Earthquake damage in Christchurch - an ironic billboard

This billboard, which predates the Darfield earthquake, was attached to a building in the Central Business District of Christchurch in New Zealand:

Do you think this is what they had in mind when they described the "open plan office with balcony access" and "cool funky office environment"?:

Images of the Darfield (Canterbury) earthquake fault rupture

Yesterday I was exceptionally fortunate to be able to spend the morning looking at the surface expression of the fault responsible for the Darfield earthquake, which hit the Canterbury plains area of New Zealand a fortnight ago.  I was kindly guided around by Russ Van Dissen of GNS Science, and the visit was organised by Chris Massey, also of GNS - so many thanks to them.  This GNS map shows the surface expression of the fault across the Canterbury Plain:

These pictures will work from east to west.

The east-most expression of the fault occurs close to the town of Rolleston, where a railway track crossed the fault.  The rails have been repaired, but the kink in the formerly straight railway track is fairly obvious.

Just around the corner a road crosses the fault as well.  Here the damage, again to the formerly straight road, is unrepaired as the fault is expressed as a broad deformation zone accommodating about 60 cm of movement:

If you are struggling to see the feature, remember that the road stretching into the distance (not the bit at the very bottom of the picture) was straight before the earthquake.  You should be able to see that from the middle of the image the road has been shifted to the right.  In this area there is little evident vertical change, bearing in mind that the surface was not perfectly flat before the earthquake.

A few kilometres to the west there is another formerly-straight road crossing the fault.  Here we see a little more lateral movement - actually about a metre.  Again, there is no vertical movement.  The movement is evident in this image - look at the alignment of the edge of the road:

Lets now jump a few more kilometres to the west, where things start to get really interesting!  Another formerly straight road is our indicator of strain - but now it is becoming difficult to believe that this happened in a single 30 second event (I can assure you it did):

Note here the highway people have resurfaced the road, so the original cracks are no longer visible.  There is a ditch running down the side of the road that also shows the deformation rather clearly:

The movement here is about 3 metres or so.  Again there is little evidence of vertical deformation.

The farmer at this site very kindly allowed us to enter his field (please do not do this without permission), where the array of cracks, and associated deformation, is astonishing.  GNS have an aerial view of the field here; below is the ground view:

The movement of the fault is evident in the power lines that cross the fault here.  The movement of the fault has put the cables under tension, meaning that the insulators (the pieces that join the cable to the pylon) are no longer hanging vertically:

A few more kilometres to the west and we are into the maximum displacement area.  Here we see over 3 metres of horizontal deformation and about 1.5 metre vertically.  This is the view from the hanging wall side - the drop down onto the footwall, and the lateral motion should be evident:

The picture below was taken on the footwall side looking back towards the fault - note the horizontal motion (the road has been patched up) and the vertical change.  Remember that this was a straight road across a flat plain before the earthquake:

The maximum deformation is recorded a little to the west again, where a road is offset by almost its entire width, indicating movement of about 4 metres.  There is some vertical deformation too, but this appears to be more of a ground roll than a true vertical movement of the hanging wall block:

Our last site is at the western end of the fault trace.  Here the surface expression of the fault is reducing, leaving a small step in the road that is quite hard to see.  The best evidence is from the power cables, some of which are now very tight (those on the upper right), whilst others are very slack (those linking to the pole on the far right).  Note how the tension cable supporting the pole on the left has also gone loose - this would have been taut before the earthquake:

It is at this point, almost perfectly on the fault, that the highest accelerations were measured.

I hope this gives a useful overview of the fault.  I am happy to answer any questions, though Geonet and GNS Science are the experts. 

Comments welcome

Images of the Meager Creek landslide in Canada

The Meager Creek landslide in British Columbia, Canada on Friday was a very large and very energetic event.  The latest estimates suggest that it had a volume of about 40 million cubic metres, making it one of the largest slides in Canada in recent decades.  Indeed, the Vancouver Sun quotes Rick Guthrie in stating that the slide travelled at 30 metres per second over a distance of 10 km.

