Paddlefest, plate tectonics


Staff Reports



5th Annual Parkersburg Paddlefest Weekend Slated for Sept. 14-16

PARKERSBURG, W.Va. (August 13, 2018) – Parkersburg Paddlefest Weekend will is slated to take place September 14-16, 2018 and will once again coincide with the craft brew and BBQ event, Downtown Throwdown on Sept. 15.

This fun-filled three-day festival is dedicated to people-powered watercraft. Kayaks, canoes, and stand-up paddleboards are welcome to come and participate. Point Park, at the confluence of the Ohio and Little Kanawha Rivers, is the setting for the first two days of activities. The weekend concludes with a lake excursion on Sunday at North Bend State Park Lake.

Paddlefest weekend begins on Friday night (Sept. 14) with a glow paddle at 8 p.m. Electric lights and glow sticks will illuminate boats as the group paddles up the Little Kanawha River from Point Park. The boat with the most spectacular light display will win a prize!

On Friday and Saturday evenings, the 2nd Annual Riverfest returns to Point Park bringing with it a group of iconic Sternwheelers for well-loved local food and music. The event is free and family-friendly.

The main event on Saturday (Sept. 15) 8 a.m. to 2 p.m., provides a unique opportunity to paddle a three-mile stretch of the Ohio River, from Point Park downriver to Blennerhassett Island and back, while commercial traffic is restricted on the Ohio River. No worries about being run over by barges. Safety watercraft will be on hand to slow private motorized craft passing through. On Blennerhassett Island, the staff and volunteers at Blennerhassett Island Historical State Park will welcome Paddlefest participants to tour Blennerhassett Mansion, enjoy horse-drawn wagon rides, special events and activities. (Please note: You will need to bring cash if you are interested in taking tours of Blennerhassett Mansion, horse-drawn wagon ride, or purchasing anything from the concession stand while on Blennerhassett Island.)

Temple Challenge, Full Circle Yoga, and Appalachian Disc Golf will all be offering additional activities for those interested once they reach the island. These activities will be free.

Saturday evening (Sept. 15), 6 to 10 p.m., Paddlefest participants are encouraged to attend “The Downtown Throwdown”. The event is a craft brew and barbecue blowout that features fantastic food, frosty beverages and live local performers making inspired music! It takes place in Parkersburg’s Bi-Centennial Park, just three blocks from Point Park in historic downtown Parkersburg.

On Sunday (Sept 16), before heading home, the festival offers a farewell lake paddling excursion on North Bend State Park Lake beginning at 11 a.m. The lake, located 40 minutes east of Parkersburg, is only 17 years old and still has lots of standing trees in the water which have become habitat for what is arguably the largest congregation of Red-headed woodpeckers in the United States. It offers a scenic and serene final paddling trip with which to end a wonderfully wet weekend!

Registered Parkersburg Paddlefest Participants are insured by the American Canoe Association (ACA) throughout the duration of the event. If you are planning on registering on the morning of Paddlefest, please bring cash of the correct amount of $20 per paddler.

To learn more about Greater Parkersburg and these events, visit www.GreaterParkersburg.com, call the Greater Parkersburg Convention & Visitors Bureau office at 304-428-1130 or email Hannah Duffield at hduffield@greaterparkersburg.org.

Nathan Winterroth of Westerville receives University of Nebraska-Lincoln degree

LINCOLN, NE (08/13/2018)— Nathan Winterroth of Westerville was among 751 graduates who received degrees from the University of Nebraska-Lincoln during the summer commencement ceremony Aug. 11 at Pinnacle Bank Arena.

Winterroth earned a Master of Business Administration from the Office of Graduate Studies.

Chancellor Ronnie Green presided over the ceremony, in which undergraduate and graduate degrees were awarded.

Donde Plowman, executive vice chancellor and chief academic officer at Nebraska, delivered the commencement address.

The graduates are from 38 countries, 38 states and the District of Columbia, and more than 75 Nebraska communities. For a complete list of graduates, visit https://go.unl.edu/vk96.

