The next time you speak to someone from Japan or California, you may wish to have a topic to shake things up a bit. Indeed, earthquakes are a lot more complex than they first seem and often happen without anyone even noticing.
Due to the fact that some forms of earthquake are predictions of other natural disasters and may result in strong aftershocks or a tsunami with corresponding flooding, having a better understanding of earthquake types and their effects can go a long way to making life safer, especially in earthquake prone zones.
Types of Earthquakes
1. Collapse Earthquakes
These may be man-made or natural in nature and tend to occur in underground areas such as caves and mines. Breaking of rock from an explosion or settling can cause a seismic disruption that results in cave-ins.
Collapse earthquakes tend to be very low magnitude, but may still result in significant property damage when the collapsed cavities are underneath structures.
2. Explosive Earthquake
A purely man-made form of earthquake, not a lot is known about how these progress. They’re created from the detonation of nuclear or chemical weapons.
First observed during nuclear weapons tests, the amount of energy released upon detonation causes massive seismic upheaval. In the case of the two atomic bombs dropped on Hiroshima and Nagasaki, the tremors were felt or detected all around the world.
Thankfully, explosive earthquakes are the one type of quake which we can prevent. Detonation of powerful bombs have many consequences, of which earthquakes are only one. What additional effects or how this form of earthquake may affect faults and other sources of natural earthquake has yet to be discovered.
3. Tectonic Earthquakes
According to the Pangaea theory, our planet once had a single supercontinent. An unknown cataclysm caused the Earth’s crust to crack and begin shifting. The pieces of crust are known as tectonic plates. A similar event occurred on Venus, only the fracturing there led to the planet’s crust flipping entirely, leaving the surface molten.
Floating on the mantle, Earth’s tectonic plates migrate slowly along the surface of the planet. As they collide, the edges are either broken up or one side forces the other underneath. This latter scenario is how mountain ranges are formed.
In both cases, the grinding of the crust cause earthquakes. Two plates may pass without causing an earthquake so long as there are no irregularities. However, there usually are irregularities that caused passing plates to catch.
Known as stick-slip behavior, the two plates continue to move despite being locked together, creating increased strain along the fault surface which continues to increase until the irregularity is broken and the plates are allowed to continue along their relative paths.
The resulting energy released from this fracture is a combination of cracking rock, frictional heating, and radiated seismic waves caused by the elastic strain. Oddly enough, this process (known as elastic rebound theory) consists almost entirely of friction-based heat and the actual fracturing. The seismic energy we equate to an earthquake is actually less than 10 percent of this total force.
Note that minor tectonic earthquakes may occur far from the plate’s edges due to the way stress translated throughout the entire plate.
4. Volcanic Earthquake
The place where tectonic plates meet give access to the molten mantle. As a result, these fissures are a major source of volcanic activity. Volcanoes are openings in the Earth’s crust where pressure buildups are released along with molten materials, preventing the planet from overheating and exploding.
They’re not always found along fault lines, but frequently mark the edge of a tectonic plate. The Ring of Fire in the Pacific is a prime example of this phenomenon.
Volcanic earthquakes are a form of tectonic earthquake where volcanic activity coincides with tectonic forces. There are actually two forms of volcanic earthquake, although only one can be noticed without untra-sensitive equipment.
The first type is the volcano-tectonic earthquake, which occurs beneath a volcano. In this variation, magma begins pushing upwards towards the lava tubes and cone of the volcano. As it does, chunks of rock are broken off and sink to the bottom to fill the void left by the rising magma. These tremors are so faint they’re only observable with special seismic equipment.
More pronounced, long-period earthquakes are caused when the magma forces its way into the surrounding rock. This results in a pressure change that’s easily measured and has a significant effect on the ecosystem.
Long-period earthquakes signal a pending eruption, as (unlike volcanic-tectonic quakes) the magma has reached a level where it begins actively trying to vent out. Detecting a long-period earthquake allows local disaster relief to enact preventative measures that can save numerous lives when the eruption comes.