Seattle Fault

from Wikipedia, the free encyclopedia
The Seattle Fault runs across the Puget Sound into Seattle itself. Restoration Point in the foreground, Alki Point is faintly visible on the right edge of the picture.

The Seattle Fault is a zone of shallow thrusts that crosses the Puget Sound Lowland and Seattle in Washington State ; it is adjacent to Interstate 90 . The Seattle Fault was first recognized as a significant seismic hazard in 1992 when a series of studies showed that the zone was the cause of a major earthquake with a magnitude of 7 some 1,100 years ago - an event that entered the oral legends of the Native people found. Intensive research since then has shown that the Seattle Fault is part of a regional system of faults .

Heavy earthquake

After initial assumptions as a result of mapping gravity anomalies in 1965 and the uplift of a marine plateau at Restoration Point (in the picture above in the foreground), the existence and the possible dangers of the Seattle Fault were made known in 1992 through several publications in Science . These publications looked at the timing of the sudden rise and fall around Restoration Point and Alki Point (the latter on the far right of the picture), the deposition of tsunamites in Puget Sound, turbulence in the ancient lake deposits, rock avalanches, and multiple landslides around Lake Washington , and determined that all of this happened about 1,100 years ago (between 900 and 930 AD ) most likely due to a magnitude 7 earthquake on the Seattle Fault.

Representation of the a'yahos spirit

Although the 900-930 earthquake was more than a thousand years ago, local indigenous legends have the connection between a powerful supernatural spirit - a'yahos, associated with tremors, waterfalls, and landslides - with five locations along the course of the Seattle- Fault preserved, including the “Psai-Yah-hus” near the ferry terminal in Fauntleroy in West Seattle, known as “Spirit Boulder”.

geology

Approximate location of the Seattle fault zone (and other faults). The section of the fault zone directly below “Seattle” corresponds to the red line in the first picture. (Extract from the geological map of the Division of Geology and Earth Resources [DGER] of the Washington State Department of Natural Resources)
A model of the Seattle Uplift: profile (south to north) along the east side of central Puget Sound looking west. TB = Tacoma Basin, EPZ = East Passage Zone (Maury Island), SFZ = Seattle Fault Zone (Alki Point). The gray dots are hypocenters of earthquakes of magnitude 2 or greater between 1970 and 2001.

The Seattle Fault represents the structural boundary at which 50… 60 million year old ( early Tertiary ) basalts of the Crescent Formation were raised in the south (Seattle Uplift ), and advances into the Seattle Basin, where the Tertiary basement is below at least Seven kilometers thick, relatively softer and lighter layers of sediment from the younger Blakeley and Blakely Harbor Formations was buried. This resulted in a 4 to 7 kilometer wide complex fault zone with at least three south facing large thrusts. Most faulting processes are “blind” (that is, they do not reach the surface); they are generally difficult to locate as the surface is covered by dense vegetation or settlements / infrastructure. Three main strands have been identified and their location determined by high-resolution seismic and aeromagnetic surveys. The northernmost strand is near the course of Interstate 90 and then under Lake Sammamish . The central section of the fault zone - where it crosses the apparent location of the Olympic-Wallowa lineament - shows marked variations in the strands and underlying structures, but the properties and meaning of this are still unknown.

The fault extends approximately 70 km (43 miles) from near Fall City in the east, where it appears to be bounded by the South Whidbey Island fault , to the Hood Canal in the west (not shown on the map). The western limit, however, is unclear (see here and Anderson et al. (2008)). It forms the north edge of the Seattle Uplift, of which the Tacoma Fault forms the south edge. One of the models sees the Seattle and Tacoma faults as convergent; they form a wedge in the depths, which is pushed upwards by the north-southward compression, which in turn is driven by the plate tectonics. Another model (see graphic) interprets the Seattle uplift as a slab of rock that is pushed up over a ramp. Subsequent work suggests that the structure of the Seattle Fault could vary from east to west, making both models applicable to the affected sections. A later model sees part of the northward warped plate as a wedge between the sediment formations of the Seattle Basin and the basement below.

