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(2021) Glissements de terrain déclenchés par le tremblement de terre du 14 août 2021, de magnitude 7,2 à Nippes, Haïti

(2021) Glissements de terrain déclenchés par le tremblement de terre du 14 août 2021, de magnitude 7,2 à Nippes, Haïti

U.S. Department of the Interior, U.S. Geological Survey 2021 26 pages
Resume — Ce rapport évalue les risques géologiques liés aux glissements de terrain sur la péninsule de Tiburon suite au tremblement de terre de magnitude 7,2 qui a frappé Nippes, Haïti, le 14 août 2021. Il présente une carte préliminaire des glissements de terrain déclenchés par le séisme et les précipitations ultérieures, en soulignant les zones préoccupantes nécessitant une évaluation et une surveillance détaillées.
Constats Cles
Description Complete

Le tremblement de terre de magnitude 7,2 qui a frappé Nippes, Haïti, le 14 août 2021, a déclenché des milliers de glissements de terrain sur la péninsule de Tiburon, causant des décès, des dommages et entravant les efforts de réponse. Ce rapport présente une évaluation des risques géologiques potentiels liés aux glissements de terrain après le tremblement de terre pour la péninsule de Tiburon et une carte préliminaire des glissements de terrain déclenchés par le tremblement de terre et les précipitations ultérieures du cyclone tropical Grace. L'évaluation est basée sur une analyse d'urgence des images satellite disponibles après le tremblement de terre, soulignant les zones de préoccupation spécifiques qui pourraient bénéficier d'une évaluation détaillée et d'une surveillance à plus long terme. Les efforts de cartographie ont révélé qu'au moins 4 893 glissements de terrain ont été déclenchés à travers la péninsule de Tiburon, avec des centaines de dépôts de glissements de terrain susceptibles de restreindre le débit des rivières et des cours d'eau et d'affecter les routes.

Sujets
EnvironnementRéduction des risques
Geographie
National, Ouest, Sud, Grand'Anse, Nippes
Periode Couverte
2021 — 2021
Mots-cles
landslides, earthquake, Haiti, Nippes, Tiburon Peninsula, geologic hazards, landslide dams, road obstructions, flooding, sediment
Entites
U.S. Geological Survey, USAID, Tropical Cyclone Grace, Enriquillo-Plantain Garden fault zone, Pic Macaya National Park
Texte Integral du Document

Texte extrait du document original pour l'indexation.

