Strong Magnitude 6.4 Earthquake Strikes Indonesia

A powerful magnitude 6.4 earthquake has struck off Indonesia’s central island of Sumbawa, but no tsunami warning was issued and there were no immediate reports of damage.

The tremor on Tuesday followed a pair of offshore quakes in the same area earlier Tuesday, including one that was magnitude 6.1 south of the city of Raba.

The latest one struck about 85km south of the town of Kahale, according to the United States Geological Survey.

There were no immediate reports of damage or casualties.

Disaster-prone Indonesia, which sits on the geologically active so-called Pacific Ring of Fire, where tectonic plates collide, suffered its deadliest year in more than a decade in 2018 as a series of earthquakes and tsunamis killed thousands of people.

The vast Southeast Asian archipelago of more than 17,000 islands is still reeling from a devastating tsunami at the end of December triggered by an erupting volcano in the middle of the Sunda Strait between Java and Sumatra islands that killed more than 400 people.

The tsunami was Indonesia’s third major natural disaster in six months.

It followed a series of powerful earthquakes on the island of Lombok in July and August and a quake-tsunami in September that killed around 2,200 people in Palu on Sulawesi island, with thousands more missing and presumed dead.

Nepal Earthquake: Waiting For The Complete Rupture

In April 2015, Nepal — and especially the region around the capital city, Kathmandu — was struck by a powerful tremor. An earthquake with a magnitude of 7.8 destroyed entire villages, traffic routes and cultural monuments, with a death toll of some 9,000.

However, the country may still face the threat of much stronger earthquakes with a magnitude of 8 or more. This is the conclusion reached by a group of earth scientists from ETH Zurich based on a new model of the collision zone between the Indian and Eurasian Plates in the vicinity of the Himalayas.

Using this model, the team of ETH researchers working with doctoral student Luca Dal Zilio, from the group led by Professor Taras Gerya at the Institute of Geophysics, has now performed the first high-resolution simulations of earthquake cycles in a cross-section of the rupture zone.

“In the 2015 quake, there was only a partial rupture of the major Himalayan fault separating the two continental plates. The frontal, near-surface section of the rupture zone, where the Indian Plate subducts beneath the Eurasian Plate, did not slip and remains under stress,” explains Dal Zilio, lead author of the study, which was recently published in the journal Nature Communications.

Normally, a major earthquake releases almost all the stress that has built up in the vicinity of the focus as a result of displacement of the plates. “Our model shows that, although the Gorkha earthquake reduced the stress level in part of the rupture zone, tension actually increased in the frontal section close to the foot of the Himalayas. The apparent paradox is that ‘medium-sized’ earthquakes such as Gorkha can create the conditions for an even larger earthquake,” says Dal Zilio.

Tremors of the magnitude of the Gorkha earthquake release stress only in the deeper subsections of the fault system over lengths of 100 kilometres. In turn, new and even greater stress builds up in the near-surface sections of the rupture zone.

According to the simulations performed by Dal Zilio and his colleagues, two or three further Gorkha quakes would be needed to build up sufficient stress for an earthquake with a magnitude of 8.1 or more. In a quake of this kind, the rupture zone breaks over the entire depth range, extending up to the Earth’s surface and laterally — along the Himalayan arc — for hundreds of kilometres. This ultimately leads to a complete stress release in this segment of the fault system, which extends to some 2,000 kilometres in total.

Historical data shows that mega events of this kind have also occurred in the past. For example, the Assam earthquake in 1950 had a magnitude of 8.6, with the rupture zone breaking over a length of several hundred kilometres and across the entire depth range. In 1505, a giant earthquake struck with sufficient power to produce an approximately 800-kilometre rupture on the major Himalayan fault. “The new model reveals that powerful earthquakes in the Himalayas have not just one form but at least two, and that their cycles partially overlap,” says Edi Kissling, Professor of Seismology and Geodynamics. Super earthquakes might occur with a periodicity of 400 to 600 years, whereas “medium-sized” quakes such as Gorkha have a recurrence time of up to a few hundred years. As the cycles overlap, the researchers expect powerful and dangerous earthquakes to occur at irregular intervals.

However, they cannot predict when another extremely large quake will next take place. “No one can predict earthquakes, not even with the new model. However, we can improve our understanding of the seismic hazard in a specific area and take appropriate precautions,” says Kissling.

The two-dimensional and high-resolution model also includes some research findings that were published after the Gorkha earthquake. To generate the simulations, the researchers used the Euler mainframe computer at ETH Zurich. “A three-dimensional model would be more accurate and would also allow us to make statements about the western and eastern fringes of the Himalayas. However, modelling the entire 2,000 kilometres of the rupture zone would require enormous computational power,” says Dal Zilio.

Santorini Volcano (Greece): Earthquake Swarm Southwest Off The Island

An earthquake swarm has been occurring near the island since this morning. So far, 16 quakes of magnitudes between 2 and 3.9 and at depths ranging between about 30-6 km have been detected.

The quakes are clustered about half way between Santorini’s SW end and the Christiana Island group.

The strongest shock with magnitude 3.9 occurred at 10:27 local time and might have been felt weakly by residents of the southern part of Santorini.

Although the quakes are near the Kameni line, a tectonic lineament in SW-NE direction which has been the preferred location for magma ascent (i.e. formation of volcanic vents) in the volcano’s past few 100,000 years of history, there is currently no indication that the earthquakes are volcanic in origin. It is much more likely that they represent a normal tectonic event.

