Saturday, July 6, 2013

DELUGE: Landslides And Floods In Nepal Kill 50 - 7,000 Displaced; 800 Houses Completely Destroyed; Death Toll Likely To Rise!

July 06, 2013 - NEPAL - Landslides and floods triggered by several weeks of monsoon rains have killed at least 50 people in mainly remote parts of Nepal, a government official said Thursday.

"So far, 50 people from across the country have been killed by landslides and floods," said Lakshmi Prasad Dhakal, chief of National Emergency Operation Centre, which monitors natural disasters in Nepal.

The death toll is likely to rise, with some 19 people still missing after floods hit mostly farming communities in the country's southern plains and remote western hills, Dhakal said.

"We are forming a committee headed by the minister for physical planning, which will present a report on how to rebuild the infrastructure damaged by the landslides and floods," said Dhakal.

A total of 7,000 people have also been displaced, while 800 houses have been completely destroyed and 1500 partly damaged, after heavy monsoon rains began in mid-June and eased two weeks later, he said.

"Over 1000 livestock have also been killed and we are still assessing the damage in monetary terms," Dhakal said, adding that the government has distributed 7.5 million rupees ($78,000) in total to victims.

Hundreds of people die every year from flooding and landslides during the monsoon season in Nepal.

Monsoon rains have also struck over the border in India, with landslides and flash floods leaving at least one thousand people dead. - Space Daily.

PLANETARY TREMORS: Strong 6.0 Magnitude Earthquake Strikes Off The Coast Of Sumatra, Indonesia!

July 06, 2013 - INDONESIA - A strong 6.4-magnitude quake struck off the Indonesian island of Sumatra on Saturday, the US Geological Survey said, but no tsunami warning was issued.

USGS earthquake location.

The quake struck at a shallow depth of just 23kms (14 miles), off the west coast of the vast island and 154 kilometers southwest of Sungaipenuh and was later downgraded to a 6.0 event, said the USGS.

Suharjono, an official from the local meteorology, climatology and geophysics agency who goes by one name, said there was no threat of a tsunami.

The earthquake came just days after a strong inland tremor in Aceh province, on the northern tip of Sumatra, which killed dozens of people and left thousands homeless.

USGS earthquake shakemap intensity.

Indonesia sits on the Pacific “Ring of Fire” where tectonic plates collide, causing frequent seismic and volcanic activity. - Hindustan Times.

Tectonic Summary - Seismotectonics of the Sumatra Region
The plate boundary southwest of Sumatra is part of a long tectonic collision zone that extends over 8000 km from Papua in the east to the Himalayan front in the west. The Sumatra-Andaman portion of the collision zone forms a subduction zone megathrust plate boundary, the Sunda-Java trench, which accommodates convergence between the Indo-Australia and Sunda plates. This convergence is responsible for the intense seismicity and volcanism in Sumatra. The Sumatra Fault, a major transform structure that bisects Sumatra, accommodates the northwest-increasing lateral component of relative plate motion.

Relative plate motion between the Indo-Australia and Sunda plates is rapid, decreasing from roughly 63 mm/year near the southern tip of Sumatra (Australia relative to Sunda) to 44 mm/year north of Andaman Islands (India relative to Sunda) and rotating counterclockwise to the northwest, so that relative motion near Jakarta is nearly trench-normal but becomes nearly trench-parallel near Myanmar. As a result of the rotation in relative motion along the strike of the arc and the interaction of multiple tectonic plates, several interrelated tectonic elements compose the Sumatra-Andaman plate boundary. Most strain accumulation and release occurs along the Sunda megathrust of the main subduction zone, where lithosphere of the subducting Indo-Australia plate is in contact with the overlying Sunda plate down to a depth of 60 km. Strain release associated with deformation within the subducting slab is evidenced by deeper earthquakes that extend to depths of less than 300 km on Sumatra and 150 km or less along the Andaman Islands. The increasingly oblique convergence between these two plates moving northwest along the arc is accommodated by crustal seismicity along a series of transform and normal faults. East of the Andaman Islands, back- arc spreading in the Andaman Sea produces a zone of distributed normal and strike-slip faulting. Similar to the Sumatran Fault, the Sagaing Fault near Myanmar also accommodates the strike-slip component of oblique plate motion. Plate-boundary related deformation is also not restricted to the subduction zone and overriding plate: the subducting Indo-Australian plate actually comprises two somewhat independent plates (India and Australia), with small amounts of motion relative to one another, that are joined along a broad, actively-deforming region producing seismicity up to several hundred kilometers west of the trench. This deformation is exemplified by the recent April 2012 earthquake sequence, which includes the April 11 M 8.6 and M 8.2 strike-slip events and their subsequent aftershocks.