Black male youth more fearful when visiting whiter neighborhoods

Aug. 13, 2018

Study tracked youth via smartphones to see where they felt safe

COLUMBUS, Ohio – Young black males feel less safe when they go to neighborhoods with a larger white population than occurs in areas they normally visit, a new study suggests.

Researchers gave 506 black youths in Columbus smartphones that tracked their locations for a week and asked the participants to rate how safe they felt (among other questions) five times per day.

Results showed that African American boys felt less safe even in areas that were only modestly more white than where they usually spent time, said Christopher Browning, lead author of the study and professor of sociology at The Ohio State University.

“It doesn’t have to be a majority white neighborhood for African American boys to feel more threatened,” Browning said. “It just has to be more white than what they typically encounter.”

When outside their own neighborhoods, black teens in the study visited areas that were, on average, 13 percent more white.

Unlike boys, black girls did not report feeling significantly less safe in whiter areas.

Browning presented the research Aug. 13 in Philadelphia at the annual meeting of the American Sociological Association.

The results are consistent with the hypothesis that young black males expect increased scrutiny, surveillance and even direct targeting when they are in white areas, according to Browning.

“We’ve seen a lot of stories in the media lately about the police being called on black people going about their business in white areas,” he said.

“This may help explain why black youth felt more threatened in parts of town where they were exposed to more white people.”

Data for the study came from the Adolescent Health and Development in Context study, which Browning leads. The AHDC is examining the lives of 1,405 representative youths living in 184 neighborhoods in Franklin County, Ohio. This includes Columbus and its suburbs.

This particular study involved 506 black youths aged 11 to 17 when the study was done from 2014 to 2016. They carried a smartphone with a GPS function that reported their location every 30 seconds. Five times a day they were sent a mini-survey to answer on their phones. By the end of the study, the researchers had collected 7,398 of these surveys.

In one question, participants were asked to rate on a scale of 1 (strongly disagree) to 5 (strongly agree) if the place they were currently at was a safe place to be.

Participants reported either strongly agreeing or agreeing that they were in a safe place about 91 percent of the time. That makes sense, Browning said, because the teens reported being at home about 71 percent of the time when they received the survey.

Much of the research that examines safety among black youth focuses on the neighborhood they live in. But this research suggests that the immediate neighborhood may not be the most important area to focus on, he said.

What seemed to matter was how the places they visited differed from the areas where they spent most of their time.

Black boys felt less safe when they were in neighborhoods that were significantly poorer than ones they generally frequented, as well as in neighborhoods that were whiter.

“Part of the experience for black kids is having to leave their home neighborhoods to go to places that might not be as welcoming,” Browning said.

“They are typically going to places with amenities like restaurants and movie theaters that may not be available in their neighborhoods. And these places are probably going to be whiter than the places they live.”

The findings were similar for African American boys no matter where they lived in the Columbus area.

“Even black boys who were regularly exposed to integrated neighborhoods felt less safe when they went to white-dominated areas,” he said.

Although African American girls in this study didn’t report feeling less safe in whiter areas, Browning said that doesn’t necessarily mean they aren’t experiencing negative effects.

It may be that there are different features of neighborhoods not picked up in this study, such as the number of men in the immediate vicinity, that may affect whether black girls felt safe in a particular location, he said.

Browning, who is a member of Ohio State’s Translational Data Analytics Institute and Institute for Population Research, co-authored the study with Ohio State colleagues Catherine Calder, professor of statistics; Bethany Boettner, senior research associate at the IPR; Jodi Ford, associate professor of nursing; and Lesley Schneider and Jake Tarrence, graduate students in sociology.

This research was supported by the National Institute on Drug Abuse, the Eunice Kennedy Shriver National Institute of Child Health and Development, and the William T. Grant Foundation.

10th of the Month Club

Your donations toward our undergarment drive totaled…2,965 items…:)

neighborhood bridges has inventoried everything and we believe that your generosity will impact children in up to 18 of our schools here in Westerville.

