AbstractSeismic response records were retrieved from the monitored 21-story (53.26-m-tall) typical Puerto Rican reinforced-concrete shear-wall dominated El Castillo Building in Mayaguez, 50 km from the mainshock epicenter of the January 7, 2020, Mw6.4 offshore Indios, Puerto Rico earthquake. The shear-wall-to-floor areas of the building are 0.97 and 3.49 in the longitudinal and transverse directions, respectively, and have a slenderness ratio of 3.0 in the transverse direction. Basement and top-floor peak accelerations were 5% g and 12.8% g, respectively. Additionally, records from a nearby free-field station indicate a site period of 0.16 s. No visible damage was observed in the building after the earthquake. Spectral ratios and system identification allow identification of the transverse, longitudinal, and torsional fundamental periods as 0.97, 0.88, and 0.81 s, respectively, and are consistent with ASCE/SEI 7-16 (2017) formula. Damping percentages are 4.5%, 3.4%, and 2.2%, respectively. The maximum drift ratios are 0.20% and 0.12% in the longitudinal and transverse directions, well below the damage threshold for structural elements of ∼0.5%.