Post Mortem

So we finished the wall and decided it was important to put all our thoughts on the process and result up here.

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Joel:

The idea of creating an Earthbag wall for this assessment stemmed from the floods hitting most of Queensland earlier this year, with the initial thought of sandbags being something quite easy to come across.  Unfortunately that wasn't the case, and I spent a good 3 weeks trying to locate a good supply of the polypropylene sandbags.  This would have been easier if we were after 1000+ bags but wanting between 20-30 it just wasn't going to happen.  So we were left using Hessian bags which were never going to work as well and given all the rain we did have between our build days we ended up with some quite waterlogged bags.  We also ran into issues with the window opening and having enough materials to correctly waterproof it.  Lacking sealant and a decent window frame really hurt us here.  The final area I felt we fell short was in the 'finish' of the wall.  We had run out of money from our $100 budget.  To get render and wire mesh to properly finish off the front of the wall would have really made a difference.  This wasn't as much a structural problem as it was purely aesthetic, an aesthetic that would have really made the wall go from amateur to fantastic!

That's what didn't work as well as I would have liked, but looking at the things that worked I was really impressed with how well the team worked together to get the wall built in just two Saturday sessions.  The earthbags themselves I originally thought had no chance of sitting upright beyond about 3 courses high.  But we did a really good job in lining the bags up and shaping them to ensure every course remained level and the overall sturdiness of the earthbag section of the wall was quite impressive.  The timber frame section also came together really well with both timber we purchased from Bunnings and wood from mates / scrap.  The roof was the best 'win' for the team in regards to effort vs result.  We pretty much decided the day before we wanted to incorporate a green roof and we just got it done.

If we had the chance to do it all again, I'd want to do it will polypropylene bags,  a window frame, render and i'd want to do a full size wall with a corner.  I think this would be a true test of 'waterproofness', as we really did lack some materials by the end of it.  It was a heap of fun to put together, and I learnt a whole heap about general construction and what does and doesn't work.

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Leah:

When I heard about the Earthbag for the first time, I felt surprised and impressed at the same time. A structure of sandbags, it is easy to understand what it is and how it gets build as it sounds. But the actual building process was not easy as it seemed. We only built a little part of the wall but there was a lot of work that needed to be done. The bags were heavy when it was filled and carrying and stacking them needed a lot of energy. To build a whole building, it should take huge amount of materials, time and power.

 If I had a chance to work on Earthbag construction again, I would want to test different types of soil and content for the filling although it is already proven what is best to use. Just for an experiment, and in different parts of the world maybe there are more suitable material to suit the land.

I would also like to do some kind of rendering on the exterior wall which we didn’t get to do it this time. 

 A lot of parts in the world are working on and experimenting with Earthbags. I think it is a good idea because of its simple method of constructing and easy to get the materials, so it can be used for the land that has been destroyed by disasters and those countries which are developing.

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Shakiba:

Earth bag structure was the new way of constructing the building .It was a good experience , and qeit challenging cause it was`nt a common method  ,so we need to discuss and decide about each single step.

But I found it very useful for areas with lots of rain and natural disaster ,and I hope it helps to save lots life by making building or at least use some part of Earth bag method for their our buildings.

In this method we first discuss about our material .which kind of material are we going to use for filling our bag .Or which size of timber should we use for our frame .

The next step was thinking about safety and making it as a sustainable wall. how are we going to make the wall and roof water proofing ?,how are we suppose to support the roof?  and connection between our timber frame and Earth bags are all questions that we are faced for making the wall as perfect as we could

Also for Using Earh tbag needs to be aware of materials and power that we are going to use for it. I think preparing all of the bags  ,filling them all up , carry them too the right spot , and the kinds of material that are going to be used are all the issues that need to be considered for this project .

The Earth bag wall was simple sample of actual projects that have been done in different countries. I hope we hear lots of of progress in this project in all around the world.

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Daniel:

With the initial idea of Earthbag construction, I can’t say I was too confident we would achieve what we had planned on paper. Images of a weak and waterlogged wall were all I could think about and with winter setting in, the idea of filling bags of wet dirt and sand was not my idea of a good time.

As we wanted to steer away from traditional (third world) Earthbag construction and modernise with our own version, we set out to incorporate a timber frame for the internal wall, allowing us to clad the internal walls with something other than tradition bagging techniques. With our initial ideas having too much wastage of timber, we opted to halve the amount of timber used, not only saving cost but also saving the environment.

