Earth Watch Report  -  Earthquakes

China - Seven  EQ April 19th  2013 photo ChinasevenEQApril19th2013_zpsf0b2671f.jpg

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Instrumental Intensity

ShakeMap Intensity Image

6.6 50km WSW of Linqiong, China 2013-04-20 00:02:47 30.284°N 102.956°E 12.3

M6.6 – 50km WSW of Linqiong, China 2013-04-20 00:02:47 UTC

Earthquake location 30.284°N, 102.956°E

Event Time

  1. 2013-04-20 00:02:47 UTC
  2. 2013-04-20 08:02:47 UTC+08:00 at epicenter
  3. 2013-04-19 19:02:47 UTC-05:00 system time

Location

30.284°N 102.956°E depth=12.3km (7.6mi)

Nearby Cities

  1. 50km (31mi) WSW of Linqiong, China
  2. 99km (62mi) ENE of Kangding, China
  3. 111km (69mi) NW of Leshan, China
  4. 114km (71mi) WSW of Chengdu, China
  5. 1065km (662mi) NNW of Ha Noi, Vietnam

4.8 31km WSW of Linqiong, China 2013-04-20 00:31:36 30.352°N 103.142°E 10.0

M4.8 – 31km WSW of Linqiong, China 2013-04-20 00:31:36 UTC

Earthquake location 30.352°N, 103.142°E

Event Time

  1. 2013-04-20 00:31:36 UTC
  2. 2013-04-20 08:31:36 UTC+08:00 at epicenter
  3. 2013-04-19 19:31:36 UTC-05:00 system time

Location

30.352°N 103.142°E depth=10.0km (6.2mi)

Nearby Cities

  1. 31km (19mi) WSW of Linqiong, China
  2. 95km (59mi) WSW of Chengdu, China
  3. 103km (64mi) SW of Tianpeng, China
  4. 106km (66mi) NW of Leshan, China
  5. 1068km (664mi) NNW of Ha Noi, Vietnam

4.8 42km WSW of Linqiong, China 2013-04-20 00:37:11 30.274°N 103.044°E 10.1

M4.8 – 42km WSW of Linqiong, China 2013-04-20 00:37:11 UTC

Earthquake location 30.274°N, 103.044°E

Event Time

  1. 2013-04-20 00:37:11 UTC
  2. 2013-04-20 08:37:11 UTC+08:00 at epicenter
  3. 2013-04-19 19:37:11 UTC-05:00 system time

Location

30.274°N 103.044°E depth=10.1km (6.3mi)

Nearby Cities

  1. 42km (26mi) WSW of Linqiong, China
  2. 105km (65mi) NW of Leshan, China
  3. 107km (66mi) WSW of Chengdu, China
  4. 107km (66mi) ENE of Kangding, China
  5. 1062km (660mi) NNW of Ha Noi, Vietnam

4.7 46km WSW of Linqiong, China 2013-04-20 01:02:56 30.281°N 103.002°E 10.3

M4.7 – 46km WSW of Linqiong, China 2013-04-20 01:02:56 UTC

Earthquake location 30.281°N, 103.002°E

Event Time

  1. 2013-04-20 01:02:56 UTC
  2. 2013-04-20 09:02:56 UTC+08:00 at epicenter
  3. 2013-04-19 20:02:56 UTC-05:00 system time

Location

30.281°N 103.002°E depth=10.3km (6.4mi)

Nearby Cities

  1. 46km (29mi) WSW of Linqiong, China
  2. 103km (64mi) ENE of Kangding, China
  3. 108km (67mi) NW of Leshan, China
  4. 110km (68mi) WSW of Chengdu, China
  5. 1064km (661mi) NNW of Ha Noi, Vietnam

5.0 60km WSW of Linqiong, China 2013-04-20 01:11:51 30.218°N 102.876°E 10.0

Event Deleted

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4.8 35km WSW of Linqiong, China 2013-04-20 01:20:10 30.294°N 103.121°E 11.9

M4.8 – 35km WSW of Linqiong, China 2013-04-20 01:20:10 UTC

Earthquake location 30.294°N, 103.121°E

Event Time

  1. 2013-04-20 01:20:10 UTC
  2. 2013-04-20 09:20:10 UTC+08:00 at epicenter
  3. 2013-04-19 20:20:10 UTC-05:00 system time

Location

30.294°N 103.121°E depth=11.9km (7.4mi)

Nearby Cities

  1. 35km (22mi) WSW of Linqiong, China
  2. 99km (62mi) WSW of Chengdu, China
  3. 102km (63mi) NW of Leshan, China
  4. 109km (68mi) SW of Tianpeng, China
  5. 1062km (660mi) NNW of Ha Noi, Vietnam

4.6 41km WNW of Linqiong, China 2013-04-20 01:26:02 30.503°N 103.037°E 12.4

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M4.6 – 41km WNW of Linqiong, China 2013-04-20 01:26:02 UTC

Earthquake location 30.503°N, 103.037°E

Event Time

  1. 2013-04-20 01:26:02 UTC
  2. 2013-04-20 09:26:02 UTC+08:00 at epicenter
  3. 2013-04-19 20:26:02 UTC-05:00 system time