Some good images of this event are now available, despite the smoke-filled air (the smoke is from local forest fires).  Worth a look is the Global Winnipeg gallery of the slide here, from which these images are derived:

This image shows the location at which the slide entered the main valley and then spread.  Note the way that the trees on the far valley wall have been stripped off by the flow.  This is called super-elevation and is an indication of the speed of the flow.  To generate this degree of super-elevation the flow must have been moving very quickly.

This is a view from the opposite side of the valley looking up the main flow.  Note the small lake forming upstream of the blockage.  This problem has now apparently been resolved.

This image shows the flow path of the slide down the valley.  Again, note the stripping of vegetation up the valley walls, suggesting a very considerable flow depth.

This is the upper reaches of the main slide, giving a great perspective on the magnitude of the flow.

The very best images of the slide are available on the Flickr page of DBSteers, a member of the Search and Rescue team that flew over the slide.  The images are explicitly copyrighted, so I will not reproduce them here, but I strongly recommend that you take a look.  The page is here:


http://www.flickr.com/photos/dbsteers/

Take a look - you won't regret it!

New images of the Attabad landslide

The Pamir Times has today run a pictorial article on the state of the Attabad landslide (NB see my new site for the latest monitoring data for the landslide).  A few of the images are worth reproducing here.

First, the third in the sequence of images showing the water level rise.  The first was taken by me in late February, the second (on the upper row on the right) is from about a week ago, and the final one was taken in the last few days: 

 However, this image shows just how much higher the water has to rise before the spillway is reached:

Finally, this image shows ongoing rockfall activity on the landslide scar:

Teachers First presentation on the hazards associated with the Wenchuan (Sichuan) earthquake

This is a 45 minute presentation that I gave today at a seminar for sixth form (High School) teachers on the impact of the Wenchuan (Sichuan) Earthquake in May 2008. You should be able to view or download the presentation below. Please feel free to use it as appropriate for educational purposes, but please acknowledge me.

Teachers First Talk 14th October 2009

See more presentations by Dr_Dave | Upload your own PowerPoint presentations

If the above presentation does not work you should be able to access the presentation here.

More images of the earthquake-triggered landslides in Sumatra

I thought it would be useful to provide a compilation of images of the landslides triggered by the Sumatra earthquake. ReliefWeb is reporting that over 1000 landslides were triggered: "Landslides have hindered relief efforts in some areas. The West Sumatra Satkorlak reported at least 1,000 landslide spots in Gunung Tigo highlands, located between Padang Pariaman and Agam districts. Six helicopters carrying food and medical supplies were dispatched to the highlands as landslides blocked roads." Interestingly, the landslides appear to be highly mobile, (comparatively but not very) shallow flows in deeply weathered soils. They have run out over quite large distances and in some of the images there appears to be large amounts of water present.

From here, "A highway is severely damaged by a landslide after an earthquake occured near the Padang Alai village area in Pariaman, West Sumatra province"
From Reuters, "A motorbike is covered in mud after it was unearthed in the earthquake ravaged village of Tandikat, Indonesia's West Sumatra province October 6, 2009".


From Reuters, "An aerial view of a village hit by a landslide which occurred when an earthquake hit the area in Pariaman district, West Sumatra province October 6, 2009."


From Reuters, "An aerial view of villages hit by a landslide which occurred when an earthquake hit the area in Pariaman district, West Sumatra province October 6, 2009."


From Reuters, "An aerial view of villages hit by a landslide which occurred when an earthquake hit the area in Pariaman district, West Sumatra province October 6, 2009."

From Reuters, "Indonesian soldiers and police search victims buried after a quake-triggered landslide in Jumanak in Padang Pariaman district, Indonesia, Monday, Oct. 5, 2009."

From Reuters, "An aerial view of the damage after a landslide caused by a powerful earthquake in Limo Koto Timur village in Padang , Indonesia's West Sumatra province, October 4, 2009."

