Global & Disaster Medicine

Archive for the ‘Earthquake’ Category

6/17/2019: M 5.8 – 19km S of Changning, China: Left 12 people dead and 135 others injured.

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The June 17, 2019, M 5.8 earthquake in the Chinese province of Sichuan occurred as the result of oblique reverse and strike-slip faulting at shallow depths in the crust of the Eurasia plate. Focal mechanism solutions for the event indicate rupture occurred on either a steeply dipping fault striking towards the south, or on a more moderately dipping fault striking towards the northwest. The location, depth and preliminary focal mechanism solution for this earthquake indicate the event occurred as the result of intraplate faulting within the Eurasia plate.

On a continental scale, the seismicity of central and eastern Asia is a result of northward convergence of the India plate against the Eurasia plate at a velocity of about 50 mm/yr. The convergence of the two plates is broadly accommodated by the uplift of the Asian highlands and by the motion of crustal material to the east away from the uplifted Tibetan Plateau.  The June 17 event occurred near the edge of a major uplifted plateau to the south and the Sichuan Basin to the north and may relate to the active tectonics of this juxtaposition.

Seismicity in the region is relatively common, with five earthquakes above M 6.0 within 250 km distance since 1900.  The most recent such event was the August 3, 2014 M 6.2 event near Wenping China, about 200 to the southwest.  Slightly further away, the very large May 12, 2008, M 7.9 Wenchuan earthquake occurred about 330 km northwest of June 17 event.  That event killed more than 69,000 people, with an estimated economic loss of 86 Billion US dollars.


6/16/1896: A tsunami originating from an earthquake in the Japan Trench claims up to 27,000 lives

HxC


4.0M quake east of Cleveland

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M 4.0 – 4km NNW of Eastlake, Ohio

  • 2019-06-10 14:50:44 (UTC)
  • 41.695°N 81.466°W
  • 5.0 km depth

Tectonics

Tectonic Summary

Earthquakes in the Northeast Ohio Seismic Zone

The Northeast Ohio seismic zone has had moderately frequent earthquakes at least since the first one was reported in 1823. The largest earthquake (magnitude 4.8) caused damage in 1986 in northeasternmost Ohio, and the most recent damaging shock (magnitude 4.5) occurred in 1998 at the seismic zone’s eastern edge in northwestern Pennsylvania. Earthquakes too small to cause damage are felt two or three times per decade.

Earthquakes in the central and eastern U.S., although less frequent than in the western U.S., are typically felt over a much broader region. East of the Rockies, an earthquake can be felt over an area as much as ten times larger than a similar magnitude earthquake on the west coast. A magnitude 4.0 eastern U.S. earthquake typically can be felt at many places as far as 100 km (60 mi) from where it occurred, and it infrequently causes damage near its source. A magnitude 5.5 eastern U.S. earthquake usually can be felt as far as 500 km (300 mi) from where it occurred, and sometimes causes damage as far away as 40 km (25 mi).

Faults

Earthquakes everywhere occur on faults within bedrock, usually miles deep. Most of the seismic zone’s bedrock was formed as several generations of mountains rose and were eroded down again over the last billion or more years.

At well-studied plate boundaries like the San Andreas fault system in California, often scientists can determine the name of the specific fault that is responsible for an earthquake. In contrast, east of the Rocky Mountains this is rarely the case. The Northeast Ohio seismic zone is far from the nearest plate boundaries, which are in the center of the Atlantic Ocean and in the Caribbean Sea. The seismic zone is laced with known faults but numerous smaller or deeply buried faults remain undetected. Even the known faults are poorly located at earthquake depths. Accordingly, few, if any, earthquakes in the seismic zone can be linked to named faults. It is difficult to determine if a known fault is still active and could slip and cause an earthquake. As in most other areas east of the Rockies, the best guide to earthquake hazards in the Northeast Ohio seismic zone is the earthquakes themselves.

