Project Grant G23AP00081

PROJECT TITLE HIGH PRECISION 3D GRAVITY INVESTIGATION OF THE 2020 MW5.1 SPARTA, NC EPICENTRAL AND AFTERSHOCKZONEPERIOD OF PERFORMANCE 1 1 2023 THROUGH 12 31 2023THE MAGNITUDE 5.1 SPARTA, NC EARTHQUAKE WAS THE LARGEST EASTERN U.S. SHOCK IN THE PAST DECADE, CAUSING AT LEAST 24 MILLION IN DAMAGE AND CREATING THE FIRST OBSERVED SURFACE RUPTURE EAST OF THE MISSISSIPPI. IT OCCURRED ON THE SHALLOW ( 1 KM), PREVIOUSLY UNKNOWN LITTLE RIVER FAULT AND SET OFF ABOUT 300 SIMILARLY SHALLOW AFTERSHOCKS THAT ILLUMINATE A NETWORK OF DISTINCT, CROSS CUTTING FAULTS. BECAUSE DAMAGING EARTHQUAKES IN THE CEUS ARE SO RARE, AND THIS SURFACE RUPTURE IS UNIQUE, THIS DISASTER PROVIDES AN IMPORTANT OPPORTUNITY TO IMPROVE OUR UNDERSTANDING OF THE FORCES AND FAULTS RESPONSIBLE FOR INTRAPLATE EARTHQUAKES. TO MAP AND CHARACTERIZE THE FAULT ZONE IN THREE DIMENSIONS, THE RECIPIENT WILL MEASURE AND MODEL IMPERCEPTIBLE VARIATIONS IN THE PULL OF GRAVITY DUE TO DIFFERENCES IN THE ROCK TYPES ON EITHER SIDE OF FAULTS AND DUE TO THE DAMAGED ZONE ALONG FAULTS. REGULARLY SUCH STUDIES IN SUPPORT OF MAJOR CONSTRUCTION PROJECTS, GEOHAZARDS INVESTIGATIONS, AND GEOTHERMAL PROSPECTING, AMONG OTHER APPLICATIONS, AND HAVE DEVELOPED AN EXTENSIVE TOOLKIT OF GRAVITY BASED METHODS SPECIFICALLY DESIGNED FOR FAULT AND FAULT ZONE IMAGING WILL BE CONDUCTED. SHALLOW FAULTS LIKE THE LITTLE RIVER FAULT CREATE ESPECIALLY HIGH AMPLITUDE, NARROW GRAVITY SIGNALS THAT ARE VERY SENSITIVE INDICATORS OF SUBSURFACE STRUCTURE. WE PROPOSE A MICROGAL PRECISION GRAVITY SURVEY REPRODUCIBLY MEASURING GRAVITY VARIATIONS OF PARTS IN 1 BILLION OF THE SPARTA EPICENTRAL AND AFTERSHOCK ZONE. GOALS INCLUDE MAPPING THE LITTLE RIVER FAULT ZONE IN 3D AND DELINEATING THE COMPLEX NETWORK OF FAULTS ILLUMINATED BY AFTERSHOCKS WITH DECAMETER RESOLUTION. ONE KEY OUTCOME OF THIS WORK WILL BE TO ASCERTAIN THE SEISMOGENIC POTENTIAL OF THE LITTLE RIVER FAULT BY DETERMINING WHETHER THERE ARE PERSISTENT STRUCTURAL OR LITHOLOGIC BARRIERS TO RUPTURE THAT LIMIT EARTHQUAKES NEAR M5, STEPS OR OVERLAPS THAT TYPICALLY SEGMENT THE FAULT BUT COULD LINK IN A LARGE FUTURE EARTHQUAKE, OR NO PARTICULAR FEATURES THAT WOULD PREVENT LONGER RUPTURES AND THUS LARGER FUTURE EARTHQUAKES. A SECOND LINE OF INVESTIGATION WILL FOCUS ON HOW SLIP AT DEPTH WAS TRANSFERRED TO THE SURFACE AND PARTITIONED ACROSS THE SHALLOW NETWORK OF ANTECEDENT FAULTS, AND HOW UP DIP SLIP TRANSFER MAY INFLUENCE THE PROBABILITY OF SURFACE RUPTURES AND THE OUTSIZED DAMAGE THEY CAUSE. FINALLY, SYNTHESIZING PRELIMINARY WORK DOCUMENTING REGIONAL GEOLOGIC STRUCTURES, THE PROPOSED GRAVITY IMAGING OF THE EPICENTRAL ZONE, AND GEOMECHANICAL CONSTRAINTS WILL DETERMINE IF THE LITTLE RIVER FAULT IS AN ISOLATED SEISMOGENIC STRUCTURE OR IF THERE ARE ADDITIONAL FAULTS IN THE REGION CAPABLE OF SIMILAR OR LARGER EARTHQUAKES IN THE FUTURE. THE PROPOSED WORK WILL THEREFORE IMPROVE OUR UNDERSTANDING OF THE SPARTA EARTHQUAKE AND HAZARDS ASSOCIATED WITH THE NEWLY IDENTIFIED LITTLE RIVER FAULT, REGIONAL HAZARDS ALONG THE CENTRAL SOUTHERN APPALACHIAN FRONT, AND INTRAPLATE EARTHQUAKE SOURCE PROCESSES NATIONWIDE.