Landslide round-up: Philippines, India and Italy

1. Philippines
Typhoon Parma (known as Pepeng in the Philippines) has churned its way across the northern part of Luzon in the Philippines. Fortunately, its track took it north of the most vulnerable area, which is the first bit of good news for a while:


However, early reports are that the storm has triggered some landslides:

"Rains in Benguet province set off landslides in which at least 12 people were killed, police said. The victims included seven small-scale miners who were sleeping in a shelter when they were buried by one landslide, said provincial police chief Loreto Espeneli."

And this from GMA News in the Philippines:

"At least 12 people were killed in two landslides that hit their homes in Benguet province in" the wake of typhoon “Pepeng" (Parma), a radio report said Sunday. Radio dzBB’s Benjie Liwanag Jr. reported that seven people, including a family and two guests, were killed in a landslide in Sitio Manganese in Ampukao village in Itogon town. The incident occurred at about 2 a.m., the report said. The fatalities were not immediately named, but the report said the two guests were from Ifugao province."

"On the other hand, dzBB said five members of a family were buried in their house at Beckel village in La Trinidad town Saturday night. Their bodies were recovered Sunday morning."

2. India
The very heavy rain in southern India is continuing to cause major problems. On Friday it has been reported that a landslide struck Kadwad in Uttara Kannada district in North Karnataka:

"In Kadwad village, a landslide occurred in the Madibag area on Friday afternoon, where 24 people were buried alive when the nine houses collapsed. While a minor landslide had already occurred later, the people residing between the railway track and the hillock area of the village did not expect another landslide. But, by evening boulders and mud from the hill began rolling down and seven families bore the brunt of this negligence." (note I suspect that the use of the term "negligence" here may be a mistranslation"

3. Italy
The Italian news agency ANSA is now reporting that the loss of life in the mudslides in Messina at the end of last week is 22, but that this is likely to continue to rise. There appears to be growing anger about the links between this disaster and illegal construction.

Emerging news of landslides triggered by the Sumatra earthquake

It is interesting to note that in all three of the large earthquakes upon which I have worked (1999 Taiwan, 2005 Pakistan, 2008 China), the media has tended to initially focus their coverage upon urban areas, whilst the real story has actually been in the rural hinterland. The reasons for this are complex of course, and include the power of the imagery of people buried / being rescued from buildings. However, the main reason is of course that in upland rural areas landslides kill large numbers of people whilst also destroying communications links and power infrastructure. Thus, the disaster in these areas goes unreported for some time; even the government is often unaware of this situation. As I tell my students, in this case no news is definitely bad news - if no information is coming out about these upland rural areas then the situation is probably dire.

And so it has proven once again in the Sumatra earthquakes. It appears that yesterday communications infrastructure reached the point in which aid, and of course journalists, could start to get into the upland areas, whereupon it became clear that there has been a substantial disaster during this earthquake. AP have distributed this aerial overview shot, showing a series of large flow type failures in Padang Pariaman district:

There are various reports about the impact of this landslide, which appears to have destroyed four hamlets: Pulau Aie, Lubuk Laweh, Cumanak and Gunung Tiga. Some reports suggest quite high fatality totals (>650 people). In this case local knowledge may be the most reliable, so I have taken a look at the Jakarta Post report, which says:

"Three hamlets have gone and 400 people are feared dead as the earthquake that shook West Sumatra on Wednesday produced a landslide that pushed the hamlets of Kapalo Koto, Cumanak and Lubuk Laweh into a river. An area of at least five square kilometers was buried by a huge landslide falling down from the nearby hills. A mosque which had stood 30 meters high disappeared with the hamlets. "

The higher death tolls being quoted elsewhere from this slide may be because the media are conflating estimates of the loss of life from all landslides with the losses from this single event. This is a Reuters quote from a Health Ministry Official:

"In the villages in Pariaman, we estimate about 600 people died," said Rustam Pakaya, head of the Health Ministry's crisis centre. Pariaman, closer to the epicentre, is one of the worst-affected.
In one of the villages, there's a 20-metre-high minaret, it was completely buried, there's nothing left, so I presume the whole village is buried by a 30-metre deep landslide."