Thank you to the Westerville Public Library and the City of Westerville for adding donation centers. Thank you to the great folks at our Fire Station on W. Main Street for receiving all of our donations for neighborhood bridges. Thank you to Neighbor 2 Neighbor and the 10th of the Month Club for coming together to offer kindness and honor our heroes.

This has gone so well that we are planning ANOTHER collaboration for the November/December time frame.

Opinion: Rare Earth Minerals — Think Competitiveness, Not Tariffs

By James Clad

InsideSources.com

Now moving from rhetoric to reality, the Great Trade War of 2018 has kicked off a scramble for preferred commercial outcomes felt in the corridors of Congress and logged in White House phone calls.

Over the last months, U.S. manufacturers, the agricultural export lobby and primary commodity firms have moved into the trading trenches as reciprocal multi-billion dollar tariffs begin to hit home. But lost in the uproar is a sense of the wider goals of this conflict.

Reciprocal trade “fairness” remains the dominant public rationale, but there are bigger fish to fry: a monopolistic mindset must come under sustained fire, especially China’s mercantilist, possessive and beggar-thy-neighbor industrial policy.

Yet while the U.S. administration has good reason to challenge China on the thrust of trading policy, tariffs invariably cause indiscriminate damage, doing little to derail or even moderate China’s advanced manufacturing and tech sector plans.

Lifting American competitiveness across the board is a more enduring goal that requires renewed attention to domestic impediments to competitive productivity, whether regulatory overload or infrastructure shortcomings.

In many respects, we have been our own enemy when one surveys eroding U.S. competitiveness and the steady diminution of our industrial and manufacturing sector. We have also acquiesced in the widening of glaring strategic vulnerabilities — notably the nearly complete American dependence on China’s rare earth minerals, a situation shaped in equal parts by China’s strategic mercantilism and by our own domestic policy.

It is not far-fetched to see in China’s monopoly of the global rare earth minerals market something like a “nuclear option,” employable as and when the trade tariffs conflict escalates further. Rare earth minerals (REM) have become critical to the production of such products as wind turbines and electric engines, and to dominant U.S. defense technologies like smart bombs and night-vision goggles.

The various minerals counted as REM, which include yttrium and neodymium, remain essential to a dizzying variety of advanced technologies in which, until the early 1990s, the United States had long been the world’s largest developer. Since then the Chinese have come to dominate the rare earth marketplace. Astonishingly, not a single American rare earths mine remains in operation today.

Glaring vulnerabilities like this sound a drumbeat for a coherent effort to rebuild the U.S. industrial base, and to reduce self-imposed impediments to strategic American competitiveness.

In this quest, the decline of U.S. mining should stand as both warning and a call for action. Its decline exemplifies the varied challenges facing U.S. industry. As a former defense official focused on China’s strategic assertiveness, I have a view of the market and production vulnerabilities that favor that country’s across-the-board challenge to the United States.

Despite our bottomless appetite for minerals and metals indispensable to the manufacture of smart phones, lithium-ion batteries and solar panels, we impose many obstacles to mining those very same minerals. The result: mining investment and minerals production has gone elsewhere.

This trend stands in total contrast to America’s resource position. The United States has some of the world’s largest mineral reserves (the U.S. Geological Survey estimates their value at $6.2 trillion). But our dependence on imported minerals is stark. The United States has become 100 percent import-dependent on 21 critical minerals, and we are now 50 percent, or more, import dependent on an additional 29 minerals.

Ask the mining industry what can be done to reverse this trend. Its answer: Reform the current mine permitting system. It regularly takes a decade or more to open a new mine in the United States. A redundant, broken mine permitting process has become an anchor on U.S. producers.

Despite the environmental sensitivities, no permitting process need take a decade. In Canada and Australia, nations with environmental safeguards on par with our own, mine permitting takes just two to three years.

The current focus on imbalanced trade should therefore lead to a new appreciation of our own self-imposed impediments to our own competitiveness. Glaring strategic vulnerabilities resulting from our REM dependency should further heighten awareness of the China Challenge. Tackling the self-imposed competitiveness barriers, like the cumbersome mine permitting process, may lack the political flair of new tariff announcements. But it counts for just as much, if not more.

