AP Notes - Earthquakes
Earthquakes
Earthquakes occur during abrupt movement on an existing fault, along tectonic plate boundary or along mid-oceanic ridges. A massive amount of stored energy, held in place by friction, is released during a very short period of time. The area where the energy is released and the earthquake begins is called the focus. From the focus, seismic waves travel outward in all directions. Directly above the focus, on Earth’s surface is the epicenter.
Earthquakes occur during abrupt movement on an existing fault, along tectonic plate boundary or along mid-oceanic ridges. A massive amount of stored energy, held in place by friction, is released during a very short period of time. The area where the energy is released and the earthquake begins is called the focus. From the focus, seismic waves travel outward in all directions. Directly above the focus, on Earth’s surface is the epicenter.
The strength or magnitude of an earthquake is commonly measured by the logarithmic Richter scale and is recorded by a seismograph (devised by Charles Richter in 1935).
THE RICHTER SCALE
Richter Magnitudes Description Earthquake Effects Frequency of Occurrence
Less than 2.0 Micro Micro-earthquakes, not felt. About 8,000 per day
2.0-2.9 Minor Generally not felt, but recorded. About 1,000 per day
3.0-3.9 Minor Often felt, but rarely causes damage. 49,000 per year (est.)
4.0-4.9 Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.)
5.0-5.9 Moderate Can cause major damage to poorly constructed buildings over small regions.
At most slight damage to well-designed buildings. 800 per year
6.0-6.9 Strong Can be destructive in areas up to about 160 kilometers (100mi) across in
populated areas. 120 per year
7.0-7.9 Major Can cause serious damage over larger areas. 18 per year
8.0-8.9 Great Can cause serious damage in areas several hundred miles across. 1 per year
9.0-9.9 Extreme Devastating in areas several thousand miles across. 1 per 20 years
10.0+ Epic Never recorded Extremely rare
Richter magnitude scale is really comparing amplitudes of waves on a seismogram, not the strength (energy) of the quakes. It is the energy of strength of the earthquake that knocks down buildings and causes damages. The following chart relates changes in the Richter magnitude scale with the strength of energy of earthquakes:
RICHTER MAGNITUDE
Richter Magnitude Change Ground Motion Change (Displacement) Energy Change
1.0 10 times ~32 times
0.5 3.2 times ~5.5 times
0.3 2 times ~3 times
0.1 1.3 times ~1.4 times
Types of Waves
There are two classes of seismic waves: body waves and surface waves.
1. Body waves travel through the interior of the earth. There are two types: P and S.
THE RICHTER SCALE
Richter Magnitudes Description Earthquake Effects Frequency of Occurrence
Less than 2.0 Micro Micro-earthquakes, not felt. About 8,000 per day
2.0-2.9 Minor Generally not felt, but recorded. About 1,000 per day
3.0-3.9 Minor Often felt, but rarely causes damage. 49,000 per year (est.)
4.0-4.9 Light Noticeable shaking of indoor items, rattling noises. Significant damage unlikely. 6,200 per year (est.)
5.0-5.9 Moderate Can cause major damage to poorly constructed buildings over small regions.
At most slight damage to well-designed buildings. 800 per year
6.0-6.9 Strong Can be destructive in areas up to about 160 kilometers (100mi) across in
populated areas. 120 per year
7.0-7.9 Major Can cause serious damage over larger areas. 18 per year
8.0-8.9 Great Can cause serious damage in areas several hundred miles across. 1 per year
9.0-9.9 Extreme Devastating in areas several thousand miles across. 1 per 20 years
10.0+ Epic Never recorded Extremely rare
Richter magnitude scale is really comparing amplitudes of waves on a seismogram, not the strength (energy) of the quakes. It is the energy of strength of the earthquake that knocks down buildings and causes damages. The following chart relates changes in the Richter magnitude scale with the strength of energy of earthquakes:
RICHTER MAGNITUDE
Richter Magnitude Change Ground Motion Change (Displacement) Energy Change
1.0 10 times ~32 times
0.5 3.2 times ~5.5 times
0.3 2 times ~3 times
0.1 1.3 times ~1.4 times
Types of Waves
There are two classes of seismic waves: body waves and surface waves.
1. Body waves travel through the interior of the earth. There are two types: P and S.
- P waves travel through the earth and are caused by expansion and contraction of bedrock.
- S waves are produced when material moved either vertically or horizontally and travel only within the uppermost layers of the earth.
The severity of an earthquake depends on:
Primary effects are due to the shaking and resulting damage to buildings and infrastructure and due to the loss of life or injury. Secondary effects include rock-slides, flooding due to subsidence (sinking of land, liquefaction or recent sediments, fires and tsunamis).
Damage due to earthquakes can be reduced through mapping faults, preparing computer models and simulations, strengthening building codes, preparing emergency teams with adequate training, upgrading communication technology and availability, storing energy supplies, and educating the public.
Facts
Largest earthquake in US occurred in Prince William Sound in 1964. 9.2 on Richter scale
Number 1 state in the US for quantity of earthquakes is Alaska, followed by California, and Hawaii.
Earthquake that caused the most deaths (~830,000) occurred in Shansi, China in 1556. In the US, it was in San Francisco, California in 1906 (3,000 died including deaths due to the fires that resulted).
In 2004 Indian Ocean undersea earthquake (Sumatra-Andaman earthquake) occurred in 12/26/2004 and was the second largest earthquake ever recorded. The earthquake generates a tsunami (giant wave). Killed over 240,000 people. An estimated 1,200 km (750 miles) of fault line slipped about 15m (50 ft) along a subduction zone where Indian Plate is subducted under the Burma Plate. The slip took place in two phases and occurred over several minutes.
At this point - Proceed to the next subtopic: AP Notes - Volcanoes
- The amount of potential energy that has been stored.
- The distance the rock mass moved when the energy was released.
- How far below the surface the movement occurred.
- The makeup of the rock material.
Primary effects are due to the shaking and resulting damage to buildings and infrastructure and due to the loss of life or injury. Secondary effects include rock-slides, flooding due to subsidence (sinking of land, liquefaction or recent sediments, fires and tsunamis).
Damage due to earthquakes can be reduced through mapping faults, preparing computer models and simulations, strengthening building codes, preparing emergency teams with adequate training, upgrading communication technology and availability, storing energy supplies, and educating the public.
Facts
Largest earthquake in US occurred in Prince William Sound in 1964. 9.2 on Richter scale
Number 1 state in the US for quantity of earthquakes is Alaska, followed by California, and Hawaii.
Earthquake that caused the most deaths (~830,000) occurred in Shansi, China in 1556. In the US, it was in San Francisco, California in 1906 (3,000 died including deaths due to the fires that resulted).
In 2004 Indian Ocean undersea earthquake (Sumatra-Andaman earthquake) occurred in 12/26/2004 and was the second largest earthquake ever recorded. The earthquake generates a tsunami (giant wave). Killed over 240,000 people. An estimated 1,200 km (750 miles) of fault line slipped about 15m (50 ft) along a subduction zone where Indian Plate is subducted under the Burma Plate. The slip took place in two phases and occurred over several minutes.
At this point - Proceed to the next subtopic: AP Notes - Volcanoes