Filling the bags and stacking them into a wall was not a pleasurable task, however once it was completed I was quite surprised at how structurally sound it actually was. Bracing the bags to the timber frame turned out to also be a beneficial idea and improved the walls strength greatly.

Having planned, analysed and designed our wall thoroughly before commencement of construction, we managed not only to save time, but effectively and successfully put our plan into action with only minor hiccups along the way.

Constructing the wall in only two short days is a great achievement for our group and something I am quite proud of. Along the way I have learnt a great deal about environmentally friendly materials and construction methods which I hope to incorporate in future building designs. The last minute idea of a green roof turned out to be the finishing touch on our wall and also something I found very interesting to research.

All in all I am proud of our team and the achievements we have made, even if I wasn’t too sure about the whole idea in the first place. Earthbag construction is a worthy contender and has great elements with regards to sustainability, however I do believe it has a while to go before it is applied and incorporated into the modern day world we live in today.

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Bao:

Earthbags is definitely a challenge for our group. From materials to structural, it is an impressive way, unusual try.

We have learned a lot from the whole process of this project. We build up our knowledge and at the same time improved our team cooperating. It is really awesome!

It is a very impressive job. The buildings are cool in summer and warm in winter, probably the most environmentally friendly homes. They meet all building codes, are energy efficient, weather tight, and so solid they passed the most gruelling stress tests.

Although Lack of sealant, it seems all right after testing. Everything is under control :) We've done a successful job. The earth bag wall is not only sustainable, doable but also affordable, simple.

Putting It To The Test!

Now that the wall is completed, it's time to test its strength against the elements!

VIDEO TESTING

Earthbag - Rain Simulation Test: Dan hoses down the wall to simulate 
                          the affects of rain on the completed wall.

Earthbag - Rain Simulation Conclusion: Dan investigates the results of
                                         the water soaked wall.

How we intend to test the wall

We are now in stage of testing the wall if it is waterproofed or not. We have a foil covering up the timber frame and up to roofing to avoid water from getting in inside. There is also a additional plastic sheet for the roofing.

Generally, this test will be pouring water on the roof and the wall for 5 minutes as a simulation of rain. For the water that we are using, we can collect them to reuse in order to not wasting water. But it might turn out that the Earthbags soaking up the water, but we will see what happens after the experiment.

Written by Leah Oikawa and Shakiba Moradi

Build Completed - Finished Wall!

The wall is finished!  Here is a video of the completed wall and a video talking to the team about how they felt the wall construction phase went.

VIDEOS:

Earthbag - Finished Wall:  Joel has a look at the completed wall and explains the structure of the final parts.

Earthbag - Construction Final Thought: Joel asks the team how they felt the construction phase of the build went.

Now, Testing!

Build Day 02 - Video Diary

Along with the Photo diary we are keeping, we have taken a selection of short videos to explain and show in a bit of detail some of the processes involved in creating the Earthbag wall.

VIDEO DIARY:


Earthbag - Bags in Place:  Shakiba Shows off the earthbag section of the wall.

Earthbag - Timber Frame Explained:  Leah Explains the timber frame, then Bao cuts the hole for the window.

Earthbag - Structure 01:  Some of the bags were unusable at the top course of the wall so new bags were required.

Earthbag - Adding a Course:  The team is filmed adding the top layer of earthbags to the wall.

Earthbag - Window Frame:  Dan finds some wood to use for the window frame.

Earthbag - Window:  Shakiba shows us the window! Hi Bao!

Earthbag - Flashing:  Bao shows us the flashing used between the earthbags.

Case Study

Earthbag constructions are becoming populor in many places of the world. This is mostly because of environmental issues such as climate change, shortage of resources and alternative construction for those places being damaged by disasters like tsunamis. Also, economical issues can be the reason for using Earthbags.

When researching about use of Earthbag constructions around the world, I have came across with an article called "Earthbag Building in the Humid Tropics; Simple Structures", this blog will be an introduction of it. 

