5- Chapter More United States and Canadian Earthquakes Earthquake- significant- USGS deems magnitude of 6.5 of higher Western North America: Plate Tectonic-Related Earthquakes North American plate is moving into the Pacific plate at 2.5 cm/yr and that a tremendous volume of the Farallon plate has subducted beneath N. America. April 1949, Puget Sound Washington- Down-to-the-east movements of the subducting Juan de Fuca plate, surface wave magnitude was 7.1 with eight deaths. $150M. April 1965, Tacoma- Seattle area- 6.5 M killing seven people totaling $50M. Because of subducting Juan de Fuca plate is only 10 to 15 million years old and is warm and buoyant enough to couple with the North American plate. Seattle fault zone occurred 1,100 years ago 1) Restoration Point was uplifted about 7 m. 2) Large landslides carried trees in growth position to the bottom of Lake Washington. 3) Tsunamis buried logs and trunks. 4) Major rock avalanches occurred around same time. 5) Redeposition of sediment in deeper waters (turbidites). 1872, Owens Valley, CA- fault of western side broke loose along length of 160 km, making it the third longest fault rupture in CA history. Western Great Basin Seismic Trend- runs through eastern CA and western NV with recognizable line of epicenters. Between the eastern Sierra Nevada in CA and the Wasatch Mountain front in central Utah. 1915, south of Winnemucca in Pleasant Valley, NV- magnitude 7.7 event. August 1959, Hebgen Lake, Montana- Enormous rock slide of 43 million cubic yards- killing 26 campers buried canyon to depths of 67 m and created a natural dam known as Earthquake Lake. Seiche- water sloshes back and forth for 11.5 hours, causing a drop down of 50 mi squared of land on the northern side of Hebgen Lake. Intermountain Seismic Belt- northerly trending zone at 1,500 km long and about 100-200 km wide, from southern Nevada and northern Arizona into northwestern Montana. Scarps- steep clifflike face/slope Rio Grande Rift: New Mexico, Colorado, Westernmost Texas, and Mexico- continental crust is being heated and stretched below from involving extensional (normal) faulting. Intraplate Earthquakes: Stable Central United States December 1811-March 1812- 1,874 earthquakes, located where Mississippi and Ohio Rivers come together at the upper end of Mississippi River, NEW MADRID earthquakes- taking name from town of 1,000 people. New Madrid felt from Canada to the Gulf of Mexico and from the Rocky Mountains to the Atlantic seaboard because of rigid basement rocks in continental interior. VS- SF EQ which had younger, tectonically fractured rocks that quickly damped out seismic energy. Reelfoot Rift: Missouri, Arkansas, Tennessee, Kentucky, Illinois- line up along the Mississippi river valley, formed 550M years ago- FAILED RIFT- zones of weakness that may be reactivated by later plate-tectonic stresses to once again generate earthquakes. 83 percent of the large earthquakes recorded in the central US are at or near the sites of ancient rifts. E.G: 1) St. Louis arm corresponds to the Ste. Genevieve fault 2) Southern Indiana arm is overlain by the Wabash Valley fault zone 3) Rough Creek rift is expressed as the Rough Creek fault zone, appearing to continue eastward as the Kentucky River fault zone. 4) Southern Oklahoma rift corresponds with the frontal-fault system of the Wichita Mountains. Eastern US June 1638, Cape Ann- Mercalli intensity range all the way up to IX. 1727, East Coast from Maine to Deleware- quicksand conditions were common during the earthquake. St. Lawrence River Valley Earthquakes- seisms reach magnitude 7 and may reach magnitude 5 range. Transform faults continue northwestward as great fracture zones that seem to line up with some onland seismic zones. New England seamounts are a chain of submerged, extinct volcanoes extending under New England and lining upw itht he Cape Ann epicenters and the northwest-trending belt of sesisms etending through Boston and into Ottawa, Canada.
1886, Carleston, SC- 60 people died, with body wave of 6.7 and surface wave of 7.7. Hawaii- Magma is on the move at shallow depths commonly generating harmonic tremors.