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.
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