Misplaced Pages

#415584

28-592: Technically, a fracture zone is not a transform fault, but in the case of the Mendocino, the term has been loosely applied to the active fault segment east of the Gorda Ridge as well as to the true fracture zone segment west of it. Many seismologists refer to the active segment as the Mendocino Fault or Mendocino fault zone . The fault section demarcates the boundary between the northwestward-moving Pacific plate and

56-484: A natural disaster in the United States", further predicting "widespread and catastrophic" damage across Alabama, Arkansas, Illinois, Indiana, Kentucky, Mississippi, Missouri, and particularly Tennessee, where a 7.7 or greater magnitude quake would cause damage to tens of thousands of structures affecting water distribution , transportation systems , and other vital infrastructure. The quakes caused extensive changes to

84-552: A series of intense intraplate earthquakes beginning with an initial earthquake of moment magnitude 7.2–8.2 on December 16, 1811, followed by a moment magnitude 7.4 aftershock on the same day. Two additional earthquakes of similar magnitude followed in January and February 1812. They remain the most powerful earthquakes to hit the contiguous United States east of the Rocky Mountains in recorded history. The earthquakes, as well as

112-605: Is a fault that is likely to become the source of another earthquake sometime in the future. Geologists commonly consider faults to be active if there has been movement observed or evidence of seismic activity during the last 10,000 years. Active faulting is considered to be a geologic hazard – one related to earthquakes as a cause. Effects of movement on an active fault include strong ground motion , surface faulting, tectonic deformation , landslides and rockfalls , liquefaction , tsunamis , and seiches . Quaternary faults are those active faults that have been recognized at

140-553: Is employed with other factors to determine the potential earthquake hazard. The geologic conditions and plate tectonic setting in much of the Western U.S. has resulted in the region being underlain by relatively thin crust and having high heat flow, both of which can favor relatively high deformation rates and active faulting. In contrast, in the Central and Eastern U.S. (CEUS) the crust is thicker, colder, older, and more stable. Furthermore,

168-634: Is now North America began to split or rift apart during the breakup of the supercontinent Rodinia in the Neoproterozoic era (about 750 million years ago). Faults were created along the rift, and igneous rocks formed from magma that was being pushed towards the surface. The resulting rift system failed to split the plate, but has remained as an aulacogen (a scar or weak zone) deep underground. In recent decades, minor earthquakes have continued. The epicenters of over 4,000 earthquakes can be identified from seismic measurements since 1974, originating from

196-481: Is unknown; as a frontier area, the region was sparsely populated, and communications and records were poor. The predominantly wooden buildings resisted collapse, though the intense shaking caused many chimneys to fall, wood structures to crack, and trees to fall on buildings, particularly in the epicentral area during the first earthquake on December 16, 1811. Rated at VII on the Mercalli Intensity Scale,

224-681: The seismic zone of their occurrence, were named for the Mississippi River town of New Madrid , then part of the Louisiana Territory and now within the U.S. state of Missouri . The epicenters of the earthquakes were located in an area that at the time was at the distant western edge of the American frontier , only sparsely settled by European settlers. Contemporary accounts have led seismologists to estimate that these stable continental region earthquakes were felt strongly throughout much of

252-450: The 16th of December 1811, about two o'clock, a.m., we were visited by a violent shock of an earthquake, accompanied by a very awful noise resembling loud but distant thunder, but more hoarse and vibrating, which was followed in a few minutes by the complete saturation of the atmosphere, with sulphurious vapor, causing total darkness. The screams of the affrighted inhabitants running to and fro, not knowing where to go, or what to do—the cries of

280-593: The CEUS is thousands of miles from active plate boundaries, so the rates of deformation are low in this region. Nevertheless, the CEUS has had some rather large earthquakes in historical times, including a series of major earthquakes near New Madrid, Missouri in 1811–1812 , a large earthquake near Charleston, South Carolina in 1886, and the Cape Ann earthquake northeast of Boston in 1755. 1811%E2%80%9312 New Madrid earthquakes The 1811–1812 New Madrid earthquakes were

308-657: The Prophet must be supported. The many more aftershocks include one magnitude 7 aftershock to the December 16, 1811, earthquake which occurred at 6:00 UTC (12:00 am local time) on December 17, 1811, and one magnitude 7 aftershock to the February 7, 1812, earthquake which occurred on the same day at 4:40 UTC (10:40 pm local time). Susan Hough , a seismologist of the United States Geological Survey , has estimated

SECTION 10

#1732852190416

336-771: The adjacent swamps as water levels rose by 8 to 9 meters. Waves on the Mississippi River caused boats to wash ashore; river banks rose, sand bars were destroyed, and some islands completely disappeared. Sand blows occurred in Missouri, Tennessee, and Arkansas, covering farmland. The continuous underlying rock mass, uninterrupted by fractures or faults, conducted the seismic waves from the earthquakes over great distances, with perceptible ground shaking as far away as Canada. Intense effects were widely felt in Illinois, Arkansas, Tennessee, Kentucky and Missouri. The number of people who died

364-450: The area of any given plate. The fact that intraplate regions may also present seismic hazards has only recently been recognized. Various geologic methods are used to define the boundaries of an active fault such as remote sensing and magnetic measurements, as well as other ways. Several types of data, such as seismologic reports or records over time, are used to gauge fault activity. Activity and fault area are correlated, and risk analysis

