Wednesday, February 12, 2014

PLANETARY TREMORS: Powerful 6.9 Magnitude Earthquake Shakes Western China - Casualties Or Damage Unclear!

February 12, 2014 - CHINA - A powerful earthquake struck a sparsely populated area of China's far western region of Xinjiang on Wednesday. It was not immediately clear if it caused any casualties or significant damage.

USGS earthquake location.

The U.S. Geological Survey said the magnitude-6.9 quake was centered 268 kilometers (167 miles) east-southeast of Hotan at a depth of 10 kilometers (6.2 miles). The China Earthquake Networks Center measured the quake at magnitude 7.3 and said it was followed by at least seven smaller quakes within the following half hour.

The epicenter was in Yutian county, a mountainous area several thousand meters above sea level on the edge of the Taklamakan desert. A magnitude-7.2 quake in that area in March 2008 collapsed some houses but caused no injuries.

China Earthquake Networks Center researcher Sun Shihong said any casualties from Wednesday's quake would likely be low.

USGS earthquake shakemap intensity.

The director of the Yutian Civil Affairs Bureau, Zhang Chong, said officials were still gathering information. A police officer in Yutian said he had felt tremors shaking the police station and ran outside.

Wang Gang, a fire brigade chief in Yutian County, told the national CCTV broadcaster he was heading from the county seat to the earthquake zone, about 100 kilometers (60 miles) away, with a team of police and firefighters.

China's worst earthquake in recent years was a magnitude-7.9 temblor that struck the southwestern province of Sichuan in 2008, leaving about 90,000 people dead or missing. - ABC News.

Seismotectonics O 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 (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 M8.1 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.

USGS plate tectonics for the 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.

GLOBAL VOLCANISM: Global Volcano Report For February 11, 2014 - Very Large Pyroclastic Flow At Italy's Mount Etna; Seismic Swarm At Kelut Volcano In Indonesia, Alert Level Increased; Intense Activity At Ecuador's Tunguruhua Volcano With Continuous Ash Emissions; 32 Earthquakes Beneath Hawaii's Kilauea Volcano; Indonesian Officials Sends People Back To Areas Outside The 5km Exclusion Zone Around Mount Sinabung And Small Earthquake Swarm At Mammoth Mountain In California! [PHOTOS+VIDEOS]

February 12, 2014 - WORLDWIDE VOLCANOES - The following constitutes the new activity, unrest and ongoing reports of volcanoes across the globe.

Etna (Sicily, Italy): Another new effusive vent opened up on the eastern side of the New SE crater around 04:00 this morning, erupting a new short-lived lava flow that stopped being active around 09:00.

The lava flow last night (Photo: Emanuela / VolcanoDiscovery Italia)

No significant changes were observed last night: the lava flow and strombolian activity at the New SE crater have continued similar to the days before.

This morning at 10:20 (local time),after an ash explosion, a new vent opened over the vents that alimented the active lava flow.

WATCH: The following time-lapse video shows the evolution of lava flows from the various vents, as well as pulses of strombolian activity since the start of the ongoing eruptive episode:

Tremor is fluctuating, but there's a slow overall rising trend

A (for Etna standards) very large pyroclastic flow descended this morning on the eastern flank from the area of the new vents that opened yesterday on the eastern side beneath the summit of the New SE crater.

Photo of the pyroclastic flow on Etna this morning (Photo: Mike Schüler, Facebook)

Most likely, explosive lava-snow interaction and destabilization of this area where new magma was pushing its way outside caused a sector to collapse and descend the Valle del Bove flank as a hot turbulent avalanche (=pyroclastic flow). It reached the bottom of Valle del Bove in less than 3 minutes and traveled about 3 km length, which implies an average speed of 60 km/h, with maximum speed probably in excess of 100 km/h (approx. 65 mph).

