Yesterday I gave a talk to the Manchester branches of the Geographical Association and the Geological Association on the causes of the Sichuan (Wenchuan) earthquake disaster. As usual I promised to make my slides available via Authorstream. You should be able to download the presentation as well as viewing it below.:
Showing posts with label sichuan. Show all posts
Showing posts with label sichuan. Show all posts
Thursday, March 11, 2010
Monday, August 10, 2009
A dreadful weekend of landslides
The last few days have been a dreadful period for landslides. I really cannot cover all that has happened in enough detail, so all I can do is to outline the main events:
1. Rotorua rockfall, New Zealand
Actually the period started with a very lucky escape in New Zealand on Thursday when a rockfall on a slope under maintenance crushed a car with two passengers. Both were trapped but were extracted from the car with minimal injuries. Given the size of the blocks and the state of the car this is pretty remarkable image from here:
2. Shunhe township, Hanyuan county, Sichuan province, China
The large valley-blocking landslide in Hanyuan County also occurred on Thursday. This slide, which is reported here, is believed to have killed 31 people. The partial blockage of the river continues to cause problems:
6. Typhoon Marakot, Taiwan
The true impact of Typhoon Marakot is far from clear, with reports of debris flows that might have killed hundreds. It is important to stress that these are unconfirmed, but with 2.4 m of rainfall in a weekend who knows? A slightly clearer report suggests that Taoyuan Village in the county of Kaohsiung was hit by a debris flow that killed 16. We will wait for the morning to see whether the reports of much higher loss of life are correct.
1. Rotorua rockfall, New Zealand
Actually the period started with a very lucky escape in New Zealand on Thursday when a rockfall on a slope under maintenance crushed a car with two passengers. Both were trapped but were extracted from the car with minimal injuries. Given the size of the blocks and the state of the car this is pretty remarkable image from here:
2. Shunhe township, Hanyuan county, Sichuan province, China
The large valley-blocking landslide in Hanyuan County also occurred on Thursday. This slide, which is reported here, is believed to have killed 31 people. The partial blockage of the river continues to cause problems:
3. Mount Pinatubo, Philippines
On Friday the Philippines was hit with very intense rainfall that appears to be from the outer edges of Typhoon Marakot, which hit Taiwan and then China. There were two disastrous landslides - in the first a lahar hit a tour group and their guides on the flanks of Mount Pinatubo, killing two locals and three tourists.
4. Kias, Baguio, Philippines
In the second incident, also on Friday, a landslide hit a group of miners at Kias, near to Baguio in the Philippines. A group who went to their rescue were then hit by a second landslide, killing 14 people in total.
5. Pithoragarh district, Uttarakhand
On Saturday a large landslide occurred in northern India (see image below from here). The true impact of this is a little unclear, but the current estimate of loss of life appears to be 43 people. Thanks to David Hopkins for the heads-up on this one, and to Sekhar for the photo).
6. Typhoon Marakot, TaiwanThe true impact of Typhoon Marakot is far from clear, with reports of debris flows that might have killed hundreds. It is important to stress that these are unconfirmed, but with 2.4 m of rainfall in a weekend who knows? A slightly clearer report suggests that Taoyuan Village in the county of Kaohsiung was hit by a debris flow that killed 16. We will wait for the morning to see whether the reports of much higher loss of life are correct.
Friday, August 7, 2009
Update - emergency evacuations below the Dadu River landslide in China
The Chinese language website www.scol.com.cn has some images of the area upstream of the landslide dam at Dadu here. This also links to what appears to be a Chinese language bulletin board here in which people are posting images of the situation. If this is as it seems then this area has serious problems. although reports do seem to indicate that the river is not completely blocked.
For example, this is a bridge across the Dadu River under normal conditions:
And this is it today:
More details here as well, with some images of the low flow downstream. It appears that the authorities are organising a large-scale evacuation.
For example, this is a bridge across the Dadu River under normal conditions:
And this is it today:
More details here as well, with some images of the low flow downstream. It appears that the authorities are organising a large-scale evacuation.
Sunday, July 26, 2009
Two recent landslides at hydroelectric sites in China
In the past week China has suffered two rather extraordinary landslide accidents at hydroelectric plants.
The first occurred an 20th July 2009 near to the Xiaowan hydroelectric power station in Yunnan province. The dam, shown in the artist's impression below, will apparently be the world's tallest arched dam, standing 292 m high when finished. It is still under construction, with the first turbine expected to be operational later this year:
The image above is a bit fanciful as it doesn't show the lake or the extensive slope works that have been needed. The image below, taken in an earlier phase of construction, gives an idea of the state of the slopes:
Now interestingly, late last month there was a rather triumphant article in the Chinese media about the second stage filling of the site. The Google translation of the article says this:
"It is reported that the second phase of Xiaowan storage power station will be carried out in two steps, 20 July, water power stations will reach 1125 meters elevation; the end of August, water storage, power generation water level will reach 1160 meters elevation, the first unit into operation by the end of September this year power generation is just around the corner" (excuse the rather mangled English).
In other words, the lake level was being elevated for the first time to 1125 m elevation on 20th July. The landslide occurred on that day. The landslide itself was described thus:
"Waves up to 30 metres high swept 14 people into the turbulent upper reaches of the Mekong River following a huge landslide into the river in south-western China's Yunnan province, state media said on Tuesday. Rescue workers recovered two bodies from the river, which is known as the Lancang in China, and were still searching for 12 others missing since they were swept away in the early hours of Monday, the semi-official China News Service said. An estimated 13 hectares of land plunged into the river near the Xiaowan hydroelectric power station, creating giant waves that engulfed 14 farmers as they camped nearby, the agency said. "
This slide apparently had a surface area of 130,000 square metres and created displacement waves 30 m high. That is a very large landslide!
