And like the SCF, strike-slip motion died out between 44 and 41 MA (due to plutonic intrusions). [61], North of Everett is an area of parallel ridges and stream drainages oriented approximately NW-SE, evident even on non-geological maps. [153] For these reasons this is now a questioned fault, and is indicated on the map as a dashed line. "We. [75], The strongly expressed topographical lineaments at the north end of the Rogers Belt pose a perplexing problem, as they show no definite offset where they are bisected by the left-lateral oblique-slip Devils Mountain Fault. There is a general pattern where most of these faults partition a series of basins and uplifts, each about 20km wide. Black squares are urban sewer outfalls, which don't match the bubble plumes' locations. [51] The length of the Doty Fault is problematical: the report in 2000 gave it as 65km (40 miles), but without comment or citation. 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). And since those models for the Seattle Fault were published, there've actually been many more Puget Sound faults discovered. [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. This interpretation suggests that the Seattle Uplift acts as a rigid block, and possibly explains the kinematic linkage by which large earthquakes may involve ruptures on multiple faults: the Seattle, Dewatto, and Tacoma faults represent the northern, western, and southern faces of a single block. [76], The Cherry Creek fault zone (CCFZ) was discovered in 2010 while mapping the area at the north end of the Rattlesnake Mountain fault zone (RMFZ). [42] Marine seismic reflection surveys show it striking northwest across the eastern end of the Strait of Juan de Fuca. 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. normal. 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. [47], To the southeast the SWIF passes through Admiralty Inlet (past Port Townsend) and across the southern part of Whidbey Island, crossing to the mainland between Mukilteo and Edmonds. If so, this would be a major fault system (over 185km long), connecting the Puget Lowland with the Yakima Fold Belt on the other side of the Cascades, with possible implications for both the OlympicWallowa Lineament (which it parallels) and geological structure south of the OWL. However, there are indications that the fault is segmented, which might limit rupturing and earthquake magnitude.[36]. Thick glacial and other deposits, heavy vegetation, urban development, and a topography of sharp relief and rapid erosion obscures the surface expression of faults in this region, and has hindered their discovery. 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). 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. With inland, Puget Sound faults, like the Seattle Fault, the risk is comparatively smaller. [109] It extends as far east as (and probably terminates at) the Rattlesnake Mountain Fault Zone (RMFZ; the southern extension of the SWIF) near Fall City. This is because the Olympic terrane is moving (relative to North America) northeast; its continued clockwise rotation is akin to a giant wheel rolling up the western side of the North Cascade crystalline core. [213] Seismicity sometimes occurs in zones, such as has been observed under Mercer Island, or from downtown Seattle towards Kirkland[214] but whether particular zones reflect undiscovered faults, or might be the source of damaging earthquakes, is generally unknown. Job Description. 09 Feb 2023 03:01:00 In the wedge model of Pratt et al. (Enter only one word per blank.) [103] Other seismic tomography has tantalizingly suggested three north-striking strands under Seattle, and a fourth just east of Lake Washington. It's the other counties in the Puget . This is being obliquely overridden by the North American plate coming out of the northeast, which has formed a bend in the subducting plate and in the forearc basin above it. to the north, past Lummi Island is contrary to the prevailing consensus that the DMF is not offset. 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. More than a millennium ago, a quake estimated at a magnitude 7 on the Seattle Fault thrust land upward as much as 23 feet and submerged 200-acre chunks of forest in central Puget Sound and Lake . [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. [206] This line may also mark the northwestern boundary of the SWCC. Nor does this uplift delineate any significant basin between it and the Devils Mountain Fault. About 1,100 years ago, a major earthquake rocked Puget Sound, suddenly shooting what is now Restoration Point on Bainbridge Island up about 23 feet while Seattle 's West Point sunk more than. [96] As the juxtaposition of various disparate tectonic structures in northwest Washington requires significant strike-slip movement, it is further expected that this contact will be a major fault.