Overall summary of general principles;

1. Light materials are effective for cooling the building. 

2. Use as little metal and timber as possible to stay away from rust and termites.

3. Make sure to waterproof base course no less than 600mm high.

4. Consider rainwater flow on walls and have slopes.

5. Wide roof overhangs are needed to avoid strong sunlight.

6. Test materials for exterior rendering.

Soil Test

As for soil tests, there are 2 types that is need to be considered, the (soil) ball test and the bag test.

Ball test is to see the hardness of the soil by dropping 40mm size balls from 1500mm height. Depending on the results, there are several ways of use for the soil.

Bag test is to see if the bags will have any cracks or shrinkage or not after being filled.

Layouts for non-hazardous areas

There are many options for plan layouts to fit the area. But Earthbags being not stable enough to tolerate hazardous such as hurricanes, tsunamis or earthquakes, it is only suitable for non-hazardous areas. The following is the examples of layouts.

• Square outside corners / Piers at outside corners - the corner will help the structure stand for buildings without steel reinforcement.
  
  
  
  
  

• Straight walls - piers are needed for this layout.
  
  
• Circles - strong structure within 5m radius.
• Corrugated walls - straight walls coming in and out every 4m to work as support without piers.
  
  
  
  

Exterior Finishes
Wall must be protected from rain which cause erosion. Clay based material works well including lime, ash, and animal products. Oil mixture is used often as well. If possible, getting local product for free or low cost would be ideal.

Cement stucco is not recomended due to its charactaristics of absorbing water but emitting water very slowly.

Build Day 02 - Photo Diary

The second day of building the wall has come and passed.  With another afternoon hard at it with the wall we found ourselves with a completed wall!  

Knowing we had a few materials still required to finish up, Joel managed to locate some Plasterboard, Insulation Foil and Flashing, while Dan got his hands on some Perspex (for the window).  For the newly decided upon green roof we decided that the local oval would be able to help us on the day.

PHOTO DIARY:

During the down time between Build day 01 and 02 (approx 1 month) there had been some consistent rainfall some of the bags were that saturated filling new ones was required.

All the bags sitting in a pile that resembles a wall!  Window opening left, barbed wire used between the bag to hold them better int place.

With the wall put together, we put the foil onto the frame constructed the last build day.  One bracket had been put on the frame before the foil (we realized that it should have gone on after, which is why the second isn't on yet).

After the foil goes on, we cut a dirty big hole in it!.

With the earthbag front face of the wall and the frame ready we put them together with an approximate 100mm gap.

After this point we got a bit carried away and just went and finished up the rest of the wall without any progress photos (there are a few videos).  So here are some beauty shots of the finished wall. Perspective.

Front - showing the green roof (which is sitting on perspex and foil) and the fascia. Window below is perspex with some wood from a palette used as the frame.

Side - here you can see the flashing, and how we have used a continuous length of the foil to wrap around to the roof to provide a water seal.

Behind - Showing a section of the wall were we attached some plasterboard to show the intended finished look.

Video: Video's of this Build Day will be posted in a separate post shortly.

The Team and their wall.

Why should 'I' use Earthbag ?

SUSTAINABLE

Energy efficiency is a strong plus in favor of building with bags. The massive earth walls stabilize interior temperatures in hot climates. In cold and hot climates, earthbags can be filled with an insulating material, such as lava rock, pumice, vermiculite or perlite. Some builders are experimenting with rice hulls for insulation, which are often free for the taking. In general, lightweight insulating materials (such as those just mentioned) require far less labor than those of tamped earth and provide comfort through the harshest winters or hottest summers.
Earthbag buildings are sustainable since they are made primarily of earth from or near the building site. Earthbag domes do not require wood, thereby reducing pressure on our forests. Expensive concrete foundations are not required if you use gravel-filled bags. In addition, these structures are safe, quiet, nontoxic, rodent proof, and fire, hurricane and flood resistant.

SIMPLE

Earthbags are ideal for owner-builders. The necessary skills for each step of construction can be learned in a few minutes. It boils down to simply filling bags with an appropriate fill material (typically subsoil or gravel) and tamping them solid. It doesn't get much simpler than that. Also, few tools are required - shovels, buckets, garden hose. The few additional tools needed (tamper, slider) can be made cheaply and easily.
Earthbag building can be designed to suit a wide variety of climates. Since the woven polypropylene bags are virtually rot proof, earthbags are an excellent choice for underground structures: root cellars, storm shelters, bermed homes and greenhouses. In climates where wood is scarce, whole houses can be built exclusively with earthbags including the foundation and roof, as is the case for corbelled earthbag domes. Earthbags also combine well with other natural building materials that can be combined together to create hybrid structures. Straw bales can be interlocked with earthbags to build sturdy arch entryways or to add thermal mass to the interior wall of an attached sunroom. Or we may choose to use earthbags for the sunken first level of a structure and then switch to strawbale, post-and-beam, cob or adobe brick for the rest of the wall above grade to make use of an available resource or add aesthetic variety.

