More Like this

1. The 5 April 2024 Mw $${\mathrm{M}}_{\mathrm{w}}$$4.8 Tewksbury, New Jersey Aftershock Sequence Resolved With Machine‐Learning‐Enhanced Detection Methods

   https://doi.org/10.1029/2024GL113598  

   Beaucé, Eric; Waldhauser, Felix; Schaff, David; Kim, Won‐Young; Kolawole, Folarin (June 2025, Geophysical Research Letters)

   Abstract The Ramapo Seismic Zone (RSZ) in the Northeastern United States hosts frequent but poorly understood intraplate earthquakes, potentially posing a significant hazard to the nearby New York metropolitan area. The 5 April 2024, 4.8, Tewksbury, New Jersey earthquake, provides a rare opportunity to study the RSZ seismicity. We applied machine‐learning‐enhanced backprojection, matched‐filtering, correlation‐timing and double‐difference methods to continuous waveforms recorded at local and regional stations to detect and locate about 2,000 aftershocks ( 0.0) within the 74 days following the mainshock. They reveal a single, 51° east‐southeast dipping fault plane possibly abutting the Ramapo fault at depth to the north. Aftershock locations are consistent with a shallow (4 km) mainshock hypocenter with rupture propagating downward and terminating at a depth of about 6 km. A relatively high Gutenberg‐Richterb‐value and a low aftershock spatial fall‐off rate suggest that the Tewksbury sequence activated a rough, immature fault. 

   more » « less
2. Ground-Motion Simulations for the 2024 Mw 4.8 Tewksbury, New Jersey, Earthquake

   https://doi.org/10.1785/0220250333  

   Boyd, Oliver S; Bozdağ, Ebru; Kehoe, Haiyang L; Moschetti, Morgan P (January 2026, Seismological Research Letters)

   Abstract Ground-motion simulations of notable earthquakes in the central and eastern United States are limited and typically assume 1D Earth structure. In this study, we use a 3D seismic velocity model to better constrain the depth and focal mechanism of the 5 April 2024, moment magnitude 4.8 Tewksbury earthquake and investigate the spatial variability of earthquake ground motions and the effects of nearby sedimentary basins. We perform earthquake ground-motion simulations up to 0.5 Hz using the 3D spectral-element wave-propagation solver SPECFEM3D over a region 280 km wide by 260 km long by 77 km deep. Topography and subsurface geophysical structure are assigned using the U.S. Geological Survey (USGS) National Crustal Model with a minimum shear-wave velocity of 200 m/s. We use earthquake time series from 13 broadband seismic stations in the region that have a uniform azimuthal distribution and epicentral distances ranging from 76 to 131 km to compare with synthetics and explore the effects of 1D versus 3D seismic structure on focal mechanism and depth solutions. Ground-motion intensity metrics are also presented relative to the Next Generation Attenuation-East Project (NGA-East) ground-motion models (GMMs) currently used in seismic hazard assessments for the region. We find that the 3D model, which reveals a wide spatial variability of period-dependent ground motions, yields better predictions of earthquake ground motions relative to the 1D model and the NGA-East ergodic GMM, with a 76% reduction of residual variance in observed ground motions averaged over 3, 5, 7, and 10 s periods. Use of the 3D model to solve for a focal mechanism yields a shallower focal depth at 4 km and a shallower east-dipping focal plane relative to the USGS regional moment tensor and Global Centroid Moment Tensor. Our study demonstrates that use of 3D seismic velocity models can improve estimates of earthquake focal mechanisms, ground motions, and seismic hazard. 

   more » « less
3. Bi‐Segment Fault Rupture and Long‐Lasting Intraslab Aftershock Activity During the 2017 Mw 8.2 Tehuantepec, Mexico Earthquake

   https://doi.org/10.1029/2024JB030699  

   Chen, Fang; Wang, Dun; Xu, Shenghui; Yan, Bing; Zhang, Junfeng; Guo, Yicun; Yao, Dongdong; Zhuang, Jiancang; Suárez, Gerardo; Shearer, Peter (June 2025, Journal of Geophysical Research: Solid Earth)

   Abstract The 8 September 2017 Mw 8.2 Tehuantepec, Mexico earthquake was the second largest normal‐faulting earthquake to occur in a shallow subduction environment since 1976 (GCMT catalog), and the earthquake sequence featured an extremely long‐lasting and productive aftershock activity that deviated from typical intraslab earthquakes. Here we relocated the early aftershocks within 5 days following the mainshock and investigated the source process of the mainshock using back‐projection and finite fault inversion methods. Our results showed that the earthquake rupture propagated along a ∼150‐km‐long, NW‐striking normal fault. After rupturing approximately 100 km, it triggered activity on a ∼40‐km‐long fault located ∼50 km to the northeast. We employed a stochastic branching model to isolate the background seismicity rate, and compared this rate to those of five other earthquakes of similar magnitudes. The results indicated that the background seismicity of the Mexico event occurred at a much higher rate than those of the other five representative earthquakes. Considering that the rupture planes showed similar dip angles and strikes to those of the outer‐rise normal faults, we suggest that the ruptures of the Mw 8.2 earthquake are possibly the reactivation of hydrated outer‐rise normal faults in the subducting slab. 