Location

30.503°N 103.037°E depth=12.4km (7.7mi)

Nearby Cities

  1. 41km (25mi) WNW of Linqiong, China
  2. 100km (62mi) W of Chengdu, China
  3. 101km (63mi) WSW of Tianpeng, China
  4. 115km (71mi) ENE of Kangding, China
  5. 1086km (675mi) NNW of Ha Noi, Vietnam

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5.1 46km WSW of Linqiong, China 2013-04-20 01:37:28 30.283°N 103.001°E 12.0

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M5.1 – 46km WSW of Linqiong, China 2013-04-20 01:37:28 UTC

Earthquake location 30.283°N, 103.001°E

Event Time

  1. 2013-04-20 01:37:28 UTC
  2. 2013-04-20 09:37:28 UTC+08:00 at epicenter
  3. 2013-04-19 20:37:28 UTC-05:00 system time

Location

30.283°N 103.001°E depth=12.0km (7.5mi)

Nearby Cities

  1. 46km (29mi) WSW of Linqiong, China
  2. 103km (64mi) ENE of Kangding, China
  3. 108km (67mi) NW of Leshan, China
  4. 110km (68mi) WSW of Chengdu, China
  5. 1064km (661mi) NNW of Ha Noi, Vietnam

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4.5 42km WSW of Linqiong, China 2013-04-20 02:19:04 30.297°N 103.040°E 12.4

M4.5 – 42km WSW of Linqiong, China 2013-04-20 02:19:04 UTC

Earthquake location 30.297°N, 103.040°E

Event Time

  1. 2013-04-20 02:19:04 UTC
  2. 2013-04-20 10:19:04 UTC+08:00 at epicenter
  3. 2013-04-19 21:19:04 UTC-05:00 system time

Location

30.297°N 103.040°E depth=12.4km (7.7mi)

Nearby Cities

  1. 42km (26mi) WSW of Linqiong, China
  2. 106km (66mi) WSW of Chengdu, China
  3. 107km (66mi) NW of Leshan, China
  4. 107km (66mi) ENE of Kangding, China
  5. 1064km (661mi) NNW of Ha Noi, Vietnam

4.6 36km WSW of Linqiong, China 2013-04-20 02:38:35 30.260°N 103.129°E 12.1

M4.6 – 36km WSW of Linqiong, China 2013-04-20 02:38:35 UTC

Earthquake location 30.260°N, 103.129°E

Event Time

  1. 2013-04-20 02:38:35 UTC
  2. 2013-04-20 10:38:35 UTC+08:00 at epicenter
  3. 2013-04-19 21:38:35 UTC-05:00 system time

Location

30.260°N 103.129°E depth=12.1km (7.5mi)

Nearby Cities

  1. 36km (22mi) WSW of Linqiong, China
  2. 98km (61mi) NW of Leshan, China
  3. 100km (62mi) WSW of Chengdu, China
  4. 111km (69mi) SW of Tianpeng, China
  5. 1058km (657mi) NNW of Ha Noi, Vietnam

5.1 57km WSW of Linqiong, China 2013-04-20 03:34:16 30.181°N 102.928°E 12.3

M5.1 – 57km WSW of Linqiong, China 2013-04-20 03:34:16 UTC

Earthquake location 30.181°N, 102.928°E

Event Time

  1. 2013-04-20 03:34:16 UTC
  2. 2013-04-20 11:34:16 UTC+08:00 at epicenter
  3. 2013-04-19 22:34:16 UTC-05:00 system time

Location

30.181°N 102.928°E depth=12.3km (7.6mi)

Nearby Cities

  1. 57km (35mi) WSW of Linqiong, China
  2. 94km (58mi) E of Kangding, China
  3. 105km (65mi) NW of Leshan, China
  4. 121km (75mi) WSW of Chengdu, China
  5. 1055km (656mi) NNW of Ha Noi, Vietnam

 

Tectonic Summary

The April 20, 2013 UTC Mw6.6 earthquake in the Sichuan province of China occurred as the result of east-west oriented reverse-type motion on a north-south striking fault. A preliminary source location suggest the event likely occurred on the Longmenshan fault or a tectonically related fault at a depth of 12km. The Longmenshan fault was the source fault of the May 12, 2008 Mw7.9 Sichuan earthquake. The preliminary April 20 event location is approximately 85km from the hypocentral location of the 2008 Sichuan earthquake. The April 20 earthquake reflects tectonic stresses resulting from the convergence of crustal material slowly moving from the high Tibetan Plateau, to the west, against strong crust underlying the Sichuan Basin and southeastern China.

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 with a velocity of about 50 mm/y. 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.

Four events of Mw6.0 or greater have occurred within 200km of the April 19 event in the past 40 years, including the May 2008 Sichuan earthquake and a subsequent aftershock. The northwestern margin of the Sichuan Basin has previously experienced destructive earthquakes. The magnitude 7.5 earthquake of August 25, 1933, killed more than 9,300 people, while the May 12, 2008 killed 69,197.

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.

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