U.S. Department of the Interior U.S. Geological Survey Open-File Report 2021–1112 Earthquake Hazards Program and Landslide Hazards Program Landslides Triggered by the August 14, 2021, Magnitude 7.2 Nippes, Haiti, Earthquake Landslides Triggered by the August 14, 2021, Magnitude 7.2 Nippes, Haiti, Earthquake By Sabrina N. Martinez, Kate E. Allstadt, Stephen L. Slaughter, Robert Schmitt, Elaine Collins, Lauren N. Schaefer, and Sonia Ellison Earthquake Hazards Program and Landslide Hazards Program Open-File Report 2021–1112 U.S. Department of the Interior U.S. Geological Survey U.S. Geological Survey, Reston, Virginia: 2021 For more information on the USGS—the Federal source for science about the Earth, its natural and living resources, natural hazards, and the environment—visit https://www.usgs.gov or call 1–888–ASK–USGS. For an overview of USGS information products, including maps, imagery, and publications, visit https://store.usgs.gov/. Any use of trade, firm, or product names is for descriptive purposes only and does not imply endorsement by the U.S. Government. Although this information product, for the most part, is in the public domain, it also may contain copyrighted materials as noted in the text. Permission to reproduce copyrighted items must be secured from the copyright owner. Suggested citation: Martinez, S.N., Allstadt, K.E., Slaughter, S.L., Schmitt, R., Collins, E., Schaefer, L.N., and Ellison, S., 2021, Landslides triggered by the August 14, 2021, magnitude 7.2 Nippes, Haiti, earthquake: U.S. Geological Survey Open-File Report 2021–1112, 17 p., https://doi.org/​10.3133/​ofr20211112 . Associated data for this publication: Martinez, S.N., Allstadt, K.E., Slaughter, S.L., Schmitt, R.G., Collins, E., Schaefer, L.N., and Ellison, S., 2021, Rapid response landslide inventory for the 14 August 2021 M7.2 Nippes, Haiti, earthquake: U.S. Geological Survey data release, https://doi.org/10.5066/P99MYPXK. ISSN 2331-1258 (online) iii Acknowledgments Funding for the preparation of this report was provided by the U.S. Agency for International Development’s Bureau for Humanitarian Assistance and the U.S. Geological Survey. We thank Robert Mason, Karl Winters, and Allen Gellis for their insights on channel sedimentation and flooding and Jeff Coe, Randall Jibson, David Wald, and Ryan Gold for reviewing the report (U.S. Geological Survey). v Contents Acknowledgments����������������������������������������������������������������������������������������������������������������������������������������iii Abstract�����������������������������������������������������������������������������������������������������������������������������������������������������������1 Introduction����������������������������������������������������������������������������������������������������������������������������������������������������1 Data and Analysis������������������������������������������������������������������������������������������������������������������������������������������3 Coseismic Landslides������������������������������������������������������������������������������������������������������������������������������������4 Ongoing Hazards������������������������������������������������������������������������������������������������������������������������������������������13 Landslide Dams�����������������������������������������������������������������������������������������������������������������������������������13 Landslide Hazards to Roads��������������������������������������������������������������������������������������������������������������13 Increased Landslide Activity������������������������������������������������������������������������������������������������������������13 Channel Sedimentation and Flooding����������������������������������������������������������������������������������������������14 Summary�������������������������������������������������������������������������������������������������������������������������������������������������������15 References Cited�����������������������������������������������������������������������������������������������������������������������������������������16 Figures 1. Overview of the Tiburon Peninsula showing contours of estimated peak ground acceleration for the 2021 Nippes, Haiti, earthquake��������������������������������������������������������������2 2. Overview map of the Haiti 2021 earthquake landslide inventory showing landslide dams, road hazards, and flagged landslides����������������������������������������������������������3 3. Flagged landslide features in Camp-Perrin commune, identified from satellite imagery after the 2021 Haiti earthquake�����������������������������������������������������������������������������������8 4. Flagged landslide features in Pestel, Beaumont, Chantal, and Roseaux communes, identified from satellite imagery after the 2021 Haiti earthquake�������������������9 5. Flagged landslide features in Maniche commune, identified from satellite imagery after the 2021 Haiti earthquake���������������������������������������������������������������������������������10 6. Flagged landslide features in L’Asile commune, identified from satellite imagery after the 2021 Haiti earthquake������������������������������������������������������������������������������������������������11 7. Flagged landslides in Cavaillon, Saint Louis du Sud, and Baradères communes, identified from satellite imagery after the 2021 Haiti earthquake���������������������������������������12 8. Satellite imagery from Haiti after the 2021 earthquake and examples of two landslide dams that were flagged as warranting continued monitoring��������������������������14 9. Map showing the relative density of landslides along 1,000-meter river segments on the Tiburon Peninsula, Haiti, after the 2021 earthquake������������������������������15 Table 1. Notable landslide dams and road obstructions after the 2021 Nippes, Haiti, earthquake�������������������������������������������������������������������������������������������������������������������������������������5 vi Conversion Factors International System of Units to U.S. customary units Multiply By To obtain Length meter (m) 3.281 foot (ft) kilometer (km) 0.6214 mile (mi) kilometer (km) 0.5400 mile, nautical (nmi) meter (m) 1.094 yard (yd) Area square kilometer (km 2 ) 247.1 acre square kilometer (km 2 ) 0.3861 square mile (mi 2 ) Datum Coordinate information is referenced to the