Then, on 23rd July 2009, another landslide disaster occurred, this time at the site of the Changheba Hydroelectric power (HEP) works in Kangding County, Sichuan Province. It appears that in this case a debris flow hit a construction camp for the dam, which will be a 2.2 GW plant across the Dadu river. Unfortunately, the very large (500,000 cubic metre) debris flow occurred at about the worst possible time, 3 am. It hit a major road and 136 temporary buildings housing workers. It is believed to have killed 57 people. The site of the landslide appears to be shown in this Xinhua image:
The rescue operations have been hampered by another large failure, this time on the access road to the site. Here it appears that a failure has occurred in a hillside store of boulders that are to be used in the construction of the dam:
The boulders clearly have been generated recently, as this close up image shows:
It appears that they were being retained by gabian walls above the road:
The collapse has blocked the highway, meaning that until today heavy machinery could not access the disaster site. This has hampered the rescue operation, although to be honest there seems to be very little chance that there could be any survivors from an event of this size.
If anything, 57 fatalities from 136 temporary houses would seem to be a surprisingly low number.
The first occurred an 20th July 2009 near to the Xiaowan hydroelectric power station in Yunnan province. The dam, shown in the artist's impression below, will apparently be the world's tallest arched dam, standing 292 m high when finished. It is still under construction, with the first turbine expected to be operational later this year:
The image above is a bit fanciful as it doesn't show the lake or the extensive slope works that have been needed. The image below, taken in an earlier phase of construction, gives an idea of the state of the slopes:
Now interestingly, late last month there was a rather triumphant article in the Chinese media about the second stage filling of the site. The Google translation of the article says this:"It is reported that the second phase of Xiaowan storage power station will be carried out in two steps, 20 July, water power stations will reach 1125 meters elevation; the end of August, water storage, power generation water level will reach 1160 meters elevation, the first unit into operation by the end of September this year power generation is just around the corner" (excuse the rather mangled English).
In other words, the lake level was being elevated for the first time to 1125 m elevation on 20th July. The landslide occurred on that day. The landslide itself was described thus:
"Waves up to 30 metres high swept 14 people into the turbulent upper reaches of the Mekong River following a huge landslide into the river in south-western China's Yunnan province, state media said on Tuesday. Rescue workers recovered two bodies from the river, which is known as the Lancang in China, and were still searching for 12 others missing since they were swept away in the early hours of Monday, the semi-official China News Service said. An estimated 13 hectares of land plunged into the river near the Xiaowan hydroelectric power station, creating giant waves that engulfed 14 farmers as they camped nearby, the agency said. "
This slide apparently had a surface area of 130,000 square metres and created displacement waves 30 m high. That is a very large landslide!
Then, on 23rd July 2009, another landslide disaster occurred, this time at the site of the Changheba Hydroelectric power (HEP) works in Kangding County, Sichuan Province. It appears that in this case a debris flow hit a construction camp for the dam, which will be a 2.2 GW plant across the Dadu river. Unfortunately, the very large (500,000 cubic metre) debris flow occurred at about the worst possible time, 3 am. It hit a major road and 136 temporary buildings housing workers. It is believed to have killed 57 people. The site of the landslide appears to be shown in this Xinhua image:
The rescue operations have been hampered by another large failure, this time on the access road to the site. Here it appears that a failure has occurred in a hillside store of boulders that are to be used in the construction of the dam:
The boulders clearly have been generated recently, as this close up image shows:
It appears that they were being retained by gabian walls above the road:
The collapse has blocked the highway, meaning that until today heavy machinery could not access the disaster site. This has hampered the rescue operation, although to be honest there seems to be very little chance that there could be any survivors from an event of this size.
If anything, 57 fatalities from 136 temporary houses would seem to be a surprisingly low number.
Tuesday, June 23, 2009
Chongqing landslide rescue update - 23rd June
Xinhua has a video report about the ongoing rescue attempts at the Chongqing landslide site. The report suggests that remotely sensed imagery allowed a number of locations in which the crags in the head scar area were found to be unstable and threatening the rescue teams. To this end, two artillery pieces were brought in and shells were fired at the crags to try to dislodge the unstable sections. This failed unfortunately, so now dynamite will be used instead.
Unfortunately there is no news of the rescue attempt itself.
Unfortunately there is no news of the rescue attempt itself.
Thursday, June 18, 2009
Chongqing landslide - NASA satellite image
NASA have provided the first decent overview of the Chongqing landslide via a high resolution satellite image. This can be found here.
The morphology of this is decidedly odd - I will spend some time trying understand it better. According to the NASA page the source is to the north and the landslide has moved southwards and then spread out to the southwest.
Meanwhile, the search for victims continues according to Xinhua.
The morphology of this is decidedly odd - I will spend some time trying understand it better. According to the NASA page the source is to the north and the landslide has moved southwards and then spread out to the southwest.
Meanwhile, the search for victims continues according to Xinhua.
Tuesday, June 16, 2009
The Chongqing landslide - update 16th June
The latest update on the Chongqing landslide rescue is provided by Xinhua. Key points:
- Rescue operations continue, with 3,000 people working on site;
- Ten small-scale landslides have occurred at the landslide site since Friday;
- southwest China's Chongqing Municipality from Friday, and rescuers continued to search for 64 missing for the 10th day on Tuesday.
- The water level in the barrier lake has dropped to 10 m below the top of the temporary embankment;
- The rescuers have not yet found the mine entrance.
Sunday, June 14, 2009
The Chongqing landslide - the rescue is probably about to be abandoned
Xinhua is reporting that the rescue at the Chongqing landslide is likely to be abandoned shortly. Given the length of time that has elapsed since the failure the chances of rescuing the miners alive are now very small. More worryingly, there is an increasing risk of further failures at the site:
"According to a geologist with the rescue headquarters who declined to be identified, cracks with the span of eight to ten meters wide and up to 30 meters deep have appeared on the landslide-induced hills. "If the 1.75 million cubic meters of soil and rocks fell down from 80 to 100 meters high, another massive landslide shall occur," he said. Four remaining big stones that stood on the edge of the mountains are also likely to slip off when it rains, he said. Two landslides of smaller scale forced suspension of rescue work twice early Friday morning. The landslide site has entered the flood season, and landslide-induced lakes are likely to trigger mud-rock flows, said Zhu Xiansheng, head of the water conservancy bureau of Chongqing."
