7) Earthquake Hazards - Quito and Las Sierras

Las Sierras

The types of earthquake in this region and the hazards they present can be entirely different from the coastal areas. However as I'm sure you will see, there are always similar hazards when it comes to earthquakes.

There are a variety of different sources for earthquakes in this region. Firstly this area is still affected by the subduction of the Nazca plate. However the effects of these earthquakes are minimised greatly. Firstly any earthquakes that occurs beneath the Andes have a long way to travel through the hard, crystalline volcanic rock until they reach the surface. As a consequence of this, the earthquakes from this source that hit these areas are usually very deep and have very high attenuation (see entry 3) rates, so they do not pose that much of an issue. Even for any massive earthquakes that strike the coastal regions, the waves produced still need to travel a long distance and through solid rock.

The greatest hazard in this region comes from the complex plate boundary with the mini North Andean plate (see entry 1 for more info). This boundary has created many potentially earthquake producing faults. Although these faults aren't large or can produce particularly large earthquakes (6.5M are usually the largest you would find) they are close to the surface, meaning the surface waves do not lose a lot of energy and can potentially be more damaging than a much larger but deeper earthquake. The majority of these faults are not as well understood as the subduction zone is, so prediction is much harder. Earthquakes from these faults could strike anywhere from Quito to Riobamba (Bell 2016).

Initial Hazards

For these two 'hazard' type sections, I will solely focus on this unusual plate boundary as the subduction type earthquakes will be briefly discussed later on. However most of if not all the initial hazards mentioned for the coastal areas apply here.
The hazards these 'intra-plate' earthquakes create will be much more acute than most of the earthquakes down by the coast. As mentioned the shallow depth of the earthquakes will result in much larger surface waves (Bell 2016). This will destroy many buildings, roads and other parts of the infrastructure that cannot deal with the strong earth movements.
This is a real threat in this region, for example Quito has a complex series of faults these can be seen to be the narrow ridges that run through the city that could trigger a potentially devastating earthquake. Also Quito is based on top of weaker rock than the surrounding volcanic rock, so the wave movement will be amplified if the earthquake comes from one of these faults.
Of course landslides are an obvious hazard in this mountainous, steep sided region. As mentioned in the previous entry, always be aware of potentially hazardous slopes in your area. One factor in these regions that could affect landslides is volcanism. Volcanic activity can weaken the sides of the volcano slopes (eg loose material deposited on the side, lava pushing at the sides of the mountain etc.) or even ash fall from eruptions can produce a weak, loosely packed layer of soil that could come loose.

Secondary Hazards

Although there is no tsunami risk, the hazards are much the same as the coastal regions. The majority of the damage done by these earthquakes will be done within the event, the hazards afterwards mostly come from damage control. There will be lacks in supply for the most simple things such as water, food and medicine. Also if Quito is near (or on) the epicentre the government will need to reestablish itself elsewhere before it can run itself again. There will be emergency protocols in place in case of this so there is nothing to worry about.

#Quaketips8
Stick together in any time of crisis. A community is stronger if it works together, and may make any disaster seem just a little better.

6) Earthquake Hazards - La Costa

Earthquake Producing Factors

As we have discussed, the largest earthquakes occur where the Nazca plate subducts underneath the South American plate. This means the areas most at risk from these earthquakes are generally along the coast, as these areas are nearest the plate boundary. The process that triggers earthquakes here has been explained in previous entries. The earthquakes along this boundary are deeper in the earth but can have very high magnitudes (can reach up to 8.8M as an earthquake in 1906 did, the effects of which still affects earthquake production today (https://earthquake.usgs.gov/earthquakes/world/events/1906_01_31.php).