[97]. Document name Date Description Additional versions; 2809: 4/1/2021: . Over 7,000 people are dead after a magnitude 7.8 earthquake shook southern Turkey, near the Turkish-Syrian border. This map of Puget Sound shows the location of the methane plumes (yellow and white circles) detected along the ship's path (purple). They interpreted it as "simple folds in Eocene bedrock", though Sherrod (1998) saw sufficient similarity with the Seattle Fault to speculate that this is a thrust fault. The mapped surface traces are only 5km long, but LIDAR-derived imagery shows longer lineaments, with the traces cutting Holocene alluvial traces. The Seattle fault isn't a single strand, but a zone of subterranean fractures that extends across Puget Sound, passing under Seattle and reaching as far east as Issaquah. 2-5 Cruises Age 60s. Here, the Cherry Creek and Tokul Creek faults zones on the east side of the RMFZ are conjugate to the SWIF on the west side. [113], Determination of the western terminus of the Seattle Fault has been problematic, and has implications for the entire west side of the Puget Lowland. The answer is still unresolved. Most of these "faults" are actually zones of complex faulting at the boundaries between sedimentary basins (synclines, "") and crustal uplifts (anticlines, ""). It may also be the original location of the DarringtonDevils Mountain Fault (the dashed line "X" at the top of the following map). 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. Energize Eastside project is building a new substation and upgrading approximately 16 miles of existing transmission lines from Redmond to Renton. It has been speculated that the OS might connect with the seismically active Saint Helens Zone (discussed below), which would imply that the OS is both locked and being stressed, raising the possibility of a major earthquake. Puget Sound Energy Maps and Records Non-Disclosure Agreement: (NDA ONLY) ko ru zh es vi hi: PSE Map Request Form and Non-Disclosure Agreement: 07/29/2022: The worst of the tsunami would hit the Pacific Coast and San Juan Islands area but the interior of Puget Sound between Edmonds, Tacoma, and Hoodsport could see waves 10 feet or higher, the. Combined with continued aggressive electric conservation efforts, Energize . The question of where on Puget Sound the line would ultimately end was intentionally left open, and the region's fledgling cities began competing furiously for the good fortune of a major railroad terminus. Although the largely unstudied White River Fault (WRF) appears to lie just outside the Puget Lowland, it may actually connect under the Muckleshoot Basin to the East Passage Zone and the Tacoma Fault (map). One of these faults, the Sequim Fault Zone (striking east from the town of Sequim), crosses Discovery Bay (and various possible extensions of the Hood Canal Fault) and bounds the Port Ludlow Uplift ("uplift of unknown origin" on the map); it appears to extend to the Southern Whidbey Island Fault. Rainier, along the DDMFZ, and under Puget Sound between Olympia and approximately the Southern Whidbey Island Fault. According to the Washington state Department of Natural Resources, more than 1,000 earthquakes happen in Washington state each year! 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). One problem with this is that the parts of the SWIF east of Puget Sound do not show the velocity contrasts that would indicate contrasting rock types. [190] These faults also cross the Saint Helens Zone (SHZ), a deep, north-northwest trending zone of seismicity that appears to be the contact between different crustal blocks. If entirely analogous, then "roof duplex" might also apply, and the Olympia Fault would be a reverse fault similar to the Tacoma Fault. [139] The Dewatto linement extends from the western end of the Tacoma fault (see map immediately above) northward towards Green Mountain at the western end of the Seattle fault. A similar line aligns with the termination of the WRZ, SHZ, and Gales Creek Fault Zone (northwest of Portland), with faulting along the upper Nehalem River on the Oregon coast,[211] and a topographical contrast at the coast (between Neahkahnie Mountain and the lower Nehalem River valley) distinct enough to be seen on the seismicity map above (due west of Portland). The Pacific Northwest Seismic Network (PNSN) reported at least three earthquakes within the past few days. The discovery was an alarm bell for engineers and emergency