AFFORDABLE

Earthbag is surely one of the lowest cost, most practical building methods. It has the advantage of being able to use a wider range of filling materials. A simple earthbag dome, for example, using recycled grain bags and earth can be built for around US$100. A larger, more comfortable home can be built for around US$500-1000. It is more durable than tarps and more comfortable than tents, earthbags work perfectly since even unskilled workers can build their own shelters - all without destroying local resources.

Roof Construction

Having taken such a natural approach to our wall construction, it only seemed logical to incorporate this approach into the design of our roof. The roof can be the cause of great internal heat loss in winter and rising temperatures in summer from the penetrating sun rays.

Traditionally a conventional roof system is put in place with insulation batts to improve thermal efficiency. However our approach was to use a fairly new a currently uncommon method of Green Roofing.

Environmental Advantages of Green Roofing

Reduce Urban Heat Island Effect (UHIE):

Built up urban areas experience increased temperature during warmer months, compared to rural areas. One of the major culprits are Commercial Office buildings, whose construction materials consist largely of glass, steel and concrete – most of which have high thermal mass properties, meaning they heat up and re-radiate heat back into the atmosphere during the night.

Green roofs can help lower ambient air temperatures. Studies have shown that temperatures in built up areas can be reduced by up to 2 Degrees Celsius if just 8% of buildings have green roofs.

Storm water management:
One of the more significant problems facing Melbourne is its underground storm water infrastructure and capacity to service the city’s growing development. Green roofs reduce storm water volume and calm water flow, thus helping to ease the pressure on storm water infrastructure.

Green roofs also filter and cool water runoff. They can help prevent nitrogen, phosphorus and toxins from entering waterways.

Sketch(up)s V03! - Final Wall

Some tweaks to make the wall a bit less wide.

VERSION 03 - Final

Still retaining an air gap, but letting the earthbags do the work on their own. This allows for only 1 stud frame.

Profile depth - 400- 460mm. (will depend on how wide we want the air gap (40-100mm)

Thoughts - A reduced profile makes for a more usable wall. Think we are on the money with this now.

What now?

Well we have the Earthbags filled and the frame constructed. So we now need to identify what we still need to complete the wall, and start putting all the elements together. Still required:
- Window frame
- Window glass*
- Plasterboard
- Render*
- Wire mesh
- Flashing
- Foil

Then we need to look at the roof!...

Build Day 01 - Videos

Along with the Photo diary we are keeping, we have taken a selection of short videos to explain and show in a bit of detail some of the processes involved in creating the Earthbag wall.

VIDEO DIARY:

Earthbag - Sourcing the Soil:  Joel explains what Dan is up to loosening the dirt and gravel with a pick.

Earthbag - Filling the bags:  Dan explains what Joel and Leah are doing.



Earthbag - Stacking the bags: Joel explains how the team intends to put the earthbags together.



Earthbag - Preparing the Frame:  Dan cuts some of the timber for the frame to length.



Earthbag - Building the Frame: Shakiba nailing together the frame ready.

Frame complete and bags filled, construction to begin very soon.

Build Day 01 - Photo Diary

The group has been quite busy with life in general over the last few weeks, so getting the blog posts up haven't been highest on the list of priorities.  Unfortunately its taken almost a month to put up one of the more important posts.  Build Day 01!

With Build Day 02 quickly approaching, its important for us to show how much we have done so far.  With the design 80% locked in when we began the day (16th April) we headed to Bunnings to pick up a few items we would require to begin the build.

PHOTO DIARY:

Before any shopping could begin Joel introduced Shakiba, Leah and Bao to their first ever Bunnings Sausage Sizzle. YUM!!

Leaving Dan to scout ahead and find some of the timber we needed for the frame.

After about 30minutes we'd picked up the required timber, nails and other items we were short on and headed to Dan's house.