ABOUT THE WRITER

James Clad is a senior fellow at the American Foreign Policy Council in Washington and a former U.S. deputy assistant secretary of defense for Asia. He wrote this for InsideSources.com.

LINK

Devin Nunes Is the Exact Constitution-Shredding Miscreant the Founders Feared

https://www.thenation.com/article/devin-nunes-exact-constitution-shredding-miscreant-founders-feared/?utm_source=Sailthru&utm_medium=email&utm_campaign=Daily%2008132018&utm_term=daily

Capital gains and why they matter – a tax expert explains

August 8, 2018

It’s a game for the rich.

Author

Stephanie Leiser

Lecturer in Public Policy, University of Michigan

Disclosure statement

Stephanie Leiser does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Partners

University of Michigan

University of Michigan provides funding as a founding partner of The Conversation US.

The Trump administration wants to change the way capital gains are taxed to factor in inflation.

To many, this may sound like a technical change of little consequence. To others, such as the Tax Policy Center’s Len Burman, it’s a “windfall” for the very rich who are still adding up their gains from the 2017 tax cut.

As a tax policy expert, I agree that the proposed change could make sense as part of broader tax reform that simplifies the tax code and benefits all taxpayers. But on its own, this policy would only make the tax code more regressive and less efficient.

To understand why, let’s review some of the basics.

What are capital gains?

In economics, a person’s income in a given year should include all inflows of new financial resources that can be used for either consumption or gains in net worth.

A familiar example is your paycheck. But financial resources don’t always come in the form of cash. Income can also come from the appreciation of non-cash assets such as stocks and real estate, also known as capital gains.

Most Americans get the vast majority of their income from wages and salaries. Among the top 1 percent, however, capital gains make up 36 percent of total income.

How are gains calculated and taxed?

The IRS needs to know how much money a taxpayer makes in a year in order to tax her properly under the 16th amendment, which was ratified in 1913 and gave the U.S. the power to tax incomes “from whatever source.”

Unlike wages, capital gains are harder to calculate – and harder to tax.

Ideally, we’d need to know how much value her investments gained. The value of some assets like stocks and mutual funds is straightforward because they are bought and sold frequently. But that’s not the case for assets like real estate or fine art that don’t change hands often. So it’s harder to know their value.

The solution has been to only tax capital gains when they are realized – that is, when the asset is sold. The gain is the difference between the sale price and the original purchase price, ignoring the impact of inflation, which erodes its real value.

As long as you hold onto an asset, you don’t have to pay capital gains taxes on it. In fact, if you die, your heirs don’t have to pay either and the gain will never be taxed.

How much is the tax?

In the early years of the income tax, capital gains were taxed at the same rates as ordinary income, or as high as 77 percent in 1918 as the rate soared to cover the cost of World War I.

After the war, conservatives began to make the case for tax cuts. So Congress lowered the top individual tax rate to 58 percent in 1922 and split off capital gains from regular income, slashing the rate to 12.5 percent.

Since then, capital gains tax rates have been changed frequently, climbing as high as 40 percent but typically remaining much lower than the top rate on ordinary income.

What are the effects of capital gains taxes?

Supporters of lower rates for capital gains argue that it stimulates economic growth, mitigates double taxation of corporate income and alleviates the “lock-in” effect that discourages investors from selling assets to avoid taxes. They also point out that inflation erodes the real value of capital gains. Lower rates help offset this penalty – as would the administration’s proposal.

Other research, however, suggests that capital gains tax breaks have no significant effect on economic growth and create other distortions that hurt economic efficiency. For example, hedge fund managers exploit the “carried interest” loophole to categorize their income as capital gains instead of wages.

Whether capital gains tax policy actually increases economic efficiency, we do know it makes the tax system more regressive. Since capital gains are highly concentrated among high-income taxpayers, tax breaks for capital gains primarily benefit the wealthy. The Tax Policy Center estimates that in 2016 taxpayers with incomes over US$1 million received over three quarters of the benefits of lower rates while taxpayers earning less than $75,000 received just 2 percent.

