This map of Puget Sound shows the location of the methane plumes (yellow and white circles) detected along the ship's path (purple). Movement on the southern segment of the DDMFZ that converges with the SCF the Darrington Fault was, as on the SCF itself, right-lateral. [203] This line is the southernmost of a band of NE trending faults and topographical lineaments that extend from the Oregon coast into the North Cascades. [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. [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]. Accommodation of strain (displacement) between the Seattle Fault and the Saddle Mountain deformation zone is likely distributed across the more pliable sediments of the Dewatto Basin; this, and the greater depth to the Crescent Formation, may account for the subdued expression of the Seattle Fault west of Green Mountain. These are usually fairly short, and not believed to be significantly seismogenic. 48), along the edge of a formation known as the Southern Washington Cascades Conductor. Faults running on the Snohomish County-Skagit County line and between Port Townsend and Whidbey Island point toward Vancouver Island. Let's make your home safer With inland, Puget Sound faults, like the Seattle Fault, the risk is comparatively smaller. 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. While there is a short zone (not shown) of fainter seismicity near Goat Rocks (an old Pliocene volcano[196]) that may be associated with the contact, the substantially stronger seismicity of the WRZ is associated with the major Carbon RiverSkate Mountain anticline. (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. 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.. The Seattle uplift, and possibly the Black Hills uplift, consist of Crescent Formation basalt that was exposed when it was forced up a ramp of some kind. Somewhere between Puget Sound and Cascades foothills these two geological provinces come into contact. [73] The presence of detritus from the Idaho Batholith[72] indicates a former location closer to southern Idaho. Relatively shallow crustal earthquakes, generally less than 25km (16 miles) deep, caused by stresses and faulting in the near-surface crustal structures. Black squares are urban sewer outfalls, which don't match the bubble plumes' locations. The Puget Sound region is not just potentially seismic, it is actively seismic. [185] The prospect of a major earthquake on the Doty Fault poses a serious hazard to the entire Puget Sound region as it threatens vital economic lifelines: At Chehalis there is but a single freeway (Interstate 5) and a single rail line connecting the Puget Sound region with the rest of the west coast; the only alternate routes are very lengthy.[186]. [54], It has been suggested that the SWIF might extend past its intersection with the RMFZ (with only peripheral strands turning to join the RMFZ) to cross the Cascades and eventually merge with or cross the OlympicWallowa Lineament;[55] a study of regional features suggests such a pattern. 10+ Cruises Age 2020s. [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. Black lines show the South Whidbey Island Fault Zone, the . In some places, such as along the South Fork of the Stillaguamish River between Arlington and Granite Falls, there are also contrasting geological contacts. [198], Does the SHZ extend north? 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. [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. 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 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]. 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 1949, 1965, and 2001 Puget Sound earthquakes were the result of _____ fault movement within the Juan de Fuca plate. The alternative, that younger faulting in the Rogers Belt has offset the DMF Cheney argued that the MVF had offset the DMF 47km. (See, There is a preliminary report of aeromagnetic and gravity mapping placing the eastern edge of the Siletz terrane under Lake Washington. [125] While some coherency is developing, the story is not complete: identified faults do not yet account for much of the region's seismicity. Some of these faults possibly developed in the Mesozoic, when these deposits were in the accretionary wedge;[72] the cross-cutting NE and NNE-striking faults that form the various basins resulted from a subsequent change to transtension. The discovery was an alarm bell for engineers and emergency planners. Tacoma, WA. It stands out in regard of its eastwest orientation, depth to bedrock, and hazard to an urban population center. This ramp could be either in the lower crustal blocks, or where the thrust sheet has split and one part is being forced over the next. This fault produced a large earthquake that left a geologic record of surface offsets about 1100 years ago. [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. and Fault Location. [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. 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. This map shows areas of seismic risk from high (red) to low (grayish-green). [38] These earthquakes probably caused tsunamis, and several nearby locations have evidence of tsunamis not correlated with other known quakes. Where it intersects the northwest-trending Johnsons Swamp fault zone, easternmost member of the RMFZ. The history and capabilities of the Frigid Creek Fault are not known. Energy builds up as elastic strain in rocks. [132], Scarps associated with Holocene uplift of the Tacoma fault have been traced westward to Prickett Lake (southwest of Belfair, see map). [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. 