Blue Hill Observatory Begins Earthquake Monitoring

Blue Hill Observatory has been watching the weather since 1885, and Boston College’s Weston Observatory has been watching the Earth quake since 1931. We are now joining forces to monitor the Earth with a recently installed seismograph at Blue Hill.

In collaboration with Dr. Alan Kafka, Director of Weston Observatory, Blue Hill purchased and installed a seismograph in Fall 2019 to begin a program of earthquake monitoring on the summit of Great Blue Hill. The monitoring equipment measures seismic waves from earthquakes around the world. These seismic waves travel from the earthquake epicenter, propagate through and around the Earth, and arrive at the Blue Hill seismograph. Since these waves vary with the location and type of earthquakes, and are altered by the material they pass through, differences in the amplitude and arrival times of the waves at different locations can reveal information about the characteristics of the earthquakes and the interior of the Earth.

Several earthquakes have been observed by the equipment on Blue Hill since it was installed. Figure 1 shows a series of seismograph recordings for multiple sites along the U.S. East Coast following a strong magnitude 7.7 earthquake that occurred near Jamaica on January 28, 2020. Notice the differing amplitudes and arrivals times of the seismic waves at each location as the waves generated by the earthquake moved northward after the earthquake and arrived about 10 seconds earlier in Florida than in Maine, which is much farther from the epicenter than Florida. Figure 2 shows the seismic wave recordings of that earthquake as they were measured at Weston Observatory and at Blue Hill.

**Figure 1.** Seismograph recordings of seismic waves as measured at multiple locations along the U.S. East Coast from a magnitude 7.7 earthquake near Jamaica on January 28, 2020.

**Figure 2.** Seismograph recordings measured at Weston Observatory and at Blue Hill Observatory from a magnitude 7.7 earthquake near Jamaica on January 28, 2020.

A magnitude 6.2 earthquake on February 5, 2020 with an epicenter much farther away in Indonesia was also observed along the East Coast and in the local area. Figure 3 shows seismograph recordings for several sites along the U.S. East Coast following the Indonesia earthquake. In this case, these instruments observed what are called “PKP” seismic waves that are refracted by the Earth’s core on their way through the planet, providing valuable information about the nature of Earth’s interior. Differing amplitudes and arrivals times of these seismic waves at each location were also seen in this case. Figure 4 shows the detailed “PKP” seismic wave recordings that were measured for this event at two locations at Boston College, at Weston Observatory and at Blue Hill Observatory.