As for the administration’s proposal, given the vast complexity of our tax system, it would be a very minor fix that benefits a small number of wealthy people.

Or in the words of Burman, also a professor of public administration and international affairs at Syracuse University, the proposal would result in tax savings of “up to $20 billion a year for the richest Americans and open the door to a raft of new, inefficient tax shelters.”

The Conversation

The Conversation

Parts of the Pacific Northwest’s Cascadia fault are more seismically active than others – new imaging data suggests why

August 1, 2018

What’s going on 150 kilometers below the Earth’s surface?

Authors

Miles Bodmer

PhD Student in Earth Sciences, University of Oregon

Doug Toomey

Professor of Earth Sciences, University of Oregon

Disclosure statement

Doug Toomey receives funding from National Science Foundation and the United States Geological Survey.

Miles Bodmer does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.

Partners

University of Oregon

University of Oregon provides funding as a member of The Conversation US.

The Pacific Northwest is known for many things – its beer, its music, its mythical large-footed creatures. Most people don’t associate it with earthquakes, but they should. It’s home to the Cascadia megathrust fault that runs 600 miles from Northern California up to Vancouver Island in Canada, spanning several major metropolitan areas including Seattle and Portland, Oregon.

This geologic fault has been relatively quiet in recent memory. There haven’t been many widely felt quakes along the Cascadia megathrust, certainly nothing that would rival a catastrophic event like the 1989 Loma Prieta earthquake along the active San Andreas in California. That doesn’t mean it will stay quiet, though. Scientists know it has the potential for large earthquakes – as big as magnitude 9.

Geophysicists have known for over a decade that not all portions of the Cascadia megathrust fault behave the same. The northern and southern sections are much more seismically active than the central section – with frequent small earthquakes and ground deformations that residents don’t often notice. But why do these variations exist and what gives rise to them?

Our research tries to answer these questions by constructing images of what’s happening deep within the Earth, more than 100 kilometers below the fault. We’ve identified regions that are rising up beneath these active sections which we think are leading to the observable differences along the Cascadia fault.

Cascadia and the ‘Really Big One’

The Cascadia subduction zone is a region where two tectonic plates are colliding. The Juan de Fuca, a small oceanic plate, is being driven under the North American plate, atop which the continental U.S. sits.

The Juan de Fuca plate meets the North American plate beneath the Cascadia fault. USGS, CC BY

Subduction systems – where one tectonic plate slides over another – are capable of producing the world’s largest known earthquakes. A prime example is the 2011 Tohoku earthquake that rocked Japan.

Cascadia is seismically very quiet compared to other subduction zones – but it’s not completely inactive. Research indicates the fault ruptured in a magnitude 9.0 event in 1700. That’s roughly 30 times more powerful than the largest predicted San Andreas earthquake. Researchers suggest that we are within the roughly 300- to 500-year window during which another large Cascadia event may occur.

Many smaller undamaging and unfelt events take place in northern and southern Cascadia every year. However, in central Cascadia, underlying most of Oregon, there is very little seismicity. Why would the same fault behave differently in different regions?

Over the last decade, scientists have made several additional observations that highlight variations along the fault.

One has to do with plate locking, which tells us where stress is accumulating along the fault. If the tectonic plates are locked – that is, really stuck together and unable to move past each other – stress builds. Eventually that stress can be released rapidly as an earthquake, with the magnitude depending on how large the patch of fault that ruptures is.

A GPS geosensor in Washington. Bdelisle, CC BY

Geologists have recently been able to deploy hundreds of GPS monitors across Cascadia to record the subtle ground deformations that result from the plates’ inability to slide past each other. Just like historic seismicity, plate locking is more common in the northern and southern parts of Cascadia.

Geologists are also now able to observe difficult-to-detect seismic rumblings known as tremor. These events occur over the time span of several minutes up to weeks, taking much longer than a typical earthquake. They don’t cause large ground motions even though they can release significant amounts of energy. Researchers have only discovered these signals in the last 15 years, but permanent seismic stations have helped build a robust catalog of events. Tremor, too, seems to be more concentrated along the northern and southern parts of the fault.

