Observations of Ground Failure in the 2020 M6.4 Indios, Puerto Rico Earthquake Sequence

Session: Early Results from the 2020 M6.4 Indios, Puerto Rico Earthquake Sequence
Type: Oral
Date: 4/30/2020
Time: 01:30 PM
Room: 115
Description: 

In the days following the January 7, 2020 magnitude 6.4 earthquake in Puerto Rico, the U.S. Geological Survey (USGS) coordinated with the University of Puerto Rico Mayagüez to survey earthquake-induced ground failures, including landslides and liquefaction. The USGS near-real-time ground failure product predicted that both landslides and liquefaction were likely to have been triggered by this earthquake, but that only a limited area would be affected. Because this event appears to be near the threshold of shaking required to trigger ground failure in this region, documentation of the ground failure occurrences is especially useful for improving near-real-time ground failure models.

Our field observations indicate that many landslides occurred, but the majority were small rock falls in road cuts. Due to their size, road cuts are not captured by the digital elevation model that we use for global earthquake response, and so the model is not able to accurately predict these sites. We observed liquefaction features in the coastal communities including Playa de Guayanilla, Playa de Guánica and Ponce, where water table was very shallow. The liquefaction models also predicted elevated likelihood of occurrences in more distant locations from the epicenter, where we were not able to identify any evidence of liquefaction. We observed liquefaction associated with important infrastructure, including cracks and tilted piers at a port and a power plant, lateral spreading near power plant infrastructure and rock falls that posed an ongoing risk to natural gas tanks and schools. While ground failure did occur in this event, the structural damage due to shaking appears to far exceed the damage due to ground failure.

Presenting Author: Eric M. Thompson

Authors