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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. The study was. 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. 4 earthquakes in the past 30 days. 10+ Cruises Age 2020s. [127], The Tacoma Fault (at right, and also between lines C and D on the Uplift and basin map, above) just north of the city of Tacoma, Washington has been described as "one of the most striking geophysical anomalies in the Puget Lowland". Cluster of earthquakes in Puget Sound considered 'normal', earthquake researchers say. From the north these are (see the map at right): The Hood Canal Fault (and its possible extensions) and Saddle Mountain faults to the west are believed to form the western boundary to all this. ), 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". If the entire 125km length ruptured in a single event the resulting earthquake could be as large as magnitude 7.5. The Devils Mountain Fault is seismically active, and there is evidence of Holocene offsets. On this Wikipedia the language links are at the top of the page across from the article title. 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. Though the Olympia Structure (a suspected fault) runs towards the SHZ, and delineates the northern edge of an exposed section of the Crescent Formation, it appears to be an upper crustal fold, part of a pattern of folding that extends southeast to cross the Columbia River near The Dalles, and unrelated to the mid and lower crustal SHZ. The WRZ and SHZ are associated with the southern Washington Cascades conductor (SWCC), a formation of enhanced electrical conductivity[194] lying roughly between Riffe Lake and Mounts St. Helens, Adams, and Rainier, with a lobe extending north (outlined in yellow, right). Click a second point on the map, this will be the right side of the cross-section. [160] The Canyon River Fault is a major fault in itself, associated with a 40km long lineament and distinct late Holocene scarps of up to 3 meters.[161]. The lowest exposed strata of Tiger Mountain, the mid-Eocene marine sediments of the Raging River formation, may be correlative with the SWCC. Plot. West of Puget Sound the tectonic basement of the Coast Range geologic province is the approximately 50 million year (Ma) old marine basalts of the Crescent Formation, part of the Siletzia terrane that underlies western Washington and Oregon. [92] This is where the SWIF encounters the edge of the Western and Eastern Melange Belts (remnants of a mid-Cretaceous subduction zone[93]); the RMFZ is where the Seattle Uplift is being forced against the Western Melange belt[94], To the north the Melange Belt is manifested as the Rogers Belt, a zone of low-amplitude folding stretching from Monroe to Mount Vernon; the apparent western edge of this zone is on-strike with the RMFZ. They are also on-strike with a swarm of faults on the Columbia River, bracketing The Dalles. These are usually fairly short, and not believed to be significantly seismogenic. Review for American Spirit to U.S.A. Gilliancruise. 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 . That wave is quite severe, quite high. 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. slope, need not be high. These lineaments have been associated with possible zones of faulting in the crust and subducting plate.[212]. It's the other counties in the Puget . 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. The length of the Doty Fault is problematical: the report in 2000 gave it as 65km (40 miles), but without comment or citation. [37] Trenching on the UPF (at a scarp identified by LIDAR) shows at least one and probably two Holocene earthquakes of magnitude 6.7 or more, the most recent one between AD 1550 to 1850, and possibly triggered by the 1700 Cascadia earthquake. 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. But. According to the recent seismological studies, the Seattle Fault is believed to be a zone of thrust or reverse faults that strikes through Seattle in the densely populated Puget Lowland of western Washington (Johnson et al., 1999). 0 magnitude subduction earthquake off the Washington coast would generate a tsunami capable of submerging not only coastal areas but also most of the Puget Sound shoreline . Of great interest here is that both the northern lobe of the SWCC and the Carbon River anticline are aligned towards Tiger Mountain (an uplifted block of the Puget Group of sedimentary and volcanic deposits typical of the Puget Lowland) and the adjacent Raging River anticline (see map). [45] The Leech River Fault has been identified as the northern edge of the Crescent Formation (aka Metchosin Formation, part of the Siletzia terrane that underlies much of western Washington and Oregon). PNSN staff will continue to develop this section of the web site but to find more good information now, visit these resources: The alternative, that younger faulting in the Rogers Belt has offset the DMF Cheney argued that the MVF had offset the DMF 47km. 