Jessica E. Pilarczyk - US grants

There is an extensive instrumental, historical, and geological record of tsunamigenic-earthquakes originating from the northern and middle parts of the Japan Trench that documents the last several thousand years of earthquakes and tsunamis, including the magnitude 9 Tohoku earthquake in 2011. This earthquake ruptured five segments along the northern and middle parts of the Trench, but failed to rupture through the southern part, which is near metropolitan Tokyo. The seismic risk for this portion of the trench is uncertain because of the possibility that stress transferred southwards during the 2011 earthquake and that this part of the subduction zone is locked. Furthermore, the instrumental and historical record is sparse with only one tsunamigenic-earthquake on record (CE 1677 Empo earthquake) and lack of long-term geological data. A research team from University of Southern Mississippi and Rutgers University in collaboration with Japanese researchers will employ an innovative combination of field, laboratory (sedimentary, microfossil, and radiometric analyses), statistical, and modeling techniques to a series of possible tsunami deposits in order to determine the tsunami and earthquake history of the southern Japan Trench, data which is very important for anticipating future disasters. Besides providing an improved understanding of seismic risk in the Tokyo region, additional benefits to society include improved STEM education though outreach to middle school students and development of a globally competitive STEM workforce through training of graduate and undergraduate students and post-doctoral fellow mentoring.

The detection and characterization of tsunami deposits preserved in coastal sediments provides a long-term record of past earthquakes. This project focuses on three candidate-tsunami sands that are preserved in coastal rice fields in the Kujukuri beaches, a strand plain located on the Boso Peninsula approximately 50 km east of Tokyo. The identification of tsunami deposits using proxy analyses (grain size and microfossil), with Bayesian age-depth models and tsunami simulation models, will resolve whether the southern part of the trench can produce future earthquakes that are similar in size as the 2011 Tohoku event. Well-constrained ages for each candidate tsunami will permit an accurate estimation of the shoreline position, and thus, inundation distance at the time of deposition. By integrating these changing shoreline positions into previously developed tsunami simulation models (e.g., 2011 Tohoku and CE 1677 Empo models), the research team will test whether previous middle/northern or southern trench ruptures could have deposited the tsunami sands on the Boso Peninsula.

With four intense storms making landfall on American and Caribbean coastlines this year, the 2017 hurricane season highlights the need to better understand the geographic and temporal controls on hurricanes in the Atlantic region. This RAPID project represents a unique opportunity to understand the impact of a Category 5 hurricane on the existing paleo-overwash record at previously-studied field sites on Anegada, British Virgin Islands (BVI), one of the islands that sustained the greatest impact from Hurricane Irma. The research team will make careful comparisons between pre- and post-Irma coastal deposits resulting from extreme wave inundation as an important step towards improving the assessment of hazard risk for coastlines that are vulnerable to both hurricane and tsunami inundation. This work will provide important new information regarding hurricane and tsunami hazards, not only for the British Virgin Islands, but for other Caribbean islands including those of the U.S. Virgin Islands and Puerto Rico. By assessing the sediments deposited by Hurricane Irma, the team will develop an important modern analog of a Category 5 storm that will help interpret long-term geologic records of overwash (and episodic tsunami) deposits for the Caribbean region, which will enable Caribbean countries to better prepare for, respond to, recover from, and mitigate future hurricane impacts.

The distribution of overwash sediments and boulders at Anegada, BVI captures important information regarding Hurricane Irma's storm surge (flow depths, inundation distances). Through detailed multidisciplinary field and laboratory analyses the team intends to investigate the environmental impacts and overwash deposits associated with Hurricane Irma's landfall on Anegada to: (1) document the storm surge characteristics and associated sedimentary deposit of a known Category 5 hurricane; (2) assess the depth of scour and distance of sediment and boulder transport by storm surge; and (3) use the Hurricane Irma deposit as a basis of comparison with older overwash records, including a series of inferred tsunami deposits within coastal ponds at Anegada. These data will be used to reassess previously documented overwash records that span the last several thousand years and will identify similarities and differences between the sedimentary deposits emplaced by past major storms (e.g., hurricanes in 2010 and 2017) and tsunamis (1755 Lisbon earthquake) at this location. This reassessment of the overwash record at Anegada, based on lessons learned from Hurricane Irma, can be used to reconstruct millennial scale patterns of frequency, intensity, and physical impacts associated with both storms and tsunamis. This refined understanding of extreme wave events will improve hazard prediction, preparedness, and assessment for coastlines impacted by both forms of marine inundation.