PhD opportunity: Holocene palaeoseismicity and sea-level change in Chile

The Department of Geography, Northumbria University, seeks to appoint a PhD student to work on Holocene sea-level change and palaeoseismicity in Chile. Funding is available to UK and international students. The closing date is 20th January 2017. Read on for more details about the position.  

On this day in 1960

A sand layer deposited by the 1960 tsunami,
deposited on top of and later covered by peat

Today, 22nd May 2016, marks the 56th anniversary of the 1960 Great Chilean earthquake. With a magnitude estimated at 9.5, this still stands as the largest instrumentally documented earthquake worldwide. 

Palaeoseismologists have sought to characterise the geological evidence for this earthquake and the subsequent tsunami in a range of different settings.

Vulnerable Coastal Areas

Philipp Kempf, Renard Centre of Marine Geology, Ghent University,
presents on his research into tsunamis in Chile

The Belgian Royal Academy for Overseas Sciences held a multidisciplinary workshop on Vulnerable Coastal Areas on 10th December. The workshop, chaired by Cecile Baeteman, brought together researchers from Belgium, the UK and Chile, with presentations on hazard, risk and resilience in a variety of different settings.

Magnitude 8.3 earthquake, central Chile, 16th September 2015

USGS Shakemap: available here

A great earthquake struck central Chile yesterday, with severe to extreme shaking felt in the Coquimbo region. The initial magnitude is estimated at 8.3, making this larger than the 2014 Iquique earthquake and the largest to strike Chile since the magnitude 8.8 earthquake of 2010.

The earthquake occurred along the Chilean Subduction Zone, a fault between the Nazca and South American Plates. The Nazca Plate subducts beneath South America, with the strain that accumulates over time episodically released during earthquakes. Great subduction zone earthquakes such as this are accompanied by intense shaking that may last several minutes. They also frequently generate tsunamis, which may be damaging both close to the source and across ocean basins. Wave heights of over 4m have been reported in Chile. The Pacific Tsunami Warning Centre suggests large waves are unlikely for most Pacific countries, however Chile and French Polynesia remain on alert for waves exceeding 1m.

So, what happens when a giant tsunami inundates coastal lakes?

This blog post is by Philipp Kempf, PhD student at Ghent University, who writes about his recently published Sedimentary Geology paper on tsunami deposits in coastal lakes in south central Chile. Philipp is now on twitter too, tweeting as @TsunamiPhil.

Pan Pacific Palaeoseismology symposium

Last week I was delighted to welcome fellow academics, friends and collaborators from Potsdam Universty, Ghent University, Durham University and The Geological Survey of Belgium to join me for a symposium on subduction zone palaeoseismology. The day-long meeting was an opportunity to present and discuss the different approaches that we use when studying past earthquakes, tsunamis and subduction zone behaviour.

The 1877 and 2014 earthquakes

We provided a brief introduction to the 1st April 2014 Iquique earthquake earlier. It's struck the Northern Chilean (or Iquique) seismic gap, an area that hasn't ruptured in a major megathrust earthquake since 1877 (though a magnitude 7.7 earthquake did rupture a deeper section of the interface in 2007). GPS data published in 2004 suggested the Nazca and South American plates were fully coupled, with none of the plate convergence being offset by slip between the plates. An update just last year identified three zones of high coupling - the Camarones, Loa and Paranal segments - separated by weaker zones. Potentially any of these segments would individually be capable of producing an earthquake of the size of the one seen yesterday. The authors

Magnitude 8.2 earthquake north of Iquique, Chile, April 2014

A major earthquake struck the north of Chile yesterday (1st April 2014), with intense shaking felt in the cities of Iquique and Arica. Less intense shaking was also felt across northern Chile and in Bolivia, Peru, Brazil and Costa Rica..The USGS maintains 'did you feel it?' pages, where anyone can report shaking that they have experienced. Here's the page for the 1st April earthquake: Did you feel it?. Initial reports placed the magnitude in the region of 8.0, with subsequent analysis upgrading this to 8.2. This USGS page will continue to be updated as further information on the earthquake becomes available. For comparison, the 2010 Maule (Chile) earthquake measured 8.8, the 2011 Tohoku (Japan) earthquake registered

Recent magazine article highlighting our work

While we've been busy on fieldwork and analysing the sediments we've collected, we're also keen to keep publishing our findings and updating people on where we're at with our research. Back in September our first academic paper on Chilean earthquakes was published in Quaternary Science Reviews. This month we've written an article in International Innovation magazine, produced by Research Media Ltd. The Environment issue of this magazine disseminates current global environmental issues to the wider

Coring, coring, coring (+Videos)

Much of our last field season was spent coring tidal marsh sediments. See previous posts for more details on what we do both in the field and back in the labs. In order to sample sediments several metres below the ground surface we use a sediment corer - either a gouge corer (for reasonably consolidated sediments) or a Russian corer (in peats or more unconsolidated sediments). Here is a short video showing us using a gouge corer at Chaihuin, with the invaluable help of Bill Austin from St Andrews University.