Such rescues are always a balance between the benefits of successfully rescuing the victims and the risks to the search teams. Given the time that has elapsed, the difficulties involved in the operation and the lack of indications that the miners are alive, the increasing risks to the rescue teams do suggest that stopping the operation is probably prudent, even though it is a very difficult decision to make. Thirty metre deep cracks that are widening are a strong indication that all is not well on the hillside, although failure is certainly not inevitable.
"According to a geologist with the rescue headquarters who declined to be identified, cracks with the span of eight to ten meters wide and up to 30 meters deep have appeared on the landslide-induced hills. "If the 1.75 million cubic meters of soil and rocks fell down from 80 to 100 meters high, another massive landslide shall occur," he said. Four remaining big stones that stood on the edge of the mountains are also likely to slip off when it rains, he said. Two landslides of smaller scale forced suspension of rescue work twice early Friday morning. The landslide site has entered the flood season, and landslide-induced lakes are likely to trigger mud-rock flows, said Zhu Xiansheng, head of the water conservancy bureau of Chongqing."
Such rescues are always a balance between the benefits of successfully rescuing the victims and the risks to the search teams. Given the time that has elapsed, the difficulties involved in the operation and the lack of indications that the miners are alive, the increasing risks to the rescue teams do suggest that stopping the operation is probably prudent, even though it is a very difficult decision to make. Thirty metre deep cracks that are widening are a strong indication that all is not well on the hillside, although failure is certainly not inevitable.
Friday, June 12, 2009
The latest update on the Chongqing landslide rescue
Xinhua and CCTV have published updates on the Chongqing landslide rescue. The picture is looking increasingly grim given that the estimated survival time of the miners was five to seven days, and it is now a week since the landslide. Highlights of the reports are as follows:
- Drilling continues but to date no signs of life have been detected. Drilling (or is this tunnel construction - see below) is only progressing at 5 m per day as they are creating an inclined hole to try to prevent secondary failures;
- Unfortunately the mine plans were buried in the landslide, so the exact location of the mine entrances is unknown. The chances of being able to build a tunnel that will intersect the mine entrance is considered to be less than 20%;
- A small landslide that a the drilling platform interrupted rescue operations today. No-one was injured. However, it is now believed that over a million cubic metres of the slope above the site is unstable, and the possibility of more landslides is considered to be "very high".
- The heavy lift helicopter is transporting heavy equipment onto the site (see image above). This is expected to increase the rate at which excavation can occur;
- The barrier lake now contains 40,000 cubic meters of water (this is a big increase in estimated volume compared with yesterday - but is still not a huge amount of water as these things go); The lake level rose by 0.5 m in the last 24 hours.
- The team continues to build an embankment to keep the water away from the rescue site. The water level is now 1 m below the embankment
- However, the drainage pipe is now in place and will start pumping today. With a capacity of 15,000 cubic metres per day this should keep the level below the maximum under current conditions;
- In due course a proper drainage channel will be needed, but at the moment the focus is on the rescue.
1. The news that the authorities do not know the actual location of the mine entrances is new - and very candid. One should not be critical of them for this - a characteristic of the Guinsaugon (Leyte) landslide was the huge difficulties that the rescuers, including the US Marine Corps, had in determining the former location of buildings and infrastructure;
2. It seems to me that there are two operations occurring simultaneously here - one to drill bore holes to allow detection equipment to be located and, I suspect, to try to find the mine entrances. This explains why 40 rigs are being used.
3. There is a double race occurring here - one associated with the limited survival time of the miners and the other to beat the seasonal rains. Unfortunately the slope could collapse even without further rain (i.e. through a progressive failure), so the danger to the rescuers is real and very immediate.
Thursday, June 11, 2009
Latest update on the Chongqing landslide
The desperate rescue attempts continue at the site of the Chongqing landslide, but time is now clearly running out for the miners. The heavy lift helicopter, the same one that assisted at Tangjiashan, is now in full operation, and the drilling continues using 20 machines according to this report. The drilling operations have now reached 100 m below the surface and thus have reached the position of the portal. Unfortunately this appears to have collapsed (unsurprisingly). Additionally, the rescue teams have had to abandon their use of explosives due to the instability of the landslide mass.
There can be little hope for the trapped miners now, although it is still worth trying to get to them.
Meanwhile, according to this report the barrier lake volume has now reached 10,000 cubic metres (this is not a huge volume). Operations to lay a drainage pipe are ongoing.
There can be little hope for the trapped miners now, although it is still worth trying to get to them.
Meanwhile, according to this report the barrier lake volume has now reached 10,000 cubic metres (this is not a huge volume). Operations to lay a drainage pipe are ongoing.
Tuesday, June 9, 2009
Chongqing landslide update - 9th June
Image source: http://uk.news.yahoo.com/19/20090609/img/pwl-china-landslide-death-9-6f14af6c0f4b.htmlThe latest news from the Chongqing landslide site is as follows:
- Attempts to build a tunnel to the trapped miners continue. The heavy lift helicopter is now in operation. Electric cables and a generator have been installed to provide power to the ongoing operations;
- Heavy rain has now reduced to drizzle, but the water depth in the barrier lake increased by a metre in 24 hours;
- Operations to create a channel to drain the lake continue. The image above appears to show the barrier lake in the background;
- The rescue teams are using sandbags to try to prevent water from the barrier lake entering the mine - this would of course be disastrous for the trapped miners.
- Satellite imagery was expected to be available from today (I would like to see this!). Meanwhile, monitoring points have been established to provide warning of any further landslides.