WATCH: Here are the impressive videos from INGV Catania:

The following is a comparison of some characteristic stages of the vents and lava flows on the eastern flank of the New SE cone:

Comparison of thermal images showing the evolution of the eastern flank of the NSEC during the past 36 hours

Mammoth Mountain (California, USA): An small earthquake swarm at shallow depths (around 5 km) occurred east of Mammoth Mountain during the past week. The largest quake was a magnitude 3.0 event on 5 Feb.

Location of recent earthquakes near Mammoth Mountain (CA)

This latest (of many in the past years) seismic swarm is weak in terms of number and energy of earthquakes compared to long-term averages of seismic activity at the Long Valley caldera, an active volcanic system that is capable to erupt (probably not in a near future, though) and is being closely monitored by very experienced staff from USGS.

Number of earthquakes in the Long Valley caldera over the 30 days, showing the recent swarm (USGS)

It could be related to a small intrusion of magma, but is unlikely to be a precursor of a new eruption in any near future. USGS has not changed the status code of the volcanic system (at green=normal).

Kilauea (Hawai'i):  32 earthquakes were strong enough to be located beneath Kilauea Volcano in the past 24 hours, including 21 scattered broadly beneath the summit caldera.

Tungurahua (Ecuador): Activity of the volcano remains intense, but the style of the eruption has changed towards near continuous ash emissions as opposed to discrete, but potentially much more violent explosions. The ash plume still rises up to 4 km above Tungurahua's summit at times.

Abundant degassing and steaming accompanies the ash emissions. Ash falls frequently occur in nearby villages.

Kelut (East Java, Indonesia):  Another Indonesian volcano looks to be headed for new eruptive activity. The BPBD (Disaster Management) placed towns around Kelut (also known as Kelud) on their highest alert and the PVMBG (Volcano Monitoring) has the volcano at Orange, the second-highest alert possible.

The dome within the crater at Kulet in Indonesia. This dome formed during the 2007 eruption of the volcano —
seen here in 2010. Image: Zahidayat / Flickr.

This elevated status is due to a trio of signs: increased shallow earthquakes under the volcano, an inflation of the volcanic edifice and increasing temperatures of water in the crater of the volcano. These signs combined would all suggest that new magma is rising up under Kelut.  has a history of fatal eruptions, with over 5,100 deaths during an eruption in 1919 and 34 deaths in 1990. Apparently, the local residents are taking this rumbling seriously — partially due to the warnings but also due to more colloquial beliefs about animal behavior prior to an eruption.

Seismic activity at Kelut volcano during the past weeks (VSI)

Hypocenters of recent earthquakes under Kelut volcano (VSI)

Kelut is one of the few places on the planet where people have tried to use a massive engineering project to try to mitigate against volcanic disaster. The largest hazard present at Kelut is the generation of lahars (volcanic mudflows) due to presence of a crater lake. Chris Rowan wrote a post during the 2007 activity (that built an impressive dome in the main crater – see above) about how, after the 1919 eruption, tunnels were dug to try to drain the crater lake to help prevent the generation of these lahars. The plan did work … for awhile, but the eruption in 1951 deepened the crater lake, so new tunnels had to be dug during the 1960s. However, these tunnels might have actually made the eruption in 1966 worse. You can read the full story of these eruption and the attempts to “fix” the problem in a report from the Commission on Crater Lakes.

The PVMBG has an active webcam pointed at Kelut as well.

Sinabung (Indonesia): Meanwhile, Indonesian officials are sending people back to villages outside the 5-km exclusion zone around Sinabung. Now, this move might seem troubling considering the recent deaths at Sinabung, however, those deaths occurred within that 5-km exclusion zone (in fact, the people were close to 3 km of the active vent). The villages within the 5-km exclusion zone are likely to remain evacuated for much longer and some will be abandoned permanently. Even at a distance of 7 km from the volcano, these villages will be slowly repopulated as the government cleans up the copious ash that has fallen.

Complete Earthquake list (worldwide) for February 11, 2014.

SOURCES: Volcano Discovery | WIRED.