It is easy to read that quote as suggesting that 600 died in a single slide, but actually he is suggesting that this might be the loss "in the villages of Pariaman".

The high loss of life in that particular landslide appears to be related to the fact that one of the villages was hosting a wedding party at the time of the landslide. There are a couple of other AP images of what is reported to be this landslide (although it could also be a different failure):


Unfortunately this landslide is certainly not the only one to have caused fatalities. The image below appears to show a different landslide (and note that in the background another failure can just be seen). Here it appears that a building has been incorporated into the slide:

Meanwhile the BBC have a report here from another village affected by landslides, including a large failure in which the reporter suggests that ten people died.

Whilst the main concern at the moment must be the emergency response, a serious medium term worry will be that the rainy season for this area starts in November. Landslides will pose a very substantive hazard during that period.

Photos and text from a visit to the Shiaolin landslide in Taiwan

The aim of this post is to present an initial interpretation of the Shiaolin landslide, based upon a couple of days of fieldwork by Chris Massey and myself over the past two days. The interpretation here, which I have written (so don't blame Chris!) should be considered to be provisional at best. At the end of the post there are some thoughts about future work. We have no intention at this stage of publishing our analysis - that is for others to do - and so are happy for others to develop the ideas presented here. If so, we would just ask for acknowledgement in any resulting publications and that you let us know what you have found.

Disclaimer - please note that this is a personal assessment based on a very provisional walk over survey. Far more work is needed to produce a definitive evaluation - this is not that! Please do not use this in any formal sense - that is not its purpose.

Geological setting
The basic geology of the landslide is an interbedded sandstone and mudstone sequence. The structure is quite complex - on the west side of the river the beds are steeply dipping, as the image below shows. The steeply dipping bedding is clearly evident on the left (west) side of the image:


Steep dips are also seen at the toe of the slope on the east side of the river near to the location of the old bridge. Further up the slope the bedding is difficult to discern, and we did not have time to get that far. There are clear planar surface visible - we interpreted these as being bedding, perhaps dipping approximately parallel to the slope, although these could have been joints. On the south edge of the landslide bedding is visible, but as the slope is steep we could not get a proper idea of the dip and dip direction. The upshot of this is that it is clear that the simple geological sections that appear to indicate a simple syncline and with failure occurring as a dipslope may not be supported by field evidence. An initial interpretation would be that there is a fault running through the valley close to the toe of the slope (probably on the right side of the image above), but this needs a great deal more detailed work.

Landslide morphology
This is an attempt to calculate some crude initial details and statistics of the landslide:

Landslide type: Rock-slide/debris-flow
Volume: 30 to 45 million cubic metres
Source area: 1.4 square kilometres
Depth (average): 20 to 30 m
Distance from crown to assumed toe (western side of river): 3,400 m
Vertical fall: 1,000 m
Angle of reach: 16°

The morphology of the slide is indicated below. To the left is the original image, to the right is the same image with annotation. The labels are meant to be indicative only - a much more robust mapping exercise would be needed to do this properly.

(Base image taken from a helicopter by Mr Chi)

The key points are as follows:

1. There are effectively two slides at this site - the main one to the south (in the centre of the image above), and the other to the north, which is a much smaller (though still very substantial) slide. The slides are divided by a bedrock ridge for essentially their entire length;
2. The main slide is a structurally controlled failure in bedrock. A large promontary high on the slope has failed and collapsed. At this point the failure is quite deep. The detachment surfaces are likely to be joints and/or bedding.
   
3. The debris from the main failure has travelled directly downslope, unfortunately through the location of the village. In this central part the landslide appears to have been highly disrupted and to have bulldozed everything in its path;
4. Most of the debris was deposited in the river channel. The river was blocked near to the old bridge, but there would also have been substantial amounts downstream. Much of this debris has been removed in the subsequent flood. It is likely that this is also the case for the remains of the village;
5. The main rockslope failure was followed by a complex series of debris flows that have deposited finer grained, matrix supported materials on top of, and on the flanks of, the main slide deposit. The flows form distinct lobes that could be mapped. In some cases there is intact vegetation associated with them;
6. The final phase of deposition was of fluvially reworked sediments.
   