Meanwhile, some additional pieces of background information have been published in China Daily:
- The iron ore mine, which was called Sanlian, produced only 100 tonnes per day. This is very low.
- A similar accident occurred 0n 30th April 1994, creating a landslide deposit that blocked the river;
- Two days before the accident rockfalls were observed from the slope;
- The local authorities warned the villagers about the potential for a landslide in 2003. They were offered 5,000 yuan (c.£450 or 520 Euros) to move. Most villagers refused to leave.
Monday, June 8, 2009
Background to the Chongqing landslide
According to this report, rescue operations for the 27 miners trapped in a mine beneath the Chongqing landslide have been suspended due to bad weather. As I mentioned in my earlier post, working on a fresh rockslide deposit is exceptionally dangerous, so this is a wise decision. However, the outlook for the trapped miners must be looking increasingly bleak, given that it now appears that they are trapped 200 m underground and heavy machinery is not being used.
The above article has some very interesting and pertinent information about the context of the landslide. It quotes local residents as saying that the mine in question, which opened in 1949, was closed in 2000 "after being labelled dangerous by an official geological survey team". However, work resumed in 2004 under private ownership, whereupon landslides started to occur from the slope. In 2004 "masses fell from the mountain into the valley... after which the Tiekuang government offices, local school and circa 70 residencies were moved. But 40 of those people buried by the landslide decided to stay in the area, after local officials assured them that there were no problems."
The mine owner has been arrested, but the local people are critical that the local media is reporting the landslide as having been natural: “it wasn’t a natural disaster; human error is the only thing to blame for the tragedy”.
The above article has some very interesting and pertinent information about the context of the landslide. It quotes local residents as saying that the mine in question, which opened in 1949, was closed in 2000 "after being labelled dangerous by an official geological survey team". However, work resumed in 2004 under private ownership, whereupon landslides started to occur from the slope. In 2004 "masses fell from the mountain into the valley... after which the Tiekuang government offices, local school and circa 70 residencies were moved. But 40 of those people buried by the landslide decided to stay in the area, after local officials assured them that there were no problems."
The mine owner has been arrested, but the local people are critical that the local media is reporting the landslide as having been natural: “it wasn’t a natural disaster; human error is the only thing to blame for the tragedy”.
Sunday, June 7, 2009
The race against time to save 27 miners trapped below the Chongqing landslide
In China there is now a dramatic race against time being played out as rescuers race to reach 27 miners trapped below the Chongqing landslide. Xinhua is reporting that the two entrances to the Jiwei Mountain Iron Ore mine were blocked by the landslide. The trapped miners are likely to be able to survive for five to seven days, so there is very limited time available. Rescuers are now trying to blast a 40 m deep shaft through the landslide debris to reach the miners, as this Xinhua image shows:
To facilitate this the rescuers have build a road to bring in heavy machinery and now have access to a heavy lift helicopter.
However, we should not under-estimate the difficulties of this task. First, the landslide debris looks to be incredibly coarse, which will mean that digging a shaft or a tunnel is very difficult indeed, as this Xinhua image shows (note the rescuers for scale):
Third, the debris will be at its dry angle of repose and so is only just stable. Therefore, digging into will potentially destabilise the mass above. Supporting a tunnel or shaft in this material is not going to be easy. Finally, of course, rainfall would be very dangerous. The rainy season is just starting. Therefore, there are substantial risks to the rescuers as well as the miners.
Meanwhile, the slide, which is now estimated to have a volume of 12 million cubic metres, has also blocked the valley, such that a lake is forming. Once again the Chinese are having to build a drainage channel and evacuate people downstream and within the lake area.
The number killed by the landslide is very unclear at present, but the best estimate seems to be 79 buried by the landslide plus the 27 miners.
Saturday, June 6, 2009
Illustration of the scale of the Chongqing rockslope failure
The landslide at Chongqing is very large - it has an estimated volume of 3.5 million cubic metres. The scale of this is well-illustrated by this image from Suomen Kuvalehti, which shows rescuers walking across the landslide debris:
Update on the Chongqing landslide
Xinhua is now reporting that 79 people have been killed in the catastrophic landslide in Chongqing. In addition, 27 miners are trapped in a mine whose adit has been buried.
Xinhua has also released an image of the source zone of the landslide (showing continued rockfall activity):
And also the landslide deposit. It is now appears that this is a massive and catastrophic rock slope failure:
Xinhua has also released an image of the source zone of the landslide (showing continued rockfall activity):
And also the landslide deposit. It is now appears that this is a massive and catastrophic rock slope failure:
Friday, May 22, 2009
Sinorock conference report - the Wenchuan Earthquake session
Yesterday there was a special session of the Sinorock Conference in Hong Kong, focused on the Wenchuan Earthquake. This involved six presentations and then a lively round-table discussion. This is a brief review.
The first talk was given by colleagues from Chengdu University of Technology on the topic of the landslides triggered by the earthquake. This was visually spectacular, emphasising the scale, density and impact of the landslides that were triggered. The CDUT team have completed an impressive amount of analysis of the data that they have collected now. An interesting addition was some small scale shaking table tests to investigate whether the morphologies that they observed can be replicated in the laboratory - the conclusion was that they can - and the videos made good viewing, although great care is needed in the interpretations due to the well-known problems of scaling the stresses and displacements.
Next up was Li Yong, also from CDUT, who talked about the mechanics of the earthquake itself. Interestingly, he highlighted the work that he and his co-workers had done with my colleague at Durham Dr Alex Densmore, in particular noting that their 2007 paper on the Longmenshan fault system had highlighted before the earthquake the threat posed by this active fault system. Dating of the sediments excavated from trenches along the fault suggest that the last major rupture was about 950 years before the present. However, his final note was quite chilling - this is that there are three large parallel faults in the Longmenshan system, but only two ruptured...
