Foreshock productivity and rupture nucleation in injection-induced earthquakes in western Canada.

Cascading Ruptures of the 2022 Chihshang Earthquake Sequence Constrained by Seismic and InSAR Data

Foreshocks are closely linked to the mainshock’s rupture, and they can either accelerate or inhibit the nucleation of the mainshock. Resolving the source processes is therefore essential for understanding the trigger mechanisms during earthquake sequences. In September 2022, a strong earthquake sequence comprising an Mw 6.6 foreshock and an Mw 7.0 mainshock struck Taitung County, Taiwan, providing a valuable opportunity to study earthquake nucleation. We combine seismic waveforms and Interferometric Synthetic Aperture Radar (InSAR) deformation data to construct a three-fault model for this earthquake sequence. Using Pn/Pg and Rayleigh surface waves, we determine the relative hypocenter and centroid locations, respectively. The results, which integrate these two types of data, are verified by relative location measurements. In addition, other available geodetic data (InSAR and Global Navigation Satellite System) are used to validate our model, and the results reproduce the observations well. Finally, static Coulomb stress changes are calculated based on the three-fault model. The results show that subsequent subevents were triggered by preceding ones, indicating that the sequence ruptured in a cascading manner. According to the high historical seismicity in the region, special attention should be paid to the seismic risk in the stress-increased regions caused by the current earthquake.

Transient aseismic slip and two-stage evolution of the 2023-2025 Lesotho-South Africa earthquake swarm

Rupture dynamics of a moderate intraplate earthquake sequence in the Târgu Jiu region, Romania

A significant seismic sequence occurred in 2023 in the Târgu Jiu region (Romania), at the boundary between the Getic Depression and the Southeastern Carpathians. The sequence began with two moderate mainshocks (Mw 4.9 and Mw 5.4) located in the active crust (~ 20 km depth) and was followed by intense aftershock activity lasting more than one year. This well-recorded sequence provides an opportunity to investigate rupture dynamics in a complex intraplate extensional setting. We combine relocated hypocenters, focal-mechanism solutions, waveform inversion results, and simplified self-similar dynamic rupture modeling to explore the fault geometry, slip distribution, and stress conditions associated with the mainshocks. The rupture scenarios suggest predominantly unilateral upward rupture propagation toward northwest along a southeast-dipping normal fault. The modeled ruptures are characterized by stress drops of ~ 3.6 MPa (Mw 4.9) and ~ 4.7 MPa (Mw 5.4), and source duration of ~ 1.3 s and ~ 2.0 s, respectively. The simulated rupture evolution indicates heterogeneous slip, with peak slip values of ~ 0.05 m and ~ 0.12 m concentrated near the nucleation area. Possible rupture directivity effects toward the northwest are qualitatively compatible with the modeled waveform patterns and the asymmetric aftershock distribution. The spatial distribution of more than 4400 aftershocks highlights the role of complex pre-existing crustal structures in controlling rupture propagation and seismicity in the region and possible fluid-driven effects.

Foreshocks and Nucleation Process of the 2018 Ms 4.8 and 5.2 Chengduo Doublet, China

Foreshocks may offer critical insights into the nucleation process of an upcoming mainshock, yet their underlying physical mechanisms remain a topic of ongoing debate. On 5 and 6 May 2018, two significant earthquakes with magnitudes of Ms 4.8 and 5.2, respectively, struck Chengduo, China. Notably, a sequence of foreshocks began three days prior to the Ms 4.8 earthquake. In this study, we conduct a comprehensive analysis of the earthquake sequence, including earthquakes detection and relocation, focal mechanisms inversion of two mainshocks, rupture dimension estimation and stress perturbation analysis of the large foreshocks, and repeating foreshocks identification. A total of 638 earthquakes were detected, which is about 3.4 times that of the catalog. The spatial-temporal evolution of earthquakes shows the foreshocks and the Ms 4.8 mainshock occurred on the same unmapped northeast-east–southwest-west-trending, near-vertical fault. The foreshock activity process can be divided into two stages. The rupture patches of foreshocks within the same stage exhibit significant overlap, and two groups repeating earthquakes identified in foreshock sequence, indicate aseismic slip occurred during the period of foreshock activity. The epicenters of two stages are concentrated in two adjacent regions, and some large foreshocks occurred in the stress increased region, suggest that stress transfer may also play an important role in the triggering process. Our results support a combination effort of aseismic preslip and cascade stress triggering in the nucleation process of the 2018 Chengduo doublet.

Is Seismic Forecasting Possible with Physics-based AI?

Slow slip events within subduction zones offer a unique window into earthquake prediction. The subducting plate drives dehydration reactions in the fault, causing cyclical slip and observable surface displacements. Earthquake footprints can then be identified in these displacement series through coupling the multi-physics governing the subduction process with regional seismic activity. However, data noise and traditional filtering methods obscure the underlying mechanisms. Here, we alleviate this constraint with our physics-based attractor. By accounting for the physics of subduction paired with AI-assisted manifold detection, we are able to predict an earthquake in New Zealand's Hikurangi trench one week early. Additionally, predictability limits extend to 5-6 weeks with decadal repeatability, pointing to the fundamental determinism of the suggested mechanism through which physics-based seismic forecasting is possible.

On the Multimodel Nature of Earthquake Sources and Their Prediction: the Baikal Rift Zone Case Study