What would cause this situation, with the area beneath Oregon relatively less active by all these measures? To explain we had to look deep, over 100 kilometers below the surface, into the Earth’s mantle.

Green dots and blue triangles show locations of seismic monitoring stations. Bodmer et al., 2018, Geophysical Research Letters, CC BY-ND

Imaging the Earth using distant quakes

Physicians use electromagnetic waves to “see” internal structures like bones without needing to open up a human patient to view them directly. Geologists image the Earth in much the same way. Instead of X-rays, we use seismic energy radiating out from distant magnitude 6.0-plus earthquakes to help us “see” features we physically just can’t get to. This energy travels like sound waves through the structures of the Earth. When rock is hotter or partially molten by even a tiny amount, seismic waves slow down. By measuring the arrival times of seismic waves, we create 3D images showing how fast or slow the seismic waves travel through specific parts of the Earth.

Ocean bottom seismometers waiting to be deployed during the Cascadia Inititive. Emilie Hooft, CC BY-ND

To see these signals, we need records from seismic monitoring stations. More sensors provide better resolution and a clearer image – but gathering more data can be problematic when half the area you’re interested in is underwater. To address this challenge, we were part of a team of scientists that deployed hundreds of seismometers on the ocean floor off the western U.S. over the span of four years, starting in 2011. This experiment, the Cascadia Initiative, was the first ever to cover an entire tectonic plate with instruments at a spacing of roughly 50 kilometers.

What we found are two anomalous regions beneath the fault where seismic waves travel slower than expected. These anomalies are large, about 150 kilometers in diameter, and show up beneath the northern and southern sections of the fault. Remember, that’s where researchers have already observed increased activity: the seismicity, locking, and tremor. Interestingly, the anomalies are not present beneath the central part of the fault, under Oregon, where we see a decrease in activity.

Regions where seismic waves moved more slowly, on average, are redder, while the areas where they moved more quickly are bluer. The slower anomalous areas 150 km beneath the Earth’s surface corresponded to where the colliding plates are more locked and where tremor is more common. Bodmer et al., 2018, Geophysical Research Letters, CC BY-ND

So what exactly are these anomalies?

The tectonic plates float on the Earth’s rocky mantle layer. Where the mantle is slowly rising over millions of years, the rock decompresses. Since it’s at such high temperatures, nearly 1500 degrees Celsius at 100 km depth, it can melt ever so slightly.

These physical changes cause the anomalous regions to be more buoyant – melted hot rock is less dense than solid cooler rock. It’s this buoyancy that we believe is affecting how the fault above behaves. The hot, partially molten region pushes upwards on what’s above, similar to how a helium balloon might rise up against a sheet draped over it. We believe this increases the forces between the two plates, causing them to be more strongly coupled and thus more fully locked.

A general prediction for where, but not when

Our results provide new insights into how this subduction zone, and possibly others, behaves over geologic time frames of millions of years. Unfortunately our results can’t predict when the next large Cascadia megathrust earthquake will occur. This will require more research and dense active monitoring of the subduction zone, both onshore and offshore, using seismic and GPS-like stations to capture short-term phenomena.

Our work does suggest that a large event is more likely to start in either the northern or southern sections of the fault, where the plates are more fully locked, and gives a possible reason for why that may be the case.

It remains important for the public and policymakers to stay informed about the potential risk involved in cohabiting with a subduction zone fault and to support programs such as Earthquake Early Warning that seek to expand our monitoring capabilities and mitigate loss in the event of a large rupture.

Two types of tectonic plate activity create earthquake and tsunami risk on Lombok

August 6, 2018

Shallow but powerful earthquakes on Lombok have resulted in around 100 deaths and destroyed buildings. EPA/AAP

Authors

Jane Cunneen

Research Fellow, Curtin University

Phil R. Cummins

Professor, Australian National University

Disclosure statement

The authors do not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.

Partners

Curtin University

Australian National University

Curtin University and Australian National University provide funding as members of The Conversation AU.