However there appears to be a large gap in earthquake activity in the central Esmereldas and the Santo Domingo de los Tsachilas regions.This is due to a change in the subduction, caused by the Carnegie ocean ridge (look at the map in the previous entry). See the lighter blue area of ocean off the coast of Manabi? This is an ocean ridge, created through volcanic activity around the Galapagos islands and slowly moved towards the coast in a conveyor belt kind of system (subduction of the Nazca plate pulls the ridge towards the coast). This results in this part of the plate not subducting normally. As the plate along the ridge is thicker, it is harder to subduct beneath the South American plate, so it almost floats along beneath for much further than the other parts of the Nazca plate, until it finally fully sinks into the mantle somewhere after the Andes. This results in an earthquake gap in the mentioned regions as earthquakes only tend to occur when the Nazca plate first hits the South American plate, and then when it subducts. These two points are spread apart due to the slower subduction of the plate here. However it seems when this ridge first does hit the South American plate, more earthquakes are produced as the ridge is harder to subduct so it needs to be forced to sink.

Hazards

The hazards of the earthquakes present here are numerous. First lets talk about the initial impacts of an earthquake in this region. Earthquakes here tend to occur at around 20km beneath the surface, due to the subduction process. This means the surface waves produced will not be as dangerous as a shallower earthquake as they need to travel further. However as these earthquakes are generally more powerful, this does not really affect the hazards in a large event (7.8M and above).

Immediate Effects

As we have talked about, it is these body waves that do the most damage. The usual hazards are associated with this: buildings not designed to withstand strong earth movement will buckle and collapse, roads will be torn apart by the combination of movements from Love waves and Rayleigh waves (see entry 2) and electrical power lines and pipes will collapse or break, cutting services in the area.

However there are other hazards in an earthquake that may not instantly come to mind. Firstly a process called liquefaction. 

This can be explained by thinking about sand on a beach. Let's say you are standing still in wet sand, the sand remains solid and you can stand on it without sinking in. However if you begin to stomp or walk on the spot, you move the grains of sand about which allows water to seep through. As a result the sand acts more like a liquid and you begin to sink into it (try this yourself next time you are on a beach if you'd like). The same process can be applied when an earthquake hits. If there is water beneath sandy or loose soil, the shaking will move the soil about and water will seep through and anything that is heavy enough will sink into it. This can affect building foundations to cars. This image is a good visual aid: 

(sourced from Stuff.co.nz)

Unfortunately, a large portion of the coastal regions (especially around Guayaquil) have soils and high water tables (level of water beneath the ground) that could create conditions to allow liquefaction.

Another hazard that could occur during (and after) an earthquake is landslides. I am sure you are all familiar with landslides being a major issue, especially in the rainy season. However, as the ground is violently shook during an earthquake landslides could get triggered. This is an issue not only from large earthquakes but also small ones. Landslides could be triggered by slopes that are already weakened or under threat from landslides only need a little nudge from seismic activity to trigger them. The threat of landslides created by earthquakes is increased during times of rain, where the soil is already soaked through and has very little grip. 

Secondary effects

These effects are either effects that are not immediately obvious or occurring during the earthquake, or effects that occur after all the physical hazards have happened. Probably the most widespread and dangerous hazard for these regions are tsunamis. 

For those of you who don't know, a tsunami is an earthquake triggered wave. Think of the puddle analogy, as you drop a pebble into water it displaces the liquid around it (as in moves the water in order to make space for itself), creating a wave. The same is for earthquakes. As the plate moves suddenly in an earthquake, it displaces the water around it, creating a wave. This wave is dependent on the moment magnitude (see previous entry), and can reach heights of over 20m for large earthquakes. This presents a dangerous hazard for coastal towns such as La Libertad, Manta and Guayaquil. Large scale evacuation measures need to be in place for these towns as even with a 5m high tsunami could inundate most of the towns adjacent to the earthquake, causing massive damage and potentially loss of life.

#Quaketips4

If you live by the coast and you feel a medium/strong earthquake, you may want to reach higher ground as soon as possible a precaution, even if there has been no official warning. It may just save your life.

As mentioned, landslides also come under this category so always be wary of slopes that have been known to have them as the earthquake may weaken the slope even further.

It is not only physical hazards that could spell disaster but also the after-effects.

Some examples of this are buildings that have been weakened during the earthquake but are still standing still do have the potential to collapse hours or even days after the event.

#Quaketips5

Do not attempt to enter any large or clearly weakened structures after an earthquake until you are told it is safe to do so. This may seem obvious but these buildings could be your house, resist the temptation to retrieve valuable items until you know for sure it is safe.

