20-21. Analysis of active tectonics and fault systems in Puerto Rico

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Background: Puerto Rico is one of the most tectonically active areas of the United States. Caught between the Caribbean and North American plates, the island and surrounding regions are being subjected to oblique subduction and uplift that causes a complex distribution of faults and accompanying seismicity. Oblique subduction along the Puerto Rico trench north of the island affects backarc thrusting in the Muertos Trough on the south side of the island (e.g., tenBrink et al., 2009), causing the development of fault systems in and around the island (e.g., Bruña et al., 2015). Information about the kinematics and slip rates of these faults, or how they are driven by the deeper subduction zone, is lacking (e.g., Prentice and Mann, 2005). Additional submarine fault systems beneath Mona Passage to the west and Anegada Trough to the east have been mapped (Chaytor and ten Brink, 2010; 2014), but their exact relationship to the subduction system is unknown. Most recently, the ongoing earthquake sequence in southwest Puerto Rico, including a M6.4 earthquake, landslides and shoreline subsidence, highlights a complex system of faults with a variety of motions (López et al., 2020). The island has substantial seismic and tsunami hazard potential and serves as a natural laboratory for studying tectonics and faulting in an oblique-slip subduction environment.

A wealth of new data is currently or soon will be available to study the region using geophysical and/or geologic methods. The Puerto Rico seismic network has been upgraded since Hurricane Maria, portable seismic instrumentation is available within the USGS, new lidar data spanning nearly the entire island were acquired after Hurricane Maria, and a National Science Foundation crustal-scale onshore-offshore seismic reflection and refraction experiment is planned for 2023 that will involve the deployment of a marine multichannel seismic array and a substantial number of temporary seismometers onshore and offshore. These capabilities and new data sets present an opportunity to characterize crustal deformation and the development of fault systems within Puerto Rico and the greater Caribbean/North American plate boundary, and convergent oblique plate boundaries in general.

The U.S. Territories of Puerto Rico and the Virgin Islands are densely populated and are also major tourist destinations. The combination of a dense population and a relatively high level of seismicity make the northern Caribbean one of the highest earthquake, tsunami, and landslide risks in the U.S. The active tectonics also influences coastal morphology and landforms, with implications for the response to hurricanes and storms. It is a priority for the USGS Natural Hazards Mission area to understand and assess these hazards, with results informing updates of future probabilistic hazard maps and emergency preparedness efforts.

Description of the Research Opportunity: The selected Fellow will integrate multiple data sets and/or techniques, leverage and synthesize new and existing datasets, and/or develop new models or methods to analyze active tectonics in the region. The Fellow will be based in one of three locations depending upon the specific project: the Geologic Hazards Science Center in either Golden Colorado, or Reston, Virginia, or the Coastal and Marine Science Center in Woods Hole, Massachusetts. We also encourage the Fellow to work closely with researchers at the University of Puerto Rico at Mayaguez, with the possibility of extended stays on the island.

The exact research effort will be determined by the candidate’s interests and background but should broadly align with the research opportunity goals. The work ideally will bridge the USGS Earthquake Hazards and Coastal and Marine Programs, although this is not a requirement.

Potential topics may include, but are not limited to:

• Analyses of seismicity to better define and characterize the active tectonics and fault systems;
• Fault studies either onshore or offshore to understand the geologic history and earthquake hazards of the island, including understanding the earthquake histories or fault slip rates, timing and triggering between subduction zone and crustal fault earthquakes, landscape response to active tectonics, and/or fault geometries and kinematics;
• Quantitative comparisons of fault systems and seismicity in Puerto Rico with analogs elsewhere;
• Imaging or modeling of the subduction interface, the backarc thrust complex, and the island arc using seismic reflection and refraction methods;
• Imaging or modeling of sedimentary deformation in response to fault motion;
• Geodetic or topographic analyses of vertical and horizontal motions and their relations to faulting and subduction;
• Understanding the evolution of oblique plate boundaries through kinematic and fault modeling.

Applicants are encouraged to propose research aligning with the above goals and consistent with their research interests and background. The project will need to be focused to ensure a high probability of success within the two-year appointment. Substantial resources to collect data already exist or are planned, and are available for use in the project, although the applicant can propose to acquire additional resources necessary for their proposed work. In addition to the data sets mentioned above, the USGS has facilities and equipment to date geologic samples, collect and analyze seismic reflection/refraction/GPR data and sediment cores, and deploy portable seismic networks.

A successful applicant must show evidence of the following: 

• Demonstrated record of peer-reviewed publications related to the proposed work; 
• Excellent oral (including public speaking) and written communication skills; 

• Experience building and/or working in collaborative, diverse, and inclusive team environments;
• Knowledge of Spanish is not required, but would facilitate work on the island and interactions with researchers there. 

Interested applicants are strongly encouraged to contact the Research Advisor(s) early in the application process to discuss project ideas.

References:

Bruña, J.L. Granja, U.S. ten Brink, A. Muñoz-Martín, A. Carbó-Gorosabel, and P. Llanes Estrada (2015). Shallower structure and geomorphology of the southern Puerto Rico offshore margin, Marine and Pedtrolum Geology, v. 67, p. 30-56; doi: 10.1016/j.marpetgeo.2015.04.014

Chaytor, J.D., and U.S. ten Brink (2010). Extension in Mona Passage, Northeast Caribbean, Tectonophysics, 493, 74-92.

Chaytor, J.D. and U.S. ten Brink (2014). Event sedimentation in low-latitude deep-water carbonate basins, Anegada Passage, Northeast Caribbean, Basin Research, doi: 10.1111/bre.12076.

López, A.M., K.S. Hughes, and E. Vanacore (2020). Puerto Rico’s Winter 2019-2020 Seismic Sequence Leaves the Island On Edge, Temblor, http://doi.org/10.32858/temblor.064.

Prentice, C. S., and P. Mann (2005). Paleoseismic study of the South Lajas fault: First documentation of an onshore Holocene fault in Puerto Rico, in Mann, P., ed., Active tectonics and seismic hazards of Puerto Rico, the Virgin Islands, and offshore areas: Geological Society of America Special Paper 385, p. 215-222.

ten Brink, U.S., Marshak, S. and Bruña, J.L. Granja (2009). Bivergent thrust wedges surrounding oceanic island arcs: Insight from observations and sandbox models of the northeastern Caribbean plate, GSA Bulletin; November/December 2009; v. 121; no. 11/12; p. 1522–1536; doi: 10.1130/B26512.1

Proposed Duty Station: Golden, Colorado; Woods Hole, Massachusetts; or Reston, Virginia

Areas of PhD: Geology, seismology, geophysics, oceanography, numerical modeling, or related fields (candidates holding a Ph.D. in other disciplines, but with extensive knowledge and skills relevant to the Research Opportunity may be considered).

Qualifications: Applicants must meet the qualifications for one of the following: Research Geologist, Research Geophysicist, Research Oceanographer, Research Physical Scientist

(This type of research is performed by those who have backgrounds for the occupations stated above.  However, other titles may be applicable depending on the applicant's background, education, and research proposal. The final classification of the position will be made by the Human Resources specialist.)

Human Resources Office Contact:  Megan Agy, 303-236-9584, magy@usgs.gov