Energy builds up as elastic strain in rocks. [42] Marine seismic reflection surveys show it striking northwest across the eastern end of the Strait of Juan de Fuca. These maps are based on only one Cascadia scenario. Mapping from the Pacific Northwest Seismic Network shows that the bulk of the earthquakes in western Washington are concentrated in four places: in two narrow zones under Mt. The most striking concentrations of mid-crustal seismicity in western Washington outside of Puget Sound are the Saint Helens Zone (SHZ) and Western Rainier Zone (WRZ) at the southern edge of the Puget Lowland (see seismicity map, right). [156], The Saddle Mountain Faults ("East" and "West", and not to be confused with a different Saddle Mountains Fault in Adams county, eastern Washington[157]), are a set of northeast trending reverse faults on the south-east flank of the Olympic Mountains near Lake Cushman first described in 1973 and 1975. The Seattle Fault, a zone of east-west thrust faults under the Puget Sound and Seattle, last ruptured in a magnitude-7.0 to -7.5 earthquake about 1,100 years ago. [68] Both of these faults (and some others) appear to terminate against the left-lateral Sultan River Fault at the western margin of the NNE-striking Cherry Creek Fault Zone (CCFZ; see next section). Sail Date . [207] North of the RMFZ it follows a topographical lineament that can be traced to Rockport (on Hwy. The Seattle Fault was first recognized as a significant seismic hazard in 1992, when a set of reports showed that about 1,100 years ago it was the scene of a major earthquake of about magnitude 7 - an event that entered Native American oral legend. Some upper-crustal formations (such as the Western and Eastern Melange Belts, see, There is a general north or northeast directed compression within the Lowland causing folds, which eventually break to become, This page was last edited on 11 January 2023, at 17:28. [78] It is projected to extend past Lake Chaplain, and perhaps to the east end of Mount Pilchuck. It is not known to be seismic indeed, there is very little seismicity south of the Tacoma Basin as far as Chehalis[169] and not even conclusively established to be a fault. The earthquake scenario used in the modeling is a "very large, low-probability" magnitude 7.5 earthquake on the Seattle Fault, which runs east-west through Puget Sound and downtown Seattle.. See. The Olympia structure also known as the Legislature fault[168] is an 80km long gravitational and aeromagnetic anomaly that separates the sedimentary deposits of the Tacoma Basin from the basalt of the Black Hills Uplift (between lines A and B on the map). [100], However, gravity and other data suggest that near the southern tip of Whidbey Island the Crescent Formation contact may turn away from the SWIF, and may even be reentrant under north Seattle,[101] forming the northwestern side of the Seattle Basin, and possibly connecting with the recently reported "Bremerton trend" of faulting running from the southern end of Hood Canal, through Sinclair Inlet (Bremerton), and across Puget Sound. This map shows areas of seismic risk from high (red) to low (grayish-green). Puget Sound Lidar Consortium Finding faults scarp(n). The Doty Fault/Chehalis Basin sequence follows the cross-section X-X' shown on the, The long-range mapping plan area and current status of planned mapping can be seen at, For the County's interpretation of the geological hazard and anticipated impacts of a major earthquake, see the, Interstate 5 runs nearly due north from Everett to Mount Vernon, except for a stretch southeast of Conway that parallels one of these low-amplitude folds. Display Faults. [38] These earthquakes probably caused tsunamis, and several nearby locations have evidence of tsunamis not correlated with other known quakes. What makes the DotySalzer Fault (and the short Chehalis Fault striking due east from Chehalis) stand out from the many other faults south of Tacoma is its eastwest strike; the significance of this is not known. [192] Indeed, it is mainly by their seismicity that these faults are known and have been located, neither showing any surface faulting. How the CRBF might run north of Seattle (specifically, north of the OWL, which Seattle straddles) is unknown, and even questioned, as there is no direct evidence of such a fault. [16] For the past 50 million years or so (since the early Eocene epoch) these have been thrust by subduction up against the North Cascades ("fixed block" in the diagram), which sit on the North American Plate. [183] While the towns of Centralia and Chehalis in rural Lewis County may seem distant (about 25 miles) from Puget Sound, this is still part of the Puget Lowland, and these faults, the local geology, and the underlying tectonic basement seem to be connected with that immediately adjacent to Puget Sound. The Devils Mountain Fault separates two similar but distinctive ensembles