The third presentation was by the ever-impressive Chen Zuyu, who gave a wonderful talk about the mitigation of the Tangjiashan barrier lake, of which most readers will be very familiar. Prof. Chen focussed on the pressures that were on them during the successful drainage operation, the unanswerable questions that they faced, and the scientific data that they collected during the breaching. They measured the discharge as the breach proceeded and have a paper in with the ASCE at the moment. He pledged to release the data once the paper is published - so please can the ASCE make a quick decision!
An interesting issue that he highlighted was the state of Tangjiashan now. How noted that a debris flow blocked the river again on 24th September, forcing a 7 m rise in the lake level. The channel has now been widened and deepened ahead of the monsoon (this is what they were doing when I was there). More worrying, he noted that above the back scarp of the landslide scar there are tension cracks. Monitoring suggested very substantial amounts of ongoing movement, but this has now been terminated due to a lack of funds. This must be a very serious concern given the impending monsoon.
Finally before the break, He Chuan reviewed damage to lifeline engineering. Most of this went over my head, but I was interested in the fact that they examined the behaviour of rockslope reinforcement and retaining walls. In the case of rockslope reinforcement they noted that rock anchors and grids worked much better than mesh and shotcrete (not a surprise actually). The case of retaining walls they noted that walls on convex bends in the road performed poorly, whilst those on straight sections did OK. I am not sure whether this is because of the underlying materials (maybe walls on bends are holding up large colluvial bodies) or something to do with the dynamics of the earthquake shaking, or something else (presence of water?), but it is an intriguing result.
After coffee there were two brief presentations. The first was by Alexander Strom, who compared the impact of the earthquake in China with a potential event in the Tien Shan, noting that the presence of similar earthquake landforms (fault scarps, offset terraces, large landslides) suggest that an area that is considered to be of low seismic hazard may actually be quite risky. The second was by Xu Wenjie, who considered the ways in which the Xiajiapiao landslide blocked a river, and the ways in which it was breached. The fact that 14 tonnes of explosives were used to drain it sticks in the mind. I was also good to see some outcomes of modelling of the slides, but this did highlight the concerns about using models with rigid blocks to simulate materials that can fracture and fragment. The use of rigid blocks generates very high local stresses that cause ballistic behaviour of debris within the lodel. This does not mean that the the landslide did this (to be fair the author did not suggest that it did, but the audience might misinterpret the plots).
The discussion focused upon the availability of seismic data (apparently it has now been released in a book - I will try to get a copy), models of landslide initiation, topographic amplification, and the ways in which we understand the behaviour of coarse materials in landslide dams. It was all pretty interesting and there was some disagreement, which was good.
Overall I learnt a great deal but I am increasingly concerned that the opportunities presented by the event to gain scientific knowledge about landslides might be getting away from us. This is not the fault of our Chinese academic colleagues - who are impressively proactive and skilled - more of the global scientific system. This is very frustrating!
Incidentally, the Great Firewall of China has now blocked access to blogger across the whole of China. This is a great shame, and a retrograde step in terms of sharing knowledge.
The first talk was given by colleagues from Chengdu University of Technology on the topic of the landslides triggered by the earthquake. This was visually spectacular, emphasising the scale, density and impact of the landslides that were triggered. The CDUT team have completed an impressive amount of analysis of the data that they have collected now. An interesting addition was some small scale shaking table tests to investigate whether the morphologies that they observed can be replicated in the laboratory - the conclusion was that they can - and the videos made good viewing, although great care is needed in the interpretations due to the well-known problems of scaling the stresses and displacements.
Next up was Li Yong, also from CDUT, who talked about the mechanics of the earthquake itself. Interestingly, he highlighted the work that he and his co-workers had done with my colleague at Durham Dr Alex Densmore, in particular noting that their 2007 paper on the Longmenshan fault system had highlighted before the earthquake the threat posed by this active fault system. Dating of the sediments excavated from trenches along the fault suggest that the last major rupture was about 950 years before the present. However, his final note was quite chilling - this is that there are three large parallel faults in the Longmenshan system, but only two ruptured...
The third presentation was by the ever-impressive Chen Zuyu, who gave a wonderful talk about the mitigation of the Tangjiashan barrier lake, of which most readers will be very familiar. Prof. Chen focussed on the pressures that were on them during the successful drainage operation, the unanswerable questions that they faced, and the scientific data that they collected during the breaching. They measured the discharge as the breach proceeded and have a paper in with the ASCE at the moment. He pledged to release the data once the paper is published - so please can the ASCE make a quick decision!
An interesting issue that he highlighted was the state of Tangjiashan now. How noted that a debris flow blocked the river again on 24th September, forcing a 7 m rise in the lake level. The channel has now been widened and deepened ahead of the monsoon (this is what they were doing when I was there). More worrying, he noted that above the back scarp of the landslide scar there are tension cracks. Monitoring suggested very substantial amounts of ongoing movement, but this has now been terminated due to a lack of funds. This must be a very serious concern given the impending monsoon.
Finally before the break, He Chuan reviewed damage to lifeline engineering. Most of this went over my head, but I was interested in the fact that they examined the behaviour of rockslope reinforcement and retaining walls. In the case of rockslope reinforcement they noted that rock anchors and grids worked much better than mesh and shotcrete (not a surprise actually). The case of retaining walls they noted that walls on convex bends in the road performed poorly, whilst those on straight sections did OK. I am not sure whether this is because of the underlying materials (maybe walls on bends are holding up large colluvial bodies) or something to do with the dynamics of the earthquake shaking, or something else (presence of water?), but it is an intriguing result.
