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               Figure 1. (A) Topographic map of Puerto Rico showing the storm track of Hurricane Maria. (B) Relative density of landslides mapped from
               the rapid classification of satellite and aerial imagery and site visits following Hurricane Maria (updated from Bessette-Kirton et al., 2017).

          1340 m (U.S. Geological Survey, 2017c;   complex is unconformably overlain by a   maximum rainfall values range from
          Fig. 1A). Broad lowlands and coastal   cover sequence of Oligocene–Pliocene   353 to 1431 mm (see [A] in the GSA Data
          plains ring most of the island. Present-   carbonates and associated siliciclastic   Repository  for a summary of rainfall
                                                                                        1
          day tectonic uplift resulting from the    deposits (Monroe, 1976; Ortega-Ariza    data). Doppler estimates are not available
          convergence of the North American    et al., 2015).                   due to the destruction of radar during
          and Caribbean plates is one of the main                               the storm (National Weather Service,
          drivers of the rugged topography that is   HURRICANE MARIA            2017b). Although rainfall estimates from
          expressed across much of the island   Hurricane Maria made landfall along    Hurricane Maria vary, multiple data sets
          (Taggart and Joyce, 1991; Brocard et al.,   the southeast coast of Puerto Rico as a   indicate that at least 250 mm of rain fell
          2015, 2016). The average annual rainfall   Category 4 hurricane at 6:15 a.m. local   across Puerto Rico’s mountainous terrain,
          varies dramatically across micro-climate   time (Atlantic Standard Time [AST]) on    much of which had received 254–381 mm
          zones, with the highest annual rainfall   20 September 2017 (Pasch et al., 2018)    of rainfall from Hurricane Irma two weeks
          usually reported around the Sierra de   and moved across Puerto Rico with a    prior to Maria (5–7 September 2017;
          Luquillo (Fig. 1A) in the northeastern part   west-northwest trajectory (Fig. 1A).   Cangialosi et al., 2018).
          of the island (Ravalo et al., 1986; Daly et   Rainfall data from Hurricane Maria vary
          al., 2003). High rainfall, temperature, and   both in absolute magnitude and spatial   LANDSLIDE DISTRIBUTION
          humidity contribute to widespread sapro-  distribution. Estimates of average island-  AND CHARACTERISTICS
          lite formation (Murphy et al., 2012).  wide rainfall from the National Hurricane   To rapidly assess the areas that were
            Puerto Rico is part of an extinct volcanic   Center (NHC; Pasch et al., 2018), the   most severely impacted by landslides, we
          island arc that lies along the North America–   National Centers for Environmental   used post-hurricane satellite (DigitalGlobe
          Caribbean plate boundary and is underlain   Prediction (NCEP; National Weather   Inc.) and aerial imagery (Sanborn and
          by a faulted basement assemblage of Upper   Service, 2018), and the PERSIANN-Cloud   Quantum Spatial; Vexcel Imaging, 2017)
          Jurassic ocean crustal fragments and   Classification System (CCS; Center for   collected between 26 September and
          Cretaceous to Eocene volcaniclastic and   Hydrometeorology and Remote Sensing,   8 October 2017 to map landslide density.
          intrusive units (Jolly et al., 1998). This arc   2018) range from 280 to 543 mm, while   A few of the landslides that we mapped


          1  GSA Data Repository item 2019079, (A) summaries of published rainfall and soil moisture data from Hurricane Maria and (B) database of past hurricanes and
          tropical storms in Puerto Rico with landslide occurrences described when applicable, is available online at www.geosociety.org/datarepository/2019.

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