Problem 23 - An Introduction to Physical Science

Question

What is measured by the Richter scale? What is measured by the Mercalli scale?

Step-by-Step Solution

Answer

The Richter scale measures earthquake magnitude, while the Mercalli scale measures earthquake intensity.

Step 1: Understanding the Richter Scale

The Richter scale is a logarithmic scale used to measure the magnitude of an earthquake. It quantifies the energy released at the source of the earthquake, providing a single value that represents the earthquake's overall size.

Step 2: Understanding the Mercalli Scale

The Mercalli scale is a qualitative scale used to measure the intensity of an earthquake. It assesses the event's effects on people, buildings, and the Earth's surface, with readings ranging from I (not felt) to XII (total destruction).

Key Concepts

Richter Scale

The Richter scale is a popular method used to evaluate the magnitude of earthquakes. It works as a logarithmic scale, which means each whole number increase on the scale represents a tenfold increase in measured amplitude and roughly 31.6 times more energy release. For example, an earthquake with a magnitude of 6.0 has an amplitude ten times greater than one with a magnitude of 5.0. This scale focuses on measuring the energy released at the earthquake's origin, creating a consistent numerical value to describe the quake's strength.

• A logarithmic scale measures how much the ground shakes.
• Developed in 1935 by Charles F. Richter.
• Provides a numerical value to convey the earthquake's size.

The Richter scale is especially useful in comparing different earthquakes, as it offers a standardized way of quantifying their size. Despite its practicality, it has some limitations and has been largely supplanted by the moment magnitude scale for large earthquake measurements.

Mercalli Scale

The Mercalli scale is quite different from the Richter scale as it measures the intensity of an earthquake rather than its magnitude. Intensity refers to the earthquake's effects on people, structures, and the Earth's surface. This scale uses Roman numerals ranging from I to XII to describe the observed impact of the quake, with I being hardly noticeable and XII involving total destruction.

• Qualitative measure based on observations and reports.
• Developed by Giuseppe Mercalli in 1902.
• Describes the earthquake's effects, not its inherent energy.

The Mercalli scale relies on human observations, which can vary widely depending on distance from the epicenter, local building codes, and geographical features. While it offers a vivid picture of what people experience during an earthquake, its subjectivity means it lacks the precision and consistency of magnitude scales like the Richter.

Magnitude vs Intensity

Magnitude and intensity are two vital concepts for comprehending earthquakes, each representing different aspects of these natural events. Magnitude, like that measured by the Richter scale, quantifies the energy released at the earthquake's source, providing an objective and consistent number.

• Magnitude is a measure of energy release, offering a precise scale.
• Independent of the earthquake's location, as it's measured at the source.

On the other hand, intensity refers to the severity of shaking at specific locations. The Mercalli scale is commonly used for this, depicting how the event is felt by people and the damage caused. Intensity can vary widely depending on proximity to the epicenter and local conditions.

• Intensity measures the impact on structures and people.
• Can vary based on local geology and distance from the source.

Understanding both aspects helps in better earthquake preparedness and assessment, allowing for deeper insights into both the power and consequences of these formidable natural phenomena.