2023-07-14 16:57:45
Tremor in the USA: How is an earthquake measured?
The magnitude of an earthquake is calculated using scales such as Richter and surface wave, which provide numerical estimates of the size of the seismic event. These scales display a logarithmic relationship, which means that each unit increase represents a 10-fold increase in the amplitude of ground motion. Intensity, on the other hand, is a measure of shaking and effects at a specific location, determined by damage reports and human reactions. The Modified Mercalli Intensity Scale is the most widely used to classify earthquakes.
The magnitude is related to the power of a radio station, while the intensity is similar to the signal strength in a radio receiver. Although an earthquake is assigned a magnitude, it can report varying intensities due to factors such as distance from the epicenter, type of construction, and local soil. Intensity maps often show complex patterns, as the most significant damage occurs near the epicenter, but it can extend over considerably greater distances.
The 6.5 magnitude Seattle-Tacoma earthquake in 1965 caused intensity VII to VIII damage near the epicenter, intensity V damage 150 km away, and faint intensity I to II damage 300 to 500 km away. The intensity of damage to buildings depends on various factors, contributing to the complexity of intensity patterns on seismic maps, notes the Pacific Northwest Seismic Network (PNSN).
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