After coffee there were two brief presentations. The first was by Alexander Strom, who compared the impact of the earthquake in China with a potential event in the Tien Shan, noting that the presence of similar earthquake landforms (fault scarps, offset terraces, large landslides) suggest that an area that is considered to be of low seismic hazard may actually be quite risky. The second was by Xu Wenjie, who considered the ways in which the Xiajiapiao landslide blocked a river, and the ways in which it was breached. The fact that 14 tonnes of explosives were used to drain it sticks in the mind. I was also good to see some outcomes of modelling of the slides, but this did highlight the concerns about using models with rigid blocks to simulate materials that can fracture and fragment. The use of rigid blocks generates very high local stresses that cause ballistic behaviour of debris within the lodel. This does not mean that the the landslide did this (to be fair the author did not suggest that it did, but the audience might misinterpret the plots).
The discussion focused upon the availability of seismic data (apparently it has now been released in a book - I will try to get a copy), models of landslide initiation, topographic amplification, and the ways in which we understand the behaviour of coarse materials in landslide dams. It was all pretty interesting and there was some disagreement, which was good.
Overall I learnt a great deal but I am increasingly concerned that the opportunities presented by the event to gain scientific knowledge about landslides might be getting away from us. This is not the fault of our Chinese academic colleagues - who are impressively proactive and skilled - more of the global scientific system. This is very frustrating!
Incidentally, the Great Firewall of China has now blocked access to blogger across the whole of China. This is a great shame, and a retrograde step in terms of sharing knowledge.
Sinorock presentation file on the Wenchuan (Sichuan) Earthquake
Today there was a session on the Wenchuan Earthquake at the Sinorock conference in Hong Kong. I was invited to participate in the panel discussion, for which I put together the following presentation highlighting a few critical issues:
Uploaded on authorSTREAM by Dr_Dave
You should be able to review the presentation above or to download it the Powerpoint file if you wish (from here if necessary).
I will write a review of the presentations and discussion over the next day or so. It was very interesting indeed!
Uploaded on authorSTREAM by Dr_Dave
You should be able to review the presentation above or to download it the Powerpoint file if you wish (from here if necessary).
I will write a review of the presentations and discussion over the next day or so. It was very interesting indeed!
Tuesday, May 12, 2009
So what have we learnt from the Wenchuan (Sichuan) Earthquake?
Driving home from work last night, and bored with listening to endless discussions on the radio about the ways in which politicians use the system to personal gain, I started pondering what we have learnt from the Wenchuan Earthquake a year ago. The media yesterday understandably focused on collapsed schools. We have known for years that critical buildings in earthquake zones need seismic reinforcement, so this is hardly new. These are the key things that I think we have learnt (you may have more, so I welcome comments):
1. Our current rapidly-generated maps of the distribution of earthquake shaking are not good enough.
In China it is clear that the area of maximum damage occurred on the hanging wall (NW side) of the fault, with the peak being very close to the surface trace of the fault. Many of the early maps suggested that maxim,um damage would be in a zone centred around the epicentre. Unfortunately this meant that at least a part of the rescue effort was misdirected. The need for strong motion instruments across an earthquake-vulnerable area that can telemeter (send) the data back to a central station is clear. This is what happened in 1999 in Taiwan. Additionally, further work is clearly needed to allow the rapid generation of reliable shake maps.
2. Communications are critical.
In China there was a major problem with communications from the most seriously-affected areas. With no telephones or power, and with all of the roads blocked by literally hundreds of landslides, getting information out about the impact proved impossible. This was compounded by a lack of understanding from the Chinese government about the likely level of damage. On the afternoon of the earthquake the Chinese Premier Wen Jiabao ordered that the roads to the epicentral areas should be reopened by before 12 p.m the day after the earthquake. Clearly there was no comprehension of what things were like in the mountain regions - and Wen is a geologist! This is not a criticism of Wen or the Chinese government - how could they possibly have known that things were so bad - but rather of the landslide community - of which I am a part - for failing to make governments aware of the implications of landslides in mountainous earthquake zones (see below).
3. Landslides play a major role in mountain area earthquakes.
Until now the earthquake community has failed to appreciate the major role that landslides cause in earthquakes in upland areas. About a third of the fatalities occurred as a result of landslides; landslides also to a large degree prevented the delivery of aid; landslides blocked valleys causing a major secondary hazard (see below); and landslides now generate much of the long term hazard in the affected areas.
4. Valley blocking landslides can be mitigated.
This is the first large earthquake in modern times that has created very large numbers of valley-blocking landslides. The Chinese demonstrated that these hazards can be successfully mitigated, but that it requires the availability of the right tools, experience and resources. The Chinese achievement is extraordinary - I wonder if the rest of the world could cope so well?
5. Satellite tools are still not up to the job.
For years we have been hearing that satellites provide the capability to get an almost instant view of what has happened in disaster zones. There are more satellites available than ever, but imagery proved to be of almost no use at all in the recovery phase. The problems remain that the instruments with the highest resolutions cannot see through clouds and it is very difficult to get the data into a format that is usable on the ground.
1. Our current rapidly-generated maps of the distribution of earthquake shaking are not good enough.
In China it is clear that the area of maximum damage occurred on the hanging wall (NW side) of the fault, with the peak being very close to the surface trace of the fault. Many of the early maps suggested that maxim,um damage would be in a zone centred around the epicentre. Unfortunately this meant that at least a part of the rescue effort was misdirected. The need for strong motion instruments across an earthquake-vulnerable area that can telemeter (send) the data back to a central station is clear. This is what happened in 1999 in Taiwan. Additionally, further work is clearly needed to allow the rapid generation of reliable shake maps.
2. Communications are critical.
In China there was a major problem with communications from the most seriously-affected areas. With no telephones or power, and with all of the roads blocked by literally hundreds of landslides, getting information out about the impact proved impossible. This was compounded by a lack of understanding from the Chinese government about the likely level of damage. On the afternoon of the earthquake the Chinese Premier Wen Jiabao ordered that the roads to the epicentral areas should be reopened by before 12 p.m the day after the earthquake. Clearly there was no comprehension of what things were like in the mountain regions - and Wen is a geologist! This is not a criticism of Wen or the Chinese government - how could they possibly have known that things were so bad - but rather of the landslide community - of which I am a part - for failing to make governments aware of the implications of landslides in mountainous earthquake zones (see below).
