Liquefaction induced by historic and prehistoric earthquakes in western Puerto Rico

Dozens of liquefaction features in western Puerto Rico probably formed during at least three large earthquakes since A.D. 1300. Many of the features formed during the 1918 moment magnitude (M) 7.3 event and the 1670 event, which may have been as large as M 7 and centered in the Añasco River Valley. Liquefaction features along Río Culebrinas, and possibly a few along Río Grande de Añasco, appear to have formed ca. A.D. 1300–1508 as the result of a M ≥ 6.5 earthquake. We conducted reconnaissance along Río Culebrinas, Río Grande de Añasco, and Río Guanajibo, where we found and studied numerous liquefaction features, dated organic samples occurring in association with liquefaction features, and performed liquefaction potential analysis with geotechnical data previously collected along the three rivers. Our ongoing study will provide additional information regarding the age and size distribution of liquefaction features along the western, northern, and eastern coasts and will help to improve estimates of the timing, source areas, and magnitudes of earthquakes that struck Puerto Rico during the late Holocene.