On Tuesday morning a magnitude 3.7 earthquake occurred about 16 miles SW of Ester, rattling folks across the Fairbanks region. Seismic instruments throughout the UAF Engineering Learning and Innovation Facility recorded the quake well. They also recorded the way the building responded to the shaking. Sensors on the lower floors are primarily sensitive to the motion of the earth itself. Sensors higher up also record the motion of the building induced by the earthquake.
During this earthquake the motion on the upper floors was strongest. That is typical and agrees with the experiences people reported. The motion in the basement was dominated by a single strong pulse that lasted less than a second. As this oscillation traveled up the building it initiated a lower-frequency resonance (i.e., swaying) that could be felt for many seconds. The earthquake essentially “kicked” the building into resonating—a bit like kicking a signpost.
Instrumented buildings, such as the ELIF, provide scientists and engineers with the ability to measure how structures respond to earthquakes. The lessons learned from these data, especially during larger damaging earthquakes, are used to adjust and update building codes and practices. The ELIF is the only building in interior Alaska that is instrumented at several levels. A prior post in this space described the 2017 installation of sensors in the building. Details about this specific earthquake can be found on the event page. Credit for Lea Gardine for the awesome figure.