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People power

2 Apr

Seismic monitoring is critical in earthquake-prone areas such as Nepal, but limited resources mean limited monitoring. EGU Science Journalism Fellowship awardee Kate Ravilious reports back on how scientists are using social media to fill the gap. 

Data gathering needn’t always involve expensive instruments or exotic fieldtrips. Here in resource strapped Nepal, seismologists are tapping into the power of local people to collect information that could ultimately save many lives.

In places like California and Japan shake-maps, as they are known, are commonplace. Houses built on thick layers of sediment will be rattled much more than houses situated on granite bedrock for example. Detailed knowledge of local geology, plus dense arrays of instruments enable geologists to accurately predict which areas are going to wobble most when an earthquake arrives. This information ensures that funding can be targeted and spent in the areas which need it most. But here in Nepal the network of instruments is sparse and without these shake-maps it is very hard to know how best to spend the very limited funds and increase earthquake resilience in this earthquake-prone land.

The view over Kathmandu. (Credit: Katie Oven, Durham University/Earthquakes Without Frontiers).

Last week I visited Nepal’s National Seismological Centre in Kathmandu. Lok Bijaya Adhikari took me to see their accelerometer – an instrument that measures the acceleration produced by an earthquake and tells you literally how much the ground moved. I enjoyed making my own very mini earthquake by jumping up and down, and watching the light come on, registering that the ground had moved. Countries that can afford a good network of accelerometers can use the data gathered during small earthquakes to assess which parts of a city shake most. But Nepal has just seven accelerometers to cover the entire country – not nearly enough to gather the local detail required to produce a shake map.

Instead Adhikari and his colleagues are tapping into a much cheaper and more plentiful resource: gossip. When something exciting happens we all love to tell our version of events. Last year the National Seismological Centre added a ‘Did you feel it?’ button to their local earthquake reports webpage and Facebook site. People are invited to submit their experience of an earthquake – how intense the shaking felt, what kind of things fell over, how long the shaking went on for, and so on.

Obviously personal accounts are subjective and nowhere near as accurate as an accelerometer, but providing there are enough accounts the exaggerated answers are smoothed out. “We can gain some information on how the ground responds and estimate which local areas are most at risk,” Adhikari told me.

Given that Nepal experiences around five earthquakes of magnitude 4 or greater every month, there are plenty of opportunities for people to submit their experiences. And the explosive rise in mobile phone uptake and interest in social media in Nepal over the last five years or so suddenly make this a viable and very powerful method of gathering data. Now all Adhikari needs to do is spread the word…

By Kate Ravilious, Science Journalist (http://www.kateravilious.net)

An earlier version of this post was originally published on the Earthquakes Without Frontiers blog at http://ewf.nerc.ac.uk/2014/03/27/people-power/

Sniffing out signs of an earthquake

28 Mar

Last year Kate Ravilious was awarded an EGU Science Journalism Fellowship to follow scientists studying continental faults. Now she’s out in Nepal alongside researchers who are working out when the county’s next big quake will be…

Sometimes the best rocks are found in the worst locations. Yesterday I was reminded of this as I watched Paul Tapponnier, from the Earth Observatory of Singapore, and his team tracing one of the most dangerous earthquake faults in the world, right next to a dusty, noisy, dirty and busy main road in southern Nepal. Hooters were blaring, bells ringing and people shouting. Clouds of fine orange dust (from quarrying down the road) coated us from head to toe and under our feet lay the rubbish chucked out of bus and car windows. Glamourous it was not.

But Tapponnier and his team are prepared to hold their noses and get on with the job in hand. They know that these rocks are likely to hold the answers to the puzzle they are trying to solve, and that studying them could eventually help to save many lives.

Chasing charcoal – the key to dating faults. (Credit: Kate Ravilious)

Chasing charcoal – the key to dating faults. (Credit: Kate Ravilious)

In Nepal earthquakes are a fact of life. India is slamming into Asia at a rate of 4 cm per year (pushing up the mighty Himalayan mountain range) and the strain that accumulates in the underlying tectonic plates releases itself periodically in the form of earthquakes. Tremors of magnitude 4 or 5 happen more than ten times every year, but the real worry is the ‘great’ earthquakes – magnitude 8 or more – which Nepal encounters once every few decades.

