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| USGS earthquake location map. |
May 16, 2015 - KATHMANDU, NEPAL -
A 5.7 magnitude earthquake has struck in Nepal, sending tremors across Bihar and parts of northern India.
Buildings shook throughout the Uttar Pradesh and Bihar regions on
Saturday, as the the US Geological Survey recorded a "shallow quake"
about 76 km east south east of the capital Kathmandu.
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| A collapsed house during a landslide after Tuesday's earthquake at Singati Village in Nepal. © Athit Perawongmetha |
Centering on Nepal, the quake is the third so far this month and lead to
fresh panic among those trying to rebuild after an earthquake killed
8,000 people in April and leveled more than 250,000 homes throughout the
region.
There has been no reports yet of deaths from this most recent quake,
though at least 17 people are thought to have been killed in northern
India.
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| USGS shakemap intensity. |
Some 117 persons were killed, and more than 1000 were injured, when a 7.3 magnitude earthquake hit Nepal on May 12.
The quake shook neighbouring countries including India, China, Pakistan, Bangladesh and China. -
Independent.
Tectonic Summary - Seismotectonics of the Himalaya and Vicinity
Seismicity in the Himalaya dominantly results from the continental
collision of the India and Eurasia plates, which are converging at a
relative rate of 40-50 mm/yr. Northward underthrusting of India beneath
Eurasia generates numerous earthquakes and consequently makes this
area one of the most seismically hazardous regions on Earth. The
surface expression of the plate boundary is marked by the foothills of
the north-south trending Sulaiman Range in the west, the Indo-Burmese
Arc in the east and the east-west trending Himalaya Front in the north
of India.
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| USGS plate tectonics for the region. (PDF) |
The India-Eurasia plate boundary is a diffuse boundary, which in the
region near the north of India, lies within the limits of the
Indus-Tsangpo (also called the Yarlung-Zangbo) Suture to the north and
the Main Frontal Thrust to the south. The Indus-Tsangpo Suture Zone is
located roughly 200 km north of the Himalaya Front and is defined by an
exposed ophiolite chain along its southern margin. The narrow
(less than 200km) Himalaya Front includes numerous east-west trending,
parallel structures. This region has the highest rates of seismicity
and largest earthquakes in the Himalaya region, caused mainly by
movement on thrust faults. Examples of significant earthquakes, in this
densely populated region, caused by reverse slip movement include the
1934 M8.0 Bihar, the 1905 M7.5 Kangra and the 2005 M7.6 Kashmir
earthquakes. The latter two resulted in the highest death tolls for
Himalaya earthquakes seen to date, together killing over 100,000 people
and leaving millions homeless. The largest instrumentally recorded
Himalaya earthquake occurred on 15th August 1950 in Assam, eastern
India. This M8.6 right-lateral, strike-slip, earthquake was widely felt
over a broad area of central Asia, causing extensive damage to
villages in the epicentral region.
The Tibetan Plateau is situated north of the Himalaya, stretching
approximately 1000km north-south and 2500km east-west, and is
geologically and tectonically complex with several sutures which are
hundreds of kilometer-long and generally trend east-west. The Tibetan
Plateau is cut by a number of large (greater than 1000km) east-west trending,
left-lateral, strike-slip faults, including the long Kunlun, Haiyuan,
and the Altyn Tagh. Right-lateral, strike-slip faults (comparable in
size to the left-lateral faults), in this region include the Karakorum,
Red River, and Sagaing. Secondary north-south trending normal faults
also cut the Tibetan Plateau. Thrust faults are found towards the north
and south of the Tibetan Plateau. Collectively, these faults
accommodate crustal shortening associated with the ongoing collision of
the India and Eurasia plates, with thrust faults accommodating north
south compression, and normal and strike-slip accommodating east-west
extension.
Along the western margin of the Tibetan Plateau, in the vicinity of
south-eastern Afghanistan and western Pakistan, the India plate
translates obliquely relative to the Eurasia plate, resulting in a
complex fold-and-thrust belt known as the Sulaiman Range. Faulting in
this region includes strike-slip, reverse-slip and oblique-slip motion
and often results in shallow, destructive earthquakes. The active,
left-lateral, strike-slip Chaman fault is the fastest moving fault in
the region. In 1505, a segment of the Chaman fault near Kabul,
Afghanistan, ruptured causing widespread destruction. In the same
region the more recent 30 May 1935, M7.6 Quetta earthquake, which
occurred in the Sulaiman Range in Pakistan, killed between 30,000 and
60,000 people.