Another hazard the damaged infrastructure. This is the same for most areas damaged by an earthquake; lack or no available drinking water, lack of sanitary facilities, lack of supplies (e.g. food) etc. However in these regions disease carried by mosquitoes can become an issue, for example the Zika virus. The earthquake may leave behind large amounts of standing water which are perfect mosquito breeding grounds.

#Quaketips6

Always have a mosquito net, even in a rushed evacuation always pack these nets as there may not be any form of protection from mosquitoes available after the event for some time.

5) Earthquake Hazards - Affected Areas

Now we understand all the processes that go into forming, sizing and predicting earthquake hazards, we can look at the hazards they present to Ecuador. These hazards vary from immediate hazards to hazards that occur after the earthquake. I will dedicate a separate entry for different regions, for both immediate hazards and hazards after the event.

Areas affected by Earthquakes

Before we look at hazards, we should look at what areas are under the most threat. From a survey taken from the USGS (http://earthquake.usgs.gov/earthquakes/search/), the ‘ANSS comprehensive catalogue’ of earthquakes has taken note of every earthquake in Ecuador since 2000 to July 2016. If we plot the location of each earthquake onto google earth, we see where roughly the areas prone to earthquakes are:

Each icon represents where an earthquake has struck. Magnitude is not shown here but the larger earthquakes occurred along the coast.

There are two general areas which contain the most earthquakes, La Costa and Las Sierras.

4) Hazard Assessment

In this entry, I will discuss how we can predict earthquakes of certain magnitude, type and also predict how hazardous the earthquake is by region. I am sure this section will be of interest to most people here as it covers how often earthquakes can and will strike in Ecuador and how these earthquakes may be more severe in certain regions.

There are two ways of predicting hazard for an earthquake; time-independent hazard and time-dependant hazard. This will split this entry into these two sections.

Time Independent Factors

This essentially means that this prediction gives the hazard of an earthquake striking at any given time and does not base the prediction on if previous events might set up the next ‘quake (these processes will be explained later). There are four major parts to these predictions:

• 1.       Sources
• 2.       Recurrence
• 3.       Attenuation 
• 4.       Probability of Exceedance ( this is more simple than it sounds don't worry)

I will start by explaining sources. Sources are areas that are known or could potentially produce earthquakes, for example at the subduction zone off the coast or the boundary between the North Andean plate and the Nazca plate. The subduction of the oceanic plate is the cause of the most frequent and biggest earthquakes.

Secondly recurrence. Simply put this is how often an earthquake of a certain magnitude will strike per given time (e.g. per day/ year / decade). So, for example, a small earthquake of magnitude 4.5 will strike in Ecuador probably twice a year. So if earthquakes of 4.5 magnitude are measured for let’s say 50 years with two striking every year on average, we could say it had a recurrence probability (likelihood) of two 4.5M earthquakes per year. From this data we can predict the recurrence of larger earthquakes through a relationship called the Gutenburg-Richter relationship.  Although the maths for this may be a little complex, this relationship can give us a value for how often an earthquake of any magnitude will strike in an area. For anyone interested and relatively good at maths, this website will give further information. http://www.eq.ccu.edu.tw/lab/lab105/public_html/members/master/93/GR.pdf.

Thirdly the attenuation. What this means is how much of the energy of the earthquake will reduce with distance. If we think back to our dropping a pebble into water analogy, the height of the wave after you drop the pebble will decrease as it moves from the impact of the pebble (the wave source). The same idea applies for earthquakes, the further from its source you go the weaker the wave will be.  This is the reason why body waves do not pose much threat. Body waves travel along the surface but also travel down into the earth in all directions.Therefore their energy is used more quickly than surface waves which just travel along the surface. Now with attenuation explained, we can see how this can be applied to hazard prediction. In simple terms, if we can predict how often a large earthquake can strike then we can also predict the area this earthquake will reach to and impact when it does strike.

