Seismometers: These instruments detect and record the vibrations caused by seismic waves. The resulting data, a seismogram, allows scientists to determine the earthquake's magnitude and
Moment Magnitude Scale: A logarithmic scale used to measure the total energy released by an earthquake. Each whole number increase represents approximately 32 times more energy.
Mercalli Scale: Unlike magnitude, this scale measures the intensity or observable damage caused by an earthquake at specific locations, ranging from I (not felt) to XII (total destruction).
Volcanic Explosivity Index (VEI): A relative measure of the explosiveness of volcanic eruptions, based on the volume of products (ash, lava), eruption cloud height, and qualitative observations.
| Boundary Type | Movement | Earthquake Characteristics | Volcanic Activity |
|---|---|---|---|
| Constructive | Moving Apart | Shallow, generally lower magnitude | Frequent; runny basaltic lava |
| Destructive | Moving Together | Can be very deep and powerful | Explosive; thick viscous lava |
| Conservative | Sliding Past | Shallow but can be high magnitude | Rare to None |
| Collision | Moving Together | Broad zones of powerful earthquakes | None (no subduction/melting) |
Identify the Boundary: When presented with a map, look for the direction of plate movement. If plates are moving toward each other, expect destructive or collision features; if moving apart, look for constructive features.
Focus vs. Epicenter: Always distinguish between the two. The focus is the internal point of origin, while the epicenter is the point on the surface directly above it. Damage is usually greatest near the epicenter.
Depth Matters: Shallow-focus earthquakes (less than 70 km deep) often cause more surface damage because the seismic waves have less distance to travel and lose less energy before reaching the surface.
Check the Scale: Be careful not to confuse the Moment Magnitude Scale (energy) with the Mercalli Scale (damage/impact).
Misconception: All plate boundaries produce volcanoes. Correction: Conservative and Collision boundaries rarely produce volcanoes because there is no subduction to melt rock or thinning of the crust to allow magma to rise.
Misconception: Earthquakes only happen at plate boundaries. Correction: While most occur there, 'intraplate' earthquakes can happen due to human activity (mining, fracking) or ancient fault lines within a plate.
Misconception: A high magnitude earthquake always causes high damage. Correction: Damage depends on depth, distance from the epicenter, local geology, and building standards (measured by the Mercalli scale).