Fieldwork in photos

We're in Valdivia at the moment, which means reliable internet, something that we've been without for the last week. We've been at Pucatrihue and Llico, coring marshes in our search for evidence of predecessors of the 1960 Chilean earthquake. Here's a quick photo roundup. 

Back in Chile

A year on from our last field season, and we’re back in Chile continuing our search for evidence of earthquakes and tsunamis. So far we’ve visited two new sites – Pucatrihue (west of Osorno) and Llico (3 hours further south). We are working on the salt marshes at these sites and are interested in the sequence of sediments which have accumulated in the marshes over time. As the environment (or elevation of the land relative to the sea) changes, the nature of the sediment which is deposited changes. We’re particularly interested in where we find a very sudden or sharp change in sediments; where we see the

Our new paper on Chilean earthquakes

Our first paper on Chilean earthquakes is now available online in the journal Quaternary Science Reviews. The paper is open access, so the full text is free for anyone to read.

The work we present sets out how we can use diatoms, microscopic algae, to quantify the changes in land level which occur during plate boundary earthquakes. We're interested in reconstructing these land level changes as they may provide a way of working out how big past earthquakes have been. Others have used similar approaches to identify and increase understanding of the threat posed by large earthquakes in Alaska, Japan and along the west coast of the United States. We apply the techniques to Chile, demonstrating that estimates of land level change using diatoms are accurate and useful.

Ed heads North

Ben, Daria and Isobel investigate the stratigraphy

Following Emma's departure back to the UK, I headed north from Valdivia for part 2 of my field season in Chile. Three buses, each slower and more decrepit than the last took me to Temuco, then Carahue and finally Tirua. Here, I met up with Marco Cisternas again, along with Lisa Ely, Alan Nelson, Rob Wesson and Isobel Hong from the US. Ben Horton and Daria Nikitina swelled our numbers to 8 when they arrived yesterday.

We've spent the last four days working at Quidico, a small river valley 20 minutes drive north of Tirua. We've been digging deep pits, cleaning river bank exposures and taking thin columns of sediment using a coring device to try to understand the sequence of sediments that has been laid down at the site. The presence of sand layers may suggest inundation by tsunamis.

Tiny bits of rock and very small living things...

Taking great care to not leave any trace of
where we've sampled on the marsh!

Our next stop has been Rio Lingue, a site about 60 km north of Valdivia. Locals have been telling us of the devastation and land subsidence caused by the 1960 earthquake, and also told us how the 2010 tsunami reached this far south.

We found an excellent marsh to work on, which allowed us to take lots of samples to help us properly understand the present day environment. In our work we need a sound understanding of what is happening today to be able to interpret what happened in the past. We take small samples along a transect across the marsh from the mudflat exposed at low tide, across the low marsh, high marsh, and up to where freshwater vegetation grows. We look at how diatom communities (small microscopic single-celled algae) change across these different zones as the amount of tidal inundation decreases the further you get from the sea. We mainly find marine diatom species in mudflat samples and freshwater diatoms in the high marsh samples. Then when we look at our sediment cores from the past, if we find lots of marine diatoms we interpret the environment at this time was most like the present day mudflat. From this we are able to reconstruct how the land level has changed through time.

Taking a modern sample from the low marsh

Freshwater diatom of the Pinnularia genus (about half the width of a
human hair - thanks to Melanie Leng for giving this comparison!)

A few less common words (part 2)

Following on from part 1, here's the rest of the explanation of the common word summary of our work. We were delayed posting this by a wild goose chase to find a highly inaccessible site...

When the shaking happens the land can go up and down. Some places change from being high up before the shaking to being lower down after. Other places change from low down to higher up.

We're describing the vertical component of coseismic deformation resulting from a subduction zone earthquake. This is typically less than a few metres (either uplift or subsidence) for sites on the Chilean mainland. R. Grapenthin, Univ. Alaska, niftily visualises this phenomenon for the 2011 Japan earthquake.

We look for things that can tell us how and when the land has changed in the past and when waves have covered the land. To do this we look at tiny bits of rock and very small living things.

We're particularly interested in working out when past earthquakes and tsunamis have happened and how big they've been. As part 1 mentioned, historical records may be too short to provide a realistic assessment of seismic hazards. Instead, we turn to sediments (tiny bits of rock) from coastal environments. Certain low energy settings, like the tidal marshes north of Valdivia, preserve evidence for both tsunami inundation and coseismic deformation. The very small living things are diatoms, single-celled algae. More on how we use diatoms to look at land-level change in the next blog post.