USGS plate tectonics for the region.

Paleoseismic studies using coral reefs as a proxy for relative land level changes associated with earthquake displacement suggest that the Sunda arc has repeatedly ruptured during relatively large events in the past, with records extending as far back as the 10th century. In northern Simeulue Island, the southern terminus of the 2004 megathrust earthquake rupture area, a cluster of megathrust earthquakes occurred over a 56 year period between A.D. 1390 and 1455, resulting in uplift substantially greater than that caused by the 2004 event. Studies that look at large sheeted deposits of sand on land interpreted as the transport of debris from a tsunami wave also indicate that this region has experienced significant tsunamis in the past centuries, albeit infrequently.

Prior to 2004, the most recent megathrust earthquakes along the Sumatran-Andaman plate boundary were in 1797 (M 8.7-8.9), 1833 (M 8.9-9.1) and 1861 (M8.5). Since 2004, much of the Sunda megathrust between the northern Andaman Islands and Enggano Island, a distance of more than 2,000 km, has ruptured in a series of large subduction zone earthquakes - most rupturing the plate boundary south of Banda Aceh. The great M 9.1 earthquake of December 26, 2004, which produced a devastating tsunami, ruptured much of the boundary between Myanmar and Simeulue Island offshore Banda Aceh. Immediately to the south of the great 2004 earthquake, the M 8.6 Nias Island earthquake of March 28, 2005 ruptured a 400-km section between Simeulue and the Batu Islands. Farther south in the Mentawai islands, two earthquakes on September 12, 2007 of M 8.5 and M 7.9 occurred in the southern portion of the estimated 1797 and 1833 ruptures zone, which extends from approximately Enggano Island to the northern portion of Siberut Island. Smaller earthquakes have also been locally important: a M 7.6 rupture within the subducting plate caused considerable damage in Padang in 2009, and a M 7.8 rupture on October 25, 2010 occurred on the shallow portion of the megathrust to the west of the Mentawai Islands, and caused a substantial tsunami on the west coast of those islands.

In addition to the current seismic hazards along this portion of the Sunda arc, this region is also recognized as having one of the highest volcanic hazards in the world. One of the most dramatic eruptions in human history was the Krakatau eruption on August 26-27, 1883, a volcano just to the southeast of the island of Sumatra, which resulted in over 35, 000 casualties.

Subduction and seismicity along the plate boundary adjacent to Java is fundamentally different from that of the Sumatran-Andaman section. Relative motion along the Java arc is trench-normal (approximately 65-70 mm/year) and does not exhibit the same strain partitioning and back-arc strike- slip faulting that are observed along the Sumatra margin. Neither has the Java subduction zone hosted similar large magnitude megathrust events to those of its neighbor, at least in documented history. Although this region is not as seismically active as the Sumatra region, the Java arc has hosted low to intermediate-magnitude extensional earthquakes and deep-focus (300-700 km) events and exhibits a similar if not higher volcanic hazard. This arc has also hosted two large, shallow tsunami earthquakes in the recent past which resulted in high tsunami run-ups along the southern Java coast. - USGS.

GLOBAL VOLCANISM: Minor Unrest And Inflation Reported At Hawaii's Mauna Lao - The Largest Volcano On Earth!

July 06, 2013 - HAWAII - Very weak unrest in the form of inflation and seismic activity continues at the largest active volcano of our earth, which has not erupted since 1984.

However, this activity is not strong enough to justify a raise of the alert level from green “normal” to yellow “unrest.”

There is currently no sign that Mauna Loa will erupt any time soon. HVO reports in its monthly update:

“Minor inflation of a shallow magma reservoir beneath Mauna Loa may be occurring.

Seismicity rates were slightly elevated. Deformation: Deformation of Mauna Loa continued to be dominated by southeasterly motion of the south flank.

However, slow uplift also continues near the summit caldera (~1cm/yr at MLSP) suggesting that some inflation of the shallow magma reservoir complex beneath the summit area is occurring. - Volcano Discovery.