World Geodetic System 1984 (WGS 84) Universal Transverse Mercator (UTM) Zone 18N projection. Abbreviations DART disaster assistance response team DEM digital elevation model g acceleration of gravity M magnitude RMT response management team UNICEF United Nations Children's Fund USAID U.S. Agency for International Development USGS U.S. Geological Survey UTC coordinated universal time UTM Universal Transverse Mercator WGS World Geodetic System Landslides Triggered by the August 14, 2021, Magnitude 7.2 Nippes, Haiti, Earthquake By Sabrina N. Martinez, 1 Kate E. Allstadt, 1 Stephen L. Slaughter, 1,2 Robert Schmitt, 1 Elaine Collins, 1 Lauren N. Schaefer, 1 and Sonia Ellison 1 1 U.S. Geological Survey 2 U.S. Agency for International Development, Bureau for Humanitarian Assistance Abstract The August 14, 2021, magnitude 7.2 Nippes, Haiti, earthquake triggered thousands of landslides on the Tiburon Peninsula. The landslides directly caused fatalities and damage and impeded response efforts by blocking roads and causing other infrastructure damage. Adverse effects of the landslides likely will continue for months to years. This report presents an assessment of potential postearthquake landslide-related geologic hazards for the Tiburon Peninsula and a preliminary map of the landslides triggered by the earthquake. This hazard assessment is based on an emergency analysis of the currently available, postearthquake satellite imagery. In this report, we highlight specific areas of concern that may benefit from more detailed assessment and longer-term monitoring. Our mapping efforts revealed that at least 4,893 landslides were triggered across the Tiburon Peninsula by the earthquake and subse- quent rainfall from Tropical Cyclone Grace. We also observed hundreds of landslide deposits potentially restricting flow in rivers and streams. In addition, we observed landslides that likely affected roads by rendering them impassable or suscep- tible to subsequent damage from existing landslides. Because of the preliminary nature of this report and the limits of remote analyses, additional investigation and monitoring would be beneficial to accurately determine the threat posed by these hazards to people and infrastructure. Introduction The magnitude (M) 7.2 Nippes, Haiti, earthquake occurred at 12:29:08 coordinated universal time (08:29:08 local time) on August 14, 2021. The rupture started in the center of the Tiburon Peninsula, about 125 kilometers (km) west of the capital, Port-au-Prince, and ruptured primarily westward with reverse and left-lateral strike-slip motion along the Enriquillo-Plantain Garden fault zone. The fault rup- ture terminated in the vicinity of Pic Macaya National Park. Shaking was estimated by the U.S. Geologial Survey (USGS) ShakeMap (ver. 14) to have exceeded 0.5 g (acceleration of gravity) along an 80-km band of steep and rugged, and there- fore landslide-susceptible, terrain in the center of the Tiburon Peninsula (fig. 1). The USGS near-real-time ground failure product (Allstadt and others, 2021) estimated that the land- slides triggered by the Nippes earthquake would be significant in number and (or) spatial extent (estimated at about 70 square kilometers) and that the number of people living near landslide hazards was significant (estimated at about 9,000 people). The landslide probability map produced by the ground failure product is shown in figure 1. The earthquake was followed by Tropical Cyclone Grace, which was estimated to have dropped 5–10 inches of rain in Haiti on August 16, 2021 ( National Oceanic and Atmospheric Administration, 2021), and likely triggered additional landslides. More information about the earthquake, including the near-real-time products, is available from the USGS earthquake event page at https://​ earthquake​ .usgs.gov/​earthquakes/​ eventpage/​ us6000f65h/​executive . During the week following the earthquake, a team of USGS scientists rapidly mapped landslides using remote methods and created a landslide inventory. By the end of this effort, 3,625 landslides had been mapped. This inven- tory, with critical daily observations, was shared with the U.S. Agency for International Development’s (USAID’s) Disaster Assistance Response Team (DART) and Response Management Team (RMT) for situational awareness and emergency response. The inventory also was made publicly available as an ArcGIS online web map for use by humanitar- ian aid organizations for situational awareness and emergency response. The original rapid inventory that was available immediately after the earthquake for situational awareness only is now superseded by the inventory associated with this report (Martinez and others, 2021). For this report, we mapped additional landslides that were missed in the initial inventory. We carefully reviewed the inventory in its entirety to identify landslides that may pose ongoing threats to people and property (fig. 2). We mapped, as best as possible, the location of each landslide’s heads- carp area as a point feature. Some mapped locations may be 2  Landslides Triggered by the August 14, 2021, Magnitude 7.2 Nippes, Haiti, Earthquake imprecise because of the poor orthorectification of some of the satellite imagery used. Landslide polygons were not mapped for this preliminary version of the inventory. Most imagery available for the affected area was obtained after the passage of Tropical Cyclone Grace; thus, the landslide inventory pre- sented could contain both earthquake- and rainfall-triggered landslides. However, we did not see many landslides with characteristics common to rainfall-triggered landslides, such as channelized flows, so we think that most of the landslides were triggered by the earthquake. In addition to landslide headscarp locations, we present an assessment of potential postearthquake landslide-related geologic hazards for the Tiburon Peninsula. We highlight specific areas of concern that may benefit from more detailed assessment and longer-term monitoring because of the poten- tial effects on people and infrastructure. Potential postearth- quake landslide hazards include (1) sudden flooding from the failure of landslide dams; (2) continued landsliding of dam- aged slopes, especially along roads and river channels; (3) an overall increase in landslide activity for multiple years; and (4) changes in river behavior from an influx of landslide sedi- ment that can lead to long-term changes in flooding risks. USGS GF model landslide probability EXPLANATION