We have found the biggest shaking and largest waves happened four times in the past 1000 years in the area we are working.

Ed's PhD, based on sites a few hundred kilometres south of this project, found sedimentary and diatom evidence for the 1960 and 1575 earthquakes, as well as two older earthquakes predating written records in Chile.

A few less common words (part 1)

We thought we'd expand on our last blog post today and use some less common words to explain what we're up to. There were many other great common word distillations of projects, research areas and whole careers in science generated in response to the Up-Goer Five text editor. You can read them in the tumblr curated by Chris and Anne from Highly Allochthonous.

So, here's what we were trying to convey in the thousand word post (or ten hundred as those pesky Americans keep saying). The common words are in italics.

When the ground shakes a lot it can kill many people.

Earthquakes! You got that bit, right?

Ground shaking can also form very big waves of water which cover lots of the land, and kill more people.

Tsunamis. Created in this instance by strain release during an earthquake resulting in deformation of the sea floor. Tsunamis can also be formed by landslides, volcanic eruptions, meteorites and iceberg roll events.

It is important to understand when and where this happens so that we can make people safer in years to come.

The past is the key to future preparedness and hazard mitigation. We want to know how frequently earthquakes and tsunamis occur and their maximum possible sizes. Historical records are valuable, but in many areas do not go back far enough. Even in Japan, home to the most comprehensive records of tsunamis, historical records may underestimate the size of previous seismic events. See this from the Japan Times for more.

Part 2 to follow...

Our research using only common words

Here's a summary of our past and present research in Chile using only the 1000 most common words used in the English language:

When the ground shakes a lot it can kill many people. Ground shaking can also form very big waves of water which cover lots of the land, and kill more people. It is important to understand when and where this happens so that we can make people safer in years to come.

When the shaking happens the land can go up and down. Some places change from being high up before the shaking to being lower down after. Other places change from low down to higher up. We look for things that can tell us how and when the land has changed in the past and when waves have covered the land. To do this we look at tiny bits of rock and very small living things. We have found the biggest shaking and largest waves happened four times in the past 1000 years in the area we are working.

Thanks to Chris Rowan and Anne Jefferson of the Highly Allocthonous blog for passing on the idea. Head over to the Up-Goer Five Words Box to try it for yourself.

Marshes, mud and crazy postmen

Since the last post, we've had a successful few days in Queule, Tolten and Rio Lingue (about 80km north of Valdivia). These locations lie on a wide coastal plain; subsidence of a couple of metres during the 1960 earthquake changed low lying but valuable farmland into waterlogged marshland. The tsunami swept up rivers and across the coastal plain, reaching several kilometres inland. As the area is so flat, with few safe higher areas, escaping the waves would have been difficult.

We collected lots of samples of sediment from intertidal marshes close to the mouths of the rivers that cross the plain. We're particularly interested in tidal marshes as they provide evidence for how the land or sea has changed in level over time. On a positive note, we found some good sites and collected lots of samples. Unfortunately we seemed to spend a lot of our time watching the tide go up and down, sometimes until it got too dark to actually see what we were doing!

Ed at Queule with sediments that we think
were deposited before and after the 1960
earthquake and tsunami

We've also been back to Valdivia and sampled a marsh on Isla del Rey, an island in the Valdivia Estuary. We're pretty pleased with the samples from here, not just because we found a good site, but also because we managed to get to the site in the first place! First we needed to find a boat to take us there, then were trapped and had to escape from a very talkative postman on the island (who wanted to tell us everything from the entire history of Chile to the material used to surface the road in response to us asking who owned the land), and finally we needed to get a boat back. The latter proved to be the most tricky, but it seems in Valdivia it's possible to hail a boat like you hail a taxi!

What are we looking for?

After a few more days looking for potential sites, we thought it was probably time we gave an update on what makes a good site and what exactly we're looking for...

Ed digging a pit / pogo-sticking!

So we're working on tidal marshes which preserve evidence of previous great earthquakes. During the largest subduction earthquakes, land may suddenly subside or uplift by up to a few metres. This coseismic deformation results from extension of the upper plate during the earthquake (as in this diagram from Natural Resources Canada). The area that we are working in subsided during the 1960 earthquake. Low lying land subsided into the sea, inundating farmland and killing trees (see picture 3 of our last blog post). 

10cm of tsunami sand (light grey)
separating two different types of sediment

We have been digging pits in marshes and looking at incised banks of rivers in the hope of finding abrupt changes in sediment type which might reflect the sudden changes in the level of the land with respect to the sea. A change from a soil with lots of organic matter to a sandier, less organic sediment could reflect a change from a freshwater to a tidal flat with no vegetation.