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. [98] This turns and runs just south of Victoria, nearly in-line with the SWIF. Other similar lineaments (such as from Astoria to Glacier Peak) align with various topographical features and changes in fault orientation. These include the: Southern Whidbey Island Fault (SWIF) Seattle Fault Devils Mountain Fault Strawberry Point fault Utsalady Point fault Calawah fault Barnes Creek 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). One animation shows the expected path of a Puget Sound tsunami generated by a quake on the Seattle Fault. On the east, the Devils Mountain Fault connects with the south striking Darrington Fault (not shown) which runs to the OWL, and the Southern Whidbey Island Fault extends via the Rattlesnake Mountain Fault Zone (dashed line) to the OWL. Though these faults have been traced for only a little ways, the southeast striking anticlines they are associated with continue as far as Riffe Lake, near Mossyrock. Harold Tobin, a researcher at the University of Washington and director of the Pacific Northwest Seismic Network, says the fault line that caused earthquake that shook southern Turkey near the Turkish-Syrian border and killed more than 7,000 people is similar to the faults under Puget Sound. 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. This is the Puget Lowland. 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. Locations of some previously mapped faults have been adjusted on the latest map. 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. Analysis of seismic profiles extending 50 km across the Puget Lowland from Lake Washington to Hood Canal indicates . [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]. 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. 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. Get directions. [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. [53] Reckoned between Victoria and approximately Fall City the length of the SWIF is around 150km (90 miles). 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. 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. Following a mega quake on the Cascadia fault, simulations show that the tiny town of La Push would get hit first by a tsunami, 10 minutes after shaking started. Most of this thrust sheet consists of the Crescent Formation (corresponding to the Siletz River volcanics in Oregon and Metchosin Formation on Vancouver Island), a vast outpouring of volcanic basalt from the Eocene epoch (about 50 million years ago), with an origin variously attributed to a seamount chain, or continental margin rifting (see Siletzia). The ultimate driver of the stresses that cause earthquakes are the motions of the tectonic plates: material from the Earth's mantle rises at spreading centers, and moves out as plates of oceanic crust which eventually are subducted under the more buoyant plates of continental crust. [40], The Southern Whidbey Island Fault (SWIF) is a significant terrane boundary manifested as an approximately four mile wide zone of complex transpressional faulting with at least three strands. In the map above these are represented by the pair of dotted lines at the lower right. Also intersecting at Mount St. Helens is a NE (045) trending line (red) of Pleistocene (about 4 Ma) plug domes and a topographic lineament (followed in part by Highway 12). [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. [46] Seismic tomography studies show that this portion of the SWIF marks a strong contrast of seismic velocities, such as is expected of Crescent Formation basalts in contact with the metamorphic basement rocks of the Cascades geologic province to the east. Geologic map of southwestern Washington (GM-34). Despite not having active plate tectonics, the eastern United States still experiences earthquakes. 4) Drag square on line to include events to plot. This map of Puget Sound shows the location of the methane plumes as yellow and white circles. It is uncertain how these faults relate to the structure, and whether they are deep-seated faults, or fractures due to bending of the shallow crust. [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. [44] The significance of this whether the edge of the Crescent Formation (and implicitly of the Siletz terrane) turns southward (discussed below), or the metamorphic basement is supplanted here by other volcanic rock is not known. Combined with continued aggressive electric conservation efforts, Energize . And the magnitude used to generate that wave is only about 7.5, as opposed to a magnitude-9 earthquake off the coast. A magnitude 7.1 earthquake in the Tacoma Fault Zone A plausible scenario for the southern Puget Sound region, Washington May 18, 2010 Citation Information. [29] This prospect is especially intriguing as a possible explanation of a cluster of seismic events around 1100 years ago.