392-400: The central and eastern United States, across an area of roughly 50,000 square miles (130,000 km ), and moderately across nearly 1 million sq mi (3 million km ). The 1906 San Francisco earthquake , by comparison, was felt moderately over roughly 6,200 sq mi (16,000 km ). The earthquakes were interpreted by Tecumseh 's pan-Indian alliance, to mean that Tecumseh and his brother

420-558: The church bell in Cahokia sounded by the agitation of the building. It is said the shock of an earthquake was felt in Kaskaskia in 1804, but I did not perceive it. The shocks continued for years in Illinois, and some have experienced it this year, 1855. The Shaker diarist Samuel Swan McClelland described the effects of the earthquake on the Shaker settlement at West Union (Busro), Indiana , where

448-455: The earthquakes contributed to the temporary abandonment of the westernmost Shaker community. The underlying cause of the earthquakes is not well understood, but modern faulting seems to be related to an ancient geologic feature buried under the Mississippi River alluvial plain , known as the Reelfoot Rift. The New Madrid seismic zone is made up of reactivated faults that formed when what

476-610: The earthquakes' magnitudes as around magnitude 7. John Bradbury , a fellow of the Linnean Society , was on the Mississippi on the night of December 15, 1811, and describes the tremors in great detail in his Travels in the Interior of America in the Years 1809, 1810 and 1811 , published in 1817: After supper, we went to sleep as usual: about ten o'clock, and in the night I was awakened by

504-643: The eastward-moving Gorda plate . The Gorda plate is subducting beneath the North American plate just offshore of Cape Mendocino. Where the Mendocino Fault intersects the undersea trench of the subduction zone, it also meets the San Andreas Fault . This seismically active intersection is called a triple junction , and specifically the Mendocino triple junction . In Tsunami studies, energy focusing around

532-535: The fowls and beasts of every species—the cracking of trees falling, and the roaring of the Mississippi— the current of which was retrograde for a few minutes, owing as is supposed, to an irruption in its bed— formed a scene truly horrible. John Reynolds , the fourth governor of Illinois , among other political posts, mentions the earthquake in his biography My Own Times: Embracing Also the History of My Life (1855): On

560-559: The fracture zone has been noted, leading to increased wave heights in the area around Crescent City, California . The fracture zone is referred to as the Mendocino Escarpment in these studies, descriptively rather than named from its geological origin. Robert W. Pease observed in 1965 that the alignment of a transverse tectonic zone extending from Mount Lassen to the Walker Lane at the north end of Honey Lake Fault , suggests it

588-407: The most tremendous noise, accompanied by an agitation of the boat so violent, that it appeared in danger of upsetting ... I could distinctly see the river as if agitated by a storm; and although the noise was inconceivably loud and terrific, I could distinctly hear the crash of falling trees, and the screaming of the wild fowl on the river, but found that the boat was still safe at her moorings. By

SECTION 20

#1732852190416

616-533: The night of the 15th of December 1811, an earthquake occurred, that produced great consternation amongst the people. The centre of the violence was in New Madrid, Missouri, but the whole valley of the Mississippi was violently agitated. Our family all were sleeping in a log cabin, and my father leaped out of bed crying aloud "the Indians are on the house" ... We laughed at the mistake of my father, but soon found out it

644-454: The region's topography. Subsidence , uplift, fissures, landslides and riverbank collapses were common. Trees were uprooted by the intense shaking; people drowned when subsided land flooded. Reelfoot Lake was formed in Tennessee by subsidence of 1.5 meters to 6 meters in some places. Lake St. Francis in eastern Arkansas was expanded by subsidence, with sand and coal being ejected from fissures in

672-519: The seismic activity of the Reelfoot Rift. Forecasts for the next 50 years estimate a 7–10% chance of a major earthquake like those of 1811–1812, and a 25–40% chance of a quake of magnitude 6 or greater. In a report filed in November 2008, the U.S. Federal Emergency Management Agency warns that a serious earthquake in the New Madrid Seismic Zone could inflict "the highest economic losses due to

700-522: The surface and which have evidence of movement during the Quaternary Period. Related geological disciplines for active-fault studies include geomorphology , seismology , reflection seismology , plate tectonics , geodetics and remote sensing , risk analysis , and others. Active faults tend to occur in the vicinity of tectonic plate boundaries, and active fault research has focused on these regions. Active faults tend to occur less within

728-499: The time we could get to our fire, which was on a large flag in the stern of the boat, the shock had ceased; but immediately the perpendicular banks, both above and below us, began to fall into the river in such vast masses, as nearly to sink our boat by the swell they occasioned ... At day-light we had counted twenty-seven shocks. Eliza Bryan in New Madrid, Territory of Missouri , wrote the following eyewitness account in March 1812: On

756-588: Was once the continental terminus of the Mendocino Fault. It forms the boundary of the Modoc Plateau and Columbia Plateau provinces with the Great Basin . Where it meets Honey Lake Fault, it bends to trend northeast across the northwest corner of Nevada, where it accompanies the geological trough that forms Black Rock Desert . 40°25′N 125°00′W  /  40.417°N 125.000°W  / 40.417; -125.000 Active fault An active fault

784-494: Was worse than the Indians. Not one in the family knew at the time that it was an earthquake. The next morning another shock made us acquainted with it, so we decided it was an earthquake. The cattle came running home bellowing with fear, and all animals were terribly alarmed on the occasion. Our house cracked and quivered, so we were fearful it would fall to the ground. In the American Bottom many chimneys were thrown down, and

#415584