Some quick discussion of who would shovel and who would hold bags we started filling up our earthbags with sand and a rock/dirt combination.  Leah & Joel filling some rock/dirt bags.

Dan & Bao filling up some of the sand earthbags.

After filling up a bunch of full and half full earthbags we put them aside and started looking at our wood framing.

Dan, cutting to size some of the studs.

Frame starting to take shape with studs and top and bottom plate cut to size.

Frame pieces all cut to size and placed together, just needs some nails now.

Bao & Shakiba tapping away with the hammer.

And the finished frame.

So after Build Day 01, we have all of our earthbags filled, and our main frame created.  Build Day 02 we will focus on putting the earthbags into a wall supported by the timber frame behind.  

Video: Video's of this Build Day will be posted in a separate post shortly.

Sketch(up)s V02!

OK so I have added stud walls to this.

VERSION 02

Second attempt, added stud walls to the back to give an air gap and provide support. 

Profile depth - 500mm.

Thoughts - The profile depth is quite deep now.  Thinking that 500mm is probably a bit extreme.  Perhaps using the double stud wall to create the air gap isn't the way.  Not sure how else to achieve it though?

Sketch(up)s V01!

So before we start building, we need to do a few things:

Step 1 - Figure out what we are going to build.

Step 2 - Buy/borrow/acquire what we need to build the wall.

Step 3 - Find somewhere to build it.

Step 4 - Start building.

Step 5 - Complete build ready for testing.

For now we are looking at Step 1.

VERSION 01

First sketch(up) of the wall done with focus on keeping the wall as simple as possible. Earthbag core with render on one side and plasterboard on the other.

Profile depth - 300mm.

Thoughts - I think we need to add something at the back to ensure that if the earthbag gets wet that it doesn't transfer directly to the plasterboard.  Like a foil?  And structurally i think it will probably start to sink a bit if we don't fix it to something but what?

Bag and Fill Materials

As can be assumed by its name, there are two important things to consider when choosing Earthbag construction.

THE EARTH

Common Materials

Essentially any type of soil can be used, but knowing the makeup of soil can help achieve the best mix. Soil is made up of clay, silt, sand and gravel. Silt is extremely fine-grained, and using too much in an Earthbag structure will weaken it. Gravel, or jagged pieces of rock, is sometimes used at a foundation level in Earthbags, however most commonly used is a mixture of clay and sand. Clay serves as the glue to hold sand together, while the loose particles of sand form the majority of the Earthwall’s stability. Earthbag builders recommend a ratio of 70 percent sand to 30 percent clay due to the clay shrinking when dry and expanding when wet.

Alternative Materials

Soil: 

Found on almost any site, soil provides a cheap and easy method of constructing Earthbags. Moistened material will also compact much more effectively creating a more stable structure. Recommended is 10% moisture content in the soil. (Soil with about 10% moisture will form a ball in your hand, but shatter if dropped)


Rice Hulls:

Often discarded and thought of as a pure waste, rice hulls start their life protecting grains of rice as they grow in the field. As it turns out, these hard shells can now be used to protect the interiors of our buildings by forming structural walls with impressive fire resistance and insulation properties. They are also resistant to moisture which eliminates insects, rodents, mold, mildew, or fungus. Typically a rice hull filled earthbag will weigh one tenth of a soil filled earthbag.

Scoria (Volcanic Rock): 

Scoria is perfect for super insulated earthbag walls.  It's low cost, all natural, rot proof, fireproof, doesn't attract pests, is lightweight and easy to work with.


Perlite: 

Perlite is a generic term for naturally occuring siliceous rock that's been heated and expanded.  It can expand 4 to 20 times its original volume.  The tiny air spaces provide excellent insulation.  Perlite is a form of natural glass and is classified as chemically inert making it perfect for Earthbag building.  Perlite however can be more expensive than other materials.

Stabilisation of Organic Material

Although the above materials are suitable for most walls, there are instances where stronger, more rigid earthbags are required, such as lintels over windows and doors. If the fill material is too fine it will not compact into a solid effectively enough in certain areas. Other elements can be added such as lime or cement which allow the fine material to bond together creating a much more rigid and firm structure.

THE BAG

Typically weighing 23-45kg, Earthbags are made of either polypropylene or burlap. Although Burlap is a cheaper and more natural material, it is less durable than polypropylene. Generally, the weaker the fill material, the stronger the bag should be.