The main rockslide
The main event appears to have been a catastrophic failure of a large area of the upper part of the landslide. Failure was without doubt structurally controlled, as evidenced by the surfaces visible in the scar:


This failure transitioned into a high speed failure that ran straight down the hill, across the first terrace and into the river, taking the lower terrace with it. The remains of this deposit are clear, including large boulders This one is on the river bed, hence the fine sediment and the rounding):


The deposit is clast (i.e. rock) supported, implying a rockslide mechanism, although there is some finer material, primarily derived from crushing and fragmentation. There are some highly shattered tree remains visible as well:


This part of the landslide appears to have run across the upper terrace, leaving some rockslide material behind, without eroding the terrace substantially. In places terraces gravels are still visible, overlain with rockslide material and underlain by bedrock:

The lower terrace has been mostly removed, and there is little evidence of debris from the village.This might indicate that it was incorporated into the landslide mass that was deposited in the river channel. Most of this debris has been removed by the dam break flood.

Just upstream from the old bridge (and from the village) the river channel is quite narrow. Landslide debris is found on top of the terrace on the far side of the river. Above this debris the slope has been stripped of trees and vegetation. This could be the outcome of a possible displacement wave. It appears that the main channel was blocked at this location by the landslide debris:

Subsequent debris flows
There is lots of evidence of subsequent debris flows overlying the main rockslide debris. These vary in character but all have a fine matrix with clasts. Some of these debris flows appear to contain little vegetation other than very splintered wood:

However, in other locations large amounts of vegetation are present, some of it still quite green with foliage:


On the margins of the slide these flows have bifurcated, leaving areas with in situ vegetation in place. In some cases there is evidence that rocks have travelled over these vegetated surfaces, leaving blocks caught in tree remains:


The dam break and flood
We did not really spend much time examining the remains of the subsequent flood. However, there are two houses left standing from the southern edge of the village. These show the after effects of the flood very clearly, even though the river was very wide at this point:

Downstream the effects are severe, with damage to bridges, embankments and even the river bed. For example, the central spans of this bridge have been washed away:

Future studies
The text here is no substitute for a detailed examination of this site. We are sure that this is being undertaken by our colleagues in Taiwan. For example, to understand this landslide properly there is a need for a full geological and geomorphological mapping exercise, including a structural geology assessment. It would be great to see an attempt to reconstruct the multiple events by mapping out the different lobes. The landslide should also have been recorded on the seismometer network, so an analysis of this might help to constrain what happened, and indeed to allow the event to be tied to the rainfall events that have been recorded from this storm. An interpretation of stallite and aerial imagery from before the slide would also be good. There is a need to reconstruct the terrain before and after the slide - using aerial images from before and ideally LIDAR data from the present. This would allow a calculation of the mass balances of the slide and of the geometry. Later on stability assessment based upon geotechnical testing could be undertaken, and ultimately even full modelling (although it is not clear what purpose this would serve). We are sure that all of the above is planned or under way (and a lot more as well) - the results will be very interesting.

A final disclaimer
All of the above is based on no more that a brief walk over survey. None of what is written here should be considered to be authorative or a substitute for a detailed survey. What is written here is the personal opinion of the author only and should not be used formally in any way.

Comments and thoughts welcome of course!

After Morakot

A new blog, called After Morakot, has been started to highlight the impact of Typhoon Morakot in Taiwan. The most recent post describes a journey by the author into the village of Namsia, which was one of the most seriously affected villages in the typhoon. The images and the commentary are remarkable.

I reproduce here two of the images, of the village of Mintsu - there are many more on the blog:

A small collection of interesting landslide images

A quick post today - I thought I'd post a small selection of impressive landslide images that I have come across recently:

Ongoing rockslide in India, from here.

Landslides resulting from deforestation in Taraza, Antioquia, Colombia, from here.

A long runout landslide from Sichuan in China, from here.

After effects of a landslide on the island of Ibiza in Spain, from here.