of Mesozoic (pre-Tertiary, before the dinosaurs died) or older rock. "[50], The contrast of seismic velocities seen to the northwest is lacking in this section, suggesting that it is not the Coast RangeCascade contact. Yet the SHZ and WRZ may be integral to the regional geology of Puget Sound, possibly revealing some deep and significant facets, and may also present significant seismic hazard. Especially as seismic reflection data[135] shows some faulting continuing east across Vashon Island and the East Passage of Puget Sound (the East Passage Zone, EPZ) towards Federal Way and an east-striking anticline. The Doty fault has been mapped from the north side of the Chehalis airport due west to the old logging town of Doty (due north of Pe Ell), paralleled most of that distance by its twin, the Salzer Creek Fault, about half a mile to the north. At Darrington it is seen to connect with the Darrington Fault, which runs nearly south 110km to converge with the Straight Creek Fault (SCF), and then to turn near Easton to align with the OlympicWallowa Lineament; together these are known as the DarringtonDevils Mountain Fault Zone (DDMFZ). The Little River Fault (see the QFFDB, Fault 556) is representative of an extensive zone of faults along the north side of the Olympic Peninsula and in the Strait of Juan de Fuca (likely connected with the fault systems at the south end of Vancouver Island, see fault database map), but these lie west of the crustal blocks that underlie the Puget Lowland, and again their possible impact on the Puget Sound region is unknown. It therefore seems reasonable that the rest of the SWIF (and its apparent extension, the RMFZ) follows the Coast RangeCascade contact, and (these faults being active) constitutes the CRBF. San Juan Island hopping on the Puget Sound, WA. This structure is shown in the gravitational mapping of 1965, but without comment. That earthquake, likely between magnitude 7 and 7.5, lifted the southern end of Bainbridge Island and West Seattle more than 20 feet (3 meters), generated a tsunami, and created landslides into Lake Washington, says Bill Steele . Just four miles (6km) south the city of Oak Harbor straddles several stands of the Utsalady Point Fault (UPF) as they head roughly east-southeast towards Utsalady Point at the north end of Camano Island. (See, There is a preliminary report of aeromagnetic and gravity mapping placing the eastern edge of the Siletz terrane under Lake Washington. 112 earthquakes in the past 365 days. [198], Does the SHZ extend north? Because the Seattle and Tacoma faults run directly under the biggest concentration of population and development in the region, more damage would be expected, but all the faults reviewed here may be capable of causing severe damage locally, and disrupting the regional transportation infrastructure, including highways, railways, and pipelines. There's a one-in-10 chance that the next . Yet the former is only the first of at least six more parallel southeast striking faults, which do cross the Salzer Creek Fault. The energy released depends on the length of the fault; the faults here are believed capable of generating earthquakes as great as M 6 or 7. This map of Puget Sound shows the location of the methane plumes (yellow and white circles) detected along the ship's path (purple). However, the Hood Canal fault has been "largely inferred"[147] due to a paucity of evidence, including lack of definite scarps and any other signs of active seismicity. Next to a 4-6 lines highways with 90db noise and cancerous pollution. [180], That Olympia and the south Sound are at risk of major earthquakes is shown by evidence of subsidence at several locations in southern Puget Sound some 1100 years ago. [170] Gower, Yount & Crosson (1985), labelling it "structure L", mapped it from Shelton (near the Olympic foothills) southeast to Olympia (pretty nearly right under the state Legislature), directly under the town of Rainier, to a point due east of the Doty Fault, and apparently marking the northeastern limit of a band of southeast striking faults in the Centralia-Chehalis area. Can be formed by differential erosion of adjacent hard and soft rock; by localized erosion, for example at the edge of a river terrace; by movement of a landslide; or by a shallow earthquake that is large enough to break the Earth's surface. [216], An Everett Fault, running east-northeast along the bluffs between Mukilteo and Everett that is, east of the SWIF and at the southern edge of the Everett Basin has been claimed, but this does not appear to have been corroborated.[217]. Tacoma's Gain is Seattle's Pain. Document name Date Description Additional versions; 2809: 4/1/2021: . TTY Relay 711. On the eastern side, where the SWCC is believed to be in contact with pre-Tertiary terranes accreted to the North American craton, matters are different. 