How are earthquakes recorded? How are earthquakes measured? How is the magnitude of an earthquake determined?
Earthquakes are recorded by a seismographic network. Each seismic station in the network measures the movement of the ground at the site. The slip of one block of rock over another in an earthquake releases energy that makes the ground vibrate. That vibration pushes the adjoining piece of ground and causes it to vibrate, and thus the energy travels out from the earthquake in a wave.
There are many different ways to measure different aspects of an earthquake:
- Magnitude is the most common measure of an earthquake's size. It is a measure of the size of the earthquake source and is the same number no matter where you are or what the shaking feels like. The Richter scale is an outdated method that is no longer used - it measured the largest wiggle on the recording, but other magnitude scales measure different parts of the earthquake. The USGS currently reports earthquake magnitudes using the Moment Magnitude scale, though many other magnitudes are calculated for research and comparison purposes.
- Intensity is a measure of the shaking and damage caused by the earthquake; this value changes from location to location.
What was the duration of the earthquake? Why don't you report the duration of each earthquake? How does the duration affect the magnitude?
What does it mean that the earthquake occurred at a depth of 0 km? How can an earthquake have a negative depth; that would mean it’s in the air. What is the geoid, and what does it have to do with earthquake depth?
What is the difference between magnitude and intensity? What is the Modified Mercalli Intensity Scale?
Moment magnitude, Richter scale - what are the different magnitude scales, and why are there so many?
How do you determine the magnitude for an earthquake that occurred prior to the creation of the magnitude scale?
The Hawaiian Volcano Observatory’s 1912–2012 Centennial—100 Years of Tracking Eruptions and Earthquakes
HAWAI‘I ISLAND, Hawaii —The history of earthquakes and seismic monitoring in Hawai‘i during the past century will be the topic of a presentation at the University of Hawai‘i at Hilo on Thursday, January 26, at 7:00 p.m.
More than $7 million in cooperative agreements will be awarded for earthquake monitoring by the U.S Geological Survey in 2010. This funding will contribute to the development and operation of the USGS Advanced National Seismic System (ANSS).
A new geologic map of surficial deposits in the nine-county San Francisco Bay region that can be used to evaluate earthquake hazards has been released in digital form by the U.S. Geological Survey in Menlo Park.
A K2 seismograph. The K2 is an accelerometer and data-logger combined into a single, portable package. The unit is the size of a large shoe box. It is usually installed in a corner of the garage or a convenient area on a patio or side walk along the house. A photo of a unit installed in a garage is shown.
With funding from the American Recovery and Reinvestment Act of 2009, The USGS Hawaiian Volcano Observatory recently upgraded its seismic monitoring network. Here, HVO staff, assisted by an HVO volunteer, installs the solar panel and antenna for one of the upgraded seismic stations on Kīlauea.
A map of ShakeOut scenario shaking in southern California.
Map of ANSS free-field seismic stations across the U.S. in 2016 (not shown are additional seismic instruments in buildings and other structures). Map colors show seismic hazard across the United States derived from the National Seismic Hazard Model. Background colors indicate the levels of shaking that have a 2% chance of being exceed in a 50-year period. Shaking is...
Bryant Platt digs a hole to install seismometers at a home in southern Kansas. Seismometers are in the foreground.