Project Grant G23AP00243

PROJECT TITLE: DETECTION THRESHOLDS FOR LARGE TO GREAT SUBDUCTION EARTHQUAKES IN ALASKA: COLLABORATIVE RESEARCH WITHDURHAM UNIVERSITY AND THE USGSPERIOD OF PERFORMANCE: 5 1 2023 THROUGH 4 30 2024PLAIN LANGUAGE DESCRIPTION: THIS PROJECT WILL UNDERTAKE FIELD AND LABORATORY INVESTIGATIONS AND SUBSEQUENT DATA ANALYSIS TO INVESTIGATE WHETHER THE UPPER PART OF COASTAL MARSHES IN THE PRINCE WILLIAM SOUND AREA OF ALASKA POSSESS RECORDS OF VERTICAL DEFORMATION OF LESS THAN 1 M CAUSED BY EARTHQUAKES MW8.0 EARTHQUAKES OVER THE PAST 4000 YEARS. THE SAMPLING DESIGN OF THESE STUDIES WHICH FOCUSES ON MARSH-FRONT LOCATIONS DOES NOT DETECT SMALLER LAND-LEVEL CHANGES CAUSED BY SMALLER EARTHQUAKES DURING THIS TIME-PERIOD. THIS NEW STUDY WILL USE A NEW, COMPLEMENTARY METHOD LOOKING AT SEDIMENTS FROM THE UPPER PART OF COASTAL MARSHES TO INVESTIGATE WHETHER WE CAN RECONSTRUCT SMALLER AMOUNTS OF DEFORMATION ( 1M) AND THEREFORE CREATE A MORE COMPLETE CATALOGUE OF EARTHQUAKE EVENTS IN THIS REGION DURING THE LAST FEW MILLENNIA.ACTIVITIES TO BE PERFORMED: THE PROJECT WILL INVOLVE COLLECTING SEDIMENT CORES FROM GIRDWOOD MARSH (PRINCE WILLIAM SOUND REGION) DURING A 10-DAY FIELD CAMPAIGN IN SUMMER 2023. WE WILL ALSO COLLECT ADDITIONAL SURFACE SEDIMENT SAMPLES TO INCLUDE IN AN EXISTING DATABASE OF MICROFOSSILS FROM ALASKAN COASTAL MARSHES. THE SEDIMENT CORE AND SURFACE SEDIMENT SAMPLES WILL BE ANALYSED FOR MICROFOSSILS (DIATOMS) THAT RECORD CHANGES IN WATER LEVEL OVER TIME, AND STATISTICAL ANALYSIS WILL ALLOW RECONSTRUCTION OF ABRUPT LAND-LEVEL CHANGES IN THE CORES. TOGETHER WITH RADIOCARBON DATING OF THE SEDIMENTS THIS WILL ALLOW ESTIMATES OF THE TIMING AND MAGNITUDE OF LAND-LEVEL CHANGES IN-BETWEEN THE 1M EVENTS ALREADY IDENTIFIED IN THE GIRDWOOD RECORD. DELIVERABLES AND EXPECTED OUTCOMES: WE WILL COLLECT SEDIMENT CORE SEQUENCES AND MODERN SEDIMENT SAMPLES DURING FIELDWORK AND ANALYSES THEM AT DURHAM UNIVERSITY, UK. COUNTS OF MODERN MICROFOSSIL DISTRIBUTIONS WILL BE ADDED TO AN EXISTING MICROFOSSIL DATABASE WIDELY USED BY RESEARCHERS IN THIS FIELD. CORE LOGS, MICROFOSSIL COUNT SHEETS AND RADIOCARBON DATING RESULTS WILL BE MADE AVAILABLE ONLINE ON PUBLICATION OF THE RESULTS OF THE PROJECT. WE WILL PRESENT THE WORK AT AN INTERNATIONAL SCIENCE MEETING, WRITE A FINAL REPORT FOR THE USGS AND SUBMIT THE RESULTS TO AN INTERNATIONAL PEER-REVIEWED JOURNAL.INTENDED BENEFICIARIES: THIS RESEARCH WILL CONTRIBUTE TOWARDS REDUCING UNCERTAINTIES REGARDING THE NATURE OF FUTURE EARTHQUAKE HAZARD IN SOUTH CENTRAL ALASKA, AND ALSO IMPROVE OUR UNDERSTANDING OF THE NATURE OF PAST EARTHQUAKE RUPTURES IN THIS REGION. THE PROJECT RESULTS WILL INFORM FUTURE RESEARCH ON IDENTIFYING SMALLER AMOUNTS OF DEFORMATION IN ALASKAN MARSHES AND CONTRIBUTE TO FUTURE UPDATES OF THE SEISMIC AND TSUNAMI HAZARD MAPS OF ALASKA.SUBRECIPIENT ACTIVITIES: N A