3. Landslides play a major role in mountain area earthquakes.
Until now the earthquake community has failed to appreciate the major role that landslides cause in earthquakes in upland areas. About a third of the fatalities occurred as a result of landslides; landslides also to a large degree prevented the delivery of aid; landslides blocked valleys causing a major secondary hazard (see below); and landslides now generate much of the long term hazard in the affected areas.
4. Valley blocking landslides can be mitigated.
This is the first large earthquake in modern times that has created very large numbers of valley-blocking landslides. The Chinese demonstrated that these hazards can be successfully mitigated, but that it requires the availability of the right tools, experience and resources. The Chinese achievement is extraordinary - I wonder if the rest of the world could cope so well?
5. Satellite tools are still not up to the job.
For years we have been hearing that satellites provide the capability to get an almost instant view of what has happened in disaster zones. There are more satellites available than ever, but imagery proved to be of almost no use at all in the recovery phase. The problems remain that the instruments with the highest resolutions cannot see through clouds and it is very difficult to get the data into a format that is usable on the ground.
Monday, May 11, 2009
The Wenchuan Earthquake - one year on
No words can do justice to the first anniversary of the Wenchuan (Sichuan) earthquake, so I won't even try. Instead I post these pictures as a silent memorial to the victims.
Wednesday, April 22, 2009
EGU Day 3
I am just going to write up one session from today's meeting as it contained the most interesting talks that I heard. This was an annual session on landslides induced by volcanoes and earthquakes, the first three talks of which focussed on the Wenchuan event. Regular readers will know that I am very interested indeed in this event (see here for example).
So first up was Ed Harp and two colleagues from USGS. They provided a pretty general overview of the landslides triggered by the earthquake, but supplemented with some very nice satellite imagery of key sites. He highlighted the death toll associated with the earthquake-induced landslides (20,000+) and the huge number of dams that needed clearing (he quoted 33 that required mitigation). The tour included Beichuan, Tangjiashan, etc. I guess there wasn't much new or scientifically-challenging here, but it was a good start. The final part of the talk highlighted the collaboration between USGS and the China Geological Survey, which is going to allow transfer of techniques for seismic landslide hazard analysis, data collation to test the USGS PAGER model and quantification of the sediment flux. In questioning Ed said that the planned seismic hazard analysis tool is Newmark Displacement. I do wonder whether this is the right tool in this part of China - it is probably appropriate for the initiation of the slides, but most of the failures that I saw have lower sections that are very complex, with massive entrainment of slope debris and colluvium. This is where the people and infrastructure are, so it seems to me that without substantial modification Newmark is going to be quite problematic.
Second up was Gorum and his colleagues from ITC. The poor chap had the misfortune of giving his first international conference talk to a packed house about a set of landslides that he had not visited! In that context he did very well indeed. He gave a slightly broader overview, making use of some of the data collected by the Chengdu University of Technology from their mapping. In particular, he highlighted that the landslide are focused close to the fault trace (NB this focus is not on the epicentral region), with many slides on the lower gorges. Using satellite imagery they have mapped an initial 11,308 landslides, compared with 1,638 before the earthquake. They also noted that they had mapped 256 valley blocking slides, with the highest concentration being on the fault trace. They are now working with the Chinese to understand the landslide distribution (very challenging) and to undertake a multi-hazard analysis. I cannot quite see how the latter will be done - the presenter seemed to imply that they will use the existing landslide distribution to drive a modelling exercise. I hope that this is not the case as the seismically-induced landslides will not give a good indication as to where rainfall-triggered slides will occur in a post-earthquake landscape.
The final talk from Wenchuan was by Chigira and his colleagues from Kyoto, with substantial co-authorship from China. This was the best judges of the three, provising a nice summary of the key points issues, well-illustrated using good images. They highlighted the role of dissolution in raising landslide susceptibility - the point being that dissolving limestone beds creates voids that allows drainage of groundwater, reducing susceptibility to rainfall induced slides, but creating point-to-point contacts that increases susceptibility to earthquake induced sliding. This is a nice point. He concluded by looking at some of the very largest slides, concluding that the geomorphology before the earthquake showed depressions and dips on the big slides that indicated that they were potentially unstable. Thus, the biggest slides were considered to be predictable. I am not sure that I agree with the latter point completely (unless all slopes with these features failed, which I don't think is the case), the observations about the morphology are well-made.
The penultimate talk upon which I will comment was by Niels Hovious from Cambridge, with co-authors from Taiwan and elsewhere. Niels used the 1999 Chi-Chi earthquake in Taiwan to examine the distribution of landslides that are generated, and then to look at the production of sediment. First, Niels argues that the landslides closely map onto the distribution of ground shaking, with which I agree, but then argued that the highest landslide density occurs around the epicentre. This may well be true for Chi-Chi, but it was not for one of jis other examples (Northridge) and it was not true for Pakistan, where the highest densities are at the fault rupture. Most importantly, it is also not true for Wenchuan, where again the highest densities lie close to the surface expression of the fault rupture and not around the epicentre. Niels then showed that the density of landslides increased remarkably in the aftermath of the Chi-Chi earthquake - in the Chenyoulan ctachment that they studied the number of landslides before the earthquake was 8123, with a further 3,800 being triggered in the event. However, in the nearly ten years since a further 48,370 landslides have been triggered. However, Niels showed that the sediment concentration in the rivers is now close to base level again, suggesting that the earthquake's impacts are now reducing. This is good stuff but, given that the landscape is affected by typhoons that are exceptionally extreme events one wonders how applicable it is to other places. It seems to me that they need to work in China! An important aside is that this talk does highlight the importance of being prepared for massive sediment production in China.
