January 2020 Puerto Rico earthquake provides valuable data for ground failure models — ScienceDaily

Cortez Deacetis

Field surveys carried out in the times following the 7 January 2020 Puerto Rico earthquake documented a lot more than 300 landslides and serious liquefaction in southern coastal areas, in accordance to a new examine by U.S. Geological Survey and University of Puerto Rico Mayagüez scientists.

The ground failure that resulted from the magnitude 6.4 earthquake wasn’t outstanding, specially in contrast to the catastrophic floor failure in latest situations these as the August 2021 Haiti earthquake. But the floor failure survey conducted by USGS analysis geophysicist Kate Allstadt and colleagues provides a useful source for Puerto Rico, which has no island-extensive hazard map for earthquake-activated landslides or liquefaction.

In their paper published in Seismological Study Letters, Allstadt and her colleagues examine how they can use the new survey facts to refine situational awareness instruments such as the USGS’ Floor Failure solution, which quickly estimates landslide and liquefaction dangers and populace exposure soon after an earthquake.

The merchandise uses statistically dependent, worldwide versions to make its estimates, but the info that go into the types is biased in favor of extremely detrimental occasions at the expenditure of extra common and moderate gatherings, said Allstadt.

“When the shaking’s truly solid, you get rid of the capability to have an understanding of the restrictions of ground failure,” she spelled out. “And which is 1 of the toughest factors to model, for the reason that typically most of the interest is specified to the truly spectacular ground failure events.”

In the 7 days soon after the earthquake, USGS and UPR Mayagüez researchers went into the area to map floor failure, guided by the USGS Ground Failure product and satellite imagery. Social media and news reviews, alongside with ideas from emergency professionals and citizens, helped Allstadt and colleagues monitor down landslides and liquefaction.


The landslides ended up mostly concentrated in areas where peak floor acceleration exceeded 30% g—a measure equivalent to a particular person sensation “very strong” shaking. Liquefaction mainly occurred in coastal spots in which peak floor acceleration was much larger than 50% g (shaking that feels “severe”), but some of the most detrimental liquefaction took area in Ponce, wherever shaking estimates were as reduced as 20% g.

In the vicinity of Ponce, “there was a stretch of houses together a creek where by people experienced to evacuate simply because their homes ended up so weakened by liquefaction,” Allstadt stated. “It was heartbreaking to see.”

The researchers observed that landslides generally transpired in limestone rock alongside the coasts, a pattern quite equivalent to the landslides that happened all through Puerto Rico’s notorious 1918 San Fermin earthquake, one of the island’s most lethal and economically devastating seismic situations. The description of landslides in a 1919 report, they note, “could quite well describe the 2020 earthquake if the location names ended up altered.”

“It does suggest that this is the characteristic variety of habits for these varieties of rock when they are shaken,” stated Allstadt.

The earthquake amazed people in Puerto Rico, who informed Allstadt and her colleagues that they are extra made use of to hurricanes which arrive almost each individual calendar year. Couple Puerto Ricans were alive the previous time a big earthquake impacted the island.


K. Stephen Hughes of UPR Mayagüez, a co-writer on the SRL paper, and his colleagues previously mapped exactly where rainfall-induced landslides are typically probably in Puerto Rico. Only about 25% of the 2020 earthquake landslides happened “where we mapped the rainfall-induced susceptibility as large, extremely significant, or particularly substantial,” Hughes famous.

“Obviously steep slopes can be inclined for all varieties of landsliding, but there are several, lots of other factors that influence how and when a slope fails—soil sort, bedrock sort, and land use, just to title a number of,” he stated.

Hughes and his colleagues are applying the datasets they have collected right after Hurricane Maria and the 2020 earthquake to help them predict long term landsliding in Puerto Rico, specifically when seismic and storm hazards coincide.

Comprehensive details like that gathered in the Puerto Rico reconnaissance study can be applied to establish regional variations of the Ground Failure products, Allstadt explained. For the minute, she and her colleagues are operating on a regional edition for Alaska, prompted by the detrimental 2018 Anchorage earthquake. “We are applying the world design as the first guess and then updating it with regional details,” she reported. “We’ll most likely do one thing like that for Puerto Rico ultimately with these knowledge.”

The paper is aspect of an upcoming exclusive target segment in SRL on Puerto Rico seismicity, tectonics, and the 2020 earthquake sequence.

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