The last great earthquake – a magnitude 8.4 – occurred in 1934. It  razed around one quarter of Nepal’s capital, Kathmandu, to the ground and killed 17,000 people across India and Nepal. Since then the population of Kathmandu has grown sevenfold and dangerous multi-story concrete buildings have sprung up everywhere. Kathmandu (which happens to be built on jelly-like ancient lake sediments) has risen to an unenviable first position in the world earthquake risk list and scientists estimate that up to one million people could be killed when the next big quake shakes the Himalayan region.

But when and where will this next big  earthquake be? For decades no-one could even locate the fault that caused the 1934 quake, let alone estimate when it might move again. But Tapponnier has an uncanny nose for sniffing out earthquake ruptures, and in 2008 he found the culprit, hidden underneath layers of Nepalese jungle down on the edge of the hot Terai plains in southern Nepal. Since then he has returned every year, to uncover the extent of this massive fault and learn more about how it operates.

Paul Tapponier searching for signs of earthquakes past. (Credit: Kate Ravilious)

Paul Tapponier searching for signs of earthquakes past. (Credit: Kate Ravilious)

And so it was that I ended up standing next to the busy road, near the small town of Bardibas, thanks to a travel grant awarded by the EGU, to learn about the work that Tapponnier and his team are doing.

This year much of the focus of the field trip has been to map out the shape of the land, using a sophisticated LIDAR (Light Detection and Ranging) technology. This sleek silver canister rotates and sends out 150,000 pulses of laser light every second. The reflections are used to build up a high resolution three-dimensional picture of the surface.

Sorvigenaleon Ildefonso, a LIDAR technician  from the Earth Observatory of Singapore, along with Aurélie Coudurier-Curveur and Çagil Karakaş, both post-doctoral researchers at the Earth Observatory of Singapore, have spent the last two weeks gathering as many measurements as possible, from a range of locations (many of which are beautiful and tranquil spots), often working until the light fades and they can no longer see what they are doing. The day I arrive they are hauling the LIDAR and associated equipment from location to location, ignoring the energy-sapping heat, blaring of horns, stink of rubbish and clouds of dust. While I am constantly distracted by what is going on around me, they are all completely focused, setting up their equipment with precision and great care, and recording their measurements meticulously.

Sorvigenaleon Ildefonso setting things up for LIDAR. (Credit: Kate Ravilious)

Sorvigenaleon Ildefonso setting things up for LIDAR. (Credit: Kate Ravilious)

What they are searching for is changes in gradient, not always visible to the naked eye under the thicket of vegetation. Much of the hillside has a step-like appearance, and each of those steps may represent one upward thrust of the earthquake. By using the LIDAR to map out these steps in detail they can work out how many times the fault has moved, and how much land it thrust upwards each time.

Meanwhile, down at the bottom of the hillside Tapponnier and his Nepalese colleague, Som Sapkota, from the Department of Mines and Geology in Kathmandu, are standing in a ditch, searching for miniscule pieces of charcoal in amongst the sand and cobbles of a small outcrop of rock. These incredibly precious fragments (often no bigger than a sesame seed) are the key to dating the timings of the fault movement and working out how often the fault moves on average.

In the pit, picking out charcoal and peering into the past. (Credit: Kate Ravilious)

In the pit, picking out charcoal and peering into the past. (Credit: Kate Ravilious)

It is hot, tiring and often tedious work, but for this group of scientists it is puzzle they refuse to leave unsolved. “We have to study these things, and do it quickly, before the next big earthquake strikes,” says Tapponnier.

By Kate Ravilious, Science Journalist (http://www.kateravilious.net)

GeoCinema Online: Hazards

7 Jun

In this week’s GeoCinema Online, we’re taking you to regions of the world that have experienced large eruptions in both the recent and distant past. These films take you through what it’s like to live in an active volcanic area or fault zone, from dealing with disasters, to how scientists are working towards better methods of earthquake and eruption forecasting:

Mayon: The Volcano Princess

Interviewing local residents, officials, and scientists, this film is about the people who live around the Mayon volcano in the Philippines: from what it’s like to live next to the unceasing threat of lahars, pyroclastic flows and eruptions. It also presents some of the strategies for dealing with volcanic disasters and the problems with evacuating the area.

 People Coral Mentawai

The Mentawai Islands in West Sumatra lie above the giant fault line that generated the Boxing Day earthquake in 2004. This documentary follows a team from the Earth Observatory of Singapore as they meet the people affected by the fault line’s disasters and study coral reefs that have been uplifted by earthquakes. This work helps them build an earthquake timeline that can aid earthquake predictions for the future.