The final talk that I shall briefly mention is that of Merri and his colleagues from Italy, who are using a finite difference model (FLAC3D to simulate the impacts of magma intrusion on the stability of the Stromboli volcanic edifice. The presentation was quite nice, but the model seems a little flawed. First, it assumes that the volcano is geologically homogenous - volcanoes certainly are not, and given that deposits are layed down in slope parallel layers, this heterogeneity can be a big factor in slope instability. Second, the model appears to ignore pore pressure affects (I asked whether pore pressures are being modelled - the presenter ducked the issue by talking about over-stress. Given that injections of hot material cause increases in pore pressure for certain, and these may well be very important in understanding slope stability - this is a substantial omission.
Comments welcome as ever, especially from the presenters and other attendees. Do feel free to comment if you disagree with what I have written. Finally, apologies for typos, spelling mistakes, etc. The spell check function isn't working and I don't have time to check.
So first up was Ed Harp and two colleagues from USGS. They provided a pretty general overview of the landslides triggered by the earthquake, but supplemented with some very nice satellite imagery of key sites. He highlighted the death toll associated with the earthquake-induced landslides (20,000+) and the huge number of dams that needed clearing (he quoted 33 that required mitigation). The tour included Beichuan, Tangjiashan, etc. I guess there wasn't much new or scientifically-challenging here, but it was a good start. The final part of the talk highlighted the collaboration between USGS and the China Geological Survey, which is going to allow transfer of techniques for seismic landslide hazard analysis, data collation to test the USGS PAGER model and quantification of the sediment flux. In questioning Ed said that the planned seismic hazard analysis tool is Newmark Displacement. I do wonder whether this is the right tool in this part of China - it is probably appropriate for the initiation of the slides, but most of the failures that I saw have lower sections that are very complex, with massive entrainment of slope debris and colluvium. This is where the people and infrastructure are, so it seems to me that without substantial modification Newmark is going to be quite problematic.
Second up was Gorum and his colleagues from ITC. The poor chap had the misfortune of giving his first international conference talk to a packed house about a set of landslides that he had not visited! In that context he did very well indeed. He gave a slightly broader overview, making use of some of the data collected by the Chengdu University of Technology from their mapping. In particular, he highlighted that the landslide are focused close to the fault trace (NB this focus is not on the epicentral region), with many slides on the lower gorges. Using satellite imagery they have mapped an initial 11,308 landslides, compared with 1,638 before the earthquake. They also noted that they had mapped 256 valley blocking slides, with the highest concentration being on the fault trace. They are now working with the Chinese to understand the landslide distribution (very challenging) and to undertake a multi-hazard analysis. I cannot quite see how the latter will be done - the presenter seemed to imply that they will use the existing landslide distribution to drive a modelling exercise. I hope that this is not the case as the seismically-induced landslides will not give a good indication as to where rainfall-triggered slides will occur in a post-earthquake landscape.
The final talk from Wenchuan was by Chigira and his colleagues from Kyoto, with substantial co-authorship from China. This was the best judges of the three, provising a nice summary of the key points issues, well-illustrated using good images. They highlighted the role of dissolution in raising landslide susceptibility - the point being that dissolving limestone beds creates voids that allows drainage of groundwater, reducing susceptibility to rainfall induced slides, but creating point-to-point contacts that increases susceptibility to earthquake induced sliding. This is a nice point. He concluded by looking at some of the very largest slides, concluding that the geomorphology before the earthquake showed depressions and dips on the big slides that indicated that they were potentially unstable. Thus, the biggest slides were considered to be predictable. I am not sure that I agree with the latter point completely (unless all slopes with these features failed, which I don't think is the case), the observations about the morphology are well-made.
The penultimate talk upon which I will comment was by Niels Hovious from Cambridge, with co-authors from Taiwan and elsewhere. Niels used the 1999 Chi-Chi earthquake in Taiwan to examine the distribution of landslides that are generated, and then to look at the production of sediment. First, Niels argues that the landslides closely map onto the distribution of ground shaking, with which I agree, but then argued that the highest landslide density occurs around the epicentre. This may well be true for Chi-Chi, but it was not for one of jis other examples (Northridge) and it was not true for Pakistan, where the highest densities are at the fault rupture. Most importantly, it is also not true for Wenchuan, where again the highest densities lie close to the surface expression of the fault rupture and not around the epicentre. Niels then showed that the density of landslides increased remarkably in the aftermath of the Chi-Chi earthquake - in the Chenyoulan ctachment that they studied the number of landslides before the earthquake was 8123, with a further 3,800 being triggered in the event. However, in the nearly ten years since a further 48,370 landslides have been triggered. However, Niels showed that the sediment concentration in the rivers is now close to base level again, suggesting that the earthquake's impacts are now reducing. This is good stuff but, given that the landscape is affected by typhoons that are exceptionally extreme events one wonders how applicable it is to other places. It seems to me that they need to work in China! An important aside is that this talk does highlight the importance of being prepared for massive sediment production in China.
The final talk that I shall briefly mention is that of Merri and his colleagues from Italy, who are using a finite difference model (FLAC3D to simulate the impacts of magma intrusion on the stability of the Stromboli volcanic edifice. The presentation was quite nice, but the model seems a little flawed. First, it assumes that the volcano is geologically homogenous - volcanoes certainly are not, and given that deposits are layed down in slope parallel layers, this heterogeneity can be a big factor in slope instability. Second, the model appears to ignore pore pressure affects (I asked whether pore pressures are being modelled - the presenter ducked the issue by talking about over-stress. Given that injections of hot material cause increases in pore pressure for certain, and these may well be very important in understanding slope stability - this is a substantial omission.
Comments welcome as ever, especially from the presenters and other attendees. Do feel free to comment if you disagree with what I have written. Finally, apologies for typos, spelling mistakes, etc. The spell check function isn't working and I don't have time to check.
Subscribe to:
Posts (Atom)