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Coupling of Brittle Crustal Fabrics and Seismic Anisotropy Near the 2024 Mw4.8 New Jersey Earthquake

The recent 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. This event represents one of the largest earthquakes in the region since the 1884 Mw5.3 New York earthquake and adds to the growing number of Mw<5 events, most of which appear to cluster within 15 km of the Ramapo Fault trace. However, all these events commonly ruptured fault planes oriented at high angles to the Ramapo Fault system and intra-rift faults. Although the Mw4.8 earthquake was an oblique strike-slip event, previously recorded events show thrust faulting kinematics, documenting a compressive stress regime with ENE-WSW-to-NE-SW-oriented SHmax. 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 structure and geomechanical characteristics of secondary basement-hosted brittle faults in the region. We present preliminary results from field geological mapping of ancient slip surfaces and fracture networks, crustal shear wave splitting analysis, frictional stability experiments on basement fault rocks, and Coulomb stress change analysis of the earthquake sequence. Field mapping reveals prominent NNE, NNW, and ~E-W -trending slip surfaces within 3 km of the epicenter area, which changes to dominantly NE, WNW, and NNW trends at greater distances from the epicenter. Fast polarization directions from shear wave splitting measurements near the mainshock are dominantly N-S and WNW but transition to NE at farther distances along the Ramapo Fault Zone. Our Coulomb stress change analysis shows that failure on an NNE-trending fault and aftershocks on N-to-NNE-trending surfaces are most compatible with the aftershock distribution. These results highlight that although the Ramapo Fault Zone may represent a mechanical weakness and topographic anomaly that localizes regional tectonic strain, the secondary pre-existing faults oriented at high-angles to it are most critically-oriented for unstable frictional failure in the modern stress state.

Session: The 5 April 2024 Magnitude 4.8 Whitehouse Station, New Jersey Earthquake [Poster Session]

Type: Poster

Room: Exhibit Hall

Date: 5/3/2024

Presentation Time: 08:00 AM (local time)

Presenting Author: Folarin Kolawole

Student Presenter: No

Additional Authors