64, on-line) that the edge of the Crescent Formation offsets west along the Seattle Fault, with the Seattle Basin resulting from a gap between the main part of Siletiza and a northern block that has broken away. The alternative, that younger faulting in the Rogers Belt has offset the DMF Cheney argued that the MVF had offset the DMF 47km. On the other hand, the contrasting character of the east-striking and southeast-striking segments is unsettling, and the change of direction somewhat difficult to reconcile with the observed fault traces. The largest intra-crustal earthquakes have about the same total energy (which is about one-hundredth of a subduction event), but since they are closer to the surface they will cause more powerful shaking, and, therefore, more damage. It is not notably seismogenic. [182], The Doty Fault the southernmost of the uplift-and-basin dividing faults reviewed here, and located just north of the Chehalis Basin is one of nearly a dozen faults mapped in the CentraliaChehalis coal district in 1958. Tobin says offshore faults tend to cause bigger earthquakes and are a larger tsunami risk. [164] Such quakes pose a serious threat to the City of Tacoma's dams at Lake Cushman,[165] located in the fault zone,[166] and to everyone downstream on the Skokomish River. The University of Puget Sound's Facilities Services Department is hiring an Electrician responsible for the inspection, installation, modification, maintenance and repair of the electrical systems across Puget Sound's beautiful residential campus community located . It has been suggested that a corresponding change in the character of the SWIF may reflect a change in the direction of regional crustal strain. A Seattle Fault quake could be as large as M7.5,160 but less than M7.0 is more probable. Geochemistry, Geophysics, Geosystems , 2021; 23 (1) DOI: 10.1029/2021GC010211 Cite This Page : [120] However, the Saddle Mountain fault zone is not quite reciprocally aligned,[121] trending more northerly to where it encounters westeast trending faults (including the Hamma Hamma fault zone) that appear to be a westward extension of the Seattle Fault zone. [59] Another study identified an unusually broad band of scarps passing between Bothell and Snohomish, with several scarps in the vicinity of King County's controversial Brightwater regional sewage treatment plant showing at least four and possibly nine events on the SWIF in the last 16,400 years. The SE striking Scammon Creek Fault seems to be terminated by the Salzer Creek Fault (the exact relationship is not clear), with the latter continuing east for another seven miles. The first item on your list though is the fault of builders and nobody else. Although these faults are west of the Hood Canal Fault (previously presumed to be the western boundary of the Puget Lowland), new studies are revealing that the Saddle Mountain and related faults connect with the Seattle fault zone. According to the Washington state Department of Natural Resources, more than 1,000 earthquakes happen in Washington state each year! [21] The OWL appears to be a deep-seated structure over which the shallower crust of the Puget Lowland is being pushed, but this remains speculative. [197] This anticline, or uplifted fold, and the narrower width of the northern part of the SWCC, reflects an episode of compression of this formation. Doubts on the connectivity of these faults led to abandonment of this name in 1986[65] when Cheney mapped the Mount Vernon fault (MVF) from near Sultan northwest past Lummi Island (west side of Bellingham Bay, visible at the top of the map), crossing the Devils Mountain Fault (DMF, part of the DarringtonDevils Mountain Fault Zone) near Mount Vernon. And since those models for the Seattle Fault were published, there've actually been many more Puget Sound faults discovered. It does bound the north side of the Chehalis basin, but the south boundary of the Black Hills Uplift is more properly the southeast striking Scammon Creek Fault that converges with the DotySalzer Creek Fault just north of Chehalis. [89] The northern end of the mountain falls off where it crosses the eastern end of the Seattle Fault, which in turn terminates at the RMFZ; Rattlesnake Mountain forms the eastern edge of the Seattle Uplift. The Devils Mountain Fault (DMF) runs about 125km (75 miles) from the town of Darrington in the Cascade foothills due west to the northern tip of Whidbey Island, and on towards Victoria, British Columbia, where the DMF is believed to join the Leech River fault system at the southern end of Vancouver Island. Methane Plume Emissions Associated With Puget Sound Faults in the Cascadia Forearc. The principal effects of this complex interplay of forces on the near-surface crust underlying the Puget Lowland are: Further complicating this is a feature of unknown structure and origin, the OlympicWallowa Lineament (OWL). This map of Puget Sound shows the location of the methane plumes as