Volcano Hazards

Just because a volcano isn’t close to a population centre doesn’t mean it won’t have widespread impacts. From the consequences of eruptions to dealing with their effects, this film takes a look at the hazards caused by explosive volcanic events.

Had your fill of hazards? Why not take a trip to the stars in the stunning space and planetary science series. Seen it already? Stay tuned for the next GeoCinema Online!

Credits

Mayon: The Volcano Princess: EOS Videos (source)

People Coral Mentawai: Isaac Kerlow (source)

Volcano Hazards: USGS (source)

Geosciences column: Spotting signs of sea-quakes

11 Jan

A French and Algerian study team seeks markers of underwater earthquakes off the Algerian coast. The team also matched the site’s paleoseismic history to land-based historical reports. Wayne Deeker reports.

The Mediterranean Sea represents the boundary between the African and Eurasian plates. Yet the fault segment off the Algerian coast is one of the most active in the western Mediterranean. It is associated with a series of moderate to large earthquakes: about 22 magnitude 6+ events since 856 CE. According to historical records, very large events in Algeria have been rare, though approximately one third of documented earthquakes would have been Mw 7+.

One of the most destructive was also the most recent. In May 2003, the Algerian coast experienced a Mw 6.8 earthquake, centred on the town of Boumerdès. It killed more than 2,300 people, injured some 10,000, and did all the usual structural damage earthquakes do in such countries. It also caused a tsunami which affected the western Mediterranean.

Building damage in the city of Boumerdes, Algeria (Credit: Ali Nour CGS; National Center of Applied Research in Earthquake Engineering)

The authors of a 2012 study published in EGU’s Open Access journal Natural Hazards and Earth System Sciences wanted to understand more about this event and earthquake recurrence intervals in the area. They found interesting clues deep underwater, where the quake likely caused landslides that resulted in almost 30 breaks of submarine telecommunications cables.

The researchers say it is especially worthwhile to investigate earthquake threats in areas that, like those surrounding the Algerian fault, have irregular, long-recurrence patterns because people there will be less prepared than where earthquakes are frequent. Another good reason motivates this research. While 2003 was a very well documented earthquake, most studies of its impact were conducted on land, with little attention paid to the effects and signatures offshore. This is unsurprising, as submarine earthquakes are difficult to monitor in real time, especially during catastrophic events. Therefore, the seafloor signatures of such events have remained elusive because they are occasional, erosive, and are a complex combination of many processes.

The damage to Algerian submarine telecommunications cables provides a clue to what happened underwater in 2003. While cable breaks often denote a definite time and place, pinpointing an event which can be interpreted in context with the landscape, the 2003 breaks were vague in all but one case. The location of the recovered cables also did not correspond to the point of damage, which suggests erosive action of turbidity currents (streams of rapidly moving sediment-rich water that deposit to form so-called turdibite sedimentary beds). Satellite images confirmed this, yet the flow pattern must have been quite complex, apparently following different paths along the underwater scarp system.

Resolving this complexity is challenging and, to do it, the researchers focused partly on seafloor morphology, in particular on the signs of seafloor rupture and instability, such as submarine landslides. Once the researchers started looking, they found the scarps had been affected by numerous landslides. The research team also found evidence of significant sediment transport, confined between salt domes and scarp walls. Sonar images showed signatures of high-energy events: ditches formed by erosion, indicating flow direction, plus perpendicular structures interpreted as pebble or gravel waves. These features probably constitute the sought-after signs of undersea earthquake activity, which can now be matched to other sites.

Direct sediment sampling compliments the scans. At the foot of the scarp slopes, the sediments are too mixed up to reveal any bedding that might be dated. Further out, this is not the case, and the presence of  turbidite beds alternating with another type of sedimentary deposit allows for some cautious dating of those layers. Preliminary results, from layers within the upper 1.5m of the core, show at least eleven turbidites accumulated during the Holocene, giving an average recurrence interval of about 800 years in this area. This matches the main seismic cycle on land, supporting the view that large earthquakes in Algeria are the main responsible for the large turbidity flows.

The authors concluded that the 2003 cable breaks were, for the most part, caused by the passage of a turbidity current triggered by the earthquake. The likely path of currents depends on the roughness and the irregularities of the sea floor: seafloor scarps in some cases deflect turbidity flow paths, while perched basins may trap them. The scarps seem prone to sediment failure, and are potential additional sources of cable breaks.

By Wayne Deeker, freelance science writer

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