Seismometers, seismographs, seismograms - what's the difference? How do they work?
Seismographs are instruments used to record the motion of the ground during an earthquake--installed in the ground throughout the world and operate as part of a seismographic network. The first one was developed in 1890. The earliest "seismoscope" was invented by the Chinese philosopher Chang Heng in A.D. 132. This did not record earthquakes, however. It only indicated that there was one occurring.
A seismograph is securely mounted onto the surface of the earth so that when the earth shakes, the entire unit shakes with it, EXCEPT for the mass on the spring which has inertia, and remains in the same place. As the seismograph shakes under (in the example below) the mass, the recording device on the mass records the relative motion between itself and the rest of the instrument, thus recording the ground motion. In reality, these mechanisms are no longer manual, but instead work by measuring electronic changes produced by the motion of the ground with respect to the mass.
A seismogram is the recording of the ground shaking at the specific location where the instrument is. On a seismogram, the HORIZONTAL axis = time (measured in seconds) and the VERTICAL axis= ground displacement (usually measured in millimeters). When there is NO EARTHQUAKE reading there is just a straight line except for small wiggles caused by local disturbance or "noise" and the time markers. Seismograms are digital now - there are no more paper recordings.
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?
How are earthquakes recorded? How are earthquakes measured? How is the magnitude of an earthquake determined?
Moment magnitude, Richter scale - what are the different magnitude scales, and why are there so many?
What is the difference between magnitude and intensity? What is the Modified Mercalli Intensity Scale?
How do you determine the magnitude for an earthquake that occurred prior to the creation of the magnitude scale?
The USGS Earthquake Hazards Program recently released a new strategic plan for earthquake monitoring entitled the “Advanced National Seismic System – Current Status, Development Opportunities, Priorities, 2017-2027.”
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.
USGS will Grant Universities $5 Million to Beef Up Public Safety Grants totaling $5 million under the American Recovery and Reinvestment Act are being awarded to 13 universities nationwide to upgrade critical earthquake monitoring networks and increase public safety.
USGS scientist John Hamilton installing a seismograph in the offices of the major-league soccer team San Jose Earthquakes’ new stadium.
A seismometer deployed near the epicenter of the Greeley earthquake in 2014.
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...
USGS seimologist Doug Given works with colleagues from the Bureau des Mines et de l'Energie to install a seismometer. Seismometers monitor the earth's movement and can detect and measure aftershocks. Given traveled to Haiti with USGS colleagues Susan Hough, Mark Meremonte, and J. Zebulon Maharrey shortly after a magnitude-7 earthquake struck on Jan. 12, 2010. The...
Bryant Platt digs a hole to install seismometers at a home in southern Kansas. Seismometers are in the foreground.