The Seattle Fault is estimated to be around 40 million years old (late Eocene ). At about this time, the northbound Straight Creek Fault stalled due to the intrusion of plutons . It appears that when the Straight Creek Fault got stuck, the north-south oriented compressive force it exerted from the transverse motion was transferred to the crust of the Puget Lowland which was eventually folded and discarded. The different blocks were pushed one over the other.

Other escarpments associated with the Seattle Fault were identified through lidar- assisted mapping; Fragmentation has generally shown that the faults are more complex than initially assumed. Many details of the Seattle fault, including the rate of recursion, remain unsolved. An examination of the sediments in Lake Washington gave evident indications of seven major earthquakes (with magnitudes> 7) over the past 3,500 years.

Superficial land steps caused by faults are rarely observed in this area due to the topography, vegetation and urbanization; an exception can be seen in Mee Kwa Mooks Park south of Alki Point. This is the location of the West Seattle Fault ; the prominent rise there results from an uplift on the north side of the fault.

hazards

Container crane in the port of Port-au-Prince (Haiti) tilted after the ground gave way due to an earthquake. The Seattle waterfront faces a similar risk.

The Seattle Fault (and the associated Tacoma Fault) is not the only source of earthquake hazard in the Puget Lowland. Other faults near the surface of the continental crust such as the South Whidbey Island Fault (near Everett) and the recently investigated Olympia Fault (near Olympia ), although historically seismically inactive, are suspected of being earthquakes with magnitudes of around 7 to be able to trigger. Earthquakes like the 2001 Nisqually earthquake originate 50… 60 kilometers below the Puget Sound in the Wadati-Benioff zone of the subducting Juan de Fuca plate ; due to the great depth, their energy is widely distributed. There are also irregular, but very energetic, subduction events such as the 9-magnitude Cascadia earthquake of 1700 when the entire Cascadia subduction zone moved from Cape Mendocino to Vancouver Island .

However, the Seattle and Tacoma Faults are possibly the largest earthquake sources in the densely populated Seattle-Tacoma region. A study from 2002 estimated on the reliability of bridges that an earthquake with a magnitude of 7 would damage on the Seattle Fault, about 80 bridges in the region, whereas a Subduktionsereignis with a magnitude of 9, only about 87 bridges throughout western Washington harm would. (The much greater energy of a subduction event would be distributed over a very large area and only concentrated near the coast, where urbanization is less.) The same study found that with damage to just six bridges (the minimal damage of an event with a magnitude of 6, 5 in the Benioff zone) an economic loss of at least USD 3 billion would be expected. Subsequent retrofitting by the Washington Department of Transportation and the City of Seattle would likely reduce the damage to key bridges. There is consensus that such an earthquake at the Seattle Fault would destroy so-called "unreinforced masonry (URM) buildings", of which around a thousand can be found in the City of Seattle, which are concentrated in the Capitol Hill and Pioneer Square neighborhoods as well as in the International District.

Damage to a brick building (Cadillac Hotel) in Seattle after the 2001 Nisqually earthquake

Another recent investigation found that the Seattle Fault can produce two types of earthquakes; both face "considerable damage" in the Seattle metropolitan area. The earthquake that struck between 900 and 930 appears to have been the only one in the past 7,000 years to cause regional uplift. The other type occurs more locally and at shallower depths (and is therefore more destructive); at least four such events occurred on the western edge of the fault in the past 3,000 years. (There is no information on the history of the central and eastern parts.)

Calculations based on the length of the fault and paleoseismological studies show that the Seattle Fault can cause a very severe earthquake with a magnitude of 7.0. In addition to the severe damage to unreinforced buildings and those on landfills (as most of the Pioneer Square area in Seattle, the industrial area and the coastal areas) can - according to computer simulations have shown - in the Elliott Bay a tsunami up to two meter high waves occur. The modeling shows that such a tsunami would inundate the industrial areas at Commencement Bay, 30 mi (48 km) south of Tacoma and low-lying areas in the delta of the Puyallup River . There is also agreement that a severe or prolonged event would cause damage to the Duwamish River or Puyallup River deltas , where Seattle and Tacoma's main port facilities are located (Harbor Island and Commencement Bay).