However, Santorini being both a popular tourist destination and an active volcano, the situation merits close monitoring.

Magnitude 6.1 Earthquake Near Adak, Tsunami Not Expected

A magnitude 6.1 earthquake struck 57 miles southwest of Adak, Alaska, at 9:47 Saturday morning. At this time, a tsunami is not expected, according to the National Weather Service Tsunami Warning Center.

The earthquake epicenter was some 37 miles south of Bobrof island, just 62 miles deep. The area is in the far western Aleutians, some 1,200 miles southwest of Anchorage.

At this time there are no reports of damage.

Strong 6.8-Magnitude Earthquake Hits Western Brazil

A strong earthquake with a preliminary magnitude of 6.8 has struck Brazil’s Amazon region, but damage is unlikely because it struck at a depth of nearly 600 kilometers (372 miles), seismologists say.

The earthquake, which struck at 2:25 p.m. local time on Saturday, was centered in the Amazon rainforest, about 89 kilometers (55 miles) west of Tarauacá in Acre state, or 739 kilometers (459 miles) northeast of Lima.

The U.S. Geological Survey measured the magnitude at 6.8 but said it struck at a depth of 575 kilometers (479 miles), making it a very deep earthquake. Peru’s seismological agency put the magnitude significantly higher, at 7.2.

Damage is unlikely because it struck far below the surface and in a remote area. Computer models from the UN estimate that nearly 5,300 people live within 50 kilometers (31 miles) of the earthquake epicenter.

Saturday’s earthquake was the strongest to hit Brazil since 2003, when a powerful 7.1-magnitude earthquake hit the same region. However, strong and deep earthquakes sometimes hit Peru in areas that are close to the border with western Brazil. They rarely cause damage.

No Tsunami Threat To Hawaii From Alaska Earthquake

The Pacific Tsunami Warning Center said a magnitude 6.1 earthquake that struck Alaska today poses no local threat of a tsunami.

 

A earthquake magnitude 6.1 (ml/mb) has struck on Sunday, 116 km SE of Cold Bay, Alaska (72 miles). Exact location, longitude -161.4719° West, latitude 54.4279° North, depth = 26.92 km.

The 6.1-magnitude earthquake has occurred at 15:35:37 / 3:35 pm (local time epicenter). A tsunami warning has been issued near Cold Bay in Alaska (Does not indicate if a tsunami actually did or will exist).

Earthquake Off Philippine Coast Hits A Region Already On High Alert

An undersea earthquake occurred Saturday off the coast of the southern Philippines. The U.S. Geological Survey says it struck at a depth of about 38 miles and had a magnitude of 7.0. According to The Associated Press, no casualties or damage had been reported as of a few hours after the quake.

It was felt in several cities in the southern Philippines and led the Pacific Tsunami Warning Center to issue a tsunami threat – which has since been lifted — for areas along the coasts of Indonesia and the Philippines.

This most recent scare, which seemed to cause little damage, is the latest seismic activity in a region reeling from disaster. On Dec. 22, a tsunami hit Indonesia and killed at least 430 people. NPR’s Anthony Kuhn reported that Indonesia’s seismic activity directors were faulty, which meant that residents were not properly warned. Kuhn also noted that Indonesians did not feel an earthquake, a common warning sign, before the tsunami struck.

A widely shared video of a concert is one of the more unsettling illustrations of how unexpected the disaster was: The local pop-rock band Seventeen was performing at a party in Java one moment and taken by a massive wave the next.

Now scientists might know why last Saturday’s disaster happened. According to a statement from the European Geosciences Union, the partial collapse of Anak Krakatau, a volcano in Indonesia’s Sunda Strait, may have caused the tsunami. Researcher Raphaël Paris says Anak Krakatau’s instability will continue to pose a risk. In the EGU statement, Paris says, “There is a big uncertainty on the stability of the volcanic cone now and the probability for future collapses and tsunamis is perhaps non-negligible.”

When Anak Krakatau lost a 64-hectare portion of its west-southwest flank, tons of rocky debris fell into the sea and brought forth powerful waves. This, according to the BBC’s Jonathan Amos, could have been the source. NPR’s Julie McCarthy reports that researchers say the volcanic cone has decreased in height from 1,108 feet to just 336 feet. Satellite images also show a significant decrease in Anak Krakatau’s size.

Paris was part of a team that modeled a very similar Anak Krakatau-induced tsunami back in 2012. Mike Burton, president of the EGU Division on Geochemistry, Mineralogy, Petrology and Volcanology, said in the EGU’s statement: “The hazard scenario were therefore understood, but the management of such a hazard obviously remains a major challenge.”

The exact details of the tsunami’s cause — the nature of the eruption that triggered the loss of the flank, for example — will not be determined until researchers can access the area of the volcano, according to the BBC’s Amos.

Anak Krakatau translates to “child of Krakatau.” Anak’s parent, Krakatau (or Krakatoa), is perhaps best known for exploding in 1883. According to Hawaii Public Radio’s Neal Conan, about 100,000 people died from that eruption’s direct effects and more than 35,000 others died from resulting tsunami waves. Anak Krakatau was formed from what remained of Krakatau.

Less than three months ago, another tsunami in Indonesia killed at least 1,400 others. And in August, a 6.9 magnitude earthquake killed at least 460. A statement issued in October by Indonesia’s National Agency for Disaster Management said 1,999 natural disasters occurred in Indonesia in 2018, leaving 3,548 dead or missing.