When an earthquake strikes, several seismic waves radiate outward from the origin of the earthquake. These seismic waves may be thought of as ripples through the Earth’s crust that are similar to the ripples in a pond after a pebble has been tossed into the water. The origin of the earthquake is known as the focus or hypocenter of the earthquake. The epicenter is the point on the Earth’s surface directly above the hypocenter.
There are 2 major types of waves that travel through Earth. The first is the P wave, the primary or pressure wave. These are lateral compression waves. I think of these as a closely packed line of people waiting for tickets. One person bumps the person next to them who bumps the person next to them and so on through the line. The people represent molecules within the Earth that bump their neighbors as the p wave passes by. The second type of seismic wave is called the S wave, the shear or secondary wave. These travel as a transverse wave. I think of like a human wave at the ball park where one person standing up causes the person next to the to stand up and so on around the park.
P waves travel much faster than S waves, thus, the further you are from the earthquake epicenter, the greater the lag between the two waves. A seismogram is a record of these waves, captured digitally or on paper. The precise arrival time of the P wave and S wave is captured on the seismogram. Using several seismic monitoring stations, one may triangulate the location of any earthquake.
The teachers at the Lawrence Hall of Science are very skilled at leading these programs and quickly cover a lot of ground while maintaining the students’ interest and understanding. They are able to lead students through the plate tectonic causes of earthquakes, then how to read seismograms, then how to find the epicenter of an earthquake.
To enroll in a program, there is a minimum enrollment of 16 and a maximum of 32 students. It costs $9.50 per student and includes access to the other exhibits, including Forces that Shape the Bay. The workshops occur at set times throughout the day: 10:00 a.m., 11:10 a.m., 12:30 p.m., or 1:30 p.m. Reservations may be made by calling: (510) 642-5134 or you may reserve online.