, K.P., 2000, Preliminary geologic map of the Wildcat Lake 7.5' quadrangle, Kitsap and Mason Counties, Washington: U.S. Geological Survey Open-File Report 00-356, scale 1:24,000.

#4727 Haeussler, P.J., Wells, R.E., Blakely, R.J., Murphy, J., and Wooden, J., L., 2000, Structure and timing of movement on the Seattle fault at Green and Gold Mountains, Kitsap Peninsula, Washington: Geological Society of America Abstracts with Programs, v. 32, no. 6, p. A-16.

#4728 Harding, D.J., and Berghoff, G.S., 2000, Fault scarp detection beneath dense vegetation cover—Airborne laser mapping of the Seattle fault zone, Bainbridge Island, Washington State: Proceedings of the American Society of Photogrammetry and Remote Sensing Annual Conference, Washington, D.C., 9 p.

#6211 Haugerud, R.A., Harding, D.J., Johnson, S.Y., Harless, J.L., Weaver, C.S., and Sherrod, B.L., 2003, High-resolution lidar topography of the Puget Lowland, Washington—A bonanza for earth science: Geological Society of America GSA Today, v. 13, no. 6, p. 4-10.

#4735 Haugerud, R.A., Weaver, C.S., and Harless, J., 2001, Finding faults with LIDAR in the Puget Lowland: Seismological Research Letters, v. 72, p. 253.

#599 Jacoby, G.C., Williams, P.L., and Buckley, B.M., 1992, Tree ring correlation between prehistoric landslides and abrupt tectonic events in Seattle, Washington: Science, v. 258, p. 1621-1623.

#4729 Johnson, S.Y., Dadisman, S.V., Childs, J.R., and Stanley, W.D., 1999, Active tectonics of the Seattle fault and central Puget Lowland—Implications for earthquake hazards: Geological Society of America Bulletin, v. 111, p. 1042-1053 and oversize insert.

#4730 Johnson, S.Y., Potter, C.J., and Armentrout, J.M., 1994, Origin and Evolution of the Seattle fault and Seattle basin: Geology, v. 22, p. 71-74 and oversize insert.

#598 Karlin, R.E., and Abella, S.E.B., 1992, Paleoearthquakes in the Puget Sound region recorded in sediments from Lake Washington, U.S.A.: Science, v. 258, p. 1617-1620.

#6713 Karlin, R.E., Holmes, M., Abella, S.E.B., and Sylwester, R., 2004, Holocene landslides and a 3500-year record of Pacific Northwest earthquakes from sediments in Lake Washington: Geological Society of America Bulletin, v. 116, p. 94-108.

#4734 Khazaradze, G.Q., Anthony, and Dragert, H., 1999, Tectonic deformation in western Washington from continuous GPS measurements: Geophysical Research Letters, v. 26, p. 3153-3156.

#4731 McCaffrey, R., Long, M.D., Goldfinger, C., Zwick, P.C., Nabelek, J.L., Johnson, C.K., and Smith, C., 2000, Rotation and pl. locking along the southern Cascadia subduction zone: Geophysical Research Letters, v. 27, p. 3117-3120.

#4732 Miller, M.M., Miller, D.J., Rubin, C.M., Dragert, H., Wang, Kelin, Qamar, Anthony, and Goldfinger, C., 2001, GPS-determination of along-strike variation in Cascadia margin kinematics—Implications for relative pl. motion, subduction zone coupling, and permanent deformation: Tectonics, v. 20, p. 161-176.

#6250 Nelson, A.R., Johnson, S.T., Kelsey, H.M., Sherrod, B.L., Wells, R.E., Okumura, K., Bradley, L., Bogar, R., and Personius, S.F., 2003, Field and laboratory data from an earthquake history of the Waterman Point fault, Kitsap County, Washington: U.S. Geological Survey Miscellaneous Field Studies Map MF-2423, 1 sheet.

#6354 Nelson, A.R., Johnson, S.Y., Kelsey, H.M., Sherrod, B.L., Wells, R.E., Bradley, L., and Okumura, K., 2003, Late Holocene earthquakes on the Waterman Point reverse fault, another ALSM-discovered fault scarp in the Seattle fault zone, Puget Lowland, Washington: Geological Society of America Abstracts with Programs.

#5868 Nelson, A.R., Johnson, S.Y., Kelsey, H.M., Wells, R.E., Sherrod, B.L., Pezzopane, S.K., Bradley, L., and Koehler, R.D., III, 2003, Late Holocene earthquakes on the Toe Jam Hill fault, Seattle fault zone, Bainbridge Island, Washington: Geological Society of America Bulletin, v. 115, no. 11, p. 16.

