NEARBY CITIES
- 35km (22mi) E of Lamjung, Nepal
- 60km (37mi) NNE of Bharatpur, Nepal
- 75km (47mi) E of Pokhara, Nepal
- 76km (47mi) NW of Kirtipur, Nepal
- 77km (48mi) NW of Kathmandu,
Nepal
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.
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 (<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 M8.1 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 (>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 (>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 >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.
Source: US Geological Survey
