GPS measured response of a tall building due to a distant M _w 7.3 earthquake

The response of a 413-m-tall building to the 12 November 2017 M _w 7.3 earthquake 642 km from the building is measured with a Global Positioning System (GPS) receiver located near the top of the building and operating with a 1 Hz sampling rate. Nearby GPS and seismic stations measure the ground motion near the building. The ground motions have amplitudes of ∼40 mm, while the top of the building moves by up to 160 mm. The building motion continues with levels greater than the noise level of the GPS measurement for about 15 min after the earthquake. After the ground-motion excitation ends, the building motion decays with a time constant of ∼2 min and the beat between the two lowest frequency modes of deformation of the building can be seen. There are two large amplitude peaks in the building motion with magnitudes of 120 and 160 mm. The timing of the peaks is consistent with ground excitation in an 8.3–6.5-s-period (120–180 mHz) band, which covers the 7.25 and 5.81 s periods (138 and 172 mHz frequencies) of the fundamental modes of the building. The ground motions in this band show two large pulses of the excitation, which have timing consistent with the large amplitude building signals. The response of the top of the building is amplified by an order magnitude over the ground motions in this band. There is no apparent permanent displacement of the top of the tower.