The Structure and Frictional Behavior of Seismogenic Faults along the Northern US East Coast: Insights from the 2024 M4.8 New Jersey Earthquake
Folarin Kolawole, Columbia University
Zachary Foster-Baril, Lamont-Doherty Earth Observatory
Rasheed Ajala, Lamont-Doherty Earth Observatory
Jacob Tielke, Lamont-Doherty Earth Observatory
Abhishek Prakash, Lamont-Doherty Earth Observatory
Sean Kinney, Lamont-Doherty Earth Observatory
Felix Waldhauser, Lamont-Doherty Earth Observatory
Leonardo Seeber, Lamont-Doherty Earth Observatory
Abstract
The recent April 5, 2024 Mw4.8 New Jersey earthquake ruptured a basement-rooted fault at ~4.7 km depth near the ~300-km long ENE-to-NE-trending Ramapo border fault system of the Newark Basin in New Jersey. This event represents one of the largest recorded earthquakes in the region since the 1884 Mw5.3 New York earthquake and adds to the growing number of Mw<5 thrust/oblique slip events, most of which appear to cluster within 15 km of the Ramapo Fault trace. The Ramapo Fault and its sub-parallel intra-rift faults are misoriented for reactivation in the current stress state, highlighting the need to understand the geological structure and geomechanical characteristics of secondary brittle faults hosted in the gneissic basement rocks dominating the region. We present results from field geological mapping of ancient slip surfaces and fracture networks around the epicenter area, geomechanical laboratory testing of the seismic behavior of epicentral basement rocks at hypocentral depth conditions and integrate the results with relocated aftershock catalog. We find that the up-dip projection of the relocated aftershock cluster is collocated with a discrete 1.7 km-wide zone in Mountainville, New Jersey that is dominated by steep sub-parallel en-echelon fracture clusters that dominantly trend NNE-SSW and dips WSW, parallel to a nodal plane on the focal mechanism and geometry of the aftershock clusters. The gneissic outcrops locally exhibit damage zones with shear morphology but lacks gouge or well-developed shear striations. This surface fault damage zone locally controls a bedrock stream channel, but only exhibits a subtle geomorphic expression on existing LiDAR topography data. The damage zone fracture set show high (>80 %) slip tendencies in the resolved effective stress field of the earthquake event, and laboratory testing of the synthetic gouges exhibit significantly unstable behavior at hypocentral loading conditions. The results indicate that the intraplate strain release in this region is being accommodated by the rupture of immature but frictionally unstable small-offset fault zones that were emplaced during the Mesozoic rifting of the Eastern North American margin.
Session
Neotectonics
earthquake geology