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. 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. 6) Click "Plot" Draw. The implications of this are not only "the possibility of a moderate to large crustal earthquake along the SHZ", but that the tectonics under Puget Sound are more complicated than yet understood, and may involve differences in the regional stress patterns not reflected in current earthquake hazard assessments. (1997) a slab of rock mainly basalts of the Crescent Formation about 20km thick is being pushed up a "master ramp" of deeper material; this forms the Seattle Uplift. [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. 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. 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 . (E.g., the Olympia Fault is aligned with and appears to be the northernmost member of a set of faults between Olympia and Chehalis that may extend to the Columbia River, and there has been a suggestion that the Tacoma Fault may connect with the White RiverNaches River fault on the east side of the Cascades.[24]). Marine seismic reflection surveys on either side of Whidbey Island extend the known length of these faults to at least 26 and 28km (about 15 miles). Geologic map of northwestern Washington (GM-50). There is a general pattern where most of these faults partition a series of basins and uplifts, each about 20km wide. The true length of the UPF is likely twice as long, as it forms the southern margin of an aeromagnetic high that extends another 25km to the southeast. This MSH-MR-GP lineament is believed to reflect a "long-lived deep-seated lithospheric flaw that has exerted major control on transfer of magma to the upper crust of southern Washington for approximately the last 25 [million years]";[203] it has been attributed to the geometry of the subducting Juan de Fuca plate.[205]. According to the Washington state Department of Natural Resources, more than 1,000 earthquakes happen in Washington state each year! Get directions. Subsidence dated to between AD 1445 and 1655 has been reported in Mud Bay (just west of Olympia). Offsets in the eastwest oriented Monroe Fault (south side of the Skykomish River), earthquake focal mechanisms, and kinematic indications show that the CCFZ is a left-lateral strike-slip fault, possibly with some oblique motion (up on the eastern side). 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. [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. A Seattle Fault quake could be as large as M7.5,160 but less than M7.0 is more probable. In the wedge model of Pratt et al. 6 earthquakes in the past 7 days. There are some interesting relationships here. Sail Date . The last major earthquake on the Seattle Fault occurred around 1,100 years ago, shifting the landscape in Puget Sound. These lineaments have been associated with possible zones of faulting in the crust and subducting plate.[212]. [32] And it is suggested that the Great Seattle Quake of approximately 1,100 years ago, and other coseismic events in southern Puget Sound around that time, were a single event that affected this entire block, with a magnitude of around 8, possibly triggered by an earthquake deeper in the crust.[33]. In this model the Tacoma fault zone is primarily the result of local adjustments as the slab bends upward at the bottom of the ramp. Ongoing mapping is revealing more faults. [28] Faults and folds may develop where the thrust sheet is being bent, or where the leading edge is thrust over softer, weaker sedimentary deposits, and breaks off and slumps. [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. Olympic Peninsula, Washington has had: (M1.5 or greater) 0 earthquakes in the past 24 hours. 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. 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). Please follow the steps below: . [Paper No. [39] On the basis of marine seismic reflection surveying in the Strait of Juan de Fuca it has been suggested that the DMF, SPF, and UPF are structurally connected (at least in the segment crossing Whidbey Island). 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. But the western segment the Devils Mountain Fault has left-lateral movement. [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. Strawberry Point and Utsalady Point faults, "The Puget Lowland is a north-south-trending structural basin that is flanked by Mesozoic and Tertiary rocks of the Cascade Range on the east and by Eocene rocks of the Olympic Mountains on the west. Cheney also mapped the Lake Chaplain Fault, parallel and just east of the MVF, from Lake Chaplain to Granite Falls. It follows the Bainbridge Island ferry route east under Puget Sound and the route of Interstate 90 toward, and possibly beyond, the Cascade Mountains. In 1870, as construction of the Northern Pacific began, Seattle numbered fewer than 1,200 souls. Posted: 12 days ago. An earthquake occurs along a south-moving fault. 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. The structure of the Seattle Fault zone still have great uncertainty and there exist a number of interpretations. The Seattle Fault crosses east-west through Puget Sound and downtown Seattle. 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. 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). Both of these are dip-slip (vertical) faults; the block between them has been popped up by compressive forces. Document name Date Description Additional versions; 2809: 4/1/2021: . But their significance to the Puget Sound area is unknown.
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