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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. 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. [74], Early Eocene igneous units in the area appear to be part of a 49- to 44- Ma magmatic belt that appeared just after the arrival of Siletzia, and possibly associated with that event. Posted: 12 days ago. [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. 10+ Cruises Age 2020s. fault Which of the following statements best describes elastic-rebound theory? [98] This turns and runs just south of Victoria, nearly in-line with the SWIF. A UW researcher says the fault line that caused earthquake that shook southern Turkey near the Turkish-Syrian border this week and killed more than 7,000 people is similar to the faults under Puget Sound. 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. 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. Conjugate faults are secondary faults that branch off from opposite sides of a strike-slip fault at approximately the same angle. A marine seismic reflection study[177] found evidence of faulting at the mouth of Budd Inlet, just north of the Olympia structure, and aligning with faint lineaments seen in the lidar imagery. This is just after the terrane carrying the Olympic Mountains came into contact with the North American continent. It stands out in regard of its eastwest orientation, depth to bedrock, and hazard to an urban population center. [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. One study of seismic vulnerability of bridges in the Seattle Tacoma area[4] estimated that an M 7 earthquake on the Seattle or Tacoma faults would cause nearly as much damage as a M 9 subduction earthquake. There is evidence that the Tacoma Fault connects with the White River River Fault (WRF) via the EPZ and Federal Way, under the Muckleshoot Basin (see map),[137] and thence to the Naches River Fault. A Coast Range Boundary Fault (CRBF, discussed above) was inferred on the basis of differences in the basement rock to the west and east of Puget Sound (the Crescent FormationCascadia core contact), and arbitrarily mapped at various locations including Lake Washington; north of the OWL this is now generally identified, with the Southern Whidbey Island Fault. 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. 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). [162] Trench studies indicate major earthquakes (in the range of M 6. to 7.8) on the Saddle Mountain faults [163] at nearly the same time (give or take a century) as the great quake on the Seattle Fault about 1100 years ago (900930 AD). [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). [132], Scarps associated with Holocene uplift of the Tacoma fault have been traced westward to Prickett Lake (southwest of Belfair, see map). 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. 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. In some places, such as along the South Fork of the Stillaguamish River between Arlington and Granite Falls, there are also contrasting geological contacts. An earthquake occurs along a south-moving fault. But the western segment the Devils Mountain Fault has left-lateral movement. (See, There is a preliminary report of aeromagnetic and gravity mapping placing the eastern edge of the Siletz terrane under Lake Washington. 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. 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. Harold Tobin, . 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. normal. [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. 6 earthquakes in the past 7 days. [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. [69] The principal zone of faulting extends from the Woods Creek Fault to the Granite Falls Fault Zone (GFFZ), slightly offset from the WCF and running under the town of Granite Falls. See Snavely et al. 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]. A parallel line ("B") about 15 miles (25 kilometers) to the west corresponds to the western limit of a zone of seismicity stretching from the WRZ to southwest of Portland. 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 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. [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. Full-Time. PNSN staff will continue to develop this section of the web site but to find more good information now, visit these resources: I've been in the business for 20 years and the way skilled labor has been treated up until very recently drove a ton of people away from the industry. 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). 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). The magnitude-4.0 earthquake that rattled people awake across the Puget Sound region last Wednesday probably struck on the western edge of the Seattle Fault, according to geologists. And since those models for the Seattle Fault were published, there've actually been many more Puget Sound faults discovered. [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. 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. It is believed that all of these faults, folds, basins, and uplifts are related. [88] (See the adjacent map. [2] All this is at risk of earthquakes from three sources:[3]. Sail Date: October 2022 . The maps show slightly lower . Marine technician Sony Brugger, right, retrieves underwater sampling equipment during a December 2020 research cruise aboard the RV Rachel Carson. This boundary would be the contact where northward movement of the basement rock of the Puget Lowland against the Olympic Peninsula is accommodated; it would be expected to be a significant seismological zone. Not until 2001 was it identified as a fault zone,[12] and only in 2004 did trenching reveal Holocene activity. [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. 