What does an earthquake look like - to a seismologist?
In order to study earthquakes, scientists deploy seismometers to measure ground motion. Seismograms are recordings of ground motion as a function of time and are the basic data which seismologists use to study the waves generated by earthquakes. These data are used to study the earthquakes themselves and to learn more about the structure of the Earth.
We have gathered several examples of earthquake recordings to illustrate the wide variety of motion. These data are derived from the Berkeley Digital Seismic Network, an array of broadband, high-dynamic range instruments in northern and central California. This network is operated by the UC Berkeley Seismological Laboratory for earthquake monitoring and research.
Seismologists generally describe earthquakes as local, regional, or teleseismic. These terms refer to distance from the earthquake to the recording instrument. For example, when the Berkeley Seismographic Station refers to a local earthquake, we mean one which has occurred within Northern California. An example of a regional earthquake might be an event in Southern California, Nevada, Utah, Oregon, or Washington. Teleseismic events are those which occur at great distances, such as earthquakes in Japan, Tonga, or Iceland.
Local and regional earthquakes are dominated by crustal waves, i.e., by waves which propagate through the crust. At greater distances, the seismic wavefield is dominated by waves which sample the body of the earth - the upper mantle, the lower mantle, and the core.
The seismic recording instruments of the BDSN are capable of "seeing" earthquakes around the globe. In this example, we will illustrate the variations in waveforms among these types of earthquakes.
Earthquake Examples
A detailed explanation of waves, seismic instrumentation, and the records they produce was prepared by Charles Ammon at St. Louis University for an introductory earthquake class.