Fourthly and finally there is the probability of exceedance. This is simply all the previous factors combined into one. It is how likely the ground is going to shake or move at any certain place. This probability is one of the most important factors into planning for earthquakes as it allows you to clearly see where the areas are that are most at risk from all of these factors. This information can be used for damage prevention in the areas most under risk, such as deciding where to put buildings or earthquake drills in schools. This type of hazard assessment is also good for using on seismic hazard maps, for example this is one for Ecuador.

(Bell, University of Edinburgh 2016)

The high hazard in the coastal region is obviously to do with the subduction on the Nazca plate. However the hazard in the mountains around Quito and Riobamba is due to the faulting of the minor plate, as mentioned in the first post.

One factor that can increase the hazard in the area is the rock on which you stand on (known as the bedrock). If the bedrock is strong and thick -lavas and other volcanic rocks are good examples of these- then the energy of the wave will be used up quicker as it tries to bend the rock. However, a weaker bedrock (for example river deposits or sandstone) can bend much easier due to their structure. The images of the recent earthquake in early 2016 show how the material below the surface can badly affect the impact of surface waves. For example in the photo below, look at the material below the road; it is mostly soft sands and mud which can easily be warped by surface waves.

(Sourced from http://www.independent.co.uk/news/world/americas/ecuador-earthquake-today-61-magnitude-quake-coast-days-deadly-tremor-a6992366.html)

Time Dependent Factors 

Unlike time independent factors, these factors are dependent of previous activity in the region. What this means is that the activities of other earthquakes (such as large earthquakes). The processes of working out these are a bit more complicated so I won't cover them in this blog but I'll explain them in general. For those of you who are still interested and quite good at maths, I recommend you read http://www.nat-hazards-earth-syst-sci.net/16/2177/2016/nhess-16-2177-2016.pdf as it gives a much more detailed description of these factors.

These factors are dependent on three parts:

• Time and slip predictable models
• Earthquake triggering
• Coulomb stress transfer

Forget the complicated names again as they are just jargon. 

Firstly the time and slip predictable models. What this in essence means is that with increase in time, the chance of the crust buckling and faulting increases.This is similar to coiling a spring very slowly but at a certain speed, after a predictable amount of time the stress in the spring will give way and it shoots back into it's original position. However this factor only works in areas where we know the average time between this stress build up and release in the earth, and unfortunately not every earthquake producing area has this predictability. Where this method does work, we can predict the recurrence of earthquakes quite successfully.

Secondly earthquake triggering. This is quite easy to understand. Essentially, when a large earthquake hits an area it weakens the crust all around it. This allows for smaller earthquakes to occur as the rock is weaker, it is more likely to slip and fault. It is this process that creates aftershocks, the mini-earthquakes after a major earthquake. It can work the other way round, where a smaller earthquake can weaken the rock just enough to be able to create a much larger, more dangerous earthquake.

Thirdly and finally we have Coulomb stress transfer. This is very similar to earthquake triggering. What this means is as the plate that creates an earthquake suddenly moves (think of the spring being released), the surrounding rocks and earth move with it and become part of the earthquake process. However there are parts in the crust that are adjacent to this movement but do not move, this part of the crust as a result becomes weakened. The part of crust that does not move has had the 'stress' transferred to it, and is more likely to fault and create another earthquake.

These processes are much more useful when they can be applied. They can be used along with the time independent factors to give an even more accurate prediction of the earthquake probability. Although the chances of an earthquake striking at any second are still very very low (around less the 1% chance), the time dependent factors can give an idea of how high an alert the area should be on, leading to stocking up supplies and temporary evacuations of vulnerable buildings (eg old churches, schools etc).

#Quaketips 3

Always be prepared if you live in an earthquake prone area. Check how strong your foundations are. Just a couple changes or fixes to the strength of it could save your house in a minor earthquake.

3) Measuring Earthquakes

For this entry, we discuss how earthquakes can be measured using the Richter scale and also how you can be involved with measuring an earthquake.

The general question for this entry is: How do you measure an earthquake?