yellow and white circles. Over 7,000 people are dead after a magnitude 7.8 earthquake shook southern Turkey, near the Turkish-Syrian border. This is a seemingly accidental alignment of topographic features that runs roughly east-southeast from the north side of the Olympic Peninsula to the Wallowa Mountains in northeastern Oregon. Most people in the United States know just one fault line by name: the San Andreas, which runs nearly the length of California and is perpetually rumored to be on the verge of unleashing "the. Review for American Spirit to U.S.A. Gilliancruise. The Puget Sound Region is crisscrossed by fault lines and zones and also located close to the Cascadia Subduction Zone, where the Juan de Fuca and North American tectonic plates meet. In particular, to the southeast of Mount St. Helens and Mount Rainier they reflect a regional pattern of NNW oriented faulting, including the Entiat Fault in the North Cascades and the Portland Hills and related faults around Portland (see QFFDB fault map). It is of interest here because the various strands of the Seattle Fault change orientation where they appear to cross the OWL,[20] and various other features, such as the Rosedale monocline and Olympia structure, and a great many local topographical features, have parallel alignments. ), The Coast Range Boundary Fault (CRBF) is hypothesized, expected on the basis of tectonic considerations, which may correlate in part with one or more currently known faults, or may involve as yet undiscovered faulting. As all of these are thrust and reverse faults, they probably result from northeast directed regional compression. E.g., HH mlange rock has been found in Manastash Ridge, 110km to the south (look for the small sliver of purple near the bottom of the diagram). [57] Mapping of areas further east that might clarify the pattern is not currently planned. The Puget Sound faults under the heavily populated Puget Sound region (Puget Lowland) of Washington state form a regional complex of interrelated seismogenic (earthquake-causing) geologic faults. At the edge of this older rock is the Rogers Belt, a geologically interesting zone running from the area of Sultan (due east of Everett) to Mount Vernon (just north of the bend in the Devils Mountain Fault). normal. While there is a bit of uplifted pre-Tertiary rock between the SPF and UPF, this does not truly fit the uplift and basin pattern described above because of the small scale (2km wide rather than around 20), and because the uplift here is entirely like a wedge being popped out between two nearly vertical faults, rather than being forced over a ramp such as is involved with the Seattle and Tacoma faults. $30 to $33 Hourly. Rainier is offset because the faults are deep and the conduits do not rise quite vertically.) This seems geologically reasonable, as both the SWIF and RMFZ appear to be the contact between Tertiary Crescent Formation basement of Puget Sound on the west and the older Mesozoic (pre-Tertiary) mlange belt basement rocks under the Cascades on the east.[110]. This follows the front of the Rosedale monocline, a gently southwest-tilting formation that forms the bluffs on which Tacoma is built. [219] Various other faults in the North Cascades are older (being offset by the Straight Creek Fault) and are unrelated to the faults in Puget Sound. ), Aeromagnetic mapping in 1999 showed a very prominent anomaly[172] (such as typically indicates a contrast of rock type); that, along with paleoseismological evidence of a major Holocene earthquake, has led to a suggestion that this structure "may be associated with faulting". [87], Rattlesnake Mountain is a prominent NNW trending ridge just west of North Bend (about 25 miles east of Seattle). [209] Between the Cherry Creek and parallel Tokul Creek faults is a contact between formations of the Western Melange Belt. They are also on-strike with a swarm of faults on the Columbia River, bracketing The Dalles. Seven times in the past 3,500 years, the CSZ has buckled and fractured to produce an earthquake so massive that it left a mark in the geologic record. [178] Alternately, the OS appears to coincide with a gravitational boundary in the upper crust that has been mapped striking southeast to The Dalles on the Columbia River,[179] where there is a swarm of similarly striking faults. These bends are located where they intercept a "subtle geological structure"[202] of "possible fundamental importance",[203] a NNE striking zone (line "A" on the map) of various faults (including the Tokul Creek Fault NNE of Snoqualmie) and early-Miocene (about 24 Ma) volcanic vents and intrusive bodies (plutons and batholiths) extending from Portland to Glacier Peak;[204] it also marks the change in regional fault orientation noted above. . Newport Inglewood Rose Canyon Fault Zone. These faults also form the north and south boundaries of uplifted pre-Tertiary rock, suggesting