Web links

Individual evidence

  1. ^ ZF Daneš, MM Bonno, E. Brau, WD Gilham, TT Hoffman, D. Johansen, MH Jones, B. Malfait, J. Masten, GO Teague: Geophysical investigation of the Southern Puget Sound area, Washington . In: Journal of Geophysical Research . 70, No. 22, November 15, 1965, pp. 5573-5580. doi : 10.1029 / JZ070i022p05573 .
  2. ^ A b c R. C. Bucknam, E. Hemphill-Haley, EB Leopold: Abrupt Uplift Within the Past 1700 Years at Southern Puget Sound, Washington . In: Science . 258, No. 5088, December 4, 1992, pp. 1611-1614. doi : 10.1126 / science.258.5088.1611 .
  3. ^ BF Atwater, AL Moore: A Tsunami About 1000 Years Ago in Puget Sound, Washington . In: Science . 258, No. 5088, December 4, 1992, pp. 1614-1617. doi : 10.1126 / science.258.5088.1614 .
  4. ↑ a b R. E. Karlin, SEB Abella: Paleoearthquakes in the Puget Sound Region Recorded in Sediments from Lake Washington, USA . In: Science . 258, No. 5088, December 4, 1992, pp. 1617-1620. doi : 10.1126 / science.258.5088.1617 . PMID 17742527 .
  5. ^ RL Schuster, RL Logan, PT Pringle: Prehistoric Rock Avalanches in the Olympic Mountains, Washington . In: Science . 258, No. 5088, December 4, 1992, pp. 1620-1621. doi : 10.1126 / science.258.5088.1620 .
  6. ^ GC Jacoby, PL Williams, BM Buckley: Tree Ring Correlation Between Prehistoric Landslides and Abrupt Tectonic Events in Seattle, Washington . In: Science . 258, No. 5088, December 4, 1992, pp. 1621-1623. doi : 10.1126 / science.258.5088.1621 .
  7. ^ Radiocarbon dating of a Seattle earthquake to AD 900-930. . In: Seismological Research Letters . 70, p. 232. doi : 10.1785 / gssrl.70.2.190 .
  8. ↑ RS Ludwin, CP Thrush, D. Buerge, C. Jonientz-Trisler, J. Rasmussen, K. Troost, A. de los Angeles: Serpent Spirit-power Stories along the Seattle Fault Archived from the original on May 12, 2008. Info : The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Seismological Research Letters . 76, No. 4, July-August 2005, pp. 426-431. doi : 10.1785 / gssrl.76.4.426 . Retrieved January 18, 2009. @1@ 2Template: Webachiv / IABot / www.pnsn.org
  9. ↑ DM Buerge: Lost Seattle, our shameful neglect of a rich archeological past . In: Seattle Weekly . 06-13 March 1985.
  10. ^ EH Brown, JD Dragovich: Tectonic elements and evolution of northwest Washington . In: Washington Division of Geology and Earth Resources . Geologic Map GM – 52, December 2003, p. 12. "1 map sheet, scale 1: 625,000"
  11. ↑ a b Active shortening of the Cascadia forearc and implications for seismic hazards of the Puget Lowland Archived from the original on June 7, 2011. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. In: Tectonics . 23, No. TC1011, pp. 1-27. doi : 10.1029 / 2003TC001507 . Retrieved September 11, 2017. @1@ 2Template: Webachiv / IABot / earthquake.usgs.gov
  12. ↑ a b c T. L. Pratt, SY Johnson, CJ Potter, WJ Stephenson: Seismic reflection images beneath Puget Sound, western Washington State: The Puget Lowland thrust sheet hypothesis Archived from the original on August 20, 2008. Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. In: Journal of Geophysical Research . 102, No. B12, December 10, 1997, pp. 27,469-27,490. doi : 10.1029 / 97JB01830 . Retrieved June 30, 2010. @1@ 2Template: Webachiv / IABot / faculty.washington.edu