Bag size can vary, depending on manufacturer and builder preference, but the most common size for housing construction is approximately 457 mm wide and 762 mm long (usually specified as 18”x 30”).. This size has been accepted by the Earthbag community as having an optimal balance of strength and workability, based on construction experience. Bags are also available in larger dimensions such as 508 mm x 914 mm and 635 mm x 1016 mm.

Supply we demand!

We hit our first hurdle in creating our Earthbag wall only days after we began.  Finding sandbags!?  With all the recent flooding along the entire East coastline of Australia you would think they would be one of the easiest things to get a hold of.  However if you are only after 10 or so, you are hard pressed to find any!

After a lot of research and calling around we have found a supplier of burlap sandbags (thanks for the tipoff Victorian SES)  So we can begin our tests on contents.  We are still looking for a supply of polypropylene bags to get a good comparison of how each performs.

Know a supplier of Woven Polypropylene bags, please comment below and let us know!

History of Earthbag

ORIGINS

The sandbag has been used in construction of shelter, fortification and flood breaks since around the 18th century.  However the use of sandbags as Earthbags has only been adopted since around the 1970's.  Traditionally made from burlap/Hessian, commonly sandbags are now made from woven polypropylene.

One of the earliest images of an 'Earthbag' like structure is a bunker used in the Korean war.  In the picture you can see a wall structure with a door and simple window.

TIMELINE

1976 - Gernot Minke in Research Laboratory for Experimental Building at Kassel Polytechnic College in Germany began to investigate the question of how natural building materials like sand and gravel could be used for building houses without the necessity of using binders.

Gernot Minke Director of Building Research Institute, Architecture Department University of Kassel, Germany.  One of the construction methods commonly used is earthbag, first developed by Gernot Minke, using bags filled with pumice to build walls.

1978 - A prototype house using an earthquake-proof stacked-bag type of construction was built in Guatemala.

1984 - An Iranian-born architect named Nader Khalili who has popularized the notion of building permanent structures with bags filled with earthen materials. Actually his first concept was to fill the bags with moon dust! Attending a 1984 NASA symposium for brainstorming ways to build shelters on the moon.

Nader Khalili, received his architectural education in Iran, Turkey, and the United States.In 1970 he was licensed by the State of California and practiced architecture in the U.S. and around the world. Khalili was known for his innovation into the Earthbag Construction technique called super adobe.

1986 - CalEarth was founded by its director - Nader Khalili, its scope spans technical innovations published by NASA for lunar and Martian construction, to housing design and development for the world's homeless for the United Nations.

1997 - Kelly Hart first began experimenting with earth bag building.  He has built his own home using the earth bag technique.

Kelly Hart is the host of:

earthbagbuilding.com | greenhomebuilding.com | dreamgreenhomes.com

1999 - Nader Khalili was continuing the promotion of his "Super adobe" technique and eventually decided to patent the idea, which he obtained in the U. S.

2001 - Paulina Wojciechowska was the first to write an entire book on the topic of earth bag building: Building with Earth: A Guide to Flexible-Form Earth bag Construction was published in 2001. This featured some of her early experiments done at Khalili's CalEarth, along with several other case histories.

2004 - Kaki Hunter and Doni Kiffmeyer (a couple) became enamored with earthbag construction after studying with Khalili, and worked on a variety of projects, both for themselves and for clients. In 2004 they wrote and got published another book, Earthbag Building: the Tools, Tricks and Techniques , based on their particular experience.

2006 - at the request of Dr. Owen Geiger of the Geiger Research Institute of Sustainable Building, the Department of Civil and Mechanical Engineering of the U.S. Military Academy at West Point conducted several controlled and computer-monitored tests to determine the ability of polypropylene earthbags filled with sand, local soil, and rubble to withstand vertical loads.

Dr. Owen Geiger is the founder and director of the Geiger Research Institute of Sustainable Building and has two engineering degrees and a Ph.D. in Social and Economic Development. His lifelong goal is to alleviate substandard housing by using natural building materials and sustainable building methods.

2010 - Haiti was struck by a magnitude 7.0 earthquake, since then there have been a number of Earthbag structures built and currently being built.  This method has been adopted for its cost effective nature and proven resistance to earthquakes.