planners. [52], Subsequent mapping shows the SWIF wrapping around the eastern end of the Seattle Basin to merge with the Rattlesnake Mountain Fault Zone (RMFZ); the RMFZ, despite the approximately 15 bend and different context, is now believed to be the southern extension of the SWIF. external structure, lines, and riggings; stand deck watches, such as helmsman and lookout underway; stand pier sentry, fire security, anchor, and . [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. [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. Black lines show the South Whidbey Island Fault Zone, the Seattle Fault Zone and the Tacoma. If the pattern is continued to the southwest, along cross-section A-A' in Pratt's figure 11 (and missing the mapped trace of the Doty Fault), then the next basin is at Grays Harbor (not shown here). fault Which of the following statements best describes elastic-rebound theory? 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.. South of Monroe the folds of the Rogers Belt are obscured by subsequent volcanic formations, but other faults parallel to the RMFZ (e.g., the Snoqualmie Valley and Johnson's Swamp fault zones) extend the general trend of NNW faulting as far as Monroe. A 2001 study[148] using high-resolution seismic tomography questioned its existence. Arcos' work suggests. This map is useful in showing the location and approximate length of faults but does not provide the impact an earthquake from a fault could have on the area surrounding. Yet the former is only the first of at least six more parallel southeast striking faults, which do cross the Salzer Creek Fault. Based on this and geophysical anomalies it was inferred that there is a major, active strike-slip fault zone running from the south end of Hood Canal, up Dabob Bay, and continuing north on land. This formation, up to 15km thick, is largely buried (from one to ten kilometers deep), and known mainly by magnetotellurics and other geophysical methods. San Juan Island hopping on the Puget Sound, WA. It is not notably seismogenic. Methane Plume Emissions Associated With Puget Sound Faults in the Cascadia Forearc CC BY 4.0 Authors: H. Paul Johnson University of Washington Seattle S. G. Merle National Oceanic and. [138] It arises from the contrast between the denser and more magnetic basalt of the Crescent Formation that has been uplifted to the east, and the glacial sediments that have filled the Dewatto basin to the west. This is the Dewatto lineament, believed to result from an east-dipping low-angle thrust fault where the western flank of the Seattle Uplift has been pushed into the northwestern corner of the Tacoma Basin. Just past them is the parallel Olympia Structure, which as a geophysical lineament has been traced to a point due east of Chehalis;[189] these would seem to be related somehow, but the nature of that relationship is not yet known. [38] These earthquakes probably caused tsunamis, and several nearby locations have evidence of tsunamis not correlated with other known quakes. Very little is known about the structure of the deep crust (below about 30km or 19 miles), though this and other seismic tomography studies (such as Ramachandran 2001) provide tantalizing glimpses. slope, need not be high. [44] Another problem with the SWIF/RMFZ as CRBF is that a large westward step is required to connect from the RMFZ to the Saint Helens Zone (SHZ; see map), whereas the RMFZ turns easterly to align with the OWL. [115] This seems reasonable enough, as Hood Canal is a prominent physiographic boundary between the Olympic Mountains and Puget Lowlands, and believed to be the location of a major fault. 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. [145] This is conformable with some regional tectonic interpretations[146] that put a major terrane boundary between the Olympics and the Puget Lowland, and imply a connection (either via the Discovery Bay Fault, or closer to Port Townsend) to the various faults in the Strait of Juan de Fuca. 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). "[50], The contrast of seismic velocities seen to the northwest is lacking in this section, suggesting that it is not the Coast RangeCascade contact. (A tsunami generated by a quake on the offshore Cascadia Subduction Zone would be . 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. Full-Time. And the magnitude used to generate that wave is only about 7.5, as opposed to a magnitude-9 earthquake off the coast. It appears that the Seattle Uplift is acting as a rigid block, with the Tacoma, Dewatto, and Seattle faults being the southern, western, and northern faces.
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