For the majority of measuring methods, we must use a seismograph. A seismograph is essentially an ink pen on a ball which is attached to the ground by either springs or wire. As the land moves with the earthquake, the ball will sway and ink draws out the shape and direction of ground movement. The paper produced by seismographs look something like this:

 (Sourced from http://earthquake.usgs.gov/learning/kids/coloring/seismograph.gif)

Once the seismograph has drawn a line, the result will usually look like this:

(Sourced from http://www.geo.mtu.edu/UPSeis/reading.html)

If you read the previous entry, you will be familiar with each type of wave. As we can see, the smaller body waves arrive first and then the larger surface waves. The timing between each wave is usually quite short but intense (ie 5/120 seconds, the duration of the earthquake), as we are concerned with earthquakes that are from Ecuador.

Now with this explained, we can talk about the Richter scale.

You probably have heard of the Richter scale when measuring earthquakes. This is simply a measure of the maximum surface wave height (see diagram) measured against the distance from the source of that earthquake. This done by using the time between the arrival of the first P-wave and the first S-wave is used to work out this distance by using the graph.  This will give us a value of 1-10, the numbers we are used to seeing when talking about earthquake magnitude. This scale is logarithmic, which in essence means a magnitude 7 earthquake is ten times stronger than one of 6, which is ten times bigger than one of 5 etc. A way to think of it is like when a doctor asked you to rate your pain on a scale of 1- 10 if you are more than 6 then take cover as your insides must be collapsing.
A Richter Scale diagram looks like this:

(Source http://www.bgs.ac.uk/discoveringGeology/hazards/earthquakes/MeasuringQuakes.html) 
As we can see from this diagram, the amplitude is the measure of the highest recorded wave (in this case 20mm) measured against the distance (or the S-P wave lag time of 25 seconds). These results are measured in a straight line from each other and from this we can clearly see it this is a magnitude 5 earthquake.
However there is are problems with this method. The main problem with using the Richter scale is that it becomes inaccurate at high magnitudes. Also as seismographs are a relatively recent invention, there are no records of historical earthquakes using this method (ie there are no Richter scale records of earthquakes before the 20th century).

Nowadays there is more complicated and more accurate method of measuring the size of an earthquake of higher magnitude; The moment magnitude. To do this out you need to work out the seismic moment. The seismic moment of an earthquake is the combination of how much the land is moved by the earthquake or the displacement of land, the area that was moved and the strength/stiffness of rocks in the affected area (for example you can get weaker rocks, like sandstone that are not very stiff). The process of working out the moment magnitude from this are far too complicated to be covered in this blog but if you are interested click this link https://earthquake.usgs.gov/learn/topics/measure.php.

Now, the method which you can be a part of and help scientists work out the magnitude/ severity of the earthquake is the Mercalli Scale. Don’t be intimidated by the name, it is rather simple. It is a scale that is simply someone's perception of how intense the earthquake is. It is measured from I (one) to XII (12). This figure should explain it better;

(Taken from http://dnr.mo.gov/geology/geosrv/geores/richt_mercali_relation.htm)
This is a good short term method of measuring an earthquake. However, it can be a bad measurement of an earthquake's size. For example the scale is from a person’s point of view, so it might change from person to person.

#Quaketips 2

Now, you can be involved when an earthquake strikes your area. By using the USGS website, if you feel any unusual ground shaking or obvious seismic activity in your area you can report it online and become a part of the research and damage control process, and help your country. The website will only give you a few simple questions about the earthquake. https://earthquake.usgs.gov/.

2) Wave Types

In this blog, unlike the last one, we will touch on the hazards of earthquakes.

One of the most important features about earthquakes are the ‘waves’ they produce. Similar to dropping a pebble into a pool of water, an earthquake is a series of waves that move the ground like the pebble moves the water into an up and down motion. There are two types of waves that earthquakes make; body waves and surface waves. 

If we continue with the pebble into water analogy, the body wave would be the relatively small ripple underwater caused by the pebble. As the names suggest, body-waves travel through the ‘body’ of the earth (they can travel all the way through the earth to the other side of the globe). There are two types of body waves, S-waves and P-waves. The S waves are more familiar as they move in the same way as a normal wave does, in an up and down motion. P-waves work differently as they pull the rock together and then apart again. This diagram should explain: 

  

(Source http://www.earth.northwestern.edu/individ/seth/202/lectures/Seismology/p&swaves.htm)

These waves, although they can be powerful and they are faster than surface waves, are generally not as hazardous. It is surface waves that cause the majority of the damage from an earthquake. 