Several large earthquakes have struck the Indonesian island of Lombok in the past week, with the largest quake killing at least 98 people and injuring hundreds more.

Thousands of buildings are damaged and rescue efforts are being hampered by power outages, a lack of phone reception in some areas and limited evacuation options.

The majority of large earthquakes occur on or near Earth’s tectonic plate boundaries – and these recent examples are no exception. However, there are some unique conditions around Lombok.

The recent earthquakes have occurred along a specific zone where the Australian tectonic plate is starting to move over the Indonesian island plate – and not slide underneath it, as occurs further to the south of Lombok.

This means there is earthquake and tsunami risk not only along the plate boundary south of Lombok and Bali, but also from this zone of thrusting to the north.

Read more: Bali’s Agung – using ‘volcano forensics’ to map the past, and predict the future

Jammed subduction zone

Tectonic plates are slabs of the Earth’s crust that move very slowly over our planet’s surface. Indonesia sits along the “Pacific Ring of Fire” where several tectonic plates collide and many volcanic eruptions and earthquakes occur.

Some of these earthquakes are very large, such as the magnitude 9.1 quake off the west coast of Sumatra that generated the 2004 Indian Ocean tsunami. This earthquake occurred along the Java-Sumatra subduction zone, where the Australian tectonic plate moves underneath Indonesia’s Sunda plate.

Hospital patients were moved to an emergency tent after an earthquake struck northern Lombok. EPA/AAP

But to the east of Java, the subduction zone has become “jammed” by the Australian continental crust, which is much thicker and more buoyant than the oceanic crust that moves beneath Java and Sumatra.

The Australian continental crust can’t be pushed under the Sunda plate, so instead it’s starting to ride over the top of it. This process is known as back-arc thrusting.

The data from the recent Lombok earthquakes suggest they are associated with this back-arc zone. The zone extends north of islands stretching from eastern Java to the island of Wetar, just north of Timor (as shown in map below).

Earthquake hazards along plate boundaries near Indonesia. The dates in the map show historical earthquakes, and Mw indicates earthquake magnitude. Edited by P. Cummins from an original by Koulali and co-authors

Historically, large earthquakes have also occurred along this back-arc thrust near Lombok, particularly in the 19th century but also more recently. (Dates and sizes of past earthquakes are shown in the map above).

It is thought that this zone of back-arc thrusting will eventually form a new subduction zone to the north along from eastern Java to the island of Wetar just north of Timor.

Read more: I’ve always wondered: do nuclear tests affect tectonic plates and cause earthquakes or volcanic eruptions?

Tsunami risk

Lombok’s recent earthquakes – the August 5 6.9 magnitude quake plus a number of aftershocks, and the 6.4 magnitude earthquake just a week before it – occurred in northern Lombok under land, and were quite shallow.

Recent earthquakes on Lombok were also felt on the neighbouring island of Bali. US Geological Survey

Earthquakes on land can sometimes cause undersea landslides and generate a tsunami wave. But when shallow earthquakes rupture the sea floor, much larger and more dangerous tsunamis can occur.

Due to the large number of shallow earthquakes along the plate boundaries, Indonesia is particularly vulnerable to tsunamis. The 2004 Indian Ocean tsunami killed more than 165,000 people along the coast of Sumatra, and in 2006 over 600 people were killed by a tsunami impacting the south coast of Java.

Read more: Explainer: after an earthquake, how does a tsunami happen?

The region around Lombok has a history of tsunamis. In 1992 a magnitude 7.9 earthquake occurred just north of the island of Flores and generated a tsunami that swept away coastal villages, killing more than 2,000.

Nineteenth century earthquakes in this region also caused large tsunamis that killed many people.

The areas around Lombok and the islands nearby, including Bali, are at high risk for earthquakes and tsunamis occurring both to the north and the south of the island.

Unfortunately, large earthquakes like the ones this week cannot be predicted, so an understanding of the hazards is vital if we are to be prepared for future events.

The Conversation US, Inc.

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Staff Reports