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Reactivation of the Flemington Fault by the 2024 Mw4.8 Whitehouse Station Earthquake: Slip Potential of the Southwestern Ramapo Fault System, Central NJ

Description: 

The 2024 Mw4.8 Whitehouse Station, NJ earthquake occurred on or near a known NNE-striking strand of the Flemington Fault, the southwestern continuation of the Ramapo fault system. In 1983, two scientific cores were drilled through this strand 1 km from the 2024 epicenter. These indicate a strike/dip (right-handed) of N1–10E/~35° that comports with N11E/45° mainshock and N8E/36° Mw3.7 aftershock focal planes but contrasts with N30–45E/45–55° at other sites along the Ramapo system. Similarly, much of the Ramapo system is reactivated in the modern stress field to accommodate ENE-WSW shortening, yet focal planes differ from the system’s overall NE trend, instead striking between NW and NNE. Stress inversions indicate near-horizontal N65E-trending maximum stress and a stress ratio that favors oblique shortening, both similar to the mainshock and aftershock source mechanisms. Fault slip potential modeling delineates several previously mapped fault strands in the epicentral area amenable to reactivation. The ~N10E strand of the Flemington Fault is well oriented with respect to this stress field, while the overall NE trend of the Ramapo system is not. Aftershock epicenters delineate two primary NE trends, separated by an aseismic patch (of Jurassic basalts?). Aftershocks have been restricted to within 6 km of the epicenter and rates have decayed with time^-0.84, consistent with the ≤15 km and time^-0.88 typical of eastern U.S. sequences. However—just as seismicity along the Ramapo system activates favorably oriented NNW-striking (±30°) planes within an overall NE-trending zone that itself is comparatively stable—the NE aftershock alignments may not illuminate the operative fault planes. The Whitehouse Station earthquake reinforces the pattern that modern intraplate seismicity typically exploits fault zones inherited from prior tectonism, but it also demonstrates that the active fault planes may be highly oblique to the overall trend of the reactivated tectonic belt that contains them. Thus, epicentral alignments may not illuminate the causative faults in intraplate settings.

Session: The 5 April 2024 Magnitude 4.8 Whitehouse Station, New Jersey Earthquake - I

Type: Oral

Date: 5/3/2024

Presentation Time: 02:15 PM (local time)

Presenting Author: Will

Student Presenter: No

Invited Presentation: 

Authors