Question

Three sites (L1, L2, L3) record earthquake magnitude and earthquake intensity for the same earthquake. \(\mathrm{Ll}\) is located closest to the focus and L3 is farthest away. Where is the intensity greatest, and what happens to the earthquake magnitude calculated at the different sites? a) Intensity is greatest at Ll; calculated magnitude is the same at each site. b) Intensity is greatest at L3; calculated magnitude is the same at each site. c) Intensity is greatest at Ll; calculated magnitude decreases with distance from the focus. d) Intensity is greatest at L3; calculated magnitude decreases with distance from the focus.

Short answer

Intensity is greatest at L1; magnitude is the same at each site (option a).

Step-by-step solution

Understanding Earthquake Intensity and Magnitude

Earthquake intensity refers to the effects of an earthquake observed at different locations, which can vary based on the distance from the earthquake's focus. Generally, the closer a location is to the focus, the greater the intensity experienced at that location. Earthquake magnitude, on the other hand, is a measure of the energy released at the source of the earthquake and is consistent regardless of where it is recorded.

Examining Intensity at Different Sites

Since L1 is the closest to the earthquake's focus, it is logical that L1 will experience the greatest earthquake intensity. As distance increases from the focus, the effects lessen, causing L2 to experience less intensity than L1 and L3 to experience the least of all.

Checking Magnitude Consistency

Earthquake magnitude is a measure of the earthquake's size and is not affected by the location of measurement. Therefore, the calculated magnitude should be the same at L1, L2, and L3, despite any differences in the intensity recorded at these sites.

Answer Selection

Based on understanding of intensity and magnitude, option (a) is accurate as it states that intensity is greatest at L1, and that the calculated magnitude is the same at each site.

Key concepts

Earthquake Magnitude

Earthquake magnitude is a crucial concept in understanding seismic events. It measures the amount of energy released at the earthquake's source, often referred to as the focus. This measurement is uniform and does not change based on location. This is important because it helps scientists and seismologists compare different earthquakes on a consistent scale. The Richter scale is a well-known method for measuring earthquake magnitude, but other scales, such as the moment magnitude scale, are also used. Magnitude remains constant no matter where the earthquake is observed, providing a reliable way to assess the energy of the seismic event.

Seismology

Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth. This field plays a vital role in understanding and predicting earthquakes. Seismologists study the origin, frequency, and intensity of earthquakes. They use this data to understand the Earth's internal structure and dynamics. By analyzing seismic waves, they gain insights into the locations of faults and the potential for future seismic activity. Seismology is crucial for improving earthquake preparedness and developing engineering solutions to minimize earthquake damage.

Seismic Waves

Seismic waves are the waves of energy that travel through the Earth as a result of an earthquake. They are vital for understanding how earthquakes affect different areas:

• Primary waves (P-waves): These are the fastest seismic waves and are the first to be detected by seismographs. They compress and expand the ground like an accordion.
• Secondary waves (S-waves): Arriving after P-waves, S-waves shake the ground up and down and side to side. They cause more destruction due to their higher amplitude.
• Surface waves: These waves travel along the Earth's surface and typically cause the most damage during an earthquake.

Seismic waves are essential for understanding how energy is dispersed through the Earth and how intensity varies at different locations.

Earthquake Measurement

Measuring earthquakes involves assessing both magnitude and intensity.
Magnitude is measured using seismographs, which detect the energy of seismic waves. This helps provide a consistent scale for comparing earthquakes globally.
Intensity examines the earthquake's effects at specific locations. The Modified Mercalli Intensity (MMI) Scale is commonly used to describe the intensity and observable effects of an earthquake. While magnitude provides information about the earthquake as a whole, intensity varies based on proximity to the earthquake's epicenter, local geology, and building structures. Understanding both these measurements ensures a comprehensive analysis of an earthquake's impact.