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M 6.1 – 8km N of Canoas, Costa Rica

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Tectonic Summary

Seismotectonics of the Caribbean Region and Vicinity

Extensive diversity and complexity of tectonic regimes characterizes the perimeter of the Caribbean plate, involving no fewer than four major plates (North America, South America, Nazca, and Cocos). Inclined zones of deep earthquakes (Wadati-Benioff zones), ocean trenches, and arcs of volcanoes clearly indicate subduction of oceanic lithosphere along the Central American and Atlantic Ocean margins of the Caribbean plate, while crustal seismicity in Guatemala, northern Venezuela, and the Cayman Ridge and Cayman Trench indicate transform fault and pull-apart basin tectonics.

Along the northern margin of the Caribbean plate, the North America plate moves westwards with respect to the Caribbean plate at a velocity of approximately 20 mm/yr. Motion is accommodated along several major transform faults that extend eastward from Isla de Roatan to Haiti, including the Swan Island Fault and the Oriente Fault. These faults represent the southern and northern boundaries of the Cayman Trench. Further east, from the Dominican Republic to the Island of Barbuda, relative motion between the North America plate and the Caribbean plate becomes increasingly complex and is partially accommodated by nearly arc-parallel subduction of the North America plate beneath the Caribbean plate. This results in the formation of the deep Puerto Rico Trench and a zone of intermediate focus earthquakes (70-300 km depth) within the subducted slab. Although the Puerto Rico subduction zone is thought to be capable of generating a megathrust earthquake, there have been no such events in the past century. The last probable interplate (thrust fault) event here occurred on May 2, 1787 and was widely felt throughout the island with documented destruction across the entire northern coast, including Arecibo and San Juan. Since 1900, the two largest earthquakes to occur in this region were the August 4, 1946 M8.0 Samana earthquake in northeastern Hispaniola and the July 29, 1943 M7.6 Mona Passage earthquake, both of which were shallow thrust fault earthquakes. A significant portion of the motion between the North America plate and the Caribbean plate in this region is accommodated by a series of left-lateral strike-slip faults that bisect the island of Hispaniola, notably the Septentrional Fault in the north and the Enriquillo-Plantain Garden Fault in the south. Activity adjacent to the Enriquillo-Plantain Garden Fault system is best documented by the devastating January 12, 2010 M7.0 Haiti strike-slip earthquake, its associated aftershocks and a comparable earthquake in 1770.

Moving east and south, the plate boundary curves around Puerto Rico and the northern Lesser Antilles where the plate motion vector of the Caribbean plate relative to the North and South America plates is less oblique, resulting in active island-arc tectonics. Here, the North and South America plates subduct towards the west beneath the Caribbean plate along the Lesser Antilles Trench at rates of approximately 20 mm/yr. As a result of this subduction, there exists both intermediate focus earthquakes within the subducted plates and a chain of active volcanoes along the island arc. Although the Lesser Antilles is considered one of the most seismically active regions in the Caribbean, few of these events have been greater than M7.0 over the past century. The island of Guadeloupe was the site of one of the largest megathrust earthquakes to occur in this region on February 8, 1843, with a suggested magnitude greater than 8.0. The largest recent intermediate-depth earthquake to occur along the Lesser Antilles arc was the November 29, 2007 M7.4 Martinique earthquake northwest of Fort-De-France.

The southern Caribbean plate boundary with the South America plate strikes east-west across Trinidad and western Venezuela at a relative rate of approximately 20 mm/yr. This boundary is characterized by major transform faults, including the Central Range Fault and the Boconó-San Sebastian-El Pilar Faults, and shallow seismicity. Since 1900, the largest earthquakes to occur in this region were the October 29, 1900 M7.7 Caracas earthquake, and the July 29, 1967 M6.5 earthquake near this same region. Further to the west, a broad zone of compressive deformation trends southwestward across western Venezuela and central Colombia. The plate boundary is not well defined across northwestern South America, but deformation transitions from being dominated by Caribbean/South America convergence in the east to Nazca/South America convergence in the west. The transition zone between subduction on the eastern and western margins of the Caribbean plate is characterized by diffuse seismicity involving low- to intermediate-magnitude (M<6.0) earthquakes of shallow to intermediate depth.