#4733 Nelson, A.R., Johnson, S.Y., Pezzopane, S.K., Wells, R.E., Kelsey, H.M., Sherrod, B.L., Koehler, R.D., Bradley, L.A., Bucknam, R.C., LaPrade, W.T., Cox, J.W., and Narwold, C.F., 2000, Postglacial and Late Holocene earthquakes on the Toe Jam strand of the Seattle fault, Bainbridge Island, Washington: Geological Society of America Abstracts with Programs, v. 32, p. A-58.

#4736 Nelson, A.R., Johnson, S.Y., Wells, R.E., Pezzopane, S.K., Kelsey, H.M., Sherrod, B.L., Bradley, L.A., Koehler, R.D.I., Bucknam, R.C., Haugerud, R.A., and LaPrade, W.T., 2002, Field and laboratory data from an earthquake history study of the Toe Jam Hill fault, Bainbridge Island, Washington: U.S. Geological Survey Open-File Report 02-0060, 19 p., 2 sheets.

#6237 Porter, S.C., and Swanson, T.W., 1998, Radiocarbon age constraints on rates of advance and retreat of the Puget lobe of the Cordilleran ice sheet during the last glaciation: Quaternary Research, v. 50, p. 205-213.

#4737 Pratt, T.L., Johnson, S.Y., Potter, C.J., and Stephenson, W., 1997, Seismic reflection images beneath Puget Sound, western Washington State: The Puget Lowland thrust sheet hypothesis: Journal of Geophysical Research, v. 102, p. 27,469-27,490.

#6712 Prunier, C.F., Karlin, R.E., Holmes, M., Abella, S.E.B., and Pratt, T.L., 1997, Holocene neotectonic deformation and earthquake history in sediments from Lake Washington, Lake Sammamish, and Port Orchard: Eos, Transactions of the American Geophysical Union, v. 78, no. 46, p. 440.

#4738 Rogers, W.P., 1970, A geological and geophysical study of the central Puget Sound Lowland: Seattle, University of Washington, unpublished Ph.D. dissertation, 123 p., 9.

#600 Schuster, R.L., Logan, R.L., and Pringle, P.T., 1992, Prehistoric rock avalanches in the Olympic Mountains, Washington: Science, v. 258, p. 1620-1621.

#4740 Sherrod, B.L., 2001, Evidence for earthquake-induced subsidence about 1100 years ago in coastal marshes of southern Puget Sound, Washington: Geological Society of America Bulletin, v. 113, p. 1299-1311.

#4741 Sherrod, B.L., Bucknam, R.C., and Leopold, E.B., 2000, Holocene relative sea level changes along the Seattle fault at Restoration Point, Washington: Quaternary Research, v. 54, p. 384-393.

#4739 Sherrod, B.L., Haeussler, P.J., Wells, R., Troost, K., and Haugerud, R., 2001, Surface rupture in the Seattle fault zone near Bellevue, Washington: Seismological Research Letters, v. 72, p. 253.

#4171 Sherrod, D.R., 1985, Geologic setting of the Breitenbush-Austin Hot Springs area, Cascade Range, north-central Oregon—Chapter 1, in Sherrod, D.R., ed., Geology and geothermal resources of the Breitenbush-Austin Hot Springs area, Clackamas and Marion Counties, Oregon: State of Oregon, Department of Geology and Mineral Industries Open-File Report 0-88-5, p. 1-14.

#6353 ten Brink, U.S., Molzer, P.C., Fisher, M.A., Blakely, R.J., Bucknam, R.C., Parsons, T., Crosson, R.S., and Creagher, K.C., 2002, Subsurface geometry and evolution of the Seattle fault zone and the Seattle basin, Washington: Bulletin of the Seismological Society of America, v. 92, p. 1737-1753.

#4743 Wells, R.E., and Johnson, S.Y., 2000, Neotectonics of western Washington and the Puget Lowland from northward migration of the Cascadia forearc: Geological Society of America Abstracts with Programs, v. 32, p. A-75.

#4742 Wells, R.E., Weaver, C.S., and Blakely, R.J., 1998, Forearc migration in Cascadia and its neotectonic significance: Geology, v. 26, p. 759-762.

#4744 Yount, J.C., and Gower, H.D., 1991, Bedrock geologic map of the Seattle 30' by 60' quadrangle, Washington: U.S. Geological Survey Open-File Report 91-147, 37 p., 4, scale 1:100,000.

#4745 Yount, J.C., and Holmes, M.L., 1992, The Seattle fault—A possible Quaternary reverse fault beneath Seattle Washington: Geological Society of America Abstracts with Programs, v. 24, p. 93.

#4746 Yount, J.C., Dembroff, G.R., and Barats, G.M., 1985, Map showing depth to bedrock in the Seattle 30' by 60' quadrangle, Washington: U.S. Geological Survey Miscellaneous Field Studies Map MF-1692, scale 1:100,000.