[30]. [6] The first definite indications of most of these faults came from gravitational mapping in 1965,[7] and their likely existence noted on mapping in 1980 and 1985. There are other tsunami scenarios that are not accounted for in these maps, such as tsunamis caused by . [218] This would pose significantly greater seismic hazard than currently recognized, especially as the White River Fault is believed to connect with the Naches River Fault that extends along Highway 410 on the east side of the Cascades towards Yakima. King County Emergency Management. [134] Most authors align it with the strong gravitational anomaly (which typically reflects where faulting has juxtaposed rock of different density) and topographical lineament down Commencement Bay. [42] Marine seismic reflection surveys show it striking northwest across the eastern end of the Strait of Juan de Fuca. Page 2 of 4 / 2012-2013 Type of Earthquake Most earthquake hazards result from ground shaking caused by seismic waves that radiate out from a fault when it ruptures. Western Washington lies over the Cascadia subduction zone, where the Juan de Fuca Plate is subducting towards the east (see diagram, right). Faults running on the Snohomish County-Skagit County line and between Port Townsend and Whidbey Island point toward Vancouver Island. An informal consortium of regional agencies has coordinated LIDAR mapping of much of the central Puget Lowland, which has led to discovery of numerous fault scarps which are then investigated by trenching (paleoseismology). However, there are indications that the fault is segmented, which might limit rupturing and earthquake magnitude.[36]. [83], The CCFZ appears to be related to the parallel Tokul Creek fault zone to the south; both appear to be conjugate faults[84] to the northwest-trending SWIF. 2-5 Cruises Age 60s. [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. This is supported by geologically recent scarps and other signs of active faulting on the Saddle Mountain faults, and also discovery of a geophysical lineament running through Pleasant Harbor (south of Brinnon) that appears to truncate strands of the Seattle Fault. 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). (1997), while observing the "remarkable straight boundaries that we interpret as evidence of structural control",[171] refrained from calling this structure a fault. The geology also suggests that the DMF is moving obliquely up a ramp that rises to the east,[35] possibly an ancient coastal shore. It is believed that all of these faults, folds, basins, and uplifts are related. All this is explained by right-lateral strike-slip motion on the Straight Creek Fault, which initiated about 50 to 48 Ma (millions of years ago). "[31] More particularly, the concentration of seismicity under Puget Sound south of the Seattle Fault is attributed to uplift of that block, bounded by the Seattle, Tacoma, and Dewatto faults on the north, south, and west (the eastern boundary is not determined), creating the Seattle Uplift. 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). OLYMPIA, Wash. - A 9. 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). 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. Plot Type: X-Section Depth Cumulative # Mag-Time. [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. 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. 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. [60] Such seismic hazards were a major issue in the siting of the plant, as it is tucked between two active strands, and the influent and effluent pipelines cross multiple zones of disturbed ground. [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. Seismic tomography studies show a change in seismic velocities across the northern end of the SWIF, suggesting that this is also part of the Coast RangeCascade contact. [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]. [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. Newport Inglewood Rose Canyon Fault Zone. Even before Washington became a state in 1889, Puget Sound beaches had been exploited as log dumps, farmed for shellfish, occupied as homesites and enjoyed for recreation. [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. This follows the front of the Rosedale monocline, a gently southwest-tilting formation that forms the bluffs on which Tacoma is built. Geochemistry, Geophysics, Geosystems , 2021; 23 (1) DOI: 10.1029/2021GC010211 Cite This Page : 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. It follows the Bainbridge Island ferry route east under Puget Sound and the route of Interstate 90 toward, and possibly beyond, the Cascade Mountains. 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. [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 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. The last major earthquake on the Seattle Fault occurred around 1,100 years ago, shifting the landscape in Puget Sound. Folding and faulting has exposed these basalts in some places (black areas in diagram); the intervening basins have been filled by various sedimentary formations, some of which have been subsequently uplifted. The Doty Fault appears to terminate against, or possibly merge with, the Salzer Creek Fault at Chehalis; the Salzer Creek Fault is traced another seven miles east of Chehalis. 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.

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