  13. ^ SY Johnson, CJ Potter, JM Armentrout: Origin and evolution of the Seattle Fault and Seattle Basin, Washington . In: Geology . 22, No. 1, January 1994, pp. 71-74. doi : 10.1130 / 0091-7613 (1994) 022 <0071: OAEOTS> 2.3.CO; 2 .
  14. ↑ a b c A. R. Nelson, SY Johnson, HM Kelsey, RE Wells, BL Sherrod Pezzopane, SK Bradley, L. Koehler, RD Bucknam, RC: Late Holocene earthquakes on the Toe Jam Hill fault, Seattle fault zone, Bainbridge Island, Washington Archived from the original on June 14, 2010. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: Geological Society of America Bulletin . 115, No. 11, November 2003, pp. 1368-1403. doi : 10.1130 / B25262.1 . Retrieved April 14, 2010. @1@ 2Template: Webachiv / IABot / web.cocc.edu
  15. ↑ a b S. Y. Johnson, RJ Blakely, TM Brocher, RC Bucknam, PJ, Haeussler, TL Pratt, AR Nelson, BL Sherrod Wells, RE Lidke, DJ Harding, DJ Kelsey, HM: Fault number 570, Seattle fault zone . In: US Geological Survey (Ed.): Quaternary fault and fold database for the United States 2004.
  16. ↑ SY Johnson, SV Dadisman, JR Childs, WD Stanley: Active Tectonics of the Seattle Fault and Central Puget Sound, Washington: Implications for earthquake hazards Archived from the original on January 29, 2012. Information: The archive link was automatically inserted and not yet checked . Please check the original and archive link according to the instructions and then remove this notice. In: Geological Society of America Bulletin . 111, No. 7, July 1999, pp. 1042-1053. doi : 10.1130 / 0016-7606 (1999) 111 <1042: ATOTSF> 2.3.CO; 2 . Retrieved September 11, 2017. @1@ 2Template: Webachiv / IABot / earthquake.usgs.gov
  17. ↑ a b c d R. J. Blakely, RE Wells, CS Weaver, SY Johnson: Location, structure, and seismicity of the Seattle fault zone, Washington: Evidence from aeromagnetic anomalies, geologic mapping, and seismic-reflection data . In: Geological Society of America Bulletin . 114, No. 2, February 2002, pp. 169-177. doi : 10.1130 / 0016-7606 (2002) 114 <0169: LSASOT> 2.0.CO; 2 .
  18. ^ Geologic map of the North Bend 7.5-minute quadrangle, King County, Washington . In: Washington Division of Geology and Earth Resources . Geological Map GM – 73, p. 39. "1 map sheet, scale 1: 24,000"
  19. ^ The Saddle Mountain Fault Deformation Zone, Olympic Peninsula, Washington: Western Boundary of the Seattle Uplift . In: Geosphere . 5, No. 2, pp. 105-125. doi : 10.1130 / GES00196.1 .
  20. ↑ The western extension of the Seattle fault: new insights from seismic reflection data Archived from the original on January 28, 2017. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. In: US Geological Service . NEHRP. Retrieved September 11, 2017. "Project Award Number 08HQGR0075" @1@ 2Template: Webachiv / IABot / earthquake.usgs.gov
  21. ↑ ML Anderson, JD Dragovich, RJ Blakely, R. Wells, TM Brocher: Where Does the Seattle Fault End? Structural Links and Kinematic Implications , abstract # T23B-2022, American Geophysical Union Fall Meeting 2008, 2008.
  22. Jump up ↑ TM Brocher, T. Parsons, RJ Blakely, NI Christensen, MA Fisher, RE Wells the SHIPS Working Group: Upper crustal structure in Puget Lowland, Washington: Results from the 1998 Seismic Hazards Investigation in Puget Sound . In: Journal of Geophysical Research . 106, No. B7, July 10, 2001, pp. 13,541-13,564. doi : 10.1029 / 2001JB000154 .
