[102] Or the Crescent margin may simply (and quietly) just run south-southeast under Seattle to the WRZ. [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. [174] Although no surface traces of faulting have been found in either the Holocene glacial sediments or the basalts of the Black Hills,[175] on the basis of well-drilling logs a fault has been mapped striking southeast from Offut Lake (just west of Rainier); it appears to be in line with the easternmost fault mapped in the CentraliaChehalis area.[176]. (Their model of the Black Hills Uplift is analogous with their "wedge" model of the Seattle Uplift, discussed above, but in the opposite direction. 6) Click "Plot" Draw. [Paper No. Puget Sound Energy. 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). A Seattle Fault quake could be as large as M7.5,160 but less than M7.0 is more probable. Extensive research has since shown the Seattle Fault to be part of a regional system of faults . [5] The southern limit nearly matches the southern limit of the glaciation; possibly the seismicity reflects rebound of the upper crust after being stressed by the weight of the glacial ice. 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. These faults are: the Kopiah Fault (note the curious curve), Newaukum Fault, Coal Creek Fault, and three other unnamed faults. Prior to 2000, prominent aeromagnetic anomalies strongly suggested that the fault zone continued southeast, perhaps as far as the town of Duvall, but this was uncertain as the SWIF is largely concealed, and the faint surface traces generally obliterated by urban development. Its capable magnitude is a megathrust quake exceeding 9.0. It appears the entire DDMFZ and Leech River fault system was pushed onto the early continental margin from an original alignment along the OWL. There are numerous other faults (or fault zones) in the Puget Lowland, and around its edges, sketchily studied and largely unnamed. The map is from a 2007 report (click here to download) on seismic design categories in Washington. Rainier, along the DDMFZ, and under Puget Sound between Olympia and approximately the Southern Whidbey Island Fault. The alternative, that younger faulting in the Rogers Belt has offset the DMF Cheney argued that the MVF had offset the DMF 47km. to the north, past Lummi Island is contrary to the prevailing consensus that the DMF is not offset. 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. 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. 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. 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). These include (from north to south, see map) the: Devils Mountain Fault Strawberry Point and Utsalady Point faults Southern Whidbey Island Fault (SWIF) Gonzalez: That Seattle Fault tsunami has been modeled by others. Both the SPF and UPF are said to be oblique-slip transpressional; that is, the faults show both horizontal and vertical slip as the crustal blocks are pressed together. See. [67] However, subsequent mapping shows that the Woods Creek Fault (WCF), a four-mile wide strip of oblique-slip and strike-slip faults just to the west and passing directly under Sultan, appears to be the more significant fault, and better aligned with Mount Vernon. 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. (See, There is a preliminary report of aeromagnetic and gravity mapping placing the eastern edge of the Siletz terrane under Lake Washington. It's due for another one,. [70] Although the intervening section has not been mapped, geologists believe the GFFZ connects with the McMurray FZ to the north, and forms the eastern boundary of the Everett Basin. Review for American Spirit to U.S.A. Gilliancruise. [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. The Woods Lake Fault, running past Lake Chaplain, corresponds closest to the mapped position of the southern end of Cheney's Mount Vernon Fault. The northern end of the Crescent Formation (aka Metchosin Formation) has been identified as the eastwest trending Leech River Fault on the southern tip of Vancouver Island. 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. There are some interesting relationships here. 112 earthquakes in the past 365 days. It is believed capable of generating earthquakes of at least magnitude 7, and there is evidence of such a quake approximately 1,000 years ago, possibly the same earthquake documented on the Seattle Fault 24 miles (38km) to the north. 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. 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. [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]. 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. This bend has distorted the subducting slab into an arch that has lifted the Olympic Mountains and prevented them from subducting. Rainier is offset because the faults are deep and the conduits do not rise quite vertically.) They estimate the fault is within a few miles of the surface and was active as recently as 1,000 to 1,100 years ago. These lineaments have been associated with possible zones of faulting in the crust and subducting plate.[212]. The passive roof duplex model of Brocher et al. [130] This is likely not coincidental, as it appears that the Tacoma and Seattle faults converge at depth (see diagram above) in a way that northsouth compression tends to force the Seattle Uplift up, resulting in dip-slip movement on both fault zones. We use an extensive network of marine high-resolution and conventional industry seismic-reflection data to constrain the location, shallow structure, and displacement rates of the Seattle fault zone and crosscutting high-angle faults in the Puget Lowland of western Washington. ), 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". Strands of the east-striking Devils Mountain Fault cross the northern tip of Whidbey Island at Dugualla Bay and north side of Ault Field (Whidbey Island Naval Air Station). In the map above these are represented by the pair of dotted lines at the lower right. The fault type is subducting. Black lines show the South Whidbey Island Fault Zone, the Seattle Fault Zone and the Tacoma. The DotySalzer Creek Fault does not fully fit the regional pattern of basins and uplifts bounded by faults described above. The Seattle Fault is a zone of complex thrust and reverse faults between lines E and F on the map up to 7km wide and over 70km long that delineates the north edge of the Seattle Uplift. Interpretation of the eastern part of the Tacoma Fault is not entirely settled. [49] Yet it is also notable that "most seismicity in the northern Puget Sound occurs along and southwest of the southern Whidbey Island fault at typical depths of 1527 km within the lower part of the Crescent Formation. It's the other counties in the Puget . 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. Newport Inglewood Rose Canyon Fault Zone. The Seattle Fault crosses east-west through Puget Sound and downtown Seattle. [173] One reason for caution is that a detailed gravity survey was unable to resolve whether the Olympia structure is, or is not, a fault. In some places, such as along the South Fork of the Stillaguamish River between Arlington and Granite Falls, there are also contrasting geological contacts. They run . [9] Not until 1992 was the first of the lowland faults, the Seattle Fault, confirmed to be an actual fault with Holocene activity, and the barest minimum of its history established.[10]. 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). [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. ), and headed for the definitely active Saint Helens Zone; this appears to be a large-scale structure. The Canyon River Fault is believed to have caused a similar-sized earthquake less than 2,000 years ago;[167] this is a particular hazard to the Wynoochee Dam (to the west). There are other tsunami scenarios that are not accounted for in these maps, such as tsunamis caused by . Deep quakes are the most common large earthquakes that occur in the Puget Sound region. It follows the Bainbridge Island ferry route east under Puget Sound and the route of Interstate 90 toward, and possibly beyond, the Cascade Mountains. This is only one of a series of active large crustal faults in the Puget Lowland. external structure, lines, and riggings; stand deck watches, such as helmsman and lookout underway; stand pier sentry, fire security, anchor, and . Full-Time. [143] Such interconnection also suggests a capability for larger earthquakes (> M7 for the Seattle Fault); the amount of increased risk is unknown.[144]. [195] The southwestern boundary of the SWCC, where it is believed to be in near vertical contact with the Eocene basalts of the Crescent Formation, forms a good part of the 90km (56 mile) long SHZ. The EPZ is active, being the locale of the 1995 M 5 Point Robinson earthquake.[136]. . 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).
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