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. Black squares are urban sewer outfalls, which don't match the bubble plumes' locations. [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. Arcos' work suggests. 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). Active faults and earthquakes in Washington state Seismic Scenario Catalog NEHRP site class and liquefaction susceptibility Seismic design categories Hazardous Minerals Lahar Hazards Landslides and landforms Inactive and abandoned mines Contact Us Susan Schnur Editor-in-Chief 360-701-6122 DNR is led by Commissioner of Public Lands Hilary Franz (Not included in QFFDB. 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. [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. One animation shows the expected path of a Puget Sound tsunami generated by a quake on the Seattle Fault. This section of the SWIF forms the southwestern side of the Everett Basin[48] (see map), which is notably aseismic in that essentially no shallow (less than 12km deep) earthquakes have occurred there, or on the section of the SWIF adjoining it, in the first 38 years of instrumental recording. 112 earthquakes in the past 365 days. [200], Mount St. Helens and Mount Rainier are located where their associated fault zones make a bend (see map, above).[201](Mt. [11] Marine seismic reflection surveys on Puget Sound where it cuts across the various faults have provided cross-sectional views of the structure of some of these faults, and an intense, wide-area combined on-shore/off-shore study in 1998 (Seismic Hazards Investigation in Puget Sound, or SHIPS)[12] resulted in a three-dimensional model of much of the subsurface geometry. 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. Puget Sound Lidar Consortium Finding faults scarp(n). 39 earthquakes in the past 365 days. It aligns with the West Coast fault and Queen Charlotte Fault system of strike-slip fault zones (similar to the San Andreas Fault in California) on the west side of Vancouver Island, but does not itself show any significant or through-going strike-slip movement. [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. 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. Initially it was not specified, and rather vaguely indicated to be west of Restoration Point (i.e., west of Puget Sound). [Paper No. [56] But detailed mapping just past the intersection shows only a complex and confused pattern of faulting, with no indication that there is, or is not, through-going faulting. [57] Mapping of areas further east that might clarify the pattern is not currently planned. Get directions. 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). [107], The Seattle Fault was first identified in 1965[108] but not documented as an active fault until 1992 with a set of five articles establishing that about 1100 years ago (AD 900930) an earthquake of magnitude 7+ uplifted Restoration Point and Alki Point, dropped West Point (the three white triangles in the Seattle Basin on the map), caused rockslides in the Olympics, landslides into Lake Washington, and a tsunami on Puget Sound. Geologic map of southwestern Washington (GM-34). Puget Sound and San Juan islands. 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. On this Wikipedia the language links are at the top of the page across from the article title. It may also be the original location of the DarringtonDevils Mountain Fault (the dashed line "X" at the top of the following map). [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. 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. Seattle Fault Zone in Central Puget Sound Washington Military Department FEMA Emergency Management Division . Although Washington State's Puget Sound has been shaken every few decades, damage in the region's largest cities, including Seattle, Tacoma and Olympia, has only ever been modest. 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. 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. Washington's fault lines tend to sweep east-west. . East of Puget Sound the basement of the Cascades province is various pre-Tertiary (older than 65 Ma) metamorphic rock. These faults are: the Kopiah Fault (note the curious curve), Newaukum Fault, Coal Creek Fault, and three other unnamed faults. [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). 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. This formation, up to 15km thick, is largely buried (from one to ten kilometers deep), and known mainly by magnetotellurics and other geophysical methods. [53] Reckoned between Victoria and approximately Fall City the length of the SWIF is around 150km (90 miles). Though a 2012 study[149] interpreted a different variety of tomographic data as showing the Hood Canal fault, other mapping has "found no convincing evidence for the existence of this fault",[150] considers it doubtful,[151] depicted it "with low level of confidence",[152] or omits it entirely. With inland, Puget Sound faults, like the Seattle Fault, the risk is comparatively smaller. The most recent Seattle Fault earthquake was about 1,100 years ago; The Seattle Fault has been active about three or four times in the past 3,000 years. [199] It has been speculated that the SHZ might extend under the Kitsap Peninsula (central Puget Sound), possibly involved with a section of the subducting Juan de Fuca plate that is suspected of being stuck. [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. [123] Other studies have faults extending NW or WNW from the SF towards Dabob Bay;[124] these are now recognized as part of the Dabob Bay fault zone. [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. [61], North of Everett is an area of parallel ridges and stream drainages oriented approximately NW-SE, evident even on non-geological maps. 