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Slip Kinematics, Radiation Pattern, and Rupture Directivity Effects on the Peak Ground Velocity (PGV) of the 2024 Mw4.8 Tewksbury, New Jersey, Earthquake

The 2024 Mw4.8 Tewksbury, New Jersey, intraplate earthquake produced strong shaking that was widely felt by >170,000 people across the northeast US, from Virginia to northern New Hampshire. The earthquake ruptured a southeast-dipping fault 70 km west-southwest of New York City, with a right-lateral oblique-thrust slip motion, as suggested by focal mechanism, field surveys, and aftershock analyses. Interestingly, the observed Peak Ground Velocity (PGV) and the USGS Did You Feel It (DYFI) reports show stronger ground shaking northeast of the earthquake, which coincided with the more populated area.

We analytically calculate synthetic PGVs accounting for the Tewksbury earthquake’s radiation pattern and rupture directivity, and investigate whether its ground motions can be explained by slip obliquity and rupture directivity. The radiation pattern is estimated from the USGS focal mechanism, assuming that S-waves in an elastic whole space generate the strongest motions. We account for rupture directivity effects using the rupture speed and the directivity of the line-source model by Han et al. (2024), in which the rupture propagates obliquely northeastward and down-dip.

We find that the synthetic ground motion matches the spatial pattern observed in the PGV and DYFI reports. Areas ENE and NE of the fault experienced stronger shaking because of two reasons: (i) The S-wave radiation pattern of the right-lateral, thrust slip motion on the southeast-dipping fault has the largest amplitude along the northeast-southwest axis; (ii) The northeast rupture directivity causes the apparent source time function for northeast stations to be of a larger amplitude and narrower. We argue that, to first order, a combination of coseismic slip obliquity and unidirectional rupture directivity produces the highly asymmetric coseismic radiation pattern. Our simple source model can be further improved using a more sophisticated velocity structure or accounting for dynamic effects. Nevertheless, our simple source representation may help inform seismic hazard assessment for intraplate seismicity in the New Jersey-New York region.

Session: Regional Source, Path and Site Effects in Earthquake Ground Motions - III

Type: Oral

Room: Ballroom A

Date: 4/15/2026

Presentation Time: 02:30 PM (local time)

Presenting Author: Baoning Wu

Student Presenter: No

Invited Presentation: 

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Additional Authors