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Inventory of liquefaction features triggered by the 7 January 2020 M6.4 Puerto Rico earthquake

September 21, 2021

This dataset consists of an inventory of the locations of liquefaction-related phenomena triggered by the 7 January 2020 M6.4 Puerto Rico earthquake. The inventory is primarily based on field observations collected during post-earthquake reconnaissance conducted by the USGS and partners (Allstadt and others, 2020, Interactive Dashboard). Some additional locations were added based on reconnaissance reports by other groups (Miranda and others, 2020; Morales-Velez and others, 2020). We delineated 43 polygons of liquefaction areas and lateral spreading where we had sufficient evidence to do so (liquefaction_polygons_20210913.zip), but all outlines are approximate because liquefaction is primarily a subsurface process and surface expression may not extend over the entire area where liquefaction occurred at depth (and sometimes surface expression may not be present at all, though we are not able to map those cases). We used scientific judgment to group larger areas of fissuring, spreading, sand boils, and settlement into polygons that enclosed these clusters of features while maintaining relatively simple geometries. All other locations are point features, one file contains 32 points of occurrences (liquefaction_points_20210913.zip) and a separate file contains 81 null points, or non-occurrences (liquefaction_nullpoints_20210913.zip), which are locations in environments susceptible to liquefaction that we visited but did not observe any evidence that ground failure occurred. This inventory is not a complete mapping of all areas where liquefaction or lateral spreading occurred; it represents areas that were visited in the field and where evidence of liquefaction was visible at the surface. There were likely other liquefaction-related ground failure occurrences that are not mapped here. For the files that contain liquefaction occurrences, we defined the following attributes: "Type": Polygons were defined as one of three types: The "liquefaction area" type indicates areas where liquefaction surface manifestations (fissures, sand ejecta, sand boils, settlement) were pervasive but there was no obvious lateral displacement. The "lateral spreading" type indicates locations where lateral displacements, often towards bodies of water and likely related to liquefaction, were observed. The "settlement" type indicates areas where vertical deformation was noted but lacked definitive evidence of liquefaction. The latter two types may or may not have sand ejecta. Points have a wider variety of types because they refer to specific individual occurrences of possible manifestations of liquefaction and lateral spreading (bridge abutment damage, sand boils, broken pipes, compressional features, raised manhole). "Ejecta": This attribute has a value of 1 if sand ejecta were noted, 0 if it was not noted. The value is left as Null if the presence of absence of ejecta could not be determined with certainty. "Disp": We did not make precise measurements of displacements, but we include this attribute to note whether there was little to no vertical or horizontal displacement. Displacement estimates were primarily based on horizontal displacements because we did not have reference points to measure vertical displacement except in a few cases where adjacent structures did not settle and provided a point of reference. The displacement categories are defined as follows: mild displacement (on the order of 1 cm), moderate displacement (on the order of 10 cm), or major displacements (on the order of a meter or larger). "Certainty": This attribute represents the confidence that each feature was related to liquefaction or caused by the earthquake. This is categorized on a scale from one to three in which 1 indicates the feature was field checked, its location is well-known, and it was likely related to liquefaction, 2 indicates the feature was field checked but it is unclear if the feature is actually related to liquefaction (e.g., bridge abutment damage) or if it was actually caused by the earthquake (e.g., some crab burrows in the area resemble sand boils), and 3 indicates the feature was mapped using satellite imagery and was not field checked. "Comments": This attribute includes additional relevant information. The null point dataset only has the "Comments" attribute and an id ("fieldobs_id") that corresponds to the entry of the field observations dataset (Allstadt et al., 2020) that the point comes from. Null points were taken directly from that field observations dataset. However, the original dataset contained many null observations collected for different purposes so for this subset we have screened out only those null observations that are from locations where liquefaction susceptibility was estimated to be high but liquefaction did not occur. High susceptibility refers to areas with elevated probabilities on the USGS Ground Failure product liquefaction model map (https://earthquake.usgs.gov/data/ground-failure/background.php) and/or areas where the environment was conducive to liquefaction (strong shaking, close to bodies of water, soft soils). We did not include any landslides in this inventory except those classified as lateral spreading. Landslides were mapped separately by (Knoper and others, 2020). References: Allstadt, K.E., Thompson, E.M., Bayouth Garcia, D., Brugman, E.I., Hernandez, J.L., Schmitt, R.G., Hughes, S.K., Fuentes, Z., Martinez, S.N., Cerovski-Darriau, C., Perkins, J.P., Grant, A.R., and Slaughter, S.L., 2020, Field observations of ground failure triggered by the 2020 Puerto Rico earthquake sequence: U.S. Geological Survey data release. https://doi.org/10.5066/P96QNFMB. Knoper, L., Allstadt, K.E., Clark, M.K., Thompson, E.M., and Schmitt, R.G., 2020, Inventory of landslides triggered by the 2020 Puerto Rico earthquake sequence: U.S. Geological Survey data release. https://doi.org/10.5066/P9U0IXLP. Miranda, E., Archbold, J., Heresi, P., Messina, A., Rosa, I., Kijewski-Correa, T., Mosalam, K., Prevatt, D., Robertson, I., and Roueche, D., 2020, StEER - Puerto Rico Earthquake Sequence December 2019 to January 2020: Early Access Reconnaissance Report (EARR). https://doi.org/10.17603/ds2-h0kd-5677 Morales-Velez, A.C., Bernal, J., Hughes, K.S., Pando, M., Perez, J.C., Rodriguez, L.A., and Suarez, L.E., 2020, Geotechnical Reconnaissance of the January 7, 2020 M6.4 Southwest Puerto Rico Earthquake and Associated Seismic Sequence: Geotechnical Extreme Event Reconnaissance Association GEER-066, accessed July 28, 2020, at http://www.geerassociation.org/component/geer_reports/?view=geerreports….

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