# Physical Processes

## Processes at Plate Margins

Earthquake Processes:

Seismic Waves:

When the strength of the rocks under pressure is overcome, they fracture along cracks called faults sending a series of seismic shockwaves to the surface.

The breaking point is called the hypocentre of the earthquake. The epicenter is the point on the surface directly above the focus. The distance between the hypocentre and the epicentre is called the focal depth. The epicenter commonly experiences the most severe ground shaking. The shaking then becomes progressively less severe with distance from the epicentre, like ripples spreading outwards in a pond.

Earthquake tremors usually last for less than a minute followed by several weeks of aftershocks as the crust settles.

1. Volcanic Processes
2. ﻿These are two different types of volcano. Their lava is very different, as is their eruption and shape. The table demonstrates this.

Describe the anatomy of an earthquake
Your answer should include: Fault / epicentre / focus / pressure / energy / seismic waves
Examine the difference between the Richter and Mercalli scales. Which is most accurate in measuring earthquakes?
Your answer should include: Logarithmic / numerical / observed effects / scale

## Impact of Processes

Initial impact:

The impact of earthquakes depends on 3 factors:

1. Magnitude of the earthquake.

2. The distance from the epicentre.

3. Local geological conditions.

## Magnitude of Hazards

Richter Scale:

The magnitude of an earthquake is determined from the logarithm of the amplitude of waves recorded by seismographs. Adjustments are included for the variation in the distance between the various seismographs and the epicenter of the earthquakes. On the Richter Scale, magnitude is expressed in whole numbers and decimal fractions.

Because of the__ logarithmic basis __of the scale, each whole number increase in magnitude represents a tenfold increase in measured amplitude; as an estimate of energy, each whole number step in the magnitude scale corresponds to the release of about 31 times more energy than the amount associated with the preceding whole number value.

Mercalli Scale:

Although numerous intensity scales have been developed over the last several hundred years to evaluate the effects of earthquakes, the one currently used in the United States is the Modified Mercalli (MM) Intensity Scale. This scale, composed of increasing levels of intensity that range from imperceptible shaking to catastrophic destruction, is designated by Roman numerals. It does not have a mathematical basis; instead it is an arbitrary ranking based on __observed effects. __