Environmental Hazards - Earthquakes Flashcards
How do earthquakes form at conservative plate boundaries
Conservative plate margins form where two tectonic plates slide past each other. They can either be moving in the same direction at different rates, or in the opposite direction from each other. The plates often stick together. Pressure builds up and eventually they snap apart creating an earthquake
Explain how earthquakes form at diverging plate boundaries
Tension forms when two plates move apart. They may suddenly break apart creating seismic waves that radiate outwards and upwards towards the Earth’s surface. This creates an earthquake
How can gas detectors be used to predict earthquakes
Gas detectors - gases are often emitted prior to earthquakes, gas detectors can be used to detect changes in gases in earthquake prone areas
How can seismographs predict an earthquake
These pieces of equipment are very sensitive to movements in the Earth’s crust. Often prior to a large earthquake there will be a series of tremors that increase in frequency and strength. Seismographs can detect and measure these tremors
How can earthquake history predict earthquakes
Scientists can predict earthquakes by looking at the history of them along fault lines. They can detect where the pressure is building along fault lines. Looking at other earthquakes can also help to predict them as often one earthquake can trigger another earthquake further along a fault line or plate boundary
How can animal behavior predict an earthquake
Some animal behaviour can tell us if an earthquake is likely to occur. For example the common toad is able to detect seismic activity several days prior to an earthquake. An article published by the Journal of Zoology in 2010 suggested that 5 days prior to an earthquake male toads would abandon their breeding sites. It’s believed that toads can detect the gases that are often released before an earthquake. Birds go extremely quiet and animals such as dogs, horse and cats will become agitated prior to an earthquake
How does an earthquake form at converging plate boundaries - where two crustal plates meet -
At some plate margins two crustual plates meet. The plates have the same density, so they push against each other. The impact created when the plates collide form earthquakes.
How do earthquakes form at convergent plate boundaries - where oceanic and crustal plates meet -
The heavier oceanic plate collides with the lighter continental plate. Due to the difference in densities, the heavier oceanic plate is dragged down underneath the lighter continental plate. These plates have rough jagged edges and often stick together, when this happens pressure will build up. When the pressure becomes too much the plates will snap apart. Seismic waves travel outwards from the point underground where the plates have snapped apart, this point is known as the focus. The seismic waves spread upwards and outwards. The point directly above the focus on the earth’s surface is called the epicentre of the volcano, this is where the earthquake will be strongest
How should individuals prepare for an earthquake
- Have an emergency kit (similar items to a volcanic emergency kit)
- Tall items of furniture should be anchored to floors or walls with strong volts to prevent them from falling and injuring someone and causing more damage
- Heavy items, glassware and other breakable items should be stored in floor level cupboards as they could cause head injuries and facial lacerations if they fall out during or after an earthquake
- People should learn how to cut gas, electricity and water supplies in homes and workplaces. Because fractured gas pipes and falling electricity cables can create explosions and fires
- Households should create an evacuation plan and practise the Drop, Cover and Hold
Drop - to the floor so you don’t fall over and get injured
Cover - you should seek cover under a sturdy desk or table, to protect yourself from falling objects
Hold - you should hold onto an anchored item
How can the government prepare for an earthquake
Early warning systems - these provide citizens to prepare or evacuate for an earthquake. The government should have early warning apps the public can download and in earthquake prone areas loudspeakers should be installed so that if an earthquake occurs it will broadcast announcements with instructions on when and where the people should evacuate
Building codes - The government controls building codes. These building codes ensure modern bridges, buildings and roads are designed to withstand earthquakes. They also ensure that older structures have adaptations that will reduce the effects of earthquakes
Providing advice - to the public on evacuation routes and emergency rest centres. They should also encourage the public to have an emergency kit, an evacuation plan, have tall items of furniture anchored to the floor and walls and where to store breakable items
How can buildings be made earthquake proof
Shear walls in buildings reduce the risk of wall collapse. Shear walls can resist lateral movement during earthquakes, while supporting vertical weight. This prevents buildings from collapsing
Cross braces attach to a building’s frame by bracing stud to stud in an X pattern to increase load capacity. The use of cross-bracing keeps buildings stable against high winds and seismic activity.
Using damping methods such as vibrational control devices. This method involves placing dampers at each level of a building between columns and beams. Each damper consists of piston heads inside a cylinder filled with silicone oil. When an earthquake occurs, the building transfers the vibrational energy into the pistons, which push against the oil. The energy is then transformed into heat, dissipating the force of the vibrations.
How to earthquakes cause tsunamis
They form where seawater is displaced by the movement of a plate
boundary/fault line, under the ocean. This creates waves. Out in the open sea, the waves are not particularly large. However, as the sea shallows
near the coastline the waves slow down and compress. This causes the height of the waves to increase.