The plate boundary offshore of Colombia is also characterized by convergence, where the Nazca plate subducts beneath South America towards the east at a rate of approximately 65 mm/yr. The January 31, 1906 M8.5 earthquake occurred on the shallowly dipping megathrust interface of this plate boundary segment. Along the western coast of Central America, the Cocos plate subducts towards the east beneath the Caribbean plate at the Middle America Trench. Convergence rates vary between 72-81 mm/yr, decreasing towards the north. This subduction results in relatively high rates of seismicity and a chain of numerous active volcanoes; intermediate-focus earthquakes occur within the subducted Cocos plate to depths of nearly 300 km. Since 1900, there have been many moderately sized intermediate-depth earthquakes in this region, including the September 7, 1915 M7.4 El Salvador and the October 5, 1950 M7.8 Costa Rica events.

The boundary between the Cocos and Nazca plates is characterized by a series of north-south trending transform faults and east-west trending spreading centers. The largest and most seismically active of these transform boundaries is the Panama Fracture Zone. The Panama Fracture Zone terminates in the south at the Galapagos rift zone and in the north at the Middle America trench, where it forms part of the Cocos-Nazca-Caribbean triple junction. Earthquakes along the Panama Fracture Zone are generally shallow, low- to intermediate in magnitude (M<7.2) and are characteristically right-lateral strike-slip faulting earthquakes. Since 1900, the largest earthquake to occur along the Panama Fracture Zone was the July 26, 1962 M7.2 earthquake.

References for the Panama Fracture Zone:
Molnar, P., and Sykes, L. R., 1969, Tectonics of the Caribbean and Middle America Regions from Focal Mechanisms and Seismicity: Geological Society of America Bulletin, v. 80, p. 1639-1684.

 


At least one earthquake happens every three minutes across Southern California.

Weather Channel

Science

“…….When they started their research, the earthquake catalog for the region of Southern California they studied listed 181,000 temblors recorded between 2008 and 2017. After wading through the data and scanning it through high-power computers, that number was increased to 1.8 million.

The nearly 2 million “new” earthquakes range in magnitude from negative 2.0 to 1.7……”

satellite image of southern California showing superposed fault lines

Satellite image of southern California showing superposed fault lines (image sources: (1) faults from Jennings, 1994; (2) Landsat image from Jet Propulsion Laboratory of the California Institute of Technology). [Jennings, C.W., 1994, Fault activity map of California and adjacent areas: California Division of Mines and Geology, California Geologic Data Map Series, Map No. 6, scale 1:750,000. ]
 

Diagram of southern California showing the San Andreas Fault as a master player in a tectonic setting that includes other faults and compressional fold belts

Oblique aerial photograph of the trace of a fault on the desert floor of southern California
Oblique aerial photograph of the trace of a fault on the desert floor of southern California; view looking east at the Coachella Valley trace of the Banning Fault in the northern Coachella Valley. The linear trace on the desert floor occurs where a fault plane that is vertical in the subsurface intersects the land surface. Thus, a cross-sectional view of a fault in a road cut expresses translates into a trace on the ground surface when viewed from above in this photograph. The linear is formed by scarps (topographic expression of fault movement), by vegetation concentrated along the fault trace where ground-water ponds up-slope from the fault, and by sand dunes that form where wind-blown sand is trapped by the vegetation. Photo by J.C. Matti, USGS, December, 1979.
Diagram illustrating the plate-tectonic setting of southern California Diagram illustrating the plate-tectonic setting of southern California (image source: USGS general-interest publication “This dynamic earth: the story of plate tectonics” (Kious and Tilling, 1996).

April 25, 2015: A magnitude 7.8 earthquake tore through Nepal, killing nearly 9,000 and injuring 16,800.

HxC

 


The Philippines: Monday and Tuesday tremors kill 11 and 30 remain trapped in rubble

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CNN


4/18/1906: At 5:13 a.m., an earthquake estimated at close to 8.0 on the Richter scale strikes San Francisco, California, and killed an estimated 3,000 people, destroyed some 30 000 buildings and created 20 000 refugees

HxC

Timeline


Indonesia lifted a tsunami warning but urged people to remain vigilant and evacuate to higher ground after an earthquake of magnitude 6.8 struck off the coast of its island of Sulawesi.

CNBC

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3/29/1982: The combination of an earthquake and a volcanic eruption at El Chichon in southern Mexico converts a hill into a crater, kills thousands of people and destroys acres of farmland

HxC


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