   more » « less
4. ML-Enhanced catalog of the 5 April 2024 Tewksbury aftershocks

   https://doi.org/10.5281/zenodo.14058325  

   Beaucé, Eric (January 2024, Zenodo)

   {"Abstract":["Machine-learning-enhanced catalog of the aftershocks of the 5 April 2024 M4.8 Tewksbury, New Jersey earthquake. It accompanies the following article submitted to Geophysical Research Letters:\n\nThe 5 April 2024 Tewksbury, New Jersey aftershock sequence resolved with machine-learning-enhanced detection methods\n\nThis repository contains the pre-relocation catalog (catalog_Tewksbury_aftershocks_before_relocation.csv) and the relocated catalog (catalog_Tewksbury_aftershocks_relocated.csv).\n\n \n\nColumns of the pre-relocation catalog:\n\n\n\nevent_id: Unique string identifying an event.\n\nMw: Moment magnitude, computed when possible only (so, most of the events have NaNs because they were too small to estimate Mw).\n\nMw_err: Error on moment magnitude.\n\nMw*: Approximate moment magnitude.\n\nlongitude: Event longitude.\n\nlatitude: Event latitude.\n\ndepth: Event depth in km.\n\norigin_time: Event UTC origin time.\n\norigin_time_local: Event local origin time.\n\nhmax_unc: Event location maximum horizontal 1-std uncertainty, in km.\n\nhmin_unc: Event location minimum horizontal 1-std uncertainty, in km.\n\nvmax_unc: Event location maximum horizontal 1-std uncertainty, in km.\n\naz_hmax_unc: Azimuth of the event location maximum horizontal uncertainty.\n\ntt_rms: Residual travel-time, in sec.\n\nn_dev: Network-averaged correlation coefficient in units of CC RMS (matched-filtering).\n\npotential_quarry_blast: True or False. Flags potential quarry blast, ie, anthropogenic earthquake.\n\n\nColumns of the relocated catalog:\n\n\n\nevent_id: Unique string identifying an event.\n\norigin_time: Event UTC origin time.\n\nlongitude: Event longitude.\n\nlatitude: Event latitude.\n\ndepth: Event depth in km.\n\nMw*: Approximate moment magnitude.\n\nhmax_unc: Event location maximum horizontal uncertainty, 95% CI, in km. Computed with bootstrapping.\n\nhmin_unc: Event location minimum horizontal uncertainty, 95% CI, in km. Computed with bootstrapping.\n\nvmax_unc: Event location maximum horizontal uncertainty, 95% CI, in km. Computed with bootstrapping.\n\naz_hmax_unc: Azimuth of the event location maximum horizontal uncertainty.\n\nquality: "A" or "B". "A" events were relocated with stronger inter-event linkage in HypoDD."]} 

   more » « less
5. The Role of Stress Transfer in Rupture Nucleation and Inhibition in the 2023 Kahramanmaraş, Türkiye, Sequence, and a One-Year Earthquake Forecast

   https://doi.org/10.1785/0220230252  

   Toda, Shinji; Stein, Ross S (January 2024, Seismological Research Letters)

   Abstract We probe the interaction of large earthquakes on the East Anatolian fault zone, site of four Mw ≥ 6.8 events since 2020. We find that the 2023 Mw 7.8 Pazarcık shock promoted the Mw 7.7 Elbistan earthquake 9 hr later, largely through unclamping of the epicentral patch of the future rupture. Epicentral unclamping is also documented in the 1987 Superstition Hills, 1997 Kagoshima, and 2019 Ridgecrest sequences, so this may be common. The Mw 7.7 Elbistan earthquake, in turn, is calculated to have reduced the shear stress on the central Pazarcık rupture, producing a decrease in the aftershock rate along that section of the rupture. Nevertheless, the Mw 7.7 event ruptured through a Çardak fault section on which the shear stress was decreased by the Mw 7.8 rupture, and so rupture propagation was not halted by the static stress decrease. The 2020 Mw 6.8 Doğanyol–Sivrice earthquake, located beyond the northeast tip of the Mw 7.8 Pazarcık rupture, locally dropped the stress by ∼10 bars. The 2023 Mw 7.8 earthquake then increased the stress there by 1–2 bar, leaving a net stress drop, resulting in a hole in the 2023 Pazarcık aftershocks. We find that many lobes of calculated stress increase caused by the 2020–2023 Mw 6.8–7.8 earthquakes are sites of aftershocks, and we calculate 5–10 faults in several locations off the ruptures brought closer to failure. The earthquakes also cast broad stress shadows in which most faults were brought farther from failure, and we observe the beginnings of seismicity rate decreases in some of the deepest stress shadows. Some 41 Mw ≥ 5 aftershocks have struck since the Mw 7.8 mainshock. But based on these Coulomb interactions and on the rapid Kahramanmaraş aftershock decay, we forecast only about 1–3 Mw ≥ 5 earthquakes during the 12–month period beginning 1 December 2023, which is fortunately quite low. 

   more » « less