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. The Doty fault particularly seems to have gained prominence with geologists since it was associated with an aeromagnetic anomaly,[184] and a report in 2000 credited it capable of a magnitude 6.7 to 7.2 earthquake. [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. [102] Or the Crescent margin may simply (and quietly) just run south-southeast under Seattle to the WRZ. [158] Vertical movement on these faults has created prominent scarps that have dammed Price Lake and (just north of Saddle Mountain) Lilliwaup Swamp. And like the SCF, strike-slip motion died out between 44 and 41 MA (due to plutonic intrusions). The first item on your list though is the fault of builders and nobody else. Base map is hillshaded DEM derived from LiDAR data (pixel size 1.8 m) from Puget Sound LiDAR Consortium; illumination from azimuth 05, at 5 above the horizon; datum is NAD83, UTM zone 10N. But. 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. ecc.kc@kingcounty.gov. It follows the Bainbridge Island ferry route east under Puget Sound and the route of Interstate 90 toward, and possibly beyond, the Cascade Mountains. There are numerous other faults (or fault zones) in the Puget Lowland, and around its edges, sketchily studied and largely unnamed. The alternative, that younger faulting in the Rogers Belt has offset the DMF Cheney argued that the MVF had offset the DMF 47km. 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 fault type is subducting. There is no firm evidence that this has occurred in the Seattle fault zone near Puget Sound, although a low terrace of 1 m or less formed during a moderate earthquake would be difficult to. A single earthquake in Seattle could cause a catastrophic situation for the northwest corner of the state, a new report from Washington's Department of Natural Resources found. As all of these are thrust and reverse faults, they probably result from northeast directed regional compression. [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. 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. But their significance to the Puget Sound area is unknown. NW-striking black lines are right-lateral bedrock faults thought to be subsidiary to Dar- rington-Devils Mountain fault zone (Dragovich and DeOme, 2006). These include (from north to south, see map) the: Devils Mountain Fault Strawberry Point and Utsalady Point faults Southern Whidbey Island Fault (SWIF) Large plumes of methane bubbles have been discovered throughout the waters of Puget Sound prompting questions about the Puget Sound food web, studies of earthquake faults and climate-change research. 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. 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. slope, need not be high. [142]) This reflects westward thrusting of the Seattle Uplift into the Dewatto basin, a northwestern extension of the Tacoma basin. 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). (1997), while observing the "remarkable straight boundaries that we interpret as evidence of structural control",[171] refrained from calling this structure a fault. The discovery was an alarm bell for engineers and emergency planners. 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. This map of Puget Sound shows the location of the methane plumes (yellow and white circles) detected along the ship's path (purple). Over 7,000 people are dead after a magnitude 7.8 earthquake shook southern Turkey, near the Turkish-Syrian border. 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). Fault lines in the New Madrid seismic zone are being mapped, thanks in part to . to the north, past Lummi Island is contrary to the prevailing consensus that the DMF is not offset. E.g., mapping along the Rattlesnake Mountain Fault Zone has revealed a complex network of active or potentially active faults across (and likely beyond) the lower Snoqualmie Valley, including the Cherry Creek Fault Zone, scene of the 1996 M 5.3 Duvall earthquake. 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. 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). [78] It is projected to extend past Lake Chaplain, and perhaps to the east end of Mount Pilchuck. 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. A new view is developing that the regional tectonic boundary is not under Hood Canal, but just to the west, involving the Saddle Mountain fault zone (discussed below) and associated faults. The Bellingham BayChaplain fault zone was first mapped by Cheney in 1976 as running from near Chaplain Lake (north of Sultan) NNW past Bellingham Bay. 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). This structure is shown in the gravitational mapping of 1965, but without comment. 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 . The geology also suggests that the DMF is moving obliquely up a ramp that rises to the east,[35] possibly an ancient coastal shore.