Using our pebble into water analogy, the surface waves would be the relatively large ripple on the surface of the water. These waves, as the name also might show, travel along the surface of the earth. Although they cannot travel very fast, these waves have far greater strength than body waves and cause far more damage.

There are two types of these surface waves; Love Waves and Rayleigh Waves. Love waves move the ground from side to side, just think of the pictures of farmer’s fences that don’t match up after an earthquake. For Rayleigh waves, the motion is very similar to that of a wave at sea, it moves up and down in a rolling motion.

It is important to understand that the body waves arrive before the surface waves as they travel faster. In it’s simplest form, the thunder comes before the lightning. If you feel the ground starting to shake moderately you now understand the most dangerous waves are yet to come. 

#Quaketips1

There is always an important notion with earthquake hazards; earthquakes don’t kill people, buildings do.

1) Plate Tectonics

This part of the blog may seem boring or irrelevant but for those who are genuinely interested into what causes these earthquakes, I strongly encourage you to read on. For those just wanting to know about the hazards, that is further up the blog.

Although it may seem obvious, it is good to sometimes ask ‘what is an earthquake?’. To understand this, we must first understand plate tectonics. As I am sure most of you are familiar with, plate tectonics describes the process of movement of solid sections of the earth’s surface. These plates all interact with each other, much like different cheeses on top of hot pizza or ice cubes in a glass of water.

Sometimes one plate can sink beneath another one. This is called a subduction zone, where one, denser (heavier per m³) plate gradually sinks beneath another. The most relevant example of this is when an oceanic crust is subducted (sinks beneath) a continental crust. This is called a cnvergent plate boundary, as the plates move into each other In this situation, as the oceanic plate sinks it forms an ocean trench. These trenches can be many kilometres deep. This is relevant to Ecuador as just 100km off the coast there is a convergent plate boundary and a trench. The two plates interacting here are the Pacific plate (the ocean bit) and the Nazca plate (the land bit). These zones are usually associated with seismic activity, which is why this blog exists.

Now with the boring (albeit necessary) background out of the way, we can answer the first question: What is an earthquake?

An earthquake an be compared to a coiled spring, both have the common point of stress. When the spring is released a huge amount of energy is passed through it. We can use this analogy in close relation to Ecuador, an earthquake in Ecuador is created when the stress is built up through friction; as the subducted plate passes the other plate it builds up stress until it is suddenly released.There are other causes of stress in the crust, however it is this process that creates the largest earthquakes.

The diagram will hopefully better explain the idea of a subduction zone. The lithosphere means the surface of the earth that is solid, the asthenosphere means the part that has melted.

(Sourced from http://study.com/academy/lesson/subduction-zone-definition-location-example.html)

However, unfortunately for Ecuador this is not the only plate movements and interactions. In the northern parts of the Andes, there is a smaller plate that is not as obvious as the Nazca or South American plates. It is called the North Andean Plate. This plate has a boundary (the edge of a plate, where plate interactions occur) with the Nazca plate that runs through the high valleys in the Andean parts of Ecuador around Quito and Riobamba. This is what forms the large mid-Andean valley where these two cities are. This boundary has created numerous and complex faults. A fault is a part of the earth's surface that has cracked into two or more obvious sides due to earth movements. These faults run down the spine of the Andean regions of Ecuador and finish in the Gulf of Guayaquil. The nature of this plate boundary and these faults is still under research and quite complex, so I will not cover them in much detail.

Introduction to the Blog

Introduction to our Blog

I welcome any and all viewers to my blog from Ecuador and beyond! The purpose of this blog is simple, to inform anyone interested in the science behind earthquakes occurring in Ecuador and how to prepare for if (and when) they strike.

The first posts of this blog will be explaining the geology behind earthquakes in Ecuador and hazards associated with them. 

I hope you enjoy the blog and remember, be prepared!