On the north-western side of the Tibetan Plateau, beneath the
Pamir-Hindu Kush Mountains of northern Afghanistan, earthquakes occur
at depths as great as 200 km as a result of remnant lithospheric
subduction. The curved arc of deep earthquakes found in the Hindu Kush
Pamir region indicates the presence of a lithospheric body at depth,
thought to be remnants of a subducting slab. Cross-sections through the
Hindu Kush region suggest a near vertical northerly-dipping subducting
slab, whereas cross-sections through the nearby Pamir region to the
east indicate a much shallower dipping, southerly subducting slab. Some
models suggest the presence of two subduction zones; with the Indian
plate being subducted beneath the Hindu Kush region and the Eurasian
plate being subducted beneath the Pamir region. However, other models
suggest that just one of the two plates is being subducted and that the
slab has become contorted and overturned in places.
Shallow crustal earthquakes also occur in this region near the Main
Pamir Thrust and other active Quaternary faults. The Main Pamir Thrust,
north of the Pamir Mountains, is an active shortening structure. The
northern portion of the Main Pamir Thrust produces many shallow
earthquakes, whereas its western and eastern borders display a
combination of thrust and strike-slip mechanisms. On the 18 February
1911, the M7.4 Sarez earthquake ruptured in the Central Pamir
Mountains, killing numerous people and triggering a landside, which
blocked the Murghab River.
Further north, the Tian Shan is a seismically active
intra-continental mountain belt, which extends 2500 km in an ENE-WNW
orientation north of the Tarim Basin. This belt is defined by numerous
east-west trending thrust faults, creating a compressional basin and
range landscape. It is generally thought that regional stresses
associated with the collision of the India and Eurasia plates are
responsible for faulting in the region. The region has had three major
earthquakes (greater than M7.6) at the start of the 20th Century, including the
1902 Atushi earthquake, which killed an estimated 5,000 people. The
range is cut through in the west by the 700-km-long,
northwest-southeast striking, Talas-Ferghana active right-lateral,
strike-slip fault system. Though the system has produced no major
earthquakes in the last 250 years, paleo-seismic studies indicate that
it has the potential to produce M7.0+ earthquakes and it is thought to
represent a significant hazard.
The northern portion of the Tibetan Plateau itself is largely
dominated by the motion on three large left-lateral, strike-slip fault
systems; the Altyn Tagh, Kunlun and Haiyuan. The Altyn Tagh fault is
the longest of these strike slip faults and it is thought to
accommodate a significant portion of plate convergence. However, this
system has not experienced significant historical earthquakes, though
paleoseismic studies show evidence of prehistoric M7.0-8.0 events.
Thrust faults link with the Altyn Tagh at its eastern and western
termini. The Kunlun Fault, south of the Altyn Tagh, is seismically
active, producing large earthquakes such as the 8th November 1997, M7.6
Manyi earthquake and the 14th November 2001, M7.8 Kokoxili earthquake.
The Haiyuan Fault, in the far north-east, generated the 16 December
1920, M7.8 earthquake that killed approximately 200,000 people and the
22 May 1927 M7.6 earthquake that killed 40,912.
The Longmen Shan thrust belt, along the eastern margin of the Tibetan
Plateau, is an important structural feature and forms a transitional
zone between the complexly deformed Songpan-Garze Fold Belt and the
relatively undeformed Sichuan Basin. On 12 May 2008, the thrust belt
produced the reverse slip, M7.9 Wenchuan earthquake, killing over
87,000 people and causing billions of US dollars in damages and
landslides which dammed several rivers and lakes.
Southeast of the Tibetan Plateau are the right-lateral, strike-slip
Red River and the left-lateral, strike-slip Xiangshuihe-Xiaojiang fault
systems. The Red River Fault experienced large scale, left-lateral
ductile shear during the Tertiary period before changing to its present
day right-lateral slip rate of approximately 5 mm/yr. This fault has
produced several earthquakes greater than M6.0 including the 4 January 1970, M7.5
earthquake in Tonghai which killed over 10,000 people. Since the start
of the 20th century, the Xiangshuihe-Xiaojiang Fault system has
generated several M7.0+ earthquakes including the M7.5 Luhuo earthquake
which ruptured on the 22 April 1973. Some studies suggest that due to
the high slip rate on this fault, future large earthquakes are highly
possible along the 65km stretch between Daofu and Qianning and the 135km
stretch that runs through Kangding.
Shallow earthquakes within the Indo-Burmese Arc, predominantly occur
on a combination of strike-slip and reverse faults, including the
Sagaing, Kabaw and Dauki faults. Between 1930 and 1956, six M7.0+
earthquakes occurred near the right-lateral Sagaing Fault, resulting in
severe damage in Myanmar including the generation of landslides,
liquefaction and the loss of 610 lives. Deep earthquakes (200km) have
also been known to occur in this region, these are thought to be due to
the subduction of the eastwards dipping, India plate, though whether
subduction is currently active is debated. Within the pre-instrumental
period, the large Shillong earthquake occurred on the 12 June 1897,
causing widespread destruction. -
USGS.