that the faults come together at a lower level, much like one model of the Seattle and Tacoma faults, but at a smaller scale. Curiously, the extension of line "B" north of the OWL is approximately the eastern limit of Puget Sound seismicity, the rest of southwestern Washington and the North Cascades being relatively aseismic (see the seismicity map, above). Discovery of faults has been greatly facilitated with the development of LIDAR, a technique that can generally penetrate forest canopy and vegetation to image the actual ground surface with an unprecedented accuracy of approximately one foot (30cm). (Not included in QFFDB. (2001),[111] relying on seismic tomography data from the "Seismic Hazards Investigation in Puget Sound" (SHIPS) experiment, retains the thrusting slab and master ramp concepts, but interprets the Tacoma fault as a reverse fault (or back thrust) that dips north towards the south dipping Seattle fault (see diagram); as a result the Seattle Uplift is being popped up like a horst. Tacoma, WA. Western Washington lies over the Cascadia subduction zone, where the Juan de Fuca Plate is subducting towards the east (see diagram, right). [102] Or the Crescent margin may simply (and quietly) just run south-southeast under Seattle to the WRZ. [133] The Tacoma fault was initially suspected of following a weak magnetic anomaly west to the Frigid Creek fault,[127] but is now believed to connect with a steep gravitational, aeromagnetic, and seismic velocity gradient that strikes north towards Green Mountain (Blue Hills uplift). The western flank of the Seattle Uplift forms a strong gravitational, aeromagnetic, and seismic velocity gradient known as the Dewatto lineament. If entirely analogous, then "roof duplex" might also apply, and the Olympia Fault would be a reverse fault similar to the Tacoma Fault. These features suggest that the southern Puget Lowland is influenced by the deep crust and even the subducting Juan de Fuca plate, but the details and implications are not yet known. Kinematic analysis suggests that if shortening (compression) in the Puget Lowland is directed to the northeast (i.e., parallel to Hood Canal and the Saddle Mountain deformation zone) and thus oblique to the Dewatto lineament, it should be subject to both strike-slip and dip-slip forces, implying a fault. These faults are: the Kopiah Fault (note the curious curve), Newaukum Fault, Coal Creek Fault, and three other unnamed faults. The SWCC appears to be Tertiary marine sediments, not the pre-Tertiary metamorphic rock of the Cascades province; this would seem to make it part of the Coast Range province, with the Coast RangeCascade contact further east. [72] The WMB is an assemblage of Late Jurassic and Cretaceous rock (some of it as much as 166 million years old) collected in the accretionary wedge (or prism) of a subduction zone. There are numerous other faults (or fault zones) in the Puget Lowland, and around its edges, sketchily studied and largely unnamed. According to the preeminent model, the "Puget Lowland thrust sheet hypothesis",[26] these faults, etc., occur within a sheet of crust about 14 to 20km deep that has separated from and is being thrust over deeper crustal blocks. News Media at VA Puget Sound health care, 206-764-2435, 206-764-2317. The Seattle Fault is the most studied of the regional faults, which has led to several models of its structure, which may also be relevant to other faults. [43] Just south of Victoria, British Columbia it intersects the west-striking Devils Mountain Fault (reviewed above), and either merges with it,[44] or crosses (and possibly truncates) it to connect with the Leech River Fault. Where it intersects the northwest-trending Johnsons Swamp fault zone, easternmost member of the RMFZ. The geology also suggests that the DMF is moving obliquely up a ramp that rises to the east,[35] possibly an ancient coastal shore. The San Juan Island and Leach River faults crossing the southern end of Vancouver Island are significant and undoubtedly connected with the DarringtonDevils Mountain and Southern Whidbey Island faults, and certainly of particular interest to the residents of Victoria, B.C. Conjugate faults are secondary faults that branch off from opposite sides of a strike-slip fault at approximately the same angle. After all, Olympia, which is the closest of the cities to the megathrust fault, is estimated to experience the least severe shaking; at the same time, many cities on the east side of the Puget Sound further away from the fault experience much stronger shaking. But the western segment the Devils Mountain Fault has left-lateral movement. [210] The zone between these two lines, reflecting changes in regional structure, seismicity, fault orientation, and possibly the underlying lithospheric structure, appears to be a major structural boundary in the Puget Lowland.
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