  23. ↑ a b c H. M. Kelsey, BL Sherrod, AR Nelson, TM Brocher: Earthquakes generated from bedding plane-parallel reverse faults above an active wedge thrust, Seattle fault zone. . In: Geological Society of America Bulletin . 120, No. 11/12, November – December 2008, pp. 1581–1597. doi : 10.1130 / B26282.1 .
  24. ^ Another look at the Fraser River-Straight Creek Fault (FRSCF) [abstract] . In: Geological Society of America 1994 Annual Meeting, Abstracts with Programs . 24, p. 88.
  25. ↑ RW Tabor, VA, Jr. Frizzell, JA Vance, CW Naeser: Ages and stratigraphy of lower and middle Tertiary sedimentary and volcanic rocks of the central Cascades, Washington: Application to the tectonic history of the Straight Creek fault . In: Geological Society of America Bulletin . 95, No. 1, January 1984, pp. 26-44. doi : 10.1130 / 0016-7606 (1984) 95 <26: AASOLA> 2.0.CO; 2 .
  26. ↑ RA Haugerud, DJ Harding, SY Johnson, JL Harless, CS Review, BL Sherrod: High-resolution lidar topography of the Puget Lowland, Washington - A Bonanza for Earth Science . In: GSA Today . June 2003, pp. 4-10.
  27. ^ RE Karlin, M. Holmes, SEB Abella, R. Sylvester: Holocene landslides and a 3500-year record of Pacific Northwest earthquakes from sediments in Lake Washington . In: Geological Society of America Bulletin . 116, No. 1-2, February 2004, pp. 94-108. doi : 10.1130 / B25158.1 .
  28. ^ KG Troost, DB Booth: Geology of Seattle: City of Seattle Field Trip . Seattle-Area Geologic Mapping Project Department of Earth and Space Sciences University of Washington, May 22, 2004.  ( Page no longer available , search in web archives )  Info: The link was automatically marked as broken. Please check the link according to the instructions and then remove this notice.@1@ 2Template: Dead Link / geomapnw.ess.washington.edu  
  29. ^ Crustal Structure and Earthquake Hazards of the Subduction Zone in Southwestern British Columbia and Western Washington . In: US Geological Survey . Professional Paper 1661-C.
  30. ↑ a b D. Ballantyne, M. Pierepiekarz, S. Chang: Seismic Vulnerability Assessment of the Seattle – Tacoma Highway Corridor using HAZUS 2002. Archived from the original on September 20, 2009 Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. (Accessed April 21, 2010). @1@ 2Template: Webachiv / IABot / www.mmiengineering.com
  31. ↑ DB Swanson, A. Findlay: City of Seattle Unreinforced Masonry Building Seismic Hazards Study Archived from the original on June 2, 2010. Information: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. In: City of Seattle Department of Planning and Development . December 2007. Retrieved April 23, 2010. @1@ 2Template: Webachiv / IABot / www.seattle.gov
  32. ↑ Inundation modeling of local tsunamis in Puget Sound, Washington, due to potential earthquakes . In: ITS 2001 Proceedings . No. Session 7, Number 7-18, pp. 861-873.
  33. Jump up ↑ TJ Walsh, D. Arcas, AJ Venturato, VV Titov, HO Mofjeld, CC Chamberlin, FI González: Tsunami hazard map of Tacoma, Washington — Model results for Seattle fault and Tacoma fault earthquake tsunamis . In: Washington Division of Geology and Earth Resources . Open File Report 2009-9, July 2009.
  34. ↑ FI González, BL Sherrod, BF Atwater, AP Frankel, SP Palmer, ML Holmes, RE Karlin, BE Jaffe Titov, VV Mofjeld, HO Venturato, AJ: Puget Sound Tsunami Sources - 2002 Workshop Report . In: NOAA . June 2003.
  35. ^ Seismic stability of the Duwamish River delta, Seattle, Washington . In: US Geological Survey . Professional Paper 1661-E.